17,558 research outputs found
Phases of granular segregation in a binary mixture
We present results from an extensive experimental investigation into granular
segregation of a shallow binary mixture in which particles are driven by
frictional interactions with the surface of a vibrating horizontal tray. Three
distinct phases of the mixture are established viz; binary gas (unsegregated),
segregation liquid and segregation crystal. Their ranges of existence are
mapped out as a function of the system's primary control parameters using a
number of measures based on Voronoi tessellation. We study the associated
transitions and show that segregation can be suppressed is the total filling
fraction of the granular layer, , is decreased below a critical value,
, or if the dimensionless acceleration of the driving, , is
increased above a value .Comment: 12 pages, 12 figures, submitted to Phys. Rev.
Broad Iron Emission from Gravitationally Lensed Quasars Observed by Chandra
Recent work has demonstrated the potential of gravitationally lensed quasars
to extend measurements of black hole spin out to high-redshift with the current
generation of X-ray observatories. Here we present an analysis of a large
sample of 27 lensed quasars in the redshift range 1.0<z<4.5 observed with
Chandra, utilizing over 1.6 Ms of total observing time, focusing on the
rest-frame iron K emission from these sources. Although the X-ray
signal-to-noise (S/N) currently available does not permit the detection of iron
emission from the inner accretion disk in individual cases in our sample, we
find significant structure in the stacked residuals. In addition to the narrow
core, seen almost ubiquitously in local AGN, we find evidence for an additional
underlying broad component from the inner accretion disk, with a clear red wing
to the emission profile. Based on simulations, we find the detection of this
broader component to be significant at greater than the 3-sigma level. This
implies that iron emission from the inner disk is relatively common in the
population of lensed quasars, and in turn further demonstrates that, with
additional observations, this population represents an opportunity to
significantly extend the sample of AGN spin measurements out to high-redshift.Comment: 5 pages, 2 figures, accepted for publication in Ap
Crossover in the scaling of island size and capture zone distributions
Simulations of irreversible growth of extended (fractal and square) islands
with critical island sizes i=1 and 2 are performed in broad ranges of coverage
\theta and diffusion-to-deposition ratios R in order to investigate scaling of
island size and capture zone area distributions (ISD, CZD). Large \theta and
small R lead to a crossover from the CZD predicted by the theory of Pimpinelli
and Einstein (PE), with Gaussian right tail, to CZD with simple exponential
decays. The corresponding ISD also cross over from Gaussian or faster decays to
simple exponential ones. For fractal islands, these features are explained by
changes in the island growth kinetics, from a competition for capture of
diffusing adatoms (PE scaling) to aggregation of adatoms with effectively
irrelevant diffusion, which is characteristic of random sequential adsorption
(RSA) without surface diffusion. This interpretation is confirmed by studying
the crossover with similar CZ areas (of order 100 sites) in a model with
freezing of diffusing adatoms that corresponds to i=0. For square islands,
deviations from PE predictions appear for coverages near \theta=0.2 and are
mainly related to island coalescence. Our results show that the range of
applicability of the PE theory is narrow, thus observing the predicted Gaussian
tail of CZD may be difficult in real systems.Comment: 9 pages, 7 figure
Interfollicular epidermal stem cells: boosting and rescuing from adult skin
Publicado na série "Methods in Molecular Biology", vol. 989 (2013), ISSN 1064-3745Epidermal stem cells isolation struggle remains, mainly due to the yet essential requirement of well-defined approaches and markers. The herein proposed methodology integrates an assemblage of strategies to
accomplish the enrichment of the interfollicular epidermal stem cells multipotent fraction and their subsequent
separation from the remaining primary human keratinocytes culture. Those include rapid adherence
of freshly isolated human keratinocytes to collagen type IV through the β 1-integrin ligand and Rho-
Associated Protein Kinase Inhibitor Y- 27632 administration to the cultures, followed by an immunomagnetic
separation to obtain populations based in the combined CD49f bri /CD71 dim expression. Flow
cytometry is the supporting method to analyze the effect of the treatments over the expression rate of early
epidermal markers keratins19/5/14 and in correlation to CD49f bri /CD71 dim subpopulations. The stepby-
step methodology herein described indulges the boosting and consecutive puri fi cation and separation
of interfollicular epidermal stem cells from human keratinocytes cultures.(undefined
Thromboembolic Complications During Endovascular Treatment of Ruptured Intracranial Aneurysms - Prevention and Therapy
As complicações tromboembólicas são as mais frequentemente reportadas durante a terapêutica endovascular de aneurismas intracranianos com espiras metálicas. A frequência deste tipo de complicação varia na literatura, contudo autores referem uma incidência entre 2,5 e 28%.
Diversos mecanismos poderão estar envolvidos na formação e migração do trombo: pode ser já preexistente no interior do aneurisma
a tratar e deslocar-se para o vaso portador; pode formar-se de novo na superfície das espiras ou dos cateteres utilizados; ou ainda no eventual colo residual se o grau de oclusão não for completo. Estudos demonstraram maior incidência de complicações tromboembólicas em aneurismas de colo largo.
Neste trabalho discutimos a importância e justificação de medidas utilizadas na prevenção de complicações tromboembólicas durante e após a terapêutica endovascular de aneurismas rotos intra-cranianos. Referem-se ainda as opções e estratégias a adoptar na eventualidade de uma oclusão vascular ser detectada durante o procedimento, como a administração de inibidores da glicoproteina IIb/IIIa ou mesmo a libertação de stents intra-cranianos. Diversos casos exemplificativos são exibidos.
A prevenção de complicações tromboembólicas e a rápida actuação perante a oclusão vascular são essenciais para a melhoria do
prognóstico dos doentes submetidos a terapêutica endovascular de aneurismas rotos. O conhecimento profundo das opções disponíveis é essencial para a persecução desse objectivo
Modified electrodes for electrochemical reduction of carbon dioxide
The efforts to constrain greenhouse gas emissions and concerns over security of fossil fuels have led to increased attention for renewable energy for the past decade. Renewable energy is one of the key solutions to the actual energy challenges. Omnidea in collaboration with Research Institutes is developing a technology based upon a regenerative energy storage cycle that could be a contribution to a low-carbon energy future. In this cycle the recharge system, which is composed of an electrochemical cell, converts CO2 into fuel (hydrocarbons and hydrogen) using an external source of power (e.g. solar power). The discharge system produces electric energy when hydrocarbons and oxygen from the recharge system are directly supplied to a Solid Oxide Fuel Cell (SOFC). Currently state of the art systems for direct electrochemical reduction of CO2 exhibit low current densities and or low Faradaic efficiencies. Thus considerable research activity is still needed to develop electrodes with a performance suitable for an industrial application. This paper describes the progress to date and the work carried out with the aim of achieving this goal. It addresses particularly the modification of electrodes for electrochemical conversion of CO2 and reports voltammetric studies as a tool for screening and optimizing electrodes for CO2 conversio
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