2,874 research outputs found
Coexistence in neutral theories: interplay of criticality and mild local preferences
Neutral theories have played a crucial and revolutionary role in fields such
as population genetics and biogeography. These theories are critical by
definition, in the sense that the overall growth rate of each single
allele/species/type vanishes. Thus each species in a neutral model sits at the
edge between invasion and extinction, allowing for the coexistence of
symmetric/neutral types. However, in finite systems, mono-dominated states are
ineludibly reached in relatively short times owing to demographic fluctuations,
thus leaving us with an unsatisfactory framework to rationalize
empirically-observed long-term coexistence. Here, we scrutinize the effect of
heterogeneity in quasi-neutral theories, in which there can be a local mild
preference for some of the competing species at some sites, even if the overall
species symmetry is maintained. As we show here, mild biases at a small
fraction of locations suffice to induce overall robust and durable species
coexistence, even in regions arbitrarily far apart from the biased locations.
This result stems from the long-range nature of the underlying critical bulk
dynamics and has a number of implications, for example, in conservation ecology
as it suggests that constructing local specific "sanctuaries" for different
competing species can result in global enhancement of biodiversity, even in
regions arbitrarily distant from the protected refuges.Comment: Accepted for publication in Journal of Statistical Mechanics: Theory
and Experimen
Temporal disorder in up-down symmetric systems
The effect of temporal disorder on systems with up-down Z2 symmetry is
studied. In particular, we analyze two well-known families of phase
transitions: the Ising and the generalized voter universality classes, and
scrutinize the consequences of placing them under fluctuating global
conditions. We observe that variability of the control parameter induces in
both classes "Temporal Griffiths Phases" (TGP). These recently-uncovered phases
are analogous to standard Griffiths Phases appearing in systems with quenched
spatial disorder, but where the roles of space and time are exchanged. TGPs are
characterized by broad regions in parameter space in which (i) mean
first-passage times scale algebraically with system size, and (ii) the system
response (e.g. susceptibility) diverges. Our results confirm that TGPs are
quite robust and ubiquitous in the presence of temporal disorder. Possible
applications of our results to examples in ecology are discussed
Inferencia del origen del bovino Criollo Cubano a través del análisis de patri- y matrilinajes
Antes de descubrimiento, no existÃan bovinos en América. Los primeros, fueron introducidos en la Antillas Mayores (La Española, Puerto Rico, Jamaica y Cuba), y desde allà trasladados al resto de Latinoamérica. Actualmente, existen en Cuba alrededor de 1300 bovinos Criollos, concentrados principalmente en la región oriental. Con el objetivo de analizar el origen materno de esta raza y detectar eventos contemporáneos de flujo génico por vÃa paterna, se analizó un fragmento de 240 pb del D-loop mitocondrial (mtADN) y 5 microsatélites del cromosoma Y (BTY), en 36 hembras y 21 machos respectivamente. La diversidad genética se estimó mediante el número de haplotipos, el número de sitios polimórficos, el número de diferencias nucleotÃdicas entre pares de secuencias y el Ãndice de diversidad nucleotÃdica, mientras que el análisis filogenético se realizó utilizando el método de median joining network. Dicho análisis permitió detectar 15 haplotipos mitocondriales (10 del haplogrupo europeo T3, 3 del africano T1, 1 del cercano oriente T2 y 1 ambiguo T1-T3) y 3 haplotipos en el BTY, ambos del haplogrupo cebuÃno Y3. En el mtADN se detectaron 23 sitios polimórficos con una diversidad nucleotÃdica de 0,014 y 3,36 diferencias medias entre pares de secuencias. En conclusión, la población de bovinos Criollos Cubanos presentó una composición haplotÃpica mitocondrial comparable a la de otras razas criollas y mediterráneas, hecho que concuerda con su origen histórico. El BTY evidenció altos niveles de introgresion paterna de genes del zebú.Cattle was absent from America before the discovery. Initially, bovine were brought to Greater Antilles (La Española, Puerto Rico, Jamaica and Cuba islands), and in the course of a few years, they were taken from Caribbean islands to the rest of Latin America. Nowadays, Cuban Creole cattle population is about 1300 heads, mainly located in the eastern region of the island. With the aim of analyzing the maternal origin of Cuban Creole cattle and detect possible contemporaneous, male