共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
A. Avella F. Mancini 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):27-33
The magnetic properties of the La2CuO4 are analyzed by means of the paramagnetic solution of the Hubbard model within the composite operator method. The experimental
findings of the inelastic neutron magnetic scattering [R. Coldea et al., Phys. Rev. Lett. 86, 5377 (2001)] for the spin spectrum, the spin-wave intensity and the behavior of the dispersion at the zone boundary are
well described by our results although the difference in phase. The Hubbard model emerges has a minimal model capable to describe
the anomalous magnetic behavior of such a strongly correlated material.
Received 29 July 2002 / Received in final form 2 January 2003 Published online 14 March 2003 相似文献
3.
R. Leone G. Odriozola L. Mussio A. Schmitt R. Hidalgo-Álvarez 《The European physical journal. E, Soft matter》2002,7(2):153-161
Coupled aggregation and sedimentation processes were studied by means of three-dimensional computer simulations. For this
purpose, a large prism with no periodic boundary conditions for the sedimentation direction was considered. Furthermore, three
equally sized and mutually excluded regions were defined inside the prism, a top, a middle and a bottom region. This allows
to study the time evolution of the cluster size distribution and the cluster structure separately for each region. The mass
distribution profile and the center-of-mass position were also accessed as a function of time. For the bottom region, the
effects of the sediment formation on the kinetics of growth and on the cluster structure were clearly observed. The obtained
results not only agree with the experimental data obtained by Allain et al. (C. Allain, M. Cloitre, M. Wafra, Phys. Rev. Lett. 74, 1478 (1995)) and with the simulations made by Gonzalez (A.E. Gonzalez, Phys. Rev. Lett. 86, 1243 (2001)), but also allow to gain further insight into the details.
Received 7 November 2001 相似文献
4.
T. Aichele A.I. Lvovsky S. Schiller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):237-245
A detailed theoretical analysis of the spatiotemporal mode of a single photon prepared via conditional measurements on a photon pair generated in the process of parametric down-conversion is presented. The maximum
efficiency of coupling the photon into a transform-limited classical optical mode is calculated and ways for its optimization
are determined. An experimentally feasible technique of generating the optimally matching classical mode is proposed. The
theory is applied to a recent experiment on pulsed homodyne tomography of the single-photon Fock state [A.I. Lvovsky et al., Phys. Rev. Lett. 87, 050402 (2001)].
Received 16 July 2001 相似文献
5.
G. Costanza 《Physica A》2003,330(3-4):421-441
The analytical continuous equations for the Tang and Leschhorn (Phys. Rev. A 45 (1992) R8309) and the Buldyrev et al. (Phys. Rev. A 45 (1992) R8313) models are derived from the microscopic rules using a regularization procedure. As was shown in a previous paper (Phys. Rev. E 62 (2000) 6970) the continuous equation for the Tang and Leschhorn model is formally different to the Kardar–Parisi–Zhang equation (Phys. Rev. Lett. 56 (1986) 889) with quenched noise (QKPZ). Nevertheless, after expanding the multiplicative noise, it is shown that we recover the usual QKPZ, demonstrating analytically that both equations belong to the same universality class. 相似文献
6.
D.F. Zheng P.M. Hui K.F. Yip N.F. Johnson 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(2):213-218
We present generalized dynamical models describing the sharing of information, and the corresponding herd behavior, in a population
based on the recent model proposed by Eguıluz and Zimmermann (EZ) [Phys. Rev. Lett. 85, 5659 (2000)]. The EZ model, which is a dynamical version of the herd formation model of Cont and Bouchaud (CB), gives a
reasonable model for the formation of clusters of agents and for actions taken by clusters of agents. Both the EZ and CB models
give a cluster size distribution characterized by a power law with an exponent -5/2. By introducing a size-dependent probability
for dissociation of a cluster of agents, we show that the exponent characterizing the cluster size distribution becomes model-dependent
and non-universal, with an exponential cutoff for large cluster sizes. The actions taken by the clusters of agents generate
the price returns, the distribution of which is also characterized by a model-dependent exponent. When a size-dependent transaction
rate is introduced instead of a size-dependent dissociation rate, it is found that the distribution of price returns is characterized
by a model-dependent exponent while the exponent for the cluster-size distribution remains unchanged. The resulting systems
provide simplified models of a financial market and yield power law behaviour with an easily tunable exponent.
Received 31 December 2001 相似文献
7.
