Second-harmonic generation of ZnO nanoparticles synthesized by laser ablation of solids in liquids

We report the synthesis of small zinc oxide nanoparticles (ZnO NPs) based colloidal suspensions and the study of second-harmonic generation from aggregated ZnO NPs deposited on glass substrates. The colloidal suspensions were obtained using the laser ablation of solids in liquids technique, ablating a Zn solid target immersed in acetone as the liquid medium, with ns-laser pulses (1064 nm) of a Nd-YAG laser. The per pulse laser fluence, the laser repetition rate frequency and the ablation time were kept constant. The absorption evolution of the obtained suspensions was optically characterized through absorption spectroscopy until stabilization. Raman spectroscopy, SEM and HRTEM were used to provide evidence of the ZnO NPs structure. HRTEM results showed that 5–8 nm spheroids ZnO NPs were obtained. Strong second-harmonic signal is obtained from random ZnO monocrystalline NPs and from aggregated ZnO NPs, suggesting that the high efficiency of the nonlinear process may not depend on the NPs size or aggregation state

Effects of forest fragmentation on the vertical stratification of neotropical bats

Vertical stratification is a key component of the biological complexity of rainforests. Understanding community- and species-level responses to disturbance across forest strata is paramount for evidence-based conservation and management. However, even for bats, known to extensively explore multiple layers of the complex three-dimensional forest space, studies are biased towards understory-based surveys and only few assessments of vertical stratification were done in fragmented landscapes. Using both ground and canopy mist-nets, we investigated how the vertical structure of bat assemblages is influenced by forest fragmentation in the experimentally fragmented landscape of the Biological Dynamics of Forest Fragments Project, Central Amazon, Brazil. Over a three year-period, we captured 3077 individuals of 46 species in continuous forest (CF) and in 1, 10 and 100 ha forest fragments. In both CF and forest fragments, the upper forest strata sustained more diverse bat assemblages than the equivalent understory layer, and the midstory layers had significantly higher bat abundance in fragments than in CF. Artibeus lituratus and Rhinophylla pumilio exhibited significant shifts in their vertical stratification patterns between CF and fragments (e.g. R. pumilio was more associated with the upper strata in fragments than in CF). Altogether, our study suggests that fragmentation modulates the vertical stratification of bat assemblages

Black holes die hard: can one spin-up a black hole past extremality?

A possible process to destroy a black hole consists on throwing point particles with sufficiently large angular momentum into the black hole. In the case of Kerr black holes, it was shown by Wald that particles with dangerously large angular momentum are simply not captured by the hole, and thus the event horizon is not destroyed. Here we reconsider this gedanken experiment for a variety of black hole geometries, from black holes in higher dimensions to black rings. We show that this particular way of destroying a black hole does not succeed and that Cosmic Censorship is preserved.Comment: 10 pages, 7 figures. RevTex4

Los imaginarios populares sobre México en Corea del Sur

Public image analysis involves the process of managing a country’s image internationally. Such examination is particularly important to gain an understanding of a policy’s effectiveness in the target country and to reflect S-F / Shutterstock.com 39 MAP | REVISTA MUNDO ASIA PACÍFICO | Vol. 9, No. 17 upon its undesired signals to design positioning strategies in a partner country’s society. Therefore, public opinion surveys are the key to achieving specific desired aims in other societies. This research paper provides hard data to inquire about popular Korean perceptions of Mexico as the main pillar of the latter’s positioning in Asian society. Analysis of the responses reveals several enriching elements that are not highlighted by media images.El análisis de la imagen pública forma parte del proceso de gestión de la imagen de nación en el exterior. Su importancia se torna esencial para que pueda entenderse la eficiencia de la política hacia la nación de destino, reflexionar en torno a las señales no deseadas para desarrollar, a partir de estas, las estrategias del posicionamiento en la sociedad del país-socio. Por este motivo, los sondeos de la opinión pública constituyen elementos clave para lograr fines específicos deseados en otras sociedades. La presente investigación brinda datos valiosos para indagar en las per-cepciones populares sobre México en Corea como uno de los ejes centrales del posicionamiento del país latinoamericano en la sociedad asiática. El análi-sis de las respuestas permite revelar elementos enriquecedores que no salen a la luz en las imágenes de los medios de comunicación