mediated, gene flow, a 240 pb fragment of mitochondrial D-loop (mtDNA) and five microsatellites of Y chromosome (BTY) were studied in 36 dams and 21 sires, respectively. Genetic diversity was evaluated through number of haplotypes, mean number of pairwise differences and nucleotide diversity. The phylogenetic analysis was performed using a median joining. A total of 15 mtDNA haplotypes were detected in the studied population (10 from the European haplogroup T3, 3 from the African T1, 1 from the Nearern East T2, and 1 ambiguous T1-T3). The number of polymorphic sites, the mean nucleotide diversity, and the mean number of pairwise differences were 23, 0.014 and 3.36, respectively. Two patrilinages were detected, both belonging to the Y3 Zebu haplogroup. In conclusion, Cuban Creole cattle population had a mtDNA haplotypic composition similar to the observed in Creole and Mediterranean breeds, what is in concordance with its historical origin. Y chromosome analysis evidenced a male mediated process of zebu introgression.Fil: Liron, Juan Pedro. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; ArgentinaFil: Acosta, A.. Centro Nacional de Sanidad Agropecuaria. Laboratorio de Genética Molecular; CubaFil: Rogberg Muñoz, Andres. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; ArgentinaFil: Uffo, O.. Centro Nacional de Sanidad Agropecuaria. Laboratorio de Genética Molecular; CubaFil: Posik, Diego Manuel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; ArgentinaFil: Garcia, J.. Ministerio de la Agricultura. Dirección Nacional de Genética; CubaFil: Peral Garcia, Pilar. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; ArgentinaFil: Giovambattista, Guillermo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico CONICET- La Plata. Instituto de Genética Veterinaria "Ing. Fernando Noel Dulout". Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias. Instituto de Genética Veterinaria; Argentin
Simultaneous ultrafast optical pulse train bursts generation and shaping based on Fourier series developments using superimposed fiber Bragg gratings
We propose an all-fiber method for the generation of ultrafast shaped pulse train bursts from a single pulse based on Fourier Series Developments (FDSs). The implementation of the FSD based filter only requires the use of a very simple non apodized Superimposed Fiber Bragg Grating (S-FBG) for the generation of the Shaped Output Pulse Train Burst (SOPTB). In this approach, the shape, the period and the temporal length of the generated SOPTB have no dependency on the input pulse rate
Formation in-situ of metallic nanoclusters of Mn interlayered into bentonite previously pillared with Al
Hasta el momento, el crecimiento de agregados polinucleares en el espacio interlaminar de diferentes aluminosilicatos por reacción en el estado sólido requiere de tiempos prolongados de contacto (alrededor de 4 meses). En consecuencia, en el presente trabajo se ha evaluado una metodologÃa novedosa para llevar a cabo tal sÃntesis, especÃficamente para el crecimiento in-situ de MnS en el espacio interlaminar de una bentonita que involucra un tiempo aproximado de 10 horas de reacción. Sin embargo, los resultados han evidenciado que hay varias condiciones que se deben controlar por cuanto afectan la estabilidad de los clusters; entre estos factores están el tratamiento quÃmico, térmico, el tipo de atmósfera empleado en la calcinación y la densidad de los pilares de Al
Laser performance of Coumarin 540A dye molecules in polymeric host media with different viscosities: From liquid solution to solid polymer matrix
11 pages, 12 figures, 3 tables.-- PACS: 42.70.Hj; 42.55.Rz; 42.55.Mv; 66.20.+d; 78.55.Bq; 78.55.KzPhotophysical parameters and lasing properties of Coumarin 540A dye molecules are studied in solutions of increasing viscosity, from liquid solutions in 1,4-dioxane to solid solutions in poly(methyl methacrylate). The fluorescence quantum yield and lasing efficiencies decrease as the viscosity of the solution increases, reflecting the strong influence of the rigidity of the medium on the radiative processes. The photodegradation mechanisms acting on the fluorophores are analyzed by following the dependence of laser induced fluorescence and laser output on the number of pump laser pulses. The fluorescence redistribution after pattern photobleaching technique is used, and Fick's second law is applied to study the diffusion of dye molecules in the highly viscous polymer solutions. The diffusion coefficients of the dye molecules as a function of the increased viscosity of the medium are determined.This work was supported by the Spanish
CICYT Project MAT94-0757.Peer reviewe
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