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981.
The operation of a torsional oscillator for detection, of flow-driven textural transitions in, 3He-A is described. The detection technique, tracking the shift of the resonant frequency of the torsional oscillator, allows us to observe textural changes and the presence of vortices in zero magnetic field. It relies on. the anisotropic superfluid density of 3He-A and its change due to reorientation of the Î-texture caused by counterflow.  相似文献   
982.
In this paper the problem of determining a manipulator design so that its workspace corresponds to a prescribed workspace is considered. Two different strategies, resulting in two different types of optimization problem are considered. The first strategy attempts to obtain a good overall approximation to the prescribed workspace and results in an unconstrained optimization problem. The second strategy entails designing a manipulator so that its workspace fully encloses the prescribed workspace and results in a constrained optimization problem. Two specific formulations of the constrained problem are proposed. The first constrained problem simply aims to fit the manipulator workspace as exactly as possible to the prescribed workspace, while still ensuring that the prescribed workspace is fully enclosed. The second constrained optimization formulation is used to design a manipulator, the workspace of which fully encloses the prescribed workspace, but which is also well‐conditioned throughout the workspace with respect to some performance measure. The particular manipulator used to illustrate and evaluate these formulations is a simple 2‐dof planar parallel manipulator, and the final formulation is also applied to a 3‐dof planar parallel manipulator. Although the manipulators studied here are simple, the objective of this study is to obtain a robust numerical methodology which can be extended to more practical and complex manipulators. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
983.
The thick film of Zn-Sb-O was prepared by coating the paste of nanoparticles mixture (Sb2O3:ZnO=1:3) on the alumina substrate, followed by sintering at 500-900 °C for 2 h in air. The electrical resistance and gas-sensing properties to benzene, alcohol and acetone of Zn-Sb-O films were found to be dependent on the change of phase structure caused by sintering temperature.  相似文献   
984.
The spatial structure of visible emission from plasma of a transverse nanosecond pulsed electric discharge in a gas-filled diode with a hollow (slit) cathode has been experimentally studied. A relation is established between the regime of electron energy relaxation and the plasma-beam discharge structure formation. High values of the electron emission coefficient are observed in the experiment, which cannot be explained using the notion of electron emission from a cathode bombarded by fast heavy particles.  相似文献   
985.
Broadband chaotic oscillations were monitored in a depressed potential collector of a traveling-wave oscillator (TWO). This signal appears due to the oscillations of a virtual cathode, which is formed in the spent electron beam under the action of retarding fields existing in the multistage depressed collector.  相似文献   
986.
The optical properties of heterostructures comprising InAs/InGaAsN quantum wells in strain-compensated GaAsN/InGaAsN superlattices have been studied. It is demonstrated that, using such superlattices of various design and thickness and with additional InAs monolayer spacers, it is possible to control the wavelength of room-temperature emission from InGaAsN quantum wells within 1.3–1.6 μm without deteriorating the output radiation characteristics, which opens additional prospects for the development of lasers on GaAs substrates for telecommunication applications.  相似文献   
987.
A considerable (~1.4-fold) increase in the average output power of a chemical current source has been achieved by means of a periodic pulsed manipulation of the load. A scheme used for the pulse-train loading is presented and mechanisms ensuring an increase in the average output power of the current source are considered.  相似文献   
988.
This paper considers problems on the rolling of rigid driven and driving cylinders slipping on a compactible viscoelastic base. As a result of the investigation of the process of propagation of viscoelastic decaying strain waves in a deformable medium caused by a cylinder rolling over it and the action of the sliding friction forces, formulas and calculation algorithms have been obtained for determining the indices of the stressed-strained state and compactness of the base, the rolling resistance of the driven and diving cylinders, and the driving force of the driving cylinder. Calculations of these indices have been performed for the cases of cylinders rolling over a soil whose viscoelastic properties have been investigated experimentally. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 5, pp. 122–132, September–October, 2007.  相似文献   
989.
Numerical simulations of the heating of a carbon dust particle (pellet) in hydrogen plasma showed that the character of heating depends in a threshold manner on the initial temperature of the pellet. The heating proceeds at a high rate if the initial temperature is above a certain threshold (“hot” regime), and at a much lower rate for an initial temperature below this threshold (“cold” regime). An important factor in this process is thermionic emission, which leads to positive charging of a pellet in hydrogen plasma due to electron emission from the surface in the hot regime. In the cold regime, the pellet acquires a negative charge that retards the electron flux from plasma to the particle. A method for the experimental observation of this effect is proposed.  相似文献   
990.
We have studied the structure and thermo emf of a nanotubular carbon deposit formed in electric arc discharge plasma. The deposit contains flocky granules with dimensions of 15–20 μm within a 20–60 μm-thick layer on the substrate surface. This deposit is characterized by a sufficiently high thermo emf (60 μV/K) and electric conductivity (600 Ω−1 m−1).  相似文献   
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