71,954 research outputs found
Moving grid method without interpolations
In their method, to solve a one—dimensional moving boundary problem, Crank and Gupta suggest a grid system which moves with the Interface. The method requires some interpolations to be carried out which they perform by using a cubic spline or an ordinary polynomial. In the present paper these interpolations are avoided by employing a Taylor's expansion in space and time dimensions. A practical diffusion problem is solved and the results are compared with those obtained from other methods
Observations of Dissipation of Slow Magneto-acoustic Waves in a Polar Coronal Hole
We focus on a polar coronal hole region to find any evidence of dissipation
of propagating slow magneto-acoustic waves. We obtained time-distance and
frequency-distance maps along the plume structure in a polar coronal hole. We
also obtained Fourier power maps of the polar coronal hole in different
frequency ranges in 171~\AA\ and 193~\AA\ passbands. We performed intensity
distribution statistics in time domain at several locations in the polar
coronal hole. We find the presence of propagating slow magneto-acoustic waves
having temperature dependent propagation speeds. The wavelet analysis and
Fourier power maps of the polar coronal hole show that low-frequency waves are
travelling longer distances (longer detection length) as compared to
high-frequency waves. We found two distinct dissipation length scales of wave
amplitude decay at two different height ranges (between 0--10 Mm and 10--70 Mm)
along the observed plume structure. The dissipation lengths obtained at higher
height range show some frequency dependence. Individual Fourier power spectrum
at several locations show a power-law distribution with frequency whereas
probability density function (PDF) of intensity fluctuations in time show
nearly Gaussian distributions. Propagating slow magneto-acoustic waves are
getting heavily damped (small dissipation lengths) within the first 10~Mm
distance. Beyond that waves are getting damped slowly with height. Frequency
dependent dissipation lengths of wave propagation at higher heights may
indicate the possibility of wave dissipation due to thermal conduction,
however, the contribution from other dissipative parameters cannot be ruled
out. Power-law distributed power spectra were also found at lower heights in
the solar corona, which may provide viable information on the generation of
longer period waves in the solar atmosphere.Comment: corrected typos and grammar, In press A&
Weighted Density Approximation Description of Insulating YH and LaH
Density functional calculations within the weighted density approximation
(WDA) are presented for YH and LaH. We investigate some commonly used
pair-distribution functions G. These calculations show that within a consistent
density functional framework a substantial insulating gap can be obtained while
at the same time retaining structural properties in accord with experimental
data. Our WDA band structures agree with those of approximation very well,
but the calculated band gaps are still 1.0-2.0 eV smaller than experimental
findings.Comment: 6 Pages, 3 figure
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A moving boundary problem arising from the diffusion of oxygen in absorbing tissue
Approximate analytical and numerical solutions of a partial differential equation are obtained which describe the
diffusion of oxygen in an absorbing medium. Essential
mathematical difficulties are associated with the presence
of a moving boundary which marks the furthest penetration
of oxygen into the medium and also with the need to allow
for an initial distribution of oxygen through the medium
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A method for solving moving boundary problems in heat flow Part I: Using cubic splines
A new approach to a heat-flow problem involving a moving boundary makes use of a grid system which moves with the boundary. The necessary interpolations are performed by using cubic splines. The method smooths out irregularities in the motion of the boundary which were evident in previous calculations based on a fixed grid system
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