共查询到20条相似文献,搜索用时 43 毫秒
1.
Milton Dean Slaughter 《Nuclear Physics A》2004,740(3-4):383-399
A parameter-free, nonperturbative calculation of the ΔNγ electromagnetic transition amplitudes GM*(q2), GE*(q2), and the resonant multipole ratio REM(q2)≡E1+3/2(q2)/M1+3/2(q2) is performed in terms of the well-known nucleon isovector Sachs form factor GMV. Our methods are fully relativistic with conservation of the electromagnetic current guaranteed. We find that GM*(q2) decreases more rapidly than the nucleon dipole form factor when −q21 GeV2/c2 and that REM(q2) remains small even for very high four-momentum transfer implying that the perturbative QCD prediction REM(q2)→1 is purely asymptotic and is valid only for extremely high |q2|. 相似文献
2.
M. Hamedoun M. Houssa N. Benzakour A. Hourmatallah 《Physica B: Condensed Matter》1999,270(3-4):384-390
By making use of high-temperature series expansions (HTSE) of the correlation functions, we study the thermal and disorder variation of the short-range order (SRO) in the particular B-spinel ZnCr2xAl2−2xS4. We developed the HTSE for the q-dependent static structure factor S(q) to the order 6 in reciprocal temperature including both the nearest- and next-nearest-neighbour interactions J1 and J2, respectively. Respecting the experimental fact that the broad diffuse peak of the neutron is situated at the particular wave vector q0=[0 0 0.79] and is insensitive to the temperature for a given ratio of dilution x, we have estimated the thermal variation of J1 and J2 in the case of the pure compound.
The bond percolation threshold xp of the ZnCr2xAl2−2xS4 is determined by studying the disorder variation of the correlation length ξ. The xp is considered as the concentration at which ξ vanishes. The obtained values are xp=0.27 when only J1 is considered and 0.23 when both J1 and J2 are taken into account. 相似文献
3.
4.
The q-deformed traces and orbits for the two parametric quantum groups GLqp(2) and GLqp(1¦1) are defined, they are subsequently used in the construction of q-orbit invariants for these groups. General qp-(super)oscillator commutation relations are obtained, which remain invariant under the coactions of groups GLqp(2) and GLqp(1¦1). The GLqp(2)-covariant deformed algebra is deduced in terms of the bilinears of bosonic qp-oscillators, which turns out to be a central extension of the Witten-type deformation of sl(2) algebra. In the case of the supergroup GLqp(1¦1), the corresponding covariant algebras contain the N = 2 supersymmetric quantum mechanical subalgebras. 相似文献
5.
J. Weyers 《Physics letters. [Part B]》1990,240(3-4):396-400
It is shown that for deformation parameters q = 1, the bilinear product relations which define the quantum groups GLq(n) can be recast as Weyl-Heisenberg relations, provided some invertibility conditions are met. Finite- and infinite-dimensional representations of GLq(n) are then easily constructed, as shown in a few examples. 相似文献
6.
The classical Hamiltonian H = p2/2m + ε(q2/2)Σδ[s-(t/T)] has an integrable mapping of the plane, [qn+1, pn+1]= [qn+1+pn, qn+2pn], as its equations of motion. But then by introducing periodic boundary conditions via (mod 1) applied to both q and p variables, the equations of motion become the Arnol'd cat map, [qn+1, pn+1] = [qn + pn, qn + 2pn], (mod 1), revealing it to be one of the simplest fully chaotic systems which can be derived from a Hamiltonian and analyzed. Consequently, we here quantize the Arnol'd cat and examine its quantum motion for signs of chaos using algorithmic complexity as the litmus. Our analysis reveals that the quantum cat is not chaotic in the deep quantum domain nor does it become chaotic in the classical limit as required by the correspondence principle. We therefore conclude that the correspondence principle, as defined herein, fails for the quantum Arnol'd cat. 相似文献
7.
