32,693 research outputs found
Fine particulate capture device
To capture fine particulate matter in a gas such as air, a dielectric fluid is directed to the center of whichever face of a rotating disc is exposed to the air flow. The disc is comprised of two or more segments which bear opposite electrostatic potentials. As the dielectric fluid is centrifuged towards the periphery of the rotating disc, the fluid becomes charged to the same potential as the segment over which it is passing. Particulate matter is attracted to the charged segment and is captured by the fluid. The fluid then carries the captured particulate matter to a collection device such as a toroidal container disposed around the periphery of the disc. A grounded electrically-conductive ring may be disposed at the outer periphery of the disc to neutralize the captured particles and the fluid before they enter the container
Surface-gravity determinations for main-sequence B stars
Astronomical models for computing surface gravity of B stars from hydrogen line equivalent width
Selection of the SIM Astrometric Grid
We investigate the choice of stellar population for use as the Astrometric
Grid for the Space Interferometry Mission (SIM). SIM depends on the astrometric
stability of about 2000 stars, the so called Grid, against which the science
measures are referenced. Low metallicity, and thus relatively high luminosity K
giants are shown to be the population of choice, when available. The
alternative, nearby G dwarfs, are shown to be suseptable to unmodeled motions
induced by gas-giant planetary companions, should there be a significant
population of such companions.
Radial velocity filtering is quite efficient in selecting Grid members from
the K giants with yields exceeding 50% if filtering at 30m/s (1-sigma) is
available. However if the binary fraction of the G dwarfs approaches 100% as
some studies suggest, the yield of stable systems would be in the range of 15%
at best (with 10m/s filtering). Use of the initial SIM measurement as a final
filter is shown not to be critical in either case, although it could improve
the yield of stable grid members.
For a Grid composed of weak-lined K giants, the residual contamination by
large unmodeled motions will amount to about 3% (and rises to about 6% if a
60m/s radial velocity criterion is used). The selective introduction of
quadratic terms in the proper motion solutions during the post-mission phase of
data reduction can reduce contamination to a remarkable 1% or better in either
case.
Analytic estimates based on circular orbits are developed which show how
these results come about.Comment: 42 pages including 13 eps figures. To be published Sept 2002 in PAS
Evaluation of bistable systems versus matched filters in detecting bipolar pulse signals
This paper presents a thorough evaluation of a bistable system versus a
matched filter in detecting bipolar pulse signals. The detectability of the
bistable system can be optimized by adding noise, i.e. the stochastic resonance
(SR) phenomenon. This SR effect is also demonstrated by approximate statistical
detection theory of the bistable system and corresponding numerical
simulations. Furthermore, the performance comparison results between the
bistable system and the matched filter show that (a) the bistable system is
more robust than the matched filter in detecting signals with disturbed pulse
rates, and (b) the bistable system approaches the performance of the matched
filter in detecting unknown arrival times of received signals, with an
especially better computational efficiency. These significant results verify
the potential applicability of the bistable system in signal detection field.Comment: 15 pages, 9 figures, MikTex v2.
Preliminary results of the University of California X-ray experiment on the OSO-3
Cosmic and solar X ray data obtained by Orbiting Solar Observatory /OSO-3
Long term variability of the Broad Emission Line profiles in AGN
Results of a long-term monitoring ( years) of the broad line and
continuum fluxes of three Active Galactic Nuclei (AGN), 3C 390.3, NGC 4151, and
NGC 5548, are presented. We analyze the H and H profile
variations during the monitoring period and study different details (as bumps,
absorption bands) which can indicate structural changes in the Broad Line
Region (BLR). The BLR dimensions are estimated using the time lags between the
continuum and the broad lines flux variations. We find that in the case of 3C
390.3 and NGC 5548 a disk geometry can explain both the broad line profiles and
their flux variations, while the BLR of NGC 4151 seems more complex and is
probably composed of two or three kinematically different regions.Comment: 10 pages, 9 figures, New Astronomy Reviews (Proceeding of 7th
SCSLSA), in pres
Hard X-ray imaging facility for space shuttle: A scientific and conceptual engineering study
A shuttle-accommodated instrument for imaging hard X-rays in the study of nonthermal particles and high temperature particles in various solar and cosmic phenomena was defined and its feasibility demonstrated. The imaging system configuration is described as well as the electronics, aspect systems, mechanical and thermal properties and the ground support equipment
Evidence for Supermassive Black Holes in Active Galactic Nuclei from Emission-Line Reverberation
Emission-line variability data for Seyfert 1 galaxies provide strong evidence
for the existence of supermassive black holes in the nuclei of these galaxies,
and that the line-emitting gas is moving in the gravitational potential of that
black hole. The time-delayed response of the emission lines to continuum
variations is used to infer the size of the line-emitting region, which is then
combined with measurements of the Doppler widths of the variable line
components to estimate a virial mass. In the case of the best-studied galaxy,
NGC 5548, various emission lines spanning an order of magnitude in distance
from the central source show the expected velocity proportional to inverse
square root of the distance correlation between distance and line width, and
are thus consistent with a single value for the mass. Two other Seyfert
galaxies, NGC 7469 and 3C 390.3, show a similar relationship. We compute the
ratio of luminosity to mass for these three objects and the narrow-line Seyfert
1 galaxy NGC 4051 and find that that the gravitational force on the
line-emitting gas is much stronger than radiation pressure. These results
strongly support the paradigm of gravitationally bound broad emission-line
region clouds.Comment: 10 pages, 2 figures, Accepted for publication in Astrophysical
Journal Letter
b-quark decay in the collinear approximation
The semileptonic decay of a b-quark, b--> c l nu, is considered in the
relativistic limit where the decay products are approximately collinear.
Analytic results for the double differential lepton energy distributions are
given for finite charm-quark mass. Their use for the fast simulation of
isolated lepton backgrounds from heavy quark decays is discussed.Comment: 7 pages, 1 figure, submitted to Phys.Rev.
First Steps Toward Change in Teacher Preparation for Elementary Science
Unless introductory undergraduate science classes for prospective elementary teachers actively incorporate the philosophy of inquiry-based learning called for in K-l2 science education refom little will change in elementary science education. Thus, at James Madison University, we have developed a new integrated science core curriculum called Understanding our World [1]. This course sequence was not only designed to fulfill general education science requirements. but also to focus on content areas our students will need to know as teachers. The objectives of these courses are based on the National Science Education Standards and Virginia’s Science Standards of Learning, including earth and space science, chemistry, physics, life sciences, and environmental science [2,3]. As an integrated package, this course sequence addresses basic science content, calculation skills, the philosophy and history of science, the process of how science is done, the role of science in society, and applications of computers and technology in science. Keeping in mind that students tend to teach in the same way they were taught, Understanding our World core classes embrace the concepts associated with reform in elementary math and science
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