Measuring Chern numbers in Hofstadter strips

Topologically non-trivial Hamiltonians with periodic boundary conditions are characterized by strictly quantized invariants. Open questions and fundamental challenges concern their existence, and the possibility of measuring them in systems with open boundary conditions and limited spatial extension. Here, we consider transport in Hofstadter strips, that is, two-dimensional lattices pierced by a uniform magnetic flux which extend over few sites in one of the spatial dimensions. As we show, an atomic wavepacket exhibits a transverse displacement under the action of a weak constant force. After one Bloch oscillation, this displacement approaches the quantized Chern number of the periodic system in the limit of vanishing tunneling along the transverse direction. We further demonstrate that this scheme is able to map out the Chern number of ground and excited bands, and we investigate the robustness of the method in presence of both disorder and harmonic trapping. Our results prove that topological invariants can be measured in Hofstadter strips with open boundary conditions and as few as three sites along one direction.Comment: v1: 17 pages, 10 figures; v2: minor changes, reference added, SciPost style, 26 pages, 10 figures; v3: published versio

Flexural isostatic response of the Alps to increased Quaternary erosion recorded by foreland basin remnants, SE France

International audienceWe test the hypothesis that flexural isostatic compensation of the mass removed by enhanced Quaternary erosion is responsible for uplift of the Western European Alps and their forelands. We use two well-preserved and well-dated (1.8 Ma) abandonment surfaces of foreland basin remnants in SE France (the Chambaran and Valensole plateaux) as passive benchmarks for tilting of the foreland. Estimating their initial slope from morphometric scaling relationships, we determine bulk post-depositional tilting of 0.5–0.8% for these surfaces. The calculated isostatic response of the Alpine lithosphere to erosional unloading, using the method recently proposed by Champagnac et al. [Geology 35 (2007) 195–198], yields a predicted tilting of 0.3–0.4% in the considered areas, explaining approximately half of the determined post-depositional tilting. Such long-term deformation being insensitive to cyclic loading/unloading because of glaciations, we suspect the other half to be related to as yet undetermined long-wavelength and long-lived tectonic process(es)

JaxPruner: A concise library for sparsity research

This paper introduces JaxPruner, an open-source JAX-based pruning and sparse training library for machine learning research. JaxPruner aims to accelerate research on sparse neural networks by providing concise implementations of popular pruning and sparse training algorithms with minimal memory and latency overhead. Algorithms implemented in JaxPruner use a common API and work seamlessly with the popular optimization library Optax, which, in turn, enables easy integration with existing JAX based libraries. We demonstrate this ease of integration by providing examples in four different codebases: Scenic, t5x, Dopamine and FedJAX and provide baseline experiments on popular benchmarks.Comment: Jaxpruner is hosted at http://github.com/google-research/jaxprune

Cerebrospinal fluid biomarker candidates associated with human WNV neuroinvasive disease

During the last decade, the epidemiology of WNV in humans has changed in the southern regions of Europe, with high incidence of West Nile fever (WNF) cases, but also of West Nile neuroinvasive disease (WNND). The lack of human vaccine or specific treatment against WNV infection imparts a pressing need to characterize indicators associated with neurological involvement. By its intimacy with central nervous system (CNS) structures, modifications in the cerebrospinal fluid (CSF) composition could accurately reflect CNS pathological process. Until now, few studies investigated the association between imbalance of CSF elements and severity of WNV infection. The aim of the present study was to apply the iTRAQ technology in order to identify the CSF proteins whose abundances are modified in patients with WNND. Forty-seven proteins were found modified in the CSF of WNND patients as compared to control groups, and most of them are reported for the first time in the context of WNND. On the basis of their known biological functions, several of these proteins were associated with inflammatory response. Among them, Defensin-1 alpha (DEFA1), a protein reported with anti-viral effects, presente

Le glissement du Chambon : évolution du phénomène et gestion de crise

Le déclenchement d’un grand glissement de terrain a entraîné la fermeture totale à la circulation du grand tunnel du Chambon le 10 avril 2015 et, par conséquent, de la route RD1091, reliant Grenoble et Briançon par la vallée de la Romanche dans les Alpes françaises (département de l’Isère). La coupure de cet axe routier, unique en fond de vallée et sans déviation possible, pour une longue période, a eu et a toujours de lourdes conséquences sur la vie quotidienne des habitants et sur l’économie de la haute vallée de la Romanche. Au mois de juillet 2015, les mesures de sécurité supplémentaires adoptées lors de deux phases de grands déplacements du glissement de terrain, pendant lesquelles une rupture brutale était redoutée, ont rendu encore plus difficiles les communications entre les deux parties de la vallée, malgré le déploiement de mesures exceptionnelles pour rétablir la continuité des déplacements locaux. Le présent article fait le point sur la compréhension actuelle du phénomène et de son évolution temporelle, et présente notamment une interprétation des désordres géologiques comme les manifestations d’une rupture progressive du versant

Quantification des déplacements 3D par la méthode PLaS − application au glissement du Chambon (Isère)

Une méthode de suivi de l'évolution des mouvements de versant sans végétation, facile à mettre en œuvre et à bas coût, est développée : la méthode PLaS (Photogrammetry-based method for Landslide Study). Elle est basée sur le principe de la photogrammétrie qui est utilisée à la fois pour la génération du modèle 3D de la surface sous la forme de nuages de points et pour le calcul des déplacements 3D en surface pour le suivi de son évolution. Cette méthode est appliquée à l'étude de l'évolution du glissement du Chambon entre avril 2016 et juillet 2016. Elle permet d'identifier les zones stables et en mouvement et fournit une valeur et une direction des déplacements 3D sensiblement égales aux valeurs mesurées

Measuring Chern numbers in Hofstadter strips

Topologically non-trivial Hamiltonians with periodic boundary conditions are characterized by strictly quantized invariants. Open questions and fundamental challenges concern their existence, and the possibility of measuring them in systems with open boundary conditions and limited spatial extension. Here, we consider transport in Hofstadter strips, that is, two-dimensional lattices pierced by a uniform magnetic flux which extend over few sites in one of the spatial dimensions. As we show, an atomic wavepacket exhibits a transverse displacement under the action of a weak constant force. After one Bloch oscillation, this displacement approaches the quantized Chern number of the periodic system in the limit of vanishing tunneling along the transverse direction. We further demonstrate that this scheme is able to map out the Chern number of ground and excited bands, and we investigate the robustness of the method in presence of both disorder and harmonic trapping. Our results prove that topological invariants can be measured in Hofstadter strips with open boundary conditions and as few as three sites along one direction

Measuring Chern numbers in Hofstadter strips

Topologically non-trivial Hamiltonians with periodic boundary conditions are characterized by strictly quantized invariants. Open questions and fundamental challenges concern their existence, and the possibility of measuring them in systems with open boundary conditions and limited spatial extension. Here, we consider transport in Hofstadter strips, that is, two-dimensional lattices pierced by a uniform magnetic flux which extend over few sites in one of the spatial dimensions. As we show, an atomic wavepacket exhibits a transverse displacement under the action of a weak constant force. After one Bloch oscillation, this displacement approaches the quantized Chern number of the periodic system in the limit of vanishing tunneling along the transverse direction. We further demonstrate that this scheme is able to map out the Chern number of ground and excited bands, and we investigate the robustness of the method in presence of both disorder and harmonic trapping. Our results prove that topological invariants can be measured in Hofstadter strips with open boundary conditions and as few as three sites along one direction.Peer Reviewe