10,469 research outputs found
Arsenic in the Water, Soil Bedrock, and Plants of the Ester Dome Area of Alaska
Concentrations of arsenic as large as 10 ppm (200 times the safe
limit for drinking water) occur in the groundwater of a mineralized
residential area near Fairbanks. Bedrock of the area contains 750 ppm
As, primarily as arsenopyrite and scorodite. The oxygen-poor groundwater
is enriched in As(III) and ferrous iron while the surface waters
are iron free and contain less than 50 ppb As(V). Arsenic is removed
from the water by coprecipitation with ferric hydroxide. Some iron-rich
stream sediments contain as much as 1,400 ppm arsenic.
The distribution of arsenic in the groundwater is controlled by the
distribution of arsenic in the bedrock. The arsenic content of the B soil
horizon over mineralized veins is about 150 ppm, while that over barren
rock is 30 ppm. The vegetation over the veins is not significantly
enriched in arsenic.
Lettuce, radishes and tomatoes grown with arsenic-rich water (5 ppm) contain 16, 8 and 1 ppm As, respectively; these amounts are significantly
greater than plants not treated with arsenic.
Preliminary studies by state and federal health agencies show no
detrimental effects on the health of persons drinking these arsenic-rich
waters.The work upon which this publication is based was supported in part by
funds provided by the Office of Water Research and Technology (Project
B-037-ALAS, Agreement No. 14-34-0001-8056), U.S. Department of the
Interior, Washington, D.C., as authorized by the Water Research and
Development Act of 1978
Modelling the impacts of pasture contamination and stocking rate for the development of targeted selective treatment strategies for Ostertagia ostertagi infection in calves
A simulation study was carried out to assess whether variation in pasture contamination or stocking rate impact upon the optimal design of targeted selective treatment (TST) strategies. Two methods of TST implementation were considered: 1) treatment of a fixed percentage of a herd according to a given phenotypic trait, or 2) treatment of individuals that exceeded a threshold value for a given phenotypic trait. Four phenotypic traits, on which to base treatment were considered: 1) average daily bodyweight gain, 2) faecal egg count, 3) plasma pepsinogen, or 4) random selection. Each implementation method (fixed percentage or threshold treatment) and determinant criteria (phenotypic trait) was assessed in terms of benefit per R (BPR), the ratio of average benefit in weight gain to change in frequency of resistance alleles R (relative to an untreated population). The impact of pasture contamination on optimal TST strategy design was investigated by setting the initial pasture contamination to 100, 200 or 500 O. ostertagi L3/kg DM herbage; stocking rate was investigated at a low (3calves/ha), conventional (5 calves/ha) or high (7 calves/ha) stocking rates. When treating a fixed percentage of the herd, treatments according to plasma pepsinogen or random selection were identified as the most beneficial (i.e. resulted in the greatest BPR) for all levels of initial pasture contamination and all stocking rates. Conversely when treatments were administered according to threshold values ADG was most beneficial, and was identified as the best TST strategy (i.e. resulted in the greatest overall BPR) for all levels of initial pasture contamination and all stocking rates
Mirror Map as Generating Function of Intersection Numbers: Toric Manifolds with Two K\"ahler Forms
In this paper, we extend our geometrical derivation of expansion coefficients
of mirror maps by localization computation to the case of toric manifolds with
two K\"ahler forms. Especially, we take Hirzebruch surfaces F_{0}, F_{3} and
Calabi-Yau hypersurface in weighted projective space P(1,1,2,2,2) as examples.
We expect that our results can be easily generalized to arbitrary toric
manifold.Comment: 45 pages, 2 figures, minor errors are corrected, English is refined.
