共查询到20条相似文献,搜索用时 0 毫秒
1.
Valery V. Kiselev 《Central European Journal of Physics》2004,2(3):523-534
We calculate the leptonic constant for the pseudoscalar ground state of the B
c
meson in the framework of a QCD-motivated potential model taking into account the two-loop anomalous dimension for the heavy
quark current in nonrelativistic QCD as matched with full QCD. 相似文献
2.
S. V. Dmitriev N. N. Medvedev R. R. Mulyukov O. V. Pozhidaeva A. I. Potekaev M. D. Starostenkov 《Russian Physics Journal》2008,51(8):858-865
The possibility of existence of nonlinear localized vibrational modes in an A3B two-dimensional crystal with pairwise interatomic bonds is demonstrated. Such modes are easily realized when the difference
between masses of atoms A and B is significant and the spectrum of small-amplitude crystal vibrations has a sufficiently wide
gap. The influence of the uniform tension/compression deformation on the small-amplitude crystal vibration spectrum and on
the existence of nonlinear localized modes is investigated.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 73–79, August, 2008. 相似文献
3.
T.-J. Wang J.-C. Gao Yu. M. Andreev S. A. Bereznaya T. N. Kopylova Z. V. Korotchenko G. V. Lanskii T. D. Malinovskaya A. N. Morozov S. Yu. Sarkisov 《Russian Physics Journal》2007,50(6):560-565
The most probable parameters of the pure, doped, and mixed GaSe1−xSx (x ≤ 0.4) crystals (solid solutions) are presented together with the results of investigations of their crystal structure
and defects, optical and mechanical properties, and damage thresholds.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 35–40, June, 2007. 相似文献
4.
5.
M. Davier S. Descotes-Genon A. Höcker B. Malaescu Z. Zhang 《The European Physical Journal C - Particles and Fields》2008,56(3):305-322
We revisit the determination of α
S
(m
τ
2) using a fit to inclusive τ hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient K
4 in the expansion of the Adler function, (2) new precision measurements from BABAR of e+e− annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions,
and (3) improved results from BABAR and Belle on τ branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty,
introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative
prediction of two different methods: fixed-order perturbation theory (FOPT) and contour-improved perturbative theory (CIPT).
The corresponding theoretical uncertainties are studied at the τ and Z mass scales. The CIPT method is found to be more stable with respect to the missing higher order contributions and to renormalization
scale variations. It is also shown that FOPT suffers from convergence problems along the complex integration contour. Nonperturbative
contributions extracted from the most inclusive fit are small, in agreement with earlier determinations. Systematic effects
from quark-hadron duality violation are estimated with simple models and found to be within the quoted systematic errors.
The fit based on CIPT gives α
S
(m
τ
2)=0.344±0.005±0.007, where the first error is experimental and the second theoretical. After evolution to M
Z
we obtain α
S
(M
Z
2)=0.1212±0.0005±0.0008±0.0005, where the errors are respectively experimental, theoretical and due to the evolution. The result
is in agreement with the corresponding N3LO value derived from essentially the Z width in the global electroweak fit. The α
S
(M
Z
2) determination from τ decays is the most precise one to date. 相似文献
6.
We developed a self-consistent method for the calculation of spatial current distributions in high-T c grain-boundary junctions. It is found that crystallographic anisotropy of high-T c superconducting electrodes results in the effects, which previously were not taken into account for interpretations of experimental data. Among them is a significant redistribution of electrical currents in superconducting electrodes in the vicinity of a grain boundary. In particular in the case of [100]-tilt bicrystal junctions, this current redistribution results in a substantial focusing to the top or bottom part of a thickness of the grain boundary, depending on “roof”- or “valley”-type of the grain boundary. This redistribution is accompanied by generation of vortex currents around the grain boundary, which leads to self-biasing of grain-boundary junctions by magnetic field nucleated by these vortex currents. It is shown that twinning or variation of geometrical shape of the high-T c electrode may also result in intensive redistribution of electrical currents and nucleation of local magnetic fields inside a high-T c superconducting electrodes. 相似文献
7.
Yong-Yeon Keum 《Pramana》2004,63(6):1151-1170
We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two-bodyB-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approach. PQCD
results are compatible with present experimental data for charmless B-meson decays. We predict the possibility of large direct
CP asymmetry in B0 → π+π− (23 +7%) and B0 →K
+π− (− 17 ± 5%). We also investigate the branching ratios, CP asymmetry and isospin symmetry breaking in radiativeB →(K*/ρ)γ decays. 相似文献
8.
A.A. Kordyuk V.B. Zabolotnyy D.V. Evtushinsky D.S. Inosov T.K. Kim B. Büchner S.V. Borisenko 《The European physical journal. Special topics》2010,188(1):153-162
We review the search for a mediator of high-T
c superconductivity focusing on ARPES experiment. In case of HTSC cuprates, we summarize and discuss a consistent view of electronic
interactions that provides natural explanation of both the origin of the pseudogap state and the mechanism for high temperature
superconductivity. Within this scenario, the spin-fluctuations play a decisive role in formation of the fermionic excitation
spectrum in the normal state and are sufficient to explain the high transition temperatures to the superconducting state while
the pseudogap phenomenon is a consequence of a Peierls-type intrinsic instability of electronic system to formation of an
incommensurate density wave. On the other hand, a similar analysis being applied to the iron pnictides reveals especially
strong electron-phonon coupling that suggests important role of phonons for high-T
c superconductivity in pnictides. 相似文献
9.
