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Eisenbud Lecture Series in Mathematics and Physics
Berko Symposium
All colloquium videos are under copyright and may not be reproduced, in part or in total, without written permission of the speaker and of the Physics Department.
Department Colloquia
Martin Weiner Lecture Series
Department of Physics Colloquium
4:00 pm, Abelson 131
Refreshments at 3:30pm outside Abelson 131
Fall 2012 Colloquia
Craig Blocker, Brandeis University
Discovery of the Higgs Boson at the LHC
Abstract: In summer 2012, the two large detectors at the Large Hadron Collider, ATLAS and CMS, presented evidence for the discovery of a new particle consistent with the long sought Higgs boson. This talk will cover that evidence and discuss further measurements to determine the exact nature of this new particle.
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Tuesday, September 18, 2012
No colloquium (Rosh Hashanah)
Tuesday, September 25, 2012
Heinrich Jaeger, University of Chicago
Dense suspensions of particles in a liquid exhibit a number of counter-intutive, non-Newtonian flow behaviors. Most remarkably, the application of stress can dramatically harden the material, transforming it from a liquid state at rest into a solid-like state when driven strongly. Shear-thickening-based models developed over the last 25 years cannot explain the observed large normal stresses (large enough to support a grown person's weight when running across a pool filled with a suspension such as cornstarch in water). This talk surveys some of the key issues, discusses the stress scales associated with shear thickening in dense suspensions, and outlines a new scenario for impact response. In particular, using high-speed video and x-ray imaging during sudden impact, we are able to link the nonlinear suspension dynamics in a new way to the jamming phase transition.
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Tuesday, October 2, 2012
Christine Thomas, Brandeis University
Fundamental Aspects of Catalyst Design for Renewable Energy Applications
Abstract: In the search for alternatives to fossil fuels, a fundamental challenge is finding energy sources that are both renewable and naturally abundant. While solar power fits both of these criteria, variations in the sun's intensity necessitate storage of this energy. One strategy that has emerged is the storage of solar energy in the form of chemical bonds - that is, using solar energy make energy intensive molecules that can be stored for later use as energy sources. A typical example of this is the photocatalyzed splitting of water (H2O) into hydrogen (H2) and oxygen (O2). Other examples of such small molecule activation will be discussed, along with the challenges of designing efficient and economically viable catalysts for these purposes. Fundamental contributions from the Thomas laboratory will be presented with a particular emphasis on the tools used by synthetic inorganic chemists to probe their molecules and their properties.
Tuesday, October 9, 2012
No colloquium. Brandeis Monday.
Tuesday - Thursday October 16, 17, and 18, 2012
Eisenbud Lectures in Mathematics and Physics
Craig A. Tracy, UC Davis
Integrable Systems, Operator Determinants and Probabilistic Models
Abstract: This project involves the study of current fluctuations in the asymmetric simple exclusion process for a variety of initial configurations. This is a model of interacting particles on a one-dimensional lattice. The model has attracted wide attention from both mathematicians and physicists since it is one of the simplest models to incorporate far from equilibrium behavior with nonclassical fluctuations. These fluctuations are expected to have a new universal behavior similar in their applicability to the famous bell-shaped curve (the Gaussian distribution) of classical probability. A long-term goal of research in this area is the establishment of new limit laws similar in nature to the classical central limit theorem. Already these new universal distributions are being applied to various problems in growth processes, population genetics, and finance. This project will extend our knowledge of fluctuations to a much wider class of growth models.
