Coupled electric and magnetic dipole formulation for planar arrays of dipolar particles: metasurfaces with various electric and/or magnetic meta-atoms per unit cell

The optical properties of infinite planar array of scattering particles, metasurfaces and metagratings, are attracting special attention lately for their rich phenomenology, including both plasmonic and high-refractive-index dielectric meta-atoms with a variety of electric and magnetic resonant responses. Herein we derive a coupled electric and magnetic dipole (CEMD) analytical formulation to describe the reflection and transmission of such periodic arrays, including specular and diffractive orders, valid in the spectral regimes where only dipolar multipoles are needed. Electric and/or magnetic dipoles with all three orientations arising in turn from a single or various meta-atoms per unit cell are considered. The 2D lattice Green function is rewritten in terms of a 1D (chain) version that fully converges and can be easily calculated. Modes emerging as poles of such lattice Green function can be extracted. This formulation can be applied to investigate a wealth of plasmonic, all-dielectric, and hybrid metasurfaces/metagratings of interest throughout the electromagnetic spectrum.Comment: 8 pages, 4 figure

Effect of Non Gaussian Noises on the Stochastic Resonance-Like Phenomenon in Gated Traps

We exploit a simple one-dimensional trapping model introduced before, prompted by the problem of ion current across a biological membrane. The voltage-sensitive channels are open or closed depending on the value taken by an external potential that has two contributions: a deterministic periodic and a stochastic one. Here we assume that the noise source is colored and non Gaussian, with a $q$-dependent probability distribution (where $q$ is a parameter indicating the departure from Gaussianity). We analyze the behavior of the oscillation amplitude as a function of both $q$ and the noise correlation time. The main result is that in addition to the resonant-like maximum as a function of the noise intensity, there is a new resonant maximum as a function of the parameter $q$.Comment: Communication to LAWNP01, Proceedings to be published in Physica D, RevTex, 8 pgs, 5 figure

Effects of quark family nonuniversality in SU(3)_c X SU(4)_L X U(1)_x models

Flavour changing neutral currents arise in the $SU(3)_c\otimes SU(4)_L\otimes U(1)_X$ extension of the standard model because anomaly cancellation among the fermion families requires one generation of quarks to transform differently from the other two under the gauge group. In the weak basis the distinction between quark families is meaningless. However, in the mass eigenstates basis, the Cabibbo-Kobayashi-Maskawa mixing matrix motivates us to classify left-handed quarks in families. In this sense there are, in principle, three different assignments of quark weak eigenstates into mass eigenstates. In this work, by using measurements at the Z-pole, atomic parity violation data and experimental input from neutral meson mixing, we examine two different models without exotic electric charges based on the 3-4-1 symmetry, and address the effects of quark family nonuniversality on the bounds on the mixing angle between two of the neutral currents present in the models and on the mass scales $M_{Z_2}$ and $M_{Z_3}$ of the new neutral gauge bosons predicted by the theory. The heaviest family of quarks must transform differently in order to keep lower bounds on $M_{Z_2}$ and $M_{Z_3}$ as low as possible without violating experimental constraints.Comment: 27 pages, 10 tables, 2 figures. Equation (19) and typos corrected. Matches version to appear in Phys. Rev.

Kink dynamics in spatially inhomogeneous media: the role of internal modes

The phenomenon of length-scale competition in soliton-bearing equations perturbed by spatially dependent terms A. Sánchez and A. R. Bishop, SIAM Rev. 40, 579 1998 is analyzed from a general viewpoint. We show that the perturbation gives rise to an effective potential for solitons, which consists of wells and barriers. We calculate the effect of these potential features on the solitons, establishing a direct relationship between the maxima, minima, and curvature of the potential with soliton deformations. When the typical wavelength of the perturbation is of the order of the soliton width, these deformations are seen to correspond to the excitation of shape modes and can lead to the dissipation of the soliton kinetic energy and, further, to the impossibility of soliton propagation. Thus, we demonstrate that the mechanism for length-scale competition is related to changes in the dynamics of the internal modes. We study different examples where the perturbation is introduced parametrically and nonparametrically to make it clear that our results apply to a wide class of equations.This work was supported by MEC Spain under Grants MOSAICO and No. NAN2004-9087-C03-03 and by the Comunidad Autónoma de Madrid (Spain) under Grants No. UC3M-FI-05-007 and SIMUMAT-CM. The work by J.G. was done in part during a stay at Universidad Carlos III de Madrid, whose financial support is acknowledged, and S.C. is supported by the Consejería de Educación de la Comunidad Autónoma de Madrid and the Fondo Social Europeo.Publicad

Trapping Dynamics with Gated Traps: Stochastic Resonance-Like Phenomenon

We present a simple one-dimensional trapping model prompted by the problem of ion current across biological membranes. The trap is modeled mimicking the ionic channel membrane behaviour. Such voltage-sensitive channels are open or closed depending on the value taken by a potential. Here we have assumed that the external potential has two contributions: a determinist periodic and a stochastic one. Our model shows a resonant-like maximum when we plot the amplitude of the oscillations in the absorption current vs. noise intensity. The model was solved both numerically and using an analytic approximation and was found to be in good accord with numerical simulations.Comment: RevTex, 5 pgs, 3 figure

Dinámica espacial del mero Epinephelus morio (Pisces: Serranidae) en el Banco de Campeche, Golfo de México

