Isostaticity and the solidification of semiflexible polymer melts

Using molecular dynamics simulations of a tangent-soft-sphere bead-spring polymer model, we examine the degree to which semiflexible polymer melts solidify at isostaticity. Flexible and stiff chains crystallize when they are isostatic as defined by appropriate degree-of-freedom-counting arguments. Semiflexible chains also solidify when isostatic if a generalized isostaticity criterion that accounts for the slow freezing out of configurational freedom as chain stiffness increases is employed. The dependence of the average coordination number at solidification $Z(T_s)$ on chains' characteristic ratio $C_\infty$ has the same functional form [$Z \simeq a - b\ln(C_\infty)$] as the dependence of the average coordination number at jamming $Z(\phi_J)$ on $C_\infty$ in athermal systems, suggesting that jamming-related phenomena play a significant role in thermal polymer solidification

Biological synthesis of fluorescent nanoparticles by cadmium and tellurite resistant Antarctic bacteria: exploring novel natural nanofactories

Indexación: Web of ScienceBackground: Fluorescent nanoparticles or quantum dots (QDs) have been intensely studied for basic and applied research due to their unique size-dependent properties. There is an increasing interest in developing ecofriendly methods to synthesize these nanoparticles since they improve biocompatibility and avoid the generation of toxic byproducts. The use of biological systems, particularly prokaryotes, has emerged as a promising alternative. Recent studies indicate that QDs biosynthesis is related to factors such as cellular redox status and antioxidant defenses. Based on this, the mixture of extreme conditions of Antarctica would allow the development of natural QDs producing bacteria. Results: In this study we isolated and characterized cadmium and tellurite resistant Antarctic bacteria capable of synthesizing CdS and CdTe QDs when exposed to these oxidizing heavy metals. A time dependent change in fluorescence emission color, moving from green to red, was determined on bacterial cells exposed to metals. Biosynthesis was observed in cells grown at different temperatures and high metal concentrations. Electron microscopy analysis of treated cells revealed nanometric electron-dense elements and structures resembling membrane vesicles mostly associated to periplasmic space. Purified biosynthesized QDs displayed broad absorption and emission spectra characteristic of biogenic Cd nanoparticles. Conclusions: Our work presents a novel and simple biological approach to produce QDs at room temperature by using heavy metal resistant Antarctic bacteria, highlighting the unique properties of these microorganisms as potent natural producers of nano-scale materials and promising candidates for bioremediation purposes.http://microbialcellfactories.biomedcentral.com/articles/10.1186/s12934-016-0477-

El resentimiento público.

La impunidad ha sido en los últimos tiempos un material televisivo y noticioso de numerosos es pectadores y lectores, de tal forma que cualquier ciudadano colombiano está mínimamente enterado de lo que ocurre en nuestro país: señalo al menos dos ejemplos, no por escabrosos, menos válidos: se han encontrado más de mil fosas con restos, en muchos casos descuartizados, de las víctimas de los paramilitares; ya se ha reconocido públicamente, pero el ciudadano menos informado tendrá alguna “sospecha confirmada” de la cooptación del Estado por parte de los grupos paramilitares en sus nexos con congresistas de la coalición de gobierno

Plasmon enhanced energy-transfer up-conversion in Yb3+-Er3+ co-doped LiNbO3 crystal

We have analyzed the effect of linear chains of metallic Ag nanoparticles on the optical properties of a periodically poled Yb 3+ -Er 3+ co-doped LiNbO 3 crystal. By exploiting the broad plasmonic response supported by linear chains of strongly coupled Ag nanoparticles, we demonstrate a 50% of enhancement of the up-converted Er 3+ emission under excitation in the f-f transition of Yb 3+ ions. The observed intensification is explained in terms of the broad plasmonic spectral response supported by the Ag chains, which overlaps both the Er 3+ visible emissions and the Yb 3+ absorption band, and the two-photon character of the Yb 3+ → Er 3+ energy-transfer up-conversion process. The results are of interest for applications involving luminescence up-conversion such as sensing, solar energy conversion, biological imaging or solid-state nanolasersThis work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under project MAT2013- 43301-R and Comunidad de Madrid under grant S2013/MIT-274

