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1.
R. Tarumi  H. Nitta  H. Ogi  M. Hirao 《哲学杂志》2013,93(16):2140-2153
A complete set of elastic constants C ij and piezoelectric coefficients e ij of a La3Ga5SiO14 (langasite) single crystal was determined from 5.5 to 275.5?K by resonant ultrasound spectroscopy. Unlike a conventional crystal, the elastic constants C ij of the langasite crystal showed three types of temperature dependence: (i) monotonic elastic stiffening upon cooling (C 44 and C 14); (ii) monotonic elastic softening (C 66); and (iii) a stiffening-to-softening transition below 150?K (C 11, C 12, C 13 and C 33). In addition, a strong correlation between C 66 and the piezoelectric coefficient e 11 was confirmed. Group theoretical lattice dynamics analysis revealed that the novel phenomena of elastic softening and strong correlation are explained on the basis of two types of optical mode internal displacements which have the totally symmetric A 1 and doubly degenerated E symmetries in the point group D 3.  相似文献   

2.
We first show how, from the general 3rd order ODE of the form , one can construct a natural Lorentzian conformal metric on the four-dimensional space . When the function satisfies a special differential condition the conformal metric possesses a conformal Killing field, , which in turn, allows the conformal metric to be mapped into a three dimensional Lorentzian metric on the space ) or equivalently, on the space of solutions of the original differential equation. This construction is then generalized to the pair of differential equations, z ss =S(z,z s ,z t ,z st ,s,t) and z tt =T(z,z s ,z t ,z st ,s,t), with z s and z t the derivatives of z with respect to s and t. In this case, from S and T, one can again, in a natural manner, construct a Lorentzian conformal metric on the six dimensional space (z,z s ,z t ,z st ,s,t). When the S and T satisfy differential conditions analogous to those of the 3rd order ode, the 6-space then possesses a pair of conformal Killing fields, and which allows, via the mapping to the four-space of (z,z s ,z t ,z st ) and a choice of conformal factor, the construction of a four-dimensional Lorentzian metric. In fact all four-dimensional Lorentzian metrics can be constructed in this manner. This construction, with further conditions on S and T, thus includes all (local) solutions of the Einstein equations. Received: 10 October 2000 / Accepted: 26 June 2001  相似文献   

3.
We report a study of the 4 A 2g 2 T 1g absorption band of Mn4+ in Cs2SiF6. The band shows several lines or groups of lines associated with transitions from the 4 A 2g ground state to the spin-orbit components (2 T 1g 8 and (2 T 1g 6 coupled to the three odd-parity vibrations v 6(t 2u ), v 4(t 1u ) and v 3(t 1u ). The absorptions associated with the (2 T 1g 8 electronic state have structure whereas those associated with the (2 T 1g 6 do not. It is shown that the structure is a consequence of splitting of the Γ8 × v vibronic multiplets by electron-vibration interaction. The intensity of the 4 A 2g →(2 T 1g i + vj vibronic transitions are expressed in terms of a small number of parameters; two parameters for v(t 1u ) modes and three for v(t 2u ) modes. Plausible but not good fits to the low temperature Zeeman data and vibronic splitting patterns are obtained. The excitation spectrum of the Cs2SiF6 : Mn4+ in the region of the 4 A 2g 2 Eg and 4 A 2g 2 T 1g is recorded using a c.w. dye laser. This reveals numerous weaker lines involving combinational modes and even-parity modes v5 (t 2g ), v 2(eg ) and v 1(a 1g ). Several interesting electron-vibrational effects are observed. These are illustrated and discussed qualitatively.  相似文献   

4.
The rotational analysis of the infrared absorption spectrum of CH3 79Br and CH3 81Br between 2150 and 2510 cm-1 was performed on a Fourier transform spectrum with a resolution of 0·007 cm-1. The bands v 2 + v 6(E) and v 5 + v 6(A 1 + A 2 + E) occur in this region, giving rise to several perturbations as in the corresponding system of methyl chloride [3]. Forbidden transitions, observed in correspondence of the level crossing of the x-y Coriolis coupling between v 2 + v 6 and v 5 + v 6(E), enabled us to estimate the value of A″ - 225DK at 5·16186 cm-1 for CH3 79Br and 5·16173 cm-1 for CH3 81Br. The parallel system of v 5 + v 6 exhibits a perpendicular structure, and an l-type resonance couples those levels of the parallel and perpendicular components of v 5 + v 6 involved in transitions from the K″ = 0 levels of the ground state. The QQ 0 branches of the A 2 component of v 5 + v 6, made active by this resonance, are observed for both isotopic species.  相似文献   

