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1.
The solid solutions Eu(Ir1–x Pd x )2Si2, which exist for 0x0.125 and 0.75x1. cristallize with the tetragonal ThCr2Si2-type structure. The variation of the europium valence with composition has been thoroughly studied at temperatures 4.2T293 K by151Eu Mössbauer resonance. For 0x0.125 the europium valence at room temperature decreases asx increases. For 0.75x1 the valence transition temperature Eu3+Eu2+ increases asx increases.  相似文献   

2.
Successive band-splitting transitions occur in the one-dimensional map xi+1=g(xi),i=0, 1, 2,... withg(x)=x, (0 x 1/2) –x +, (1/2 <x 1) as the parameter is changed from 2 to 1. The transition point fromN (=2n) bands to 2Nbands is given by=(2)1/N (n=0, 1,2,...). The time-correlation function i=xix0/(x0)2,xi xi–xi is studied in terms of the eigenvalues and eigenfunctions of the Frobenius-Perron operator of the map. It is shown that, near the transition point=2, i–[(10–42)/17] i,0-[(102-8)/51]i,1 + [(7 + 42)/17](–1)ie–yi, where2(–2) is the damping constant and vanishes at=2, representing the critical slowing-down. This critical phenomenon is in strong contrast to the topologically invariant quantities, such as the Lyapunov exponent, which do not exhibit any anomaly at=2. The asymptotic expression for i has been obtained by deriving an analytic form of i for a sequence of which accumulates to 2 from the above. Near the transition point=(2)1/N, the damping constant of i fori N is given by N=2(N-2)/N. Numerical calculation is also carried out for arbitrary a and is shown to be consistent with the analytic results.  相似文献   

3.
Let t be an analytic solution of the Schrödinger equation with the initial condition . Let t be the solution of the Schrödinger equation with the initial condition =, where is an analytic function. When 0, then t (x) t (x)1 ( t (x)), where t (x) trajectory starting from x. We relate this result to Feynman's sum over trajectories and complex stochastic differential equations.  相似文献   

4.
The ergodic properties of two stochastic models I and II are investigated. Each model is described by a fieldx(t),t > 0, on the lattice =Z d,d < . For I,x(t) evolves according to the equations wherex s (t) R for eachs eF. Here the {ws(t): s } are independent, one-dimensional Wiener processes, 2 is a bounded interaction between adjacent lattice sites, and the potentials 1 and 2 satisfy appropriate regularity conditions. It is shown that for each model,x(t) is a Markov process on an infinite-dimensional phase spaceX. The probability measures onX that satisfy the Dobrushin-Lanford-Ruelle (DLR) conditions are stationary for this process and have a mixing property. Moreover, for I any stationary, time-reversal-invariant probability measure that has certain regularity properties must satisfy the DLR conditions.This paper is based on a portion of the author's Ph.D. thesis.(2)  相似文献   

5.
The measurements of the proton (NMR) spinlattice relaxation times have been made in a series of ytterbium hydrides, YbH x . Results are reported forx=1.80, 1.95, 2.00 and 2.62 and temperatures 4.2T297K. In the orthorhombic phase (1.80x2.00), the spin-lattice relaxation times are dominated by the hyperfine interaction of protons with conduction electrons and the spin diffusion mechanism. In the cubic phase (x=2.62), the relaxation times are five orders of magnitude shorter than in the orthorhombic one. This is interpreted in terms of the proton coupling with the Yb3+ ion spin fluctuations.  相似文献   

6.
LetN, be a von Neumann algebras on a Hilbert space , a common cyclic and separating vector. Assume to be cyclic and also separating forN . Denote by , N , N the modular operators to (, ), (N, ), resp (N , ). Assume now -it N it N for allt 0. (Such type of inclusions ((N U, ) , ) are called half-sided modular.) Then the modular groups it , N ir , N is ,t, r, s generate a unitary representation of the group S1(2, )/Z 2 of positive energy.Another result is related to two half-sided modular inclusions (1 , ) and (2 , ). Under proper conditions the three modular groups it , 1 ir , 2 is ,t, r, s generate the three-dimensional subgroup of O(2, 1) of two commuting translations and the Lorentz transformation.Partly supported by the DFG, SFB 288 Differentialgeometrie und Quantenphysik.  相似文献   

