Folding model analysis of alpha radioactivity

Radioactive decay of nuclei via emission of $\alpha$ particles has been studied theoretically in the framework of a superasymmetric fission model using the double folding (DF) procedure for obtaining the $\alpha$-nucleus interaction potential. The DF nuclear potential has been obtained by folding in the density distribution functions of the $\alpha$ nucleus and the daughter nucleus with a realistic effective interaction. The M3Y effective interaction has been used for calculating the nuclear interaction potential which has been supplemented by a zero-range pseudo-potential for exchange along with the density dependence. The nuclear microscopic $\alpha$-nucleus potential thus obtained has been used along with the Coulomb interaction potential to calculate the action integral within the WKB approximation. This subsequently yields microscopic calculations for the half lives of $\alpha$ decays of nuclei. The density dependence and the exchange effects have not been found to be very significant. These calculations provide reasonable estimates for the lifetimes of $\alpha$ radioactivity of nuclei.Comment: 7 pages including 1 figur

Initiation of ensemble data assimilation

A B S T R A C T The specification of the initial ensemble for ensemble data assimilation is addressed. The presented work examines the impact of ensemble initiation in the Maximum Likelihood Ensemble Filter (MLEF) framework, but is also applicable to other ensemble data assimilation algorithms. Two methods are considered: the first is based on the use of the KardarParisi-Zhang (KPZ) equation to form sparse random perturbations, followed by spatial smoothing to enforce desired correlation structure, while the second is based on the spatial smoothing of initially uncorrelated random perturbations. Data assimilation experiments are conducted using a global shallow-water model and simulated observations. The two proposed methods are compared to the commonly used method of uncorrelated random perturbations. The results indicate that the impact of the initial correlations in ensemble data assimilation is beneficial. The root-mean-square error rate of convergence of the data assimilation is improved, and the positive impact of initial correlations is notable throughout the data assimilation cycles. The sensitivity to the choice of the correlation length scale exists, although it is not very high. The implied computational savings and improvement of the results may be important in future realistic applications of ensemble data assimilation

Vortices in a cylinder: Localization after depinning

Edge effects in the depinned phase of flux lines in hollow superconducting cylinder with columnar defects and electric current along the cylinder are investigated. Far from the ends of the cylinder vortices are distributed almost uniformly (delocalized). Nevertheless, near the edges these free vortices come closer together and form well resolved dense bunches. A semiclassical picture of this localization after depinning is described. For a large number of vortices their density $\rho(x)$ has square root singularity at the border of the bunch ($\rho(x)$ is semicircle in the simplest case). However, by tuning the strength of current, the various singular regimes for $\rho(x)$ may be reached. Remarkably, this singular behaviour reproduces the phase transitions discussed during the past decade within the random matrix regularization of 2d-Gravity.Comment: 4 pages, REVTEX, 2 eps figure

Microsatellite markers for the grapevine pathogen, Eutypa lata

Abstract We isolated and characterized nine polymorphic microsatellite markers for Eutypa lata, a fungal pathogen responsible for Eutypa dieback of grapevine, in populations from two California vineyards (24 isolates per vineyard). Allele frequency ranged from two to 11 alleles per locus and haploid gene diversity ranged from 0.33 to 0.83. All samples comprised unique haplotypes. Our results suggest that there is sufficient allelic polymorphism to estimate fine-scale spatial structure, and to identify possible sources of inoculum from habitats outside of vineyards. Keywords: Ascomycota, Diatrypaceae, Eutypa dieback, Eutypa lata, plant pathogen, Vitis vinifera Received 19 May 2008; revision accepted 10 June 2008 The means of spread of Eutypa dieback from vine-to-vine within vineyards is likely due to dispersal of Eutypa lata sexual spores (ascospores), and not asexual spores (conidia), based on evidence of distributions of vegetative compatibility groups, reproductive structures (perithecia), and symptomatic grapevines Genomic DNA was extracted from an isolate of E. lata from Switzerland [isolate 208.87; Centraalbureau voor Schimmelcultures, Utrecht, the Netherlands], purified (GENECLEAN III Kit, MP Biomedicals), digested with Taq αI (New England BioLabs), and enriched for both a trinucleotide, CAC 10 , and a tetranucleotide mixture (AAAC 6 , AAAG 6 , AAAT 8 , AGAT 8 ; Integrated DNA Technologies). Digested DNA was ligated to linker oligonucleotides 20B (5′-GCGGTTCCCGGTCGAGTTGG-3′) and 22B (5′-pCGCCAACTCGACCGGGAACCGC-3′

