Field dependence of the vortex core size in a multi-band superconductor

The magnetic field dependence of the vortex core size in the multi-band superconductor NbSe2 has been determined from muon spin rotation measurements. The spatially extended nature of the quasiparticle core states associated with the smaller gap leads to a rapid field-induced shrinkage of the core size at low fields, while the more tightly bound nature of the states associated with the larger gap leads to a field-independent core size for fields greater than 4 kOe. A simple model is proposed for the density of delocalized core states that establishes a direct relationship between the field-induced reduction of the vortex core size and the corresponding enhancement of the electronic thermal conductivity. We show that this model accurately describes both NbSe2 and the single-band superconductor V3Si.Comment: 4 pages, 4 figures. Version accepted for publication in Physical Review Letter

Tuning Fermi-surface properties through quantum confinement in metallic meta-lattices: New metals from old atoms

We describe a new class of nanoscale structured metals wherein the effects of quantum confinement are combined with dispersive metallic electronic states to induce modifications to the fundamental low-energy microscopic properties of a three-dimensional metal: the density of states, the distribution of Fermi velocities, and the collective electronic response.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let

Existence of multi-site intrinsic localized modes in one-dimensional Debye crystals

The existence of highly localized multi-site oscillatory structures (discrete multibreathers) in a nonlinear Klein-Gordon chain which is characterized by an inverse dispersion law is proven and their linear stability is investigated. The results are applied in the description of vertical (transverse, off-plane) dust grain motion in dusty plasma crystals, by taking into account the lattice discreteness and the sheath electric and/or magnetic field nonlinearity. Explicit values from experimental plasma discharge experiments are considered. The possibility for the occurrence of multibreathers associated with vertical charged dust grain motion in strongly-coupled dusty plasmas (dust crystals) is thus established. From a fundamental point of view, this study aims at providing a first rigorous investigation of the existence of intrinsic localized modes in Debye crystals and/or dusty plasma crystals and, in fact, suggesting those lattices as model systems for the study of fundamental crystal properties.Comment: 12 pages, 8 figures, revtex forma

Added value of the regional climate model MAR for simulating the surface mass balance of the Antarctic ice sheet compared to a global climate model (ACCESS1.3)

Due to their ability to produce climate projections, General circulation models (GCM) are often used to provide estimates of the surface mass balance (SMB) of the Antarctic ice sheet that can be used to constrain ice sheet models. However, GCM still benefit from a poor representation of polar climate specificities such as stable boundary layers, polar clouds or interactions between snow-covered surfaces and the atmosphere. In this study, we highlight the importance of downscaling GCM outputs from the Fifth Climate Model Intercomparison Project (CMIP5) with a regional climate model to provide accurate estimates of the Antarctic SMB. For that purpose, the regional climate model MAR is forced by 6-hourly outputs from ACCESS1.3 that is currently considered as one of the best GCM from CMIP5 over the Antarctic ice sheet. Estimates of the SMB computed by MAR and ACCESS1.3 are evaluated against SMB observations. Even if the temporal variability of the SMB is forced by the driving GCM, the comparison shows that MAR improves the spatial variability of the Antarctic SMB, emphasizing the added value of using a polar RCM for downscaling GCM outputs at high latitudes

The hadron-quark transition with a lattice of nonlocal confining solitons

We use a lattice of nonlocal confining solitons to describe nuclear matter in the Wigner-Seitz approximation. The average density is varied by changing the size of the Wigner-Seitz cell. At sufficiently large density quark energy bands develop. The intersection of the filled valence band with the next empty band at a few times standard nuclear density signals a transition from a color insulator to a color conductor and is identified with the critical density for quark deconfinement.Comment: 12 pages Latex with one PS figur

Mechanism of Thermal Atomic Layer Etch of W Metal Using Sequential Oxidation and Chlorination:A First-Principles Study

Thermal atomic layer etch (ALE) of W metal can be achieved by sequential self-limiting oxidation and chlorination reactions at elevated temperatures. In this paper, we analyze the reaction mechanisms of W ALE using the first-principles simulation. We show that oxidizing agents such as O2, O3, and N2O can be used to produce a WOx surface layer in the first step of an ALE process with ozone being the most reactive. While the oxidation pulse on clean W is very exergonic, our study suggests that runaway oxidation of W is not thermodynamically favorable. In the second ALE pulse, WCl6 and Cl2 remove the oxidized surface W atoms by the formation of volatile tungsten oxychloride (WxOyClz) species. In this pulse, each adsorbed WCl6 molecule was found to remove one surface W atom with a moderate energy cost. Our calculations further show that the desorption of the additional etch products is endothermic by up to 4.7 eV. Our findings are consistent with the high temperatures needed to produce ALE in experiments. In total, our quantum chemical calculations have identified the lowest energy pathways for ALE of tungsten metal along with the most likely etch products, and these findings may help guide the development of improved etch reagents

Comparison Between Surface Melt Estimation From Sentinel-1 Synthetic Aperture Radar and a Regional Climate Model. Case Study Over the Roi Baudouin Ice Shelf, East Antarctica

peer reviewedAntarctica is the largest potential contributor to sea-level rise and needs to be monitored. It is also one of the first victims of global warming. However, it is often difficult to obtain high-resolution data on this vast and distant continent. Thanks to the Copernicus space program providing free and open access to high-quality data, this paper aims to show the complementarity between Sentinel-1 images and Modèle Atmosphérique régional (MAR) data over Antarctica. This study is conducted over Roi Baudouin Ice Shelf. The complementarity between the two datasets is established by a quantitative, temporal, and spatial comparison of the amplitude information of the radar signal and several variables modelled by MAR. Comparisons show strong spatial correlations between MAR variables representing melt and the backscatter coefficient recorded by the satellite. While temporal and quantitative analyses also give impressive results, further investigations are required to explain contrasting behaviors in other different areas of the ice shelf

PARASO, a circum-Antarctic fully coupled ice-sheet–ocean–sea-ice–atmosphere–land model involving f.ETISh1.7, NEMO3.6, LIM3.6, COSMO5.0 and CLM4.5

We introduce PARASO, a novel five-component fully coupled regional climate model over an Antarctic circumpolar domain covering the full Southern Ocean. The state-of-the-art models used are the fast Elementary Thermomechanical Ice Sheet model (f.ETISh) v1.7 (ice sheet), the Nucleus for European Modelling of the Ocean (NEMO) v3.6 (ocean), the Louvain-la-Neuve sea-ice model (LIM) v3.6 (sea ice), the COnsortium for Small-scale MOdeling (COSMO) model v5.0 (atmosphere) and its CLimate Mode (CLM) v4.5 (land), which are here run at a horizontal resolution close to 1/4°. One key feature of this tool resides in a novel two-way coupling interface for representing ocean–ice-sheet interactions, through explicitly resolved ice-shelf cavities. The impact of atmospheric processes on the Antarctic ice sheet is also conveyed through computed COSMO-CLM–f.ETISh surface mass exchange. In this technical paper, we briefly introduce each model's configuration and document the developments that were carried out in order to establish PARASO. The new offline-based NEMO–f.ETISh coupling interface is thoroughly described. Our developments also include a new surface tiling approach to combine open-ocean and sea-ice-covered cells within COSMO, which was required to make this model relevant in the context of coupled simulations in polar regions. We present results from a 2000–2001 coupled 2-year experiment. PARASO is numerically stable and fully operational. The 2-year simulation conducted without fine tuning of the model reproduced the main expected features, although remaining systematic biases provide perspectives for further adjustment and development.This research has been supported by the Fonds De La Recherche Scientifique – FNRS (grant no. O0100718F).Peer ReviewedArticle signat per 23 autors/es: Charles Pelletier (1), Thierry Fichefet (1), Hugues Goosse (1), Konstanze Haubner (2), Samuel Helsen (3), Pierre-Vincent Huot (1), Christoph Kittel (4), François Klein (1), Sébastien Le clec'h (5), Nicole P. M. van Lipzig (3), Sylvain Marchi (3), François Massonnet (1), Pierre Mathiot (6,7), Ehsan Moravveji (3,8), Eduardo Moreno-Chamarro (9), Pablo Ortega (9), Frank Pattyn (2), Niels Souverijns (3,10), Guillian Van Achter (1), Sam Vanden Broucke (3), Alexander Vanhulle (5), Deborah Verfaillie (1), and Lars Zipf (2) // (1) Earth and Life Institute (ELI), UCLouvain, Louvain-la-Neuve, Belgium / (2) Laboratoire de Glaciologie, Université Libre de Bruxelles, Brussels, Belgium / (3) Department of Earth and Environmental Sciences, KU Leuven, Leuven, Belgium / (4) Laboratory of Climatology, Department of Geography, SPHERES, University of Liège, Liège, Belgium / (5) Earth System Science and Departement Geografie, Vrije Universiteit Brussel, Brussels, Belgium, (6) Met Office, Exeter, United Kingdom / (7) Université Grenoble Alpes/CNRS/IRD/G-INP, IGE, Grenoble, France / (8) ICTS, KU Leuven, Leuven, Belgium / (9) Barcelona Supercomputing Center (BSC), Barcelona, Spain / (10) Environmental Modelling Unit, Flemish Institute for Technological Research (VITO), Mol, BelgiumPostprint (published version

Surface versus internal fatigue crack initiation in steel : Influence of mean stress

Stress-controlled fatigue tests were run at different R ratios (= sigma min / sigma max) up to at most 3 million cycles on a 2.5%Cr–1%Mo steel (ASTM A182 F22) used in riser tubes connectors for offshore oil drilling. The fatigue lives, as well as the slope of the S – N curves were found to decrease with increasing R and the endurance limit to follow Gerber’s parabola. Surface crack initiation without any defect involved, was most often observed for R=-1, 0.5 and 0, while an R ratio of 0.25 triggered crack initiation from either surface or internal pores or chemically inhomogeneous areas, leading, in the latter case, to fish-eye patterns for relatively low numbers of cycles. A further increase in R ratio to 0.5 promoted only defect-initiated surface cracks, while no fatigue fracture was observed within 10 million cycles above R=0.6. These transitions in crack initiation mode are discussed based on X-ray diffraction analyses of residual stresses, elastic–plastic F.E. computations on a unit cell model containing a pore and some fracture mechanics analyses, with a particular attention to environmental effects.The authors acknowledge the assistance of Dr. E. Heripre for FIB sectioning and observations with a dual beam microscope bought within the Equipex Matmeca funding program

Calculating and visualizing the density of states for simple quantum mechanical systems

We present a graphical approach to understanding the degeneracy, density of states, and cumulative state number for some simple quantum systems. By taking advantage of basic computing operations, we define a straightforward procedure for determining the relationship between discrete quantum energy levels and the corresponding density of states and cumulative level number. The density of states for a particle in a rigid box of various shapes and dimensions is examined and graphed. It is seen that the dimension of the box, rather than its shape, is the most important feature. In addition, we look at the density of states for a multi-particle system of identical bosons built on the single-particle spectra of those boxes. A simple model is used to explain how the N-particle density of states arises from the single particle system it is based on