Failure modes observed on worn surfaces of W-C-Co sputtered coatings

During scratch testing, the indenter gives rise to a distribution of stresses similar to that observed in tribocontacts. In this work, rJ.- sputtered W-C-Co coatings deposited from sintered WC + Co (6,10 and 15 Wl.% Co) at various substrate biases were scratched and tested tribologically and the morphology of the damaged surfaces was analysed. The cobalt content of the coatings is the main factor determining their tribological characteristics. The failure modes observed on the worn pin-on-disc tested surfares are explained and compared with those obtained by scratch testing. In spite of it not being possible to establish quantitative results for the wear resistance ofW-C-Co coatings from scratch testing, an estimation can be performed based on the observation ofthe failure modes in the scratch track. Thus scratch testing can i:>eused to predict the tribological behaviour of coated surfaces. This possibility can reduce the number and cost of tribological tests

Strategies for recommendation of common bean lines tested for value of cultivation and use in different environments.

The purpose of this study was to develop strategies for the recommendation of common bean cultivars tested in VCU trials with regard to the performance of lines with different growth habits, at different fertilizer rates and sowing densities. It was found that the grain yield of lines is more affected by variations in fertilizer rates than of the sowing density; the response of the lines to higher planting density and fertilizer rate varies with the environment of evaluation and does not depend on the growth habit, the interactions between fertilizer rates and sowing densities were significant, demonstrating the importance of VCU trials with different fertilizer rates and sowing densities

Molecular Dynamics Simulation of HIV Fusion Inhibitor T-1249: Insights on Peptide-Lipid Interaction

T-1249 is a peptide that inhibits the fusion of HIV envelope with the target cell membrane. Recent results indicate that T-1249, as in the case of related inhibitor peptide T-20 (enfuvirtide), interacts with membranes, more extensively in the bilayer liquid disordered phase than in the liquid ordered state, which could be linked to its effectiveness. Extensive molecular dynamics simulations (100 ns) were carried out to investigate the interaction between T-1249 and bilayers of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and POPC/cholesterol (1 : 1). It was observed that T-1249 interacts to different extents with both membrane systems and that peptide interaction with the bilayer surface has a local effect on membrane structure. Formation of hydrogen bonding between certain peptide residues and several acceptor and donor groups in the bilayer molecules was observed. T-1249 showed higher extent of interaction with bilayers when compared to T-20. This is most notable in POPC/Chol membranes, owing to more peptide residues acting as H bond donors and acceptors between the peptide and the bilayer lipids, including H-bonds formed with cholesterol. This behavior is at variance with that of T-20, which forms no H bonds with cholesterol. This higher ability to interact with membranes is probably correlated with its higher inhibitory efficiency

Accessing Nuclear Structure for Field Emission, in Lens, Scanning Electron Microscopy (FEISEM)

Scanning electron microscopy (SEM) has had a shorter time course in biology than conventional transmission electron microscopy (TEM) but has nevertheless produced a wealth of images that have significantly complemented our perception of biological structure and function from TEM information. By its nature, SEM is a surface imaging technology, and its impact at the subcellular level has been restricted by the considerably reduced resolution in conventional SEM in comparison to TEM. This restriction has been removed by the recent advent of high-brightness sources used in lensfield emission instruments (FEISEM) which have produced resolution of around 1 nanometre, which is not usually a limiting figure for biological material. This communication reviews our findings in the use of FEISEM in the imaging of nuclear surfaces, then associated structures, such as nuclear pore complexes, and the relationships of these structures with cytoplasmic and nucleoplasmic elements. High resolution SEM allows the structurally orientated cell biologist to visualise, directly and in three dimensions, subcellular structure and its modulation with a view to understanding its functional significance. Clearly, intracellular surfaces require separation from surrounding structural elements in vivo to allow surface imaging, and we review a combination of biochemical and mechanical isolation methods for nuclear surfaces

The Transcriptionally Permissive Chromatin State of Embryonic Stem Cells Is Acutely Tuned to Translational Output

A permissive chromatin environment coupled to hypertranscription drives the rapid proliferation of embryonic stem cells (ESCs) and peri-implantation embryos. We carried out a genome-wide screen to systematically dissect the regulation of the euchromatic state of ESCs. The results revealed that cellular growth pathways, most prominently translation, perpetuate the euchromatic state and hypertranscription of ESCs. Acute inhibition of translation rapidly depletes euchromatic marks in mouse ESCs and blastocysts, concurrent with delocalization of RNA polymerase II and reduction in nascent transcription. Translation inhibition promotes rewiring of chromatin accessibility, which decreases at a subset of active developmental enhancers and increases at histone genes and transposable elements. Proteome-scale analyses revealed that several euchromatin regulators are unstable proteins and continuously depend on a high translational output. We propose that this mechanistic interdependence of euchromatin, transcription, and translation sets the pace of proliferation at peri-implantation and may be employed by other stem/progenitor cells

