Semiclassical Dynamics of Electrons in Magnetic Bloch Bands: a Hamiltonian Approach

y formally diagonalizing with accuracy $\hbar$ the Hamiltonian of electrons in a crystal subject to electromagnetic perturbations, we resolve the debate on the Hamiltonian nature of semiclassical equations of motion with Berry-phase corrections, and therefore confirm the validity of the Liouville theorem. We show that both the position and momentum operators acquire a Berry-phase dependence, leading to a non-canonical Hamiltonian dynamics. The equations of motion turn out to be identical to the ones previously derived in the context of electron wave-packets dynamics.Comment: 4 page

DeepKSPD: Learning Kernel-matrix-based SPD Representation for Fine-grained Image Recognition

Being symmetric positive-definite (SPD), covariance matrix has traditionally been used to represent a set of local descriptors in visual recognition. Recent study shows that kernel matrix can give considerably better representation by modelling the nonlinearity in the local descriptor set. Nevertheless, neither the descriptors nor the kernel matrix is deeply learned. Worse, they are considered separately, hindering the pursuit of an optimal SPD representation. This work proposes a deep network that jointly learns local descriptors, kernel-matrix-based SPD representation, and the classifier via an end-to-end training process. We derive the derivatives for the mapping from a local descriptor set to the SPD representation to carry out backpropagation. Also, we exploit the Daleckii-Krein formula in operator theory to give a concise and unified result on differentiating SPD matrix functions, including the matrix logarithm to handle the Riemannian geometry of kernel matrix. Experiments not only show the superiority of kernel-matrix-based SPD representation with deep local descriptors, but also verify the advantage of the proposed deep network in pursuing better SPD representations for fine-grained image recognition tasks

From Feynman Proof of Maxwell Equations to Noncommutative Quantum Mechanics

In 1990, Dyson published a proof due to Feynman of the Maxwell equations assuming only the commutation relations between position and velocity. With this minimal assumption, Feynman never supposed the existence of Hamiltonian or Lagrangian formalism. In the present communication, we review the study of a relativistic particle using ``Feynman brackets.'' We show that Poincar\'e's magnetic angular momentum and Dirac magnetic monopole are the consequences of the structure of the Lorentz Lie algebra defined by the Feynman's brackets. Then, we extend these ideas to the dual momentum space by considering noncommutative quantum mechanics. In this context, we show that the noncommutativity of the coordinates is responsible for a new effect called the spin Hall effect. We also show its relation with the Berry phase notion. As a practical application, we found an unusual spin-orbit contribution of a nonrelativistic particle that could be experimentally tested. Another practical application is the Berry phase effect on the propagation of light in inhomogeneous media.Comment: Presented at the 3rd Feynman Festival (Collage Park, Maryland, U.S.A., August 2006

Évaluation du sous-dénombrement de la population lors du recencement de la population et du logement du Canada de 1976

La contre-vérification des dossiers constitue l’une des principales études de la qualité des données produites lors du recensement de la population et du logement du Canada de 1976. Elle vise à analyser le sous-dénombrement de la population lors du recensement et ses effets sur les chiffres de la population pour le Canada, les provinces et certains sous-groupes importants. La méthode consiste à choisir un échantillon de personnes à partir de sources indépendantes du recensement de 1976, à établir l’adresse de chacune au moment du recensement et à vérifier dans les documents du recensement si elles ont ou non été recensées. Le présent document décrit d’une manière générale la méthodologie de la contre-vérification des dossiers de 1976 et donne les principaux résultats obtenus

Orientation and distribution of recent gullies in the southern hemisphere of Mars: observations from HRSC/MEX and MOC/MGS data

