Decays Z' -> \gamma\gamma\gamma{} and Z -> \gamma\gamma\gamma{} in the minimal 331 model

The possibility of a significant effect of exotic particles on the Z'->\gamma\gamma\gamma{} and Z->\gamma\gamma\gamma{} decays is investigated in the context of the minimal 331 model. This model, which is based in the SU_C(3)xSU_L(3)xU_X(1) gauge group, predicts the existence of many exotic charged particles that can significantly enhance the decay widths. It is found that the standard model prediction for the Z->\gamma\gamma\gamma{} decay remains essentially unchanged, as the new physics effects quickly decouples. On the other hand, it is found that the contributions of the new exotic quarks and gauge bosons predicted by this model lead to a branching fraction for the Z'->\gamma\gamma\gamma{} decay of about 10^(-6), which is about three orders of magnitude larger than that of the Z->\gamma\gamma\gamma{} decay.Comment: 20 pages and 20 figure

A blue sky catastrophe in double-diffusive convection

A global bifurcation of the blue sky catastrophe type has been found in a small Prandtl number binary mixture contained in a laterally heated cavity. The system has been studied numerically applying the tools of bifurcation theory. The catastrophe corresponds to the destruction of an orbit which, for a large range of Rayleigh numbers, is the only stable solution. This orbit is born in a global saddle-loop bifurcation and becomes chaotic in a period doubling cascade just before its disappearance at the blue sky catastrophe.Comment: 4 pages, 6 figures, REVTeX, To be published in Physical Review Letter

Bilepton effects on the WWV^* vertex in the 331 model with right-handed neutrinos via a SU_L(2)XU_Y(1) covariant quantization scheme

In a recent paper, we investigated the effects of the massive charged gauge bosons (bileptons) predicted by the minimal 331 model on the off-shell vertex WWV^* (V=gamma, Z) using a SU_L(2) X U_Y(1) covariant gauge-fixing term for the bileptons. We proceed along the same lines and calculate the effects of the gauge bosons predicted by the 331 model with right-handed neutrinos. It is found that the bilepton effects on the WWV^* vertex are of the same order of magnitude than those arising from the SM and several of its extensions, provided that the bilepton mass is of the order of a few hundred of GeVs. For heavier bileptons, their effects on the WWV^* vertex are negligible. The behavior of the form factors at high energies is also discussed as it is a reflect of the gauge invariance and gauge independence of the WWV^* Green function obtained via our quantization method.Comment: Replaced to match published versio

Strong covalent bonding between two graphene layers

We show that two graphene layers stacked directly on top of each other (AA stacking) form strong chemical bonds when the distance between planes is 0.156 nm. Simultaneously, C-C in-plane bonds are considerably weakened from partial double-bond (0.141 nm) to single bond (0.154 nm). This polymorphic form of graphene bilayer is meta-stable w.r.t. the one bound by van der Waals forces at a larger separation (0.335 nm) with an activation energy of 0.16 eV/cell. Similarly to the structure found in hexaprismane, C forms four single bonds in a geometry mixing 90^{0} and 120^{0} angles. Intermediate separations between layers can be stabilized under external anisotropic stresses showing a rich electronic structure changing from semimetal at van der Waals distance, to metal when compressed, to wide gap semiconductor at the meta-stable minimum.Comment: tar gzip latex 4 pages 4 figure

Branchiosyllis salazari sp. n. (Polychaeta, Syllidae) del Caribe noroccidental y comentarios sobre el material tipo de B. exilis (Gravier, 1900)