Downward pumping of magnetic flux as the cause of filamentary structures in sunspot penumbrae

The structure of a sunspot is determined by the local interaction between magnetic fields and convection near the Sun's surface. The dark central umbra is surrounded by a filamentary penumbra, whose complicated fine structure has only recently been revealed by high-resolution observations. The penumbral magnetic field has an intricate and unexpected interlocking-comb structure and some field lines, with associated outflows of gas, dive back down below the solar surface at the outer edge of the spot. These field lines might be expected to float quickly back to the surface because of magnetic buoyancy, but they remain submerged. Here we show that the field lines are kept submerged outside the spot by turbulent, compressible convection, which is dominated by strong, coherent, descending plumes. Moreover, this downward pumping of magnetic flux explains the origin of the interlocking-comb structure of the penumbral magnetic field, and the behaviour of other magnetic features near the sunspot

Spectral stability of noncharacteristic isentropic Navier-Stokes boundary layers

Building on work of Barker, Humpherys, Lafitte, Rudd, and Zumbrun in the shock wave case, we study stability of compressive, or "shock-like", boundary layers of the isentropic compressible Navier-Stokes equations with gamma-law pressure by a combination of asymptotic ODE estimates and numerical Evans function computations. Our results indicate stability for gamma in the interval [1, 3] for all compressive boundary-layers, independent of amplitude, save for inflow layers in the characteristic limit (not treated). Expansive inflow boundary-layers have been shown to be stable for all amplitudes by Matsumura and Nishihara using energy estimates. Besides the parameter of amplitude appearing in the shock case, the boundary-layer case features an additional parameter measuring displacement of the background profile, which greatly complicates the resulting case structure. Moreover, inflow boundary layers turn out to have quite delicate stability in both large-displacement and large-amplitude limits, necessitating the additional use of a mod-two stability index studied earlier by Serre and Zumbrun in order to decide stability

Threading holder based on axial metal cylinder pins to reduce tap risk during reversion instant

Internal thread profiles are used widely in manufacturing processes with the aim of assembling/disassembling different components during maintenance activities from the aeronautics sector until common industrial parts. The threading process is one of the last operations carried out to obtain those components, and consequently, it is an operation of high added value. Threading is a complex operation that must carefully synchronize the rotation with the feed movements to avoid tool breakage during the instant of tapping reversion stage. In order to avoid this risk, several toolholders were developed present in the literature but deficiencies in terms of stability and productivity. Therefore, in this work, a new toolholder is proposed in which the common springs used to mitigate the lack of perfect synchronization between rotation and feed movements are replaced by elastic metal pins achieving a torsional compliance toolholder. The results show that the use of the proposed toolholder implies not only a productivity increase but also a surface integrity improvement as well as a stress reduction that the cutting tap is subjected and thus, achieving a substantial improvement in the current tapping processes. In particular, the use of the proposed toolholder implied a 75% reduction of the maximum stress achieved in the reversal instant, improving 20% tool life with an increase of 30% cutting speed. Therefore, the use of the proposed toolholder implies a substantial improvement in the current tapping processes

