Equilibrium Dynamics of Microemulsion and Sponge Phases

The dynamic structure factor $G({\bf k},\omega)$ is studied in a time-dependent Ginzburg-Landau model for microemulsion and sponge phases in thermal equilibrium by field-theoretic perturbation methods. In bulk contrast, we find that for sufficiently small viscosity $\eta$, the structure factor develops a peak at non-zero frequency $\omega$, for fixed wavenumber $k$ with $k_0 < k {< \atop \sim} q$. Here, $2\pi/q$ is the typical domain size of oil- and water-regions in a microemulsion, and $k_0 \sim \eta q^2$. This implies that the intermediate scattering function, $G({\bf k}, t)$, {\it oscillates} in time. We give a simple explanation, based on the Navier-Stokes equation, for these temporal oscillations by considering the flow through a tube of radius $R \simeq \pi/q$, with a radius-dependent tension.Comment: 24 pages, LaTex, 11 Figures on request; J. Phys. II France 4 (1994) to be publishe

Ultraviolet photography and spectroscopy using a spectrally selective image converter

Ultraviolet spectroscopy and photography using spectrally selective image converte

Active depinning of bacterial droplets: the collective surfing of Bacillus subtilis

How systems are endowed with migration capacity is a fascinating question with implications ranging from the design of novel active systems to the control of microbial populations. Bacteria, which can be found in a variety of environments, have developed among the richest set of locomotion mechanisms both at the microscopic and collective levels. Here, we uncover experimentally a new mode of collective bacterial motility in humid environment through the depinning of bacterial droplets. While capillary forces are notoriously enormous at the bacterial scale, even capable of pinning water droplets of millimetric size on inclined surfaces, we show that bacteria are able to harness a variety of mechanisms to unpin contact lines, hence inducing a collective slipping of the colony across the surface. Contrary to flagella-dependent migration modes like swarming we show that this much faster `colony surfing' still occurs in mutant strains of \textit{Bacillus subtilis} lacking flagella. The active unpinning seen in our experiments relies on a variety of microscopic mechanisms which could each play an important role in the migration of microorganisms in humid environment.Comment: 6 pages, 7 figures, SI: 5 movies, 10 figures, 1 tabl

Active Matter Alters the Growth Dynamics of Coffee Rings

How particles are deposited at the edge of evaporating droplets, i.e. the {\em coffee ring} effect, plays a crucial role in phenomena as diverse as thin-film deposition, self-assembly, and biofilm formation. Recently, microorganisms have been shown to passively exploit and alter these deposition dynamics to increase their survival chances under harshening conditions. Here, we show that, as the droplet evaporation rate slows down, bacterial mobility starts playing a major role in determining the growth dynamics of the edge of drying droplets. Such motility-induced dynamics can influence several biophysical phenomena, from the formation of biofilms to the spreading of pathogens in humid environments and on surfaces subject to periodic drying. Analogous dynamics in other active matter systems can be exploited for technological applications in printing, coating, and self-assembly, where the standard coffee-ring effect is often a nuisance.Comment: 7 pages, 5 figure

Identification of small-molecule modulators that enhance the ability of the immune system to eliminate cancer cells

The ability of the immune system to fight cancer is long-established whereas an in-depth understanding of how cancer cells can escape from immunosurveillance has only emerged over the last 20 year. This led to the development of the first groundbreaking cancer immunotherapies. However, the variety of cancer cell escape mechanisms is still not entirely elucidated, e.g., how cancer cells establish their immunosuppressive tumor microenvironment (TME). Although key components of the TME have been identified, only a few could be established as drug targets for the development of novel small-molecule drugs. To discover new mechanisms to modulator the immunosuppressive features of the TME, two chemical genetic approaches were developed in the course of this thesis. The TME harbors various tumor-derived suppressive factors that inhibit effector immune cells, like natural killer (NK) cells, from eliminating cancer cells. In order to prevent NK cell suppression within the TME and to identify proteins or pathways involved in NK cell inhibition, a phenotypic assay was developed that facilitated the investigation of a small molecule library. In addition, the kynurenine (Kyn) metabolic pathway and its rate limiting enzyme indolamine 2, 3-dioxygenase (IDO1) plays a key role in immunosuppression within the TME. To prevent IDO1 activity a new cell-based assay was established to screen for small-molecule modulators that inhibit the Kyn pathway. Thereby, iDeg-1 was identified, the first monovalent small molecule degrader of IDO1

