2,994 research outputs found
Synthetic redesign of plant lipid metabolism
Plant seed lipid metabolism is an area of intensive research, including many examples of transgenic events in which oil composition has been modified. In the selected examples described in this review, progress towards the predictive manipulation of metabolism and the reconstitution of desired traits in a non-native host is considered. The advantages of a particular oilseed crop, Camelina sativa, as a flexible and utilitarian chassis for advanced metabolic engineering and applied synthetic biology are considered, as are the issues that still represent gaps in our ability to predictably alter plant lipid biosynthesis. Opportunities to deliver useful bio-based products via transgenic plants are described, some of which represent the most complex genetic engineering in plants to date. Future prospects are considered, with a focus on the desire to transition to more (computationally) directed manipulations of metabolism
Chandra Observation of the Globular Cluster NGC 6440 and the Nature of Cluster X-ray Luminosity Functions
As part of our campaign to determine the nature of the various source
populations of the low-luminosity globular cluster X-ray sources, we have
obtained a Chandra X-ray Observatory ACIS-S3 image of the globular cluster NGC
6440. We detect 24 sources to a limiting luminosity of ~2 times 10^31 erg/s
(0.5-2.5keV) inside the cluster's half-mass radius, all of which lie within ~2
core radii of the cluster center. We also find excess emission in and around
the core which could be due to unresolved point sources. Based upon X-ray
luminosities and colors, we conclude that there are 4-5 likely quiescent
low-mass X-ray binaries and that most of the other sources are cataclysmic
variables. We compare these results to Chandra results from other globular
clusters and find the X-ray luminosity functions differ among the clusters.Comment: 9 pages, 4 figures, accepted by ApJ, minor changes, added table of
clusters' physical parameter
Neutral Gas Distribution and Kinematics of the Nearly Face-on Spiral Galaxy NGC 1232
We have analyzed high velocity resolution HI synthesis observations of the
nearly face-on Sc galaxy NGC 1232. The neutral gas distribution extends well
beyond the optical extent of the galaxy. As expected, local peaks in the HI
column density are associated with the spiral arms. Further, the HI column
density drops precipitously near the center of the galaxy. Closed contours in
the velocity field suggest either that the system is warped, or that the
rotation curve declines. The velocity dispersion is approximately constant
throughout the system, with a median value of 9.9 +/- 1.8 km/s. When corrected
for rotational broadening, there is no indication of a radial trend in the
neutral gas velocity dispersion in this galaxy.Comment: 14 pages of text, 10 pages of figures. Accepted to the A
Departures From Axisymmetric Morphology and Dynamics in Spiral Galaxies
New HI synthesis data have been obtained for six face-on galaxies with the
Very Large Array. These data and reanalyses of three additional data sets make
up a sample of nine face-on galaxies analyzed for deviations from axisymmetry
in morphology and dynamics. This sample represents a subsample of galaxies
already analyzed for morphological symmetry properties in the R-band. Four
quantitative measures of dynamical nonaxisymmetry are compared to one another
and to the quantitative measures of morphological asymmetry in HI and R-band to
investigate the relationships between nonaxisymmetric morphology and dynamics.
We find no significant relationship between asymmetric morphology and most of
the dynamical measures in our sample. A possible relationship is found,
however, between morphology and dynamical position angle differences between
approaching and receding sides of the galaxy.Comment: 24 pages, 19 figures, AASTeX, accepted for publication in AJ,
postscript figures available at
ftp://culebra.tn.cornell.edu/pub/david/figures.tar.g
The Structure of Rapidly Rotating Late-Type Spiral Galaxies: I. Photometry, HI and Optical Kinematics
We present I-band photometry, long-slit optical spectroscopy, and new
aperture synthesis HI observations for eight late-type spirals with rotation
velocities in the range 243 km/s < V_{rot} < 308 km/s. The sample will be used
to study the structure and angular momentum of disks at the high-mass end of
the spiral galaxy population; here we discuss the basic properties of these
``fast rotators'', and derive hybrid optical/HI rotation curves for each.
Despite the presence of HI warps and low-mass companions in many systems, their
kinematics are regular and there is excellent agreement between optical and HI
tracers near the optical radius r_{opt}. At high inclinations at which
projection effects are negligible, the sample galaxies exhibit flat,
featureless rotation curves out to their last measured points at
1.7r_{opt}--3.5 r_{opt}. The intermediate inclination systems are also
consistent with a constant rotation amplitude for r > 0.5 r_{opt}. We therefore
find no evidence for declining rotation curves at the high-mass end of the
late-type spiral galaxy population. Combining our data with the compilation of
spirals with reliable outer HI kinematics from the work of Casertano & van
Gorkom, we find no convincing trends between logarithmic outer rotation curve
slopes and rotation amplitudes or surface brightnesses for galaxies with
V_{rot} > 220 km/s. Correlations between these slopes and morphological types
or disk scale lengths are also marginal in this regime.Comment: v2: minor changes to match proofs. 23 pages, 15 figures, AJ in press.
For version with high resolution figures, see
http://www.physics.rutgers.edu/~spekkens/papers/fast1.pd
The genetics of the Lp Antigen
Several genetic models were considered to explain the distribution of qualitatively positive and negative children in 204 Caucasian families. A model which best describes the inheritance of the Lp antigenic expression involves a major genetic locus which distinguishes two overlapping continuously distributed modes of quantitative activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66139/1/j.1469-1809.1974.tb01992.x.pd
The 74MHz System on the Very Large Array
The Naval Research Laboratory and the National Radio Astronomy Observatory
completed implementation of a low frequency capability on the VLA at 73.8 MHz
in 1998. This frequency band offers unprecedented sensitivity (~25 mJy/beam)
and resolution (~25 arcsec) for low-frequency observations. We review the
hardware, the calibration and imaging strategies, comparing them to those at
higher frequencies, including aspects of interference excision and wide-field
imaging. Ionospheric phase fluctuations pose the major difficulty in
calibrating the array. Over restricted fields of view or at times of extremely
quiescent ionospheric ``weather'', an angle-invariant calibration strategy can
be used. In this approach a single phase correction is devised for each
antenna, typically via self-calibration. Over larger fields of view or at times
of more normal ionospheric ``weather'' when the ionospheric isoplanatic patch
size is smaller than the field of view, we adopt a field-based strategy in
which the phase correction depends upon location within the field of view. This
second calibration strategy was implemented by modeling the ionosphere above
the array using Zernike polynomials. Images of 3C sources of moderate strength
are provided as examples of routine, angle-invariant calibration and imaging.
Flux density measurements indicate that the 74 MHz flux scale at the VLA is
stable to a few percent, and tied to the Baars et al. value of Cygnus A at the
5 percent level. We also present an example of a wide-field image, devoid of
bright objects and containing hundreds of weaker sources, constructed from the
field-based calibration. We close with a summary of lessons the 74 MHz system
offers as a model for new and developing low-frequency telescopes. (Abridged)Comment: 73 pages, 46 jpeg figures, to appear in ApJ
A Study of Cosmic Ray Composition in the Knee Region using Multiple Muon Events in the Soudan 2 Detector
Deep underground muon events recorded by the Soudan 2 detector, located at a
depth of 2100 meters of water equivalent, have been used to infer the nuclear
composition of cosmic rays in the "knee" region of the cosmic ray energy
spectrum. The observed muon multiplicity distribution favors a composition
model with a substantial proton content in the energy region 800,000 -
13,000,000 GeV/nucleus.Comment: 38 pages including 11 figures, Latex, submitted to Physical Review
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