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971.
T.?A.?Prokof’evEmail author B.?A.?Polezhaev A.?V.?Kovalenko 《Journal of Applied Spectroscopy》2005,72(6):865-871
The mechanisms of photoluminescence excitation of Mn2+ ions in ZnS crystals have been investigated on the basis of complex analysis of the temperature dependences of the photoluminescence
and photoluminescence-excitation spectra of ZnS:Mn crystals. The activation energy of a manganese luminescence center was
estimated at Ea = 0.17 ± 0.05 eV. It is shown that Ea represents an energy band with a width ΔEa = 0.1 eV, within which a manganese luminescence center can experience radiationless recombination.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 788–793, November–December, 2005. 相似文献
972.
Influence of hydrostatic pressure and temperature on electronic band parameters for zinc-blende AlxGa1–xAs was investigated by means of pseudopotential calculations. The agreement between our results and the available experimental data is generally satisfactory. Our results showed that the effect of pressure leads to a decrease of the crossing point and the optical bowing parameter. However, the temperature effect was found to be insignificant on both crossing point and bowing parameter. 相似文献
973.
R. S. Castro S. Prasad R. M. Gomes I. C. E. S. G Lima A. G. Souza T. A. A Melo S. J. G. Lima 《Journal of Thermal Analysis and Calorimetry》2004,75(2):649-654
Co80Nb14B6, Co80Nb12B8 and Co80Nb10B10 amorphous alloys were obtained through the melt-spinning process. The ribbons structure was investigated by X-ray diffractometry
and the crystallization process and the thermal stability were studied by means of differential thermal analysis and thermomechanical
technique. It was observed that the crystallization temperature depends on the alloy composition and occurs in a temperature
range between 420 and 730°C. The coercive field of all alloys was determined by magnetic susceptibility measurements, the
values of which range from 2.78 to 5.95 A m-1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
974.
J.K. Baria 《Czechoslovak Journal of Physics》2004,54(5):575-595
A simple pseudopotential model is used for the calculation of the temperature dependence of lattice mechanical properties which also depend on the phonon density of states such as lattice heat capacity C
V
, Debye temperature D, harmonic contribution to free energy, thermal pressure, isothermal bulk modulus corrected to the fourth order, volume thermal expansion coefficient , Debye-Waller factor, mean-square displacement, Debye-Waller temperature parameter, and X-ray characteristic temperature M of Cu, Ag, Au, Ni, Pd, Pt, Rh, and Ir. The contribution of d-like electrons is taken into account by introducing repulsive short-range Born-Mayer-like term. Very recently proposed screening function due to Sarkar et al. has been used to obtain the screened form factor. The theoretical results are compared with experimental findings wherever possible. A good agreement between theoretical investigations and experimental findings show the ability of our model potential to reproduce wide class of properties in noble and transition metals. 相似文献
975.
We describe the construction and operation of a variable temperature (VT) system for a high field fast magic angle spinning (MAS) probe. The probe is used in NMR investigations of biological macromolecules, where stable setting and continuous measurement of the temperature over periods of several days are required in order to prevent sample overheating and degradation. The VT system described is used at and below room temperature. A vortex tube is used to provide cooling in the temperature range of -20 to 20 degrees C, while a liquid nitrogen-cooled heat exchanger is used below -20 degrees C. Using this arrangement, the lowest temperature that is practically achievable is -140 degrees C. Measurement of the air temperature near the spinning rotor is accomplished using a fiber optic thermometer that utilizes the temperature dependence of the absorption edge of GaAs. The absorption edge of GaAs also has a magnetic field dependence that we have measured and corrected for. This dependence was calibrated at several field strengths using the well-known temperature dependence of the (1)H chemical shift difference of the protons in methanol. 相似文献
976.
