Department of Physics & Astronomy
Previous Colloquia and Videos
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Department of Physics & Astronomy
May 31, 2018 Susan Kassin - Space Telescope Science Institute Toward a New Understanding of Disk Galaxy Formation One of the most important open issues in astronomy is the assembly of galactic disks. Over the last decade this has been addressed with large surveys of internal galaxy kinematics spanning the last 10 billion years of the universe. I will discuss recent results from my group that show the kinematic assembly of disk galaxies since a redshift of 2. Our results strongly challenge traditional analytic models of galaxy formation and provide an important benchmark for simulations. Furthermore, I will discuss our plans for using the multi-object spectrograph on JWST to enrich our understanding of galaxy kinematics at intermediate redshifts, and to extend our measurements to potentially unvirialized systems in the much earlier universe. From mock JWST observations of zoom-in simulations of galaxies, we are finding that interpreting these observations is not necessarily straightforward. May 24, 2018 Vid Irsic - University of Washington Small Scale Structure of the IGM: A Dark Matter Tale The intergalactic medium (IGM) plays a unique role in constraining the (small scale) matter power spectrum, since the low-density, high redshift IGM filaments are particularly sensitive to the small-scale properties of dark matter. The main observable manifestation of the IGM, the Lyman-alpha forest, has provided important constraints on the linear matter power spectrum, especially when combined with cosmic microwave background data. This includes, most notably, the tightest constraints on warm dark matter (WDM) and fuzzy dark matter (FDM) models, that I will present in this talk. May 17, 2018 Smadar Naoz - University of California, Los Angeles (UCLA) Triples are Here and There, Triples are Everywhere

(Triples in Planets, Stars, and Balck holes) Many observed triple systems in our Universe are in a hierarchical configuration: two objects orbit each other in a relatively tight inner binary while the third object is on a much wider orbit. In this case, the secular approximation (i.e., phase-averaged, long-term evolution) can be applied, where the interactions between two non-resonant orbits are equivalent to treating the two orbits as massive wires. Thus, the orbits may change shape and orientation, on timescales longer than the orbital periods, but the semi-major axes are constant. This approximation has been proven to be very useful in many astrophysical contexts, from planetary to triple-star systems and even black holes. I will discuss recent developments in that field and will show that hierarchical triple systems are richer and far more exciting than considered of before. In particular, the tight orbit can reach extremely high eccentricities and undergo chaotic flips of its orientation. This behavior has important implications for the evolution of many systems, and I will present some seminal examples, such as retrograde hot Jupiters, blue stragglers, and black-hole binaries. May 10, 2018 Andrew Fruchter - Space Telescope Science Institute (STScI) Refusing to Go Quietly: Gamma-Ray Bursts, Superluminous Supernovae and their Progenitors Gamma-ray bursts (GRBs) are the most brilliant objects in the universe. Some are initially bright enough to be seen by the unaided eye to a redshift of one. Yet the majority of GRBs, the so-called long-soft GRBs (LGRBs) are, like most supernovae, produced by the collapse of a massive star. I will discuss the environmental conditions and stellar progenitors which in rare circumstances create these unusually brilliant explosions and with them the most relativistic bulk motion known. I will show that properties of an unusual GRB, GRB 111209a, and strong similarities between the hosts hydrogen-poor Superluminous Supernovae (SLSNe) and LGRB hosts suggest that LGRBs and SLSNe may have been particularly prevalent the early universe, and that the similar local environments in which they are found may be an important component in the formation of the central engines that power these events. I will also use measurements of the relativistic outflow of LGRBs to place some limits on the central engines. Short Bio: Andy Fruchter received his PhD working with Joe Taylor at Princeton on millisecond pulsars, then went on to a Teagle Fellowship at the Department of Terrestrial Magnetism of the Carnegie Institution and a Hubble Fellowship at Berkeley. After Berkeley he joined the staff of the Space Telescope Science Institute (STScI) where, working with Richard Hook, he developed the Drizzle algorithm for handling the image processing of the Hubble Deep Field, which became the primary algorithm for combining Hubble Space Telescope (HST) images. At STScI he continued his work on compact objects and their progenitors. He was a member of the Supernova Cosmology Project which was one of the two teams responsible for discovering the acceleration of the expansion of the universe. He has also lead a number of large programs studying gamma-ray bursts and their host environments, and has most recently been involved in HST observations of the merging neutron star binary, GW 170817. May 3, 2018 Adrian Liu - UC Berkeley & McGill University 21cm Cosmology in the Detection Era Although it is a crucial part of our cosmic timeline, Cosmic Dawn—when the first stars and galaxies formed and systematically reionized the intergalactic medium—remains relatively unexplored. By tracing the distribution and state of neutral hydrogen, 21cm cosmology promises to provide the first direct observations of Cosmic Dawn. The Hydrogen Epoch of Reionization Array (HERA) is a low-frequency radio interferometer that is poised to realize this promise within the next few years by making large-scale observations of the 6 < z < 20 universe. In this talk, I will provide an overview of the scientific capabilities of HERA as well as a status update on high-z 21cm cosmology. As part of this update, I will discuss a recently claimed first detection of the 21cm line at z~17 from the Experiment to Detect the Global EoR Signal (EDGES). If confirmed, the EDGES result would have broad-ranging implications not just on the astrophysics of the first stars, but possibly also the physics of dark matter. April 19, 2018 Miguel Mostafa - Pennsylvania State University Multi-Te V Particle Astrophysics with the HAWC Observatory High-energy gamma-ray observations are an essential probe of cosmic-ray acceleration mechanisms. The detection of the highest energy gamma rays and the shortest timescales of variability are the key to improve our understanding of the acceleration processes and the environment of the cosmic accelerators. The High Altitude Water Cherenkov (HAWC) experiment is a large field of view, multi-Te V, gamma-ray observatory continuously operating at 14,000 ft since March, 2015. The HAWC observatory has an order of magnitude better sensitivity, angular resolution, and background rejection than the previous generation of water-Cherenkov arrays. The improved performance allows us to discover Te V sources, to detect transient events, to study the Galactic diffuse emission at Te V energies, and to measure or constrain the Te V spectra of Ge V gamma-ray sources. In addition, HAWC is the only ground-based instrument capable of detecting prompt emission from gamma-ray bursts above 100 Ge V. In this colloquium I will present the most recent results using the first three years of data from the HAWC observatory. I will also briefly mention the exciting perspectives of building a next-generation gamma-ray experiment at a very high altitude in the Southern Hemisphere. Short Bio: Miguel Mostafa is a professor of physics and of astronomy & astrophysics at Penn State University. After obtaining his Ph.D. in high energy particle physics from Instituto Balseiro in Argentina, he was a fellow of the Instituto Nazionale di Fisica Nucleare in Italy, and a postdoctoral research associate at the University of New Mexico. He was an assistant professor of physics at the University of Utah, and an associate professor of physics at Colorado State University before joining Penn State in 2013. He has been working on ultra-high energy cosmic rays as a member of the Pierre Auger Collaboration, and he is the PI of the Astrophysical Multi-Messenger Observatory Network at Penn State since 2013. His research interests are in high energy particle astrophysics, including the origin of cosmic rays, acceleration mechanisms, particle physics at energies above terrestrial accelerators, gamma-ray astronomy and the structure of the Galaxy, and the nature and properties of dark matter. He was elected fellow of the American Physical Society in 2016, and his teaching awards include the C.I. Noll Award for Excellence in Teaching at Penn State, Best Teacher Awards and the Outstanding Mentor Award at Colorado State University, and the Students Choice Award at the University of Utah. April 12, 2018 David Reitze - California Institute of Technology The Gravitational Wave Astronomical Revolution We are witnessing a revolution in astrophysics brought about by the first direct detections of gravitational waves by LIGO and Virgo. Twenty years ago many wondered when or even if gravitational waves could be detected on earth; today observations of binary black hole mergers detected through their gravitational wave emissions are becoming routine. The first observation of two colliding neutron stars in August 2017, captured both in gravitational waves and in light, has given us new insights into gamma ray bursts, kilonovae, the formation of heavy elements, and even gravity itself. Gravitational waves provide unique information about the most energetic astrophysical events, revealing insights into the nature of gravity, matter, space, and time. In this talk, I’ll cover gravitational waves and what makes them so difficult to detect and at the same time such powerful and unique probes of the universe. Most of the presentation will focus on the interferometers, the LIGO-Virgo detections and their astrophysical implications. Time permitting, I’ll give a preview of where LIGO intends to go in the next decade and beyond. April 5, 2018 Yuval Grossman - Cornell University Neutrinos as the Key to the Universe as We Know It Why is there only matter around us? How neutrinos acquire their tiny masses? Why all particles in Nature have integer electric charges? It turns out that these open questions maybe related. In this talk I will explain these open questions, the connection between them, and describe the on-going theoretical and experimental efforts in understanding them. March 15, 2018 Alexander Grosberg - New York University Activity Driven Segregation of Phases in Particles and (Bio)Polymers Big nuts segregate from small ones; oil segregates from water; but there is also another novel type of segregation, activity driven, which may be important for the functioning of our chromosomes. Video March 8, 2018 Rafael Lang - Purdue University Xenon and the Hunt for Dark Matter The Nature of Dark Matter is one of the biggest outstanding problems in physics. I will review the evidence for Dark Matter from cosmological and astrophysical arguments, spanning vast time and length scales. Some leading candidate models will be introduced. In particular, the search for WIMP particles is led by Xenon-based detectors. With target masses exceeding a tonne, these detectors are now also sensitive to signals from solar and supernova neutrinos. With their extraordinary sensitivity even to single electrons, new experiments to search for sub-GeV dark matter become possible. I will report on results and the status of the XENON1T experiment as well as its upgrade XENONnT, will introduce the LBECA experiment to search for sub-GeV dark matter, and will give an outlook both for the search for dark matter as well as for neutrinoless double-beta decay. Video March 1, 2018 Benjamin Lev - Stanford Exploring quantum thermalization with a magnetic quantum Newton’s cradle The question of how chaos arises in nature touches on widely disparate phenomena. For example, the fact that chaos emerges gradually in weakly nonlinear systems unpins our explanation for why the solar system remains stable. While the work of Kolmogorov and others in the 1950’s