The third lecture will take place at 4:30pm instead of 4pm (all lectures in Abelson 131)
Lecture I: Watch the video
Lecture III: Watch the video
Tuesday, October 23, 2012
Royce Zia, Virginia Tech
Non-equilibrium Statistical Mechanics: a growing frontier of “pure and applied” theoretical physics
Abstract: Founded over a century ago, statistical mechanics (SM) for systems in thermal equilibrium has been so successful that, nowadays, it forms part of our physics core curriculum. On the other hand, most of "real life" phenomena occur under non-equilibrium conditions. Unfortunately, statistical mechanics for such systems is far from being well established. The goal of understanding complex collective behavior from simple microscopic rules (of evolution, say) remains elusive. As an example of the difficulties we face, consider predicting the existence of a tree from an appropriate collection of
H,C,O,N,... atoms! Over the last two decades, an increasing number of condensed matter theorists are devoting their efforts to this frontier. After a brief summary of the crucial differences between text-book equilibrium SM and non-equilibrium SM, I will give a bird's-eye view of some key issues, ranging from the "fundamental" to (a small set of) the "applied." The methods used also span a wide spectrum, from "easy" computer simulations to sophisticated field theoretic techniques. These will be illustrated in the context of an overview of our work, as well as a simple model for transport.
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Douglas Weibel, University of Wisconsin, Madison
Co-sponsored with the Quantitative Biology Program
Protein regulation at curved bacterial membranes
Abstract: Using a combination of cell biological, biochemical, and biophysical techniques, we demonstrate that the Escherichia coli recombination repair enzyme, RecA is temporally localized and regulated by its interaction with anionic phospholipids at regions of large, negative membrane curvature. Early studies on RecA function in vivo demonstrated large amounts of protein associating with membrane fractions during DNA damage (Garvey et al. 1985, J. Biol. Chem. 285, 18984). A fundamental unanswered question is why does RecA bind the membrane and is this interaction conserved across organisms? To test whether this mechanism is evolutionarily conserved between bacteria and mitochondria, we are extending our studies to Rad51, which is a mitochondrial homolog of RecA. Recent studies have implicated Rad51 in mtDNA repair during damage due to lipid peroxidation. In this presentation I discuss several possible hypotheses that support our data.
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Tuesday, November 6, 2012
No colloquium.
Tuesday, November 13, 2012
John Crocker, University of Pennsylvania
Interactions, directed assembly and transformations of colloids using DNA handshaking
Abstract: DNA is a versatile tool for directing the controlled self-assembly of nanoscopic and microscopic objects. The interactions between microspheres due to the hybridization of DNA strands grafted to their surface have been measured and can be modeled in detail, using well-known polymer physics and DNA thermodynamics. Knowledge of the potential, in turn, enables the exploration of the complex phase diagram and self-assembly kinetics in simulation. In experiment, at high densities of long grafted DNA strands, and temperatures where the binding is reversible, these system readily form colloidal crystals having several different structures. For interactions that favor alloying between two same-sized colloidal species, our experimental observations compare favorably to a simulation framework that predicts the equilibrium phase behavior, crystal growth kinetics and solid-solid transitions. We will discuss the crystallography of the novel alloy structures formed, and the interesting diffusionless transformations they undergo that resemble shape memory alloys.
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Tuesday, November 20, 2012
Pankaj Mehta, Boston UniversityThermodynamics of cellular computation
Abstract: Cells often perform computations in response to environmental cues. On general theoretical grounds (Landauer's Principle), it is expected that such computations require cells to consume energy. We discuss the thermodynamics of cellular computations using two simple examples. First, we consider the classic problem, first considered by Berg and Purcell, of determining the concentration of a chemical ligand in the surrounding media. We show that learning about external concentrations necessitates the breaking of detailed balance and consumption of energy, with greater learning requiring more energy. Our calculations suggest that the energetic costs of cellular computation may be an important constraint on networks designed to function in resource poor environments such as the spore germination networks of bacteria. We will then discuss how Landauer's principle can be used to inform the design of synthetic memory modules in cells, focusing on protein-based switches and DNA-based memory.
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David Nelson, Harvard University
Life at High Reynolds Number
Abstract: Microorganisms living in the ocean can be subject to strong turbulence with cell division times in the middle of a Kolmogorov-like cascade of eddy turnover times. We explore the dynamics of a Fisher equation describing cell proliferation in one and two dimensions, as well as turbulent advection and diffusion. Because of inertial effects and cell buoyancy, we argue that the effective advecting velocity field is compressible. For strong enough compressible turbulence, bacteria, for example, can track, in a quasilocalized fashion (with remarkably long persistence times), sinks in the turbulent field. An important consequence is a large reduction in the carrying capacity of the fluid medium.
