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51.
We investigate the temperature dependence of the dielectric constant of BaTiO3 ceramic with coarse to nanograin size under different hydrostatic high pressures up to 5000 bar in the range between room temperature and 200℃. The ferroelectric-to-paraelectric phase transition temperatures Tc are determined from the peak of dielectric constant versus temperature. The values of average grain-size are estimated from the SEM images. It is found that the magnitude of dTc/dp varies considerably from sample to sample depending on grain size. The Curie point Tc of the sample with small grain size decreases more sharply than that of samples with larger one. 相似文献
52.
A completely antisymmetrized Green’s function approach to the inclusive quasielastic (e, e′) scattering, including a realistic one-body density, is presented. The single-particle Green’s function is expanded in terms of the eigenfunctions of the non-hermitian optical potential. This allows one to treat final state interactions consistently in the inclusive and in the exclusive reactions. Nuclear correlations are included in the one-body density. Numerical results for the response functions of 16O and 40Ca are presented and discussed. 相似文献
53.
D. G. Middleton J. R. M. Annand C. Barbieri P. Barneo H. P. Blok R. Böhm M. O. Distler J. Friedrich C. Giusti D. I. Glazier P. Grabmayr T. Hehl J. Heim W. H. A. Hesselink E. Jans M. Kohl L. Lapikás I. J. D. MacGregor I. Martin J. C. McGeorge H. Merkel F. Moschini G. Rosner M. Seimetz H. de Vries Th. Walcher D. P. Watts B. Zihlmann 《The European Physical Journal A - Hadrons and Nuclei》2006,29(3):261-270
This paper reports on the first measurement of the 16O(e, e'pn)14N reaction. Data were measured in kinematics centred on a super-parallel geometry at energy and momentum transfers of 215MeV
and 316MeV/c. The experimental resolution was sufficient to distinguish groups of states in the residual nucleus but not good enough to
separate individual states. The data show a strong dependence on missing momentum and this dependence appears to be different
for two groups of states in the residual nucleus. Theoretical calculations of the reaction using the Pavia code do not reproduce
the shape or the magnitude of the data.
An erratum to this article is available at. 相似文献
54.
O. Benhar S. Fantoni G.I. Lykasov 《The European Physical Journal A - Hadrons and Nuclei》2000,7(3):415-419
The production of backward pions in lepton-nucleus collisions is analyzed. We show that a large yield of high momentum backward
pions can be explained by the Regge asymptotic of the distribution of nucleons carrying a large momentum fraction in the nuclear
target. The calculated spectra of pions emitted in the ν+ Ne →μ+π−+ X and ν+2H →μ+π−+ X reactions are in satisfactory agreement with the available experimental data.
Received: 22 July 1999 / Revised version: 22 November 1999 相似文献
55.
L. L. Frankfurt W. R. Greenberg G. A. Miller M. M. Sargsyan M. I. Strikman 《Zeitschrift für Physik A Hadrons and Nuclei》1995,352(1):97-113
High momentum transfer electrodisintegration of polarized and unpolarized deuterium targets,d(e, ep)n is studied. We show that the importance of final state interactions FSI, occuring when a knocked out nucleon interacts with the other nucleon, depends strongly on the momentum
of the spectator nucleon. In particular, these FSI occur when the essential contributions to the scattering amplitude arise from internucleon distances 1.5 fm. But the absorption of the high momentum
* may produce a point like configuration, which evolves with time. In this case, the final state interactions probe the point like configuration at the early stage of its evolution. If the point like configuration is still small after propagating about 1.5 fm, the FSI are suppressed. The result is that significant color transparency effects, which can either enhance or suppress computed cross sections, are predicted to occur forQ
24GeV2. We suggest searching for color transparency phenomenon by examining ratios of experimentally measured quantities. Possible theoretical uncertainties of the calculations, including those due to the deuteron wave function and relativistic effects, are found to be small.This work was supported in part by the USA — Israel Binational Science Foundation Grant No. 9200126 and by the US Department of Energy under Contract Nos. DE-FG02-93ER40771 and DE-FG06-88ER40427. 相似文献
56.