provided a firm connection between the theories of classical mechanics and classical statistical mechanics by showing how classical chaos and thermalization emerge, the analogous question in quantum physics remains a key unresolved question. How, specifically, does quantum chaos—and hence, thermalization—emerge in isolated quantum systems? We will present a new experiment that explores this question by studying the dynamics of the momentum in a dipolar quantum Newton's cradle consisting of highly magnetic dysprosium atoms. This system constitutes the first dipolar strongly interacting 1D Bose gas. The dipolar interactions provide tunability of both the strength of the integrability-breaking perturbation and the nature of the near-integrable dynamics. The work sheds light on the mechanisms by which isolated quantum many-body systems thermalize and on the temporal structure of the onset of thermalization. February 22, 2018 Nitya Kallivayalil - University of Virginia Probing the Dark Halo of the Milky Way The Local Group, the regime in which detailed star-by-star studies can be done, is becoming a major testbed for the cold dark matter-based model of the Universe. Critical to these tests is a better estimate of the total Milky Way halo mass. The most reliable means by which to constrain the properties of the Milky Way dark halo is through assessing the 6-D phase space distributions of tracers of its gravitational potential. This requires accurate proper motions (tangential velocities) in addition to generally known radial velocities for field stars, streams, and satellite galaxies widely distributed throughout the halo. In turn, these measurements allow us to investigate the past histories of these tracers, and thus the accretion history of the Milky Way. I will discuss some novel approaches we have been developing to obtain proper motions for a variety of tracers in the Milky Way halo, including streams, globular clusters, and satellite galaxies, to definitively constrain the Milky Way's dark halo mass, shape and distribution. These techniques involve space-based imagers (HST), wide-field ground-based imagers, as well as imagers equipped with adaptive optics systems. I will also discuss the future prospects for this work, and the trade-off between Gaia, space missions (JWST, WFIRST, EUCLID), and ELTs. Video February 15, 2018 Abhay Deshpande - Stony Brook University The Science and Status of the U.S. Electron Ion Collider Quantum Chromodynamics (QCD) is no doubt the correct theory of strong interaction within the Standard Model of Physics. However, despite decades of significant theoretical progress made based on a broad range of experimental observations, some of the most intellectually compelling questions remain unanswered. For example, how do quark, gluons and their interactions & dynamics, collectively result in the observed fundamental properties of hadrons such as the spin and mass? What is the QCD/partonic origin of the nucleon-nucleon forces in nuclei? How does nuclear environment impact the parton’s momentum distribution in confined nucleons? Does the gluon density in nucleons and nuclei saturate at extremely high energy, and form a universal form of gluonic matter? What connections can be made between the understanding of cold QCD matter in a nucleus to the hot Quark Gluon Plasma that emerges when two nuclei collide at the LHC and RHIC? Such questions can now be addressed qualitatively through a polarized high-energy high-luminsity Electron Ion Collider (EIC). Along with the advances in accelerator technology, lessons from the limitations experience in past fixed target and collider experiments will impact the future detector and interaction region designs for this future collider. Last, but certainly not the least, the theoretical frame work is mature enough to put the resulting measurements in to comprehensive picture within QCD that could answer the above compelling questions. The Electron ion collider (EIC) was recommended in the 2015 US Longe Range Plan prepared by the US Nuclear Science Advisory Committee (NSAC) as the highest priority for new construction for a new facility within the US. In this talk, I will summarize its science case, and present the status and plans for its realization. Video February 8, 2018 Sayantani Ghosh - UC Merced Directed nano-assembly of adaptive functional structures The design and development of adaptive functional structures using artificially synthesized nano-constituents as building blocks is one of the most compelling current research areas. The typical approach is bottom-up assembly of nanoparticles (NPs), and while this has led to the successful creation of two- and three-dimensional super-lattices, these tend to simply exhibit the combined properties of the constituent NPs, instead of exhibiting a novel functionality arising from synergistic inter-particle interactions. The route we use involves utilizing soft materials such as liquid crystals as templates for NP assembly, which removes rigid constraints in the way the individual components can be combined and make novel architectures possible, such as non-planar structures. Additionally, it allows us to modulate the NP assembly in situ via external controls, such as temperature, mechanical strain and electromagnetic fields, which lead not just to greater versatility in functionality, but to the emergence of entirely novel behavior. Following this approach, we demonstrate “cluster assembly” of metallic, magnetic and semiconducting NPs that form structures with interesting new properties and diverse applications in magneto-optical sensing, photothermal therapy, and tissue engineering. This work was funded by NSF and UCMEXUS-CONACYT. Video February 1, 2018 Chetan Nayak - UCSB Thermalization and its Discontents Thermalization is the process by which a typical closed quantum system in a generic initial state approaches local thermal equilibrium. Its occurrence precludes some fascinating and potentially useful equilibrium states of matter. However, under certain conditions, thermalization only occurs after an exponentially long time. During the intervening time interval, which is called the prethermal regime, most of the beneficial properties associated with thermal equilibrium continue to hold, but some of the limitations are removed. As a result, states of matter such as time crystals and self-correcting quantum memories can occur. Video January 25, 2018 Joshua Lui - UCR Observation of Valley-Exclusive Bloch-Siegert Shift in Monolayer WS2 Coherent interaction with off-resonance light can be used to shift the energy levels of atoms, molecules, and solids. The dominant effect is the optical Stark shift, but there is an additional contribution from the so-called Bloch-Siegert shift that has eluded direct and exclusive observation in solids. We observed an exceptionally large Bloch-Siegert shift in monolayer tungsten disulfide (WS2) under infrared optical driving. By controlling the light helicity, we could confine the Bloch-Siegert shift to occur only at one valley, and the optical Stark shift at the other valley, because the two effects obey opposite selection rules at different valleys. Such a large and valley-exclusive Bloch-Siegert shift allows for enhanced control over the valleytronic properties of two-dimensional materials. Reference: Large, valley-exclusive Bloch-Siegert shift in monolayer WS2. E. J. Sie, C. H. Lui, Y.-H. Lee, L. Fu, J. Kong & N. Gedik Science 355, 1066-1069 (2017) Biography: Prof. Chun Hung (Joshua) Lui joined the Department of Physics at UC Riverside as an assistant professor in July 2015. Before that he was a postdoc at MIT. He obtained his Ph.D. in physics at Columbia University in 2011. His group investigates the light-matter interactions in 2D layered materials, such as graphene and transition-metal dichalcogenides, by means of Raman, infrared, and ultrafast pump-probe laser spectroscopy and imaging. Video January 18, 2018 Jim Thomas - Lawrence Berkeley National Laboratory The Chiral Magnetic Effect in Hot QCD I will give a brief introduction to the world of Hot QCD at the Relativistic Heavy Ion Collider and the unusual opportunities that it provides for the experimentalist. Heavy Ion Collisions allow us to study nuclear matter at high temperature (150 MeV) and high density (10x normal nuclear matter densities). These are conditions that are similar to the conditions in the early Universe a few microseconds after the Big Bang. Heavy ion collision also provide systems with high angular momentum (1000 h-bar), and they create extremely large magnetic fields (10^17 gauss). One application of these high magnetic fields is the Chiral Magnetic Effect. If the CME can be found experimentally, it would be the smoking gun for Chiral symmetry restoration in heavy ion collisions, as well as the observation of parity violation in the strong interaction (in hot QCD). I will discuss the phenomenology of the CME and give an update on the status of the experimental search for it. January 11, 2018 Yun-Tse Tsai - SLAC Exploring Neutrino Territory: Using LArTPC Technology Neutrinos are the electrically neutral elementary particles with finite mass. The discovery of the non-zero masses is the first instance of a conflict with the Standard Model of particle physics, which has successfully described elementary particles and interactions but leaves questions unanswered. The fruitful results from neutrino experiments in the past two decades have opened a window to a new territory, and further measurements are required to address fundamental questions. In this talk, I will introduce the core topics of neutrino physics, the requirements of neutrino experiments, focusing on the technology of liquid argon time projection chamber (LArTPC). In particular, I will discuss measuring neutrinos from supernova explosions and searching for exotic physics with LArTPCs. I will talk about the MicroBooNE experiment, the first large LArTPC in the U.S., its recent results, and the future LArTPC experiments. December 7, 2017 Jay Wacker Physicists at Startups I recently left an academic physics career to join a tech startup called Quora Quora is questions and answer knowledgebase whose mission is to share and grow the world's knowledge. I'll discuss why I made this career change, why physicists can make a great impact at startups, and my observations from my time outside of physics. Video November 30, 2017 Wilson Ho STM Inelastic Electron Tunneling Spectroscopy and Microscopy Inelastic electron tunneling in a scanning tunneling microscope (STM) provides a unique way to measure and image the excitation of an atom or molecule adsorbed on a solid surface with sub-Ångstróm resolution. Inelastic electron tunneling spectroscopy (IETS) and microscopy was first reported in 1998 for the detection of vibrational excitation in a single molecule and has since been extended to the excitation of a single electron spin and the rotation of a single molecule. This talk illustrates by three examples the use of STM-IETS to image the nature of the chemical bond in molecular structure and intermolecular interactions, spin-vibration coupling in single molecule magnetism, and single molecule vibration and dynamics in the time domain. Video November 16, 2017 Andrea Young Topological order and symmetry breaking in van der Waals heterostructures

Correlated quantum states of matter can be distinguished by their symmetry, their topology, or both. Examples of symmetry-breaking in solid state systems abound, and include most familiar phases of matter, such as ferromagnetism, superconductivity, and crystalline order. Topological order is much rarer experimentally, having only been definitively observed at partial filling of Landau levels—flat bands of electronic states that develop when two-dimensional electrons are subjected to a large magnetic field. Topological order manifests through global properties of the many-body wavefunction, encoded in the fractionally quantized Hall effect and fractional quantum numbers of the collective excitations supported by the interacting electron system. Theoretically, topological order can also arise within generalized ‘Chern bands,’ of which Landau levels are a limiting case. Most famously, electrons subjected simultaneously to a periodic potential and magnetic field are confined to the fractal bands of the Hofstadter butterfly, each of which is a Chern band.

