403,683 research outputs found
A study of shock impacts and vibration dose values onboard highspeed marine craft
The shocks and impacts encountered on small high-speed craft exceed the limits set for safe working practice according to current standards. European legislation regarding the exposure to vibration will have far reaching effects on the operators of such craft with respect to the safety of their employees. This paper sets out to highlight the vibration dose values that can be expected during typical transits onboard high-speed craft and attempts to clarify some of the controversy currently surrounding vibration dose measurement in such circumstances. In order to relate vibration dosage to the impacts encountered and to boat motion, an algorithm was developed that identifies the timing and magnitude of impacts
Waveforms for Gravitational Radiation from Cosmic String Loops
We obtain general formulae for the plus- and cross- polarized waveforms of
gravitational radiation emitted by a cosmic string loop in transverse,
traceless (synchronous, harmonic) gauge. These equations are then specialized
to the case of piecewise linear loops, and it is shown that the general
waveform for such a loop is a piecewise linear function. We give several simple
examples of the waveforms from such loops. We also discuss the relation between
the gravitational radiation by a smooth loop and by a piecewise linear
approximation to it.Comment: 16 pages, 6 figures, Revte
Weakly nonlinear waves in magnetized plasma with a slightly non-Maxwellian electron distribution. Part 1, Stability of solitary waves
Weakly nonlinear waves in strongly magnetized plasma with slightly non-isothermal electrons are governed by a modified ZakharovâKuznetsov (ZK) equation, containing both quadratic and half-order nonlinear terms, which we refer to as the SchamelâKortewegâde VriesâZakharovâKuznetsov (SKdVZK) equation. We present a method to obtain an approximation for the growth rate, Îł, of sinusoidal perpendicular perturbations of wavenumber, k, to SKdVZK solitary waves over the entire range of instability. Unlike for (modified) ZK equations with one nonlinear term, in this method there is no analytical expression for kc, the cut-off wavenumber (at which the growth rate is zero) or its corresponding eigenfunction. We therefore obtain approximate expressions for these using an expansion parameter, a, related to the ratio of the nonlinear terms. The expressions are then used to find Îł for k near kc as a function of a. The approximant derived from combining these analytical results with the ones for small k agrees very well with the values of Îł obtained numerically. It is found that both kc and the maximum growth rate decrease as the electron distribution becomes progressively less peaked than the Maxwellian. We also present new algebraic and rarefactive solitary wave solutions to the equation
Dense H-free graphs are almost (Χ(H)-1)-partite
By using the Szemeredi Regularity Lemma, Alon and Sudakov recently
extended the classical Andrasfai-Erdos-Sos theorem to cover general graphs. We
prove, without using the Regularity Lemma, that the following stronger statement
is true.
Given any (r+1)-partite graph H whose smallest part has t vertices, there exists
a constant C such that for any given Îľ>0 and sufficiently large n the following is
true. Whenever G is an n-vertex graph with minimum degree
δ(G)âĽ(1 â
3/3râ1 + Îľ)n,
either G contains H, or we can delete f(n,H)â¤Cn2â1/t edges from G to obtain an
r-partite graph. Further, we are able to determine the correct order of magnitude
of f(n,H) in terms of the Zarankiewicz extremal function
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