3,765 research outputs found
Évaluation d'un système de mesure des pertes de contaminants agricoles par ruissellement et drainage souterrain en régions froides
Cette note technique présente un système automatique de mesure des pertes de polluants agricoles par ruissellement et drainage souterrain pouvant opérer durant la période estivale et la fonte nivale. Le système de mesure du ruissellement est composé d'une trappe à sédiments, d'un déversoir en V et d'un système automatique de mesure du débit et de contrôle de l'échantillonnage. Le système de mesure du drainage souterrain consiste en un auget à bascule, relié à un compteur d'impulsions, et un partiteur de débit. Ces systèmes ont été utilisés sur neuf parcelles expérimentales pour mesurer les masses de contaminants agricoles perdues par ruissellement et drainage souterrain. La hauteur totale de ruissellement durant les deux années (4,6 mm an-1) a été faible comparée au drainage (227 mm an-1). Soixante-seize pourcent du ruissellement annuel s'est produit durant la fonte des neiges. Les principaux avantages de ce système sont de pouvoir mesurer simultanément les volumes et les débits de ruissellement tout en prélevant des échantillons d'eau.This technical note presents an automatic measurement system for measuring losses of agricultural pollutants in surface runoff and subsurface drainage outflow. This system can be operated during rainfall events and snowmelt periods. The runoff system was composed of a sediment trap, a V-notch weir and an automatic system for flow measurement and sampling. The subsurface drainage system consisted of a tipping bucket, connected to a pulse counter, and a sampling unit. This system was used on nine experimental plots for the measurement of pollutant losses by surface runoff and subsurface drainage. The total depth of surface runoff measured was low for the two years of measurement (4.6 mm y-1) compared to subsurface drainage (227 mm y-1). Seventy six percent of the annual surface runoff occurred during the snowmelt period. The principal advantage of this system is to measure runoff volume and flow while taking water samples
Unravelling the Mysteries of the Leo Ring: An Absorption Line Study of an Unusual Gas Cloud
Since the 1980's discovery of the large (2x10^9 Msun) intergalactic cloud
known as the Leo Ring, this object has been the center of a lively debate about
its origin. Determining the origin of this object is still important as we
develop a deeper understanding of the accretion and feedback processes that
shape galaxy evolution. We present HST/COS observations of three sightlines
near the Ring, two of which penetrate the high column density neutral hydrogen
gas visible in 21 cm observations of the object. These observations provide the
first direct measurement of the metallicity of the gas in the Ring, an
important clue to its origins. Our best estimate of the metallicity of the ring
is ~10% Zsun, higher than expected for primordial gas but lower than expected
from an interaction. We discuss possible modifications to the interaction and
primordial gas scenarios that would be consistent with this metallicity
measurement.Comment: 11 pages, 7 figures, accepted Ap
Metallicity and Ionization in High Velocity Cloud Complex C
We analyze HST and FUSE ultraviolet spectroscopic data for eleven sight lines
passing through the infalling high velocity cloud (HVC) Complex C. These sight
lines pass through regions with HI column densities ranging from N(HI) =
10^(18.1) to 10^(20.1). From [OI/HI] abundances, we find that Complex C
metallicities range from 0.09 to 0.29 Z_solar, with a column density weighted
mean of 0.13 Z_solar. Nitrogen (NI) is underabundant by factors of (0.01-0.07)
(N/H)_solar, significantly less than oxygen relative to solar abundances. This
pattern suggests nucleosynthetic enrichment by Type II SNe, consistent with an
origin in the Galactic fountain or infalling gas produced in winds from Local
Group galaxies. The range of metallicity and its possible (2 sigma) dependence
on N(HI) could indicate some mixing of primordial material with enriched gas
from the Milky Way, but the mixing mechanism is unclear. We also investigate
the significant highly ionized component of Complex C, detected in CIV, SiIV,
and OVI, but not in NV. High-ion column density ratios show little variance and
are consistent with shock ionization or ionization at interfaces between
Complex C and a hotter surrounding medium. Evidence for the former mechanism is
seen in the Mrk 876 line profiles, where the offset in line centroids between
low and high ions suggests a decelerating bowshock.Comment: Submitted to Ap
Correction to: Genetic characterization and expression analysis of wheat (\u3ci\u3eTriticum aestivum\u3c/i\u3e) line 07OR1074 exhibiting very low polyphenol oxidase (PPO) activity
The above mentioned article was published in 2015 with an error in the naming of one of the allele sequences for the PPO gene on the D genome. The PPO-D1f allele was incorrectly named as it is identical to the PPO-D1c allele previously published in GenBank by the authors on March 11th, 2014. An alignment between the previously published PPOD1c allele and a resequencing of the parental line 07OR1074 shows that the PPO-D1f allele is identical to the PPO-D1c allele. The allele in the paper referred to as PPO-D1f should be treated as PPO-D1c and can be accessed at NCBI with the following GenBank ID
New HST Observations of the Halo Gas of NGC 3067: Limits on the Extragalactic Ionizing Background at Low Redshift and the Lyman Continuum Escape Fraction
We present UV spectroscopy from HST/GHRS and reanalyze existing H_alpha
images of the quasar/galaxy pair 3C 232/NGC 3067 and of the halo gas associated
with NGC 3067. The spectra permit measurement of, or limits on, the column
densities of Fe I, Fe II, Mg I, and Mg II in the absorbing cloud. Two distinct
models of the extragalactic radiation field are considered: (1) the ionizing
spectrum is dominated by a power-law extragalactic continuum, and (2) the
power-law spectrum contains a Lyman break, implying enhanced flux longward of
912 A relative to the hydrogen-ionizing flux. The H_alpha images constrain the
escape fraction of Lyman continuum photons from the galaxy to f_esc <= 0.02.
With the assumption that the cloud is shielded from all galactic contributions,
we can constrain the intensity and shape of the extragalactic continuum. For an
AGN-dominated power-law extragalactic spectrum, we derive a limit on the
extragalactic ionizing flux Phi_ion >= 2600 photons cm^-2 s^-1, or I_0 >=
10^-23 erg cm^-2 s^-1 Hz^-1 sr^-1 for an ionizing spectrum with power-law index
of 1.8 and a cloud of constant density. When combined with previous upper
limits from the absence of H_alpha recombination emission from intergalactic
clouds, our observations require 2600 <= Phi_ion <= 10000 photons cm^-2 s^-1.
We show that if galactic contributions to the incident radiation are important,
it is difficult to constrain Phi_ion. These results demonstrate that galactic
halo opacities and their wavelength dependence are crucial to understanding the
abundance of low-ionization metals in the IGM.Comment: 25 Pages LaTex, 8 PostScript Figures, accepted for publication in AJ,
Nov. 99 issu
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