42,841 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
Closed expression of the interaction kernel in the Bethe-Salpeter equation for quark-antiquark bound states
The interaction kernel in the Bethe-Salpeter equation for quark-antiquark
bound states is derived from the Bethe-Salpeter equations satisfied by the
quark-antiquark four-point Green's function. The latter equations are
established based on the equations of motion obeyed by the quark and antiquark
propagators, the four-point Green's function and some other kinds of Green's
functions which follow directly from the QCD generating functional. The B-S
kernel derived is given an exact and explicit expression which contains only a
few types of Green's functions. This expression is not only convenient for
perturbative calculations, but also suitable for nonperturbative
investigations.Comment: 27 pages,no figure
Enhanced acoustic transmission through a slanted grating
It is known that an acoustic wave incident on an infinite array of aligned
rectangular blocks of a different acoustic material exhibits total transmission
if certain conditions are met [1] which relate the unique "intromission" angle
of incidence with geometric and material properties of the slab. This
extraordinary acoustic transmission phenomenon holds for any slab thickness,
making it analogous to a Brewster effect in optics, and is independent of
frequency as long as the slab microstructure is sub-wavelength in the
length-wise direction. Here we show that the enhanced transmission effect is
obtained in a slab with grating elements oriented obliquely to the slab normal.
The dependence of the intromission angle is given explicitly in
terms of the orientation angle. Total transmission is achieved at incidence
angles , with a relative phase shift between the transmitted
amplitudes of the and cases. These effects are shown
to follow from explicit formulas for the transmission coefficient. In the case
of grating elements that are rigid the results have direct physical
interpretation. The analytical findings are illustrated with full wave
simulations.Comment: 15 page, 16 figure
Non-damping oscillations at flaring loops
Context. QPPs are usually detected as spatial displacements of coronal loops
in imaging observations or as periodic shifts of line properties in
spectroscopic observations. They are often applied for remote diagnostics of
magnetic fields and plasma properties on the Sun. Aims. We combine imaging and
spectroscopic measurements of available space missions, and investigate the
properties of non-damping oscillations at flaring loops. Methods. We used the
IRIS to measure the spectrum over a narrow slit. The double-component Gaussian
fitting method was used to extract the line profile of Fe XXI 1354.08 A at "O
I" window. The quasi-periodicity of loop oscillations were identified in the
Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected
in the line properties of Fe XXI, HXR emissions in GOES 1-8 A derivative, and
Fermi 26-50 keV. The Doppler velocity and line width oscillate in phase, while
a phase shift of about Pi/2 is detected between the Doppler velocity and peak
intensity. The amplitudes of Doppler velocity and line width oscillation are
about 2.2 km/s and 1.9 km/s, respectively, while peak intensity oscillate with
amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period
of about 155 s is identified in the Doppler velocity and peak intensity of Fe
XXI, and AIA 131 A intensity. Conclusions. The oscillations at about 40 s are
not damped significantly during the observation, it might be linked to the
global kink modes of flaring loops. The periodicity at about 155 s is most
likely a signature of recurring downflows after chromospheric evaporation along
flaring loops. The magnetic field strengths of the flaring loops are estimated
to be about 120-170 G using the MHD seismology diagnostics, which are
consistent with the magnetic field modeling results using the flux rope
insertion method.Comment: 9 pages, 9 figures, 1 table, accepted by A&
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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
Similarity between the primary and secondary air-assisted liquid jet breakup mechanism
we report an ultrafast synchrotron x-ray phase contrast imaging study of the
primary breakup mechanism of a coaxial air-assisted water jet. We demonstrate
that there exist great similarities in the phenomenology of primary breakup
with that of the secondary breakup. Especially, a membrane-mediated breakup
mechanism dominates the breakup process for a wide range of air speeds. This
finding reveals the intrinsic connections of these two breakup regimes and has
deep implications on the unified theoretical approach in treating the breakup
mechanism of high speed liquid jet.Comment: 15 pages, 4 figure
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