The long-term evolution of the X-ray pulsar XTE J1814-338: a receding jet contribution to the quiescent optical emission?

We present a study of the quiescent optical counterpart of the Accreting Millisecond X-ray Pulsar XTE J1814-338, carrying out multiband (BVR) orbital phase-resolved photometry using the ESO VLT/FORS2. The optical light curves are consistent with a sinusoidal variability modulated with the orbital period, showing evidence for a strongly irradiated companion star, in agreement with previous findings. The observed colours cannot be accounted for by the companion star alone, suggesting the presence of an accretion disc during quiescence. The system is fainter in all analysed bands compared to previous observations. The R band light curve displays a possible phase offset with respect to the B and V band. Through a combined fit of the multi-band light curves we derive constraints on the companion star and disc fluxes, on the system distance and on the companion star mass. The irradiation luminosity required to account for the observed day-side temperature of the companion star is consistent with the spin-down luminosity of a millisecond radio pulsar. The flux decrease and spectral evolution of the quiescent optical emission observed comparing our data with previous observations, collected over 5 years, cannot be well explained with the contribution of an irradiated companion star and an accretion disc alone. The progressive flux decrease as the system gets bluer could be due to a continuum component evolving towards a lower, bluer spectrum. While most of the continuum component is likely due to the disc, we do not expect it to become bluer in quiescence. Hence we hypothesize that an additional component, such as synchrotron emission from a jet was contributing significantly in the earlier data obtained during quiescence and then progressively fading or moving its break frequency toward longer wavelengths.Comment: 7 pages, 8 figures, accepted for publication in Section 7. Stellar structure and evolution of Astronomy and Astrophysic