S. Wallentowitz R.L. de Matos Filho S.-C. Gou W. Vogel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(3):397-405
We present a method for the direct measurement of the Wigner-function matrix for complex vibronic states of a trapped atom,
that is suited to analyse the entanglement between two motional degrees of freedom and the internal electronic dynamics. It
is a generalisation of the method for the determination of vibronic quantum states [S. Wallentowitz, R.L. de Matos Filho,
W. Vogel, Phys. Rev. A 56, 1205 (1997)] in conjunction with the scheme for the direct observation of the Wigner function of a single motional degree
of freedom [L.G. Lutterbach, L. Davidovich, Phys. Rev. Lett. 78, 2547 (1997)]. The major advantage of the present method is that it reduces the experimental efforts substantially. On the
other hand, it is demonstrated that the nonlinear vibronic coupling necessary for this method turns out to be its main limitation.
Received: 5 August 1998 相似文献
8.
J. Le Cochec F. Ladieu 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):13-26
We have calculated the real part of the nonlinear dielectric susceptibility of amorphous insulators in the kHz range, by using the two-level system model
and a nonperturbative numerical quantum approach. At low temperature T, it is first shown that the standard two-level model should lead to a decrease of when the measuring field E is raised, since raising E increases the population of the upper level and induces Rabi oscillations cancelling the ones induced from the ground level.
This predicted E-induced decrease of is at odds with experiments. However, a better, though still not perfect, agreement with low-frequency experimental nonlinear data is
recovered if, in our fully quantum simulations, interactions between defects are taken into account by a new relaxation rate
whose efficiency increases as , as was proposed recently by Burin et al. [Phys. Rev. Lett. 86, 5616 (2001)]. In this approach, the behavior of at low T is mainly explained by the efficiency of this new relaxation channel. Since a quantitative understanding of glasses is still missing, we finally discuss experiments whose results should yield a refined understanding
of this new relaxation mechanism: i) a completely new nonlinear behavior should be found for samples whose thickness is ≃
10 nm; ii) a decrease of nonequilibrium effects should be found when E is increased.
Received 19 September 2002 / Received in final form 4 December 2002 Published online 14 March 2003 相似文献
9.
H.-P. Breuer U. Dorner F. Petruccione 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):377-386
In a recent experiment the progressive decoherence of a mesoscopic superposition of two coherent field states in a high-Q cavity, known as Schr?dinger cat state, has been measured for the first time [Brune et al., Phys. Rev. Lett. 77, 4887 (1996)]. Here, the full master equation governing the coupled dissipative dynamics of the atom-field system studied
in the experiment is formulated and solved numerically for the experimental parameters. The model simulated avoids the approximations
underlying an analytically solvable model which is based on a harmonic expansion of the energies of the dressed atomic states
and on a treatment of their dynamics within the adiabatic approximation. In particular, the numerical simulations reveal that
the coupling of the cavity field mode to its environment causes important decoherence effects already during the initial preparation
phase of the Schr?dinger cat state. This phenomenon is investigated in detail with the help of a measure for the purity of
states. Moreover, the Hilbert-Schmidt distance of the intended target state, the Schr?dinger cat, to the state that is actually
prepared in the experiment is determined.
Received 13 September 2000 and Received in final form 22 December 2000 相似文献
10.
I. M. Herbauts S. Bettelli H. Hübel M. Peev 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):395-406
Some MIT researchers [Phys. Rev. A
75, 042327 (2007)] have recently claimed that
their implementation of the Slutsky-Brandt attack [Phys. Rev. A
57, 2383 (1998); Phys. Rev. A 71, 042312 (2005)] to
the BB84 quantum-key-distribution (QKD) protocol puts the security of this
protocol “to the test” by simulating “the most powerful
individual-photon attack” [Phys. Rev. A 73, 012315
(2006)].
A related unfortunate news feature by a
scientific journal [G. Brumfiel, Quantum cryptography is hacked, News @ Nature (april 2007); Nature 447, 372 (2007)]
has spurred some concern in the QKD community and among the general public
by misinterpreting the implications of this work. The present article
proves the existence of a stronger individual attack on QKD protocols with
encrypted error correction, for which tight bounds are shown, and clarifies
why the claims of the news feature incorrectly suggest a contradiction with
the established “old-style” theory of BB84 individual attacks.
The full implementation of a quantum cryptographic protocol includes a
reconciliation and a privacy-amplification stage, whose choice alters in
general both the maximum extractable secret and the optimal eavesdropping
attack. The authors of [Phys. Rev. A
75, 042327 (2007)] are concerned only with the error-free
part of the so-called sifted string, and do not consider faulty bits,
which, in the version of their protocol, are discarded. When using the
provably superior reconciliation approach of encrypted error correction
(instead of error discard), the Slutsky-Brandt attack is no more optimal
and does not “threaten” the security bound derived by Lütkenhaus [Phys. Rev. A 59, 3301 (1999)].
