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61.
V. Rusanov H. Winkler C. Ober A.X. Trautwein 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):191-198
M?ssbauer studies were performed on single crystals of guanidinium nitroprusside with different orientations of their principal
crystallographic axes (a, b, c) with respect to the incident radiation. The markedly anisotropic Lamb-M?ssbauer factor f
LM
, i.e.
f
LM
(a) = 0.118(8), f
LM
(b) = 0.174(8), f
LM
(c) = 0.202(8) is in contrast to that of nitroprussides with inorganic anions. The observed anisotropy is ascribed to the anisotropic
vibrational mean-square displacement of the nitroprusside anions as a whole which is due to the specific packing of both,
anions and cations, as well as the very weak chemical bonding between the ions, typical only for guanidinium nitroprusside.
The vibrational anisotropy of iron atoms in barium nitroprusside that has been observed by X-ray structural investigations
has a different origin and therefore does not result in an anisotropic Lamb-M?ssbauer factor. We have also investigated metastable
states in guanidinium nitroprusside that have been populated by means of incoherent irradiation from light-emitting diodes.
With a specific orientation of the guanidinium nitroprusside single crystal a population of the metastable states up to 26%
could be achieved. Populations of comparable size on lithium, sodium and potassium nitroprussides have only been reached using
coherent laser irradiation.
Received 15 December 1998 and Received in final form 3 March 1999 相似文献
62.
M. Pinterić M. Miljak N. Biškup O. Milat I. Aviani S. Tomić D. Schweitzer W. Strunz I. Heinen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):217-225
We report a detailed characterization of the magnetism and AC transport in single crystals of the organic conductor -(BEDT-TTF)2Cu[N(CN)2]Cl by means of magnetic anisotropy measurements and low-frequency dielectric spectroscopy. Magnetic anisotropy obeys Curie-Weiss
law with negative Curie-Weiss temperature in the temperature range 300 K-70 K. An antiferromagnetic transition with concomitant
canted antiferromagnetic state is established at 22 K. A large hysteresis in the spin-flop transition and magnetic field reversal
of the weak ferromagnetic magnetization are documented for the first time. A broad dielectric relaxation mode of moderate
strength () emerges at 32 K, and weakens with temperature. The mean relaxation time, much larger than that expected for single-particle
excitations, is thermally activated in a manner similar to the DC conductivity and saturates below 22 K. These features suggest
the origin of the broad relaxation as an intrinsic property of the weak ferromagnetic ground state. We propose a charged domain
wall in a random ferromagnetic domain structure as the relaxation entity. We argue that the observed features might be well
described if Dzyaloshinsky-Moriya interaction is taken into account. A Debye relaxation with similar temperature dependence
was also observed and seems to be related to an additional ferromagnetic-like, most probably, field-induced phase. We tentatively
associate this phase, whose tiny contribution was sample dependent, with a Cu2+ magnetic subsystem.
Received 15 June 1998 and Received in final form 1 February 1999 相似文献
63.
The aim of this paper is to evaluate the influence of the surface free energy upon the propagation of the eigenmodes of structures, by studying successively (a) the Rayleigh wave for an elastic half-space, (b) the Lamb waves for an elastic layer, and (c) the guided modes for a tri-layer structure (e.g., metal/adhesive/metal). The surface free energy is a parameter which appears in the jump conditions of stresses and displacements at each interface, and which consequently modifies the eigenmodes, solutions of the boundary conditions system. As expected, the Rayleigh wave is dispersive and its velocity increases when the surface free energy increases. In the same way, the velocity of Lamb waves also increases except at normal angle of propagation where the surface free energy does not arise. Moreover, near the Rayleigh angle, the behaviour of the A0 and S0 Lamb modes varies strongly according to the surface free energy. Similar results are observed for the tri-layer structure. 相似文献
64.
A. López-Ortega 《General Relativity and Gravitation》2006,38(5):743-771
We extensively study the exact solutions of the massless Dirac equation in 3D de Sitter spacetime that we published recently. Using the Newman-Penrose formalism, we find exact solutions of the equations of motion for the massless classical fields of spin s= 12,1,2 and to the massive Dirac equation in 4D de Sitter metric. Employing these solutions, we analyze the absorption by the cosmological horizon and de Sitter quasinormal modes. We also comment on the results given by other authors. 相似文献
65.
A. López-Ortega 《General Relativity and Gravitation》2006,38(12):1747-1770
Using the monodromy method we calculate the asymptotic quasinormal frequencies of an electromagnetic field moving in D-dimensional Schwarzschild and Schwarzschild de Sitter black holes (D ≥ 4). For the D-dimensional Schwarzschild anti-de Sitter black hole we also compute these frequencies with a similar method. Moreover, we calculate the electromagnetic normal modes of the D-dimensional anti-de Sitter spacetime. 相似文献
66.
BEPCⅡ500MHz超导腔是BEPCⅡ储存环的关键设备,腔中高次模的分布和阻抗将很大程度上直接影响束流的稳定.因此,研究BEPCⅡ超导腔的高次模分布和高次模吸收器的吸收效果对实现BEPCⅡ指标至关重要.为此,通过改变高次模吸收器的位置、铁氧体吸收材料的长度、厚度以及腔的渐变过渡波导的角度等对BEPCⅡ超导腔高次模阻抗抑制进行了模拟优化研究,从而找到并确定了吸收器对高次模阻抗抑制的最优值.同时,为证实模拟计算结果的正确性,对BEPCⅡ超导模型腔进行了高次模分布和吸收测量,得到了与计算一致的结果.结果表明,经过细致优化腔的高次模吸收器,腔中大部分高次模被深度吸收了,那些具有潜在危险的高次模阻抗值降到了阈值以下,满足BEPCⅡ束流阻抗要求 相似文献
67.
在一新型三维轴对称腔CO2激光器的基础上提出了一种对此激光器位相锁定的方法。通过在输出镜后放置一具有反射和整形作用的凹凸镜,让作为输出注入光束的谐振腔优先起振。此腔输出的光束到达凹凸镜时被其反射。利用重新定义光斑半径的方法,证明此光束能够覆盖其他放电管输出的光束,根据几何光学,此光束能反射进入各个放电管。然后利用光子简并度的概念证明了反射光束能够控制腔内的本征模式,并且数值分析了注入锁定后腔内模式匹配。在反射注入锁定的情况下,给出了数值计算的光强输出及其模拟,结果证明经位相锁定后,激光器输出光束的质量有了很大的提高。 相似文献
68.
We propose a two-color scheme of atom waveguides and one-dimensional (1D) optical lattices using evanescent wave fields of different transverse modes around an optical micro/nano-fiber. The atom guide potential can be produced when the optical fiber carries a red-detuned light with TE01 mode and a blue-detuned light with HEll mode, and the 1D optical lattice potential can be produced when the red-detuned light is transformed to the superposition of the TE01 mode and HE11 mode. The two trapping potentials can be transformed to each other for accurately controlling mode transformation for the red-detuned light. This might provide a new approach to realize flexible transition between the guiding and trapping states of atoms. 相似文献
69.
70.
B. Sen B. Das P. Chatterjee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(2):211-216
Nonlinear dust acoustic solitary waves in a dusty plasma are studied for nonzero kinematic viscosity. Sagdeev’s potential
can be obtain upto any order in ϕ. The existence of soliton solution is determined by pseudopotential approach. It is seen
that the electron inertia has a significant effect on the existence of solitary waves in presence of kinematic viscosity. 相似文献