Une aide à la décision pour le choix des interventions en zone inondable

Cet article a été réalisé dans le cadre d'un projet de trois ans visant à développer une méthodologie d'analyse, de prévision et de contrôle des risques d'inondation au Québec. Il présente une approche concrète pour calculer les impacts potentiels et le risque d'inondation et utiliser ces résultats afin d'évaluer la situation du risque local, de décider si les impacts doivent être minimisés et de choisir les moyens d'intervention appropriés. Le risque d'inondation est considéré comme étant le produit de la probabilité d'occurrence des crues et des conséquences occasionnées par ces événements. Les pertes de vies potentielles et les dommages directs sont évalués en simulant les niveaux d'eau de différents scénarios d'inondation à partir d'un modèle d'écoulement unidimensionnel non permanent, et en intégrant ces résultats à un logiciel géoréférencé de calcul des dommages d'inondation. L'analyse des impacts et du risque calculé permet de dresser un portrait du montant des dommages annuels potentiels sur les sites habités le long du cours d'eau et un portrait de l'évolution des impacts en fonction de l'amplitude des crues. Cette analyse mène à l'identification des sites où existe un risque jugé inacceptable selon des critères préétablis. Pour chaque site où des interventions sont justifiées par le niveau de risque, des scénarios de minimisation des impacts tenant compte des mécanismes d'inondation sont élaborés et ensuite simulés afin d'en mesurer l'efficacité. Un exemple d'application à un site de la rivière Châteauguay illustre la méthode et les gains pouvant découler de son utilisation.Each year, several rivers in Quebec are responsible for severe flooding and these events generate major socio-economic impacts. The frequency and magnitude of these episodes highlight the existence of a real flood risk. Using global information concerning level and extent of flood risk, authorities would be more likely to make appropriate decisions in the management of flood risk. This article results from a three year project aimed at developing a methodology for the analysis, forecasting and control of flood risk in Quebec. It suggests a concrete approach for the evaluation of the potential impact of floods in order to obtain a better knowledge of local risk in inhabited areas and exploits there results to evaluate the acceptability of the calculated risk and to plan appropriate risk minimisation interventions.Risk is defined as the product of the mathematical expectation of a specified occurrence with the expected consequences of the event. In floodplain studies, flood risk is the probability of the occurrence at a given flood multiplied by the expected consequences resulting from this event. Different types of consequences may be observed, clearly the easiest to evaluate being direct or material damages and potential loss of life. The risk calculated using the proposed definition is attributable in variable proportions to the frequency of the floods and the amount of damages. A given calculated global risk on a site could be the result of frequent floods, each causing moderate damage or of a single (or more) extreme event, with very low probability of occurrence, but causing severe damage. Risk associated with rare events could be considered as an acceptable risk, a risk we decide to live with, since the resources available to prevent flood damage are often limited and a decision is taken to optimise the allocation of these resources. The flood level corresponding to the limit between acceptable and unacceptable risk must be determined by the population concerned and be based on a good knowledge of the risk situation.The proposed methodology to evaluate and minimise flood risk for a site localised in a river flood plain involves six steps:1. the realisation of a hydrologic frequency analysis to determine the amplitude of the floods associated with the flood frequency,2. the hydraulic simulation of floods to predict water level and velocity in the stream for each scenario, 3. the assessment of direct damage and potential loss of life for each flood simulated, 4. the calculation of risk, 5. the risk analysis considering the limit of acceptable risk and 6. the choice and planning of appropriate intervention to eliminate unacceptable risk.This approach has been applied to the study of a site along the Châteauguay River, a tributary of the St Laurence River, a river that experiences flood events every two years or so. Seven flood scenarios (the 2, 3, 10, 20, 100, 1 000, and 10 000 year flood) are used to evaluate the risk for a site localised in the village of Huntingdon. Hydraulic characteristics, water level and velocity, associated with each flood scenario are determined using the DAMBRK model, a one-dimensional unsteady flow model. The results are incorporated in DOMINO, a geo-referenced software calculating flood impacts. This software allows the user to create a three-dimensional numerical model of the site based on topographic information. The superposition of hydraulic results provides the flow depth at any point within the site. Damage is evaluated by integrating the municipal roll number of Huntingdon, which provide the site location and value of each building, and gives an estimate of the population threatened by each flood event at the site. These results of direct damages are used to calculate the risk related to each flood event simulated on the Huntingdon site. For this application, the unacceptable risk has generally been agreed to be the risk resulting from the 20 year flood, or more frequent floods, for the material damages and to the number of potential losses of life associated with the 100 year flood or more frequent flood. The analysis indicates that an unacceptable risk of 23 993 $ per year for material damages and potential loss of life of 50 persons exist. Different site scale interventions to eliminate this risk have been simulated and proven to be efficient only if complemented with a few local modifications to the more exposed buildings.This approach may be extended to the study of any river because it takes into consideration local hydrologic and hydraulic conditions. It has the advantage of being based on existing information and to be automated, which limits the time and resources required to obtain the base data and perform the necessary simulations

Continued evaluation of potential for geologic storage of carbon dioxide in the southeastern United States

Southern States Energy Board Duke Energy Santee Cooper Power Southern CompanyBureau of Economic Geolog

Promotional benefits of 99-ending prices: the moderating role of intuitive and analytical decision style

Evidence suggests that retailers use 99-ending prices as a promotional technique. This paper explores the consumer perceived benefits of such promotional practices and the information processing conditions under which hedonic benefits are higher (lower) than utilitarian ones. In line with the benefit framework of sales promotion proposed by Chandon, Wansink, and Laurent (2000), 99-ends are not expected to be strictly associated to monetary savings benefit but also to a more hedonic benefit, fulfilling consumer’s needs for exploration. In addition, the analytic or intuitive consumer decision style (Mantel & Kardes, 1999) is likely to activate either the utilitarian benefit of savings or the hedonic benefit of exploration with more strength. The analysis of an on-line survey among 317 shoppers shows that both perceived savings and exploration benefits have a positive impact on proneness to buy 99-ends products with the saving benefits being stronger (weaker) for analytical decision makers (intuitive decision makers). The findings contribute to the better understanding of the image effect of 99-ends underlying its individual differences and help retailers and also pricing managers in their use of 99-ends as a promotional technique

Stress response function of a two-dimensional ordered packing of frictional beads

