2017-2018 Academic Year

Upcoming Colloquia

December 13, 2017
Erdal Toprak, UT Southwestern
Title: Evolution of Antibiotic Resistance on A Multidimensional Hypercube
Abstract: Antibiotic resistance is a growing public health problem. Prolonged treatment times due to drug resistant pathogens increase human suffering and health care costs. Understanding the genetic changes responsible for elevated drug resistance can inform novel strategies for combating drug resistance. In this seminar, I will first introduce a novel automated microbial selection device, the “morbidostat”, which we developed to study the long term evolution of antibiotic resistance. Following that, I will summarize our recent work where we synthetically construct and analyze all possible combinations of six antibiotic resistance conferring mutations. Our results show that resistance evolves through an extremely rugged adaptive landscape with direct and indirect paths leading to distinct resistance peaks. High-order interactions between adaptive mutations create this highly rugged fitness landscape, where the distributions of most mutations’ effects are indistinguishable from increasing or decreasing resistance by flipping a coin.

November 29, 2017
Jessica Ramella-Roman, Florida International University
Title: Improving the diagnosis of pathologies of the extracellular matrix through optical imaging
Abstract: The Extra Cellular Matrix (ECM) provides structural and biomechanical support to cellular constituents in organs and tissue, with variation in composition and function depending on its environment. The ultrastructure of the ECM consists in part of proteins (collagen and elastin for example) whose organization can be observed from the nanoscopic to the macroscopic level through various optical techniques.
Understanding the ECM functional role in biological environments may be used to pinpoint early pathological events and consequently devise new treatment paradigms. To translate this knowledge into clinical methods, a new understanding of nanoscopic to macroscopic light-tissue interaction needs to be achieved.
By utilizing non-linear microscopic techniques such as Second Harmonic Generation and Adaptive Optics we obtain extreme high-resolution structural assessment of the living ECM. We utilize this data as a framework for our computational models of light transfer to ultimately refine our understanding of the complex interaction between light and biological matter.
Based on this knowledge we ultimately aim at improving full field optical techniques, such as Mueller matrix polarimetry, and create quantitative diagnostic tools for the clinical setting. In this context, we are interested in understanding the role of cervical collagen during parturition and determine if early signs of preterm labor can be observed through Mueller matrix polarimetry, we are also interested in studying the ECM organization in the human cornea and heart valves to guide early intervention.

November 1, 2017
Peter Milonni, University of Rochester
Title: Zero-Point Energy, Fluctuations, and Dissipation: A (Mostly) Quantum-Optical Perspective
Abstract: Following a brief review of how the concept of zero-point energy first appeared in quantum theory, I will describe some of the evidence for electromagnetic zero-point energy and quantum field fluctuations. Attention will then be focused on fluctuation-dissipation relations which allow different physical interpretations of effects usually associated with changes in zero-point field energy, and which bear on the question of whether equations of motion determine commutation relations. Quantum Langevin equations with zero-point fluctuations and dissipation will be shown to lead straightforwardly to expressions for quantized electromagnetic fields in dissipative media. Implications of vacuum field fluctuations and zero-point energy will be discussed in the context of recent experiments on spontaneous parametric down-conversion and for a proposed experiment probing Planck-scale physics.

October 25, 2017
Max Zenghui Wang, University of Electronic Science and Technology, China
Title: A Vibrant New World—Exploring New Physics and Materials with Nanoelectromechanical Systems (NEMS).
Abstract: The advent of low-dimensional nanostructures has enabled a plethora of new devices and systems. Among them, nanoelectromechanical systems (NEMS) offers the unique capability of coupling the exquisite material properties found in these atomically-defined nanostructures with their mechanical degree of freedom, opening new opportunities for exploring exotic phenomena at the nanoscale. In this talk I will discuss two such examples: 1) using an individual carbon nanotube as a nanoscale balance to study low-dimensional phase transition, and 2) using multimode resonance in black phosphorus NEMS resonator to resolve the intrinsic anisotropy in these nanoscale crystals.
Zenghui Wang et al., Science 327, 552 (2010)
Zenghui Wang et al., Nanoscale 7, 877 (2015)
Zenghui Wang and Philip X.-L. Feng, 2D Materials 2, 021001 (2015)
Zenghui Wang et al., Nano Letters 16, 5394-5400 (2016).

October 11, 2017
Ata Sarjedini, Florida Atlantic University
Title: RR Lyrae Variable Stars in M31, M32, and M33
Abstract: I will review some of the recent work on the RR Lyrae populations in M31, M32, and M33. The capabilities of the Hubble Space Telescope and 10-meter class ground-based telescopes have made it possible to reliably identify and characterize RR Lyrae variables in these two galaxies. This is important because RR Lyraes are the 'Swiss Army knives' of astronomy in the sense that they have multiple and varied uses for probing the formation and evolution of galaxies. I will describe the diversity of ways that RR Lyraes are useful in this regard and what they reveal about the properties of M31, M32, and M33.

Colloquium date TBA
Comert Kural, Ohio State University
Title: Mechanobiology of clathrin-mediated endocytosis
Abstract: Clathrin-mediated endocytosis is the best characterized and most extensively studied mechanism by which cells internalize molecules from their environment. The interplay between mechanical forces and dynamics of the molecular assemblies performing the internalization has important roles during development of complex multicellular organisms. Due to technical limitations, however, effects of mechanical cues generated during development of organisms on formation and dissolution of internalization agents are not characterized. In the first part of my talk, I will focus on the strategies we developed for determining the variations in clathrin dynamics within tissues of a developing organism. In the second part, I will highlight our work on characterizing the tension-based regulation of internalization dynamics and our long term aims for utilizing this information as non-invasive membrane tension sensors applicable to tissues.

Past Colloquia

February 20, 2017
Shawn Henderson, Cornell University
Title: Probing fundamental physics and astrophysics with Advanced ACT and future CMB surveys
Abstract: A worldwide experimental effort is underway to precisely map the polarization of the cosmic microwave background (CMB). These measurements will significantly improve our knowledge of the standard model of cosmology and will probe for signs of new physics in the early and late Universe. Measurements of the CMB in the next decade, and in particular its polarization, have the potential to radically transform our understanding of fundamental physics, from the ultra high energy physics of inflation to the basic properties of fundamental particles like the masses of the neutrinos.  The Advanced Atacama Cosmology Telescope Polarimeter (Advanced ACT) is a new polarization-sensitive microwave receiver on the Atacama Cosmology Telescope that we are using to tackle these exciting problems by more precisely mapping the polarization anisotropies of the CMB on arcminute scales. In addition to probing the physics of the very early Universe, we expect Advanced ACT to significantly improve our understanding of large-scale astrophysics by discovering thousands of new galaxy clusters and high-redshift galaxies. To accomplish these goals Advanced ACT will measure the CMB over roughly half the sky in five frequency bands (28-230 GHz) using the largest monolithic superconducting detector arrays yet deployed by a CMB experiment. I will also discuss our efforts with the Simons Observatory, CCAT-prime, and the Stage IV CMB survey to extract all the primordial information from the CMB polarization in the next decade.

February 15, 2017
Ivan Medvedev, Wright State University, Dayton, Ohio, 45435
Title: Bio-Chemical Respiratory Sensing in the Terahertz Spectral Range – Science, Technology, and Applications
Abstract: The translation of high resolution molecular-spectroscopy into technological solutions with high potential for societal impact in health care has been the motivation of the research conducted by our group. Chemical analysis of expired human breath is a rapidly developing field with significant promise for use in medicine (clinical and research) as well as occupational and chemical safety applications. The majority of existing breath analysis research relies on the golden standard of gas sampling - Gas Chromatography – Mass Spectrometry (GC-MS), which is costly, complex in operation, and is somewhat preclusive of large data set collections (>1000) much needed for human respiratory modeling. Our laboratory has pioneered the use of Terahertz (THz) chemical sensors for human breath sensing (doi: 10.1063/1.4823544), and has since demonstrated its capabilities for detection of breath analytes related to blood glucose metabolism and sleep deprivation induced fatigue. By sampling a single human breath (200 cc sample volume), THz sensors are capable of detecting a wide range of bio-relevant Volatile Organic Compounds at a part per trillion level of dilution, with ‘absolute’ specificity (vanishingly small probability of false alarm), and total sampling time of under 5 minutes, thus significantly improving upon competing techniques. Unlike GC-MS, THz sensors do not require daily calibration and facilitate detection based on unique rotational spectral signatures. These signatures are much valued by astronomers trying to understand the origins of star formation in the interstellar space. Most important, THz sensors enable collection of large data sets. These data sets will facilitate the development of machine learning algorithms unavoidably needed for human metabolic modeling. The remarkable sensitivity of THz devices allows for the ongoing study of the viral infection effects on respiratory expression of lung cell cultures, opening a window for the development of multiscale respiratory models.

In this talk I will provide our vision for applying THz spectroscopy to bio-sensing and details of our multidisciplinary projects interfacing physics with medicine, biology, astronomy, and engineering. I will also describe our ongoing efforts in design, miniaturization, and evolving THz chemical sensor technology towards affordable and compact implementations.

Bio: Ivan R. Medvedev received his B.S. and M.S. degrees from the Moscow Institute of Physics and Technology (Russia) in 1996 and 1998, respectively. He received his Ph.D. degree from the Ohio State University in 2005. He is currently an Associate Professor of Physics at Wright State University. Prior to joining WSU, Dr. Medvedev worked as a research scientist in the Department of Physics at the Ohio State University. He has expertise in THz and IR point and stand-off sensor development. His research interests include the development of millimeter-wave and terahertz systems for in-situ and remote sensing applications. His scope of expertise spans AMO physics, analytical chemistry, molecular spectroscopy, bio-physics, electrical and computer engineering. His laboratory is at the forefront of THz respiratory sensing with focus on sensor development and applications. He has authored and co-authored 48 peer-reviewed publications. His research has been funded by a range of commercial and governmental agencies.

February 13, 2017
Nico Cappelluti, Yale University
Title: The Billions problem: finding the progenitors of Supermassive Black Holes in the first Gyr of cosmic history.
Abstract: Supermassive Black Holes are the most enigmatic objects in the Universe, their growth and evolution have been  witnessed by X-ray and multi-wavelength cosmological surveys from the present day back to when the Universe was about 1 Gyr old (redshift z~7). Impressively, by that time the Universe has been capable of growing Black Holes to a billion solar masses,  as discovered by the Sloan Digital Sky Survey. There is no known accretion process capable of growing an ordinary stellar black hole  to such a high mass in such a short time. This is the so-called “Billions Problem.” However, the lack of metals in the early Universe  means that the first generation of black holes was probably unusually massive (100-10^5 M_☉), arising either from evolved first-generation  stars or from Direct Collapse to a Black Hole. Both types should be visible in the X-ray band. To date there have been no direct X-ray detections of this first generation of black holes. However, studies of cosmic  background fluctuations provide clues to their demography and environment. In particular, we discovered, using NASA’s Chandra  and Spitzer Great Observatories, that the Cosmic Background Light angular fluctuations are coherent at several wavelengths from  FAR-IR to X-ray (after removing all the detected sources). These, strong, joint fluctuations can be explained with a population of very  high-redshift (z>>7), low metallicity, Compton-thick, massive black holes, likely produced by the collapse of pristine clouds of molecular  hydrogen. Cosmic backgrounds are therefore extremely information rich tools. They also carry important information on the nature of Dark  Matter or the existence of a sterile neutrino with mass of a few keV. Over the next few years, new facilities like JWST, Euclid, WFIRST,  eROSITA, and Athena---and STAR-X, Lynx, and equivalent X-ray missions---will allow to both directly detect the first black holes in  the Universe and to make 1% measurements of the Cosmic Background fluctuations in as many as 20 wavelength bands. 

February 8, 2017
Seyed Hashemi, Institute of Optics, Univ. Rochester
Title: Quantum Optics With Structured Light
Abstract: Today, quantum information science is moving passed its infancy into an era when its promise of dramatic improvements in applications such as metrology, cryptography, and computation are no longer merely a dream. The transverse profile of the light field provides an unbounded Hilbert space that can be used for encoding information. The ease of control, the large dimensionality, and the weak interaction of photons with the environment makes structured light a prime candidate for long-range applications such as quantum key distribution

To establish control over the transverse structure of light, we need to meet challenges in characterization of such states at the single photon level. I provide a summary of where we currently stand in terms of our capabilities to characterize a priori unknown states. Direct measurement of a quantum state, originally proposed by Lundeen et al, provides a simple means of characterization of quantum states by using complex weak values. I will explain how we can combine the power of compressive sensing with direct measurement to characterize a large-dimensional quantum states. For example, in our implementation we have shown a 350-fold speed up in the process of characterizing a 19200-dimensional state.

I will also give an example of what we can do with structured light. I will discuss the importance of entanglement in quantum physics and delve into some of the recent controversies surrounding the idea of entanglement. I will present a classical counterpart to quantum teleportation that uses classical entanglement. This analog protocol allows us to teleport an arbitrary OAM state, in the subspace spanned by any two OAM states, to the polarization of the same beam.

February 6, 2017
Gerhard Ulbricht, University of California - Santa Barbara
Title: Microwave Kinetic Inductance Detectors (MKIDs) for IR-optical and X-ray Astronomical Instrumentation
Abstract: Microwave Kinetic Inductance Detectors (MKIDs) are novel superconducting detectors with very attractive properties for observational astronomy as they offer significant advantages over time-tested CCD technology as well as competing low temperature detectors. I will explain their basic working principle and show how every MKID pixel can count single photons, achieve µSec time resolution and measure individual photon energies at the same time. I’ll also demonstrate how frequency domain multiplexing allows MKID arrays to scale up to kilo- or even megapixel sizes, a unique advantage among competing low temperature detectors. Thermal Kinetic Inductance Detectors (TKIDs) are a variation of the MKID principle optimized to detect soft X-rays. As TKIDs are partly suspended on a freestanding membrane they operate as microcalorimeters and have the potential to achieve time and energy resolutions comparable to transition edge sensors. As they still profit from the passive MKID multiplexibility, they present a unique and feasible way to large detector arrays for X-ray imaging spectroscopy. I will present how our TKID prototypes, even though considerably saturated, achieved an energy resolution of 75 eV at 5.9 keV and will explain how by slightly sacrificing dynamic range, TKIDs should in principle be able to reach unmatched energy resolutions. Finally, I will present our latest progress with the UV-optical-IR MKIDs we developed at UCSB. We were able to demonstrate their potential for time-domain astronomy and multi-object spectroscopy and are currently working on several instruments for the direct imaging of exoplanets. As MKIDs offer several unique advantages for high contrast imaging they promise to increase attainable contrast ratios by up to 2 orders of magnitude and thus could significantly increase the potential number of exoplanetary targets for the search for life outside our own solar system.

