Reaction-diffusion processes and non-perturbative renormalisation group

This paper is devoted to investigating non-equilibrium phase transitions to an absorbing state, which are generically encountered in reaction-diffusion processes. It is a review, based on [Phys. Rev. Lett. 92, 195703; Phys. Rev. Lett. 92, 255703; Phys. Rev. Lett. 95, 100601], of recent progress in this field that has been allowed by a non-perturbative renormalisation group approach. We mainly focus on branching and annihilating random walks and show that their critical properties strongly rely on non-perturbative features and that hence the use of a non-perturbative method turns out to be crucial to get a correct picture of the physics of these models.Comment: 14 pages, submitted to J. Phys. A for the proceedings of the conference 'Renormalization Group 2005', Helsink

A flexible route to new spirodioxanes, oxathianes and morpholines

International audienceThis work describes a modular efficient route to 10-aza-4-thia-, 10-aza-4-oxa-, and 10-oxa-4-thia-1,7-dioxaspiro[5.5]undecanes. The synthetic pathway relies upon the iterative nucleophilic substitution of 1,3-dichloropropan-2-one O-benzyloxime by solketal derivatives. The oxime key-intermediates, submitted to an acidic deprotection–spiroacetalization process, afforded these original spiroketal compounds in three steps, few purifications, and very good yields

Influence of deformation rate and degree of compression on textural parameters of potato and apple tissues in texture profile analysis

The influence of the degree of compression, at deformation rates of 50, 250 and 500 mm min-1, on the textural parameters in the texture profile analysis (TPA) of cylindrical samples of potato and apple tissues was examined. The tests were performed at up to eight different deformation levels ranging from 10% to 80%. The values of all the parameters measured in the samples of both tissues were influenced more by the degree of compression than by the deformation rate. Degrees of compression greater than 40% and 20% caused the rupture of potato and apple specimens, respectively. Regression models were fitted to express the variation of cohesiveness and chewiness with deformation rate and degree of compression. In apple and potato tissues, the degree of compression had a quadratic effect on the cohesiveness while the effect of the deformation rate was only linear. Cohesiveness was the most appropriate textural parameter for detecting effects of deformation rate and degree of compression in TPA tests of potato and apple tissues. Recoverable instantaneous springiness offers a high potential to differentiate the structural natures of different tissues. © Springer-Verlag 2002.Peer Reviewe

Numerical simulation of fiber reinforced composite materials––two procedures

In this work, two methodologies for the analysis of unidirectional fiber reinforced composite materials are presented. The first methodology used is a generalized anisotropic large strains elasto-plastic constitutive model for the analysis of multiphase materials. It is based on the mixing theory of basic substance. It is the manager of the several constitutive laws of the different compounds and it allows to consider the interaction between the compounds of the composite materials. In fiber reinforced composite materials, the constitutive behavior of the matrix is isotropic, whereas the fiber is considered orthotropic. So, one of the constitutive model used in the mixing theory needs to consider this characteristic. The non-linear anisotropic theory showed in this work is a generalization of the classic isotropic plasticity theory (A Continuum Constitutive Model to Simulate the Mechanical Behavior of Composite Materials, PhD Thesis, Universidad Politécnica de Cataluña, 2000). It is based in a one-to-one transformation of the stress and strain spaces by means of a four rank tensor. The second methodology used is based on the homogenization theory. This theory divided the composite material problem into two scales: macroscopic and microscopic scale. In macroscopic level the composite material is assuming as a homogeneous material, whereas in microscopic level a unit volume called cell represents the composite (Tratamiento Numérico de Materiales Compuestos Mediante la teorı́a de Homogeneización, PhD Thesis, Universidad Politécnica, de Cataluña 2001). This formulation presents a new viewpoint of the homogenization theory in which can be found the equations that relate both scales. The solution is obtained using a coupled parallel code based on the finite elements method for each scale problem

Wilson-Polchinski exact renormalization group equation for O(N) systems: Leading and next-to-leading orders in the derivative expansion

With a view to study the convergence properties of the derivative expansion of the exact renormalization group (RG) equation, I explicitly study the leading and next-to-leading orders of this expansion applied to the Wilson-Polchinski equation in the case of the $N$-vector model with the symmetry $\mathrm{O}(N)$. As a test, the critical exponents $$ and $\nu$ as well as the subcritical exponent $\omega$ (and higher ones) are estimated in three dimensions for values of $N$ ranging from 1 to 20. I compare the results with the corresponding estimates obtained in preceding studies or treatments of other $\mathrm{O}(N)$ exact RG equations at second order. The possibility of varying $N$ allows to size up the derivative expansion method. The values obtained from the resummation of high orders of perturbative field theory are used as standards to illustrate the eventual convergence in each case. A peculiar attention is drawn on the preservation (or not) of the reparametrisation invariance.Comment: Dedicated to Lothar Sch\"afer on the occasion of his 60th birthday. Final versio

Near-field scanning optical microscopy to study nanometric structural details of LiNbO3 Zn-diffused channel waveguides

