Origin of density clustering in a freely evolving granular gas

The physical mechanisms leading to the development of density inhomogeneities in a freely evolving low density granular gas are investigated. By means of the direct simulation Monte Carlo method, numerical solutions of the inelastic Boltzmann equation are constructed for both a perturbed system and also for an initially homogeneous state. Analysis of the Fourier components of the fields indicates that the nonlinear coupling contributions of the transversal velocity play a crucial role in the initial setup of clustering. A simple hydrodynamic model is proposed to describe what is observed in the simulations. Finally, the nature of the inhomogeneous state is briefly discussed.This research was partially supported by Grant No. PB95-0534 from the Dirección General de Investigación Científica yTécnica ~ Spai

On the validity of linear hydrodynamics for low-density granular flows described by the Boltzmann equation

The direct Monte Carlo simulation method is used to check the validity of the hydrodynamic description of a low-density granular flow in the linear region about the homogeneous cooling state. Good agreement is found between the simulation results and the hydrodynamic equations obtained recently from the Boltzmann equation by using a generalized Chapman-Enskog procedure. In particular, the dependence of the transport coefficients on the coefficient of restitution predicted by the theory is verified.Grant No. PB98-1124 from the Dirección General de Investigación Científica y Técnica (Spain)

High energy tail in the velocity distribution of a granular gas

The Enskog-Boltzmann equation for a homogeneous freely evolving system of smooth hard disks colliding inelastically is solved by means of the direct simulation Monte Carlo method. The distribution function shows an exponential high velocity tail, while it is Gaussian for small velocities. The numerical results are compared with recent predictions of approximate analytical theories and quite good agreement is found.This research was partially supported by Grant No. PB96-0534 from the Dirección General de Investigación Científica y Técnica (Spain

Homogeneous cooling state of a low-density granular flow

The homogeneous cooling state of a granular flow of smooth spherical particles described by the Boltzmann equation is investigated by means of the direct simulation Monte Carlo method. The velocity moments and also the velocity distribution function are obtained and compared with approximate analytical results derived recently. The accuracy of a Maxwell-Boltzmann approximation with a time-dependent temperature is discussed. Besides, the simulations show that the state of uniform density is unstable to long enough wavelength perturbations so that clusters and voids spontaneously form throughout the system. The instability has the characteristic features of the clustering instability which has been observed in molecular dynamics simulations of dense fluids and predicted by hydrodynamic models of granular flows.This research was partially supported by Grant No. PB96- 0534 from the Dirección General de Investigación Científica y Técnica (Spain

Fourier state of a fluidized granular gas

It is shown that the Boltzmann equation for smooth inelastic hard disks or spheres admits a solution describing a steady state characterized by uniform pressure and linear temperature profile. Such a state has been observed previously both in numerical solutions of the Boltzmann equation and in molecular dynamics simulations. Quite peculiarly, pressure and temperature gradient are not independent but their ratio is a function of the coefficient of restitution. Several properties of the solution are discussed. In particular, it is shown that a linear Fourier-like law is verified for arbitrary temperature gradient.Grant No. PB98-1124 from the Dirección General de Investigación Científica y Técnica (Spain)

Oregano Essential Oil and Purple Garlic Powder Effects on Intestinal Health, Microbiota Indicators and Antimicrobial Resistance as Feed Additives in Weaning Piglets

Finding alternatives to zinc oxide is a pressing issue for the pig production sector. We studied the impact of the bioactive components degradation of oregano essential oil (OEO) and purple garlic powder (PGP) during storage in silos, their effect on the morphometry of the jejunum and ileum and the cecal microbiota as intestinal health indicators in piglets during the post-weaning period. We also monitored antimicrobial resistance in the commensal indicator E. coli. Histological parameters and intestinal microbiota were measured in 140 piglets weaned at 21 days of age. Seven dietary treatments were used: a negative control group (basal diet), a positive control group with ZnO (3000 mg/kg of food), two groups with OEO at 0.4% and 1.2%, respectively, two groups with PGP 0.4% and 2%, respectively, and a group with OEO with 1.2% combined with PGP with 2%. Each group of piglets received the treatment for seven weeks, from weaning, before samples were taken. Antibiotic resistance profiles were measured in 81 E. coli strains. On this occasion, only the control groups, ZnO, OEO 1.2%, PGP 2% and OEO 1.2% + PGP 2% were used, and the samples were obtained from the cecal content. A progressive loss of the bioactive components of OEO and PGP was observed during the 34 days of storage (p < 0.05). PGP 2%, OEO 1.2% and their combination showed results similar to ZnO (p > 0.05), or superior in the study of intestinal morphometry and the values of E. coli and Lactobacillus. All categories showed high levels of resistance. Only the strains isolated from the OEO 1.2% group did not show resistance to colistin and presented the lowest resistance values. In general, high doses of the additives studied showed the best results, obtaining levels like or higher than those offered by ZnO