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Angelo Cacciuto, Columbia University
Abstract: Understanding how nanocomponents spontaneously organize into complex macroscopic structures is one of the great challenges in the field of complex fluids today. The process of self-assembly is in fact relevant to several biological processes, such as protein aggregation and intracellular trafficking, and has numerous applications in materials science. The ability to predict and control the phase behavior of a solution given a set of nanocomponents may open the way to the development of materials with novel optical, mechanical, and electronic properties. The main objective of our research is to establish rigorous links between the microscopic properties of nanocomponents and their ability to form ordered aggregates via the process of self-assembly. In this talk we will discuss two specific cases: (1) The phase behavior of hard irregularly shaped particles and their crystallizability limits, and (2) the exotic behavior (fanta-packing) of ultra-soft nanoparticles, such as dendrimers and star-polymers, at large densities.
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Tuesday, December 11, 2012
Alan Marscher, Boston University
Black Holes, Jets, and Gamma Rays in Active Galactic Nuclei
Abstract: Although black holes consume most of the matter that falls toward them, a small fraction gets heated and shot out along the poles in the form of ultra-high energy plasma jets having flow velocities very close to the speed of light. The most powerful jets are found in active galactic nuclei, where the mass of the central black hole is millions or even billions of solar masses. I will describe recent observations at gamma-ray, microwave, infrared, optical, and X-ray frequencies that probe the jets closer to the black hole than has been possible previously. The data so far are consistent with prevailing theoretical models, according to which the jets are propelled by magnetic forces. But the gamma rays originate mostly from regions parsecs from the black hole, contrary to most previous models.
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Spring 2013 Colloquia
Tuesday, January 15, 2013
Physics Department Colloquium
4pm in Abelson 131
Jane Luu, MIT
The New Solar System
Abstract: By the early 1990s, astronomers thought they knew all the major types of objects in the solar system: planets, satellites, comets, asteroid, etc. They also thought they had a good idea how the solar system obtained its current configuration. In 1992, the discovery of a new population of objects beyond Neptune, called the Kuiper Belt, turned this view upside down. Not only were astronomers far from knowing what the solar system contained, the original configuration is now up for debate. This talk describes the discovery of the Kuiper Belt and how it changed our view of the solar system.
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Tuesday, January 22, 2013
Doug Jerolmack, University of Pennsylvania
Surprising connections among aerodynamics, vegetation and groundwater in a desert dune field
Abstract: Desert dunes often exhibit remarkable pattern changes over short distances. For example, sediment-rich dunes can break up into smaller, isolated features, and then become stabilized by plants, over distances of kilometers. Such pattern transitions often coincide with spatial variations in sediment supply, transport rate, hydrology and vegetation, but have not been linked mechanistically. Here we hypothesize that the abrupt increase in roughness at the upwind margins of dune fields trips the development of an internal boundary layer, which thickens downwind and causes a spatial decrease in the surface wind stress. We demonstrate that this mechanism forces a downwind decline in sand flux at White Sands, New Mexico, using a combination of physical theory and field observations. Declining sand flux triggers an abrupt increase in vegetation density, which in turn drives changes in groundwater depth and salinity – showing that aerodynamics, sediment transport and ecohydrology are tightly interconnected in this landscape. Despite the complex climatic and geologic history of White Sands, internal boundary layer theory explains many of the observed first-order patterns of the dune field.
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Tuesday, January 29, 2013
Joseph Lehar, Novartis Institutes for BioMedical Research and Boston University
An astrophysicist turns to drugs
Abstract: Novartis is undertaking a large-scale effort to comprehensively describe cancer through the lens of cell cultures and tissue samples. In collaboration with academic and industrial partners, we have generated mutation status, gene copy number, and gene expression data for a library of 1,000 cancer cell lines, representing most cancer lineages and common genetic backgrounds. Most of these cell lines have been tested for chemosensitivity against ~1,200 cancer-relevant compounds, and we are systematically exploring drug combinations for synergy against ~100 prioritized CCLE lines. We expect this large-scale campaign to enable efficient patient selection for clinical trials on existing cancer drugs, reveal many therapeutically promising drug synergies or anti-resistance combinations, and provide unprecedented detail on functional interactions between cancer signaling pathways. I will discuss early highlights of this work and describe our plans to make use of this resource.