February 1, 2017
Miranda van Iersel, The Netherlands Institute for Applied Scientific Research
Title: Observing objects: determining the influence of environmental parameters
Abstract: Imaging systems can be found in many different objects nowadays (car, cell phones, drones, satellites, etc.). We use these imaging systems for a wide variety of tasks (observation / detection of persons, remote sensing, laser communication, etc.). The performance of these imaging systems is usually limited by the atmosphere, which interacts with the optical wave when it propagates from the object to the imaging sensor. The fluctuations of the index of refraction, but also absorption and scattering, taking place in the atmosphere are perturbing the optical wave front. These processes cause propagation effects like refraction, turbulence, and transmission losses, which in turn are responsible for distortions (e.g. blurring, scintillation) in images. This results in images in which details are less visible or even have disappeared completely. A better understanding of the influence of the environment on these effects can help to get images of a better (more detailed) quality. To gain a better understanding, several outdoor experiments were performed in different locations (the Netherlands, South Africa). During these experiments a geometric object (CUBI) or a small vessel was used as an object. The object was monitored by visual and/or infrared (IR) cameras, while at the same time the environment was characterized using standard meteorological equipment, scintillometers, etc. In this talk I will elaborate on the experiments that were performed and show examples of how the environment influences the observation of an object. One example will focus on the dynamic IR signature of an object. Besides monitoring the influence of the diurnal temperature change on the IR signature, dynamic changes (changing the orientation, wetting the object) were (intentionally) made to the object to study the influence of certain parameters. In addition to these examples, several future research topics will be identified and discussed.

January 30, 2017
Abigail T Crites, California Institute of Technology
Title: Innovative Approaches in mm-Wavelength Cosmology: From Inflation to the Epoch of Reionization and Beyond
Abstract: I will describe how I use mm-wavelength instruments (both spectrometers and photometers) to explore our universe across cosmic time. I will discuss instruments such as SPT-pol, CMB-S4, TIME, and future even more powerful mm-wavelength spectrometers that will allow us to probe the universe, from the first fractions of a second after the big bang to the present day.  These new instruments and the detector technologies being developed in the field can be used to study 1) inflation and neutrinos via the CMB; 2) the epoch of reionization; and 3) galaxies at the peak of star formation.

I will discuss one instrument in depth, TIME (the Tomographic Ionized-carbon Intensity Mapping Experiment) which is a new instrument designed to probe the epoch of reionization (EoR) by measuring the 158 um ionized carbon emission line [CII] from redshift 5 - 9 using line intensity mapping.  I will describe the instrument which is an R of ~100 spectrometer sensitive to the 200-300 GHz radiation.  This instrument will detect the [CII] clustering fluctuations from faint galaxies during EoR and compare these measurements to predicted [CII] amplitudes from current models. The [CII] intensity mapping measurements are complimentary to both 21-cm measurements of the EoR and direct detections of high redshift galaxies with HST, ALMA, and, in the future, JWST.

January 26, 2017
Luc Vinet, Centre de Recherches Mathematiques, Montreal, Canada
Title: The Bannai-Ito algebra in many guises
Abstract: This talk will offer a review of the Bannai-Ito algebra and of its higher rank extension. It will first be explained that it is in a Schur-Weyl duality with the super algebra osp(1,2). Its occurrence as the symmetry algebra of the Dirac-Dunkl equation will be discussed and its relation to orthogonal polynomials will also be presented.

January 25, 2017
Chungqiang Li, University of Texas, El Paso
Title: Advanced Optical Imaging Techniques for Deep Penetration, Super Resolution, and High 3D Imaging Speed
Abstract: Deeper penetration can access much larger volume in scattering tissue for in vivo imaging. Nanometer resolution is needed to visualize molecular trafficking and interactions. Imaging speed in kHz range is necessary for studying fast cellular and molecular events such as transient neural signaling. The first part of this talk is focused on using non-diffracting laser beams, such as Bessel beams and Airy beams, as the light source for deeper penetration. The propagation of non-diffracting beams is immune to diffraction and scattering, i.e. they can maintain their intensity profiles through a long propagation length, and preserve their intensity profiles after distortion. Super resolution fluorescence microscopy has achieved success with the 2014 Nobel Prize in Chemistry. The second part of this talk is to develop super resolution microscope without molecular fluorescence using a femtosecond laser pump-probe method. The last part of this talk will discuss developing high-speed two-photon microscope for imaging fluorescent objects and simultaneously tracking their fast motion in 3D. The idea is to integrate two ultrafast laser techniques, temporal focusing and pulse shaping, to achieve fast 3D scanning without mechanical motion.

November 30, 2016
Matteo Baggioli, University of Crete
Title: Gravity and Condensed Matter: an unexpected love story
Abstract: Strongly coupled/correlated (and often many body) systems represent a big challenge for modern theoretical physics because standard perturbative techniques are neither efficient nor suitable for computations. Condensed matter (CM) provides a plethora of such strongly coupled phenomena which are interesting from both the theoretical and experimental perspectives. I will introduce a new tool, known as AdS-CFT, for computing observables in strongly coupled field theories using a dual gravitational picture. I will focus in particular on applications of the duality toward the CM world (AdS-CMT) and upon recent developments to deal with the introduction of momentum dissipation into such a framework. We will aim to discuss the possibility of describing strongly coupled insulators and metal-insulator transitions using particular black holes solutions in higher-dimensional spacetimes.

November 2, 2016
P. Scott Carney, University of Illinois
Title: Lens vs algorithm: optical imaging in the age of computers
Abstract:  Optical elements may be thought of as effecting a linear transformation of the optical field.  Given access to the field, those same transformation, and many more, may be performed with a computer and so hardware may be replaced with software. I will mainly discuss the application of this idea in optical coherence tomography (OCT) where we have replaced complicated hardware with physics-based algorithms to produce a high-resolution 3-d imaging system with infinite depth of field in a compact form factor. I will give  examples of the method in use in biological systems and results from a recent clinical trial in breast cancer.

Bio: P. Scott Carney holds a BS in Engineering Physics from UIUC (1994), and a PhD in Physics from the University of Rochester (1999).  He was a post-doctoral associate at Washington University from 1999 to 2001 when he joined the faculty of UIUC ECE.  He is a theorist with research interests in inverse problems, imaging, coherence theory and other branches of optical physics.   He is also the cofounder of Diagnostic Photonics, Inc., a company bringing innovations in computed imaging to the surgical market. He is active in the community beyond his research,  serving as the editor-in-chief of the Journal of the Optical Society of America A and General Co-Chair of the 2016 Frontiers in Optics conference.

October 5, 2016
Misak Sargsian, Florida International University
Title: Dynamics of Superdense nuclear Matter: from Atomic Nuclei to Neutron Stars
Abstract: One of the most fascinating stellar objects are the Neutron Stars which represent the last stage of the visible matter before it collapses to the black hole. I will discuss the history of the prediction and discovery of neutrons stars and how the progress of understanding the inner workings of the star is associated with the progress of understanding the nuclear forces at very short distances. I will report on some recent developments in studies of nuclear forces at very short distances and demonstrate that if they are correct then they will require reevaluation of the several key properties of neutron stars.

September 14, 2016
Heather Bloemhard, American Astronomical Society
Title: Science Policy for Scientists
Abstract: Science policy is the interdisciplinary field where science and policy intersect. Science policy includes a wide array of topics where science and policy rely on each other. In this talk, we will focus on the ways that policy impacts science and how you, as individuals, can influence policy. This will include an overview of some of the relevant topics and a discussion of why you should and how you can get involved in science policy. This presentation is designed to be an interactive conversation, with an expectation that the audience will participate. Our goal will be gain a better understanding of how to utilize your leverage as scientists and constituents to help your members of Congress make policy decisions that will benefit you.  PDF version of this abstract here Heather Bloemhard Colloquium

September 7, 2016
Stefan Kautsch, Nova Southeastern Univ.
Title: Too thin or too beautiful? - The Mystery of Superthin Galaxies Revealed
Abstract: Superthin galaxies have extremely thin, low-density stellar disks with low star-formation rates. They are heavily dark-matter dominated. Thus, superthins provide a unique opportunity to study dark matter, and how it influences galaxy formation and morphological evolution. I present new observations which will help to establish them as a diverse class of extragalactic objects.

April 20, 2016
Eduardo H. da Silva Neto, UBC
Title: Universal Charge Order in the Cuprate High-Tc Superconductors
Abstract: Superconductivity at temperatures much higher than what is predicted by the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity are obtained in some copper-oxide (cuprate) materials. In these cuprates, an antiferromagnetic state can be destabilized toward high-temperature superconductivity by either hole or electron doping the material. Besides these two phases, a periodic distribution of the electronic density, or charge order (CO), was recently detected in the Y-based cuprates [1], and echoed the long-known presence of stripe order in the La-based cuprates [2]. However, at that point, the universality of the CO phenomenon to the cuprates remained to be determined.

In this talk I will first discuss a novel combined scanning tunneling microscopy (STM) and resonant X ray scattering (RXS) experimental approach that established the universality of a CO competing with superconductivity in the holed-doped cuprates [3]. Still, the universality of charge order remained in question, with several experiments and theories pointing to hole-doping as a critical ingredient to its formation.

Here I will also present RXS measurements that demonstrated for the first time the presence of charge order in the electron-type cuprate Nd2-xCexCuO4 (NCCO) [4]. A comprehensive study of CO in NCCO as a function of doping, temperature, and magnetic fields, shows that CO does not require a pseudogap precursor state. We also find that while CO is universal to all cuprates, its relationship with superconductivity is not. Finally, open questions in the field, as well as prospects for future experiments, will also be discussed.

[1] G. Ghiringhelli, et al. Science 337, 821 (2012).
[2] J. M. Tranquada, et al. Nature 375, 561 (1995).
[3] E. H. da Silva Neto, et al. Science 343, 393 (2014).
[4] E. H. da Silva Neto, et al. Science 347, 282 (2015).
[5] E. H. da Silva Neto, et al. Science Advances (submitted) (2016).

March 30, 2016
Cyrus Hirjibehedin, Univ. College, London (UCL)
Title: Atomically Precise Magnetic Nanostructures: From Physics to Information Technology
Abstract: In his 1959 speech "There’s plenty of room at the bottom", Richard Feynman drew attention to the powerful consequences of being able to manipulate matter at the atomic scale. Beyond examining the frontiers of data storage by discussing the viability of writing "the entire 24 volumes of the Encyclopedia Britannica on the head of a pin", Feynman foresaw many other revolutionary outcomes, including atomically precise materials synthesis and new forms of computation. Today, using a range of bottom-up techniques from self-assembly to direct atomic manipulation, it is possible to construct a variety of atomically precise nanostructures on solid-state surfaces that display intriguing quantum phenomena. There has also been dramatic recent progress in developing a variety of complementary experimental probes for extracting the magnetic properties of these nanostructures with atomic spatial resolution.

Using scanning tunneling microscopy (STM), we have built individual magnetic nanostructures one atom at a time [1]. By measuring their magnetic excitations with inelastic electron tunneling spectroscopy, we can extract the magnetic anisotropies of individual magnetic atoms [2] as well as the coupling between atoms in an antiferromagnetic chain [1]. Using numerical and analytic techniques, we consider the capacity of such quantum spin chains to carry classical binary information. Furthermore, we show that we can gate the flow of information across the chain by inducing quantum fluctuations with an externally applied magnetic field. These results highlight our ever-growing ability to design and characterize more complex atomic-scale systems of physical interest, including those that may have applications in novel device paradigms.

[1] C.F. Hirjibehedin et al., Science 312, 1021 (2006)
[2] C.F. Hirjibehedin et al., Science 317, 1199 (2007)

March 23, 2016
Beverly Berger, LIGO Scientific Collaboration
Title: Observation of gravitational waves from a binary black hole merger: a new window on the universe
Abstract: LIGO’s detection of gravitational waves from a binary black hole merger inaugurates a completely new mode of observational astronomy and represents the culmination of a quest lasting half a century. After a brief review of gravitational waves in general relativity, I will discuss the detection itself. How do the LIGO instruments work? How do we know the signal was caused by a binary black hole merger? What does this detection tell us about binary black holes? Then I will focus on how this moment came to pass. The detection required many ingredients to be in place including (1) developments in theoretical relativity to allow proof that gravitational waves were not coordinate artifacts; (2) a bold vision to recognize that gravitational wave detection was not impossible; (3) technological developments of novel vacuum systems, lasers, optical coatings, active seismic isolation, etc.; (4) the successful conclusion of a 35 year effort to simulate binary black holes on the computer; (5) development of sophisticated, new data analysis methods to tease a waveform from noisy data; (5) the growth of the field of gravitational wave science from a handful of practitioners to the more than 1000 authors on the detection paper; and finally (6) the (nearly) unwavering support of the National Science Foundation. Finally, I will discuss the future — more binary black holes, other sources of gravitational waves and what we might learn, instrument upgrades, new facilities — and other ways to detect gravitational waves — from space and from monitoring millisecond pulsars.

See full poster here

March 2, 2016
Aziz Boulesbaa, Oak Ridge National Laboratory - Center for Nanophase Materials Sciences
Title: From vibrational dynamics of interfacial water to the formation and dissociation of quasiparticles in nanomaterials
Abstract: Abstract: One of the challenges in the 21st century is finding alternative energy resources, and solar energy has emerged as an attractive choice due to its availability, affordability, and environmental friendliness. However, improving the efficiencies of photovoltaic conversion and water photocatalytic reactions still remains a challenge. Because the conversion processes in these systems often proceed on ultrashort time-scales, femtosecond spectroscopy emerged as one of the most suitable tools to comprehend, and possibly control, the fundamental aspects and factors limiting them. My talk will focus on this idea, and will be presented in four parts: 1) the first topic concerns ultrafast vibrational coherence and energy dynamics in interfacial water as characterized using one of the shortest mid-infrared laser pulses that we are aware of to date. In particular, I will outline how O-H bonds oriented away from the bulk water are easier to dissociate than their inward facing counterparts. 2) In the next topic, I will illustrate my contributions to the field of energy and charge transfers at the interface of semiconducting quantum dots (0D) and molecular adsorbates. Most notably, the dependence of dissociation efficiency of photogenerated excitons on the number of adsorbed molecules on the 0D particle will be emphasized. 3) Following the second topic, I will present the ultrafast dynamics of the generation of exciton and trion quasiparticles in two-dimensional (2D) materials and their interfaces. In particular, the formation of a hybrid-exciton (HX) at the 2D/0D interface, and the coupling between excitonic and photonic modes at the 2D/plasmonics interface will be outlined. 4) Lastly, I will present my visions of the future and emerging horizons relating to performing fundamental research on, and the potential applications of, nanomaterials and their interfaces.


Aziz Boulesbaa graduated with a BSc & MSc in "Physics of Radiations” in 2002 from the University of Sciences and Technology of Algiers, Algeria. In 2004, he graduated with an MSc in "Physics of Lasers & Metrology” from the University of Paris 13, France. From 2007 to 2013 he pursued Ph.D. studies in "Physical-Chemistry” at Emory University in Atlanta and Temple University in Philadelphia, and graduated in December 2013. Since 2014, he has been working at Oak Ridge National Laboratory as a Post-Doctoral Research Fellow.

