7,690 research outputs found
Dairy Cow Ownership and Child Nutritional Status in Kenya
This study examines the hypothesis that dairy cow ownership improves child nutritional status. Using household data from coastal and highland Kenya, three econometric model formulations are estimated. Positive impacts on chronic malnutrition are observed for coastal Kenya. No negative effects on acute or chronic malnutrition are found for either region.Food Consumption/Nutrition/Food Safety, Livestock Production/Industries,
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Potential impact of iodine on tropospheric levels of ozone and other critical oxidants
A new analysis of tropospheric iodine chemistry suggests that under certain conditions this chemistry could have a significant impact on the rate of destruction of tropospheric ozone. In addition, it suggests that modest shifts could result in the critical radical ratio HO2/OH. This analysis is based on the first ever observations of CH3I in the middle and upper free troposphere as recorded during the NASA Pacific Exploratory Mission in the western Pacific. Improved evaluations of several critical gas kinetic and photochemical rate coefficients have also been used. Three iodine source scenarios were explored in arriving at the above conclusions. These include: (1) the assumption that the release of CH3I from the marine environment was the only iodine source with boundary layer levels reflecting a low-productivity source region, (2) same as scenario 1 but with an additional marine iodine source in the form of higher molecular weight iodocarbons, and (3) source scenario 2 but with the release of all iodocarbons occurring in a region of high biological productivity. Based on one-dimensional model simulations, these three source scenarios resulted in estimated Ix (Ix =I + IO + HI + HOI + 2I2O2 +INOx) yields for the upper troposphere of 0.5, 1.5, and 7 parts per trillion by volume (pptv), respectively. Of these, only at the 1.5 and 7 pptv level were meaningful enhancements in O3 destruction estimated. Total column O3 destruction for these cases averaged 6 and 30%, respectively. At present we believe the 1.5 pptv Ix source scenario to be more typical of the tropical marine environment; however, for specific regions of the Pacific (i.e., marine upwelling regions) and for specific seasons of the year, much higher levels might be experienced. Even so, significant uncertainties still remain in the proposed iodine chemistry. In particular, much uncertainty remains in the magnitude of the marine iodine source. In addition, several rate coefficients for gas phase processes need further investigating, as does the efficiency for removal of iodine due to aerosol scavenging processes. Copyright 1996 by the American Geophysical Union
Florence Valley : An Abandoned Stream Valley, Florence Township, Erie County, Ohio
Author Institution: U.S.D.A. Soil Conservation Service, Sandusky, OhioAn abandoned stream valley, here called Florence Valley, was found in eastern Erie County, Ohio. Florence Valley is about one mile long and connects the valleys of Chappel Creek and the Vermilion River. There is evidence that Florence Valley was formed as a result of the capture of a tributary of the Vermilion River by Chappel Creek. Chappel Creek, at the junction of Florence Valley and the valley of Chappel Creek, has a rightangled bend, which displays morphology characteristic of an "elbow-of-capture." The gradient of the eastern two-thirds of Florence Valley slopes toward the Vermilion River. Because the Vermilion River is more deeply entrenched than is Chappel Creek, this stream capture must have taken place at a time when the base level was at a higher elevation, when Chappel Creek had a shorter course and steeper gradient than did the Vermilion River. These conditions are believed to have existed during the time of Lake Maumee III
Characterisation of the L-mode Scrape Off Layer in MAST: decay lengths
This work presents a detailed characterisation of the MAST Scrape Off Layer
in L-mode. Scans in line averaged density, plasma current and toroidal magnetic
field were performed. A comprehensive and integrated study of the SOL was
allowed by the use of a wide range of diagnostics. In agreement with previous
results, an increase of the line averaged density induced a broadening of the
midplane density profile.Comment: 30 pages, 11 figure
Achromatizing a liquid-crystal spectropolarimeter: Retardance vs Stokes-based calibration of HiVIS
Astronomical spectropolarimeters can be subject to many sources of systematic
error which limit the precision and accuracy of the instrument. We present a
calibration method for observing high-resolution polarized spectra using
chromatic liquid-crystal variable retarders (LCVRs). These LCVRs allow for
polarimetric modulation of the incident light without any moving optics at
frequencies >10Hz. We demonstrate a calibration method using pure Stokes input
states that enables an achromatization of the system. This Stokes-based
deprojection method reproduces input polarization even though highly chromatic
instrument effects exist. This process is first demonstrated in a laboratory
spectropolarimeter where we characterize the LCVRs and show example
deprojections. The process is then implemented the a newly upgraded HiVIS
spectropolarimeter on the 3.67m AEOS telescope. The HiVIS spectropolarimeter
has also been expanded to include broad-band full-Stokes spectropolarimetry
using achromatic wave-plates in addition to the tunable full-Stokes
polarimetric mode using LCVRs. These two new polarimetric modes in combination
with a new polarimetric calibration unit provide a much more sensitive
polarimetric package with greatly reduced systematic error.Comment: Accepted in PAS
Stresses in isostatic granular systems and emergence of force chains
Progress is reported on several questions that bedevil understanding of
granular systems: (i) are the stress equations elliptic, parabolic or
hyperbolic? (ii) how can the often-observed force chains be predicted from a
first-principles continuous theory? (iii) How to relate insight from isostatic
systems to general packings? Explicit equations are derived for the stress
components in two dimensions including the dependence on the local structure.
The equations are shown to be hyperbolic and their general solutions, as well
as the Green function, are found. It is shown that the solutions give rise to
force chains and the explicit dependence of the force chains trajectories and
magnitudes on the local geometry is predicted. Direct experimental tests of the
predictions are proposed. Finally, a framework is proposed to relate the
analysis to non-isostatic and more realistic granular assemblies.Comment: 4 pages, 2 figures, Corrected typos and clkearer text, submitted to
Phys. Rev. Let
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