共查询到20条相似文献,搜索用时 46 毫秒
1.
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
2.
M. Angeloni C. Aruta G. Balestrino P. Orgiani A. Tebano P.G. Medaglia 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):561-566
In this report we demonstrate that high quality epitaxial heterostructures, based on metallic SrRuO3 and insulating SrTiO3 individual blocks a few unit cells thick, can be grown in a purely 2D, layer-by-layer mode, using pulsed laser deposition
with in situ reflection high energy electron diffraction (RHEED) diagnostics. The thickness of each constituent block can be controlled
at the level of a single unit cell. A detailed investigation carried out at the synchrotron facility, ESRF, by various X-ray
techniques has demonstrated that each intensity oscillation of the RHEED specular spot corresponds strictly to the growth
of a single perovskite unit cell, either SrRuO3 or SrTiO3. Furthermore, we show that, in these structures, the interfaces between the different constituent blocks are very sharp with
a roughness of only one unit cell.
Received 3 July 2002 / Received in final form 12 September 2002 Published online 31 October 2002
RID="a"
ID="a"e-mail: tebano@uniroma2.it 相似文献
3.
J. de Vries S. Luther D. Lohse 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):503-509
When a 2-4 mm diameter bubble rising with constant velocity hits a thin wire, bubble shape oscillations can be induced. As
a consequence also the bubble rise velocity strongly oscillates. With the help of a force balance we show that these velocity
oscillations are an added-mass effect.
Received 9 April 2002 / Received in final form 11 July 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: lohse@tn.utwente.nl 相似文献
4.
J.M. Cerveró A. Rodrıguez 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):239-251
We present the exact diagonalization of the Schr?dinger operator corresponding to a periodic potential with N deltas of different couplings, for arbitrary N. This basic structure can repeat itself an infinite number of times. Calculations of band structure can be performed with
a high degree of accuracy for an infinite chain and of the correspondent eigenlevels in the case of a random chain. The main
physical motivation is to modelate quantum wire band structure and the calculation of the associated density of states. These
quantities show the fundamental properties we expect for periodic structures although for low energy the band gaps follow
unpredictable patterns. In the case of random chains we find Anderson localization; we analize also the role of the eigenstates
in the localization patterns and find clear signals of fractality in the conductance. In spite of the simplicity of the model
many of the salient features expected in a quantum wire are well reproduced.
Received 24 June 2002 Published online 29 November 2002 相似文献
5.
A. Khelif B. Djafari-Rouhani Ph. Lambin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):437-445
The vibrational and electronic spectra of a semi-infinite crystal with a planar surface are modified by the presence of surface
inhomogeneities or roughness such as ridges or grooves, quantum wires or tips. We develop a Green's function formalism to
investigate the localized and resonant acoustic modes of shear horizontal polarization associated with the surface of a substrate
supporting a single and a periodic array of wires. Each material is assumed to be an isotropic elastic medium. The calculation
can be applied to an arbitrary choice of the shape and elastic parameters of the wires. The surface modes are obtained as
well-defined peaks of the densities of states (DOS). In this paper, we calculate the variation of the density of states associated
with the adsorption of a single wire, and the dispersion curves of the surface modes for a periodic array of wires on the
flat surface of a substrate. We discuss their behaviors as a function of the elastic parameters and the relationship between
resonant modes of the single wire and dispersion curves of the surface modes for a periodic structure.
Received 6 December 2000 相似文献
6.
Pil H. Song ILki Kim 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):299-303
We study the effects of dissipation or leakage on the time evolution of Grover's algorithm for a quantum computer. We introduce
an effective two-level model with dissipation and randomness (imperfections), which is based upon the idea that ideal Grover's
algorithm operates in a 2-dimensional Hilbert space. The simulation results of this model and Grover's algorithm with imperfections
are compared, and it is found that they are in good agreement for appropriately tuned parameters. It turns out that the main
features of Grover's algorithm with imperfections can be understood in terms of two basic mechanisms, namely, a diffusion
of probability density into the full Hilbert space and a stochastic rotation within the original 2-dimensional Hilbert space.
