Very long-range attractive and repulsive forces in Model Colloidal Dispersions

Experiments with polymer latex solutions show the coexistence of order-disorder structures of macroions. Because of the large macroions' sizes, this order-disorder phase coexistence imply the existence of very long-range attractive and repulsive forces, which can not be explained in terms of conventional direct interaction potentials, which are short-range. Here we apply an integral equations theory to a simple model for colloidal dispersions, at finite concentrations, calculate the particles distribution functions and the involved effective forces. We find very long-range attractive and repulsive forces among the like-charged macroions. The distribution functions are in qualitative agreement with experimental results. The origin of these forces are discussed in terms of an energy-entropy balance.Comment: 16 pages, seven figures. ECIS-201

The primitive model of ionic fluids near its critical point in the Poisson–Boltzmann and modified Poisson–Boltzmann theories

The Poisson–Boltzmann (PB) and modified Poisson–Boltzmann (MPB) theories are used to investigate the primitive model of ionic fluids in the low density–large coupling regime where the liquid–vapor transition is situated. The PB and MPB spinodal curves for the restricted primitive model are calculated from the virial route and compared with those from the mean spherical approximation (energy route) and the hybrid hypernetted‐chain/mean spherical approximation (virial route). The effect of unequal ion sizes on the critical point and spinodal curves is also considered.National Sanitation Foundation (NSF) EE.UU. CHE-8907130Fondo Institucional para la Investigación (FIPI) de la Universidad de Puerto RicoComunidad Europea (beca Marie Curie)Dirección General de Investigación Científica y Técnica (DGICYT). España PBgl / 060

Multiscale assessment of woody species recruitment in Mediterranean shrublands: facilitation and beyond

Forest recovery in Mediterranean environments is influenced by factors such as aridity, herbivory and facilitation by shrubs, as well as by seed limitation in the case of highly fragmented forests. How these various factors interact can determine the direction of secondary succession, yet these interactions are poorly understood. We assessed the relative importance of several factors in forest species recruitment in Retama sphaerocarpa (L.) Boiss (Retama) shrublands at different spatial scales.Ministerio de Economía y CompetitividadComunidad de Madri

Perforación de ciego por colitis isquémica asociada a uso de cocaína. Reporte de caso

Resumen Introducción: El consumo de cocaína es un problema mayor a nivel mundial; los usuarios crónicos presentan complicaciones médicas graves que afectan el aparato vascular, los cuales pueden derivar en accidentes isquémicos serios. A continuación presentamos un caso de perforación intestinal secundaria a colitis isquémica por uso de cocaína. Caso clínico: Un hombre de 21 anos de edad con antecedente de uso de cocaína inició su pade- ˜ cimiento 5 días antes de su ingreso con dolor abdominal, náuseas y vómitos. Con el diagnóstico de perforación de víscera hueca se realizó una laparotomía exploradora, en la cual se encontró una perforación en la cara anterior del ciego. Se realizó una hemicolectomía derecha con una ileostomía y una fístula mucocutánea de colon transverso. Discusión: La causa de las perforaciones es la isquemia local en la mucosa y la necrosis parietal. En este paciente obtuvimos una prueba de orina positiva para cocaína; además, con el antecedente de uso intenso de esta sustancia y el resultado en el reporte histopatológico pudimos llegar a este diagnóstico. Conclusión: La colitis isquémica asociada a uso de cocaína debe ser considerada como diagnóstico diferencial en pacientes jóvenes con dolor abdominal agudo y/o sangrado rectal. © 2017 Sociedad de Cirujanos de Chile. Publicado por Elsevier Espana, S.L.U. Este es un art ˜ ´ıculo Open Access bajo la licencia CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4. 0/). KEYWORDS Surgery; Colorectal Perforation of the cecum by isquemic colitis associated with cocaine use. A case report Abstract Introduction: Cocaine use is a major problem worldwide. Chronic users have serious medical complications that affect the vascular system, which can lead to serious ischemic events. We describe a case of intestinal perforation secondary to ischemic colitis caused by cocaine. Case report: A 21-year-old man with a history of cocaine started 5 days before with abdominal pain, nausea and vomiting. With a diagnosis of a perforated intestine, a exploratory laparotomy was performed, in which a perforation of the anterior wall of the cecum was found. A right hemicolectomy with ileostomy and a mucocutaneous fistula of the transverse colon were carried out. Discussion: Perforations are caused by local ischemia of the mucosa and parietal necrosis. In this patient, a urine test for cocaine was positive, in addition to the history of intensive use of this substance and a pathology report. Conclusion: Ischemic colitis associated with cocaine use should be considered as a differential diagnosis in young patients with acute abdominal pain and/or rectal bleeding. © 2017 Sociedad de Cirujanos de Chile. Published by Elsevier Espana, S.L.U. This is an open ˜ access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/)

A simulational and theoretical study of the spherical electrical double layer for a size-asymmetric electrolyte: the case of big coions

