Seminars and Colloquia - Fall 2008
Tuesday, September 9, 2008
Martin Weiner Lecture Series
Physics Colloquium
Eugene Shakhnovich
Harvard University
Title: Bridging scales in biological evolution: From atoms to organisms
Host: Mike Hagan
Abstract:
One of the key unsolved problems in Biology today is understanding impact of classical evolution, on organismal and population level on molecular evolution of genes and proteins. In this lecture I will present a microscopic physical model of early, biological evolution, where phenotype - organism life expectancy - is directly related to genotype – the stability of its proteins and interactions between them which can be determined exactly in the model. Simulating the model on a computer, we consistently observe the ‘’Big Bang’’ scenario whereby exponential population growth ensues as favorable sequence-structure combinations (precursors of stable proteins) are discovered. After that, random diversity of the structural space abruptly collapses into a small set of preferred proteins. The key feature of evolved proteins is their remarkable robustness with respect to point mutations. Further, we noted that evolution of populations of organisms each carrying M genes is isomorphic to the problem of M-dimensional random walkers in space of protein sequences with two adsorbing boundary conditions: at high energies of protein native conformations where proteins become unviable and organisms carrying their genes die and at lower energies where proteins are depleted of possible stable sequences. This problem can be solved exactly and we obtained the relation between mutation rates, duplication rate and stability range of the proteins at which populations remain viable. This formula predicts the universal speed limit on molecular evolution at 6 mutations per genome per replication. It provides important insights into genomic organization and evolution of viruses and simple organisms. Further analysis highlights relationship between selection and mutations – an exact solution of the selection-mutation equation provides insights into evolution of bacteria viruses and immune response.
Refreshments will be served outside room 131 at 3:30pm
Tuesday, September 16, 2008
2:00pm
Theory Seminar
Abelson 229
Hajar Ebrahim
"Black Holes and Qubits"
Tuesday, September 16, 2008
Martin Weiner Lecture Series
Physics Colloquium
4:00pm -- Abelson 131
Albion Lawrence
Brandeis University
Title: (De)constructing spacetime in string theory
Abstract:
The famous difficulty of combining Einstein's theory of gravity with quantum mechanics teaches us that the degrees of freedom of nature should change drastically at short distances and high energies. String theory provides such a change of perspective by positing that the fundamental constituents of nature are extended objects. In this scenario, there is no operational notion of a "point" in space or in time. To probe this new description of spacetime, we will describe explicit examples of "stringy" spacetimes which have features that are very different from those that we are used to (these generalizations also have applications to particle physics and cosmology). We will then discuss how two familiar concepts -- time, and the dimension of space -- arise in string theory. We will close by discussing current work on recovering the physics of black holes.
Refreshments will be served outside room 131 at 3:30pm
Tuesday, September 23, 2008
Martin Weiner Lecture Series
Physics Colloquium
4:00pm -- Abelson 131
Jim Bensinger
Brandeis University
A Precision Muon Detector for the ATLAS Experiment at the LHC
The muon detector, the outermost part of the ATLAS experiment at the LHC, was built to an unprecedented size and with unprecedented precision. The muon system occupies a volume 40 meters long and 25 meters in diameter. It contains approximately 300,000 wires and the position of each one has to be known to 40 mm. This system is expected to measure the momentum of muons up to 1 TeV/c with 10% accuracy. As muons and electrons are expected to be significant signatures of new phenomenon, this is a critical part of the ATLAS experiment. I will describe the experiment and in particular the muon system and discuss the technological developments and advances that enabled us to build this system with emphasis on those developments achieved at Brandeis.
Refreshments will be served outside room 131 at 3:30pm
Tuesday, September 23, 2008
Theory Seminar
2:00pm -- Abelson 229
Cecilia Garraffo
Brandeis Univeristy
"Ultra Violet Corrections to Einstein-Hilbert Action"
Monday, September 29, 2008
(Brandeis Tuesday)
Martin Weiner Lecture Series
Physics Colloquium
No Colloquium today.
Refreshments will be served outside room 131 at 3:30pm
Monday, September 29, 2008
String Theory Seminar
2:00pm
Abelson 229
"Tachyon actions in string theory: a no-go theorem"
Matthew Headrick
Brandeis University
Tuesday, October 7, 2008
Martin Weiner Lecture Series
Physics Colloquium
Paul Miller
Biology Department
Brandeis University
"Learning associations while retaining specificity: competing
demands on network plasticity rules"
Host: Mike Hagan
Abstract:
Many cognitive tasks require behavioral responses to specific pairings or combinations of stimuli (A with B or X with Y) that differ from responses to the same individual stimuli, but in alternative combinations (A with Y or X with B). Such pair-specific responses can require logic equivalent to XOR, and can not be solved with a single layer neural network. Generation of a neurons with responses to specific pairs of stimuli becomes essential. We assess how various plasticity rules, which describe how connections between neurons alter as a function of neural activity, can assist or detract from the necessary generation of neurons with responses to specific associations. We find that standard rules for spike-timing dependent plasticity tends to produce over-association (so that any cell responding to the pair "A and B" would also respond to "A and Y" or to "X and B". However, the more recently discovered long-term potentiation of inhibitory connections counters such over-association by generating cross-inhibition, which suppresses the unwanted responses. We show how such association-specific neurons can arise in an initially random network. We also address which types of network structure can generate stimulus-specific memory activity, which is needed when pairs of stimuli are separated in time. Some of these memory networks can retain information about the order of stimuli as well as the specific pairing.