In this talk, I will describe the experimental observation of ‘fractional Chern insulators’ in van der Waals heterostructures created by combining atomically thin graphite and insulating hexagonal boron nitride. van der Waals heterostructures provide an ideal experimental platform for investigating the correlated physics of Chern bands, allowing superlattice potentials (engineered from the interference of the mismatched graphene and boron nitride lattices) to be combined with exceptionally low disorder and strong interactions. I will describe how we distinguish the fractional Chern insulators—which feature fractionally charged excitations--from the other gapped electronic phases in these devices including those that break lattice symmetries. Finally, I will describe prospects for using fractional Chern insulators as a substrate for engineering and detecting novel emergent quasiparticles with unconventional quantum statistics.

Video November 9, 2017 Alex Travesset Nanoparticle Assemblies as a New Form of Matter Materials whose fundamental units are nanoparticles, instead of atoms or molecules, are a new form of matter that is gradually emerging as major candidates to solve many of the technological challenges of our century. Those materials display unique structural, dynamical and thermodynamical properties, often reflecting deep underlying geometric and topological constraints. In this colloquia, I will discuss the assembly of these materials into crystals or quasi-crystals, so-called nanoparticle superlattices. I will introduce three successful strategies to induce crystallization into simple and binary lattices: DNA programmable self-assembly, crystallization of nanoparticle neutral (uncharged) polymer brushes by electrostatic phase separation and also, by controlling self-assembly through hydrocarbon and polystyrene capping ligands. I will show that the structure of superlattices follows from considering capping ligands as Skyrmions with vortex textures, which determine the bonding very much like atomic orbitals in lattices of simple atoms. I will also discuss the underlying icosahedral order present in all experimental superlattices reported so far, and discuss a wealth of experimental data and numerical simulations providing confirmation of the theoretical predictions. I will finish with an outlook for this fascinating new materials. November 2, 2017 Nathaniel Gabor Why Are Terrestrial Plants Green? And Other Essential Questions About Emerging Quantum Optoelectronic Technologies Nature realizes a vast array of complex structures composed of molecular building blocks, the electronic structure of which can be well described by quantum mechanics. In photosynthetic light harvesting, for example, quantum behavior within complex nanoscale structures has generated tremendous recent interest. While there is remarkable potential that photosynthetic systems are, in a sense, behaving as quantum devices, the exact relationship between structure and the properties of quantum states (e.g., coherence) remains a topic of vigorous debate. In this talk, I describe a new paradigm – based on internal thermodynamic fluctuations in a QHE photocell – that attempts to describe highly efficient light energy harvesting in complex quantum structures. By understanding the connection between electronic structure and energy fluctuations, I describe an intrinsic regulation mechanism that emerges from quantum structure alone. Beyond gaining a deeper understanding of quantum optoelectronics, the natural regulation process described here promises to have applications across various disciplines ranging from quantum nanoscience and computing to bionanoscience and astrobiology. Natural regulation may also explain the predominance of green plants on Earth. Video October 26, 2017 Yaroslav Tserkovnyak Spin hydrodynamics in insulators I will review recent progress in understanding novel transport phenomena in magnetic insulators. Central to this will be conservation laws that are rooted in topological invariance of certain types of magnetic field configurations. The continuity relations associated with such dynamic spin textures can mimic superfluid phenomena, even at high temperatures. Key examples will include easy-plane magnetic films, materials that harbor skyrmionic textures, and, surprisingly, disordered glassy spin systems. Recently developed magnetoelectric and thermoelectric techniques (e.g., based on spin Hall and spin Seebeck effects) are now allowing us to systematically access this physics in a range of materials, both old and new. Video October 19, 2017 Carl Wieman Taking a scientific approach to teaching physics (and most other subjects)

Guided by experimental tests of theory and practice, science has advanced rapidly in the past 500 years. Guided primarily by tradition and dogma, science education meanwhile has remained largely medieval. Research on how people learn is now revealing much more effective ways to teach and evaluate complex thinking and learning than what is in use in the traditional science class. Students and instructors find such innovative research-based teaching more rewarding, because they involve the physics expertise of the instructor much more extensively and transfer that expertise more effectively. This research is setting the stage for a new approach to teaching and learning that can provide the relevant and effective science education for all students that is needed for the 21st century. I will also cover more meaningful and effective ways to measure the quality of teaching. Although the focus of the talk is on undergraduate science and engineering teaching, particularly physics, the underlying principles come from studies of the general development of expertise and apply widely.

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October 12, 2017 Hilke E. Schlichting Planet Formation at Home and Abroad Recent observations by the Kepler space telescope have led to the discovery of more than 4000 exoplanet candidates consisting of many systems with Earth- to Neptune-sized objects that reside well inside the orbit of Mercury, around their respective host stars. How and where these close-in planets formed is one of the major unanswered questions in planet formation. I will present new results that self-consistently treat the nebular gas accretion onto rocky cores and the subsequent evolution of gas envelopes due to cooling and photo-evaporation following the dispersal of the protoplanetary disk. I will demonstrate that planets shed their outer layers (dozens of percent in mass) following the disk's dispersal (even without photo-evaporation), and that their atmospheres shrink in a few Myr to a thickness comparable to the radius of the underlying rocky core. In addition, I will discuss the importance of collisions in shaping the architecture and composition of super-Earths. Finally, I will conclude with comparing our new results with observations and discussing the implications for the origin and formation of terrestrial planets in our solar system and for close in exoplanets. Video October 5, 2017 David Simmons-Duffin The conformal bootstrap: magnets, boiling water, and quantum gravity

Conformal Field Theory (CFT) describes the long-distance dynamics of quantum and/or statistical many-body systems. Often, this dynamics is so complicated that traditional computational tools fail.

However, powerful new techniques for understanding CFTs have emerged in the last decade, based on the old idea of the "conformal bootstrap". I will describe how the bootstrap lets us calculate critical exponents in the 3d Ising Model to world-record precision, how it explains striking relations between magnets and boiling water, and how it can be applied to questions across theoretical physics.

Video September 28, 2017 Jianwei (John) Miao Exploring the #D Nano and Atomic World: Coherent Diffractive Imaging and Atomic Electron Tomogrpahy Crystallography has been fundamental to the development of many fields of science over the past century It has now matured to a point that as long as good quality crystals are available, their atomic structure can be routinely determined in three dimensions. However, many samples in nature are non-crystalline and their three-dimensional (3D) structures are not accessible by crystallography. Overcoming this hurdle has required the development of new structure determination methods. In this talk, I will present two methods that can go beyond crystallography: coherent diffractive imaging (CDI) and atomic electron tomography (AET). In CDI, the diffraction pattern of a non-crystalline sample or a nanocrystal is first measured and then directly phased to obtain an image. The well-known phase problem is solved by combining the oversampling method with iterative algorithms. In the first part of the talk, I will illustrate several important CDI methods and highlight some important applications in the physical and biological sciences using 3rd generation synchrotron radiation and X-ray free electron lasers. In the second part of the talk, I will present a general tomographic method, termed AET, for 3D structure determination of crystal defects and disordered materials at the individual atomic level. By combining advanced electron microscopes with novel data analysis and tomographic reconstruction algorithms, AET has been used to reveal the 3D atomic structure of crystal defects and chemical order/disorder such as grain boundaries, anti-phase boundaries, stacking faults, dislocations and point defects, and to precisely localize the 3D coordinates of individual atoms in materials without assuming crystallinity. As coherent X-ray sources and powerful electron microscopes are under rapid development in the world, it is anticipated that CDI and AET will find broad applications across different disciplines. June 8, 2017 Raphael Flauger - University of California, San Diego Deciphering the Beginning The cosmic microwave background contains a wealth of information about cosmology as well as high energy physics. It tells us about the composition and geometry of the universe, the properties of neutrinos, dark matter, and even the conditions in our universe long before the cosmic microwave background was emitted. After a general introduction, I will discuss lessons from the recently released Planck full mission data for models of the early universe. Finally, I will turn to the search for primordial gravitational waves and provide an outlook what we may hope to learn from current and future CMB experiments. Video May 25, 2017 Rob Myers - Perimeter Institute Scanning New Horizons: Information, Holography & Gravity New advances and insights often emerge from the confluence of different ideas coming from what appeared to be disconnected research areas. The theme of my talk will review an ongoing collision between the three topics listed in the title above which has been generating interesting new insights about the nature of quantum gravity, as well as other fields, eg, condensed matter physics and quantum field theory. Video May 18, 2017 Rychard Bouwens - Leiden University Young Galaxies Forming in the High-Redshift Universe Over the last few years, enormous progress has been made in studying galaxies in the first two billion years thanks to the incredible capabilities of the Hubble and Spitzer Space Telescopes. Already, more than 1500 probable galaxies are known at redshifts above z~6, and now the current frontier is at z~9-10, with 50 plausible galaxy identifications to date, and a spectroscopic redshift measurement to z=11.1. Noteworthy advances are also being made in characterizing the physical properties of these distant galaxies, with probes of the nebular emission lines and specific star formation rates to z~8.5 and new constraints on dust-enshrouded star formation at z>~2 from ALMA. One area where there has been particularly exciting activity is in the study of ultra-faint galaxies in the early universe with the Hubble Frontier Fields (HFF) program, combining the power of long exposures with Hubble and Spitzer with gravitational lensing by massive galaxy clusters. In this colloquium, I survey these and other highlights of current research on high redshift galaxies, while looking forward to future work with JWST. Video May 11, 2017 Daniel Whiteson - University of California, Irvine Deep Learning in High Energy Physics Recent advances in artificial intelligence offer