Microscopic origin of granular ratcheting

Numerical simulations of assemblies of grains under cyclic loading exhibit ``granular ratcheting'': a small net deformation occurs with each cycle, leading to a linear accumulation of deformation with cycle number. We show that this is due to a curious property of the most frequently used models of the particle-particle interaction: namely, that the potential energy stored in contacts is path-dependent. There exist closed paths that change the stored energy, even if the particles remain in contact and do not slide. An alternative method for calculating the tangential force removes granular ratcheting.Comment: 13 pages, 18 figure

Indeterminacy, Memory, and Motion in a Simple Granular Packing

We apply two theoretical and two numerical methods to the problem of a disk placed in a groove and subjected to gravity and a torque. Methods assuming rigid particles are indeterminate -- certain combinations of forces cannot be calculated, but only constrained by inequalities. In methods assuming deformable particles, these combinations of forces are determined by the history of the packing. Thus indeterminacy in rigid particles becomes memory in deformable ones. Furthermore, the torque needed to rotate the particle was calculated. Two different paths to motion were identified. In the first, contact forces change slowly, and the indeterminacy decreases continuously to zero, and vanishes precisely at the onset of motion, and the torque needed to rotate the disk is independent of method and packing history. In the second way, this torque depends on method and on the history of the packing, and the forces jump discontinuously at the onset of motion.Comment: 11 pages, 7 figures, submitted to Phys Rev

Weight bias internalization among adolescents in Spain: psychological correlates across gender diversity and weight status

Weight bias internalization refers to the negative weight-related attributions applied to oneself, but it does not just occur in the highest weight statuses, but rather exists across the entire weight spectrum. There is a negative impact associated to increase psychological problems in adults, however, it has been less studied among the adolescent Spanish population. In this study, we assess the relationship between the internalization of weight bias, social attitudes towards appearance, body appreciation and self-esteem, and potential differences regarding gender and weight status. A community sample of 1258 Spanish adolescents between 12 and 18 years old (46.3% male gender; Mage = 15.58; SD = 1.59; 49.5% female gender; Mage = 15.59; SD = 1.67; and 4.1% non-binary gender; Mage = 14.86; SD = 2.86) participated in the study. The Modified Weight Bias Internalization Scale (WBIS-M), the Rosenberg Self-Esteem Scale (RSES), and the Sociocultural Attitudes Towards Appearance Questionnaire (SATAQ-4) were used. ANOVA’s test and bivariate correlations were performed. The results suggest that females (t = -.55; p ≤ .001) and non-binary adolescents (t = .64; p ≤ .01) have higher levels of WBI-M compared to males. Regarding weight status, the group with obesity (t = 1.39; p ≤ .001) and the group with overweight (t = -.81; p ≤ .001) have higher levels of WBI-M compared to the normal weight group. Significant correlations between WBI-M and the assessed psychological variables were found in the total sample, and across all-gender and weight categories, except for the underweight group. These results are a first approximation to the internalization of weight bias in a Spanish adolescent sample and highlight the need to introduce this concept in prevention and psychological interventions in school context.La internalización de los prejuicios de peso entre los y las adolescentes en España: correlatos psicológicos en función del género y el estatus de peso. La internalización de los prejuicios de peso hace referencia a las atribuciones negativas relacionadas con el peso aplicadas a uno mismo/a, lo cual no ocurre únicamente en las personas con un estatus de peso elevado, sino en todo el rango de pesos. En adultos, existe evidencia de su impacto negativo asociados a incrementar problemas psicológicos; aunque se ha estudiado en menor medida en la población adolescente. El objetivo de este estudio fue examinar la relación entre la internalización de prejuicios de peso, las actitudes socioculturales hacia la apariencia, la apreciación corporal y el nivel de autoestima, y analizar las posibles diferencias en función del género y del estatus de peso. Participaron 1.258 adolescentes españoles de una muestra comunitaria entre 12 y 18 años (46.3% género masculino; Medad = 15.58; DT = 1.59; 49,5% género femenino; Medad = 15.59; DT = 1.67; y 4.1% género no binario; Medad = 14.86; DT = 2.86). Se utilizaron la escala de internalización de prejuicios de peso modificado (WBIS-M), la escala de autoestima de Rosenberg (RSES) y el cuestionario de actitudes socioculturales hacia la apariencia (SATAQ-4). Se realizó la prueba ANOVA y correlaciones bivariadas. Los resultados sugieren que el grupo identificado con el género femenino (t = -.55; p ≤ .001) y con el no binario (t = .64; p ≤ .01) muestran niveles más altos de internalización del sesgo de peso en comparación con el género masculino. En cuanto al estado ponderal, el grupo con obesidad (t = 1.39; p ≤ .001) y el grupo con sobrepeso (t = -.81; p ≤ .001) presentan niveles más altos de internalización de prejuicios de peso en comparación con el grupo con normopeso. Se encontraron correlaciones significativas entre las puntuaciones del WBIS-M y las variables psicológicas evaluadas en la muestra total y en todas las categorías de género y peso, con la excepción del grupo de bajo peso. Estos resultados son una primera aproximación a la interiorización del estigma del peso en una muestra adolescente española y resalta la necesidad de incluir esta dimensión en la prevención de las alteraciones de la imagen corporal y los problemas psicológicos relacionados con la autoestima entre adolescentes en el contexto escolar

Langerin-Heparin Interaction: Two Binding Sites for Small and Large Ligands as revealed by a combination of NMR Spectroscopy and Cross-Linking Mapping Experiments

