Optical conductivity study of screening of many-body effects in graphene interfaces

Theoretical studies have shown that electron-electron (e-e) and electron-hole (e-h) interactions play important roles in many observed quantum properties of graphene making this an ideal system to study many body effects. In this report we show that spectroscopic ellipsometry can enable us to measure this interactions quantitatively. We present spectroscopic data in two extreme systems of graphene on quartz (GOQ), an insulator, and graphene on copper (GOC), a metal which show that for GOQ, both e-e and e-h interactions dominate while for GOC e-h interactions are screened. The data further enables the estimation of the strength of the many body interaction through the effective fine structure constant, $\alpha_{g}^{*}$. The $\alpha_{g}^{*}$ for GOQ indicates a strong correlation with an almost energy independent value of about 1.37. In contrast, $\alpha_{g}^{*}$ value of GOC is photon energy dependent, is almost two orders of magnitude lower at low energies indicating very weak correlation.Comment: Main Article (4 pages, 4 figures); Supporting Online Material (12 pages, 9 figures

Depth dependent local structures in thin films unraveled by grazing incidence x-ray absorption spectroscopy

A method of using X-ray absorption spectroscopy (XAS) together with resolved grazing incidence geometry for depth profiling atomic, electronic, chemical or magnetic local structures in thin films is presented. The quantitative deconvolution of thickness-dependent spectral features is performed by fully considering both scattering and absorption formalisms. Surface oxidation and local structural depth profiles in nanometric FePt films are determined, exemplifying the application of the method.Comment: 5 pages, 3 figure

Petrografia e química mineral do Stock Granítico Serra do Barriga (Sobral, CE, nordeste do Brasil)

The Serra do Barriga Granitic Stock (SGSB), located at NNW of the Ceará, northeast of Brazil, presents faciological variation that permits commercial exploitation in four types of ornamental rocks: Rosa Iracema (RI), Rosa Olinda (RO), Branco Savana (BS) and White Crystal Quartz (BCQ). The aim of this paper is to investigate mineral association, chemical composition and classification of the main minerals phases, as well as genetic relationships among the granitic facies. Petrographic analyzes were made using thin section and analyzes of mineral chemistry through electron microprobe. Petrographic and mineral chemistry analyzes show that SBGS lithotypes varies from inequigranular to porphyritic syenogranites and monzogranites and different facies do not show significant differences in mineral composition, except for small variations of Or amount in K-feldspar. Potassium feldspar is orthoclase and plagioclase ranges from albite to oligoclase (Ab-Or- to Ab-Or). Biotite corresponds to annita to siderophyllite, while amphibole corresponds to iron-edenite. Post-magmatic or hydrothermal mineral transformations such as exsolution, potassification, albitization, chloritization, sericitization and neoformation of fluorite are common and control discoloration from the pink to the white facies (BS and BCQ). In the plagioclase of the white granites frequent sericitization occurs superimposed to the microclinization, with neoformation of fluorite. The whole data converge to the knowledge that all the facies were formed at the same magmatic event, being the syenogranites (RI, RO and BCQ) originated by an unique magma, followed by a new, more mafic magmatic pulse, represented by porphyritic monzogranite (RO).O Stock Granítico Serra do Barriga (SGSB), localizado a NNW do Ceará, nordeste do Brasil, apresenta variação faciológica que permite exploração comercial em quatro tipos de rochas ornamentais: Rosa Iracema (RI), Rosa Olinda (RO), Branco Savana (BS) e Branco Cristal Quartzo (BCQ). O objetivo deste trabalho é determinar a paragênese, a composição química e a classificação dos principais minerais, além das relações genéticas entre as fácies graníticas. Foram realizadas análises petrográficas, utilizando-se lâminas delgadas e análises de química mineral através de microssonda eletrônica. As análises petrográfica e de química mineral mostram que o SGSB varia de sienogranitos e monzogranitos inequigranulares a porfiríticos e não ocorrem diferenças significativas nas composições dos minerais entre as fácies, exceto ligeiras variações no teor de Or nos KF. O feldspato potássico é ortoclásio, o plagioclásio mostra transição de albita para oligoclásio. A biotita corresponde a annita com tendência a siderofilita, enquanto o anfibólio corresponde a ferro-edenita. As transformações minerais pós-magmáticas ou hidrotermais como exsolução, potassificação, albitização, cloritização, sericitização e neoformação de fluorita são comuns no SGSB e contribuem na “descoloração” das fácies rosas para as brancas. No plagioclásio dos granitos brancos ocorre frequente sericitização sobreposta à microclinização, com neoformação de fluorita. Todos os dados convergem para a ideia de que as fácies foram formadas por um mesmo evento magmático, sendo que os sienogranitos (RI, RO e BCQ) correspondem à faciologias originadas por um mesmo magma, seguido por um novo pulso magmático mais máfico, representado pelo monzogranito porfirítico (RO)

