共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Dr. Göran Niklasson 《Zeitschrift für Physik B Condensed Matter》1972,14(2):138-184
Numerical calculations of phonon dispersion curves and phonon damping in solid Argon are presented. Particular emphasis is
given to the transition between the low-frequency hydrodynamic regime, where collective effects are dominant, and the high-frequency
“zero sound” regime, where phonons propagate essentially as single particles. An important quantity in this context is the
Peierls' collision operator which is treated through a single relaxation time approximation. The calculations are based on
an MLJ (6.12)-potential, and the effects of non-linear dispersion and anisotropy are fully taken into account. This article
contains also a summary of the underlying theoretical work which has been presented in more detail in earlier publications.
Supported by the Swedish Council for Atomic Research. 相似文献
3.
Dispersion of the high-frequency sound velocity in the aqueous solution of 4-methylpyridine with the concentration 0.06 mole
fraction corresponding to the singular point in the temperature-concentration phase diagram is studied. Along with observation
of positive dispersion of the speed of sound in going over from ultrasound to hypersound frequencies (5.4 MHz to 4.8 GHz),
negative dispersion (a decrease in velocity with increasing frequency) was also observed in a narrow interval of hypersound
frequencies from 4.8 to 6.1 GHz. 相似文献
4.
5.
J. Schuyer 《Molecular physics》2013,111(6):597-599
The quantum yields of naphthalene vapour fluorescence at 225°c and of phenanthrene vapour fluorescence at 365°c excited by the Hg 313 μ line are independent of concentration up to 0·014 and 0·007 moles/l. respectively; this is attributed to fast dissociation relaxation of the excimer at these temperatures. The fluorescence of naphthacene vapour excited at temperatures of 355–435°c by the group of Hg lines at 365 μ decreases with increasing pressure at pressures below that at which absorption of the incident radiation is virtually complete, and is attributed to a combination of self-quenching and reabsorption of fluorescence. An analysis of the data for the limiting cases of complete and negligible fluorescence reabsorption provides upper and lower limits for self-quenching constant which are consistent with unit collisional quenching efficiency and a lifetime of 5·3 ± 2·2 + 10-9 sec at 355°c. 相似文献
6.
7.
We have measured the sound velocity of liquid Te70Se30, Te50Se50 and Te30Se70 mixtures and obtained their adiabatic compressibility βs. There appear prominent maxima in the temperature variations of βS. It is concluded that the pressure-induced semiconductor-to-metal transition previously observed for liquid Te-Se mixtures is associated with the structural change from Se-like loosely packed to Te-like densely packed structure. 相似文献
8.
We report the first measurements of the sound velocity in liquid La, Ce, Pr and Yb and deduce the adiabatic and isothermal compressibilities. The temperature coefficient of the sound velocity in liquid Ce is positive, which we interpret as support for the suggestion that there is increasing delocalization of the 4f electrons in the liquid state. 相似文献
9.
理论上分析了超声光栅衍射和液体表面波光栅衍射,得到了表面波光栅衍射图样与表面波参数的解析关系.实验上得到清晰的衍射图样,利用表面波光栅衍射法测量了液体表面波波速,实验结果与理论值误差不超过1%. 相似文献
10.
设计并搭建了超声光栅,观察了激光经过光栅形成的衍射斑纹,测量了声速;并利用超声光栅测定了不同温度、不同浓度的NaCl溶液中的声速,给出了声速-水温和声速-溶液浓度的依赖关系.水的温度每升高1℃,3.974 MHz的超声波的声速增加2.09 m/s,16.574 MHz的超声波的波速增加2.04m/s;声速随着NaCl溶液浓度的增大线性增加,NaCl溶液浓度每升高1%,3.974 MHz的超声波声速增加13.637 m/s,16.574 MHz的声波声速增加11.757 m/s.在此基础上,分析了不同频率的超声波对实验规律的影响,认为不同频率的超声波在相同条件下测量的溶液中声速大小的不同源于测量的随机误差. 相似文献
11.
J.B. Mehl 《Physics letters. A》1974,47(1):15-16
An explanation of the decrease of the velocity of second sound due to heat currents in liquid helium is given. The explanation is based on Hall and Vinen's theory of the interaction of second sound with vortex lines. The predictions are in reasonable agreement with experiment. 相似文献
12.
