Superposition rheology of shear-banding wormlike micelles

Wormlike micelle solutions are submitted to small-amplitude oscillatory shear superimposed to steady shear in the shear banding regime. By imposing a shear oscillation, the interface between high- and low-shear regions oscillates in time. A two-fluid semi-phenomenological model is proposed for superposition rheology in the shear banding regime, which allows us to extract a characteristic velocity for the interface dynamics from experiments involving only a standard rheometer. Estimates of the stress diffusion coefficient ${\cal D}$ can also be inferred from such superposition experiments. The validity of our model is confirmed by directly recording the interface displacement using ultrasonic velocimetry.Comment: 24 pages, 13 figure

Wall slip and flow of concentrated hard-sphere colloidal suspensions

We present a comprehensive study of the slip and flow of concentrated colloidal suspensions using cone-plate rheometry and simultaneous confocal imaging. In the colloidal glass regime, for smooth, non-stick walls, the solid nature of the suspension causes a transition in the rheology from Herschel-Bulkley (HB) bulk flow behavior at large stress to a Bingham-like slip behavior at low stress, which is suppressed for sufficient colloid-wall attraction or colloid-scale wall roughness. Visualization shows how the slip-shear transition depends on gap size and the boundary conditions at both walls and that partial slip persist well above the yield stress. A phenomenological model, incorporating the Bingham slip law and HB bulk flow, fully accounts for the behavior. Microscopically, the Bingham law is related to a thin (sub-colloidal) lubrication layer at the wall, giving rise to a characteristic dependence of slip parameters on particle size and concentration. We relate this to the suspension's osmotic pressure and yield stress and also analyze the influence of van der Waals interaction. For the largest concentrations, we observe non-uniform flow around the yield stress, in line with recent work on bulk shear-banding of concentrated pastes. We also describe residual slip in concentrated liquid suspensions, where the vanishing yield stress causes coexistence of (weak) slip and bulk shear flow for all measured rates

Osteoporosis transitoria de la cadera: revisión de aspectos clínicos y terapéuticos a propósito de un caso

Presentamos el caso de una mujer de 17 años con osteoporosis transitoria de cadera (OTC). La OTC es una enfermedad infrecuente, difícil de etiquetar, que afecta a hombres sanos de mediana edad, y a mujeres en el tercer trimestre del embarzo. Su etiología todavía no está clara. Los principales signos clínicos son dolor en la cadera y cojera. La RM muestra en la cabeza y cuello femoral hipointensidad en las imágenes ponderadas en T1, e hiperintensidad en las imágenes ponderadas en T2. Se acepta que los cambios en la RM se producen por incremento de líquido en la cavidad medular de la cabeza femoral. Es importante el diagnóstico diferencial con otras enfermedades de la cadera. El propósito de esta publicación es aclarar los aspectos diagnósticos y terapéuticos de la OTC.A case of transient osteoporosis of the hips in a 17-year-old-woman is reported. Transient osteoporosis of the hip (TOH) is an uncommon but possibly underdiagnosed condition. The TOH affects previous healthy middle-age men, and women in the third trimester of pregnancy. Its etiology is still unclear. Pain in the hip area and limp are the main clinical signs. The MRI study shows low signal intensity on the Tl weighted images and limp signal intensity on the T2 weighted images in the femoral head and neck. It is generally accepted that the change in MRI is caused by an increase in fluid within the marrow cavities of the femoral head. Differential diagnosis of hip problems is required. The purpose of this report is to review the diagnostic and therapeutic aspects of TOH

Colloidal gels under shear: Strain rate effects

Attractive colloidal particles are trapped in metastable states such as colloidal gels at high attraction strengths and attractive glasses and high volume fractions. Under shear such states flow via a two step yielding process that relates to bond and cluster or cage breaking. We discuss the way the structural properties and related stress response are affected by the shear rate. At low rates colloidal gels yield during start-up shear essentially in a single step, exhibiting a single stress overshoot due to creation of compact flowing clusters. With increasing shear rate a second stress overshoot, linked with further cluster breaking up to individual particles, is becoming more pronounced. We further present the age dependence of the two step yielding and wall slip effects often taking place during rheological experiments of colloidal gels. The latter is related both with the shear rate dependent gel structure as well as the time evolution of the near wall structure

