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DTSTART;TZID=America/New_York:20221103T103000
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SUMMARY:Asymptotic geometry of null hypersurface in Schwarzschild spacetime and null Penrose inequality
DESCRIPTION:General Relativity Seminar \n\nSpeaker: Pengyu Le (BIMSA) \nTitle: Asymptotic geometry of null hypersurface in Schwarzschild spacetime and null Penrose inequality \nAbstract: Null Penrose inequality is an important case of the well-known Penrose inequality on a null hypersurface. It conjectures the relation between the area of the outmost marginally trapped surface and the Bondi mass at null infinity. Following the proposal of Christodoulou and Sauter\, we employ the perturbation method to study the asymptotic geometry of null hypersurfaces at null infinity in a perturbed vacuum Schwarzshild spacetime. We explain how to apply this perturbation theory to prove null Penrose inequality on a nearly spherically symmetric null hypersurface in a perturbed vacuum Schwarzschild spacetime.
URL:https://cmsa.fas.harvard.edu/event/gr_11322/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:General Relativity Seminar
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DTSTART;TZID=America/New_York:20221103T130000
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SUMMARY:Force transmission informs the collective behavior of active cell layers
DESCRIPTION:Active Matter Seminar \nSpeaker: Siavash Monfared\, Niels Bohr Institute\, Copenhagen \nTitle: Force transmission informs the collective behavior of active cell layers \nAbstract: Collective cell migration drives numerous physiological processes such as tissue morphogenesis\, wound healing\, tumor progression and cancer invasion. However\, how the interplay of mechanical interactions and the modes of collective self-organization among cells informs such processes is yet to be established. In this talk\, I will focus on the role of three-dimensional force transmission\, from a theoretical and computational perspective\, on two phenomena: (1) cell extrusion from a cellular monolayer and (2) density-independent solid-like to fluid-like transition of active cell layers. For the first topic\, I will focus on how increasing cell-cell adhesion relative to cell-substrate adhesion enables cells to collectively exploit distinct mechanical pathways – leveraging defects in nematic and hexatic phases associated with cellular arrangement – to eliminate an unwanted cell. For the second topic\, I will show how solid-like to fluid-like transition in active cell layers is linked to the percolation of isotropic stresses. This is achieved via two distinct and independent paths to model this transition by increasing (a) cell-cell adhesion and (b) active traction forces. Additionally\, using finite-size scaling analyses\, the phase transition associated with each path is mapped onto the 2D site percolation universality class. Our results highlight the importance of force transmission in informing the collective behavior of living cells and opens the door to new sets of questions for those interested in connecting the physics of cellular self-organization to the dynamics of biological systems. \n 
URL:https://cmsa.fas.harvard.edu/event/am-113022/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Active Matter Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Active-Matter-Seminar-11.03.22.png
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