A near-field scanning optical microscope (NSOM) is used to perform structural and optical characterization of the surface layer after Zn diffusion in a channel waveguide fabricated on lithium niobate. A theoretical approach has been developed in order to extract refractive index contrast from NSOM optical transmission measurements (illumination configuration). As a result, different solid phases present on the sample surface can be identified, such as ZnO and ZnNb2O6. They appear like submicrometric crystallites aligned along the domain wall direction, whose origin can be ascribed to some strain relaxation mechanism during the annealing process after Zn [email protected]

El sistema skarn-epitermal de Zn–(Pb–Cu) de Velardeña, Durango (México): Nuevos datos fisicoquímicos de los procesos de mineralización

[eng] The Velardeña mining district is economically the most important of Durango state. The ore deposits occur in different skarn zones developed within the intrusive contact between Mesozoic limestones and Eocene granitic stocks and dikes. The most important ore deposits are related to the Santa María dike and Reyna de Cobre porphyritic stock (separated from each other by 10 km). They occur as irregularly shaped replacement masses developed near the intrusive contact and have a skarn paragenesis dominated by calc-silicates and sulfides. The mineral assemblages show replacement textures and are dominated by calcic clinopyroxene (Di97-53Hd42-02Jh04-01) and garnet (Ad100-57Grs43-00) in the exoskarn, with wollastonite particularly abundant in the endoskarn. Hydrous silicates are actinolite, epidote, and chlorite, whereas sulfides include pyrite, sphalerite, pyrrhotite, galena, chalcopyrite, and sulfosalts. Scheelite, hematite, quartz, and calcite are also present. According to sphalerite geobarometry, the skarns formed at hypabyssal depths (~3-4 km). They developed by a succession of replacive mineralizing events, including (a) a prograde stage at temperatures from ≥470 to 335 °C in conditions of low f (CO2), followed by (b) a retrograde stage from 335 to 220 °C. There was a general increase in f (O2), accompanying the temperature decline during the formation of the system, which accounts for a process of mixing with cooler, oxidizing, and dilute water. During the retrograde stage, wollastonite, calcic garnet and clinopyroxene formed. On the other hand, hydrous silicates, sulfides, sulfosalts, scheelite, and hematite crystallized during the retrograde stage. Skarn mineralization is crosscut by veins of calcite, fluorite, adularia, and sphalerite. The vein mineralization formed at temperatures below 200 °C. The different ore deposits of Velardeña constitute a telescoped skarn-epithermal mineral system.[spa]El distrito minero Velardeña es económicamente el más importante del estado de Durango. En él, las mineralizaciones comprenden diferentes zonas de skarn, desarrolladas entre el contacto de calizas mesozoicas, stocks y diques del Eoceno. Los depósitos de Velardeña más importantes están relacionados al dique Santa María, y el stock porfídico Reyna de Cobre (separados entre sí ~10 km). La mineralización ocurre como reemplazamiento, formando cuerpos irregulares cerca del contacto con los intrusivos, caracterizados por una paragénesis típica de skarn (calcisilicatos y sulfuros). Las asociaciones minerales muestran texturas de reemplazo dominados por clinopiroxeno cálcico (Di53Hd42-02Jh04-01) y granate (Ad100-57Grs43-00) en el exoskarn, y wollastonita particularmente abundante en el endoskarn. Los hidrosilicatos son actinolita, epidota y clorita; los sulfuros incluyen pirita, esfalerita, pirro tita, galena, calcopirita y sulfosales. Scheelita, hematita, cuarzo y calcita también están presentes. El geobarómetro de esfalerita estima que las mineralizacionestipo skarn de Velardeña se formaron a profundidades hipabisales (~ 3-4 km). La mineralización metálica se desarrolló por una sucesión de eventos de reemplazamiento, que incluyen (a) una etapa prógrada a ≥470 a 335 °C y baja f(CO ), seguida por (b) la etapa retrógrada de 335 a 2202°C. Hubo un aumento general de f(O ), durante el descenso de temperatura en laformación del yacimiento, debido a la mezcla de fluidos mineralizantes con agua más fría, oxidante y diluida. Durante la etapa retrógrada, se formaron wollastonita, granate cálcico y clinopiroxeno. La etapa prógrada dio lugar a la formación de hidrosilicatos, sulfuros (inclu- yendo sulfosales), scheelita y hematita. Además de las mineralizaciones tipo skarn en Velardeña, hay vetas epitermales de calcita, fluorita, adularia y esfalerita, cortando los calcosilicatos. La mineralización en estas vetas se estima que se formó a <200 °C. Por ello, es plausible proponer que los depósitos minerales que conforman el distrito minero Velardeña constituyen un sistema skarn-epitermal telescópeado

Estudio Mineralógico de los Sediementos de las Cuencas de WAGNER y CONSAG. Golfo de California (México)

Las cuencas de Wagner y de Consag se encuentran localizadas en la parte más septentrional del Golfo de California (GC). Con una profundidad máxima de 216 m, son las cuencas más someras del golfo y presentan una actividad gasohidrotermal submarina intensa (Canet et al., 2008)

Estudio mineralógico de los sedimentos de las cuencas de Wagner y Consag, Golfo de California (México)

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