678 research outputs found
Laser scanning methods and a phase comparison, modulated laser range finder for terrain sensing on a Mars roving vehicle
Two areas of a laser range finder for a Mars roving vehicle are investigated: (1) laser scanning systems, and (2) range finder methods and implementation. Several ways of rapidly scanning a laser are studied. Two digital deflectors and a matrix of laser diodes, are found to be acceptable. A complete range finder scanning system of high accuracy is proposed. The problem of incident laser spot distortion on the terrain is discussed. The instrumentation for a phase comparison, modulated laser range finder is developed and sections of it are tested
Clarifying and expanding the focus of Environmental Toxicology and Chemistry
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92138/1/1869_ftp.pd
Editorial
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95638/1/2035_ftp.pd
The importance of scientific peer review at SETAC
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102196/1/etc2449.pd
The Amateur Sky Survey Mark III Project
The Amateur Sky Survey (TASS) is a loose confederation of amateur and
professional astronomers. We describe the design and construction of our Mark
III system, a set of wide-field drift-scan CCD cameras which monitor the
celestial equator down to thirteenth magnitude in several passbands. We explain
the methods by which images are gathered, processed, and reduced into lists of
stellar positions and magnitudes. Over the period October, 1996, to November,
1998, we compiled a large database of photometric measurements. One of our
results is the "tenxcat" catalog, which contains measurements on the standard
Johnson-Cousins system for 367,241 stars; it contains links to the light curves
of these stars as well.Comment: 20 pages, including 4 figures; additional JPEG files for Figures 1,
2. Submitted to PAS
Asymptotics and local constancy of characters of p-adic groups
In this paper we study quantitative aspects of trace characters
of reductive -adic groups when the representation varies. Our approach
is based on the local constancy of characters and we survey some other related
results. We formulate a conjecture on the behavior of relative to
the formal degree of , which we are able to prove in the case where
is a tame supercuspidal. The proof builds on J.-K.~Yu's construction and the
structure of Moy-Prasad subgroups.Comment: Proceedings of Simons symposium on the trace formul
Stationary phase expression of the arginine biosynthetic operon argCBH in Escherichia coli
BACKGROUND: Arginine biosynthesis in Escherichia coli is elevated in response to nutrient limitation, stress or arginine restriction. Though control of the pathway in response to arginine limitation is largely modulated by the ArgR repressor, other factors may be involved in increased stationary phase and stress expression. RESULTS: In this study, we report that expression of the argCBH operon is induced in stationary phase cultures and is reduced in strains possessing a mutation in rpoS, which encodes an alternative sigma factor. Using strains carrying defined argR, and rpoS mutations, we evaluated the relative contributions of these two regulators to the expression of argH using operon-lacZ fusions. While ArgR was the main factor responsible for modulating expression of argCBH, RpoS was also required for full expression of this biosynthetic operon at low arginine concentrations (below 60 ÎŒM L-arginine), a level at which growth of an arginine auxotroph was limited by arginine. When the argCBH operon was fully de-repressed (arginine limited), levels of expression were only one third of those observed in ÎargR mutants, indicating that the argCBH operon is partially repressed by ArgR even in the absence of arginine. In addition, argCBH expression was 30-fold higher in ÎargR mutants relative to levels found in wild type, fully-repressed strains, and this expression was independent of RpoS. CONCLUSION: The results of this study indicate that both derepression and positive control by RpoS are required for full control of arginine biosynthesis in stationary phase cultures of E. coli
Impact of temperature dependence on the possible contribution of organics to new particle formation in the atmosphere
Secondary particles formed via new particle formation (NPF)
dominate cloud condensation nuclei (CCN) abundance in most parts of the
troposphere and are important for aerosol indirect radiative forcing (IRF).
Laboratory measurements have shown that certain organic compounds can
significantly enhance the binary nucleation of sulfuric acid and H2O.
According to our recent study comparing particle size distributions measured
in nine forest areas in North America with those predicted by a global
size-resolved aerosol model, current H2SO4âorganics nucleation
parameterizations appear to significantly overpredict NPF and particle
number concentrations in summer. The lack of temperature dependence in
the current H2SO4âorganics nucleation parameterization has been
suggested to be a possible reason for the observed overprediction. In this
work, H2SO4âorganics clustering thermodynamics from
quantum chemical studies has been employed to develop a scheme to
incorporate temperature dependence into H2SO4âorganics nucleation
parameterization. We show that temperature has a strong impact on
H2SO4âorganics nucleation rates and may reduce the nucleation rate by
ââŒââŻ1 order of magnitude per 10âŻK of temperature increase.
The particle number concentrations in summer over North America based on the
revised scheme is a factor of more than 2 lower, which is in much better agreement
with the observations. With the temperature-dependent
H2SO4âorganics nucleation parameterization, the summer CCN
concentrations in the lower troposphere in the Northern Hemisphere are about
10â30âŻ% lower compared to the temperature-independent parameterization. This study
highlights the importance of the temperature effect and its impacts on NPF
in the global modeling of aerosol number abundance
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