ABSTRACT
We have systematically studied the single-particle states in quantum rings produced by a set of concentric circular gates over a graphene sheet placed on a substrate. The resulting potential profiles and the interaction between the graphene layer and the substrate are considered within the Dirac Hamiltonian in the framework of the envelope function approximation. Our simulations allow microscopic mapping of the character of the electron and hole quasi-particle solutions according to the applied voltage. General conditions to control and operate the bound state solutions are described as functions of external and controllable parameters that will determine the optical properties ranging from metallic to semiconductor phases. Contrasting behaviors are obtained when comparing the results for repulsive and attractive voltages as well as for variation of the relative strength of the graphene-substrate coupling parameter.
Subject(s)
Graphite/chemistry , Graphite/radiation effects , Models, Chemical , Models, Molecular , Nanostructures/chemistry , Nanostructures/ultrastructure , Computer Simulation , Electromagnetic Fields , Macromolecular Substances/chemistry , Macromolecular Substances/radiation effects , Materials Testing , Molecular Conformation/radiation effects , Nanostructures/radiation effects , Particle Size , Surface Properties/radiation effectsABSTRACT
We examine the morphological and chemical changes in the pulp chamber dentin after using endodontic agents by scanning electron microscopy (SEM), Fourier transform Raman spectroscopy (FT-Raman), and micro energy-dispersive x-ray fluorescence spectrometry (µEDXRF). Thirty teeth were sectioned exposing the pulp chamber and divided by six groups (n=5): NT-no treatment; CHX-2% chlorhexidine; CHXE-2% chlorhexidine+17% EDTA; E-17% EDTA; SH5-5.25% NaOCl; SH5E-5.25% NaOCl+17% EDTA. The inorganic and organic content was analyzed by FT-Raman. µEDXRF examined calcium (Ca) and phosphorus (P) content as well as Ca/P ratio. Impressions of specimens were evaluated by SEM. Data were submitted to Kruskal-Wallis and Dunn tests (p<0.05). Differences were observed among groups for the 960 cm(-1) peak. Ca and P content differences were significant (SH5>NT=SH5E>CHX>E>CHXE). CHXE and E presented the highest Ca/P ratio values compared to the other groups (p<0.05). The SEM images in the EDTA-treated groups had the highest number of open tubules. Erosion in the tubules was observed in CHX and SH5E groups. Endodontic agents change the inorganic and organic content of pulp chamber dentin. NaOCl used alone, or in association with EDTA, was the most effective agent considering chemical and morphological approaches.
Subject(s)
Dentin/chemistry , Dentin/ultrastructure , Microscopy, Electron, Scanning , Mouthwashes/pharmacology , Root Canal Irrigants/pharmacology , Spectrometry, X-Ray Emission , Spectroscopy, Fourier Transform Infrared , Dentin/drug effects , Humans , Materials Testing , Molecular Conformation/radiation effectsABSTRACT
A nematic liquid crystal with high, positive dielectric anisotropy (5CB) has been studied under the influence of the combined action of a dc and an ac electric field. Broad frequency, voltage, and cell thickness ranges were considered. Pattern morphologies were identified; the thresholds and critical wave numbers were measured and analyzed as a function of frequency, dc-to-ac voltage ratio, and thickness. The current-voltage characteristics were simultaneously detected.
Subject(s)
Liquid Crystals/chemistry , Liquid Crystals/radiation effects , Models, Chemical , Models, Molecular , Molecular Conformation/radiation effects , Computer Simulation , Electromagnetic Fields , RefractometryABSTRACT
This paper describes the development of ZnO nanoparticles by a chemical method, to test them in the photocatalysis of the degradation of textile dyes, using Rhodamine B (RhB) as a probe reaction. The samples were submitted to different heat treatments in order to observe the annealing effects on the photocatalytical properties, surface decontamination and the consequent particle change, in terms of crystallinity. The as-prepared samples (ZOA) correspond to a metastable phase (oxy or hydroxy zinc acetate) and post annealing leads to ZnO crystallization. In spite of the XRD patterns showing only the ZnO phase for heat treatment at 100 degrees C, FTIR data show that carboxylate groups remains attached to the ZnO surface up to 300 degrees C. Up to 300 degrees C the presence of these carboxylate groups, provided by the synthesis method, showed to be more relevant to photoactivity than the specific surface area. At higher temperatures, crystallinity becomes the dominant factor and an increasing of crystallinity favors the photoactivity.
