12,243 research outputs found
Braneworlds, Conformal Fields and the Gravitons
We investigate the dynamics of Randall-Sundrum AdS5 braneworlds with
5-dimensional conformal matter fields. In the scenario with a compact fifth
dimension the class of conformal fields with weight -4 is associated with exact
5-dimensional warped geometries which are stable under radion field
perturbations and describe on the brane the dynamics of inhomogeneous dust,
generalized dark radiation and homogeneous polytropic dark energy. We analyse
the graviton mode flutuations around this class of background solutions and
determine their mass eigenvalues and wavefunctions from a Sturm-Liouville
problem. We show that the localization of gravity is not sharp enough for large
mass hierarchies to be generated. We also discuss the physical bounds imposed
by experiments in particle physics, in astrophysics and in precise measurements
of the low energy gravitational interaction.Comment: LaTeX, 9 pages, 2 figures. Based on talk given in the Second
International Conference on Quantum Theories and the Renormalization Group in
Gravity and Cosmology, CSIC and University of Barcelona, Barcelona, Spain,
11-15 July 2006. Submitted to be published in the Conference Proceedings, J.
Phys. A: Math. Ge
Braneworlds and Dark Energy
In the Randall-Sundrum scenario, we analyse the dynamics of an AdS5
braneworld when conformal matter fields propagate in five dimensions. We show
that conformal fields of weight -4 are associated with stable geometries which
describe the dynamics of inhomogeneous dust, generalized dark radiation and
homogeneous polytropic dark energy on a spherically symmetric 3-brane embedded
in the compact AdS5 orbifold. We discuss aspects of the radion stability
conditions and of the localization of gravity in the vicinity of the brane.Comment: 12 pages, latex, 3 eps figures. Talk given at the Seventh Workshop on
Quantum Field Theory under the Influence of External Conditions, IEEC, CSIC
and University of Barcelona, Barcelona, Catalonia, Spain, 5-9 September 2005.
Revised version published in the workshop proceedings, J. Phys. A:
Mathematical and General. Typos corrected and some changes introduced for
clarit
A strong form of almost differentiability
We present a uniformization of Reeken's macroscopic differentiability (see [5]), discuss its relations to uniform differentiability (see [6]) and classical continuous differentiability, prove the corresponding chain rule, Taylor's theorem, mean value theorem, and inverse mapping theorem. An attempt to compare it with the observability (see [1, 4]) is made too. © 2009 Springer Science+Business Media, Inc.CEOCFCTFEDER/POCT
Probing features of the Lee-Wick quantum electrodynamics
In this paper we discuss some aspects concerning the electromagnetic sector
of the abelian Lee-Wick (LW) quantum electrodynamics (QED). Using the Dirac's
theory of constrained systems, the higher-order canonical quantization of the
LW electromagnetism is performed. A quantum bound on the LW heavy mass is also
estimated using the best known measurement of the anomalous magnetic moment of
the electron. Finally it is shown that magnetic monopoles can coexist
peacefully in the LW scenario.Comment: Replaced with published versio
Retroreflecting curves in nonstandard analysis
We present a direct construction of retroreflecting curves by means of Nonstandard Analysis. We construct non self-intersecting curves which are of class C(1), except for a hyper-finite set of values, such that the probability of a particle being reflected from the curve with the velocity opposite to the velocity of incidence, is infinitely close to 1. The constructed curves are of two kinds: a curve infinitely close to a straight line and a curve infinitely close to the boundary of a bounded convex set. We shall see that the latter curve is a solution of the problem: find the curve of maximum resistance infinitely close to a given curve.CEOCFCTFEDER/POCT
Dynamic analysis of the train-bridge interaction: an accurate and efficient numerical method
The dynamic behavior of railway bridges carrying high-speed trains can be analyzed with or
without the consideration of the vehicle's own structure. However, due to the amount of
kinetic energy carried at high speeds, the train may interact significantly with the bridge,
especially when resonance occurs. Equally important is the riding comfort and the stability of
the track and train cars, which are usually the most critical limit states in the design of this
type of structures. With the aim of studying this problem a computer code was developed,
being the interaction between the bridge and the train implemented by means of contact
conditions between each train wheel (nodal point) and the structure (point inside a finite
element). The treatment of the interaction between a train wheel and a point on the surface of
a finite element is directly and efficiently implemented by means of an extended stiffness
matrix, which includes stiffness, flexibility and additional terms that stem from the
compatibility equations between the displacements of the vehicle and the bridge. This
methodology was applied to the study of the dynamic behavior of a bowstring arch bridge and
proved to be very accurate and efficien
Development of an efficient finite element model for the dynamic analysis of the train-bridge interaction
The design of high-speed railway bridges comprises a set of demands, from safety
and serviceability aspects, to new types of equipment and construction solutions. In order to perform
an accurate and realistic evaluation of the corresponding dynamic behavior, adequate
analysis tools that take into account the complexity of the train-bridge system are required.
These computational tools must be based on efficient algorithms to allow for the completion of
detailed dynamic analyses in a reasonable amount of time. The classical methods of analysis
may be unsatisfactory in the evaluation of the dynamic effects of the train-bridge system and
fully assessment of the structural safety, track safety and passenger comfort. A direct and versatile
technique for the simulation of the train-bridge interaction was implemented in the FEMIX
code, which is a general purpose finite element computer program. The presented case study is
an application of the proposed formulation, which proved to be very accurate and efficient
Specification of spatial relationships in directed graphs of cell signaling networks
Graph theory provides a useful and powerful tool for the analysis of cellular signaling networks. Intracellular components such as cytoplasmic signaling proteins, transcription factors and genes are connected by links, representing various types of chemical interactions that result in functional consequences. However, these graphs lack important information regarding the spatial distribution of cellular components. The ability of two cellular components to interact depends not only on their mutual chemical affinity but also on co-localization to the same subcellular region. Localization of components is often used as a regulatory mechanism to achieve specific effects in response to different receptor signals. Here we describe an approach for incorporating spatial distribution into graphs, and for the development of mixed graphs where links are specified by mutual chemical affinity as well as colocalization. We suggest that such mixed graphs will provide more accurate descriptions of functional cellular networks and their regulatory capabilities and aid in the development of large-scale predictive models of cellular behavior
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