February 29, 2016
Laura Newburgh, University of Toronto
Title: New Probes of Old Structure: Cosmology with 21cm Intensity Mapping and the Cosmic Microwave Background
Abstract: Current cosmological measurements have left us with deep questions about our Universe: What caused the expansion of the Universe at the earliest times? How did structure form? What is Dark Energy and does it evolve with time? New experiments like CHIME, HIRAX, and ACTPol are poised to address these questions through 3-dimensional maps of structure and measurements of the polarized Cosmic Microwave Background. In this talk, I will describe how we will use 21cm intensity measurements from CHIME and HIRAX to place sensitive constraints on Dark Energy between redshifts 0.8 -- 2.5, a poorly probed era corresponding to when Dark Energy began to impact the expansion history of the Universe. I will also discuss how we will use data from new instruments on the ACT telescope to constrain cosmological parameters like the total neutrino mass and probe structure at late times.  

February 24, 2016
Steve Hailey-Dunsheath, Caltech
Title: Probing Star Formation in the Early Universe with Submillimeter-Wave Survey Spectroscopy
Abstract: The far-infrared spectral regime contains a number of bright atomic fine-structure lines from carbon, nitrogen, and oxygen that often sum to more than 1% of the total luminosity in star-forming galaxies. These lines are sensitive, extinction-free probes of the physical conditions of neutral and moderately ionized gas in galaxies, and of the nature of star formation in these systems. I will describe efforts to develop a miniaturized spectrometer technology (SuperSpec) that will enable the construction of submillimeter-wave spectrometers capable of rapid extragalactic surveys. These instruments will be optimized for detecting [CII] 158 micron line emission from the Epoch of Reionization (z > 5), as well as carbon monoxide rotational emission from galaxies at moderate redshifts (z = 1-3). Surveys will target the spectral line emission from individual galaxies, as well as the statistical detection of galaxy emission fluctuations using the technique of line intensity mapping. I will review the current status of the fundamental technology, and prospects for instrumentation on large ground-based telescopes.

February 22, 2016
David K. Campbell, Boston University
Title: FPU and the Birth of Experimental Mathematics
Abstract: In the summer of 1953, at Los Alamos Scientific Laboratory, Enrico Fermi, John Pasta, and Stanislaw Ulam initiated a series of studies on the MANIAC-1 digital computer. These studies were aimed at exploring how simple, multi-degree of freedom nonlinear mechanical systems obeying reversible deterministic dynamics evolve in time, presumably to an equilibrium state describable by statistical mechanics. FPU’s goal was to gain insight into the fundamental question of “the arrow of time.” Their expectation was that the approach to equilibrium would occur by mixing behavior among the many linear modes. Their intention was then to study more complex nonlinear systems, with the eventual hope of modeling turbulence computationally.

The results of this first study of the so-called “Fermi-Pasta-Ulam (FPU) problem,” which were published in 1955 and characterized by Fermi as a “little discovery, ” showed instead of the expected mixing of linear modes a striking series of (near) recurrences of the initial state and no evidence of equipartition. This work heralded the beginning of both computational physics and (modern) nonlinear science. In particular, the work marked the first systematic study of a nonlinear system by digital computers (“experimental mathematics”). I will review the consequences of this remarkable numerical experiment and show how it remains of active interest still today, more than sixty years later.

See full poster here

February 15, 2016
John Appel, John Hopkins University
Title: Searching for the signature of primordial gravitational waves in the polarization of the Cosmic Microwave Background
Abstract: The detection of the Cosmic Microwave Background (CMB) in 1965 opened a window into the earliest moments of our Universe, thirteen billion years ago. Measurements of the CMB’s 2.725 K blackbody spectrum and tens of micro-Kelvin temperature anisotropies provide crucial evidence in favor of the ΛCDM cosmological model, which describes an expanding, flat Universe composed of dark energy, dark matter, and baryons. The Inflation paradigm extends ΛCDM by proposing a period of exponential expansion in the first 10-35 seconds. This expansion enlarged quantum fluctuations to macroscopic scales that seeded the CMB anisotropies and large-scale structure we see today. In particular, Inflation models predict primordial gravitational waves that leave a characteristic “B-mode” imprint in the polarization pattern of the CMB. In this talk, I will review the state of B-mode measurements and describe two current efforts: 1) The Atacama B-mode Search (ABS) began observing from the Atacama Desert of Chile in 2012 with a novel warm Half-Wave Plate (HWP) polarization modulation scheme and a 150 GHz feedhorn-coupled Transition Edge Sensor (TES) bolometer array. Ongoing analysis will yield new constraints on the B-mode amplitude over a 2,400 deg2 sky patch. 2) The Cosmology Large Angular Scale Surveyor (CLASS) will distinguish the CMB from polarized dust and synchrotron emission through multi-frequency coverage (40, 90, 150, 220 GHz). It will take advantage of Variable Delay Polarization Modulators (VPM) and access to 70% of the sky to map large-scale CMB B-modes. Deployment to the Atacama site has begun.

February 10, 2016
Elena Rasia, University of Michigan and Observatory of Trieste
Title: Clusters of galaxies as a window into cosmology and astrophysics
Abstract: Future extragalactic surveys aim at elucidating the formation and the evolution of cosmic structures and, ultimately, the interaction between the constituents of the universe: baryons, dark matter, and dark energy. Clusters of galaxies are optimal targets for such investigations since their structural and thermodynamical properties facilitate multi-wavelength observations up to high redshift.  I will review my past and recent efforts to establish a robust theoretical framework crucial for the interpretation of the large amount of upcoming data from future missions.

February 8, 2016
He Wang, UC Berkeley and Lawrence Berkeley National Laboratory
Title: Interfacial Engineering and Optical Dynamics in Organic and Perovskite Solar Cells
Abstract: Organic and organic-inorganic hybrid perovskite semiconductors have been utilized in optoelectronic devices including solar cells due to their unique optoelectronic properties. The fundamental understanding of the static and dynamic processes in organic and perovskite solar cells could provide a guide for optimized device efficiency.

The interface between inorganic electrodes and organic active layers plays an important role in organic electronic devices since this interface dictates energy level alignment as well as the injection, extraction, and recombination of carriers. We elucidate the structural and electronic characteristics of the interfaces between organic semiconductors and inorganic electrodes and study how such interfaces affect device characteristics of organic solar cells.

The relationship between crystal structure and the strength of the exciton binding energy could provide a guide for rational design of organic-inorganic hybrid perovskite, a material for high power conversion efficiency solar cell devices. We explore exciton and free charge dynamics in perovskite via temperature-dependent ultrafast laser spectroscopy. Our findings suggest that methylammonium lead iodide behaves like a non-excitonic semiconductor in the tetragonal phase and an excitonic semiconductor in the orthorhombic phase.

February 3, 2016
Norbert Werner, Stanford University
Title: Sculpting the visible Universe: Mergers, supermassive black holes and star formation
Abstract: In the course of structure formation, only a small fraction of the baryons turned into stars - most remain in a diffuse intergalactic medium. The growth and evolution of galaxies is controlled by mergers and by feedback processes, such as energy and momentum input from supernovae, and from the jets and winds of accreting supermassive black holes. I will start my talk by presenting recent observational results on the role of supermassive black holes in suppressing star formation in the most massive galaxies, keeping them 'red and dead’. Then, I will show how merger induced `weather’ in the intergalactic medium, including cold fronts, affects the evolution of clusters of galaxies. Eventually, I will `zoom out' to the outskirts of galaxy clusters where X-ray observations with the Suzaku satellite reveal a remarkably homogeneous distribution of iron, requiring that most of the metal enrichment of the intergalactic medium occurred before the clusters formed, probably more than ten billion years ago, during the period of maximal star formation and black hole activity. Finally, I will talk about the upcoming ASTRO-H satellite which will revolutionize X-ray spectroscopy and our understanding of how feedback processes couple to the hot intergalactic medium.

February 1, 2016
Tang Ba Hoang, Duke University
Title: Tailoring light-matter interaction at nanoscale for new generation of high efficiency optoelectronics
Abstract: Recent advances in materials science have driven research activities in the fields of optoelectronics and nanophotonics to a new high level where the generation, control and detection of light at the nanoscale are critically important. Because of this, study of how optical and electronic properties are modified in individual nanostructures has become crucial and subsequently drives the optimization of nanostructures for desired applications. Furthermore, in order to move current proof-of-concept nanodevices to high-performance, compact optoelectronic devices, nanoscale materials have to fulfill a list of challenges such as broadband, room-temperature operation and highly efficient. Fortunately, these challenges can be addressed thanks to recent developments in the field of nanophotonics which offers great opportunities to control the light-matter interaction at the nanoscale. In this talk, I will discuss new approaches in the design and use of nanoscale optical cavities and antennas to manipulate the spontaneous emission rate of nanomaterials. I will show that by engineering photonic crystal cavities and plasmonic nanopatch antennas, one can achieve great flexibility in tailoring the light-matter interaction at the single quantum emitter level. For instance, the spontaneous emission rate of colloidal quantum dots can be increased by a 1000-fold while having a high radiative quantum efficiency. I will also illustrate in detail how to engineer plasmonic nanostructures which can achieve almost 100% light absorption at a selective wavelength. By interfacing plasmonic nanostructures with 0D and 2D materials, I will discuss how to develop next generation of optoelectronic devices such as high efficiency solar cells and photo-detectors.

January 27, 2016
Tom Essinger-Hileman, John Hopkins University
Title: Searching for the Signature of Inflation in CMB Polarization: the ABS and CLASS experiments
Abstract: The cosmic microwave background (CMB) offers a unique glimpse into the state of the young universe, providing a wealth of information about its structure and constituents. CMB polarization also provides a window onto the first moments after the Big Bang through its sensitivity to inflationary gravitational waves, which leave a distinctive curl (B mode) component in the CMB polarization, as opposed to the dominant divergence (E mode) component. I will describe two experiments based in the Atacama Desert of Chile that aim to detect and characterize B modes: (1) the Atacama B-Mode Search (ABS) operated for three seasons with ongoing data analysis yielding new constraints on B modes soon; and (2) the Cosmology Large Angular Scale Surveyor (CLASS), a multi-frequency array of telescopes that is unique in aiming to measure the B mode signal on the largest angular scales from the ground. CLASS will also make cosmic-variance-limited measurements of large-scale E mode polarization, improving constraints on the redshift of reionization and the sum of the neutrino masses. Measuring and characterizing B mode polarization would provide confirmation that inflation occurred, our first evidence of quantum gravitational effects, and a probe of physics at grand-unified theory (GUT) energy scales. I will review the observational challenges in making these measurements and prospects for the future.

January 20, 2016
Eric Detsi, University of California at Los Angeles (UCLA)
Title: Earth-Abundant Nanoporous Metals: New Avenues for Large-Scale Energy Conversion and Storage Applications
Abstract: Meeting our society’s energy challenge remains a significant research topic and nanostructured materials are expected to play a central role in future energy harvesting & storage technologies. In line with these goals, dealloyed nanoporous metals and their composites exhibit unique properties that cannot be observed in dense metal counterparts. These exceptional properties include electric charge-induced reversible strain, localized surface plasmon resonances, and some remarkable catalytic properties. In this talk, I will present research involving the exploitation of nanoporous metals and their composites in energy conversion and storage technologies. The first topic will focus on the potential of high surface-to-volume ratio nanoporous metals as energy-efficient actuators, which can operate at lower voltages than standard piezoelectric actuators. The second section will explore plasmon-induced hot carrier science and technology in nanoporous metals. Here I will show that monolithic nanoporous metal films can be used to capture sunlight and convert it into an electrical current. The third topic will involve the sustainable production of hydrogen. Here I will present our recent work on the development of earth-abundant nanoporous metal composites for usage as highly active and robust water oxidation electrocatalysts [1]. Finally, the last topic will be on the development of earth-abundant nanoporous metals for next generation Li-ion and Na-ion battery anodes. In all cases, the unique nanoscale architecture of these materials enables new science and new applications.
[1] E. Detsi et al. Energy & Environmental Science (2016). DOI: 10.1039/c5ee02509e

January 13, 2016
Mohamed A. Gharbi, Department of Physics, McGill University
Title: Energy Stored in Soft Matter: A New Toolkit for Directed Assembly of Advanced Materials.
Abstrat: The opportunities for guiding assembly using elastic energy stored in soft matter are wide open. The emerging scientific frontiers in this field show an exceptional promise for significant new applications. Since soft materials can be readily reconfigured, there are unplumbed opportunities to make responsive devices including smart windows for energy efficiency, and responsive optical structures. In the other hand, the trapping of colloidal objects at interfaces between immiscible fluids has proven to exhibit incredible abilities to template the arrangement of particles into rich ordered structures. These structures are controlled by lateral forces that compete with capillary forces. However, these interactions are still unexplored when particles are trapped at the interface of an ordered fluid, such as a liquid crystal. In this talk, I will present recent progress in understanding the mechanisms that govern interactions between particles at liquid crystal interfaces. I will report how the resulting potential induced by the interplay between elasticity and capillarity could lead to new opportunities for genuine spontaneous self-assembly and create new strategies for making new generation of advanced materials that may find relevance in many applications in the field of energy technology.

November 11, 2015
John Howell, University of Rochester
Title: Physics of Invisibility
Abstract: Invisibility has fascinated mankind for thousands of years. It represents the ultimate protection, evasion and ability for reconnaissance. In this talk, I will outline some informal definitions of cloaking and invisibility. I will then discuss several techniques that are currently being pursued to achieve broadband omni-directional invisibility ranging from metamaterials to ray optics.

October 14, 2015
Guoqing Lin, Dept. of Marine Geosciences, RSMAS, Univ. of Miami
Title: Seismic imaging in tectonically and volcanically active regions
Abstract: Seismic velocity and attenuation of compressional (P) and shear (S) waves (Vp, Vs, Qp, and Qs) and their respective ratios provide essential constraints on Earth properties because of their sensitivity to rock composition, fluid content, thermal effect, and other factors. Seismic tomography has been an important tool for the determination of three-dimensional velocity structure. However, attenuation inversion has generally fallen behind velocity studies mainly because of the data scattering, inversion complexity and interpretation difficulty. Here, I use the Island of Hawaii as a case study to show how seismologists combine results from earthquake relocation, focal mechanism, seismic velocity inversion, and attenuation tomography to study the seismic-volcanic-tectonic relationships in a magmatic system. I also apply a state-of-the-art technique to estimate in situ Vp/Vs ratios for similar event clusters by using P- and S-wave differential times from waveform cross-correlation. This approach provides highly precise results for near-source regions because cross-correlation can measure differential times to within a few milliseconds and can achieve a precision of 0.001 in the estimated Vp/Vs ratio, corresponding to about 0.0004 in Poisson’s ratio. These recent seismological studies provide a complementary definition of the magmatic system in Hawaii to the existing velocity models.

