Three-body description of direct nuclear reactions: Comparison with the continuum discretized coupled channels method

The continuum discretized coupled channels (CDCC) method is compared to the exact solution of the three-body Faddeev equations in momentum space. We present results for: i) elastic and breakup observables of d-12C at E_d=56 MeV, ii) elastic scattering of d-58Ni at E_d=80 MeV, and iii) elastic, breakup and transfer observables for 11Be+p at E_{11Be}/A=38.4 MeV. Our comparative studies show that, in the first two cases, the CDCC method is a good approximation to the full three-body Faddeev solution, but for the 11Be exotic nucleus, depending on the observable or the kinematic regime, it may miss out some of the dynamic three-body effects that appear through the explicit coupling to the transfer channel.Comment: 12 pages, 10 figures, accepted for publication in Physical Review

Late-Variscan multistage hydrothermal processes unveiled by chemical ages coupled with compositional and textural uraninite variations in W-Au deposits in the western Spanish Central System Batholith

The scheelite skarn from Los Santos and the W-Au veins from El Cabaco district, located in the Spanish Central System Batholith (SCSB), are some of the best-known tungsten ore deposits in Spain. Uraninite is an accessory mineral in both deposits, which underwent several hydrothermal flow events. Chemical and textural characteristics, as well as electron microprobe U-Th-Pb uraninite chemical data from the different stages of the skarn and the vein-type mineralizations, are presented here. Based on these data the uraninite was able to be classified into two groups. Group I uraninite has an octahedral habit and occurs as inclusions in K-feldspar relicts of the leucogranite related to Los Santos skarn formation. It shows high Th (6.95 to 8.51wt.% ThO2) and high Rare Earth Elements (REEs) contents (0.55 to 1.38wt.% ∑REE2O3). Group II uraninite occurs i) associated to El Cabaco granite, in a greenish selvage-style greisen and its reddish envelope and in the mineralized rimming quartz veins and ii) in Los Santos high-temperature endoskarn and anorthite skarn, where it is associated with U-rich mica. This uraninite type has lower Th and ∑REE2O3contents than Group-I uraninite. The mineral chemistry and the assemblage and textural relationships suggest that Group-I uraninite is magmatic and the attained U-Th-Pb chemical age of 300±4Ma is interpreted as the magmatic age of the skarn-forming aplite granites in the western part of the SCSB. Group-II uraninite includes two events: i) hydrothermal uraninite, which yields an age of 295±2Ma, dates a strong alkali mobilization and early tungsten deposition and ii) a later hydrothermal process, around 287±4Ma, that resulted in sulfides and late scheelite precipitation and widespread silicification. Finally, the gold deposition is younger than this silicification according to textural criteria. Therefore, W-Au deposits in the western part of the SCSB were formed by superposition of several processes that took place some 15Ma after the skarn-forming granite crystallized. Comparable W, W-Au and U deposits in the Variscan orogenic belt show a similar timing of hydrothermal events, suggesting that the hydrothermal history was controlled by large-scale Late-Variscan tectonic processes

Exportação de nutrientes em povoamentos de Pinus taeda L. baseada em volume estimado pelo sistema sispinus.

Os plantios de Pinus ocorrem preferencialmente em regiões com menores preços de terras, localizados em áreas com solos de baixa fertilidade natural e conseqüentemente baixa produtividade. Essa condição, associada ao fato da não-fertilização dos plantios, via de regra, e à exportação de nutrientes nos desbastes e na colheita final, leva invariavelmente a perdas de produtividade futuras dos povoamentos. Nesse contexto, este trabalho teve como objetivo avaliar a aplicabilidade de modelos matemáticos, desenvolvidos em área florestais descritas por Moro (2005), ao SisPinus, para estimativa de nutrientes exportados na madeira, nas ocasiões da colheita da floresta. Para a realização deste estudo, foram selecionados plantios de P. taeda com 8, 12, 18 e 23 anos de idade, localizados em povoamentos comerciais, situados na região de Guarapuava (PR). Determinaram-se os nutrientes nos diversos segmentos do tronco, a cada metro, da base à altura comercial, no lenho e na casca. As equações desenvolvidas por Moro (2005) foram inseridas ao estimador de biomassa SisPinus, possibilitando a estimativa dos nutrientes exportados. O ajuste das equações desenvolvidas, dentro da variação de idade, qualidade do sítio, intensidade de manejo, entre outras variáveis, foi extremamente elevado, permitindo alta confiabilidade nas equações para estimativa de exportação dos nutrientes

Dermanyssus gallinae in layer farms in Kosovo: a high risk for salmonella prevalence

Background The poultry red mite (PRM), Dermanyssus gallinae (D.g.) is a serious ectoparasitic pest of poultry and potential pathogen vector. The prevalence of D. g. and the prevalence of Salmonella spp. within mites on infested laying poultry farms were investigated in Kosovo. Findings In total, 14 populated layer farms located in the Southern Kosovo were assessed for D. g. presence. Another two farms in this region were investigated 6 months after depopulation. Investigated flocks were all maintained in cages, a common housing system in Kosovo. A total of eight farms were found to be infested with D. g. (50%) at varying levels, including the two depopulated farms. The detection of Salmonella spp. from D. g. was carried out using PCR. Out of the eight layer farms infested with D. g., Salmonella spp. was present in mites on three farms (37.5%). Conclusions This study confirms the high prevalence of D. g. in layer flocks in Kosovo and demonstrates the link between this mite and the presence of Salmonella spp. on infested farms