Refreshments will be served outside room 131 at 3:30pm
Tuesday, October 7 , 2008
String Theory Journal Club
2:00pm
Abelson 229
"Quantum entropy function from AdS2/CFT1 correspondence"
Hajar Ebrahim
Tuesday, October 14, 2008
String Theory Seminar
2:00 pm.
Abelson 229
"An overview of thte closed string tachyon"
Ian Swanson
MIT
Thursday, October 16, 2008
String Theory Seminar
2:00pm
Abelson 229
"M2 branes and maximal gauged supergravities in D=3"
Hermann Nicolai
AEI Potsdam
Tuesday, October 21, 2008
String Theory Seminar
2:00pm
Abelson 229
"Holographic superconductors"
Sean Hartnoll
Harvard University
Tuesday, October 28, 2008
String Theory Seminar
2:00pm
Abelson 229
"Regge behavior in N=4 super-Yang-Mills theory"
Howard Schnitzer
Brandeis University
Tuesday, October 28, 2008
Martin Weiner Lecture Series
Physics Colloquium: Co-sponsored with Quantitative Biology Program
Rudi Podgornik
Josef Stefan Institute and NIH
Title: The Nature and Characterization of Order in High Density DNA Mesophases
Host: Jane' Kondev
Abstract: I will describe the nature of known mesophases of DNA at high densities (cholesteric, line hexatic, hexagonal columnar, hexagonal and orthorhombic) and invoke some recent advances in their understanding. Concerted rotations and translations of long helical molecules around their long axes in bulk samples lead to a new mesophase with a screw-like order. This screw-like order actually expels the cholesteric twist from a line hexatic phase and allows it to show a typical sixfold hexatic scattering intensity. Next I will describe a partially constrained system like DNA fibers where the molecules are allowed to rotate but are not allowed to fluctuate translationally. In this case, general considerations based on angular dependence of the DNA-DNA interaction potential, lead to new phases with non-hexagonal symmetry as already seen in classical DNA X- ray scattering studies in the '50s. I will also show how the azimutal interactions lead to crystallization of the fiber with an orthorhombic unit cell which can be observed in DNA at high density.
Refreshments will be served outside room 131 at 3:30pm
Tuesday, November 4, 2008
String Theory Seminar
2:00pm
Abelson 229
"TBA"
Alessandro Tomasiello
Harvard University
Tuesday, November 4, 2008
Martin Weiner Lecture Series
Physics Colloquium
MIT
Title TBA
Host: Albion Lawrence
Refreshments will be served outside room 131 at 3:30pm
Tuesday, November 11, 2008
String Theory Seminar
2:00pm
Abelson 229
"TBA"
Cynthia Keeler
Harvard University
Tuesday, November 11, 2008
Martin Weiner Lecture Series
Physics Colloquium
Syracuse University
Title: TBA
Host: Bulbul Chakraborty
Refreshments will be served outside room 131 at 3:30pm
Tuesday, November 18, 2008
Martin Weiner Lecture Series
Physics Colloquium
Alexander Grosberg
NYU
Title: TBA
Host: Jane' Kondev
Refreshments will be served outside room 131 at 3:30pm
Tuesday, November 25, 2008
String Theory Seminar
2:00pm
Abelson 229
"TBA"
Delia Schwartz-Perlov
Tufts University
Tuesday, November 25, 2008
Martin Weiner Lecture Series
Physics Colloquium
Dr. Steffi Baum
Director, Center for Imaging Science, Rochester Institute of Technology
Title: TBA
Host: John Wardle
Refreshments will be served outside room 131 at 3:30pm
Tuesday, December 2, 2008
String Theory Seminar
2:00pm
Abelson 229
"Duality between non-rational CFTs and their string theory interpretation"
Gaston Giribet
University of Buenos Aires
Tuesday, December 2, 2008
Martin Weiner Lecture Series
Physics Colloquium
Priya Natarajan
Prof. of Physics and Astronomy at Yale Univ. and Fellow at the Radcliffe Institute for Advanced Study, Harvard Univ.
Title: TBA
Host: Albion Lawrence
Refreshments will be served outside room 131 at 3:30pm
Tuesday, December 9, 2008
String Theory Seminar
2:00pm
Abelson 229
"Duality between non-rational CFTs and their string theory interpretation"
Chethan Gowdigere
University of Buenos Aires
Tuesday, December 9, 2008
Martin Weiner Lecture Series
Physics Colloquium
Erik Luijten
University of Illinois, Urbana-Champagne
Title: TBA
Host: Mike Hagan
Refreshments will be served outside room 131 at 3:30pm