Interfacial and coexistence properties of soft spheres with a short-range attractive Yukawa fluid: molecular dynamics simulations.

Molecular dynamics simulations have been carried out to obtain the interfacial and coexistence properties of soft-sphere attractive Yukawa (SAY) fluids with short attraction range, κ = 10, 9, 8, 7, 6, and 5. All our simulation results are new. These data are also compared with the recently reported results in the literature of hard-core attractive Yukawa (HAY) fluids. We show that the interfacial and coexistence properties of both potentials are different. For the surveyed systems, here we show that all coexistence curves collapse into a master curve when we rescale with their respective critical points and the surface tension curves form a single master curve when we plot γ* vs. T/T(c).

Excess chemical potential of thiophene in [C4MIM] [BF4, Cl, Br, CH3COO] ionic liquids, determined by molecular simulations.

The excess chemical potential of thiophene in imidazolium-based ionic liquids [C4mim][BF4], [C4mim][Cl], [C4mim][Br], and [C4mim][CH3COO] were determined by means of molecular dynamics in conjunction with free energy perturbation techniques employing non-polarizable force fields at 300 K and 343.15 K. In addition, energetic and structural analysis were performed such as: interaction energies, averaged noncovalent interactions, radial, and combined distribution functions. The results from this work revealed that the ionic liquids (ILs) presenting the most favorable excess chemical potentials ([C4mim][BF4], [C4mim][CH3COO]) are associated with the strongest energetic interaction between the thiophene molecule and the ionic liquid anion, and with the weakest energetic interaction between the thiophene molecule and the ionic liquid cation.

Thermodynamic, structural and dynamic properties of ionic liquids [C4mim][CF3COO], [C4mim][Br] in the condensed phase, using molecular simulations.

In this work a series of thermodynamic, structural, and dynamical properties for the 1-butyl-3-methylimidazolium trifluoroacetate ([C4mim][CF3COO]) and 1-butyl-3-methylimidazolium bromide, ([C4mim][Br]) ionic liquids (ILs) were calculated using Non-polarizable Force Fields (FF), parameterized using a methodology developed previously within the research group, for condensed phase applications. Properties such as the Vapor-Liquid Equilibrium (VLE) curve, critical points (ρ c, T c), Radial, Spatial and Combined Distribution Functions and self-diffusion coefficients were calculated using Equilibrium Molecular Dynamics simulations (EMD); other properties such as shear viscosities and thermal conductivities were calculated using Non-Equilibrium Molecular Dynamics simulations (NEMD). The results obtained in this work indicated that the calculated critical points are comparable with those available in the literature. The calculated structural information for these two ILs indicated that the anions interact mainly with hydrogen atoms from both the imidazolium ring and the methyl chain; the bromide anion displays twice the hydrogen coordination number than the oxygen atoms from the trifluoroacetate anion. Furthermore, Non-Covalent interactions (NCI index), determined by DFT calculations, revealed that some hydrogen bonds in the [C4mim][Br] IL displayed similar strength to those in the [C4mim][CF3COO] IL, in spite of the shorter O--H distances found in the latter IL. The majority of the calculated transport properties presented reasonable agreement with the experimental available data. Nonetheless, the self-diffusion coefficients determined in this work are under-estimated with respect to experimental values; however, by escalating the electrostatic atomic charges for the anion and cation to ±0.8e, only for this property, a remarkable improvement was obtained. Experimental evidence was recovered for most of the calculated properties and to the best of our knowledge, some new predictions were done mainly in thermodynamic states where data are not available. To validate the FF, developed previously within the research group, dynamic properties were also evaluated for a series of ILs such as [C4mim][PF6], [C4mim][BF4], [C4mim][OMs], and [C4mim][NTf2] ILs.

The Wolf method applied to the liquid-vapor interface of water.

The Wolf method for the calculation of electrostatic interactions is applied in a liquid phase and at the liquid-vapor interface of water and its results are compared with those from the Ewald sums method. Molecular dynamics simulations are performed to calculate the radial distribution functions at room temperature. The interface simulations are used to obtain the coexisting densities and surface tension along the coexistence curve. The water model is a flexible version of the extended simple point charge model. The Wolf method gives good structural results, fair coexistence densities, and poor surface tensions as compared with those obtained using the Ewald sums method.

Molecular dynamics simulations of 2-(dimethylamino)ethanol (DMEA).