opportunities to disrupt the traditional techniques for data analysis in high energy physics. I will describe the new machine learning techniques, explain why they are particularly well suited for particle physics, and present selected results that demonstrate their new capabilities. Video May 4, 2017 Oleg Gnedin - University of Michigan Progress in Simulations of Galaxy Formation I will discuss recent progress in numerical modeling of galaxy formation. Cosmological simulations can now resolve galactic structure on the spatial scale of parsecs, and follow the build-up and dissociation of giant molecular clouds. A lot of effort is going into understanding the drivers of turbulence in the interstellar medium and the effects of young stars. I will present a novel approach to modeling galactic star formation as a composition of individual star clusters, which allows new powerful tests of galaxy formation simulations. In a few years we should have fairly reliable predictions for full star formation histories of galaxies. Video April 27, 2017 Sima Setayeshgar - Indiana University Optimal strategies in single cell sensing and response Biochemical reactions constitute the cell's computing language, carrying out the processes of life from cell growth and death to response to environmental cues. In a classic work, Berg and Purcell showed that bacterial chemotaxis, where a single-celled organism responds to small changes in the concentration of chemicals outside the cell, is limited directly by molecule counting noise and that aspects of the bacteria's computational and behavioral strategies are optimal given the physical constraints. In this talk, I will revisit and extend their arguments: For the ubiquitous case of sensing by multiple, cooperatively interacting biological receptors, I will show that while the sensiti?vity of response to the change in concentration of signaling molecules is enhanced, the accuracy is limited by the irreducible noise related to the random arrival of diffusing molecules. I will compare theoretical limits with quantitative experimental results for the bacterial flagellar motor demonstrating performance consistent with physical limits. I will also discuss related work aimed at understanding system-level properties of the chemotaxis signaling network from the standpoint of network adaptation and information transmission. Video April 20, 2017 Yannick Meurice - University of Iowa Application of the tensor renormalization group method to quantum simulations and machine learning The renormalization group method has played a key role in establishing the standard model of electroweak and strong interactions. It connects the short and large distance behaviors of field theoretical models and provides an unified way to approach lattice models in condensed matter and high energy physics. I describe a recently proposed computational method called tensor renormalization group which applies to spin and gauge models. I discuss applications in the context of quantum simulations on optical lattice and machine learning. Video April 13, 2017 Michael Roukes - Caltech Nanotechnology for Massively-Parallel, Multi-Physical Interrogation of Brain Activity Although our understanding of the properties of individual neurons and their role in brain computations has advanced significantly over the past several decades, we are still far from elucidating how complex assemblies of neurons – that is, brain circuits – interact to process information. In 2011, six U.S. scientists from different disciplines banded together, outlined a vision [1,2], and managed to convince the Obama administration of the unprecedented opportunity that exists to launch a coordinated, large-scale international effort to map brain activity. This culminated in the U.S. BRAIN Initiative (Brain Research through Advancing Innovative Neurotechnologies), which was launched in 2013. Our perspective was predicated, in part, on the current level of maturity of diverse fields of nanotechnology and silicon very-large-scale integration (VLSI) that can now be coalesced to create unprecedented tools for massively parallel interrogation of brain activity. We will outline the immense complexity of such pursuits, the hopes we articulated, survey the existing technological landscape for assembling the requisite instrumentation, and then focus upon our own collaborative efforts toward tools enabling multi-physical interrogation of brain activity. We believe this technology will engender a spectrum of new possibilities for neuroscience and clinical neuromedicine. April 6, 2017 Kai Mueller - Technical University of Munich Nanostructure Quantum Photonics Optically active semiconductor nanostructures are promising candidates for building blocks in future photonic quantum technologies, including quantum information processing, quantum communication, quantum sensing and quantum metrology. By embedding a single quantum emitter inside a nanoresonator that strongly localizes the optical field, it is possible to achieve a very strong light–matter interaction. The strength of this interaction is characterized by the coherent emitter-field coupling strength (g), which increases with reduction in the optical mode volume and which also sets the limit on the operational speed of such a system. With InAs quantum dots inside GaAs photonic crystal cavities, coupling strengths of 40 GHz can be reached (much greater than the record values in atom-cavity QED systems). This allows the system to be operated in the strong coupling regime where the formation of hybridized light-matter states results in effective photon-photon interactions and enables the on-chip generation of nonclassical light [1-2]. Exploiting interference effects which are intrinsic to the photonic crystal platform [3] allows to significantly improve the signal to noise ratio and enables the on-chip generation of indistinguishable photons with state-of-the-art metrics [4]. Finally, I will discuss possibilities for generating nonclassical states of light beyond single photons, such as photon bundles. Specifically, I will show that resonantly driven two-level systems which are well established as single-photon sources can also act as sources of two-photon pulses [5]. March 16, 2017 Leslie Rosenberg - University of Washington Searching for Dark-Matter Axions The axion is a hypothetical elementary particle whose existence would explain the baffling absence of CP violation in the strong interactions. Axions also happen to be a compelling dark-matter candidate. Axions could comprise the overwhelming majority of mass in the universe, yet they would be extraordinarily difficult to detect. However, several experiments, either under construction or in operation, would be sensitive to even the more pessimistically coupled dark-matter axions. This talk reviews the state of these searches. Video March 9, 2017 Elena Pierpaoli - USC The Cosmos seen through the Planck satellite eyes The Cosmic Microwave Background (CMB) radiation allows us to study processes of the very early Universe. The detailed study of its anisotropies with the Planck satellite allowed to determine cosmological parameters at unprecedented level of precision. As a byproduct, it also provided important results in several areas of astrophysics such as the detection of clusters through their Sunyavev-Zeldovich signature and characterization of Galactic emission at microwave and infrared wavelengths. The Planck satellite, which was launched in 2009, has completed collecting data and most results have recently been released. I will review the main achievements of the latest data release and interpretation, including the determination of main cosmological parameters, epoch of star formation, galaxy clusters detection and use. I will also discuss future prospects in CMB studies. Video March 2, 2017 Christoph Haselwandter - USC Physical Mechanisms of Membrane Protein Organization and Collective Function Cell membranes are one of the fundamental hallmarks of life. For many of their biological functions, cell membranes rely on the collective properties of lattices of interacting membrane proteins. Here we explore the general physical mechanisms and principles underlying supramolecular organization and collective function of membrane proteins, based on three model systems: (1) We show how the interplay of protein-induced lipid bilayer curvature deformations, topological defects in protein packing, and thermal effects can explain the observed symmetry and size of membrane protein polyhedral nanoparticles; (2) We predict that the observed four- and five-fold symmetric states of mechanosensitive ion channels yield characteristic lattice architectures of channel clusters, with distinctive collective gating properties; (3) We show that lipid bilayer-mediated elastic interactions between chemoreceptor trimers provide a physical mechanism for the observed self-assembly of chemoreceptor lattices, and may contribute to the cooperative signaling response of the chemotaxis system. Video February 23, 2017 Harry Nelson - UCSB Touch the Dark Matter We know from astrophysical evidence that the vast majority of matter in our Universe neither absorbs nor emits light. Does this `Dark Matter' have any relation to the strong, electromagnetic, or weak interactions that comprise our `Standard Model' of particle physics? I'll discuss the current & future world program to detect the dark matter in terrestrial experiments, with particular emphasis on the intense competition among experiements that utilize liquid xenon. The flagship US dark matter experiment, LZ, is part of that competition, and just received final Department of Energy approval. Video February 16, 2017 Nathaniel Craig - UCSB Is Nature Natural? The discovery of the Higgs boson at the LHC marks the culmination of a decades-long quest for the final piece of the Standard Model. But the discovery of the Higgs also adds new urgency to the hierarchy problem, namely the question of why the Higgs boson is so light despite its unique quantum sensitivity to much higher energy scales. This puzzle is made all the more challenging by the lack of evidence for conventional approaches to the hierarchy problem at the LHC and other experiments. In this talk I'll discuss the essential features of the hierarchy problem and its possible solutions, with a particular focus on new approaches to the problem that have emerged in the years following the Higgs discovery. These new approaches feature novel experimental signatures, add urgency to the measurement of Higgs properties, and may shed light on dark matter and other mysteries of the Standard Model. Video February 9, 2017 ALice Shapley - UCLA The MOSFIRE Deep Evolution Field (MOSDEF) Survey: A Detailed Census of the Physics of Galaxy Formation in the Early Universe Understanding the formation and evolution of galaxies remains one of the great challenges of modern cosmology. Key outstanding questions include: What are the physical processes driving the formation of stars in individual galaxies? How do galaxies exchange material with their intergalactic environments? How do the impressive variety of galactic structures that we observe today assemble? How do supermassive black holes affect the evolution of their host galaxies? We present new results from the MOSFIRE Deep Evolution Field (MOSDEF) survey, a comprehensive census of the galaxy population during the peak epoch of activity in the universe ~10 billion years ago. In addition to providing an overview of the MOSDEF survey and its science, we focus on new results regarding the evolving physical conditions in star-forming regions towards higher redshift. Our new results suggest many exciting future observational directions for untangling the detailed nature of star formation in the early universe. Video February 2, 2017 Hendrik Ohldag - Stanford Synchrotron Radiation Laboratory Ultrafast and Very Small: Discover Nanoscale Magnetism With Picosecond Time Resolution Using X-Rays Today’s magnetic device technology is based on complex magnetic alloys or multilayers that are patterned at the nanoscale and operate at gigahertz frequencies. To better understand the behavior of such devices one needs an experimental approach that is capable of detecting magnetization with nanometer and picosecond sensitivity. In addition, since devices contain different magnetic elements, a technique is needed that provides element-specific