A stochastic-dynamic model for global atmospheric mass field statistics

A model that yields the spatial correlation structure of atmospheric mass field forecast errors was developed. The model is governed by the potential vorticity equation forced by random noise. Expansion in spherical harmonics and correlation function was computed analytically using the expansion coefficients. The finite difference equivalent was solved using a fast Poisson solver and the correlation function was computed using stratified sampling of the individual realization of F(omega) and hence of phi(omega). A higher order equation for gamma was derived and solved directly in finite differences by two successive applications of the fast Poisson solver. The methods were compared for accuracy and efficiency and the third method was chosen as clearly superior. The results agree well with the latitude dependence of observed atmospheric correlation data. The value of the parameter c sub o which gives the best fit to the data is close to the value expected from dynamical considerations

Collective resonances in plasmonic crystals: Size matters

Periodic arrays of metallic nanoparticles may sustain Surface Lattice Resonances (SLRs), which are collective resonances associated with the diffractive coupling of Localized Surface Plasmon Resonances (LSPRs). By investigating a series of arrays with varying number of particles, we traced the evolution of SLRs to its origins. Polarization resolved extinction spectra of arrays formed by a few nanoparticles were measured, and found to be in very good agreement with calculations based on a coupled dipole model. Finite size effects on the optical properties of the arrays are observed, and our results provide insight into the characteristic length scales for collective plasmonic effects: for arrays smaller than 5 x 5 particles, the Q-factors of SLRs are lower than those of LSPRs; for arrays larger than 20 x 20 particles, the Q-factors of SLRs saturate at a much larger value than those of LSPRs; in between, the Q-factors of SLRs are an increasing function of the number of particles in the array.Comment: 4 figure

Eight New Species of Poechiliid Fishes of the Genus Limia from Hispaniola

Pending revision of the genus, eight new species of Limia are described to make the names available. The genus Is divided into two subgenera, one of which, Odontollmia, is proposed as new. The two subgenera are characterized and the number of species In Odontollmia is six and in Limia 13

Semiclassical Coherent States propagator

In this work, we derived a semiclassical approximation for the matrix elements of a quantum propagator in coherent states (CS) basis that avoids complex trajectories, it only involves real ones. For that propose, we used the, symplectically invariant, semiclassical Weyl propagator obtained by performing a stationary phase approximation (SPA) for the path integral in the Weyl representation. After what, for the transformation to CS representation SPA is avoided, instead a quadratic expansion of the complex exponent is used. This procedure also allows to express the semiclassical CS propagator uniquely in terms of the classical evolution of the initial point, without the need of any root search typical of Van Vleck Gutzwiller based propagators. For the case of chaotic Hamiltonian systems, the explicit time dependence of the CS propagator has been obtained. The comparison with a \textquotedbl{}realistic\textquotedbl{} chaotic system that derives from a quadratic Hamiltonian, the cat map, reveals that the expression here derived is exact up to quadratic Hamiltonian systems.Comment: 13 pages, 2 figure. Accepted for publication in PR

Character Displacement and Coexistence in Two Poeciliid Fishes of the Genus Poecilia (Mollienesia) from Hispaniola

Character displacement in animals, particularly in fishes, is reviewed and the new approach of Grant (1975) is used in this study to demonstrate character displacement in P. hispaniolana and P. dominicensis, two closely related and partly sympatric species of mollies endemic to Hispaniola. Background information is given on the probable origin, evolution, attainment of present partial sympatry and length of coexistence of the two species, as indicated by their present distribution and the paleogeography of Hispaniola. It is hypothesized that a common ancestor to both species existed on the island prior to the Miocene about 20 million years ago. It is also hypothesized that the ancestral population was split during the Miocene-Pliocene for a period of about 18 million years, that the two species evolved during that time, and that the barrier to their dispersal was eliminated in late Pliocene about two million years ago. It is assumed that during that last period the present distribution and partial sympatry were attained, and that the two species have coexisted twice as long in the localities where character displacement shows greater magnitude. Analyses of meristics, morphometries, and reproduction are given to demonstrate character displacement in fin ray, scale, and gill-raker number, and in body size and fecundity. Divergent, convergent, and parallel displacement were found to occur as well as a change of reproductive strategy for P. dominicensis in sympatry. Causes and effects of displacement in the two species are discussed and later summarized in combination with tentative conclusions

A New Species of Poeciliid Fish of the Genus Poecilia from Hispaniola, with Reinstatement and Redescription of P. dominicensis (Evermann and Clark)

