摘要:

AbstractThe dynamics of a driven interface in a medium with random pinning forces is analyzed. The interface undergoes a depinning transition where the order parameter is the interface velocityv, which increases asv∼(FFc)θfor driving forcesFclose to its threshold valueFc. We consider a Langevin‐type Eq. which is expected to be valid close to the depinning transition of an interface in a statistically isotropic medium. By a functional renormalization group scheme the critical exponents characterizing the depinning transition are obtained to the first order in ϵ = 4 —D>0, whereDis the interface dimension. The main results were published earlier [T. Nattermann et al., J. Phys. II France2(1992) 1483]. Here, we present details of the perturbative calculation and of the derivation of the functional flow Eq. for the random‐force correlator. The fixed point function of the correlator has a cusp singularity which is related to a finite value of the thresholdFc, similar to the mean field theory. We also present extensive numerical simulations and compare them with our analytical results for the critical exponents. For ϵ = 1 the numerical and analytical results deviate from each other by only a few percent. The deviations in lower dimensions ϵ = 2, 3 are larger and suggest that the roughness exponent is somewhat larger than the value ξ =e/3 of an interface in thermal

ISSN:0003-3804    

DOI:10.1002/andp.19975090102

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractCalculations are reported of the total energies and related quantities of sequences of small clusters of the form AmPbn, where A is an alkali atom,n<6 andm<9. The object of this study is to shed light on the stoichiometry and the possible formation of complexes in A‐Pb liquid alloys. The calculations are performed using empty core pseudopotentials and the spherical average approximation for the cluster. The results are insensitive to the choice of alkali atom apart from a smooth trend with the progression from Li to Cs. The calculated total energies suggest that clusters with compositions A4Pb and A4Pb4are very stable against a change in the number of Pb or A atoms and support the possibility of these clusters forming in the liquid alloys. This stability arises from an electronic shell‐closing eff

ISSN:0003-3804    

DOI:10.1002/andp.19975090103

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractWe study the density of states (DOS) as a function of the interactionUin the half‐filled simplified Hubbard model in a magnetic field. This model is considered on the Bethe lattice in the limit of high dimensions. We show that the DOS can be calculatedexactly, and that many of its properties have an astonishingly simple form. In particular, the DOS can be investigatedexplicitlyin the limits of weak and strong coupling and near the metal‐insulator transition. E.g., we find an explicit result for the critical valueUc, at which the metal‐insulator transition occurs, as a function of the magnetization. The relation between the magnetization and the magnetic field is calculated numerically. An important result is that the metal‐insulator transition, occurring in the model withB= 0, is continuously connected to the metal‐insulator transition in the subspace of single s

ISSN:0003-3804    

DOI:10.1002/andp.19975090104

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe total nuclear level density is obtained for periodic single particle spectra. First, we express the canonical partition function in terms of Jacobi theta functions for degenerated fermion systems. Secondly, we use a relation for the number of representations of an integer number as sums of smaller numbers to find an exact formula for the nuclear level density. The shell structure is incorporated in the result in a simple way. An asymptotic relation can be easily obtained from the exact result and shown to be the well known back‐shifted Bethe‐form

ISSN:0003-3804    

DOI:10.1002/andp.19975090105

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19975090101

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY