13,306 research outputs found
A model for water uptake by plant roots.
We present a model for water uptake by plant roots from unsaturated soil. The model includes the simultaneous flow of water inside the root network and in the soil. It is constructed by considering first the water uptake by a single root, and then using the parameterized results thereby obtained to build a model for water uptake by the developing root network. We focus our model on annual plants, in particular the model will be applicable to commercial monocultures like maize, wheat, etc. The model is solved numerically, and the results are compared with approximate analytic solutions. The model predicts that as a result of water uptake by plant roots, dry and wet zones will develop in the soil. The wet zone is located near the surface of the soil and the depth of it is determined by a balance between rainfall and the rate of water uptake. The dry zone develops directly beneath the wet zone because the influence of the rainfall at the soil surface does not reach this region, due to the nonlinear nature of the water flow in the partially saturated soil. We develop approximate analytic expressions for the depth of the wet zone and discuss briefly its ecological significance for the plant. Using this model we also address the question of where water uptake sites are concentrated in the root system. The model indicates that the regions near the base of the root system (i.e. close to the ground surface) and near the root tips will take up more water than the middle region of the root system, again due to the highly nonlinear nature of water flow in the soil
Differences between stellar and laboratory reaction cross sections
Nuclear reactions proceed differently in stellar plasmas than in the
laboratory due to the thermal effects in the plasma. On one hand, a target
nucleus is bombarded by projectiles distributed in energy with a distribution
defined by the plasma temperature. The most relevant energies are low by
nuclear physics standards and thus require an improved description of
low-energy properties, such as optical potentials, required for the calculation
of reaction cross sections. Recent studies of low-energy cross sections suggest
the necessity of a modification of the proton optical potential. On the other
hand, target nuclei are in thermal equilibrium with the plasma and this
modifies their reaction cross sections. It is generally expected that this
modification is larger for endothermic reactions. We show that there are many
exceptions to this rule.Comment: 4 pages, Proceedings of Nuclear Physics in Astrophysics 4, Frascati,
Italy; to appear in J. Phys. Conf. Serie
Electrostatic Analyzer for 1.5-Mev Protons
A system for analyzing the ion beam of an electrostatic generator is described. A weak magnetic field separates protons from heavier components and a 90° electrostatic deflection gives the required energy resolution. With the analyzer controlling the generator voltage, a proton beam of one microampere with an energy spread of the order of 300 volts in one million is obtained
Grid enabling legacy applications for scalability – Experiences of a production application on the UK NGS
A mathematical model of plant nutrient uptake
The classical model of plant root nutrient uptake due to Nye. Tinker and Barber is developed and extended. We provide an explicit closed formula for the uptake by a single cylindrical root for all cases of practical interest by solving the absorption-diffusion equation for the soil nutrient concentration asymptotically in the limit of large time. We then use this single root model as a building block to construct a model which allows for root size distribution in a more realistic plant root system, and we include the effects of root branching and growth. The results are compared with previous theoretical and experimental studies
The application of remote sensing to the development and formulation of hydrologic planning models
A hydrologic planning model is developed based on remotely sensed inputs. Data from LANDSAT 1 are used to supply the model's quantitative parameters and coefficients. The use of LANDSAT data as information input to all categories of hydrologic models requiring quantitative surface parameters for their effects functioning is also investigated
The application of remote sensing to the development and formulation of hydrologic planning models
For abstract, see N76-18632
Comparative Microbial Dynamics in Crassostrea virginica and Crassostrea ariakensis
Considerations to introduce the Suminoe or Asian oyster Crassostrea ariakensis along the East Coast have raised many questions regarding ecology, economics, and human health. To date, research has focused primarily on the ecological and socioeconomic implications of this initiative, yet few studies have assessed its potential
impact on public health. Our work compares the rates of bioaccumulation, depuration and post harvest decay of indicator organisms (such as E. coli) and Vibrio sp. between
Crassostrea virginica and Crassostrea ariakensis in the laboratory. Preliminary results suggest that the rates of bioaccumulation of E. coli in Crassostrea ariakensis were
significantly lower than those for Crassostrea virginica, depuration of E. coli was variable between the two species, and Crassostrea ariakensis post harvest decay rates of
Vibrio sp. were significantly lower than Crassostrea virginica. This research provides coastal managers with insight into the response of Crassostrea ariakensis to bacteria, an important consideration for determining appropriate management strategies for this species. Further field-based studies will be necessary to elucidate the mechanisms responsible for the differences in rates of bioaccumulation and depuration. (PDF contains 40 pages
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