A canonical family of multiple orthogonal polynomials for Nikishin systems

16 pages.-- MSC2000 codes: Primary 42C05, 33C25; Secondary 41A21.-- Submitted paper.For any pair of compact intervals Δ1 and Δ2 of the real line such that Δ1∩Δ2 = ø we obtain two pairs of absolutely continuous probability measures (μ1,μ2) and (τ1,τ2) supported on Δ1 and Δ2, respectively, such that:- for appropriate constants C1 and C2, (μ1,μ2) is the Nikishin system generated by (μ1,C1τ1) and (τ1,τ2) the Nikishin system generated by (τ1,C2μ1),- the polynomials of multiple orthogonality with respect to the Nikishin system (μ1,μ2) and indices {..., (n,n), (n+1,n), ...} satisfy a recurrence relations with constant coe±cients of period 2,- 1/hat-μ1(z) and 1/hat-μ2(z) are the functions which describe the ratio asymptotics of multiple orthogonal polynomials with respect to an arbitrary Nikishin system N(σ1,σ2) verifying supp(σi) = Δi, and σi' > 0, i = 1,2, almost everywhere on Δi. Analogously, 1/hat-τ1(z) and 1/hat-τ2(z) give the ratio asymptotics for N(σ1,σ2).The research of both authors was supported by research grant MTM 2006-13000-C03-02 of Ministerio de Ciencia e Innovación, Spain. I.A. Rocha also received support from Universidad Politécnica de Madrid through Grupo de Investigación TACA.No publicad

Modeling Star counts in the Monoceros stream and the Galactic anti-centre

There is a continued debate as to the form of the outer disc of the Milky Way galaxy, which has important implications for its formation. Stars are known to exist at a galacto-centric distance of at least 20 kpc. However, there is much debate as to whether these stars can be explained as being part of the disc or whether another extra galactic structure, the so called Monoceros ring/stream, is required. To examine the outer disc of the Galaxy toward the anti-centre to determine whether the star counts can be explained by the thin and thick discs alone. Using Sloan star counts and extracting the late F and early G dwarfs it is possible to directly determine the density of stars out to a galacto-centric distance of about 25 kpc. These are then compared with a simple flared disc model. A flared disc model is shown to reproduce the counts along the line of sights examined, if the thick disc does not have a sharp cut off. The flare starts at a Galacto-centric radius of 16 kpc and has a scale length of 4.5+/-1.5 kpc. Whilst the interpretation of the counts in terms of a ring/stream cannot be definitely discounted, it does not appear to be necessary, at least along the lines of sight examined towards the anti centre.Comment: 11 pages, 4 figures, accepted to be published in A&

COMPORTAMENTO DE MOVIMENTAÇÃO HORIZONTAL E VERTICAL DA TARTARUGA-DE-COURO Dermochelys coriacea

The general biology of the leatherback turtle (Dermochelys coriacea) still remains poorly understood, mainly because of its life-history characteristics. D. coriacea is a highly pelagic cosmopolitan species that spends most of its life in the open sea, and is able to perform transoceanic migrations from reproductive to foraging zones and back. Over their long travels throughout the sea, the leatherback turtle moves both horizontally (e.g., migrations) and vertically (i.e. dives) in response to different factors, like searching for suitable habitats for growth, feeding and reproduction. The present article is a  comprehensive review of the current knowledge about the horizontal and vertical behavioral movements performed by D. coriacea. An analysis of how these behaviors are influenced by different factors governing the ecology of this species is presented. Some studies indicate that oceanographic features are the key factors determining the movement patterns observed for D. coriacea, mainly during their geographic migrations and residence in feeding zones. In short, the leatherback turtle employs different navigation and dispersion strategies while in each different oceanic zone. On certain occasions, individuals may disperse in different directions while on other occasions they may follow a roughly uniform path across the sea. Movement trends during the nesting period vary between different oceanic zones depending on local topography and on the behavioral strategy adopted by the nesting females with respect to how to invest energy during the reproductive season (e.g., actively searching for prey versus limiting activity to reduce metabolic rate).La biología de la tortuga laúd (Dermochelys coriacea) aún es relativamente poco conocida, fundamentalmente debido a sus hábitos de vida. D. coriacea es una especie altamente pelágica y cosmopolita que pasa la mayor parte da su vida en el océano abierto, y que puede realizar migraciones transoceánicas entre áreas de reproducción y de alimentación. En sus extensos desplazamientos a través del océano,la tortuga de laúd ejecuta movimientos tanto horizontales (ej.  migraciones) como verticales (ej. buceos) que constituyen respuestas de comportamiento a diferentes factores como búsqueda de un ambiente apropiado para el crecimiento, alimentación y reproducción, entre otros. En este trabajo, presentamos una amplia revisión acerca del estado actual del conocimiento de los movimientos horizontales y verticales realizados por D. coriacea, analizando como estos comportamientos son influenciados por diferentes factores que determinan la ecología de la especie. Los estudios indican que las características oceanográficas constituyen factores claves en la determinación de los patrones de movimiento registrados para D. coriacea, principalmente durante lasmigraciones y durante su permanencia en áreas de alimentación. En general la tortuga laúd utiliza diferentes estrategias de navegación y dispersión en las diferentes regiones del océano, en algunos casos, los individuos de la especie se dispersan ampliamente en varias direcciones y en otros casos siguen un patrón relativamente uniforme y persistente a través del océano. Las tendencias de movimiento durante el período de desove varían en las diferentes zonas oceánicas, influenciadas por la topografía del lugar y por la estrategia de comportamiento  de las hembras en relación a los costos energéticos durante la temporada reproductiva (ej. comportamiento de búsqueda de alimento versus poca actividad para reducir el gasto metabólico).A biologia da tartaruga-de-couro (Dermochelys coriacea) é ainda relativamente pouco conhecida,fundamentalmente devido a seus hábitos de vida. D. coriacea é uma espécie altamente pelágica e cosmopolita que passa a maior parte da sua vida no oceano aberto, e que pode realizar migrações transoceânicas entre áreas de reprodução e de alimentação. Ao longo de sua extensa movimentação por porções oceânicas, a tartarugade-couro executa movimentos horizontais (ex. migrações) e verticais (ex. mergulhos) que constituem respostas comportamentais a diferentes fatores, como busca de ambiente apropriado para o crescimento, a alimentação e a reprodução, entre outros. No presente artigo, apresentamos uma revisão abrangente acerca do estado atual do conhecimento sobre os movimentos comportamentais horizontais e verticais realizados por D. coriacea, analisando como estes comportamentos são influenciados por diferentes fatores que regem a ecologia da espécie. Os estudos indicam que as feições oceanográficas constituem fatores-chave na determinação dos padrões de movimentação registrados para D. coriacea, principalmente durante as migrações e durante sua permanência em áreas de alimentação. Em geral a tartaruga-de-couro utiliza diferentes estratégias de navegação e dispersão nas diferentes regiões oceânicas, em alguns casos, os indivíduos da espécie se dispersam amplamente em varias direções e, em outros casos, seguem um padrão relativamente uniforme e persistente através do oceano. As tendências de movimentação durante o período de desova variam nas diferentes regiões oceânicas, influenciadas pela topografia do local e pela estratégia comportamental das fêmeas em relação aos custos energéticos durante a temporada reprodutiva (ex. comportamento de busca de alimento versus pouca atividade para reduzir o gasto metabólico)

