Polarons in Carbon Nanotubes

We use ab initio total-energy calculations to predict the existence of polarons in semiconducting carbon nanotubes (CNTs). We find that the CNTs' band edge energies vary linearly and the elastic energy increases quadratically with both radial and with axial distortions, leading to the spontaneous formation of polarons. Using a continuum model parametrized by the ab initio calculations, we estimate electron and hole polaron lengths, energies and effective masses and analyze their complex dependence on CNT geometry. Implications of polaron effects on recently observed electro- and opto-mechanical behavior of CNTs are discussed.Comment: Revtex preprint format, 12 pages, 2 eps figures, source in LaTeX. Accepted for publication in Physical Review Letter

Highly-confined spin-polarized two-dimensional electron gas in SrTiO3_{3}/SrRuO3_{3} superlattices

We report first principles characterization of the structural and electronic properties of (SrTiO$_{3}$)$_{5}$/(SrRuO$_{3}$)$_{1}$ superlattices. We show that the system exhibits a spin-polarized two-dimensional electron gas, extremely confined to the 4$d$ orbitals of Ru in the SrRuO$_{3}$ layer. Every interface in the superlattice behaves as a minority-spin half-metal ferromagnet, with a magnetic moment of $\mu$ = 2.0 $\mu_{\rm B}$/SrRuO$_{3}$ unit. The shape of the electronic density of states, half metallicity and magnetism are explained in terms of a simplified tight-binding model, considering only the $t_{2g}$ orbitals plus (i) the bi-dimensionality of the system, and (ii) strong electron correlations.Comment: 5 pages, 4 figure

First-principles modeling of the thermoelectric properties of SrTiO3_3/SrRuO3_3 superlattices

Using a combination of first-principles simulations, based on the density functional theory and Boltzmann's semiclassical theory, we have calculated the transport and thermoelectric properties of the half-metallic two dimensional electron gas confined in single SrRuO$_3$ layers of SrTiO$_3$/SrRuO$_3$ periodic superlattices. Close to the Fermi energy we find that the semiconducting majority spin channel displays a very large in-plane component of the Seebeck tensor at room temperature, $S$ = 1500 $\mu$V/K, and the minority spin channel shows good in-plane conductivity $\sigma$ = 2.5 (m$\Omega$cm)$^{-1}$. However, contrary to the expectation of Hicks and Dresselhaus model about enhanced global thermoelectric properties due to the confinement of the metallic electrons, we find that the total power factor and thermoelectric figure of merit for reduced doping is too small for practical applications. The reason for this failure can be traced back on the electronic structure of the interfacial gas, which departs from the free electron behaviour on which the model was based. The evolution of the electronic structure, electrical conductivity, Seebeck coefficient, and power factor as a function of the chemical potential is explained by a simplified tight-binding model. We find that the electron gas in our system is composed by a pair of one dimensional electron gases orthogonal to each other. This reflects the fact the physical dimensionality of the electronic system can be even smaller than that of the spacial confinement of the carriers.Comment: 9 pages, 7 figure

First-principles modeling of the thermoelectric properties of SrTiO3/SrRuO3 superlattices

peer reviewedUsing a combination of first-principles simulations, based on density functional theory and Boltzmann’s semiclassical theory, we have calculated the transport and thermoelectric properties of the half-metallic twodimensional electron gas confined in single SrRuO3 layers of SrTiO3/SrRuO3 periodic superlattices. Close to the Fermi energy, we find that the semiconducting majority-spin channel displays a very large in-plane component of the Seebeck tensor at room temperature, S ∼ 1500 μV/K, and the minority-spin channel shows good in-plane conductivity, σ = 2.5 (m cm)−1. However, we find that the total power factor and thermoelectric figure of merit for reduced doping is too small for practical applications. Our results support that the confinement of the electronic motion is not the only thing that matters to describe the main features of the transport and thermoelectric properties with respect the chemical doping, but the shape of the electronic density of states, which in our case departs from the free-electron behavior, is also important. The evolution of the electronic structure, electrical conductivity, Seebeck coefficient, and power factor as a function of the chemical potential is explained by a simplified tight-binding model. We find that the electron gas in our system is composed by a pair of one-dimensional electron gases orthogonal to each other. This reflects the fact the physical dimensionality of the electronic system (1D) can be even smaller than that of the spacial confinement of the carriers (2D)

Central mucoepidermoid carcinoma: Report of 2 cases

Central mucoepidermoid carcinoma is a rare mandibular neoplasm. The objective of this paper was to report two cases. (C) 2007 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved

Transformação anaplásica em carcinoma papilífero de tireóide

OBJETIVO: Escrever a transformação de um Carcinoma Papilífero de Tireóide em Carcinoma Anaplásico. MÉTODOS: relato de caso de uma paciente portadora de Carcinoma Papilífero de glândula tireóide e tratada no Serviço de Cirurgia de Cabeça e Pescoço do HCMRPUSP. Espécimes histológicos foram colhidas durante o decorrer do tratamento e estudos anatomopatológico e imuno-histoquímico foram realizados para direcionar conduta médica. RESULTADOS: A análise anatomopatológica e imuno-histoquímica realizada mostrou mudança de padrão de diferenciação celular durante a evolução da doença em questão. Tais dados, correlatados às características clínico-radiológicas tornam o caso compatível com a transformação anaplásica tireoideana a partir de um tumor bem diferenciado-Carcinoma Papilífero de tireóide. CONCLUSÕES: Observa-se nítida diferença das características evolutivas dos dois tipos de tumores malignos presentes nesta paciente: a primeira com comportamento "benigno" e indolente e a segunda agressiva, e fatal, sugerindo transformação anaplásica - como já descrita previamente na literatura.<br>Anaplastic transformation of a differentiated (papillary or folicular) tyroid carcinoma is a very rare event. Ocasionally, indiffentiated and well differentiated carcinomas occur simultaneously at the same metastatic focci. All well-differentiated tyroid carcinomas could have this evolution. Some authors suggest that this transformation is induced by radioactive iodine, external radiotherapy or long term goiter. The purpose of this article is to show an anaplastic transformation in a 69 year old woman with papillary thyroid carcinoma operated by Head and Neck Surgery team at Hospital das Clinicas da Faculdade de Medicina de Ribeirão Preto - USP

Synthesis, anticancer activity and mechanism of action of new phthalimido-1,3-thiazole derivatives

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Studies toward the structural optimization of novel thiazolylhydrazone-based potent antitrypanosomal agents

In previous studies, we identified promising anti-Trypanosoma cruzi cruzain inhibitors based on thiazolylhydrazones. To optimize this series, a number of medicinal chemistry directions were explored and new thiazolylhydrazones and thiosemicarbazones were thus synthesized. Potent cruzain inhibitors were identified, such as thiazolylhydrazones 3b and 3j, which exhibited IC(50) of 200-400 nM. Furthermore, molecular docking studies showed concordance with experimentally derived structure-activity relationships (SAR) data. In the course of this work, lead compounds exhibiting in vitro activity against both the epimastigote and trypomastigote forms of T. cruzi were identified and in vivo general toxicity analysis was subsequently performed. Novel SAR were documented, including the importance of the thiocarbonyl carbon attached to the thiazolyl ring and the direct comparison between thiosemicarbazones and thiazolylhydrazones. (C) 2010 Elsevier Ltd. All rights reserved.Pernambuco State Foundation for Science and Technology (FACEPE)[APQ-0123-4.03/08]Pernambuco State Foundation for Science and Technology (FACEPE)Brazilian National Council of Research (CNPq)[472880/2009-8]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CAPE