A. S. Pine M. Dang-Nhu 《Journal of Quantitative Spectroscopy & Radiative Transfer》1993,50(6):565-570
Intensities have been measured for individual transitions in the Q and R branches of the ν1 band of NH3 using a difference-frequency laser spectrometer. The data yield an integrated band strength of S0v=219.36±1.03 cm-2/MPa at 297 K, corresponding to a transition moment of μv = 8.535(20) × 10-32 C·m, and a Herman-Wallis correction factor, (1 + jm)2, where j = 0.0209(20). The intensities of a few lines for K 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2ν4 (E, L = 2), so were excluded from the fit. A small sample of ν3 band lines occurring in the ν1 band scans also yields a rough estimate of the ν3 band intensity with evident irregular perturbations. 相似文献
8.
N. Kijima R. Gronsky
X. -D. Xiang
W. A. Vareka A. Zettl J. L. Corkill Marvin L. Cohen 《Physica C: Superconductivity and its Applications》1992,190(4):597-605The crystal structure of stage-3 iodine-intercalated superconducting IBi6Sr6Ca3Cu6Ox has been determined by transmission electron microscopy to belong to the space group Pma2 with lattice parameters a=5.4Å, B=5.4Å and C=49.4Å. Ioidine atoms intercalated between every three Bi---O bilayers expand the distance between the Bi---O layers by 3.6Å and alter the atomic stacking across Bi---O layers from the staggered configuration characteristic of host superconducting Bi2Sr2CaCu2Ox to an aligned configuration characteristic of stage-1 iodine-intercalated superconducting IBi2Sr2CaCu2Ox. Higher-stage intercalation has also been observed as stacking faults which predominantly contain both stage-2 and stage-3 phases. The space groups and c-axis dimensions of the higher-stage phases have been deduced to be Pma2 with c=3.6+15.3n Å when stage number n is odd, and Bbmb with c=2(3.6+15.3n) Å when n is even. 相似文献
9.
Vacancy-assisted diffusion of a neutral probe nanoparticle with a radius Rp of a few lattice constants in a quantum crystal with a narrow vacancy band is considered. The diffusion coefficient of the probe Dp(T) in such a crystal should fall exponentially near Tmelt, and it can go through a maximum at temperatures Ttr, where the transition from thermally activated hopping of localized vacancies to a proper band motion of delocalized vacancions takes place, under the condition that the mean free path of the vacancions lv(T) at Ttr is less than Rp and increases with lowering the temperature quicker than the inverse value of the relative concentration of vacancies Xv(T). Below Ttr, where lv is much longer than the probe diameter, the value of Dp should fall proportionally to Xv(T). 相似文献
10.
A. Butera M. Vsquez Mansilla A. Fainstein G. V. M. Williams 《Physica B: Condensed Matter》2002,320(1-4):316-318
We have made high-temperature (250 K<T<800 K) DC susceptibility measurements in the compounds RuSr2Eu2−xCexCu2O10 for x=0.6,0.8, and 1.0 in order to determine the Ru effective magnetic moment. After carefully subtracting all contributions to the magnetic susceptibility except that of the Ru ions, we have been able to fit the Ru susceptibility with a law χRu=χ0+CRu/(T−ΘRu). We have found that the Ru effective moment
falls between the values expected for Ru5+ in spin states
and
. We have also found a dependence of μeff(Ru) and ΘRu with the Ce content x. 相似文献
11.
Within a real-space renormalization-group framework, we approach the cubic lattice through a D = 3 diamond-like hierarchical lattice. The model is a standard, nearest-neighbor, Ising spin glass with coupling constants {Jij} distributed according to the family of continuous probability distributions Pq(Jij) ∝ 1/[1 + (q − 1)Jij2/2J2]1/(q − 1) (if 1 + (q − 1) Jij2/2J2 > 0, and zero otherwise; q
). Such distributions, which arise naturally in the treatment, within the recently proposed nonextensive thermostatistics, of anomalous diffusion, reproduce the usual, Gaussian case, for q → 1. Moreover, they present a second moment Jij2 proportional to (5 − 3q)−1 for q < 5/3, diverging for q ≥ 5/3, but keeping a finite width at midheight. In the limit q → 3, Pq(Jij) collapses with the abscissa, and so the width at midheight diverges. We compute the q-dependence of the spin-glass critical temperature Tc. We show numerically that Tc does not scale with Jij21/2 (contrary to the usual belief), but rather with the width at midheight of Pq(Jij). Our results suggest that Tc vanishes as −1/q when q → −∞; furthermore, we verified that Tc diverges exponentially when q approaches 3 from below. 相似文献
12.
