Dynamic Surface Tension of Aqueous Solutions of Ionic Surfactants: Role of Electrostatics

The adsorption kinetics of the cationic surfactant dodecyltrimethylammonium bromide at the air-water interface has been studied by the maximum bubble pressure method at concentrations below the critical micellar concentration. At short times, the adsorption is diffusion-limited. At longer times, the surface tension shows an intermediate plateau and can no longer be accounted for by a diffusion limited process. Instead, adsorption appears kinetically controlled and slowed down by an adsorption barrier. A Poisson-Boltzmann theory for the electrostatic repulsion from the surface does not fully account for the observed potential barrier. The possibility of a surface phase transition is expected from the fitted isotherms but has not been observed by Brewster angle microscopy.Comment: 13 pages, 5 figure

La enseñanza de las matemáticas en contextos de riesgo de exclusión social. Buenas prácticas educativas

En contextos de riesgo de exclusión social referirnos a buenas prácticas en el ámbito de las matemáticas se asocia a características como flexibilidad, adaptación, individualización, etc., apoyadas en valores democráticos y participativos en pos de contrarrestar el fracaso escolar y fomentar la cohesión social. Por ello, partiendo de una metodología cualitativa de investigación nos aproximamos a tres Institutos de Educación Secundaria (IES) públicos ubicados en contextos de exclusión social dentro de la comunidad autónoma de Andalucía con el objetivo de identificar dichas buenas prácticas educativas. Como resultado, hemos podido seleccionarlas y clasificarlas en diferentes sub-categorías que reflejan, de forma organizada, las actuaciones del profesorado de matemáticas que fundamentan la categoría de buenas prácticas educativas en el área de las matemáticas en las distintas medidas de atención a la diversidad

An exploratory study of attitudes toward African migrants and migration among students at the University of the Western Cape

Magister Psychologiae - MPsychIn the context of recent attacks that occurred against foreign nationals (migrants) in South Africa, this study sought to explore attitudes toward migrants and immigration among a sample of students at the University of the Western Cape. Previous studies in South Africa and elsewhere have suggested that in most countries, nationals tend to hold negative attitudes toward migrants and express protectionist attitudes toward migration policies. Research around students' attitudes toward migrants and immigration has shown similar trends. The present study employed a sample survey design to investigate: a) Students' attitudes toward African migrants, b) Students' attitudes toward migration into South Africa and c) Degree of contact that students have with African Migrants. A convenience sample of 183 undergraduate psychology students was used. Students‟ age ranged between 18 and 38 years of age (x = 20 years). Data was collected using a questionnaire comprising of 27 questions related to attitudes towards migrants and immigration as well as a section on contact with migrants. The results show that students showed exclusionary attitudes in terms of immigration, limited contact with migrants and negative attitudes toward African migrants. However, attitudes toward migrant‟s rights were positive. The implications of these findings are discussed

Reaction Kinetics in the Production of Pd Nanoparticles in Reverse Microemulsions. Effect on Particle Size

In the synthesis of metallic nanoparticles in microemulsions, we hypothesized that particle size is mainly controlled by the reaction rate. Thus, the changes observed on the particle sizes as reaction conditions, such as concentrations, temperature, type of surfactant used, etc., are varied should not be correlated directly to the modification of those conditions but indirectly to the changes they produce on the reaction rates. By means of time resolved UV-vis spectroscopy, we measured the reaction rates in the production of Pd nanoparticles inside microemulsions at different reactant concentrations, keeping all the other parameters constant. The measured reaction rates were then correlated with the particle sizes measured by transmission electron microscopy (TEM). We found that nanoparticle size increases linearly as the reaction rates increases, independently of the actual reactant concentrations. We proposed that the kinetics is controlled mainly by the diffusion of the reducing agent through the surfactant monolayer covering the microemulsion membrane. With this model, we predicted that particle size should depend indirectly, via the reaction kinetics, on the micelle radius (v0 ~ r^-3), the water volume (v0~vw^3) and the total microemulsion volume (v0~vT^-3), and temperature (Arrhenius). Some of these predictions were explored in this article

Impact of the Assessment and Diagnosis Test in public schools in the province of Granada (Andalusia). The perspective of the educational actors

El “movimiento de mejora y calidad del sistema educativo” (LOE, 2006) posibilita la aplicación de las Pruebas de Evaluación y Diagnóstico sobre los centros escolares andaluces. Investigaciones en el ámbito internacional constatan efectos a nivel escolar cuando se aplica la evaluación externa. La necesidad de evidencia empírica (cualitativa) en el contexto andaluz impulsa el objetivo del estudio: analizar las percepciones y valoraciones de los actores educativos acerca del impacto de las PED en los centros escolares. La investigación se realizó en seis centros de educación primaria públicos de la Provincia de Granada (Andalucía) diferenciados geográficamente y por tipo de alumnado. Se utilizo metodología cualitativa y “análisis de contenido” para reducir los datos. Los resultados reflejan las categorías emergentes. Su índice de frecuencia categorial (IFC) evidenció que el efecto del diagnóstico se incrementa mientras la tipología del centro decrece. También permitió organizar las sub-categorías en relación con su grado de impacto.The "improvement and quality movement of the education system" (LOE, 2006) enable the application of the evaluation and diagnostic tests (EDT) on Andalusia schools. International research shows the effects in the school when applied external evaluation. The need for empirical evidence (qualitative) in the Andalusia context promotes the objective of the study: analyze the perceptions of the educational stakeholders about the impact of the EDT in schools. The research was carried out in six public elementary schools in the province of Granada (Andalusia) differentiated geographically and by type of students. Qualitative methodology and "content analysis" was used to reduce the data. The results reflect the emerging categories. Index of categorical frequency (ICF) showed that the effect of diagnosis increases while the typology of the center decreases. It also allowed organized the sub-categories in relation to their degree of impact

