共查询到20条相似文献,搜索用时 46 毫秒
1.
T. Mazet J. Tobola B. Malaman 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):183-191
The electronic structure of the RFe
6
Ge
6
compounds ( R
=
Sc, Lu, Ti, Zr, Hf and Nb) of HfFe
6
Ge
6
-type structure has been studied using the muffin-tin Korringa-Kohn-Rostoker method in a non-relativistic approach. The chemical
bonding is analyzed based on the l-decomposed site projected densities of states. Spin-dependent changes in the R nd- Fe 3d covalent bond are shown to be responsible for the experimentally observed rise in the Fe moment and hyperfine field upon
increasing the R valency. The limited quantitative agreement between theoretical and experimental values is interpreted as
being due to a non-negligible orbital moment and to a significant asphericity in the spin density at the iron site. The theoretical
results also forecast a strong increase of the Ge(2e) transferred hyperfine field with the R valency.
Received 20 December 2002 Published online 4 June 2003
RID="a"
ID="a"e-mail: Thomas.Mazet@lcsm.uhp-nancy.fr
RID="b"
ID="b"Associé au CNRS (UMR 7555) 相似文献
2.
P. Parneix 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):375-383
The isomerization and evaporation processes in the neutral homogeneous (CH3CN)n molecular clusters (n
= 2-7) have been investigated using classical molecular dynamics simulations. The evaporation rate constants and the kinetic energy
release in the dissociation have been analysed as a function of the cluster size and as a function of the internal energy
in the parent cluster. The competition between monomer and dimer ejections has been also carefully studied. All the dynamical
properties in these dissociative processes have been discussed in relation to the static properties of the clusters involved
in the dissociation and also in relation to the solid-liquid like transition which appears in these homogeneous molecular
clusters.
Received 19 November 2002 / Received in final form 5 February 2003 Published online 29 April 2003
RID="a"
ID="a"e-mail: pascal.parneix@ppm.u-psud.fr
RID="b"
ID="b"Laboratoire associé à l'université Paris-Sud. 相似文献
3.
H. Belich O.M. Del Cima M.M. Ferreira Jr. J.A. Helayël-Neto 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):145-155
We start from a parity-breaking MCS QED3 model with spontaneous breaking of the gauge symmetry as a framework for evaluation of the electron-electron interaction
potential and for attainment of numerical values for the e
-
e
-
- bound state. Three expressions ( V
eff
, V
eff
, V
eff
) are obtained according to the polarization state of the scattered electrons. In an energy scale compatible with condensed
matter electronic excitations, these three potentials become degenerated. The resulting potential is implemented in the Schr?dinger
equation and the variational method is applied to carry out the electronic binding energy. The resulting binding energies
in the scale of 10-100 meV and a correlation length in the scale of 10-30 ? are possible indications that the MCS-QED3 model adopted may be suitable to address an eventual case of e
-
e
-
pairing in the presence of parity-symmetry breakdown. The data analyzed here suggest an energy scale of 10-100 meV to fix the breaking of the U
(1)-symmetry.
Received 24 September 2002 / Received in final form 15 January 2003 Published online 1st April 2003
RID="a"
ID="a"e-mail: belich@cbpf.br
RID="b"
ID="b"e-mail: delcima@cbpf.br
RID="c"
ID="c"e-mail: manojr@cbpf.br
RID="d"
ID="d"e-mail: helayel@cbpf.br 相似文献
4.
H. Salehi N. Shahtahmasebi S.M. Hosseini 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):177-180
The electronic structure, total density of states DOS and electronic density in ferroelectric tetragonal crystal BaTiO3 are studied using WIEN2k package. This employs the full potential-linearized augmented plan wave FP-LAPW method in the framework
of the density functional theory DFT with the generalized gradient approximation (GGA). The results show an indirect band
gap of 2.30 eV at the Γ point in the Brillouin zone. The calculated band structure and density of states of BaTiO3 agree with the previous experimental and theoretical results, as do the charge distribution and the prediction of the nature
of the chemical bonding.
Received 11 December 2002 / Received in final form 3 February 2003 Published online 1st April 2003
RID="a"
ID="a"e-mail: salehihamid@yahoo.com 相似文献
5.
