JUMPSAT: Qualifying three equipments in the CubeSat mission

JUMPSAT is a 3-Unit CubeSat mission expected for launch in 2017. It is a collaborative project involving the French research institutes CNES and ONERA as well as two universities, the Institut Supérieur de l'Aéronautique et de l'Espace and TELECOM Bretagne. The main mission objectives are the technological verification of both the three-axis attitude control system as well as the verification of two embedded payloads: A low cost Star Tracker developed by ISAE-Supaero for future small satellite missions and a directional radiation sensor for precise mapping of the Earth radiation belt. This article focuses on the mission concept and the status of the mission design in fall 2013. Main mission parameters are introduced, with emphases on the characteristic properties of the Jumpsat mission, as for example the choice of a sun-synchronous elliptical low-Earth Orbit, which is necessary to be in compliance with the payload requirements and at the same time to ensure space debris prevention. Furthermore, due to the limited observation time of a polar satellite, it was decided to utilize a distributed ground station network on S-band frequency for ensuring the necessary communication bandwidth for up- and downlink. The space segment will be equipped with deployable solar panels for improving the thermal and power budget of the overall system. Finally, a brief overview of the specifications and design of the attitude control system and both payloads are also given in the article

Magnetic states at the surface of alpha Fe2O3 thin films doped with Ti, Zn, or Sn

The spin states at the surface of epitaxial thin films of hematite, both undoped and doped with 1% Ti, Sn or Zn, respectively, were probed with x-ray magnetic linear dichroism (XMLD) spectroscopy. Morin transitions were observed for the undoped (T_M~200 K) and Sn-doped (T_M~300 K) cases, while Zn and Ti-doped samples were always in the high and low temperature phases, respectively. In contrast to what has been reported for bulk hematite doped with the tetravalent ions Sn4+ and Ti4+, for which T_M dramatically decreases, these dopants substantially increase T_M in thin films, far exceeding the bulk values. The normalized Fe LII-edge dichroism for T<T_M does not strongly depend on doping or temperature, except for an apparent increase of the peak amplitudes for T<100 K. We observed magnetic field-induced inversions of the dichroism peaks. By applying a magnetic field of 6.5 T on the Ti-doped sample, a transition into the T>T_M state was achieved. The temperature dependence of the critical field for the Sn-doped sample was characterized in detail. It was demonstrated the sample-to-sample variations of the Fe LIII-edge spectra were, for the most part, determined solely by the spin orientation state. Calculations of the polarization-depedent spectra based on a spin-multiplet model were in reasonable agreement with the experiment and showed a mixed excitation character of the peak structures.Comment: 8 pages, 8 figure

The spin temperature of high-redshift damped Lyman-α\alpha systems

We report results from a programme aimed at investigating the temperature of neutral gas in high-redshift damped Lyman-$\alpha$ absorbers (DLAs). This involved (1) HI 21cm absorption studies of a large DLA sample, (2) VLBI studies to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet spectroscopy to determine DLA metallicities and velocity widths. Including literature data, our sample consists of 37 DLAs with estimates of the spin temperature $T_s$ and the covering factor. We find a strong $4\sigma$) difference between the $T_s$ distributions in high-z (z>2.4) and low-z (z<2.4) DLA samples. The high-z sample contains more systems with high $T_s$ values, $\gtrsim 1000$ K. The $T_s$ distributions in DLAs and the Galaxy are also clearly (~$6\sigma$) different, with more high-$T_s$ sightlines in DLAs than in the Milky Way. The high $T_s$ values in the high-z DLAs of our sample arise due to low fractions of the cold neutral medium. For 29 DLAs with metallicity [Z/H] estimates, we confirm the presence of an anti-correlation between $T_s$ and [Z/H], at $3.5\sigma$ significance via a non-parametric Kendall-tau test. This result was obtained with the assumption that the DLA covering factor is equal to the core fraction. Monte Carlo simulations show that the significance of the result is only marginally decreased if the covering factor and the core fraction are uncorrelated, or if there is a random error in the inferred covering factor. We also find evidence for redshift evolution in DLA $T_s$ values even for the z>1 sub-sample. Since z>1 DLAs have angular diameter distances comparable to or larger than those of the background quasars, they have similar efficiency in covering the quasars. Low covering factors in high-z DLAs thus cannot account for the observed redshift evolution in spin temperatures. (Abstract abridged.)Comment: 37 pages, 22 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Is Mislocalization during saccades related to the position of the saccade target within the image or to the gaze position at the end of the saccade?