It is shown that the method of Slutsky and collaborators [Phys. Rev. A
57, 2383 (1998)] can
be adapted to reconciliation with error correction, and that the optimal
entangling probe can be explicitly found. Moreover, this attack fills
Lütkenhaus bound, proving that it is tight (a fact which was not
previously known). 相似文献
11.
L.V. Grigorenko R.C. Johnson I.G. Mukha I.J. Thompson M.V. Zhukov 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):125-129
The theoretical approach to the two-proton radioactivity and three-body decays developed in (L.V. Grigorenko, R.C. Johnson,
I.G. Mukha, I.J. Thompson, M.V. Zhukov, Phys. Rev. Lett. 85, 22 (2000) and to be published in Phys. Rev. C) is applied to the range of light nuclear systems. We study nuclear structures,
widths, and momentum correlations for the decay fragments. Strong contradictions with experiment, as well as effects of special
interest, are found in 12O and 16Ne nuclei.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: l.grigorenko@surrey.ac.uk 相似文献
12.
G. Apaydın E. Tıraşoğlu Ö. Söğüt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(3):487-492
The M X-ray production differential cross sections in Re, Bi and U elements
have been measured at the 5.96 keV incident photon energy in an angular
range 135°–155°. The measurements were performed using a 55Fe
source and a Si(Li) detector. The present results contradict the predictions
of Cooper and Zare [Atomic Collision Processes, Gordon and Breach, New York (1969)]
and experimental results of Kumar et al. [J. Phys. B: At. Mol. Opt. 34,
613 (2001)]. that, after photoionization of inner shells, the vacancy state has equal
population of magnetic substates and the subsequent X-ray emission is
isotropic, but confirm the predictions of the calculations of Flügge et
al. [Phys. Rev. Lett. 29, 7 (1972)] and experimental results of Sharma and Allawadhi [J. Phys. B: At. Mol. Opt. 32, 2343 (1999)] and Ertugrul [Nucl. Instrum. Meth. B 119, 345 (1996)].
Total M X-ray production cross sections from the decay at the 5.96 keV
photon energies are found to be in good agreement with the calculated
theoretical results using the theoretical values of M shell photoionization
cross section. 相似文献
13.
J. P. Santos F. Parente 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(3):339-350
Total ionization cross sections of neutral phosphorus, arsenic,
antimony, and bismuth atoms by electron impact are reported and
compared to the only available experimental results by Freund et al. [Phys. Rev. A 41, 3575 (1990)]. These calculations take into account the possibilities that some
target atoms used in the experiments were in metastable states close
to the ground state, the excitation-autoionization of nsnp4
excited states may be substantial, and the ions produced in
experiments may be in excited, low-lying metastable states. The cross sections for direct ionization calculations are based
on
the BEB model by Kim and Rudd [Phys. Rev. A 50, 3954 (1994)].
Plane-wave Born cross sections scaled by the method developed by Kim
[Phys. Rev. A 64, 3954 032713 (2001)] are used to determine the
contributions from excitation-autoionization. The combination of the BEB model and the scaled Born cross sections
is in agreement with the experimental data by Freund et al. These theoretical data are useful to experimentalists and can
be
used to complete data tables needed for plasma or astrophysical
studies. 相似文献
14.
R.S. Mendes S.F. Kwok E.K. Lenzi J.N. Maki 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):353-359
By using integral representations the perturbation expansion and the Bogoliubov inequality in nonextensive Tsallis statistics
are investigated in a unified way. This procedure extends the analysis performed recently by Lenzi et al. [Phys. Rev. Lett. 80, 218 (1998)] to the quantum (discrete spectra) case, for q<1. An example is presented in order to illustrate the method.
Received 19 November 1998 相似文献
15.
W. Ekardt W.-D. Schöne R. Keyling 《Applied Physics A: Materials Science & Processing》2000,71(5):529-535
Experience has shown that theoretically determined lifetimes of bulk states of hot electrons in real metals agree quantitatively
with the experimental ones, if theory fully takes into account the crystal structure and many-body effects of the investigated
metal, i.e., if the Dyson equation is solved at the ab initio level and the effective electron–electron interaction is determined beyond the plasmon-pole approximation. Therefore the
hitherto invoked transport effect [Knoesel et al.: Phys. Rev. B 57, 12812 (1998)] does not seem to exist. In this paper we show that likewise neither virtual states [Hertel: et al. Phys. Rev.
Lett. 76, 535 (1996)] nor damped band-gap states [Ogawa: et al.: Phys. Rev. B 55, 10869 (1997)] exist, but that the hitherto unexplained d-band catastrophe in Cu [Cu(111), Cu(110)] can be naturally resolved
by the concept of the transient exciton. This is a new quasiparticle in metals, which owes its existence to the dynamical character of dielectric screening at the microscopic level. This means that excitons, though they do not exist under stationary
conditions, can be observed under ultrafast experimental conditions.
