Parallel waveform extraction algorithms for the Cherenkov Telescope Array Real-Time Analysis

The Cherenkov Telescope Array (CTA) is the next generation observatory for the study of very high-energy gamma rays from about 20 GeV up to 300 TeV. Thanks to the large effective area and field of view, the CTA observatory will be characterized by an unprecedented sensitivity to transient flaring gamma-ray phenomena compared to both current ground (e.g. MAGIC, VERITAS, H.E.S.S.) and space (e.g. Fermi) gamma-ray telescopes. In order to trigger the astrophysics community for follow-up observations, or being able to quickly respond to external science alerts, a fast analysis pipeline is crucial. This will be accomplished by means of a Real-Time Analysis (RTA) pipeline, a fast and automated science alert trigger system, becoming a key system of the CTA observatory. Among the CTA design key requirements to the RTA system, the most challenging is the generation of alerts within 30 seconds from the last acquired event, while obtaining a flux sensitivity not worse than the one of the final analysis by more than a factor of 3. A dedicated software and hardware architecture for the RTA pipeline must be designed and tested. We present comparison of OpenCL solutions using different kind of devices like CPUs, Graphical Processing Unit (GPU) and Field Programmable Array (FPGA) cards for the Real-Time data reduction of the Cherenkov Telescope Array (CTA) triggered data.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

Alluvionnement des retenues par courants de turbidité

Reservoir sedimentation by turbidity currents All lakes created on natural rivers are subjected to reservoir sedimentation. The construction of a dam significantly modifies the flow conditions of natural streams inside and downstream of an artificial lake. Considering the sediment concentration, often high during the flood season, the entering flow shows a greater density than the ambient fluid. Suspended load can therefore be entrained along the reservoir bottom all the way down to the dam in the form of turbidity currents. Research was undertaken to better understand the physical phenomena that contribute to reservoir sedimentation. The study of turbidity currents at the bottom of a lake is based on a review of the relevant literature, on measurements of water and sediment motion on site, on physical modelling of turbidity currents and on numerical flow simulation. The two-year on site investigation in the test site of Luzzone in southern Switzerland showed the relationship between precipitation, water and sediment flow and turbidity current in the reservoir even for minor events. A simple relationship describing the inflow hydrograph and the sediment transport for small floods in the incoming river was established as a set of non-dimensional equations. These relations were implemented in the numerical flow code as an upstream boundary condition. No significant occurrence of high water was observed. It was therefore impossible to establish the necessary elements for extrapolation to important flood events with their implication for the reservoir sedimentation process. The laboratory investigation confirmed the results from numerical simulation of turbidity currents. The progressing flow proceeded as predicted by theory and numerical simulation. The numerical model developed is based on the general Navier-Stokes solver code CFX-F3D from Computational Fluid Dynamics Services. User defined sediment deposition and erosion modules were added in order to take into account sedimentation and the interactions between the turbidity current and the bottom of the reservoir. The flow in the physical model as well as in the real reservoir geometry was simulated with exactly the same boundary conditions. Comparison between computer simulation, physical model and on site measurement results showed a satisfactory agreement. The code was then used to simulate turbidity currents in two dimensions in a simplified reservoir geometry with all available flow - sediment interaction models for three different particle sizes. The results were compared to data from an existing 2Dflow simulation programme and they agreed well. The study of a thousand-year flood in the Luzzone reservoir using the developed computer model revealed the potential of such a tool. In particular, the impact on the sediment deposits was analysed. A Rapid evaluation of the incidence of such an extreme turbidity flow was made. Through this study, considerable knowledge has been acquired. It can be used to formulate proposals in order to allow limited transit of sediments through the lake during floods to evacuate them directly downstream of the dam. This operation has to take place during flood periods, when the upstream and downstream reaches carry enough water. The bottom outlet therefore participates partially in the sediment evacuation at the moment of their major occurrence during floods. Another advantage of this procedure would be the reduced impact on wildlife and vegetation in the downstream river

Les rives lacustres et le génie biologique

La Suisse est un pays de lacs avec une longueur totale de leurs rives de plus de 2000 km. Les lacs et rives façonnent le paysage. Les rives lacustres constituent des habitats quasi linéaires définissant la frontière entre espaces terrestres et lacustres, créant par la même occasion des zones tampon très actives. La forte pression démographique a fait perdre à nos rives la majorité de ses espaces naturels. C'est en remblayant les zones à faible profondeur et la construction de murs devancés par des enrochements que les roselières ont disparu pour faire place à des parcs et promenades, immeubles, infrastructure portuaires et autres voies de communication. Les rives lacustres se trouvent aujourd'hui en grande partie dans un état non naturel ou artificiel. Mais plusieurs projets de revitalisation des rives sont à l'étude, en exécution ou ont déjà été réalisés. Un groupe de travail «Rives Lacustres » a été fondé en 2008 au sein de l'association pour le génie biologique afin de soutenir ces projets et fournir des bases scientifiques et pratiques à leur réalisation