Self-diffusion in freely evolving granular gases

A self-diffusionequation for a freely evolving gas of inelastic hard disks or spheres is derived starting from the Boltzmann–Lorentz equation, by means of a Chapman–Enskog expansion in the density gradient of the tagged particles. The self-diffusion coefficient depends on the restitution coefficient explicitly, and also implicitly through the temperature of the system. This latter introduces also a time dependence of the coefficient. As in the elastic case, the results are trivially extended to the Enskog equation. The theoretical predictions are compared with numerical solutions of the kinetic equation obtained by the direct simulation Monte Carlo method, and also with molecular dynamics simulations. An excellent agreement is found, providing mutual support to the different approaches.The Dirección General de Investigación Científica y Técnica (Spain) through Grant No. PB98-112

Education Via the Educational Discourse. Educational Practices and Discursive Building of Knowledge in the Classroom

El marco teórico en el que se sitúa nuestra investigación es el de los principios y las estrategias metodológicas desarrollados por la psicología histórico-cultural, las perspectivas constructivistas, el análisis del discurso (DA) y el análisis conversacional (CA). El objeto del trabajo que aquí se presenta es el de describir y analizar las estrategias de comunicación y la naturaleza del discurso utilizado por profesores y alumnos en las actividades del aula, específicamente respecto a dos cuestiones principales: la descripción de los procesos por medio de los cuales se crea la intersubjetividad en el discurso educativo y los procesos por los que se construye una versión legítima del conocimiento en las aulas. En nuestro trabajo, adoptamos un enfoque cualitativo y etnográfico. La actividad del aula se registra mediante la grabación en vídeo del desarrollo de unidades temáticas completas. El análisis de los datos se realiza sobre la transcripción de las sesiones de trabajo del aula, y consiste en la búsqueda de patrones sistemáticos en el discurso educativo, y el análisis de sus funciones y consecuencias. Este análisis nos ha permitido no sólo identificar un conjunto de dispositivos y recursos semióticos que utilizan los profesores y los alumnos, sino también comprender y mostrar cómo las acciones orientadas a la instrucción que se plasman en un conocimiento escolar específico, se llevan a cabo mediante el discurso. Nuestras conclusiones indican que existe una relación entre el tipo de discurso del profesor de un aula y el discurso que promueve en sus alumnos, y, por lo tanto, en los recursos que los alumnos emplean en el proceso de socialización científica en un aula.The theoretical framework of our work is that offered by the principles and methodological strategies developed by cultural and historical psychology, constructivist perspectives, discourse analysis (DA) and conversational analysis (CA). The paper sets out to describe and analyze the strategies for communication and the nature of the discourse used by teachers and students in classroom activities, specifically those related to two main aspects: the description of the processes involved in creating inter-subjectivity in the educational discourse and the processes taking part in the construction of a legitimated version of knowledge in the classroom. A qualitative and ethnographic perspective has been adopted for this study. Classroom activity is registered by videotaping complete thematic sessions of work. Data analysis is made from the transcription of the sessions of classroom work and it consists in looking for systematic patterns in the educational discourse and analyzing its functions and its consequences. This analysis allowed us to identify several devices and semiotic resources used by teachers and students, and also to understand and show how the instructional actions that construct a specific educational knowledge are developed by means of discourse. Our conclusions show that there exists a relationship between the kind of discourse used by a teacher in the classroom and the discourse it leads to in the students and, therefore, in the resources that students use in the process of scientific socialization in the classroom.Ministerio de Ciencia y Tecnología BSO2000-0474Ministerio de Ciencia y Tecnología BSO2003-0360

Assignment of a Reference Value of Total Cow’s Milk Protein Content in Baked Cookies Used in an Interlaboratory Comparison

