Equilibration of Concentrated Hard Sphere Fluids

We report a systematic molecular dynamics study of the isochoric equilibration of hard-sphere fluids in their metastable regime close to the glass transition. The thermalization process starts with the system prepared in a non-equilibrium state with the desired final volume fraction {\phi} but with a prescribed non-equilibrium static structure factor S_0(k; {\phi}). The evolution of the {\alpha}- relaxation time {\tau}{\alpha} (k) and long-time self-diffusion coefficient DL as a function of the evolution time tw is then monitored for an array of volume fractions. For a given waiting time the plot of {\tau}{\alpha} (k; {\phi}, tw) as a function of {\phi} exhibits two regimes corresponding to samples that have fully equilibrated within this waiting time ({\phi} \leq {\phi}(c) (tw)), and to samples for which equilibration is not yet complete ({\phi} \geq {\phi}(c) (tw)). The crossover volume fraction {\phi}(c) (tw) increases with tw but seems to saturate to a value {\phi}(a) \equiv {\phi}(c) (tw \rightarrow \infty) \approx 0.582. We also find that the waiting time t^(eq)_w({\phi}) required to equilibrate a system grows faster than the corresponding equilibrium relaxation time, t^(eq)({\phi}) \approx 0.27 \times [{\tau}{\alpha} (k; {\phi})]^1.43, and that both characteristic times increase strongly as {\phi} approaches {\phi}^(a), thus suggesting that the measurement of equilibrium properties at and above {\phi}(a) is experimentally impossible

Incidencia de la violencia social, en Baja california: pobreza y desigualdad

ResumenEste artículo explora el aumento de la incidencia de violencia social en el estadofronterizo de Baja California, México en los últimos quince años. Se analizan losprincipales determinantes de los crímenes violentos en la región al confrontar dosperspectivas comúnmente propuestas por las ciencias sociales como catalizadoras dela violencia: la pobreza y la desigualdad. Mediante la utilización del modelo de Becker(1968) y, también, mediante la presentación de una caracterización jurídico-social dela región se propone un modelo empírico que incluye a la pobreza y a la desigualdad.Los resultados son sugerentes, pues, mientras que la pobreza y la desigualdad afectanla incidencia de crímenes violentos, la desigualdad tiene un mayor impacto en el casode Baja California.

Comparison of greenhouse gas emissions from Mexican intensive dairy farms

The objectives of this study were to compare estimates of greenhouse gas emissions (GHG) as CH4 (enteric-manure), N2O (manure), and CO2 (fuel and energy use), the use of water and soil, the excretion of nutrients in manure, and feed efficiency from Mexican intensive dairy farms. Data from 26 dairy farms were analysed with a multivariable cluster analysis. Three grades of intensifications were identified (low, medium and high). Mathematical models were used to estimate GHG. Feed efficiency (kg milk per kg DMI) was better in high intensive production systems. Enteric methane was identified as the major source of GHG in all types of systems. High intensive dairies generated the lowest emissions of CH4, N2O and CO2 equivalent by unit of product, 18.6 g, 0.12 g and 828 g, respectively. Water footprint was lower in low intensive dairies using 427 L of water/L of milk. Cropland was highest in intensive systems but milk yield per area was better (30,938 kg/ha). Excretions of N, P, and K were lower in intensive dairies per kg of milk, at 13.2, 2.4, and 6.4 g, respectively. As intensification in the dairy system increased feed efficiency (kg milk/kg DMI) was better. Per unit of product (kg of milk), dairies with the highest intensification generated the lowest GHG emissions, nutrient excretion values and land and water use as compared to dairies with medium and low intensification. Increasing intensification and therefore feed efficiency of Mexican dairy systems could help to decrease GHG emissions, natural resources use and nutrient excretion.Keywords: Carbon footprint, environmental impact, methane, milk productio

La educación en ciencias de la naturaleza en la secundaria vista por universitarios colombianos

Se presentan los resultados de unainvestigación relacionada con la percepción del estudiantado universitario acerca de la contribución de la Educación en Ciencias de la Naturaleza recibida durante la secundariaa la formación en las competencias científicas planteadas por el Ministerio deEducación Nacional de Colombia.Los resultados muestran que un mayor número de estudiantes considera que la educación en ciencias contribuyó al desarrollo de las diversas competencias analizadas. Los factores que más influyeron en esta formación fueron la motivación propia del estudiante, las estrategias de enseñanza y las características de personalidad de los profesores. Para aquellos estudiantes que consideraron que la educación en ciencias no contribuyó a su formación, los resultados muestran que los factores que más influyeron en sus respuestas fueron las estrategias de enseñanza de los profesores, la motivación propia del estudiante y los contenidos temáticos tratados en los cursos de ciencias

Comparison of forest regeneration in two sites with different primate abundances in Northwestern Ecuador

