Long lasting instabilities in granular mixtures

We have performed experiments of axial segregation in the Oyama's drum. We have tested binary granular mixtures during very long times. The segregation patterns have been captured by a CCD camera and spatio-temporal graphs are created. We report the occurence of instabilities which can last several hours. We stress that those instabilities originate from the competition between axial and radial segregations. We put into evidence the occurence of giant fluctuations in the fraction of grain species along the surface during the unstable periods.Comment: 10 pages, 10 figures, (2002

The transportation sector and low-carbon growth pathways: modeling urban, infrastructure and spatial determinants of mobility

International audienceThere is still a controversy as to the effect of spatial organization on CO2 emissions. This paper contributes to this debate by investigating the potentials offered by infrastructure measures favoring lower mobility in the transition to a low-carbon economy. This is done by embarking a detailed description of passenger and freight transportation in an energy-economy-environment (E3) model. In addition to the standard representation of transport technologies, this framework considers explicitly the "behavioural" determinants of mobility that drive the demand for transport but are often disregarded in mitigation assessments: constrained mobility needs (essentially commuting) imposed by the spatial organization of residence and production, modal choices triggered by installed infrastructure and the freight transport intensity of production processes. This study demonstrates that the implementation of measures fostering a modal shift towards low-carbon modes and a decoupling of mobility needs from economic activity significantly modifies the sectoral distribution of mitigation efforts and reduces the carbon tax levels necessary to reach a given climate target relatively to a "carbon price only" policy. This result is robust to a wide range of assumptions about exogenous parameters

Patterns in hydraulic ripples with binary granular mixtures

An experimental study of a binary granular mixture submitted to a transient shear flow in a cylindrical container is reported. The formation of ripples with a spiral shape is observed. The appearance of phase segregation in those spiral patterns is shown. The relative grain size bewteen sand species is found to be a relevant parameter leading to phase segregation. However, the relative repose angle is an irrelevant parameter. The formation of sedimentary structures is also presented. They result from a ripple climbing process. The ``sub-critical'' or ``super-critical'' character of the lamination patterns is shown to depend on the rotation speed of the container.Comment: 9 pages, 9 figures, LateX (using elsart package), submitted to Phys.

Clay fine fissuring monitoring using miniature geo-electrical resistivity arrays

Abstract This article describes a miniaturised electrical imaging (resistivity tomography) technique to map the cracking pattern of a clay model. The clay used was taken from a scaled flood embankment built to study the fine fissuring due to desiccation and breaching process in flooding conditions. The potential of using a miniature array of electrodes to follow the evolution of the vertical cracks and number them during the drying process was explored. The imaging technique generated two-dimensional contoured plots of the resistivity distribution within the model before and at different stages of the desiccation process. The change in resistivity associated with the widening of the cracks were monitored as a function of time. Experiments were also carried out using a selected conductive gel to slow down the transport process into the cracks to improve the scanning capabilities of the equipment. The main vertical clay fissuring network was obtained after inversion of the experimental resistivity measurements and validated by direct observations

Enfermedades producidas por priones en los Animales

Las encefalopatías espongiformes transmisibles (EETs) o enfermedades producidas por priones, son un grupo de enfermedades neurodegenerativas, de progresión lenta y fatales. Afectan tanto a los humanos como a los animales. Dentro de este grupo se encuentra la Encefalopatía Espongiforme Bovina (EEB), que se diagnosticó en Gran Bretaña y que posteriormente ha afectado a otros países. Esta patología ha causado gran impacto por el daño que ha provocado en la salud animal, en la economía y por su relevancia en la salud pública de estos países, al ser una enfermedad zoonótica. El agente etiológico de todas las EETs, se denomina "prión", que corresponde a la forma alterada (PrPSc) de una proteína constitutiva de la membrana celular (PrPC). La forma patológica es infectiva, capaz de producir la enfermedad, extremadamente resistente al calor y a otros métodos tradicionales de esterilización, que son efectivos contra otros patógenos. Entre las características comunes de estas patologías, se incluyen su curso con un largo periodo de incubación, el que puede durar hasta 3 años, posterior a la exposición. Los signos clínicos aparecen después de este período, los animales afectados presentan signos neurológicos progresivos y cambios morfológicos degenerativos del sistema nervioso central, que terminan con la muerte del individuo. Las principales EETs en los animales, que se describen en este trabajo son: el scrapie de ovinos y caprinos, la Encefalopatía Espongiforme Bovina (EEB), la Encefalopatía Transmisible del Visón (ETV), la Enfermedad del Desgaste Crónico (EDC) en ciervos y alces y la Encefalopatía Espongiforme Felina (EEF).  

