An Exactly Solvable Phase-Field Theory of Dislocation Dynamics, Strain Hardening and Hysteresis in Ductile Single Crystals

An exactly solvable phase-field theory of dislocation dynamics, strain hardening and hysteresis in ductile single crystals is developed. The theory accounts for: an arbitrary number and arrangement of dislocation lines over a slip plane; the long-range elastic interactions between dislocation lines; the core structure of the dislocations resulting from a piecewise quadratic Peierls potential; the interaction between the dislocations and an applied resolved shear stress field; and the irreversible interactions with short-range obstacles and lattice friction, resulting in hardening, path dependency and hysteresis. A chief advantage of the present theory is that it is analytically tractable, in the sense that the complexity of the calculations may be reduced, with the aid of closed form analytical solutions, to the determination of the value of the phase field at point-obstacle sites. In particular, no numerical grid is required in calculations. The phase-field representation enables complex geometrical and topological transitions in the dislocation ensemble, including dislocation loop nucleation, bow-out, pinching, and the formation of Orowan loops. The theory also permits the consideration of obstacles of varying strengths and dislocation line-energy anisotropy. The theory predicts a range of behaviors which are in qualitative agreement with observation, including: hardening and dislocation multiplication in single slip under monotonic loading; the Bauschinger effect under reverse loading; the fading memory effect, whereby reverse yielding gradually eliminates the influence of previous loading; the evolution of the dislocation density under cycling loading, leading to characteristic `butterfly' curves; and others

Radio numbers for generalized prism graphs

A radio labeling is an assignment $c:V(G) \rightarrow \textbf{N}$ such that every distinct pair of vertices $u,v$ satisfies the inequality d(u,v)+|c(u)-c(v)|\geq \diam(G)+1. The span of a radio labeling is the maximum value. The radio number of $G$, $rn(G)$, is the minimum span over all radio labelings of $G$. Generalized prism graphs, denoted $Z_{n,s}$, $s \geq 1$, $n\geq s$, have vertex set $\{(i,j)\,|\, i=1,2 \text{and} j=1,...,n\}$ and edge set $\{((i,j),(i,j \pm 1))\} \cup \{((1,i),(2,i+\sigma))\,|\,\sigma=-\left\lfloor\frac{s-1}{2}\right\rfloor\,\ldots,0,\ldots,\left\lfloor\frac{s}{2}\right\rfloor\}$. In this paper we determine the radio number of $Z_{n,s}$ for $s=1,2$ and $3$. In the process we develop techniques that are likely to be of use in determining radio numbers of other families of graphs.Comment: To appear in Discussiones Mathematicae Graph Theory. 16 pages, 1 figur

Diabetic retinopathy: could the alpha-1 antitrypsin be a therapeutic option?

Diabetic retinopathy is one of the most important causes of blindness. The underlying mechanisms of this disease include inflammatory changes and remodeling processes of the extracellular-matrix (ECM) leading to pericyte and vascular endothelial cell damage that affects the retinal circulation. In turn, this causes hypoxia leading to release of vascular endothelial growth factor (VEGF) to induce the angiogenesis process. Alpha-1 antitrypsin (AAT) is the most important circulating inhibitor of serine proteases (SERPIN). Its targets include elastase, plasmin, thrombin, trypsin, chymotrypsin, proteinase 3 (PR-3) and plasminogen activator (PAI). AAT modulates the effect of protease-activated receptors (PARs) during inflammatory responses. Plasma levels of AAT can increase 4-fold during acute inflammation then is so-called acute phase protein (APPs). Individuals with low serum levels of AAT could develop disease in lung, liver and pancreas. AAT is involved in extracellular matrix remodeling and inflammation, particularly migration and chemotaxis of neutrophils. It can also suppress nitric oxide (NO) by nitric oxide sintase (NOS) inhibition. AAT binds their targets in an irreversible way resulting in product degradation. The aim of this review is to focus on the points of contact between multiple factors involved in diabetic retinopathy and AAT resembling pleiotropic effects that might be beneficial.Fil: Ortiz, Gustavo Alfredo. Universidad Austral. Facultad de Ciencias Biomédicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Salica, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Austral. Facultad de Ciencias Biomédicas; ArgentinaFil: Chuluyan, Hector Eduardo. Universidad de Buenos Aires. Facultad de Medicina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gallo, Juan Eduardo Maria. Universidad Austral. Facultad de Ciencias Biomédicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

