Events Archive

Nov
28
2012
Bubble instabilities in constricted geometries
PLEASE NOTE: This is a WEBINAR The displacement of a liquid by an air bubble is a generic two-phase flow that underpins applications as diverse as microfluidics, thin-film coating, enhanced oil recovery, and biomechanics of the lungs. I will present two intriguing examples of such flows where, firstly, oscillations in the shape of propagating bubbles are induced by a simple change in tube geometry, and secondly, flexible vessel boundaries that enable streamwise variations of the channel depth...
Nov
27
2012
Conformational dynamics that allow repair proteins to detect DNA mismatches
The DNA mismatch repair system is critical for accurate DNA replication.  This system is highly conserved across organisms ranging from bacteria to humans reflecting the importance of minimizing genomic defects during cell division. The mismatch repair protein MutS has been identified the key factor that detects base-base mismatches and insertion-deletion mismatches in double stranded DNA and signals for their repair.  Despite intense study, a temporally resolved understanding of the molecular details of the MutS:DNA interactions during mismatch repair initiation has been difficult to...
Nov
27
2012
Collective interactions in Metamaterials and Cold Atomic Gases: Manipulating Light in Ensembles of Electromagnetic Emitters
In this seminar, we will discuss how interactions between discrete electromagnetic (EM) emitters lead to a cooperative response of a metamaterial or cold atomic gas to an incident field.  We will examine a number of ways the cooperative response can be engineered and exploited. The interactions responsible arise from repeated scattering of the field between its discrete constituent elements. Our focus will be on metamaterials, which are composed of subwavelength circuit elements - or meta-atoms - whose electric and magnetic multipole interactions are governed by their design.  We also...
Nov
26
2012
From Social Intelligence of Bacteria to Cyber-war on Cancer
Cancer continues to elude us. Metastasis, relapse and drug resistance are all still poorly understood and clinically insuperable. Evidently, the prevailing paradigms need to be re-examined and out-of-the-box ideas ought to be explored. Recently, has become acknowledged that transformative convergence of physical sciences with life sciences can bring forth new perspectives for addressing major questions and challenges relating to cancer. Drawing upon recent discoveries demonstrating the parallels between collective behaviors of bacteria and cancer, I will present a new picture of cancer as a...
Nov
20
2012
Percolation, Phase Transitions and Speciation on a Neutral Landscape
The problem of speciation and species aggregation on a neutral landscape, subject to random mutational fluctuations without selective drive, has been a focus of research since the seminal work of Kimura on genetic drift. This problem, which has received increased attention due to the recent development of a neutral ecological theory by Hubbell, bears comparison with mathematical problems such as percolation and...
Nov
19
2012
How worms wiggle
Directed locomotion requires coordinated motor activity throughout an animal’s body. The nematode C. elegans, with only 302 neurons, offers an opportunity to understand how locomotion is organized by an entire motor system. We discovered that the mechanism that organizes undulatory locomotion in C. elegans is a novel form of sensory feedback within the motor circuit. Stretch-sensory feedback simply compels each body segment to bend in the same direction and shortly after the bending of the adjacent anterior segment. Remarkably, the entire...
Nov
17
2012
When galaxies collide, what happens to their supermassive black holes?
Galaxy collisions and mergers are a common consequence of the structure formation in the universe. We know that they happen because we see a number of beautiful examples on the sky through the "eyes" of many astronomical observatories. It is also thought that almost every galaxy (including our own, the Milky Way) harbors a supermassive black hole at its center. I will discuss the "knowns" and "unknowns" in the evolution of supermassive black hole pairs that form in collisions of their host galaxies and end their cosmic journey when the two black holes merge due to the emission of gravitational waves....
Nov
15
2012
Physics Graduate & Undergraduate In-reach Series: Computational Neuroethology: A physicist’s journey into wet lab studies of the brain’s neural code
Dr. Robert Liu trained as a condensed matter experimentalist working on quantum transport and noise in mesoscopic semiconductors, but always believed that the true value of a physics doctorate was in learning how to think through and solve problems. As a graduate student at Stanford, he became fascinated with questions about the brain and memory, and decided to apply his quantitative training from physics to the study of neuroscience. He moved to the University of California at San Francisco’s Sloan-Swartz Center for Theoretical Neurobiology to begin postdoctoral work on studying the neural...
Nov
14
2012
Interrogating a granular material: force networks, state variables, and acoustics
Granular materials exhibit large spatial variations in their response to external loading, whether static or dynamic. As such, continuum models of properties such as the shear modulus and sound speed often fail. A promising alternative is to build an understanding of bulk behaviors from measurements at the particle scale, by analogy with the statistical mechanics of thermal systems. I will describe experiments in which we utilize photoelastic particles and piezo-embedded 'smart' particles to explore how two familiar properties -- temperature equilibration and...
Nov
13
2012
Immunophysics of host-pathogen interactions: An immune-cell perspective
Motile immune cells like neutrophils (the most abundant type of white blood cell) track down invading microbes by chemotaxis, keep hold of them by adhesion, and neutralize them by phagocytosis.  We integrate concepts and tools from immunobiology and biophysics to examine the mechanistic underpinnings of this amazing, cross-disciplinary feat.  Single-live-cell experiments using micropipette manipulation, optical tweezers, and a new type of horizontal atomic force microscope allow us to assess the nano-to-microscale ingredients of one-on-one encounters between human neutrophils and their targets (such as opsonized...

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