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PHYSICS COLLOQUIUM SCHEDULE
Fall 2018
The Colloquia are in Room 1002 NPB on Thursday at 4:05 PM
Refreshments will be served starting at 3:15 PM in NPB 2205

Contact: A. Hebard afh@phys.ufl.edu)
Department of Physics Colloquium Committee:
Hebard (chair), Fulda, Matchev, Mitselmakher, Wang


August 23

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August 30
  Speaker Graduate Student Meeting with Dr. Xiaoguang Zhang 4:00pm in 1002 NPB
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September 6
  Speaker Doug Soltis, Florida Museum of Natural History and Department of Biology
  Title Building the tree of life
  Abstract Why did it take over 150 years from the time of Darwin who referred to “The Great Tree of Life” in the mid 1800s to build the first tree of all life in 2015? With more than 2 million species already described, and many more millions undiscovered or extinct, the size of the Tree of Life is immense. As a result, the task of assembling a comprehensive tree for all life was long considered not just daunting but impossible. Put simply, building huge family trees of relationships (phylogenetic trees) is very hard, rivaling the most difficult problems in physics and astronomy. In fact, building large trees of relationships for just a few hundred species was once deemed impossible because of the mathematically challenges. For example, the number of ways that just 20 species can be connected into trees of relationships is approaching Avogadro’s number, that is a mole of trees (6.02 x 1023). Thus, building the first tree of all named Life (all 2.3 million species) was a true “grand challenge” or a “moonshot” for biology. Accomplishing that moonshot required the perfect storm of algorithm development, computer power, DNA sequencing improvements as well as international collaboration and teamwork. Furthermore, building the first Tree of Life provides an enormously important tool for human-well-being with numerous downstream applications.
  Host Hebard

September 13
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September 20
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September 27
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October 4
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October 11
  Speaker Chenglong Li (Medicinal Chemistry)
  Title The Role of Computational Biophysics in Drug Design
  Abstract With modern advances of molecular simulation and computing power, rational drug design becomes more and more attractive. This talk focuses on two application examples: nAChR and Survivin. Based on homology modeling and molecular dynamics sampling, we have identified a negative allosteric binding site on the ectodomain of a4ß2 nAChR (nicotinic acetylcholine receptor) – an anti-smoking addiction target. For the anti-cancer drug target survivin, we used REMD (replica exchange MD) and free energy analysis to elucidate ligand binding mechanism and optimized the drug lead compound. These examples demonstrate the potential of computational molecular biophysics for functional molecular design and engineering.
Host Zhang

October 18
  Speaker Angel Garcia (Center for NonLinear Studies (CNLS), Los Alamos National Laboratory)
  Title Proteins under Pressure
  Abstract Proteins are heteropolymers that self-assemble into a compact ordered structure known as the folded state. Although the folded state is a compact state, proteins will unfold under high hydrostatic pressure. This effect seems contradictory, given that high pressures should drive the system toward lower volume states. However, pressure denaturation can be easily explained in terms of the pressure effects of hydrophobic interactions (i.e., how non polar molecules interact with water). We use molecular simulations to model pressure folding/unfolding equilibrium of small peptides that form alpha helices, beta sheets, and a model protein (the trp-cage mini protein). These calculations show a rich P-T stability diagram in which a protein can unfold at high pressures, or can unfold upon cooling (cold denature) at elevated pressures. I will describe the role of the interactions of water with proteins in describing these effects. The simulation results in small, model proteins will be used to interpret experimental data in larger, complex protein systems.
Host Maslov and Wang

October 25
  Speaker Kyle Shen (Cornell)
  Title Shedding Light on Artificial Quantum Materials
  Abstract Quantum materials host a vast array of emergent electronic phenomena, including high-temperature superconductivity, colossal magnetoresistance, and nanoscale charge / spin ordering. One of the grand challenges of this field is to be able to precisely and deterministically manipulate the properties of quantum materials. To achieve this control, we employ molecular beam epitaxy (MBE) to synthesize "artificial quantum materials" in thin film form with atomic layer precision, which allows for new control knobs such as the creation of interfaces, the stabilization of metastable phases, or imposing large epitaxial strains. We combine MBE growth with angle-resolved photoemission spectroscopy (ARPES) which provides direct insights into the electronic structure and quantum many-body interactions to understand how strong quantum many-body interactions can influence the electronic and magnetic properties of quantum materials. In particular, I will focus on some very recent developments where we have used interfacial engineering and thin film epitaxy to manipulate and control exotic superconductors, including the odd-parity superconductor Sr2RuO4 and monolayer FeSe grown on SrTiO3.
Host Amlan Biswas

