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A method is proposed to find the digital input signals to enter in nonlinear acoustical systems (power amplifiers, transducers, etc.) in order to obtain desired arbitrary response signals. The searched input signals are found by performing a Monte Carlo search guided by a simulated annealing process applied to a hidden model with a small number of parameters. The physical system is actually used in the optimization procedure, in a real-time manner, so that no theoretical model of the system response is required. The main aspects of the algorithm are described and illustrated with several examples. 相似文献
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Doubly‐Charged Xe Ions Evidenced by Time Resolved RPA Measurement in the Far Field Plume of a Low‐Power HET
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A low power Hall Effect Thruster (HET), based on a permanent magnet circuit, was investigated in the GREMI laboratory facility. The thruster operated in the working range between 50 and 300 W and the previously measured thrust is between 4 and 16 mN for an anodic efficiency respectively between 15% and 27%. The pulsed character of the thruster current is an important feature of this HET. The ion current's bursts are recorded at 30 and 70 cm from the exit plane in the thruster plume and are time‐resolved, which lead to a preliminary analysis of the time of flight (TOF) phenomena. This paper presents a detailed study of these bursts of ion current in the plume. The total ion current is shown to be a superposition of 2 distinct contributions of charged species. In complement, a controlled single current interruption in stable anodic current condition leads to exactly the same features than in oscillating mode. This crucial verification garantees the validity of the time of flight origine of the two distinct contributions. Then, the slower one is the more intense and is proportional to the ion Xe+ current whereas the faster one could be attributed either to doubly‐charged Xe++ or to superfast Xe+. The work presents a way to determine unambiguously the nature of the fast contribution by recording the Retardated Potential Analyser (RPA) signals at various repelling grid potentials with respect to time. The energy distribution of the 2 wellseparated contributions are reconstructed and confirms the contribution of doubly‐charged xenon ions (Xe++) in the plume. This way of RPA collecting data and interpretation presents the main advantage tobe an easy way for the identification of the nature of the charged species in the plume. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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P. Gibert 《Journal of sound and vibration》1984,97(3):499-511
New methods of analysis of slender bodies in the low- and medium-frequency ranges are introduced. In the medium-frequency range, the modes can be expected to be very oscillatory along the axis of the body. For this reason, the use of standard numerical calculation methods, such as the finite element method, is accompanied by severe practical difficulties. The alternative technique proposed here is of W.K.B.J. type, well-known in quantum mechanics. It is shown in particular that in the medium-frequency range, there are two types of modes: global modes and spatially localized modes. 相似文献
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The performance of the most common and also some other less common CE buffers has been tested for the pKa determination of several types of compounds (pyridine, amines, and phenols). The selected buffers cover a pH ranging from 3.7 to 11.8. Whereas some buffers, like acetic acid/acetate, BisTrisH+/BisTris, TrisH+/Tris, CHES/CHES-, and CAPS/CAPS- can be used with all type of analytes, others like ammonium/ammonia, butylammonium/butylammonia, ethylammonium/ethylammonia, diethylammonium/diethylammonia, and hydrogenphosphate/phosphate are not recommended because they interact with a wide range of compounds. The rest of the tested buffers (dihydrogenphosphate/hydrogenphosphate, MES/MES-, HEPES/HEPES-, and boric acid/borate) can show specific interactions depending on the nature of the analytes, and their use in some applications should be restricted. 相似文献
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Marie Violay Benoit Gibert Pierre Azais Philippe A. Pezard Gérard Lods 《Transport in Porous Media》2012,91(1):303-318
Electrical resistivity soundings are used by geophysicists to determine the structure and composition of the Earth’s crust
and mantle and to explore natural resources (ore, oil, gas, water). Their interpretations in terms of composition and in-situ
physical conditions depend mainly on laboratory measurements of electrical conductivity of rocks at simulated crustal conditions
of temperature, pressure, saturation and pore pressures. These measurements present a numbers of limitations, in particular,
in the case where conductive pore fluids are present, as in the case of deep reservoir conditions, where temperature exceeds
250 °C. Here, we present a new cell capable of measuring electrical conductivity of large saturated samples at confining pressure
up to 200 MPa, pore pressure up to 50 MPa, and temperature up to 500 °C. The measurement cell has been developed in a commercial,
internally heated, gas pressure apparatus (Paterson press). It is based on the concept of “guard ring” electrode, which is
adapted to samples that are jacketed by a very conductive, metallic material. Numerical modeling of the current flow in the
electrical cell allowed defining the optimal cell geometry. Calibration tests have been performed on Fontainebleau sandstones
saturated with electrolytes of different conductivities, up to 350 °C. The resulting electrical formation factor and temperature
dependence of electrical conductivity are in very good agreement with previous studies. This new cell will improve the exploration
and exploitation of deep fluid reservoirs, as in unconventional, high enthalpy geothermal fields. In particular, the investigations
address possible effects of fluid-rock interactions on electrical resistivity of a reservoir host rock. 相似文献
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Fabien Gibert Dimitri Edouart Claire Cénac Florian Le Mounier 《Applied physics. B, Lasers and optics》2014,116(4):967-976
We report on the development and the demonstration of a two-wavelength single-frequency laser oscillator based on Ho:YLF crystal. This laser is especially suitable for application as a transmitter in differential absorption lidar (DIAL)/integrated path differential absorption (IPDA) measurements of atmospheric carbon dioxide (CO2) using the R30 CO2 absorption line at 2,050.967 nm. The oscillator consists in a fiber-coupled and free-space solid-state hybrid system and can be used in high-energy middle-rate or moderate-energy high-rate configurations. The latter produced On and Off sequentially single-frequency laser pulses with 13 mJ of energy at a repetition rate of 2 kHz and pulse duration of 42 ns. The pulse energy and frequency stabilities are specially documented in free-running, single-frequency and two-frequency seeding single-mode operations. Standard deviation is 7.7 % for pulse energy and 2 MHz for frequency stability for the two-wavelength seeding operation. Allan variance plot shows that frequency fluctuations are reduced below 70 kHz for 10 s of averaging which is suitable for accurate CO2 DIAL or IPDA measurements. 相似文献
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Sarah HisChristophe Meyer Janine Cossy Gibert EmericAlfred Greiner 《Tetrahedron letters》2003,44(47):8581-8584
In the presence of trifluoroacetic acid, ketoxime benzyl carbonates undergo a Beckmann rearrangement to the corresponding amides. This reaction was translated to a solid support by immobilizing oximes in the form of mixed carbonates derived from hydroxymethylpolystyrene in order to produce a diversity of amides with high efficiency. 相似文献