6,733 research outputs found
The scaling of model test results to predict intake hot gas reingestion for STOVL aircraft with augmented vectored thrust engines
The difficulties of modeling the complex recirculating flow fields produced by multiple jet STOVL aircraft close to the ground have led to extensive use of experimental model tests to predict intake Hot Gas Reingestion (HGR). Model test results reliability is dependent on a satisfactory set of scaling rules which must be validated by fully comparable full scale tests. Scaling rules devised in the U.K. in the mid 60's gave good model/full scale agreement for the BAe P1127 aircraft. Until recently no opportunity has occurred to check the applicability of the rules to the high energy exhaust of current ASTOVL aircraft projects. Such an opportunity has arisen following tests on a Tethered Harrier. Comparison of this full scale data and results from tests on a model configuration approximating to the full scale aircraft geometry has shown discrepancies between HGR levels. These discrepancies although probably due to geometry and other model/scale differences indicate some reexamination of the scaling rules is needed. Therefore the scaling rules are reviewed, further scaling studies planned are described and potential areas for further work are suggested
Gaussian limits for multidimensional random sequential packing at saturation (extended version)
Consider the random sequential packing model with infinite input and in any
dimension. When the input consists of non-zero volume convex solids we show
that the total number of solids accepted over cubes of volume is
asymptotically normal as . We provide a rate of
approximation to the normal and show that the finite dimensional distributions
of the packing measures converge to those of a mean zero generalized Gaussian
field. The method of proof involves showing that the collection of accepted
solids satisfies the weak spatial dependence condition known as stabilization.Comment: 31 page
Interpreting doubly special relativity as a modified theory of measurement
In this article we develop a physical interpretation for the deformed
(doubly) special relativity theories (DSRs), based on a modification of the
theory of measurement in special relativity. We suggest that it is useful to
regard the DSRs as reflecting the manner in which quantum gravity effects
induce Planck-suppressed distortions in the measurement of the "true" energy
and momentum. This interpretation provides a framework for the DSRs that is
manifestly consistent, non-trivial, and in principle falsifiable. However, it
does so at the cost of demoting such theories from the level of "fundamental"
physics to the level of phenomenological models -- models that should in
principle be derivable from whatever theory of quantum gravity one ultimately
chooses to adopt.Comment: 18 pages, plain LaTeX2
The Seeds of Cosmic structure as a door to New Physics
There is something missing in our understanding of the origin of the seeds of
Cosmic Structuture.
The fact that the fluctuation spectrum can be extracted from the inflationary
scenario through an analysis that involves quantum field theory in curved
space-time, and that it coincides with the observational data has lead to a
certain complacency in the community, which prevents the critical analysis of
the obscure spots in the derivation. The point is that the inhomogeneity and
anisotropy of our universe seem to emerge from an exactly homogeneous and
isotropic initial state through processes that do not break those symmetries.
This article gives a brief recount of the problems faced by the arguments based
on established physics, which comprise the point of view held by a large
majority of researchers in the field.
The conclusion is that we need some new physics to be able to fully address
the problem. The article then exposes one avenue that has been used to address
the central issue and elaborates on the degree to which, the new approach makes
different predictions from the standard analyses.
The approach is inspired on Penrose's proposals that Quantum Gravity might
lead to a real, dynamical collapse of the wave function, a process that we
argue has the properties needed to extract us from the theoretical impasse
described above.Comment: Prepared for the proceedings of the conference NEBXII " Recent
Developments in Gravity", Napfio Grece June 2006. LateX, 15 page
Spin-3/2 Fermions in Twistor Formalism
Consistency conditions for the local existence of massless spin 3/2 fields
has been explored that the field equations for massless helicity 3/2 are
consistent iff the space-time is Ricci-flat and that in Minkowski space-time
the space of conserved charges for the fields is its twistor space itself.
After considering the twistorial methods to study such massless helicity 3/2
fields, we derive in flat space-time that the charges of spin-3/2 fields
defined topologically by the first Chern number of their spin-lowered self-dual
Maxwell fields, are given by their twistor space, and in curved space-time that
the (anti-)self-duality of the space-time is the necessary condition. Since in
N=1 supergravity torsions are the essential ingredients, we generalize our
space-time to that with torsion (Einstein-Cartan theory) and have investigated
the consistency of existence of spin 3/2 fields in it. A simple solution is
found that the space-time has to be conformally (anti-)self-dual, left-(or
right-)torsion-free. The integrability condition on -surface shows that
the (anti-)self-dual Weyl spinor can be described only by the covariant
derivative of the right-(left-)handed-torsion.Comment: 13 pages, Latex2e. The derivations and the conclusions are improve
Mathematics of random growing interfaces
We establish a thermodynamic limit and Gaussian fluctuations for the height
and surface width of the random interface formed by the deposition of particles
on surfaces. The results hold for the standard ballistic deposition model as
well as the surface relaxation model in the off-lattice setting. The results
are proved with the aid of general limit theorems for stabilizing functionals
of marked Poisson point processes.Comment: 12 page
Growing Perfect Decagonal Quasicrystals by Local Rules
A local growth algorithm for a decagonal quasicrystal is presented. We show
that a perfect Penrose tiling (PPT) layer can be grown on a decapod tiling
layer by a three dimensional (3D) local rule growth. Once a PPT layer begins to
form on the upper layer, successive 2D PPT layers can be added on top resulting
in a perfect decagonal quasicrystalline structure in bulk with a point defect
only on the bottom surface layer. Our growth rule shows that an ideal
quasicrystal structure can be constructed by a local growth algorithm in 3D,
contrary to the necessity of non-local information for a 2D PPT growth.Comment: 4pages, 2figure
Limit theory for point processes in manifolds
Let , be i.i.d. random variables having values in an
-dimensional manifold and consider sums
, where is a real
valued function defined on pairs , with
and locally finite. Subject to
satisfying a weak spatial dependence and continuity condition, we show that
such sums satisfy weak laws of large numbers, variance asymptotics and central
limit theorems. We show that the limit behavior is controlled by the value of
on homogeneous Poisson point processes on -dimensional hyperplanes
tangent to . We apply the general results to establish the limit
theory of dimension and volume content estimators, R\'{e}nyi and Shannon
entropy estimators and clique counts in the Vietoris-Rips complex on
.Comment: Published in at http://dx.doi.org/10.1214/12-AAP897 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Twistors, special relativity, conformal symmetry and minimal coupling - a review
An approach to special relativistic dynamics using the language of spinors
and twistors is presented. Exploiting the natural conformally invariant
symplectic structure of the twistor space, a model is constructed which
describes a relativistic massive, spinning and charged particle, minimally
coupled to an external electro-magnetic field. On the two-twistor phase space
the relativistic Hamiltonian dynamics is generated by a Poincare scalar
function obtained from the classical limit (appropriately defined by us) of the
second order, to an external electro-magnetic field minimally coupled, Dirac
operator. In the so defined relativistic classical limit there are no Grassman
variables. Besides, the arising equation that describes dynamics of the
relativistic spin differs significantly from the so called Thomas Bergman
Michel Telegdi equation.Comment: 39 pages, no figures, few erronous statements (not affecting anything
else in the papper) on page 23 delete
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