Generation of Fourier transform limited heralded single photons

In this paper we study the spectral (temporal) properties of heralded single photon wavepackets, triggered by the detection of an idler photon in the process of parametric downconversion. The generated single photons are studied within the framework of the chronocyclic Wigner function, from which the single photon spectral width and temporal duration can be computed. We derive specific conditions on the two-photon joint spectral amplitude which result in both pure and Fourier- transform limited heralded single photons. Likewise, we present specific source geometries which lead to the fulfilment of these conditions and show that one of these geometries leads, for a given pump bandwidth, to the temporally shortest possible heralded single photon wavepackets.Comment: 10 pages, 3 figure, PHYSICAL REVIEW A 75, 02381

Patrones de reclutamiento, crecimiento, mortalidad y orientación de Balanus trigonus (Crustacea: Cirripedia) durante sucesión en placas de ‘fouling’

Succession studies on artificial substrates in the Bay of Santa Marta, Colombian Caribbean showed Balanus trigonus (Darwin) as one of the more prominent members of the fouling community. This fact prompted the interest for a closer examination of its biology. Four aspects were touched upon: recruitment, growth and mortality rates, and orientation with respect to the horizon line. Two hypotheses were tested. First, that orientation of individuals was random within the orientation range observed during succession, and second, that there was no relationship between orientation and age of the individuals. Larvae settling was found to occur throughout the year but with a well delimited peak in the dry season (January to April). The availability of competent larvae is reflected in the abundance of the species during succession. Growth and mortality proceed rapidly. Maximal growth (6.2 mm average carino-rostral distance) is reached in 20 weeks after settlement. Mortality is substantial: 50% of recruits, on average, died after 3-4 weeks from settlement. Orientation at settlement was found to be not random: for instance, 64% of individuals orientated between 0°-60° from the horizon. With age the orientation patterns at settlement changed statistically. Biological and ecological implications of these findings are discussed and comparisons made with other studies. It is concluded that Balanus trigonus could act as a model species for latitudinal comparisons in view of its wide distribution, adaptability and sessile habit.En el curso de un estudio sobre sucesión en sustratos artificiales en la Bahía de Santa Marta, Caribe colombiano, se encontró que Balanus trigonus (Darwin) era uno de los miembros más prominentes de la comunidad de ‘fouling’ que se desarrolló sobre los sustratos. La oportunidad se aprovechó para tocar cuatro aspectos de la biología de B. trigonus según se manifestaron en la población de los sustratos: reclutamiento, tasas de crecimiento y mortalidad, y orientación respecto a la línea del horizonte. Se probaron dos hipótesis: primero, que la orientación de los individuos dentro del rango de orientaciones encontrado es al azar; segundo, que la orientación es independiente de la edad de los individuos. El asentamiento de larvas cubre todo el año, si bien con un pico bien marcado en la estación seca (enero a abril). Esta disponibilidad se refleja en la abundancia de la especie durante la sucesión. Crecimiento y mortalidad son rápidos. El crecimiento máximo (6.2 mm en promedio, distancia carino-rostral) se alcanza en aproximadamente 20 semanas desde el asentamiento. La mortalidad es sustancial. En promedio 50 % de los reclutas han perecido después de 3- 4 semanas del asentamiento. La orientación en el asentamiento se encontró que sigue un patrón no azaroso: por ejemplo, 64 % de los individuos se orientaron entre los 0º y los 60º del horizonte. Con la edad los patrones de orientación cambiaron estadísticamente. Se discuten las implicaciones biológicas y ecológicas de estos resultados y se compara con estudios hechos sobre la misma especie en otras latitudes. Se concluye que Balanus trigonus en razón a su hábito sesil, amplia distribución y capacidad de adaptación podría servir de modelo para estudios latitudinales comparativos

