A three-dimensional full Stokes model of the grounding line dynamics: effect of a pinning point beneath the ice shelf

The West Antarctic ice sheet is confined by a large area of ice shelves, fed by inland ice through fast flowing ice streams. The dynamics of the grounding line, which is the line-boundary between grounded ice and the downstream ice shelf, has a major influence on the dynamics of the whole ice sheet. However, most ice sheet models use simplifications of the flow equations, as they do not include all the stress components, and are known to fail in their representation of the grounding line dynamics. Here, we present a 3-D full Stokes model of a marine ice sheet, in which the flow problem is coupled with the evolution of the upper and lower free surfaces, and the position of the grounding line is determined by solving a contact problem between the shelf/sheet lower surface and the bedrock. Simulations are performed using the open-source finite-element code Elmer/Ice within a parallel environment. The model's ability to cope with a curved grounding line and the effect of a pinning point beneath the ice shelf are investigated through prognostic simulations. Starting from a steady state, the sea level is slightly decreased to create a contact point between a seamount and the ice shelf. The model predicts a dramatic decrease of the shelf velocities, leading to an advance of the grounding line until both grounded zones merge together, during which an ice rumple forms above the contact area at the pinning point. Finally, we show that once the contact is created, increasing the sea level to its initial value does not release the pinning point and has no effect on the ice dynamics, indicating a stabilising effect of pinning points

The PELskin project—part I: fluid–structure interaction for a row of flexible flaps: a reference study in oscillating channel flow

Previous studies of flexible flaps attached to the aft part of a cylinder have demonstrated a favourable effect on the drag and lift force fluctuation. This observation is thought to be linked to the excitation of travelling waves along the flaps and as a consequence of that, periodic shedding of the von Kármán vortices is altered in phase. A more general case of such interaction is studied herein for a limited row of flaps in an oscillating flow; representative of the cylinder case since the transversal flow in the wake-region shows oscillating character. This reference case is chosen to qualify recently developed numerical methods for the simulation of fluid–structure interaction in the context of the EU funded ‘PELskin’ project. The simulation of the two-way coupled dynamics of the flexible elements is achieved via a structure model for the flap motion, which was implemented and coupled to two different fluid solvers via the immersed boundary method. The results show the waving behaviour observed at the tips of the flexible elements in interaction with the fluid flow and the formation of vortices in the gaps between the flaps. In addition, formation of vortices upstream of the leading and downstream of the trailing flap is seen, which interact with the formation of the shear-layer on top of the row. This leads to a phase shift in the wave-type motion along the row that resembles the observation in the cylinder case

The PELskin project: part II—investigating the physical coupling between flexible filaments in an oscillating flow

The fluid-structure interaction mechanisms of a coating composed of flexible flaps immersed in a periodically oscillating channel flow is here studied by means of numerical simulation, employing the Euler-Bernoulli equations to account for the flexibility of the structures. A set of passively actuated flaps have previously been demonstrated to deliver favourable aerodynamic impact when attached to a bluff body undergoing periodic vortex shedding. As such, the present configuration is identified to provide a useful test-bed to better understand this mechanism, thought to be linked to experimentally observed travelling waves. Having previously validated and elucidated the flow mechanism in Paper 1 of this series, we hereby undertake a more detailed analysis of spectra obtained for different natural frequency of structures and different configurations, in order to better characterize the mechanisms involved in the organized motion of the structures. Herein, this wave-like behaviour, observed at the tips of flexible structures via interaction with the fluid flow, is characterized by examining the time history of the filaments motion and the corresponding effects on the fluid flow, in terms of dynamics and frequency of the fluid velocity. Results indicate that the wave motion behaviour is associated with the formation of vortices in the gaps between the flaps, which itself are a function of the structural resistance to the cross flow. In addition, formation of vortices upstream of the leading and downstream of the trailing flap is seen, which interact with the formation of the shear-layer on top of the row. This leads to a phase shift in the wave-type motion along the row that resembles the observation in the cylinder case

High level software for 4.8 GHz LHC Schottky system

The performance of the LHC depends critically on the accurate measurements of the betatron tunes. The betatron tune values of each LHC beam may be measured without excitation using a newly installed transverse Schottky monitor. A high-level software package written in Java has been developed for the Schottky system. The software allows end users to monitor and control the Schottky system, and provides them with non-destructive and continuous bunch-by-bunch measurements for the tunes, momentum spreads, chromaticities and emittances of the LHC beams. It has been tested with both proton and lead ion beams at the LHC with very successful results.Comment: 3 pp. Particle Accelerator, 24th Conference (PAC'11) 2011. 28 Mar - 1 Apr 2011. New York, US

Optimality Clue for Graph Coloring Problem

In this paper, we present a new approach which qualifies or not a solution found by a heuristic as a potential optimal solution. Our approach is based on the following observation: for a minimization problem, the number of admissible solutions decreases with the value of the objective function. For the Graph Coloring Problem (GCP), we confirm this observation and present a new way to prove optimality. This proof is based on the counting of the number of different k-colorings and the number of independent sets of a given graph G. Exact solutions counting problems are difficult problems (\#P-complete). However, we show that, using only randomized heuristics, it is possible to define an estimation of the upper bound of the number of k-colorings. This estimate has been calibrated on a large benchmark of graph instances for which the exact number of optimal k-colorings is known. Our approach, called optimality clue, build a sample of k-colorings of a given graph by running many times one randomized heuristic on the same graph instance. We use the evolutionary algorithm HEAD [Moalic et Gondran, 2018], which is one of the most efficient heuristic for GCP. Optimality clue matches with the standard definition of optimality on a wide number of instances of DIMACS and RBCII benchmarks where the optimality is known. Then, we show the clue of optimality for another set of graph instances. Optimality Metaheuristics Near-optimal