Received 12 August 2002 / Received in final form 14 October 2002 Published online 4 February 2003 相似文献
7.
O. Civitarese J. Suhonen H. Ejiri 《The European Physical Journal A - Hadrons and Nuclei》2003,16(3):353-358
We have performed a theoretical analysis of the ground-state-to-ground-state transitions in 100Mo and 116Cd, based on the quasiparticle random-phase approximation and on a straightforward perturbative scheme. The results show that
the single-state dominance found in the realistic calculations of the nuclear matrix elements, which is consistent with data,
can be viewed as a result of the interference between few two-quasiparticle configurations.
Received: 12 August 2002 / Accepted: 23 October 2002 / Published online: 18 February 2003
RID="a"
ID="a"e-mail: civitarese@fisica.unlp.edu.ar
Communicated by V.V. Anisovich 相似文献
8.
The modeling of the elastic properties of disordered or nanoscale solids requires the foundations of the theory of elasticity
to be revisited, as one explores scales at which this theory may no longer hold. The only cases for which microscopically
based derivations of elasticity are documented are (nearly) uniformly strained lattices. A microscopic approach to elasticity
is proposed. As a first step, microscopically exact expressions for the displacement, strain and stress fields are derived.
Conditions under which linear elastic constitutive relations hold are studied theoretically and numerically. It turns out
that standard continuum elasticity is not self-evident, and applies only above certain spatial scales, which depend on details
of the considered system and boundary conditions. Possible relevance to granular materials is briefly discussed.
Received 18 March 2002 and Received in final form 29 May 2002 相似文献
9.
M. Johansson A.M. Morgante S. Aubry G. Kopidakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):279-283
Modulational instability of travelling plane waves is often considered as the first step in the formation of intrinsically
localized modes (discrete breathers) in anharmonic lattices. Here, we consider an alternative mechanism for breather formation,
originating in oscillatory instabilities of spatially periodic or quasiperiodic nonlinear standing waves (SWs). These SWs
are constructed for Klein-Gordon or Discrete Nonlinear Schr?dinger lattices as exact time periodic and time reversible multibreather
solutions from the limit of uncoupled oscillators, and merge into harmonic SWs in the small-amplitude limit. Approaching the
linear limit, all SWs with nontrivial wave vectors (0 < Q < π) become unstable through oscillatory instabilities, persisting for arbitrarily small amplitudes in infinite lattices.
The dynamics resulting from these instabilities is found to be qualitatively different for wave vectors smaller than or larger
than π/2, respectively. In one regime persisting breathers are found, while in the other regime the system thermalizes.
Received 6 October 2001 / Received in final form 1st March 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: mjn@ifm.liu.se 相似文献
10.
G. Bollen 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):237-243
Today ion traps are an important experimental tool. Applications range from high-precision measurements of masses and moments,
realization of atomic clocks, to the study of ion chemical reactions. Ion traps have gained particular importance in the field
of nuclear physics where they are used for the precise determination of nuclear binding energies, decay studies, and radioactive
ion beam manipulation.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: bollen@nscl.msu.edu 相似文献
11.
N.-K. Lee T.A. Vilgis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):451-465
We study the elastic properties of single A/B random copolymer chains, with a specific sequence and use them as theoretical
model for so called HP proteins. HP proteins carry hydrophilic (P) and hydrophobic (H) monomers. We predict a rich structure
in the force-extension relations which can be attributed to the information in the sequence. The variational method is used
to probe local minima on the path of stretching and releasing for the chain molecules. At a given force, we find multiple
configurations which are separated by energy barriers. A collapsed globular configuration consists of several domains which
unravel cooperatively. Upon stretching, the unfolding path shows a stepwise pattern corresponding to the unfolding of each
domain. While releasing, several cores can be created simultaneously in the middle of the chain, resulting in a different
path of collapse. The long-range interactions and stiffness of the chain simplify the potential landscape given by the disorder
in sequence.
