The camera of the fifth H.E.S.S. telescope. Part I: System description

In July 2012, as the four ground-based gamma-ray telescopes of the H.E.S.S. (High Energy Stereoscopic System) array reached their tenth year of operation in Khomas Highlands, Namibia, a fifth telescope took its first data as part of the system. This new Cherenkov detector, comprising a 614.5 m^2 reflector with a highly pixelized camera in its focal plane, improves the sensitivity of the current array by a factor two and extends its energy domain down to a few tens of GeV. The present part I of the paper gives a detailed description of the fifth H.E.S.S. telescope's camera, presenting the details of both the hardware and the software, emphasizing the main improvements as compared to previous H.E.S.S. camera technology.Comment: 16 pages, 13 figures, accepted for publication in NIM

AIM (Artery in microgravity): Design and development of an ice cubes mission

The Artery In Microgravity (AIM) project is the first experiment to be selected for the “Orbit Your Thesis!” programme of ESA Academy. It is a 2U experiment cube designed for the ICE Cubes facility on board of the International Space Station. The experiment is expected to be launched on SpaceX-20 in early 2020. The project is being developed by an international group of students from ISAE-SUPAERO and Politecnico di Torino, under the supervision of the ISAE-SUPAERO and Politecnico di Torino staff. The experiment is a test-bench for investigating haemodynamics in microgravity focusing on coronary heart disease, the most common form of cardiovascular disease and the cause of approximately 9 million deaths every year. Coronary heart disease is caused by stenosis of the coronary artery due to the build-up of plaque. While the development of atherosclerosis is not fully understood, the primary event seems to be subtle and repeated injury to the artery walls through various mechanisms including physical stresses from flow disturbances as well as from systemic and biological risk factors. In the presence of severe stenosis, patients are treated with the implantation of one or more coronary stents, which are tubular scaffolds devoted to restore and maintain myocardial perfusion. The coronary stenting procedure is largely applied (e.g., 1.8 million stents per year implanted in USA) In view of the impact that coronary artery disease has on humans, as well as of the increasing number of people that will be involved in space flights in the future, the way astronauts in space coronary hemodynamics is affected by the absence of gravity in the presence of stenosis or of stenting needs to be investigated in depth. In addition, as most stents are metallic objects, the radiation exposure in space might interact with their surface, altering blood flow, inducing particles release and ultimately leading to stent failure. Therefore, the aim of AIM is to start studying the vascular haemodynamics in a stented and a stenosed coronary artery on Earth and in microgravity and the stent-radiation coupling. This will allow to learn about the effect gravity plays on coronary artery haemodynamics, the effects of microgravity and radiation on the performance of implantable devices and ultimately the risks of myocardial infarction to astronauts on long-distance spaceflight. The experimental setup consists of a closed hydraulic loop containing two models of a coronary artery in series. An electric pump and reservoir will control the flow of a blood-mimicking fluid through the system. One model of the coronary artery will contain a coronary stent. The pressure of the fluid will be studied along its path using a series of pressure sensors and a camera will visualise the flow. The same experiments will be repeated on the ground with the same conditions as the in-flight model for comparison. The paper will outline in detail the design and development of the AIM experiment cube and the results of testing. The full data and results will be available after the completion of the mission which is expected to be between March and June 2020

Food-web structure in relation to environmental gradients and predator-prey ratios in tank-bromeliad ecosystems

Little is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators: prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests

Biological traits of European pond macroinvertebrates

Whilst biological traits of river macroinvertebrates show unimodal responses to geographic changes in habitat conditions in Europe, we still do not know whether spatial turnover of species result in distinct combinations of biological traits for pond macroinvertebrates. Here, we used data on the occurrence of 204 macroinvertebrate taxa in 120 ponds from four biogeographic regions of Europe, to compare their biological traits. The Mediterranean, Atlantic, Alpine, and Continental regions have specific climate, vegetation and geology. Only two taxa were exclusively found in the Alpine and Continental regions, while 28 and 34 taxa were exclusively recorded in the Atlantic and Mediterranean regions, respectively. Invertebrates in the Mediterranean region allocated much energy to reproduction and resistance forms. Most Mediterranean invertebrate species had narrow thermal ranges. In Continental areas, invertebrates allocated lesser energy to reproduction and dispersal, and organisms were short lived with high diversity of feeding groups. These characteristics suggest higher resilience. The main difference between ponds in the Alpine and Atlantic regions was their elevation. Alpine conditions necessitate specific adaptations related to rapid temperature fluctuations, and low nutrient concentrations. Even if our samples did not cover the full range of pond conditions across Europe, our analyses suggest that changes in community composition have important impacts on pond ecosystem functions. Consistent information on a larger set of ponds across Europe would be much needed, but their low accessibility (unpublished data and/or not disclosed by authors) remains problematic. There is still, therefore, a pressing need for the incorporation of high quality data sets into a standardized database so that they can be further analyzed in an integrated European-wide manner

