89,645 research outputs found

    Moving grid method without interpolations

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    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

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    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&

    Barrier modification in sub-barrier fusion reactions using Wong formula with Skyrme forces in semiclassical formalism

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    We obtain the nuclear proximity potential by using semiclassical extended Thomas Fermi (ETF) approach in Skyrme energy density formalism (SEDF), and use it in the extended â„“\ell-summed Wong formula under frozen density approximation. This method has the advantage of allowing the use of different Skyrme forces, giving different barriers. Thus, for a given reaction, we could choose a Skyrme force with proper barrier characteristics, not-requiring extra ``barrier lowering" or ``barrier narrowing" for a best fit to data. For the 64^{64}Ni+100^{100}Mo reaction, the â„“\ell-summed Wong formula, with effects of deformations and orientations of nuclei included, fits the fusion-evaporation cross section data exactly for the force GSkI, requiring additional barrier modifications for forces SIII and SV. However, the same for other similar reactions, like 58,64^{58,64}Ni+58,64^{58,64}Ni, fits the data best for SIII force. Hence, the barrier modification effects in â„“\ell-summed Wong expression depends on the choice of Skyrme force in extended ETF method.Comment: INPC2010, Vancouver, CANAD

    Weighted Density Approximation Description of Insulating YH3_3 and LaH3_3

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    Density functional calculations within the weighted density approximation (WDA) are presented for YH3_3 and LaH3_3. 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 GWGW 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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