共查询到20条相似文献,搜索用时 781 毫秒
1.
A. Lindner H. Freese G. Quehl D. Reiß K. Schiller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):99-112
The time evolution of a damped two-level atom coupled to a damped field mode at resonance is calculated analytically as well
as numerically in the basis of dressed states. We study the dynamics of the density matrix and of observables, e.g. the number of field quanta. For the initial states we consider the field to be in a Fock or Glauber state and the atom in
the ground or excited state. We show the significant influence of the damping on the well-known phenomena of this model, e.g. collapse and revival.
Received 22 January 2001 and Received in final form 16 May 2001 相似文献
2.
N. Liu W. Gao J. Yin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):137-145
A new scheme to magnetically guide cold, neutral atoms using a V-shaped current-carrying conductor is proposed. The spatial
distributions of the magnetic fields, potentials and forces generated by the V-shaped current-carrying conductor are calculated,
and the relationship between the magnetic field and the parameters of the V-shaped current-carrying conductor are analyzed
in detail. Our study shows that the V-shaped current-carrying conductor proposed here can be used to guide cold atoms in the
weak-field-seeking state, and to construct various atom-optical elements, such as atomic funnel, atomic beam-splitter and
atom interferometer and so on, and even to realize a single-mode atomic waveguiding under certain conditions.
Received 17 November 2000 and Received in final form 26 May 2001 相似文献
3.
4.
G. Sharma S.K. Ghosh 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):79-86
Using hydrodynamic model of semiconductor plasmas and coupled-mode theory of interacting waves, we have analytically investigated
parametric interaction in a magnetised piezoelectric semiconductor plasma in non-relativistic domain. The temperature dependence
of momentum transfer collision frequency of electrons due to their heating by the pump is assumed to induce nonlinearity in
the medium. We have derived a dispersion relation which finally gives four unstable acoustic modes; two forward amplifying
modes and two backscattered attenuating modes. We have also obtained an expression for the critical pump amplitude ( ) at and around which gains and phase velocities of amplifying acoustic modes become least dependent on the pump amplitude
and static magnetic field . The required can be readily obtained from a pulsed 10.6 μm CO2 laser. The magnetic field is found to shift the critical point towards lower pump amplitudes.
Received 5 September 2000 and Received in final form 5 March 2001 相似文献
5.
B.S. Kandemir T. Altanhan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):517-526
We investigate the stability condition of large bipolarons confined in a parabolic potential containing certain parameters
and a uniform magnetic field. The variational wave function is constructed as a product form of electronic parts, consisting
of center of mass and internal motion, and a part of coherent phonons generated by Lee-Low-Pines transformation from the vacuum.
An analytical expression for the bipolaron energy is found, from which the ground and excited-state energies are obtained
numerically by minimization procedure. The bipolaron stability region is determined by comparing the bipolaron energy with
those of two separate polarons, which is already calculated within the same approximation. It is shown that the results obtained
for the ground state energy of bipolarons reduce to the existing works in zero magnetic field. In the presence of a magnetic
field, the stability of bipolarons is examined, for three types of low-dimensional system, as function of certain parameters,
such as the magnetic-field, the electron-phonon coupling constant, Coulomb repulsion and the confinement strength. Numerical
solutions for the energy levels of the ground and first excited states are examined as functions of the same parameters.
Received 7 March 2002 and Received in final form 22 April 2002 Published online 25 June 2002 相似文献
6.
A simple model for systems of dipolarly interacting single-domain ultrafine ferromagnetic particles is studied by Monte Carlo
simulations of zero field cooling and field cooling as well as relaxation experiments. By investigating systems characterized
by an identical moderate concentration but different types of particle positions' disorder, it is shown that the positional
disorder has a crucial influence on the magnetic behavior of the system. For extreme values of positional disorder, the interplay
between spatial disorder and dipolar interaction can even lead to a cooperative freezing at low temperatures.
Received 28 November 2001 相似文献
7.
P. Fulde A. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):623-627
We study the magnetic field dependence of the dielectric response of large cylindrical molecules such as nanotubes. When a
field-induced level crossing takes place, an applied electric field has two effects: it may cause a linear instead of the
usual quadratic Stark effect or the difference in the quadratic Stark coefficient of the two levels leads to a discontinuity
in the polarization. Explicit calculations are performed for doped nanotubes and a rich structure in the real part of the
low-frequency dielectric function is found when a magnetic field is applied along the cylinder axis. It is suggested that studies of can serve as a spectroscopic tool for the investigation of large ring-shaped or cylindrical molecules.
Received 11 January 2000 and Received in final form 19 May 2000 相似文献
8.
