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1.
A recent conjecture on two-dimensional foams suggested that for fixed topology with given bubble areas there is a unique state
of stable equilibrium. We present counter-examples, consisting of a ring of bubbles around a central one, which refute this
conjecture. The discussion centres on a novel form of instability which causes symmetric clusters to become distorted. The
stability of these bubble clusters is examined in terms of the Hessian of the energy.
Received 8 November 2001 相似文献
2.
We have examined a number of candidates for the minimum-surface-energy arrangement of two-dimensional clusters composed of
N bubbles of area 1 and N bubbles of area λ ( λ≤1). These include hexagonal bubbles sorted into two monodisperse honeycomb tilings, and various mixed
periodic tilings with at most four bubbles per unit cell. We identify, as a function of λ, the minimal configuration for N → ∞. For finite N, the energy of the external (i.e., cluster-gas) boundary and that of the interface between honeycombs in “phase-separated” clusters have to be taken into account.
We estimate these contributions and find the lowest total energy configuration for each pair (N,λ). As λ is varied, this alternates between a circular cluster of one of the mixed tilings, and “partial wetting” of the
monodisperse honeycomb of bubble area 1 by the monodisperse honeycomb of bubble area λ.
Received 1 August 2002
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ID="a"e-mail: paulo@ist.utl.pt 相似文献
3.
P. Lazić D.K. Sunko 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):595-603
A bond-disordered two-dimensional Ising model is used to simulate Kauzmann's mechanism of vitrification in liquids, by a Glauber
Monte Carlo simulation. The rearrangement of configurations is achieved by allowing impurity bonds to hop to nearest neighbors
at the same rate as the spins flip. For slow cooling, the theoretical minimum energy configuration is approached, characterized
by an amorphous distribution of locally optimally arranged impurity bonds. Rapid cooling to low temperatures regularly finds
bond configurations of higher energy, which are both a priori rare and severely restrictive to spin movement, providing a simple realization of kinetic vitrification. A supercooled liquid
regime is also found, and characterized by a change in sign of the field derivative of the spin-glass susceptibility at a
finite temperature.
Received 3 August 2000 and Received in final form 9 March 2001 相似文献
4.
Amongst the two-dimensional cellular patterns that fill a plane, dry foams at stable equilibrium typify a particular subset for which the total perimeter P of cell boundaries ( i.e., films between bubbles) has a local minimum. For a given set of bubble areas Ai (i=1,..., N), P can be written in the form P=R(SigmaN(i=1) square root Ai)/2, where R is topology dependent. We seek the set of areas Ai and the cluster topology that minimise R, and propose lower bounds for R that set lower bounds for the surface energy of i) individual bubbles, with circular edges meeting at 2pi/3 angles at vertices (Plateau cells), and ii) infinite periodic bubble clusters. 相似文献
5.
D. Bar L.P. Horwitz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):505-518
We discuss the properties of a large number N of one-dimensional (bounded) locally periodic potential barriers in a finite interval. We show that the transmission coefficient,
the scattering cross section σ, and the resonances of σ depend sensitively upon the ratio of the total spacing to the total
barrier width. We also show that a time dependent wave packet passing through the system of potential barriers rapidly spreads
and deforms, a criterion suggested by Zaslavsky for chaotic behaviour. Computing the spectrum by imposing (large) periodic
boundary conditions we find a Wigner type distribution. We investigate also the S-matrix poles; many resonances occur for certain values of the relative spacing between the barriers in the potential.
Received 1st August 2001 and Received in final form 18 November 2001 相似文献
6.
A lattice of magneto-optical and magnetic traps for cold atoms 总被引:1,自引:0,他引:1
A. Grabowski T. Pfau 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):347-354
We describe basic periodic trapping configurations for ultracold atoms above surfaces. The approach is based on a simple wire
grid and can be scaled to provide large arrays of periodically arranged magnetic or magneto-optical traps. The unit cells
of the trap lattices are based on crossed wire segments. By alternating the current directions in the wires of the grid it
can be distinguished between 3 basic lattice configurations. As a first demonstration, we used macroscopic wires in a 2 layer
configuration to realize the unit cells of the lattices. With this experimental setup, we observe two of the basic unit cells
and an array of 2×2 magneto optical traps.
Received 29 August 2002 / Received in final form 12 December 2002 Published online 18 February 2003 相似文献
7.
8.