The paper presents an analysis of energy fluctuations of high-frequency (2–4.5 kHz) sound signals propagating in a shallow water in the presence of nonlinear (soliton-like) internal waves (2006 Shallow Water experiment, US Atlantic shelf). Signals were received by three single hydrophones in different directions at distances of ~4, ~12, and ~5 km from the source. The angle between the first two acoustic tracks was ~15°. The third track was almost an extension of the first and was on the other side of the source. A relatively short (one to two solitons) nonlinear internal wave packet first moved approximately along the first two tracks and then along the third track. It is demonstrated that in the presence of solitons on the track in the frequency spectrum of energy fluctuations, there is an isolated frequency that depends, in particular, on the angle between the soliton front and the acoustic track. The experimental results agree well with the theory previously proposed by the authors, where the occurrence mechanism of fluctuations is explained using the ray approach. 相似文献
13.
R. J. Wojciechowski 《Zeitschrift für Physik B Condensed Matter》1986,63(2):169-171
The influence of the quasiparticle-phonon interaction on a sound velocity in heavy fermion systems in the presence of an external magnetic field is studied. It is shown that for temperatures less than spin fluctuation temperatureT
* the change of sound velocity depends strongly on the detailed shape of the quasiparticle density of states. 相似文献
14.
Large amplitude quantum oscillations of the longitudinal sound velocity, |ΔV/V| ~ 10-3, were observed in single crystal zinc. The effective masses associated with the ‘cigar’ and ‘butterfly’ were determined from the temperature dependence of the amplitudes of the oscillations in the region 1.5?T?4.2K. The experimental data are compared with the results of theoretical treatments. 相似文献
15.
Hideji Yamada 《Solid State Communications》1981,37(11):841-843
The longitudinal sound velocity in an itinerant-electron antiferromagnet is studied, using a jellium model for the ions and a two-sub-band model for the itinerant electrons with an energy gap caused by the antiferromagnetic spin ordering. It is shown that the longitudinal sound velocity decreases with decreasing temperature, due to the electron-photon interaction. The exchange interaction between itinerant electrons is seen to play a particularly important role in the phonon softening phenomena for such a system; and although the model is a great simplification of reality it gives reason to believe that the observed elastic anomalies in the face-centred-cubic 3d transition metal alloys are directly related to their tendency towards antiferromagnetism. 相似文献
16.
G. N. Kuznetsov V. M. Kuz’kin S. A. Pereselkov D. Yu. Prosovetskiy 《Acoustical Physics》2016,62(5):559-574
We describe an algorithm for estimating the radial component of the velocity of a sound source based on information about frequency shifts of the interference maxima of the field and consider the problem of its interference immunity. We obtain the limit estimate for the value of the input signal/noise ratio when the algorithm is working effectively. We present results of computational and field experiments using a single receiver and a horizontal array. We compare the experimental data with analytic interference immunity estimates. 相似文献
17.
18.
Sound velocity and density were measured in six binary liquid mixtures namely,n-heptane+toluene (I);n-heptane+n-hexane (II); toluene+n-hexane (III); cyclohexane+n-heptane (IV); cyclohexane+n-hexane (V), andn-decane+n-hexane (VI) at 298.15 K. The experimental isothermal compressibility has been evaluated from measured values of density and
sound velocity. The isothermal compressibility of these mixtures has been calculated theoretically using different models
for the hard sphere equation of state and also using Flory’s statistical theory. The computed values of isothermal compressibility
were also compared with the experimentally evaluated values. A satisfactory agreement has been observed. 相似文献
19.
Abstract The pressure dependence of the refractive index n(P) and of the longitudinal acoustic velocities of 4.1 methanol-ethanol solution have been measured in a diamond anvil cell up to 8.1 GPa. We utilize Brillouin scattering methods for this determination and detect, in the same back scattering configuration, acoustic wave propagation parallel to the faces of the diamond anvils as well as along the incident laser radiation direction. We also deduce that the polarizability of the fluid is reduced by about 15% over the pressure range studied. 相似文献
20.
声速测量实验有关问题的研究 总被引:1,自引:3,他引:1
在物理实验中常利用在1对换能器之间形成的驻波测量声速.该实验是通过调节两换能器之间的距离观察接收换能器上声压(幅度或相位)变化规律获得波长.但部分文献在陈述换能器上声压随两换能器之间的距离的变化关系时,没有表达清楚或者表述错误.本文以一维黏性媒质波动方程为基础,详细给出了声压随两换能器之间的距离的变化关系. 相似文献