Zig-zag instability of an Ising wall in liquid crystals

We present a theoretical explanation for the interfacial zigzag instability that appears in anisotropic systems. Such an instability has been experimentally highlighted for an Ising wall formed in a nematic liquid crystal cell under homeotropic anchoring conditions. From an envelope equation, relevant close to the Freedericksz transition, we have derived an asymptotic equation describing the interface dynamics in the vicinity of its bifurcation. The asymptotic limit used accounts for a strong difference between two of the elastic constants. The model is characterized by a conservative order parameter which satisfies a Cahn-Hilliard equation. It provides a good qualitative understanding of the experiments.Comment: 4 pagess, 4 figures, lette

Single polymer dynamics: coil-stretch transition in a random flow

By quantitative studies of statistics of polymer stretching in a random flow and of a flow field we demonstrate that the stretching of polymer molecules in a 3D random flow occurs rather sharply via the coil-stretch transition at the value of the criterion close to theoretically predicted.Comment: 4 pages, 5 figure

Ring-Pattern Dynamics in Smectic-C* and Smectic-C_A* Freely Suspended Liquid Crystal Films

Ring patterns of concentric 2pi-solitons in molecular orientation, form in freely suspended chiral smectic-C films in response to an in-plane rotating electric field. We present measurements of the zero-field relaxation of ring patterns and of the driven dynamics of ring formation under conditions of synchronous winding, and a simple model which enables their quantitative description in low polarization DOBAMBC. In smectic C_A* TFMHPOBC we observe an odd-even layer number effect, with odd number layer films exhibiting order of magnitude slower relaxation rates than even layer films. We show that this rate difference is due to much larger spontaneous polarization in odd number layer films.Comment: 4 RevTeX pgs, 4 eps figures, submitted to Phys. Rev. Let

The French Didactic Tradition in Mathematics

This chapter presents the French didactic tradition. It first describes theemergence and development of this tradition according to four key features (role ofmathematics and mathematicians, role of theories, role of design of teaching andlearning environments, and role of empirical research), and illustrates it through two case studies respectively devoted to research carried out within this traditionon algebra and on line symmetry-reflection. It then questions the influence of thistradition through the contributions of four researchers from Germany, Italy, Mexicoand Tunisia, before ending with a short epilogue

Coalescence in the 1D Cahn-Hilliard model

We present an approximate analytical solution of the Cahn-Hilliard equation describing the coalescence during a first order phase transition. We have identified all the intermediate profiles, stationary solutions of the noiseless Cahn-Hilliard equation. Using properties of the soliton lattices, periodic solutions of the Ginzburg-Landau equation, we have construct a family of ansatz describing continuously the processus of destabilization and period doubling predicted in Langer's self similar scenario

Roteiros de aprendizagem a partir da transposição didática reflexiva

Este artigo busca socializar o produto da dissertação de mestrado profissional em Ensino de Matemática. Apresentamos roteiros de aprendizagem como uma possibilidade educacional para que professores de matemática do Ensino Médio possam aplicá-los de modo a desenvolver a matemática a partir de dados reais. Os roteiros foram adaptados de trabalhos oriundos do Projeto de Iniciação Científica do IFC - Campus Rio do Sul. A pesquisa foi embasada na teoria da Transposição Didática e na Educação Matemática Crítica. Essa abordagem foi denominada de Transposição Didática Reflexiva, com o intuito de unir as duas teorias num processo em que o saber a ser ensinado seja adaptado de forma a provocar reflexões, instituindo um cenário para investigação que propicie a participação do aluno no processo, provoque discussões e tomada de decisão, de modo a instigar o sujeito a ser transformador de sua própria realidade. De modo particular, o artigo apresenta, em linhas gerais, um dos roteiros detalhados na dissertação, aplicado em uma turma do IFC - Campus Rio do Sul

Simulating JWST deep extragalactic imaging surveys and physical parameter recovery

International audienceWe present a new prospective analysis of deep multi-band imaging with the James Webb Space Telescope (JWST). In this work, we investigate the recovery of high-redshift 5  6 and redshifts of 0   5 galaxy samples can be reduced to < 0.01 arcmin−2 with a limited impact on galaxy completeness. We investigate multiple high-redshift galaxy selection techniques and find that the best compromise between completeness and purity at 5 <  z <  10 using the full redshift posterior probability distributions. In the EGS field, the galaxy completeness remains higher than 50% at magnitudes mUV <  27.5 and at all redshifts, and the purity is maintained above 80 and 60% at z ≤ 7 and 10, respectively. The faint-end slope of the galaxy UV luminosity function is recovered with a precision of 0.1–0.25, and the cosmic star formation rate density within 0.1 dex. We argue in favor of additional observing programs covering larger areas to better constrain the bright end

El matemático como un profesional en los recorridos de estudio e investigación

In this paper we describe a new didactic device: the trajectories of study and research (TSR). These didactic devices allow to articulate teaching and learning sequences.&lt;br&gt;&lt;br&gt;En este trabajo se describe un nuevo dispositivo didáctico que estamos diseñando y completando, los Recorridos de Estudio e Investigación (REI), que quieren contribuir a crear secuencias de enseñanza-aprendizaje

Tryptase as a marker of severity of aortic valve stenosis

Background: Severe aortic valve stenosis is one of the most common cause of mortality in adult patients affected with metabolic syndrome, a condition associated with an active inflammatory process involving also mast cells and their mediators, in particular tryptase. The aim of this study was to characterize the possible long-term prognostic role of tryptase in severe aortic valve stenosis. Case presentation: The baseline serum tryptase was measured in 5 consecutive patients admitted to our Hospital to undergo aortic valve replacement for severe acquired stenosis. Within 2years after, the patients were evaluated for the occurrence of major cardiovascular events (MACE). The tryptase measurements were higher in patients experiencing MACE (10.9, 11.7 and 9.32ng/ml) than in non-MACE ones (5.69 and 5.58ng/ml). Conclusions: In patients affected with severe aortic stenosis, baseline serum tryptase may predict occurence of MACE. Further studies are needed to demonstrate the long-term prognostic role of this biomarker

O Fenômeno Didático Institucional da Rigidez e a Atomização das Organizações Matemáticas Escolares

Nesta investigação estudamos um fenômeno didático complexo que se manifesta na desconexão dos conteúdos matemáticos que constituem o programa oficial do ensino secundário/médio e que está fortemente relacionado com a rigidez e a atomização da Matemática escolar. Para tal estudo utilizamos as ferramentas teóricas e metodológicas que nos proporciona a Teoria Antropológica do Didático (TAD) cujo objeto primário de investigação é a análise da atividade matemática escolar institucional. Assim, realizamos estudos exploratórios nos manuais escolares de Matemática do ensino secundário de Portugal e da Espanha, contrastando e comprovando cinco conjeturas relacionadas, por exemplo, com a ausência de questionamento e justificação das técnicas utilizadas. Concluimos que nestes países as praxeologias matemáticas apresentam-se desarticuladas, rígidas,e, consequentemente, surgem isoladas atividades de modelagem matemática nas instituições escolares