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1.
Existence of a phase transition is proved for a one-dimensional lattice gas with long-range interaction and nearest neighbor exclusion.  相似文献   

2.
We consider a lattice model with a repulsive hard core and an attractive short range interaction. We show that this model has at least three independent equilibrium states, when the temperature is sufficiently low and the chemical potential is suitably chosen.  相似文献   

3.
An equation of state is proposed for a system of rods interacting only through hard core repulsions. A quantitative comparison is made with recently proposed equations of state based upon the scaled-particle and Percus-Yevick theory.  相似文献   

4.
5.
Using field theory and Monte Carlo (MC) simulation we investigate the finite-size effects of the magnetization M for the three-dimensional Ising model in a finite cubic geometry with periodic boundary conditions. The field theory with infinite cutoff gives a scaling form of the equation of state where is the reduced temperature, h is the external field and L is the size of system. Below and at the theory predicts a nonmonotonic dependence of f(x,y) with respect to at fixed and a crossover from nonmonotonic to monotonic behaviour when y is further increased. These results are confirmed by MC simulation. The scaling function f(x,y) obtained from the field theory is in good quantitative agreement with the finite-size MC data. Good agreement is also found for the bulk value at . Received 20 July 1999 and Received in final form 11 November 1999  相似文献   

6.
A mapping theorem leading to exact many-body dynamics of impenetrable bosons in one dimension reveals dark and gray solitonlike structures in a toroidal trap which is phase imprinted. On long time scales revivals appear that are beyond the usual mean-field theory.  相似文献   

7.
M. Moradi  S. Hashemi 《Physica A》2010,389(21):4510-2467
The structural and thermodynamic properties of a confined hard ellipse fluid are studied using Monte Carlo simulation. The angular, average number densities and order parameters of hard ellipses confined between hard parallel walls are obtained for various bulk densities, aspect ratios and wall separations. The results show that the effect of the existence of the wall on the molecular fluid structure, either on their directions or their locations, with respect to the bulk, especially close to the walls, is significant. For this system the pressure is also obtained and it is shown that the average density at the wall is proportional to the pressure, βP=〈ρw〉. Our simulation results show that the order parameters depend on the number of the particles in the box unless it exceeds thousand.  相似文献   

8.
A theory of hysteresis in superconductors based on an approximation to the fluxoid-fluxoid interaction is used to fit experimental data on highly hysteretic Nb wires. No adjustable parameters were used in the comparison, but only data pertaining to the shape of the magnetization curves. The qualitative agreement of the calculated and experimental curves is good, and quantitative agreement is reached on the curve of increasing field.  相似文献   

9.
The system of hard core particles interacting via slowly decreasing repulsions of a finite range is investitated both theoretically and experimentally. The exponential (EXP) approximation of simple fluids is extended to pure repulsive potentials and is found as an accurate and rapid method to obtaining the radial distribution function. While the results based on the blip-function approximation are accurate only for a short interaction range and/or very low densities, agreement between the EXP results and Monte Carlo simulation data is excellent for all the interaction ranges and densities considered.  相似文献   

10.
We describe efficient Monte Carlo computer simulation techniques to calculate conditional distribution functions for pairs of hard-sphere (HS) cavities in a hard slit pore of width L, n* (z 1,z 2,r), and use these as an efficient route to calculating the corresponding dimensionless excess chemical potentials μ e (z 1,z 2,r). zi is the distance of an HS centre from a (specified) wall and r is the distance between the cavity centres. This is the first calculation of such functions, which are of interest in their own right and provide data for the testing of theories, in addition to providing data for a simple model for the infinite dilution behaviour of a polyatomic solute in a simple molecularly confined solvent. Results are presented for special cases for the cavity functions n* (z 1,z 2,r) which occur when the spheres are in the same plane, when the line of sphere centres is perpendicular to the walls, and when the spheres are in contact. We compare results obtained using the Kirkwood superposition approximation in conjunction with results obtained from the computer simulation data using the first member of the BGY integral equation hierarchy. The approximation is found to be exact in certain limiting geometrical situations, but in general is quantitatively poor.  相似文献   