In vivo assembling of bacterial ribosomal protein L11 into yeast ribosomes makes the particles sensitive to the prokaryotic specific antibiotic thiostrepton

Article available at http://dx.doi.org/10.1093/nar/gkm773Eukaryotic ribosomal stalk protein L12 and its bacterial orthologue L11 play a central role on ribosomal conformational changes during translocation. Deletion of the two genes encoding L12 in Saccharomyces cerevisiae resulted in a very slow-growth phenotype. Gene RPL12B, but not the RPL12A, cloned in centromeric plasmids fully restored control protein level and the growth rate when expressed in a L12-deprived strain. The same strain has been transformed to express Escherichia coli protein EcL11 under the control of yeast RPL12B promoter. The bacterial protein has been found in similar amounts in washed ribosomes from the transformed yeast strain and from control E. coli cells, however, EcL11 was unable to restore the defective acidic protein stalk composition caused by the absence of ScL12 in the yeast ribosome. Protein EcL11 induced a 10% increase in L12-defective cell growth rate, although the in vitro polymerizing capacity of the EcL11-containing ribosomes is restored in a higher proportion, and, moreover, the particles became partially sensitive to the prokaryotic specific antibiotic thiostrepton. Molecular dynamic simulations using modelled complexes support the correct assembly of bacterial L11 into the yeast ribosome and confirm its direct implication of its CTD in the binding of thiostrepton to ribosomesThis work was funded by Ministerio de Educación y Ciencia, Spain (BFU2006-00365 to J.P.G.B., GEN2003-206420-C09-08 and BIO2005-0576 to A.R.O.); Fundación Ramón Areces (institutional grant to CBMSO)Peer reviewe

The short-term debt choice under asymmetric information

This paper investigates whether the market level of information asymmetry affects firms’ debt financing decisions. Using a sample of non-financial listed firms and a composite index based on microstructure measures of information asymmetry, we find that firms with more information asymmetry use shorter debt maturities. In addition, we find that these firms face more difficulties to access public debt and bank debt (particularly, short-term bank debt), and they have to rely on trade credit as an alternative source of short-term financing. Analyzing the associations in two subsamples based on firm size, we find that our results essentially driven by smaller companies, which are those affected by higher information asymmetries. Our findings support the information asymmetry theories of trade credit: as information asymmetry increases and, consequently, listed firms face more constraints in the credit markets, they increase the use of financing provided by their suppliers.David Abad acknowledges financial support from the Ministerio de Economía y Competitividad through Grants ECO2013-4409-P and ECO2014-58434-P. José Yagüe acknowledges financial support from Fundación Caja Murcia

Slip and flow of hard-sphere colloidal glasses

We study the flow of concentrated hard-sphere colloidal suspensions along smooth, non-stick walls using cone-plate rheometry and simultaneous confocal microscopy. In the glass regime, the global flow shows a transition from Herschel-Bulkley behavior at large shear rate to a characteristic Bingham slip response at small rates, absent for ergodic colloidal fluids. Imaging reveals both the `solid' microstructure during full slip and the local nature of the `slip to shear' transition. Both the local and global flow are described by a phenomenological model, and the associated Bingham slip parameters exhibit characteristic scaling with size and concentration of the hard spheres.Comment: 4 pages, 4 figures. Accepted for publication in PR

Three-dimensional jamming and flows of soft glassy materials

Various disordered dense systems such as foams, gels, emulsions and colloidal suspensions, exhibit a jamming transition from a liquid state (they flow) to a solid state below a yield stress. Their structure, thoroughly studied with powerful means of 3D characterization, exhibits some analogy with that of glasses which led to call them soft glassy materials. However, despite its importance for geophysical and industrial applications, their rheological behavior, and its microscopic origin, is still poorly known, in particular because of its nonlinear nature. Here we show from two original experiments that a simple 3D continuum description of the behaviour of soft glassy materials can be built. We first show that when a flow is imposed in some direction there is no yield resistance to a secondary flow: these systems are always unjammed simultaneously in all directions of space. The 3D jamming criterion appears to be the plasticity criterion encountered in most solids. We also find that they behave as simple liquids in the direction orthogonal to that of the main flow; their viscosity is inversely proportional to the main flow shear rate, as a signature of shear-induced structural relaxation, in close similarity with the structural relaxations driven by temperature and density in other glassy systems.Comment: http://www.nature.com/nmat/journal/v9/n2/abs/nmat2615.htm