November 1
  Speaker George Christou (Department of Chemistry)
Title The Power of Molecular Chemistry in Nanoscale Materials Research
  Abstract Molecular chemistry can bring many powerful advantages to the study of nanoscale materials of various kinds, and this area of ‘molecular nanoscience’ is therefore a rapidly growing field. The advantages include monodisperse (single-size) products and a shell of organic ligation that imparts solubility and crystallinity, allowing structural characterization to atomic resolution by X-ray crystallography. The ligands can usually also be modified as desired, allowing tuning of redox properties and atom/isotope labelling (e.g. 2H, 19F, etc.) for various studies in solution and the solid state, such as NMR spectroscopy. In the molecular nanomagnetism arena, the above advantages have been absolutely crucial in the study of single-molecule magnets (SMMs), individual molecules that function as nanoscale magnets. They have greatly assisted the synthesis and structural characterization of numerous SMMs, and they have led to discovery of new quantum physics phenomena within nanomagnetism important to new 21st century technologies. These include quantum tunneling of the magnetization vector (QTM) and other phenomena that could not be reliably detected from the study of traditional nanoparticles. Our giant (~4 nm) SMMs have also bridged the gap between the ‘top-down’ world of traditional magnetic nanoparticles and the ‘bottom-up’ world of molecular nanomagnets. In one extension of the SMM project, we have been developing controlled ways to form supramolecular oligomers of 2 or more covalently-linked Mn3 SMMs to study the resulting quantum properties introduced by the weak inter-SMM exchange coupling, such as exchange-biased QTM and quantum superposition states, including in solution for the first time. More recently still, we have extended our molecular approach to other interesting materials and have been targeting molecular clusters that can be considered ‘molecular nanoparticles’ of certain metal oxides, such as cerium(IV) dioxide, and mixed-metal oxides with the perovskite structure. The syntheses, structures, and properties of a selection of these materials will be described.
Host Hebard

November 8
  Speaker Eugene Shakhnovich (Harvard)
Title Understanding evolution on multiple scales: from protein physics to population genetics and back
  Abstract Biological phenomena unfold in a broad range of scales ranging from molecules to cells to populations and ecosystems. Variation of molecular properties of biomolecules profoundly impacts the ability of cells to survive and propagate (fitness). Finally, the fate of a mutation is decided by Darwinian selection on the level of the population, where three outcomes are possible: fixation in the population, elimination by purifying selection or separation in the population in a subdominant clone (polymorphism). In this lecture I will outline my lab’s and others efforts in an emerging new field which merges molecular biophysics with evolution. I will discuss new models of evolutionary dynamics on biophysical fitness landscapes. Traditional population genetics models are agnostic to the physical-chemical nature of mutational effects. Rather they operate with an a’priori assumed distributions of fitness effects (DFE) of mutations from which evolutionary dynamics are derived. In departure with this tradition the novel multiscale models integrate the molecular effects of mutations on physical properties of proteins into physically intuitive yet detailed genotype-phenotype relationship (GPR) assumptions. I will briefly present a range of models from simple analytical diffusion-based model on biophysical fitness landscapes to more sophisticated computational models of populations of model cells where genetic changes are mapped into molecular effects using biophysical modeling of proteins and ensuing fitness changes determine the fate of mutations in realistic population dynamics. Examples of insights derived from biophysics-based multiscale models include the fundamental limit on mutation rates in living organisms, physics of thermal adaptation, co-evolution of protein interactions and abundances in cytoplasm and related results, some of which I will briefly present and discuss. In parallel, my lab has been developing experimental approaches to explore, top down, the relationship between molecular scale biophysical effects and ensuing effects on phenotype and evolutionary dynamics. Experimental examples include evolution of antibiotic resistance and evolution upon horizontal gene transfer
Host Maslov

November 15

  Speaker Premi Chandra, Rutgers University
  Title The Inner Universe of Quantum Materials
  Abstract Historically the study of physics in our local environment has led to an improved understanding of Nature well beyond our planetary bounds. As a physicist who has worked in academia and industry, in this talk I hope to convey my excitement for the study of quantum materials both for their application to the everyday and for their fundamental properties that may help us understand our greater Universe. The combination of quantum mechanics and complexity leads to the emergence of rich, exotic states of matter where the number of constituent electrons is comparable to the number of stars in our observable Universe. In this sense quantum materials can be viewed as tunable Universes where their behaviors under extreme conditions can be probed in the laboratory with far-reaching implications. After discussing some speci?c examples, I will end with our “Dark Matter” challenges and our many hopes for the future. The
Host Maslov

November 29

  Speaker Robert Kleinberg, Schlumberger/APS Distinguished Lecturer
  Title mK to km: How Millikelvin Physics is Reused to Explore the Earth Kilometers Below the Surface
  Abstract It is a common, but still surprising observation that many physics students have never met a physicist outside of an academic setting. Thus many undergraduate and graduate students know of few sources of information to help them understand what opportunities may exist university environments. The purpose of the APS Distinguished Lecturer program is to show how some physicists have navigated the transition to the “real world”.

