摘要:

An exact analysis of the Ising model with infinite‐range interactions in a random field and a local mean‐field theory in three dimensions is carried out leading to a phase diagram with several coexistence surfaces and lines of critical points. Our results show that the phase diagram depends crucially on whether the distribution of random fields is symmetric or not. Thus, Ising‐like phase transitions in a porous medium (the asymmetric case) are in a different universality class from the conventional random‐field model (symmetric case).

ISSN:0094-243X    

DOI:10.1063/1.44724

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We describe the results of studies of a random‐anisotropy Blume‐Emery‐Griffiths spin‐1 Ising model using mean‐field theory, transfer‐matrix calculations, and position‐space renormalization‐group calculations. The interplay between the quenched randomness of the anisotropy and the annealed disorder introduced by the spin‐1 model leads to a rich phase diagram with a variety of phase transitions and reentrant behavior. Our results may be relevant to the study of the phase separation of3He–4He mixtures in porous media in the vicinity of the superfluid transition.

ISSN:0094-243X    

DOI:10.1063/1.44725

出版商:AIP    

年代:1992

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.44726

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The first passage time of random walks from one end to the other, of a segment of adisorderedlattice is considered. Disorder is modeled by prescribing random nearest neighbor jump probabilities to the lattice sites. We consider lattices with random barriers, random traps, and Sinai disorder. We present exact results on mean first passage time (MFPT) and disorder averaged MFPT. We investigate the nature of the distribution of MFPT over the disorder.

ISSN:0094-243X    

DOI:10.1063/1.44727

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Stronger then exponential localization, or ‘‘superlocalization,’’ on the infinite cluster in a percolating system is expected to arise due to the fractal nature of the percolating cluster. This assertion is substantiated here through the calculation of the fractal dimension of the percolating cluster using results on inverse‐participation‐ratio versus composition calculations.

ISSN:0094-243X    

DOI:10.1063/1.44748

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We estimate the transmittance of the quantum percolation model on square lattices of various sizes using the vector recursion method. We note from arguments of finite size scaling theory that there is no delocalization transition for any degree of disorder in two dimensions. We also locate resonating states in this model by studying the variation of transmittance vs energy. The resonating states found by us appeu, to be necklace states described by Pendry.

ISSN:0094-243X    

DOI:10.1063/1.44728

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We propose a new type of localization namely subexponential localization, and our finite‐size scaling analysis tends to indicate that it exists in a model potential with varying period in one dimension.

ISSN:0094-243X    

DOI:10.1063/1.44729

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Here we have probed the effects of dislocations on channeling radiation from 56 MeV positrons channeled along ⟨110⟩ axis of a silicon single crystal using shell model axial potential and calculated the fractional increase in radiation frequency due to dislocations.

ISSN:0094-243X    

DOI:10.1063/1.44730

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Electron Paramagnetic Resonance (EPR) spectra of VO(II), Mn(II), Cu(II), and Gd(III) ions in lithium fluoroborate glasses have been studied at room temperature.

ISSN:0094-243X    

DOI:10.1063/1.44731

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Beta silver iodide with a wurtzite structure undergoes the well known beta‐alpha phase transition (1st order) to the Ag+disordered bcc phase at 147°C. Besides the fast Ag+ion conductivity which continues to baffle researchers, recent work on &agr;‐AgI has thrown up many surprises of a fundamental nature, notably, strongly coupled one component plasma behavior and the fractal nature of Ag+diffusion. The present paper attempts to capture the current excitement in this area and to cite some interesting experimental results.

ISSN:0094-243X    

DOI:10.1063/1.44732

出版商:AIP    

年代:1992

数据来源: AIP