Guest lectures and seminars - Page 46
Abstract: Swimming bacteria, growing cell tissues, molecular motors, and microtubule systems confined to a substrate are examples of active matter films that exhibit long-range nematic (orientational) order. Intrinsic activity in these systems builds mechanical stresses that tend to destroy local nematic order through topological defects, which act as sources of persistent active flows. The overall evolution and functionality of biological matter is greatly influenced by these orientational defects. Yet, their formation and dynamics are driven by a complex interplay between topological singularities in the nematic order and active flow instabilities, and this is not completely understood.
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For many real-life phenomena one may assume that the units of observation, typically patients, transition through a set of discrete states on their way towards an absorbing state. The states often constitute various stages of a disease, from perfect health through various stages of dementia for example. Multi-state models are a class of statistical models which allow us to study the time spent in different states, the probability of transitioning between states, and the relationship between these quantities and covariates of interest. In many applications the transition times between states are not observed exactly; instead, the current state of the patients is queried at arbitrary times. The transition times are therefore interval censored, and this makes inference and modelling challenging. Most current approaches are based on the Markov assumption, for example the simplest parametric model available - the time-homogeneous Markov model. Here, we propose a new, general framework for parametric inference with interval censored multi-state data. Our models allow non-Markovian behaviour. I will present the framework and an algorithm for the automatic construction of the likelihood function, along with real-data examples. This talk is based on joint work with Marthe Aastveit and Nils Lid Hjort.
Abstract: Exchange processes across a porous-medium free-flow interface occur in a wide range of environmental, technical, and bio-mechanical systems. In the course of these processes, flow dynamics in the porous domain and in the free-flow domain exhibit strong coupling, often controlled by mechanisms at the common interfaces. Such processes need to be analyzed on small scales and new scale-bridging modeling concepts need to be developed for an accurate description also on larger scales (REV scale). Recent developments within the Collaborative Research Center "Interface-Driven Multi-Field Processes in Porous Media – Flow, Transport and Deformation" and the Cluster of Excellence SimTech at the University Stuttgart regarding such aspects for coupled free-flow and porous-medium flow systems will be presented in this talk.
This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.
Abstract: We present a second-order numerical scheme to compute capillary bridges between arbitrary solids by minimizing the total energy of all interfaces. From a theoretical point of view, this approach can be interpreted as the computation of generalized minimal surfaces using a Newton-scheme utilizing the shape Hessian. In particular, we give an explicit representation of the shape Hessian for functionals on shells involving the normal vector without reverting back to a volume formulation. From an algorithmic perspective, we combine a resolved interface via a triangulated surface for the liquid with a level-set description for the constraints stemming from the arbitrary geometry. The actual shape of the capillary bridge is then computed via finite elements provided by the FEniCS environment, minimizing the shape derivative of the total interface energy.
This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.