共查询到20条相似文献,搜索用时 15 毫秒
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CHENBao-Zhen HUANGZu-Qia 《理论物理通讯》2004,42(3):431-434
The theoretical signal-pressure curves are calculated from approximate analytical solutions of the coupled equations describing the third order parametric wave mixing in a gas-filled capillary of femto-second laser pulses, The comparison with the corresponding experimental curves suggests that the following three factors exert important influences on the degree of fitting between the theoretical and experimental results: the walk-off, the phase modulation, and the third order harmonic of idler pulse. 相似文献
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A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic
obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation,
to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these
metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the
experimental and theoretical phonon dispersion curves. 相似文献
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MgO(001) surfaces prepared by three different heat treatments were studied by LEED. The first was the surface just after the vacuum cleavage; the second was that after the annealing of the first one at 300°C in UHV. The third was prepared by cleaving in air and heating in oxygen until the carbon Auger peak disappear. LEED I-V curves of the diffraction spots, (10), (11) and (20), were recorded and compared carefully. No remarkable difference corresponding to the preparing methods was found. Therefore, the atomic structures of the surfaces seem to be similar to each other. These experimental I-V curves were compared with the theoretical curves obtained by dynamical calculations for several grades of surface relaxation. The theoretical curves with no relaxation or with the smallest one in the calculation (2.5% expand) fitted best with the experimental curves. The experimental curves were also compared with the theoretical ones calculated for the rumpled surface. But no effect induced by the rumpling was found in the experimental curves. 相似文献
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S. V. Pavlov 《Moscow University Physics Bulletin》2013,68(2):139-142
A phenomenological model that describes the sequence of phase transitions in lawsonite is considered. A phase diagram of the model is constructed and theoretical temperature dependences of order parameters and inverse permittivity in low-symmetry phases are calculated. The comparison of theoretical curves with experimental results showed satisfactory qualitative agreement. 相似文献
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C.S. MenonR. Ramji Rao 《Journal of Physics and Chemistry of Solids》1972,33(6):1325-1334
The lattice dynamics and the anharmonic properties of the hexagonal Zirconium are worked out using Keating's approach. The dispersion curves are fitted using twelve second order parameters and the six second order elastic constants are evaluated. The ten third order elastic constants are calculated using five third order parameters. The experimental measurements on the pressure derivatives of the second order elastic constants in Zirconium are in good agreement with the calculated values. The low-temperature limit of the lattice thermal expansion is calculated which agrees well with the value obtained from thermal expansion data. The variation of the generalised GPs of the elastic modes with the direction of propagation is illustrated by polar diagram. 相似文献
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《Current Applied Physics》2014,14(1):93-98
We report on the third order non linearity of TiN/PVA nanocomposites. Linear and nonlinear optical properties were studied from theoretical and experimental method. Theoretical method involved Tichy and Ticha relation pooled with generalised Miller's rule. During the study dispersion of refractive index is analysed using the Wemple–Di Domenico single oscillator model. Z-Scan was used as the experimental tool. The results derived from theoretical method deviated greatly from the experimental. We believe that such incongruity is due to the SPR property of the TiN nanoparticle whose SPR peak almost coincides with the irradiated laser wavelength. 相似文献
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In this paper are studied the possibilities of investigating the structure of B+ -implanted Si single crystals by measuring X-ray rocking curves (the Bragg case). From the viewpoint of the dynamical diffraction of X-rays the structure of an implanted layer is described by a depth-profile of the statistical disorder of the layer structure and by a depth-profile of the relative change in the specific volume. These quantities take place in a modified form of the Takagi equations which are numerically computed for various values of the parameters of the layer, in order to trace their influence to the shape of the rocking curve. A great amount of free parameters and the complexity of their influence on the rocking curves make it impossible to fit the experimental and theoretical curves. On the basis of the theoretical study of the rocking curves the experimental curves measured on Si samples (dose 5×1015 cm–2 of B+, energy 50–200 keV) are interpreted qualitatively. 相似文献
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A mechanism is proposed to explain the double phase transitions found in K2PbCu(NO2)6 and Tl2PbCu(NO2)6. The higher temperature transition is caused by the cooperative Jahn-Teller effect. The lower temperature transition occurs as the fourth order anharmonic interaction restabilizes the lattice against instabilities caused by static distortions in the third order anharmonic interaction. Calculated curves of the order parameter and heat capacity reproduce all the features in the experimental curves. 相似文献
