Spherically symmetric models: separating expansion from contraction in models with anisotropic pressures

We investigate spherically symmetric spacetimes with an anisotropic fluid and discuss the existence and stability of a dividing shell separating expanding and collapsing regions. We find that the dividing shell is defined by a relation between the pressure gradients, both isotropic and anisotropic, and the strength of the fields induced by the Misner-Sharpe mass inside the separating shell and by the pressure fluxes. This balance is a generalization of the Tolman-Oppenheimer- Volkoff equilibrium condition which defines a local equilibrium condition, but conveys also a non- local character given the definition of the Misner-Sharpe mass. We present a particular solution with dust and radiation that provides an illustration of our results.Comment: 4pp Towards New Paradigms: Proceeding Of The Spanish Relativity Meeting 2011. AIP Conference Proceedings, Volume 1458, pp. 487-490 (2012). Published in AIP Conf.Proc. 1458 (2011) 487-49

Liquid mixtures involving fluorinated alcohols: The equation of state (p, r, T, x) of (Ethanol + Trifluoroethanol) Experimental and Simulation

Liquid mixtures involving fluorinated alcohols: The equation of state (p, r, T, x) of (Ethanol + Trifluoroethanol) Experimental and Simulation Pedro Duartea, Djêide Rodriguesa, Marcelo Silvaa, Pedro Morgadoa, Luís Martinsa,b and Eduardo J. M. Filipea* aCentro de Química Estrutural, Instituto Superior Técnico, 1049-001 Lisboa, Portugal bCentro de Química de Évora, Universidade de Évora, 7000-671 Évora, Portugal Fluorinated alcohols are substances with unique properties and high technological value in the pharmaceutical and chemical industries. Trifluoroethanol (TFE), in particular, displays a number of unusual properties as a solvent. For example, it dissolves nylon at room temperature and is effectively used as solvent in bioengineering. The presence of the three fluorines atoms gives the alcohol a high ionization constant, strong hydrogen bonding capability and stability at high temperatures. In the pharmaceutical industry, TFE finds use as the major raw material for the production of inhalation anesthetics. Mixtures of TFE and water (known as Fluorinols®) are used as working fluids for Rankine cycle heat engines for terrestrial and space applications, as a result of a unique combination of physical and thermodynamic properties such as high thermal efficiency and excellent turbine expansion characteristics. Environmentally, TFE is a CFC substitute with an acceptable short lifetime and with small ozone depletion potential. Additionally, TFE is known to induce conformational changes in proteins and it is used as a co-solvent to analyze structural features of partially folded states. The (ethanol + TFE) system displays an interesting and peculiar behaviour, combining a negative azeotrope with high positive excess volumes. In this work, liquid mixtures of (ethanol + TFE) were investigated. The densities of the mixtures were measured as a function of composition between 278K and 338K and at pressures up to 700 bar. The corresponding excess volumes as a function of temperature and pressure, the isothermal compressibilities and thermal expansivities were calculated from the experimental results. The mixtures are highly non-ideal with excess volumes ranging from 0.8 - 1.0 cm3mol-1. Finally, molecular dynamic simulations were performed to model and interpret the experimental results. The Trappe force field was used to simulate the (TFE + ethanol) mixtures and calculate the corresponding excess volumes. The simulation results are able to reproduce the correct sign and order of magnitude of the experimental VE without fitting to the experimental data. Furthermore, the simulations suggest the presence of a particular type of hydrogen bridge between ethanol and TFE, that can help to rationalize the experimental results

Fundamental Limits to Position Determination by Concentration Gradients

Position determination in biological systems is often achieved through protein concentration gradients. Measuring the local concentration of such a protein with a spatially-varying distribution allows the measurement of position within the system. In order for these systems to work effectively, position determination must be robust to noise. Here, we calculate fundamental limits to the precision of position determination by concentration gradients due to unavoidable biochemical noise perturbing the gradients. We focus on gradient proteins with first order reaction kinetics. Systems of this type have been experimentally characterised in both developmental and cell biology settings. For a single gradient we show that, through time-averaging, great precision can potentially be achieved even with very low protein copy numbers. As a second example, we investigate the ability of a system with oppositely directed gradients to find its centre. With this mechanism, positional precision close to the centre improves more slowly with increasing averaging time, and so longer averaging times or higher copy numbers are required for high precision. For both single and double gradients, we demonstrate the existence of optimal length scales for the gradients, where precision is maximized, as well as analyzing how precision depends on the size of the concentration measuring apparatus. Our results provide fundamental constraints on the positional precision supplied by concentration gradients in various contexts, including both in developmental biology and also within a single cell.Comment: 24 pages, 2 figure

SAFT-γ force field for the simulation of molecular fluids: 8. hetero-group coarse-grained models of perfluoroalkylalkanes assessed with new vapour-liquid interfacial tension data