Physical and land-cover variables influence ant functional groups and species diversity along elevational gradients

Of particular importance in shaping species assemblages is the spatial heterogeneity of the environment. The aim of our study was to investigate the influence of spatial heterogeneity and environmental complexity on the distribution of ant functional groups and species diversity along altitudinal gradients in a temperate ecosystem (Pyrenees Mountains). During three summers, we sampled 20 sites distributed across two Pyrenean valleys ranging in altitude from 1,009 to 2,339 m by using pitfall traps and hand collection. The environment around each sampling points was characterized by using both physical and land-cover variables. We then used a self-organizing map algorithm (SOM, neural network) to detect and characterize the relationship between the spatial distribution of ant functional groups, species diversity, and the variables measured. The use of SOM allowed us to reduce the apparent complexity of the environment to five clusters that highlighted two main gradients: an altitudinal gradient and a gradient of environmental closure. The composition of ant functional groups and species diversity changed along both of these gradients and was differently affected by environmental variables. The SOM also allowed us to validate the contours of most ant functional groups by highlighting the response of these groups to the environmental and land-cover variables

Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA

An elastic lidar system for the H.E.S.S. Experiment

International audienceThe H.E.S.S. experiment in Namibia, Africa, is a high energy gamma ray telescope sensitive in the energy range from ~100 Gev to a few tens of TeV, via the use of the atmospheric Cherenkov technique. To minimize the systematic errors on the derived fluxes of the measured sources, one has to calculate the impact of the atmospheric properties, in particular the extinction parameter of the Cherenkov light (~300–650 nm) exploited to observe and reconstruct atmospheric particle showers initiated by gamma-ray photons. A lidar can provide this kind of information for some given wavelengths within this range. In this paper we report on the hardware components, operation and data acquisition of such a system installed at the H.E.S.S. site

A Nanosatellite Optoelectronic Payload Dedicated to Radiation-Induced Degradation Measurement in Erbium-Doped Fiber

International audienceRadio over optical fiber (RoF) technologies appears as good candidates to address flexible payload requirements of the next generation of telecommunication satellites operating in Ku and Ka bands. In this context we have started the assembly of a 3U nanosatellite dedicated to the qualification of several erbium-doped fibers by using an optoelectronic metrology technique. The objective is hence to quantify the gain and noise figure degradation of the erbium-doped fiber amplifier (EDFA) due to cosmic ray exposure during a two years mission at a low earth orbit (LEO). This educational project is called NIMPH for "Nanosatellite to Investigate Microwave Photonics Hardware". It started in 2013 and involves students from the University of Toulouse with the support of Thales Alenia Space and CNES, the French national space agency

The fire ant Solenopsis saevissima and habitat disturbance alter ant communities

The fire ant Solenopsis saevissima is a major pest frequent in human-disturbed areas of its native range where it forms 'supercolonies'. We determined that its natural habitat in French Guiana is likely the sporadically flooded riparian forest and aimed to evaluate this ant's impact on the abundance and diversity of other ants by comparing different habitats at two sites. We noted a significant decrease in ant species richness between the rainforest and human-disturbed habitats (but not between the former and the naturally disturbed riparian forest), and between extreme habitats and all others. The number of ant nests per surface unit (i.e., quadrats of equal surface area), a proxy of ant abundance, globally followed this pattern. S. saevissima was absent from pristine rainforest (as expected) and from extreme habitats, showing the limits of its adaptability, whereas some other native ants can develop in these habitats. Ant species richness was significantly lower in the presence of S. saevissima in the riparian forest, forest edges and meadows, illustrating that this ant species has a negative impact on the ant communities in addition to the impact of natural- and man-made disturbances. Only some ant species can develop in its presence, and certain of these can even thrive. Because it has been recorded in Africa, Guadeloupe and the Galapagos Islands, we concluded that, due to the increasing volume of global trade and forest destruction, S. saevissima could become a pantropical invasive species