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Past years' colloquia
Archive of videos - Fall 2012
Archive of videos - Spring 2013
Archive of videos - Fall 2013
Eisenbud Lecture Series in Mathematics and Physics
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.
Martin Weiner Lecture Series
Department of Physics Colloquium
4:00 pm, Abelson 131
Refreshments at 3:30pm outside Abelson 131
Fall 2013 Colloquia
Tuesday, September 3
Arup Chakraborty, MIT
How to hit HIV where it hurts
HIV continues to wreak havoc around the world, especially in poor countries. A vaccine is urgently needed to overcome this major global health challenge. I will describe key challenges that must be confronted to achieve this goal. I will then focus on some work that aims to address a part of these challenges by bringing together theory and computation (rooted in statistical physics), consideration of structures of multi-protein assemblies, basic immunology, and human clinical data. The results of these studies suggest the design of immunogens that could be components of vaccines that might elicit immune responses which might be able to hit HIV where it hurts upon natural infection. I shall also briefly touch upon some potentially generic features of viral evolution, which are superficially reminiscent of critical phenomena.Watch the video.
Tuesday, September 10
Boris Shraiman, KITP
Statistical Genetics and the Dynamics of Natural Selection
Evolution works through natural selection that acts on genetic variation. A mounting body of evidence suggests that large populations harbor a great deal of such “selectable” variation. This implies that in order to understand how genetic variants (a.k.a. polymorphisms) spread through populations, theoretical models must account for interactions between polymorphisms at different genetic loci and in different individuals. The problem is further encumbered by the effect of sex and recombination that reassort polymorphisms between individual genomes. Yet, this “many-body problem” of evolutionary dynamics lends itself to a “Statistical Genetics” approach with many parallels to Statistical Physics. This lecture will present a statistical physicist’s view of natural selection acting in populations with high levels of genetic diversity and describe some of the new insights into the effects of different genetic interactions.
Watch the video.
Tuesday, September 17 (Brandeis Thursday)
Robert Holyst, Polish Academy of Sciences
Biologistics:Mobility in cytoplasm of the eukaryotic and prokaryotic cells
Biologistics and biochemistry in a crowded environment are two emerging interdisciplinary fields of science. They provide quantitative analysis of transport of proteins and their interactions involved in gene expression and regulation. These processes inside living cells strongly depend on the physics of liquids at the nanoscale. As I will try to convince you during my talk, the length-scale dependent nanoviscosity [1-4] characterizing motion of proteins at the nanoscale is a key to quantitative analysis of biochemical reactions in living cells. Genes are activated and repressed by proteins referred to as transcription factors (TF). The binding of TFs to the operator region on DNA is diffusion limited. TFs search for operators by performing a combination of three-dimensional (3D) diffusion in a defined volume and one-dimensional (1D) diffusion along DNA molecule. The diffusion coefficients for 3D diffusion, D, and 1D diffusion, D1, are inversely proportional to the viscosity. For the model Gram-negative bacterium Escherichia coli, the nanoviscosity of the cytoplasm depends on the size of diffusing objects. This scale dependent nanoviscosity changes by a factor of >104 between 0.001 Pas for water molecules (size 0.14 nm) and 18 Pas for large plasmids (size 300 nm). Accordingly D for biomolecules in E. coli varies by a factor of ~108. An understanding of how D, D1 and the reaction rates for gene expression depend on the length-scale dependent nanoviscosity and non-specific interactions between DNA and proteins is an essential step for understanding metabolic and proteomic networks. The final outcome of the work of my group is a database (6600 records) of diffusion coefficients for all proteins and their complexes from the proteome of E.coli. This is the first such database for any organism. Only 10-20 measurements of diffusion coefficients are needed to construct the databases for any cell or its organelles (nucleus, mitochondria).
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Tuesday, September 24
David Huse, Princeton University
Thermalization and localization in quantum statistical mechanics
Progress in atomic physics and quantum information science has motivated much recent study of the behavior of many-body quantum systems fully isolated from their environment, and thus undergoing coherent quantum time evolution. What does it mean for such a system to go to thermal equilibrium? I will explain the Eigenstate Thermalization Hypothesis (ETH), which says that each individual exact eigenstate of the system's Hamiltonian is at thermal equilibrium, and which appears to be true for most quantum many-body systems. But there are systems that do not obey this hypothesis, namely systems that are Anderson localized. These "many-body localized" systems can retain local memory of their initial state for infinite time and thus do not thermally equilibrate. A key issue here is whether or not the system itself constitutes a "thermal reservoir" that can equilibrate its parts.
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Tuesday, October 1
Peter J. Lu, Harvard University
Modern math in medieval islamic architecture
The conventional view holds that girih (geometric star-and-polygon) patterns in medieval Islamic architecture were conceived by their designers as a network of zigzagging lines, and drafted directly with a straightedge and a compass. I will describe recent findings that, by 1200 C.E., a conceptual breakthrough occurred in which girih patterns were reconceived as tessellations of a special set of equilateral polygons (girih tiles) decorated with lines. These girih tiles enabled the creation of increasingly complex periodic girih patterns, and by the 15th century, the tessellation approach was combined with self-similar transformations to construct nearly-perfect quasicrystalline patterns. Quasicrystal patterns have remarkable properties: they do not repeat periodically, and have special symmetry---and were not understood in the West until the 1970s. I will discuss some of the properties of Islamic quasicrystalline tilings, and their relation to the Penrose tiling, perhaps the best known quasicrystal pattern..
