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The materials science and engineering of high-power lasersJohn Ballato, PhD Friday, February 5, 2021 Continued progress in the development of optical fiber-based lasers has led to the present state where further improvements in performance are limited by intrinsic optical nonlinearities. In order to manage such limitations, laser designers have largely adopted the approach of microstructuring the fiber to shift nonlinear thresholds to high optical powers. The nonlinearities are accepted as fixed and performance is enhanced through fiber geometric complexity. This talk treats a different option, which is to mitigate optical nonlinearities at their fundamental origin: the materials with which the light interacts. This work provides a road-map for the development of simple core/clad optical fibers whose enhanced performance – in particular, marked reductions in optical nonlinearities – is achieved materially and not through the more conventional present routes of geometrically complex fiber design. More specifically, the material properties that give rise to Brillouin, Raman, and Rayleigh scattering, transverse mode instabilities (TMI), and n2-mediated nonlinear effects are compiled and results on a wide range of optical fibers are discussed with a focus on trends in performance with glass composition. Further, optical power scaling estimations as well as binary and ternary property diagrams associated with Rayleigh scattering, the Brillouin gain coefficient (BGC) and the thermo-optic coefficient (dn/dT) are developed and employed to graphically represent general trends with composition along with compositional targets for a single intrinsically low nonlinearity, silica-based optical fiber that can achieve the power-scaling goals of future high energy fiber laser applications. |
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Physics of wound healing in biological tissuesShiladitya Banerjee, PhD Friday, March 19, 2021 Biological tissues are inevitably damaged from time to time and must therefore have robust repair mechanisms. The physical behaviour of tissues depends on their mechanical properties and those of the surrounding environment. However, it remains poorly understood how tissue mechanical properties regulates collective cell motion during wound healing. Here we show that by tuning mechanical tension in tissues, we can alter the rate of wound healing. We observe cells moving past each other at the wound edge by exchanging neighbors, like molecules in a fluid, resulting in seamless wound closure. Using theory and experiments, we discover that a solid-to-fluid phase transition in tissues, via a reduction in tissue tension, can accelerate the rate of wound healing. This is contrary to previous evidence that tensile forces are important for driving wound healing. The role we describe for tissue fluidity in wound healing, in addition to its known roles in developing and mature tissues, reinforces the importance of the fluid state of a tissue. |
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How life shapes timeSrividya Iyer-Biswas, PhD Friday, April 23, 2021 There has been a longstanding quest for uncovering the quantitative laws governing the stochastic growth and division of individual cells. While great strides have been made in unravelling and modeling the details of the gene regulatory networks which dictate growth and division for different organisms, there is a regrettable paucity of quantitative physical laws derived from the complementary “top down” perspective. Introducing the unique combination of technologies that facilitated probing stochastic cellular dynamics with unprecedented precision, I will first summarize the "scaling laws" that govern fluctuations in growth and division of individual cells under steady-state growth conditions. Taking a minimalist perspective, I will argue for how these scaling laws reveal an elegant physical principle governing these complex biological processes: a single cellular unit of time, which scales with external conditions, governs all aspects of stochastic cell growth and division at a given condition. I will then focus on applications of the technology to probe more complex growth conditions, the corresponding generalizations of the physical principle, and the implications for the underlying biological systems design. Finally, I propose an integrative perspective of microbial growth dynamics under balanced conditions, by introducing a multi-scale theoretical framework that takes observables at both scales, single-cell and population, into account. |
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Seminar series organizers:
Seminar series sponsored by: Augusta University Research Institute, College of Science and Mathematics, Department of Chemistry and Physics