Localized spoof plasmons arise while texturing closed surfaces

We demonstrate that textured closed surfaces, i.e., particles made of perfect electric conductors (PECs), are able to support localized electromagnetic resonances with properties resembling those of localized surface plasmons (LSPs) in the optical regime. Because of their similar behavior, we name these types of resonances as spoof LSPs. As a way of example, we show the existence of spoof LSPs in periodically textured PEC cylinders and the almost perfect analogy to optical plasmonics. We also present a metamaterial approach that captures the basic ingredients of their electromagnetic respons

New foam stabilising additive for alumnium

Liquid metals are mostly made foamable by Ca additions followed by a thickening period. There is a need for an additive that can be easily admixed to an aluminium alloy melt and makes this melt foamable. We have selected aluminium-based grain refiner composites to test their foamability. TiB2, TiC or TiAl3 particles were produced in the melt by flux-assisted melting using fluoride salts. The particle size was kept below 1 im for TiB2 and TiC and around 10µm for TiAl3. The composites were heated to above their melting point (700°C) and were then foamed by either the addition of TiH2 or by injecting gases into the melt directly. Foams were successfully produced using TiB2 and TiC particles, while TiAl3 did not lead to any foam. Foam stability increased from TiB2 to TiC. Ex-situ characterisation of the foams by SEM showed that the particles segregate to the surfaces of the cell walls and lead to almost dense coverages there. Even after dilution of the initial composite a significant amount of foam can be still produced, indicating that these composites are suitable foam stabilizing additive for aluminium alloys and that foams based on small volume fractions of nonmetallic additives can be produced

Spanish Translation and Psychometric Validation of a Measure of Acculturative Stress among Latinx Immigrants in the USA

BACKGROUND: In the U.S., the Latinx community is growing at a faster rate than any other racial and ethnic minority group. Members of this community have been found to experience a number of acculturative stressors after immigrating including xenophobia, racism, and discrimination. Although several scales have been created in recent years to measure acculturative stress in Spanish-speaking immigrants, they are long, do not have nuanced subscales, or have not been validated in an extremely diverse sample of Latinx immigrants. OBJECTIVE: The purpose of the current study was to translate and psychometrically validate the Riverside Acculturative Stress Inventory (RASI) in a diverse sample of Spanish-speaking immigrants. METHODS: A sample of 202 Latinx immigrants in the U.S. completed the RASI as well as measures of depression and anxiety. RESULTS: An initial confirmatory factor analysis suggested at the overall subscale factor structure was not an ideal fit for the data. Exploratory factor analysis suggested the retention of four subscales, each with three items, forming a 12-item Spanish RASI short form. As indices of convergent validity, the RASI total score was positively associated with depression and anxiety. CONCLUSIONS: Findings from the study contribute to the literature a brief and valid assessment of acculturative stress in Spanish-speaking immigrants. The RASI Spanish short form holds promise to stimulate research on the unique adversities experienced by Latinx immigrants.https://scholarscompass.vcu.edu/uresposters/1418/thumbnail.jp

U B V R I Photometry of Stellar Structures throughout the Disk of the Barred Galaxy NGC 3367

We report new detailed surface U, B, V, R, and I photometry of 81 stellar structures in the disk of the barred galaxy NGC 3367. The images show many different structures indicating that star formation is going on in the most part of the disk. NGC 3367 is known to have a very high concentration of molecular gas distribution in the central regions of the galaxy and bipolar synchrotron emission from the nucleus with two lobes (at 6 kpc) forming a triple structure similar to a radio galaxy. We have determined the U, B, V, R, and I magnitudes and U - B, B - V, U - V, and V - I colors for the central region (nucleus), a region which includes supernovae 2003 AA, and 79 star associations throughout NGC 3367. Estimation of ages of star associations is very difficult due to several factors, among them: filling factor, metallicity, spatial distribution of each structure and the fact that we estimated the magnitudes with a circular aperture of 16 pixels in diameter, equivalent to $6''.8\sim1.4$ kpc. However, if the colors derived for NGC 3367 were similar to the colors expected of star clusters with theoretical evolutionary star tracks developed for the LMC and had a similar metallicity, NGC 3367 show 51 percent of the observed structures with age type SWB I (few tens of Myrs), with seven sources outside the bright surface brightness visible disk of NGC 3367.Comment: Accepted for publication (abr 2007) in The Astronomical Journal (July 2007 issue