The dominant role of the 2D van Hove saddle point singularity on the Fermi surface (FS) and generalized susceptibility, χ(q), in the quasi-2D superconductor La2-xMxCuO4 is shown for varying compositions x of divalent additions M=Sr, Ba …. Dramatic topological changes in the FS with x indicate that composition can play the role of pressure in the classic work of Lifshitz. Very close correlations of large peaks in χ(q) with Fermi surface nesting features are found, along the Γ-X and Γ-N directions in the Brillouin zone, for varying x. The peak at X and N for x=0 which apparently drives, via a soft phonon mode, the transition from the bct to the orthorhombic phase is shifted to smaller q values. These results are consistent with the semiconducting behavior of La2CuO4 and superconductivity when stabilized with x>0 additions. Finally, orbital frequencies (areas) and masses are given which show the range required for de Haas-van Alphen or other experiments. 相似文献
13.
K. Fischer A. Rojek S. Thierfeldt H. Lippert R. R. Arons 《Physica C: Superconductivity and its Applications》1989,160(5-6):466-470
Unsubstituted and lead-antimony substituted 2223 BiSrCaCu Oxygen compounds have been synthesized and compared by resistivity R(T) and susceptibility χ(T) measurements and chemical analysis. The R(T) and χ(T) measurements show that interface effects occur which are reflected in the R(T) characteristics. The chemical analysis of samples with a resistance zero Tc(0)=114 K and a diamagnetic onset at 115 K yields a severe loss of lead from nominally 40 at% down to about 3 at%, whereas the Tc(0)=110 K samples contain up to about 30 at% of lead. It is assumed that for the formation of the 115 K phase lead oxide acts as a catalyst not being incorporated to a considerable amount into the lattice. 相似文献
14.
15.
Tamara A. Leskova Ingve Simonsen Alexei A. Maradudin 《Waves in Random and Complex Media》2002,12(3):307-319
We study the statistical properties of the scattering matrix S(q|k) for the problem of the scattering of light of frequency ω from a randomly rough one-dimensional surface, defined by the equation x3=ζ(x1), where the surface profile function ζ(x1) constitutes a zero-mean, stationary, Gaussian random process. This is done by studying the effects of S(q|k) on the angular intensity correlation function C(q,k|q',k')=〈I(q|k)I(q'|k')〉-〈I(q|k)〉〈I(q'|k')〉, where the intensity I(q|k) is defined in terms of S(q|k) by I(q|k)=L-11(ω/c)|S(q|k)|2, with L1 the length of the x1 axis covered by the random surface. We focus our attention on the C(1) and C(10) correlation functions, which are the contributions to C(q,k|q',k') proportional to δ(q-k-q'+k') and δ(q-k+q'-k'), respectively. The existence of both of these correlation functions is consistent with the amplitude of the scattered field obeying complex Gaussian statistics in the limit of a long surface and in the presence of weak surface roughness. We show that the deviation of the statistics of the scattering matrix from complex circular Gaussian statistics and the C(10) correlation function are determined by exactly the same statistical moment of S(q|k). As the random surface becomes rougher, the amplitude of the scattered field no longer obeys complex Gaussian statistics but obeys complex circular Gaussian statistics instead. In this case the C(10) correlation function should therefore vanish. This result is confirmed by numerical simulation calculations. 相似文献
16.
V. Kleber 《Progress in Particle and Nuclear Physics》2003,50(2):1115-559
A program to investigate the light scalar resonances a0(980)/ƒ0(980) in hadronic interactions via their decay into the πη and
channels has started at the ANKE spectrometer of COSY-Jülich. As the first step the reactions pp → dπ+X and pp → dK+X have been measured at two energies, Tp = 2.65 GeV and 2.83 GeV. The status of the analysis at Tp = 2.65 GeV is presented. A total cross section of about 50 nb has been determined for the reaction
. 相似文献
17.
18.