information about not only ferromagnetic but antiferromagnetic materials as well. Synchrotron based X-ray microscopy provides exactly these capabilities because a synchrotron produces tunable and fully polarized X-rays with energies between several tens of electron volts up to tens of kiloelectron volts. The interaction of tunable X-rays with matter is element-specific, allowing us to separately address different elements in a device. The polarization dependence or dichroism of the X-ray interaction provides a path to measure a ferromagnetic moment and its orientation or determine the orientation of the spin axis in an antiferromagnet. The wavelength of X-rays is on the order of nanometers, which enables microscopy with nanometer spatial resolution. And finally, a synchrotron is a pulsed X-ray source, with a pulse length of tens of picoseconds, which enables us to study magnetization dynamics with a time resolution given by the X-ray pulse length in a pump-probe fashion. The goal of this talk is to present an introduction to the field and explain the capabilities of synchrotron based X-ray microscopy, which is becoming a tool available at every synchrotron, to a diverse audience. The general introduction will be followed by a set of examples, depending on the audience, that may include properties of magnetic materials in rocks and meteorites, magnetic inclusions in magnetic oxides, interfacial magnetism in magnetic multilayers, and dynamics of nanostructured devices due to field and current pulses and microwave excitations. Video January 19, 2017 Xiaoping Hu - UCR MRI: A Field with Endless Advances and Diverse Biomedical Applications Although MRI was invented more than 40 years ago and has been a routine diagnostic imaging modality in clinical practice for more than 30 years, it is still an area of active research with advances being continuously made. These advances have been brought about by technological developments and introduction of new biomedical applications. This talk will provide a brief review major milestones in MRI and highlight some recent advances, particularly those related to neuroimaging. Video January 12, 2017 Mark Alber - UCR Combined Multi-scale Computational and Experimental Studies of Bacterial Swarming and Blood Clot Formation Surface motility such as swarming is thought to precede biofilm formation during infection. Population of bacteria P. aeruginosa, major infection in hospitals, will be shown to efficiently propagate as high density waves that move symmetrically as rings within swarms towards the extending tendrils. Multi-scale model simulations suggest a mechanism of wave propagation as well as branched tendril formation at the edge of the population that depend upon competition between the changing viscosity of the bacterial liquid suspension and the liquid film boundary expansion caused by Marangoni forces. This collective mechanism of cell-cell coordination was shown to moderate swarming direction of individual bacteria to avoid antibiotics. In the second half of the talk, a novel three-dimensional multi-scale model will be described for simulating receptor-mediated adhesion of deformable platelets at the site of vascular injury under different shear rates of blood flow. The modeling approach couples submodels at three biological scales crucial for the early clot formation: novel hybrid cell membrane submodel to represent physiological elastic properties of a platelet, stochastic receptor–ligand binding submodel to describe cell adhesion kinetics and lattice Boltzmann submodel for simulating blood flow. Predictive model simulations revealed that platelet deformation, interactions between platelets in the vicinity of the vessel wall as well as the number of functional GPIba platelet receptors played significant roles in platelet adhesion to the injury site. Lastly, macro-scale model of blood clot deformation and deformation of blood vessel will be described. The model represents clot as a ternary complex fluid made of heterogeneously distributed platelets, fibrin network and plasma phases and takes into account mechanical properties of different phases. Video December 1, 2016 Dr. Zvi Bern - UCLA A curious story of quantum gravity in the ultraviolet For the past 30 years nearly all theoretical physicists have believed that quantum field theories based on Einstein's general relativity necessarily must be ill-defined in the ultraviolet. This is the well known nonrenormalizability problem of gravity. But is it actually true, in general? We describe recent calculations that cast doubt on this simple picture and show that quantum gravity is much tamer in the ultraviolet than believed possible. The new calculations make use of enormous advances in our ability to compute scattering amplitudes in quantum field theory by relating gravity theories to gauge theories. Applications to black holes will be mentioned. Video November 17, 2016 Dr. Boris Shraiman - KITP Physics and Biology of Morphogenesis One hundred years ago, D'Arcy Thompson – a nineteenth century polymath, working at the turn of the twentieth century – wrote a monograph, "On Growth and Form", in which he pondered the geometry of living forms and how it emerges in the process of Morphogenesis. Thompson was ahead of his time. Since then, progress of Developmental Biology and Molecular Genetics uncovered many if not most of key genes and molecules involved in Morphogenesis, yet Thompson's agenda of understanding how developmental processes actually specify the geometry of tissues, limbs and organs is far from complete. A particular challenge is to bridge the gap between microscopic scales, where molecular mechanisms operate, and the macroscopic scales of animal "shape and form". This challenge offers much for a Physicist to think about. This talk will focus in particular on the mechanical aspects of morphogenesis i) examining the role of mechanical stress in regulation of growth and ii) seeking a quantitative understanding of tissue flows observed in morphogenesis. At the interface of Physics and Biology we will find some new biology and new physics. Video November 10, 2016 Dr. Rui-Rui Du - Rice Electronic Superhighway in Topological Insulators Electrical insulators commonly refer to the materials that prevent the flow of electricity. However, recent research demonstrates a type of topological insulators which has novel properties. Although electricity cannot flow through them, it can flow around their narrow outer edges. The material, called a "quantum spin Hall topological insulator", acts as an electronic superhighway. It is one of the building blocks needed to create future electronics and computers. In this talk I will show such insulators can be built from common compound semiconductors containing a double-layer of electrons and holes, which are created by band-gap engineering using molecular beam epitaxy and electrostatic gates. The material supports quantized helical edge modes. Amazingly, due the interactions between electron and holes, the material can become a superconductor, where the pairing of electron and holes resembles the Cooper pair in ordinary superconductors. Video November 3, 2016 Dr. Ehud Altman - Berkeley Ergodicity, entanglement and many-body localization in quantum dynamics. Do quantum many-body systems necessarily come to thermal equilibrium after a long enough time evolution? The conventional wisdom has long been that they do and that, in the process, any quantum information encoded in the initial state is lost irretrievably. Thus the dynamics of many interacting particles becomes effectively classical. But these ingrained notions of thermalization and ergodicity have recently been called into question. In this talk I will discuss how ergodicity can break down in disordered quantum systems through the phenomenon of many-body localization. In contrast to thermalizing fluids, quantum correlations can persist through time evolution of the localized state even at high energy densities. Thus, investigating the many-body localization transition offers a concrete route to address fundamental unsolved questions concerning the boundary between classical and quantum physics in the macroscopic world. I will emphasize the important role that quantum entanglement plays in current attempts to understand this fascinating dynamical phase transition. Finally I will present recent progress in confronting the emerging theoretical understanding of many-body localization with experimental tests using systems of ultra-cold atoms. Video October 27, 2016 Dr. Barry Barish - Caltech LIGO and the Detection of Gravitational Waves Einstein predicted the existence of gravitational waves 100 years ago. They have been recently observed from pairs of merging Black Holes by the Laser Interferometer Gravitational-wave Observatory (LIGO). The physics of gravitational waves, the detection technique, the observations, including latest results, and implications will all be discussed. Video October 13, 2016 Stephen Kane - San Francisco State University Analyzing Alien Worlds: A Multidisciplinary Approach to Characterizing Exoplanets About the Speaker: Stephen Kane has been researching planets orbiting other stars for more than 20 years. He has discovered and characterized hundreds of exoplanets, including Kepler-186f, which is the smallest planet yet found in the Habitable Zone of a star. After spending many years working at the NASA Exoplanet Science Institute, Kane is now an Associate Professor of Astrophysics at San Francisco State University (SFSU). He is the Chair of the Kepler Habitable Zone Working Group and the Director of the Planetary Research Laboratory at SFSU. Stephen is involved in several upcoming and ongoing NASA missions in ways that dovetail seamlessly with the UCR-based team of the NASA Astrobiology Institute. His work with the Deep Space Climate Observatory is the first major effort to use Earth's rotation and albedo to model modern Earth as an exoplanet. He is also leading a project to use the future James Webb Space Telescope to detect evidence for volcanic activity on terrestrial planets discovered with TESS, the Transiting Exoplanet Survey Satellite scheduled for launch in 2017. Abstract: The number of exoplanet discoveries has increased dramatically over the past several decades, requiring a planetary classification system to encompass the enormous diversity among worlds. Exoplanetary science can be broadly divided into categories of detection, characterization, and habitability. Kane's research has allowed him to address leading questions in all three areas: detecting multi-planet systems, determining the stability of planetary orbits, analyzing planetary atmospheres, and predicting the effects of both planetary orbit and geological activity on habitability. In this seminar, he will present highlights from his survey of potentially transiting exoplanets and his role in recent exoplanet discoveries. He will also present the results from his newly published catalog of Kepler planets in the habitable zones of their host stars and describe the methodology he developed for distinguishing between Earth and Venus analogs. Finally, he will describe future opportunities from both ground and space-based observatories that will be used to provide a more complete understanding of comparative planetology. October 6,2016 Jesse Thaler - MIT New Physics Gets a Boost: Jet Substructure at the Large Hadron Collider Collisions at the Large Hadron Collider (LHC) are dominated by jets, collimated sprays of particles that arise from quantum chromodynamics (QCD) at high energies. With the remarkable performance of the ATLAS and CMS detectors, jets can now be characterized not just by their overall direction and energy but also by their substructure. In this talk, I highlight the increasingly important role that jet substructure is playing in searches for dark matter and other new physics at the LHC, especially when exploring extreme kinematic regimes involving large Lorentz boosts. I also explain how innovative theoretical studies of jet substructure have taught us surprising lessons about QCD, revealing new probes of hot dense matter and universal features of gauge theories. September 29, 2016 DR. Samindranath Mitra - PRL Editor Physics after the lab and the desk: Your work in PRL Physics research takes place mostly at your desk, at the keyboard, in the lab. You communicate results through posters, talks, and