We develop a multipurpose force field to investigate the properties of the condensed phases of 2-(dimethylamino)ethanol (DMEA). We use ab initio computations at the HF/6-311++G(2d,2p) level to derive partial charges, obtain force constants, and compute the electrostatic potential of the DMEA. We find that the HF predictions for the dipole moment are in excellent agreement with the experimental result (2.6 D). The computations also show the strong preference of DMEA to form intramolecular hydrogen bonds between the hydrogen in the alcohol group and nitrogen. We have tested the accuracy of our force field by computing coexistence and interfacial properties as well as thermal conductivities in wide range of thermodynamic states. In all these instances we find excellent agreement with the available experimental data. We have further investigated the structure of the liquid by computing pair correlations. Our results indicate a clear preference for DMEA to form low-dimensional structures, such as linear and bifurcated chains, which are driven by the association of the DMEA molecules via the alcohol group. Overall, our force field provides a good basis to compute the bulk and interfacial properties of DMEA.

Los grupos informales y su relación con el rendimiento de las MiPyMES en México / Informal groups and their relationship with the performance of MSMEs in Mexico / Grupos informais e sua relação com a atuação das MPMEs no México

Resumen Introducción: en la actualidad, el liderazgo, la cultura y el clima organizacional que ejercen los grupos informales representan algunos de los factores clave en el rendimiento empresarial de las MiPyMES debido a que fortalece el incremento de la productividad en un mercado altamente competitivo. Objetivo: el propósito de la investigación es identificar la influencia conjunta del liderazgo transformacional, la cultura clan y el clima organizacional que presentan los grupos informales de trabajo sobre el rendimiento empresarial de las MiPyMES de la región del bajío del estado de Guanajuato, México. Materiales y métodos: el diseño metodológico fue cuantitativo, explicativo, observacional y transversal. Se empleó una muestra de 225 participantes. Para la comprobación de hipótesis se desarrolló un modelo de ecuación estructural (SEM). En cuanto a los índices de bondad y ajuste del SEM (χ2=146.10 gl=52; CFI=0.969 y TLI=0.960; RMSEA=.06) fueron absolutamente aceptables. Resultados: de acuerdo con los resultados obtenidos a través del SEM, se demuestra que el liderazgo transformacional influye positiva y significativamente sobre el clima organizacional (β1=0.26; p<0.001) como también en la cultura clan (β2=0.81; p<0.001) de los grupos informales. Asimismo, la cultura clan de los grupos informales influye (β3=0.61; p<0.001) positiva y significativamente sobre el clima organizacional. Finalmente, el clima organizacional de los grupos informales influye (β4=0.68; p<0.001) positiva y significativamente sobre el rendimiento empresarial de las MiPyMES. Conclusión: Los grupos informales representan un recurso promueve en el éxito de las MiPyMES y con ello, potencializar el rendimiento del sector empresarial de las MiPyMES en estado de Guanajuato.

Abstract Introduction: At present, the leadership, culture and organizational climate exercised by informal groups represent some of the key factors in the business performance of MSMEs because it strengthens the increase in productivity in a highly competitive market. Objective: the purpose of the research is to identify the joint influence of transformational leadership, clan culture and organizational climate presented by informal work groups on the business performance of MSMEs in the Bajio region of the state of Guanajuato, Mexico. Materials and methods: the methodological design was quantitative, explanatory, observational and transversal. A sample of 225 participants was used. For hypothesis testing, a structural equation model (SEM) was developed. Regarding the goodness and fit indices of the SEM (χ2 = 146.10 gl = 52; CFI = 0.969 and TLI = 0.960; RMSEA = 0.06) they were absolutely acceptable. Results: according to the results obtained through the SEM, it is shown that transformational leadership positively and significantly influences the organizational climate (β1 = 0.26; p <0.001) as well as clan culture (β2 = 0.81; p <0.001) of informal groups. Likewise, the clan culture of informal groups influences (β3 = 0.61; p <0.001) positively and significantly on the organizational climate. Finally, the organizational climate of informal groups has a positive and significant influence (β4 = 0.68; p <0.001) on the business performance of MSMEs. Conclusions: informal groups represent a resource that promotes the success of MSMEs and with it, potentiates the performance of the business sector of MSMEs in the state of Guanajuato.

