A molecular dynamics framework to explore the structure and dynamics of layered double hydroxides

It is presented a straightforward procedure based on the CLAYFF force field to perform molecular dynamics (MD) computer simulations with the GROMACS open source package of layered double hydroxide (LDH) materials with different intercalated anions. This procedure enables running very long simulations of systems where all atomic positions are allowed to move freely, while maintaining the integrity of the LDH structure intact. Therefore, it has the potential to model different important applications of LDH involving ion-exchange and interlayer equilibrium processes in diverse areas as drug delivery, water purification, and corrosion protection. The magnesium-aluminium based LDH with a metallic ratio 2:1 (Mg2Al) was chosen to validate our computer simulation framework, because of the comprehensive experimental and computational studies reported in the literature devoted to the understanding of the structure of Mg2Al LDH. Potential parameters from the literature were used to model the Mg2Al LDH with different intercalated anions using a new set of atomic point charges calculated with the DDEC6 formalism. Once the model was validated through careful comparisons of the simulated and experimental structures, the procedure was adapted to the Zn2Al LDH materials. Lennard-Jones parameters had to be developed for zinc (II) cations and calibrated using the experimental structural data found in the literature for Zn2Al LDH and the height of the galleries determined experimentally in this work for Zn2Al with intercalated nitrate anions. The consistency of the model is proved by carrying out MD simulations to reproduce in the computer the typical experimental conditions in which the Zn2Al LDH is immersed in a sodium chloride water solution to act as a nanotrap for aggressive anions in corrosion protection applications. The LDH structure is maintained in the MD simulation in which the LDH is free to move alongside the solution and allowing a natural anion exchange between the LDH and the solution as well as dehydration/hydration of the basal space.publishe

Vibrational energy transfer in N(2D)+N2 collisions: a quasiclassical trajectory study

Rate coefficients for the N(2D)+N2 collisions were calculated employing quasiclassical trajectories and the first available set of potential energy surfaces for such excited nitrogen interactions. The details of the vibrational energy transfer are discussed, such as the contributions from reactive and non-reactive trajectories as well as the contribution of each electronic symmetry. The calculated state-to-state and state-to-all rate coefficients show that deactivation is far more probable than excitation, and multi-quanta deactivation play an important role

Entanglement measure for general pure multipartite quantum states

We propose an explicit formula for an entanglement measure of pure multipartite quantum states, then study a general pure tripartite state in detail, and at end we give some simple but illustrative examples on four-qubits and m-qubits states.Comment: 5 page

Caracterização biométrica e físico-química dos frutos de acessos de manga 'Ubá'.

Este trabalho teve como objetivo avaliar a dissimilaridade genética de acessos de manga ?Ubá? na região leste de Minas Gerais, por meio da caracterização biométrica e físico-química dos frutos, visando a identificar materiais de interesse industrial para futuros trabalhos de melhoramento. Frutos de 67 acessos de mangueira Ubá provenientes do leste de Minas Gerais foram caracterizados, avaliando-se: massa da fruta, massa do endocarpo, relação polpa/endocarpo, diâmetro longitudinal, diâmetro transversal, sólidos solúveis totais, acidez total titulável, relação sólidos solúveis total/acidez total titulável e pH. Os resultados foram avaliados por estatística descritiva, utilizando-se de medida de tendência central (média) e de variabilidade de dados (desvio-padrão). Foram realizadas análises estatísticas, utilizando-se das técnicas de agrupamento e medidas de dissimilaridade. Os frutos que apresentaram melhores características para o processamento foram os provenientes dos acessos 10; 22; 23; 24; 35; 38; 40; 42; 52; 55 e 63. A análise de agrupamento mostrou a formação de dois grupos de acessos com base nas características biométricas e físico-químicas dos frutos, o que demonstra variabilidade genética em mangueiras Ubá, no leste de Minas Gerais

Elucidating structure–property relationships in aluminum alloy corrosion inhibitors by machine learning

Organic corrosion inhibitors are playing a crucial role to substitute traditional protective technologies, which have acute toxicity problems associated. However, why some organic compounds inhibit corrosion and others do not, is still not well understood. Therefore, we tested different machine learning (ML) methods to distinguish efficient corrosion inhibitors for aluminum alloys commonly used in aeronautical applications. In this work, we have obtained information that can greatly contribute to automate the search for new and more efficient protective solutions in the future: i) a ML algorithm was selected that is able to classify correctly efficient inhibitors (i.e., with more than 50 % efficiency) and non-inhibitors (i.e. with lower-equal than 50 % efficiency), even when information about different alloys at different pHs is included in the same dataset, which can significantly increase the information available to train the model; ii) new descriptors related to the self-association of the molecules were evaluated, but improvements to the predictive power of the models are limited; iii) average differences concerning the descriptors in this work were identified for inhibitors and non-inhibitors, having the potential to serve as guidelines to select potentially inhibitive molecular systems. This work demonstrates that ML can significantly accelerate research in the field by serving as a tool to perform an initial virtual screen of the molecules.publishe

Diferenças entre adubação sulfurada e calda sulfocálcica nos níveis de dissulfeto de carbono em mamão.

Abakerli et al. (2003), demonstraram que o mamão pode gerar CS2 sob as condições de análise de resíduos de etilenobis(ditiocarbamatos) conduzindo a erros de interpretação quanto ao uso desse fungicida. Nas brássicas a fonte provável de CS2 é a existência do sistema glicosinolato/mirosinase, que desempenha um papel importante no sistema de defesa das plantas contra microrganismos e insetos, por meio dos seus produtos de hidrólise (Bones, 2005). Outra função desse sistema é a remobilização do enxofre presente no glicosinolato, como sulfato, pois durante estresse de S, ocorre um aumento da atividade da mirosinase. Os glicosinolatos contêm uma proporção significativa de S e de N e, portanto, pode-se esperar que os fertilizantes influenciem as concentrações dos mesmos nas brássicas. Neste trabalho visou-se verificar a influência de dois tratamentos com agroquímicos sulfurados nos níveis de CS2 em mamão, calda sulfocálcica e sulfato de amônio

Electric field inversion asymmetry: Rashba and Stark effects for holes in resonant tunneling devices

We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeeman effect, produced by a combination of the Rashba spin-orbit interaction, Stark shift and charge screening. The electric-field-induced modulation of the spin-splitting are studied during the charging and discharging processes of p-type GaAs/AlAs double barrier resonant tunneling diodes (RTD) under applied bias and magnetic field. The abrupt changes in the photoluminescence, with the applied bias, provide information of the charge accumulation effects on the device.Comment: 4 pages, 2 figure