September 16, 2015
Akira Chiba, Department of Biology, University of Miami
Title: The social proteins
Abstract: Proteins are social just like we humans are. An atypical way to study the network of people would be to isolate individuals and then line them up. A more commonsensical way would be to observe them socialize naturally. The challenge that applies to all forms of life, however, is that an individual protein comes in about a billionth of us in size. Since its 1994 introduction, green fluorescent protein has been used to tag numerous proteins. We employ a simple imaging logic: with proteins A and B each tagged with a spectrally overlapping fluorescent protein variant, resonance energy transfer described by Förster (FRET) that occurs between such tags serves as a proxy for interaction between A and B. In our experiment, we quantify the protein-to-protein FRET that results from re-introducing an unspecified number of wild type proteins back to their natural environment after equipping each with a ‘wearable’ fluorescent tag and then capturing their otherwise natural interactions en masse over a period of at least a hundred times longer than their typically short-lived rendezvous within a living animal. This seminar will take you along our recent expedition into the brain of a Drosophila embryo.

2014-2015 Academic Year

March 24, 2015
Prof. Eduardo Guendelman, Ben Gurion University of the Negev, Beer Sheva, Israel
Title: Schwarzschild metric and Friedmann equations from Newtonian gravitational collapse
Abstract: As is well known, the $0-0$ component of the Schwarzschild space can be obtained by the requirement that the geodesic of slowly moving particles match the Newtonian equation. Given this result, I will show that the remaining components can be obtained by requiring that the inside of a Newtonian ball of dust matched at a free falling radius with the external space determines that space to be Schwarzschild, if no pathologies exist. Also I am able to determine that the constant of integration that appears in the Newtonian cosmology coincides with the spatial curvature of the FLRW metric. These result are interesting by themselves and also suggest a new way to approach how one could teach GR.

February 11, 2015
Prof. Robert Brewster, California Institute of Technology
Title: Noise and competition in gene expression: the biophysics of cellular inconveniences
Abstract: Resources in the cell are limited and typically shared. This is especially acute in the process of transcription where the proteins involved often exist in similar copy number to their total number of DNA target sites. This shared demand for and scarcity of protein resources contributes to the difficulty inherent in quantitative predictions for transcription: the cellular environment is noisy and interconnected. In this talk I'll show how an approach combining rigorous theoretical models with precision measurements made possible by synthetic biology techniques provides a powerful framework for finding the biophysical rules controlling these cellular inconveniences and their influence on gene expression.

February 9, 2015
Prof. Mason Klein, Harvard University Center for Brain Science
Abstract: What do animals do, and how do they go about doing it? More specifically, what physically occurs at each step starting with an animal sensing a stimulus input and ending with it performing a meaningful behavioral output? These fundamental neuroscience questions become tractable when applied to simpler model organisms. I will describe recent work investigating the fruit fly larva's response to temperature changes, from sensory input, to neuronal circuit processing, to navigational output. A modified 3D microscope system optically measures calcium and voltage dynamics in neurons in vivo, revealing temperature-sensing cells and downstream processing circuitry. And precise quantification of crawling motion in navigating larvae establishes rules that govern transitions between behavioral modes, even leading to mathematical filters that can predict the animal population's actions. Taken together, the results point toward a more complete understanding of the path from sensing to response, with devices and techniques that should readily apply to other stimuli and other organisms.

Wednesday, February 4
Prof. Frank Weinert, California Institute of Technology
Title: The Transcription Factor Titration Effect
Abstract: Models of gene regulation in cells are often built around a picture of regulatory proteins called transcription factors acting on a single copy of their target gene. However, this idealization ignores that fact that transcription factors are often shared between multiple genes simultaneously, with the binding strength from one to the next being quite different. Beyond that, genes often exist at high copy numbers, in multiple, identical copies on the chromosome or on plasmids or viral vectors with copy numbers in the hundreds, making this competition effect even more acute.
In my talk I will present a statistical mechanical model that characterizes the interplay between the supply and demand for transcription factors in cells and the resulting effect on gene expression. Using video microscopy, we measure this effect and demonstrate the parameter-free predictive power of the thermodynamic model as a function of the transcription factor copy number and the number and affinities of the available specific binding sites; such predictive control is important for the understanding of gene regulation and the desire to quantitatively design the output of genetic circuits. With our understanding of the titration effect in hand, I then show how to use these experiments to measure the dynamics of the plasmid copy number during the cell cycle.

February 2, 2015
Prof. Nan Jing, Department of Chemistry, Northwestern University
Title: An Insight into Single-Molecule Processes via Nanoimaging and Nanospectroscopy
Abstract: This talk explores a new path forward toward the goal of probing single-molecule processes via Nanoimaging and Nanospectroscopy. The combination of scanning tunneling microscopy imaging and optical spectroscopy will be discussed as a means to raise both the spatial and spectral resolution of molecules to an unprecedented level. At the beginning of this lecture, I will show how imaging with sub-molecular resolution has been achieved by either inserting buffer layer under the molecules or modifying the scanning probes. Then, I will discuss methods for controlling the formation of nanostructures by tuning (i) the coverage of molecular adsorbates, (ii) the temperature of the substrate, and (iii) the external electric field. Next, I will focus on recent advances in a new nanoscale vibrational spectroscopy (tip-enhanced Raman spectroscopy): quantitatively identifying multiple vibrational modes of large polyatomic molecular adsorbates with molecular resolution imaging, understanding the interaction between adsorbates and the surface with intramolecular vibrational distribution. Finally, I will discuss how this improved understanding of single-molecule processes on surfaces presents new opportunities for the study of solar energy conversion and storage.

January 29, 2015
Prof. Christoph Keplinger, Department of Chemistry and Chemical Biology, Harvard University
Title: Soft Machines: From Artificial Muscles and Renewable Energy to Stretchable Ionics and Bionic Skin
Abstract: The biological world and the engineered world differ in terms of mechanics: man-made machines are built from hard materials, while nature predominantly uses soft materials. The elegance of nature’s design inspires scientists to create soft machines. This talk starts with an elementary component: artificial muscles, materials that deform in response to external stimuli. Two approaches are presented to achieve giant voltage-induced deformation of an elastomer: electrode-free actuators, and actuators that harness snap-through instabilities. Subsequently, soft generators are identified as unique tools for electricity generation. Based on principles used in classical thermodynamics, experimental and theoretical methods are introduced to assess the maximum electrical energy that can be generated. Natural rubber is found to be a prime material for sustainable, high-power energy generation from ocean waves. Soft machines require electrical conductors with special properties, such as stretchability, biocompatibility and transparency. This talk introduces stretchable ionics – a new class of devices enabled by ionic conductors that are highly stretchable, fully transparent, biocompatible and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilovolts. The electromechanical transduction is achieved without electrochemical reaction. Initial demonstrations include: i) a transparent, large-strain actuator, ii) a transparent, full-range loudspeaker, and iii) bionic skin that senses strain and pressure. Ideas for future research give an outlook on exciting opportunities in soft matter science.

January 26, 2015
Prof. Albert Siryaporn, Department of Molecular Biology, Princeton University
Title: Regulation of bacterial pathogenesis by mechanical cues
Abstract: My work explores the role of mechanical forces in bacterial pathogenesis at the interface of biophysics and molecular genetics. During the course of an infection, bacteria encounter a variety of mechanical forces such as adhesive forces during contact with the host cells that they infect and shear stresses in fluidic environments. Using a mechano-genetic approach that I have developed, I found that bacteria use mechanical cues (1) to detect the presence of host cells and (2) to guide the expansion of large bacterial populations within host organisms. In particular, my work shows that the major pathogen Pseudomonas aeruginosa detects the presence of host cell surfaces, akin to a bacterial sense of touch. This mechanical cue activates virulence and consequently P. aeruginosa, unlike other pathogens, does not rely on a chemical signal specific to any one host. This novel paradigm provides a long-sought explanation for understanding how P. aeruginosa can infect a broad range of hosts including humans, animals and plants. My findings highlight mechano-sensation as an important signaling class for pathogenesis and suggest alternative strategies for combatting bacterial infections. The ubiquity and diversity of mechanical forces in all aspects of a bacterium’s life have far-reaching consequences within and beyond pathogenesis and thus constitutes an important novel avenue of research. Moving forward, my laboratory will employ mechano-genetic techniques to understand how diverse bacteria sense, interpret and translate mechanical signals.

January 21, 2015
Prof. Xuefeng Wang, Physics Department & Institute of Genomic Biology, University of Illinois at Urbana-Champaign
Title: Cellular Forces Studied by DNA-based Molecular Force Sensor and Modulator
Abstract: Mammalian cells are remarkable force processors. Cells adhere through membrane protein integrins and generate forces on integrins to probe the local environment. These forces regulate many fundamental cellular functions such as cell adhesion, proliferation, migration, and ultimately stem cell differentiation and cancer progression. Because of its critical importance, integrin force has long been a central topic in the field of cell mechanics. To study integrin forces at the molecular level, I developed a DNA-based force sensor and modulator termed tension gauge tether (TGT) which quantitatively reports and controls cellular forces on integrin molecules. Using TGT, I systematically studied the ranges and physiological roles of integrin forces and discovered two distinct force regimes: cell membrane generates ~40 pN molecular force on integrins to regulate cell adhesion and spreading, while cytoskeleton generates >54 pN molecular force on integrins to regulate cell polarization and migration. This work demonstrated the versatility of integrins and shed light on the mechanism how cells adjust integrin molecular tensions to regulate different cellular functions. TGT was also applied to study other mechano-sensitive proteins including cadherins and Notch receptors. Overall, TGT provides a novel avenue for the study of cell mechanics at the molecular level. In the future, I will apply TGT to study a series of mechanical–involved cellular processes such as kinase activation, durotaxis and endocytosis, and develop TGT-derived biomaterials for biomedical applications.

January 14, 2015
Prof. Raul Monsalve
Title: Characterizing Cosmic Dawn through Observations of the 21-cm Line
Abstract: A key objective in cosmology consists of characterizing the evolution of the universe after the release of the cosmic microwave background (CMB). One way of tracking the formation of the first generations of compact objects in the range 40 > z > 6 is through observations of the 21-cm line emitted by neutral atomic hydrogen (HI) in the intergalactic medium (IGM) due to the hyperfine splitting of its ground state. Models have been developed for this observable as a function of redshift, and precise estimation of their parameters would allow constraining the physics of structure formation before 1 Gyr after the Big Bang. Due to expansion, the HI signal must have been shifted from 1.4204 GHz down to the VHF range, and therefore its detection is being attempted through interferometric and global (spatially averaged) observations at frequencies between 40 and 200 MHz. The talk will describe my participation in the project called “Experiment to Detect the Global EoR Signature (EDGES)”, which is currently operating in the desert of Western Australia. This instrument represents the state of the art in global measurements of the 21-cm signal from the epoch of reionization (EoR), corresponding to 15 > z > 6. In addition, the talk will summarize the goals and status of low-frequency radio astronomy, which extends beyond cosmology into several areas of astrophysics. Finally, it will describe the efforts of a project called MARI-UCSC that attempts to find radio-quiet locations in the chilean Atacama Desert, which could become sites for conducting competitive low-frequency observations.

January 12, 2015
Prof. Matthew White
Title: Thin-film organic and hybrid optoelectronics
Abstract: Organic and hybrid materials offer unique physical properties and challenges. Their application in optoelectronic devices, including photovoltaic cells and LEDs, creates a promising pathway towards future technologies. The active devices are large-area but only several hundred nanometers thick, on the order of the wavelength of visible light. The quasi-two-dimensional nature may be exploited in realizing flexible, stretchable, lightweight devices and potentially large-scale power generation from solar energy. Unsolved fundamental and technical challenges remain in the pursuit of these goals.

I will present advances in the electron selective contact materials, the device substrates, and in organic semiconductors themselves. Zinc oxide, cross-linked polyethylenimine, and combinations of the two are demonstrated as air-stable electron selective contacts. The low cost of these materials render them very attractive options for mass production of photovoltaics. Substrate materials constitute nearly 100% of the mass and volume of organic photovoltaic devices. Ultrathin plastic foils and even printing paper are demonstrated as the physical supporting substrate for photovoltaics and LEDs. The unique substrate materials provide remarkable physical and processing properties, but present distinct challenges. Lastly, I will discuss the potential of inter- and intra- molecular charge transfer to realize high efficiency without sacrificing cost, production volume, or toxicity.

December 3, 2014
Prof. Paul Francois
Title: In silico evolution and application to immune detection
Abstract: Despite recent advances in systems biology, it is unclear how specific dynamical properties (the “phenotype”) emerge from the complexity of biochemical interactions. I will describe an inverse problem approach: I am using computational evolution to reconstruct simplified networks performing a predefined biological function. I will illustrate the predictive aspect of this approach on the problem of immune detection, that led us to the discovery of a general mechanism that we named “adaptive sorting”, an instance of which is present in mammalian T-cell biochemical networks.

November 19, 2014
Prof. Armin Fuchs
Title: Diffusion Tensor Imaging and its Applications to Concussions in Football Players
Abstract: Mild traumatic brain injuries (MTBI), in most cases, cannot be detected using imaging modalities like CT or MRI. However, diffusion tensor imaging (DTI) reveals subtle changes in white matter integrity as a result of head trauma and plays an important role in refining diagnosis and management of MTBI. We use DTI to detect the microstructural changes in collegial football players induced by axonal injuries and to monitor their evolution during the recovery process. Three players suffered a MTBI during play or practice and underwent scanning within 24h with follow-ups after one and two weeks. Scalar diffusion indices were derived from diffusion tensors and analyzed using tract-based spatial statistics (TBSS) and voxel-wise t-tests to detect brain regions showing significant group differences between the injured subjects and controls. Both analyses revealed overlapping regions in the corticospinal tract with significant increase in fractional anisotropy and decreases in transverse and mean diffusivity within 24h. In voxel-wise t-tests strong indications for recovery were found spatially and temporally. For mean and transverse diffusivity, regions showing significant differences shrunk between the first and the follow-up scans. Although the sample size is small, these findings are remarkably consistent across all subjects and scans.

November 12, 2014
Jose' Feliciano Benitez
Title: Status of the Higgs Boson Measurements at the Large Hadron Collider
Abstract: Following the discovery of a new Higgs-like particle in 2012, the 2013 Nobel Prize in Physics was awarded for the theoretical prediction of the Higgs mechanism in the 1960’s. This mechanism describes the process by which fundamental particles attain their mass and predicts the existence of a scalar particle: the Higgs boson. An intense search for this particle has been ongoing with the experiments at the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland. I will present an overview of the current observations made with the CMS and the ATLAS experiments and will show the progress in the studies of the compatibility of the new particle with the Higgs boson of the Standard Model. Finally, I will report on the status of the experiments and their expected restart after a two year shutdown.