Subject(s)
Crystallization/methods , Nanostructures/chemistry , Nanostructures/ultrastructure , Zinc Oxide/chemistry , Zinc Oxide/radiation effects , Catalysis , Hardness , Hot Temperature , Light , Materials Testing , Molecular Conformation/radiation effects , Nanostructures/radiation effects , Particle Size , Surface Properties/radiation effectsABSTRACT
Raman scattering is used to study the effect of low energy (90 eV) Ar(+) ion bombardment in graphene samples as a function of the number of layers N. The evolution of the intensity ratio between the G band (1585 cm(-1)) and the disorder-induced D band (1345 cm(-1)) with ion fluence is determined for mono-, bi-, tri- and â¼50-layer graphene samples, providing a spectroscopy-based method to study the penetration of these low energy Ar(+) ions in AB Bernal stacked graphite, and how they affect the graphene sheets. The results clearly depend on the number of layers. We also analyze the evolution of the overall integrated Raman intensity and the integrated intensity for disorder-induced versus Raman-allowed peaks.
Subject(s)
Graphite/chemistry , Graphite/radiation effects , Models, Chemical , Nanostructures/chemistry , Nanostructures/radiation effects , Spectrum Analysis, Raman/methods , Computer Simulation , Heavy Ions , Macromolecular Substances/chemistry , Macromolecular Substances/radiation effects , Materials Testing , Molecular Conformation/radiation effects , Nanostructures/ultrastructure , Particle Size , Radiation Dosage , Surface Properties/radiation effectsABSTRACT
Os autores fizeram algumas revisões sobre informações básicas de algumas questões da química orgânica como a isomeria e mais especificamente a isomeria espacial ou estereoisomeria, no sentido de esclarecer os conceitos de quiralidade, enantiômeros e mistura racêmica. Além disso, descrevem o desenvolvimento de um novo antidepressivo, S-Citalopram usando um único enantiômero, que resultou em um aumento da potência, início mais rápido de ação e diminuição dos efeitos colaterais quando comparado com mistura racêmica.
Subject(s)
Antidepressive Agents , Molecular Conformation/radiation effects , IsomerismABSTRACT
La erradicación de los insectos vectores Trypanosornci cruzt (agente etiológico del mal de Chagas) ha causado cambios inesperados en el comportamiento poblacional de éstos, reemplazando los vectores primarios por otros secundarios, como Triatoma sordida y T. guasayana (en Bolivia). Estos vectores han mostrado una alta capacidad de adaptación al hábitat humano. Por eso es importante identificar y estudiar la dinámica de poblaciones de estos insectos, sobre la base de marcadores de especie, una de las herramientas moleculares para este efecto propuesta en este trabajo es el RAPD. A partir de ADN extraido de especimenes de Triatoma guasayana, 7'. sordida Ql. T. sordida G2 y T. infestans, clasificadas anteriormente por isoenzimas; se amplificó fragmentos con 10 cebadores decaméricos del MT A (OPERON), 9 de los 10 cebadores utilizados presentaron perfiles RAPD, obteniéndose 170 perfiles de 1 a 8 fragmentos. Se pudo evidenciar la existencia de dos marcadores RAPD específicos: (1) un fragmento de 995 pb con el cebador OPAO1 para 7'. sordida G2, (2) un fragmento de 986 pb con el cebador OPAO2 para 7' sordida Gi