13,324 research outputs found
The pulsed air gust generator Final report
Wind tunnel simulation of jet pulsing apparatus for controlled gust
The construction and evaluation of four series of lessons to stimulate the flow of ideas in the creative writing of fourth, fifth, and sixth grade pupils.
Thesis (Ed.M.)--Boston Universit
Bargmann representations for deformed harmonic oscillators
Generalizing the case of the usual harmonic oscillator, we look for Bargmann
representations corresponding to deformed harmonic oscillators. Deformed
harmonic oscillator algebras are generated by four operators
and the unity 1 such as , and . We discuss the conditions of existence of
a scalar product expressed with a true integral on the space spanned by the
eigenstates of (or ). We give various examples, in particular we
consider functions that are linear combinations of , and
unity and that correspond to q-oscillators with Fock-representations or with
non-Fock-representations.Comment: 23 pages, Late
Point sets that minimize -edges, 3-decomposable drawings, and the rectilinear crossing number of
There are two properties shared by all known crossing-minimizing geometric
drawings of , for a multiple of 3. First, the underlying -point set
of these drawings has exactly -edges, for all . Second, all such drawings have the points divided into three
groups of equal size; this last property is captured under the concept of
3-decomposability. In this paper we show that these properties are tightly
related: every -point set with exactly -edges for
all , is 3-decomposable. As an application, we prove that the
rectilinear crossing number of is 9726.Comment: 14 page
M31's Heavy Element Distribution and Outer Disk
Hubble Space Telescope imaging of 11 fields in M31 were reduced to
color-magnitude diagrams. The fields were chosen to sample all galactocentric
radii to 50 kpc. Assuming that the bulk of the sampled stellar populations are
older than a few Gyr, the colors of the red giants map to an abundance
distribution with errors of order 0.1 dex in abundance. The radially sampled
abundance distributions are all about the same width, but show a mild abundance
gradient that flattens outside ~20 kpc. The various distributions were weighted
and summed with the aid of new surface brightness profile fits to obtain an
abundance distribution representative of the entirety of M31. M31 is a system
near chemical maturity. This ``observed closed box'' is compared to analytical
closed box models. M31 suffers from a lack of metal-poor stars and metal-rich
stars relative to the simplest closed-box model in the same way as the solar
neighborhood.Comparing to several simple chemical evolution models, neither
complete mixing of gas at all times nor zero mixing, inhomogeneous models give
the most convincing match to the data. As noted elsewhere, the outer disk of
M31 is a factor of ten more metal-rich than the Milky Way halo, ten times more
metal-rich than the dwarf spheroidals cospatial with it, and more metal-rich
than most of the globular clusters at the same galactocentric radius.
Difficulties of interpretation are greatly eased if we posit that the M31 disk
dominates over the halo at all radii out to 50 kpc. In fact, scaling from
current density models of the Milky Way, one should not expect to see halo
stars dominating over disk stars until beyond our 50 kpc limit. A corollary
conclusion is that most published studies of the M31 "halo" are actually
studies of its disk.Comment: 28 pages, 11 black-and-white figures, in press, Astrophysical Journa
Upper Limits on the Extragalactic Background Light from the Gamma-Ray Spectra of Blazars
The direct measurement of the extragalactic background light (EBL) is
difficult at optical to infrared wavelengths because of the strong foreground
radiation originating in the Solar System. Very high energy (VHE, E100 GeV)
gamma rays interact with EBL photons of these wavelengths through pair
production. In this work, the available VHE spectra from six blazars are used
to place upper limits on the EBL. These blazars have been detected over a range
of redshifts and a steepening of the spectral index is observed with increasing
source distance. This can be interpreted as absorption by the EBL. In general,
knowledge of the intrinsic source spectrum is necessary to determine the
density of the intervening EBL. Motivated by the observed spectral steepening
with redshift, upper limits on the EBL are derived by assuming that the
intrinsic spectra of the six blazars are . Upper limits are
then placed on the EBL flux at discrete energies without assuming a specific
spectral shape for the EBL. This is an advantage over other methods since the
EBL spectrum is uncertain.Comment: 33 pages, 14 figures, accepted by Ap
Evidence for a Young Stellar Population in NGC 5018
Two absorption line indices, Ca II and Hdelta/FeI4045, measured from high
resolution spectra are used with evolutionary synthesis models to verify the
presence of a young stellar population in NGC 5018. The derived age of this
population is about ~2.8 Gyr with a metallicity roughly solar and it completely
dominates the integrated light of the galaxy near 4000 A.Comment: 13 pages, 7 figures (figs 3-7 are color figures), to be published in
the May 2000 issue of the Astrophysical Journa
V1647 Ori (IRAS 05436-0007) in Outburst: the First Three Months
We report on photometric (BVRIJHK) and low dispersion spectroscopic
observations of V1647 Ori, the star that drives McNeil's Nebula, between 10
February and 7 May 2004. The star is photometrically variable atop a general
decline in brightness of about 0.3-0.4 magnitudes during these 87 days. The
spectra are featureless, aside from H-alpha and the Ca II infrared triplet in
emission, and a Na I D absorption feature. The Ca II triplet line ratios are
typical of young stellar objects. The H-alpha equivalent width may be modulated
on a period of about 60 days. The post-outburst extinction appears to be less
than 7 mag. The data are suggestive of an FU Orionis-like event, but further
monitoring will be needed to definitively characterize the outburst.Comment: Accepted for publication in the Astronomical Journa
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