Biography: Dr. Benitez obtained his Ph.D. at Stanford University (2011) working in the BABAR experiment at the SLAC Linear Accelerator Center in Menlo Park, California. Since 2011 he worked as a research fellow at CERN in Geneva, Switzerland on the search for Higgs boson decays to tau leptons in the CMS experiment and was one of the leaders for the recent publication of this search. Dr. Benitez is now a member of the ATLAS collaboration and a postdoctoral scholar at the University of Iowa.

November 5, 2014
Prof. Boris Ya. Zeldovich
Title: Up and Down Asymmetry of Light’s Electric Field and Other Properties of Polarization.
Abstract: Are up and down directions of electrical field of light always equivalent? No, there are important and common cases when they are not equivalent. Theory and experiments on the fields with spectrum broader than octave will be described. Those include Second Harmonic Generation (SHG) and Nobel-Prize awarded technique of femtosecond Laser Frequency Combs (LFC). Other polarization properties of optical processes will be described in the talk, accompanied by the demonstration of the educational tool on the floor (bi-frequency pendulum on a rotary platform, developed by Prof. M. J. Soileau and B. Ya. Z.)

Boris Zeldovich received his Doctor of Physical and Mathematical Sciences degree from the Lebedev Physics Institute in Moscow, Russia and is currently a Professor of Optics and Physics at CREOL-UCF. He is the co-discoverer of optical phase conjugation. He predicted and discovered experimentally the giant optical nonlinearity of liquid crystals, which is 10^10 times stronger than for usual media. He predicded and discovered expeimentally polar asymmetry of optical fields He is currently pursuing theoretical description of electrodynamics of Volume Bragg Gratings (VBG). He is a Member of the USSR (nowadays Russian) Academy of Science. Awards & Honors: Elevated to the status of Fellow of the Optical Society of America 1997 OSA Max Born Award in Physical Optics 1987 Elected Member of the USSR Academy of Sciences 1983 USSR State Prize

October 29, 2014
Prof. Laura Newburgh
Title: Measuring Dark Energy with CHIME
Abstract: The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a new radio transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use the 21cm emission line of neutral hydrogen to map baryon acoustic oscillations between 400-800MHz across 3/4 of the sky. These measurements will yield sensitive constraints on the dark energy equation of state between redshifts 0.8 -- 2.5, a fascinating but poorly probed era corresponding to when dark energy began to impact the expansion history of the Universe. I will describe theCHIME instrument, the analysis challenges, the calibration requirements, and current status.

Biography: Dr. Laura Newburgh is currently a postdoctoral fellow at the Dunlap Institute at the University of Toronto working on CHIME, a new radio telescope. Her previous experience has focused on polarized measurements of the Cosmic Microwave Background: first at Columbia University where she received her Ph.D. in 2010, and then at her first postdoctoral position at Princeton University from 2010-2013.

October 15, 2014
Prof. Michael Smith
Title: Jets in Astrophysics: the known unknowns.
Abstract: Supersonic jets are observed to emanate and propagate vast distances from many objects including tiny comets, protostars and supermassive black holes. In this Colloquium, the physics will be discussed. Why are they almost ubiquitous? How diverse are the driving mechanics, composition and structure? These questions will be discussed before going deep into how they feed back into their environments, often regulating their own formation and inhibiting surrounding star formation and galaxy growth. Current unexplained phenomena will be listed and answers requested.

Biography: Michael Smith is Professor of Astronomy at the University of Kent where he is Director of the Centre for Astrophysics and Planetary Science and Director of the Kent Space School. He is also a Fellow of the Royal Astronomical Society and a member of the International Astronomical Union. He studied at Imperial College, London, and Magdalen College, Oxford. Neils Bohr is his PhD great-grandfather. He has gone on to write two books, written over 200 scientific papers and is Editor-in-Chief of an international journal. He has lived in Australia, USA, Germany, Italy and the Netherlands, as well as Ireland, Scotland and England. In the USA, he worked at the universities of Illinois, Iowa and Maryland. He has used space and earth telescopes as well as computer simulations to study stars, galaxies and black holes. He has recently been commissioned by UNESCO, NASA and the Saudi Arabian government as a reviewer. He has contributed to television, radio and newspapers, acted as expert witness, and held many public lectures.

September 24, 2014
Prof. Jin He
Title: Nanopore for sensing and imaging
Abstract: In recent years, molecular scale nanopores formed in thin biological and synthetic membranes have emerged as versatile new tools for single molecule analysis and detection. One outstanding example of nanopore application is DNA sequencing. In this talk, I will review the recent progress of nanopore research and present our research of fabricating new types of nanopores and using them for single molecule analysis. To improve the sensing capability of nanopore, recognition tunneling technique has been explored as a new sensing method for nanopore devices. In the end, I will also show our research of using nanopore as a probe in scanning probe microscopy for living cell imaging.

2013-2014 Academic Year

March 31, 2014
Prof. Pedro Ferreira
Title: Testing General Relativity with Cosmology
Abstract: With the successes of observational cosmology, a new window has opened up on to gravitational physics. By carefully measuring the morphology and growth of structure in the Universe it may be possible to constrain general relativity on a completely new range of scales. It also allows us to explore a plethora of modified gravity theories that have emerged as an attempt to explain the observational evidence for dark energy. I will discuss the challenges and approaches which are being taken in this new field

February 17, 2014
Prof. Sunxiang Huang
Title: Broken Symmetry and Magnetic Skyrmions
Abstract: Broken symmetry is a fundamental concept in physics. The broken symmetries at phase transitions, such as those at the gaseous/solid and the paramagnetic/ferromagnetic transitions,are familiar examples. In cubic B20 magnets, however, it is the inversion symmetry and the 4-fold rotation symmetry that are broken. The broken inversion symmetry leads to the Dzyaloshinskii-Moriya (D-M) interaction, which dictates not an aligned ground state but a spin helix, and in addition,an exotic magnetic skyrmion state with a new type of topological spin texture. Magnetic skyrmions, with a double-twist spin structure on the nanometer scale, carry a topological charge and a Berry phase in real space. Magnetic skyrmions not only provide a novel route to study the topological nature of magnetic defects but also exhibit spectacular static and dynamic properties. Among the various unusual properties, I'll describe our experimental results of the direct consequence of the broken rotation symmetry in the electric transport properties, and the determination of the intrinsic resistance of the spin helix. In bulk B20 crystals, the skyrmion state exists only in a very small region in the phase space of a few K and a narrow magnetic field range, which is not amenable to exploration of magnetic skyrmions for new spintronic phenomena let alone devices. I will describe the realization of epitaxial B20 FeGe thin films with greatly expanded skyrmion state in phase space covering the entire temperature range up to the Curie temperature and in a much larger field range.

February 13, 2014
Prof. Emil Mottola, Los Alamos National Laboratory
Title: New Horizons on Gravity: Dark Energy & Condensate Stars Abstract: Both the black hole information paradox and the existence of vacuum dark energy indicate that something basic is missing in the gravitational sector of the Standard Model at macroscopic distance scales. In an Effective Field Theory (EFT) approach the trace anomaly must play a special role in the EFT of low energy gravity. The conformal anomaly implies the existence of a new long range massless scalar degree of freedom in gravity, not present in the classical Einstein theory, which have long range gravitational effects, significant in the vicinity of black hole horizons.
The fluctuations of the anomaly scalar also imply that the cosmological term is not a constant but a kind of gravitational condensate which is state dependent and runs to zero in the infrared. These considerations suggest a completely non-singular quantum final state of gravitational collapse in which the classical black hole event horizon is replaced by a thin shell, and its interior is replaced by a vacuum condensate with dark energy eq. of the state, p= - rho. Gravitational condensate stars have a modest entropy and do not suffer an information paradox. Cosmological dark energy then appears as a finite volume Casimir effect of the Hubble scale.

February 12, 2014
Prof. Rhoda Dzakpasu, Georgetown University
Title: The balance of plasticity and stability in an in vitro network of neurons
Abstract: The brain is a unique complex dynamical system. Not only does its emergent properties stem from the complex interactions between its fundamental unit, the neuron, but the individual neurons themselves are also complex systems. Emergent activity, detectable in the form of collective rhythmic dynamics, arises from networks of neurons and these dynamics are vital for cognitive functions such as attention, memory formation, learning and sleep. A major challenge for the brain is to maintain a stable operating state while retaining sufficient adaptability to grow while experiencing the requisite plasticity to response to external stimuli. As a result, the manner in which these two opposing constraints reconcile remains an open question. I will discuss the complexity of neurons and some results from our lab that explores how an in vitro network of hippocampal neurons attempts to achieve this balance.
My talk will be tailored towards a broad audience. I will provide an introduction of the topic of our research along with the general context of some of the big questions and outstanding issues in dynamical neuroscience. This will also help to motivate why a physicist would be interested in this field of study. I will finish with a discussion of how our current research fits into this wider context.

February 5, 2013
Prof. Askin Kocabas, Harvard University
Title: Controlling neural dynamics to evoke complex behaviors in C. elegans
Abstract: The brain is the most complex network in nature. Remarkably, its massive interactions can orchestrate complex internal dynamics to generate precise and robust behavioral outputs. Understanding the detailed network dynamics leading specific behaviors is a challenging task even in the simplest nervous system of nematode Caenorhabditis elegans (C. elegans), which has only 302 neurons interconnected through 7000 synapses. To approach this challenge we asked whether we could control the dynamics of neural network well enough to be able to evoke specific behaviors. To make this approach possible, we combined optogenetics and novel imaging systems that could visualize, identify and specifically illuminate the neuron(s) of interest to drive any pattern of electrical activity in the nervous system of freely moving C. elegans. As a particular example, we used this system to control chemotactic behavior of C. elegans. During chemotaxis, the nervous system processes environmental information received through the sensory neurons and coordinates all necessary motor activities leading animal to food. We discovered that controlling the dynamics of activity in one key pair of interneurons was sufficient to evoke this complex behavior. By remotely controlling this pair of neurons we could make the animal to turn right or left, go forward or backward and finally make it to track virtually defined chemoatractive gradients or more complex spatial profiles. In this talk, I will start by describing the challenges and our achievements to control neural activity patterns to evoke behavior in a virtual environment. Next, I will describe our recent complementary tools and techniques for brain-wide imaging of neural activities in a freely moving C. elegans. Finally, I will argue that combination of these control and imaging-based approaches will provide powerful avenues for studying the complex dynamics of entire nervous systems.

February 3, 2014
Prof. Christianne Beekman, Oak Ridge National Laboratory
Title: Novel Ways to Manipulate Nanoscale Phase Separation in Complex Oxides Abstract: Complex oxides are one of the most widely studied classes of materials often composed of many elements (including transition metals), which usually results in complex lattice structures. The interplay between many competing interactions involving spin, charge, orbital and lattice degrees of freedom results in the many remarkable physical properties of complex oxides. Due to the closeness in energy of these interactions only small perturbations are required to dramatically change the physical properties of these compounds. Hence, these materials provide an excellent basis for current and future (applied) research in a number of exciting areas, such as multiferroics, magneto-optics, data storage devices and solid oxide fuel cells. An example of a perturbation that is often used is epitaxial strain, i.e. intentional lattice mismatch between a thin film and the substrate that it is grown on. Recent studies have shown that the application of strain can control and/or enhance a variety of scientifically and technologically important properties such as magnetoresistance[1], ferroelectricity and multiferroicity[2-4]. Certain transition metal oxides are of particular interest since a large amount of strain is not always accommodated through partial relaxation (i.e. uncontrolled defect formation), but rather by forming an additional polymorph with lower symmetry, resulting in well-ordered structural, electronic and/or magnetic phase separation[5]. I will discuss several examples of complex oxide thin films for which minute changes in crystal lattice (i.e. application of strain) lead to large changes in physical properties, phase coexistence and sometimes even completely new phases. Furthermore, perturbations such as magnetic and electric fields and optical excitation can be used to manipulate the phase coexistence, increase our understanding of these systems and pave the way for designing novel functionality in oxide heterostructures[6].
[1] C. Beekman et al., Phys Rev. B 83, 235128 (2011)
[2] V. Moshnyaga et al., Nat. Mater. 2, 247 (2003)
[3] H.N. Lee et al. Nature, 433, 395 (2005)
[4] G. Catalan et al. Nat. Mater. 10, 963 (2011)
[5] C. Beekman et al. Adv. Mat., 25, 5561 (2013)
[6] H.Y. Hwang et al., Nat. Mater. 11, 103 (2012)

January 29, 2014
Prof. Bharat Ratra, Kansas State University
Title: The "Standard" Model of Cosmology ... and Open Questions
Abstract: Experiments and observations over the last decade have provided strong support for a "standard" model of cosmology that describes the evolution of the universe from an early epoch of inflation to the complex hierarchy of structure seen today. I review the basic physics, astronomy, and history of ideas on which this model is based. I describe the data which persuade cosmologists that (as yet undetected) dark energy and dark matter are by far the main components of the energy budget of the universe. I conclude with a list of open cosmological questions.

January 24, 2014
Prof. Oscar Varela, Hrvard University
Title: The holography of electric/magnetic duality breaking
Abstract: he field theory defined on a stack of N M2-branes is thought to correspond to that introduced by ABJM. At large N, an important sector of this theory can be described, holographically, by the D=4 N=8 SO(8)-gauged supergravity of de Wit and Nicolai. Since its inception, the latter has been tacitly assumed to be unique. Recently, however, a one-parameter family of SO(8) gaugings of N=8 supergravity has been discovered, the de Wit-Nicolai theory being just a member in this class. I will explain how this overlooked family of SO(8)-gauged supergravities is deeply related to electric/magnetic duality breaking in four dimensions. I will then discuss some predictions that can be made about the possible family of dual field theories, focusing on the structure of conformal phases and the RG flows between them.

January 22, 2014
Prof. Johannes Seelig, Howard Hughes Medical Institute
Title: Neural circuits and representations underlying visuomotor integration in Drosophila
Abstract: The fruit fly Drosophila melanogaster performs a range of interesting behaviors, solving the task of transforming sensory information into motor output (sensorimotor integration) with a nervous system that is numerically simpler than those of most vertebrates. In addition to the increased tractability this provides for mechanistic understanding, Drosophila has many other experimental advantages, including the ability to genetically target specific sub-populations of neurons (enabling, for example, cell-type-specific activity sensing and manipulation). This makes the fruit fly an attractive model system for identifying general computational algorithms that might be conserved across species, and to understand how they are implemented in neural circuits. To understand how the brain enables sensorimotor integration, it is important to study the dynamics of neural circuits in the context of the behaviors that they are involved in. To this end, I have developed an experimental setup for two-photon calcium imaging while the fly performs visually guided tethered walking and flight behavior. This setup allows us to record the activity of selected, genetically identified populations of neurons while the fly performs a task. I have used this setup to investigate the function of neural circuits in the fly's visual system and in its central brain. I particularly focused on neural representations and dynamics in a region in the central brain of the fly that is required for innate attraction to particular visual features, for visual short- and long-term memory (including spatial memory or place learning) as well as motor coordination, and I will discuss the results of these experiments in my talk.

