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991.
A. GAJEWSKI 《Journal of sound and vibration》2002,249(3):447-463
This paper presents a study on the influence of the physical non-linearity of material in creep conditions on vibration and stability of non-uniform annular plates subjected to a follower force radially distributed at the outer edge. The stability analysis requires first the calculation of a membrane stress distribution and then the application of the kinetic stability criterion, making use of small superposed vibrations. The differential equations of the membrane and vibration states have been integrated by means of the transfer matrix method which allowed the determination of the relationships between the real and imaginary parts of the complex frequency and compressive force (characteristic curves). The results have been presented in numerous figures. 相似文献
992.
Afraimovich É. L. Vodyannikov V. V. Voyeikov S. V. Perevalova N. P. Yakovets A. F. 《Radiophysics and Quantum Electronics》2002,45(10):741-757
Using the COPHASE method and the GPS interferometry method for travelling ionospheric disturbances, we analyze in detail the spatio-temporal properties of travelling wave packets (TWP) of total electron content (TEC) disturbances. The analysis is performed on the example of a clearest TWP manifestation observed in California, USA, in October 18, 2001, using the GLOBDET technique, developed at the Institute of Solar-Terrestrial Physics of the Siberian Branch of RAS for global detection and monitoring of natural and technogenic ionospheric disturbances on the basis of TEC variations retrieved from the global network of GPS receivers. In the time domain, TWPs are quasi-periodic TEC oscillations of duration about 1 h, period of 10–20 min, and amplitude exceeding that of the background TEC fluctuations by at least one order of magnitude. The velocity and direction of TWP motion are similar to those of mid-latitude mesoscale travelling ionospheric disturbances, as obtained earlier from the analysis of phase parameters of HF radio signals and the signals of geostationary satellites and discrete space radio sources. 相似文献
993.
R.S. Gonnelli A. CalzolariD. Daghero G.A. UmmarinoV.A. Stepanov P. FinoG. Giunchi S. CeresaraG. Ripamonti 《Journal of Physics and Chemistry of Solids》2002,63(12):2319-2323
We studied the voltage and temperature dependency of the dynamic conductance of normal metal-MgB2 junctions obtained either with the point-contact technique (with Au and Pt tips) or by making Ag-paint spots on the surface of MgB2 samples. The fit of the conductance curves with the generalized BTK model gives evidence of pure s-wave gap symmetry. The temperature dependency of the gap, measured in Ag-paint junctions (dirty limit), follows the standard BCS curve with 2Δ/kBTc=3.3. In out-of-plane, high-pressure point-contacts we obtained almost ideal Andreev reflection characteristics showing a single small s-wave gap Δ=2.6±0.2 meV (clean limit). 相似文献
994.
995.
We use the adiabatic hyperspheric expansion and the Faddeev decomposition of the wave function with only s-waves. We derive for a fixed hyperradius an integro-differential equation for the angular eigenvalue and wave function. The
correlations lower the interaction energy for N = 20 by about a factor of 5.
Received October 22, 2001; accepted for publication November 5, 2001 相似文献
996.
The high-temperature cubic phase of non-stoichiometric strontium ferrite SrFeOx (2.5≤x≤3.0) has been studied by in situ neutron powder diffraction in air over the temperature range 300-1273 K. The composition of SrFeOx changes within the range 2.56≤x≤2.81 from 1273 to 673 K, respectively.Rietveld refinements of the diffraction patterns show that the high-temperature cubic phase of SrFeOx is consistent with a face-centred Fm3c structure. This structure leads to agreement with previous density measurements. This cell allows the high-temperature structure of SrFeOx to be described in terms of a solid solution of the composition end members. Cubic SrFeOx at high temperature is found to closely obey Vegard's law. The density of cubic SrFeOx is also found to exhibit a linear relationship with composition. 相似文献
997.
TOPOLOGY DESIGN OF STRUCTURES SUBJECTED TO PERIODIC LOADING 总被引:5,自引:0,他引:5
C.S. JOG 《Journal of sound and vibration》2002,253(3):687-709
Although a lot of attention in the topology optimization literature has focused on the optimization of eigenfrequencies in free vibration problems, relatively little work has been done on the optimization of structures subjected to periodic loading. In this paper, we propose two measures, one global and the other local, for the minimization of vibrations of structures subjected to periodic loading. The global measure which we term as the “dynamic compliance” reduces the vibrations in an overall sense, and thus has important implications from the viewpoint of reducing the noise radiated from a structure, while the local measure reduces the vibrations at a user-defined point. Both measures bring about a reduction in the vibration level by moving the natural frequencies which contribute most significantly to the measures, away from the driving frequencies, although, as expected, in different ways. Quite surprisingly, the structure of the dynamic compliance optimization problem turns out to be very similar to the structure of the static compliance optimization problem. The availability of analytical sensitivities results in an efficient algorithm for both measures. We show the effectiveness of the measures by presenting some numerical examples. 相似文献
998.
Yu. A. Pobedin 《JETP Letters》2002,75(12):625-630
The states of a charged particle with a finite free path are determined in the field of a resonant electromagnetic wave. The exact resonance conditions, the modulation and beam instability mechanisms, the charge and current densities (Ohm's law) are obtained for the collisionless beam of resonance particles. Quantum theory of radiation is developed for the resonant adiabatic interaction between a particle and a wave taking into account the interaction with a constant magnetic field induced at the grating surface by the charge and nonresonant waves. The radiation power, the spectrum, and the range of generated frequencies are determined. The results obtained can be used in the plasma and solid-state theories and in electronics. 相似文献
999.
A. M. Zheltikov 《Optics and Spectroscopy》2002,93(2):286-290
A harmonic oscillator model is used to demonstrate the possibility of coherent control of acoustic vibrations of metal nanoparticles and thin films with sequences of femtosecond laser pulses. When the interval between the pulses in such a sequence is chosen equal to the oscillation period of the expansion mode of a nanoscale system, the relevant acoustic vibrations can be excited in a resonant and selective way. Sequences of femtosecond pulses with picosecond time intervals between the pulses are shown to be ideally suited for a resonant excitation and coherent control of acoustic modes of silver nanoparticles. 相似文献
1000.
INTERACTION OF A SPHERICAL SHOCK WAVE AND A SUBMERGED FLUID-FILLED CIRCULAR CYLINDRICAL SHELL 总被引:1,自引:0,他引:1
S. IAKOVLEV 《Journal of sound and vibration》2002,255(4):615-633
The complete three-dimensional interaction between a spherical shock wave and a submerged fluid-filled elastic circular cylindrical shell is considered. A hybrid analytical-numerical solving procedure is established. An exact analytical solution in the form of double Fourier series with time-depending coefficients is obtained for the hydrodynamic pressure. Displacements of a shell are approached analytically to reduce the problem to a set of systems of ordinary differential equations, which are treated numerically. Detailed analysis of the interaction is performed with emphasis given to the stress-strain state. A few important features of the interaction process have been found. In particular, it has been shown that the interior fluid not only substantially affects the magnitude of displacements and stresses, but also dramatically changes the nature of the interaction. It has been found that the absolute maximum of stresses can neither be caused by a direct action of a shock wave nor by a constructive superpose of elastic waves in the shell, but by the pressure wave propagating in the interior fluid. This fact seems to be of essential importance for engineering applications, especially when safety is a primary design concern. Another important result is that the maximum stresses are attained at large times, which makes use of early time asymptotics leading to incorrect results. The proposed semi-analytical approach seems to be computationally attractive and suitable for extensive numerical simulations. 相似文献