Abstract not available

Cross-dimensional Weighting for Aggregated Deep Convolutional Features

We propose a simple and straightforward way of creating powerful image representations via cross-dimensional weighting and aggregation of deep convolutional neural network layer outputs. We first present a generalized framework that encompasses a broad family of approaches and includes cross-dimensional pooling and weighting steps. We then propose specific non-parametric schemes for both spatial- and channel-wise weighting that boost the effect of highly active spatial responses and at the same time regulate burstiness effects. We experiment on different public datasets for image search and show that our approach outperforms the current state-of-the-art for approaches based on pre-trained networks. We also provide an easy-to-use, open source implementation that reproduces our results.Comment: Accepted for publications at the 4th Workshop on Web-scale Vision and Social Media (VSM), ECCV 201

Turbulent nitrate fluxes in the Lower St. Lawrence Estuary, Canada

Turbulent vertical nitrate fluxes were calculated using new turbulent microstructure observations in the Lower St. Lawrence Estuary (LSLE), Canada. Two stations were compared: the head of the Laurentian Channel (HLC), where intense mixing occurs on the shallow sill that marks the upstream limit of the LSLE, and another station located about 100 km downstream (St. 23), more representative of the LSLE mean mixing conditions. Mean turbulent diffusivities and nitrate fluxes at the base of the surface layer for both stations were, respectively (with 95% confidence intervals): inline image and inline image. Observations suggest that the interplay between large isopleth heaving near the sill and strong turbulence is the key mechanism to sustain such high turbulent nitrate fluxes at the HLC (two to three orders of magnitude higher than those at Station 23). Calculations also suggest that nitrate fluxes at the HLC alone can sustain primary production rates of inline image over the whole LSLE, approximately enough to account for a large part of the phytoplankton bloom and for most of the postbloom production. Surfacing nitrates are also believed to be consumed within the LSLE, not leaving much to be exported to the rest of the Gulf of St. Lawrence

Lorenz partial order: the best known logical framework to define evenness indices

Evenness is generally regarded as the constituent of species diversity which is independent of species richness. The group of most popular evenness indices has recently changed, following the influential work of Smith and Wilson (1996). My first point is to argue that this work failed to define coherently what evenness should be and thus advocated the use of indices of different nature. Instead, I propose to use the Lorenz partial order to choose indices that have a behaviour compatible with it. I then suggest a list of such evenness indices and build four series of . new. evenness indices. Finally, I discuss the interest of the Lorenz partial order and of the various evenness indices that are compatible with it

A Black Hills-Madison Aquifer Origin for Dakota Aquifer Groundwater in Northeastern Nebraska

Previous studies of the Dakota Aquifer in South Dakota attributed elevated groundwater sulfate concentrations to Madison Aquifer recharge in the Black Hills with subsequent chemical evolution prior to upward migra¬tion into the Dakota Aquifer. This study examines the plausibility of a Madison Aquifer origin for groundwater in northeastern Nebraska. Dakota Aquifer water samples were collected for major ion chemistry and isotopic analysis (18O, 2H, 3H, 14C, 13C, 34S, 18O-SO4, 87Sr, 37Cl). Results show that groundwater beneath the eastern, un¬confined portion of the study area is distinctly different from groundwater sampled beneath the western, con¬fined portion. In the east, groundwater is calcium-bicarbonate type, with δ18O values (−9.6‰ to −12.4‰) simi¬lar to local, modern precipitation (−7.4‰ to −10‰), and tritium values reflecting modern recharge. In the west, groundwater is calcium-sulfate type, having depleted δ18O values (−16‰ to −18‰) relative to local, modern precipitation, and 14C ages 32,000 to more than 47,000 years before present. Sulfate, δ18O, δ2H, δ34S, and δ18O-SO4 concentrations are similar to those found in Madison Aquifer groundwater in South Dakota. Thus, it is pro¬posed that Madison Aquifer source water is also present within the Dakota Aquifer beneath northeastern Ne¬braska. A simple Darcy equation estimate of groundwater velocities and travel times using reported physical parameters from the Madison and Dakota Aquifers suggests such a migration is plausible. However, discrep¬ancies between 14C and Darcy age estimates indicate that 14C ages may not accurately reflect aquifer residence time, due to mixtures of varying aged water