papers -- leading to, hopefully, wide dissemination and recognition. This sequence entails interacting with journal editors, referees, conference chairs, journalists, and so on. I will focus on this post-research collaborative process in physics, primarily through the lens that is Physical Review Letters. September 22, 2016 Dr. Brian Siana - UCR Dwarf Galaxies in the Early Universe: Finding and Characterizing the Other Half of Star Formation Small galaxies in the early universe are incredibly important. They comprise the majority of early star formation, reionized the hydrogen in the intergalactic medium and populated it with heavier elements. Furthermore, mysteries about the abundance and dynamics of dwarf galaxies today may be giving insights into the properties of dark matter or, alternatively, may arise from baryonic process during early star formation episodes. To understand these star formation episodes, we first have to see the dwarf galaxies. I will summarize our research using gravitational lenses to get a census of these previously unobservable dwarf galaxies, and to better characterize their star formation histories and ionizing emission. June 2, 2016 Henri Orland - CEA- Saclay, Paris Pseudoknots and knots in RNA After reviewing some elementary properties of RNA, we recall how secondary structures of RNA without pseudoknots can be computed using simple concepts of statistical physics. The situation is much more complex when dealing with RNA structures with pseudoknots. In that case, inspired by matrix field theory, we introduce a classification of pseudoknots in terms of their topological genus. The standard free energy parametrization is modified to include a penalty proportional to the genus of the RNA structure, and we present two algorithms to efficiently predict RNA structures with pseudoknots. In the last part of the talk, we address the question: Are there knots in RNA? To try to answer this question, we present a thorough study of the database of all known RNA structures. May 26, 2016 Harry Teplitz - IPAC Infrared Grism Spectroscopy from Space: Hubble Results and Preparing for New Missions Slitless grism spectroscopy is an efficient way for space telescopes to obtain large samples of low resolution spectra in the near infrared wavelength range. The Hubble Space Telescope’s Wide Field Camera 3 (WFC3) offers a powerful example of this technique. I will review current results from WISPs (WFC3 Infrared Spectroscopic Parallel survey), which observes “random” parallel fields 5 to 8 arcminutes away from primary observations taken by other instruments. The WISPs dataset includes almost 2000 hours of HST data, which have led to a range of discoveries in the study of galaxy evolution. In addition, WISP is the ideal pathfinder for planning the future WFIRST and Euclid missions, which will both employ near infrared grisms over thousands of square degrees of the extragalactic sky. May 19, 2016 Laura Sales - UCR Dwarf galaxies and their satellites as extreme probes of LCDM The cosmological scenario (Lambda Cold Dark Mater, LCDM) makes three clear predictions for the dark matter halos surrounding galaxies: 1) the number of halos steeply rises towards low-mass objects, 2) halos are "cuspy" at their centers and 3) there should be a wealth of substructure swarming around each of these halos. We use cosmological numerical simulations of halos and galaxies to explore these predictions and to compare them with available observational constraints, such as the Baryonic Tully-Fisher relation and the inventory of dwarfs (low-mass galaxies) in the Local Volume. The recent detection of several dwarf galaxies potentially associated with the Magellanic Clouds is an exciting discovery that confirms that the hierarchical nature of galaxy formation extends down to the faintest limits probed, just as predicted by LCDM. On the other hand, the extreme baryon content of some isolated dwarfs together with the large variety of rotation curve profiles for these objects presents a newly recognized challenge to the paradigm that still awaits resolution. Do we need to move beyond Cold Dark Matter? May 12, 2016 Arjun Dey - NOAO Mapping the Universe: A New Generation of Sky Surveys The Dark Energy Spectroscopic Instrument project, which will begin operations in 2019, will measure the expansion history of the universe to unprecedented precision and provide sub-percent constraints on the distance scale and the equation of state of dark energy. I will describe the current state of the project and the wide-field imaging surveys that are being undertaken in preparation for the DESI spectroscopic survey. These imaging surveys are using state-of-the-art red-sensitive cameras and will benefit a wide range of astrophysical studies. The data sets being created will have lasting legacy value, well into the LSST era. May 5, 2016 Tony Tyson - UC Davis LSST and the physics of the dark universe The physics that underlies the accelerating cosmic expansion is unknown. This, "dark energy" and the equally mysterious "dark matter" comprise 96% of the mass-energy of the universe and are outside the standard model. Recent advances in optics, detectors, and information technology, has led to the design of a facility that will repeatedly image an unprecedented volume of the universe: LSST. For the first time, the sky will be surveyed wide, deep and fast. The history of astronomy has taught us repeatedly that there are surprises whenever we view the sky in a new way. I will focus on the technology of LSST, and review several independent probes of the nature of dark energy and dark matter. These new investigations will rely on the statistical precision obtainable with billions of galaxies. April 28, 2016 Kirill Shtengel - UCR Anyonics: Exotic circuitry with anyons, or how to build a Flux Capacitor Anyons (particularly non-Abelian anyons) are widely sought for the exotic fundamental physics they harbour as well as for their possible applications for quantum information processing. Currently, there are numerous blueprints for stabilizing the simplest type of non-Abelian anyon, a Majorana zero energy mode bound to a vortex or a domain wall. One such candidate system, a so-called "Majorana wire" can be made by judiciously interfacing readily available materials; the experimental evidence for the viability of this approach is presently emerging. Following this idea, we introduce a device fabricated from conventional fractional quantum Hall states, s-wave superconductors and insulators with strong spin-orbit coupling. Similarly to a Majorana wire, the ends of our “quantum wire” would bind "parafermions", exotic non-Abelian anyons which can be viewed as fractionalized Majorana zero modes.I will briefly discuss their properties and describe how such parafermions can be used to construct new and potentially useful circuit elements which include current and voltage mirrors, transistors for fractional charge currents and "flux capacitors". April 21, 2016 Daniel Cox - UC Davis Proteins as Molecular Legos: How Lessons Learned from Mad Cow Disease can be Applied to Novel Materials and Biotechnology The unregulated yet ordered self-assembly of large disordered proteins such as prion and tau contribute to neurodegenerative diseases like mad cow and Alzheimer’s. Nevertheless, organisms as diverse as yeast, spiders, lacewings, and E. coli bacteria have evolved mechanisms to harness these protein aggregation processes for their benefit, using the proteins effectively as “Molecular Legos”. In this talk I will discuss how related “beta solenoid” proteins can be engineered to undergo this self-assembly in a controlled way to produce remarkably stable and beautifully ordered structures that can be harnessed for nanotechnology and biotechnology applications including energy harvesting and biosensing. I will discuss the physics of the aggregation process, how you can measure it with Rayleigh scattering, and how you can measure the mechanical toughness with both computer simulations and high intensity ultrasound. We find that the filaments of our engineered beta solenoid proteins are stiff against bending and twist, and have a mechanical toughness comparable to Kevlar. April 14, 2016 Bharat Ratra - Kansas State University Dark Energy: constant or time variable? (... and other open questions) Experiments and observations over the last two decades have persuaded cosmologists that (as yet undetected) dark energy is by far the main component of the energy budget of the universe. I review a few simple dark energy models and compare their predictions to observational data, to derive dark energy model-parameter constraints and to test consistency of different data sets. I conclude with a list of open cosmological questions. April 7, 2016 Alex Rudolph - California State Polytechnic University CAMPARE and Cal-Bridge: Engaging Underrepresented Students in Physics and Astronomy The level of participation by underrepresented minority (URM) and female students in physics and astronomy PhD programs is shamefully low (2-4% for URM v. 30% in the general population; 20% for women v. 50% in the general population). I will begin by discussing research into why these participation rates are so low for these groups, highlighting role the physics and general GRE tests play in suppressing diversity in our field, while providing little to no benefit in helping predict long-term success. I will then describe some alternative methods of conducting graduate admissions, including the role of programs like Cal-Bridge and CAMPARE. I will then describe these two California-wide, multi-institutional programs, CAMPARE and Cal-Bridge, with the common mission of increasing participation of underrepresented minorities and women in astronomy and physics through summer research opportunities, in the case of CAMPARE, scholarships in the case of Cal-Bridge, and significant mentoring and professional development in both programs, leading to an increase in their numbers completing bachelor’s degrees, and successfully pursuing a PhD in these fields. There are plans for an expansion of the Cal-Bridge program to include students interested in physics PhDs, as well as to make it statewide. I will be talking about how UCR physics and astronomy faculty can get involved in the program and these expansion efforts. March 31, 2016 Joshua Lui - UCR Shedding light on two-dimensional electrons in graphene and beyond Graphene, a single layer of carbon atoms, has stimulated intense scientific interest due to its distinctive electronic and mechanical properties. Graphene exhibits strong interactions with light over a broad spectral range. This enables us to examine its electronic and vibrational properties through optical spectroscopy. In addition to gaining understanding of the properties of single-layer graphene, we can also probe the behavior of electrons in few-layer graphene. This reveals the unique electronic and vibrational properties for graphene of each layer thickness and stacking order, as well as their distinct capability to induce an electrically tunable band gap. I will also highlight recent development of 2D materials beyond graph March 10, 2016 Evan Kirby - Caltech Dwarf Galaxies: Laboratories for Nucleosynthesis and Dark Matter The Milky Way is surrounded by dozens of dwarf galaxies. Although these galaxies contain as few as 1000 stars (compared to 100 billion stars in the Milky Way), they have masses equivalent to millions of stars. The extra mass suggests that dwarf galaxies are reservoirs for dark matter. March 3, 2016 Micahel M. Fogler - UC San Diego Hyperbolic waves in Nature: from nano to Terra Waves with hyperbolic dispersion relation are exotic yet surprisingly widespread phenomena that occur in anisotropic media with internal resonances. Such media have been investigated in numerous fields, ranging from engineering to condensed matter physics to optics to fluid dynamics and geophysics. Hyperbolic waves can be found in magnetic materials, in both usual and topological insulators, in superconductors, as well as in our oceans, beaches, atmosphere, and space. The characteristic lengths and frequencies of such waves vary vastly, from atomic to cosmic. However, they all exhibit certain common attributes, such as strict directionality, diverging density of states, and anomalous reflection. This talk will contain a primer on hyperbolic materials, a recipe for a death ray, and