32,479 research outputs found
SkyMapper and the Southern Sky Survey - a resource for the southern sky
SkyMapper is amongst the first of a new generation of dedicated, wide-field
survey telescopes. The 1.3m SkyMapper telescope features a 5.7 square degree
field-of-view Cassegrain imager and will see first light in late 2007. The
primary goal of the facility is to conduct the Southern Sky Survey a six
colour, six epoch survey of the southern sky. The survey will provide
photometry for objects between 8th and 23rd magnitude with global photometric
accuracy of 0.03 magnitudes and astrometry to 50 mas. This will represent a
valuable scientific resource for the southern sky and in addition provide a
basis for photometric and astrometric calibration of imaging data.Comment: 6 pages, 4 figures, proceedings of ESO Calibration Workshop 200
Design guide for helicopter transmission seals
A detailed approach for the selection and design of seals for helicopter transmissions is presented. There are two major types of seals presently being used and they are lip type seals and mechanical type seals. Lip type seals can be divided in conventional lip seals and hydrodynamic lip seals. Conventional lip seals can be used for slow-speed, low-pressure, low-temperature sealing. Hydrodynamic lip seals although they are as pressure and temperature limited as conventional lip seals, can operate at a higher speed. Mechanical types seals are comprised of face seals and circumferential seals. Face seals are capable of high speed, high pressure, and high temperature. Circumferential seals can be used in high-speed and high-temperature applications, but will leak excessively at moderate pressures. The performance goals of transmission seals are a life that is at least equal to the scheduled overhaul interval of the gearbox component and a leakage rate of near zero
Homotopy Method for the Large, Sparse, Real Nonsymmetric Eigenvalue Problem
A homotopy method to compute the eigenpairs, i.e., the eigenvectors and eigenvalues, of a given real matrix A1 is presented. From the eigenpairs of some real matrix A0, the eigenpairs of
A(t) ≡ (1 − t)A0 + tA1
are followed at successive "times" from t = 0 to t = 1 using continuation. At t = 1, the eigenpairs of the desired matrix A1 are found. The following phenomena are present when following the eigenpairs of a general nonsymmetric matrix:
• bifurcation,
• ill conditioning due to nonorthogonal eigenvectors,
• jumping of eigenpaths.
These can present considerable computational difficulties. Since each eigenpair can be followed independently, this algorithm is ideal for concurrent computers. The homotopy method has the potential to compete with other algorithms for computing a few eigenvalues of large, sparse matrices. It may be a useful tool for determining the stability of a solution of a PDE. Some numerical results will be presented
Stellar Associations and their Field East of LMC 4 in the Large Magellanic Cloud
We report about the stellar content and the luminosity and mass functions of
three stellar associations and their field located on the north-east edge of
the super-bubble LMC 4 in the Large Magellanic Cloud.Comment: To be appeared in the meeting Proceedings of ``Modes of Star
Formation and the Origin of Field Populations'', Heidelberg, Germany, October
2000; to be published in the ASP Conference Series, edited by E. K. Grebel
and W. Brandne
The effect of electron-electron correlation on the attoclock experiment
We investigate multi-electron effects in strong-field ionization of Helium
using a semi-classical model that, unlike other commonly used theoretical
approaches, takes into account electron-electron correlation. Our approach has
an additional advantage of allowing to selectively switch off different
contributions from the parent ion (such as the remaining electron or the
nuclear charge) and thereby investigate in detail how the final electron angle
in the attoclock experiment is influenced by these contributions. We find that
the bound electron exerts a significant effect on the final electron momenta
distribution that can, however, be accounted for by an appropriately selected
mean field. Our results show excellent agreement with other widely used
theoretical models done within a single active electron approximation
Finding RR Lyrae Stars with SkyMapper: an Observational Test
One of the major science goals of the SkyMapper Survey of the Southern
Hemisphere sky is the determination of the shape and extent of the halo of the
Galaxy. In this paper we quantify the likely efficiency and completeness of the
survey as regards the detection of RR Lyrae variable stars, which are excellent
tracers of the halo stellar population. We have accomplished this via
observations of the RR Lyrae-rich globular cluster NGC 3201. We find that for
single epoch uvgri observations followed by two further epochs of g, r imaging,
as per the intended three-epoch survey strategy, we recover known RR Lyraes
with a completeness exceeding 90%. We also investigate boundaries in the
gravity-sensitive single-epoch two-color diagram that yield high completeness
and high efficiency (i.e., minimal contamination by non-RR Lyraes) and the
general usefulness of this diagram in separating populations.Comment: 10 pages, 5 figures, to appear in the Publications of the
Astronomical Society of Australia (PASA), published by Cambridge University
Pres
Assessing the Effectiveness of a Computer Simulation in Introductory Undergraduate Environments
We present studies documenting the effectiveness of using a computer simulation, specifically the Circuit Construction Kit (CCK) developed as part of the Physics Education Technology Project (PhET) [1, 2], in two environments: an interactive college lecture and an inquiry-based laboratory. In the first study conducted in lecture, we compared students viewing CCK to viewing a traditional demonstration during Peer Instruction [3]. Students viewing CCK had a 47% larger relative gain (11% absolute gain) on measures of conceptual understanding compared to traditional demonstrations. These results led us to study the impact of the simulation's explicit representation for visualizing current flow in a laboratory environment, where we removed this feature for a subset of students. Students using CCK with or without the explicit visualization of current performed similarly to each other on common exam questions. Although the majority of students in both groups favored the use of CCK over real circuit equipment, the students who used CCK without the explicit current model favored the simulation more than the other grou
Constraining the Circumbinary Envelope of Z CMa via imaging polarimetry
Z CMa is a complex binary system, composed of a Herbig Be and an FU Ori star.
The Herbig star is surrounded by a dust cocoon of variable geometry, and the
whole system is surrounded by an infalling envelope. Previous
spectropolarimetric observations have reported a preferred orientation of the
polarization angle, perpendicular to the direction of a large, parsec-sized jet
associated with the Herbig star. The variability in the amount of polarized
light has been associated to changes in the geometry of the dust cocoon that
surrounds the Herbig star. We aim to constrain the properties of Z CMa by means
of imaging polarimetry at optical wavelengths. Using ExPo, a dual-beam imaging
polarimeter which operates at optical wavelengths, we have obtained imaging
(linear) polarimetric data of Z CMa. Our observations were secured during the
return to quiescence after the 2008 outburst. We detect three polarized
features over Z CMa. Two of these features are related to the two jets reported
in this system: the large jet associated to the Herbig star, and the micro-jet
associated to the FU Ori star. Our results suggest that the micro-jet extends
to a distance ten times larger than reported in previous studies. The third
feature suggests the presence of a hole in the dust cocoon that surrounds the
Herbig star of this system. According to our simulations, this hole can produce
a pencil beam of light that we see scattered off the low-density envelope
surrounding the system.Comment: Accepted for publication in A\&
- …