150,791 research outputs found
Gravitational waveforms from the evaporating ACO cosmic string loop
The linearly polarized gravitational waveforms from a certain type of
rotating, evaporating cosmic string - the Allen-Casper-Ottewill loop - are
constructed and plotted over the lifetime of the loop. The formulas for the
waveforms are simple and exact, and describe waves which attenuate
self-similarly, with the amplitude and period of the waves falling off linearly
with time.Comment: 30 pages, 16 figure
Knots and Classical 3-Geometries
It has been conjectured by Rovelli that there is a correspondence between the
space of link classes of a Riemannian 3-manifold and the space of 3-geometries
(on the same manifold). An exact statement of his conjecture will be
established and then verified for the case when the 3-manifold is compact,
orientable and closed.Comment: 14p. type-set in AmS-TeX version 2.
Coherent instabilities of intense high-energy "white" charged-particle beams in the presence of nonlocal effects within the context of the Madelung fluid description
A hydrodynamical description of coherent instabilities that take place in the
longitudinal dynamics of a charged-particle coasting beam in a high-energy
accelerating machine is presented. This is done in the framework of the
Madelung fluid picture provided by the Thermal Wave Model. The well known
coherent instability charts in the complex plane of the longitudinal coupling
impedance for monochromatic beams are recovered. The results are also
interpreted in terms of the deterministic approach to modulational instability
analysis usually given for monochromatic large amplitude wave train propagation
governed by the nonlinear Schr\"odinger equation. The instability analysis is
then extended to a non-monochromatic coasting beam with a given thermal
equilibrium distribution, thought as a statistical ensemble of monochromatic
incoherent coasting beams ("white" beam). In this hydrodynamical framework, the
phenomenon of Landau damping is predicted without using any kinetic equation
governing the phase space evolution of the system.Comment: 14 pages, 1 figur
Aeolian sans ripples: experimental study of saturated states
We report an experimental investigation of aeolian sand ripples, performed
both in a wind tunnel and on stoss slopes of dunes. Starting from a flat bed,
we can identify three regimes: appearance of an initial wavelength, coarsening
of the pattern and finally saturation of the ripples. We show that both initial
and final wavelengths, as well as the propagative speed of the ripples, are
linear functions of the wind velocity. Investigating the evolution of an
initially corrugated bed, we exhibit non-linear stable solutions for a finite
range of wavelengths, which demonstrates the existence of a saturation in
amplitude. These results contradict most of the models.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett. Title changed,
figures corrected and simplified, more field data included, text clarifie
Learning guide for the terminal configured vehicle advanced guidance and control system mode select panel
This learning guide is designed to assist pilots in taking the PLATO presimulator training course on the advanced guidance and control system mode select panel. The learning guide is divided into five sections. The first section, the introduction, presents the course goals, prerequisites, definition of PLATO activities, and a suggested approach to completing the course. The remaining four sections present the purpose, learning activities and summary of each lesson of the AGCS PLATO course, which consists of (1) AGCS introduction; (2) lower order modes; (3) higher order modes; and (4) an arrival route exercise
On a Order Reduction Theorem in the Lagrangian Formalism
We provide a new proof of a important theorem in the Lagrangian formalism
about necessary and sufficient conditions for a second-order variational system
of equations to follow from a first-order Lagrangian.Comment: 9 pages, LATEX, no figures; appear in Il Nuovo Cimento
Improving fertiliser management: redefining the relationship between soil tests and crop responses for wheat in WA
Most soils in Western Australia (WA) are highly weathered with very low levels of phosphorus. WA soils initially contained adequate indigenous soil potassium for cropping but removal of potassium over time in harvested grain has gradually resulted in the some soils becoming potassium-deficient for grain production.
Fertiliser costs represent a significant part of the variable costs of growing crops in WA. Chen et al. (2009) identified the need for updated soil test interpretations due to substantial changes in farming systems, fertiliser practices and crop yield potential. The aims of this study were (1) to compile experimental data containing the standard soil test measurements and observed wheat crop yield responses for both nil and fertilised treatments across different soil types and seasons from published or unpublished sources, and (2) to critically analyse soil test-crop response relationships to derive better critical soil test values in soils and environments suitable for wheat grain production in WA
Development of lightweight, fire-retardant, low-smoke, high-strength, thermally stable aircraft floor paneling
Extensive fire resistance and mechanical property tests were conducted on sandwich configurations composed of resin-fiberglass laminates bonded with adhesive to Nomex honeycomb and foam core. The test results were used to select a combination of materials that would improve the fire safety of the airplane without sacrificing mechanical performance of the aircraft floor panels. A test panel is being service evaluated in a commercial aircraft
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