4,810 research outputs found
Detection of Interstellar C_2 and C_3 in the Small Magellanic Cloud
We report the detection of absorption from interstellar C_2 and C_3 toward
the moderately reddened star Sk 143, located in the near 'wing' region of the
SMC, in optical spectra obtained with the ESO VLT/UVES. These detections of C_2
(rotational levels J=0-8) and C_3 (J=0-12) absorption in the SMC are the first
beyond our Galaxy. The total abundances of C_2 and C_3 (relative to H_2) are
similar to those found in diffuse Galactic molecular clouds -- as previously
found for CH and CN -- despite the significantly lower average metallicity of
the SMC. Analysis of the rotational excitation of C_2 yields an estimated
kinetic temperature T_k ~ 25 K and a moderately high total hydrogen density n_H
~ 870 cm^-3 -- compared to the T_01 ~ 45 K and n_H ~ 85-300 cm^-3 obtained from
H_2. The populations of the lower rotational levels of C_3 are consistent with
an excitation temperature of about 34 K.Comment: accepted to MNRAS; 10 pages, 6 figure
FUSE Observations of the Magellanic Bridge Gas toward Two Early-Type Stars: Molecules, Physical Conditions, and Relative Abundance
We discuss FUSE observations of two early-type stars, DI1388 and DGIK975, in
the low density and low metallicity gas of Magellanic Bridge (MB). Toward
DI1388, the FUSE observations show molecular hydrogen, O VI, and numerous other
atomic or ionic transitions in absorption, implying the presence of multiple
gas phases in a complex arrangement. The relative abundance pattern in the MB
is attributed to varying degrees of depletion onto dust similar to that of halo
clouds. The N/O ratio is near solar, much higher than N/O in damped Ly-alpha
systems, implying subsequent stellar processing to explain the origin of
nitrogen in the MB. The diffuse molecular cloud in this direction has a low
column density and low molecular fraction. H2 is observed in both the
Magellanic Stream and the MB, yet massive stars form only in the MB, implying
significantly different physical processes between them. In the MB some of the
H2 could have been pulled out from the SMC via tidal interaction, but some also
could have formed in situ in dense clouds where star formation might have taken
place. Toward DGIK975, the presence of neutral, weakly and highly ionized
species suggest that this sight line has also several complex gas phases. The
highly ionized species of O VI, C IV, and Si IV toward both stars have very
broad features, indicating that multiple components of hot gas at different
velocities are present. Several sources (a combination of turbulent mixing
layer, conductive heating, and cooling flows) may be contributing to the
production of the highly ionized gas in the MB. Finally, this study has
confirmed previous results that the high-velocity cloud HVC 291.5-41.2+80 is
mainly ionized composed of weakly and highly ions. The high ion ratios are
consistent with a radiatively cooling gas in a fountain flow model.Comment: Accepted for publication in the ApJ (October 10, 2002). Added
reference (Gibson et al. 2000
The Magellanic System: What have we learnt from FUSE?
I review some of the findings on the Magellanic System produced by the Far
Ultraviolet Spectroscopic Explorer (FUSE) during and after its eight years of
service. The Magellanic System with its high-velocity complexes provides a
nearby laboratory that can be used to characterize phenomena that involve
interaction between galaxies, infall and outflow of gas and metals in galaxies.