a report on our nano-optics studies of hyperbolic phonon-polaritons in new quasi-2D materials such as graphene and hexagonal boron nitride. February 25, 2016 Jim Olsen - Princeton University Dispatches from the Energy Frontier: Latest results from the Large Hadron Collid In May, 2015 the Large Hadron Collider (LHC), the world’s highest energy particle collider, resumed operations after a two year shutdown. The downtime was used to prepare the machine and detectors for proton collisions at higher energy and intensities than have ever been achieved before. Following the discovery of the Higgs boson in 2012, which led to the awarding of the Nobel Prize in Physics to Peter Higgs and Rene Englert, the primary focus on the two large experiments, ATLAS and CMS, operating at the LHC is to search for signs of new particles or interactions that could either shed light on unexplained mysteries of the Standard Model of particle physics, or even provide evidence of unexpected phenomena not previously predicted. One interesting example of such a scenario was recently reported by ATLAS and CMS, where both experiments see an excess of events containing two photons that could be the first hint of a new particle with a mass near 750 GeV. In this colloquium I will present recent results from the LHC, including the diphoton excess and searches for supersymmetric particles and other exotic phenomena, as well as a host of new measurements establishing the Standard Model at the unprecedented energy of 13 TeV. I will close with a brief outlook on expectations for the LHC in the near and long term. February 18, 2016 Marusa Bradac - UC Davis Dark Matter and First Galaxies Light Up The Bullet Cluster has been the subject of intense research in the last few years. This system is remarkably well-suited to addressing outstanding issues in both cosmology and fundamental physics. I will present measurements of the composition of this system, show the evidence for existence of dark matter, and describe limits that we placed on the intrinsic properties of dark matter particles. I will also present results from a much larger sample of Bullet-like clusters, MACSJ0025-1222, A520, and DLSCL J0916.2+2951 among others. February 11, 2016 Itai Cohen - Cornell University Flight of the Fruit Fly There comes a time in each of our lives where we grab a thick section of the morning paper, roll it up and set off to do battle with one of nature’s most accomplished aviators - the fly. If however, instead of swatting we could magnify our view and experience the world in slow motion we would be privy to a world-class ballet full of graceful figure-eight wing strokes, effortless pirouettes, and astonishing acrobatics. After watching such a magnificent display, who among us could destroy this virtuoso? How do flies produce acrobatic maneuvers with such precision? What control mechanisms do they need to maneuver? More abstractly, what problem are they solving as they fly? Despite pioneering studies of flight control in tethered insects, robotic wing experiments, and fluid dynamics simulations that have revealed basic mechanisms for unsteady force generation during steady flight, the answers to these questions remain elusive. In this talk I will discuss our strategy for investigating these unanswered questions. I will begin by describing our automated apparatus for recording the free flight of fruit flies and our technique called Hull Reconstruction Motion Tracking (HRMT) for backing out the wing and body kinematics. I will then show that these techniques can be used to reveal the underlying mechanisms for flight maneuvers, wing actuation, and flight stability. Finally, I will comment on the implications of these discoveries for investigations aimed at elucidating the evolution of flight. February 4, 2016 Dan Stark - University of Arizona Galaxies in the Reionization Era Deep infrared images from the Hubble and Spitzer Space Telescopes have recently pushed the cosmic frontier back to just 500 million years after the Big Bang, delivering the first large sample of galaxies at redshifts between 7 and 10. Sometime in this redshift window the hydrogen in the intergalactic medium transitioned from mostly neutral to ionized. Over the past five years, our understanding of this process of reionization has improved greatly. The census of early galaxies derived from deep Hubble imaging has provided new insight into the role of star forming galaxies in driving reionization, while follow-up spectroscopy has constrained the timescale over which the transition happened. Most recently, deep MOSFIRE spectra have begun to provide the first glimpse of the physical nature of early galaxies, hinting at a very different population from what has been observed at lower redshifts. I will review the latest progress in our understanding of the first billion years of cosmic history and discuss the remaining challenges that must be addressed in advance of JWST. January 28, 2016 Mlke Roney - University of Victoria Applying Quantum Entanglement to Search for New Physics at TeV Energies Collisions of electrons and positrons can create B-meson particles in an entangled state. I will explain how the BABAR experiment has applied the associated Einstein–Podolsky– Rosen effect to study differences between matter and antimatter known as CP violation, as well as how it has used the effect to observe the “quantum arrow of time”. The Belle II/SuperKEKB facility that is currently being commissioned in Japan will extend these studies and will be sensitive to new physics at energies well above those available at the Large Hadron Collider. I will describe how it will do so and investigate the evidence for new physics published by BABAR and recently corroborated by the Belle and LHCb experiments. January 21, 2016 Tony Heinz - Departments of Applied Physics and Photon Science, Stanford University Two-Dimensional Materials - Graphene and Beyond Graphene, a single atomic layer of carbon atoms, has attracted great attention worldwide because of its potential for novel science and technology. Recently, this interest has expanded to the much wider class of two-dimensional materials that occur naturally as 2D layers of van-der-Waals crystals. While preserving graphene’s flexibility and tunability by external perturbations, atomically thin layers of this broader set of materials provides access to more varied electronic and optical properties, including semiconducting and insulating behavior. In our presentation, we will discuss the distinctive properties of these atomically thin 2D materials, emphasizing how they can be probed by light. For the prototypical system of graphene, the electronic response has been investigated from the THz to the UV, revealing many interesting physical properties of 2D Dirac fermions. Atomically thin layers of semiconductors in the family of transition metal dichalcogenides (MX2 where M = Mo, W and X = S, Se, Te) have also been investigated. Although weak light emitters as bulk crystals, at monolayer thickness these materials emit light efficiently. We will describe some of the surprising characteristics exhibited by these materials in the 2D limit, from their strong and anomalous excitonic effects to valley selective excitation and control. January 14, 2016 Bertrand Echenard - Caltech The Mu2e experiment: finding a needle in a trillion haystacks The Mu2e experiment at Fermilab will be the world's most sensitive search for neutrinoless muon-to-electron conversion, a charged lepton-flavor violating process. Although neutral lepton-flavor violation has been clearly established in the neutrino sector, no sign of charged lepton-flavor violation has been detected so far, despite decades of experimental searches. An observation would constitute an unambiguous sign of physics beyond the standard model, and severely constrain new theoretical models. The Mu2e experiment will improve the current sensitivity to muon-to-electron conversion by four orders of magnitude, and indirectly probe energy scales well beyond the reach of the LHC. January 7, 2016 Henk Postma - Cal State Northridge Towards rapid sequencing of individual DNA molecules with graphene nanogaps I will describe our lab's latest efforts in realizing a graphene nanogap device that may be used for sequencing individual DNA molecules. The technique is based on reading the base sequence of a single DNA molecule using a graphene nanogap to read the DNA’s transverse conductance. Because graphene is a single atom thick, single-base resolution of the conductance is readily obtained. The nonlinear current-voltage characteristic is used to determine the base type independent of nanogap-width variations that cause the current to change by 5 orders of magnitude. The expected sequencing error rate is 0% up to a nanogap width of 1.6 nm. December 3, 2015 James Bullock - UCI Dwarf Galaxies, the Local Group, and Cosmology The Local Group and the tiny galaxies that surround the Milky Way provide unique and detailed data sets for testing ideas in cosmology and galaxy formation. In this talk I will discuss how numerical simulations coupled with local "near-field" observations are informing our understanding of dark matter, the formation of the first galaxies, and the physical processes that act at the threshold of galaxy formation. November 19, 2015 DR. Thorsten Emig - MIT and CNRS Paris Geometrically constrained fluctuations The modification of (quantum and thermal) fluctuations due to geometrical constraints give rise to a plethora of effects in equilibrium and non-equilibrium systems. Prominent examples include QED and critical Casimir interactions between macroscopic bodies, van der Waals forces between atoms and surfaces, and heat radiation and transfer. I shall review recent theoretical and experimental progress in the field, with applications extending from nano-systems over soft matter to urban physics. November 12, 2015 John Chalker - Oxford Geometrically frustrated magnets and spin liquids Magnetic materials and theoretical models of them provide standard paradigms in condensed matter physics for the idea of ordering, in which interactions lead to a limited number of symmetry-related low-temperature states. Geometrical frustration is interesting as a way of making something different happen. Frustrated magnets have interactions that compete with each other, and they fluctuate between many different states even at low temperature. In this sense they provide an analogue for spin systems of the liquid phase of ordinary matter. Spin liquids, however, turn out to be much more interesting in important ways than ordinary liquids: in their low-energy states the microscopic magnetic moments are ``dissolved" by fluctuations and re-form as new degrees of freedom, often involving emergent gauge fields and fractionalised quasiparticles. I aim to present a simple overview of ideas in this field and to summarise some recent work on the dynamics of an exactly solvable model -- the Kitaev honeycomb model -- that has a spin liquid ground state. November 5, 2015 Qian Niu - UT Austin Orbital Magnetism and Landau Levels A semiclassical theory of electron dynamics is derived which is accurate to second order in the magnetic field. We show how various geometric effects exhibit in the magnetic susceptibility as well as in the orbital magnetization. We also obtain a simple relation between the Landau level index and the magnetic response functions. One can thus obtain accurate Landau levels from first principles calculations, or measure the magnetic response functions from Landau level data. October 29, 2015 Alan Rein - NCI Putting the Pieces Together: The Building Block of HIV-1 Virus Particles and How it is Assembled AIDS is caused by a virus called HIV-1. We will describe the replication cycle of the virus. A single virus-coded protein, “Gag”, is the building block of HIV-1 virus particles. We are studying the mechanisms by which several thousand Gag molecules are assembled into an “immature” HIV-1 particle and analyzing the structure of these particles. In a subsequent step in the viral life cycle, the Gag proteins in the immature particle are cleaved. These “maturation cleavages” result in a global reorganization of the particle and are absolutely required for viral infectivity. New results on a molecular switch triggering particle assembly will be presented. October 22, 2015 Arun Paramekanti - U Toronto Band topology meets