11.
《Physics letters. A》2006,356(6):397-401
The Letter describes a 2D simulation of a system of regular polygons moving within the unit square. The polygons, having 4n sides, are not allowed to rotate and their interactions are of the hard body type. The requirement that the simulation be reversible necessitates the use of rational values for positions and velocities. The latter then enable to introduce the notion of absolute age which gives a novel look at the irreversibility. It is observed that with growing n the dynamics approaches the hard disk one with the Maxwell–Boltzmann distribution of speeds. The simulation also enables to demonstrate the gradual appearance of hydrodynamic behavior with growing n, retaining at the same time the reversibility of the dynamics.  相似文献   

12.
An hf discharge in CCl4, is studied by probe and optical emission spectroscopy. The experiments were performed in a diode type reactor in which a discharge was maintained at a frequency of 440 kHz. A measurement method based on simultaneous use of single and double probes is described. The plasma was studied spectrographically to identify radicals present in the CCl4 hf discharge.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 5–8, September, 1990.  相似文献   

13.
The electronic second hyperpolarizability γ of the carbon tetrachloride molecule is calculated by the ab initio molecular orbital method considering electron correlation with large basis sets. The static electronic γ value with the CCSD(T) method is 1.65 times the Hartree-Fock value, indicating a considerable electron correlation effect. Taking account of the frequency dispersion and vibrational effects, we estimate the most probable theoretical γ value at 800 nm to be around 17900au (9.0 × 10?36 esu). On the other hand, the experimental value recently observed by optical Kerr effect method is 10.6 × 10?36 esu at 800nm. It is concluded that the major part of the experimental χ(3) value of carbon tetrachloride can account for the static electronic hyperpolarizability.  相似文献   

14.
A theoretical investigation of boson versions of the t-J and t-J(z) models on the square lattice is carried out. In the t-J(z) model, phase separation between a hole-rich and a hole-free phase occurs, at sufficiently low hole doping, for arbitrarily small values of J(z). The boson t-J model, instead, features a uniform ground state at any doping for J/t< or =1.5. No evidence of a striped ground state is found. Relevance of this study to the corresponding fermion models is discussed. Fermi statistics is found to enhance the tendency toward phase separation; in particular, phase separation is predicted, at low doping, in the fermion t-J(z) model, at all values of J(z).  相似文献   

15.
We present a new method of analyzing the gas of hard core spheres. We investigate analytic properties of the thermodynamic function over the circle of convergence of the cluster expansion and describe the way in which phase transition occurs.  相似文献   

16.
We use Hanbury-Brown-Twiss interferometry (HBTI) to study various quantum phases of hard core bosons (HCBs) and ideal fermions confined in a one-dimensional quasi-periodic (QP) potential. For HCBs, the QP potential induces a cascade of Mott-like band-insulator phases in the extended regime, in addition to the Mott insulator, Bose glass, and superfluid phases. At critical filling factors, the appearance of these insulating phases is heralded by a peak to dip transition in the interferogram, which reflects the fermionic aspect of HCBs. On the other hand, ideal fermions in the extended phase display various complexities of incommensurate structures such as devil’s staircases and Arnold tongues. In the localized phase, the HCB and the fermion correlations are identical except for the sign of the peaks. Finally, we demonstrate that HBTI provides an effective method to distinguish Mott and glassy phases.  相似文献   

17.
18.
For a three-level atom interacting with two modes of the quantized radiation field the time dependence of transition operators, photon amplitudes, and of operators of level populations and photon numbers is examined rigorously. It is shown that the availability of a mode detuning leads to the splitting of the “soft branch” of frequencies of two-photon Rabi oscillations.  相似文献   

19.
A K Sinha  S K Sinha 《Pramana》1979,13(4):367-371
A cluster expansion theory, in which the quantum hard sphere system is taken as a reference system and the attractive interactions as a perturbation, is applied to calculate the equilibrium properties of the square-well fluid in the semiclassical limit. The radial distribution function and direct correlation function are obtained using the exponential approximation. The isothermal compressibility is also evaluated.  相似文献   

20.
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