January 20, 2014
Prof. Benjamin Hunt, Massachusetts Institute of Technology
Title: Engineering New Electronic States in Graphene Heterostructures: Massive Dirac Fermions, Hofstadter's Butterfly and the Quantum Spin Hall Effect
Abstract: Van der Waals heterostructures represent a new and surprising direction in nanoscale device engineering: we stack isolated two-dimensional crystals to create layered structures with atomic precision. The layer-by-layer assembly allows us to introduce a new design parameter - the interlayer twist angle - which can have profound consequences for the engineering of electronic states based on tunable interactions between adjacent layers. In this talk, I will discuss recent experiments at MIT in which we have used a hexagonal boron nitride (hBN) layer to modify the electronic bands of monolayer graphene in a van der Waals heterostructure, inducing a sizable bandgap at the charge neutrality point and imparting a mass to the normally massless Dirac charge carriers. The bandgap occurs only in samples in which the twist angle between the graphene and hBN crystals is small, resulting in a long-wavelength moiré that acts as a superlattice potential; by adjusting the twist angle the bandgap can be tuned. The moiré superlattice potential also allows us to study the problem of a charged particle in a periodic potential and magnetic field - the so-called Hofstadter problem - whose theoretical solution exhibits a rare instance of fractal behavior in a quantum-mechanical energy spectrum.
I will also discuss our recent studies of weakly-coupled graphene-hBN heterostructures in which massless Dirac fermions in graphene exhibit a quantum spin Hall effect, a fascinating example of a ''symmetry-protected topological phase'' of which the more familiar contemporary examples are the edge and surface states of the topological insulators.

January 15, 2014
Prof. Chunlei Wang, Florida International University
Title: Development of C-MEMS based micropower and biosensor systems: challenge, solution and beyond
Abstract: Carbon microelectromechanical systems (C-MEMS) and carbon nanoelectromechanical systems (C-NEMS) have received much attention because of their various potential applications, such as: microbatteries and DNA arrays. Microfabrication of carbon structures using current processing technology, including focused ion beam (FIB) and reactive ion etching (RIE), is time consuming and expensive. Low feature resolution, and poor repeatability of the carbon composition as well as widely varying properties of the resulting devices limits the use of screen printing of commercial carbon inks for C-MEMS. Our newly developed 3D C-MEMS/NEMS microfabrication technique is based on the pyrolysis of photo patterned resists at high temperatures in an oxygen free environment. It is possible to use the C-MEMS/NEMS technique to create various complex 3D carbon structures, such as: high aspect ratio carbon post arrays and suspended carbon nano wires. They can have a wide variety of shapes, resistivities and mechanical properties. We demonstrat that C-MEMS/NEMS with sizes ranging from the millimeter to the micrometer and even nanometer is very possible to provide solutions, alone or in combination with silicon and other organic, inorganic, and biological materials, in miniaturized power systems (Li-ion batteries, ultracapacitors, biofuel cells) and biosensors (such as: glucose sensors and aptamer sensors).
Chunlei (Peggy) Wang is an associate professor in the Mechanical and Materials Engineering Department at Florida International University. She received her MS (1993) and PhD (1997) in Solid State Physics from Jilin University (China). Before joining FIU, she held various research positions at Osaka University (1995-2001) and University of California Irvine (2001-2006). At FIU, her group focuses on the development of micro and nanofabrication methods for building novel micro and nanostructures and synthesizing nanomaterials that have unique structures and useful properties for energy and biological applications. She published in 5 book chapters, 90 peer reviewed journal publications, and 10 patent. She is a recipient of FIU faculty award in research and creative activities (2013), FIU Kauffman Professor Award (2009), and DARPA Young Faculty Award (2008). She was a co-founder of Carbon Microbattery Corporation (now: Enevate Corp), a consultant at Intel Lab, and a guest scientist at Max Planck Institute.

December 4th, 2013
Prof. Casey W. Miller, University of South Florida
Title: Diversity Challenges Facing Physics
Abstract: The National Academies have suggested that increasing diversity in Science, Technology, Engineering, and Math will be critical to the future competitiveness of the US in these areas [1], and the leadership of both the National Science Foundation [2] and the American Physical Society is taking this seriously. Physics and Astronomy programs grant, on average, only one PhD every 5 and 10 years, respectively, to members of underrepresented groups [3]. We are therefore not surprisingly the least diverse of the sciences [4]. In this talk, I will discuss several opportunities that may help our community move toward meeting these goals, and, importantly, the potential benefits to programs and individual investigators willing to take on these challenges. The most universally applicable and easily implementable actions regard perturbing graduate admissions policies and practices [5], and employing key features of successful Bridge Programs into graduate programs [6].
[1] National Academy of Sciences, National Academy of Engineering, and Institute of Medicine, "Expanding Underrepresented Minority Participation: America's Science and Technology Talent at the Crossroads," The National Acadamies Press (2011); link
[2] Joan Ferrini-Mundy, "Driven by Diversity," Science 340, 278 (2013).
[3] Stassun, K.G., "Building Bridges to Diversity", Mercury, 34, 3 (2005).
[4] http://www.aps.org/programs/education/statistics/minoritydegrees.cfm
[5] Casey W. Miller, "Admissions Criteria and Diversity in Graduate School,"APS News, The Back Page, February 2013. link
[6] Stassun, K.G., Sturm, S., Holley-Bockelmann, K., Burger, A., Ernst, D., & Webb, D., "The Fisk-Vanderbilt Masters-to-PhD Bridge Program: Broadening Participating of Underrepresented Minorities in the Physical Sciences. Recognizing, enlisting, and cultivating 'unrealized or unrecognized potential' in students", American Journal of Physics 79, 374 (2011).

Biography: Casey W. Miller is presently Associate Professor of Physics at the University of South Florida in Tampa, where he studies nanoscale magnetism and related devices. He is Director of the new APS-Bridge Site at USF, as well as Associate Director of Physics Graduate Studies. He graduated summa cum laude from Wittenberg University in 1999 with University and Physics Departmental Honors and, where he was also elected to PhiBetaKappa. He earned his PhD from the University of Texas at Austin in 2003, notably earning the Department's Best Dissertation Award for work combining Magnetic Resonance Imaging with Scanning Probe Microscopy. He joined USF in 2007 after completing a post-doctoral fellowship at the University of California, San Diego, where he worked on spin-dependent tunneling.

November 20, 2013
Prof. Jonathan Engle, Florida Atlantic University
Title: Gravity, quantum, loops, and cosmology
Abstract: In Einstein's theory of gravity, general relativity (GR), space-time geometry is not a fixed background, but is dynamical, acting on, and reacting to, matter. A quantum theory of gravity should thus be a quantum field theory in which there is no fixed background space-time geometry, a so-called "background independent" QFT. Such a QFT is necessarily very different in structure from all previously studied QFTs. In this colloquium, we introduce the background independent quantization of GR known as Loop Quantum Gravity, as well as the path integral formulation of its dynamics, known as Spin Foams. We summarize some recent developments in the definition of the Spin Foam dynamics, as well as some recent work in application of the theory to early universe cosmology.

November 6, 2013
Prof. Mark Reeves, George Washington University
Title: From Random Walks to Brownian Motion, from Diffusion to Entropy: Statistical Principles in Introductory Physics
Abstract: Entropy changes underlie the physics that dominates biological interactions. Indeed, introductory biology courses often begin with an exploration of the qualities of water that are important to living systems. However, one idea that is often not addressed is dominant contribution of the entropy of water molecules in driving biologically important processes towards equilibrium. For students, this slight is compounded by many introductory physics courses that have deemphasized entropy, almost to the point of eliminating it entirely. In contrast, we are teaching this concept in our introductory physics and biology classes, and are collaborating to bring the pedagogical approaches of Scale-Up Physics teaching into biology instruction. From a content point of view, we strive to bring quantitative modeling into the biology class and life into the physics course.

In this talk, I will present some of the examples of cellular interactions that we use to model processes from Brownian motion, to diffusion, to packing DNA, to ligand binding. These are based on simple statistical modeling that can be taught in a way that is accessible to beginning students, and brings together ideas that they learn in their biology class with approaches to quantitative modeling that they learn in physics.

October 30, 2013
Prof. Sefaattin Tongay, University of California, Berkeley
Title: Novel Functional Two-dimensional Materials & Derivatives
Abstract: Two-dimensional (2D) materials at the quantum confinement limit are emerging as an important class of materials for innovative information, optoelectronics, and energy conversion technologies. Recent advances in 2D materials beyond graphene have opened our eyes to a new class of low-dimensional materials with extraordinary properties ranging from insulating to semiconducting and metallic and even to superconducting. 2D materials enable access to a wide range of chemical, optical, magnetic, electrical, and mechanical properties that are otherwise unattainable. These materials are not only significantly different when compared to their bulk counter-parts but they also display unusual phenomena due to the much enhanced quantum confinement in two-dimensions.
This talk will introduce these novel '2D materials' and present recent progress and discoveries made by the '2D materials & interfaces' team lead by Dr. Tongay at the University of California, Berkeley. Such discoveries include (1) tuning physical properties of 2D semiconductors by defect engineering, molecular gating and thermal decoupling, (2) unusual layered materials that behave as monolayers in the bulk limit, (3) alloys and vertical heterostructures of 2D materials, and (4) novel synthesis routes to realize large-area 0.7 nm thick monolayer materials. This talk will also address the many challenges in the emerging field of 2D materials and propose an interdisciplinary cutting-edge research program at the University of Miami.
Biography: Sefaattin Tongay is presently a postdoctoral researcher in the Department of Materials Science and Engineering at the University of California, Berkeley where he leads the '2D materials & interfaces' team. He has published 37 SCI-indexed research articles and holds 2 patents on these subjects. His work has received wide media coverage from Nature publications, Scientific American, Science Daily, Phys.org, IOP nanotechweb, Gizmag, and various other media sources. He graduated from Ege University in 2002 with the University and Physics Departmental Honors. He earned his M.Sc in Physics from Bilkent University in 2004 and Ph.D in Physics from the University of Florida in 2010. He is the winner of Tom Scott Memorial award (2009), Ege University Scientific achievement award (2002), prestigious presidential, private scholarship awards, and has been recently nominated for the Eni awards and the Chinese Academy of Sciences Fellowship Young International Scientist award.

October 16, 2013
Prof. Prem Chapagain, Florida International University
Title: Computational investigations of protein structure and dynamics
Abstract: Computational and statistical mechanical techniques have been valuable tools for investigating how a protein folds to its biologically functional configuration. In this talk, I will discuss computer simulations of protein structural conversion in amyloid proteins as well as protein dynamics of fluorescent proteins. Alpha-helix to beta-sheet transition is a frequently observed process in protein aggregation and fibrilization of amyloidogenic proteins. Such structural transitions are implicated in a variety of neurodegenerative diseases such as Alzheimer's, Parkinson, Huntington and prion diseases and are considered to be the result of protein misfolding. A detailed molecular-level understanding of the formation process of amyloid fibrils is crucial for developing methods to slow down or prevent these horrific diseases. Another topic of the talk will be the protein-chromophore interactions in Fluorescent Proteins (FP). Fluorescent proteins are extremely valuable biochemical to! ols in molecular and cell biology research. Computational investigations of the protein barrel flexibility and chromophore interaction provide important insights that can help design novel fluorescent proteins (RFP) with improved photophysical properties.

October 2nd, 2013
Prof. Alex Mahalov, The Wilhoit Foundation Dean’s Distinguished Professor, Arizona State University
Title: Multi-Scale Dynamics and Laminated Structures in the Upper Troposphere and Lower Stratosphere (UTLS)
Abstract: This talk focuses on physics-based predictive modeling of shear-stratified dynamics and multi-scale mechanical and optical turbulence. High-resolution mesoscale and microscale simulations of wave breaking and laminated structures induced by jetsream and mountain waves in the upper troposphere and lower stratosphere (UTLS) are presented for the Terrain-induced Rotor Experiment (T-REX), Owens Valley, CA and Hawaii campaigns of atmospheric measurements. To resolve multi-scale physical processes in the UTLS region, vertical nesting and adaptive vertical gridding have been developed and applied in the nested mesoscale/microscale simulations. The fully three dimensional, moist, compressible Navier-Stokes equations are solved to characterize multi-scale, shear-stratified dynamics in the UTLS region. For nesting, both lateral and vertical boundary conditions are treated via relaxation zones where the velocity and temperature fields are relaxed to those obtained from the mesoscale inner nest. Real-case simulations based on initial and boundary conditions from high resolution analysis datasets are conducted. Localized sharp shear layers and stiff gradients of vertical velocity and temperature characterize mechanical and optical turbulence within the embedded microscale nests. Three-dimensional laminated structures and multi-scale shear-stratified dynamics in the UTLS are compared with in situ radiosonde and aircraft measurements.
Bio: Dr. Alex Mahalov earned a PhD in applied mathematics from Cornell University in 1991. After a postdoc position in the Department of Mechanical Engineering at UC Berkeley, he joined Arizona State University where he was promoted to the Wilhoit Foundation Dean's Distinguished Professor in 2008. Recent research efforts are focusing on problems at the interface of high performance computing, multiscale atmospheric physics, optical turbulence and predictive modeling. Dr. Mahalov's research has been supported by grants from AFOSR, NSF, NASA and contracts from industry.

2012-2013 Academic Year

May 1st, 2013
Dr. Martin Stringer, Observatoire de Paris, France
Title: Galaxy properties as a fingerprint of cosmology and fundamental physics
Abstract: Any viable theory of the formation and evolution of galaxies should be able to broadly account for the emergent properties of the galaxy population, and their evolution with time, in terms of fundamental physical quantities. Yet, when citing the key processes we believe to be central to the story, we often find ourselves listing from a vast and confusing melee of modelling strategies & numerical simulations, rather than appealing to traditional analytic derivations where the connections to the underlying physics are more tangible. By re-examining both complex models and recent groundbreaking observational surveys in the spirit of the classic theories, we investigate to what extent the trends in the galaxy population can still be seen as an elegant fingerprint of cosmology and fundamental physics.

April 30, 2013
Dr. Marco Notarianni, Queensland University of Technology, Brisbane, Australia
Title: Novel Nanomaterials for Organic Photovoltaics
Click here for abstract

April 24, 2013
Prof. Megan Eckart, NASA/GSFC and UMBC
Title: X-ray Astrophysics with Non-Dispersive Imaging Spectrometers: Astro-H and Beyond
High-resolution spectroscopy in the soft X-ray waveband (0.1-10 keV) is a key component of probing the physics of high-energy phenomena. Unique line diagnostics available in this waveband allow transformative scientific observations, including studies of clusters of galaxies and probes of the accretion and outflow processes near black holes. I will introduce the microcalorimeter, a low-temperature detector capable of x-ray photon counting with high spectral resolution, and the scientific potential of upcoming space-based experiments using arrays of such detectors. I will discuss the Soft X-ray Spectrometer, a pioneering microcalorimeter instrument that will launch aboard the Japanese-led Astro-H mission in 2015, and recent advances in superconducting transition-edge-sensor (TES) microcalorimeters, a detector technology that enables the larger field of views required for sounding rocket experiments and future space-based astrophysics missions.

