f.c.c./f.c.c.LUCS的电子结构

在只计入最近邻间相互作用的紧束缚近似下,计算了由两种面心立方金属组成的多层超薄共格结构(LUCS)的电子能谱和态密度。 关键词：     

On the occurrence of b.c.c.–h.c.p. structural phase transition in Mo under pressure

Abstract

To resolve the controversy on the occurrence of a b.c.c.–h.c.p. transition in shock as well as static measurements in Mo, we have done more accurate total energy electronic structure calculations. Our results show that this phasetransition should occur at much higher pressures than suggested by earlier calculations.     

The deformation potential and the deformation operator associated with a 〈110〉-screw dislocation in an f.c.c. crystal

The influence of a 〈110〉-screw dislocation in a f.c.c. crystal on nearly free electrons is analysed by means of the deformation potential theory. The Fermi surface is assumed to intersect the faces of the first Brillouin zone and electrons near those faces are considered in the two wave approximation. The pure shear strain around the screw dislocation yields the deformation potential. The phase-dismatching caused by the deformation operator takes the value π when the incident electron is on one of four faces of the first zone.     

Ratchet potential in d.c. SQUID’s and reduced two-junction interferometer models

For finite values of the parameter and in the presence of small structural asymmetry and inhomogeneity of the junctions parameters, the two-junction interferometer model can be described by means of a single non-linear differential equation in such a way that a ratchet potential for SQUIDs can be deduced. The resulting dynamical equation, derived for first-order corrections with respect to a symmetric and homogeneous model with =0, presents an additional second-harmonic term and a cosine term in the expression for the effective current-phase relation. For opportune values of the perturbation parameters a ratchet potential with pre-definite characteristics can be obtained.     

Antiproton-proton interactions at 5·7 Gev/c I. Nonannihilation channels

We present an analysis of nonannihilation channels in four-pronged interactions at 5·68 GeV/c. The transverse momenta and azimuthal angles distributions of nucléons and -mesons are compared with phase space. No essential influence of production on azimuthal correlation has been found. The seen difference of azimuthal angle distributions for like and unlike charged pions in annihilations appears to be more pronounced for small transverse momenta and for small transverse masses. For 10971 events of the reaction ¯pp¯pp^–+ we present cross sections for production and differential cross sections. The reaction is dominated by the strong quasi-two-body channel with cross section (1·66 ±±0·10) mb. We study in detail the production mechanism of this channel in terms of the absorption model.Dedicated to Academician Václav Votruba on the occasion of his seventieth birthday.The authors are indebted to the CERN-Prague collaboration on ¯pp interactions at 5·7 GeV/c for experimental data used in this paper and to Dr. M. Novak for valuable comments.     

c MESONS

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The molecular systems composed of the charmed mesons in the H\bar{S}+h.c. doublet

We study the possible heavy molecular states composed of a pair of charm mesons in the H and S doublets. Since the P-wave charm-strange mesons D _s0(2317) and D _s1(2460) are extremely narrow, the future experimental observation of the possible heavy molecular states composed of $D_{s}/D_{s}^{\ast}$ and D _s0(2317)/D _s1(2460) may be feasible if they really exist. Especially the possible J ^PC =1^?? states may be searched for via the initial state radiation technique.     

ηb decay into charmonium in association with c(c) pair

We calculate the inclusive decay rates of ηb into charmonium via double cc pairs for S- and P-wave states ηc, J/ψ and χcJ within the framework of non-relativistic QCD (NRQCD) factorization at leading order in αs. Besides calculating the contributions of the color-singlet channels ηb→c(c)[2S+1Sl(1)]+c(c), the effects of c(c) pair in the color-octet configurations are also considered. We find that ηb→c(c)[3S1(8)]+c(c) make a small contribution to Br(ηb→J/ψ(ηc)+c(c)). While in ther ηb→χcJ+c(c) case, the color octet contributions are significant, for they are of the same αs4vc5 order as the color-singlet processes. We predict Br(ηb → J/ψ(ηc)+c(c)) = 2.99(2.75) × 10-5 for S-vrave states J/ψ and ηc, and Br(ηb→χcJ +c(c))= (4.37,3.40,2.83)×10-5 (for J = 0,1,2) for P-wave states χcJ. In the end, we also find Br(ηb → c(c)c(c)) is almost saturated by ηb decay into charmonium in association with cc pair from the point of view of duality.     

Precise evaluation of h→ c(c) and axion-like particle production

We study the decay of the SM Higgs boson to a massive charm quark pair at the next-to-next-to-leading order QCD and next-to-leading order electroweak.At the sec...     

Laser Raman spectral studies under d.c. bias on fast proton transport in molybdic acid (MoO3· 2H2O)

Laser Raman spectroscopy on samples across which a d.c. field has been applied is suggested as a new technique for studying ionic solids. As an example, the laser Raman spectra of a solid state proton conductor MoO₃ · 2H₂Ois reported with the d.c. field “on”. Two new peaks at 795 and 414 cm⁻¹ appear in the laser Raman spectra and their intensities grow with increasing time and applied d.c. voltage. Their appearance has been explained by assuming that H₃O⁺ ions are created by the d.c. field as the mobile charged ionic species. By monitoring the peak intensities of the 795 and 414cm⁻¹ bands at different places in the sample between the cathode and the anode, the diffusion coefficient has been estimated.     