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Three related aspects of the magnetic phase diagram are presented here: the first deals with the disruption of the antiferromagnetic
order in the electron rich phase obtained by Ce doping, the second concern the role of Bi planes as a sink-buffer of carriers,
the third focuses the magnetization vs. temperature curves in a variety of different bilayer materials as seen by the muons
and discusses the “anomalous” behaviour in relation to theoretical predictions and neutron scattering data. 相似文献
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This work aims to validate a time domain numerical model for the nonlinear propagation of a short pulse of finite amplitude sound beam propagation in a tissue-mimicking liquid. The complete evolution equation is simply derived by a superposition of elementary operators corresponding to the 'one effect equation'. Diffraction LD, absorption and dispersion LAD, and nonlinear distortion LNL effects are treated independently using a first order operator-splitting algorithm. Using the method of fractional steps, the normal particle velocity and the acoustical pressure are calculated plane by plane, at each point of a two-dimensional spatial grid, from the surface of the plane circular transducer to a specified distance. The LA operator is a time convolution between the particle velocity and the causal attenuation filter built after the Kramers-Kroning relations. The LNL operator is a time-based transformation obtained by following an implicit Poisson analytic solution. The LD operator is the usual Rayleigh integral. We present a comparison between theoretical and experimental temporal pressure waveform and axial pressure curves for fundamental (2.25 MHz), second, third and fourth harmonics, obtained after spectral analysis. 相似文献
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在有效质量近似下,利用量子力学的密度矩阵理论,采用无限深势阱模型导出了三层球型量子点的三阶非线性光学极化率(自聚焦)的解析表达式.通过数值计算,分析了ZnS/CdSe/ZnS球型核壳结构量子点的三阶极化率(自聚焦)与量子点尺寸和入射光频率之间的关系.结果显示,量子点尺寸增大时,自聚焦效应三阶极化率(自聚焦)的峰值高度增大,峰值位置红移.本文的讨论为实验研究和实际应用提供了理论依据,对于光电器件的研究和改进有参考价值. 相似文献
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The temperature dependence of the mean square displacements for atoms on the (100) and (110) surfaces of chromium has been studied theoretically using the harmonic approximation. Calculations were carried out for crystals with periodic boundary conditions in two directions and free boundary conditions in the third direction using a Born-van Karman model with central interactions up to third nearest neighbors and non-central angular stiffness interaction between nearest and next nearest neighbors. The values of the force constants were chosen to give good fits to the elastic constants and to the bulk phonon dispersion curves in the three major directions [100], [110] and [111]. The ratio of the mean-square displacements at a surface to that in the bulk was calculated as a function of temperature for both the (100) and (110) surfaces. The theoretical, results are compared with the available experimental data from low-energy electron diffraction. 相似文献
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This article is devoted to an experimental validation of a theoretical model presented in an earlier contribution by the same authors. The non-linear forced vibrations of circular plates, with the excitation frequency close to the natural frequency of an asymmetric mode, are investigated. The experimental set-up, which allows one to perform precise measurements of the vibration amplitudes of the two preferential configurations, is presented. Experimental resonance curves showing the amplitude and the phase of each configuration as functions of the driving frequency are compared to the theoretical ones, leading to a quantitative validation of the predictions given by the model. Finally, all the approximations used are systematically discussed, in order to show the scope and relevance of the approach. 相似文献
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Y C Lee 《Ultrasonics》2001,39(4):297-306
This paper presents a new method of measuring dispersion curves of leaky Lamb waves propagating in a thin plate. The measurement system is based on a lens-less line-focus transducer and its defocusing measurement technique. A new waveform processing method known as V(f, z) method is introduced for analyzing the measured waveforms and for extracting the dispersion relation. For two thin-plate samples, namely a 150 microm thick alumina plate and a 320 microm thick stainless steel plate, the dispersion curves of several lower order modes of leaky Lamb waves have been experimentally determined in the frequency range of few to 25 MHz. The experimental dispersion curves have then been compared with the theoretical ones. Excellent agreement is observed. It is then verify that this method indeed provides a convenient and accurate way for experimentally measuring dispersion curves of leaky Lamb waves of thin-plate samples. 相似文献
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In this paper we report on both a theoretical model for the transients in optical bistability in a Fabry-Perot cavity and the corresponding experimental results. An analytical calculation permits to predict the shape of the transient curves and the order of magnitude of their time duration in the case of a slow sweep of the length of the cavity. The experiment, which uses the nonlinearity arising from a two-photon transition in rubidium, yields results in good agreement with the theoretical calculation.Work supported by the D.R.E.T. 相似文献