Theory and simulation of the confined Lebwohl-Lasher model

We discuss the Lebwohl-Lasher model of nematic liquid crystals in a confined geometry, using Monte Carlo simulation and mean-field theory. A film of material is sandwiched between two planar, parallel plates that couple to the adjacent spins via a surface strength $\epsilon_s$. We consider the cases where the favoured alignments at the two walls are the same (symmetric cell) or different (asymmetric or hybrid cell). In the latter case, we demonstrate the existence of a {\it single} phase transition in the slab for all values of the cell thickness. This transition has been observed before in the regime of narrow cells, where the two structures involved correspond to different arrangements of the nematic director. By studying wider cells, we show that the transition is in fact the usual isotropic-to-nematic (capillary) transition under confinement in the case of antagonistic surface forces. We show results for a wide range of values of film thickness, and discuss the phenomenology using a mean-field model.Comment: 40 pages 19 figures (preprint format). Part of the text and some figures were modified. New figure was include

Exact Quantum States for all Two-Dimensional Dilaton Gravity Theories

It is shown that the recently obtained quantum wave functionals in terms of the CJZ variables for generic 2d dilaton gravity are equivalent to the previously reported exact quantum wave functionals in geometrical variables. A third representation of these exact quantum states is also presented

Efficient and Effective Query Auto-Completion

Query Auto-Completion (QAC) is an ubiquitous feature of modern textual search systems, suggesting possible ways of completing the query being typed by the user. Efficiency is crucial to make the system have a real-time responsiveness when operating in the million-scale search space. Prior work has extensively advocated the use of a trie data structure for fast prefix-search operations in compact space. However, searching by prefix has little discovery power in that only completions that are prefixed by the query are returned. This may impact negatively the effectiveness of the QAC system, with a consequent monetary loss for real applications like Web Search Engines and eCommerce. In this work we describe the implementation that empowers a new QAC system at eBay, and discuss its efficiency/effectiveness in relation to other approaches at the state-of-the-art. The solution is based on the combination of an inverted index with succinct data structures, a much less explored direction in the literature. This system is replacing the previous implementation based on Apache SOLR that was not always able to meet the required service-level-agreement.Comment: Published in SIGIR 202

A strategy for the design of skyrmion racetrack memories

Magnetic storage based on racetrack memory is very promising for the design of ultra-dense, low-cost and low-power storage technology. Information can be coded in a magnetic region between two domain walls or, as predicted recently, in topological magnetic objects known as skyrmions. Here, we show the technological advantages and limitations of using Bloch and Neel skyrmions manipulated by spin current generated within the ferromagnet or via the spin-Hall effect arising from a non-magnetic heavy metal underlayer. We found that the Neel skyrmion moved by the spin-Hall effect is a very promising strategy for technological implementation of the next generation of skyrmion racetrack memories (zero field, high thermal stability, and ultra-dense storage). We employed micromagnetics reinforced with an analytical formulation of skyrmion dynamics that we developed from the Thiele equation. We identified that the excitation, at high currents, of a breathing mode of the skyrmion limits the maximal velocity of the memory

The impact of cultural dissonance and acculturation orientations on immigrant students' academic performance

Indexación: Scopus; Scielo; Redalyc.Prior research has documented meaningful differences between school performance of immigrant and native students. Multicultural education has been associated with academic failure of foreign students. e aim of this study was to examine the impact of a set of psychosocial variables on the perceived academic achievement of first generation immigrant adolescents from public secondary schools in Northern Spain. Results showed that 46% of the variability in foreign students’ perceived academic performance was explained by home-school cultural dissonance. We also explored the impact of acculturation orientation to separation, perception of discrimination from teachers, school adjustment, and psychological well-being in academic performance. Any multicultural education context should take into account psychosocial adjustment, given its influence on academic performance of all studentsSe han hallado diferencias significativas entre el rendimiento académico de los inmigrantes y el de los estudiantes nativos. Sin embargo, hay una escasa evidencia acerca de los aspectos psicosociales de este fenómeno. El objetivo de este estudio fue examinar el impacto de un conjunto de variables psicosociales: disonancia cultural y orientaciones de aculturación en el rendimiento académico percibido de adolescentes inmigrantes de primera generación de centros de Educación Secundaria en el Norte de España. Los resultados mostraron que alrededor del 46% de la variabilidad en el rendimiento era explicada por la disonancia cultural entre escuela y hogar. Cualquier contexto de educación multicultural ha de tomar en consideración el ajuste psicosocial, dada su influencia en el rendimiento académico de los estudiantes.http://www.redalyc.org/jatsRepo/647/64753989003/index.htm