Received: 30 March 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
16.
Jun Cai Jian-Sheng Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):45-48
The tight-binding potential combined with a simulated annealing method is used to study the generalized stacking fault (GSF)
structure and corresponding energy of gold. The potential is chosen to fit band structures and total energies from a set of
first-principle calculations [Phys. Rev. B 54, 4519 (1996)]. It is found that the relaxed stacking fault energy (SFE) and unstable SFE are equal to 46 and 102 mJ/m2, respectively, and are in good agreement with first principles calculations and experiment. In addition, the structure properties
of the relaxed GSF of metal Au are also presented.
Received 13 December 2001 Published online 9 July 2002 相似文献
17.
Using small-angle X-ray scattering, the repeat distance vs. temperature is measured for a homologous series of multilamellar vesicles of lecithins with varying acyl chain length in
excess water condition around the lipid main transition. A systematic chain length dependence is found which is in accordance
with a bending rigidity renormalization and critical unbinding of the lamellae close to the transition, as previously suggested
in H?nger et al. [Phys. Rev. Lett. 72, 3911 (1994)].
Received 13 January 1999 and Received in final form 6 September 1999 相似文献
18.
B. Audoin M. Perton N. Chigarev C. Rossignol 《The European physical journal. Special topics》2008,153(1):235-237
Investigation of thin metallic film properties by means
of picosecond ultrasonics [C. Thomsen et al., Phys. Rev. Lett. 53, 989 (1984)] has been under the scope of several studies.
Generation of longitudinal and shear waves [T. Pézeril et al., Phys. Rev. B 73, 132301 (2006); O. Matsuda et al., Phys. Rev. Lett. 93, 095501 (2004)] with a wave vector normal
to the film free surface has been demonstrated. Such measurements cannot
provide complete information about properties of anisotropic films. Extreme
focusing of a laser pump beam (≈0.5 μm) on the sample surface
has recently allowed us to provide evidence of picosecond acoustic
diffraction in thin metallic films (≈1 μm) [C. Rossignol et al., Phys. Rev. Lett. 94, 166106 (2005)]. The resulting
longitudinal and shear wavefronts propagate at group velocity through the
bulk of the film. To interpret the received signals, source directivity
diagrams are calculated taking into account material anisotropy, optical
penetration, and laser beam width on the sample surface. It is shown that
acoustic diffraction increases with optical penetration, so competing with
the increasing of directivity caused by beam width. Reflection with mode
conversion at the film-substrate interface is discussed. 相似文献
19.
C. Giordano A.R. Plastino M. Casas A. Plastino 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):361-368
Nonlinear diffusion equations provide useful models for a number of interesting phenomena, such as diffusion processes in
porous media. We study here a family of nonlinear Fokker-Planck equations endowed both with a power-law nonlinear diffusion
term and a drift term with a time dependent force linear in the spatial variable. We show that these partial differential
equations exhibit exact time dependent particular solutions of the Tsallis maximum entropy (q-MaxEnt) form. These results constitute generalizations of previous ones recently discussed in the literature [C. Tsallis,
D.J. Bukman, Phys. Rev. E 54, R2197 (1996)], concerning q-MaxEnt solutions to nonlinear Fokker-Planck equations with linear, time independent drift forces. We also show that the present
formalism can be used to generate approximate q-MaxEnt solutions for nonlinear Fokker-Planck equations with time independent drift forces characterized by a general spatial
dependence.
Received 25 April 2001 and Received in final form 6 June 2001 相似文献
20.
A new realislic local model of light propagation and detection is described. The authors propose a novel stochastic model of low-intensity photon detection in which background noise is added to a part of the photon prior to absorption. In this model, in agreement with Planck, there is no quantization of the propagating field. The model has some similarities to theories advanced by E. Santos and T. Marshall in the last decade, but also has substantial deviations from these. A mechanism, conserving energy and momentum, is proposed by which a sudden collapse of the wave-packet is avoided. The experimental Bell inequality violation of Aspect. Grangier and Roger [Phys. Rev. Lett.47, 460 (1981)]is discussed. The authors have carried out a computer simulation of a radio frequency (RF) analogue of the Einstein-Podolsky-Rosen thought experiment to illustrate how the manipulation of certain factors, especially signal to noise ratio, detector threshold and characteristics of the noise, enables the same Bell inequality to be either satisfied or violated by a realistic local model. Building on arguments by Santos. [Phys. Rev. A46. 3646 (1992)],the appropriateness of this Bell lest is discussed. Neither the authors' stochastic-optical model, nor their RF analogue, involves an enhancement assumption of the type defined by Clauser and Horne [Phys. Rev. D10, 526 (1974)]. 相似文献