Hyperbolic reflections as fundamental building blocks for multilayer optics

We reelaborate on the basic properties of lossless multilayers by using bilinear transformations. We study some interesting properties of the multilayer transfer function in the unit disk, showing that hyperbolic geometry turns out to be an essential tool for understanding multilayer action. We use a simple trace criterion to classify multilayers into three classes that represent rotations, translations, or parallel displacements. Moreover, we show that these three actions can be decomposed as a product of two reflections in hyperbolic lines. Therefore, we conclude that hyperbolic reflections can be considered as the basic pieces for a deeper understanding of multilayer optics.Comment: 7 pages, 7 figures, accepted for publication in J. Opt. Soc. Am.

General unit-disk representation for periodic multilayers

We suggest a geometrical framework to discuss periodic layered structures in the unit disk. The band gaps appear when the point representing the system approaches the unit circle. We show that the trace of the matrix describing the basic period allows for a classification in three families of orbits with quite different properties. The laws of convergence of the iterates to the unit circle can be then considered as universal features of the reflection.Comment: 3 pages, 2 eps-figures. To be published in Optics Letter

How is star formation fed and quenched in massive galaxies at high redshift?

Observations of the location and kinematics of the atomic gas (HI) and the continuum radio emission from high redshift galaxies would mean a huge step forward in our understanding of galaxy evolution. We now have a secure global picture of the stellar content of massive galaxies and their precursors up to z~4. But we still have to understand why star formation in these systems started early and quenched some time after, a scenario known as downsizing which, at face value, conflicts with the predictions from the current hierarchical galaxy formation paradigm. SKA will provide the missing piece to solve the puzzle: information about the amounts of gas falling into galaxies to form stars, as well as data to measure when and how the star formation turns off as the gas stops cooling due to still to be understood feedback mechanisms, such as (radio mode) obscured nuclear activity.PGP-G acknowledges support from Spanish Government MINECO AYA2012-31277 Grant. JIGS acknowledges support from the Spanish Ministry for Economy and Competitiveness AYA2011-29517-C03-02. AFS acknowledges support from the Spanish Ministry for Economy and Competitiveness and FEDER funds through grants AYA2010-22111-C03-02 and AYA2013-48623-C2-2, and Generalitat Valenciana project PROMETEOII/2014/060.Peer reviewe

Diagnóstico Del Uso Y Manejo De Plaguicidas En Fincas Productoras De Cebolla Junca Allium Fistulosum En El Municipio De Pasto

