3,937 research outputs found
Dimensional reduction of the massless limit of the linearized "New Massive Gravity"
The so called "New Massive Gravity" in consists of the
Einstein-Hilbert action (with minus sign) plus a quadratic term in curvatures
(-term). Here we perform the Kaluza-Klein dimensional reduction of the
linearized -term to . We end up with a fourth-order massive
electrodynamics in described by a rank-2 tensor. Remarkably, there
appears a local symmetry in which persists even after gauging away the
Stueckelberg fields of the dimensional reduction. It plays the role of a
gauge symmetry. Although of higher-order in derivatives, the new massive
electrodynamics is ghost free, as we show here. It is shown, via master action,
to be dual to the Maxwell-Proca theory with a scalar Stueckelberg field.Comment: 12 pages, one more reference and text slightly modified accordingl
Pressure-induced phase transitions in AgClO4
AgClO4 has been studied under compression by x-ray diffraction and density
functional theory calculations. Experimental evidence of a structural phase
transition from the tetragonal structure of AgClO4 to an orthorhombic
barite-type structure has been found at 5.1 GPa. The transition is supported by
total-energy calculations. In addition, a second transition to a monoclinic
structure is theoretically proposed to take place beyond 17 GPa. The equation
of state of the different phases is reported as well as the calculated
Raman-active phonons and their pressure evolution. Finally, we provide a
description of all the structures of AgClO4 and discuss their relationships.
The structures are also compared with those of AgCl in order to explain the
structural sequence determined for AgClO4.Comment: 38 pages, 11 figures, 4 table
QED in external fields from the spin representation
Systematic use of the infinite-dimensional spin representation simplifies and
rigorizes several questions in Quantum Field Theory. This representation
permutes ``Gaussian'' elements in the fermion Fock space, and is necessarily
projective: we compute its cocycle at the group level, and obtain Schwinger
terms and anomalies from infinitesimal versions of this cocycle. Quantization,
in this framework, depends on the choice of the ``right'' complex structure on
the space of solutions of the Dirac equation. We show how the spin
representation allows one to compute exactly the S-matrix for fermions in an
external field; the cocycle yields a causality condition needed to determine
the phase.Comment: 32 pages, Plain TeX, UCR-FM-01-9
Visco-hyperelastic model with damage for simulating cyclic thermoplastic elastomers behavior applied to an industrial component
In this work a nonlinear phenomenological visco-hyperelastic model including damage consideration is developed to simulate the behavior of Santoprene 101-73 material. This type of elastomeric material is widely used in the automotive and aeronautic sectors, as it has multiple advantages. However, there are still challenges in properly analyzing the mechanical phenomena that these materials exhibit. To simulate this kind of material a lot of theories have been exposed, but none of them have been endorsed unanimously. In this paper, a new model is presented based on the literature, and on experimental data. The test samples were extracted from an air intake duct component of an automotive engine. Inelastic phenomena such as hyperelasticity, viscoelasticity and damage are considered singularly in this model, thus modifying and improving some relevant models found in the literature. Optimization algorithms were used to find out the model parameter values that lead to the best fit of the experimental curves from the tests. An adequate fitting was obtained for the experimental results of a cyclic uniaxial loading of Santoprene 101-73
Kidney disease in primary anti-phospholipid antibody syndrome
APS is an autoimmune disease defined by the presence of arterial or venous thrombotic events and/or pregnancy morbidity in patients who test positive for aPL. APS can be isolated (primary APS) or associated with other autoimmune diseases. The kidney is a major target organ in APS, and renal thrombosis can occur at any level within the vasculature of the kidney (renal arteries, intrarenal vasculature and renal veins). Histological findings vary widely, including ischaemic glomeruli and thrombotic lesions without glomerular or arterial immune deposits on immunofluorescence. Renal involvement in patients with definite APS is treated with long-term anticoagulants as warfarin, but new treatments are being tried. The aim of this article is to review the links between primary APS and kidney disease
Efficient formalism for large scale ab initio molecular dynamics based on time-dependent density functional theory
A new "on the fly" method to perform Born-Oppenheimer ab initio molecular
dynamics (AIMD) is presented. Inspired by Ehrenfest dynamics in time-dependent
density functional theory, the electronic orbitals are evolved by a
Schroedinger-like equation, where the orbital time derivative is multiplied by
a parameter. This parameter controls the time scale of the fictitious
electronic motion and speeds up the calculations with respect to standard
Ehrenfest dynamics. In contrast to other methods, wave function orthogonality
needs not be imposed as it is automatically preserved, which is of paramount
relevance for large scale AIMD simulations.Comment: 5 pages, 3 color figures, revtex4 packag
Local covariant quantum field theory over spectral geometries
A framework which combines ideas from Connes' noncommutative geometry, or
spectral geometry, with recent ideas on generally covariant quantum field
theory, is proposed in the present work. A certain type of spectral geometries
modelling (possibly noncommutative) globally hyperbolic spacetimes is
introduced in terms of so-called globally hyperbolic spectral triples. The
concept is further generalized to a category of globally hyperbolic spectral
geometries whose morphisms describe the generalization of isometric embeddings.
Then a local generally covariant quantum field theory is introduced as a
covariant functor between such a category of globally hyperbolic spectral
geometries and the category of involutive algebras (or *-algebras). Thus, a
local covariant quantum field theory over spectral geometries assigns quantum
fields not just to a single noncommutative geometry (or noncommutative
spacetime), but simultaneously to ``all'' spectral geometries, while respecting
the covariance principle demanding that quantum field theories over isomorphic
spectral geometries should also be isomorphic. It is suggested that in a
quantum theory of gravity a particular class of globally hyperbolic spectral
geometries is selected through a dynamical coupling of geometry and matter
compatible with the covariance principle.Comment: 21 pages, 2 figure
Rebuilding public trust in government administrations through e-government actions
AbstractCitizen trust in the public administration has been reduced worldwide due to recent events such as the current economic situation, corruption cases or disclosure of classified information. This work analyzes whether e-government related actions could be strategically employed to increase citizen trust in the public administration. This research confirms that perceived quality of public e-services has a positive effect on trust in the public administration. In turn, public administration communication (i.e., campaigns to promote the benefits and use of e-government) only influence trust in the public administration for citizens with a favorable attitude towards e-government. These results have interesting implications suggesting in which ways public administration should invest their limited resources in order to recover the levels of citizen trust
On the ultraviolet behaviour of quantum fields over noncommutative manifolds
By exploiting the relation between Fredholm modules and the
Segal-Shale-Stinespring version of canonical quantization, and taking as
starting point the first-quantized fields described by Connes' axioms for
noncommutative spin geometries, a Hamiltonian framework for fermion quantum
fields over noncommutative manifolds is introduced. We analyze the ultraviolet
behaviour of second-quantized fields over noncommutative 3-tori, and discuss
what behaviour should be expected on other noncommutative spin manifolds.Comment: 10 pages, RevTeX version, a few references adde
- …