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

Market forces, strategic management, HRM practices and organizational performance, a model based in european sample

This study uses structural equation modeling to test a model of the impact of human resources management practices on perceived organizational performance, on a large sample of European companies. The influences of competitive intensity, industry attractiveness and strategic management are considered in the model, and their direct and indirect influence on organizational performance is assessed. The model produced an adequate fit and results show that strategic management does influence human resource practices. Human resource flexibility practices and performance management have a positive impact on organizational performance, while training was not found to have a significant impact. A direct positive impact of competitive intensity and industry attractiveness on strategic management was supported by the data, as well as a direct positive effect of industry attractiveness on perceived organizational performance.

Anisotropic Energy Distribution in Three-Dimensional Vibrofluidized Granular Systems

We examine the energy distribution in a three-dimensional model granular system contained in an open cylinder under the influence of gravity. Energy is supplied to the system by a vibrating base. We introduce spatially resolved, partial particle-particle ``dissipations'' for directions parallel and perpendicular to the energy input, respectively. Energy balances show that the total (integrated) ``dissipation'' is less than zero in the parallel direction while greater than zero in the perpendicular directions. The energy supplied to the perpendicular directions is dissipated by particle-wall collisions. We further define a fractional energy transfer, which in the steady state represents the fraction of the power supplied by the vibrating base that is dissipated at the wall. We examine the dependence of the fractional energy transfer on the number of particles, the velocity of the vibrating base, the particle-particle restitution coefficient, and the particle-wall restitution coefficient. We also explore the influence of the system parameters on the spatially dependent partial dissipations.Comment: 10 pages, 10 figures, RevTeX forma

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

Suprabenthos distribution in a shallow temperate estuary (Mondego estuary, western Portugal)

For this paper we studied the suprabenthos distribution in the Mondego estuary's southern arm. Samples were taken monthly at two stations from October 1999 to May 2000. The collections were made during high spring tides, using a suprabenthic net mounted on a sledge (40 cm diameter, 500 mm mesh) in suprabenthic tows. Mollusca and Crustacea, especially Mysidacea, dominated the suprabenthos. Other important groups were the Copepoda, Isopoda, eggs and post larvae of Pisces, and larval stages of Decapoda. The high densities of Hydrobia ulvae (Pennant, 1777) post-larvae caught in the downstream station, which decreased species evenness due to the dominance of this species, led to a spatial diversity pattern with higher diversities in the upstream area. The mysid species Mesopodopsis slabberi (Van Beneden, 1861), together with the calanoid copepod Acartia tonsa (Dana, 1848), dominated in the upstream area. Significant differences were found in community structure between the two selected areas of the estuary, with a dominance of the spatial structure in the cluster analysis.Para este artículo, estudiamos la distribución del suprabentos en el brazo sur del estuario del río Mondego. Las muestras se tomaron mensualmente entre octubre de 1999 y mayo de 2000 en dos áreas: una de mayor flujo, río arriba, y otra en la zona de encuentro con el mar. Las recolecciones se hicieron durante las mareas vivas, utilizando una red suprabentónica de 40 cm de diámetro y 500 mm de luz de malla. Los moluscos y los crustáceos, especialmente los misidáceos, fueron los grupos que dominaron el suprabentos. Otros grupos importantes fueron los copépodos, los isópodos, los huevos y poslarvas de peces y las larvas de decápodos. La captura de altas densidades de poslarvas de Hydrobia ulvae (Pennant, 1777) en el área de encuentro desvela que su predominio es el causante de la disminución en la uniformidad de las especies en esta zona y, como consecuencia, se ha desarrollado para ella un patrón mayor de diversidad espacial. La especie Mesopodopsis slabberi (Van Beneden, 1861), junto con el copépodo calanoide Acartia tonsa (Dana, 1848), dominaron el área de mayor flujo, río arriba. Se encontraron diferencias significativas entre las estructuras de la comunidad de las dos áreas del estuario seleccionadas, dominando la estructura espacial en el análisis por agrupación (efectuado mediante cluster).Instituto Español de Oceanografí

