13,998 research outputs found
The practical implementation of fatigue requirements to military aircraft and helicopters in the United Kingdom
The methods adopted in the United Kingdom to ensure the structural integrity of military aeroplanes and helicopters from the fatigue point of view are described. The procedure adopted from the writing of the specification to the monitoring of fatigue life in service are presented along with the requirements to be met and the way in which they are satisfied. Some of the outstanding problems that remain to be solved are indicated
A non-existence result for a generalization of the equations of the conformal method in general relativity
The constraint equations of general relativity can in many cases be solved by
the conformal method. We show that a slight modification of the equations of
the conformal method admits no solution for a broad range of parameters. This
suggests that the question of existence or non-existence of solutions to the
original equations is more subtle than could perhaps be expected.Comment: minor changes from previous versio
Transport and Helfand moments in the Lennard-Jones fluid. I. Shear viscosity
We propose a new method, the Helfand-moment method, to compute the shear
viscosity by equilibrium molecular dynamics in periodic systems. In this
method, the shear viscosity is written as an Einstein-like relation in terms of
the variance of the so-called Helfand moment. This quantity, is modified in
order to satisfy systems with periodic boundary conditions usually considered
in molecular dynamics. We calculate the shear viscosity in the Lennard-Jones
fluid near the triple point thanks to this new technique. We show that the
results of the Helfand-moment method are in excellent agreement with the
results of the standard Green-Kubo method.Comment: Submitted to the Journal of Chemical Physic
A model problem for conformal parameterizations of the Einstein constraint equations
We investigate the possibility that the conformal and conformal thin sandwich
(CTS) methods can be used to parameterize the set of solutions of the vacuum
Einstein constraint equations. To this end we develop a model problem obtained
by taking the quotient of certain symmetric data on conformally flat tori.
Specializing the model problem to a three-parameter family of conformal data we
observe a number of new phenomena for the conformal and CTS methods. Within
this family, we obtain a general existence theorem so long as the mean
curvature does not change sign. When the mean curvature changes sign, we find
that for certain data solutions exist if and only if the transverse-traceless
tensor is sufficiently small. When such solutions exist, there are generically
more than one. Moreover, the theory for mean curvatures changing sign is shown
to be extremely sensitive with respect to the value of a coupling constant in
the Einstein constraint equations.Comment: 40 pages, 4 figure
Hard Discs on the Hyperbolic Plane
We examine a simple hard disc fluid with no long range interactions on the
two dimensional space of constant negative Gaussian curvature, the hyperbolic
plane. This geometry provides a natural mechanism by which global crystalline
order is frustrated, allowing us to construct a tractable model of disordered
monodisperse hard discs. We extend free area theory and the virial expansion to
this regime, deriving the equation of state for the system, and compare its
predictions with simulation near an isostatic packing in the curved space.Comment: 4 pages, 3 figures, included, final versio
Tunneling mechanism of light transmission through metallic films
A mechanism of light transmission through metallic films is proposed,
assisted by tunnelling between resonating buried dielectric inclusions. This is
illustrated by arrays of Si spheres embedded in Ag. Strong transmission peaks
are observed near the Mie resonances of the spheres. The interaction among
various planes of spheres and interference effects between these resonances and
the surface plasmons of Ag lead to mixing and splitting of the resonances.
Transmission is proved to be limited only by absorption. For small spheres, the
effective dielectric constant can be tuned to values close to unity and a
method is proposed to turn the resulting materials invisible.Comment: 4 papges, 5 figure
Fault detection and accommodation testing on an F100 engine in an F-15 airplane
The fault detection and accommodation (FDA) methodology for digital engine-control systems may range from simple comparisons of redundant parameters to the more complex and sophisticated observer models of the entire engine system. Evaluations of the various FDA schemes are done using analytical methods, simulation, and limited-altitude-facility testing. Flight testing of the FDA logic has been minimal because of the difficulty of inducing realistic faults in flight. A flight program was conducted to evaluate the fault detection and accommodation capability of a digital electronic engine control in an F-15 aircraft. The objective of the flight program was to induce selected faults and evaluate the resulting actions of the digital engine controller. Comparisons were made between the flight results and predictions. Several anomalies were found in flight and during the ground test. Simulation results showed that the inducement of dual pressure failures was not feasible since the FDA logic was not designed to accommodate these types of failures
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