Unit cell of graphene on Ru(0001): a 25 x 25 supercell with 1250 carbon atoms

The structure of a single layer of graphene on Ru(0001) has been studied using surface x-ray diffraction. A surprising superstructure has been determined, whereby 25 x 25 graphene unit cells lie on 23 x 23 unit cells of Ru. Each supercell contains 2 x 2 crystallographically inequivalent subcells caused by corrugation. Strong intensity oscillations in the superstructure rods demonstrate that the Ru substrate is also significantly corrugated down to several monolayers, and that the bonding between graphene and Ru is strong and cannot be caused by van der Waals bonds. Charge transfer from the Ru substrate to the graphene expands and weakens the C-C bonds, which helps accommodate the in-plane tensile stress. The elucidation of this superstructure provides important information in the potential application of graphene as a template for nanocluster arrays.Comment: 9 pages, 3 figures, paper submitted to peer reviewed journa

Characterization of nanometer-sized, mechanically exfoliated graphene on the H-passivated Si(100) surface using scanning tunnelling microscopy

We have developed a method for depositing graphene monolayers and bilayers with minimum lateral dimensions of 2-10 nm by the mechanical exfoliation of graphite onto the Si(100)-2x1:H surface. Room temperature, ultra-high vacuum (UHV) tunnelling spectroscopy measurements of nanometer-sized single-layer graphene reveal a size dependent energy gap ranging from 0.1-1 eV. Furthermore, the number of graphene layers can be directly determined from scanning tunnelling microscopy (STM) topographic contours. This atomistic study provides an experimental basis for probing the electronic structure of nanometer-sized graphene which can assist the development of graphene-based nanoelectronics.Comment: Accepted for publication in Nanotechnolog

Fontes florais usadas por abelhas (Hymenoptera, Apoidea) em área de cerrado no Município de Cassilândia, Mato Grosso do Sul, Brasil.

Conduziu-se este trabalho, com o objetivo de inventariar as plantas visitadas por abelhas em uma área de cerrado no município de Cassilândia/MS (19°06 48"S; 51°44 03"W), classificando-as para a elaboração de umcatálogo de pasto apícola. Os dados foram obtidos quinzenalmente, de março/2003 a fevereiro/2004, em uma trilha com 3000 metros de extensão. A flora apícola foi representada por 49 espécies pertencentes a 41 gêneros e 26 famílias. A família Malpighiaceae apresentou maior número de espécies visitadas (12,2%) e a família Sapindaceae o maior número de abelhas coletadas (18%). Com relação ao nicho trófico ocupado pelas abelhas, apenas Apis mellifera e Trigona spinipes apresentaram atividade de forrageamento em um grande número de plantas, sendo 36,7% do total de espécies identificadas visitados pelas duas espécies. Os diferentes períodos de florescimento das espécies vegetais existentes no cerrado garantem oferta de recurso alimentar durante todo o ano

Novel Cu(I)-5-nitropyridine-2-thiol Cluster with NIR Emission: Structural and Photophysical Characterization

A novel Cu(I) cluster compound has been synthesized by reacting CuI with the 2,2′-dithiobis(5-nitropyridine) ligand under solvothermal conditions. During the reaction, the original ligand breaks into the 5-nitropyridine-2-thiolate moiety, which acts as the coordinating ligand with both N- and S-sites, leading to a distorted octahedral Cu6S6 cluster. The structure has been determined by single-crystal X-ray diffraction and FT-IR analysis, and the photophysical properties have been determined in the solid state by means of steady-state and time-resolved optical techniques. The cluster presents a near-infrared emission showing an unusual temperature dependence: when passing from 77 to 298 K, a blue-shift of the emission band is observed, associated with a decrease in its intensity. Time-dependent-density functional theory calculations suggest that the observed behavior can be ascribed to a complex interplay of excited states, basically in the triplet manifold

Charge Transport Properties in CZT Detectors Grown by the Vertical Bridgman Technique

Great efforts are being presently devoted to the development of CdTe and CdZnTe detectors for a large variety of applications, such as medical, industrial, and space research. We present the spectroscopic properties of some CZT crystals grown by the standard vertical Bridgman method and by the boron oxide encapsulated vertical Bridgman method, which has been recently implemented at IMEM-CNR. By this technique the crystal is grown in an open quartz crucible fully encapsulated by a thin layer of liquid boron oxide. This technique prevent the crystal-crucible contact allowing larger single grains with lower dislocation density to be obtained. Several mono-electrode detectors were realized with two planar gold contacts. The samples are characterized by an active area of ≈4x4 mm2 or ≈7x7 mm2 and with thickness ranging from 1 to 2 mm. The charge transport properties of the detectors have been studied by mobility-lifetime (μτ) product measurements, carried out at the European Synchrotron Radiation Facility (Grenoble) in PTF configuration, where the impinging beam direction is orthogonal to the collecting electric field. We have performed several fine scans between the electrodes with a beam spot of 10x10 μm2 at different energies from 60 keV to 400 keV. In this work we present the test results in terms of μτ product of both charge carriers and an evaluation of the spectroscopic response uniformity across the sensitive volume of tested samples

Acute rejection features in dual kidney transplant recipients from elderly donors: comparison of calcineurin inhibitor-based and calcineurin inhibitor-free immunosuppressive protocols.

