10,188 research outputs found
Physical observations of comets: Their composition, origin and evolution
Observations of Comet P/Schwassmann-Wachmann 1 (SW1) during one observing run each in 1989 and 1990 are discussed, and the new significant information that was obtained is presented. Also discussed are near-UV observations of comets. The near-UV is a mostly unexplored spectral region for comets since it is not visible to spacecraft such as IUE and most ground-based detectors and spectrographs are not sensitive in the near-UV
Physical observations of comets: Their composition, origin and evolution
The composition, origins, and evolution of comets were studied. The composition was studied using spectroscopic observations of primarily brighter comets at moderate and high resolution for the distribution of certain gases in the coma. The origins was addressed through an imaging search for the Kuiper belt of comets. The evolution was addressed by searching for a link between comets and asteroids using an imaging approach to search for an OH coma
Observations of O (1S) and O (1D) in Spectra of C/1999 S4 (LINEAR)
We report on high spectral resolution observations of comet C/1999 S4
(LINEAR) obtained at McDonald Observatory in June and July 2000. We report
unequivocal detections of the O (1S) and O (1D) metastable lines in emission in
the cometary spectrum. These lines are well separated from any telluric or
cometary emission features. We have derived the ratio of the two red doublet
lines and show they are consistent with the predictions of the branching ratio.
We also derived a ratio of 0.06+/-0.01 for the green line flux to the sum of
the red line fluxes. This ratio is consistent with H2O as the dominant parent
for atomic oxygen. We have measured the widths of the lines and show that the
widths imply that there must be some parent of atomic oxygen in addition to the
H2O.Comment: 26 pages includes 6 figures and 3 tables; accepted for Icaru
Research Progress Report, No. 17
Legumes are notable for their ability to convert atmospheric dinitrogen into forms of
nitrogen which are usable by plants. This is done in association with bacteria (called
Rhizobium) which inhabit nodules of the plant roots. This process is called nitrogen-fixation. Legumes are important as forage and food crops due to their high protein content. Some are also useful for soil conservation purposes. There was no information on nitrogen fixation by legume crops in Alaska. This research was initiated to determine how much nitrogen different types of legumes can fix in interior Alaska
Analysis of Fisher Information and the Cram\'{e}r-Rao Bound for Nonlinear Parameter Estimation after Compressed Sensing
In this paper, we analyze the impact of compressed sensing with complex
random matrices on Fisher information and the Cram\'{e}r-Rao Bound (CRB) for
estimating unknown parameters in the mean value function of a complex
multivariate normal distribution. We consider the class of random compression
matrices whose distribution is right-orthogonally invariant. The compression
matrix whose elements are i.i.d. standard normal random variables is one such
matrix. We show that for all such compression matrices, the Fisher information
matrix has a complex matrix beta distribution. We also derive the distribution
of CRB. These distributions can be used to quantify the loss in CRB as a
function of the Fisher information of the non-compressed data. In our numerical
examples, we consider a direction of arrival estimation problem and discuss the
use of these distributions as guidelines for choosing compression ratios based
on the resulting loss in CRB.Comment: 12 pages, 3figure
The Health of Aging Lesbian, Gay and Bisexual Adults in California
Examines rates of diabetes, hypertension, poor mental health, physical disability, and fair or poor self-reported health status among homosexual adults ages 50 to 70 compared with their heterosexual peers. Recommends enhancing policies and practices
Homology and Derived Series of Groups II: Dwyer's Theorem
We give new information about the relationship between the low-dimensional
homology of a group and its derived series. This yields information about how
the low-dimensional homology of a topological space constrains its fundamental
group. Applications are given to detecting when a set of elements of a group
generates a subgroup ``large enough'' to map onto a non-abelian free solvable
group, and to concordance and grope cobordism of links. We also greatly
generalize several key homological results employed in recent work of
Cochran-Orr-Teichner, in the context of classical knot concordance.
In 1963 J. Stallings established a strong relationship between the
low-dimensional homology of a group and its lower central series quotients. In
1975 W. Dwyer extended Stallings' theorem by weakening the hypothesis on the
second homology groups. The naive analogues of these theorems for the derived
series are false. In 2003 the second author introduced a new characteristic
series, associated to the derived series, called the torsion-free derived
series. The authors previously established a precise analogue, for the
torsion-free derived series, of Stallings' theorem. Here our main result is the
analogue of Dwyer's theorem for the torsion-free derived series. We also prove
a version of Dwyer's theorem for the rational lower central series. We apply
these to give new results on the Cochran-Orr-Teichner filtration of the
classical link concordance group.Comment: 26 pages. In this version, we have included a new proof of part of
the main theorem. The new proof is somewhat simpler and stays entirely in the
world of group homology and homological algebra rather than using
Eilenberg-Mac Lane spaces. Other minor corrections. This is the final version
to appear in Geometry & Topolog
The Spin-Orbit Alignment of the HD17156 Transiting Eccentric Planetary System
We present high precision radial velocity observations of HD17156 during a
transit of its eccentric Jovian planet. In these data, we detect the
Rossiter-McLaughlin effect, which is an apparent perturbation in the velocity
of the star due to the progressive occultation of part of the rotating stellar
photosphere by the transiting planet. This system had previously been reported
by Narita et al. (2008) to exhibit a lambda = 62 +/- 25 degree misalignment of
the projected planetary orbital axis and the stellar rotation axis. We model
our data, along with the Narita et al. data, and obtain lambda = 9.4 +/- 9.3
degrees for the combined data set. We thus conclude that the planetary orbital
axis is actually very well aligned with the stellar rotation axis.Comment: 4 pages, 1 figure, Ap.J. Letters in pres
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