Analyse expérimentale et modélisation du comportement mécanique d'aciers duplex Fe-Mn-Al-C

Une nouvelle variété d'aciers biphasés austénite-ferrite dit duplex à forte teneur en manganèse et en aluminium a été élaborée par ARCELOR RESEARCH. Ces aciers combinent les meilleurs caractéristiques des aciers austénitiques et ferritiques. Quatre nuances sont étudiées se différenciant par leur teneur en carbone qui conduit à quatre fractions volumiques de l'austénite. L'évolution des contraintes internes dans les deux phases a été déterminée par diffraction des rayons X au cours d'un essai de traction in situ. Les résultats des mesures ont été utilisés pour déterminer le comportement mécanique de l'acier duplex en utilisant une approche micromécanique par transition d'échelles pour les essais de traction. Un bon accord entre les expériences et les simulations est obtenu au niveau macroscopique tandis que les contraintes internes calculées de la phase austénitique ne correspondent pas aux résultats expérimentaux. Ces divergences sont attribuées (i) à une mauvaise estimation de la limite d'élasticité de l'austénite ou (ii) à la présence de l'écrouissage cinématique dans la phase austénitique. On propose alors une nouvelle étape pour vérifier ces deux hypothèses

The Warburg Effect Is Genetically Determined in Inherited Pheochromocytomas

The Warburg effect describes how cancer cells down-regulate their aerobic respiration and preferentially use glycolysis to generate energy. To evaluate the link between hypoxia and Warburg effect, we studied mitochondrial electron transport, angiogenesis and glycolysis in pheochromocytomas induced by germ-line mutations in VHL, RET, NF1 and SDH genes. SDH and VHL gene mutations have been shown to lead to the activation of hypoxic response, even in normoxic conditions, a process now referred to as pseudohypoxia. We observed a decrease in electron transport protein expression and activity, associated with increased angiogenesis in SDH- and VHL-related, pseudohypoxic tumors, while stimulation of glycolysis was solely observed in VHL tumors. Moreover, microarray analyses revealed that expression of genes involved in these metabolic pathways is an efficient tool for classification of pheochromocytomas in accordance with the predisposition gene mutated. Our data suggest an unexpected association between pseudohypoxia and loss of p53, which leads to a distinct Warburg effect in VHL-related pheochromocytomas

AIM (Artery in microgravity): Design and development of an ice cubes mission

The Artery In Microgravity (AIM) project is the first experiment to be selected for the “Orbit Your Thesis!” programme of ESA Academy. It is a 2U experiment cube designed for the ICE Cubes facility on board of the International Space Station. The experiment is expected to be launched on SpaceX-20 in early 2020. The project is being developed by an international group of students from ISAE-SUPAERO and Politecnico di Torino, under the supervision of the ISAE-SUPAERO and Politecnico di Torino staff. The experiment is a test-bench for investigating haemodynamics in microgravity focusing on coronary heart disease, the most common form of cardiovascular disease and the cause of approximately 9 million deaths every year. Coronary heart disease is caused by stenosis of the coronary artery due to the build-up of plaque. While the development of atherosclerosis is not fully understood, the primary event seems to be subtle and repeated injury to the artery walls through various mechanisms including physical stresses from flow disturbances as well as from systemic and biological risk factors. In the presence of severe stenosis, patients are treated with the implantation of one or more coronary stents, which are tubular scaffolds devoted to restore and maintain myocardial perfusion. The coronary stenting procedure is largely applied (e.g., 1.8 million stents per year implanted in USA) In view of the impact that coronary artery disease has on humans, as well as of the increasing number of people that will be involved in space flights in the future, the way astronauts in space coronary hemodynamics is affected by the absence of gravity in the presence of stenosis or of stenting needs to be investigated in depth. In addition, as most stents are metallic objects, the radiation exposure in space might interact with their surface, altering blood flow, inducing particles release and ultimately leading to stent failure. Therefore, the aim of AIM is to start studying the vascular haemodynamics in a stented and a stenosed coronary artery on Earth and in microgravity and the stent-radiation coupling. This will allow to learn about the effect gravity plays on coronary artery haemodynamics, the effects of microgravity and radiation on the performance of implantable devices and ultimately the risks of myocardial infarction to astronauts on long-distance spaceflight. The experimental setup consists of a closed hydraulic loop containing two models of a coronary artery in series. An electric pump and reservoir will control the flow of a blood-mimicking fluid through the system. One model of the coronary artery will contain a coronary stent. The pressure of the fluid will be studied along its path using a series of pressure sensors and a camera will visualise the flow. The same experiments will be repeated on the ground with the same conditions as the in-flight model for comparison. The paper will outline in detail the design and development of the AIM experiment cube and the results of testing. The full data and results will be available after the completion of the mission which is expected to be between March and June 2020

Optical properties of MgH2 measured in situ in a novel gas cell for ellipsometry/spectrophotometry

The dielectric properties of alpha-MgH2 are investigated in the photon energy range between 1 and 6.5 eV. For this purpose, a novel sample configuration and experimental setup are developed that allow both optical transmission and ellipsometric measurements of a transparent thin film in equilibrium with hydrogen. We show that alpha-MgH2 is a transparent, colour neutral insulator with a band gap of 5.6 +/- 0.1 eV. It has an intrinsic transparency of about 80% over the whole visible spectrum. The dielectric function found in this work confirms very recent band structure calculations using the GW approximation by Alford and Chou [J.A. Alford and M.Y. Chou (unpublished)]. As Pd is used as a cap layer we report also the optical properties of PdHx thin films.Comment: REVTeX4, 15 pages, 12 figures, 5 table