W. H. Fietz R. Quenzel H. A. Ludwig K. Grube S. I. Schlachter F. W. Hornung T. Wolf A. Erb M. Klser G. Müller-Vogt 《Physica C: Superconductivity and its Applications》1996,270(3-4):258-266
The pressure effect on Tc of polycrystalline and single crystalline YBa2Cu3Ox investigated as a function of oxygen content x by ac-susceptibility measurements under helium pressure. In the overdoped region x> 6.93 the single crystals show a negative dTc/d p, as expected from the charge transfer model. For optimally doped samples with x = 6.93 we find dTc/d P = 0.4 K/GPa which points to pressure effects on Tc aside from charge transfer. In the underdoped region x < 6.93 the dTc/d p values obtained from the experiment depend strongly on the storage temperature of the sample during the experiment. When the samples are stored at temperatures well below 240 K throughout the entire experiment including pressure application and pressure release, dTc/d p increases to approx. 7 K/GPa at x = 6.7 but with a further decrease of the oxygen content the dTc/d p drops to approx. 2 K/GPa at x = 6.4. These effects are intrinsic to the YBa2Cu3Ox structure and can be explained by considering the anisotropic structure of YBa2Cu3Ox. The decrease of the c-axis lattice parameter results in a charge transfer to the CuO2-planes mainly [1], whereas the compression of the a- and b-axis lattice parameter is known to produce different pressure effects which are responsible for the peak in dTc/d p at x = 6.7 [2]. When pressure is changed at room temperature oxygen ordering effects occur which cause a relaxation of Tc to the equilibrium value Tc(p) at this pressure with a time constant depending on the oxygen content x. A decrease x results in a peak effect in dTc/d p at x = 6.7 again, which is enhanced to approx. 12 K/GPa. If the oxygen content is decreased further, dTc/d p first drops to 5 K/GPa at x = 6.6, but the increases to values of more than 20 K/GPa for x < 6.42. These giant pressure effects at low oxygen contents are mainly caused by a reversible Tc increase (dTc/d p)O due to pressure induced oxygen ordering via oxygen motion between unit cells. 相似文献
19.
We have measured the resistivity of textured Bi1.84Pb0.4Sr2Ca2Cu3Oy silver-clamped thick films as a function of temperature, current density ranging from 10 to 1×103 A/cm2 and magnetic field up to 0.3 T. We find that the effective activation energy Ue follows Ue(T,J,H)=U0(1−T/Tp)mln(Jc0/J)H− with m=1.75 for Hab-plane and 2.5 for Hc-axis and =0.76 for Hab and 0.97 for Hc, for the current density regime above 100 A/cm2, where Tp is a function of applied magnetic field and current density. This result suggests the effective activation energy Ue be correlated with the temperature, current density and magnetic field. The possible dissipative mechanisms responsible for the temperature, current density and magnetic field dependence of the effective activation energy are discussed. 相似文献
20.
O. Chmaissem L. Wessels Z. Z. Sheng 《Physica C: Superconductivity and its Applications》1994,230(3-4):231-238
We have successfully prepared the first three members of the mercury-based superconducting compounds Hg--- Ba2Can−1CunO2n+2+δ, namely Hg---1201, Hg---1212 and Hg---1223 with high purity and very good quality. T he influence of the synthesis parameters is studied in detail. Using the sealed quartz tube method, very simple procedures are found to ensure a 100% reproducibility of nearly 100% pure Hg---1201 and 85–90% Hg---1212 and Hg---1223. Oxygen annealing of the sample Hg---1201 at 300°C for 18 h results in an enhancement of its critical temperature up to 97 K. The symmetry of the first and second members is tetragonal with lattice parameters a = 3.8831 (1) Å, C = 9.5357 (2) Å, and A = 3.8624 (1) Å, C = 12.7045 (2) Å, respectively. X-ray diffraction lines of Hg---1223 can be indexed in a tetragonal cell with a = 3.8564 (1) Å and C = 15.8564 (9) Å as well as in an orthorhombic cell with lattice parameters a = 5.4537 (1) Å, B = 5.4247 (1) Å, and C = 15.8505 (7) Å. 相似文献