Theoretical study of the structure and stability of NbxOy, and NbxOy+ (x = 1-3; y = 2-5, 7, 8) clusters

Geometric, thermodynamic and electronic properties of cluster neutrals NbxOy and cations NbxOy+ (x = 1-3; y = 2-5, 7, 8) have been characterized theoretically. A DFT calculation using a hybrid combination of B3LYP with contracted Huzinaga basis sets. Numerical results of the relative stabilities, ionization potentials and band gaps of different clusters are in agreement with experiment. Analysis of dissociation channels supports the more stable building blocks as formed by NbO2, NbO2+ NbO3 and NbO3+ stoichiometries. The net atomic charges suggest that oxygen donor molecules can interact more favorably on central niobium atoms of cluster cations, while the interaction with oxygen acceptor molecules is more favorable on the terminal oxygen atoms of neutral clusters. A topological analysis of the electron localization function gradient field indicates that the clusters may be described as having a strong ionic interaction between Nb and O atoms. Published by Elsevier B.V. B.V.

Bounded solutions of fermions in the background of mixed vector-scalar Poeschl-Teller-like potentials

The problem of a fermion subject to a convenient mixing of vector and scalar potentials in a two-dimensional space-time is mapped into a Sturm-Liouville problem. For a specific case which gives rise to an exactly solvable effective modified Poschl-Teller potential in the Sturm-Liouville problem, bound-state solutions are found. The behaviour of the upper and lower components of the Dirac spinor is discussed in detail and some unusual results are revealed. The Dirac delta potential as a limit of the modified Poschl-Teller potential is also discussed. The problem is also shown to be mapped into that of massless fermions subject to classical topological scalar and pseudoscalar potentials. Copyright (C) EPLA, 2007.

Vacuumless kink systems from vacuum systems: An example

Some years ago, Cho and Vilenkin, introduced a model which presents topological solutions, despite not having degenerate vacua as is usually expected. Here we present a new model with topological defects, connecting degenerate vacua but which in a certain limit recovers precisely the one proposed originally by Cho and Vilenkin. In other words, we found a kind of parent model for the so called vacuumless model. Then the idea is extended to a model recently introduced by Bazeia et al. Finally, we trace some comments the case of the Liouville model.

Extended class of exact twistons and crystalline polyethylene

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Schwarzschild generalized black hole horizon and the embedding space

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Exotic dark spinor fields

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Improvements for ZCS-PWM commutation cell in high-power-factor preregulator application

A Summary of different topological arrangements concerning a ZCS-PWM cell is presented, based on the analysis of its application in boost rectifying preregulators, controlled by the technique of instantaneous average values of input current, with the purpose of obtaining high-input-power-factor rectifier and high efficiency in single-phase applications in telecommunication systems. The main characteristics of each switching cell are described, providing conditions to establish a qualitative comparison among the structures. In addition, experimental results are presented for a prototype of the latest version of the ZCS-PWM boost rectifier, implemented for processing normal values of 1200 W output power and 400 V output average voltage, at 220 V Input RMS voltage and 50 kHz switching frequency.

Algoritmos evolutivos dedicados à reconfiguração de redes radiais de distribuição sob demandas fixas e variáveis: estudo dos operadores genéticos e parâmetros de controle

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Planning and Projects of Secondary Electric Power Distribution Systems

This paper proposes a methodology to achieve integrated planning and projects for secondary distribution circuits. The planning model is formulated as a mixed integer nonlinear programming problem (MINLP). In order to resolve this problem, a tabu search (TS) algorithm is used, with a neighborhood structure developed to explore the physical characteristics of specific geographies included in the planning and expansion of secondary networks, thus obtaining effective solutions as well as low operating costs and investments. The project stage of secondary circuits consists of calculating the mechanical efforts to determine the support structures of the primary and secondary distribution systems and determining the types of structures that should be used in the system according to topological and electrical parameters of the network and, therefore, accurately assessing the costs involved in the construction and/or reform of secondary systems. A constructive heuristic based on information of the electrical and topological conditions between the medium voltage and low voltage systems is used to connect the primary systems and secondary circuits. The results obtained from planning and design simulations of a real secondary system of electric energy distribution are presented.

