2,138 research outputs found
Detecting a rotation in the epsilon Eridani debris disc
The evidence for a rotation of the epsilon Eridani debris disc is examined.
Data at 850 micron wavelength were previously obtained using the Submillimetre
Common User Bolometer Array (SCUBA) over periods in 1997-1998 and 2000-2002. By
chi-square fitting after shift and rotation operations, images from these two
epochs were compared to recover proper motion and orbital motion of the disc.
The same procedures were then performed on simulated images to estimate the
accuracy of the results.
Minima in the chi-square plots indicate a motion of the disc of approximately
0.6'' per year in the direction of the star's proper motion. This
underestimates the true value of 1'' per year, implying that some of the
structure in the disc region is not associated with epsilon Eridani,
originating instead from background galaxies. From the chi-square fitting for
orbital motion, a counterclockwise rotation rate of ~2.75 degrees per year is
deduced. Comparisons with simulated data in which the disc is not rotating show
that noise and background galaxies result in approximately Gaussian
fluctuations with a standard deviation +/-1.5 degrees per year. Thus
counterclockwise rotation of disc features is supported at approximately a
2-sigma level, after a 4-year time difference. This rate is faster than the
Keplerian rate of 0.65 degrees per year for features at ~65 AU from the star,
suggesting their motion is tracking a planet inside the dust ring.
Future observations with SCUBA-2 can rule out no rotation of the epsilon
Eridani dust clumps with ~4-sigma confidence. Assuming a rate of about 2.75
degrees per year, the rotation of the features after a 10-year period could be
shown to be >1 degree per year at the 3-sigma level.Comment: 8 pages, 6 figure
The feasibility of inventorying native vegetation and related resources form space photography
Photointerpretation of Gemini 4 photographs for inventorying native vegetatio
Neutron scattering study of a quasi-2D spin-1/2 dimer system Piperazinium Hexachlorodicuprate under hydrostatic pressure
We report inelastic neutron scattering study of a quasi-two-dimensional S=1/2
dimer system Piperazinium Hexachlorodicuprate under hydrostatic pressure. The
spin gap {\Delta} becomes softened with the increase of the hydrostatic
pressure up to P= 9.0 kbar. The observed threefold degenerate triplet
excitation at P= 6.0 kbar is consistent with the theoretical prediction and the
bandwidth of the dispersion relation is unaffected within the experimental
uncertainty. At P= 9.0 kbar the spin gap is reduced to 0.55 meV from 1.0 meV at
ambient pressure.Comment: 4 pages, 5 figure
Monte Carlo simulations for Ising spins with spin greater than 1/2 applied to the square and triangular lattices with antiferromagnetic interactions and comparing results using Kawasaki and Glauber dynamics
This paper has a pedagogical introduction. We describe the correct method for performing Monte Carlo simulations of Ising model systems with spin greater than one half. Correct and incorrect procedures are clearly outlined and the consequences of using the incorrect procedure are shown. The difference between Kawasaki and Glauber dynamics is then outlined and both methods are applied to the antiferromagnetic square and triangular lattices for S =1
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