Gauge transformations in the Lagrangian and Hamiltonian formalisms of generally covariant theories

We study spacetime diffeomorphisms in Hamiltonian and Lagrangian formalisms of generally covariant systems. We show that the gauge group for such a system is characterized by having generators which are projectable under the Legendre map. The gauge group is found to be much larger than the original group of spacetime diffeomorphisms, since its generators must depend on the lapse function and shift vector of the spacetime metric in a given coordinate patch. Our results are generalizations of earlier results by Salisbury and Sundermeyer. They arise in a natural way from using the requirement of equivalence between Lagrangian and Hamiltonian formulations of the system, and they are new in that the symmetries are realized on the full set of phase space variables. The generators are displayed explicitly and are applied to the relativistic string and to general relativity.Comment: 12 pages, no figures; REVTeX; uses multicol,fancyheadings,eqsecnum; to appear in Phys. Rev.

Noether's theorem and gauge transformations. Application to the bosonic string and CP(2,n-1) model

New results on the theory of constrained systems are applied to characterize the generators of Noethers symmetry transformations. As a byproduct, an algorithm to construct gauge transformations in Hamiltonian formalism is derived. This is illustrated with two relevant examples

Canonical Noether symmetries and commutativity properties for gauge systems

For a dynamical system defined by a singular Lagrangian, canonical Noether symmetries are characterized in terms of their commutation relations with the evolution operators of Lagrangian and Hamiltonian formalisms. Separate characterizations are given in phase space, in velocity space, and through an evolution operator that links both spaces.Comment: 22 pages; some references updated, an uncited reference deleted, minor style change

Temperature dependence of the magnetization processes in Co/Al oxide/Permalloy trilayers

The magnetization process of Co/Al oxide/Py trilayers and its evolution with the temperature have been analyzed. The particular behavior of the Co layers, including the shift of the hysteresis loops and a coercivity increase with the decrease of temperature, is related with the apparition of a CoO layer at the Co/Al-oxide interface

Tissue distribution and kinetics of endogenous porphyrins synthesized after topical application of ALA in different vehicles

The use of 5-aminolaevulinic acid (ALA) is gaining increasing attention for photosensitization in photodynamic therapy of superficially localized tumours. The aim of this work was to determine the kinetics of porphyrin generation in tissues after topical application of ALA delivered in different vehicles on the skin overlying the tumour and normal skin of mice. Maximal accumulation was found in tumour 3 h after ALA application in both cream and lotion preparations. Normal and overlying tumour skin tissues showed different kinetic patterns, reflecting histological changes when the latter is invaded by tumour cells. Liver, kidney, spleen and blood porphyrins also raised from basal levels, showing that ALA and/or ALA-induced porphyrins reach all tissues after topical application. During the first 24 h of ALA topical application, precursors and porphyrins are excreted by both urine and faeces. ALA lotion applied on the skin overlying the tumour induced higher accumulation of tumoural porphyrins than cream, and lotion applied on normal skin appeared to be the most efficient upon inducing total body porphyrins. This work has demonstrated the great influence of the formulation of ALA vehicle on penetration through the skin. Knowledge of the kinetics of porphyrin generation after different conditions of ALA application is needed for the optimization of diagnosis and phototherapy in human tumours. © 1999 Cancer Research Campaig

Sistemas de partidos multinivel en contextos unitarios en América Latina: los casos de Ecuador, Perú, Bolivia y Colombia (1978-2011)

