226 research outputs found
Numerical Techniques for Scattering from Submerged Objects
To represent the final results in terms of matrices, one expands all appropriate physical quantities in terms of partial wave basis states. This includes expansions for the incident and scattered fields and the surface quantities. The method then utilizes the Huygen-Poincare integral representation for both the exterior and interior solutions, leading to the required matrix equations. One thus deals with matrix equations, the complexity of which depends on the nature of the problem. It is shown that in general a transition matrix T can be obtained relating the incident field A with the scattered field f having the form T = PQ(-1), where f = TA. The structure of Q can be quite complicated and can itself be composed of other matrix inversions such as arise from layered objects. Recent improvements in this method appropriate for a variety of physical problems are focused on, and on their implementation. Results are outlined from scattering simulations for very elongated submerged objects and resonance scattering from elastic solids and shells. The final improvement concerns eigenfunction expansions of surface terms, arising from solution of the interior problem, obtained via a preconditioning technique. This effectively reduces the problem to that of obtaining eigenvalues of a Hermitian operator. This formalism is reviewed for scattering from targets that are rigid, sound-soft, acoustic, elastic solids, elastic shells, and elastic layered objects. Two sets of the more interesting results are presented. The first concerns scattering from elongated objects, and the second to thin elastic spheroids
A Supervisor Αgent-Based on the Markovian Decision Process Framework to Optimize the Behavior of a Highly Automated System
In this paper, we explore how MDP can be used as the framework to design and develop an Intelligent Decision Support System/Recommender System, in order to extend human perception and overcome human senses limitations (because covered by the ADS), by augmenting human cognition, emphasizing human judgement and intuition, as well as supporting him/her to take the proper decision in the right terms and time. Moreover, we develop Human-Machine Interaction (HMI) strategies able to make “transparent” the decision-making/recommendation process. This is strongly needed, since the adoption of partial automated systems is not only connected to the effectiveness of the decision and control processes, but also relies on how these processes are communicated and “explained” to the human driver, in order to achieve his/her trust
Bringing closure to microlensing mass measurement
Interferometers offer multiple methods for studying microlensing events and
determining the properties of the lenses. We investigate the study of
microlensing events with optical interferometers, focusing on narrow-angle
astrometry, visibility, and closure phase. After introducing the basics of
microlensing and interferometry, we derive expressions for the signals in each
of these three channels. For various forecasts of the instrumental performance,
we discuss which method provides the best means of measuring the lens angular
Einstein radius theta_E, a prerequisite for determining the lens mass. If the
upcoming generation of large-aperture, AO-corrected long baseline
interferometers (e.g. VLTI, Keck, OHANA) perform as well as expected, theta_E
may be determined with signal-to-noise greater than 10 for all bright events.
We estimate that roughly a dozen events per year will be sufficiciently bright
and have long enough durations to allow the measurement of the lens mass and
distance from the ground. We also consider the prospects for a VLTI survey of
all bright lensing events using a Fisher matrix analysis, and find that even
without individual masses, interesting constraints may be placed on the bulge
mass function, although large numbers of events would be required.Comment: 23 pages, aastex, submitted to Ap
Long-Baseline Interferometric Multiplicity Survey of the Sco-Cen OB Association
We present the first multiplicity-dedicated long baseline optical
interferometric survey of the Scorpius-Centaurus-Lupus-Crux association. We
used the Sydney University Stellar Interferometer to undertake a survey for new
companions to 58 Sco-Cen B- type stars and have detected 24 companions at
separations ranging from 7-130mas, 14 of which are new detections. Furthermore,
we use a Bayesian analysis and all available information in the literature to
determine the multiplicity distribution of the 58 stars in our sample, showing
that the companion frequency is F = 1.35 and the mass ratio distribution is
best described as a power law with exponent equal to -0.46, agreeing with
previous Sco-Cen high mass work and differing significantly from lower-mass