Section 1 and Section 2 are enlarged. Especially in Section 2, confusion
between the notion of resolution and the notion of compactification is
resolved. Computation under non-zero equivariant parameters are added in
Section
Modelling the consequences of targeted selective treatment strategies on performance and emergence of anthelmintic resistance amongst grazing calves
The development of anthelmintic resistance by helminths can be slowed by maintaining refugia on pasture or in untreated hosts. Targeted selective treatments (TST) may achieve this through the treatment only of individuals that would benefit most from anthelmintic, according to certain criteria. However TST consequences on cattle are uncertain, mainly due to difficulties of comparison between alternative strategies. We developed a mathematical model to compare: 1) the most ‘beneficial’ indicator for treatment selection and 2) the method of selection of calves exposed to Ostertagia ostertagi, i.e. treating a fixed percentage of the population with the lowest (or highest) indicator values versus treating individuals who exceed (or are below) a given indicator threshold. The indicators evaluated were average daily gain (ADG), faecal egg counts (FEC), plasma pepsinogen, combined FEC and plasma pepsinogen, versus random selection of individuals. Treatment success was assessed in terms of benefit per R (BPR), the ratio of average benefit in weight gain to change in frequency of resistance alleles R (relative to an untreated population). The optimal indicator in terms of BPR for fixed percentages of calves treated was plasma pepsinogen and the worst ADG; in the latter case treatment was applied to some individuals who were not in need of treatment. The reverse was found when calves were treated according to threshold criteria, with ADG being the best target indicator for treatment. This was also the most beneficial strategy overall, with a significantly higher BPR value than any other strategy, but its degree of success depended on the chosen threshold of the indicator. The study shows strong support for TST, with all strategies showing improvements on calves treated selectively, compared with whole-herd treatment at 3, 8, 13 weeks post-turnout. The developed model appeared capable of assessing the consequences of other TST strategies on calf populations
A stochastic model to investigate the effects of control strategies on calves exposed to Ostertagia ostertagi
Predicting the effectiveness of parasite control strategies requires accounting for the responses of individual hosts and the epidemiology of parasite supra- and infra-populations. The first objective was to develop a stochastic model that predicted the parasitological interactions within a group of first season grazing calves challenged by Ostertagia ostertagi, by considering phenotypic variation amongst the calves and variation in parasite infra-population. Model behaviour was assessed using variations in parasite supra-population and calf stocking rate. The model showed the initial pasture infection level to have little impact on parasitological output traits, such as worm burdens and FEC, or overall performance of calves, whereas increasing stocking rate had a disproportionately large effect on both parasitological and performance traits. Model predictions were compared with published data taken from experiments on common control strategies, such as reducing stocking rates, the ‘dose and move’ strategy and strategic treatment with anthelmintic at specific times. Model predictions showed in most cases reasonable agreement with observations, supporting model robustness. The stochastic model developed is flexible, with the potential to predict the consequences of other nematode control strategies, such as targeted selective treatments on groups of grazing calves
Damp Mergers: Recent Gaseous Mergers without Significant Globular Cluster Formation?
Here we test the idea that new globular clusters (GCs) are formed in the same
gaseous ("wet") mergers or interactions that give rise to the young stellar
populations seen in the central regions of many early-type galaxies. We compare
mean GC colors with the age of the central galaxy starburst. The red GC
subpopulation reveals remarkably constant mean colors independent of galaxy
age. A scenario in which the red GC subpopulation is a combination of old and
new GCs (formed in the same event as the central galaxy starburst) can not be
ruled out; although this would require an age-metallicity relation for the
newly formed GCs that is steeper than the Galactic relation. However, the data
are also well described by a scenario in which most red GCs are old, and few,
if any, are formed in recent gaseous mergers. This is consistent with the old
ages inferred from some spectroscopic studies of GCs in external systems. The
event that induced the central galaxy starburst may have therefore involved
insufficient gas mass for significant GC formation. We term such gas-poor
events "damp" mergers.Comment: 17 pages, 5 figures, ApJ accepte
Germination and Early Development of the Silky Prairie Clover
Field and laboratory studies of the silky prairie clover (Petalostemon villosum Nutt.) in central Minnesota indicated that seeds of this plant require scarification but do not require an overwintering period, to germinate. Germination and primary root growth are rapid; shoot growth appears to be quite slow. Methods of associating shoot growth with age are suggested and several notes on the life history of the plant ore presented
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