84 research outputs found
Quantifying surfactant interaction effects on soil moisture and turf quality
Soil water repellency occurs widely in horticultural and agricultural soils when very dry. The gradual accumulation and breakdown of surface organic matter over time produces wax-like organic acids, which coat soil particles preventing uniform entry of water into the soil. Water repellency is usually managed by regular surfactant applications. Surfactants, literally, are surface active agents (SURFace ACTive AgeNTS). Their mode of action is to reduce the surface tension of water, allowing it to penetrate and wet the soil more easily and completely. This practice improves water use efficiency (by requiring less water to wet the soil and by capturing rainfall and irrigation more effectively and rapidly). It also reduces nutrient losses through run-off erosion or leaching. These nutrients have the potential to pollute the surrounding environment and water courses. This project investigated potential improvements to standard practices (product combination and scheduling) for surfactant use to overcome localised dry spots on water repellent soils and thus improve turf quality and water use efficiency. Weather conditions for the duration of the trial prevented the identification of improved practices in terms of combination and scheduling. However, the findings support previous research that the use of soil surfactants decreased the time for water to infiltrate dry soil samples taken from a previously severely hydrophobic site. Data will be continually collected from this trial site on a private contractual basis, with the hope that improvements to standard practices will be observed during the drier winter months when moisture availability is a limiting factor for turfgrass growth and quality
Climate Study of the Learning Environment for Faculty, Staff, and Students at a U.S. Dental School: Foundation for Culture Change
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153619/1/jddjde017073.pd
M-theory and Characteristic Classes
In this note we show that the Chern-Simons and the one-loop terms in the
M-theory action can be written in terms of new characters involving the
M-theory four-form and the string classes. This sheds a new light on the
topological structure behind M-theory and suggests the construction of a theory
of `higher' characteristic classes.Comment: 8 pages. Error in gravitational term fixed; minor corrections;
reference and acknowledgement adde
On a computer-aided approach to the computation of Abelian integrals
An accurate method to compute enclosures of Abelian integrals is developed.
This allows for an accurate description of the phase portraits of planar
polynomial systems that are perturbations of Hamiltonian systems. As an
example, it is applied to the study of bifurcations of limit cycles arising
from a cubic perturbation of an elliptic Hamiltonian of degree four
Exact SU(2)*U(1) Stringy Black Holes
Extreme magnetic dilaton black holes are promoted to exact solutions of
heterotic string theory with unbroken supersymmetry. With account taken of
alpha' corrections this is accomplished by supplementing the known solutions
with SU(2) Yang-Mills vectors and scalars in addition to the already existing
Abelian U(1) vector field. The solution has a simple analytic form and includes
multi-black-holes. The issue of exactness of other black-hole-type solutions,
including extreme dilaton electrically charged black holes and Taub-NUT
solutions is discussed.Comment: 10 pages, SU-ITP-94-27 and QMW-PH-94-34 (version accepted for
publication in Phys. Rev., contains a discussion of (4.1) supersymmetry of
the black hole sigma model
Topological String Amplitudes, Complete Intersection Calabi-Yau Spaces and Threshold Corrections
We present the most complete list of mirror pairs of Calabi-Yau complete
intersections in toric ambient varieties and develop the methods to solve the
topological string and to calculate higher genus amplitudes on these compact
Calabi-Yau spaces. These symplectic invariants are used to remove redundancies
in examples. The construction of the B-model propagators leads to compatibility
conditions, which constrain multi-parameter mirror maps. For K3 fibered
Calabi-Yau spaces without reducible fibers we find closed formulas for all
genus contributions in the fiber direction from the geometry of the fibration.
If the heterotic dual to this geometry is known, the higher genus invariants
can be identified with the degeneracies of BPS states contributing to
gravitational threshold corrections and all genus checks on string duality in
the perturbative regime are accomplished. We find, however, that the BPS
degeneracies do not uniquely fix the non-perturbative completion of the
heterotic string. For these geometries we can write the topological partition
function in terms of the Donaldson-Thomas invariants and we perform a
non-trivial check of S-duality in topological strings. We further investigate
transitions via collapsing D5 del Pezzo surfaces and the occurrence of free Z2
quotients that lead to a new class of heterotic duals.Comment: 117 pages, 1 Postscript figur
An Implementation of Tarjan's Algorithm for the Block Triangularization of a Matrix
An implementation of Tarj an's algorithm for symmetrically permuting a given matrix to block tmangular form is described. The discussion includes a flowchart of the algorithm, a com-plexity analysis, and a comparison with the earlier widely used algorithm of Sargent and Westerberg. T~ming results are presented from several experiments using the code developed by the authors
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