Conceptos Claves en el Trabajo Comunitario

Introducción. En el marco de la investigación sobre características del Trabajo Comunitario (TC) en la ciudad de Córdoba desde la perspectiva de distintos actores, plantearemos aquí la visión de las Organizaciones Políticas Territoriales (OPT). Abordaremos algunos resultados respecto del eje Conceptos Claves en el TC, conformado por las dimensiones: participación, importancia de la participación, lo construido en común (tres sub dimensiones: lo destacable, lo que aporta y lo difícil en el construir en común) y lecturas sobre TC. Se realizarán relaciones con el eje Sentimientos y con la dimensión Relación entre TC y políticas públicas. Metodología. Estudio descriptivo-cualitativo. Muestra conformada por OPT que realicen TC-territorial. Recolección de datos desde entrevista semiestructurada. Análisis cuantitativo y cualitativo. Comparación de las características del TC y sus cambios según estudios anteriores; análisis de semejanzas y diferencias entre la OPT y otros actores. Resultados. Configuran el conjunto de conceptos claves “organización” y “lo colectivo”, destacándose como central “participación”. En lo construido en común se destaca: “El hacer cosas juntos”: nuevos sentidos, vínculos, organización, cambios, aprendizajes; y “sentidos y sentimientos de pertenencia a la comunidad”. Como dificultades: “Lograr acuerdos”, “La “participación”, “indiferencia”. Discusión. Son nombrados solo una vez, “confianza” y “cambio social”. Relacionado con el campo de los sentimientos: “lo que motiva a seguir” y “lo que desanima”, en ambos se alude al cambio. El Estado es nombrado escasamente. Aquí articularemos con la dimensión “relación entre Políticas Publicas y TC” y con las matrices política-ideológicas. Se afirma una fuerte relación entre lo construido en común y participación

Plasmon assisted Nd3+-based solid-state nanolaser

Solid-state lasers constitute essential tools in a variety of scientific and technological areas, being available in many different designs. However, although nanolasing has been successfully achieved for dyes and semiconductor gain media associated with plasmonic structures, the operation of solid-state lasers beyond the diffraction limit has not been reported yet. Here, we demonstrate room temperature laser action with subwavelength confinement in a Nd3+-based solid-state laser by means of the localized surface plasmon resonances supported by chains of metallic nanoparticles. We show a 50% reduction of the pump power at threshold and a remarkable 15-fold improvement of the slope efficiency with respect to the bulk laser operation. The results can be extended to the large diversity of solid-state lasers with the subsequent impact on their applicationsThis work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under projects MAT2013-43301-R and FIS2013-41184-P and Comunidad de Madrid under grant S2013/MIT-2740

Fit-Fat Index is better associated with heart rate variability compared to fitness and fatness alone as indicators of cardiometabolic human health

ObjectivesCardiorespiratory fitness and fatness indicators have been related to heart rate variability (HRV) parameters. The Fit-Fat Index (FFI) is a single index combining cardiorespiratory fitness and fatness indicators. To the best of our knowledge, no studies have previously analyzed whether FFI are related to cardiac autonomic nervous system activity assessed through HRV parameters. This study aimed (i) to examine the association of cardiorespiratory fitness, fatness indicators, and FFI with HRV parameters; and (ii) to report what of the different fatness indicators included in FFI is better associated with HRV parameters in sedentary adults. MethodsOne hundred and fifty healthy adults (74 women; 76 men), aged between 18 and 65 years old, participated in this cross-sectional study. We measured cardiorespiratory fitness (maximal oxygen consumption) and fatness indicators (waist-to-height ratio [WHR], fat mass percentage [FM%] and visceral adipose tissue [VAT]). Three FFIs were calculated as the quotient between cardiorespiratory fitness and one out of three possible fatness indicators: Fit-Fat Index calculated waist-to-height ratio (FFIWHR), Fit-Fat Index calculated with FM% (FFIFM%), and Fit-Fat Index calculated with VAT (FFIVAT). HRV parameters were measured in resting conditions using a Polar RS800CX. ResultsFFI(WTHR), FFIFM% and FFIVAT were related to different HRV parameters (beta ranges between -0.507 and 0.529; R-2 ranges between 0.096 and 0.275; all p < .001) and the association was stronger with HRV parameters than the isolated fitness or fatness indicators (beta ranges between -0.483 and 0.518; R-2 ranges between 0.071 and 0.263; all p < .001). FFIVAT was the index more consistently associated with HRV parameters (beta ranges between -0.507 and 0.529; R-2 ranges between 0.235 and 0.275; all p < .001). ConclusionOur study suggests that compound FFIs are better predictors of HRV parameters than either cardiorespiratory fitness or fatness indicators alone. The FFIVAT was the best index in terms of its association to HRV.Spanish Ministry of Education FPU16/02760, FPU14/04172United States Department of Health & Human Services National Institutes of Health (NIH) - USA U01 TR00200