No video available.
Tuesday, October 8
Greg Bearman, Snapshot Spectra, USC Keck School of Medicine and the Israeli Antiquities Authority
Imaging Methods Applied to Conservation of Cultural Heritage
Spectral and computational imaging are two relatively new technologies to be applied to cultural heritage. There are two applications of imaging, content and conservation and imaging can work for both. Content, reading text, inscriptions and seals, for example, is typically the province of those interested in what the objects say or mean. Conservation, insuring the continued state of the object, is the field of conservation or site management in the case of outside sites. Dr. Bearman will discuss the application of spectral imaging as a conservation monitoring tool, using examples drawn from the Leon Levy Dead Sea Scrolls Digital Library, for which he is the technology and imaging consultant. Other imaging methods, such as reflectance transform imaging (RTI), will also be used to illustrate how digital imaging can significantly help conservators.
The key to developing a monitoring tool is a calibrated, repeatable, stable quantitated imaging system. Without such a system, one cannot compare images datasets over time; the user does not know if measured changes are due to changes in the object itself, system drift or just a poor imaging system with larger uncertainties in measured parameters, such as absolute reflectance. Spectral and RTI imaging systems will be used to illustrate the important parameters for monitoring.
Tuesday, October 15
Marin Soljacic, MIT
Exploring nanophotonics to tailor the laws of physics
By nano-structuring materials at length scales smaller than the wavelength of light, one can create effective materials, exhibiting optical properties unparalleled in any naturally occurring materials. The power of this approach is illustrated with two particularly important examples. Firstly, it is shown that the control over the density of photonic states via such effective materials provides a control over black body emission, which can now be tailored almost at-will. And since over 90% of all primary energy sources are converted into electrical and mechanical energy via thermal processes, exciting energy-related applications could be enabled. Secondly, a new way of confining light is presented. The ability to confine light is important both scientifically and technologically. Many light confinement methods exist, but they all achieve confinement with materials or systems that forbid outgoing waves. It is predicted and shown experimentally that light can be perfectly confined in a patterned dielectric slab, even though outgoing waves are allowed in the surrounding medium. Technically, this is an observation of an ‘embedded eigenvalue’—namely, a bound state in a continuum of radiation modes—that is not due to symmetry incompatibility.
No video available.
Tuesday, October 22
Patrick Charbonneau, Duke University
High-dimensional surprises near the glass and the jamming transitions
The glass problem is notoriously hard and controversial. Even at the mean-field level, there is little agreement about how a fluid turns sluggish while exhibiting but unremarkable structural changes. It is clear, however, that the process involves self-caging, which provides an order parameter for the transition. It is also broadly assumed that this cage should have a Gaussian shape in the mean-field limit. Here we show that this ansatz does not generally hold when increasing the dimension of space, and explore some its materials consequences. We notably examine the complex relationship between non-Gaussian caging, dynamical fluctuations, and dimensionality in the breakdown of the Stokes-Einstein relation near the glass transition. Non-Gaussian caging also persists in the jamming limit of infinitely compressed hard spheres, which affects the mechanical stability of these packings. The dimensional perspective thus establishes clear mileposts for the emergence of a complete mean-field description of the glass and the jamming transitions.
Watch the video.
Tuesday, October 29
Gabriella Sciolla, Brandeis University
The Higgs Boson: One Year Later
Particle physicists have been hunting for the elusive Higgs boson for over 40 years. On July 4th, 2012, a new particle was discovered at the Large Hadron Collider at CERN. The new particle had the potential of being the Higgs boson predicted by the Standard Model of Particle Physics. Unfortunately, the first measurement revealed only the mass of the new particle, the one parameter that the theory did not predict. In this colloquium I will discuss the measurements that the two LHC experiments have performed in the past year in order to shed light on the identity of the new particle.
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Tuesday, November 5
Efi Efrati, University of Chicago
Orientation dependent handedness and chiral design
(co-sponsored by MRSEC)
Handed phenomena are of central importance in fields ranging from biological self-assembly to the design of optical meta-materials. The definition of chirality (Greek for handedness), as given by lord Kelvin, associates it with the lack of mirror symmetry: the inability to superpose an object on its mirror image. While this definition has guided the classification of chiral objects for over a century, the quantification of handed phenomena based on this definition has proven elusive, if not impossible as manifest in the paradox of chiral connectedness. In this talk I will put forward a quantification scheme in which the handedness of an object depends on the direction in which it is viewed and thus best quantified by a pseudo-tensor. While consistent with familiar chiral notions, such as the right hand rule, this framework allows objects to be simultaneously right and left handed. The trace of the suggested handedness tensors recover Lord Kelvin's definition, yet their full structure is richer, and proven to be in quantitative agreement with the direction-dependent handed behavior of phenomena ranging from fluid flow to optical activity. I will review specific examples of handedness tensors, and discuss how the tensorial approach resolves the existing paradoxes and naturally enables the design of handed meta materials from symmetry principles.