We study the stress profile of an ordered two-dimensional packing of beads in response to the application of a vertical overload localized at its top surface. Disorder is introduced through the Coulombic friction between the grains which gives some indeterminacy and allows the choice of one constrained random number per grain in the calculation of the contact forces. The so-called `multi-agent' technique we use, lets us deal with systems as large as $1000\times1000$ grains. We show that the average response profile has a double peaked structure. At large depth $z$, the position of these peaks grows with $cz$, while their widths scales like $\sqrt{Dz}$. $c$ and $D$ are analogous to `propagation' and `diffusion' coefficients. Their values depend on that of the friction coefficient $\mu$. At small $\mu$, we get $c_0-c \propto \mu$ and $D \propto \mu^\beta$, with $\beta \sim 2.5$, which means that the peaks get closer and wider as the disorder gets larger. This behavior is qualitatively what was predicted in a model where a stochastic relation between the stress components is assumed.Comment: 7 pages, 7 figures, accepted version to Europhys. Let

Enhancing the performance of a diazonium-modified carbon supercapacitor by controlling the grafting process

The activated Norit carbon was modified by grafting the 4-nitrobenzenediazonium salt in the presence or in the absence of a radical scavenger (DPPH: 2,2-diphenyl-1-picrylhydrazyl) to produce modified carbon powders having different surface organic layers going from monolayer to multilayer. The surface chemistry and pore texture of carbon products were studied by TGA, chemical elemental analysis and nitrogen gas adsorption measurements. The resulting powders were used as active components in supercapacitors working in alkaline media to investigate the impact of the grafting on the electrochemical performances. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the charge/discharge process in aqueous 1 M KOH. The present work demonstrates that the high double-layer capacitance and the low ionic resistance of the pristine carbon can be preserved by limiting the growth of the grafted layer with DPPH

Potential Sinks for Geologic Storage of CO2 Generated in the Carolinas

This document summarizes a scoping study of the current state of knowledge of carbon storage options for our geographic area. The focus is on one aspect of carbon capture and storage—identification of deep saline aquifers in which carbon dioxide (CO2 ) generated in the Carolinas might be stored. The study does not address other aspects of CO2 storage projects, such as capture and compression of the gas, well construction and development, or injection. Transport of CO2 is touched upon in this study but has not been fully addressed. The information contained in this document is primarily from review of published geologic literature and unpublished data. No field data collection has been completed as part of this study. Further work will be necessary to increase confidence in the suitability of the potential CO2 storage sites identified in this report. This study does not address the regulatory, environmental, or public policy issues associated with carbon storage, which are under development at this time.Duke Energy, Progress Energy, Santee Cooper Power, South Carolina Electric and Gas, Electric Power Research Institute (EPRI), Southern States Energy Board (SSEB)Bureau of Economic Geolog

Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface

Although the creation of spin polarization in various non-magnetic media via electrical spin injection from a ferromagnetic tunnel contact has been demonstrated, much of the basic behavior is heavily debated. It is reported here for semiconductor/Al2O3/ferromagnet tunnel structures based on Si or GaAs that local magnetostatic fields arising from interface roughness dramatically alter and even dominate the accumulation and dynamics of spins in the semiconductor. Spin precession in the inhomogeneous magnetic fields is shown to reduce the spin accumulation up to tenfold, and causes it to be inhomogeneous and non-collinear with the injector magnetization. The inverted Hanle effect serves as experimental signature. This interaction needs to be taken into account in the analysis of experimental data, particularly in extracting the spin lifetime and its variation with different parameters (temperature, doping concentration). It produces a broadening of the standard Hanle curve and thereby an apparent reduction of the spin lifetime. For heavily doped n-type Si at room temperature it is shown that the spin lifetime is larger than previously determined, and a new lower bound of 0.29 ns is obtained. The results are expected to be general and occur for spins near a magnetic interface not only in semiconductors but also in metals, organic and carbon-based materials including graphene, and in various spintronic device structures.Comment: Final version, with text restructured and appendices added (25 pages, 9 figures). To appear in Phys. Rev.