Investigations of the superfluid phases of liquid helium-3 would seem to have little application to the study of rock formations thousands of meters below the surface of the earth. However, the physicist’s tool box is versatile, and techniques used in one field of study can be reused, with appropriate adaptation, in very different circumstances.

The temperature of liquid helium-3 in the millikelvin range can be measured using an unbalanced-secondary mutual inductance coil set designed to monitor the magnetic susceptibility of a paramagnetic salt. The loss signal is discarded by phase sensitive detection. Now consider the task of measuring the electrical conductivity, at centimeter scale, of the earth surrounding a borehole. Turn the mutual inductance coil set inside out, with secondary coils arranged to be unbalanced with respect to the rock wall. Instead of discarding the loss signal, use it to measure conductivity. A sensor based on this principle has been implemented in a widely deployed borehole geophysical instrument, used to estimate the prevailing direction of the wind millions of years ago, or to decide where to drill the next well in an oilfield.

Nuclear magnetic resonance may seem a very improbable measurement of the rock surrounding a borehole. Conventionally, we place the sample (which might be a human being) inside the NMR apparatus. In borehole deployment, the instrument is placed inside the sample, the temperature is as high as 175°C, pressure ranges to 140 MPa, and measurements must be made while moving at 10 cm/s. Apparatus with these specifications have been deployed worldwide, and are used to measure a number of rock properties, including the distribution of the sizes of pores in sedimentary rock, and the viscosity of oil found therein. They have also been used for geological and oceanographic studies in northern Alaska, and at the seafloor offshore Monterey, California.
Host Kumar



PHYSICS COLLOQUIUM SCHEDULE

Spring 2019
The Colloquia are in Room 1002 NPB on Thursday at 4:05 PM
Refreshments will be served starting at 3:15 PM in NPB 2205

Contact: A. Hebard afh@phys.ufl.edu)
Department of Physics Colloquium Committee:
Hebard (chair), Fulda, Matchev, Mitselmakher, Wang


January 10
  Speaker Bingkan Xue - Theoretical Biophysics Candidate Seminar
  Title How organisms adapt to varying environments: Emergent patterns of responses through evolution
  Abstract The response of physical systems to external conditions can be understood using principles such as symmetries and conservation laws.  What are the general principles for understanding biological organisms that exhibit diverse and adaptive responses to their environment? In this talk, I show that evolution gives rise to common patterns among the organisms' responses to the environment. I present a theoretical framework that describes the emergence of such patterns, and discuss how the framework can be further developed to study biological as well as physical systems with history-dependent responses.
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January 17 - (room 2205)
  Speaker This colloquium slot is reserved for a faculty search candidate presentation
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January 24 (room 2205)
  Speaker This colloquium slot is reserved for a faculty search candidate presentation
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January 31
  Speaker Daniel Wolf Savin, Columbia University
  Title Laboratory Astrophysics Studies along the Cosmic Cycle of Gas
  Abstract Tracing the evolution of baryonic matter from atoms in space to stars and planets hinges on an accurate understanding of the underlying physics controlling the properties of the gas at every step along this pathway. Here I will explain some of the key epochs in this cosmic cycle and highlight our laboratory studies into the underlying atomic, molecular, plasma, and surface physics which control the observed properties of the cosmos.
  Host Imre Bartos

February 7 (room 2205)
  Speaker This colloquium slot is reserved for a faculty search candidate presentation
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February 8 Special Colloquium - Room 1002 at 4:05pm
  Speaker Gabriela González, LSU, LIGO
  Title Gravitational Waves Astronomy
  Abstract The first detection of gravitational waves in 2015 by the LIGO detectors, created by the merger of black holes more than a billion years ago, was followed by several other signals from black holes. In 2017, the merger of neutron stars was detected by LIGO and Virgo detectors and by gamma-ray telescopes, and was found by many electromagnetic observations too: a new era of gravitational wave astrophysics has started with very bright prospects for the future. We will describe the technology involved in the LIGO gravitational wave detectors, details of the latest discoveries and the exciting prospects for more detections in the next years.
  Host David Tanner

February 14 (room 2205)
  Speaker This colloquium slot is reserved for a faculty search candidate presentation
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February 21
  Speaker This colloquium slot is reserved for a faculty search candidate presentation
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February 28
  Speaker This colloquium slot is reserved for a faculty meeting
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March 7
  Speaker APS meeting and spring break
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March 14
  Speaker Pierre Ramond
  Title Feynman Centenary Colloquium
  Abstract TBD
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March 21