5.
It is shown that the Coulomb energy U of fully ionized ionic mixture can be written as a sum over partial contributions of ion species j: U = T Σj Njuj, yj) (generalized linear mixing rule). In contrast to the traditional linear mixing rule ULM = T Σj NjuOCPj), applicable for strong coupling, the partial contribution function u depends not only on Γj, but on an additional parameter yj = (rD/rDOCP)2 also. Here rD and rDOCP are Debye radiuses in the mixture and in the one component plasma at coupling parameter Γj, correspondingly. The parameter yj does not depend on a specific composition of the mixture, but on the Debye radius rD only, making function uj, yj) universal. The generalized linear mixing rule can be applied at any coupling parameter, if ionic mixture is not crystallized. It reproduces results of the Debye‐Hückel theory at weak coupling and traditional linear mixing rule at strong coupling. It can be easily applied to the complicated mixtures, composed of a large number of ion species. Since yj is temperature independent, the Coulomb contribution to Helmholtz free energy of the mixture can also be presented in a form of generalized linear mixing rule (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
7.
When a solution of a porphin in n-octane is slowly frozen the guests predominantly occupy a single site (A) in which the porphin has been shown to replace a number of host molecules displaced along the b-direction; if the solution is quickly frozen the optical spectra reveal the presence of a second site (B). In the present paper it is shown that the occurrence of these two types of sites, A and B, is a common phenomenon throughout the series from n-heptane (C7) to n-decane (C 10) as hosts and phenomenological criteria are formulated to distinguish between the two kinds of sites.

The orientation of palladiumporphin (PdP) in the A and B sites of a C7 host is determined from Zeeman experiments on the S 1S 0 and T 0S 0 transitions in a single crystal of C7 doped with PdP. The porphin nuclei in the B sites replace a number of alkanes displaced along the a-axis. In the course of the experiments signals related to a third type of site, B', grew in intensity in the spectra. This site is coplanar with the B site and it differs from the latter by an in-plane rotation of the trapped molecule over 20°. The origins of the S 1S 0 transition for the two types of site are assigned for H2P, ZnP and PdP as solutes in C7, C8, C9 and C10 as hosts.

Finally, the Zeeman shifts observed in the S 1S 0 transition of PdP in the three sites of C7 yield an effective orbital angular momentum for PdP in the state S 1 of (4·4 ± 0·1)?, in excellent agreement with previous determinations.  相似文献   

8.
We calculate the screening properties of a boson superlattice with distanced between the planes at temperature zero. The screened Coulomb potentialV s (r,d) of a test charge located in one plane is calculated in the neighboring plane. It is found that this interplane potential is attractive with a maximal atraction at the intraplane distancer m:V s (r m ,d)<0.V s (r m ,d) versusd shows a minimum atd m , indicating a maximal attraction for anoptimal superlattice period dm. The attraction could give rise topairing of bosons between different planes.  相似文献   

9.
杨娟  卞保民  闫振纲  王春勇  李振华 《物理学报》2011,60(10):100506-100506
建立了一种能够描述随机信号结构基本特征的双参数脉冲信号统计模型.基于此模型,脉冲信号群幅度计数分布q(lV),宽度计数分布p(lτ)及给定宽度信号子集的幅度计数分布εlτ(lV),给定幅度信号子集的宽度计数分布δlV(lτ)均能很稳定的服从以序列自然数为自变量的对数正态分布.且计数分布的统计特征量μlnVlnτlnVlnτ与信号的特征参数lV,lτ之间存在内在联系,这种联系的形式即随机信号分形特性的表现,表明随机信号特征参数的统计分布之间具有非整数维分形特征. 关键词: 分形 随机信号 双参数 统计  相似文献   

10.
The temperature dependences of the real part R s and the imaginary part X s of the surface impedance Z s =R s +iX s of the superconductor Ba0.6K0.4BiO3 (T c ≃30 K) are measured at a frequency of 9.4 GHz. Its temperature dependence Z s (T) and that of the complex conductivity σ s (T) can be described on the basis of a two-fluid model under two assumptions: The density of superconducting carriers increases linearly, and the relaxation time increases as a power law (∝1/T 5), with decreasing temperature T<T c . This model also describes well the curves Z s (T) and σs (T) recently measured for YBa2Cu3O6.95 and Bi2Sr2CaCu2O8 single crystals. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 11, 783–788 (10 December 1996)  相似文献   

11.
We consider the construction of a nilpotent BRST charge for extensions of the Virasoro algebra of the form {T a ,T b }=f ab c T c +V ab cd T c T d , (classical algebras in terms of Poisson brackets) and [T a ,T b ]=h ab I+f ab c T c +V ab cd (T c T d )(quantum algebras in terms of commutator brackets; normal ordering of the product (T c T d ) is understood). In both cases we assume that the set of generators {T a } splits into a set {H i } generating an ordinary Lie algebra and remaining generators {S }, such that only theV ij are nonvanishing. In the classical case a nilpotent BRST charge can always be constructed; for the quantum case we derive a condition which is necessary and sufficient for the existence of a nilpotent BRST charge. Non-trivial examples are the spin-3 algebra with central chargec=100 and theso(N)-extended superconformal algebras with levelS=–2(N–3).  相似文献   