Interlaboratory comparisons (ILC) in the food allergens field mainly rely on the use of consensus values per applied methodology or even per type of an ELISA test kit. Results suggest good reproducibility; however, possible biases may not be recognized since metrological traceability to an independent reference is lacking. The work presented here utilizes isotope dilution mass spectrometry (IDMS) to assign a reference value of the total cow’s milk protein (TCMP) content in a baked cookie and its associated uncertainty. TCMP consists of several individual proteins, of which five (representing 92%) served us as markers for TCMP. Per marker, one to four proteotypic peptides were selected for the quantification. These were synthesized, and the mass fractions of respective reference solutions were determined with peptide-impurity-corrected amino acid analysis to establish traceability to SI units. Stable isotope labelled (“heavy”) analogues of the proteotypic peptides were also synthesized and blended with extracts of the test material or the reference solutions for IDMS. Through careful measurement design minimizing biases, well-defined model equations were developed, allowing appropriate estimation of the associated uncertainty. The determined reference value of 11.8 ± 1.1 mg TCMP/kg cookie was used for scoring of a novel ILC

Aprendizaje colaborativo en comunidades de práctica en entornos de exclusión social. : Un análisis de las interacciones

En este artículo se analizan las interacciones educativas que permiten crear un entorno de colaboración. El estudio se realiza en una comunidad de práctica particular, la Quinta Dimensión (5D), un modelo de actividad educativa basado en la cooperación entre universidad y comunidad, donde se promueve el aprendizaje colaborativo mediado por las TIC. Diseñado por el Laboratory of Comparative Human Cognition de la Universidad de California, bajo la dirección de Michael Cole, y fundamentada en la concepción del enfoque histórico cultural del desarrollo humano, se ha adaptado a las culturas locales en diversos países. En España existe una red 5D cuya primera experiencia ha sido la Casa de Shere Rom (CSR), diseñada para desarrollar formas de aprendizaje significativo para poblaciones que presentan altos índices de absentismo, abandono y fracaso escolar. La CSR, objeto de análisis en este artículo, es un espacio comunitario en horario extraescolar que atiende a niños de etnia gitana. Se trata de un proyecto de investigación-acción participativa, al tiempo que un laboratorio para el desarrollo de nuevas formas de aprendizaje colaborativo que posteriormente se han implementado en horario lectivo en diversas escuelas situadas en entornos con riesgo de exclusión social. Con el fin de analizar los procesos de incorporación a la comunidad de prácticas, las formas de colaboración para el aprendizaje y la creación colectiva de una 'ideocultura' de significados compartidos, se examinan aquí las interacciones en parejas de niños y estudiantes universitarios que colaboran para resolver tareas. Mediante un estudio cualitativo, cuyo análisis se ha realizado con el apoyo del programa ATLAS.ti, se pretende responder a las siguientes preguntas: ¿Qué hacen los participantes para que la interacción funcione? ¿Y para colaborar? ¿Qué indica que forman parte de esta comunidad? ¿Y qué indica que tienen un conocimiento compartido del juego o de la tarea concreta?In this paper, we analyse the educational interactions that promote a collaborative environment. The study is developed in a particular kind of community of practice, the Fifth Dimension (5D), an educational activity model based on cooperation between university and community, where it is promoted ICT supported collaborative learning. Designed by the Laboratory of Comparative Human Cognition of the University of California, under Michael Cole's leadership, it is based on the conception of the cultural-historical approach of human development and has been adapted to the local cultures in several countries. In Spain exists a 5D network, the first experience was the House of Shere Rom (CSR), designed to develop meaningful learning for population that present high indexes of absenteeism, drop-out and school failure. The CSR, object of analysis in this paper, is an after-school community space where attends Roma children. It is a participatory action-research project. Moreover, it is a laboratory for new kinds of collaborative learning development, for later implementation in several schools situated in social exclusion risk environments. We examine here, the interactions of children's and university students couples, who collaborate in tasks resolution, with the purpose to analyse the incorporation's processes to the community of practice, the kinds of collaboration addressed to learn and the collective construction of an 'ideoculture' of shared meanings. By means of a qualitative study, the analysis of which has been realised with the support of the software Atlas.ti, we pretend answer to the following questions: What do the participants do for the working of the interaction? What do they do to collaborate? What do indicate that they are part of this community? What do indicate they have a shared knowledge of the activity or of the concrete task