Bulletin of the American Physical Society
78th Annual Meeting of the Southeastern Section of the APS
Volume 56, Number 9
Wednesday–Saturday, October 19–22, 2011; Roanoke, Virginia
Session GA: Biological Physics and Biomechanics |
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Chair: Rahul Kulkarni, Virginia Polytechnic Institute and State University Room: Crystal Ballroom A |
Friday, October 21, 2011 8:30AM - 9:00AM |
GA.00001: The physics of bat biosonar Invited Speaker: Bats have evolved one of the most capable and at the same time parsimonious sensory systems found in nature. Using active and passive biosonar as a major - and often sufficient - far sense, different bat species are able to master a wide variety of sensory tasks under very dissimilar sets of constraints. Given the limited computational resources of the bat's brain, this performance is unlikely to be explained as the result of brute-force, black-box-style computations. Instead, the animals must rely heavily on in-built physics knowledge in order to ensure that all required information is encoded reliably into the acoustic signals received at the ear drum. To this end, bats can manipulate the emitted and received signals in the physical domain: By diffracting the outgoing and incoming ultrasonic waves with intricate baffle shapes (i.e., noseleaves and outer ears), the animals can generate selectivity filters that are joint functions of space and frequency. To achieve this, bats employ structural features such as resonance cavities and diffracting ridges. In addition, some bat species can dynamically adjust the shape of their selectivity filters through muscular actuation. [Preview Abstract] |
Friday, October 21, 2011 9:00AM - 9:30AM |
GA.00002: How Do Songbirds Produce Precise Vocalizations? Invited Speaker: Many species of songbirds do not sing instinctively but learn their songs by a process of auditory-guided vocal learning that starts with a kind of babbling that converges over several months and through tens of thousands of iterations to a highly precise adult song. How the neural circuitry of the songbird brain learns, generates, and recognizes temporal sequences related to song are important questions for neurobiologists and also interest an increasing number of physicists with interests in biophysics, statistical mechanics, nonlinear dynamics, and networks. I will discuss some interesting questions posed by recent experiments on songbirds, especially in regard to extremely sparse neuronal firing associated with song production. I will then discuss a theoretical model known as a synfire chain that my group and others have invoked and analyzed to explain some features of the experimental data. [Preview Abstract] |
Friday, October 21, 2011 9:30AM - 10:00AM |
GA.00003: Dissecting cellular biomechanics with a laser Invited Speaker: The biological tissues of a developing organism are built and reshaped by the mechanical behavior of individual cells. We probe the relevant cellular mechanics \textit{in vivo} using laser-microsurgery -- both qualitatively, to assess whether removal of specific cells alters the dynamics of tissue reshaping, and quantitatively, to measure sub-cellular mechanical properties and stresses. I will detail two quantitative microsurgical measurements. The first uses a laser to drill a sub-cellular hole in a sheet of cells. The subsequent retraction of surrounding cells allows one to infer the local mechanical stress. The second uses a laser to isolate a single cell from the rest of a cell sheet. Isolation is accomplished on a microsecond time scale by holographically shaping a single laser pulse. The subsequent retraction (or expansion) of the isolated cell allows one to separate and quantify the effects of internal and external stresses in the determination of cell shape. I will discuss application of these techniques to the time-dependent biomechanics of epithelial tissues during early fruit fly embryogenesis -- specifically during the processes of germband retraction and dorsal closure. [Preview Abstract] |
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