Signatures of Planets in Spatially Unresolved Disks

Main sequence stars are commonly surrounded by debris disks, composed of cold dust continuously replenished by a reservoir of undetected dust-producing planetesimals. In a planetary system with a belt of planetesimals (like the Solar System's Kuiper Belt) and one or more interior giant planets, the trapping of dust particles in the mean motion resonances with the planets can create structure in the dust disk, as the particles accumulate at certain semimajor axes. Sufficiently massive planets may also scatter and eject dust particles out of a planetary system, creating a dust depleted region inside the orbit of the planet. In anticipation of future observations of spatially unresolved debris disks with the Spitzer Space Telescope, we are interested in studying how the structure carved by planets affects the shape of the disk's spectral energy distribution (SED), and consequently if the SED can be used to infer the presence of planets. We numerically calculate the equilibrium spatial density distributions and SEDs of dust disks originated by a belt of planetesimals in the presence of interior giant planets in different planetary configurations, and for a representative sample of chemical compositions. The dynamical models are necessary to estimate the enhancement of particles near the mean motion resonances with the planets, and to determine how many particles drift inside the planet's orbit. Based on the SEDs and predicted $\it{Spitzer}$ colors we discuss what types of planetary systems can be distinguishable from one another and the main parameter degeneracies in the model SEDs.Comment: 40 pages (pre-print form), including 16 figures. Published in ApJ 200

A data-driven approach to predict first-year students’ academic success in higher education institutions

This study presents a data mining approach to predict academic success of the first-year students. A dataset of 10 academic years for first-year bachelor’s degrees from a Portuguese Higher Institution (N = 9652) has been analysed. Features’ selection resulted in a characterising set of 68 features, encompassing socio-demographic, social origin, previous education, special statutes and educational path dimensions. We proposed and tested three distinct course stage data models based on entrance date, end of the first and second curricular semesters. A support vector machines (SVM) model achieved the best overall performance and was selected to conduct a data-based sensitivity analysis. The previous evaluation performance, study gaps and age-related features play a major role in explaining failures at entrance stage. For subsequent stages, current evaluation performance features unveil their predictive power. Suggested guidelines include to provide study support groups to risk profiles and to create monitoring frameworks. From a practical standpoint, a data-driven decision-making framework based on these models can be used to promote academic success.info:eu-repo/semantics/acceptedVersio

Modelling piezoelectric energy harvesters by a finite integration technique formulation for electromechanical coupled problems

A detailed analysis and optimization of piezoelectric devices, which nowadays are of widespread use in electronic applications, requires numerical analysis. Numerical models based on the Finite Element Method (FEM) have already been proposed in literature. The Finite Integration Technique (FIT) provides stable and consistent discretization schemes for coupled multiphysics problems. A FIT formulation with unstructured meshes, for 2-D/3-D coupled electromechanical static or dynamic problems, is presented. Piezoelectric bimorph cantilevers, with a realistic multilayered geometry, can be analyzed. Comparisons with FEM show the validity and the accuracy of the method

Modelos matemáticos para estimativa de exportação de nutrientes em povoamentos de Pinus taeda L.

Este trabalho teve como objetivo desenvolver e avaliar a aplicabilidade de modelos matemáticos para quantificar a exportação de nutrientes, na colheita de floresta de Pinus sp. O estudo ocorreu em plantios de P. taeda em 4 idades, localizados na região de Guarapuava (PR). As amostras foram retiradas na base, 1,0 m, 1,3 m, 2,0 m de altura e deste ponto em diante a cada metro até altura comercial. Destas amostras foram determinados os teores dos macronutrientes, do lenho e casca, no laboratório da EMBRAPA - Florestas - Colombo (PR). A amostragem aleatória em povoamentos de P. taeda em diferentes idades, nos estágios vegetativos: dominante, co-dominante e dominada e em diferentes condições de manejo e produtividade, permite obter equações de estimativas de acúmulo nutrientes com altos índices de correlações e confiabilidade. A obtenção de amostragem em segmentos até 4,0 m de altura possibilita determinar o conteúdo total dos nutrientes, sem necessidade de amostragens nos segmentos de posição mais elevada da árvore. A determinação do nutriente nitrogênio apresenta um maior grau de complexidade e requer basicamente que outros macronutrientes também sejam determinados, o que demanda maiores custos amostrais e laboratoriais

alpha-particle production in the scattering of 6He by 208Pb at energies around the Coulomb barrier

New experimental data from the scattering of 6He+208Pb at energies around and below the Coulomb barrier are presented. The yield of breakup products coming from projectile fragmentation is dominated by a strong group of $\alpha$ particles. The energy and angular distributions of this group have been analyzed and compared with theoretical calculations. This analysis indicates that the $\alpha$ particles emitted at backward angles in this reaction are mainly due to two-neutron transfer to weakly bound states of the final nucleus.Comment: 20 pages, 5 figures. Nuclear Physics A792 (2007) 2-1