Klein tunneling and electron optics in Dirac-Weyl fermion systems with tilted energy dispersion

The outstanding electronic properties of relativistic-like fermions have been extensively studied in solid state systems with isotropic linear dispersions such as graphene. Here, we show that 2D and 3D Dirac-Weyl (DW) materials exhibiting tilted energy dispersions could induce drastically different transport phenomena, compared to the non-tilted case. Indeed, the Klein tunneling of DW fermions of opposite chiralities is predicted to appear along two separated oblique directions. In addition, valley filtering and beam splitting effects are easily tailored by dopant engineering techniques while the refraction of electron waves is dramatically modified by the tilt, thus paving the way for emerging applications in electron optics and valleytronics.Comment: 5 pages, 5 figures and Supplemental Material, submitted for publicatio

Stepped Graphene-based Aharonov-Bohm Interferometers

Aharonov-Bohm interferences in the quantum Hall regime are observed when electrons are transmitted between two edge channels. Such a phenomenon has been realized in 2D systems such as quantum point contacts, anti-dots and p-n junctions. Based on a theoretical investigation of the magnetotransport in stepped graphene, a new kind of Aharonov-Bohm interferometers is proposed herewith. Indeed, when a strong magnetic field is applied in a proper direction, oppositely propagating edge states can be achieved in both terrace and facet zones of the step, leading to the interedge scatterings and hence strong Aharonov-Bohm oscillations in the conductance in the quantum Hall regime. Taking place in the unipolar regime, this interference is also predicted in stepped systems of other 2D layered materials.Comment: 6 pages + 6 figures and a supplemental material, revised and resubmitte

Topography influence on the Lake equations in bounded domains

We investigate the influence of the topography on the lake equations which describe the two-dimensional horizontal velocity of a three-dimensional incompressible flow. We show that the lake equations are structurally stable under Hausdorff approximations of the fluid domain and $L^p$ perturbations of the depth. As a byproduct, we obtain the existence of a weak solution to the lake equations in the case of singular domains and rough bottoms. Our result thus extends earlier works by Bresch and M\'etivier treating the lake equations with a fixed topography and by G\'erard-Varet and Lacave treating the Euler equations in singular domains

Improving Texture Categorization with Biologically Inspired Filtering

Within the domain of texture classification, a lot of effort has been spent on local descriptors, leading to many powerful algorithms. However, preprocessing techniques have received much less attention despite their important potential for improving the overall classification performance. We address this question by proposing a novel, simple, yet very powerful biologically-inspired filtering (BF) which simulates the performance of human retina. In the proposed approach, given a texture image, after applying a DoG filter to detect the "edges", we first split the filtered image into two "maps" alongside the sides of its edges. The feature extraction step is then carried out on the two "maps" instead of the input image. Our algorithm has several advantages such as simplicity, robustness to illumination and noise, and discriminative power. Experimental results on three large texture databases show that with an extremely low computational cost, the proposed method improves significantly the performance of many texture classification systems, notably in noisy environments. The source codes of the proposed algorithm can be downloaded from https://sites.google.com/site/nsonvu/code.Comment: 11 page

Optical Hall effect in strained graphene

When passing an optical medium in the presence of a magnetic field, the polarization of light can be rotated either when reflected at the surface (Kerr effect) or when transmitted through the material (Faraday rotation). This phenomenon is a direct consequence of the optical Hall effect arising from the light-charge carrier interaction in solid state systems subjected to an external magnetic field, in analogy with the conventional Hall effect. The optical Hall effect has been explored in many thin films and also more recently in 2D layered materials. Here, an alternative approach based on strain engineering is proposed to achieve an optical Hall conductivity in graphene without magnetic field. Indeed, strain induces lattice symmetry breaking and hence can result in a finite optical Hall conductivity. First-principles calculations also predict this strain-induced optical Hall effect in other 2D materials. Combining with the possibility of tuning the light energy and polarization, the strain amplitude and direction, and the nature of the optical medium, large ranges of positive and negative optical Hall conductivities are predicted, thus opening the way to use these atomistic thin materials in novel specific opto-electro-mechanical devices.Comment: 20 pages, 9 figures, submitted for publicatio

Who Suffers the Penalty? A Panel Data Analysis of Earnings Gaps in Vietnam

In spite of its predominant economic weight in developing countries, little is known about informal sector income dynamics vis-à-vis the formal sector. Some works have been done in this field using household surveys, but they only consider some emerging Latin American countries and a few African countries. As a matter of consequence, there is still no way to generalize the (diverging) results to other part of the developing world. Taking advantage of the rich VHLSS dataset in Vietnam, in particular its three waves panel data (2002, 2004, 2006), we assess the magnitude of various formal/informal earnings gaps while addressing heterogeneity issues at three different levels: the worker, the job (wage employment vs. selfemployment) and the earnings distribution.We estimate fixed effects and quantile regressions to control for unobserved individual characteristics. Our results suggest that the informal sector earnings gap highly depends on the workers' job status and on their relative position in the earnings distribution. Penalties may in some cases turn into premiums. By comparing our results with studies in other developing countries, we draw conclusions highlighting the Vietnam's labour market specificity. --informal employment,earnings gap,transition matrix,quantile regressions,panel data,Vietnam

Confidence criterion for speech balloon segmentation

International audienceThis short paper investigates how to improve the confidence of speech balloon segmentation algorithms from comic book images. It comes from the need of precise indications about the quality of automatic processing in order to accept or not each segmented regions as a valid result, according to the application and without requiring any ground truth. We discuss several applications like result quality assessment for companies and automatic ground truth creation from high confidence results to train machine learning based systems.We present some ideas to combine several domain knowledge information (e.g. shape, text, etc.) and produce an improved confidence criterion

Modelling of piezoelectric actuators used in forging processes: principles and experimental validation

This paper deals with the modelling of a piezo- electric stack actuator used to generate specific low frequency vibration waveforms to assist forging processes. Experimental results show that such waveforms reduce the necessary forging force during upsetting tests. The main problems which remain are defining the appropriate waveforms, predicting their in- fluence on the process and the actuator and designing the control. Due to the complexity of the interactions between the different components of the system, a complete model of the process is needed. Such a model is developed here using an energetic macroscopic representation to preserve causality throughout the modelling. Simulation results are then compared to representative experimental results