  Speaker Cliff Will, UF Physics (Winner of the 2019 Albert Einstein Medal)
  Title Is Einstein Still Right?
  Abstract Einstein formulated general relativity just over 100 years ago. Although it is generally considered a great triumph, the theory's early years were characterized by conceptual confusion, empirical uncertainties and a lack of relevance to ordinary physics. But in recent decades, a remarkably diverse set of precision experiments has established it as the "standard model" for gravitational physics. Yet it might not be the final word. We review a century of measurements that have verified general relativity, including the recent detections of gravitational waves, and describe some of the opportunities and challenges involved in testing Einstein’s great theory in new regimes of strong fields and gravitational radiation.
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March 28
  Speaker Kunie Ishioka from NIMS (National Institute for Materials Science), Tsukuba Japan
  Title Ultrafast spectroscopy for materials science - and an experience as a female scientist in Japan
  Abstract Opto-electronic devices, such as photocatalysts, photovoltatics, light emitting diodes and lasers convert light into electric current or vice versa in metals and semiconductors. The opto-electronic conversion processes occur typically on time scales ranging from femtosecond (10^-15 s) to nanoseconds (10^-9 s), and are often affected by collective atomic vibrations or phonons. In the present seminar I will introduce fundamental studies on ultrafast carrier and phonon dynamics at semiconductor interfaces in lead halide perovskite solar cells and lattice-matched GaP/Si(001). I will also talk about my personal experiences of being one of the few female physicists in Japan.
  Host Chris Stanton

April 4
  Speaker Erik Deumens, Director / UF Information Technology – Research Computing and scientist in the Department of Chemistry and Department of Physics
Sponsored by the Department of Physics and Molecular Magnets for Quantum Materials (M2QM)
Title Quantum mechanics: How Einstein and Bohr led everybody astray
Abstract For over 90 years, since quantum mechanics was formulated in 1926, physicists, mathematicians and philosophers have argued about the meaning of the mathematical entities in the quantum formalism. Bohr and Einstein argued that classical experimental concepts needed to be the basis, the young Heisenberg wanted to follow the formalism, explore it, and see where it would lead. Bohr and Einstein won the argument, leaving us with a mess of multiple inconsistent interpretations. But the basic rules are simple and precise and work exquisitely well.
The main problem with quantum mechanics is the probabilistic nature of quantum phenomena. In this talk we present a framework to discuss the deterministic foundation of quantum mechanics that is governed by the Schrödinger equation, introduce a probability measure to describe the statistics (different from von Neumann's statistical operator or density matrix, which Schrödinger showed in 1932 to be inadequate), derive dispersionless variables that satisfy classical Hamilton equations. This then allows a clear and detailed description of the measurement in quantum mechanics. It turns out that experiments have very limited access to the inner workings of quantum processes, most of which remain hidden. This is because physical systems are described at the quantum level by functions, not values as in classical theories.
Host Henk Monkhorst

April 11
  Speaker Zoltan Haiman (Columbia University )
  Title Merging Supermassive Black Hole Binaries
Abstract Supermassive black hole (SMBH) binaries are inevitably produced during galaxy formation, but observational evidence for them remains elusive. I will discuss the coupled dynamics of a SMBH binary with a circumbinary gas disk, and the expected characteristics of electromagnetic (EM) emission from such a system. In particular, the emission is likely time-variable, and contain unique spectral signatures, which should aid in the identification of SMBH binaries. We have performed hydrodynamical simulations and found that binaries can be fueled efficiently, and that the accretion rates onto the BHs have quasi-periodic modulations. The periodicity pattern depends on the mass ratio, and the strong periodic emission persists all the way to the merger. This may be used to identify unique counterparts of gravitational wave sources expected to be detected by Pulsar Timing Arrays and by LISA, and to discover wider binary SMBHs in time-domain EM surveys. We have identified a handful of quasars with periodic optical variability on the timescale of O(year). I will comment on the interpretation of these quasars as SMBH binary candidates, and on the possibility of seeing an analogous "X-ray chirp" during the late-stage inspiral a LISA binary.
  Host Bartos

APRIL 18
Speaker Francis Halzen, University of Wisconsin
  Title IceCube: Opening a New Window on the Universe from the South Pole
Abstract : The IceCube project has transformed a cubic kilometer of natural Antarctic ice into a neutrino detector. The instrument detects more than 100,000 neutrinos per year in the GeV to PeV energy range. Among those, we have isolated a flux of high-energy neutrinos of cosmic origin, with an energy density similar to that of high-energy photons and cosmic rays in the extreme universe. We recently identified their first source: on September 22, 2017, several astronomical telescopes pinpointed a flaring galaxy, powered by an active supermassive black hole, as the source of a cosmic neutrino with an energy of 290 TeV. Archival IceCube data subsequently revealed in 2014 a flare of more than a dozen neutrinos from the same direction. At a distance of four billion light-years, ten times further than the nearest such sources, the first cosmic ray accelerator seems to belong to a special class of active galaxies that may be responsible for the origin of the highest energy particles in the Universe.
  Host Bartos