1,236 research outputs found
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
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
NĂ©lida ARCHENTI y MarĂa InĂ©s TULA (coords.). «La representaciĂłn imperfecta. Logros y desafĂos de las mujeres polĂticas». Buenos Aires: Eudeba, 2014. 270 pp. ISBN: 978-950-23-2329-9.
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 fragmentaciĂłn que tiene lugar en Ă©stas a lo largo del periodo estudiado, capturado por la medida de congruencia del sistema de partidos (Gibson y Suárez Cao, 2010). Los resultados que Ă©ste arroja son analizados a la luz de los procesos polĂticos que han atravesado los sistemas de partidos con el objetivo de encontrar diferencias y similitudes en tĂ©rminos de los cambios o continuidades en el formato de la competencia de los paĂses estudiados.
En ese sentido, los objetivos especĂficos de esta investigaciĂłn son: a) superar la concepciĂłn del sistema de partidos como un espacio homogĂ©neo y relacionado, especĂficamente, con el ámbito nacional; b) volver la mirada hacia los sistemas polĂticos 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 allĂ carece de interĂ©s 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
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