Role of a Transbilayer pH Gradient in the Membrane Fusion Activity of the Influenza Virus Hemagglutinin: Use of the R18 Assay to Monitor Membrane Merging

It had been suggested that influenza virus-mediated membrane fusion might be dependent on a pH gradient across a target membrane. We have designed experiments in which this issue could be addressed. Two populations of liposomes were prepared, both simulating the plasma membrane of target cells, but with the pH of the internal aqueous medium buffered either at pH 7.4 (physiological cytosol pH) or at pH 5.0 (endosomal pH at which influenza virus displays maximal fusion activity). By monitoring fusion using the R18 assay, we found that the internal pH of the target liposomes did not influence membrane merging as mediated by the influenza virus hemagglutinin, thus demonstrating that a transmembrane pH gradient is not required in this fusion process

Avaliação de propriedades estruturais de membranas lipídicas após substituição do colesterol por análogos fluorescentes

A espectroscopia e a microscopia de fluorescência têm sido usadas em biofísica de membranas há décadas. Como a unidade estrutural básica das membranas biológicas é a bicamada de lípidos e estes não fluorescem, o uso de sondas extrínsecas de membrana é uma necessidade. Contudo, duas questões preocupantes se levantam quanto ao uso de sondas extrínsecas de fluorescência em estudos de membranas. Em primeiro lugar, o comportamento das moléculas de sonda na bicamada (que região da bicamada elas reportam, as suas dinâmicas translacional e rotacional) é frequentemente mal conhecido. Em segundo lugar, na interpretação de resultados de experiências de fluorescência, pode ser difícil distinguir entre propriedades legítimas da membrana e efeitos de perturbação resultantes da incorporação da sonda. Para este efeito, as simulações por dinâmica molecular (MD), ao providenciarem informação detalhada à escala atómica, representam um meio valioso para caracterizar a localização e dinâmica de sondas na bicamada, assim como a magnitude de perturbação que elas induzem na estrutura lipídica [1]. Neste contexto, optimizaram-se, com recurso ao programa Firefly, as estruturas do colesterol e de dois análogos fluorescentes (desidroergoesterol e colestatrienol) ao nível de teoria DFT/R-B3LYP/6-31G(d) e submeteram-se em seguida ao servidor de topologias ATB, inscrevendo simultaneamente as cargas parciais calculadas na topologia molecular. Estas topologias foram utilizadas na construção de modelos de membranas lipídicas constituídas por POPC, colesterol e uma das sondas fluorescentes acima identificadas. Os modelos assim obtidos foram hidratados e sujeitos a simulações de MD, donde se calculou a área por lípido, a espessura e densidade da bicamada, os coeficientes de difusão lateral para as espécies presentes e os parâmetros de ordem das cadeias acilo. As simulações foram efectuadas em ensemble NPT através do pacote de software GROMACS. Análises preliminares permitiram a comparação dos comportamentos na bicamada dos esteróis fluorescentes com o do colesterol, informação vital para validar o uso dos primeiros como análogos fluorescentes do segundo. REFERÊNCIAS [1] Loura, L.M.S.; Prates Ramalho, J.P. Biophys. Rev. 1 (2009), 141

Electromagnetic form factors of the Delta with D-waves

The electromagnetic form factors of the Delta baryon are evaluated within the framework of a covariant spectator quark model, where S and D-states are included in the $\Delta$ wave function. We predict all the four Delta multipole form factors: the electric charge GE0, the magnetic dipole GM1, the electric quadrupole GE2 and the magnetic octupole GM3. We compare our predictions with other theoretical calculations. Our results are compatible with the available experimental data and recent lattice QCD data.Comment: Accepted for publication in PRD. Version with typographic and orthographic corrections. 30 pages, 11 figure

Qualidade industrial da população de terras altas Primavera x Douradão em Porangatu.

O objetivo deste trabalho foi avaliar a qualidade industrial de famílias provenientes do cruzamento entre as cultivares de arroz de terras altas BRS Primavera e Douradão, conduzido em Porangatu ? GO, em delineamento látice 12 x 19 (repetições) sob irrigação em 2011.Pôster - graduação