Energy exchanges in a damped Langevin-like system with two thermal baths and an athermal reservoir

We study the properties of energy transfers in a Langevin-like model which describes an inertial particle in a one-dimensional harmonic potential and subjected to two heat baths and one athermal environment. The thermal noises are white and Gaussian, and the temperatures of heat reservoirs are different. The athermal medium act through an external non-Gaussian noise of Poisson type. We discuss the long-time behavior of first cumulants of time-integrated power due to the athermal reservoir. The averages and covariances of heat exchanged with thermal baths are also evaluated for stationary states. The properties of these cumulants are investigated in terms of the characteristics of external noise.Comment: 23 pages, 7 figure

HEMATOSALPINX TORSION IN AN ADOLESCENT

Introdução: A torção da trompa de Falópio é uma causa rara de dor abdominal aguda. A gravidez ectópica, hidro ou hematossalpinge, endometriose, tumefações anexiais e outras causas de patologia anexial são fatores predisponentes. O diagnóstico é difícil de estabelecer, uma vez que os sinais clínicos, laboratoriais e imagiológicos são pouco específicos. O diagnóstico definitivo requer uma abordagem cirúrgica. Caso clínico: Os autores apresentam um caso de hematossalpinge e torção da mesma numa adolescente virgem sem fatores de risco conhecidos. Discussão: O caso evidencia a importância da reflexão sobre causas de hematossalpinge e recorda esta patologia como diagnóstico diferencial.Introduction: Isolated fallopian tube torsion is an uncommon cause of acute lower abdominal pain. Ectopic pregnancy, hydro or hematosalpinx, endometriosis, adnexal masses and other causes of adnexal disease are predisposing factors. The diagnosis is difficult and often delayed due to the lack of pathognomonic symptoms, characteristic physical signs, and specific imaging and laboratory studies. Definitive diagnosis requires a surgical approach. Case report: The authors present a case of hematosalpinx and its tubal torsion in a virgin teenager with no prior predisposing factors. Discussion: This rare case may highlight a new insight into pathophysiology of tubal torsion and recalls hematosalpinx as a differential diagnosi

Testosterone and Cholesterol Vasodilation of Rat Aorta Involves L-Type Calcium Channel Inhibition

Testosterone has rapid nongenomic vasodilator effects which could be involved in protective cardiovascular actions. Several authors suggested specific mechanisms to explain this effect, but this matter was not clarified yet. We studied the actions of testosterone and cholesterol on endothelium-denuded rat aorta and their effects on the L-type Ca2+ current (ICa,L) and potassium current (IK). Testosterone (1–100 μM) totally relaxed, in a rapid and concentration-dependent way, the aortic rings contracted by KCl or by (−)-Bay K8644 (BAY). Cholesterol also fully relaxed the contractions induced by KCl. None of the potassium channel antagonists tested (glibenclamide, tetraethylammonium and 4-aminopyridine) modified significantly the relaxant effect of testosterone. The antagonist of classic testosterone receptors, flutamide, did not modify the vasorelaxant effect of testosterone. Furthermore, testosterone and cholesterol inhibited either basal and BAY-stimulated ICa,L in A7r5 cells and they have no effects on IK. In summary, our results demonstrate that cholesterol and testosterone relax rat aorta by inhibiting LTCC. This effect of testosterone is not mediated by the classic hormone receptor or by potassium channel activation. These results suggest that the vasodilator mechanism of cholesterol and testosterone is the same

Universal and Automatic Elbow Detection for Learning the Effective Number of Components in Model Selection Problems

We design a Universal Automatic Elbow Detector (UAED) for deciding the effective number of components in model selection problems. The relationship with the information criteria widely employed in the literature is also discussed. The proposed UAED does not require the knowledge of a likelihood function and can be easily applied in diverse applications, such as regression and classification, feature and/or order selection, clustering, and dimension reduction. Several experiments involving synthetic and real data show the advantages of the proposed scheme with benchmark techniques in the literature