April 10, 2013
Prof. Kevin Huffenberger, University of Miami, Coral Gables, Florida
Title: The Universe's Baby Picture: Cosmology results from the Planck mission
Abstract: The Planck satellite mission has recently released the most detailed full-sky maps of fluctuations in the Cosmic Microwave Background (CMB), the radiation afterglow of the Big Bang. The statistics of these maps (chiefly the angular power spectra) place strong constraints on the structure and contents of the Universe, and on small angular scales provides robust support for the standard, six-parameter Lambda-Cold-Dark-Matter (LCDM) model of cosmology. The Planck-measured values for some of these six parameters are in tension with previously-determined values (we find a lower Hubble constant and a higher matter density), but they are in excellent agreement with with constraints from baryon acoustic oscillation (BAO) surveys. Based on Planck CMB data alone, the Universe's spacetime shows no evidence for spatial curvature to percent-level precision. We place an upper limit of 0.23 eV on the summed mass of neutrinos, and find no evidence for additional neutrino-like relativistic particles. Our results are in excellent agreement with models and measurements of Big Bang nucleosynthesis. Despite the success of the standard LCDM model, this cosmology does not provide a good fit to the CMB power spectrum at large angular scales, and Planck confirms several large-scale anomalies in the CMB temperature distribution that were detected earlier by Wilkinson Microwave Anisotropy Probe. Planck has measured the gravitational lensing of the CMB at a significance of about 25 sigma. Although the analysis of polarization data is not now mature, we can show the robust detection of the E-mode polarization signal.

April 3, 2013
Steven M. Reppert, UMass Medical School, Worcester, Massachussets
Title: Neurobiology of monarch butterfly migration
Abstract: Studies of the iconic migration of the eastern North American monarch butterfly have revealed mechanisms behind its navigation using a time-compensated sun compass. Skylight cues, such as the sun itself and polarized light, are processed through both eyes and integrated in the brain's central complex, the presumed site of the sun compass. Circadian clocks that have a distinct molecular mechanism and that reside in the antennae provide time compensation. The draft sequence of the monarch genome has been presented, and gene-targeting approaches have been developed to manipulate putative migration genes. The monarch butterfly is an outstanding system to study the neural and molecular basis of long-distance migration.
Suggested readings:
Reppert SM, Gegear RJ, Merlin C (2010). Navigational mechanisms of migrating monarch butterflies.TINS 33:399-406.
Heinze S, Reppert SM (2011). Sun compass integration of skylight cues in migratory monarch butterflies. Neuron 69:345-358.
Zhan S, Merlin C, Boore JL, Reppert SM. The monarch genome yields insights into long-distance migration. Cell 2011; 147:1171-1185.

April 1, 2013
Prof. Chaoming Song, Northeaster University, Boston, Massachussets
Title: Scaling Theory of Complex networks
Abstract: Fueled by a wealth of data supplied by a wide range of high-throughput tools and technologies, the study of complex systems is currently reshaping a number of research fields from cell biology to computer science. This data-rich reality calls for new approaches and techniques to harvest the hidden information and devise new models to explain the underlying principles of various complex systems. While from a functional standpoint different systems may appear to be distinct from one another, there is an increasing realization that they often share similar structural and dynamic properties. Such similarities offer new perspectives and unique opportunities for physicists to apply their methodologies on a much broader set of phenomena. Over the past few years, we witnessed rapid advances in network science that focuses on unveiling universal structure and dynamics of complex interactions observed in diverse fields. By applying scaling analysis to real-world networks, we find the self-similar nature of network structure that allows us to reveal the origin of ubiquitous power law degree distribution. Our finding further suggests a unified scaling theory that plays an essential role in our understanding of networks emerged in biological and other systems.

March 20, 2013
Prof. Daniel James, University of Toronto, Canada
Title: Quantum Computing, Cryptography and Teleportation
This talk will present an intuitive explanation of the promise of a new generation of proposed technologies intended to exploit fundamentally quantum mechanical phenomena in order to perform tasks such as communication, metrology and computation in a dramatically more efficient manner than conventional devices in use today. We will also discuss the physical principals behind the devices and the latest progress toward realizing some of these ambitious goals.
Bio:   Daniel James was born in rainy Manchester (within sight of Manchester United, the most successful sports team in recorded human history). He was educated at New College, Oxford (which, despite the name, was founded in 1379) and at The Institute of Optics, University of Rochester, where he earned his Ph.D. in Optics under the tutelage of Prof. Emil Wolf. After a period working at the Theoretical Division of Los Alamos National Laboratory, he became the Canada Research Chair in Atomic and Optical Physics at the University of Toronto in 2005. His scientific accomplishments include the first tomographic characterization of an entangled quantum state; the demonstration of quantum teleportation with atoms, and the implementation of a simplified version of the Shor factor-finding algorithm with entangled photons.

November 7, 2012
Prof. Christopher G. A. Harrison, University of Miami - RSMAS
Title: Causality between climate and human activity
We now understand that climate has probably been affected by human activity (the most important being the burning of fossil fuel). But less is known of the reverse, i.e. the effect of climate on human activity. In this presentation, I examine data recently published by Zhang et al. (2011) consisting of sixteen data sets of annual values lasting between 1500 and 1800 A.D., totaling 301 data, and in addition other data sets by Phelps Brown and Hopkins (1956), Clark (2004), Biondi et al. (1999), Bray (1982), Cook et al. (2002) amongst others. These data sets consist of information about climate change, bioproductivity, prices and wages, and many socioeconomic data sets, such as wars, war fatalities, population, health etc., and mostly related to Europe. I shall show that many of the strong correlations between the sixteen data sets claimed by Zhang et al (2011) are in fact not as strong as they claimed. This is due to three factors; (1) Six of the data had far fewer than 301 data points and the data sets with fewer points were interpolated to achieve annual values: (2) Five of the data were detrended, causing there to be long period signals in the detrended data not present in the original data: (3) The data were subjected to a Butterworth filter which filtered out short period signals but also removed information, i.e. reduced the effective number of data below the 301 standard. Yet there are still some strong correlations. Because of the interconnection between the data sets, I feel that it is much better to study them using multiple linear regression. When this is done, the connection between the socially based data sets and the climatic data sets is much reduced. But there are some strong correlations between many of the socially based data sets which I shall discuss.

November 28, 2012
Prof. Edward F. Redish, University of Maryland
Title: Rethinking Physics for Biologists: Adapting to a major new service course constituency
Abstract: Though many physics departments offer a variety of introductory physics classes, most of the larger departments offer (and support themselves on) two main year-long service courses - a calculus-based one an algebra-based introductory one. At universities with engineering schools, the calculus-based course is primarily designed to serve the needs of engineers. Traditionally, the algebra-based course serves a variety of populations: pre-meds, nurses, architects, kinesiologists, and students looking for a lab course to satisfy a distribution requirement. Looking at the texts for the algebra-based class it's pretty clear that this is a 'cut down version of the calculus-based class - as if it were designed to serve potential engineers with limited skills in mathematics. But over the past decade, a growing fraction of this class are students who are not weak engineering students, but strong biology students. Furthermore, the biology community has been increasingly calling for stronger, more appropriate, and more interdisciplinary science classes for biologists and pre-health care professionals. Physicists around the country have begun collaborating with biologists to create an "Introductory Physics for Life Sciences" (IPLS) class. In this talk I will describe one such effort at the University of Maryland. As part of the "National Experiment in Undergraduate Science Education" (NEXUS) a large team of physicists biologists, and chemists working with our Physics and Biology Education Research Groups (PERG & BERG) have been rethinking and redesigning introductory physics for biology majors. I will present some of our observations, difficulties, ideas, and present preliminary results from the first trial year of this class.
E. F. Redish and D. Hammer, "Reinventing College Physics for Biologists: Explicating an Epistemological Curriculum," Am. J. Phys., 77, 629-642 (2009). [http://arxiv.org/abs/0807.4436]
"Collaboration seeks to create interdisciplinary undergraduate curriculum", http://www.hhmi.org/news/nexus20110608.html

October 17, 2012
Prof. Sukanya Chakrabarti, Florida Atlantic University
Title: A New Probe of Dark Matter in Spiral Galaxies
Abstract: The cold dark matter paradigm of structure formation is successful at recovering the basic skeletal structure of the universe -- the large-scale distribution of galaxies. However, the agreement between theory and observation is less secure when this model is applied to galactic (and sub-galactic) scales. Problems such as the missing satellites problem, the lack of massive dark satellites, and the unexpected distribution of galactic satellites in the Milky Way, suggest that the current paradigm is not complete in its description of galaxy evolution. The extended atomic hydrogen disks of galaxies provide an unique probe of galaxy evolution. They are ideal tracers of tidal interactions with satellites and the galactic gravitational potential well. We have recently developed a method whereby one can infer the mass, and relative position (in radius and azimuth) of satellites from analysis of observed disturbances in outer gas disks, without requiring knowledge of their optical light. I will present the proof of principle of this method by applying it to galaxies with known optical companions. I will end by presenting recent work that extends earlier our earlier results to constrain the density profile of dark matter in local spiral galaxies. I will also compare and contrast this method to gravitational lensing as a means of probing dark matter in galaxies.

2011-2012 Academic Year

April 25, 2012
Prof. Tamier Epstein, Moffitt Cancer Center
Title: Quantitative imaging of biophysical processes and biochemical parameters
Comprehensive and accurate measurements of biophysical and biochemical parameters, such as electric fields and ionic strength, have been of prime interest for decades. These are the fundamental building blocks of complex cellular processes, and thus are relevant to biological, medical, pharmaceutical and toxicological studies. In spite of much recent progress, current techniques are still limited in many ways and there is a substantial need for improvements. I present several basic biophysical questions I have been studying, discussing their importance and implications for the understanding of biological processes, and I highlight the development of PEBBLE nanosensor technology and advanced microscopy techniques for studying these questions.

April 17, 2012
Prof. Gourab Ghoshal, Northeastern University
Title: Role of topology in ranking processes on complex networks.
Many systems of scientific or technological interest can be represented as networks, such as the worldwide web, citation networks, and social and biological networks. These networks are often found to share both commonalities and differences in topological properties, whose detection and characterization has been the subject of a considerable volume of recent research. The role of topology in particular plays an important factor in diffusion processes on networks and resilience to targeted and random attacks. In this talk we will discuss some recent developments highlighting the interplay between a network's structure and the efficacy of ranking content. In particular we focus on Pagerank, a network-based diffusion algorithm, that has emerged as the leading method to rank web content, ecological species and even scientists. Despite its wide use, it remains unknown how the structure of the network on which it operates affects its performance. We will show that the ! ranking returned by Pagerank on certain real world networks is extremely sensitive to perturbations in their structure, making it unreliable for incomplete or noisy systems. In contrast, in a few cases, we predict analytically the emergence of super-stable nodes whose ranking is exceptionally stable to perturbations. We calculate the dependence of the number of super-stable nodes on network characteristics and demonstrate their presence in real networks, in agreement with analytical predictions. We end with a discussion of the implications of these results.

March 28, 2012
Prof. Sheyum Syed, Rockefeller University, New York
Title: Complexity without all the complications: the fruit fly circadian clock as a gateway towards quantitative understanding of complex behavior.
In the natural world, complex behaviors such as learning, aggression and sleep are regulated by interconnected networks of genes and their products. Owing to their nontrivial topology and large number of components, most of these networks are poorly understood and consequently, our knowledge of how diverse behaviors arise remains limited. In this talk, I will argue that the fruit fly circadian clock, a genetic circuit that signals to and modulates several key behavioral networks, is an ideal system with which to dissect the fundamental principles that govern organismal behavior. I will discuss recent results from experimental studies at the transcriptional and post-translational levels of the fly clock as well as simple mathematical models aimed at understanding fruit fly locomotion. The talk will end with an outline of future studies using the fly that will provide novel mechanistic insights into how complex behavior emerges from simple molecular events.

November 30, 2011
Prof. Gabriel Popescu, University of Illinois at Urbana-Champaign
Title: Cell dynamics and cancer diagnosis studied by quantitative phase imaging
Light transmitted through a live cell undergoes a slight time delay, of the order of a femtosecond or less, which depends on the refractive index and thickness of the specimen. The fluctuations in this pathlength (or phase) are informative regarding both cell membrane fluctuations (thickness component) and intracellular mass transport (refractive index component). Measuring these minute pathlength changes, with nanometer accuracy over broad time scales (fractions of seconds to days) is extremely challenging. Quantitative phase imaging (QPI) is an emerging field that aims at measuring these pathlength maps with the required sensitivity. I will review our efforts in developing QPI methods and applications in studying fluctuations in live cells and cancer diagnosis.

October 26, 2011
Prof. Pavel Winternitz, Centre de recherches mathematiques,
University of Montreal, Montreal, Canada
Title: Superintegrability, exact solvability and hidden symmetries
We review the present status of superintegrable systems, i.e. finite Hamiltonian systems with more integrals of motion than degrees of freedom. The emphasis is on conceptual questions and on new developments such as the discovery of infinite families of superintegrable systems with integrals of motion of arbitrary order in the momenta and the role of Painleve transcendents as superintegrable potentials.

October 19, 2011
Prof. Zoltan Bajnok, Hungarian Academy of Sciences
Title: Casimir effect and boundary quantum field theories
By placing two mirrors close to each other, an attractive force can be experienced. The force, being proportional to the fourth power of the inverse distance of the mirrors, is called the Casimir force, and is the manifestation of the quantum nature of the vacuum. This force, used by geckos to walk on the ceiling, is relevant at nano-scales; and changing its attractive nature to repulsive could give rise to levitation. In my talk I will provide a novel description of the Casimir force as a boundary finite size effect: The force comes from the reflections of virtual vacuum particles on the surfaces.

October 5, 2011
Prof. Mohamed Iskandarani, University of Miami - RSMAS
Title: Stochastic Modelling of Oceanic Flows
Forecasting oceanic flow realistically is a challenging problem due to the multi-scale nature of the flows, the complicated coastlines and forcing mechanisms, the size of ocean basins compared to dynamical length scales, and the inherent difficulties of modelling stratified rotating flows. The problem is compounded by the space-time scarcity of observations that inhibit a full description of the ocean state. Uncertainties in the input data limits confidence in the model output. Stochastic modelling provide a mechanism that allows us to propagate uncertainties in the input data to estimate uncertainties in the output data. In this talk we provide a brief overview of ocean modelling and on our polynomial chaos based approach to quantify its associated uncertainties.

