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当k的值不大时(例如k≤4),诸系数γiγi*,βkρ,βkρ*易于手工计算。但对大的k值(例如k≥5),手工计算已非易事。利用著名的计算机代数软件:REDUCE[a],我们可以很容易地计算出诸系数γi,γi*,βkρ,βkρ*。 相似文献
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本文从广义协变的运动方程和麦克斯韦方程出发,导出了电子等离子体波各量的解析表达式。指出△ω=2ωp的等离子体波是完全简谐的。完全共振的条件由△ω=2ω(p0)[1+(e2(A2((1)2)+(A2((2)2))/(2m2c4)+(3e2A2(1)A2(2))/(m2c4)]-1/2 给出。
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本文计算了双星的辐射阻尼。按照广义相对论,在广义坐标变换下,星体的运动方程中出现的力是与坐标的选择有关的。不同坐标条件将原则上导致不同的阻尼力。现在人们已经成功地观察到双星辐射阻尼效应。这表明应该找出一个物理的坐标系。在这个坐标系中算出的阻尼力等于观察到的值。我们提出下面物理条件代替通常的坐标条件。这个条件就是不存在时间方向和纵向极化的引力波。这个条件在所要求的近似下决定了我们认为是物理的坐标系。在这个坐标系中得出双星公转周期p的变化为P=-6.5×10-12(m1m2)/M⊙2((m1+m2)/m⊙)-1/3。
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为了解释Au1-xNix合金(x=0.30—0.42)低温出现电阻率极小值的实验结果,本文提出一个低浓度自旋集团顺磁态合金的模型,得到自旋集团孤立近似下和自旋集团耦合作用下的电阻率公式,并和晶格散射的贡献(由Au80Ni20合金或Au-Cu合金的ρi(T)实验数据代替)联合起来,得到ρ(T)的计算曲线,和实验结果符合得很好。当Tmin,电阻率随温度增高而下降,主要是自旋集团孤立近似下的Kondo效应引起的。自旋集团之间的RKKY耦合作用对电阻率的贡献在低温时大,随着温度增高按1/T规律迅速减小,所以ρ(T)-ρi(T)实验值在相当宽温度范围出现logT关系。随着温度增高,晶格散射对电阻率的贡献将变得重要,当T=Tmin,电阻率出现极小值。
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实验研究了温度对液相外延石榴石磁泡薄膜中条状普通硬磁畴壁内的垂直布洛赫线(VBL)链解体临界面内磁场区间的影响。发现存在一对特征温度T(1)0 和 T(2)0(前者比后者略低但均高于室温),在从室温到T(2)0的每个温度T下,使VBL逐渐消失的面内磁场Hip都分布于一个与T有关的区间[Hip(1)(T), Hip(2)(T)]内,称为临界面内磁场区间:Hip<Hip(1)(T)时,VBL链保持不变;Hip(1)(T)< Hip < Hip(2)(T)时,随着Hip的增加,越来越多的VBL消失;Hip > Hip(2)(T)时,所有VBL都消失。Hip(1)(T),Hip(2)(T)及Hip(2)(T)-Hip(1)(T)均随T的升高而下降,前二者分别于T(1)0 和 T(2)0降为零。比值Hip(2)(T)/Hip(1)(T)随T的升高而升高,在低温段(包括室温)升高缓慢且约为21/2,在T(1)0附近急剧升高且至T(1)0时趋于∞。对以上结果做了理论分析。
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本文利用虚坐标方法研究了两个共线Kerr黑洞迭加的时空结构;首次得到了这种情况下视界以内的时空区域,并给出了2z0>(M12-a12)1/2+(M22-a22)1/2时内外无限红移面和奇点随z0变化的情况。由此我们可以看到,对于角动量平行及反平行的两个共线的全同Kerr解来说,当z0→(M2-a2)1/2时,尽管它们视界以外的时空结构分别趋于一个Kerr时空及一个Schwarzschild-NUT时空,但就整个时空结构而言,并非如此。同时,我们还可看到,当2z0>(M12-a12)1/2+(M22-a22)1/2时,Einstoin场方程存在无裸奇点(而不是没有奇点)的解。
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E. M. Darwish A. Abd El-Daiem M. M. Abd El-Wahab 《Physics of Particles and Nuclei Letters》2017,14(6):822-835
Single and double spin asymmetries in the elastic electron-deuteron (e-d ) scattering were investigated. The tensor-deuteron asymmetries T2i(i = 0, 1, 2) and the beam-vector-deuteron asymmetries T e 1i(i = 0, 1) were calculated and compared with the available experimental data. The sensitivity of the results for these spin asymmetries to the deuteron wave function has been investigated. The predicted asymmetries were found to be agree with one another and with experiment. It was found that, the double spin asymmetry T e 10 is much smaller than the T e 11-asymmetry. Therefore, in addition to the single tensor-deuteron asymmetry T20, the doubly beam-vector-deuteron asymmetry T e 11 can be used as an another tool for extracting the deuteron electromagnetic form factors. 相似文献
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The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb4As3 have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT
2 with huge and nearly field-independent coefficient A ≈ 3 μΩ cm/K2 is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the
isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m
0 and a charge-carrier mean-free path of 215 ? are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed. 相似文献
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A system of equations and inequalities that allows one to determine the constraints on central density ρ c and the chemical composition, which is governed by parameter μ e , of the white dwarf RX J0648.0- 4418 with a record short period of rotation T = 13.18s and mass m = (1.28 ± 0.05)m⊙, has been derived. The analysis of numerical solutions of this system reveal a complex dependence of μ e on ρ c . The intervals of variation of μ e and ρ c are as follows: 1.09 ≤ μ e ≤ 1.21 and 9.04 ≤ μ e /ρ0 ≤ 103 (ρ0 = 0.98 × 106 g/cm3). This range of μ e values suggests that the white dwarf RX J0648.0-4418 is not made of pure hydrogen and should contain 9–21% of heavy elements. Calculations have been performed with the equation of state of an ideal degenerate electron gas. Approximate analytic expressions (with an accuracy of 10-3) for the minimum period T min and mass m of the white dwarf are obtained. It is demonstrated that the white-dwarf mass is almost doubled (compared to the case of no rotation at a fixed central density) as period T approaches T min. 相似文献
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A.G. Mostafa E.K. Abdel-Khalek W.M. Daoush S.F. Moustfa 《Journal of magnetism and magnetic materials》2008
