Fall 2006 - Mondays
September
11th
4:10 pm - 428 Pupin Hall
Speaker:
Professor Andrei Beloborodov, Columbia University Physics
Title:
"Neutron Stars with Ultra-Strong Magnetized Fields"
Abstract:
At least 10% of neutron stars are born with ultra-strong magnetic fields B > 1014 G. These "magnetars" are qualitatively different from normal neutron stars. Their crust is sporadically broken in spectacular star quakes, creating giant X-ray flares -- the brightest transients in the sky. Besides the flares, magnetars produce persistent X-ray emission with luminosity ~ 1000 times brighter than the Sun. It is now established observationally that magnetars have a bright plasma corona. The mysterious coronal activity is likely fed by gradual dissipation of non-potential (twisted) magnetic fields around the neutron star. A twist of ultrastrong magnetic field initiates electron-positron discharge that continues to operate quasi-steadily, in the regime of self-organized criticality. The stochastic discharge around the star converts magnetic energy to plasma energy and explains the formation of magnetar corona.
18th
4:10 pm - 428 Pupin Hall
Speaker:
Professor Philip Kim, Columbia University Physics
Title:
"Quantum Physics at Your Pencil Tips: Dirac Fermion in Graphitic Carbon"
Abstract:
The massless Dirac particle moving at the speed of light has been a fascinating subject in relativistic quantum physics. Graphene, an isolated single atomic layer of graphite, now provides us an opportunity to investigate such an exotic effect in low-energy condensed matter systems. The unique electronic band structure of graphene lattice provides a linear dispersion relation where the Fermi velocity replaces the role of the speed of light in the usual Dirac Fermion spectrum. In this presentation I will discuss the experimental consequence of the Dirac Fermion spectrum in charge transport, realized in two representative low dimensional graphitic carbon systems: 1-dimensional carbon nanotubes and 2-dimensional graphene. Combined with semiconductor device fabrication techniques and the development of new methods of nanoscaled material synthesis/manipulation enables us to investigate mesoscopic transport phenomena in these materials. The exotic quantum transport behavior discovered in these materials, Postsuch as room temperature ballistic transport, unusual half-integer quantum Hall effect, and a non-zero Berry's phase in magneto-oscillations will be discussed in the connection to the Dirac Fermion description in graphitic systems.
25th
4:10 pm - 428 Pupin Hall
Speaker:
Professor Dan Kabat, Columbia University Physics
Title:
"Strings, gauge theory and gravity"
Abstract:
String theory plays a prominent role in the search for theoretical structures beyond the standard model. I'll give some motivation for string theory and present some of its remarkable consequences. In particular it leads to a relationship between gravitational (string) and non-gravitational (gauge) theories. As I'll discuss, this provides a new calculational tool for studying gauge theories and gives a new perspective on the traditional problems of quantum gravity.
29th
TD Lee 80th Birthday & 50th Anniversary of the Discivery of Parity Non-Conservation
Room: 301 Pupin (note special room)
Time: 1:10-5:30 (note special time)
Introduction and Welcome - Andy Millis
T.D. Lee: Relativistic Heavy Ion (RHIC) and Riken BNL Research Center (RBRC) - Nick Samios
Quantum Chromodynamics: a Numerical Solution - Norman Christ
Particle Physics Past; Particle Physics Future - Fred Gilman
The Origin of Mass and the Feebleness of Gravity - Frank Wilczek
A Unification of Light and Fermi Statistics - Xiao-Gang Wen
The Downfall of Parity: a 36-Hour Experiment - Leon Lederman
Talk by TD Lee
October
2nd - No Colloquium
9th
4:10 pm - 428 Pupin Hall
Speaker:
Professor Stefan Westerhoff, Columbia University Physics
Title:
"The Origin of the Highest Energy Cosmic Rays"
Abstract:
Ultrahigh energy cosmic ray physics is undergoing a rapid development. Triggered by new data of unprecedented quantity and quality that has been collected over the last few years, our view of cosmic rays in the universe has changed in many aspects. This summer, the question of anomalous ultrahigh energy cosmic rays was resolved. Crucial to this was the spectrum measurement of HiRes, an air fluorescence detector which operated in Utah. HiRes stereo data has also recently revealed the remarkable isotropy of the cosmic ray sky, which so far shows no apparent "hot spots." The cosmic ray uniformity needs to be confirmed by better, more inclusive coverage, which is now becoming available with the Pierre Auger Observatory, a large hybrid detector under construction in Argentina. The HiRes and Auger measurements will be critical in addressing several important questions: Why is the arrival direction distribution so isotropic even at the highest energies? What is the chemical composition of the primary cosmic ray flux, and what does it reveal about the sources? What is the exact shape of the spectrum at the highest energies? This talk presents recent results from the HiRes and Auger experiments, and summarizes future strategies to solve the longstanding problem of the origin of ultrahigh energy cosmic rays.