R. Eryiğit C. Parlak R. Eryiğit 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):251-254
We have performed a first-principles study of structural, dynamical, and dielectric properties of the chalcopyrite semiconductor
CuInS2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials
and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin
zone center and mode oscillator strengths are calculated using density functional perturbation theory. The calculated properties
agree with infrared and Raman measurements.
Received 12 December 2002 / Received in final form 17 March 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: resul@ibu.edu.tr 相似文献
6.
D. Bucurescu A. Gadea Ghe. Căta-Danil I. Căta-Danil M. Ivaşcu N. Mărginean C. Rusu L. Stroe C.A. Ur 《The European Physical Journal A - Hadrons and Nuclei》2003,16(4):469-474
High-spin states in the 97Tc nucleus have been studied by in-beam γ-ray spectroscopy with the reaction 82Se(19F,4nγ) at 68 MeV incident energy. Excited states have been observed up to about 8 MeV excitation and spin 43/2. The observed
level scheme is compared with results of shell model calculations.
Received: 22 November 2002 / Accepted: 23 December 2002 / Published online: 18 March 2003
RID="a"
ID="a"e-mail: bucurescu@tandem.nipne.ro
RID="b"
ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy.
RID="b"
ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy.
RID="b"
ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy.
RID="c"
ID="c"Present address: Università di Padova, Padova, Italy.
Communicated by C. Signorini 相似文献
7.
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
8.
A.V. Kisselev V.A. Petrov R.A. Ryutin 《The European Physical Journal C - Particles and Fields》2003,26(4):597-600
Quark mass effects are analyzed at high Q2 in the current fragmentation region of DIS. It is found that the linear combination F
2
-2.75F
c
2 scales at large Q2 and small x. We obtained a lower bound for the ratio F
c
2/F
2
which lies very close to the data from HERA.
Received: 14 January 2002 / Revised version: 9 October 2002 Published online: 9 December 2002
RID="a"
ID="a" e-mail: ryutin@th1.ihep.su 相似文献
9.
H.-F. Zhang J.-H. Wu J.-Y. Gao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):443-447
A five-level system to control the wavelength of the in-line amplifier by the quantum interference is proposed. It is found
that the gains of the first and the second probe can be adjusted by changing the coherent field and the incoherent pumping.
The new scheme may find its application in optical switch and optical communications.
Received 9 October 2002 Published online 24 April 2003
RID="a"
ID="a"e-mail: qol@mail.jlu.edu.cn 相似文献
10.
We calculate the , (P is the light pseudoscalar meson, V the light vector meson) form factors in the large-recoil limit in the perturbative QCD approach, including both the vector
(axial vector) and tensor operators. In general there are two leading components and for the B meson wave functions. We consider both contributions of them. Sudakov effects ( and threshold resummation) are included to regulate the soft end-point singularity. By choosing the hard scale as the maximum
virtualities of the internal particles in the hard b quark decay amplitudes, Sudakov factors can effectively suppress the long-distance soft contribution. The hard contribution
can be dominant in these approaches.
Received: 27 December 2002 / Published online: 5 May 2003
RID="a"
ID="a" e-mail: lucd@mail.ihep.ac.cn
RID="b"
ID="b" e-mail: yangmz@mail.ihep.ac.cn 相似文献
11.
Ch. Lisdat N. Vanhaecke D. Comparat P. Pillet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(3):299-309
Two-photon photoassociation spectra in a Λ-type excitation scheme are analysed under the systematically varied experimental conditions of frequency detunings and laser
intensities. Line shape fits are presented as well as the investigation of intensity and detuning dependent line shifts. From
both we determine the attained spectroscopic precision, that is corrected for a systematic line shift due to the thermal distribution
of atoms in the trap. An energy correction for this effect is given. Information about the feasibility of generating translationally
cold molecules in a well defined rotational and vibrational level by the photoassociation process is derived from the analysis.
Received 21 May 2002 Published online 15 October 2002
RID="a"
ID="a"Current address e-mail: christian.lisdat@ptb.de
RID="b"
ID="b"e-mail: pierre.pillet@lac.u-psud.fr 相似文献
12.