ALGORITHM FOR PROBABILISTIC ANALYSIS of DISTRIBUTION SYSTEMS WITH DISTRIBUTED GENERATION

In this paper an efficient algorithm for probabilistic analysis of unbalanced three-phase weakly-meshed distribution systems is presented. This algorithm uses the technique of Two-Point Estimate Method for calculating the probabilistic behavior of the system random variables. Additionally, the deterministic analysis of the state variables is performed by means of a Compensation-Based Radial Load Flow (CBRLF). Such load flow efficiently exploits the topological characteristics of the network. To deal with distributed generation, a strategy to incorporate a simplified model of a generator in the CBRLF is proposed. Thus, depending on the type of control and generator operation conditions, the node with distributed generation can be modeled either as a PV or PQ node. To validate the efficiency of the proposed algorithm, the IEEE 37 bus test system is used. The probabilistic results are compared with those obtained using the Monte Carlo method.

Estudo teórico QTAIM e DFT dos compostos de coordenação: efeito quelato, titanocenos e ligação química

This work is a study of coordination compounds by quantum theory of atoms in molecules (QTAIM), based on the topological analysis of the electron density of molecular systems, both theoretically and experimentally obtained. The coordination chemistry topics which were studied are the chelate effect, bent titanocene and chemical bond in coordination complexes. The chelate effect was investigated according to topological and thermodynamic parameters. The exchange of monodentate ligands on polydentate ligands from same transition metal increases the stability of the complex both from entropy and enthalpy contributions. In some cases, the latter had a higher contribution to the stability of the complex in comparison with entropy. This enthalpic contribution is explained according to topological analysis of the M-ligand bonds where polidentate complex had higher values of electron density of bond critical point, Laplacian of electron density of bond critical point and delocalization index (number of shared electrons between two atoms). In the second chapter, was studied bent titanocenes with bulky cyclopentadienyl derivative π-ligand. The topological study showed the presence of secondary interactions between the atoms of π-ligands or between atoms of π-ligand and -ligand. It was found that, in the case of titanocenes with small difference in point group symmetry and with bulky ligands, there was an nearly linear relationship between stability and delocalization index involving the ring carbon atoms (Cp) and the titanium. However, the titanocene stability is not only related to the interaction between Ti and C atoms of Cp ring, but secondary interactions also play important role on the stability of voluminous titanocenes. The third chapter deals with the chemical bond in coordination compounds by means of QTAIM. The quantum theory of atoms in molecules so far classifies bonds and chemical interactions in two categories: closed shell interaction (ionic bond, hydrogen bond, van der Waals interaction, etc) and shared interaction (covalent bond). Based on topological parameters such as electron density, Laplacian of electron density, delocalization index, among others, was classified the chemical bond in coordination compounds as an intermediate between closed shell and shared interactions

Desenvolvimento de misturas ternárias para remoção de reboco de fluido de perfuração sintético

The construction of wells is one of the most important activities of the oil industry. The drilling process is the set of activities and operations to design, program and perform the opening thereof. During this process, the cuttings are removed by the drilling fluid, or mud, and carted to the surface. This fluid is injected into the drill string and returns to the surface through the annular space between the well walls and the drill string. After the descent of the column casing, the annular space between the casing string and the walls of the borehole is filled with cement so as to secure the spine and prevent any migration of fluids between the various permeable zones traversed by the well behind of the coating. To ensure the good quality of the cementation scrubbers are used mattresses which are pumped ahead of the cement slurry so as to avoid contamination of the drilling fluid paste, or vice versa, and assist in the removal of plaster, formed by drilling fluid of the borehole walls, thus enabling a better cement bond to the well. Within this context, this work aims to evaluate the efficiency of mattresses scrubbers, the basis of ionic and nonionic surfactants, on the removal of nonaqueous drilling fluid, based on n-paraffin in oil wells, and the compatibility between the Mattress relations washer / drilling fluid bed scrubber / cement paste mattress washer / cement slurry / drilling fluid and the drilling fluid / cement slurry using laboratory tests rheology, thickening time and compressive strength. Also technique was performed X-ray diffraction (XRD) for a more detailed analysis of these mixtures with hydrated cement paste. In compatibility tests the conditions of temperature and pressure used in the same laboratory procedure simulating the conditions of oil wells, the well is considered the depth of 800 m. The results showed that the compositions of the mattress washer nonionic, KMS obtained a 100% efficient in removing the non-aqueous drilling fluid, and the best formulation showed good results with respect to compliance testing