16th
4:10 pm - 428 Pupin Hall
Speaker:
Professor Amber Miller, Columbia University Physics
Title:
"Peeking in Ancient Holes and Seeking the Holy Grail"
Abstract:
The Cosmic Microwave Background (CMB) consists of a bath of photons
emitted when the universe was 380,000 years old. Carrying the imprint of primordial fluctuations that seeded the formation of structure in the universe, the CMB is one of the most valuable known tools for studying the early universe. In our modern, post WMAP era, the utility of studying temperature anisotropies in the CMB is clear and much of the work has been done. I will describe two exciting new directions in which the field is currently heading: small-scale secondary CMB anisotropy and CMB polarization anisotropy. In this context, I will discuss preliminary results from our small-scale secondary anisotropy experiment, the Sunyaev-Zel'dovich Array (SZA). I will also briefly describe our two upcoming CMB polarization experiments, the Q U Imaging Experiment (QUIET) and the E B Experiment (EBEX).
23rd:
4:10 pm - 428 Pupin Hall
Speaker:
Professor Licia Verde, University of Pennsylvania
Title:
"Connecting the Cosmos with Quarks: The Promise of Precision Cosmology"
Abstract:
Cosmology has recently made the transition from a data starved science to a data driven science. Cosmological parameters are today known with unprecedented precision, making "precision cosmology" possible.
The decadal survey "Astronomy and Astrophysics in the New Millennium" published by NAS in 2002 was entitled "connecting quarks with the cosmos". It presented 11 fundamental questions to be addressed, and recognized that physics and astronomy are inextricably tied together in both the answering and the answers to these questions.
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The ultimate goal of precision cosmology is to connect the cosmos with quarks. I will review some recent advances in this direction, brought about by new data sets, and will outline some forthcoming and future prospects.
30th
4:10 pm - 428 Pupin Hall
Speaker:
Professor David Shoemaker, MIT
Title:
"Progress Toward an Astronomy of Gravitational Waves"
Abstract:
The LIGO interferometric gravitational-wave detectors are now observing at a sensitivity exceeding their original design target, and other similar detectors are observing or commissioning. The instrument science must confront fundamental physics -- quantum and thermal noise -- to achieve this sensitivity. The data from the LIGO science runs have been analyzed for gravitational-wave events and to put upper limits on gravitational-wave flux and to look for gravitational waves from a variety of sources. The present run, to end in Fall 2007, will be followed by some incremental advances in sensitivity and further science runs in coordination with the other worldwide gravitational-wave detectors. LIGO -- the combined Laboratory and Scientific Collaboration -- have also progressed with the Advanced LIGO upgrade, which will start observing in 2014, and will lead to more than a factor of 10 improvement in the sensitivity, covering a volume of space 1000x greater than initial LIGO. This will allow detailed studies of such astrophysical events as neutron-star or black-hole binary inspirals, pulsars, and supernovae from a unique perspective, and will push forward the search for the stochastic background from the Big Bang. Plans are being made for other instruments, both ground-based and space-based, to join this very promising field.
November
6th – No Colloquium – Academic Holiday
13th
4:10 pm - 428 Pupin Hall
Speaker:
Professor Peter Fisher, MIT
Title:
How will we know it when we have found weakly interacting dark matter?
Abstract:
Dark matter has been with us for almost seventy five years and there has been an intensive search for
weakly interacting dark matter for the last twenty five years. This talk will describe the experimental signatures for weakly interacting dark matter and discuss some of the current and planned experiments.
The talk will be at the level of undergraduate seniors, i.e. those who will actually execute the experiments.