Basándonos en el estudio de 195 ejemplares procedentes del Caribe Noroccidental, se describe una nueva especie de Branchiosyllis Ehlers, 1887. Branchiosyllis salazari sp. n. tiene tres pares de ojos (dos pares pequeños en el margen anterior del prostomio, el tercer par está en una línea transversal), sin branquias, sedas con artejo en forma de ganchos grandes ya en los setígeros medios, y proventrículo sin línea mediodorsal. El material tipo de B. exilis (Gravier, 1900), una especie aparentemente circuntropical, fue revisado para clarificar su presencia en el Mar Caribe. Sus características diagnósticas son: dos pares de ojos en una línea transversa, sin branquias, sedas con artejo en forma de gancho grande restringidas a los setígeros posteriores y proventrículo con una línea mediadorsal de células en forma de diamante. Se anexa una clave para las siete especies de Branchiosyllis en el Gran Caribe. Palabras clave: Branchiosyllis salazari sp. n., Taxonomía, Gran Caribe, Syllidae, Polychaeta.On the basis of 195 specimens from the Northwestern Caribbean Sea, a new species of Branchiosyllis Ehlers, 1887 is described. Branchiosyllis salazari n. sp. has three pairs of eyes (two small pairs above the anterior margin of the prostomium, the third pair in a transverse line), without branchia, setae with large hooked blades in median setigers, and proventricle without middorsal line. The type material of B. exilis (Gravier, 1900), an apparently circumtropical species, was revised to clarify its presence in the Caribbean Sea. Its diagnostic features are: two pairs of eyes in a transverse line, no branchia, setae with large hooked blades in posterior setigers only, and proventricle with a middorsal line of Diamond-shaped cells. A key for the seven species of Branchiosyllis in the Grand Caribbean is included. Key words: Branchiosyllis salazari n. sp., Taxonomy, Grand Caribbean, Syllidae, Polychaeta.Basándonos en el estudio de 195 ejemplares procedentes del Caribe Noroccidental, se describe una nueva especie de Branchiosyllis Ehlers, 1887. Branchiosyllis salazari sp. n. tiene tres pares de ojos (dos pares pequeños en el margen anterior del prostomio, el tercer par está en una línea transversal), sin branquias, sedas con artejo en forma de ganchos grandes ya en los setígeros medios, y proventrículo sin línea mediodorsal. El material tipo de B. exilis (Gravier, 1900), una especie aparentemente circuntropical, fue revisado para clarificar su presencia en el Mar Caribe. Sus características diagnósticas son: dos pares de ojos en una línea transversa, sin branquias, sedas con artejo en forma de gancho grande restringidas a los setígeros posteriores y proventrículo con una línea mediadorsal de células en forma de diamante. Se anexa una clave para las siete especies de Branchiosyllis en el Gran Caribe. Palabras clave: Branchiosyllis salazari sp. n., Taxonomía, Gran Caribe, Syllidae, Polychaeta

Locally Most Powerful Invariant Tests for Correlation and Sphericity of Gaussian Vectors

In this paper we study the existence of locally most powerful invariant tests (LMPIT) for the problem of testing the covariance structure of a set of Gaussian random vectors. The LMPIT is the optimal test for the case of close hypotheses, among those satisfying the invariances of the problem, and in practical scenarios can provide better performance than the typically used generalized likelihood ratio test (GLRT). The derivation of the LMPIT usually requires one to find the maximal invariant statistic for the detection problem and then derive its distribution under both hypotheses, which in general is a rather involved procedure. As an alternative, Wijsman's theorem provides the ratio of the maximal invariant densities without even finding an explicit expression for the maximal invariant. We first consider the problem of testing whether a set of $N$-dimensional Gaussian random vectors are uncorrelated or not, and show that the LMPIT is given by the Frobenius norm of the sample coherence matrix. Second, we study the case in which the vectors under the null hypothesis are uncorrelated and identically distributed, that is, the sphericity test for Gaussian vectors, for which we show that the LMPIT is given by the Frobenius norm of a normalized version of the sample covariance matrix. Finally, some numerical examples illustrate the performance of the proposed tests, which provide better results than their GLRT counterparts

Stochastic rainfall interpolation and downscaling

No Abstract

Ethylene epoxidation in microwave heated structured reactors

In the present work we show the microwave-induced heating of monolithic reactors containing a thin-layered catalyst that exhibits a strong and selective heating susceptibility under microwave irradiation. The combination of microwave radiation and structured reactors has been successfully applied for the intensification of the selective oxidation of ethylene to ethylene oxide (epoxidation) while operating at lower power consumptions and with higher energy efficiencies than in conventional heating conditions. The microwave radiation selectively heats the catalyst and the monolith walls while maintaining a relatively colder gas stream thereby creating a gas/solid temperature gradient of up to ~70 °C at a reaction temperature of 225 °C. Moreover, the influence of different parameters such as the distribution of the catalyst onto the structured monoliths or the temperature measurement techniques employed to determine the heating profiles (Optic Fibers and/or IR thermography) have been also thoroughly evaluated to justify the obtained catalytic results