111 research outputs found
Superstatistical random-matrix-theory approach to transition intensities in mixed systems
We study the fluctuation properties of transition intensities applying a
recently proposed generalization of the random matrix theory, which is based on
Beck and Cohen's superstatistics. We obtain an analytic expression for the
distribution of the reduced transition probabilities that applies to systems
undergoing a transition out of chaos. The obtained distribution fits the
results of a previous nuclear shell model calculations for some electromagnetic
transitions that deviate from the Porter-Thomas distribution. It agrees with
the experimental reduced transition probabilities for the 26A nucleus better
than the commonly used chi-squared distribution.Comment: 14 pages, 3 figure
Kappa-deformed random-matrix theory based on Kaniadakis statistics
We present a possible extension of the random-matrix theory, which is widely
used to describe spectral fluctuations of chaotic systems. By considering the
Kaniadakis non-Gaussian statistics, characterized by the index {\kappa}
(Boltzmann-Gibbs entropy is recovered in the limit {\kappa}\rightarrow0), we
propose the non-Gaussian deformations ({\kappa} \neq 0) of the conventional
orthogonal and unitary ensembles of random matrices. The joint eigenvalue
distributions for the {\kappa}-deformed ensembles are derived by applying the
principle maximum entropy to Kaniadakis entropy. The resulting distribution
functions are base invarient as they depend on the matrix elements in a trace
form. Using these expressions, we introduce a new generalized form of the
Wigner surmise valid for nearly-chaotic mixed systems, where a
basis-independent description is still expected to hold. We motivate the
necessity of such generalization by the need to describe the transition of the
spacing distribution from chaos to order, at least in the initial stage. We
show several examples about the use of the generalized Wigner surmise to the
analysis of the results of a number of previous experiments and numerical
experiments. Our results suggest the entropic index {\kappa} as a measure for
deviation from the state of chaos. We also introduce a {\kappa}-deformed
Porter-Thomas distribution of transition intensities, which fits the
experimental data for mixed systems better than the commonly-used
gamma-distribution.Comment: 18 pages, 8 figure
Remote sensing and geographic information systems: charting Sin Nombre virus infections in deer mice.
We tested environmental data from remote sensing and geographic information system maps as indicators of Sin Nombre virus (SNV) infections in deer mouse (Peromyscus maniculatus) populations in the Walker River Basin, Nevada and California. We determined by serologic testing the presence of SNV infections in deer mice from 144 field sites. We used remote sensing and geographic information systems data to characterize the vegetation type and density, elevation, slope, and hydrologic features of each site. The data retroactively predicted infection status of deer mice with up to 80% accuracy. If models of SNV temporal dynamics can be integrated with baseline spatial models, human risk for infection may be assessed with reasonable accuracy
Nuclear Shell Model Calculations of Neutralino-Nucleus Cross Sections for Silicon 29 and Germanium 73
We present the results of detailed nuclear shell model calculations of the
spin-dependent elastic cross section for neutralinos scattering from \si29 and
\ge73. The calculations were performed in large model spaces which adequately
describe the configuration mixing in these two nuclei. As tests of the computed
nuclear wave functions, we have calculated several nuclear observables and
compared them with the measured values and found good agreement. In the limit
of zero momentum transfer, we find scattering matrix elements in agreement with
previous estimates for \si29 but significantly different than previous work for
\ge73. A modest quenching, in accord with shell model studies of other heavy
nuclei, has been included to bring agreement between the measured and
calculated values of the magnetic moment for \ge73. Even with this quenching,
the calculated scattering rate is roughly a factor of 2 higher than the best
previous estimates; without quenching, the rate is a factor of 4 higher. This
implies a higher sensitivity for germanium dark matter detectors. We also
investigate the role of finite momentum transfer upon the scattering response
for both nuclei and find that this can significantly change the expected rates.