Consumer reactions to unsustainable luxury: a cross-country analysis

Purpose – This paper investigates why and when messages regarding unsustainable luxury products lead to negative word-of-mouth (NWOM) through a focus on the role of guilt, need to warn others and consumers’ cultural orientation. Design/methodology/approach – Three experiments test whether messages describing unsustainable versus sustainable luxury manufacturing processes elicit guilt and a need to warn others and whether and how the need to warn others affects consumers’ NWOM depending on their cultural orientation. Findings – Consumers experience guilt in response to messages emphasizing the unsustainable (vs sustainable) nature of luxury products. In turn, guilt triggers a need to warn other consumers, which leads to NWOM about the luxury company. Furthermore, the results suggest that two dimensions of Hofstede’s model of national culture – namely individualism/collectivismand masculinity/femininity – moderate the effect of the need to warn others on NWOM. Practical implications – Luxury managers should design appropriate strategies to cope with consumers’ different reactions to information regarding luxury brands’ unsustainability. Managers should be aware that the risk of NWOM diffusion may be higher in countries characterized by a collectivistic and feminine orientation rather than an individualistic and masculine orientation. Originality/value – Consumer reaction to unsustainable luxury, especially across different cultural groups, is a neglected area of investigation. This work contributes to this novel area of research by investigatingNWOM stemming from unsustainable luxury manufacturing practices in different cultural contexts

The puzzling source IGR J17361-4441 in NGC 6388: a possible planetary tidal disruption event

On 2011 August 11, INTEGRAL discovered the hard X-ray source IGR J17361-4441 near the centre of the globular cluster NGC 6388. Follow up observations with Chandra showed the position of the transient was inconsistent with the cluster dynamical centre, and thus not related to its possible intermediate mass black hole. The source showed a peculiar hard spectrum (Gamma \approx 0.8) and no evidence of QPOs, pulsations, type-I bursts, or radio emission. Based on its peak luminosity, IGR J17361-4441 was classified as a very faint X-ray transient, and most likely a low-mass X-ray binary. We re-analysed 200 days of Swift/XRT observations, covering the whole outburst of IGR J17361-4441 and find a t^{-5/3} trend evident in the light curve, and a thermal emission component that does not evolve significantly with time. We investigate whether this source could be a tidal disruption event, and for certain assumptions find an accretion efficiency epsilon \approx 3.5E-04 (M_{Ch}/M) consistent with a massive white dwarf, and a disrupted minor body mass M_{mb}=1.9E+27(M/M_{Ch}) g in the terrestrial-icy planet regime. These numbers yield an inner disc temperature of the order kT_{in} \approx 0.04 keV, consistent with the blackbody temperature of kT_{in} \approx 0.08 keV estimated by spectral fitting. Although the density of white dwarfs and the number of free-floating planets are uncertain, we estimate the rate of planetary tidal disruptions in NGC 6388 to be in the range 3E-06 to 3E-04 yr^{-1}. Averaged over the Milky Way globular clusters, the upper limit value corresponds to 0.05 yr^{-1}, consistent with the observation of a single event by INTEGRAL and Swift.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal on 2014 July 16; 9 pages, 5 figures. Added references; corrected typo

Hybrid modeling of sediment management during drawdown of Räterichsboden reservoir

The Swiss utility Kraftwerke Oberhasli AG (KWO) currently implements "KWO plus", an upgrading program involving a large number of economical and ecological improvements of their hydropower schemes. A major project, the modification of the Handeck 2 power plant intake, requires total emptying of the Räterichsboden reservoir having an active volume of 25 million m3. In order to define the most efficient and ecological emptying process for these circumstances, KWO commissioned a hybrid modelling program of the sediment remobilisation processes during the planned reservoir drawdown. Hydraulic model tests were conducted at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) by means of a 1:35 scaled Froude model. Numerical simulations of sediment transport were performed by the Laboratory of Hydraulic Constructions (LCH) using the software FLOW-3D. A good agreement between both models was found for total values of the sediment concentration and its variation in time. Both the physical and the numerical model were validated by prototype data obtained during an annual functional test of the bottom outlet. These measurements were conducted at three downstream positions in the Aare River. The involved solution procedures provide the (1) sediment flux during pressure flushing, (2) influence of outlet gate opening height and opening velocity on sediment concentration, and (3) time-dependent distribution of sediment concentration along the Aare River