A stimulus that is flashed around the time of a saccade tends to be mislocalized in the direction of the saccade target. Our question is whether the mislocalization is related to the position of the saccade target within the image or to the gaze position at the end of the saccade. We separated the two with a visual illusion that influences the perceived distance to the target of the saccade and thus saccade endpoint without affecting the perceived position of the saccade target within the image. We asked participants to make horizontal saccades from the left to the right end of the shaft of a Müller-Lyer figure. Around the time of the saccade, we flashed a bar at one of five possible positions and asked participants to indicate its location by touching the screen. As expected, participants made shorter saccades along the fins-in (<->) configuration than along the fins-out (>-<) configuration of the figure. The illusion also influenced the mislocalization pattern during saccades, with flashes presented with the fins-out configuration being perceived beyond flashes presented with the fins-in configuration. The difference between the patterns of mislocalization for bars flashed during the saccade for the two configurations corresponded quantitatively with a prediction based on compression towards the saccade endpoint considering the magnitude of the effect of the illusion on saccade amplitude. We conclude that mislocalization is related to the eye position at the end of the saccade, rather than to the position of the saccade target within the image

Seamount influences on mid-water shrimps (Decapoda) and Gnathophausiids (Lophogastridea) of the South-West Indian ridge

This study was conducted under the UNDP/IUCN project, funded by the Global Environment Facility (GEF). The authors thank the School of Biology at the University of St Andrews and the National Environmental Research Council (NERC) for funding toward Tom B Letessier's PhD.Maintenance of often-observed elevated levels of pelagic diversity and biomass on seamounts, that are of relevance to conservation and fishery management, involves complex interactions between physical and biological variables that remain poorly understood. To untangle these biophysical processes we explore factors influencing the distribution of epi- and meso-pelagic (0–1000 m) micronektonic crustaceans (>15 mm; order Lophogastridea, family Gnathophausiidea; and order Decapoda) on and off seamounts along the South West Indian Ridge (SWIR, 27° to 42°S) and on a seamount off the Madagascar Ridge (31.6°S, 42.8°E). Thirty-one species of micronektic crustaceans were caught using mid-water trawls within the study are but there was no apparent latitude-related patterns in species richness or abundance. Species richness predicted by rarefraction curves and numerical abundance was highest in the vicinity (800 m). The dominant species assemblage comprised the shrimps Systellaspis debilis (37%) and Sergia prehensilis (34%), and was restricted to seamounts on the subtropical SWIR. Our observations suggest that the ‘oasis effect’ of seamounts conventionally associated with higher trophic levels is also applicable to pelagic micronektic crustaceans at lower trophic levels. We suggest that the enhanced biomass and species richness attributed is due to ‘habitat enrichment’, whereby seamounts provide favourable habitats for both pelagic and bentho-pelagic mid-water crustaceans.PostprintPeer reviewe

Using neutron activation analysis to identify scales of interaction at Kinet Höyük, Turkey

We use NAA to characterize a relatively large archaeological ceramic sample from the Late Bronze Age to Hellenistic phases of Kinet Höyük, a coastal Turkish site in the Gulf of Iskenderun at the northeast corner of the Mediterranean Sea. The geographic extent of local Kinet wares (how local is local?) is established through comparison with sediment samples across the Kinet hinterland. Four major compositional groups are identified: local and locally imported wares, imports from Cypriot, and presumed Western Anatolian and Aegean centers, and imports that appear relatively homogenous elementally but comprise typologically diverse ceramics with attributions that range from Cyprus to the coastal mainland. Comparison with other published NAA studies for this site reinforces the elemental evidence for local production, and underlines the need for caution when assuming local production always equates with local clays particularly for coastal sites. We propose that the chronological distribution of the local and non-local groups provides a useful political economic proxy. The study indicates systemic and widespread political disruption and marginalization at the transition to the Late Iron Age in this region. © 2008 Elsevier Ltd. All rights reserved

G0^0 Electronics and Data Acquisition (Forward-Angle Measurements)

The G$^0$ parity-violation experiment at Jefferson Lab (Newport News, VA) is designed to determine the contribution of strange/anti-strange quark pairs to the intrinsic properties of the proton. In the forward-angle part of the experiment, the asymmetry in the cross section was measured for $\vec{e}p$ elastic scattering by counting the recoil protons corresponding to the two beam-helicity states. Due to the high accuracy required on the asymmetry, the G$^0$ experiment was based on a custom experimental setup with its own associated electronics and data acquisition (DAQ) system. Highly specialized time-encoding electronics provided time-of-flight spectra for each detector for each helicity state. More conventional electronics was used for monitoring (mainly FastBus). The time-encoding electronics and the DAQ system have been designed to handle events at a mean rate of 2 MHz per detector with low deadtime and to minimize helicity-correlated systematic errors. In this paper, we outline the general architecture and the main features of the electronics and the DAQ system dedicated to G$^0$ forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section A. It has been written with Latex using \documentclass{elsart}. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment In Press (2007