Astrophysical factors:Zero energy vs. Most effective energy

Effective astrophysical factors for non-resonant astrophysical nuclear reaction are invariably calculated with respect to a zero energy limit. In the present work that limit is shown to be very disadvantageous compared to the more natural effective energy limit. The latter is used in order to modify the thermonuclear reaction rate formula so that it takes into account both plasma and laboratory screening effects.Comment: 7 RevTex pages. Accepted for publication in Phys.Rev.

Isomorphs in model molecular liquids

Isomorphs are curves in the phase diagram along which a number of static and dynamic quantities are invariant in reduced units. A liquid has good isomorphs if and only if it is strongly correlating, i.e., the equilibrium virial/potential energy fluctuations are more than 90% correlated in the NVT ensemble. This paper generalizes isomorphs to liquids composed of rigid molecules and study the isomorphs of two systems of small rigid molecules, the asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for both systems we find that the isochoric heat capacity, the excess entropy, the reduced molecular center-of-mass self part of the intermediate scattering function, the reduced molecular center-of-mass radial distribution function to a good approximation are invariant along an isomorph. In agreement with theory, we also find that an instantaneous change of temperature and density from an equilibrated state point to another isomorphic state point leads to no relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be more approximative than those of the asymmetric dumbbell model, which is consistent with the OTP model being less strongly correlating. For both models we find "master isomorphs", i.e., isomorphs have identical shape in the virial/potential energy phase diagram.Comment: 20 page

First Order Kaon Condensate

First order Bose condensation in asymmetric nuclear matter and in neutron stars is studied, with particular reference to kaon condensation. We demonstrate explicitly why the Maxwell construction fails to assure equilibrium in multicomponent substances. Gibbs conditions and conservation laws require that for phase equilibrium, the charge density must have opposite sign in the two phases of isospin asymmetric nuclear matter. The mixed phase will therefore form a Coulomb lattice with the rare phase occupying lattice sites in the dominant phase. Moreover, the kaon condensed phase differs from the normal phase, not by the mere presence of kaons in the first, but also by a difference in the nucleon effective masses. The mixed phase region, which occupies a large radial extent amounting to some kilometers in our model neutron stars, is thus highly heterogeneous. It should be particularly interesting in connection with the pulsar glitch phenomenon as well as transport properties.Comment: 25 pagees, 20 figures, Late

Plaquette-singlet solid state and topological hidden order in spin-1 antiferromagnetic Heisenberg ladder

Ground-state properties of the spin-1 two-leg antiferromagnetic ladder are investigated precisely by means of the quantum Monte Carlo method. It is found that the correlation length along the chains and the spin gap both remain finite regardless of the strength of interchain coupling, i.e., the Haldane state and the spin-1 dimer state are connected smoothly without any quantum phase transitions between them. We propose a plaquette-singlet solid state, which qualitatively describes the ground state of the spin-1 ladder quite well, and also a corresponding topological hidden order parameter. It is shown numerically that the new hidden order parameter remains finite up to the dimer limit, though the conventional string order defined on each chain vanishes immediately when infinitesimal interchain coupling is introduced.Comment: RevTeX, 10 pages, 9 figure

Generalized Dynamic Scaling for Critical Magnetic Systems

The short-time behaviour of the critical dynamics for magnetic systems is investigated with Monte Carlo methods. Without losing the generality, we consider the relaxation process for the two dimensional Ising and Potts model starting from an initial state with very high temperature and arbitrary magnetization. We confirm the generalized scaling form and observe that the critical characteristic functions of the initial magnetization for the Ising and the Potts model are quite different.Comment: 32 pages with15 eps-figure