The air-liquid interfacial behaviour of linear perfluoroalkylalkanes (PFAAs) is reported through a combined experimental and computer simulation study. The surface tensions of seven liquid PFAAs (perfluorobutylethane, F4H2; perfluorobutylpentane, F4H5; perfluorobutylhexane, F4H6, perfluorobutyloctane, F4H8; perfluorohexylethane, F6H2; perfluorohexylhexane, F6H6; and perfluorohexyloctane, F6H8) are experimentally determined over a wide temperature range (276 to 350 K). The corresponding surface thermodynamic properties and the critical temperatures of the studied compounds are estimated from the temperature dependence of the surface tension. Experimental density and vapour pressure data are employed to parameterize a generic heteronuclear coarse-grained intermolecular potential of the SAFT- γ family for PFAAs. The resulting force field is used in direct molecular dynamics simulations to predict with quantitative agreement the experimental tensions and to explore the conformations of the molecules in the interfacial region revealing a preferential alignment of the PFAA molecules towards the interface and an enrichment of the perfluoro-groups at the outer interface region

Interleukin-17 as a Therapeutic Target in Psoriasis

A psoríase é uma doença crónica, inflamatória, imunomediada que afecta cerca de 1-3% da população geral. O avanço no conhecimento da patogénese da psoríase levou ao desenvolvimento de novos fármacos direccionados para vias imunitárias mais específicas que os existentes. A IL-17 e os linfócitos Th17 têm um importante papel na patogénese de várias doenças auto-imunes e imunomediadas, incluindo a psoríase. A IL-17A é uma citocina pró-inflamatória, produzida pelos linfócitos Th17 juntamente com outras citocinas efetoras, como a IL-17F e IL-22. Esta citocina é igualmente expressa por outras células do sistema imune inato, incluíndo os mastócitos, neutrófilos e células dendríticas, todas elas encontradas nas lesões de psoríase. Por esta razão a IL-17 surgiu como um alvo terapêutico potencial. Vários agentes que inibem a IL-17 estão em desenvolvimento e os resultados clínicos preliminares são bastante promissores, confirmando a importância da IL-17 na fisiopatologia da psoríase. A intervenção selectiva no sistema imune desta nova classe de agentes biotecnológicos, torna-os uma abordagem terapêutica interessante no controlo de doenças auto-imunes e imunomediadas, como na psoríase. Num futuro próximo, estas novas terapêuticas poderão constituir uma alternativa válida aos agentes biológicos actualmente disponíveis.Os autores declaram não terem existido fontes de financiamento externas na realização deste trabalho

Co-infection with Onchocerca volvulus and Loa loa microfilariae in central Cameroon: are these two species interacting?

Ivermectin treatment may induce severe adverse reactions in some individuals heavily infected with Loa loa. This hampers the implementation of mass ivermectin treatment against onchocerciasis in areas where Onchocerca volvulus and L. loa are co-endemic. In order to identify factors, including co-infections, which may explain the presence of high L. loa microfilaraemia in some individuals, we analysed data collected in 19 villages of central Cameroon. Two standardized skin snips and 30 mul of blood were obtained from each of 3190 participants and the microfilarial (mf) loads of both O. volvulus and L. loa were quantified. The data were analysed using multivariate hierarchical models. Individual-level variables were: age, sex, mf presence, and mf load; village-related variables included the endemicity levels for each infection. The two species show a certain degree of ecological separation in the study area. However, for a given individual host, the presence of microfilariae of one species was positively associated with the presence of microfilariae of the other (OR=1.79, 95% CI [1.43-2.24]). Among individuals harbouring Loa microfilariae, there was a slight positive relationship between the L. loa and O. volvulus mf loads which corresponded to an 11% increase in L. loa mf load per 100 O. volvulus microfilariae. Co-infection with O. volvulus is not sufficient to explain the very high L. loa mf loads harboured by some individuals

An application of the anti-commons theory to an elderly nursing home project in Portugal

The present study evaluates the consequential economic and ethical problems which occur when bureaucracy is present in companies’ projects evaluation by governmental agencies. The delay of projects approval generates loss of value once projects may not be implemented or are implemented after the suitable time. Theory of anti-commons is presented in the contextualization of the problem. As seen in this study, when an “anti-commons” emerges, resources may be prone to under-use. In an anti-commons situation there are too many entities deciding what may lead to the under-use of the resources. In Portugal, bureaucracy in projects approval contributes to such a situation of anti-commons. The present study analyses a project for the construction of an elderly nursing home,for which is necessary a permit to be obtained from the Portuguese government. This study is made according to the framework of the anti-commons theory

Searching for a new model of governance in the high seas: Game theory applied to international commons management

In the last decade, the United Nations took important steps for the creation of a new instrument for biodiversity protection in areas beyond national jurisdiction. This put under discussion the central issues of international commons management and of the governance model for the High Seas. The aim of this paper is to discuss and evaluate critically the political negotiations already made and yet to come, as well as their rationale. For this purpose, the paper applies game theory to fisheries management to get insights. This research aims to contribute toward more qualified and grounded decisions. The key role of cooperation in the sustainable use of common resources is stressed.info:eu-repo/semantics/publishedVersio