751 research outputs found
A rigorous derivation of the stationary compressible Reynolds equation via the Navier-Stokes equations
We provide a rigorous derivation of the compressible Reynolds system as a
singular limit of the compressible (barotropic) Navier-Stokes system on a thin
domain. In particular, the existence of solutions to the Navier-Stokes system
with non-homogeneous boundary conditions is shown that may be of independent
interest. Our approach is based on new a priori bounds available for the
pressure law of hard sphere type. Finally, uniqueness for the limit problem is
established in the 1D case
Complete BFT Embedding of Massive Theory with One- and Two-form Gauge Fields
We study the constraint structure of the topologically massive theory with
one- and two-form fields in the framework of Batalin-Fradkin-Tyutin embedding
procedure. Through this analysis we obtain a new type of Wess-Jumino action
with novel symmetry, which is originated from the topological coupling term, as
well as the St\"uckelberg action related to the explicit gauge breaking mass
terms from the original theory.Comment: 22 pages, no figures, references adde
Five Dimensional Minimal Supergravities and Four Dimensional Complex Geometries
We discuss the relation between solutions admitting Killing spinors of
minimal supergravities in five dimensions and four dimensional complex
geometries. In the ungauged case (vanishing cosmological constant \Lambda=0)
the solutions are determined in terms of a hyper-Kahler base space; in the
gauged case (\Lambda<0) the complex geometry is Kahler; in the de Sitter case
(\Lambda>0) the complex geometry is hyper-Kahler with torsion (HKT). In the
latter case some details of the derivation are given. The method for
constructing explicit solutions is discussed in each case.Comment: 8 pages. Contribution to the Proceedings of the Spanish Relativity
Meeting 2008 in Salamanca, Spai
Mobile satellite service in the United States
Mobile satellite service (MSS) has been under development in the United States for more than two decades. The service will soon be provided on a commercial basis by a consortium of eight U.S. companies called the American Mobile Satellite Consortium (AMSC). AMSC will build a three-satellite MSS system that will offer superior performance, reliability and cost effectiveness for organizations requiring mobile communications across the U.S. The development and operation of MSS in North America is being coordinated with Telesat Canada and Mexico. AMSC expects NASA to provide launch services in exchange for capacity on the first AMSC satellite for MSAT-X activities and for government demonstrations
The AMSC mobile satellite system
The American Mobile Satellite Consortium (AMSC) Mobile Satellite Service (MSS) system is described. AMSC will use three multi-beam satellites to provide L-band MSS coverage to the United States, Canada and Mexico. The AMSC MSS system will have several noteworthy features, including a priority assignment processor that will ensure preemptive access to emergency services, a flexible SCPC channel scheme that will support a wide diversity of services, enlarged system capacity through frequency and orbit reuse, and high effective satellite transmitted power. Each AMSC satellite will make use of 14 MHz (bi-directional) of L-band spectrum. The Ku-band will be used for feeder links
Hamiltonian Embedding of SU(2) Higgs Model in the Unitary Gauge
Following systematically the generalized Hamiltonian approach of Batalin,
Fradkin and Tyutin (BFT), we embed the second-class non-abelian SU(2) Higgs
model in the unitary gauge into a gauge invariant theory. The strongly
involutive Hamiltonian and constraints are obtained as an infinite power series
in the auxiliary fields. Furthermore, comparing these results with those
obtained from the gauged second class Lagrangian, we arrive at a simple
interpretation for the first class Hamiltonian, constraints and observables.Comment: 13 pages, Latex, no figure
Third order perturbations of a zero-pressure cosmological medium: Pure general relativistic nonlinear effects
We consider a general relativistic zero-pressure irrotational cosmological
medium perturbed to the third order. We assume a flat Friedmann background but
include the cosmological constant. We ignore the rotational perturbation which
decays in expanding phase. In our previous studies we discovered that, to the
second-order perturbation, except for the gravitational wave contributions, the
relativistic equations coincide exactly with the previously known Newtonian
ones. Since the Newtonian second-order equations are fully nonlinear, any
nonvanishing third and higher order terms in the relativistic analyses are
supposed to be pure relativistic corrections. In this work we derive such
correction terms appearing in the third order. Continuing our success in the
second-order perturbations we take the comoving gauge. We discover that the
third-order correction terms are of -order higher than the second-order
terms where is a gauge-invariant combination related to the
three-space curvature perturbation in the comoving gauge; compared with the
Newtonian potential we have to the linear
order. Therefore, the pure general relativistic effects are of -order
higher than the Newtonian ones. The corrections terms are independent of the
horizon scale and depend only on the linear order gravitational potential
perturbation strength. From the temperature anisotropy of cosmic microwave
background we have . Therefore, our present result reinforces our
previous important practical implication that near current era one can use the
large-scale Newtonian numerical simulation more reliably even as the simulation
scale approaches near the horizon.Comment: 9 pages, no figur
Generalized BFT Formalism of Electroweak Theory in the Unitary Gauge
We systematically embed the SU(2)U(1) Higgs model in the unitary
gauge into a fully gauge-invariant theory by following the generalized BFT
formalism. We also suggest a novel path to get a first-class Lagrangian
directly from the original second-class one using the BFT fields.Comment: 14 pages, Latex, no figure
Second-order perturbations of cosmological fluids: Relativistic effects of pressure, multi-component, curvature, and rotation
We present general relativistic correction terms appearing in Newton's
gravity to the second-order perturbations of cosmological fluids. In our
previous work we have shown that to the second-order perturbations, the density
and velocity perturbation equations of general relativistic zero-pressure,
irrotational, single-component fluid in a flat background coincide exactly with
the ones known in Newton's theory. Here, we present the general relativistic
second-order correction terms arising due to (i) pressure, (ii)
multi-component, (iii) background curvature, and (iv) rotation. In case of
multi-component zero-pressure, irrotational fluids under the flat background,
we effectively do not have relativistic correction terms, thus the relativistic
result again coincides with the Newtonian ones. In the other three cases we
generally have pure general relativistic correction terms. In case of pressure,
the relativistic corrections appear even in the level of background and linear
perturbation equations. In the presence of background curvature, or rotation,
pure relativistic correction terms directly appear in the Newtonian equations
of motion of density and velocity perturbations to the second order. In the
small-scale limit (far inside the horizon), relativistic equations including
the rotation coincide with the ones in Newton's gravity.Comment: 41 pages, no figur
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