20th
4:10 pm - 428 Pupin Hall
Speaker:
Professor Jelena Vuckovic, Stanford University
Title:
"Photonic crystal chips for classical and quantum information processing"
Abstract:
Photonic crystal cavities enable localization of light into volumes below a cubic optical wavelength (smaller than any other types of optical resonators) with high quality factors. This permits a strong interaction of light and matter, which is relevant for construction of classical light sources with improved properties (e.g., low threshold lasers) and of nonclassical light sources (such as single photon sources) - crucial pieces of hardware of quantum information processing systems.
This talk will cover some of our recent experimental results enabled by such interaction, including spontaneous emission rate control (enhancement and suppression) of a single quantum dot inside a photonic crystal cavity, generation and transfer of single photons on a quantum dot-photonic crystal chip, an ultrafast nanocavity laser with low threshold, and two dimensional arrays of coherently coupled nanocavity lasers.
27th
4:10 pm - 428 Pupin Hall
Speaker:
Prof. Harmen Bussemaker, Columbia Genome Center/Biological Sciences
Title:
Data-Driven Biophysical Modeling of Gene Expression Regulation
Abstract:
It is the dynamic balance between transcription from DNA to messenger RNA and subsequent mRNA degradation that determines the steady-state mRNA abundance for each gene in a genome. However, while regulation of transcription rate by DNA binding transcription factors has been intensively studied, both experimentally and computationally, regulation of the transcript turnover rate by RNA binding factors has received far less attention. We took advantage of the fact that information about the condition-specific activity and sequence-specific affinity of RNA binding regulatory factors is implicitly represented in the steady-state mRNA abundances measured using DNA microarrays. Thus, by fitting a model based on a physical description of molecular interactions, we were able to gain quantitative insight into the mechanisms that underlie genome-wide regulatory networks. We developed a novel algorithm, MatrixREDUCE, that predicted the sequence-specific binding affinity of several known and unknown RNA-binding factors and their condition-specific activity, using only genomic sequence data and steady-state mRNA expression data as input.
We identified and computationally characterized the binding sites for six mRNA stability regulators in the yeast S. cerevisiae, which include two known RNA-binding proteins, Puf3p and Puf4p. We provide computational and experimental evidence that regulation of mRNA stability by the discovered factors is dynamic and responds to a variety of environmental stimuli. For example, little was previously known about the functional role of Puf3p, but our computational results suggest that Puf3p functions to destabilize mitochondrion-related transcripts when metabolite repressing sugars are present and in response to the drug rapamycin. We were able to experimentally confirm these predictions by growing a transformed strain expressing a hybrid mRNA designed to contain a functional Puf3p binding site in different culture conditions and measuring its half-life after a transcriptional shut-off.
Our work suggests that regulation of mRNA stability is not a special case phenomenon, but rather a pervasive regulatory mechanism that rapidly adapts cellular processes to a changing environment.
December
4th
4:10 pm - 428 Pupin Hall
Speaker:
Prof. Michael Douglas, Rutgers University
Title:
Supersymmetric gauge theory: an overview
Abstract:
Of the many suggestions for new physics to look for in upcoming collider experiments, by far the most widely accepted is supersymmetry, because of its potential for solving the theoretical problems of the Standard Model, and because of its links to unified theories such as superstring theory.
Supersymmetry is also a theoretical tool, which over the last ten years has led to many dramatic advances, including general techniques for doing nonperturbative and even exact computations. These developments led to the first analytic demonstrations of confinement in four dimensional gauge theory, and many unexpected discoveries such as the existence of non-trivial quantum critical points in four dimensions. These ideas and techniques play a central role in our modern understanding of string theory, and in proposals for how it might make contact with experiment.
We give an introduction to these ideas and discoveries for a general physics audience.
11th
4:10 pm - 428 Pupin Hall
Speaker:
Prof. Kate Scholberg, Duke University
Title:
Neutrinos from the Sky and Through the Earth
Abstract:
The progress in neutrino physics over the past ten years has been tremendous: we have learned that neutrinos have mass and oscillate. I will pick out one of the threads of the story-- the measurement of flavor oscillation in neutrinos produced by cosmic ray showers in the atmosphere. I will present the history, the current state of knowledge, and some of the puzzles remaining to be solved.
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