17,294 research outputs found
Enhancement of speed and efficiency of an Internet based gear design optimisation
An internet-based gear design optimisation program has been developed for geographically dispersed teams to collaborate over the internet. The optimisation program implements genetic algorithm. A novel methodology is presented that improves the speed of execution of the optimisation program by integrating artificial neural networks into the system. The paper also proposes a method that allows an improvement to the performance of the back propagation-learning algorithm. This is done by rescaling the output data patterns to lie slightly below and above the two extreme values of the full range neural activation function. Experimental tests show the reduction of execution time by approximately 50%, as well as an improvement in the training and generalisation errors and the rate of learning of the network
Gravitational perturbations from oscillons and transients after inflation
We study the scalar and tensor perturbations generated by the fragmentation
of the inflaton condensate into oscillons or transients after inflation, using
nonlinear classical lattice simulations. Without including the backreaction of
metric perturbations, we find that the magnitude of scalar metric perturbations
never exceeds a few , whereas the maximal strength of the
gravitational wave signal today is for standard
post-inflationary expansion histories. We provide parameter scalings for the
-attractor models of inflation, which can be easily applied to other
models. We also discuss the likelihood of primordial black hole formation, as
well as conditions under which the gravitational wave signal can be at
observationally interesting frequencies and amplitudes.
Finally, we provide an upper bound on the frequency of the peak of the
gravitational wave signal, which applies to all preheating scenarios.Comment: 18 pages, 8 figure
The charged inflaton and its gauge fields: preheating and initial conditions for reheating
We calculate particle production during inflation and in the early stages of
reheating after inflation in models with a charged scalar field coupled to
Abelian and non-Abelian gauge fields. A detailed analysis of the power spectra
of primordial electric fields, magnetic fields and charge fluctuations at the
end of inflation and preheating is provided. We carefully account for the Gauss
constraints during inflation and preheating, and clarify the role of the
longitudinal components of the electric field. We calculate the timescale for
the back-reaction of the produced gauge fields on the inflaton condensate,
marking the onset of non-linear evolution of the fields. We provide a
prescription for initial conditions for lattice simulations necessary to
capture the subsequent nonlinear dynamics. On the observational side, we find
that the primordial magnetic fields generated are too small to explain the
origin of magnetic fields on galactic scales and the charge fluctuations are
well within observational bounds for the models considered in this paper.Comment: 48 pages, 6 figures, 2 appendices, v3: references added, minor
changes to text, to appear in JCA
Resummed thermodynamic perturbation theory for bond cooperativity in associating fluids with small bond angles: Effects of steric hindrance and ring formation
In this paper we develop a thermodynamic perturbation theory for two site
associating fluids which exhibit bond cooperativity. We include both steric
hindrance and ring formation such that the equation of state is bond angle
dependent. Here the bond angle is the angle separating the centers of the two
association sites. As a test, new Monte Carlo simulations are performed, and
the theory is found to accurately predict the internal energy as well as the
distribution of associated clusters as a function of bond angle and bond
cooperativity.Comment: To appear in The Journal of Chemical Physic
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Multi-user Internet environment for gear design optimization
A Web based multi-user system has been developed to remotely execute a large size software package via the Internet. The software implements genetic algorithm to optimize the design of spur and helical gears. To accomplish this, a combination of HTML, JavaServlets, JavaApplets, JavaScript and HTTP protocol has been employed
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