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A new Monte Carlo algorithm for 2-dimensional spin glasses is presented. The use of clusters makes possible global updates and leads to a gain in speed of several orders of magnitude. As an example, we study the 2-dimensional ±J Edwards-Anderson model. The new algorithm allows us to equilibrate systems of size 1002 down to temperature T = 0.1. Our main result is that the correlation length diverges as an exponential ( ξ∼e 2βJ) and not as a power law as TT c = 0. Received 10 January 2001 and Received in final form 29 May 2001  相似文献   

3.
76 , 1985 (1996)] for quantum-state reconstruction of one-dimensional non-relativistic wave packets from position observations. We illuminate the theoretical background of the technique and show how to extend the procedure to the continuous part of the spectrum. Received: 7 July 1997  相似文献   

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New method of neutron spectrum recovery described in the paper involves accelerated deuterons (that produce neutrons in DD reaction) and allows getting neutron spectrum in any direction from computed time-velocity characteristics of deuterons. Time of flight signals registered in various distances and directions are used, that makes information involved in the recovery process (Monte-Carlo simulation) more complete than in a one-directional case, although additional assumption about axial symmetry of deuterons motion, is required. In the paper recent results of two standard tests of the proposed method are presented demonstrating its capability to recover neutron spectrum from time-of-flight signals.  相似文献   

6.
The effect of the interlayer and intralayer anisotropies on the energy gap and sublattice magnetization is investigated using the linear spin wave theory for multilayer Heisenberg models with odd number of coupled layers. In the isotropic case, such systems exhibit a long-range order and no energy gap, while, in the anisotropic case, they are still ordered and the energy gap opens for certain anisotropies.  相似文献   

7.
The completeness of the eigenfunctions of a self-adjoint Hamiltonian, which is the basic ingredient of quantum mechanics, plays an important role in nuclear reaction and nuclear-structure theory. Here we present the first formal proof of the completeness of the two-body Coulomb scattering wave functions for a repulsive unscreened Coulomb potential using Newton’s method (R. Newton, J. Math. Phys. 1, 319 (1960)). The proof allows us to claim that the eigenfunctions of the two-body Hamiltonian, with the potential given by the sum of the repulsive Coulomb plus short-range (nuclear) potentials, form a complete set. It also allows one to extend Berggren’s approach for the modification of the complete set of eigenfunctions by including the resonances for charged particles. We also demonstrate that the resonant Gamow functions with Coulomb tail can be regularized using Zel’dovich’s regularization method. Communicated by U.-G. Meiβner For the continuum spectrum the eigenfunctions are not square-integrable, strictly speaking we need to use a rigged Hilbert space which extends the normal Hilbert space by bringing together the discrete and continuum spectrum eigenstates.  相似文献   

8.
We show that the hydrogen atom possesses Yangian symmetry and integrability in terms of the RTT relation. A possible experimental test of the physical effect of Yangian is proposed.  相似文献   

9.
Spherical quantum dots with a few charged Fermi particles (electrons or holes) are studied for different total spins. Simulation by quantum path integral Monte Carlo method is performed. The dependence of the electron correlations in the quantum dot is studied at different mean interelectron separation controlled by number of electrons in the quantum dot and by steepness of electron confinement (the latter parameter can be changed by the gate voltage). The ‘cold’ melting—quantum transition from Wigner crystal-like state (i.e. from regime of strongly correlated electrons) to a Fermi liquid-like state—driven by the steepness of electron confinement is studied. The pair correlation function and radial function characterizing electron quantum delocalization are analyzed.  相似文献   

10.
Zhenya Yan 《Physics letters. A》2009,373(29):2432-2437
The three-dimensional extended quantum Zakharov-Kuznetsov (ZK) equation was investigated in dense quantum plasmas which arises from the dimensionless hydrodynamics equations describing the nonlinear propagation of the quantum ion-acoustic waves. With the aid of symbolic computation, many types of new analytical solutions of the extended quantum ZK equation are constructed in terms of some powerful ansatze, which include new doubly periodic wave, solitary wave, shock wave, rational wave, and singular wave solutions. Moreover, we analyze the nonlinear wave propagation of the obtained solutions for some chosen parameters.  相似文献   

11.
A fast simulation algorithm for the calculation of multitime correlation functions of open quantum systems is presented. It is demonstrated that any stochastic process which “unravels” the quantum Master equation can be used for the calculation of matrix elements of reduced Heisenberg picture operators, and thus for the calculation of multitime correlation functions, by extending the stochastic process to a doubled Hilbert space. The numerical performance of the stochastic simulation algorithm is investigated by means of a standard example. Received: 30 May 1997 / Revised: 4 November 1997 / Accepted: 7 November 1997  相似文献   

12.
During heavy ion collisions below the Coulomb barrier adiabatic molecular orbitals are formed for the inner electrons. For systems with total changes exceending Z=Z1 + Z2 60 relativistic effects are important and we, therefore, use the two-center Dirac Hamiltonian to describe the dynamics. We investigate the method to approximate these molecular orbitals by an expansion in a di-atomic basis of Dirac wave functions and determine the binding energies by a variation of the expansion coefficients. Deviations from adiabaticity are taken into account to first order in the relative velocityv/c 0.1) of the nuclei which is considerably smaller than the electron velocity.  相似文献   