Optimización del procedimiento de importación y operacional de hilo crudo para Textil Meka, S.A de C.V.

La empresa Textil Meka, S.A. de C.V. se dedica a la importación y teñido de hilo crudo proveniente de Korea del Sur, se encuentra en el régimen de importación definitiva. En primer lugar, debe de obtener el Padrón de Importadores, el cual es un permiso otorgado por la Secretaría de Hacienda y Crédito Público. Debe de recopilar información relativa al mercado de origen del producto y de los potenciales proveedores, conocer si existen acuerdos comerciales suscritos por México con dicho país, que permitan rebajas arancelarías o algún otro beneficio. Para formalizar la negociación con el país extranjero se tendrá que firmar un contrato estipulando las condiciones de compra y venta así como dejar en claro los Términos de Comercio Internacional (INCOTERMS) mediante los cuales se trabajará; estos incoterms se refieren a transporte, riesgos, seguros, envase y embalaje, obligaciones arancelarias y aduaneras. Implican, pues, donde acaba y empieza la responsabilidad del comprador o del vendedor. Existen varias formas de pago, de las cuales, las más usuales y de validez internacional son el crédito documentario, la cobranza extranjera y el pago de contado. El proveedor extranjero colocará la mercancía en el barco, contratando los servicios de la naviera que el consideré mejor opción tanto en seguridad como en costos. El tiempo estimado de trayecto de Korea del Sur a México es de 25 a 30 días. Cuando la mercancía arribe al puerto de Manzanillo la naviera se pondrá en contacto con el importador para notificar que ha llegado y está lista para que procedan con el despacho. La liberación de la mercancía se tendrá que gestionar por medio de un Agente Aduanal el cual es una persona física autorizada por la Secretaría de Hacienda y Crédito Público, mediante una patente

A fast Bayesian approach to discrete object detection in astronomical datasets - PowellSnakes I

A new fast Bayesian approach is introduced for the detection of discrete objects immersed in a diffuse background. This new method, called PowellSnakes, speeds up traditional Bayesian techniques by: i) replacing the standard form of the likelihood for the parameters characterizing the discrete objects by an alternative exact form that is much quicker to evaluate; ii) using a simultaneous multiple minimization code based on Powell's direction set algorithm to locate rapidly the local maxima in the posterior; and iii) deciding whether each located posterior peak corresponds to a real object by performing a Bayesian model selection using an approximate evidence value based on a local Gaussian approximation to the peak. The construction of this Gaussian approximation also provides the covariance matrix of the uncertainties in the derived parameter values for the object in question. This new approach provides a speed up in performance by a factor of `hundreds' as compared to existing Bayesian source extraction methods that use MCMC to explore the parameter space, such as that presented by Hobson & McLachlan. We illustrate the capabilities of the method by applying to some simplified toy models. Furthermore PowellSnakes has the advantage of consistently defining the threshold for acceptance/rejection based on priors which cannot be said of the frequentist methods. We present here the first implementation of this technique (Version-I). Further improvements to this implementation are currently under investigation and will be published shortly. The application of the method to realistic simulated Planck observations will be presented in a forthcoming publication.Comment: 30 pages, 15 figures, revised version with minor changes, accepted for publication in MNRA

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