3,736 research outputs found
On the stability and causality of scalar-vector theories
Various extensions of standard inflationary models have been proposed
recently by adding vector fields. Because they are generally motivated by
large-scale anomalies, and the possibility of statistical anisotropy of
primordial fluctuations, such models require to introduce non-standard
couplings between vector fields on the one hand, and either gravity or scalar
fields on the other hand. In this article, we study models involving a vector
field coupled to a scalar field. We derive restrictive necessary conditions for
these models to be both stable (Hamiltonian bounded by below) and causal
(hyperbolic equations of motion).Comment: 20 pages, references added, v2 matches published version in JCA
Raman scattering through surfaces having biaxial symmetry
Magnetic Raman scattering in two-leg spin ladder materials and the
relationship between the anisotropic exchange integrals are analyzed by P. J.
Freitas and R. R. P. Singh in Phys. Rev. B, {\bf 62}, 14113 (2000). The angular
dependence of the two-magnon scattering is shown to provide information for the
magnetic anisotropy in the Sr_14Cu_24O_41 and La_6Ca_8Cu_24O_41 compounds. We
point out that the experimental results of polarized Raman measurements at
arbitrary angles with respect to the crystal axes have to be corrected for the
light ellipticity induced inside the optically anisotropic crystals. We refer
quantitatively to the case of Sr_14Cu_24O_41 and discuss potential implications
for spectroscopic studies in other materials with strong anisotropy.Comment: To be published as a Comment in Phys. Rev.
Absolute Waterfrontage: Road Networked Artificial Islands and Finger Island Canal Estates on Australia’s Gold Coast
Receiver Architectures for MIMO-OFDM Based on a Combined VMP-SP Algorithm
Iterative information processing, either based on heuristics or analytical
frameworks, has been shown to be a very powerful tool for the design of
efficient, yet feasible, wireless receiver architectures. Within this context,
algorithms performing message-passing on a probabilistic graph, such as the
sum-product (SP) and variational message passing (VMP) algorithms, have become
increasingly popular.
In this contribution, we apply a combined VMP-SP message-passing technique to
the design of receivers for MIMO-ODFM systems. The message-passing equations of
the combined scheme can be obtained from the equations of the stationary points
of a constrained region-based free energy approximation. When applied to a
MIMO-OFDM probabilistic model, we obtain a generic receiver architecture
performing iterative channel weight and noise precision estimation,
equalization and data decoding. We show that this generic scheme can be
particularized to a variety of different receiver structures, ranging from
high-performance iterative structures to low complexity receivers. This allows
for a flexible design of the signal processing specially tailored for the
requirements of each specific application. The numerical assessment of our
solutions, based on Monte Carlo simulations, corroborates the high performance
of the proposed algorithms and their superiority to heuristic approaches
2D Fractional Supersymmetry for Rational Conformal Field Theory. Application for Third-Integer Spin States
A 2D- fractional supersymmetry theory is algebraically constructed. The
Lagrangian is derived using an adapted superspace including, in addition to a
scalar field, two fields with spins 1/3,2/3. This theory turns out to be a
rational conformal field theory. The symmetry of this model goes beyond the
super Virasoro algebra and connects these third-integer spin states. Besides
the stress-momentum tensor, we obtain a supercurrent of spin 4/3. Cubic
relations are involved in order to close the algebra; the basic algebra is no
longer a Lie or a super-Lie algebra. The central charge of this model is found
to be 5/3. Finally, we analyse the form that a local invariant action should
take.Comment: LaTex, 20 pages. Revised in response to referees' Comment
A model of gravitation with global U(1)-symmetry
It is shown that an embedding of the general relativity space into a flat
space gives a model of gravitation with the global symmetry and the
discrete one. The last one may be transformed into the symmetry
of the unified model, and the demand of independence of and
transformations leads to the estimate where
is an analog of the Weinberg angle of the standard model.Comment: 7 page
Resuming motor vehicle driving following orthopaedic surgery or limb trauma.
Following elective orthopaedic surgery or the treatment of a fracture, patients are temporarily unable to drive. This loss of independence may have serious social and economic consequences for the patient. It is therefore essential to know when it is safe to permit such patients to return to driving. This article, based upon a review of the current literature, proposes recommendations of the time period after which patients may safely return to driving. Practical decisions are made based upon the type of surgical intervention or fracture. Swiss legislation is equally approached so as to better define the decision
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