1,473 research outputs found
The problem of time and gauge invariance in the quantization of cosmological models. I. Canonical quantization methods
The paper is the first of two parts of a work reviewing some approaches to
the problem of time in quantum cosmology, which were put forward last decade,
and which demonstrated their relation to the problems of reparametrization and
gauge invariance of quantum gravity. In the present part we remind basic
features of quantum geometrodynamics and minisuperspace cosmological models,
and discuss fundamental problems of the Wheeler - DeWitt theory. Various
attempts to find a solution to the problem of time are considered in the
framework of the canonical approach. Possible solutions to the problem are
investigated making use of minisuperspace models, that is, systems with a
finite number of degrees of freedom. At the same time, in the last section of
the paper we expand our consideration beyond the minisuperspace approximation
and briefly review promising ideas by Brown and Kuchar, who propose that dust
interacting only gravitationally can be used for time measuring, and the
unitary approach by Barvinsky and collaborators. The latter approach admits
both the canonical and path integral formulations and anticipates the
consideration of recent developments in the path integral approach in the
second part of our work.Comment: 16 pages, to be published in Grav. Cosmo
Comment on the choice of time in a two-component formulation of the Wheeler--DeWitt equation
The two-component formalism in quantum cosmology is revisited with a
particular emphasis on the identification of time. Its relation with the
appearance of imaginary eigenvalues is established. It is explicitly shown how
a good choice of the global time prevents this peculiarity.Comment: 8 pages; version accepted for publication in Int. J. Mod. Phys.
Wiggly Strings in Linearized Brans-Dicke Gravity
The metric around a wiggly cosmic string is calculated in the linear
approximation of Brans-Dicke theory of gravitation. The equations of motion for
relativistic and non-relativistic particles in this metric are obtained.
Light propagation is also studied and it is shown that photon trajectories
can be bounded.Comment: 10 pages, LaTeX, added reference
Time boundary terms and Dirac constraints
Time boundary terms usually added to action principles are systematically
handled in the framework of Dirac's canonical analysis. The procedure begins
with the introduction of the boundary term into the integral Hamiltonian action
and then the resulting action is interpreted as a Lagrangian one to which
Dirac's method is applied. Once the general theory is developed, the current
procedure is implemented and illustrated in various examples which are
originally endowed with different types of constraints.Comment: 12 page
Non-Orthogonal Multiplexing of Ultra-Reliable and Broadband Services in Fog-Radio Architectures
Defect Detection System for Smartphone Front Camera Based on Improved Template Matching Algorithm
Automatic defect detection plays crucial role in resilient manufacturing in terms of product quality and cost effectiveness. With reference to the smartphone front cameras production process, the most recurrent defects can be classified into no hole, inner hole burr, outer circle damage, hole deformation, outer circle fracture and hole position offset. Due to the fast production lines and the defects micro size, Sampling-based methods has huge uncertainty and limitation, and Machine learning-based methods are characterised by low efficiency. To tackle these issues, this paper proposes a machine vision-based detection methods of smartphone front camera based on a multi-step template matching algorithm to reduce the computational effort. Specifically, in order to improve the algorithm efficiency, the images of the smartphone front cameras, acquired using industrial image acquisition devices are pre-processed by performing Hough circle and line transformations respectively, then locate the exact defect area as a region of interest (ROI). Finally, a multi-step template matching algorithm is used to detect and classify a number of common defects. Experimental results show an excellent suitability of the proposed system in detecting front camera surface defects. A benchmarking with other available technologies highlights how the proposed system yields an improvement in the detection speed by 46%, along with an improvement in the detection accuracy by 9%. The successful industrial implementation is discussed with reference to the integration into an automatic defect detection system in a smartphone front camera manufacturing context
Adiabatic renormalization in theories with modified dispersion relations
We generalize the adiabatic renormalization to theories with dispersion
relations modified at energies higher than a new scale . We obtain
explicit expressions for the mean value of the stress tensor in the adiabatic
vacuum, up to the second adiabatic order. We show that for any dispersion
relation the divergences can be absorbed into the bare gravitational constants
of the theory. We also point out that, depending on the renormalization
prescription, the renormalized stress tensor may contain finite trans-Planckian
corrections even in the limit .Comment: Typos corrected; to appear in the Proceedings of IRGAC 06, Journal of
Physics
Stability of Chaplygin gas thin-shell wormholes
In this paper we construct spherical thin-shell wormholes supported by a
Chaplygin gas. For a rather general class of geometries we introduce a new
approach for the stability analysis of static solutions under perturbations
preserving the symmetry. We apply this to wormholes constructed from
Schwarzschild, Schwarzschild-de Sitter, Schwarzschild-anti de Sitter and
Reissner-Nordstrom metrics. In the last two cases, we find that there are
values of the parameters for which stable static solutions exist.Comment: 14 pages, 5 figures; v2: minor changes and new references added.
Accepted for publication in Physical Review
A new regulator of mitochondrial OXPHOS in hepatocytes and HCC cell lines: the AAA plus ATPase RuvBL1
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