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Xalapa de Enriquez, Mexico

Bastarrachea-Magnani M.A.,National Autonomous University of Mexico | Lerma-Hernandez S.,University of Xalapas | Hirsch J.G.,National Autonomous University of Mexico
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We study the nonintegrable Dicke model and its integrable approximation, the Tavis-Cummings model, as functions of both the coupling constant and the excitation energy. Excited-state quantum phase transitions (ESQPT) are found analyzing the density of states in the semiclassical limit and comparing it with numerical results for the quantum case in large Hilbert spaces, taking advantage of efficient methods recently developed. Two different ESQPTs are identified in both models, which are signaled as singularities in the semiclassical density of states; one static ESQPT occurs for any coupling, whereas a dynamic ESQPT is observed only in the superradiant phase. The role of the unstable fixed points of the Hamiltonian semiclassical flux in the occurrence of the ESQPTs is discussed and determined. Numerical evidence is provided that shows that the semiclassical results describe very well the tendency of the quantum energy spectrum for any coupling in both models. Therefore, the semiclassical density of states can be used to study the statistical properties of the fluctuation in the spectra, a study that is presented in a companion paper. © 2014 American Physical Society.

Bastarrachea-Magnani M.A.,National Autonomous University of Mexico | Lerma-Hernandez S.,University of Xalapas | Hirsch J.G.,National Autonomous University of Mexico
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

The nonintegrable Dicke model and its integrable approximation, the Tavis-Cummings model, are studied as functions of both the coupling constant and the excitation energy. The present contribution extends the analysis presented in the previous paper by focusing on the statistical properties of the quantum fluctuations in the energy spectrum and their relation with the excited-state quantum phase transitions. These properties are compared with the dynamics observed in the semiclassical versions of the models. The presence of chaos for different energies and coupling constants is exhibited, employing Poincaré sections and Peres lattices in the classical and quantum versions, respectively. A clear correspondence between the classical and quantum result is found for systems containing between N=80 and 200 atoms. A measure of the Wigner character of the energy spectrum for different couplings and energy intervals is also presented employing the statistical Anderson-Darling test. It is found that in the Dicke model, for any coupling, a low-energy regime with regular states is always present. The richness of the onset of chaos is discussed both for finite quantum systems and for the semiclassical limit, which is exact when the number of atoms in the system tends to infinite. © 2014 American Physical Society.

Perez-Staples D.,University of Xalapas | Shelly T.E.,U.S. Department of Agriculture | Yuval B.,Hebrew University of Jerusalem
Entomologia Experimentalis et Applicata | Year: 2013

The sterile insect technique (SIT) involves the inundative release of irradiated (sterile or partially sterile) insects to decrease population levels in a target pest species. The effectiveness of SIT programs depends on sterile males mating successfully and inducing reproductive failure in wild females, or in the F1 generation in the case of lepidopteran species. Thus, from the perspective of insect control, female mating failure involves mating with a mass-reared, sterilized male, which then results in female reproductive failure. Here, we review female mating failure in the context of SIT at two stages. First, at the pre-copulatory stage we consider factors that affect female mating failure with sterile males, such as differences between sterile and wild males in terms of male courtship success, male discrimination of females, pheromone production, and dispersal. We emphasize studies with some degree of ecological realism and review certain factors that can affect female sexual development and choice, such as diet, age, and sex ratio. Second, at the post-copulatory stage we consider factors that functionally result in female reproductive failure, such as ejaculate transfer and control of female remating. Sterile insect technique operations strive to incorporate methods that increase wild female mating with sterile males so that ultimately population-wide reproductive failure is achieved in the target species. © 2012 The Netherlands Entomological Society.

Perroni Y.,University of Xalapas | Garcia-Oliva F.,National Autonomous University of Mexico | Souza V.,National Autonomous University of Mexico
Journal of Arid Environments | Year: 2014

Soil phosphorus (P) is one of the most important but least understood nutrients supporting productivity in terrestrial ecosystems. This study explored the relative importance of plant species richness or composition in the association with concentrations of different soil P forms in an oligotrophic grassland-desert scrub system in the central region of the Chihuahuan Desert (Mexico). Our results suggest that species identity, rather than richness, is more related to pools of soil P in different forms in the studied system. However, plant species richness also appears to be related to soil P patterns when analyzed alone. Differences in Allenrolfea occidentalis coverage are associated with differences of total P pool in grassland plots between 60.4 and 110.2mg/kg of dry soil. In desert scrub, Nerisyrenia camporum coverage is associated with total P between 207.2 and 243.8mg/kg of dry soil. Coverage of Jatropha dioica is associated with soluble+labile P pool between 29.7 and 22.6mg/kg of dry soil; and Larrea tridentata coverage is associated with soil organic P pool between 3.1 and 18.0mg/kg of dry soil. These results may be explained by the existence of key plant species with functional attributes that are closely related to soil P. © 2014 Elsevier Ltd.

Cortes-Perez S.,National Autonomous University of Mexico | Rodriguez-Zaragoza S.,National Autonomous University of Mexico | Mendoza-Lopez M.R.,University of Xalapas
Microbial Ecology | Year: 2014

Root exudation increases microbial activity, selecting bacterial and fungal communities that metabolize organic matter such as hydrocarbons. However, a strong contamination pulse of hydrocarbons around plant roots may reorganize the soil's microbial trophic structure toward amoebae feeding on bacteria. We conducted a microcosm experiment to elucidate the effect of Medicago sativa on the trophic structure of naked amoebae after a strong pulse of pollution (50,000 ppm of fuel oil no. 6, which is a mixture of long chains ranging from C10 to C28). Plants were seeded 24 h after contamination and species of amoebae in the microcosms were identified at 1, 30, and 60 days after pollution. Several species from three trophic groups of naked amoeba were still alive 24 h after the hydrocarbon pulse. Non-planted microcosms harbored three trophic groups after 60 days, while planted ones nourished four groups. The bacterivore group was the most diverse in all microcosms, followed by protist-eaters and omnivores. The quantity of amoebae was significantly higher (3.4×103 organisms/g soil) in the planted pots than in the non-planted ones (1.3×103 organisms/g soil after 30 days of pollution (P ≤ 0.01). The shortest hydrocarbon chains (C10-C14) disappeared or diminished in all microcosms, and the longest ones increased in the planted ones. M. sativa thus exerted a positive effect on species richness, quantity, and the composition of amoebae trophic groups in contaminated soil. This indirect effect on bacterial predators is another key factor underlying hydrocarbon assimilation by living organisms during phytoremediation. © 2013 Springer Science+Business Media New York.

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