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Department Colloquia

Martin Weiner Lecture Series
Department of Physics Colloquium
4:00 pm, Abelson 131
Refreshments at 3:30pm outside Abelson 131

Fall 2013 Colloquia

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.

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[2]. 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).

Watch the video.

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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.

Watch the video.
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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..


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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.

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Tuesday, October 15

Marin Soljacic, MIT
Title: TBA
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Tuesday, October 22

Patrick Charbonneau, Duke University
Title: TBA

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Tuesday, October 29

Gabriella Sciolla, Brandeis University
Title: TBA

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Tuesday, November 5

Efi Efrati, University of Chicago
Title: TBA

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Tuesday, November 12

Anthony Dinsmore, UMass Amherst
Title: TBA

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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.
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Tuesday, December 3

Raymond Brock, Michigan State University 
The future of High Energy Physics in the US

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

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Tuesday, January 21

Daniel Eisenstein,The Harvard-Smithsonian Center for Astrophysics
Title: TBA

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Tuesday, January 28

Leif Ristroph, Courant Institute at New York University

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Tuesday, February 4

Veronika Hubeny,University of Durham

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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.

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Tuesday, February 18

No colloquium. Midterm Recess.

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Tuesday, February 25

Bulbul Chakraborty, Brandeis University
Title: TBA
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Tuesday, March 4

No colloquium. APS Meeting.

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Tuesday, March 11

Eisenbud Lecture Series in Mathematics and Physics:
Cumrun Vafa, Harvard University

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Tuesday, March 18

Matthew Reece, Harvard University
Title: TBA



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Tuesday, March 25

Chris Rogan, Harvard University.
Title: TBA

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Tuesday, April 1

Katia Bertoldi, Harvard University
Title: TBA

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Tuesday, April 8

Daniel I. Goldman, Georgia Institute of Technology

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Tuesday, April 15

No colloquium. Spring Recess.


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Tuesday, April 22

No colloquium. Spring Recess.


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Tuesday, April 29
Michael J Naughton, Boston College
Title: TBA