We show that maximal atmospheric and large solar neutrino mixing can be implemented in SU(5) gauge theories, by making use of the U(1)
F
symmetry associated with a suitably defined family number F, together with a Z2 symmetry which does not commute with F. U(1)
F
is softly broken by the mass terms of the right-handed neutrino singlets, which are responsible for the seesaw mechanism;
in additio
n, U(1)
F
is also spontaneously broken at the electroweak scale. In our scenario, lepton mixing stems exclusively from the right-handed-neutrino
Majorana mass matrix, whereas the CKM matrix originates solely in the up-type-quark sector. We show that, despite the non-supersymmetric
character of our model, unification of the gauge couplings can be achieved at a scale 1016 GeV < m
U
< 1019 GeV; indeed, we have found a particula
r solution to this problem which yields results almost identical to the ones of the minimal supersymmetric standard model.
Received: 29 November 2002 / Published online: 3 March 2003
RID="a"
ID="a" e-mail: walter.grimus@univie.ac.at
RID="b"
ID="b" e-mail: balio@cfif.ist.utl.pt 相似文献
13.
Yu.A. Sitenko K.Yu. Rulik 《The European Physical Journal C - Particles and Fields》2003,28(3):405-414
We consider quantum electrodynamics with additional coupling of spinor fields to the space-time independent axial vector
violating both Lorentz and CPT-symmetries. The Fock-Schwinger proper-time method is used to calculate the one-loop effective action up to the second order
in the axial vector and to all orders in the space-time independent electromagnetic field strength. We find that the Chern-Simons
term is not radiatively induced and that the effective action is CPT-invariant in the given approximation.
Received: 29 January 2003 / Published online: 24 March 2003
RID="a"
ID="a" e-mail: sitenko@itp.unibe.ch
RID="b"
ID="b" e-mail: rulik@to.infn.it 相似文献
14.
A systematic investigation on the muon's anomalous magnetic moment and a related lepton flavor-violating process such as
, and is made at the two-loop level in the models with flavor-changing scalar interactions. The two-loop diagrams with double scalar
exchanges are studied and their contributions are found to be compatible with the ones from the Barr-Zee diagram. By comparing
with the latest data, the allowed ranges for the relevant Yukawa couplings Yij in the lepton sector are obtained. The results show the hierarchical structure in the physical basis if is found to be . It deviates from the widely used ansatz in which the off-diagonal elements are proportional to the square root of the products
of the related fermion masses. An alternative Yukawa coupling matrix in the lepton sector is suggested to understand the current
data. With such a reasonable Yukawa coupling ansatz, the decay rate of is found to be near the current experiment upper bound.
Received: 5 September 2002 / Revised version: 11 January 2003 / Published online: 26 February 2003
RID="a"
ID="a" e-mail: zhou@theorie.physik.uni-muenchen.de
RID="b"
ID="b" e-mail: ylwu@itp.ac.cn 相似文献
15.
F. Finkel D. Gómez-Ullate A. González-López M.A. Rodríguez R. Zhdanov 《Communications in Mathematical Physics》2003,233(2):191-209
The B
N
hyperbolic Sutherland spin model is expressed in terms of a suitable set of commuting Dunkl operators. This fact is exploited
to derive a complete family of commuting integrals of motion of the model, thus establishing its integrability. The Dunkl
operators are shown to possess a common flag of invariant finite-dimensional linear spaces of smooth scalar functions. This
implies that the Hamiltonian of the model preserves a corresponding flag of smooth spin functions. The discrete spectrum of
the restriction of the Hamiltonian to this spin flag is explicitly computed by triangularization. The integrability of the
hyperbolic Sutherland spin chain of B
N
type associated with the dynamical model is proved using Polychronakos's ``freezing trick'.
Received: 14 February 2002 / Accepted: 19 June 2002 Published online: 10 December 2002
RID="*"
ID="*" Corresponding author. E-mail: artemio@fis.ucm.es
RID="**"
ID="**" On leave of absence from Institute of Mathematics, 3 Tereschenkivska St., 01601 Kyiv-4 Ukraine
Communicated by L. Takhtajan 相似文献
16.
We obtain explicit expressions for all genus one chiral n-point functions for free bosonic and lattice vertex operator algebras. We also consider the elliptic properties of these
functions.
Received: 6 May 2002 / Accepted: 4 October 2002 Published online: 24 January 2003
RID="*"
ID="*" Partial support provided by NSF DMS-9709820 and the Committee on Research, University of California, Santa Cruz
RID="⋆⋆"
ID="⋆⋆" Supported by an Enterprise Ireland Basic Research Grant and the Millenium Fund, National University of Ireland, Galway
Communicated by L. Takhtajan 相似文献
17.
