The ArDM project: a Dark Matter Direct Detection Experiment based on Liquid Argon

The Dark Matter part of the universe presumably consists of WIMPs (Weakly Interacting Massive Particles). The ArDM project aims at measuring signals induced by WIMPs in a liquid argon detector. A 1-ton prototype is currently developed with the goal of demonstrating the feasibility of such a direct detection experiment with large target mass. The technical design of the detector aims at ind ependently measuring the scintillation light and the ionization charge originating from an interaction of a WIMP with an argon nucleus. The principle of the experiment and the conceptual design of the detector are described.Comment: 4 pages, 1 figure, Invited talk at 2nd Workshop On TeV Particle Astrophysics, 28-31 August 2006, Madison, WI, US

Nanofracture mechanics : scanning force microscopy for the investigation of adhesion and corrosion at solid-solid interfaces

Fracture processes are crucially determined by structural features on the molecular/nanometer scale (cavities, occlusions, cracks, etc.) as well as on the atomic scale (e.g. interstitial, substitutional and vacancy defects). In this work, fracture mechanics experiments were performed with fabricated nanostructures, so-called nanopillars. Furthermore, material interfaces had been introduced into these nanopillars as weak links in order to act as well-defined breaking points. By exerting calibrated forces onto these nanostructures, the threshold force for fracture incidents can be determined and hence the adhesion strengths of the interfaces involved can be studied. All such experiments were performed using a Scanning Force Microscope (SFM). Here, force and topography investigations, using a cantilever tip as a tool, reveal information about the fracture behavior of a particular interface as well as information regarding the mechanical strength. The SFM was used in the tapping (intermitted) or in the contact mode to fracture single nanopillars or an ensemble of them. For statistical examinations, an area of nanopillars was scanned with increased normal forces. Therefore, interfaces manufactured for microelectronic applications or micro-electro-mechanical systems (MEMS) can be studied by low forces applied to nanopillars exhibiting realistic interface dimensions. Due to the small dimensions of the manufactured nanopillars, slow processes, such as the weakening of the interface by fatigue (also including heat cycling in devices) or by physico-chemical processes (e.g. by tribochemical processes or corrosion which may occur in a liquid environment) can be monitored on considerably shorter time scales and under easier to control conditions than with macroscopic specimens. Additionally, such fracture experiments performed with nanopillars designed to mimic macroscopic fracture experiments, in medium (characteristic cross section ~cm2) to large scale (> ~m2) engineering, are often less cost intensive compared to large, real-world samples in time consuming (~ many load/unload heat/cool cycles, extended exposure to ambient or corrosive fluids etc.) conventional fracture experiments. Another important application comprises the study of a soft metal/polyimide interface, which is important for flexible microelectronic devices and flexible interconnect circuitry. Here, interface problems, specifically failure incidents after exposure to temperature cycling and/or mechanical load/unload cycles, have been associated with the occurrence of interfacial contamination, e.g. with residual water originating from the polyimide curing process. Hence, in a well-chosen model experiment under ultra-high vacuum (UHV) conditions, a precise amount of water was deposited on an in-situ produced polyimide sample which then was coated by a metal. Afterwards, the nanopillar structures were generated by Focused Ion Beam (FIB) milling. This work established a radically new approach to perform fracture mechanics experiments down to the few nanometers, which provides a route towards a better understanding of fracture processes down to an atomic/molecular scale