Polyelectrolyte/Surfactant Mixtures: A Pathway to Smart Foams

This review deals with liquid foams stabilized by polyelectrolyte/surfactant (PS) complexes in aqueous solution. It briefly reviews all the important aspects of foam physics at several scales, from interfaces to macroscopic foams, needed to understand the basics of these complex systems, focusing on those particular aspects of foams stabilized by PS mixtures. The final section includes a few examples of smart foams based on PS complexes that have been reported recently in the literature. These PS complexes open an opportunity to develop new intelligent dispersed materials with potential in many fields, such as oil industry, environmental remediation, and pharmaceutical industry, among others. However, there is much work to be done to understand the mechanism involved in the stabilization of foams with PS complexes. Understanding those underlying mechanisms is vital to successfully formulate smart systems. This review is written in the hope of stimulating further work in the physics of PS foams and, particularly, in the search for responsive foams based on polymer-surfactant mixtures.Fil: Ritacco, Hernán Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentin

How\u27s My Network - Incentives and Impediments of Home Network Measurements

Gathering meaningful information from Home Networking (HN) environments has presented researchers with measurement strategy challenges. A measurement platform is typically designed around the process of gathering data from a range of devices or usage statistics in a network that are specifically behind the HN firewall. HN studies require a fine balance between incentives and impediments to promote usage and minimize efforts for user participation with the focus on gathering robust datasets and results. In this dissertation we explore how to gather data from the HN Ecosystem (e.g. devices, apps, permissions, configurations) and feedback from HN users across a multitude of HN infrastructures, leveraging low impediment and low/high incentive methods to entice user participation. We look to understand the trade-offs of using a variety of approach types (e.g. Java Applet, Mobile app, survey) for data collections, user preferences, and how HN users react and make changes to the HN environment when presented with privacy/security concerns, norms of comparisons (e.g. comparisons to the local environment and to other HNs) and other HN results. We view that the HN Ecosystem is more than just “the network” as it also includes devices and apps within the HN. We have broken this dissertation down into the following three pillars of work to understand incentives and impediments of user participation and data collections. These pillars include: 1) preliminary work, as part of the How\u27s My Network (HMN) measurement platform, a deployed signed Java applet that provided a user-centered network measurement platform to minimize user impediments for data collection, 2) a HN user survey on preference, comfort, and usability of HNs to understand incentives, and 3) the creation and deployment of a multi-faceted How\u27s My Network Mobile app tool to gather and compare attributes and feedback with high incentives for user participation; as part of this flow we also include related approaches and background work. The HMN Java applet work demonstrated the viability of using a Web browser to obtain network performance data from HNs via a user-centric network measurement platform that minimizes impediments for user participation. The HMN HN survey work found that users prefer to leverage a Mobile app for HN data collections, and can be incentivized to participate in a HN study by providing attributes and characteristics of the HN Ecosystem. The HMN Mobile app was found to provide high incentives, with minimal impediments, for participation with focus on user Privacy and Security concerns. The HMN Mobile app work found that 84\% of users reported a change in perception of privacy and security, 32\% of users uninstalled apps, and 24\% revoked permissions in their HN. As a by-product of this work we found it was possible to gather sensitive information such as previously attached networks, installed apps and devices on the network. This information exposure to any installed app with minimal or no granted permissions is a potential privacy concern

«Si el hombre careciera de oído…», según Bernardo Silvestre

Durante la primera mitad del siglo XII cobró vigencia en Chartres una escuela de pensamiento filosófico-teológico caracterizada, en buena medida, por el afán de explicación del Génesis mediante el Comentario de Calcidio al Timeo de Platón. La Cosmografía de Bernardo Silvestre, dedicada a Teodorico de Chartres, permanece en las proximidades del interés cientificista y argumentativo propio de esta escuela, pero está formulada en términos literarios, en parte en prosa y en parte en verso. Dividida en dos grandes secciones: ‘Macrocosmos’ y ‘Microcosmos’, se cierra con la descripción de la naturaleza humana y su funcionamiento operativo en los procesos vitales y gnoseológicos. Los sentidos de que goza el hombre, asentados en la cabeza, son considerados instrumentos al servicio del intelecto que juzga. Ellos provienen de una única fuente pero desarrollan de diversas maneras sus operaciones. Si faltaran, no habría ni enseñanza de las letras ni sabiduría.During the first half of the XII Century, Chartres gained interest as a school of philosophical-theological thought characterized mostly by its eagerness to explain the Book of Genesis through Calcidius’ Commentary to Plato’s Timaeus. Bernardo Silvestre’s Cosmography, dedicated to Theodoric of Chartres, remains in the proximities of the school’s scientificist and argumentative interest, but it is formulated in literary terms, half prose and half verse. It is divided into two parts: ‘Macrocosmos’ and ‘Microcosmos’. It closes with the description of human nature and its operative functioning in the vital and gnoseological processes. Man’s senses, placed in the head, are considered instruments to the service of the intellect. They come from an only source but develop diverse operational ways. If they were missing, the possibility of teaching liberal arts and knowledge would not be possible.Fil: Ritacco de Gayoso, Graciela. Consejo Nacional de Investigaciones Científicas y Técnica