La educación estadística en los simposios de la SEIEM (1997-2009)

En este trabajo presentamos un análisis detallado de la producción en el ámbito de la Educación Estadística, que está recogida en las publicaciones de los Simposios de la Sociedad Española de Investigación en Educación Matemática (SEIEM) en el período comprendido entre 1997-2009. El objetivo de este estudio es caracterizar la investigación en Educación Estadística en estas publicaciones, durante el período mencionado. Para ello, mediante técnicas bibliométricas, pretendemos determinar la producción diacrónica, los autores más productivos, los temas de investigación tratados, así como los patrones de citación referidos a autores, documentos y congresos. Consideramos de interés este tipo de trabajos ya que pueden facilitar la labor de otros investigadores y contribuir a mejorar la investigación en esta área

Estudio de las situaciones problemas de probabilidad en libros de texto de bachillerato

El objetivo de este trabajo es analizar las situaciones problemas de probabilidad que se presentan en una muestra de libros de texto de Bachillerato. Se analizan los conceptos necesarios para resolver dichas situaciones, la asignación de probabilidad, los contextos empleados y el uso de recursos tecnológicos en las situaciones propuestas. Se detectan diferencias entre los diferentes textos y un tratamiento desigual de las variables analizadas

Digital humanity and self- constitution: towards a new management of digital devices

El presente trabajo se propone arrojar luz sobre la problemática relación entre los medios digitales y las formas de poder del capitalismo actual. Siguiendo esta línea, el eje central radicará en realizar una adecuada descripción del entramado constituido por la lógica algorítmica, la ontología, y la constitución de la subjetividad. A través de este método, me propongo realizar un abordaje materialista de la cuestión con dos objetivos específicos: Por un lado, exceder cierto idealismo que aún anida en la posición crítica y juzga a los medios digitales desde una añoranza nostálgica hacia un pasado supuestamente mejor; por otro, delinear una praxis filosófica capaz de señalar el lugar preciso que le caben a los medios digitales ante el avance de la dinámica de dominación del capitalismo imperante.The present work aims to shed light on the problematic relationship between digital media and the forms of power of current capitalism. Following this line, the central axis will be to make an adequate description of the framework constituted by algorithmic logic, ontology, and the constitution of subjectivity. Through this method, I intend to make a materialist approach to the issue with two specific objectives: On the one hand, to exceed certain idealism that still nests in the critical position and judges the digital media from a nostalgic longing towards a supposedly better past; on the other hand, to delineate a philosophical praxis capable of pointing out the precise place that digital media can accommodate before the dynamics of domination of the prevailing capitalism

Higher education students’ perceptions about the utility of short videos to enhance pronunciation

"This research was conducted to know students’ perceptions about the use of videos to improve pronunciation in the Bachelor of English Language Teaching in the Faculty of Languages BUAP in Puebla, Mexico. The collected data was taken from one hundred and seven participants from the first semester to the tenth. Students who participated in this research were around sixteen to over 30 years old. A non-experimental quantitative cross sectional method was used in order to answer the two theses, which stated that: students consider that videos are helpful to enhance pronunciation. Also, students have improved their pronunciation with videos. The results indicated that students have a fruitful opinion regarding the use of videos to improve pronunciation. The research findings also showed that students have a better perspective about using comedian and science fiction videos, which raise their motivation to participate during the lessons. Therefore, it can be inferred that teachers must use videos in their lessons to have a positive outcome. For further research, other methods, context, and participants' level of English may be considered"