13.
This paper describes the use of ultrasonic guided waves for identifying the mass loading due to underwater limpet mines on ship hulls. The Dynamic Wavelet Fingerprint Technique (DFWT) is used to render the guided wave mode information in two-dimensional binary images because the waveform features of interest are too subtle to identify in time domain. The use of wavelets allows both time and scale features from the original signals to be retained, and image processing can be used to automatically extract features that correspond to the arrival times of the guided wave modes. For further understanding of how the guided wave modes propagate through the real structures, a parallel processing, 3D elastic wave simulation is developed using the finite integration technique (EFIT). This full field, technique models situations that are too complex for analytical solutions, such as built up 3D structures. The simulations have produced informative visualizations of the guided wave modes in the structures as well as mimicking directly the output from sensors placed in the simulation space for direct comparison to experiments. Results from both drydock and in-water experiments with dummy mines are also shown.  相似文献   

14.
A Monte Carlo algorithm for dynamic hysteresis simulation in ferroelectric spin systems is developed based on a DIFFOUR model in which the local spontaneous polarization is defined by the double-well potential energy and the nearest-neighbor spin interaction as well as an external electrical field of variable amplitude and frequency. A direct measurement of the hysteresis loop for ferroelectric Pb(Zr0.52Ti0.48)O3 thin film capacitors using the Sawyer–Tower technique is performed. Significant dependence of the hysteresis shape and pattern on the external field is revealed. Direct imaging of the simulated domain pattern indicates serious suppression of the domain switching over the high-frequency range. The evaluated scaling relations from the simulation for remanence, coercivity, and the area of the hysteresis over the low-frequency range are supported by theoretical predictions and experiments, but the high-frequency scaling behaviors as derived are different from one and another. Received: 23 January 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001  相似文献   

15.
We study the three-body system with short-range interactions characterized by an unnaturally large two-body scattering length. We show that the off-shell scattering amplitude is cutoff independent up to power corrections. This allows us to derive an exact renormalization group equation for the three-body force. We also obtain a renormalized equation for the off-shell scattering amplitude. This equation is invariant under discrete scale transformations. The periodicity of the spectrum of bound states originally observed by Efimov is a consequence of this symmetry. The functional dependence of the three-body scattering length on the two-body scattering length can be obtained analytically using the asymptotic solution to the integral equation. An analogous formula for the three-body recombination coefficient is also obtained.  相似文献   

16.
We extend the recently presented formalism for Monte Carlo calculations of the partition function, for both even and odd particle number systems (Phys. Rev. C 59, 2500 (1999)), to the calculation of many-body matrix elements of the type <ψ| e - βℋ|ψ> where |ψ> is a many-body state with a definite angular momentum, parity, neutron and proton numbers. For large β such matrix elements are dominated by the lowest eigenstate of the many-body Hamiltonian ℋ, corresponding with a given angular momentum parity and particle number. Emphasis is placed on odd-mass nuclei. Negligible sign fluctuations in the Monte Carlo calculation are found provided the neutron and proton chemical potentials are properly adjusted. The formalism is applied to the J π = 0+ state in 166 Er and to the J π = 9/2-, 13/2+, 5/2- states in 165 Er using the pairing-plus-quadrupole model. Received: 28 April 2000 / Accepted: 20 September 2000  相似文献   

17.
The magnetic field dependence of the in-plane penetration depth λ|(H) for single crystal κ-(ET)2Cu[N(CN)2]Br has been measured at 3, 9.6, and 36 MHz. Over a limited range, λ| scales with a characteristic field that coincides with a shoulder in the λ| vs. H curves. Above that field, λ| increases sharply toward a second inflection point at that coincides with is close to the irreversibility line measured by magnetization. For fields larger than the penetration depth diverges, suggesting that the vortex lattice has melted. The field dependence at one frequency agrees qualitatively with a model of pinned vortices at low fields giving way to flux flow at higher fields. However, the observed frequency dependence deviates significantly from the predictions of this model, suggesting that collective effects play a major role. Our technique also yields a new measurement for the interplane penetration depth λ ∼ 300 μm, implying an anisotropy .  相似文献   

18.
The last full Karlsruhe PW analysis of πN scattering was finished ca. 20 years ago. After that a huge pile of new accurate πN scattering data has emerged, with which the old analysis is not completely compatible. We are making a highly modernized version of the old analysis to all (recent and old) data, aiming to pay particular attention to the discrepancies between different data sets and to the handling of the experimental errors as well as to the electromagnetic corrections and the effects of isospin breaking.  相似文献   

19.
In this Letter, we have calculated the concurrence of the pairwise thermal entanglement for the four-qubit and five-qubit Heisenberg XX chain. It is found that there is a great difference between the even-qubit and the odd-qubit chain in the aspect of the critical temperature and of the existence of the entanglement for the case of the qubit number n no more than 5.  相似文献   

20.
,Static and dynamic properties of the Potts model on the simple cubic lattice with nearest neighbor -interaction are obtained from Monte Carlo simulations in a temperature range where full thermal equilibrium still can be achieved (). For a lattice size L = 16, in this range finite size effects are still negligible, but the data for the spin glass susceptibility agree with previous extrapolations based on finite size scaling of very small lattices. While the static properties are compatible with a zero temperature transition, they certainly do not prove it. Unlike the Ising spin glass, the decay of the time-dependent order parameter is compatible with a simple Kohlrausch function, , while a power law prefactor cannot be distinguished. The Kohlrausch exponent y ( T ) decreases from at [0pt] to at [0pt] however. The relaxation time is compatible with the exponential divergence postulated by McMillan for spin glasses at their lower critical dimension, but the exponent that can be extracted still differs significantly from the theoretical value, . Thus the present results support the conclusion that the Potts spin glass in d = 3 dimensions differs qualitatively from the Ising spin glass. Received: 8 October 1997 / Accepted: 27 November 1997  相似文献   

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