The hopping motion of a classical bounded pair of two particles along a chain is investigated. It is shown that in the asymmetric
case of the system dynamics including excited states which differ from the respective ground states by the barrier to be overcome
by one of the two particles, the over- and underpopulation of these excited states leads to a directed motion of the particle
pair. Thereby, overpopulation results in one direction of motion, whereas underpopulation results in the opposite direction,
and the mean velocity is determined by the amount of over-resp. underpopulation. For small deviations from equilibrium, the
system exhibits linear response well known from other ratchet-type models. Possible generalizations and applications are discussed.
Received 17 August 2001 and Received in final form 11 October 2001 相似文献
9.
F. Mila D. Dean 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):301-306
Motivated by the observation of a spin-glass transition in almost disorder-free Kagome antiferromagnets, and by the specific
form of the effective low-energy model of the S = 1/2, trimerized Kagome antiferromagnet, we investigate the possibility to obtain a spin-glass behavior in two-component,
disorder-free models. We concentrate on a toy-model, a modified Ashkin-Teller model in a magnetic field that couples only
to one species of spins, for which we prove that a dynamic spin-glass behavior occurs. The dynamics of the magnetization is
closely related to that of the underlying Ising model in zero field in which spins and pseudo-spins are intimately coupled.
The spin-glass like history dependence of the magnetization is a consequence of the ageing of the underlying Ising model.
Received 21 September 2001 and Received in final form 16 January 2002 相似文献
10.
Yu.L. Sokolov V.P. Yakovlev V.G. Pal'chikov Yu.A. Pchelin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):27-36
The properties of two-dimensional magnetic traps for laser-cooled atoms are analysed using complex functions. The two components
of the magnetic field from a series of parallel, infinitely long, current-carrying wires are represented by a single complex
number. The regions of the field where paramagnetic atoms can be trapped occur where the magnetic field is zero. The locations
of the zeroes of the field are obtained as the solution to a polynomial and the multiplicity m of the solution determines both the 2(m + 1)-pole nature of the trap and the field gradient through the centre. The zeroes of the field can be merged or split by
varying the locations of the currents, their strengths or by applying a uniform magnetic field. The theory is applied to magnetic
traps created from long thin wires or permanent magnets on a substrate. The properties of a number of magnetic trap configurations
used for atom guides are discussed.
Received 28 February 2001 and Received in final form 6 July 2001 相似文献
11.
Column size effects of DER fluids 总被引:1,自引:0,他引:1
The static yield stress of dielectric electrorheological (DER) fluids of infinite column state and chain state are calculated
from the first principle method. The results indicate that the column surface contributions to ER effects is very small and
both states will give correct results to the real DER fluids.
Received 29 January 2001 and Received in final form 30 April 2001 相似文献
12.
The ground- and first-excited states of magnetopolarons in two-dimensional quantum dots for all coupling strengths 总被引:2,自引:0,他引:2
B.S. Kandemir T. Altanhan 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):227-232
The ground- and first-excited state energies of a magnetopolaron in a two dimensional parabolic quantum dot are studied within
a variational calculation for all coupling strength. The Lee-Low-Pines-Huybrecht variational technique that is developed previously
for all coupling strength has been extented for polarons in a magnetic field. The dependence of the polaronic correction on
the magnetic field and the confinement length is investigated. The polarization potential and the renormalized cyclotron masses
as a function of electron-phonon coupling strength and the strength of both confinement potential and magnetic field are also
studied within the same approach.
Received 16 December 2002 / Received in final form 14 April 2003 Published online 4 June 2003
RID="a"
ID="a"e-mail: kandemir@science.ankara.edu.tr 相似文献
13.
14.
R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献
15.
I.O. Kulik T. Hakioğlu A. Barone 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):219-226
We examine a generic three level mechanism of quantum computation in which all fundamental single and double qubit quantum
logic gates are operating under the effect of adiabatically controllable static (radiation free) bias couplings between the
states. Under the time evolution imposed by these bias couplings the quantum state cycles between the two degenerate levels
in the ground state and the quantum gates are realized by changing Hamiltonian at certain time intervals when the system collapses
to a two state subspace. We propose a physical implementation of the mechanism using Aharonov-Bohm persistent-current loops
in crossed electric and magnetic fields, with the output of the loop read out by using a quantum Hall effect aided mechanism.
Received 26 March 2002 / Received in final form 8 July 2002
Published online 19 November 2002 相似文献
16.
