Report of the sensor cooler technology panel

The Sensor Cooler Technology Panel identified three major areas in which technology development must be supported in order to meet the system performance requirements for the Astrotech 21 mission set science objectives. They are: long life vibration free refrigerators; mechanical refrigeration for 2 K to 5 K; and flight testing of emerging prototype refrigerators. A development strategy and schedule were recommended for each of the three areas

Limits of flexural wave absorption by open lossy resonators: reflection and transmission problems

The limits of flexural wave absorption by open lossy resonators are analytically and numerically reported in this work for both the reflection and transmission problems. An experimental validation for the reflection problem is presented. The reflection and transmission of flexural waves in 1D resonant thin beams are analyzed by means of the transfer matrix method. The hypotheses, on which the analytical model relies, are validated by experimental results. The open lossy resonator, consisting of a finite length beam thinner than the main beam, presents both energy leakage due to the aperture of the resonators to the main beam and inherent losses due to the viscoelastic damping. Wave absorption is found to be limited by the balance between the energy leakage and the inherent losses of the open lossy resonator. The perfect compensation of these two elements is known as the critical coupling condition and can be easily tuned by the geometry of the resonator. On the one hand, the scattering in the reflection problem is represented by the reflection coefficient. A single symmetry of the resonance is used to obtain the critical coupling condition. Therefore the perfect absorption can be obtained in this case. On the other hand, the transmission problem is represented by two eigenvalues of the scattering matrix, representing the symmetric and anti-symmetric parts of the full scattering problem. In the geometry analyzed in this work, only one kind of symmetry can be critically coupled, and therefore, the maximal absorption in the transmission problem is limited to 0.5. The results shown in this work pave the way to the design of resonators for efficient flexural wave absorption

Physical Basis for Spectrometer Calibration

Progress in quantitative surface analysis is hampered by the lack of experimental procedure including spectrometer calibration, sample preparation, and general experimental setting-up. Two methods for spectrometer alignment are compared: the linearization method and the elastic peak test. Experimental spectra are presented, which can be considered as stringent reference data to check the instrument response and the analyser transmission at low energies

Cephalophus ogilbyi crusalbum Grubb 1978, described from coastal Gabon, is quite common in the Forêt des Abeilles, Central Gabon

La nouvelle forme de céphalophe (Cephalophus ogilbyi crusalbum) décrite en 1978 par Grubb à partir de quelques spécimens de musée était supposée avoir une distribution limitée à la zone côtière du Gabon. De ce fait, elle fut classée comme rare et comme faisant partie des espèces nécessitant des mesures de protection urgentes. De récentes observations effectuées sur le site d'étude du Camp de la Makandé (Forêt des Abeilles) montrent que cette espèce est en fait commune dans cette région où elle est régulièrement observée. Les jarrets blancs qui la caractérisent constituent un critère d'identification aisé. Des observations complémentaires faites dans la réserve de la Lopé confirment que C. o. crusalbum est également présent sur la rive gauche de l'Offou

Intensity of Valence Auger Transitions (L23VV) of Al and Si in Metal, Oxide and Nitride

L23VV Auger transition has been studied in Si, SiO2, Al, AlN, Al2O3 by electron spectroscopy excited either by electron beam or X Rays. A strong difference is observed in intensity between pure solid and oxide or nitride under electron bombardment. Auger intensity is very sensitive to changes in the backscattering coefficient or inelastic mean free path. However transient local trapping of electrons seems to be responsible for the large change observed

Oxidation of Aluminum Studied by Ion Scattering Spectroscopy (I.S.S) in a Scanning Auger Microscope

The set up of an ion gun, producing a focused beam in the analysis chamber of a Scanning Auger Microscope permits ion scattering experiments: surface studies performed by electron spectroscopies can then be enlarged by Ion Scattering Spectroscopy (I.S.S.) to get additional information. I.S.S. appears to be very sensitive to the cleanliness of the surface: comparison between Electron Energy Loss Spectroscopy (E.E.L.S.) and I.S.S. studies on clean samples show that I.S.S. can still detect oxygen even when it is not detectable by E.E.L.S. Preliminary results on oxidation of Al (111) and Al (100) give oxidation curves in good agreement with those obtained by Auger Electron Spectroscopy (A.E.S.) and X Ray Photoemission Spectroscopy (X.P.S.)

Two-dimensional organization of a large number of stationary optical filaments by adaptive wave front control

We present an adaptive technique for the formation of multiple co-propagating and stationary filaments in a gaseous medium. Wavefront shaping of the initial beam is performed using a deformable mirror to achieve a complete two-dimensional control of the multi-spot intensity pattern in the laser focus. The spatial organization of these intensity spots yields reliable formation of up to five stable and stationary filaments providing a test bed for fundamental studies on multiple filamentatio

Variability of sulfate signal in ice core records based on five replicate cores

International audienceCurrent volcanic reconstructions based on ice core analysis have significantly improved over the past few decades by incorporating multiple-core analyses with a high temporal resolution from different parts of the polar regions into a composite common volcanic eruption record. Regional patterns of volcanic deposition are based on composite records, built from cores taken at both poles. However, in many cases only a single record at a given site is used for these reconstructions. This assumes that transport and regional meteorological patterns are the only source of the dispersion of the volcanic products. Here we evaluate the local-scale variability of a sulfate profile in a low-accumulation site (Dome C, Antarctica), in order to assess the representativeness of one core for such a reconstruction. We evaluate the variability with depth, statistical occurrence, and sulfate flux deposition variability of volcanic eruptions detected in five ice cores, drilled 1 m apart from each other. Local-scale variability, essentially attributed to snow drift and surface roughness at Dome C, can lead to a non-exhaustive record of volcanic events when a single core is used as the site reference , with a bulk probability of 30 % of missing volcanic events and close to 65 % uncertainty on one volcanic flux measurement (based on the standard deviation obtained from a five-core comparison). Averaging n records reduces the uncertainty of the deposited flux mean significantly (by a factor 1/ √ n); in the case of five cores, the uncertainty of the mean flux can therefore be reduced to 29 %