P. Ruszczynski L. Schimansky-Geier I. Dikshtein 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):569-577
A model for the motion of a single ferromagnetic domain is studied numerically and analytically. A single strip in two dimensions
and pinned at two inhomogeneities is considered. We suppose two stable configurations (positively or negatively curved with
pinned ends) due to the action of a bistable potential. Further, it is assumed that the domain is driven externally by periodic
and noisy magnetic fields. The noise makes the domain able to flip between the two configurations. The small temporally periodic
fields synchronize these flippings and the phenomenon of stochastic resonance is observed. The signal to noise ratio of the
output is investigated and shows a maximum for a nonvanishing intensity of the applied noise. Its dependency on the stiffness
of the domain is studied.
Received 14 May 1999 and Received in final form 14 October 1999 相似文献
9.
K. Pomorski K. Dietrich 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):353-364
We investigate the existence of stable charged metallic bubbles using the shell correction method. We find that for a given
mesoscopic system of n atoms of a given metal and (positive) elementary charges, a metallic bubble turns out to have a lower total energy than a compact spherical cluster,
whenever the charge number q is larger than a critical charge number qc. For a magic number (n-q) of free electrons, the spherical metallic bubble may become stable against fission.
Received: 17 November 1997 / Revised: 28 May 1998 / Accepted: 20 July 1998 相似文献
10.
L. Menzel A.A. Kosterev R.F. Curl F.K. Tittel C. Gmachl F. Capasso D.L. Sivco J.N. Baillargeon A.L. Hutchinson A.Y. Cho W. Urban 《Applied physics. B, Lasers and optics》2001,72(7):859-863
Two configurations of a continuous wave quantum cascade distributed feedback laser-based gas sensor for the detection of NO
at a parts per billion (ppb) concentration level, typical of biomedical applications, have been investigated. The laser was
operated at liquid nitrogen temperature near λ=5.2 μm. In the first configuration, a 100 m optical path length multi-pass
cell was employed to enhance the NO absorption. In the second configuration, a technique based on cavity-enhanced spectroscopy
(CES) was utilized, with an effective path length of 670 m. Both sensors enabled simultaneous analysis of NO and CO2 concentrations in exhaled air. The minimum detectable NO concentration was found to be 3 ppb with a multi-pass cell and 16 ppb
when using CES. The two techniques are compared, and potential future developments are discussed.
Received: 1 November 2000 / Revised version: 19 January 2001 / Published online: 20 April 2001 相似文献
11.
L. Wiesenfeld 《Few-Body Systems》2002,31(2-4):217-222
In reactive chaotic scattering, the relative importance of the different channels, in terms of probability, is measured classically
or semi-classically by integrals over finite areas in phase space. These areas arise in a finite time on a well chosen surface.
This is contrasted to periodic orbit theory or spectral properties, that need a very long time to be defined, as compared
to mean interaction times.
Received November 7, 2001; accepted for publication December 4, 2001 相似文献
12.
G. Carotenuto S. DeNicola G.P. Pepe L. Nicolais 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):437-441
A simple and high-reproducible method for the synthesis of polymer-protected silver cluster of controlled size is described.
UV-visible spectroscopy has been used for investigating the influence of the aging of the protective poly(vinylpyrrolidone)
layer on the cluster growth rate at different reaction temperatures and poly(vinylpyrrolidone)/ethylene glycol weight ratios.
The obtained results show that the aging time of the polymeric stabilizer solution plays a fundamental role in the reproducibility
of the cluster growth process. A model for the metal cluster formation-grow process is also proposed.
Received 18 July 2001 and Received in final form 3 October 2001 相似文献
13.
L. Spinelli G. Tissoni M. Tarenghi M. Brambilla 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):257-266
Cavity solitons are similar to spatial solitons, appearing as localized bright dots in the transverse intensity profile of
the electromagnetic field, but they arise in dissipative systems. In this paper we consider a broad-area vertical-cavity semiconductor
microresonator, driven by an external coherent field, at room temperature. The active material is constituted by a Multiple
Quantum Well GaAs/AlGaAs structure (MQW). We present a set of nonlinear dynamical equations for the electric field and the
carrier density valid for both a passive and an active (i.e. with population inversion) configuration. The complex nonlinear susceptibility is derived on the basis of a full many-body
theory, with the Coulomb enhancement treated in the Padé approximation. The linear stability analysis of the homogeneous steady
states is performed with a generalised approach, and numerical simulations demonstrating the existence of spatial patterns
and cavity solitons in experimentally achievable parameter regions are given for the two configurations.
Received 18 January 2001 相似文献
14.