Polycrystalline La0.70Sr0.30Mn1−yFeyO3 (0.05?y?0.07) samples are prepared by the co-precipitation method and have been studied. The substitution of Mn3+ by Fe3+ reduces the number of available hopping sites for the Mn eg(↑) electron and suppresses the double exchange (DE), resulting in the reduction of the metal–semiconductor transition temperature (TP) and the flux density saturation (Bs). Low-temperature resistivity (ρ) data (below TP) well fit with the relation ρ(T)=ρ0+ρ2T2, indicating the importance of grain/domain boundary effects and electron–electron scattering processes in the conduction of these materials. On the other hand, at high temperature (TP<T<θD/2) conductivity data satisfy the variable range hopping (VRH) model. For T>θD/2 the small polaron hopping model is more appropriate than the VRH model. 相似文献
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本文对高β等离子体中槽纹模低杂漂移不稳定性从迴旋动力论出发作了较系统的研究,考虑了密度梯度、电子的温度梯度以及磁场梯度漂移的共振效应,解析结果与数值计算取得了完全一致的结论。发现,当温度梯度方向与密度梯度方向相反时,与温度梯度有关的电子的磁漂移共振起不稳定作用,使模的增长率比温度均匀时明显增大;而当方向相同时,温度梯度效应加强电子磁漂移共振的稳定作用,减少模的增长率。在两种情形中随着β值的增大,模的增长率都会减小,而且最大增长率向长波方向移动。电子温度各向异性对模的性质没有影响。
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J.P. Benoit G. Hauret Y. Luspin A.M. Gillet J. Berger 《Solid State Communications》1985,54(12):1095-1098
A Brillouin scattering study of the commensurate—incommensurate transition in K2SeO4 submitted to a hydrostatic pressure was performed. It was found that an increasing pressure lowers the transition temperature (dTi/dPi = ?59 K/GPa). The strong anomalies of velocity and damping of the longitudinal acoustic wave propagating along [0 0 1] are weakly affected when pressure acts. The effect of pressure on these anomalies has been calculated on the basis of the lowest order couplings eQ2 and e2Q2 between strain e and order parameter Q. 相似文献
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The thermal conductivity of LaAl2 and of two dilute (La, Ce)Al2 alloys was measured in the normal state between 0.4 and 8 K. From the lattice conductivity of LaAl2 a high dislocation densityN d caused by the arc melting process can be inferred. After annealingN d is reduced by an order of magnitude. For the (La, Ce)Al2 samples minima are observed at 5 K in theW e ·T vs.T curves (W e =electronic thermal resistivity). Below 1 K the quantityW e ·T is linear in (— lnT). The electronic Lorenz ratioL e (T)=ρ(T)/W e (T) ·T shows a maximum at 2 K with a value 23% aboveL e (0). It is for the first time that this Kondo anomaly is established in its full temperature dependence. 相似文献
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N. A. Inogamov V. V. Zhakhovsky Yu. V. Petrov V.A. Khokhlov S. I. Ashitkov K. V. Khishchenko K. P. Migdal D. K. Ilnitsky Yu. N. Emirov P. S. Komarov V. V. Shepelev C.W. Miller I.I. Oleynik M.B. Agranat A.V. Andriyash S.I. Anisimov V.E. Fortov 《等离子体物理论文集》2013,53(10):796-810
Fundamental physical phenomena in metals irradiated by ultrashort laser pulses with absorbed fluences higher than few tens of mJ/cm2 are investigated. For those fluences, laser‐produced electron distribution function relaxes to equilibrium Fermi distribution with electron temperature Te within a short time of 10‐100 fs. Because the electron subsystem has Te highly exceeding much the ion subsystem temperature Ti the well‐known twotemperature hydrodynamic model (2T‐HD) is used to evaluate heat propagation associated with hot conductive electron diffusion and electron‐ion energy exchange. The model coefficients of electron heat conductivity κ (?, Te, Ti) and electron‐ion coupling parameter α (?, Te) together with 2T equation of state E (?, Te, Ti) and P (?, Te, Ti) are calculated. Modeling with 2T‐HD code shows transition of electron heat wave from supersonic to subsonic regime of prop‐agation. At the moment of transition the heat wave emits a compression wave moving into the bulk of met al. Nonlinear evolution of the compression wave after its separation from the subsonic heat wave till spallation of rear‐side layer of a film is traced in both 2T‐HD modeling and molecular dynamics (MD) simulation. For fluences above some threshold the nucleation of voids in frontal surface layer is initiated by strong tensile wave following the compression wave. If the absorbed fluence is ~30 % above the ablation threshold than void nucleation develops quickly to heavily foam the molten met al. Long‐term evolution of the metal foam including foam breaking and freezing is simulated. It is shown that surface nano‐structures observed in experiments are produced by very fast cooling of surface molten layer followed by recrystallization of supercooled liquid in disintegrating foam having complex geometry. Characteristic lengths of such surface nanostructures, including frozen pikes and bubbles, are of the order of thickness of molten layer formed right after laser irradiation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献