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

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.

RETRASO, a code for modeling reactive transport in saturated and unsaturated porous media

The code RETRASO (REactive TRAnsport of SOlutes) simulates reactive transport of dissolved and gaseous species in non-isothermal saturated or unsaturated problems. Possible chemical reactions include aqueous complexation (including redox reactions), sorption, precipitation-dissolution of minerals and gas dissolution. Various models for sorption of solutes on solids are available, from experimental relationships (linear KD, Freundlich and Langmuir isotherms) to cation exchange and surface complexation models (constant capacitance, diffuse layer and triple layer models). Precipitation-dissolution and aqueous complexation can be modelled in equilibrium or according to kinetic laws. For the numerical solution of the reactive transport equations it uses the Direct Substitution Approach. The use of the code is demonstrated by three examples. The first example models various sorption processes in a smectite barrier. The second example models a complex chemical system in a two dimensional cross-section. The last example models pyrite weathering in an unsaturated medium

Particle growing mechanisms in Ag-ZrO2 and Au-ZrO2 granular films obtained by pulsed laser deposition

Thin films consisting of Ag and Au nanoparticles embedded in amorphous ZrO2 matrix were grown by pulsed laser deposition in a wide range of metal volume concentrations in the dielectric regime (0.08<x(Ag)<0.28 and 0.08<x(Au)<0.52). High resolution transmission electron microscopy (TEM) showed regular distribution of spherical Au and Ag nanoparticles having very sharp interfaces with the amorphous matrix. Mean particle size determined from X-ray diffraction agreed with direct TEM observation. The silver mean diameter increases more abruptly with metal volume content than that corresponding to gold particles prepared under the same conditions. Two mechanisms of particle growing are observed: nucleation and particle coalescence, their relative significance being different in both granular systems, which yields very different values of the percolation threshold (xc(Ag)~0.28 and xc(Au)~0.52).Comment: 6 figure

Dirac's Constrained Hamiltonian Dynamics from an Unconstrained Dynamics

We derive the Hamilton equations of motion for a constrained system in the form given by Dirac, by a limiting procedure, starting from the Lagrangean for an unconstrained system. We thereby ellucidate the role played by the primary constraints and their persistance in time.Comment: 10 page

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

DISEÑO DE UNA INSTALACION FRIGORIFICA PARA OCHO CAMARAS DE 2.560 m3

El objeto del presente proyecto de final de carrera es realizar básicamente el estudio y selección de materiales de dos opciones muy diferentes de instalación frigorífica para abastecer ocho cámaras de alquiler de 2.560 m3 cada una. Estas ocho cámaras frigoríficas se ubican en una nave industrial emplazada en la provincia de Lérida. Cuatro de éstas serán exclusivamente destinadas a almacenar producto congelado mientras que las otras cuatro serán bitémperas, es decir, tendrán la posibilidad de ser utilizadas para almacenar producto congelado o fresco según lo exija la demanda del mercado. Una de las opciones de instalación frigorífica se basa en una distribución descentralizada y en cambio la otra se caracteriza por una centralización de la misma. Las dos opciones son igual de válidas como solución para la refrigeración de las ocho cámaras, consecuentemente una parte importante del proyecto se destinará a la comparación de las instalaciones des del ámbito energético, económico y ambiental entre otros. La opción de instalación descentralizada se caracteriza por una central frigorífica para cada cámara por separado situadas en el altillo de la nave. Estas ocho centrales funcionan con el refrigerante R-404A y se basan en un ciclo de refrigeración sencillo, lo que implica que realizan la compresión en una sola etapa. La opción de instalación centralizada se caracteriza por una única central situada a parte en una sala de máquinas que abastece a las ocho cámaras. Esta central funciona con el refrigerante amoníaco (NH3) y se basa en un ciclo de refrigeración booster de inyección total, lo que implica entre otras cuestiones que realiza la compresión en dos etapas. El proyecto consta de los siguientes bloques principales: • Necesidades térmicas de las cámaras frigoríficas. • Descripción y análisis de los ciclos frigoríficos en los que se basan las instalaciones. • Descripción y selección de los componentes que constituyen ambos tipos de instalación: compresores, evaporadores, condensadores, valvulería, etc. • Elementos de control y de seguridad que constituyen ambos tipos de instalación (presostatos, termostatos, cuadro eléctrico, etc.) y descripción de su función en las instalaciones. • Análisis ambiental. o Descripción y normativa vigente de los refrigerantes que utilizan las instalaciones. o Consumos eléctricos de las instalaciones. • Comparación de las instalaciones. • Presupuestos de las dos instalaciones

Evaluation of detection methods for Virus, Viroids and Phytoplasmas affecting pear and apple

The RT-PCR technique for the detection of apple stem grooving virus (ASGV), apple stem pitting virus (ASPV), apple chlorotic leaf spot virus (ACLSV), apple mosaic virus (ApMV) and pear blister canker viroid (PBCV) was evaluated for health control of fruit plants from nurseries. The technique was evaluated in purified RNA and crude extracts and also in phloem collected in autumn and from young spring shoots. The results obtained for phytoplasma detection with ribosomal and non-ribosomal primers are also presented. Keywords: Detection, fruit virus, viroids, phytoplasm