Utilizando mapas de conectividade fuzzy no desenvolvimento de algoritmos reparadores de imagens binárias 3D

A 3D binary image is considered well-composed if, and only if, the union of the faces shared by the foreground and background voxels of the image is a surface in R3. Wellcomposed images have some desirable topological properties, which allow us to simplify and optimize algorithms that are widely used in computer graphics, computer vision and image processing. These advantages have fostered the development of algorithms to repair bi-dimensional (2D) and three-dimensional (3D) images that are not well-composed. These algorithms are known as repairing algorithms. In this dissertation, we propose two repairing algorithms, one randomized and one deterministic. Both algorithms are capable of making topological repairs in 3D binary images, producing well-composed images similar to the original images. The key idea behind both algorithms is to iteratively change the assigned color of some points in the input image from 0 (background)to 1 (foreground) until the image becomes well-composed. The points whose colors are changed by the algorithms are chosen according to their values in the fuzzy connectivity map resulting from the image segmentation process. The use of the fuzzy connectivity map ensures that a subset of points chosen by the algorithm at any given iteration is the one with the least affinity with the background among all possible choices

Cistos subependimários diagnosticados pelo ultra-som transfontanelar

Objetivos: avaliar a evolução ultra-sonográfica de cistos subependimários (CSE) do ângulo externo dos ventrículos laterais, e a evolução clínica dos pacientes. Comparar os pacientes com CSE isolados e os com CSE associados a outras lesões. Métodos: foram diagnosticados um a vários cistos no ângulo externo de um ou de ambos os ventrículos laterais, por meio de ultra-som transfontanelar (US) de rotina, realizado nos primeiros dias de vida, caracterizando os CSE. Durante o período de 1981-2000, 66 recém-nascidos tiveram CSE evidenciados na UTI neonatal do Hospital de Port-Royal. Foram constituídos dois grupos: G-I, com CSE isolados (n=21), e G-II, com CSE associados a outras lesões (n=45). Resultados: os recém-nascidos do GI apresentaram maior maturidade, melhores condições de nascimento e menor morbidade respiratória em relação a GII. A incidência de malformações congênitas foi elevada em ambos os grupos. Houve baixa taxa de infecção bacteriana e ausência de infecção congênita. Os CSE foram uni ou bilaterais, únicos ou múltiplos (colar de pérolas), sem diferença entre os grupos estudados, e predominaram à esquerda. US seriados foram realizados em 49/66 pacientes (74%), mostrando aumento no tamanho do cisto em 21/49 (45%), no primeiro mês de vida, enquanto 12 CSE (24%) desapareceram. O óbito ocorreu em dez recém-nascidos com lesões neurológica graves (quatro leucomalácias periventriculares, cinco hemorragias peri e intraventriculares), e somente um com hérnia diafragmática não apresentava outras lesões ao US transfontanelar. Conclusões: as características dos CSE não diferiram quando esses estavam associados a outras lesões. O nítido predomínio no lado esquerdo sugere uma etiologia vascular. Foi encontrada uma alta taxa de malformações associadas, alertando para a possibilidade de uma etiologia malformativa. Ambas hipóteses sugerem um desvio de desenvolvimento, e não de uma fetopatia viral.

Vende-se uma vila: análise intra-urbana das vilas na Vila de Ponta Negra e no bairro de Nova Descoberta - Zona Sul de Natal

This dissertation is about low-income rental housing vilas in the South Zone in the city of Natal. Vilas are a string of houses, built privately in an urban plot of land, usually a backyard, facing a narrow street beco. This type of housing is originated in the 19th century in the Brazilian scenario. In Natal, this has become more popular since the late 1960s. This study is aimed at analyzing the urban integration of the vilas, considering that these house a low income population, vis à vis the speedy development of Natal s most economically dynamic area. The study starts with a discussion of the production of space, taking into consideration categories such as use value, exchange value, commodity and land rent. Field work was undertaken through structured interviews with dwellers of vilas in Nova Descoberta and Ponta Negra neighbourhoods. Owners of vilas were also interviewed. Data collected indicated worrisome housing conditions. Vilas, in the areas researched, are increasingly becoming unwelcome, constituting guetos in a place where landscape is changing rapidly. Gentrification is fast under way, first because of rise in rent and taxes; second because of general rise in living costs