Algebraically constrained finite element methods for hyperbolic problems with applications in geophysics and gas dynamics

The research conducted in this thesis is focused on property-preserving discretizations of hyperbolic partial differential equations. Computational methods for solving such problems need to be carefully designed to produce physically meaningful numerical solutions. In particular, approximations to some quantities of interest should satisfy local and global discrete maximum principles. Moreover, numerical methods need to obey certain conservation relations, and convergence of approximations to the physically relevant exact solution should be ensured if multiple solutions may exist. Many algorithms based on the aforementioned design principles fall into the category of algebraic flux correction (AFC) schemes. Modern AFC discretizations of nonlinear hyperbolic systems express approximate solutions as convex combinations of intermediate states and constrain these states to be admissible. The main focus of our work is on monolithic convex limiting (MCL) strategies that modify spatial semi-discretizations in this way. Contrary to limiting approaches of predictor-corrector type, their monolithic counterparts are well suited for transient and steady problems alike. Further benefits of the MCL framework presented in this thesis include the possibility of enforcing entropy stability conditions in addition to discrete maximum principles. Using the AFC methodology, we transform finite element discretizations into property-preserving low order methods and perform flux correction to recover higher orders of accuracy without losing any desirable properties. The presented methods produce physics-compatible approximations, which exhibit excellent shock capturing capabilities. One novelty of this work is the tailor-made extension of monolithic convex limiting to the shallow water equations with a nonconservative topography term. Our generalized MCL schemes are entropy stable, positivity preserving, and well balanced in the sense that lake at rest equilibria are preserved. Another desirable property of numerical methods for the shallow water equations is the capability to handle wet-dry transitions properly. We present two new approaches to dealing with this issue. To corroborate our computational results with theoretical investigations, we perform numerical analysis for property-preserving discretizations of the time-dependent linear advection equation. In this context, we prove stability and derive an a~priori error estimate in the semi-discrete setting. We also compare the monolithic convex limiting strategy to two representatives of related flux-corrected transport algorithms. Another highlight of this thesis is the chapter on MCL schemes for arbitrary order discontinuous Galerkin (DG) discretizations. Building on algorithms developed for continuous Lagrange and Bernstein finite elements, we extend our MCL schemes to the high order DG setting. This research effort involves the design of new AFC tools for numerical fluxes that appear in the DG weak formulation. Our limiting strategy for DG methods exploits the properties of high order Bernstein polynomials to construct sparse discrete operators leading to compact-stencil nonlinear approximations. The proposed numerical methods are applied to various hyperbolic problems. Scalar equations are considered mainly for testing purposes and to simplify numerical analysis. Besides the shallow water system, we study the Euler equations of gas dynamics

An Outcome Comparison of Osseointegrated and Traditional Socket-Fit Prostheses

This is one of the first studies to report on the comparison of walking ability between socket-based and osseointegrated bone-anchored prostheses of the trans-femoral amputee. Each participant\u27s hip active and passive range of motion was assessed. The Timed Up-and-Go test (TUG), 10-meter walk test (10MWT), and 6-minute walk test (6MWT) were administered to all participants with the addition of the Amputee Mobility Predictor with a Prosthesis (AMPPro). The study consists of unilateral transfemoral amputees with an activity level of K3-4. The current prosthetic users were divided into two groups based on their current intervention, socket prosthesis (S) and osseointegrated prosthesis (OI). The average completion times of each functional outcome measure is taken, recorded and compared between groups. The study provides valuable information on the impact osseointegration may have on an individual’s ability to ambulate when compared to their socket-based counterpart. The information gleaned from this study provides valuable information in determining appropriate care and outcome expectations of those undergoing the procedure

Hunters\u27 Joys : Jagerfreuden

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