Funcionalidad y recomendaciones nutricionales de ácidos grasos esenciales y sus derivados en la alimentación del lactante a partir de los 6 meses de edad

Essential fatty acids and long-chain unsaturated fatty acids are important for growth and neuronal development during the final months of gestation and the early years of life. The aim of this study is to highlight the importance of ensuring a correct intake of EFAs for nutritional requirements through the intake of foods which naturally contain these acids or which have been enriched with them. The methodology used was basee on the review of electronic databases MedLine, ScienceDirect, Scirus, Trip database and that of the scientific journal library of the University of Murcia. National and international websites such as  the Asociación Española de Pediatría (AEP), European Agency for Food Safety (EAFS) and the European Society of Pediatric, Gastroenterology, Health and Nutrition (ESPGHAN) were also consulted.   The results show how EFAs and also AGPI-CL (DHA and ARA) are essential for the correct development of breastfeeders and infants. Even though the breastfeeder is enzymatically fully equipped from the first day of life to convert EFAs into AGPI-CL and derivatives, the conversion may be insufficient  and it may be necessary to include AGPI-CL in the diet. The conclusions are that during the first 6 months of life  the provision of EFAs and AGPI-CL is assured thanks to the mother’s milk or through starter formulas; at six months the introduction of complementary foods and the adaptation to cow’s milk at  twelve months (against the recommendations of the ESPGHAN) may affect the provision of these acids. There is a legal vacuum in the issue of the provision of EFAs through complementary foods other than cereals although committees like the AEP recommend that AL in meat and fish baby foods with vegetables should suppose 3-4.5% of the energy provision, and ALN at least 0.5% in order to satisfy EFA requirements in breastfeeders ans infants.Los requerimientos de ácidos grasos esenciales (AGEs) y ácidos grasos poliinsaturados de cadena larga (AGPI-CL) durante los últimos meses de gestación y los primeros años de vida son importantes de acuerdo al crecimiento y desarrollo neuronal que está teniendo lugar durante este periodo de vida. El objetivo de este trabajo ha sido destacar la importancia de garantizar un correcta ingesta de AGEs para cubrir los requerimientos nutricionales de estos, a través de la ingesta de alimentos que contienen en su composición nutricional a estos ácidos de forma natural o han sido enriquecidos con ellos. La metodología empleada para este fin ha sido la utilización de  bases de datos electrónicas como MedLine, ScienceDirect, Scirus, Trip database y de la hemeroteca científica de la Universidad de Murcia; También han sido consultadas las páginas web de organismos nacionales e internacionales tales como la Asociación Española de Pediatría (AEP), Agencia Europea de Seguridad Alimentaria (EFSA) y European Society of Pediatric, Gastroenterology, Health and Nutrition (ESPGHAN). Los resultados obtenidos muestran como los AGEs e incluso los AGPI-CL (DHA y ARA) son esenciales para el correcto desarrollo del lactante y niño de corta edad; pues aún estando el lactante desde el primer día de vida dotado de todo el sistema enzimático necesario para la conversión de AGEs en sus correspondientes AGPI-CL y sus derivados, esta conversión podría ser insuficiente, siendo necesario y/o esencial el aporte de estos AGPI-CL a través de la dieta. Las conclusiones derivadas de este trabajo fueron que durante los seis primeros meses de vida el aporte de AGEs y AGPI-CL está asegurado a través de la leche materna o en su defecto a través de las fórmulas  de inicio; a partir de los 6 meses con la introducción de la alimentación complementaria y la introducción de la leche de vaca a partir de los 12 meses de vida (introducción en contra de las recomendaciones de ESPGHAN), podría verse comprometida la aportación de estos ácidos. Existe un vacío legal en cuanto a la aportación de AGEs a través de la alimentación complementaria distinta a los cereales; sin embargo, comités como el de la AEP recomienda que en los tarritos infantiles de carnes y pescados con verdura, el aporte de AL sea entre 3-4.5% de la energía de la dieta y al menos 0.5% desde ALN para satisfacer los requerimientos de AGEs en lactantes y niños de corta edad