Excitonic effects in the optical properties of CdSe nanowires

Using a first-principle approach beyond density functional theory we calculate the electronic and optical properties of small diameter CdSe nanowires.Our results demonstrate how some approximations commonly used in bulk systems fail at this nano-scale level and how indispensable it is to include crystal local fields and excitonic effects to predict the unique optical properties of nanowires. From our results, we then construct a simple model that describes the optical gap as a function of the diameter of the wire, that turns out to be in excellent agreement with experiments for intermediate and large diameters.Comment: submitte

Construction of the B88 exchange-energy functional in two dimensions

We construct a generalized-gradient approximation for the exchange-energy density of finite two-dimensional systems. Guided by non-empirical principles, we include the proper small-gradient limit and the proper tail for the exchange-hole potential. The observed performance is superior to that of the two-dimensional local-density approximation, which underlines the usefulness of the approach in practical applications

On the violation of a local form of the Lieb-Oxford bound

In the framework of density-functional theory, several popular density functionals for exchange and correlation have been constructed to satisfy a local form of the Lieb-Oxford bound. In its original global expression, the bound represents a rigorous lower limit for the indirect Coulomb interaction energy. Here we employ exact-exchange calculations for the G2 test set to show that the local form of the bound is violated in an extensive range of both the dimensionless gradient and the average electron density. Hence, the results demonstrate the severity in the usage of the local form of the bound in functional development. On the other hand, our results suggest alternative ways to construct accurate density functionals for the exchange energy.Comment: (Submitted on 27 April 2012

Mechanical and tribological characterization of four commercial braking formulation materials

Organic friction materials for brake linings, namely brake pads are polymer matrix composites usually containing numerous macroscopic as well as microscopic constituents such as filamentary reinforcements, solid lubricants, abrasives and fillers. Their main objective of the these composite system are that a constant and stable coefficient of friction (COF) is provided irrespective of environmental conditions such as pressure, sliding velocity, temperature, humidity etc. Brake pads performance should be maintained over a wide range of stress conditions. Although the wear of the brake pad is inevitable, it should be minimized as far as possible. While cast iron has been the dominant material for brake discs, brake pad materials are constantly evolving into more complex composites. The main objectives of the present work is to characterize the physical and the tribological behavior of four commercial braking pads material formulations. For all compositions the studied factors are normal pressure and sliding speed, considering one braking-test protocol designed with temperature and friction load data acquisition. A double pad-on-disc tribological test configuration was used to determine tribological properties of brake pad for heavy vehicles commercial. Three wear tests via increased severity of rubbing conditions for a constant braking distance.The authors acknowledge Auto Travões Viseu-recondicionamento de Travões e embraiagens Lda the support through the provision of the frictrion linning materials presented in the study

Treatment of infra-bony periodontal defects using a collagen membrane and a bone substitute of equine origin : a pilot study

Abstract in proceedings of the Fourth International Congress of CiiEM: Health, Well-Being and Ageing in the 21st Century, held at Egas Moniz’ University Campus in Monte de Caparica, Almada, from 3–5 June 2019.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.info:eu-repo/semantics/publishedVersio

Thrombophilia screening: An artificial neural network approach

Thrombotic disorders have severe consequences for the patients and for the society in general, being one of the main causes of death. These facts reveal that it is extremely important to be preventive; being aware of how probable is to have that kind of syndrome. Indeed, this work will focus on the development of a decision support system that will cater for an individual risk evaluation with respect to the surge of thrombotic complaints. The Knowledge Representation and Reasoning procedures used will be based on an extension to the Logic Programming language, allowing the handling of incomplete and/or default data. The computational framework in place will be centered on Artificial Neural Networks.This work is funded by National Funds through the FCT – Fundação para a Ciência e a Tecnologia (Portuguese Foundation for Science and Technology) within projects PEst-OE/EEI/UI0752/2014 and PEst-OE/QUI/UI0619/2012

An analytical solver for the multi-group two-dimensional neutron-diffusion equation by integral transform techniques

In this work, we present an analytical solver for neutron diffusion in a rectangular two-dimensional geometry by a two-step integral transform procedure. To this end, we consider a regionwise homogeneous problem for two energy groups, i.e. fast and thermal neutrons, respectively. Each region has its specific physical properties, specified by cross-sections and diffusion constants. The problem is set up by two coupled bi-dimensional diffusion equations in agreement with general perturbation theory. These are solved by integral transforms Laplace transform and generalized integral transform technique yielding analytical expressions for the scalar neutron fluxes. The solutions for neutron fluxes are presented for fast and thermal neutrons in the four regions

Análise e validação de metodologia para determinação de ametrina, diuron, hexazinona e tebutiuron em filé de tilápia.

Resumo: Embora os herbicidas sejam amplamente utilizados nas atividades agrícolas, o impacto desta utilização sobre a qualidade das águas é pouco conhecido e tem sido alvo de estudos em todo o mundo, sendo que efeitos mutagênicos e genotóxicos já foram observados em peixes expostos a herbicidas. Para se avaliar a toxicidade das misturas dos herbicidas tebutiuron, ametrina e do produto comercial Velpar K (diuron e hexazinone), amplamente empregados na cultura canavieira, foi necessário desenvolver e validar um método analítico capaz de detectar e quantificar a presença destes herbicidas em tilápia. A extração dos analitos foi realizada por meio do método QuECHERS (Quick, Easy, Cheap, Effective, Rugged and Safe) modificado, seguido de uma etapa de clean-up denominada extração em fase sólida dispersiva (D-SPE). As separações cromatográficas foram realizadas utilizando-se um sistema LC-MSMS, dotado de uma fonte de eletronebulização tipo electrospray, modo de ionização positivo, e analisador tipo triploquadrupolo (QqQ). As curvas analíticas obtidas para todos os compostos estudados apresentaram coeficiente de correlação linear (r2) maiores ou iguais a 0,99, limite de quantificação (LOQ) igual a 0,00125 ?g g-1 e exatidão entre 70 e 120 %