W.D. Heiss H.L. Harney 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):149-151
Exceptional points are singularities of the spectrum and wave functions of a Hamiltonian which occur as functions of a complex
interaction parameter. They are accessible in experiments with dissipative systems. We show that the wave function at an exceptional
point is a specific superposition of two configurations. The phase relation between the configurations is equivalent to a
chirality which should be detectable in an experiment.
Received 9 April 2001 and Received in final form 19 July 2001 相似文献
15.
We study the icosahedral transformations of solid Cu Co clusters with different initial configurations by using molecular dynamics with the embedded atom method. It is found that the formation of symmetric icosahedral cluster is strongly related to the atomic number and initial configuration. The transformation originates from the surface into the interior of the cluster and is a structural change which is rapid and diffusionless. The icosahedral clusters with any composition and configuration, such as core-shell or three-shell duster, can be prepared by the means of solid-solid phase transition in bimetallic clusters. 相似文献
16.
M.A. Gilmore B.L. Johnson 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):297-305
We study the effects of layer thickness variations on the collective plasmon excitation modes of finite superlattices. Unlike
other symmetry lowering mechanisms, thickness variation does not strongly localize the surface modes. We find that the reason
for this insensitivity lies in the fact that the collective modes of a given finite structure must evolve continuously from
the single-finite-superlattice at zero thickness deviation into modes of a pair of uncoupled finite structures at large thickness
variation. We also show that this behavior is analogous to the evolution of molecular orbitals from atomic orbitals as the
internuclear separation is reduced, in contrast to the analogy of the superlattice modes as a stack of coupled quantum wells.
This emphasizes the difference between the electromagnetic symmetry of the finite superlattice and the structural symmetry.
Received 16 April 2001 and Received in final form 6 July 2001 相似文献
17.
K.L. Yao G.Y. Sun W.Z. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):309-313
By using the density matrix renormalization group (DMRG) and the self-consistent numerical method, we obtain a high spin ground
state with localized spin density describing spin localization and the soliton describing the distortion of the lattice configurations
along the main chain. Different electron-phonon interactions result in different configurations of solitons. When the electron-phonon
coupling along the main chain is larger than a critical value , a transition from a single soliton-like distortion to a pair of soliton-like distortions along the main chain takes place.
Such critical value depends mainly on the intersite Coulomb interactions. The spin density wave along the main chain is always localized around
the center of soliton-like distortions.
Received 2 July 2001 and Received in final form 25 September 2001 相似文献
18.
H.I. Hidmi D.H.E. Gross H.R. Jaqaman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):87-92
The fragmentation of multiply charged atomic sodium clusters of mass 200 is investigated using the Micro-canonical Metropolis
Monte Carlo (MMMC) statistical technique for excitation energies up to 200 eV and for cluster charges up to +9e. In this work we present caloric curves and charged and uncharged fragment mass distributions for clusters with charges 0,
2, and 4. The caloric curves show a dip at the critical point implying a negative specific heat, as expected for finite systems,
while the fragment mass distributions corroborate the picture of a phase transition from one dominant liquid-like cluster
to complete vaporization.
Received 7 November 2001 / Received in final form 4 April 2002 Published online 28 June 2002 相似文献
19.
We investigate stationary and travelling wave solutions of the classical one-dimensional transverse field Ising model. Results
are given on the existence, shape and stability of kink solutions and periodic solutions. We review recent analytical results
(e.g., the proof of existence of a one-parameter family of stationary kink solutions and the proof of existence of travelling wave
kink solutions with nonzero velocity c≠ 0) and extend them by the use of numerical methods. Small oscillations arising in the tails of travelling kink solutions
are investigated numerically. In the end, stability analysis puts some light on pinning effects.
Received 23 February 2001 and Received in final form 4 October 2001 相似文献
20.
A. Moncho-Jordá G. Odriozola F. Martınez-López A. Schmitt R. Hidalgo-Álvarez 《The European physical journal. E, Soft matter》2001,5(4):471-480
A sticking probability model based on the average cluster lifetime is employed for deducing a kernel capable to describe the
kinetics of computer simulated irreversible aggregation processes in two dimensions. The deduced kernel describes not only
the time evolution of the cluster size distribution for diffusion limited aggregation (DLCA) and reaction limited aggregation
(RLCA) but also for the entire transition region between both regimes. The model predicts a crossover to diffusion limited
cluster aggregation for all sticking probabilities at long aggregation times. The time needed for reaching the DLCA limit
increases for decreasing sticking probability.
Received 16 April 2001 and Received in final form 24 May 2001 相似文献