Hopanoid lipids may facilitate aerobic nitrogen fixation in the ocean.

Cyanobacterial diazotrophs are considered to be the most important source of fixed N2 in the open ocean. Biological N2 fixation is catalyzed by the extremely O2-sensitive nitrogenase enzyme. In cyanobacteria without specialized N2-fixing cells (heterocysts), mechanisms such as decoupling photosynthesis from N2 fixation in space or time are involved in protecting nitrogenase from the intracellular O2 evolved by photosynthesis. However, it is not known how cyanobacterial cells limit O2 diffusion across their membranes to protect nitrogenase in ambient O2-saturated surface ocean waters. Here, we explored all known genomes of the major marine cyanobacterial lineages for the presence of hopanoid synthesis genes, since hopanoids are a class of lipids that might act as an O2 diffusion barrier. We found that, whereas all non-heterocyst-forming cyanobacterial diazotrophs had hopanoid synthesis genes, none of the marine Synechococcus, Prochlorococcus (non-N2-fixing), and marine heterocyst-forming (N2-fixing) cyanobacteria did. Finally, we conclude that hopanoid-enriched membranes are a conserved trait in non-heterocyst-forming cyanobacterial diazotrophs that might lower the permeability to extracellular O2 This membrane property coupled with high respiration rates to decrease intracellular O2 concentration may therefore explain how non-heterocyst-forming cyanobacterial diazotrophs can fix N2 in the fully oxic surface ocean

Barotropic thin shells with linear EOS as models of stars and circumstellar shells in general relativity

The spherically symmetric thin shells of the barotropic fluids with the linear equation of state are considered within the frameworks of general relativity. We study several aspects of the shells as completely relativistic models of stars, first of all the neutron stars and white dwarfs, and circumstellar shells. The exact equations of motion of the shells are obtained. Also we calculate the parameters of the equilibrium configurations, including the radii of static shells. Finally, we study the stability of the equilibrium shells against radial perturbations.Comment: final version; ps-version of figure is available by email request to [email protected]

Nonlinear Blend Scheduling via Inventory Pinch-based Algorithm using Discrete- and Continuous-time Models

This work uses multi-period, inventory pinch-based algorithm with continuous-time model (MPIP-C algorithm1) for scheduling linear or nonlinear blending processes. MPIP-C decomposes the scheduling problem into (i) approximate scheduling and (ii) detailed scheduling. Approximate scheduling model is further decomposed into two parts: a 1st level model which optimizes nonlinear blend models (with time periods delineated by inventory pinch points), and a 2nd level multi-period mixed-integer linear programming model (which uses fixed blend recipes from the 1st level solution) to determine optimal production plan and swing storage allocation, while minimizing the number of blend instances and product changeovers in the swing tanks. The 3rd level computes schedules using a continuous-time model including constraints based on the short-term plan solution. Nonlinear constraints are used for the Reid vapor pressure in our case studies. Excellent computational performance is illustrated by comparisons with previous approach with discrete-time scheduling model

There’s No “Me” in “Imgur”: Applying SIDE Theory and Content Analysis to Viral Posts on Imgur.com

The Social Identity model of Deindividuation Effects (SIDE) asserts that social (i.e., collective) identities are more salient under conditions of anonymity, prompting “deindividuation” as group members place more focus on community standards and downplay individual differences. As a result of deindividuation, social standards become the driving force of group interaction, and the successful practice of group norms identify individuals’ in-group status while reinforcing the social identity of the community. The current study applies the SIDE model to the anonymous image-sharing platform Imgur.com to ascertain whether self-referential posts are assessed more negatively than other-referential and non-directed content, and to examine whether posts of varying referential-type occur more frequently across post-type subcategories. A content analysis of 42 posts to Imgur’s “front page” revealed that self-referential posts receive significantly more “downvotes” (i.e., negative assessments) than non-directed content and substantially more downvotes compared to other-referential posts. Further, self-referential content was most common within the subcategories of “capitalizing” and “social support,” as compared to “community identification” and “information / mobilization” for other-referential, and “visually appealing” and “humor” for non-directed posts. The findings suggest that the Imgur community engages in voting habits that favor the maintenance of social identity over the sharing of individuating information, providing sustained support for the applicability of SIDE in anonymous online contexts such as Imgur

Mass of perfect fluid black shells

The spherically symmetric singular perfect fluid shells are considered for the case of their radii being equal to the event horizon (the black shells). We study their observable masses, depending at least on the three parameters, viz., the square speed of sound in the shell, instantaneous radial velocity of the shell at a moment when it reaches the horizon, and integration constant related to surface mass density. We discuss the features of black shells depending on an equation of state.Comment: 1 figure, LaTeX; final version + FA

Plan de mejoras técnicas para la manipulación y conservación de alimentos en el mercado municipal de durán (sector nave 2)

El presente trabajo propone establecer sistemas de buenas prácticas de manipulación y conservación de alimentos, así como brindar las recomendaciones técnicas que ayuden a mejorar la comercialización de los mismos en los diferentes mercados del país. . Para lograr el objetivo se hizo un acercamiento con la M.I. Municipalidad del cantón Durán permitiendo iniciarse la evaluación de su situación inicial. Considerando la distribución y requerimientos sanitarios para el expendio de alimentos, se diseñó un plan de mejoras referente a una redistribución de los locales con el fin de evitar la contaminación cruzada; un plan de limpieza adecuado según el tipo de alimento que se comercializa, además se consideró el diseño sanitario tomando en cuenta los requerimientos de servicios como agua para limpieza y correcto funcionamiento del mercado; la propuesta incluye asimismo el diseño de una cámara de frio con el fin de alargar el tiempo de vida útil de los alimentos. Adicionalmente, se hicieron capacitaciones direccionadas a los comerciantes de diferentes grupos de alimentos con el fin de proponer aspectos técnicos que disminuyan las pérdidas por una manipulación incorrecta. Finalmente se realizó una estimación en cuanto al costo de implementación del proyecto