These processes are crucial for understanding the evolution of galaxies and the
intergalactic medium. Among the FUSE successes I highlight are the coronal gas
about the LMC and SMC, and beyond in the Stream, the outflows from these
galaxies, the discovery of molecules in the diffuse gas of the Stream and the
Bridge, an extremely sub-solar and sub-SMC metallicity of the Bridge, and a
high-velocity complex between the Milky Way and the Clouds.Comment: A contributed paper to the FUSE Annapolis Conference "Future
Directions in Ultraviolet Spectroscopy.", 5 pages. To appear as an AIP
Conference Proceedin
On characteristic initial data for a star orbiting a black hole
We take further steps in the development of the characteristic approach to
enable handling the physical problem of a compact self-gravitating object, such
as a neutron star, in close orbit around a black hole. We examine different
options for setting the initial data for this problem and, in order to shed
light on their physical relevance, we carry out short time evolution of this
data. To this end we express the matter part of the characteristic gravity code
so that the hydrodynamics are in conservation form. The resulting gravity plus
matter relativity code provides a starting point for more refined future
efforts at longer term evolution. In the present work we find that,
independently of the details of the initial gravitational data, the system
quickly flushes out spurious gravitational radiation and relaxes to a
quasi-equilibrium state with an approximate helical symmetry corresponding to
the circular orbit of the star.Comment: 20 pages, 10 figure
Einfluss von HTC-Biokohle als Bodenverbesserer auf den Wachstums- und Entwicklungsverlauf bei Sojabohnen
The influence of biochar with an amount of 0 to 20 t/ha on growth, yield and ingredients on soybeans of different variants was compared. Differences between the variants until blooming could be found. Plants from the HTC variant have shown significantly longer stems than others. These differences diminished until the harvest. Due to extrem low precipitation values in spring and early summer, no rhizobia could be developed and nitrogen fixation for the soybean was impossible. The plants could only use nitrogen from the soil. As a result, plots prepared with mineral fertilizer have shown the significantly longest plants, highest mass of dry matter and highest yields. Further, HTC variants have shown the lowest values in oil- and sugar contents. The
highest value in sugar content was measured in the variant with mineral fertilizer, but did not differ significantly. This results show, that due to the lower amount of available
nitrogen in the year of application there can be a negative influence of biochar on the yield
Low Redshift Intergalactic Absorption Lines in the Spectrum of HE0226-4110
We present an analysis of the FUSE and STIS E140M spectra of HE0226-4110
(z=0.495). We detect 56 Lyman absorbers and 5 O VI absorbers. The number of
intervening O VI systems per unit redshift with W>50 m\AA is dN(O VI)/dz~ 11.
The O VI systems unambiguously trace hot gas only in one case. For the 4 other
O VI systems, photoionization and collisional ionization models are viable
options to explain the observed column densities of the O VI and the other
ions. If the O VI systems are mostly photoionized, only a fraction of the
observed O VI will contribute to the baryonic density of the warm-hot ionized
medium (WHIM) along this line of sight. Combining our results with previous
ones, we show that there is a general increase of N(O VI) with increasing b(O
VI). Cooling flow models can reproduce the N-b distribution but fail to
reproduce the observed ionic ratios. A comparison of the number of O I, O II, O
III, O IV, and O VI systems per unit redshift show that the low-z IGM is more
highly ionized than weakly ionized. We confirm that photoionized O VI systems
show a decreasing ionization parameter with increasing H I column density. O VI
absorbers with collisional ionization/photoionization degeneracy follow this
relation, possibly suggesting that they are principally photoionized. We find
that the photoionized O VI systems in the low redshift IGM have a median
abundance of 0.3 solar. We do not find additional Ne VIII systems other than
the one found by Savage et al., although our sensitivity should have allowed
the detection of Ne VIII in O VI systems at T~(0.6-1.3)x10^6 K (if CIE
applies). Since the bulk of the WHIM is believed to be at temperatures T>10^6
K, the hot part of the WHIM remains to be discovered with FUV--EUV metal-line
transitions.Comment: Accepted for publication in the ApJS. Full resolution figures
available at
http://www.journals.uchicago.edu/ApJ/journal/preprints/ApJS63975.preprint.pd
A Farm Bill to Help Farmers Weather Climate Change
The Farm Bill has an enormous impact on climate change. Greenhouse gas emissions from agriculture account for almost 10 percent of total U.S. emissions and up to a quarter of all emissions globally. The Farm Bill encourages the use of carbon-intensive agricultural practices and products responsible for these emissions, but nonetheless offers several opportunities to quickly expand carbon sequestration, making it a critical piece of climate legislation. This essay will examine the climate impact of the Farm Bill, focusing on the commodity, conservation, and crop insurance programs. It then proposes politically feasible changes to these programs aimed at minimizing agricultural greenhouse gas emissions and maximizing carbon storage. The essay concludes with an ambitious, long-term set of Farm Bill proposals designed to transform the U.S. agricultural sector into a carbon sink
Set-Derivability of Multidimensional Aggregates
A common optimization technique in data warehouse environments is the use of materialized aggregates. Aggregate processing becomes complex, if partitions of aggregates or queries are materialized and reused later. Most problematic are the implication problems regarding the restriction predicates. We show that in the presence of hierarchies in a multidimensional environment an efficient algorithm can be given to construct - or to derive - an aggregate from one or more overlapping materialized aggregate partitions (set-derivability)
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