Towards eulerian-eulerian large eddy simulation of reactive two-phase flows

De nombreuses applications industrielles mettent en jeu des écoulements gaz-particules. On peut citer, entre autres, les turbines aéronautiques et les réacteurs à lit fluidisé de l’industrie chimique. Dès lors, l’amélioration de ces dispositifs, imposée par les nouvelles normes européennes sur les émissions polluantes, nécessite une connaissance prédictive de la dynamique de ce type d’écoulements ainsi que l’évaluation de ses grandeurs caractéristiques telles que la ségrégation spatiale des particules. La simulation numérique est aujourd’hui largement utilisée à cet effet. Les équations de la phase gazeuse sont résolues par Simulation Numérique Directe (SND) ou par Simulation des Grandes Echelles (SGE). Le couplage avec la phase dispersée peut être envisagé de deux manières. Une première approche, dite lagrangienne, consiste à calculer les trajectoires des particules. Communément utilisée et précise, son coût numérique ne permet cependant pas d’envisager son application à des géométries complexes réalistes. Une seconde approche est fondée sur un formalisme eulérien du mouvement des particules, le couplage entre les deux phases est alors assuré par des termes d’échange interfacial. Cette méthode a d’ores et déjà été validée pour des particules dont le temps de réponse est faible comparé à la micro-échelle de temps turbulent. L’extension de cette approche à des particules plus inertielles s’avère nécessaire dans les applications industrielles de type turbines à gaz. Ceci constitue l’objectif principal de cette thèse. Les résultats fournis par l’approche lagrangienne suggèrent de décomposer la vitesse des particules en une composante corrélée et une composante décorrélée. En outre, il apparaît que l’énergie décorrélée sélève à 30% de l’énergie totale de la phase dispersée lorsque le temps de relaxation des particules et l’échelle de temps lagrangienne sont du même ordre. La prise en compte de ce mouvement décorrélé requiert l’introduction d’un tenseur de contraintes dans l’équation de quantité de mouvement. Ce travail propose différents modèles qui sont validés au travers de simulations numériques eulériennes par comparaison avec des SND lagrangiennes. Enfin, une étude du couplage entre les équations de transport des particules et des modèles de combustion est proposée. ABSTRACT : Particle laden flows occur in industrial applications ranging from droplets in gas turbines to fluidized bed in chemical industry. Prediction of the dispersed phase properties such as concentration and dynamics are crucial for the design of more efficient devices that meet the new pollutant regulations of the European community. Numerical simulation coupling Lagrangian tracking of discrete particles with DNS or LES of the carrier phase provide a well established powerful tool to investigate particle laden flows. Such numerical methods have the drawback of being numerically very expensive for practical applications. Numerical simulations based on separate Eulerian balance equations for both phases, coupled through inter-phase exchange terms might be an effective alternative approach. This approach has been validated for the case of tracer particles with very low inertia that follow the carrier phase almost instantaneously due to their small response time compared with the microscale time scales of the carrier phase. Objective of this thesis is to extend this approach to more inertial particles that occur in practical applications such as fuel droplets in gas turbine combustors. Existing results suggest a separation of the dispersed phase velocity into a correlated and an uncorrelated component. The energy related to the uncorrelated component is about 30% of the total particle kinetic energy when the particle relaxation time is comparable to the Lagrangian integral time scale. The presence of this uncorrelated motion leads to stress terms in the Eulerian balance equation for the particle momentum. Models for this stress terms are proposed and tested. Numerical simulations in the Eulerian framework are validated by comparison with simulations using Lagrangian particle tracking. Additionally coupling of the Eulerian transport equations for the particles to combustion models is tested

ArDM: a ton-scale liquid Argon experiment for direct detection of Dark Matter in the Universe

The ArDM project aims at developing and operating large noble liquid detectors to search for direct evidence of Weakly Interacting Massive Particle (WIMP) as Dark Matter in the Universe. The initial goal is to design, assemble and operate a $\approx$1 ton liquid Argon prototype to demonstrate the feasibility of a ton-scale experiment with the required performance to efficiently detect and sufficiently discriminate backgrounds for a successful WIMP detection. Our design addresses the possibility to detect independently ionization and scintillation signals. In this paper, we describe this goal and the conceptual design of the detector.Comment: 5 pages, 3 figures, Talk given at IXth international conference on Topics in Astroparticle and Underground Physics (TAUP05), Zaragoza, (Spain

Synchrotron emission from the T Tauri binary system V773 Tau A

The pre-main sequence binary system V773 Tau A shows remarkable flaring activity around periastron passage. Here, we present the observation of such a flare at a wavelength of 3 mm (90 GHz) performed with the Plateau de Bure Interferometer. We examine different possible causes for the energy losses responsible for the e-folding time of 2.3 hours of that flare. We exclude synchrotron, collisional, and inverse Compton losses because they are not consistent with observational constraints, and we propose that the fading of the emission is due to the leakage of electrons themselves at each reflection between the two mirror points of the magnetic structure partially trapping them. The magnetic structure compatible with both our leakage model and previous observations is that of a helmet streamer that, as in the solar case, can occur at the top of the X-ray-emitting, stellar-sized coronal loops of one of the stars. The streamer may extend up to 20 R and interact with the corona of the other star at periastron passage, causing recurring flares. The inferred magnetic field strength at the two mirror points of the helmet streamer is in the range 0.12 - 125 G, and the corresponding Lorentz factor, gamma, of the partially trapped electrons is in the range 20 < gamma < 632. We therefore rule out that the emission could be of gyro-synchrotron nature: the derived high Lorentz factor proves that the nature of the emission at 90 GHz from this pre-main binary system is synchrotron radiation. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).Comment: 8 pages, 5 figures, A&A in pres