Biography: Dr. Lehár heads the bioinformatics group for Novartis’s oncology translational research department, which is focused on identifying optimal treatment strategies for candidate drugs in the Novartis pipeline. Previously, he has played a central role in developing technology and analysis platforms for CombinatoRx (now Zalicus Inc.), a biotech company discovering combination therapies, in addition to researching the systems biology of drug combinations through his affiliation with BU. Prior to CombinatoRx, Dr. Lehár was a postdoctoral scientist at Whitehead Institute’s Center for Genome Research (now the Broad Institute), at the Harvard College Observatory, and at Cambridge University’s Institute of Astronomy. Dr. Lehár holds a Ph.D. in physics from MIT and a B.A. in physics from Brandeis.
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Tuesday, February 5, 2013
Jane' Kondev, Brandeis University
The physical nature of cellular decision making
Abstract: Cells make decisions all the time about what to eat, where to go, and what to become. At the heart of cellular decision making is gene regulation, the process by which cells selectively turn their genes on and off in response to environmental ques. Experiments have recently begun to probe gene regulation inside cells at the single molecule level, revealing the physical nature of this key biological process in quantitative detail. In this talk I will review recent experimental advances in single-cell gene expression measurements and the theoretical models that are being put forth to greet them. I will emphasize the interplay of theory and experiments and how it has revealed surprises about some of the best studied models of gene regulation in bacteria such as the lac operon.
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Silvan S. Schweber, Brandeis University and Harvard University
Hans Bethe and Physics in/of the 20th Century
Abstract: I will present some facets of Hans Bethe’s life to illustrate how I use biography to narrate aspects of the history of twentieth century physics. I will focus on post World War II quantum field theory, on the relation between solid state/condensed matter physics and high energy physics and make some comments regarding "revolutions" in science.
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Tuesday, February 19, 2013
No colloquium. Midterm recess.
Tuesday, February 26, 2013
Duncan J. Irschick, UMass Amherst
The making of GeckskinTM: A story of accidental science
Fortune Magazine Article about Geckskin
Gecko Feet Video
Watch the video.
Pablo Jarillo-Herrero, MIT
The Versatility of Dirac Electrons in Graphene
Abstract: Over the past few years, the physics of low dimensional electronic systems has been revolutionized by the discovery of materials with very unusual electronic structures. Among these, graphene has taken center stage due to its relativistic-like electron dynamics and potential applications in nanotechnology. Moreover, the recent discovery that hexagonal boron nitride (hBN) is a nearly-ideal substrate for high mobility graphene devices has enabled a new generation of quantum transport and optoelectronic experiments in graphene-based materials. In this talk I will review our recent experiments on graphene on hBN devices , where we explore different aspects of the "Dirac-ness" of charge carriers in graphene: from novel optoelectronic phenomena to a new type of quantum spin Hall effect.
Tuesday, March 12, 2013
Chris White, Glasgow
From gluons to gravitons: a panoramic view of long distance behaviour
Abstract: Scattering amplitudes are important quantities in quantum field theory, which govern the probabilities for particle interactions. It has been known for decades that amplitudes contain "infrared divergences" associated with the emission of force-carrying particles (e.g. photons, gluons and gravitons) at large distances. Understanding these divergences is interesting in its own right, but also allows us to increase the precision of calculations at hadron colliders such as the Tevatron and the LHC. This talk will introduce scattering amplitudes and their associated infrared divergences, before summarising recent developments in the theory of quarks and gluons (Quantum Chromodynamics). We will also look at intriguing relationships between QCD and quantum gravity, which the infrared limit helps to clarify.
Tuesday, March 19, 2013
No colloquium. APS meeting.
Tuesday, March 26, 2013
Tuesday, April 2, 2013
No colloquium. Passover and spring recess.
