Diffusion of methane in supercritical carbon dioxide across the Widom line

Diffusion of methane diluted in supercritical carbon dioxide is studied by experiment and molecular simulation in the temperature range from 292.55 to 332.85 K along the isobars 9.0, 12.5 and 14.7 MPa. Measurements of the Fick diffusion coefficient are carried out with the Taylor dispersion technique. Molecular dynamics simulation and the Green-Kubo formalism are employed to obtain Fick, Maxwell-Stefan and intradiffusion coefficients as well as shear viscosity. The obtained diffusion coefficients are on the order of 10−8 m2/s. The composition, temperature and density dependence of diffusion is analyzed. The Fick diffusion coefficient of methane in carbon dioxide shows an anomaly in the near-critical region. This behavior can be attributed to the crossing of the so-called Widom line, where the supercritical fluid goes through a transition between liquid-like and gas-like states. Further, several classical equations are tested on their ability to predict this behavior and it is found that equations that explicitly include the density are better suited to predict the sharp variation of the diffusion coefficient near the critical region predicted by molecular simulation.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Gestión de talento humano y motivación laboral en los trabajadores de la Municipalidad de Cusco, Cusco 2022

La presente investigación tuvo como objetivo: Determinar la relación entre la gestión del talento humano y motivación laboral en los trabajadores de la municipalidad de Cusco, Cusco 2022. La metodología empleada fue de investigación aplicada, de enfoque cuantitativo, nivel correlacional y diseño no experimental de corte transversal. La técnica empleada fue la encuesta y como instrumentos dos cuestionarios para las variables de estudio. La población fue de 220 trabajadores y la muestra fue de 140 trabajadores. En los resultados se destaca que el Rho de Spearman 0,475 existe relación entre la gestión del talento humano y motivación laboral en los trabajadores de la Municipalidad de Cusco, 2022. Con Rho de Spearman 0,361 existe relación entre la Gestión de Talento Humano y la Importancia de la municipalidad de Cusco, 2022. Finalmente para Rho de Spearman 0,439; existe relación de la gestión del talento humano y la Autonomía de la tarea en los trabajadores de la municipalidad de Cusco, 2022. Se concluyó que existe relación entre gestión del talento humano y motivación laboral en los trabajadores de la municipalidad Provincial del Cusco, 2022

Diffusion in liquid mixtures

The understanding of transport and mixing in fluids in the presence and in the absence of external fields and reactions represents a challenging topic of strategic relevance for space exploration. Indeed, mixing and transport of components in a fluid are especially important during long-term space missions where fuels, food and other materials, needed for the sustainability of long space travels, must be processed under microgravity conditions. So far, the processes of transport and mixing have been investigated mainly at the macroscopic and microscopic scale. Their investigation at the mesoscopic scale is becoming increasingly important for the understanding of mass transfer in confined systems, such as porous media, biological systems and microfluidic systems. Microgravity conditions will provide the opportunity to analyze the effect of external fields and reactions on optimizing mixing and transport in the absence of the convective flows induced by buoyancy on Earth. This would be of great practical applicative relevance to handle complex fluids under microgravity conditions for the processing of materials in space

First wave of COVID-19 in Venezuela:Epidemiological, clinical, and paraclinical characteristics of first cases

The coronavirus disease 2019 (COVID-19) pandemic has particularly affected countries with weakened health services in Latin America, where proper patient management could be a critical step to address the epidemic. In this study, we aimed to characterize and identify which epidemiological, clinical, and paraclinical risk factors defined COVID-19 infection from the first confirmed cases through the first epidemic wave in Venezuela. A retrospective analysis of consecutive suspected cases of COVID-19 admitted to a sentinel hospital was carried out, including 576 patient cases subsequently confirmed for severe acute respiratory syndrome coronavirus 2 infection. Of these, 162 (28.1%) patients met the definition criteria for severe/critical disease, and 414 (71.2%) were classified as mild/moderate disease. The mean age was 47 (SD 16) years, the majority of which were men (59.5%), and the most frequent comorbidity was arterial hypertension (23.3%). The most common symptoms included fever (88.7%), headache (65.6%), and dry cough (63.9%). Severe/critical disease affected mostly older males with low schooling (p < 0.001). Similarly, higher levels of glycemia, urea, aminotransferases, total bilirubin, lactate dehydrogenase, and erythrocyte sedimentation rate were observed in severe/critical disease patients compared to those with mild/moderate disease. Overall mortality was 7.6% (44/576), with 41.7% (28/68) dying in hospital. We identified risk factors related to COVID-19 infection, which could help healthcare providers take appropriate measures and prevent severe clinical outcomes. Our results suggest that the mortality registered by this disease in Venezuela during the first epidemic wave was underestimated. An increase in fatalities is expected to occur in the coming months unless measures that are more effective are implemented to mitigate the epidemic while the vaccination process is ongoing

Molecular Modeling and Simulation: Force Field Development, Evaporation Processes and Thermophysical Properties of Mixtures

To gain physical insight into the behavior of fluids on a microscopic level as well as to broaden the data base for thermophysical properties especially for mixtures, molecular modeling and simulation is utilized in this work. Various methods and applications are discussed, including a procedure for the development of new force field models. The evaporation of liquid nitrogen into a supercritical hydrogen atmosphere is presented as an example for large scale molecular dynamics simulation. System-size dependence and scaling behavior are discussed in the context of Kirkwood-Buff integration. Further, results for thermophysical mixture properties are presented, i.e. the Henry’s law constant of aqueous systems and diffusion coefficients of a ternary mixture

Density and partial molar volumes of the liquid mixture water + methanol + ethanol + 2-propanol at 298.15 K and 0.1 MPa

The density of the quaternary mixture water + methanol + ethanol + propan-2-ol and its four ternary and six binary subsystems is measured over a wide composition range at ambient temperature and pressure, that is, 298.15 K and 0.1 MPa. The resulting molar volume data are correlated with a response surface model, consisting of linear, quadratic, bilinear, and trilinear interaction terms. The density values obtained with this correlation are compared to molecular simulation results and experimental literature data. Further, the excess molar volume and the partial molar volumes are determined for the ternary and quaternary mixtures. The analytical solution for the partial molar volumes of a quaternary mixture for the response surface model is also given

The thermodynamic factor: The key to understand complex diffusion behavior in fluid mixtures

We present the results of a molecular simulation study of fluid mixtures, where complex diffusion behavior has experimentally been found and offer an explanation based on the hydrodynamic and thermodynamic components of the Fick diffusion coefficient. Special attention is paid to mixtures near critical and demixing regions, where in many cases strong discrepancies between different measurements of the Fick diffusion coefficients are found. Also molecular simulations are challenging in these regions and require extensive sampling due the presence of pronounced density fluctuations