Genes Suggest Ancestral Colour Polymorphisms Are Shared across Morphologically Cryptic Species in Arctic Bumblebees

email Suzanne orcd idCopyright: © 2015 Williams et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

The evolution of the Aristolochia pallida complex (Aristolochiaceae) challenges traditional taxonomy and reflects large-scale glacial refugia in the Mediterranean

The taxonomy of the Mediterranean Aristolochia pallida complex has been under debate since several decades with the following species currently recognized: A. pallida, A. lutea, A. nardiana, A. microstoma, A. merxmuelleri, A. croatica, and A. castellana. These taxa are distributed from Iberia to Turkey. To reconstruct phylogenetic and biogeographic patterns, we employed cpDNA sequence variation using both noncoding (intron and spacer) and protein-coding regions (i.e., trnK intron, matK gene, and trnK-psbA spacer). Our results show that the morphology-based traditional taxonomy was not corroborated by our phylogenetic analyses. Aristolochia pallida, A. lutea, A. nardiana, and A. microstoma were not monophyletic. Instead, strong geographic signals were detected. Two major clades, one exclusively occurring in Greece and a second one of pan-Mediterranean distribution, were found. Several subclades distributed in Greece, NW Turkey, Italy, as well as amphi-Adriatic subclades, and a subgroup of southern France and Spain, were revealed. The distribution areas of these groups are in close vicinity to hypothesized glacial refugia areas in the Mediterranean. According to molecular clock analyses the diversification of this complex started around 3–3.3 my, before the onset of glaciation cycles, and the further evolution of and within major lineages falls into the Pleistocene. Based on these data, we conclude that the Aristolochia pallida alliance survived in different Mediterranean refugia rarely with low, but often with a high potential for range extension, and a high degree of morphological diversity.Turkish Science Foundatio

Stabilizing entanglement autonomously between two superconducting qubits

Quantum error-correction codes would protect an arbitrary state of a multi-qubit register against decoherence-induced errors, but their implementation is an outstanding challenge for the development of large-scale quantum computers. A first step is to stabilize a non-equilibrium state of a simple quantum system such as a qubit or a cavity mode in the presence of decoherence. Several groups have recently accomplished this goal using measurement-based feedback schemes. A next step is to prepare and stabilize a state of a composite system. Here we demonstrate the stabilization of an entangled Bell state of a quantum register of two superconducting qubits for an arbitrary time. Our result is achieved by an autonomous feedback scheme which combines continuous drives along with a specifically engineered coupling between the two-qubit register and a dissipative reservoir. Similar autonomous feedback techniques have recently been used for qubit reset and the stabilization of a single qubit state, as well as for creating and stabilizing states of multipartite quantum systems. Unlike conventional, measurement-based schemes, an autonomous approach counter-intuitively uses engineered dissipation to fight decoherence, obviating the need for a complicated external feedback loop to correct errors, simplifying implementation. Instead the feedback loop is built into the Hamiltonian such that the steady state of the system in the presence of drives and dissipation is a Bell state, an essential building-block state for quantum information processing. Such autonomous schemes, broadly applicable to a variety of physical systems as demonstrated by a concurrent publication with trapped ion qubits, will be an essential tool for the implementation of quantum-error correction.Comment: 39 pages, 7 figure

Electron Beam Alignment Strategy in the LCLS Undulators

The x-ray FEL process puts very tight tolerances on the straightness of the electron beam trajectory (2 {micro}m rms) through the LCLS undulator system. Tight but less stringent tolerances of 80 {micro}m rms vertical and 140 {micro}m rms horizontally are to be met for the placement of the individual undulator segments with respect to the beam axis. The tolerances for electron beam straightness can only be met through beam-based alignment (BBA) based on electron energy variations. Conventional alignment will set the start conditions for BBA. Precision-fiducialization of components mounted on remotely adjustable girders and the use of beam-finder wires (BFW) will satisfy placement tolerances. Girder movement due to ground motion and temperature changes will be monitored continuously by an alignment monitoring system (ADS) and remotely corrected. This stabilization of components as well as the monitoring and correction of the electron beam trajectory based on BPMs and correctors will increase the time between BBA applications. Undulator segments will be periodically removed from the undulator Hall and measured to monitor radiation damage and other effects that might degrade undulator tuning