Tuesday, April 9, 2013
Robert Jaffe, MIT
Energy Critical Elements: More Precious than Gold
Elements that were once laboratory curiosities, like neodymium, tellurium, and terbium, now figure centrally when novel energy systems are discussed. Many of these elements are not at present mined, refined, or traded in large quantities. New technologies can only impact our energy needs, however, if they can be scaled from laboratory, to demonstration, to massive implementation. As a result, some previously unfamiliar elements will be needed in great quantities. Although every element has its unique story, these Energy Critical Elements have many features in common. I will describe the shared characteristics of these elements, their roles in emerging technologies, potential constraints on their availability, and government actions that can help avoid disruptive shortages. As an example, I will focus especially on elements that are required for photovoltaic technologies.
Tuesday, April 16, 2013
Adam Cohen, Harvard University
Optical tools to monitor electrical activity in neurons
Our mental state is encoded in a set of electrical spikes that propagate through our neurons. These spikes are about 100 mV tall, last about 1 ms, and travel at a few meters per second. One can record these spikes with an electrode, but an electrode only reports voltage at a single point, while a human brain has ~10^11 neurons. For decades neuroscientists have sought an optical tool to convert neuronal spikes into light, with the goal of visualizing activity in large networks of neurons. We identified a protein from a Dead Sea microorganism that achieves this goal. In the wild the protein serves as a light-driven proton pump: it absorbs sunlight and generates a transmembrane voltage which its host uses as a source of metabolic energy. We found a way to run this protein "in reverse", to convert changes in membrane voltage into light. Upon expressing this gene in neurons, we acquired movies showing electrical impulses propagating through neurons.
D. Maclaurin*, V. Venkatachalam*, H. Lee, A. E. Cohen (*Co-first authors), “Mechanism of voltage-sensitive fluorescence in a microbial rhodopsin,” PNAS 10.1073/pnas.1215595110 (2013)
J. Kralj*, A. D. Douglass*, D. R. Hochbaum*, D. Maclaurin, A. E. Cohen (*Co-first authors), “Optical recording of action potentials in mammalian neurons using a microbial rhodopsin,” Nature Methods, 9,
90-95 (2012)
J. Kralj, D. R. Hochbaum, A. D. Douglass, A. E. Cohen, “Electrical spiking in Escherichia coli probed with a fluorescent voltage-indicating protein,” Science, 333, 345-348 (2011)
Tuesday, April 23, 2013
Michael Brenner, Harvard University
Linear Algebra and the Shape of Bird Beaks
Abstract:Evolution by natural selection has resulted in a remarkable diversity of organism morphologies. But is it possible for developmental processes to create “any possible shape”? Or are there intrinsic constraints? I will discuss our recent exploration into the shapes of bird beaks. Initially, inspired by the discovery of genes controlling the shapes of beaks of Darwin's finches, we showed that the morphological diversity in the beaks of Darwin’s Finches is quantitatively accounted for by the mathematical group of affine transformations. We have extended this to show that the space of shapes of bird beaks is not large, and that a large phylogeny (including finches, cardinals, sparrows, etc) are accurately spanned by only three independent parameters-- the shapes of these bird beaks are all pieces of conic sections. After summarizing the evidence for these conclusions, I will delve into our efforts to create mathematical models that connect these patterns to the developmental mechanism leading to a beak. It turns out that there are simple (but precise) constraints on any mathematical model that leads to the observed phenomenology, leading to explicit predictions for the time dynamics of beak development in song birds. Experiments testing these predictions for the development of zebra finch beaks will be presented.
Tuesday, April 30, 2013
Hong Liu, MIT
From black holes to strange metals: many-body physics through a gravitational lens
Abstract: Ever since the end of the Stone Age, metals have fascinated humankind and have been vital in the development of civilization. During the last two decades, physicists have been mystified by a new class of “strange” metals, observed in high-temperature superconductors and other strongly interacting electron systems, and whose exotic properties challenge fundamental pillars of condensed-matter physics. I will describe how a string-theory concept called holographic duality has been applied to shed light on some of the mysteries of that novel metallic state.