Possible Existence of {(c\bar{c})} –Nucleus Bound States

Charmonium ( \({c \bar{c}}\) ) bound states in few-nucleon systems, ²H, ⁴He and ⁸Be, are studied via Gaussian Expansion Method (GEM). We adopt a Gaussian potential as an effective \({(c \bar{c})}\) –nucleon (N) interaction. The relation between two-body \({(c \bar{c})}\) –N scattering length \({a_{c\bar{c}-N}}\) and the binding energies B of \({(c \bar{c})}\) –nucleus bound states are given. Recent lattice QCD data of \({a_{c\bar{c}-N}}\) corresponds to \({B \simeq 0.5}\) MeV for \({(c \bar{c})-^{4}}\) He and 2 MeV for \({(c \bar{c})-^{8}}\) Be in our results.     

S c r a t c h软件在中学物理教学中的应用初探

介绍了S c r a t c h软件的特点和应用于中学物理教学的意义以及两个应用实例     

Single-spin asymmetry for charged hadrons produced in proton-nucleus collisions at 40 GeV for c.m. production angles in the range 40°–79°

The transverse single-spin asymmetry for charged hadrons (π ^±, K ^±, p, $\bar p$ ) produced in proton-nucleus collisions was measured for c.m. production angles in the range 40°–79°. The measurements were performed with the FODS-2 setup by using a 40-GeV polarized proton beam originating from the accelerator of the Institute for High Energy Physics (Protvino) and hitting carbon and copper nuclear targets. The data in question were obtained in the polarized-proton-fragmentation region (0.0 < x _F < 0.7, 0.6 < p T < 2.5 GeV/c). In agreement with data obtained at other energies, the single-spin asymmetry for π ^± mesons is significant at high x _F. For the first time, a sizable analyzing power, which changes sign at x _F = 0.43, is observed for protons. The dependence of the analyzing power on the target-nucleus mass is insignificant.     

Measurement of the neutron-proton spin correlation coefficient Ayy at 90° c.m. by elastic scattering of 13.7 MeV polarized neutrons from a polarized proton target

The neutron-proton spin correlation coefficient A_yy was measured at 90° c.m. by elastic scattering of 13.7 MeV polarized neutrons from a polarized proton target. The target polarization of about 60% was produced in a LMN single crystal by dynamic nuclear orientation using 70 GHz microwaves. The target was thin enough to allow the detection of the recoil protons in coincidence with the associated scattered neutrons. Our result for A_yy is the first experimental determination of a neutron-proton spin correlation parameter at such a low energy. To determine the influence of A_yy on the ³S₁-³D₁ mixing parameter ε₁, a single-energy n-p phase shift analysis was performed using the experimentally determined value of A_yy= 0.078 ± 0.014 along with analyzing power and cross section data. As expected, the result for ε₁ changes drastically upon the inclusion of A_yy. An unexpectedly small value of ε₁ = −0.16°±0.54° has been obtained in the present analysis.     

Structurally asymmetric d.c. SQUID’s in the presence of coupling energy inhomogeneity of the junctions studied by means of the reduced two-junction interferometer model

The effects of structural asymmetries and of inhomogeneities in the junction parameters on the electrodynamic response of conventional d.c. SQUIDs are studied both analytically and numerically. By a first-order perturbative expansion with respect to the parameter and to the deviation parameters describing structural asymmetry and inhomogeneity, we write the reduced dynamical equation for the average superconducting phase difference of a conventional d.c. SQUID. As in homogeneous and symmetric SQUIDs, the resulting dynamical equation is seen to be similar to that of a single junction with an unconventional current-phase relation characterized by a second harmonic contribution; in addition, a cosine term appears as a consequence of superconducting coupling inhomogeneity. By means of the reduced dynamical equation, the I-V characteristics in the presence of an external rf field and the critical current of the device are studied in the absence of noise.     

Study of inverse a.c. Josephson effect in Y–Ba–Cu–O and Y–8a–Sr–Cu–O

Microwave induced d.c. voltage due to inverse a.c. Josephson effect has been observed across bulk samples of Y-Ba-Cu-O and Y-Ba-Sr-Cu-O. The d.c. voltage is found to vary with microwave power, frequency and also with small external magnetic fields. Although the resistivity curve of Y-Ba-Cu-O does not show any appreciable resistance drop around 230 K, the microwave induced d.c. voltage due to the inverse a.c. Josephson effect has been found to exist upto 230 K. The resistivity behaviour of Y-Ba-Sr-Cu-O shows a sharp resistivity drop above 230 K. In this sample the inverse Josephson effect is found to exist upto +26 °C, indicating the presence of a phase having a superconducting onset around this temperature.