Hydrodynamic lift of vesicles under shear flow in microgravity

The dynamics of a vesicle suspension in a shear flow between parallel plates has been investigated under microgravity conditions, where vesicles are only submitted to hydrodynamic effects such as lift forces due to the presence of walls and drag forces. The temporal evolution of the spatial distribution of the vesicles has been recorded thanks to digital holographic microscopy, during parabolic flights and under normal gravity conditions. The collected data demonstrates that vesicles are pushed away from the walls with a lift velocity proportional to $\dot{\gamma} R^3/z^2$ where $\dot{\gamma}$ is the shear rate, $R$ the vesicle radius and $z$ its distance from the wall. This scaling as well as the dependence of the lift velocity upon vesicle aspect ratio are consistent with theoretical predictions by Olla [J. Phys. II France {\bf 7}, 1533--1540 (1997)].Comment: 6 pages, 8 figure

Evolution of Derwael Ice Rise in Dronning Maud Land, Antarctica, over the last millennia

Ice rises situated in the ice-shelf belt around Antarctica have a spatially confined flow regime with local ice divides. Beneath the divides, ice stratigraphy often develops arches with amplitudes that record the divide's horizontal residence time andsurface elevation changes. To investigate the evolution of Derwael Ice Rise, Dronning Maud Land, Antarctica, we combine radar and GPS data from three consecutive surveys, with a two-dimensional, full Stokes, thermomechanically-coupled, transient ice-flow model. We find that the surface mass balance (SMB) is higher on the upwind and lower on the downwind slopes. Near the crest, the SMB is anomalously low and causes arches to form in the shallow stratigraphy, observable by radar. In deeper ice, arches are consequently imprinted by both SMB and ice rheology (Raymond effect). The data show how arch amplitudes decrease as along-ridge slope increases, emphasizing that the lateral positioning of radar cross-sections is important for the arch interpretation. Using the model with three rheologies (isotropic with n = 3,4.5 and anisotropic with n = 3), we show that Derwael Ice Rise is close to steady-state, but is best explained using ice anisotropy and moderate thinning. Our preferred, albeit notunique, scenario suggests that the ice divide has existed for at least 5000 years and lowered at approximately 0.03 m a−1 over the last 3400 years. Independent of the specific thinning scenario, our modeling suggests that Derwael Ice Rise has exhibited a local flow regime at least since the Mid-Holocene

Micro-Capsules in Shear Flow

This paper deals with flow-induced shape transitions of elastic capsules. The state of the art concerning both theory and experiments is briefly reviewed starting with dynamically induced small deformation of initially spherical capsules and the formation of wrinkles on polymerized membranes. Initially non-spherical capsules show tumbling and tank-treading motion in shear flow. Theoretical descriptions of the transition between these two types of motion assuming a fixed shape are at variance with the full capsule dynamics obtained numerically. To resolve the discrepancy, we expand the exact equations of motion for small deformations and find that shape changes play a dominant role. We classify the dynamical phase transitions and obtain numerical and analytical results for the phase boundaries as a function of viscosity contrast, shear and elongational flow rate. We conclude with perspectives on timedependent flow, on shear-induced unbinding from surfaces, on the role of thermal fluctuations, and on applying the concepts of stochastic thermodynamics to these systems.Comment: 34 pages, 15 figure

K2 Y F5 crystal symmetry determined by using rare-earth ions as paramagnetic probes

The electron paramagnetic resonance angular dependences for Gd3+ and Ce3+ centers in K2 Y F5 crystals show that the Y3+ site has monoclinic Ch symmetry in these crystals. This site symmetry is compatible with the crystal structure having the Pnam space group. From the zero-field splitting parameters of the Gd3+ center, it is deduced that the symmetry of the Y3+ sites is close to trigonal around the b axis, distorted by the overall orthorhombic symmetry of the crystal structure. This information is required for the identification of radiation-induced centers in this material, which shows favorable properties for applications as thermoluminescent dosimeter. © 2007 The American Physical Society

Transferred hyperfine interactions for Yb3+ ions in CsCa F 3 and Cs2 NaY F6 single crystals: Experimental and ab initio study

The results of an electron-nuclear double resonance study of the cubic paramagnetic Yb3+ center in Cs2 NaY F6 and CsCa F3 single crystals are presented. The values and signs of the transferred hyperfine interaction (THFI) parameters for several neighboring shells are determined. It is found that the relevant parameters for the two studied matrices differ, in spite of the fact that the nearest environment of the rare earth ion is nearly identical. A first-principles theoretical analysis is performed for the THFI parameters of the first coordination shell of F- ions. Several mechanisms of metal ion-ligand coupling are considered and it is found that one of them, ligand polarization, explains the difference observed for the THFI parameters in Cs2 NaY F6 and CsCa F3. © 2009 The American Physical Society

Challenge of teaching complex, end-to-end space system design and development process: Earth Observation Satellite System Design training course

The Earth Observation Satellite System Design training course was first offered in 2018 at ESA Academy’s Training and Learning Facility at ESA’s ESEC Galaxia site in Belgium, and again in 2021 in an online format under the Covid-19 pandemic situation. The course covers the end-to-end design and development process of satellite Earth observation systems. Two major challenges were faced by the teaching experts, consisting of the active and retired ESA staff, as well as ESA Academy’s instructional designers for its development: (1) Condensing such a vast subject domain, associated with a complex, multi-disciplinary engineering undertaking, into a compact format (e.g. 4.5 days in 2018) without sacrificing the quality of the essential technical knowledge, engineering practices and logic as taught; (2) Presenting the course materials in a comprehensive form to a group of 30 M.S. and Ph.D. students with their backgrounds generally not covering all of the technical disciplines associated with the course subject domain. The 2021 online edition of the training course, which drew on lessons learnt from 2018, consisted of 18 lectures, plus 5 group project sessions where the students put their acquired knowledge into practice and learned to work in a project team environment. This paper concentrates on the approach and logic adopted by the instructional team to address the above 2 challenges. Difficulties encountered in some of the areas, e.g. remote sensing instrumentation designs, are discusse

Behandeling en stigmamanagement bij opzettelijke zelfverwonding: het smalle pad tussen te veel en te weinig interveniëren

Opzettelijke zelfverwonding wordt gedefinieerd als de intentionele directe beschadiging van het eigen lichaam, zonder bewuste suïcidale intentie. De behandeling varieert van gedwongen opname in een psychiatrische instelling (in het Britse Gemenebest), tot een permissieve aanpak zonder behandeling en uiteenlopende behandelingsmogelijkheden er tussenin. Eerst wordt de gepastheid van de mate van interveniëren besproken in functie van verschillende diagnosen. Het tweede gedeelte van het artikel bespreekt het advies dat door hulpverleners verstrekt wordt aangaande de omgang met wonden en littekens en aangaande de mogelijkheden voor een (gewezen) zelfverwonder om het stigma van een deviante identiteit te vermijden. Een rondvraag bij Belgische hulpverleners bracht aan het licht dat velen onder hen adviseren om littekens te verbergen, terwijl er anderzijds aanwijzingen zijn dat niet-verbergen een teken van herstel is. Aangezien verbergen en smoesjes verzinnen ook kunnen leiden tot de instandhouding van een deviante identiteit, wordt gewezen op meer gepaste vormen van stigmamanagement