Physics Colloquia

February 11, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)

Kyle Cranmer
New York University

Probing Fundamental Physics at the LHC... and Its Predecessor

Two months ago, the Large Hadron Collider saw its first proton collisions and became the world's highest energy particle collider. The LHC has unprecedented discovery potential and may shed light on the origin of electroweak symmetry breaking, dark matter, supersymmetry, and even extra space-time dimensions. I'll update you on some of the exciting work being done at NYU using the ATLAS detector at the LHC.... and some important results we obtained with 10 year old data while waiting for the machine to be fixed.

February 18, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)
Soft Condensed Matter Seminars (csmr)

Jasna Brujic
New York University

TBA

February 25, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)
Soft Condensed Matter Seminars (csmr)

Jerry Gollub
Haverford College

Swimming Dynamics of Algae Cells and the Fluid Motion they Produce

This talk concerns the swimming of single algae cells only 10 micrometers across. These and other algae cells produce a significant fraction of the earth's oxygen. Their swimming involves the synchronized beating of appendages known as flagella or cilia, which are also important for many other types of cells, such as those lining the interior of the lung.

In work published in Science, we showed [1] that the coordination of the two flagella of the algae cells is is possible because of forces transmitted between them through the intervening fluid. In a "Perspective" written about this work in Science, two experts in the field comment that the coordinated motion of flagella allows the cells to enhance their nutrition and may have contributed to the evolution of multi-cellular organisms.

Yet about 5% of the time the cells choose to make their flagella beat at different rates, which causes the cells to turn sharply. Why would they do this? One possibility is that the cells need to avoid contact with predators. The biochemical means by which the organism makes this choice, and the role of chance in the process, are not yet understood.

In related work that appeared in Physical Review Letters, we studied the stirring of the fluid by swimming cells, which also affects their access to nutrients. The natural Brownian motion of tracer particles immersed in the fluid is enhanced by the swimmers in a remarkable way.

This work was done in collaboration with the group of Raymond Goldstein at Cambridge UK

[1] Marco Polin, Idan Tuval, Knut Drescher, J.P. Gollub, and Raymond E. Goldstein, "Chlamydomonas swims with two "gears" in a eukaryotic version of run-and-tumble locomotion", Science 24 July 2009. Accompanied by a Perspective by Roman Stocker and William M. Durham: "Eukaryotic flaggelar synchronization: tumbling for stealth?"

March 4, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)

Adam Burrows
Princeton University

TBA

March 11, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)

Janet Conrad
MIT

Nu Adventures on the Road to New Physics

In the past decade, neutrino physics has come a long way. But for each exciting discovery, new questions have arisen. This talk reviews the most recent results in the neutrino sector and discusses the steps we need to take to form a "whole nu theory" of particle physics.

March 25, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)

David Weitz
Harvard University

TBA

April 1, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)
Soft Condensed Matter Seminars (csmr)

Jennifer Lewis
University of Illinois at Urbana-Champaign

Novel Routes for Patterning Colloidal Films, Granules, and 3D Structures

This talk will feature recent advances in the assembly of patterned colloidal films, granules, and 3D architectures. By engineering the phase transitions, rheological, and drying behavior of dense colloidal suspensions, we have developed several new patterning approaches. First, the evaporative lithographic patterning of colloidal films will be described. Next, the microfluidic assembly of colloidal granules and micro-components with controlled composition, shape, and size will be discussed. Finally, the direct-write assembly of planar and 3D structures from functional colloidal inks will be discussed. Several potential applications will be demonstrated, including printed electronics, novel granular media, and low-cost MEMs.

April 8, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)

Meg Urry
Yale University

Supermassive Black Holes and Galaxy Evolution

Black holes form in the early Universe and grow to billions of solar masses as their gravity attracts surrounding matter. This cosmic accretion releases a huge amount of energy, which is expected to have a strong influence on galaxy evolution - for example, potentially ionizing the interstellar gas and thus quenching star formation. The history of black hole growth can be traced through the detection of Active Galactic Nuclei out to very high redshifts; however, most AGN have been discovered in optical and ultraviolet surveys, which are strongly biased against obscured accretion. Deep multiwavelength surveys reveal that most AGN are heavily obscured and that obscuration is more common in the young Universe and in low-luminosity AGN, so we now have a much more complete picture of the demographics of supermassive black holes. Perhaps unexpectedly, star formation appears to turn off well before AGN reach their peak brightness, which is an important clue to the role of AGN feedback in galaxies.

April 15, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)

David Weinberg
Institute for Advanced Study

The Sloan Digital Sky Survey: I, II, III

I will describe some of the scientific highlights from the Sloan Digital Sky Survey (SDSS), concentrating on those connected to cosmology and galaxy formation. The SDSS is the most ambitious survey of the universe ever undertaken. To date, it has imaged 11,500 square degrees and detected more than 350 million objects, measured the spectra of 930,000 galaxies, 120,000 quasars, and 460,000 stars to create the largest ever 3-dimensional maps of cosmic structure, and discovered more than 500 Type Ia supernovae to measure the expansion of the universe over the last 5 billion years. Cosmological achievements from the SDSS include: probing the epoch of reionization with the most distant known quasars; comprehensively characterizing the properties of galaxies and the relations between galaxies and their parent dark matter halos; discovering ubiquitous substructure in the outer Milky Way and more than a dozen new companion satellite galaxies; and, through its precision measurements of structure on very large scales, providing a central pillar of the standard cosmological model based on inflation, cold dark matter, and dark energy. I will describe the goals of SDSS-III, the ongoing phase of the SDSS, with special attention to the Baryon Oscillation Spectroscopic Survey (BOSS), which seeks to pin down the cause of accelerating cosmic expansion through percent-level measurements of the expansion history.

April 22, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)

Alex Filippenko
UC Berkeley

TBA

April 29, 2010 Thursday 4:00 PM 
Meyer 122
Physics Colloquia (colloquia)
Soft Condensed Matter Seminars (csmr)

Itai Cohen
Cornell

Flight of the Fruit Fly: Life at Intermediate Reynolds Numbers

There comes a time in each of our lives where we grab a thick section of the morning paper, roll it up and set off to do battle with one of nature’s most accomplished aviators - the fly. If however, instead of swatting we could magnify our view and experience the world in slow motion we would be privy to a world-class ballet full of graceful figure-eight wing strokes, effortless pirouettes, and astonishing acrobatics. After watching such a magnificent display, who among us could destroy this virtuoso? How do flies produce acrobatic maneuvers with such precision? What control mechanisms do they need to maneuver? More abstractly, what problem are they solving as they fly? Despite pioneering studies of flight control in tethered insects, robotic wing experiments, and fluid dynamics simulations that have revealed basic mechanisms for unsteady force generation during steady flight, the answers to these questions remain elusive. In this talk I will discuss our strategy for investigating these unanswered questions. I will begin by describing our automated apparatus for recording the free flight of fruit flies and a new technique called Hull Reconstruction Motion Tracking (HRMT) for backing out the wing and body kinematics. I will then show that these techniques can be used to reveal the underlying mechanisms for flight maneuvers, wing actuation, and flight stability. Finally, I will comment on the implications of these discoveries for investigations aimed at elucidating the evolution of flight.