stars in Tau-Aur. Based on our analysis, we estimate that among young B-type
stars in moving groups, up to 23% are apparently single stars. This has strong
implications for the understanding of high-mass star formation, which requires
angular momentum dispersal through some mechanism such as formation of multiple
systems.Comment: 7 figures, 5 tables, accepted for publication in MNRA
Science and Technology Progress at the Sydney University Stellar Interferometer
This paper presents an overview of recent progress at the Sydney University
Stellar Interferometer (SUSI). Development of the third-generation PAVO beam
combiner has continued. The MUSCA beam combiner for high-precision differential
astrometry using visible light phase referencing is under active development
and will be the subject of a separate paper. Because SUSI was one of the
pioneering interferometric instruments, some of its original systems are old
and have become difficult to maintain. We are undertaking a campaign of
modernization of systems: (1) an upgrade of the Optical Path Length Compensator
IR laser metrology counter electronics from a custom system which uses an
obsolete single-board computer to a modern one based on an FPGA interfaced to a
Linux computer - in addition to improving maintainability, this upgrade should
allow smoother motion and higher carriage speeds; (2) the replacement of the
aged single-board computer local controllers for the siderostats and the
longitudinal dispersion compensator has been completed; (3) the large beam
reducing telescope has been replaced with a pair of smaller units with separate
accessible foci. Examples of scientific results are also included.Comment: 10 pages, 9 Figure
Orbital elements, masses and distance of lambda Scorpii A and B determined with the Sydney University Stellar Interferometer and high resolution spectroscopy
The triple system HD158926 (lambda Sco) has been observed interferometrically
with the Sydney University Stellar Interferometer and the elements of the wide
orbit have been determined. These are significantly more accurate than the
previous elements found spectroscopically. The inclination of the wide orbit is
consistent with the inclination previously found for the orbit of the close
companion. The wide orbit also has low eccentricity, suggesting that the three
stars were formed at the same time.
The brightness ratio between the two B stars was also measured at lambda =
442nm and 700nm. The brightness ratio and colour index are consistent with the
previous classification of lambda Sco A as B1.5 and lambda Sco B as B2.
Evolutionary models show that the two stars lie on the main sequence. Since
they have have the same age and luminosity class (IV) the mass-luminosity
relation can be used to determine the mass ratio of the two stars: M_B/M_A =
0.76+/-0.04.
The spectroscopic data have been reanalyzed using the interferometric values
for P, T, e and omega, leading to revised values for a_1sin i and the mass
function. The individual masses can be found from the mass ratio, the mass
function, spectrum synthesis and the requirement that the age of both
components must be the same: M_A = 10.4+/-1.3 Msun and M_B = 8.1+/-1.0 Msun.
The masses, angular semimajor axis and the period of the system can be used
to determine the dynamical parallax. We find the distance to lambda Sco to be
112+/-5 pc, which is approximately a factor of two closer than the HIPPARCOS
value of 216+/-42 pc.Comment: 8 pages, 4 figures. Accepted for publication by Monthly Notices of
the Royal Astronomical Societ
Orbital parameters, masses and distance to Beta Centauri determined with the Sydney University Stellar Interferometer and high resolution spectroscopy
The bright southern binary star beta Centauri (HR 5267) has been observed
with the Sydney University Stellar Interferometer (SUSI) and spectroscopically
with the ESO CAT and Swiss Euler telescopes at La Silla. The interferometric
observations have confirmed the binary nature of the primary component and have
enabled the determination of the orbital parameters of the system. At the
observing wavelength of 442 nm the two components of the binary system have a
magnitude difference of 0.15. The combination of interferometric and
spectroscopic data gives the following results: orbital period 357 days,
semi-major axis 25.30 mas, inclination 67.4 degrees, eccentricity 0.821,
distance 102.3 pc, primary and secondary masses M1 = M2 = 9.1 solar masses and
absolute visual magnitudes of the primary and secondary M1V = -3.85 and M2V =
-3.70. The high accuracy of the results offers a fruitful starting point for
future asteroseismic modelling of the pulsating binary components.Comment: 10 pages, 4 figures. Accepted for publication in MNRA
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