No video available.
Tuesday, November 12
Anthony Dinsmore, UMass Amherst
Liquid Interfaces and Solid particles: geometry, physics and new materials
The interface between two liquids – such as the surface of a water droplet in oil – provides a versatile platform for assembly of small particles to make functional membranes or other materials. Owing to the large interfacial tension, nanometer-to-micron-sized colloidal particles readily adsorb at the interface and become confined there. While this adsorption phenomenon has been used in industry for decades, it continues to raise fundamentally fascinating and practically relevant questions. I will describe recent work developing materials for applications ranging from encapsulation & delivery to electronics. I will also describe recent work on the adsorption of spheres at anisotropically curved liquid interfaces, where a frustration arises from the contact condition on the particle and causes extended interfacial deformations. These deformation give rise to interactions among particles bound to curved fluid interfaces or fluid membranes. The results show how interfacial geometry might be used to control long-range forces.
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Tuesday, November 19
Mark Reid, Harvard University
Measuring the Cosmos
Over 2000 years ago, Hipparcus measured the distance to the Moon by triangulation from two locations across the Mediterranean Sea. However, determining distances to stars proved much more difficult. Many of the best scientists of the 16th through 18th centuries attempted to measure stellar parallax, not only to determine the scale of the cosmos but also to test Heliocentric cosmologies. While these efforts failed, along the way they lead to many discoveries, including atmospheric refraction, precession, and aberration of light. It was not until the 19th century that Bessel measured the first stellar parallax. Distance measurement in astronomy remained a difficult problem even into the early 20th century, when the nature of galaxies ("spiral nebulae") was still debated. While we now know the distances of galaxies at the edge of the Universe, we have only just begun to measure distances accurately throughout the Milky Way. Using the Very Long Baseline Array, we now can achieve positional accuracy approaching 10 micro-arcseconds! I will present new results on parallaxes and motions of star forming regions. These measurements address the nature of the spiral structure, size, rotation speed, and mass of the Milky Way.
Watch the video.
Tuesday, December 3
Richard Gaitskell, Brown University
LUX: NOBLE TRAVAILS: First Dark Matter Search Results from the Large Underground Xenon Detector
Particle dark matter is thought to be the overwhelming majority of the matter in the Universe. Its gravitational contribution overwhelms that from the ordinary matter that we, the earth and the stars, are composed of. However, direct evidence for the existence of particle dark matter remains controversial. I will discuss the LUX Experiment which has just reported world leading results in the search for WIMPs (weakly interacting massive particles). LUX is a 350 kg liquid Xe time projection chamber, and is operating underground at the Sanford Lab, Homestake, SD. I will also review a future noble liquid experiments, including, the 7 tonne liquid Xe LZ (LUX-ZEPLIN) which is proposed to be constructed at Sanford Lab in 2016. http://luxdarkmatter.org http://particleastro.brown.edu
Spring 2014 Colloquia
Tuesday, January 14
Lyderic Bocquet, University of Lyon ,Visiting Professor at MIT
Nanofluidic Transport in Single Nanochannels: Application to Osmotic Energy Harvesting
Tuesday, January 21
Daniel Eisenstein,The Harvard-Smithsonian Center for Astrophysics
Tuesday, January 28
Leif Ristroph, Courant Institute at New York University
Tuesday, February 4
Veronika Hubeny,University of Durham
Tuesday, February 11
Herman Marshall, MIT Kavli Institute
A Soft X-ray Spectropolarimeter Telescope
We are developing instrumentation for a telescope capable of measuring linear X-ray polarization over a broad-band using conventional spectroscopic optics. Multilayer-coated mirrors are key to this approach, being used as Bragg reflectors at the Brewster angle. By laterally grading the multilayer mirrors and matching to the dispersion of a spectrometer, one may take advantage of high multilayer reflectivities and achieve modulation factors near 100% over the entire 0.2-0.8 keV band. We have a laboratory demonstration of the polarization of a pair of multilayer mirrors and will present progress on work to demonstrate the capabilities of laterally graded multilayer coated mirrors. We also present plans for a suborbital rocket experiment designed to detect a polarization level of <20% for an active galactic nucleus.
Tuesday, February 18
No colloquium. Midterm Recess.
Tuesday, February 25
Bulbul Chakraborty, Brandeis University
Tuesday, March 4
No colloquium. APS Meeting.
Tuesday, March 11
Eisenbud Lecture Series in Mathematics and Physics:
Cumrun Vafa, Harvard University
Tuesday, March 18
Matthew Reece, Harvard University
Tuesday, March 25
Chris Rogan, Harvard University.
Tuesday, April 1
Katia Bertoldi, Harvard University
Tuesday, April 8
Daniel I. Goldman, Georgia Institute of Technology
Tuesday, April 15
No colloquium. Spring Recess.
Tuesday, April 22
No colloquium. Spring Recess.
Tuesday, April 29
Michael J Naughton, Boston College