The persistence of Bacillus thuringiensis (Bt) toxins in soil is further enhanced through association with soil particles. Such persistence may improve the effectiveness of controlling target pests, but impose a hazard to non-target organisms in soil ecosystems. In this study, the equilibrium adsorption of the Bt toxin by four clay minerals (montmorillonite, kaolinite, goethite, and silicon dioxide) was investigated, and the kinetic and thermodynamic parameters were calculated. The results showed that Bt toxin could be adsorbed easily by minerals, and the adsorption was much easier at low temperature than at high temperature at the initial concentration varying from 0 to 1000 mg L−1. The adsorption fitted well to both Langmuir and Freundlich isotherm models, but the Freundlich equation was more suitable. The pseudo-second-order (PSO) was the best application model to describe the adsorption kinetic. The adsorption process appeared to be controlled by chemical process, and the intra-particle diffusion was not the only rate-controlling step. The negative standard free energy () values of the adsorption indicated that the adsorption of the Bt toxin by the minerals was spontaneous, and the changes of the standard enthalpy () showed that the adsorption of the Bt toxin by montmorillonite was endothermic while the adsorption by the other three minerals was exothermic. 相似文献
57.
This paper analyzes the approximation of a general long-memory ARFIMA (p,d,q) process by a short-memory ARMA(1, 1) process. To validate this approximation, a mean square error forecast criterion is considered, and the calculation of the mean square error between the observation Xt+l of an ARFIMA process and the l-step-ahead forecast of the ARMA(1, 1) process is presented. The performance of the ARMA(1, 1) approximation to an ARFIMA model is illustrated by using an application to a DNA sequence of orf virus. This paper gives some theoretical justification on the mean square error forecast criterion based on a selected ARMA(1, 1) model when compared to the general ARFIMA(p,d,q) process. The paper also provides a DNA sequence of orf virus analysis when the time series is originated from the tangent values of the Chaos Game Representation coordinates for each nucleotide. The conclusions of this paper work well because the estimator value of d is small (). The paper also gives the other parameter estimate of the fitted ARFIMA (0, d, 1) model and one-step predictions using ARMA(1, 1) model. 相似文献
58.
A. Bouhemadou 《Physica B: Condensed Matter》2008,403(17):2707-2713
Using first-principles calculations, we have studied the structural and elastic properties of M2SnC, with M=Ti, Zr, Nb and Hf. Geometrical optimization of the unit cell is in good agreement with the available experimental data. The effect of high pressures, up to 20 GPa, on the lattice constants shows that the contractions along the a-axis were higher than those along the c-axis. We have observed a quadratic dependence of the lattice parameters versus the applied pressure. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear dependence of the elastic stiffnesses on the pressure is found. We derived the bulk and shear moduli, Young's moduli and Poisson's ratio for ideal polycrystalline M2SnC aggregates. We estimated the Debye temperature of M2SnC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of Ti2SnC, Zr2SnC, Nb2SnC, and Hf2SnC compounds. 相似文献
59.
The density-dependent relativistic hadron (DDRH) field theory proposed recently is extended to investigate the longitudinal response function and the Coulomb sum rule in quasielastic electron scattering in the relativistic random phase approximation (RPA). The results in the DDRH model are compared with those in other models systematically. It is found that meson effective masses induced by the nonlinear terms in the nonlinear Walecka model should be used to obtain the meson Greens functions when the longitudinal response function and the Coulomb sum rule are calculated. The effects of the and mesons are clearly shown in quasielastic electron scattering, and the isospin-dependent attractive potential between nucleons due to the exchange of the -meson cancels the isospin-dependent repulsive contribution of the -meson to a certain extent. The obtained results in the DDRH model are in good agreement with experimental data except for the Coulomb sum rule in 208Pb. 相似文献
60.
J.J. Betouras V.A. Ivanov F.M. Peeters 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):349-354
We present a model of pressure effects of a two-band superconductor based on a Ginzburg-Landau free energy with two order
parameters. The parameters of the theory are pressure as well as temperature dependent. New pressure effects emerge as a result
of the competition between the two bands. The theory then is applied to MgB2. We identify two possible scenaria regarding the fate of the two σ subbands under pressure, depending on whether or not both subbands are above the Fermi energy at ambient pressure. The splitting
of the two subbands is probably caused by the E2g distortion. If only one subband is above the Fermi energy at ambient pressure (scenario I), application of pressure diminishes
the splitting and it is possible that the lower subband participates in the superconductivity. The corresponding crossover
pressure and Gr neisen parameter are estimated. In the second scenario both bands start above the Fermi energy and they move below it, either
by pressure or via the substitution of Mg by Al. In both scenaria, the possibility of electronical topological transition is emphasized. Experimental
signatures of both scenaria are presented and existing experiments are discussed in the light of the different physical pictures.
Received 3 September 2002 / Received in final form 16 December 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: joseph.betouras@ua.ac.be
RID="b"
ID="b"On leave from N.S. Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences, 31 Leninskii
prospekt, 117915, Moscow, Russia 相似文献