F. Delfino R. Procopio M. Rossi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):31-38
The evaluation of the total force of magnetic origin acting upon a body in a stationary magnetic field is often carried out
using the so-called magnetic energy (or co-energy) method, which is based on the derivation of the magnetic energy (or co-energy) with respect to a virtual rigid displacement
of the considered body. The application of this method is usually justified by resorting to the energy conservation principle,
written in terms both of electrical and of mechanical quantities. In this paper we shall re-examine the whole matter in the
context of classical thermodynamics, in order to obtain a more comprehensive and general proof of the validity of the energy
(or co-energy) approach and to point out its limitations. Two typical configurations will be discussed; in the first one,
the field sources are represented by conducting bodies carrying free currents, whereas in the second one a permanent magnet
creates the driving field. All magnetic materials are assumed to be non-hysteretic and permanent magnets are represented by
means of the well-known linear model in the second quadrant of the (B,H) plane.
Received 25 July 2001 and Received in final form 5 November 2001 相似文献
17.
B. Pilawa I. Keilhauer G. Fischer S. Knorr J. Rahmer A. Grupp 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):321-330
The magnetic properties of the cyclic compound [Fe6(bicine)6] LiClO4
. 2MeOH are reported. The cluster Fe6(bicine)6 forms an antiferromagnetically coupled ring structure of Fe III ions. The magnetic susceptibility is measured between 2 and 300 K and yields the exchange coupling of J/k
B = - 27.5±0.5 K. The field dependence of the magnetic moment is studied at 3 and 6 K in magnetic fields up to 5 T. The zero-field
splitting of the first excited spin states with S = 2 and 3 are determined by ESR at 94 GHz. The intra-molecular interactions of the Fe III ions are analyzed and the on-site anisotropy of the Fe III due to the ligand-configuration is determined to d /k
B = - 0.633±0.008K.
Received 28 October 2002 / Received in final form 22 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: bernd@piobelix.physik.uni-karlsruhe.de 相似文献
18.
B. Soep J.M. Mestdagh S. Sorgues J.P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):191-203
In the TDMAE molecule (title molecule), the time evolution has been analyzed from the very initial excitation step down to
a fluorescent state, over widely different time scales. Pump probe measurements have been performed at 3 different excitation
wavelengths 400, 266 and 200 nm. The decay has been followed over the femtosecond and subnanosecond ranges with this method
and the decay of the final charge transfer state has been detected by its fluorescence emission. This allows an overview of
the complete decay mechanism. The initial relaxation pathway is interpreted in a similar way to ethylenic molecules, where
the initial wavepacket is quickly trapped in a doubly excited state Z with charge transfer character. Then the Z state decays
slowly (10-100 picoseconds) into the final state. In difference to monoalkenes the final stage of this evolution is a charge
transfer state. The decay of transient Z state to the charge transfer state is a further assessment of the partial ionic character
of the Z state. This type of molecule with low ionization potential can be viewed as a demonstrative example of the interrelation
between the charge induced forces and the deformations in excited state reaction dynamics.
Received 17 January 2001 and Received in final form 23 February 2001 相似文献
19.
E. Ben-Naim P.L. Krapivsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):239-243
We study an elementary two-player card game where in each round players compare cards and the holder of the card with the
smaller value wins. Using the rate equations approach, we treat the stochastic version of the game in which cards are drawn
randomly. We obtain an exact solution for arbitrary initial conditions. In general, the game approaches a steady state where
the card value densities of the two players are proportional to each other. The leading small value behavior of the initial
densities determines the corresponding proportionality constant, while the next correction governs the asymptotic time dependence.
The relaxation toward the steady state exhibits a rich behavior, e.g., it may be algebraically slow or exponentially fast. Moreover, in ruin situations where one player eventually wins all cards,
the game may even end in a finite time.
Received 24 August 2001 and Received in final form 12 November 2001 相似文献
20.
P. Farmanara H.-H. Ritze V. Stert W. Radloff I.V. Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):193-209
Neutral ammonia clusters (NH3)m are photo-excited to the electronic state by a deep UV femtosecond laser pump pulse. Within a few hundred femtoseconds a significant fraction of the clusters
rearrange to form an H-transfer state (NH3)m-2NH4(3s)NH2 with the subunit NH4 in its 3s electronic ground state. This state is then electronically excited by a time-delayed infrared control pulse of variable wavelength.
Finally, a third (probe) pulse in the UV ionizes the clusters for detection. The lifetime of the excited (NH3)m-2NH4(3p)NH2 states is found to vary between 2.7 and 0.13 ps depending on cluster size and excitation energy. It increases drastically
upon deuteration. The corresponding cluster size-dependent photoelectron spectra allow us to disentangle the underlying energetics
of the excitation and ionization process and reveal additional processes, such as nonresonant ionization or dissociative ionization.
The experimental findings suggest that the excited H-transfer ammonia complexes with m > 2 are deactivated by an internal conversion process back to the electronically lowest H-transfer state followed by fast
dissociation.
Received 22 September 2001 and Received in final form 31 January 2002 相似文献