22,700 research outputs found
Speckle interferometry
We have presented the basic mathematical treatment of interferometry in the
optical domain. Its applications in astronomical observations using both the
single aperture, as well as the diluted apertures are described in detail. We
have also described about the shortcomings of this technique in the presence of
Earth's atmosphere. A short descriptions of the atmospheric turbulence and its
effect on the flat wavefront from a stellar source is given. The formation of
speckle which acts as carrier of information is defined. Laboratory experiments
with phase modulation screens, as well as the resultant intensity distributions
due to point source are demonstrated. The experimental method to freeze the
speckles, as well as data processing techniques for both Fourier modulus and
Fourier phase are described. We have also discussed the technique of the
aperture synthesis using non-redundant aperture masks at the pupil plane of the
telescope, emphasizing set on the comparison with speckle interferometry. The
various methods of image restoration and their comparisons are also discussed.
Finally, we have touched upon certain astrophysical problems which can be
tackled with the newly developed speckle interferometer using the 2.34 meter
Vainu Bappu Telescope (VBT), situated at the Vainu Bappu Observatory (VBO),
Kavalur, India.Comment: 32 pages tex files including figure
Resonance State Wave Functions of Be using Supersymmetric Quantum Mechanics
The theoretical procedure of supersymmetric quantum mechanics is adopted to
generate the resonance state wave functions of the unbound nucleus Be.
In this framework, we used a density dependent M3Y microscopic potential and
arrived at the energy and width of the 1.8 MeV (5/2) resonance state. We
did not find any other nearby resonances for Be. It becomes apparent
that the present framework is a powerful tool to theoretically complement the
increasingly important accelerator based experiments with unbound nuclei.Comment: 5 pages, 4 figures, Phys. Lett. B (2017
Control of a Circular Jet
The present study report direct numerical simulation (DNS) of a circular jet
and the effect of a large scale perturbation at the jet inlet. The perturbation
is used to control the jet for increased spreading. Dual-mode perturbation is
obtained by combining an axisymmetric excitation with the helical. In the fluid
dynamics videos, an active control of the circular jet at a Reynolds number of
2000 for various frequency ratios (both integer and non-integer) has been
demonstrated. When the frequency ratio is fixed to 2, bifurcation of the jet on
a plane is evident. However, for a non-integer frequency ratio, the
axisymmetric jet is seen to bloom in all directions.Comment: 2 page
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