¿Se pueden conseguir plásticos barrera a medida?

La Industria del Envase y Embalaje forma parte de uno de los sectores principales de aplicación de los materiales polímeros. De todos es conocido que el vidrio, papel y metales que durante muchos años se utilizaron en el embalaje y empaquetamiento de alimentos, bebidas y otros productos han sido parcialmente reemplazados en la actualidad, por sustancias de naturaleza polimérica que permiten la regularización del transporte de gases y vapores a su través. Se puede decir que uno de los principales problemas con los que se encuentran los profesionales del Sector es encontrar la mejor protección de los productos desde su empaquetamiento hasta su utilización final por el consumidor. La preservación de la calidad de los productos envasados involucra no solo la protección del sabor sino también la necesidad de evitar malos olores en el alimento envasado. De ahí la importancia que el análisis de las propiedades de transporte de masas en los filmes tiene en la industria del envasado. Sin embargo los estudios del transporte de gases y/o vapores son complejos ya que la permeabilidad del material es el resultado de diferentes etapas, por un lado la solubilidad del gas en una cara de la membrana y por otro su difusión en el interior del film hacia la otra cara y su desorción de la misma. Todas estas etapas están fuertemente influenciadas por una serie de factores, como la naturaleza del film polimérico, la temperatura de uso, los aditivos (cargas o plastificantes), etc…, que hay que tener en cuenta a la hora de diseñar un material apto para envasado. Por tanto, el objetivo de esta conferencia es revisar los factores que hay que considerar en el transporte de gases a través de membranas poliméricas densas, desde un punto de vista químico-físico, mostrando diversos ejemplos de cómo se pueden modificar estas propiedades barrera para adecuarlas a las necesidades del producto a envasar.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

RADIAL MOTIONS in DISK STARS: ELLIPTICITY or SECULAR FLOWS?

© 2016. The American Astronomical Society. All rights reserved.. Average stellar orbits of the Galactic disk may have some small intrinsic ellipticity which breaks the exact axisymmetry and there may also be some migration of stars inwards or outwards. Both phenomena can be detected through kinematic analyses. We use the red clump stars selected spectroscopically from the APO Galactic Evolution Experiment, with known distances and radial velocities, to measure the radial component of the Galactocentric velocities within 5 kpc < R < 16 kpc, , and within 20° from the Sun-Galactic center line. The average Galactocentric radial velocity is VR = (1.48 ± 0.35)[R(kpc) - (8.8 ± 2.7)] km s-1 outwards in the explored range, with a higher contribution from stars below the Galactic plane. Two possible explanations can be given for this result: (i) the mean orbit of the disk stars is intrinsically elliptical with a Galactocentric radial gradient of eccentricity around 0.01 kpc-1; or (ii) there is a net secular expansion of the disk, in which stars within R ≈ 9-11 kpc are migrating to the region R 11 kpc at the rate of ∼2 Mo yr-1, and stars with R ≲ 9 kpc are falling toward the center of the Galaxy. This migration ratio would be unattainable for a long time and should decelerate, otherwise the Galaxy would fade away in around 1 Gyr. At present, both hypotheses are speculative and one would need data on the Galactocentric radial velocities for other azimuths different to the center or anticenter in order to confirm one of the scenarios

1/fα1/f^\alpha noise and integrable systems

An innovative test for detecting quantum chaos based on the analysis of the spectral fluctuations regarded as a time series has been recently proposed. According to this test, the fluctuations of a fully chaotic system should exhibit 1/f noise, whereas for an integrable system this noise should obey the 1/f^2 power law. In this letter, we show that there is a family of well-known integrable systems, namely spin chains of Haldane-Shastry type, whose spectral fluctuations decay instead as 1/f^4. We present a simple theoretical justification of this fact, and propose an alternative characterization of quantum chaos versus integrability formulated directly in terms of the power spectrum of the spacings of the unfolded spectrum.Comment: 5 pages, 3 figures, RevTe

Quasi-exactly Solvable Lie Superalgebras of Differential Operators

In this paper, we study Lie superalgebras of $2\times 2$ matrix-valued first-order differential operators on the complex line. We first completely classify all such superalgebras of finite dimension. Among the finite-dimensional superalgebras whose odd subspace is nontrivial, we find those admitting a finite-dimensional invariant module of smooth vector-valued functions, and classify all the resulting finite-dimensional modules. The latter Lie superalgebras and their modules are the building blocks in the construction of QES quantum mechanical models for spin 1/2 particles in one dimension.Comment: LaTeX2e using the amstex and amssymb packages, 24 page