Received 5 March 2002 / Received in final form 16 May 2002 Published online 13 August 2002 相似文献
12.
T. Aspelmeier J. Magnin W. Graupner U.C. Täuber 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):441-450
We investigate random walks on a lattice with imperfect traps. In one dimension, we perturbatively compute the survival probability
by reducing the problem to a particle diffusing on a closed ring containing just one single trap. Numerical simulations reveal
this solution, which is exact in the limit of perfect traps, to be remarkably robust with respect to a significant lowering
of the trapping probability. We demonstrate that for randomly distributed traps, the long-time asymptotics of our result recovers
the known stretched exponential decay. We also study an anisotropic three-dimensional version of our model. We discuss possible
applications of some of our findings to the decay of excitons in semiconducting organic polymer materials, and emphasize the
crucial influence of the spatial trap distribution on the kinetics.
Received 23 July 2001 / Received in final form 14 May 2002 Published online 13 August 2002 相似文献
13.
A. Steyerl B.G. Yerozolimsky A.P. Serebrov P. Geltenbort N. Achiwa Yu.N. Pokotilovski O. Kwon M.S. Lasakov I.A. Krasnoshchokova A.V. Vasilyev 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):299-304
Ultracold neutrons (UCN) are lost from traps if they are quasi-elastically scattered from the wall with an energy gain sufficient
to exceed the Fermi potential for the wall. Possible mechanisms of a quasi-elastic energy transfer are, for instance, scattering
from hydrogen diffusing in an impurity surface layer or on surface waves at a liquid wall. Using two different experimental
methods at the UCN source of the Institut Laue-Langevin we have investigated both the energy-gain and the energy-loss side
of quasi-elastic UCN scattering on Fomblin grease coated walls. For Fomblin oil and similar new types of oil we report up-scattering
data as a function of temperature and energy transfer. These low-temperature oils may be used in an improved measurement of
the neutron lifetime, which requires extremely low wall reflection losses.
Received 13 March 2002 Published online 31 July 2002 相似文献
14.
M. Girod J. Libert J.-P. Delaroche P. Romain 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):209-212
The structure properties of the even-even nuclei 226, 228, 230, 232, 234Th, 230, 232, 234, 236, 238, 240U, 240, 242, 244, 246Pu, and 242, 244, 246, 248Cm have been investigated at normal and superdeformed shapes in microscopic mean-field calculations based on Gogny force.
Collective levels are predicted from constrained Hartree-Fock-Bogoliubov and configuration mixing calculations. Two quasiparticle
states are also predicted from blocking calculations for neutron and proton configurations. Predictions are shown and compared
with experimental data at superdeformed shapes.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: michel-g.girod@cla.tr 相似文献
15.
Inclusions embedded in lipid membranes undergo a mediated force, due to the tendency of the membrane to relax its excess of
elastic energy. In this paper we determine the exact shape of a two-dimensional vesicle hosting two different inclusions,
and we analyse how the inclusion conformation influences the mediated interaction. We find non-trivial equilibrium configurations
for the inclusions along the hosting membrane, and we derive the complete phase diagram of the mediated interaction. In particular,
we find a non-vanishing mediated force even when the distance between the inclusions is much greater than their size. Our
model can be applied to describe the mediated interactions of parallel, elongated inclusions embedded in three-dimensional
membranes.
Received 22 October 2001 and Received in final form 8 March 2002 相似文献
16.
Several new kinds of smectic-C twist grain boundary phases (TGBC) have been observed during the last few years. These pure
compounds or mixtures exhibit unusual textures with polygonal lattices (square or hexagonal grids) in the plane normal to
the TGB helix. The structure of these new phases seems to be complex and different from reported and predicted TGBC phases.