10.
Ctirad Klimčík 《International Journal of Theoretical Physics》2007,46(10):2443-2463
We show that D-branes in the Euclidean AdS
3 can be naturally associated to the maximally isotropic subgroups of the Lu–Weinstein double of SU(2). This picture makes very transparent the residual loop group symmetry of the D-brane configurations and gives also immediately the D-branes shapes and the σ-model boundary conditions in the de Sitter T-dual of the SL(2,C)/SU(2) WZW model. 相似文献
11.
12.
13.
Powder neutron diffraction and Hi-Q neutron diffraction data have been recorded and analysed in order to obtain the local and long range order of Cu in Cudoped
CeO2 with three doping levels of Cu. Rietveld method and MCGR techniques of data analysis for the two types of data reveal that
the Cu ion is in the 2+ oxidation state and has a vacancy in its first coordination shell. These deductions from the data
analysis fit well with the mechanism of catalysis we propose. 相似文献
14.
S. P. Baranov 《JETP Letters》2008,88(8):471-474
In the framework of k
t
-factorization approach, the process of inclusive photoproduction of J/Ψ mesons at HERA conditions is considered. The spin density matrix elements are calculated, and the predictions are compared
with recent experimental data.
The article is published in the original. 相似文献
15.
H.-Y. Cheng 《The European Physical Journal C - Particles and Fields》2003,26(4):551-565
Based on SU(3) flavor symmetry, many of the quark-graph amplitudes in two-body non-leptonic decays of charmed mesons can
be extracted from experiment, which enable us to see the relevance and importance of weak annihilation topologies and to determine
the complex parameters a1 and a2 to test the factorization approach. It is found that a
2
/a
1
in and can be different by a factor of 2, indicating that non-factorizable corrections to the latter are far more important than
the former. The relative phase between a1 and a2 is about 150°. Weak annihilation topologies induced by nearby resonances via final-state rescattering can be described in
a model-independent manner. Although the W-exchange contribution in decays is dominated by resonant final-state interactions (FSIs), its amplitude in VP decays (V: vector meson, P: pseudoscalar meson) receives little contributions from FSIs in the quark-antiquark resonance formation. As a consequence,
the sign flip of the W-exchange amplitude in and decays, which is needed to explain the relatively real decay amplitudes of , remains unexplained. SU(3) symmetry is badly broken in some Cabibbo-suppressed modes and this can be accounted for by the
accumulation of some modest SU(3) violation in individual quark-graph amplitudes.
Received: 19 July 2002 / Published online: 20 November 2002 相似文献
16.
Ville Hakulinen 《Communications in Mathematical Physics》2003,235(1):1-45
We prove estimates for the stationary state n-point functions at zero molecular diffusivity in the Kraichnan model [13]. This is done by proving upper bounds for the heat
kernels and Green's functions of the degenerate elliptic operators M
n
that occur in the Hopf equations for the n-point functions.
Received: 25 August 2001 / Accepted: 30 September 2002 Published online: 20 January 2003
Communicated by A. Kupiainen 相似文献
17.
The extended interacting boson model withs-, p-, d-, f- andg-bosons included (spdfg IBM) is investigated. The algebraic structure including the generators, the Casimir operators of the groups at theSU(5) dynamical symmetry and the branching rules of the irreducible representation reductions along the group chain are obtained.
The typical energy spectrum of the symmetry is given. 相似文献
18.
Teng Wang Tianbo Liu Da-Xin Zhang Bo-Qiang Ma 《The European Physical Journal C - Particles and Fields》2011,71(9):1758
We investigate the rare decays \(B_{c} \rightarrow D_{s}(1968)\ell \overline{\ell}\) and \(B_{c}\rightarrow D_{s}^{*}(2317) \ell \overline{\ell}\) in the framework of the light-cone quark model (LCQM). The transition form factors are calculated in the space-like region and then analytically continued to the time-like region via exponential parametrization. The branching ratios and longitudinal lepton polarization asymmetries (LPAs) for the two decays are given and compared with each other. The results are helpful for investigating the structure of B c meson and for testing the unitarity of CKM quark mixing matrix. All these results can be tested in the future experiments at the LHC. 相似文献
19.
Julia Lindberg Peter Saetre Seiji Nishino Emmanuel Mignot Elena Jazin 《BMC neuroscience》2007,8(1):34
Background
Narcolepsy causes dramatic behavioral alterations in both humans and dogs, with excessive sleepiness and cataplexy triggered by emotional stimuli. Deficiencies in the hypocretin system are well established as the origin of the condition; both from studies in humans who lack the hypocretin ligand (HCRT) and in dogs with a mutation in hypocretin receptor 2 (HCRTR2). However, little is known about molecular alterations downstream of the hypocretin signals. 相似文献20.
The experimental nuclear level density below the neutron binding energy B
n
in the mass region 40 ≤ A ≤ 200 is approximated to a high precision on the basis of the Strutinsky model combined with the assumption that the coefficient
of collective enhancement of the level density for a given number of excited quasiparticles decreases exponentially with increasing
excitation energy. This combination of model concepts makes it possible to reproduce faithfully not only the general trend
revealed by the method developed at the Joint Institute for Nuclear Research (JINR, Dubna) in the change in the level density
with increasing excitation energy in any nuclei but also the fine structure of this level density. Realistic experimental
information about the change in the relationship between the densities of quasiparticle- and vibrational-type states was obtained
for the first time for any nuclei virtually up to the neutron binding energy B
n
. 相似文献