27,118 research outputs found
Two-dimensional oscillating airfoil test apparatus
A two dimensional oscillating airfoil test apparatus is presented as a method of measuring unsteady aerodynamic forces on an airfoil or rotor blade section. The oscillating airfoil test rig, which is being built for use in an 11 X 11-foot transonic wind tunnel (speed range M = 0.4 - 1.4), will allow determination of unsteady loadings and detailed pressure distributions on representative airfoil sections undergoing simulated pitching and flapping motions. The design details of the motion generating system and supporting structure are presented. This apparatus is now in the construction phase
On Dwarf Galaxies as the Source of Intracluster Gas
Recent observational evidence for steep dwarf galaxy luminosity functions in
several rich clusters has led to speculation that their precursors may be the
source of the majority of gas and metals inferred from intracluster medium
(ICM) x-ray observations. Their deposition into the ICM is presumed to occur
through early supernovae-driven winds, the resultant systems reflecting the
photometric and chemical properties of the low luminosity dwarf spheroidals and
ellipticals we observe locally. We consider this scenario, utilising a
self-consistent model for spheroidal photo-chemical evolution and gas ejection
via galactic superwinds. Insisting that post-wind dwarfs obey the observed
colour-luminosity-metallicity relations, we conclude that the bulk of the ICM
gas and metals does not originate within their precursors.Comment: 43 pages, 8 figures, LaTeX, also available at
http://msowww.anu.edu.au/~gibson/publications.html, to appear in ApJ, Vol
473, 1997, in pres
Apparatus and process for determining the susceptibility of microorganisms to antibiotics
A process for determining the susceptibility of microorganisms to antibiotics involves introducing a diluted specimen into discrete quantities of a selective culture medium which favors a specific microorganism in that the microorganism is sustained by the medium and when so sustained will change the optical characteristics of the medium. Only the specific microorganism will alter the optical characteristics. Some of the discrete quantities are blended with known antibiotics, while at least one is not. If the specimen contains the microorganisms favored by the selective medium, the optical characteristics of the discrete quantity of pure selective medium, that is the one without antibiotics, will change. If the antibiotics in any of the other discrete quantities are ineffective against the favored microorganisms, the optical characteristics of those quantities will likewise change. No change in the optical characteristics of a discrete quantity indicates that the favored microorganism is susceptible to the antibiotic in the quantity
Constraints on Early Nucleosynthesis from the Abundance Pattern of a Damped Ly-alpha System at z = 2.626
We have investigated chemical evolution in the young universe by analysing
the detailed chemical enrichment pattern of a metal-rich galaxy at high
redshift. The recent detection of over 20 elements in the gas-phase of a damped
Lyman-alpha absorber (DLA) at z = 2.626 represents an exciting new avenue for
exploring early nucleosynthesis. Given a strict upper age of ~2.5 Gyr and a
gas-phase metallicity about one third solar, we have shown the DLA abundance
pattern to be consistent with the predictions of a chemical evolution model in
which the interstellar enrichment is dominated by massive stars with a small
contribution from Type Ia supernovae. Discrepancies between the empirical data
and the models are used to highlight outstanding issues in nucleosynthesis
theory, including a tendency for Type II supernovae models to overestimate the
magnitude of the "odd-even" effect at subsolar metallicities. Our results
suggest a possible need for supplemental sources of magnesium and zinc, beyond
that provided by massive stars.Comment: 12 pages, 7 figs. Accepted for publication in ApJ (The Astrophysical
Journal
Modeling Heterogeneous Materials via Two-Point Correlation Functions: II. Algorithmic Details and Applications
In the first part of this series of two papers, we proposed a theoretical
formalism that enables one to model and categorize heterogeneous materials
(media) via two-point correlation functions S2 and introduced an efficient
heterogeneous-medium (re)construction algorithm called the "lattice-point"
algorithm. Here we discuss the algorithmic details of the lattice-point
procedure and an algorithm modification using surface optimization to further
speed up the (re)construction process. The importance of the error tolerance,
which indicates to what accuracy the media are (re)constructed, is also
emphasized and discussed. We apply the algorithm to generate three-dimensional
digitized realizations of a Fontainebleau sandstone and a boron
carbide/aluminum composite from the two- dimensional tomographic images of
their slices through the materials. To ascertain whether the information
contained in S2 is sufficient to capture the salient structural features, we
compute the two-point cluster functions of the media, which are superior
signatures of the micro-structure because they incorporate the connectedness
information. We also study the reconstruction of a binary laser-speckle pattern
in two dimensions, in which the algorithm fails to reproduce the pattern
accurately. We conclude that in general reconstructions using S2 only work well
for heterogeneous materials with single-scale structures. However, two-point
information via S2 is not sufficient to accurately model multi-scale media.
Moreover, we construct realizations of hypothetical materials with desired
structural characteristics obtained by manipulating their two-point correlation
functions.Comment: 35 pages, 19 figure
Operator Method for Nonperturbative Calculation of the Thermodynamic Values in Quantum Statistics. Diatomic Molecular Gas
Operator method and cumulant expansion are used for nonperturbative
calculation of the partition function and the free energy in quantum
statistics. It is shown for Boltzmann diatomic molecular gas with some model
intermolecular potentials that the zeroth order approximation of the proposed
method interpolates the thermodynamic values with rather good accuracy in the
entire range of both the Hamiltonian parameters and temperature. The systematic
procedure for calculation of the corrections to the zeroth order approximation
is also considered.Comment: 22 pages, 7 Postscript figures, accepted for publication in Journal
of Physics
Gravitational hydrodynamics of large scale structure formation
The gravitational hydrodynamics of the primordial plasma with neutrino hot
dark matter is considered as a challenge to the bottom-up cold dark matter
paradigm. Viscosity and turbulence induce a top-down fragmentation scenario
before and at decoupling. The first step is the creation of voids in the
plasma, which expand to 37 Mpc on the average now. The remaining matter clumps
turn into galaxy clusters. Turbulence produced at expanding void boundaries
causes a linear morphology of 3 kpc fragmenting protogalaxies along vortex
lines. At decoupling galaxies and proto-globular star clusters arise; the
latter constitute the galactic dark matter halos and consist themselves of
earth-mass H-He planets. Frozen planets are observed in microlensing and
white-dwarf-heated ones in planetary nebulae. The approach also explains the
Tully-Fisher and Faber-Jackson relations, and cosmic microwave temperature
fluctuations of micro-Kelvins.Comment: 6 pages, no figure
The Cepheid Period-Luminosity Relation at Mid-Infrared Wavelengths: I. First-Epoch LMC Data
We present the first mid-infrared Period-Luminosity (PL) relations for Large
Magellanic Cloud (LMC) Cepheids. Single-epoch observations of 70 Cepheids were
extracted from Spitzer IRAC observations at 3.6, 4.5, 5.8 and 8.0 microns,
serendipitously obtained during the SAGE (Surveying the Agents of a Galaxy's
Evolution) imaging survey of the LMC. All four mid-infrared PL relations have
nearly identical slopes over the period range 6 - 88 days, with a small scatter
of only +/-0.16 mag independent of period for all four of these wavelengths. We
emphasize that differential reddening is not contributing significantly to the
observed scatter, given the nearly two orders of magnitude reduced sensitivity
of the mid-IR to extinction compared to the optical. Future observations,
filling in the light curves for these Cepheids, should noticeably reduce the
residual scatter. These attributes alone suggest that mid-infrared PL relations
will provide a practical means of significantly improving the accuracy of
Cepheid distances to nearby galaxies.Comment: 19 pages, 4 figures, 1 table, Accepted for publication in the
Astrophysical Journa
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