D. Sarkisyan T. Becker A. Papoyan P. Thoumany H. Walther 《Applied physics. B, Lasers and optics》2003,76(6):625-631
An extremely thin cell (ETC) with the thickness of a Rb atomic vapor layer in the range of 100–300 nm was fabricated. It is
demonstrated that a simple laser-diode technique with a single resonant light beam is sufficient to observe separately all
of the atomic hyperfine transitions of the D
2 line of Rb (780 nm) and also allows us to measure the relative transition probabilities of the hyperfine transitions. The
onset of collisional self-broadening of the hyperfine transitions as the number density of atoms increases was studied. The
detrimental role of the atoms with slow longitudinal velocity in the sub-Doppler response of the Rb ETC is demonstrated by
studies in which the cell is tilted from normal incidence of the laser beam. It is also shown that using an ETC allows us
to resolve in a moderate external magnetic field the Zeeman splitting of the hyperfine transitions of the 87Rb D
1 transition F
g=1F
e=1,2.
Received: 19 February 2003 / Revised version: 4 April 2003 / Published online: 2 June 2003
RID="*"
ID="*"Corresponding author. Fax: +374/32-31172, E-mail: david@ipr.sci.am 相似文献
18.
During the last decade, as the experimental and computing means and techniques have rapidly evolved, the experimental investigation of the f7/2-shell nuclei has gained renewed interest. TheN = Z nuclei studied with the GASP array range from 44Ti to 52Fe. The results extended the knowledge of their structure up to high spins and excitation energies, above band terminations, where the competition with the charged-particles emission was initially thought to obscure the possibility of gamma-ray spectroscopy investigation. The paper highlights some of the most outstanding properties of these nuclei such as the nuclear rotation and backbending effects, band termination states, yrast traps, non-natural parity bands, competition between T = 0 and T = 1 pn pairing modes.Received: 30 October 2002, Published online: 16 March 2004PACS:
21.10.-k Properties of nuclei; nuclear energy levels - 21.60.Cs Shell model - 23.20.Lv
transitions and level energies - 27.40. + z
C.A. Ur: On leave from NIPNE Bucharest, Romania 相似文献
19.
J.-z. Zhang 《The European Physical Journal C - Particles and Fields》2003,28(3):389-393
In the q-deformed theory the perturbation approach can be expressed in terms of two pairs of undeformed position and momentum operators.
There are two configuration spaces. Correspondingly there are two q-perturbation Hamiltonians; one originates from the perturbation expansion of the potential in one configuration space, the
other one originates from the perturbation expansion of the kinetic energy in another configuration space. In order to establish
a general foundation of the q-perturbation theory, two perturbation equivalence theorems are proved. The first is Equivalence Theorem I: Perturbation expressions
of the q-deformed uncertainty relations calculated by two pairs of undeformed operators are the same, and the two q-deformed uncertainty relations undercut Heisenberg's minimal one in the same style. The general Equivalence Theorem II is:
for any potential (regular or singular) the expectation values of two q-perturbation Hamiltonians in the eigenstates of the undeformed Hamiltonian are equivalent to all orders of the perturbation
expansion. As an example of singular potentials the perturbation energy spectra of the q-deformed Coulomb potential are studied.
Received: 6 September 2002 / Revised version: 21 October 2002 / Published online: 14 April 2003
RID="a"
ID="a" e-mail: jzzhang@physik.uni-kl.de, jzzhang@ecust.edu.cn 相似文献
20.
M. Lontano D. Ryutov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):347-351
We demonstrate the in situ detection of cold 87Rb atoms near a dielectric surface using the absorption of a weak, resonant evanescent wave. We have used this technique in
time of flight experiments determining the density of atoms falling on the surface. A quantitative understanding of the measured
curve was obtained using a detailed calculation of the evanescent intensity distribution. We have also used it to detect atoms
trapped near the surface in a standing-wave optical dipole potential. This trap was loaded by inelastic bouncing on a strong,
repulsive evanescent potential. We estimate that we trap 1.5×104 atoms at a density 100 times higher than the falling atoms.
Received 14 May 2002 Published online 8 October 2002
RID="a"
ID="a"e-mail: spreeuw@science.uva.nl 相似文献