We close with a brief discussion of the effects of some of the non-nuclear
uncertainties upon the matrix elements.Comment: 31 pages, figures avaiable on request, UCRL-JC-11408
Factors and processes shaping the population structure and distribution of genetic variation across the species range of the freshwater snail radix balthica (Pulmonata, Basommatophora)
Background: Factors and processes shaping the population structure and spatial distribution of genetic diversity across a species' distribution range are important in determining the range limits. We comprehensively analysed the influence of recurrent and historic factors and processes on the population genetic structure, mating system and the distribution of genetic variability of the pulmonate freshwater snail Radix balthica. This analysis was based on microsatellite variation and mitochondrial haplotypes using Generalised Linear Statistical Modelling in a Model Selection framework. Results: Populations of R. balthica were found throughout North-Western Europe with range margins marked either by dispersal barriers or the presence of other Radix taxa. Overall, the population structure was characterised by distance independent passive dispersal mainly along a Southwest-Northeast axis, the absence of isolation-by-distance together with rather isolated and genetically depauperated populations compared to the variation present in the entire species due to strong local drift. A recent, climate driven range expansion explained most of the variance in genetic variation, reducing at least temporarily the genetic variability in this area. Other factors such as geographic marginality and dispersal barriers play only a minor role. Conclusions: To our knowledge, such a population structure has rarely been reported before. It might nevertheless be typical for passively dispersed, patchily distributed taxa (e.g. freshwater invertebrates). The strong local drift implied in such a structure is expected to erode genetic variation at both neutral and coding loci and thus probably diminish evolutionary potential. This study shows that the analysis of multiple factors is crucial for the inference of the processes shaping the distribution of genetic variation throughout species ranges. Additional files Additional file 1: Distribution of Radix taxa. Spatial distribution of the Radix MOTU as defined in Pfenninger et al. 2006 plus an additional, newly discovered taxon. This map is the basis for the inference of the species range of R. balthica. Additional file 2: Sampling site table and spatial distribution of diversity indices, selfing estimates and inferred population bottlenecks for R. balthica. Table of sampling site code, geographical position in decimal degrees latitude and longitude, number of individuals analysed with microsatellites (Nnuc), expected heterozygosity (HE) and standard deviation across loci, mean rarefied number of alleles per microsatellite locus (A) and their standard deviation, number of individuals analysed for mitochondrial variation (Nmt), rarefied number of mitochondrial COI haplotypes (Hmt), number of individuals measured for body size (Nsize). Figures A1 - A3 show a graphical representation of the spatial distribution of He, Hmt and, s, respectively. Additional file 3: Assessment of environmental marginality. PCA (principle component analysis) on 35 climatic parameters for the period from 1960 - 2000 from publicly availableWorldClim data. Additional file 4: Inference of a recent climate driven range expansion in R. balthica. Analysis of the freshwater benthos long term monitoring data of the Swedish national monitoring databases at the Swedish University of Agricultural Sciences SLU with canonical correspondence analysis
Habitat specificity of a threatened and endemic cliff-dwelling halophyte
Research ArticleCoastal areas and other saline environments are major contributors to regional and global biodiversity
patterns. In these environments, rapidly changing gradients require highly specialized plants like halophytes.
In European coastal cliff-tops, rocky and sandy seashores, and saltmarshes, typical halophytes from the genus
Limonium are commonly found. Among them, the aneuploid tetraploid (2n ¼ 4x ¼ 35, 36, 37) Limonium multiflorum,
endemic to the west coast of Portugal, is an interesting case study for investigating the ecology and conservation
of a halophyte agamospermic species. Although it is listed in the IUCN red list of threatened species,
information on its population size or rarity, as well as its ecology, in some respects is still unknown. Field surveys
in the largest known population were performed (Raso cape, Portugal) in order to determine habitat requirements
and conservation status. A total of 88 quadrats were monitored, 43 of which contained at least one L. multiflorum
individual. For each sampled quadrat, four abiotic and four biotic variables as well as two spatially derived variables
were recorded. Principal component analysis and cluster analysis showed narrow habitat specificity for this species
which appeared to be intolerant to competition with invasive alien plants. We conclude that in situ conservation
in a local ‘hotspot’ of this rare and vulnerable species emerges as a priority in order to ensure that biodiversity is not los
Identifying metabolic pathways for production of extracellular polymeric substances by the diatom Fragilariopsis cylindrus inhabiting sea ice
Diatoms are significant primary producers in sea ice, an ephemeral habitat with steep vertical gradients of temperature and salinity characterizing the ice matrix environment. To cope with the variable and challenging conditions, sea ice diatoms produce polysaccharide-rich extracellular polymeric substances (EPS) that play important roles in adhesion, cell protection, ligand binding and as organic carbon sources. Significant differences in EPS concentrations and chemical composition corresponding to temperature and salinity gradients were present in sea ice from the Weddell Sea and Eastern Antarctic regions of the Southern Ocean. To reconstruct the first metabolic pathway for EPS production in diatoms, we exposed Fragilariopsis cylindrus, a key bi-polar diatom species, to simulated sea ice formation. Transcriptome profiling under varying conditions of EPS production identified a significant number of genes and divergent alleles. Their complex differential expression patterns under simulated sea ice formation was aligned with physiological and biochemical properties of the cells, and with field measurements of sea ice EPS characteristics. Thus, the molecular complexity of the EPS pathway suggests metabolic plasticity in F. cylindrus is required to cope with the challenging conditions of the highly variable and extreme sea ice habitat
Plant species diversity, plant biomass and responses of the soil community on abandoned land across Europe: idiosyncracy or above-belowground time lags
Evolution of Chilean colonizing populations of Drosophila subobscura: lethal genes and chromosomal arrangements
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