Análisis funcional de efectores candidatos de Podosphaera xanthii

Los oídios son patógenos biotrofos obligados que requieren células vivas para su desarrollo, por lo que deben eludir o inhibir las respuestas de defensa de la planta mediante la secreción de efectores para completar su ciclo de vida. El haustorio, estructura del hongo especializada en la toma de nutrientes, es también la vía de intercambio de factores con las células huésped. Hasta la fecha, son muy numerosos los efectores identificados en diversos hongos fitopatógenos, sin embargo, los efectores de los oídios están poco caracterizados todavía. En este trabajo hemos desarrollado un método para la identificación y el análisis de efectores candidatos de Podosphaera xanthii (ECP), el principal agente causal del oídio de las cucurbitáceas, mediante silenciamiento génico inducido por hospedador (HIGS) y la sobrexpresión de estos efectores en cotiledones de melón, utilizando para ello Agrobacterium tumefaciens. El silenciamiento de algunos de los ECP analizados provocó la acumulación en las células de la planta de compuestos relacionados con las respuestas de defensa como peróxido de hidrógeno (H2O2) y calosa, lo que sugiere un importante papel en el establecimiento de la infección. En concreto, ECPEc2 parece interferir específicamente con la formación de la papila, primera barrera de defensa de la planta que impide o ralentiza la penetración de la célula vegetal. En el caso de ECP5191, su silenciamiento se traduce un aumento del número de células que acumulaban H2O2 y calosa, así como una disminución en el número de puntos de penetración del hongo, observándose todo lo contrario cuando se sobrexpresa dicho efector. Además, la fusión traduccional CSEP5191-GFP ha permitido localizar este efector en los puntos de penetración y vesículas del haustorio del hongo.Este trabajo ha sido financiado por ayudas del Plan Nacional de I+D+I del anterior Ministerio de Ciencia e Innovación (AGL2010-21848-CO2-01), cofinanciado con fondos FEDER (UE)y una ayuda del Plan Propio de Investigación de la Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Agricultural productivity in past societies: toward an empirically informed model for testing cultural evolutionary hypotheses

Agricultural productivity, and its variation in space and time, plays a fundamental role in many theories of human social evolution. However, we often lack systematic information about the productivity of past agricultural systems on a scale large enough to test these theories properly. The effect of climate on crop yields has received a great deal of attention resulting in a range of empirical and process-based models, yet the focus has primarily been on current or future conditions. In this paper, we argue for a “bottom-up” approach that estimates potential productivity based on information about the agricultural practices and technologies used in past societies. Of key theoretical interest is using this information to estimate the carrying high quality historical and archaeological information about past societies in order to infer the temporal and geographic patterns of change in agricultural productivity and potential. We discuss information we need to collect about past agricultural techniques and practices, and introduce a new databank initiative that we have developed for collating the best available historical and archaeological evidence. A key benefit of our approach lies in making explicit the steps in the estimation of past productivities and carrying capacities, and in being able to assess the effects of different modelling assumptions. This is undoubtedly an ambitious task, yet promises to provide important insights into fundamental aspects of past societies, enabling us to test more rigorously key hypotheses about human socio-cultural evolution

Study of short cracks under biaxial fatigue

In this paper a methodology for evaluating crack initiation under biaxial conditions is presented. The methodology consists of evaluating the crack length automatically with digital processing of highmagnification images of the crack. The methodology was applied to study five different strain conditions on a low carbon ferritic-pearlitic steel specimen with tubular shape. A hole of 150 ?m diameter was drilled to enforce the crack to initiate at a particular spot. Different combinations of axial and torsional strains were analysed during the initiation stage of the crack. The setup employed allowed detection of the crack to within 6 ?m from the edge of the hole on average and monitoring of the crack during early stages. Fatigue crack propagation curves clearly showed oscillations due to microstructure. It was also observed that these oscillations decreased as the torsional component of the strain was increased