7.
We investigate one-dimensional lattice systems with (symmetric) nearest neighbor transfer ratesW n, n+1 which are independently distributed according to a probability density(w). For two general classes of(w), we rigorously determine the asymptotic behavior of the relevant single site Green function 0() near=0, and obtain exact results for the long time decay of the initial probability amplitude and for the low energy density of states. A scaling hypothesis, accurately confirmed by computer simulations, is used to relate the low frequency hopping conductivity() uniquely to 0(–i), and we conjecture that the resulting asymptotic behavior for() is also exact. The critical exponents associated with the various asymptotic laws depend on(w) and show a crossover from universal to non-universal behavior. Comparison is made with the results of several approximate treatments.  相似文献   

8.
LetH=–+V+Fx 1 withV(x 1,x ) analytic in the first variable andV(x 1+ia, x ) bounded and decreasing to zero asx for eacha . Let be an eigenvector of –+V with negative eigenvalue. Among our results we show that forF0, (,e H ) decays exponentially at a rate governed by the positions of the resonances ofH. This exponential decay is in marked contrast to conventional atomic resonances for which power law decay is the rule.Research supported by NSF Grant No. MCS 78-00101.  相似文献   

9.
We report the results of ac-susceptibility and dc-magnetization measurements for HyGd2CuO4 (0y0.54). It is shown thatH doping lowers the weak ferromagnetic component in the material. The distinct hysteresis loops observed atT=77 K for both non- and hydrogenated samples change its shape withy. The magnetic ordering temperatures T N Cu and T N Gd , as determined from the temperature dependencies of ac-susceptibility, remain unchanged with sample's hydrogenation. This result seems to indicate that extra electrons are not doped onto the Cu-O planes of Gd2CuO4. The frequency dependencies ofx(, T) andx(, T) for bothy=0 andy=0.15 samples are analysed., The maximums ofx andx found at about 200K are considered in terms of susceptibility dependence on the spin-lattice relaxation time (). The anomalies in ac-susceptibility found recently in Gd2CuO4 atT a=8 K andT b=9.5 K decrease significantly withy. Results are discussed in the context of available data on 214T-type compounds.  相似文献   

10.
Eu(Ir1–x Pd x )2Si2 solid solutions which exist only for 0x0.125 and 0.75x1 crystallize in the tetragonal ThCr2Si2-type structure. X-ray diffraction data, magnetic susceptibility and151Eu Mössbauer measurements suggest that these compounds can be characterized as homogeneous mixed valence systems. At room temperature and for 0x0.125, the europium valence decreases asx increases. For 0.75x1, a sharp continuous valence transition from Eu2+ to Eu3+ occurs near 48 K, 54 K and 78 K forx=0.75, 0.81 and 0.94 respectively. These valence changes are discussed in relation with the Eu–(Ir, Pd) interatomic distance.  相似文献   

11.
The objective of this paper is a mathematically rigorous investigation of intermittency and related questions intensively studied in different areas of physics, in particular in hydrodynamics. On a qualitative level, intermittent random fields are distinguished by the appearance of sparsely distributed sharp peaks which give the main contribution to the formation of the statistical moments. The paper deals with the Cauchy problem (/t)u(t,x)=Hu(t, x), u(0,x)=t 0(x) 0, (t, x) + × d , for the Anderson HamiltonianH = + (·), (x),x d where is a (generally unbounded) spatially homogeneous random potential. This first part is devoted to some basic problems. Using percolation arguments, a complete answer to the question of existence and uniqueness for the Cauchy problem in the class of all nonnegative solutions is given in the case of i.i.d. random variables. Necessary and sufficient conditions for intermittency of the fieldsu(t,·) ast are found in spectral terms ofH. Rough asymptotic formulas for the statistical moments and the almost sure behavior ofu(t,x) ast are also derived.  相似文献   

12.
The force-dipole tensorP , also known as the elastic dipole and the double-force tensor, is calculated for hydrogen dissolved in palladium and platinum, using a microscopic model for the interaction potentials; the so-called effective medium theory. The force-dipole tensor describes the long range displacement field induced by hydrogen dissolved in the host metal lattice in the dilute limit. It can be related to the mean elastic hydrogen-hydrogen interaction energy and the critical temperatureT c for the gas-liquid phase transition observed in systems such as PdH x and NbH x . Comparison show a fair agreement between theoretical and experimental values for the force-dipole tensor.  相似文献   

