Dynamic tight binding for large-scale electronic-structure calculations of semiconductors at finite temperatures

Calculating the electronic structure of materials at finite temperatures is important for rationalizing their physical properties and assessing their technological capabilities. However, finite-temperature calculations typically require large system sizes or long simulation times. This is challenging for non-empirical theoretical methods because the involved bottleneck of performing many first-principles calculations can pose a steep computational barrier for larger systems. While machine-learning molecular dynamics enables large-scale/long-time simulations of the structural properties, the difficulty of computing in particular the electronic structure of large and disordered materials still remains. In this work, we suggest an adaptation of the tight-binding formalism which allows for computationally efficient calculations of temperature-dependent properties of semiconductors. Our dynamic tight-binding approach utilizes hybrid-orbital basis functions and a modeling of the distance dependence of matrix elements via numerical integration of atomic orbitals. We show that these design choices lead to a dynamic tight-binding model with a minimal amount of parameters which are straightforwardly optimized using density functional theory. Combining dynamic tight-binding with machine learning molecular dynamics and hybrid density functional theory, we find that it accurately describes finite-temperature electronic properties in comparison to experiment for the prototypical semiconductor gallium-arsenide

Avaliação da produtividade da soja sob diferentes doses de Fósforo na região de Santarém - PA.

A agricultura no Brasil possui uma das maiores produções quando comparadas às principais potências mundiais no setor. As áreas agricultáveis e o próprio clima representam dentre outros fatores, um atrativo para qualificar o país como um grande produtor de alimentos e principalmente de grãos. A soja participa do Produto Interno Bruto (PIB) como um item de extrema importância na economia agrícola, inserindo diversos insumos, inerentes à qualidade de toda essa produção. Dentre os mais importantes, temos o Fósforo (P), que possui relevante papel no desenvolvimento e crescimento da soja, sendo foco de muitos estudos agronômicos relativos ao melhor manejo dos cultivos espalhados pelo Brasil. O presente trabalho aborda a utilização da adubação fosfatada na cultura da soja (FTS 4188) em diferentes dosagens, com o objetivo de avaliar a relação entre as doses aplicadas e a produtividade de grãos. Dessa forma o experimento foi realizado em blocos ao acaso, onde foram utilizados cinco tratamentos com diferentes dosagens de P2O5 sendo: 0 kg.ha-1 (Testemunha T1); 30 kg.ha-1 (T2); 60 kg.ha-1 (T3); 90 kg.ha-1 (T4) e 120 kg.ha-1 (T5) com quatro repetições. O experimento foi conduzido em Latossolo Amarelo e as dimensões das parcelas estudadas foram de 2,7 x 6,0 m. Uma vez verificada a produtividade de cada tratamento constatou-se que as médias dos dados não apresentaram diferença estatística significativa, sugerindo que em solos argilosos com altas concentrações de fósforo não existe a necessidade de adubaçã

Long-term follow-up of gliomas treated with fractionated stereotactic irradiation

Eighteen patients have been treated for gliomas with fractionated stereotactic linear accelerator (LINAC) irradiation. A plastic halo ring secured with skull pins allows daily attachment of the patient to the stereotactic frame mounted on the linear accelerator. The patients received 9-31 fractions of 1.8-3 Gy/fraction over periods of 20-49 days. Total doses delivered stereotactically where 16-60 Gy (90% isodose) delivered to 3-7 cm diameter tumors. The six patients with glioblastoma had a median survival of 16 months (range 7-60 months). The two patients with anaplastic astrocytoma survived 7 and 78 months. Most of the patients with high grade tumors also received other adjuant treatments. Of the ten patients with low grade gliomas, one expired 66 months after treatment, and the remainder are alive 22-82 months after treatment. One pediatric patient displayed evidence of focal radiation injury with visual loss. No patient developed initial recurrence of tumor outside the focally irradiated field. Stereotactic localization of irradiation protects surrounding brain tissue; fractionation improves the therapeutic ratio. These extended follow-up data indicate that stereotactic restriction of radiation fields in treatment of gliomas does not result in deterioration of survival results. Further investigation is warranted into the use of higher focal fractionated radiation doses to attempt to improve local control and survival

General cognitive principles for learning structure in time and space

How are hierarchically structured sequences of objects, events or actions learned from experience and represented in the brain? When several streams of regularities present themselves, which will be learned and which ignored? Can statistical regularities take effect on their own, or are additional factors such as behavioral outcomes expected to influence statistical learning? Answers to these questions are starting to emerge through a convergence of findings from naturalistic observations, behavioral experiments, neurobiological studies, and computational analyses and simulations. We propose that a small set of principles are at work in every situation that involves learning of structure from patterns of experience and outline a general framework that accounts for such learning

Long-Term Follow-up of Gliomas Treated with Fractionated Stereotactic Irradiation

Eighteen patients have been treated for gliomas with fractionated stereotactic linear accelerator (LINAC) irradiation. A plastic halo ring secured with skull pins allows daily attachment of the patient to the stereotactic frame mounted on the linear accelerator. The patients received 9–31 fractions of 1.8–3 Gy/fraction over periods of 20–49 days. Total doses delivered stereotactically where 16–60 Gy (90% isodose) delivered to 3–7 cm diameter tumors. The six patients with glioblastoma had a median survival of 16 months (range 7–60 months). The two patients with anaplastic astrocytoma survived 7 and 78 months. Most of the patients with high grade tumors also received other adjuant treatments. Of the ten patients with low grade gliomas, one expired 66 months after treatment, and the remainder are alive 22–82 months after treatment. One pediatric patient displayed evidence of focal radiation injury with visual loss. No patient developed initial recurrence of tumor outside the focally irradiated field. Stereotactic localization of irradiation protects surrounding brain tissue; fractionation improves the therapeutic ratio. These extended follow-up data indicate that stereotactic restriction of radiation fields in treatment of gliomas does not result in deterioration of survival results. Further investigation is warranted into the use of higher focal fractionated radiation doses to attempt to improve local control and survival