12.
In this paper the problem of the possibility of determining the cyclic Hamiltonian function of a particle moving about a magnetic vessel of the mirror type is discussed. From the Hamiltonian of the typeH=H(P 1,P 2,P 3,Q 3), derived by the author in a previous paper, the Hamiltonian functionH=H(J1,J 2,J 3,w 3) was determined whereP i ,Q i are the generalized impulses and coordinates andJ i ,w k is the action-angle coordinate system. The determination of the form H=H(J1,J 2,J 3) depends on the possibility of solving the quadrature of the Hamilton-Jacobi equation leading to an open form in the general case. Some approximative expressions, suitably replacing the mirror system, are discussed. The solution has been extended to the range of relativistic velocities. The question of the uniqueness of the expression of the Hamiltonian function in cyclic variables is analyzed; it follows from this that the class of canonical transformations leaving the Hamiltonian in a cyclic form does not allow any great simplification of the relatively complicated transformation expressions.  相似文献   

13.
We present an approximate solution of the Percus-Yevick integral equation for a binary mixture of hard spheres with non-additive diameters. Defining Rij the distance of closest approach between particles of species i and j by R 12 = ½(R 11 + R 22) + α, we obtain a closed set of equations for the direct correlation functions cij (r) when 0 < α ? min [½(R 22 - R 11), ½R 11]. Our expressions for cii (r), and for c 12(r) in the range 0 < r ? ½[R 22 - R 11] - α, agree with those previously obtained by Lebowitz and Zomick.  相似文献   

14.
Ba2−x Sr x NaNb5O15 thin films were prepared on La0.05Sr0.95TiO3 substrates by pulsed laser deposition. The structural and ferroelectric properties of the thin films depended on substrate temperature (T sub) and Sr concentration. When T sub was fixed at 700 °C, the Ba2−x Sr x NaNb5O15 (x = 0, 0.6, 1.0, and 1.4) thin films exhibited a high c-axis orientation. The thin films consisted of well-developed grains and exhibited a smooth surface. The c-axis-oriented Ba0.6Sr1.4NaNb5O15 thin film with the lowest Curie temperature also exhibited a high c-axis orientation and a P-E hysteresis loop with a high ferroelectricity at T sub 650 °C. Thus, its remanent polarization (P r) and coercive field (E c) were 2P r 24.9 μC/cm2 and 2E c 107 kV/cm, respectively. These values indicate that Ba2−x Sr x NaNb5O15 has ferroelectricity in the thin film form.  相似文献   

15.
By manipulating the integral expression for the proper radius R e of the cosmological event horizon (CEH) in a Friedmann-Robertson-Walker (FRW) universe we obtain an analytical expression for the change δR e in response to a uniform fluctuation δρ in the average cosmic background density ρ. We stipulate that the fluctuation arises within a vanishing interval of proper time, during which the CEH is approximately stationary, and evolves subsequently such that δρ/ρ is constant. The respective variations 2πR e δR e and δE e in the horizon entropy S e and enclosed energy E e should be therefore related through the cosmological Clausius relation. In that manner we find that the temperature T e of the CEH at an arbitrary time in a flat FRW universe is E e /S e , which recovers asymptotically the usual static de Sitter temperature. Furthermore it is proven that during radiation-dominance and in late times the CEH conforms to the fully dynamical First Law T e dS e =PdV e −dE e , where V e is the enclosed volume and P is the average cosmic pressure.  相似文献   

16.
张海龙  刘丰珍  朱美芳  刘金龙 《中国物理 B》2012,21(1):15203-015203
The influences of the plasma ignition condition in plasma enhanced chemical vapour deposition (PECVD) on the interfaces and the microstructures of hydrogenated microcrystalline Si (μc-Si:H) thin films are investigated. The plasma ignition condition is modified by varying the ratio of SiH4 to H2 (RH). For plasma ignited with a constant gas ratio, the time-resolved optical emission spectroscopy presents a low value of the emission intensity ratio of Hα to SiH* (I/ISiH*) at the initial stage, which leads to a thick amorphous incubation layer. For the ignition condition with a profiling RH, the higher I/ISiH* values are realized. By optimizing the RH modulation, a uniform crystallinity along the growth direction and a denser μ c-Si:H film can be obtained. However, an excessively high I/ISiH* may damage the interface properties, which is indicated by capacitance-voltage (C-V) measurements. Well controlling the ignition condition is critically important for the applications of Si thin films.  相似文献   

