994 research outputs found
Improved charge injection device and a focal plane interface electronics board for stellar tracking
An improved Charge Injection Device (CID) stellar tracking sensor and an operating sensor in a control/readout electronics board were developed. The sensor consists of a shift register scanned, 256x256 CID array organized for readout of 4x4 subarrays. The 4x4 subarrays can be positioned anywhere within the 256x256 array with a 2 pixel resolution. This allows continuous tracking of a number of stars simultaneously since nine pixels (3x3) centered on any star can always be read out. Organization and operation of this sensor and the improvements in design and semiconductor processing are described. A hermetic package incorporating an internal thermoelectric cooler assembled using low temperature solders was developed. The electronics board, which contains the sensor drivers, amplifiers, sample hold circuits, multiplexer, analog to digital converter, and the sensor temperature control circuits, is also described. Packaged sensors were evaluated for readout efficiency, spectral quantum efficiency, temporal noise, fixed pattern noise, and dark current. Eight sensors along with two tracker electronics boards were completed, evaluated, and delivered
Cross-waves induced by the vertical oscillation of a fully immersed vertical plate
Capillary waves excited by the vertical oscillations of a thin elongated
plate below an air-water interface are analyzed using time-resolved
measurements of the surface topography. A parametric instability is observed
above a well defined acceleration threshold, resulting in a so-called
cross-wave, a staggered wave pattern localized near the wavemaker and
oscillating at half the forcing frequency. This cross-wave, which is stationary
along the wavemaker but propagative away from it, is described as the
superposition of two almost anti-parallel propagating parametric waves making a
small angle of the order of with the wavemaker edge. This
contrasts with the classical Faraday parametric waves, which are exactly
stationnary because of the homogeneity of the forcing. Our observations suggest
that the selection of the cross-wave angle results from a resonant mechanism
between the two parametric waves and a characteristic length of the surface
deformation above the wavemaker.Comment: to appear in Physics of Fluid
Recent developments in CID imaging
Readout of CID imaging arrays was first performed by injecting and detecting the signal charge from each sensing site in sequence. A new readout method, termed parallel injection, has been developed in which the functions of signal charge detection and injection have been separated. The level of signal charge at each sensing site is detected during a line scan, and during the line retrace interval, all charge in the selected line is injected. The parallel injection technique is well adapted to TV scan formats in that the signal is read out at high speed, line by line. A 244 line by 248 element TV compatible imager, employing this technique and including an on chip preamplifier, has been constructed and operation demonstrated
Parametrically excited helicopter ground resonance dynamics with high blade asymmetries
The present work is aimed at verifying the influence of high asymmetries in the variation of in-plane lead-lag stiffness of one blade on the ground resonance phenomenon in helicopters. The periodical equations of motions are analyzed by using Floquet's Theory (FM) and the boundaries of instabilities predicted. The stability chart obtained as a function of asymmetry parameters and rotor speed reveals a complex evolution of critical zones and the existence of bifurcation points at low rotor speed values. Additionally, it is known that when treated as parametric excitations; periodic terms may cause parametric resonances in dynamic systems, some of which can become unstable. Therefore, the helicopter is later considered as a parametrically excited system and the equations are treated analytically by applying the Method of Multiple Scales (MMS). A stability analysis is used to verify the existence of unstable parametric resonances with first and second-order sets of equations. The results are compared and validated with those obtained by Floquet's Theory. Moreover, an explanation is given for the presence of unstable motion at low rotor speeds due to parametric instabilities of the second order
Organisation dâun contrĂŽle de la pollution radioactive du lait. Cas des radioisotopes de courtes pĂ©riodes
Michon Georges. Organisation dâun contrĂŽle de la pollution radioÂŹ active du lait, cas des radioisotopes de courtes pĂ©riodes. In: Bulletin de l'AcadĂ©mie VĂ©tĂ©rinaire de France tome 116 n°6, 1963. pp. 283-285
Eloge de Jean LeplĂątre
Michon Georges. Ăloge de Jean LeplĂątre. In: Bulletin de l'AcadĂ©mie VĂ©tĂ©rinaire de France tome 137 n°2, 1984. pp. 216-218
Organisation dâun contrĂŽle de la pollution radioactive du lait « cas des isotopes de longue pĂ©riode »
Michon G. Organisation dâun contrĂŽle de la pollution du lait. «Cas des isotopes de longues pĂ©riodes». In: Bulletin de l'AcadĂ©mie VĂ©tĂ©rinaire de France tome 116 n°10, 1963. pp. 463-465
Teneur en radium 226 des laits en France I. â IntĂ©rĂȘt de l'Ă©tude
Michon Georges. Teneur en radium 226 des laits en France. I. IntĂ©rĂȘt de lâĂ©tude. In: Bulletin de l'AcadĂ©mie VĂ©tĂ©rinaire de France tome 118 n°4, 1965. pp. 141-143
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