El control de plagas y enfermedades en el cultivo de la cebolla en Nariño, se caracteriza por el uso del control químico. Por lo tanto, el objetivo de esta investigación fue identificar las condiciones de uso y manejo de plaguicidas de este cultivo en el corregimiento Buesaquillo, del municipio de Pasto. Para determinar el tipo de productos utilizados se realizó recolección y clasificación de envases vacíos de agroquímicos durante 6 meses. En la zona de estudio se realizaron 200 encuestas con 38 preguntas relacionadas con aspectos socioeconómicos, manejo de cultivo, uso y manejo de plaguicidas y sus riesgos potenciales. Los datos fueron sometidos a análisis de correspondencia múltiple. Se recolectaron 4710 envases vacíos, de los cuales el 46,3% correspondieron a fungicidas, el 12,4% a fertilizantes y el 9,3% a insecticidas. El principal criterio para aplicación fue el recomendado por los almacenes de expendio de agroquímicos (72%), la frecuencia de aplicación depende de las condiciones ambientales que va entre 8 y 15 días, el periodo de carencia en el 80% de los encuestados es de 15 días antes de la cosecha. El 74% de los agricultores expuestos a los plaguicidas son hombres y la mayoría (85,5%) tiene estudios primarios, el 53,5% no entiende la etiqueta del producto y algunos de los encuestados (19%) dicen haber sufrido síntomas de intoxicación, y la mayoría (70%) de los productores queman los envases de los plaguicidas. Bajo las condiciones del presente estudio se concluye que el uso de los plaguicidas es similar entre los encuestados, caracterizándose por su manejo inadecuado, el cual pone en riesgo la salud de los agricultores y amenazan con el equilibrio de este agroecosistema.AbstractPests and diseases control in green onion cultivation in the department of Nariño is characterized by the use of chemical control. Therefore, the objective of the investigation was to identify the use and management conditions of pesticides on this crop in the small township of Buesaquillo, municipality of Pasto. To determine the type of products used, an empty agrochemical containers collection was carried out during six months. Two hundred surveys, with 38 questions related to socio-economic aspects, crop management, pesticide use and management and its potential risks, were carried out in the study zone. The data were submitted to multiple correspondence analyses. A total of 4710 empty containers were recollected, of which 46.3% corresponded to fungicides, 12.4% to fertilizers, and 9.3% to insecticides. The main criterion of application was the one recommended by the agrochemicals warehouse sale (72%); frequency of application depends on environmental conditions ranging between 8 and 15 days, and the grace period in 80% of the surveys is 15 days prior to the harvest. 74% of farmers exposed to pesticides are men and most of them (85.5%) have completed their primary school studies; 53.5% do not understand the product’s label, some of them (19%) claim to have suffered intoxication symptoms and most producers (70%) burn the pesticide containers. Under the conditions of this study it can be concluded that the use of pesticides is similar among the surveyed farmers, and is characterized by inadequate management, which puts farmers’ health at risk and threatens this agro ecosystem equilibrium.El control de plagas y enfermedades en el cultivo de la cebolla en Nariño, se caracteriza por el uso del control químico. Por lo tanto, el objetivo de esta investigación fue identificar las condiciones de uso y manejo de plaguicidas de este cultivo en el corregimiento Buesaquillo, del municipio de Pasto. Para determinar el tipo de productos utilizados se realizó recolección y clasificación de envases vacíos de agroquímicos durante 6 meses. En la zona de estudio se realizaron 200 encuestas con 38 preguntas relacionadas con aspectos socioeconómicos, manejo de cultivo, uso y manejo de plaguicidas y sus riesgos potenciales. Los datos fueron sometidos a análisis de correspondencia múltiple. Se recolectaron 4710 envases vacíos, de los cuales el 46,3% correspondieron a fungicidas, el 12,4% a fertilizantes y el 9,3% a insecticidas. El principal criterio para aplicación fue el recomendado por los almacenes de expendio de agroquímicos (72%), la frecuencia de aplicación depende de las condiciones ambientales que va entre 8 y 15 días, el periodo de carencia en el 80% de los encuestados es de 15 días antes de la cosecha. El 74% de los agricultores expuestos a los plaguicidas son hombres y la mayoría (85,5%) tiene estudios primarios, el 53,5% no entiende la etiqueta del producto y algunos de los encuestados (19%) dicen haber sufrido síntomas de intoxicación, y la mayoría (70%) de los productores queman los envases de los plaguicidas. Bajo las condiciones del presente estudio se concluye que el uso de los plaguicidas es similar entre los encuestados, caracterizándose por su manejo inadecuado, el cual pone en riesgo la salud de los agricultores y amenazan con el equilibrio de este agroecosistema.AbstractPests and diseases control in green onion cultivation in the department of Nariño is characterized by the use of chemical control. Therefore, the objective of the investigation was to identify the use and management conditions of pesticides on this crop in the small township of Buesaquillo, municipality of Pasto. To determine the type of products used, an empty agrochemical containers collection was carried out during six months. Two hundred surveys, with 38 questions related to socio-economic aspects, crop management, pesticide use and management and its potential risks, were carried out in the study zone. The data were submitted to multiple correspondence analyses. A total of 4710 empty containers were recollected, of which 46.3% corresponded to fungicides, 12.4% to fertilizers, and 9.3% to insecticides. The main criterion of application was the one recommended by the agrochemicals warehouse sale (72%); frequency of application depends on environmental conditions ranging between 8 and 15 days, and the grace period in 80% of the surveys is 15 days prior to the harvest. 74% of farmers exposed to pesticides are men and most of them (85.5%) have completed their primary school studies; 53.5% do not understand the product’s label, some of them (19%) claim to have suffered intoxication symptoms and most producers (70%) burn the pesticide containers. Under the conditions of this study it can be concluded that the use of pesticides is similar among the surveyed farmers, and is characterized by inadequate management, which puts farmers’ health at risk and threatens this agro ecosystem equilibrium

Perfect antireflection via negative refraction

We suggest a geometrical framework to discuss the action of slabs of negatively refracting materials. We show that these slabs generate the same orbits as normal materials, but traced out in opposite directions. This property allows us to confirm that the action of any lossless multilayer can be optically cancelled by putting it together with the multilayer constructed as the inverted mirror image, with $\epsilon$ and $\mu$ reversed in sign.Comment: Some typos corrected. New references addes. Accepted for publication in Physics Letters

NGC1600 - Cluster or Field Elliptical?

A study of the galaxy distribution in the field of the elliptical galaxy NGC1600 has been undertaken. Although this galaxy is often classified as a member of a loose group, all the neighbouring galaxies are much fainter and could be taken as satellites of NGC1600. The number density profile of galaxies in the field of this galaxy shows a decline with radius, with evidence of a background at approximately 1.3 Mpc. The density and number density profile are consistent with that found for other isolated early-type galaxies. NGC1600 appears as an extended source in X-rays, and the center of the X-ray emission seems not to coincide with the center of the galaxy. The velocity distribution of neighbouring galaxies has been measured from optical spectroscopic observations and shows that the mean radial velocity is approximately 85 km/s less than that of NGC1600, indicating that the centre of mass could lie outside the galaxy. The velocity dispersion of the `group' is estimated at 429 km/s. The inferred mass of the system is therefore of the order of 10^14 solar masses, a value that corresponds to a large group. NGC1600 therefore shares some similarities, but is not identical to, the `fossil clusters' detected in X-ray surveys. Implications of this result for studies of isolated early-type galaxies are briefly discussed.Comment: 8 pages, 5 figures and 2 table, accepted for publication in the Ap