The germanate compound Cu2Sc2Ge4O13 has been synthesized by solid-state ceramic sintering techniques between 1173 and 1423 K. The structure was solved from single-crystal data by Patterson methods. The title compound is monoclinic, a=12.336(2) Å, b=8.7034(9) Å, c=4.8883(8) Å, β=95.74(2), space group P21/m, Z=4. The compound is isotypic with Cu2Fe2Ge4O13, described very recently. The structure consists of crankshaft-like chains of edge-sharing ScO6 octahedra running parallel to the crystallographic b-axis. These chains are linked laterally by [Cu2O6]8− dimers forming a sheet of metal-oxygen-polyhedra within the a-b plane. These sheets are separated along the c-axis by [Ge4O13]10− units. Cooling to 100 K does not alter the crystallographic symmetry of Cu2Sc2Ge4O13. While the b, c lattice parameter and the unit cell volume show a positive linear thermal expansion (α=6.4(2)×10−6, 5.0(2)×10−6 and 8.3(2)×10−6 K−1 respectively), the a lattice parameter exhibits a negative thermal expansion (α=−3.0(2)×10−6 K−1) for the complete T-range investigated. This negative thermal expansion of a is mainly due to the increase of the Cu-Cu interatomic distance, which is along the a-axis. Average bond lengths remain almost constant between 100 and 298 K, whereas individual ones partly show both significant shortages and lengthening. 相似文献
977.
Consider the delay difference system
978.
Peter?EichelsbacherEmail author Matthias?L?we 《Probability Theory and Related Fields》2004,130(4):441-472
We derive moderate deviation principles for the overlap parameter in the Hopfield model of spin glasses and neural networks. If the inverse temperature is different from the critical inverse temperature c=1 and the number of patterns M(N) satisfies M(N)/N 0, the overlap parameter multiplied by N, 1/2 < < 1, obeys a moderate deviation principle with speed N1–2 and a quadratic rate function (i.e. the Gaussian limit for = 1/2 remains visible on the moderate deviation scale). At the critical temperature we need to multiply the overlap parameter by N, 1/4 < < 1. If then M(N) satisfies (M(N)6 log N M(N)2N4 log N)/N 0, the rescaled overlap parameter obeys a moderate deviation principle with speed N1–4 and a rate function that is basically a fourth power. The random term occurring in the Central Limit theorem for the overlap at c = 1 is no longer present on a moderate deviation scale. If the scaling is even closer to N1/4, e.g. if we multiply the overlap parameter by N1/4 log log N the moderate deviation principle breaks down. The case of variable temperature converging to one is also considered. If N converges to c fast enough, i.e. faster than the non-Gaussian rate function persists, whereas for N converging to one slower than the moderate deviations principle is given by the Gaussian rate. At the borderline the moderate deviation rate function is the one at criticality plus an additional Gaussian term.Research supported by the Volkswagen-Stiftung (RiP-program at Oberwolfach, Germany).Mathematics Subject Classification (2000): 60F10 (primary), 60K35, 82B44, 82D30 (secondary) 相似文献
979.
A procedure for numerical investigation of nonaxisymmetric temperature fields and the elastic stress-strain state of laminated rotational bodies of cylindrically and rectilinearly orthotropic materials under nonisothermal loading is proposed. The deformation of orthotropic materials is described by the equations of anisotropic elasticity theory. The equations of state are written in the form of Hookes law for homogeneous materials, with additional terms which take into account the thermal deformation, changes in the mechanical properties of materials in the circumferential direction, and their dependence on temperature. A semianalytic finite-element method in combination with the method of successive approximations is used. An algorithm for numerical solution of the corresponding nonlinear boundary problem is elaborated, which is realized as a package of applied FORTRAN programs. Some numerical results are presented.Translated from Mekhanika Kompozitnykh Materialov, Vol. 40, No. 6, pp. 731–752, November–December, 2004. 相似文献
980.
Acceleration waves propagating in isotropic solids at finite temperatures are studied by applying the method of singular surfaces to a new continuum model derived statistical-mechanically from a three-dimensional lattice model. The continuum model explicitly takes into account the microscopic thermal vibrations of the constituent atoms as one of the field variables. The propagation speeds and the ratios of mechanical and thermal amplitudes for both longitudinal and transverse waves are consistently determined. The differential equations that govern the time variation of the amplitudes of the waves are also derived. The analytical results, which are valid over a wide temperature range that includes the melting point, are evaluated numerically for several materials, and their physical implications are discussed. One of the findings to be emphasized is that of the singularities of the characteristic quantities at the melting point.Received: 13 March 2003, Accepted: 20 June 2003PACS:
62.30. + d, 65.40.-bM. Sugiyama: Correspondence to
Dedicated to Prof. Ingo Müller on the occasion of his 65th birthday. 相似文献