Langerin is a C-type lectin present on Langerhans cells that mediates capture of pathogens in a carbohydrate-dependent manner, leading to subsequent internalization and elimination in the cellular organelles called Birbeck granules. This mechanism mediated by langerin was shown to constitute a natural barrier for HIV-1 particle transmission. Besides interacting specifically with high mannose and fucosylated neutral carbohydrate structures, langerin has the ability to bind sulfated carbohydrate ligands as 6-sulfated galactosides in the Ca2+ dependent binding site. Very recently langerin was demonstrated to interact with sulfated glycosaminoglycans (GAGs), in a Ca2+ independent way, resulting in the proposal of a new binding site for GAGs. Based on those results, we have conducted a structural study of the interactions of small heparin (HEP) like oligosaccharides with langerin in solution. Heparin-bead cross-linking experiments, an approach specifically designed to identify HEP/HS binding sites in proteins were first carried out and experimentally validated the previously proposed model for the interaction of Lg ECD with 6 kDa HEP. High-resolution NMR studies of a set of 8 synthetic HEP-like trisaccharides harboring different sulfation patterns demonstrated that all of them bound to langerin in a Ca2+ dependent way. The binding epitopes were determined by STD NMR and the bound conformations by transferred NOESY experiments. These experimental data were combined with docking and molecular dynamics and resulted in the proposal of a binding mode characterized by the coordination of calcium by the two equatorial hydroxyl groups OH3 and OH4 at the non-reducing end. The binding also includes the carboxylate group at the adjacent iduronate residue. Such epitope is shared by all the 8 ligands, explaining the absence of any impact on binding from their differences in substitution pattern. Finally, in contrast to the small trisaccharides, we demonstrated that a longer HEP-like hexasaccharide, bearing an additional O-sulfate group at the non-reducing end, which precludes binding to the Ca2+ site, interacts with langerin in the previously identified Ca2+ independent binding site

EFFECT OF SEASON ON SERUM COPPER AND ZINC CONCENTRATIONS IN CROSSBRED GOATS HAVING DIFFERENT REPRODUCTIVE STATUS UNDER SEMIARID RANGELAND CONDITIONS IN SOUTHERN MEXICO STATE

The effect of season (rainy: RS, and dry: DS) and reproductive status on copper (Cu) and zinc (Zn) concentrations in blood serum of crossbred goats (BW= 36.01 ± 1.59 kg) were studied under semiarid rangeland conditions in Southern Mexico State. Blood samples from 80 crossbred goats were taken each season (RS and DS). The goats were clustered into 10 different groups considering their reproductive status. Concentrations of Cu and Zn in serum were assayed using atomic absorption. Data were analyzed using a general linear model procedure for a completely randomized design and differences among means were examined using a Tukey test. Blood serum concentrations of Cu and Zn were affected by reproductive status and season (P<0.001). In relation to the season, Cu and Zn serum levels were lower in RS than DS (P<0.05). Overall, kidded goats had the highest values (P<0.01) for Cu than other animals in both seasons (RS or DS). Anestrous goats had the lowest concentrations (P<0.01) for Zn during RS, while all goats at their second or more kidding, rearing single or twins, showed the highest concentrations of Zn (P<0.001) in this season. Adult goats in Southern Mexico State showed a deficiency of Cu and Zn, especially during RS. As such, mineral supplements should be provided with respect to these elements in feeding systems for goats under semiarid rangeland conditions in order to evaluate their impact on health and reproduction

Engineering and Directed Evolution of a Ca2+ Binding Site A-Deficient AprE Mutant Reveal an Essential Contribution of the Loop Leu75–Leu82 to Enzyme Activity

An aprE mutant from B. subtilis 168 lacking the connecting loop Leu75–Leu82 which is predicted to encode a Ca2+ binding site was constructed. Expression of the mutant gene (aprEΔLeu75–Leu82) produced B. subtilis colonies lacking protease activity. Intrinsic fluorescence analysis revealed spectral differences between wild-type AprE and AprEΔL75–L82. An AprEΔL75–L82 variant with reestablished enzyme activity was selected by directed evolution. The novel mutations Thr66Met/Gly102Asp located in positions which are predicted to be important for catalytic activity were identified in this variant. Although these mutations restored hydrolysis, they had no effect with respect to thermal inactivation of AprEΔL75–L82 T66M G102D. These results support the proposal that in addition to function as a calcium binding site, the loop that connects β-sheet e3 with α-helix c plays a structural role on enzyme activity of AprE from B. subtilis 168

Transversal inhomogeneities in dilute vibrofluidized granular fluids

The spontaneous symmetry breaking taking place in the direction perpendicular to the energy flux in a dilute vibrofluidized granular system is investigated, using both a hydrodynamic description and simulation methods. The latter include molecular dynamics and direct Monte Carlo simulation of the Boltzmann equation. A marginal stability analysis of the hydrodynamic equations, carried out in the WKB approximation, is shown to be in good agreement with the simulation results. The shape of the hydrodynamic profiles beyond the bifurcation is discussed

Transport coefficients for dense hard-disk systems

A study of the transport coefficients of a system of elastic hard disks, based on the use of Helfand-Einstein expressions is reported. The self-diffusion, the viscosity, and the heat conductivity are examined with averaging techniques especially appropriate for the use in event-driven molecular dynamics algorithms with periodic boundary conditions. The density and size dependence of the results is analyzed, and comparison with the predictions from Enskog's theory is carried out. In particular, the behavior of the transport coefficients in the vicinity of the fluid-solid transition is investigated and a striking power law divergence of the viscosity in this region is obtained, while all other examined transport coefficients show a drop in that density range.Comment: submitted to PR