Resumo Introdução: atualmente, a liderança, a cultura e o clima organizacional exercido pelos grupos informais representam alguns dos fatores-chave no desempenho empresarial das MPMEs, pois fortalecem o aumento da produtividade em um mercado altamente competitivo. Objetivo: o objetivo da pesquisa é identificar a influência conjunta da liderança transformacional, cultura de clã e clima organizacional apresentada por grupos de trabalho informais sobre o desempenho empresarial das MPMEs na região de Bajío, no estado de Guanajuato, México. Materiais e métodos: o desenho metodológico foi quantitativo, explicativo, observacional e transversal. Uma amostra de 225 participantes foi utilizada. Para o teste de hipótese, um modelo de equação estrutural (SEM) foi desenvolvido. Em relação aos índices de bondade e ajuste do SEM (χ2 = 146,10 gl = 52; CFI = 0,969 e TLI = 0,960; RMSEA = 0,06), eles foram absolutamente aceitáveis. Resultados: de acordo com os resultados obtidos por meio do SEM, mostra-se que a liderança transformacional influência positiva e significativamente o clima organizacional (β1 = 0,26; p <0,001) e também a cultura do clã (β2 = 0,81; p <0,001) de grupos informais. Da mesma forma, a cultura de clã dos grupos informais influência (β3 = 0,61; p <0,001) positiva e significativamente no clima organizacional. Por fim, o clima organizacional dos grupos informais influência (β4 = 0,68; p <0,001) de forma positiva e significativa no desempenho empresarial das MPMEs. Conclusões: os grupos informais representam um recurso que promove o sucesso das MPMEs e com isso potencializa a atuação do setor empresarial das MPMEs no estado de Guanajuato.

Variabilidad de la práctica médica: a 80 años del efecto Glover / Variability of medical practice: at 80 years since the Glover effect

At this moment, it seems to be clear, that the application of the epidemiological logic to the sanitary administration, by one side, to specify which are the diseases or the needs that have a greater importance in a determined population to identify which individuals are at risk situation or with unnoticed requeriments to focuse resources mainly in them, and on the other side, to planify politics at macro level or logistic to supply resources and at level meso or micro through the analysis of the configuratiion of the employement of services or their polinomic terms: patient, providers and mediating organizations. Rarefieds, however a little the atmosphere of the called variability phenomen in the medical practice, prefigurted by Glover in the decade of the 30 th. It has been however a fundational basis the study of Allison Glover on the amigdalectomies in the British school districts, chronologically the first call for attention on the wide variation over the poblational rates of the interventions (Glover 1938), to such an extent that it was coined the concept "Glover effect" to refer to this fact. These facts showd that there was in England and Wale a rate of tonsillectomies between 50% and 70%, and indication 3 times more frequent in children from more accommodated class, a higher incidence in boys than in girls, an age of higher incidence between 5 to 7 years of age, and the absence of correlatively with the so called impersonal facts as accumulation , powerty, deficient dwelling or clime. In our analysis it was proved that in the practice the Glover effect continues producing fullness. These aspects are anayzed in the study

Effect of flexibility on surface tension and coexisting densities of water.

Molecular dynamics simulations of pure water at the liquid-vapor interface are performed using direct simulation of interfaces in a liquid slab geometry. The effect of intramolecular flexibility on coexisting densities and surface tension is analyzed. The dipole moment profile across the liquid-vapor interface shows different values for the liquid and vapor phases. The flexible model is a polarizable model. This effect is minor for liquid densities and is large for surface tension. The liquid densities increase from 2% at 300 K to 9% at 550 K when the force field is changed from a fully rigid simple point charge extended (SPCE) model to that of a fully flexible model with the same intermolecular interaction parameters. The increases in surface tension at both temperatures are around 11% and 36%, respectively. The calculated properties of the flexible models are closer to the experimental data than those of the rigid SPCE. The effect of the maximum number of reciprocal vectors (h(z) (max)) and the surface area on the calculated properties at 300 K is also analyzed. The coexiting densities are not sensitive to those variables. The surface tension fluctuates with h(z) (max) with an amplitude larger than 10 mN m(-1). The effect of using small interfacial areas is slightly larger than the error in the simulations.

Doble inervación del músculo braquial en la población chilena / Dual innervation of the brachialis muscle in the Chilean population

La doble inervación del músculo braquial está dada por el nervio musculocutáneo y por ramos provenientes del nervio radial según lo describen algunos textos anatómicos y numerosos trabajos científicos. Sin embargo, no existe consenso en la frecuencia con la que ésta se presenta. El objetivo de este estudio es verificar la presencia y determinar la frecuencia de la contribución del nervio radial en la inervación del músculo braquial. En el presente trabajo se utilizaron 30 miembros superiores previamente fijados con solución fijadora y conservadora. Se realizó disección de la región braquial para determinar la presencia de ramos del nervio radial inervando al músculo braquial, verificando la presencia de ramos que penetraban en el músculo y tomando muestras de estos ramos en el sitio donde perforaban al músculo para su estudio histológico. Fue posible observar la presencia de ramos del nervio radial que penetraban en el músculo braquial en un 90 porciento de los casos; en ellos el punto motor de estos ramos se ubicó siempre en el tercio distal del músculo. De acuerdo a los resultados obtenidos en el presente trabajo, la doble inervación del músculo braquial observada por autores clásicos y reportada en estudios en diversas poblaciones, está presente en alto porcentaje de la muestra. Estos hallazgos pueden servir de referencia para procedimientos quirúrgicos, estudios electromiográficos y sonográficos.