Monte Carlo simulations of a spherical macroion, surrounded by a size-asymmetric electrolyte in the primitive model, were performed. We considered 1:1 and 2:2 salts with a size ratio of 2 (i.e., with coions twice the size of counterions), for several surface charge densities of the macrosphere. The radial distribution functions, electrostatic potential at the Helmholtz surfaces, and integrated charge are reported. We compare these simulational data with original results obtained from the Ornstein-Zernike integral equation, supplemented by the hypernetted chain/hypernetted chain (HNC/HNC) and hypernetted chain/mean spherical approximation (HNC/MSA) closures, and with the corresponding calculations using the modified Gouy-Chapman and unequal-radius modified Gouy-Chapman theories. The HNC/HNC and HNC/MSA integral equations formalisms show good concordance with Monte Carlo "experiments", whereas the notable limitations of point-ion approaches are evidenced. Most importantly, the simulations confirm our previous theoretical predictions of the non-dominance of the counterions in the size-asymmetric spherical electrical double layer [J. Chem. Phys. 123, 034703 (2005)], the appearance of anomalous curvatures at the outer Helmholtz plane and the enhancement of charge reversal and screening at high colloidal surface charge densities due to the ionic size asymmetry.Comment: 11 pages, 7 figure

Análisis de los cuellos de botella en la logística internacional de las PYMES de confecciones en Colombia.

Por medio del presente trabajo se realizará el desarrollo de la actividad Fase 10, correspondiente al repaso de las unidades 1, 2, 3 y 4, se presenta y sustenta el Proyecto Final, con el propósito de poner en práctica los conocimientos adquiridos durante el transcurso del Diplomado del Supply Chain Management y Logística, los cuales serán aplicados en el estudio de caso “Análisis de los cuellos de botella en la logística internacional de las pymes de confecciones en Colombia”, realizando un análisis para resolver con buen fundamento cada una de las preguntas que se proponen, teniendo en cuenta la guía de actividades de la fase 6 para la presentación del trabajo.Through this work, the development of the Phase 10 activity will be carried out, corresponding to the review of units 1, 2, 3 and 4, the Final Project is presented and supported, with the purpose of putting into practice the knowledge acquired during the course of the Diploma in Supply Chain Management and Logistics, which will be applied in the case study "Analysis of bottlenecks in the international logistics of SME garments in Colombia", carrying out an analysis to resolve with good foundation each of the Questions proposed, taking into account the activity guide of phase 6 for the presentation of the wor

The electrical double layer for a fully asymmetric electrolyte around a spherical colloid: an integral equation study

The hypernetted chain/mean spherical approximation (HNC/MSA) integral equation is obtained and solved numerically for a totally asymmetric primitive model electrolyte around a spherical macroparticle. The ensuing radial distribution functions show a very good agreement when compared to our Monte Carlo and molecular dynamics simulations for spherical geometry and with respect to previous anisotropic reference HNC calculations in the planar limit. We report an analysis of the potential vs charge relationship, radial distribution functions, mean electrostatic potential and cumulative reduced charge for representative cases of 1:1 and 2:2 salts with a size asymmetry ratio of 2. Our results are collated with those of the Modified Gouy-Chapman (MGC) and unequal radius Modified Gouy-Chapman (URMGC) theories and with those of HNC/MSA in the restricted primitive model (RPM) to assess the importance of size asymmetry effects. One of the most striking characteristics found is that,\textit{contrary to the general belief}, away from the point of zero charge the properties of an asymmetric electrical double layer (EDL) are not those corresponding to a symmetric electrolyte with the size and charge of the counterion, i.e. \textit{counterions do not always dominate}. This behavior suggests the existence of a new phenomenology in the EDL that genuinely belongs to a more realistic size-asymmetric model where steric correlations are taken into account consistently. Such novel features can not be described by traditional mean field theories like MGC, URMGC or even by enhanced formalisms, like HNC/MSA, if they are based on the RPM.Comment: 29 pages, 13 figure

Modificación de silla pélvica con dispositivo de apoyo al freno para descenso en personal del Ejército Nacional de Colombia

This research article arises from the modified pelvic chair project with brake support device for descent, this project is carried out based on the experiences of contingencies presented in the first man at the time of descending in the Air Assault tower of the National Army of Colombia, seeking to reduce the risk of user accidents, implementing a braking device that consists of the adaptation of a carabiner located at a specific point of the pelvic chair, being a fixed point with greater adaptability and anchoring security, allowing to continue with the tasks they are performing, giving orientation and control to the rope, avoiding knots due to oscillation when releasing the brake rope.El presente artículo de investigación surge del proyecto “Silla pélvica modificada con dispositivo de apoyo al freno para descenso”, que se realiza con base en las experiencias de contingencias presentadas en el primer hombre al momento de descender en la torre de Asalto Aéreo del Ejército Nacional de Colombia, con el fin de reducir el riesgo de accidentalidad del usuario a partir de la implementando un dispositivo de freno, que consiste en la adaptación de un mosquetón ubicado en un punto específico (parte lateral pierna izquierda o derecha) de la silla pélvica, el cual es un punto fijo con adaptabilidad y seguridad de anclaje. Esto le permite al oficial continuar con sus y da orientación y control a la cuerda, evitando nudos por oscilación al soltar la cuerda de fren