In this article, we review the main results obtained on these different new phases, and we propose new TGBC structures based
on the well-known splayed polarization --twisted director structures adopted by chiral smectic-C's in planar aligned (bookshelf)
cells. The observed square or hexagonal lattices are made of superimposed pairs of unwinding lines due to the suppression
of the helix within smectic-C blocks by the grain boundaries (unwinding walls). A lattice-free TGBC occurs if the helix within
smectic-C blocks is suppressed completely.
Received 15 March 2001 相似文献
17.
Y. Henry K. Ounadjela L. Piraux S. Dubois J.-M. George J.-L. Duvail 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):35-54
The magnetic anisotropy and domain structure of electrodeposited cylindrical Co nanowires with length of 10 or 20 μm and diameters
ranging from 30 to 450 nm are studied by means of magnetization and magnetic torque measurements, as well as magnetic force
microscopy. Experimental results reveal that crystal anisotropy either concurs with shape anisotropy in maintaining the Co
magnetization aligned along the wire or favours an orientation of the magnetization perpendicular to the wire, hence competing
with shape anisotropy, depending on whether the diameter of the wires is smaller or larger than a critical diameter of 50
nm. This change of crystal anisotropy, originating in changes in the crystallographic structure of Co, is naturally found
to strongly modify the zero (or small) field magnetic domain structure in the nanowires. Except for nanowires with parallel-to-wire
crystal anisotropy (very small diameters) where single-domain behaviour may occur, the formation of magnetic domains is required
to explain the experimental observations. The geometrical restriction imposed on the magnetization by the small lateral size
of the wires proves to play an important role in the domain structures formed.
Received 14 September 2000 相似文献
18.
Ch. Nacke H. Stolz G. Manzke K. Henneberger 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):303-312
The influence of thermalized non-coherent carriers on the dielectric function of GaAs/AlAs quantum wells is investigated by
reflection spectroscopy. Experiments are performed using the method of spectral interferometry, where both amplitude and phase
of reflected pulses can be determined. For low excitation density the complex coefficient of reflection can be described using
as dielectric function a broadened Elliot formula. With increasing carrier density pronounced nonlinearities appear in both
amplitude and phase due to many-body effects between excited carriers. The nonlinear behavior fits very well to the results
of a many-body theory based on the Semiconductor Bloch equations including memory effects in the scattering processes between
carriers and the polarization induced by the probe pulse.
Received 29 May 2002 / Received in final form 23 September 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: manzke@physik3.uni-rostock.de 相似文献
19.
G. De Smedt C. Godrèche J.M. Luck 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):215-225
We consider a ferromagnetic Ising chain evolving under Kawasaki dynamics at zero temperature. We investigate the statistics
of the blocking time, as well as various characteristics of the metastable configurations reached by the system, including
the statistics of the final energy, the spin correlations, and the distribution of domain sizes. Results of extensive numerical
simulations are compared with analytical predictions made for the a priori ensemble of all blocked configurations with equal weights. Qualitative differences are found, e.g. in the domain sizes, which are found to be neither statistically independent nor exponentially distributed.
Received 24 October 2002 / Received in final form 13 January 2003 Published online 1st April 2003
RID="a"
ID="a"e-mail: luck@spht.saclay.cea.fr
RID="b"
ID="b"URA 2306 of CNRS 相似文献
20.
We study numerically the director and orientational order parameter configurations in a nematic liquid crystal around a two-dimensional
spherical particle on the basis of the tensor order parameter formalism. To properly account for the large length scale difference
between the particle and the accompanying orientational defect, we devise an adaptive grid scheme in which the lattice spacing
is automatically and locally adjusted in response to the spatial gradient of the orientational order parameter. This adaptive
grid scheme is useful in studying dynamical as well as static orientational structures. We present a simulation result which
shows how a hedgehog defect of topological charge -1 becomes unstable in two dimensions, and splits into a defect pair of
topological charge -1/2, located symmetrically around the particle.
Received 14 September 2000 and Received in final form 27 December 2000 相似文献