Theoretical search for Chevrel phase based thermoelectric materials

We investigate the thermoelectric properties of some semiconducting Chevrel phases. Band structure calculations are used to compute thermopowers and to estimate of the effects of alloying and disorder on carrier mobility. Alloying on the Mo site with transition metals like Re, Ru or Tc to reach a semiconducting composition causes large changes in the electronic structure at the Fermi level. Such alloys are expected to have low carrier mobilities. Filling with transition metals was also found to be incompatible with high thermoelectric performance based on the calculated electronic structures. Filling with Zn, Cu, and especially with Li was found to be favorable. The calculated electronic structures of these filled Chevrel phases are consistent with low scattering of carriers by defects associated with the filling. We expect good mobility and high thermopower in materials with the composition close to (Li,Cu)$_4$Mo$_6$Se$_8$, particularly when Li-rich, and recommend this system for experimental investigation.Comment: 4 two-column pages, 4 embedded ps figure

Towards a Linear-Scaling DFT Technique: The Density Matrix Approach

A recently proposed linear-scaling scheme for density-functional pseudopotential calculations is described in detail. The method is based on a formulation of density functional theory in which the ground state energy is determined by minimization with respect to the density matrix, subject to the condition that the eigenvalues of the latter lie in the range [0,1]. Linear-scaling behavior is achieved by requiring that the density matrix should vanish when the separation of its arguments exceeds a chosen cutoff. The limitation on the eigenvalue range is imposed by the method of Li, Nunes and Vanderbilt. The scheme is implemented by calculating all terms in the energy on a uniform real-space grid, and minimization is performed using the conjugate-gradient method. Tests on a 512-atom Si system show that the total energy converges rapidly as the range of the density matrix is increased. A discussion of the relation between the present method and other linear-scaling methods is given, and some problems that still require solution are indicated.Comment: REVTeX file, 27 pages with 4 uuencoded postscript figure

A Self-Consistent First-Principles Technique Having Linear Scaling

An algorithm for first-principles electronic structure calculations having a computational cost which scales linearly with the system size is presented. Our method exploits the real-space localization of the density matrix, and in this respect it is related to the technique of Li, Nunes and Vanderbilt. The density matrix is expressed in terms of localized support functions, and a matrix of variational parameters, L, having a finite spatial range. The total energy is minimized with respect to both the support functions and the elements of the L matrix. The method is variational, and becomes exact as the ranges of the support functions and the L matrix are increased. We have tested the method on crystalline silicon systems containing up to 216 atoms, and we discuss some of these results.Comment: 12 pages, REVTeX, 2 figure

Basis Functions for Linear-Scaling First-Principles Calculations

In the framework of a recently reported linear-scaling method for density-functional-pseudopotential calculations, we investigate the use of localized basis functions for such work. We propose a basis set in which each local orbital is represented in terms of an array of `blip functions'' on the points of a grid. We analyze the relation between blip-function basis sets and the plane-wave basis used in standard pseudopotential methods, derive criteria for the approximate equivalence of the two, and describe practical tests of these criteria. Techniques are presented for using blip-function basis sets in linear-scaling calculations, and numerical tests of these techniques are reported for Si crystal using both local and non-local pseudopotentials. We find rapid convergence of the total energy to the values given by standard plane-wave calculations as the radius of the linear-scaling localized orbitals is increased.Comment: revtex file, with two encapsulated postscript figures, uses epsf.sty, submitted to Phys. Rev.

TOMATE PARA INDÚSTRIA ESTRATÉGIAS SUSTENTÁVEIS NO COMBATE A TUTA ABSOLUTA

O objetivo deste estudo foi desenvolver um sistema de apoio à decisão com base no acompanhamento técnico dos inimigos da cultura e na construção de mapas de risco para as principais zonas de produção. Outros objetivos foram o estabelecimento de uma metodologia de observação e avaliação, nomeadamente métodos expeditos de estimativa do risco, estabelecimento de regras de tomada de decisão e o estudo da bioecologia da espécie em tomate para indústria no Ribatejo. Os resultados deste projeto são uma contribuição para o uso sustentável dos produtos fitofarmacêuticos e, consequentemente, para uma maior ecoeficiência, conservação da biodiversidade e garantia de qualidade e segurança alimentar do produto final

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Measurement of D*+/- meson production in jets from pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

This paper reports a measurement of D*+/- meson production in jets from proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb^-1 for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range |eta| < 2.5. D*+/- mesons found in jets are fully reconstructed in the decay chain: D*+ -> D0pi+, D0 -> K-pi+, and its charge conjugate. The production rate is found to be N(D*+/-)/N(jet) = 0.025 +/- 0.001(stat.) +/- 0.004(syst.) for D*+/- mesons that carry a fraction z of the jet momentum in the range 0.3 < z < 1. Monte Carlo predictions fail to describe the data at small values of z, and this is most marked at low jet transverse momentum.Comment: 10 pages plus author list (22 pages total), 5 figures, 1 table, matches published version in Physical Review

Assessment of Woody Residual Biomass Generation Capacity in the Central Region of Portugal: Analysis of the Power Production Potential

Biomass is an alternative energy source with high potential to contribute to the global energy mix and to countries’ energetic independence. The case of Portugal is particularly relevant, given its biomass availability. Thus, the quantification of woody residual biomass is assumed to be urgent. To achieve the objective of quantifying residual woody biomass, various available data were used, namely the Land Cover and Soil Use Map (COS 2018), from which areas occupied by different categories were selected as being the most relevant. Then, based on coefficients previously established, the amounts of residual woody biomass were determined, namely for maritime pine forests, eucalyptus forests, scrubland, vineyards, olive groves, and orchards. Then, the potential for generating electricity was estimated. It was found that for the hypothetical scenario of the total conversion of the recently closed Pêgo coal power plant to biomass, the available amounts of residual woody biomass in the country would not be sufficient to ensure the operation. On the other hand, if the power plant only worked as a backup unit, the available quantities could ensure its operation and contribute to creating a value chain for residual woody biomass of forest and agricultural origin within a circular economy and sustainable development approachinfo:eu-repo/semantics/publishedVersio

Indoor radon exposure in Africa: A critical review on the current research stage and knowledge gaps

Indoor radon exposure poses significant health risks and has prompted testing and mitigation programs in regions such as Europe, North America, Japan, and South Korea. However, African countries have not adopted similar measures on a comparable scale. Limited research on radon exposure in Africa can be attributed to a lack of awareness among policymakers and the public, insufficient expertise in radiation protection and measurements, and restricted access to resources such as laboratories and testing equipment. This review examines existing research articles on radon exposure conducted in African countries, focusing on the efforts made by specific nations, such as Tunisia and Sudan, to address this issue. It analyzes the scope, scale, and impact of these initiatives compared to global efforts in managing radon exposure risks. The findings reveal that the study of radon exposure in Africa is still in its early stages, with limited progress and modest initiatives compared to other regions. While some efforts have been made, they are insufficient to effectively address the significant health risks associated with radon exposure. There is an urgent need for African policymakers and researchers to prioritize radon exposure as a public health issue. Developing frameworks, standards, and mitigation strategies is essential to reduce risks in homes and workplaces. This review emphasizes the importance of addressing radon exposure in African countries and offers recommendations to guide future research and policy development