¿Qué está haciendo el científico? : análisis de la actividad científica descrita por alumnos secundarios chilenos de 11° y 12° grado de distintos tipos de establecimientos educacionales

Con el objetivo de conocer la representación de estudiantes secundarios chilenos de distintos tipos de establecimientos acerca de los científicos y la actividad que estos realizan, se aplicó a una muestra de 438 estudiantes de 11° y 12° grado el Draw-a-Scientist-Test, en la versión de Türkmen (2008). En ella, los alumnos son invitados a describir de manera escrita la actividad que realiza el científico que dibujaron. Dichas narraciones fueron analizadas en función de los procesos científicos relatados, propósitos y consecuencia de la actividad descrita. Los procesos científicos más frecuentemente mencionados fueron “experimentar” y “observar”. “Formular modelos”, proceso fundamental en la actividad científica, prácticamente no fue mencionado. En relación a propósitos y consecuencias la mayoría de los alumnos tiene una imagen positiva de la actividad científica

On the families of orthogonal polynomials associated to the Razavy potential

We show that there are two different families of (weakly) orthogonal polynomials associated to the quasi-exactly solvable Razavy potential V(x)=(\z \cosh 2x-M)^2 (\z>0, $M\in\mathbf N$). One of these families encompasses the four sets of orthogonal polynomials recently found by Khare and Mandal, while the other one is new. These results are extended to the related periodic potential U(x)=-(\z \cos 2x -M)^2, for which we also construct two different families of weakly orthogonal polynomials. We prove that either of these two families yields the ground state (when $M$ is odd) and the lowest lying gaps in the energy spectrum of the latter periodic potential up to and including the $(M-1)^{\rm th}$ gap and having the same parity as $M-1$. Moreover, we show that the algebraic eigenfunctions obtained in this way are the well-known finite solutions of the Whittaker--Hill (or Hill's three-term) periodic differential equation. Thus, the foregoing results provide a Lie-algebraic justification of the fact that the Whittaker--Hill equation (unlike, for instance, Mathieu's equation) admits finite solutions.Comment: Typeset in LaTeX2e using amsmath, amssymb, epic, epsfig, float (24 pages, 1 figure

Baroque Banded Vaults: Surveying and Modeling. The Case Study of a Noble Palace in Turin

This paper presents the methodological framework set up for the analysis, interpretation, and representation of the banded vaulted systems recognized in eleven Baroque atria in Turin. In these atria, the banded vaults, locally named “a fascie”, are featured by a series of arches orthogonal to the perimeter walls on which they rest. The arches divide the room’s ceiling into spaces that can accommodate small vaults of different shapes. The atria have been the subject of bibliographical, historical and documentary analyses, laser scanner metric survey, two-dimensional graphic representations, and interpretative hypotheses through three-dimensional modeling of the design’s geometries of the vaults. The integration between terrestrial laser scanning (TLS) technique, architectural drawing and three-dimensional modeling methods led to the definition of new workflows, aimed at optimizing the use of data. From these procedures new opportunities for the research arise, such as the comparison (metric and geometric) through the superimposition of design ideal models and point clouds

Quasi-exactly solvable quartic potential

A new two-parameter family of quasi-exactly solvable quartic polynomial potentials $V(x)=-x^4+2iax^3+(a^2-2b)x^2+2i(ab-J)x$ is introduced. Until now, it was believed that the lowest-degree one-dimensional quasi-exactly solvable polynomial potential is sextic. This belief is based on the assumption that the Hamiltonian must be Hermitian. However, it has recently been discovered that there are huge classes of non-Hermitian, ${\cal PT}$-symmetric Hamiltonians whose spectra are real, discrete, and bounded below [physics/9712001]. Replacing Hermiticity by the weaker condition of ${\cal PT}$ symmetry allows for new kinds of quasi-exactly solvable theories. The spectra of this family of quartic potentials discussed here are also real, discrete, and bounded below, and the quasi-exact portion of the spectra consists of the lowest $J$ eigenvalues. These eigenvalues are the roots of a $J$th-degree polynomial.Comment: 3 Pages, RevTex, 1 Figure, encapsulated postscrip