The angiotensin II AT(1), receptor structure-activity correlations in the light of rhodopsin structure

The most prevalent physiological effects of ANG II, the main product of the renin-angiotensin system, are mediated by the AT(1) receptor, a rhodopsin-like AGPCR. Numerous studies of the cardiovascular effects of synthetic peptide analogs allowed a detailed mapping of ANG II's structural requirements for receptor binding and activation, which were complemented by site-directed mutagenesis studies on the AT(1) receptor to investigate the role of its structure in ligand binding, signal transduction, phosphorylation, binding to arrestins, internalization, desensitization, tachyphylaxis, and other properties. the knowledge of the high-resolution structure of rhodopsin allowed homology modeling of the AT(1) receptor. the models thus built and mutagenesis data indicate that physiological (agonist binding) or constitutive (mutated receptor) activation may involve different degrees of expansion of the receptor's central cavity. Residues in ANG II structure seem to control these conformational changes and to dictate the type of cytosolic event elicited during the activation. 1) Agonist aromatic residues (Phe(8) and Tyr(4)) favor the coupling to G protein, and 2) absence of these residues can favor a mechanism leading directly to receptor internalization via phosphorylation by specific kinases of the receptor's COOH-terminal Ser and Thr residues, arrestin binding, and clathrin-dependent coated-pit vesicles. On the other hand, the NH2-terminal residues of the agonists ANG II and [Sar(1)]-ANG II were found to bind by two distinct modes to the AT(1) receptor extracellular site flanked by the COOH-terminal segments of the EC-3 loop and the NH2-terminal domain. Since the [Sar(1)]-ligand is the most potent molecule to trigger tachyphylaxis in AT(1) receptors, it was suggested that its corresponding binding mode might be associated with this special condition of receptors.Universidade Federal de São Paulo, Escola Paulista Med, Dept Biophys, BR-04023062 São Paulo, BrazilUniv São Paulo, Ribeirao Preto Med Sch, Dept Biochem & Immunol, BR-14049 Ribeirao Preto, BrazilUniv São Paulo, Inst Chem, Dept Biochem, São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Biophys, BR-04023062 São Paulo, BrazilWeb of Scienc

Control of positive end-expiratory pressure (PEEP) for small animal ventilators

<p>Abstract</p> <p>Background</p> <p>The positive end-expiratory pressure (PEEP) for the mechanical ventilation of small animals is frequently obtained with water seals or by using ventilators developed for human use. An alternative mechanism is the use of an on-off expiratory valve closing at the moment when the alveolar pressure is equal to the target PEEP. In this paper, a novel PEEP controller (PEEP-new) and the PEEP system of a commercial small-animal ventilator, both based on switching an on-off valve, are evaluated.</p> <p>Methods</p> <p>The proposed PEEP controller is a discrete integrator monitoring the error between the target PEEP and the airways opening pressure prior to the onset of an inspiratory cycle. In vitro as well as in vivo experiments with rats were carried out and the PEEP accuracy, settling time and under/overshoot were considered as a measure of performance.</p> <p>Results</p> <p>The commercial PEEP controller did not pass the tests since it ignores the airways resistive pressure drop, resulting in a PEEP 5 cmH₂O greater than the target in most conditions. The PEEP-new presented steady-state errors smaller than 0.5 cmH₂O, with settling times below 10 s and under/overshoot smaller than 2 cmH₂O.</p> <p>Conclusion</p> <p>The PEEP-new presented acceptable performance, considering accuracy and temporal response. This novel PEEP generator may prove useful in many applications for small animal ventilators.</p

Response of root explants to in vitro cultivation of marketable garlic cultivars

Garlic cultivars are sexually sterile under standard growth conditions, with direct implications for commercial production costs as well as breeding programs. Garlic is propagated commercially via bulblets, which facilitates disease transmission and virus load accumulation over vegetative generations. Tissue culture produces virus-free clones that are more productive, while keeping the desired traits of the cultivar. Consequently, this technique allows studies of garlic genetics as well as guarantees genetic conservation of varieties. We aimed at analyzing the in vitroregeneration of eight marketable cultivars of garlic using root segments as explants. For each genotype, bulblet-derived explants were isolated and introduced into MS medium supplemented with 2,4-D and 2-iP. Calli were transferred to MS medium supplemented with 8.8 mM BAP and 0.1 mM NAA (regeneration medium A), or with 4.6 mM kinetin alone (regeneration medium B). The calli were then evaluated for regeneration frequency after sixty days of in vitro cultivation. The noble cultivar \u27Jonas\u27 presented the highest rates of plant regeneration among the cultivars tested. The medium A, which contained auxin and cytokinin, induced the highest regeneration rates of all cultivars. The process described herein is simple, reproducible and can potentially be used as a tool in molecular breeding strategies for other marketable cultivars and genotypes of garlic