The spatial dynamics of the red grouper Epinephelus morio plays a fundamental role in the fishery management on the Campeche Bank, where it is overfished. The objective of this study was to characterize the spatial dynamics of this population. We used a dynamic model of spatial distribution to estimate population movement rates between adjacent areas. The model was applied using information on catch per unit effort and length-frequency distributions for the Mexican mid-sized fleet that operated in the area in the period 1973-1977. These data were chosen to ensure that the information would reflect the condition of the resource before overfishing. It was possible to quantify the spatial dynamics of the red grouper and the results were consistent with previously known movement patterns. The results showed different movement rates and temporal patterns of movement for different population sectors. The spawning aggregations and the seasonal upwelling occurring in the eastern part of the Bank were considered as key factors influencing the pattern of population movements.La población del mero rojo Epinephelus morio del Banco de Campeche está sobreexplotada. La dinámica espacial del mero juega un papel fundamental en la gestión de la pesquería. El objetivo de este estudio fue caracterizar la dinámica espacial de la población del mero en el Banco de Campeche. Se utilizó un modelo dinámico de distribución espacial para estimar tasas de movimiento poblacional entre áreas adyacentes. El modelo se aplicó con información de las capturas por unidad de esfuerzo y de distribuciones de frecuencias de longitud provenientes de la flota mediana mexicana que operó en la zona de 1973 a 1977. Estos datos fueron elegidos para asegurar que la información reflejara el estado del recurso antes de la sobrepesca. Fue posible cuantificar la dinámica espacial del mero y los resultados concordaron con patrones de movimientos conocidos anteriormente. Los resultados mostraron distintos patrones temporales de movimiento para los diferentes sectores de población. Se considera que las agregaciones de desove y la surgencia estacional que ocurre en la parte oriental del Banco son factores clave que influyen en el patrón de los movimientos de población

Mathematical Visions: The Pursuit of Geometry in Victorian England (Book Review)

Reviewed Title: Joan L. Richards. Mathematical Visions: The Pursuit of Geometry in Victorian England. xiii + 266 pp., illus., figs., bibl., index. Boston/New York: Academic Press, Harcourt Brace Jovanovich, 1988

Tipología de productores de durazno en Zacatecas, México por atributos de calidad del fruto

Zacatecas se posiciona entre los cinco principales Estados productores de durazno en México. El durazno es criollo, amarillo, hueso pegado, pulpa firme, propagado sexualmente y cultivado en temporal en ˜ 81% de la superficie cultivada; lo que, destaca la baja competitividad de este cultivo. No obstante, por el número de productores dedicados a este cultivo, realza su importancia socioeconómica con relación a otros frutales. Si se pretende entender las características y problemáticas de las unidades de producción (UP) que sirvan como un instrumento para optimizar la asignación de recursos públicos, y proponer estrategias que mejoren el desarrollo de la agricultura, es necesario entender la heterogeneidad de los productores considerando sus características socioeconómicas dentro de las UP. Por ello, en esta investigación se buscó analizar y segmentar técnica y tipológicamente a los productores de durazno del estado de Zacatecas. Los datos se recopilaron a través de una encuesta a 204 productores de durazno en Zacatecas, México. Los resultados sugieren cuatro tipos de productores: 1) aquellos que plantan durazno sin objetivo; 2) los que plantan durazno a nivel de traspatio; 3) productores donde el durazno forma parte de un sistema de producción agropecuario; y 4) productores empresarios de durazno. En esta última categoría, se encontró ˜31% de los productores, lo cual podría explicar, en parte, la baja competitividad del cultivo ante otros sistemas productoPeer ReviewedPostprint (published version

Dormancy and germination in Talipariti elatum seeds

The dormancy in fresh seeds of Talipariti elatum (Sw.) Fryxell from moist evergreen forest and secondary vegetation was determined. Structural and germinative variables of the seeds were studied, and water absorption dynamics of intact and scarified seeds was determined. In seeds from both ecosystems, the dry weight of seed coats was higher than the food storage weight. Intact seeds absorbed water but lacked the triphasic pattern of absorption shown by scarified seeds. 88% intact seeds were hydrated in contact with water, though 30% ± were scarcely hydrated (up to 30% humidity) and over 50% showed hydration values surpassing 30%. Germination in intact seeds was poor and erratic, contrary to coatless seeds. Results show that fresh seeds do not have exogenous dormancy as the only impediment for avoiding germination, but a mechanical dormancy in combination with a certain degree of seed coat impermeability to water which prevent germination.Se determinó la dormancia en semillas frescas de Talipariti elatum (Sw.) Fryxell de un bosque siempreverde y una zona de vegetación secundaria. Se estudiaron las variables estructurales y germinativas de las semillas, y se determinó la dinámica de absorción de agua en semillas intactas y escarificadas. En ambas procedencias la masa seca de la cubierta seminal fue mayor que la masa seca de la reserva. Las semillas intactas absorben agua, pero no tienen el patrón trifásico de absorción que muestran las semillas escarificadas. El 88% de las semillas intactas se hidrataron una vez contacto con el agua, de ellas el 30% se hidrataron ligeramente (hasta un 30% de humedad) y más del 50% mostraron valores de hidratación superiores al 30%. La germinación de las semillas intactas fue pobre y errática, contrario a las semillas sin cubierta seminal. Los resultados muestran que las semillas frescas no tienen dormancia exógena como único impedimento para la germinación, sino prevaleció una dormancia mecánica en combinación con cierto grado de impermeabilidad de las cubiertas seminales que evitó la germinación