13.
The paper gives the results of measuring the Curie temperatureT c , the Seebeck coefficient and the activation energy of electrical conductivity on single crystal samples of manganese ferrites prepared by two different methods. In the system Mn x Fe3–x O4+y changes in the course of the quantities Tc, and are observed in the neighbourhood ofx=1 andx=1·9. A qualitative explanation of these courses is given and the influence of oxygen non-stoichiometry is discussed.The authors would like to thank Dr. S. Krupika for valuable remarks and discussions, E. Kitzinger for the X-ray analysis and A. Novák for careful chemical analysis.  相似文献   

14.
Isothermal and adiabatic susceptibilities characterize the rubies under investigation, (Cr x Al1–x )2O3 with 0.00025x0.008, as symmetric Ising spin glasses with a rms interaction of . Spin-freezing phenomena, like cusps, plateaus, and thermoremanence in the low-field magnetization are associated with a restricted heat transfer between the spin system and the thermal bath in the precritical region (TJ). At equilibrium andTJ, the scaling of the non-linear magnetization and the slowing down of the zerofield, average relaxation rate indicate a spin glass transition atT c =0. Among possible reasons for this apparent discrepancy to theT c J-hypothesis by Ogielski et al., are internal random fields.  相似文献   

15.
Hot dimers are molecules which after adsorption dissociate and each of the remaining hot monomers fly apart up to a maximum distance R from the original adsorption site. The influence of the hot-dimer adsorption mechanism on relevant aspects of the bimolecular catalyzed reaction of the type A – (1/2)B 2(hot) AB is studied by means of the Monte-Carlo simulation technique. The temporal evolution of both the reactant's coverages as well as the rate of AB-production is evaluated and discussed. Due to the enhanced probability of hot species for encounters with other adsorbed particles, the rate of AB-production becomes faster when increasing R. This behavior may be relevant in the dynamic of some catalyzed reactions such as for example the oxidation of carbon monoxide on transition metal surfaces, i.e. ACO, B 2O2, and ABCO2. Also the sticking coefficient of hot dimers and the average distance traveled by the hot monomers are evaluated and discussed.  相似文献   

16.
A cluster of two atoms described by thes-f model with Coulomb repulsion has been considered. The interaction between localized 4f electrons (S=1/2) is taken in the molecular field approximation. The thermodynamic quantities like magnetization, specific heat and correlation functions n , n , S z n , S z n , S z (n n ), n n and S + a + a as functions of temperature are presented for different band fillingN=0, 0.5, 1, 1.5, 2. The dependence of Curie temperature onN is calculated. The phase diagram forN=1 (T=0K) shows the possibility of existence of two phases: paramagnetic and ferromagnetic.The Curie temperature and the specific heat as functions ofN exhibit similar trends as found in experiments on doped magnetic semiconductors.  相似文献   

17.
Refractive-index and optical-absorption spectra of Bi-substituted yttrium iron garnet films, epitaxially grown by liquid-phase epitaxy, have been measured in the spectral regime 0.26 m1.9 m by thin-film interference for 0.52 m and by ellipsometry for0.52 m. The Y3–x–y Bi x Pb y Fe5–z Pt z O12 films contain bismuth in the range Ox 1.42, lead in the range 0.01 y0.08 and platinum in the range 0.005<=z0.03. There is satisfactory coincidence between the results from ellipsometry and thin-film interference in the overlapping wavelength region. The materials investigated are the same as reported earlier from this laboratory in ter mof their magnetic and magnetooptic properties.  相似文献   

18.
We present some inequalities for the Schattenp-norm of operators on a Hilbert space. It is shown, among other things, that ifA is an operator such that ReAa0, then for any operatorX, AX+XA* p 2aX p . Also, for any two operatorsA andB, AB 2 2 +A*B* 2 2 2AB 2 2 .  相似文献   

19.
20.
The microstructure of fiber-like SiC/Si3N4 composite particulate was investigated using high-resolution transmission electron microscopy techniques. The SiC/Si3N4 composite particulate consisted of a-SiC core and a -Si3N4 outer shell. Two kinds of composite particulate were distinguished when the observed orientation of the SiC core was <110>. In one type of the SiC/Si3N4 composite particulate, a crystal relationship of (111)-SiC | (102) -Si3N4 and (111)-SiC (114) -Si3N4 was identified; in the other type of the SiC/Si3N4 composite particulate, a crystal relationship of (111)-SiC (001) -Si3N4, and (111)-SiC (101) -Si3N4 was observed.  相似文献   

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