There is increasing evidence that large-bodied primates play important roles as seed dispersers and in the maintenance of tree diversity in forest ecosystems. In this study we compared forest regeneration at two sites with differing primate abundances in the Ecuadorian Chocoan rainforest. We predicted: (1) significant differences in primate abundance between the two sites; (2) higher understory tree species richness and density at the site with greater primate abundance; (3) the site with lower primate abundance characterized by tree species dispersed by non-primate biotic agents and/or abiotic factors. We compared two sites, Tesoro Escondido (TE) a campesino cooperative, and the El Pambilar (EP) wildlife refuge that both maintain populations of mantled howler monkey (Alouatta palliata), the brown-headed spider monkey (Ateles fusciceps fusciceps) and the capuchin monkey (Cebus capucinus). We characterized canopy structure by point-quadrant sampling, determined primate abundance and sampled seedlings/saplings in 1 m2 plots, classifying tree species based on three dispersal syndromes: adapted for primate dispersal, dispersed by other biological agents, and abiotic dispersal. We compared sites in terms of primate abundance (groups and individuals observed per day) and regeneration characteristics (overall density, species richness, and dispersal syndrome). We carried out within site comparisons and constructed understory tree species accumulation curves. Overall the forests were structurally similar - with significantly higher densities of A. f. fusciceps at TE. Encounter rates for the other two primate species were similar at both sites. Understory tree density and species richness was significantly higher in TE with no stabilization of tree species accumulation curves. The species accumulation curve for understory trees at EP stabilized. Higher densities and species richness of primate dispersed tree species were observed at TE, with non-primate biotically dispersed tree species the dominant dispersal syndrome at both sites. Our observations are consistent with those from other studies investigating the role of large-bodied frugivorous primates in forest regeneration, and point to a general pattern: future lowland tropical forest tree diversity depends on maintaining robust populations of large primate species in these systems. It is highly probable that the maintenance of high levels of tree diversity in Chocoan rainforests is dependent on the conservation of its largest resident primate, the critically endangered brown-headed spider monkey (A. f. fusciceps)

Tasa de infección en el sitio operatorio en cirugía de revascularización miocárdica en la Fundación Santa Fe de Bogotá

Antecedentesse ha reportado mediastinitis hasta en 4% de los pacientes que se someten a revascularización miocárdica, con una mortalidad cercana al 25%. Es una complicación potencialmente letal, de etiología multifactorial, que influye en la calidad de vida y en el pronóstico del paciente, y que, asimismo, genera un elevado costo derivado de su atención. Hasta en 25% de los pacientes se ha informado infección de la safenectomía, con una morbilidad asociada elevada.Objetivosdeterminar el porcentaje de tasas de infección del sitio operatorio superficial y profundo después de cirugía de revascularización miocárdica en pacientes operados en la Fundación Santa Fe de Bogotá que recibieron profilaxis con gentamicina y vancomicina según protocolo institucional.Métodosestudio de corte trasversal retrospectivo, realizado en 228 pacientes sometidos a cirugía de revascularización miocárdica en la Fundación Santa Fe de Bogotá durante un periodo de cuatro años (enero 2006 a diciembre 2009).Resultadosde los 228 pacientes, seis presentaron infecciones del sitio operatorio superficial de la safenectomía (2,63%), uno dehiscencia de la esternotomía sin mediastinitis (0,43%) y uno infección del sitio operatorio superficial de esternotomía (0,43%). No hubo infecciones profundas del sitio operatorio (esternotomía ni safenectomía).Conclusionesla profilaxis usada para cirugía cardiovascular en la Fundación Santa Fe de Bogotá ha demostrado menor incidencia de infección del sitio operatorio tanto superficial como profundo, en comparación con la que recomiendan en las guías de la ACC/AHA, sin aumentar la incidencia de resistencia a los antibióticos usados.Backgroundmediastinitis has been reported in up to 4% of patients undergoing CABG with a mortality approaching 25%. It is a potentially lethal complication of multifactorial etiology that influences patient's life quality and prognosis and generates besides a high cost. Safenectomy infection with associated high morbidity has been reported in up to 25% patients.Objectivesto determine the rate of infection of the superficial and deep surgical site after myocardial revascularization in patients operated in the Fundación Santa Fe de Bogotá that received gentamicin and vancomycin prophylaxis in accordance with the institutional protocol.Methodsretrospective cross sectional study conducted in 228 patients undergoing CABG surgery at the Fundación Santa Fe de Bogotá during a period of four years (January 2006 to December 2009).Resultsof the 228 patients, six had infection of the superficial surgical safenectomy site (2,63%), one had sternotomy dehiscence without mediastinits (0,43%) and one had surgical site superficial infection of the sternotomy (0,43%). No deep surgical site infections occurred (sternotomy or safenectomy).Conclusionsthe antibiotic prophylaxis used in the Fundación Santa Fe de Bogotá for cardiovascular surgery has demonstrated lower surgical site infection incidence, both superficial and deep, compared to the recommended in the ACC/AHA guidelines, without increment in the incidence of resistance to the antibiotics used

Atypical modulations of N170 component during emotional processing and their links to social behaviors in ex-combatants

ABSTRACT: Emotional processing (EP) is crucial for the elaboration and implementation of adaptive social strategies. EP is also necessary for the expression of social cognition and behavior (SCB) patterns. It is well-known that war contexts induce socio-emotional atypical functioning, in particular for those who participate in combats. Thus, ex-combatants represent an ideal non-clinical population to explore EP modulation and to evaluate its relation with SCB. The aim of this study was to explore EP and its relation with SCB dimensions such as empathy, theory of mind and social skills in a sample of 50 subjects, of which 30 were ex-combatants from illegally armed groups in Colombia, and 20 controls without combat experience. We adapted an Emotional Recognition Task for faces and words and synchronized it with electroencephalographic recording. Ex-combatants presented with higher assertion skills and showed more pronounced brain responses to faces than Controls. They did not show the bias toward anger observed in control participants whereby the latter group was more likely to misclassify neutral faces as angry. However, ex-combatants showed an atypical word valence processing. That is, words with different emotions yielded no differences in N170 modulations. SCB variables were successfully predicted by neurocognitive variables. Our results suggest that in ex-combatants the links between EP and SCB functions are reorganized. This may reflect neurocognitive modulations associated to chronic exposure to war experiences