Improved coining force calculations through incorporation of key process parameters

Among the sheet forming processes, coining is a specific operation which makes it possible to correct shape defects or to perform thickness reductions in the parts. This operation often requires a very high force which is likely to have an impact on the functioning of the tool or the press. It is therefore important that the coining forces be evaluated accurately, but this is not allowed by the existing analytical calculation formulas. The objective of this study is to improve the accuracy of the calculation of the coining forces via the adaptation of an existing formula. Such adaptation was carried out based on a study of the influence of the flat coining parameters. To that end, a series of experimental measurements was performed. An instrumented force measuring setup made it possible to measure the maximum coining force. Several parameters were analysed, including the coining ratio and the sheet thickness. Numerical simulations were carried out at the same time, in order to understand the influence of certain parameters on the coining force. 2D numerical models were developed using the Forge NXT2 software. The simulations and the experimental tests were analysed and the results revealed the influential phenomena which have to be taken into account in the analytical formula, in particular the coining surface and the friction. In order to study the friction more thoroughly, ring compression tests were performed so as to determine the friction coefficients, based on the Coulomb’s law limited to Tresca. This type of test is representative of the stresses undergone by the metal during the coining operation. Finally, a new calculation formula is proposed, in order to integrate the coining surface and friction more accurately

Homogeneous datasets of triple negative breast cancers enable the identification of novel prognostic and predictive signatures

Background: Current prognostic gene signatures for breast cancer mainly reflect proliferation status and have limited value in triple-negative (TNBC) cancers. The identification of prognostic signatures from TNBC cohorts was limited in the past due to small sample sizes. Methodology/Principal Findings: We assembled all currently publically available TNBC gene expression datasets generated on Affymetrix gene chips. Inter-laboratory variation was minimized by filtering methods for both samples and genes. Supervised analysis was performed to identify prognostic signatures from 394 cases which were subsequently tested on an independent validation cohort (n = 261 cases). Conclusions/Significance: Using two distinct false discovery rate thresholds, 25% and <3.5%, a larger (n = 264 probesets) and a smaller (n = 26 probesets) prognostic gene sets were identified and used as prognostic predictors. Most of these genes were positively associated with poor prognosis and correlated to metagenes for inflammation and angiogenesis. No correlation to other previously published prognostic signatures (recurrence score, genomic grade index, 70-gene signature, wound response signature, 7-gene immune response module, stroma derived prognostic predictor, and a medullary like signature) was observed. In multivariate analyses in the validation cohort the two signatures showed hazard ratios of 4.03 (95% confidence interval [CI] 1.71–9.48; P = 0.001) and 4.08 (95% CI 1.79–9.28; P = 0.001), respectively. The 10-year event-free survival was 70% for the good risk and 20% for the high risk group. The 26-gene signatures had modest predictive value (AUC = 0.588) to predict response to neoadjuvant chemotherapy, however, the combination of a B-cell metagene with the prognostic signatures increased its response predictive value. We identified a 264-gene prognostic signature for TNBC which is unrelated to previously known prognostic signatures

The SARS-CoV-2 Pandemic Impacts the Management of Swiss Pediatric Intensive Care Units.

The impact of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic on pediatric intensive care units (PICUs) is difficult to quantify. We conducted an observational study in all eight Swiss PICUs between 02/24/2020 and 06/15/2020 to characterize the logistical and medical aspects of the pandemic and their impact on the management of the Swiss PICUs. The nine patients admitted to Swiss PICUs during the study period suffering from pediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2 (PIMS-TS) and constituting 14% (9/63) of all SARS-CoV-2 positive hospitalized patients in Swiss children's hospitals caused a higher workload [total Nine Equivalents of nursing Manpower use Score (NEMS) points, p = 0.0008] and were classified to higher workload categories (p &lt; 0.0001) than regular PICU patients (n = 4,881) admitted in 2019. The comparison of the characteristics of the eight Swiss PICUs shows that they were confronted by different organizational issues arising from temporary regulations put in place by the federal council. These general regulations had different consequences for the eight individual PICUs due to the differences between the PICUs. In addition, the temporal relationship of these different regulations influenced the available PICU resources, dependent on the characteristics of the individual PICUs. As pandemic continues, reflecting and learning from experience is essential to reduce workload, optimize bed occupancy and manage resources in each individual PICU. In a small country as Switzerland, with a relatively decentralized health care local differences between PICUs are considerable and should be taken into account when making policy decisions