15,665 research outputs found
Modeling and identification of SCOLE
Vector differential equations for distributed structures; discretization (in space) of distributed structures; and parameter identification for the Spacecraft Control Laboratory Experiment (SCOLE) are examined
Effective speed of sound in phononic crystals
A new formula for the effective quasistatic speed of sound in 2D and 3D
periodic materials is reported. The approach uses a monodromy-matrix operator
to enable direct integration in one of the coordinates and exponentially fast
convergence in others. As a result, the solution for has a more closed form
than previous formulas. It significantly improves the efficiency and accuracy
of evaluating for high-contrast composites as demonstrated by a 2D example
with extreme behavior.Comment: 4 pages, 1 figur
Identification and control of structures in space
The derivation of the equations of motion for the Spacecraft Control Laboratory Experiment (SCOLE) is reported and the equations of motion of a similar structure orbiting the earth are also derived. The structure is assumed to undergo large rigid-body maneuvers and small elastic deformations. A perturbation approach is proposed whereby the quantities defining the rigid-body maneuver are assumed to be relatively large, with the elastic deformations and deviations from the rigid-body maneuver being relatively small. The perturbation equations have the form of linear equations with time-dependent coefficients. An active control technique can then be formulated to permit maneuvering of the spacecraft and simultaneously suppressing the elastic vibration
The ATLAS-SPT Radio Survey of Cluster Galaxies
Using a high-performance computing cluster to mosaic 4,787 pointings, we have
imaged the 100 sq. deg. South Pole Telescope (SPT) deep-field at 2.1 GHz using
the Australian Telescope Compact Array to an rms of 80 Jy and a resolution
of 8". Our goal is to generate an independent sample of radio-selected galaxy
clusters to study how the radio properties compare with cluster properties at
other wavelengths, over a wide range of redshifts in order to construct a
timeline of their evolution out to . A preliminary analysis of the
source catalogue suggests there is no spatial correlation between the clusters
identified in the SPT-SZ catalogue and our wide-angle tail galaxies.Comment: 9 pages, 4 figures. Submitted to Proceedings of Science for "The many
facets of extragalactic radio surveys: towards new scientific challenges",
Bologna, Italy 20-23 October 2015 (EXTRA-RADSUR2015
A Survey of the Galactic Plane for 6.7-GHz Methanol Masers I: l = 325.0 - 335.0 ; b = -0.53 - 0.53
We report the results of the first complete survey of an area of the Galactic
Plane for maser emission from the 6.7-GHz transition of methanol. The survey
covers a 10.6-square-degree region of the Galactic Plane in the longitude range
325-335 degrees and latitude range -0.53-0.53 degrees. The survey is sensitive
to masers with a peak flux density greater than approximately 2.6 Jy. The
weakest maser detected has a peak flux density of 2.3 Jy and the strongest a
peak flux density of 425 Jy. We detected a total of 50 distinct masers, 26 of
which are new detections. We show that many 6.7-GHz methanol masers are not
associated with IRAS sources, and that some are associated with sources that
have colours differing from those of a typical ultra-compact HII region
(UCHII). We estimate that the number of UCHII regions in the Galaxy is
significantly more than suggested by IRAS-based estimates, possibly by more
than a factor of two.Comment: 19 pages including 4 figures, using LaTeX formatted with mn.sty,
accepted for publication in MNRA
Quantum Operation Time Reversal
The dynamics of an open quantum system can be described by a quantum
operation, a linear, complete positive map of operators. Here, I exhibit a
compact expression for the time reversal of a quantum operation, which is
closely analogous to the time reversal of a classical Markov transition matrix.
Since open quantum dynamics are stochastic, and not, in general, deterministic,
the time reversal is not, in general, an inversion of the dynamics. Rather, the
system relaxes towards equilibrium in both the forward and reverse time
directions. The probability of a quantum trajectory and the conjugate, time
reversed trajectory are related by the heat exchanged with the environment.Comment: 4 page
Compact Radio Cores in Seyfert Galaxies
We have observed a sample of 157 Seyfert galaxies with a 275 km baseline
radio interferometer to search for compact, high brightness temperature radio
emission from the active nucleus. We obtain the surprising result that compact
radio cores are much more common in Seyfert 2 than in Seyfert 1 galaxies, which
at first seems to be inconsistent with orientation unification schemes. We
propose a model, involving optical depth effects in the narrow-line region,
which can reconcile our result with the standard unified scheme. (Accepted for
publication in ApJ 1994 Sep 10)Comment: 21 pages and 7 figures, uuencoded tar-compressed postscript files,
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