A new catalog of photometric redshifts in the Hubble Deep Field

Using the newly available infrared images of the Hubble Deep Field in the J, H, and K bands and an optimal photometric method, we have refined a technique to estimate the redshifts of 1067 galaxies. A detailed comparison of our results with the spectroscopic redshifts in those cases where the latter are available shows that this technique gives very good results for bright enough objects (AB(8140) < 26.0). From a study of the distribution of residuals (Dz(rms)/(1+z) ~ 0.1 at all redshifts) we conclude that the observed errors are mainly due to cosmic variance. This very important result allows for the assessment of errors in quantities to be directly or indirectly measured from the catalog. We present some of the statistical properties of the ensemble of galaxies in the catalog, and finish by presenting a list of bright high-redshift (z ~ 5) candidates extracted from our catalog, together with recent spectroscopic redshift determinations confirming that two of them are at z=5.34 and z=5.60.Comment: 28 pages, 12PS+4JPEG figures, aaspp style. Accepted for publication in The Astrophysical Journal. The catalog, together with a clickable map of the HDF, Tables 4 and 5 (HTML, LaTeX or ASCII format), and the figures, are available at http://bat.phys.unsw.edu.au/~fsoto/hdfcat.htm

About International Reserve Adequacy: The Case of Chile

Under a flexible exchange rate regime, international reserves contribute to reducing the risk of a financial crisis, and allow the monetary authority to intervene exceptionally in the exchange market. However, holding reserves is costly. In this paper, we analyze several issues concerning the adequate level of Chilean international reserves. First we compare the level of Chile's international reserves with those of different sets of countries, using various indicators. We then analyze empirically some of the benefits and costs of holding reserves. Our results show that Chile's international reserves are high when measured with respect to GDP or M2, but they are in line with those of countries of similar characteristics when measured as a fraction of short-term residual debt. On the other hand, given the low risk of the Chilean economy, marginal changes in reserves have a very low impact on both the probability of a financial crisis and the sovereign spread of the country. Finally, as the sovereign spread has decreased over the last years, so too has the cost of reserves. In fact, over the past few years Chile's cost of reserves as a fraction of GDP has been considerably lower than the cost of other emerging economies.

Atmospheric circulation types controlling rainfall in the Central American Isthmus

Rainfall mechanisms in the Central American Isthmus are controlled by complex physical interactions across spatial and temporal scales, which are reflected on the dynamics of atmospheric circulation patterns affecting the region. However, physical mechanisms and their relationships with thermodynamic distributions connected to overturning circulations remain elusive. Here, a set of six recurrent daily atmospheric patterns, or weather types (WT), is defined using a k-means++ clustering algorithm on standardized fields of Convective Available Potential Energy (CAPE) and winds at 925, 850, and 200 hPa. The relationships between these weather types, their temporal characteristics, and anomalous distributions of moisture flux divergence, equivalent potential temperature (saturated and unsaturated), and observed rainfall are used to describe physical processes controlling the latter, for all seasons. Regional observed rainfall is analysed from a set of 174 automatic stations from all countries from Mexico to Panama. By modulating vertically integrated moisture fluxes, these weather types, and the different climate drivers linked to them, control the temporal and spatial rainfall characteristics in the region, especially over the Pacific side of the isthmus. During some stages of the regional rainy season, described by two weather types, thermal anomalies in convective quasiequilibrium characteristic of the upward branch of the Hadley cell force westerly flow over Central America, enhancing rainfall. While during other stages, the enhancement of the trades and the displacement of convection to the ITCZ area over the eastern tropical Pacific, characteristic of the midsummer drought, diminishes rainfall. This study sets the stage for a better understanding of the mechanistic relationship between these weather types and rainfall characteristics in general, like onset, demise, and duration of rainy seasons. Hence, these results can inform process-based model diagnostics aiming at bias-correcting climate predictions at multiple timescalesUniversidad de Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigaciones Geofísicas (CIGEFI)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de FísicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

A blind test of photometric redshift prediction

Results of a blind test of photometric redshift predictions against spectroscopic galaxy redshifts obtained in the Hubble Deep Field with the Keck Telescope are presented. The best photometric redshift schemes predict spectroscopic redshifts with a redshift accuracy of |Delta-z|<0.1 for more than 68 percent of sources and with |Delta-z|<0.3 for 100 percent, when single-feature spectroscopic redshifts are removed from consideration. This test shows that photometric redshift schemes work well at least when the photometric data are of high quality and when the sources are at moderate redshifts.Comment: 14 pp., accepted for publication in A