[ES]Las preguntas fundamentales que busca resolver esta investigación se relacionan con dar cuenta del cambio en los sistemas de partidos desde una perspectiva multinivel, es decir, considerando tanto la competencia que tiene lugar en el nivel nacional como en el local. Asimismo, se busca identificar variables que puedan tener alguna incidencia sobre los cambios que atraviesan los sistemas de partidos. Puntualmente, ¿cuáles son los factores, tanto institucionales como sociológicos, que han favorecido los diferentes tipos de cambios en el modo en que se estructura la competencia en los sistemas de partidos multinivel? Para esto, se comparan las diferentes unidades territoriales locales y nacionales que componen los sistemas de partidos observando el nivel de fragmentación que tiene lugar en éstas a lo largo del periodo estudiado, capturado por la medida de congruencia del sistema de partidos (Gibson y Suárez Cao, 2010). Los resultados que éste arroja son analizados a la luz de los procesos políticos que han atravesado los sistemas de partidos con el objetivo de encontrar diferencias y similitudes en términos de los cambios o continuidades en el formato de la competencia de los países estudiados. En ese sentido, los objetivos específicos de esta investigación son: a) superar la concepción del sistema de partidos como un espacio homogéneo y relacionado, específicamente, con el ámbito nacional; b) volver la mirada hacia los sistemas políticos unitarios, confrontando la idea de que en estos sistemas el poder subnacional no es relevante y, por lo tanto, la competencia que tiene lugar en allí carece de interés y c) repensar el concepto de cambio del sistema de partidos, aplicándolo a sistemas de partidos fluidos en el marco de los cuales los cambios son más frecuentes, teniendo en cuenta tanto el nivel nacional como en el nivel local del sistema de partidos.[EN]The key questions this research seeks to address relate to accounting for the change in party systems from a multilevel perspective, ie, considering the competition that takes place at the national and local levels. It also seeks to identify variables that might have a bearing on the changes that cross party systems. Specifically, what are the factors, both institutional and sociological, that have favored different types of changes in the way it is structured competition in multi-party systems? For this, we compare the different territorial units that make up local and national party systems by observing the level of fragmentation that occurs in these throughout the study period, as captured by the congruence of the party system (Gibson and Suarez Cao , 2010). The results are analyzed it sheds light on the political processes that crossed party systems in order to find differences and similarities in terms of the changes and continuities in the competition format of the countries studied. In that sense, the specific objectives of this research are: a) overcome the conception of the party system as a homogeneous space and related specifically to national b) look back unitary political systems, confronting the idea that in these systems the power sub is not relevant and, therefore, the competition that takes place in there without interest c) rethink the concept of change in the party system, applying a fluid party systems under which changes are more frequent, taking into account both the national and local level in the party system

Electrospinning of ultra-thin polymer fibers

The electrospinning technique was used to spin ultra-thin fibers from several polymer/solvent systems. The diameter of the electrospun fibers ranged from 16 nm to 2 μm. The morphology of these fibers was investigated with an atomic force microscope (AFM) and an optical microscope. Polyethylene oxide) (PEO) dissolved in water or chloroform was studied in greater detail. PEO fibers spun from aqueous solution show a “beads on a string” morphology. An AFM study showed that the surface of these fibers is highly ordered. The “beads on a string” morphology can be avoided if PEO is spun from solution in chloroform; the resulting fibers show a lamellar morphology. Polyvinylalcohol (PVA) dissolved in water and cellulose acetate dissolved in acetone were additional polymer/solvent systems which were investigated. Furthermore, the electrospinning process was studied: different experimental lay-outs were tested, electrostatic fields were simulated, and voltage - current characteristics of the electrospinning process were recorded

Higher-Derivative Two-Dimensional Massive Fermion Theories

We consider the canonical quantization of a generalized two-dimensional massive fermion theory containing higher odd-order derivatives. The requirements of Lorentz invariance, hermiticity of the Hamiltonian and absence of tachyon excitations suffice to fix the mass term, which contains a derivative coupling. We show that the basic quantum excitations of a higher-derivative theory of order 2N+1 consist of a physical usual massive fermion, quantized with positive metric, plus 2N unphysical massless fermions, quantized with opposite metrics. The positive metric Hilbert subspace, which is isomorphic to the space of states of a massive free fermion theory, is selected by a subsidiary-like condition. Employing the standard bosonization scheme, the equivalent boson theory is derived. The results obtained are used as a guideline to discuss the solution of a theory including a current-current interaction.Comment: 23 pages, Late