Metastable states influence on the magnetic behavior of the triangular lattice: Application to the spin-chain compound Ca3Co2O6

It is known that the spin-chain compound Ca3Co2O6 exhibits very interesting plateaus in the magnetization as a function of the magnetic field at low temperatures. The origin of them is still controversial. In this paper we study the thermal behavior of this compound with a single-flip Monte Carlo simulation on a triangular lattice and demonstrate the decisive influence of metastable states in the splitting of the ferrimagnetic 1/3 plateau below 10 K. We consider the [Co2O6]n chains as giant magnetic moments described by large Ising spins on planar clusters with open boundary conditions. With this simple frozen-moment model we obtain stepped magnetization curves which agree quite well with the experimental results for different sweeping rates. We describe particularly the out-of-equilibrium states that split the low-temperature 1/3 plateau into three steps. They relax thermally to the 1/3 plateau, which has long-range order at the equilibrium. Such states are further analyzed with snapshots unveiling a domain-wall structure that is responsible for the observed behavior of the 1/3 plateau. A comparison is also given of the exact results in small triangular clusters with our Monte Carlo results, providing further support for our thermal description of this compound.Comment: 8 pages, 11 figures, submitted to PR

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

Trombocitopenia inducida por tamoxifeno y letrozol

Medicin

Human resources in dentistry and treatment needs of caries in 12-year-old teenagers in Chile

Indexación: Web of Science; ScieloEl objetivo del estudio es estimar los recursos odontológicos para resolver las necesidades de tratamiento de los adolescentes de 12 años de Chile, pertenecientes a los niveles socio económicos alto, medio y bajo. El estudio se realizó a partir de los resultados del "Estudio Diagnóstico Nacional de Salud Bucal del Adolescente de 12 Años y Evaluación del Grado de Cumplimiento de los Objetivos Sanitarios de Salud Bucal 2000-2010", proyecto FONIS el que fue realizado en una muestra de 2.232 adolescentes de 12 años, con representación regional proporcional a la población nacional. Para estratificar por nivel socioeconómico este estudio se usó la clasificación y ranking de pobreza por comuna de MIDEPLAN y la caracterización por NSE de los establecimientos del Ministerio de Educación Se calculó el recurso humano necesario mediante la aplicación de estándares de rendimiento del ministerio de salud, comparando estos parámetros en el eje de nivel socioeconómico. Se observan diferencias estadísticamente significativas en las necesidades de tratamiento entre los NSE, concentrándose la mayor necesidad en los grupos de NSE bajo y medio.Abstract: The aim of this study is to determine oral health care delivery team workforce necessary to tackle oral health treatment needs of 12-year-old adolescents from different socioeconomic status. The sample consisted of 2.232 individuals. There was a proportional representation of the Nations regions. The Socioeconomic status (SES) was stratified through the MIDEPLAN)s poverty municipality ranking and by means of description of SES of the selected school by the Ministry of Education. To determine oral health treatments needs we carried out dental examination and WHO diagnosis criteria were used. We calculated the oral health care delivery team workforce based on Ministry of Health recommendations and compare among SES. Differences upon health care delivery team workforce necessary to tackle oral health treatment needs of 12-year-old adolescents from different socioeconomic status were evident.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0719-01072011000200001&nrm=is

Geography determines genetic relationships between species of mountain pine (Pinus mugo complex) in western Europe

Aim  Our aims were to test whether morphological species of mountain pines were genetically supported in the western part of the distribution range of the Pinus mugo species complex (Pinus mugo Turra sensu lato), to resolve genetically homogeneous clusters of populations, to determine historical demographic processes, and to assess the potential hybridization of mountain pines with Scots pine, Pinus sylvestris L. Location  Populations were sampled in the Iberian System, the Pyrenees, the French Mont Ventoux, Vosges and Jura mountains, the German Black Forest and throughout the Alps. This corresponded to a range-wide sampling for mountain pine sensu stricto (Pinus uncinata Ram.) and to a sampling of the western parts of the ranges of dwarf mountain pine (Pinus mugo Turra sensu stricto) and bog pine/peatbog pine [Pinus rotundata Link/Pinus × pseudopumilio (Willk.) Beck]. Methods  In total, 786 individuals of P. mugo sensu lato from 29 natural populations, and 85 individuals of P. sylvestris from four natural populations were genotyped at three chloroplast microsatellites (cpSSRs). Populations were characterized for standard genetic diversity statistics and signs of demographic expansion. Genetic structure was explored using analysis of molecular variance, differentiation statistics and Bayesian analysis of population structure (BAPS). Results  One hundred haplotypes were identified in P. mugo sensu lato. There was a stronger differentiation between geographical regions than between morphologically identified taxa (P. mugo sensu stricto, P. uncinata and P. rotundata/P. ×pseudopumilio). Overall genetic differentiation was weak (GST = 0.070) and displayed a clear phylogeographic structure [NST = 0.263, NST > NST (permuted), P < 0.001]. BAPS identified a Pyrenean and an Alpine gene pool, along with several smaller genetic clusters corresponding to peripheral populations. Main conclusions  The core regions of the Pyrenees and Alps were probably recolonized, respectively by P. uncinata and P. uncinata/P. mugo sensu stricto, from multiple glacial refugia that were well connected by pollen flow within the mountain chains. Pinus rotundata/P. × pseudopumilio populations from the Black Forest, Vosges and Jura mountains were probably recolonized from various glacial populations that kept their genetic distinctiveness despite late glacial and early Holocene expansion. Marginal P. uncinata populations from the Iberian System are compatible with elevational shifts and long-term isolation. The causes of haplotype sharing between P. mugo sensu lato and P. sylvestris require further researc

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

Sliding window multi-curve resolution: application to gas chromatography - ion mobility spectrometry

Blind source separation (BSS) techniques aim to extract a set of source signals from a measured mixture in an unsupervised manner. In the chemical instrumentation domain source signals typically refer to time-varying analyte concentrations, while the measured mixture is the set of observed spectra. Several techniques exist to perform BSS on ion mobility spectrometry, being simple-to-use interactive self-modelling mixture analysis (SIMPLISMA) and multivariate curve resolution (MCR) the most commonly used. The addition of a multi-capillary gas chromatography column using the ion mobility spectrometer as detector has been proposed in the past to increase chemical resolution. Short chromatography times lead to high levels of co-elution, and ion mobility spectra are key to resolve them. For the first time, BSS techniques are used to deconvolve samples of the gas chromatography-ion mobility spectrometry tandem. We propose a method to extract spectra and concentration profiles based on the application of MCR in a sliding window. Our results provide clear concentration profiles and pure spectra, resolving peaks that were not detected by the conventional use of MCR. The proposed technique could also be applied to other hyphenated instruments with similar strong co-elutions

Theoretical-Experimental Study of the Effect of the External Plates on the Thermal Performance of a Plate Heat Exchanger

Abstract In this work we present a theoretical-experimental research on the thermal phenomena that the endplates present on the performance of the plate heat exchangers in a single step and with a U type configuration. The endplate effect is reflected in a reduction of the temperature difference for heat transfer. The model discusses a theoretical focus that includes the elongation factor, which is a parameter that relates the actual area to the projected area of a plate. This model was performed to 2, 3, 4, 5, and 6 channel flow; therefore the experimentation was carried out to validate the theoretical model, it was carried out for 4, 5, 6, 7, 8 and 9 flow channels. Such results show that the theoretical model deviates in a 5% of the experimental values. The results obtained for theorical temperature correction factor presents a maximum deviation of ± 0.0245 with respect to the experimental values