Exploration of the streams and lakes of Hispaniola and available collections of poeciliid fishes from that island are discussed, followed by the taxonomic history and generic status of the two species described. The genera Limia and Mollienesia were synonymized with Poecilia by Rosen and Bailey (1963) and the former Mollienesia dominicensis of Evermann and Clark (1906) became a junior homonym of Limia dominicensis of Valenciennes (1846). Rosen and Bailey, therefore, renamed M. dominicensis of Evermann and Clark as Poecilia montana. Because Mollienesia is herein retained as a synonym of Poecilia but Limia is reinstated as a valid genus, Poecilia dominicensis of Evermann and Clark is no longer a junior homonym of Limia dominicensis of Valenciennes. The name montana, therefore, becomes a junior objective synonym of Evermann and Clark\u27s dominicensis. The new species herein described, although available to previous authors, had been hitherto confused with Poecilia dominicensis of Evermann and Clark. Both species are superficially similar but clearly distinct and more closely related to each other than either is to any of the other species of Poecilia. They are restricted to the island of Hispaniola and show character displacement in the several localities where they occur together

Tolerance to mutations in the foot-and-mouth disease virus integrin-binding RGD region is different in cultured cells and in vivo and depends on the capsid sequence context.

Engineered RNAs carrying substitutions in the integrin receptor-binding Arg-Gly-Asp (RGD) region of foot-and-mouth disease virus (FMDV) were constructed (aa 141-147 of VP1 capsid protein) and their infectivity was assayed in cultured cells and suckling mice. The effect of these changes was studied in the capsid proteins of two FMDVs, C-S8c1, which enters cells through integrins, and 213hs(-), a derivative highly adapted to cell culture whose ability to infect cells using the glycosaminoglycan heparan sulfate (HS) as receptor, acquired by multiple passage on BHK-21 cells, has been abolished. The capsid sequence context determined infectivity in cultured cells and directed the selection of additional replacements in structural proteins. Interestingly, a viral population derived from a C-S8c1/L144A mutant, carrying only three substitutions in the capsid, was able to expand tropism to wild-type (wt) and mutant (mt)glycosaminoglycan-deficient CHO cells. In contrast, the 213hs(-) capsid tolerated all substitutions analysed with no additional mutations, and the viruses recovered maintained the ability of the 213hs(-) parental virus to infect wt and mt CHO cells. Viruses derived from C-S8c1 with atypical RGD regions were virulent and transmissible for mice with no other changes in the capsid. Substitution of Asp143 for Ala in the C-S8c1 capsid eliminated infectivity in cultured cells and mice. Co-inoculation with a neutralizing monoclonal antibody directed against the type C FMDV RGD region abolished infectivity of C-S8c1 virus on suckling mice, suggesting that FMDV can infect mice using integrins. Sequence requirements imposed for viral entry in vitro and in vivo are discussed

Modelling a two-dimensional spatial distribution of mycotoxin concentration in bulk commodities to design effective and efficient sample selection strategies

Mycotoxins in agricultural commodities are a hazard to human and animal health. Their heterogeneous spatial distribution in bulk storage or transport makes it particularly difficult to design effective and efficient sampling plans. There has been considerable emphasis on identifying the different sources of uncertainty associated with mycotoxin concentration estimations, but much less on identifying the effect of the spatial location of the sampling points. This study used a two-dimensional statistical modelling approach to produce detailed information on appropriate sampling strategies for surveillance of mycotoxins in raw food commodities. The emphasis was on deoxynivalenol (DON) and ochratoxin A (OTA) in large lots of grain in storage or bulk transport. The aim was to simulate a range of plausible distributions of mycotoxins in grain from a set of parameters characterising the distributions. For this purpose, a model was developed to generate data sets which were repeatedly sampled to investigate the effect that sampling strategy and the number of incremental samples has on determining the statistical properties of mycotoxin concentration. Results showed that, for most sample sizes, a regular grid proved to be more consistent and accurate in the estimation of the mean concentration of DON, which suggests that regular sampling strategies should be preferred to random sampling, where possible. For both strategies, the accuracy of the estimation of the mean concentration increased significantly up to sample sizes of 40-60 (depending on the simulation). The effect of sample size was small when it exceeded 60 points, which suggests that the maximum sample size required is of this order. Similar conclusions about the sample size apply to OTA, although the difference between regular and random sampling was small and probably negligible for most sample sizes