17.
The current-voltage characteristics of granular YBa2Cu3O6.95 high-temperature superconductor samples have been measured at a temperature of 77.3 K in external transverse magnetic fields H ext with a strength of up to H ext ≈ 500 Oe for low transport current densities (0.1 A/cm2j ≤ 0.6 A/cm2). The current-voltage characteristics obtained have been used to construct dependences of the magnetoresistance ρ on the quantities j (ρ(j) Hext=const) and H ext(ρ(H ext) j = const). It has been revealed that the current and field dependences of the magnetoresistance exhibit anomalies at H extH c1g , where H c1g is the lower critical field of superconducting grains. A comparative analysis of the dependences ρ(j)H ext = const and ρ(H ext) j = const has made it possible to develop concepts regarding the influence of the processes of redistribution of the magnetic field between grain boundaries and superconducting grains on the transport and galvanomagnetic properties of granular high-temperature superconductors. It has been established that the field dependences of the magnetoresistance exhibit specific features associated with the beginning of penetration of Josephson vortices into grain boundaries in the magnetic field H c1J and with the breaking of a continuous chain of Josephson junctions in the magnetic field H c2J .  相似文献   

18.
We determine an explicit form of a q-difference operator that transforms the continuous q-Hermite polynomials H n (x|q) of Rogers into the Askey-Wilson polynomials p n (x; a, b, c, d|q) on the top level in the Askey q-scheme. This operator represents a special convolution-type product of four one-parameter q-difference operators of the form ɛ q (c q D q ) (where c q are some constants), defined as Exton’s q-exponential function ɛ q (z) in terms of the Askey-Wilson divided q-difference operator D q . We also determine another q-difference operator that lifts the orthogonality weight function for the continuous q-Hermite polynomialsH n (x|q) up to the weight function, associated with the Askey-Wilson polynomials p n (x; a, b, c, d|q).  相似文献   

19.
A general method is presented for determining the shape and orientation of the Raman tensor of a molecule in a uniaxial crystal using a Raman microscope. First, equations are derived to connect the Raman tensor components (αxx, αyy, etc.) of a molecule to the Raman tensor components (αaa, αcc, etc.) of a crystal that is composed of molecules in a uniaxial arrangement, with an orientation specified by the two angles χ and θ. Next, a method is presented to obtain a correct set of values of the intensity ratios Iac/Iaa and Icc/Iaa from observed values of the intensity ratios measured with a Raman microscope. To augment the experimental data, the depolarization ratio ρ (for a completely random molecular orientation) is plotted as a function of r1 = αxxzz and r2 = αyyzz, so that a possible set of r1 and r2 values can be found from an observed value of ρ. The method has been applied to an aspartame IIA crystal (P41). A set of values of r1, r2, χ and θ has been determined for each of the following Raman fundamentals: 1741 cm−1 (ester CO stretch), 1667 cm−1 (amide I), 1275 cm−1 (amide III) and 1204 cm−1 (C Cphenyl stretch), excited at 488.0 nm.  相似文献   

20.
This paper examines how an electric field relaxes when a discontinuous large carrier-depleting voltage applied to high-resistance symmetric metal-semiconductor-metal (MSM) and metal-insulator-semiconductor-insulator-metal (MISIM) structures having a single impurity level, and how its energy level ɛ t=E cE t and the tunneling transparency T n,p of the metal-semiconductor or metal-insulator boundary affect the relaxation. It is shown that the relaxation of the field and the form of its steady-state distribution depend on the ratio of the time constant t p in the majority-carrier (hole) region to the ionization time τ t −1 n (n *+n 1)+α p (p *+p 1) of a deep trap in the bulk. This ratio determines the relative contributions of free ρ p,n and bound charge dnsities ρ t (where α n,p is the coefficient for capture by an impurity, and p *, n *, p 1, n 1 are equilibrium concentrations and Shockley-Read constants in the bulk). For τ t ≈(τ t )maxt p t ≫ it is found that ρ p,n and ρ t ≫ρ p,n , which corresponds to a trap energy close to , independent of the value of T n,p , decaying oscillations arise in the concentration distribution, bulk charge, and field appear in the bulk. The amplitude of these oscillations reaches a maximum at time t≈0.4τ t. Decreasing the ratio α pn causes τ t to deviate from (τ t)max. When this happens, the field no longer oscillates; instead, it increases with positive curvature in the cathode portion of the bulk. The quantity T n,p determines the behavior of the field in the neighborhood of the anode. The value of (dE/dx)0 is positive for MSM structures (T n,p ≈1), and negative for MISIM structures (T n,p ≈0). For transparencies close to a critical value T n,p 0 , the field in the structure remains almost uniform over an impurity ionization time. Fiz. Tverd. Tela (St. Petersburg) 39, 1775–1782 (October 1997)  相似文献   

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