correlations - from solid state to cold atoms. The mathematics of topology plays an important role in many recently discovered effects in solid state matter, ranging from the quantum anomalous Hall effect to the quantum spin Hall effect and its higher dimensional generalizations. Recent work on cold atoms has also realized such physics by designing novel optical lattices and using lasers to create artificial orbital magnetic fields for neutral atomic gases. The interplay of such topological phases and interparticle interactions is a largely open field of research. The talk will give an introduction to this field and discuss some of our theoretical work, including the discovery of unusual forms of magnetism in spin-orbit coupled oxides and atomic gases, oxide heterostructures as platforms to realize quantum anomalous Hall phases, and emergence of novel phases at topological quantum critical points. more details» copy to my calendar October 15, 2015 Chung-Pei Ma - UC Berkeley Supermassive Black Holes in Nearby Galaxies Black holes are among the most fascinating astrophysical objects and have long entranced the public. For over three decades, the giant elliptical galaxy Messier 87 has hosted the most massive known black hole in the local universe. New kinematic data and improved models in the past few years have substantially expanded and revised dynamical measurements of black hole masses at the centers of nearby galaxies. I will describe recent progress in discovering black holes beyond ten billion solar masses in ongoing surveys of massive elliptical galaxies. I will present updated scaling relations between the black hole mass and host galaxy properties, and discuss the implications for the formation of massive galaxies and the predicted gravity waves from merging supermassive black hole binaries. October 8, 2015 Samir D Mathur - Ohio State Resolution of the black hole information paradox Some 40 years ago Hawking found a remarkable contradiction: if we accept the standard behavior of gravity in regions of low curvature, then the evolution of black holes will violate quantum mechanics. Resolving this paradox would require a basic change in our understanding of spacetime and/or quantum theory. In recent years the paradox has found an interesting resolution through string theory. While quantum gravity is normally expected to be important only at distances of order planck length, the situation changes when a large number N of particles are involved, as for instance in the situation where we make a large black hole. Then the length scale of quantum gravity effects grows with N, altering the black hole structure to a "fuzzball"; this effect resolves the paradox. October 1, 2015 John Martinis - UCSB What’s next after Moore’s law: quantum computing As microelectronics technology nears the end of exponential growth over time, known as Moore’s law, there is a renewed interest in new computing paradigms. I will discuss recent research at UCSB on superconducting quantum bits, as well as our recent start at Google to build a useful quantum computer to solve machine learning problems. Two qubit experiments will be highlighted, one to simulate a chemical reaction that finds a cross section, and a second to extend the lifetime of a qubit state using quantum error correction. June 4, 2015 Michael Rich - UCLA The Central Bulge of our Galaxy: New Insights and Mysteries Half of the light in the local Universe arises from the old stars in elliptical galaxies and bulges of spiral galaxies. At the center of our Galaxy lies a region called the "bulge" consisting of stars older and generally more metal rich than those in the disk, and hosting the Milky Way's central black hole. The central bulge population of our Milky Way is 700 times closer than the nearest similar stars in M31, providing a remarkable opportunity to learn the age, composition, kinematics, structure, and origin of this population. Present cold dark matter models suggest that the Milky Way and similar galaxies should have been bombarded by the infall of satellite galaxies during their lifetime and galaxies with bulges like that of our Milky Way would be predicted to not have survived in the form we observe today. I will discuss two new survey programs: one uses the Dark Energy Camera at the Cerro Tololo Observatory to image the central 1000 parsecs of the Milky way, and the other survey aims to measure the composition of giants just a few parsecs distant from the Milky Way's central supermassive black hole. We also consider what the next generation of ground- and space- based telescopes may uncover. May 28, 2015 Brant Robertson - University of Arizona New Constraints on Cosmic Reionization from Planck and Hubble Space Telescope Understanding cosmic reionization requires the identification and characterization of early sources of hydrogen-ionizing photons. The 2012 Hubble Ultra Deep Field (UDF12) campaign acquired the deepest blank-field infrared images with the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time, systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicates reionization was underway. High-redshift observations with HST including UDF12, CANDELS, and the Frontier Fields provide the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize results from these HST campaigns and the most recent constraints from Planck CMB observations to infer redshift-dependent ultraviolet luminosity densities, reionization histories, and electron scattering optical depth evolution consistent with the available data. We review these results, and discuss future avenues for progress in understanding the epoch of reionization. May 21, 2015 Heather Knutson - Caltech Atmospheres of Extrasolar Planets in the Super-Earth Era Ongoing surveys of nearby stars have revealed an amazing diversity of planetary systems, many of which have characteristics that differ substantially from those of the solar system planets. Perhaps one of the biggest surprises to come out of these surveys was the discovery that "super-Earths" (planets between 1-10 times the mass of the Earth) are in fact the most common type of extrasolar planet. Despite the name we actually know very little about the compositions of these mysterious planets, and it has been suggested that this mass range may include both "water worlds" and "mini-Neptunes" with thick hydrogen envelopes in addition to more Earth-like terrestrial planets. In my talk I will explore current constraints on the compositions of planets with masses ranging from that of Neptune down into the super-Earth regime, and discuss the corresponding implications for our understanding of planet formation and evolution. May 14, 2015 Joel Primack - UCSC New Insights on Galaxy Formation from Comparisons of Simulated and Observed Galaxies Computer simulations and theoretical understanding have now reached a stage where simulations are increasingly able to tackle the complexity of galaxy formation and evolution. This talk will describe in particular the successes and challenges of high-resolution hydrodynamic galaxy simulations, now including radiative pressure feedback, in trying to understand the Hubble Space Telescope observations of galaxies during the period of most vigorous star formation (1 < z < 3, “Cosmic High Noon”) [1]. I used to think that galaxies form as disks, that forming galaxies are pretty smooth, and that galaxies generally grow in radius as they grow in mass — but we are now learning that all these statements are false. The majority of star-forming galaxies at z > 1 have recently been shown to have mostly elongated (prolate) stellar distributions [2] rather than disks or spheroids, and our simulations may explain why [3]. A large fraction of star-forming galaxies at redshifts 1 < z < 3 are found to have massive stellar clumps [4]; these originate from violent disk instabilities in our simulations [5-6], which also help to create compact spheroids (“nuggets”) through galaxy compaction [7-9]. We are trying to understand how angular momentum evolves as gas falls toward the inner galaxy and becomes stars [10]. The talk will also describe the Assembling Galaxies of Resolved Anatomy (AGORA) program to run high-resolution simulations using as much as possible the same initial conditions, physical assumptions, and output analysis procedures. AGORA will systematically compare galaxy simulations using a wide variety of computer codes with each other and with observations, and thus improve understanding of galaxy formation [11]. May 7, 2015 Zhiqiang Mao - Tulane University Interplay between magnetism and superconductivity in iron chalcogenide The interplay between magnetism and superconductivity in Fe-based superconductor systems is currently a subject of intense studies. The iron chalcogenide Fe1+y(Te1-xSex) is of particular interest due to its unique magnetic properties. While the parent compound Fe1+yTe shows antiferromagnetism with (p,0) in-plane magnetic wave vector, the optimally doped sample displays superconductivity with (p,p) spin resonance. This contrasts with iron pnictides in which both the parent compound’s antiferromagnetism and the doped samples’ superconducting (SC) spin resonance are characterized by the in-plane Fermi surface nesting wave vector Qn = (p,p). The evolution from (p,0) magnetism to superconductivity with (p,p) spin resonance in iron chalcogenides is associated with coexistence of magnetic correlations at (p,0) and (p,p). The other remarkable difference between iron chalcogenide and iron pnictide superconductors is their phase diagrams. In iron pnictides, bulk superconductivity either emerges immediately following suppression of long-range (p,p) antiferromagnetic (AFM) order, or coexists with it in a particular composition range. In contrast, in iron chalcogenides, bulk superconductivity does not appear immediately following the suppression of long-range (p,0) AFM order. Instead, an intermediate phase with weak charge carrier localization appears between AFM order and bulk superconductivity for 0.09 < x < 0.3. In this talk, I will first present an overview on the results summarized above and then introduce our recent studies on the coupling between electronic and magnetic properties in this system. I will show the doping dependences of Sommerfeld coefficient ?, Hall coefficient RH and Hall angle as well as their relations with superconductivity. The origin of superconductivity suppression and charge carrier localization in the underdoped region will be discussed in terms of these experimental results. April 23, 2015 Alex Evilevitch - Carnegie Mellon University Physical Mechanisms of Viral Life-Cycle Herpesviruses are a leading cause of human viral disease, second only to influenza and cold viruses. Herpesviruses consist of a double-stranded (ds) DNA genome contained within a protein shell, termed the capsid, that is surrounded by an unstructured protein layer (the tegument) and a lipid-envelope. During viral replication, an ATP-dependent motor packages the genome into a preformed capsid through a unique opening created by the portal complex. Herpes Simplex virus type 1 (HSV-1) is a prototypical model system to study the general infection mechanisms of herpesviruses and other viruses that release their genome into the cell nucleus without capsid disassembly. We have recently shown that HSV-1 genome packaging creates an internal pressure of tens of atmospheres within the viral capsid. This pressure results from bending stress and repulsive forces acting on the tightly packaged DNA molecule. We also found that despite its liquid crystalline state inside the capsid, the DNA is fluid-like which facilitates its ejection into the cell nucleus during infection. The fluidity or, equivalently, mobility of the closely packaged DNA strands caused by interstrand repulsive interactions is regulated by the ionic environment of the cellular cytoplasm. Between rounds of replication, the virion must be sufficiently stable to ensure that the packaged genome is retained within the capsid. Conversely, during infection the virion must be unstable enough to allow genome release into the cell nucleus. A precise balance between these physical aspects of the viral capsid and its encapsidated genome is crucial to the viral replication cycle. Using HSV-1 as our primary model system, we investigate the roles of intracapsid DNA mobility and capsid stability for viral replication with respect to retention of the 