2010-2011 Academic Year

April 27, 2011
Prof. Antao Chen, University of Washington, Seattle, WA
Title: Photonics and nanotechnology for telecommunication and sensors
Organic electro-optic materials have the unique advantage of good velocity match between radio frequency and optical frequency. As a result optical modulation can be realized with wide bandwidth of over hundreds of GHz. Silicon nano-photonic structures is able to confine optical modes in a small space due to the high refractive index of silicon. Combining the EO polymer with silicon photonics has greatly reduced the size of the EO polymer modulator and the modulator drive voltage

Nano- and micro-structures including micro optical resonators and microfluidics, with sizes matching that of biological cells and bio-molecules, are useful tools in biomedical research. Interaction of light propagating in the wave-guiding structures with the surrounding media through its evanescent field has been used to detect biochemical activities without labeling the target molecules. By introducing multiple slots in a dielectric waveguide, a much stronger evanescent field could be achieved in the surrounding media while still maintaining good optical confinement. Experimental demonstration of micro-ring resonator sensors using single mode waveguides having three slots indicates a 5-fold increase in sensitivity for homogeneous sensing and more than 3-fold increase in sensitivity for surface sensing (biotin-bovine serum albumin) in comparison to those of a waveguide without slots. Numerical simulations suggest higher sensitivity enhancement (as high as 100 times) is possible if more slots and larger waveguide widths are used.

Microstructures can be created by light. Two-photon polymerization has been used by us as a versatile and flexible means to fabricate arbitrary 3D structures of sub-micron dimensions. These structures made in functional polymers (e. g., oxygen sensitive fluorescent polymers) are useful for micro sensors and cell study. Microresonator fabricated on side-polished fiber allows fiber coupled sensor arrays to detect and identify various analytes.

Charge carrier transport in semiconducting nanowires is strongly affected by localized surface states. This property makes nanowires ideal for chemical gas sensors. We developed nanoelectronic sensors capable of detecting trace chemical gases for security, biological, and environment protection. With proper choice of the material, dimensions of nanowires, and sensor structure, detection limit in the low parts-per-trillion range have been achieved. Such sensors operate at room temperature and are self-refreshing.

April 13, 2011
Prof. Spiros S. Skourtis, University of Cyprus, Nicosia, Cyprus
Title: The control of electron transfer pathways in biomolecular and small-molecule systems: the roles of medium fluctuations and initial state preparation.
Electron transfer reactions are ubiquitous in biology and chemistry and they involve a variety of electron transport mechanisms. The electronic couplings that enable electron transfer in large biomolecular and small-molecule systems can be understood in terms of competing and interfering electron transfer pathways that are controlled by structure, dynamics, and initial state preparation. We review recent theoretical progress on the effects of conformational distributions, excited-state polarization, and electron-nuclear dynamics on tunneling electron transfer reactions in different biomolecular systems. Further, we discuss connections between biomolecular electron transfer and electron transport in small molecule devices.

March 25, 2011
Prof. Dr. Takuya Matsumoto, AEI, Potsdam
Title: Quantum affine symmetries of the q-deformed S-matrix
It is known that the AdS/CFT worldsheet S-matrix is based on the centrally extended sl(2|2) superalgebra and the associated Yangian. In this work, towards a more uniform description of the integrable structures, we have investigated the algebraic structures of its q-deformation and derived its underlying exceptional quantum affine algebra. We also show how the algebra reduces to the above mentioned Yangian. This is based on the collaboration work with Niklas Beisert and Wellington Galleas. (to appear)

March 2, 2011
Prof. Maurizio Giannotti, Barry University
Title: Astrophysics and Axions: New Models and New Constraints
Axions are hypothetical particles, whose existence is a consequence of the Peccei-Quinn solution of the strong CP problem. Today, axion research is experiencing an exciting revival in terms of new experimental efforts for its detection, as well as new theoretical ideas and models. Improvements in experimental and theoretical astrophysics research has opened up new possibilities to understand the properties of these particles. I will discuss the axion phenomenology, especially from an astrophysics point of view, and discuss some new astrophysical bounds and new possibility of detection.

February 23, 2011
Prof. Carolyne Van Vliet, University of Miami
Title: Quantizing the Hendrik Antoon Lorentz force, 1853 - 1928, University of Leyden, Holland
Click here for abstract

February 16, 2011
Prof. Demetrios Christodoulides, University of Central Florida
Title: Optical Airy beams and bullets>
Click here for abstract

February 9, 2011
Prof. Brian A. Raue, Florida International University
Title: Rewriting 50 years of nuclear physics: The search for two photon exchange.
One of the most important aspects of modern nuclear physics is understanding the structure of nucleons (protons and neutrons). This includes measurement of the proton's electric and magnetic form factors, which essentially tell us how the proton's electric charge and current are distributed. These form factors are measured through elastic scattering of electrons from a proton target. However, recent measurements of the form-factor ratio (G_E/G_M) using different techniques yield dramatically different results. One explanation for this is that the standard methods of accounting for the electromagnetic interaction between the electron and a nucleus are missing a small, but potentially important component: Two Photon Exchange (TPE). I will discuss a currently running experiment in experimental Hall B at The Thomas Jefferson National Accelerator Facility in Virginia that is directly measuring the TPE effect.

December 1, 2010
Prof. Jack Hughes, Rutgers University
Title: Clusters and Cosmology from the Atacama Cosmology Telescope
The Atacama Cosmology Telescope (ACT) is a 6-m diameter telescope with a sensitive mm-wave band camera custom designed to survey the cosmic microwave background (CMB) on arcminute angular scales. The camera observes simultaneously in three bands at frequencies of 148 GHz, 220 GHz, and 270 GHz. One of the goals of the project is to find galaxy clusters through the Sunyaev-Zel'dovich effect, which arises when hot electrons in the cluster inverse Compton scatter cold CMB photons. The SZ effect manifests as a decrement in ACT's low frequency channel, an increment in its high frequency channel and a null in the middle channel. Over the past year the ACT team has pursued an ambitious program to identify and characterize the ACT clusters and utilize them to constrain the growth of structure in the Universe. In this colloquium I will present our current results and describe our plans for the future.

November 3, 2010
Prof. Angela M. Guzman, Florida Atlantic University
Title: Quantum atom-surface interaction in the presence of optical fields
In Micro-electro-mechanical systems (MEMS) and nanoscale devices, the Casimir force plays the role that friction forces play in the macroscopic world. Optical manipulation of atoms and nanosized particles close to surfaces involve atom-surface interactions that are modified by the presence of the optical field. A better knowledge of the atom-surface interaction in the presence and absence of optical fields will find application in the design of atom-optics components, in the manipulation of ultracold atoms, and in exploring ways to obtain an increased reflectivity. Recently, a direct measurement of intermediate-range Casimir-Polder potentials by means of ultracold atom reflection in evanescent-wave mirrors [H. Bender et. al., Phys. Rev. Lett. 104, 083201, 2010] was reported. A deviation from the theoretical values was observed, which is particularly large for high laser powers. The measured barrier height exceeds the values predicted by theoretical calculations based on the idea that the Casimir force remains unchanged in the presence of an applied electromagnetic field. We have introduced an alternate theoretical model for atom-surface interactions as originated from the quantum dipole-dipole interaction. It takes into account the dipole moment induced by the electromagnetic field, which leads to a power dependent van der Waals force. Our results are in good agreement with the experimental results cited above.

October 27, 2010
Prof. Neil Johnson, University of Miami
Title: The magic of 2.5: From wars and markets to neurons and superconductivity
A devil's advocate view of many natural phenomena would say that every case is a special case. Given the lack of any general theory for how things work, it makes sense that special disciplines arise to tackle the special features of each of these special cases -- from cosmology and many-body quantum physics through to conflict studies, and from neuroscience through to quantitative finance. But what if everything turned out to be 'the same' on some level? Certainly, all the details are different -- but the issue of how collections of objects interact in space and time, is general to all these topics. Recently researchers have attempted to build analogies between the collective dynamics in such systems, giving rise to curious subfields such as 'Econophysics' -- but is there any quantitative justification for this optimism? In this talk, I will take a few tentative steps along this path by discussing how a remarkably simple mechanism of group formation provides an interpretation for the behavior across many disparate domains. In Douglas Adams' Hitchhiker's Guide to the Galaxy, the supercomputer Deep Thought (after 7½ million years of computation) arrived to the Ultimate Answer to the Ultimate Question of Life, The Universe, and Everything (i.e. the Meaning of Life), and it was 42. But maybe it should be 2.5?

October 6, 2010
Prof. Bernard S. Gertsman, Florida International University
Title: Protein Folding: Energy, Entropy, Non-Linear Dynamics, and Neurological Diseases
Living systems are the epitome of non-linear, self-organized complexity. The self-organization occurs on all scales, from the molecular up to the organismal level. The machines responsible for maintaining organization are protein molecules. However, protein molecules themselves must self-organize into highly specific shapes. The folding of proteins is a self-organizing process in which a long chain heteropolymer in a disorganized configuration spontaneously changes its shape to a highly organized structure in milliseconds. I explain how the energy and entropy landscape of protein chains is shaped to allow self-organization. I also show how these principles can be used in molecular level investigations of protein-protein interactions that lead to both beneficial dimerization of useful proteins, or disastrous, disease producing and potentially fatal protein aggregation that appears in neurological diseases such as Alzheimer's and Parkinson's.

2009-2010 Academic Year

September 9, 2009
Prof. Andy Lau, Florida Atlantic University
Title: Response and Fluctuations in Active Systems
Active complex fluid systems like living cells, assemblies of motors and filaments, flocks of birds, and vibrated granular material are nonequilibrium systems that consume and dissipate energy. These active systems exhibit phenomena that can be quite distinct from those of conventional equilibrium soft materials. Nevertheless, their long-wavelength properties can at times be described by hydrodynamic-like stochastic equations similar to those of equilibrium systems but with additional terms that break Onsager reciprocity and noise sources that violate the fluctuation dissipation theorem. In this talk, we focus on a model active system, namely, a bacterial bath, which consists of a population of rod-like motile or self-propelled bacteria suspended in a fluid environment. We discuss results of recent microrheological experiments in terms of a dynamical model for nematic liquid crystals in the isotropic state, appropriately modified to reflect the activity of bacteria. We show, in particular, that the non-equilibrium contributions to the stress arising from the swimming of the bacteria lead to a $1/\sqrt{omega}$ scaling in the power spectrum of the active stress fluctuations, as observed experimentally.

October 7, 2009
Prof. Chris Landsea, NOAA/NWS/National Hurricane Center
Title: Hurricane Analysis and Forecasting at the National Hurricane Center
The National Hurricane Center issues analyses, forecasts, and warnings over large parts of the North Atlantic and Pacific Oceans, and in support of many nearby countries. Advances in observational capabilities, operational numerical weather prediction, and forecaster tools and support systems over the past 15-20 yr have enabled the center to make more accurate forecasts, extend forecast lead times, and provide new products and services. Important limitations, however, persist. This talk discusses the current workings and state of the nation's hurricane warning program, and highlights recent improvements and the enabling science and technology. It concludes with a look ahead at opportunities to address challenges.

October 28, 2009
Prof. Jorge L. Rodriguez, Florida International University
Title: Physics at the Large Hadron Collider with the CMS Experiment: Status Fall 2009
The Large Hadron Collider (LHC) will resume operations in November of 2009. The LHC is designed to collide protons head on at 7 trillion electron volts and at collision rates higher than ever before achieved in any particle accelerator. The unprecedented energies and the large data rates will usher in a new era of exploration that will allow us to peer further into fundamental constituent of matter and processes that govern our universe. At the LHC experiments are scheduled to search for the origin of mass, the constituents of dark matter and even for the extra-special dimension predicted by string theory. In this talk I will begin by briefly introducing the field of particle physics, highlighting some of these very these basic questions and unresolved mysteries. I will then describe the experimental apparatus constructed globally but gathered at CERN including a short synopsis of the status of the accelerator after its year long hiatus. I will then spend a few minutes describing one of the two large general purpose detectors, the Compact Muon Solenoid experiment, positioned around one of the interaction points and poised to collect data from the LHC.

November 4, 2009
Prof. Stewart E. Barnes, University of Miami
Title: Taking Faraday's law for a spin - gauge theories and spin batteries
Faraday's 1831 law of induction E = - dΦ/dt relates the rate of change of magnetic flux Φ to the electromotive-force E produced in a circuit. This accounts only for the forces acting on the charge of an electron. When the forces acting on the spin are accounted for this is better stated as
E = - ( hbar / e ) dγ/dt where γ is the (1984) Berry phase acquired while the electron passes around a circuit. The Anaronov-Bohm contribution to γ gives back E = - dΦ/dt while adding the spin Berry phase leads to a spin-motive-force which in a ferromagnetic material implies an electromotive-force. Feynman, in 1948, anticipated Berry by showing the velocity commutation rule [vi,vj ] = i (e hbar / m2) εijk Bk, defining the Berry curvature Bk, implies Faraday's law.
A ferromagnetic has broken rotational symmetry and implies a result for Bk which is a Pauli matrix corresponding a a SU(2) rather than U(1) gauge group. In turn this leads to the additional spin terms in Faraday's law. Nearly all generation of electrical power reflects Faraday's law, while essentially all storage batteries convert chemical to electrical energy and both lead to currents due to the forces on the electron's charge. A spin battery converts energy stored in a magnetic material into electric power via the extended Faraday's law using the spin-transfer-torque effect and corresponds to forces acting on the electron's spin. The energy density stored in such a battery based upon nano-magnets is perhaps comparable to that of a lead-acid battery. Might this one day power electric cars?

December 2, 2009
Prof. Roland Romeiser, University of Miami/RSMAS
Title: A new remote sensing technique, called along-track interferometric synthetic aperture radar (along-track InSAR, ATI), permits a direct imaging of line-of-sight velocity fields from airborne and spaceborne platforms at spatial resolutions better than 1000 m and swath widths of up to 100 km and more. This capability is attractive for the observation of moving objects on land as well as for surface current measurements in coastal waters, rivers, and the open ocean for a variety of applications. A conventional synthetic aperture radar (SAR) uses coherent processing of signals received by a moving small antenna to synthesize a long antenna aperture with a high spatial resolution in flight direction. The along-track InSAR uses two antennas to acquire two images with a short time lag. Phase differences between the two complex images are proportional to Doppler shifts and thus to line-of-sight target velocities. This basic concept was first described by Goldstein & Zebker in (1987); first experiments with airborne ATI systems took place in the late 1980s and the 1990s. Since then, we have learned how to model the imaging mechanism of currents and waves theoretically in order to correct measured velocity fields for contributions of wave motions and imaging artifacts and to study the performance of spaceborne ATI concepts. A first demonstration of current measurements from space was possible with data from the Shuttle Radar Topography Mission (SRTM) in February 2000. The first operational satellite with (experimental) ATI capabilities is the German TerraSAR-X, which was launched in 2007. The University of Miami's satellite receiving station, the Center for Southeastern Tropical Advanced Remote Sensing (CSTARS), will begin to receive TerraSAR-X data in 2010. This presentation gives an overview of basic principles of ATI, the theory of the ATI imaging mechanism of currents and waves, example results from airborne ATI experiments, SRTM, and TerraSAR-X, and promising applications.