Self Induced Quenched Disorder: A Model for the Glass Transition

We consider a simple spin system without disorder which exhibits a glassy regime. We show that this model can be well approximated by a system with quenched disorder which is studied with the standard methods developped in spin glasses. We propose that the glass transition is a point where quenched disorder is self induced, a scenario for which the `cavity' method might be particularly well suited.Comment: Latex, LPTENS 94/14, three figures upon reques

ON A DYNAMICAL MODEL OF GLASSES

We analyze a simple dynamical model of glasses, based on the idea that each particle is trapped in a local potential well, which itself evolves due to hopping of neighbouring particles. The glass transition is signalled by the fact that the equilibrium distribution ceases to be normalisable, and dynamics becomes non-stationary. We generically find stretching of the correlation function at low temperatures and a Vogel-Fulcher like behaviour of the terminal time.Comment: 11 pages, 2 figures (available upon request

A Metric Inequality for the Thompson and Hilbert Geometries

There are two natural metrics defined on an arbitrary convex cone: Thompson's part metric and Hilbert's projective metric. For both, we establish an inequality giving information about how far the metric is from being non-positively curved.Comment: 15 pages, 0 figures. To appear in J. Inequalities Pure Appl. Mat

Hamiltonian structure of thermodynamics with gauge

The state of a thermodynamic system being characterized by its set of extensive variables $q^{i}(i=1,...,n) ,$ we write the associated intensive variables $\gamma_{i},$ the partial derivatives of the entropy $S(q^{1},...,q^{n}) \equiv q_{0},$ in the form $\gamma_{i}=-p_{i}/p_{0}$ where $p_{0}$ behaves as a gauge factor. When regarded as independent, the variables $q^{i},p_{i}(i=0,...,n)$ define a space $\mathbb{T}$ having a canonical symplectic structure where they appear as conjugate. A thermodynamic system is represented by a $n+1$-dimensional gauge-invariant Lagrangian submanifold $\mathbb{M}$ of $\mathbb{T}.$ Any thermodynamic process, even dissipative, taking place on $\mathbb{M}$ is represented by a Hamiltonian trajectory in $\mathbb{T},$ governed by a Hamiltonian function which is zero on $\mathbb{M}.$ A mapping between the equations of state of different systems is likewise represented by a canonical transformation in $\mathbb{T}.$ Moreover a natural Riemannian metric exists for any physical system, with the $q^{i}$'s as contravariant variables, the $p_{i}$'s as covariant ones. Illustrative examples are given.Comment: Proofs corrections latex vali.tex, 1 file, 28 pages [SPhT-T00/099], submitted to Eur. Phys. J.

Onsager's Wien Effect on a Lattice

The Second Wien Effect describes the non-linear, non-equilibrium response of a weak electrolyte in moderate to high electric fields. Onsager's 1934 electrodiffusion theory along with various extensions has been invoked for systems and phenomena as diverse as solar cells, surfactant solutions, water splitting reactions, dielectric liquids, electrohydrodynamic flow, water and ice physics, electrical double layers, non-Ohmic conduction in semiconductors and oxide glasses, biochemical nerve response and magnetic monopoles in spin ice. In view of this technological importance and the experimental ubiquity of such phenomena, it is surprising that Onsager's Wien effect has never been studied by numerical simulation. Here we present simulations of a lattice Coulomb gas, treating the widely applicable case of a double equilibrium for free charge generation. We obtain detailed characterisation of the Wien effect and confirm the accuracy of the analytical theories as regards the field evolution of the free charge density and correlations. We also demonstrate that simulations can uncover further corrections, such as how the field-dependent conductivity may be influenced by details of microscopic dynamics. We conclude that lattice simulation offers a powerful means by which to investigate system-specific corrections to the Onsager theory, and thus constitutes a valuable tool for detailed theoretical studies of the numerous practical applications of the Second Wien Effect.Comment: Main: 12 pages, 4 figures. Supplementary Information: 7 page

A Bijection between classes of Fully Packed Loops and Plane Partitions

It has recently been observed empirically that the number of FPL configurations with 3 sets of a, b and c nested arches equals the number of plane partitions in a box of size a x b x c. In this note, this result is proved by constructing explicitly the bijection between these FPL and plane partitions

Existence of conformal metrics with constant QQ-curvature

Given a compact four dimensional manifold, we prove existence of conformal metrics with constant $Q$-curvature under generic assumptions. The problem amounts to solving a fourth-order nonlinear elliptic equation with variational structure. Since the corresponding Euler functional is in general unbounded from above and from below, we employ topological methods and minimax schemes, jointly with a compactness result by the second author.Comment: 36 pages, revised version. To appear in Annals of Mathematic

Cuantificación de hierro total en las hojas de espinaca(basella alba) por espectrofotometría ultravioleta/visible, laboratorio de análisis físico químico de alimentos departamento de química, UNAN-Managua, Enero-Diciembre, 2015

Palabras claves: Anemia Ferropénica, Hierro Total, curva de calibrado, espectrofotometría Ultravioleta/Visible, Cenizas Totales. La presente investigación se realiza en el Laboratorio de Análisis Físico Químico de Alimentos del Departamento de Química de la UNAN-Managua por la técnica de espectrofotometría Ultravioleta/Visible utilizando el método colorimétrico de la orto-fenantrolina, para determinar la concentración de hierro total presente en las hojas de espinaca (Basella alba). La cuantificación se realiza a tres lotes de espinaca provenientes de los municipios de San Juan de Oriente (lote-MTSJ) y Catarina (lote-MCTR1, MCTR2) obteniendo un total de 58 muestras, en cada lote se obtiene un residuo seco aplicando el método de secado en estufa de convección hasta peso constante, luego se obtienen las cenizas totales por medio de combustión seca a una temperatura de 550 °C y posteriormente se digestan con ácido clorhídrico concentrado. Para cada lote de espinaca se realiza una curva de calibración para determinar la concentración de hierro total en las muestras de análisis. En el primer lote la concentración promedio es de 3.20 mg Fe/100 g de espinaca, en el segundo lote se obtiene una media de 1.97 mg Fe/100 g de espinaca y para el tercero 2.92 mg Fe/100 g de espinaca. Se estima la masa bruta de espinaca en peso seco como alimento funcional para la población que padezca anemia ferropénica en el municipio de San Juan de Oriente para adultos se obtienen 0.44 kg de peso seco una vez al día, embarazadas de 0.88 kg de peso seco una vez al día y para la población de Catarina en adultos es de 0.53 kg de peso seco una vez al día y embarazadas 1.06 kg de peso seco una vez al dí

Valued constraint satisfaction problems: Hard and easy problems

tschiexOtoulouse.inra.fr fargierOirit.fr verfailOcert.fr In order to deal with over-constrained Constraint Satisfaction Problems, various extensions of the CSP framework have been considered by taking into account costs, uncertainties, preferences, priorities...Each extension uses a specific mathematical operator (+, max...) to aggregate constraint violations. In this paper, we consider a simple algebraic framework, related to Partial Constraint Satisfaction, which subsumes most of these proposals and use it to characterize existing proposals in terms of rationality and computational complexity. We exhibit simple relationships between these proposals, try t