The dual innervation of the brachialis muscle by the musculocutaneos nerve and branches from the radial nerve has been described by some anatomical texts and several scientific papers; however, there is no consensus about the frequency with which this occurs. In this study we proposed to check the presence and determine the frequency of the contribution of radial nerve in the innervations of the brachialis muscle. In this study we used 30 upper limbs fixed in fixative and conservative solution. Dissection of the brachial region was carried out, checking the branches that penetrated the muscle and taking samples of these branches to histological study. It was possible to observe the presence of branches of the radial nerve innervating the brachialis muscle in a 90 percent of the sample used in this study; the motor point of these branches was always located in the distal third of this muscle. According with the results of this study, the dual innervations of the brachial muscles observed by classical authors and reported by several investigations is also present in a high percentage of the sample. These findings can serve as reference for surgical procedures, electromyographic and ultrasound studies.

Oscillatory surface tension due to finite-size effects.

The simulation results of surface tension at the liquid-vapor interface are presented for fluids interacting with Lennard Jones and square-well potentials. From the simulation of liquids we have reported [M. González-Melchor et al., J. Chem. Phys. 122, 4503 (2005)] that the components of pressure tensor in parallelepiped boxes are not the same when periodic boundary conditions and small transversal areas are used. This fact creates an artificial oscillatory stress anisotropy in the system with even negative values. By doing direct simulations of interfaces we show in this work that surface tension has also an oscillatory decay at small surface areas; this behavior is opposite to the monotonic decay reported previously for the Lennard Jones fluid. It is shown that for small surface areas, the surface tension of the square-well potential artificially takes negative values and even increases with temperature. The calculated surface tension using a direct simulation of interfaces might have two contributions: one from finite-size effects of interfacial areas due to box geometry and another from the interface. Thus, it is difficult to evaluate the true surface tension of an interface when small surface areas are used. Care has to be taken to use the direct simulation method of interfaces to evaluate the predicted surface tension as a function of interfacial area from capillary-wave theory. The oscillations of surface tension decay faster at temperatures close to the critical point. It is also discussed that a surface area does not show any important effect on coexisting densities, making this method reliable to calculate bulk coexisting properties using small systems.

Stress anisotropy induced by periodic boundary conditions.

Finite size effects due to periodic boundary conditions are investigated using computer simulations in the canonical ensemble. We study liquids with densities corresponding to typical liquid coexistence densities, and temperatures between the triple and critical points. The components of the pressure tensor are computed in order to analyze the finite size effects arising from the size and geometry of the simulation box. Two different box geometries are considered: cubic and parallelepiped. As expected the pressure tensor is isotropic in cubic boxes, but it becomes anisotropic for small noncubic boxes. We argue this is the origin of the anomalous behavior observed recently in the computation of the surface tension of liquid-vapor interfaces. Otherwise, we find that the bulk pressure is sensitive to the box geometry when small simulation boxes are considered. These observations are general and independent of the model liquid considered. We report results for liquids interacting through short range forces, square well and Lennard-Jones, and also long range Coulombic interactions. The effect that small surface areas have on the surface tension is discussed, and some preliminary results at the liquid vapor-interface for the square well potential are given.

Medidas fractales cardiotorácicas en radiografías de tórax / Cardiothoracic fractal measurements in thoracic x-rays

La geometría fractal caracteriza de manera adecuada las formas irregulares de la naturaleza; por ello, para obtener una descripción matemática objetiva de la irregularidad de la cavidad torácica, es necesario hacer uso de ésta.Mediante el método de box-counting se midieron las dimensiones fractales de los objetos definidos de 20 radiografías de tórax de individuos sanos, 10 de mujeres y 10 de hombres entre 18 y 32 años de edad, en la cuales se comparó la primera y segunda cifra significativa entre las dimensiones fractales de los tres objetos definidos.Las dimensiones fractales de las placas evaluadas con la primera cifra significativa, resultaron diferentes o iguales en los tres objetos evaluados, o bien iguales para dos de los tres objetos fractales, mientras que en la segunda cifra significativa fueron diferentes en los tres objetos fractales al mismo tiempo, además la mayor diferencia máxima entre los valores de las islas es de tres décimas. Estudios posteriores con radiografías de pacientes con diferentes patologías permitirán realizar una generalización de la metodología desarrollada para su aplicación clínica.