Features of acute rejection in dual kidney transplant have not been studied. The aim of this study is to compare acute rejections in dual kidney transplant recipients from elderly donors on different immunosuppressive protocols. Sixty-nine patients were evaluated: 28 received calcineurin inhibitor-based (group 1) and 41 received calcineurin inhibitor-free immunosuppression (group 2). Histology of all donor kidneys was evaluated before implantation. All rejections showed tubulitis in both groups, and were classified as T cell-mediated acute rejections. Incidence and Banff grade of rejections in the two groups were not significantly different. Late rejections however, were observed in group 1 ( P < 0.01) whereas steroid-resistant rejections occurred in group 2 ( P < 0.03). C4d deposition was only observed in group 2. Occurrence of acute rejection was significantly associated with graft loss due to interstitial fibrosis/tubular atrophy in both groups. In group 1 mean serum creatinine levels of patients with rejections at six months and one year were higher than those of patients without rejections ( P < 0.03 and P < 0.009, respectively). In group 2 they were higher at six months ( P < 0.01) but not at one year. In addition, graft loss due to interstitial fibrosis/tubular atrophy occurred in 3/28 patients in group 1 (10.7%, OR= 1.95, 95%CI 1.02–3.71), and in 1/41 patients in group 2 (2.4%, OR= 0.41, 95%CI 0.07–2.24). Taken together these results suggest better renal function in patients on calcineurin inhibitor-free immunosuppression. In conclusion, acute rejections were detrimental irrespective of the type of immunosuppression, but different features were observed with each therapy. A tailored approach should be advantageous for prevention and treatment of acute rejections

Giant Shape-Persistent Tetrahedral Porphyrin System: Light-Induced Charge Separation

Tetraphenylmethane appended with four pyridylpyridinium units works as a scaffold to self-assemble four ruthenium porphyrins in a tetrahedral shape-persistent giant architecture. The resulting supramolecular structure has been characterised in the solid state by X-ray single crystal analysis and in solution by various techniques. Multinuclear NMR spectroscopy confirms the 1 : 4 stoichiometry with the formation of a highly symmetric structure. The self-assembly process can be monitored by changes of the redox potentials, as well as by modifications in the visible absorption spectrum of the ruthenium porphyrin and by a complete quenching of both the bright fluorescence of the tetracationic scaffold and the weak phosphorescence of the ruthenium porphyrin. An ultrafast photoinduced electron transfer is responsible for this quenching process. The lifetime of the resulting charge separated state (800 ps) is about four times longer in the giant supramolecular structure compared to the model 1 : 1 complex formed by the ruthenium porphyrin and a single pyridylpyridinium unit. Electron delocalization over the tetrameric pyridinium structure is likely to be responsible for this effect

Caracterização físico-química de amostras de méis produzidas por Apis mellifera L. em fragmento de cerrado no município de Itirapina, São Paulo.

A fisionomia vegetal mais representativa do país, depois da floresta amazônica, é o cerrado, que ocupa atualmente dois milhões de km2 do território brasileiro. Este trabalho teve como objetivo determinar as características físicoquímicas de amostras de mel produzidas por Apis mellifera em um fragmento de cerrado, localizado em Itirapina, SP (22º14?S e 47º49?W). As amostras foram coletadas mensalmente, em cinco colméias, entre fevereiro e outubro de 2005 e as características avaliadas foram: açúcares redutores, redutores totais, sacarose, umidade, hidroximetilfurfural (HMF), cor, condutividade elétrica, pH, acidez, índice de formol, teor de cinzas, proteínas e viscosidade, além da análise polínica. Os resultados obtidos indicam que os limites estabelecidos pela legislação brasileira para parâmetros físico-químicos analisados são atendidos pela maioria das amostras de mel. Com relação à análise polínica, foi verificada a presença de Eucalyptus sp. como pólen dominante nos meses de fevereiro a julho e o de Citrus sp. no mês de outubro, em virtude da maior atratividade destes dois cultivos sobre as abelhas

A Flexible and Accurate Genotype Imputation Method for the Next Generation of Genome-Wide Association Studies

Genotype imputation methods are now being widely used in the analysis of genome-wide association studies. Most imputation analyses to date have used the HapMap as a reference dataset, but new reference panels (such as controls genotyped on multiple SNP chips and densely typed samples from the 1,000 Genomes Project) will soon allow a broader range of SNPs to be imputed with higher accuracy, thereby increasing power. We describe a genotype imputation method (IMPUTE version 2) that is designed to address the challenges presented by these new datasets. The main innovation of our approach is a flexible modelling framework that increases accuracy and combines information across multiple reference panels while remaining computationally feasible. We find that IMPUTE v2 attains higher accuracy than other methods when the HapMap provides the sole reference panel, but that the size of the panel constrains the improvements that can be made. We also find that imputation accuracy can be greatly enhanced by expanding the reference panel to contain thousands of chromosomes and that IMPUTE v2 outperforms other methods in this setting at both rare and common SNPs, with overall error rates that are 15%–20% lower than those of the closest competing method. One particularly challenging aspect of next-generation association studies is to integrate information across multiple reference panels genotyped on different sets of SNPs; we show that our approach to this problem has practical advantages over other suggested solutions