15,547 research outputs found
Mathematical model investigation of long-term transport of ocean-dumped sewage sludge related to remote sensing
An existing, three-dimensional, Eulerian-Lagrangian finite-difference model was modified and used to examine the transport processes of dumped sewage sludge in the New York Bight. Both in situ and laboratory data were utilized in an attempt to approximate model inputs such as mean current speed, horizontal diffusion coefficients, particle size distributions, and specific gravities. The results presented are a quantitative description of the fate of a negatively buoyant sewage sludge plume resulting from continuous and instantaneous barge releases. Concentrations of the sludge near the surface were compared qualitatively with those remotely sensed. Laboratory study was performed to investigate the behavior of sewage sludge dumping in various ambient density conditions
Remote monitoring of a thermal plume
A remote-sensing experiment conducted on May 17, 1977, over the Surry nuclear power station on the James River, Virginia is discussed. Isotherms of the thermal plume from the power station were derived from remotely sensed data and compared with in situ water temperature measurements provided by the Virginia Electric and Power Company, VEPCO. The results of this study were also qualitatively compared with those from other previous studies under comparable conditions of the power station's operation and the ambient flow. These studies included hydraulic model predictions carried out by Pritchard and Carpenter and a 5-year in situ monitoring program based on boat surveys
Stem-root flow effect on soilâatmosphere interactions and uncertainty assessments
Abstract. Soil water can rapidly enter deeper layers via vertical redistribution of soil water through the stemâroot flow mechanism. This study develops the stemâroot flow parameterization scheme and coupled this scheme with the Simplified Simple Biosphere model (SSiB) to analyze its effects on landâatmospheric interactions. The SSiB model was tested in a single column mode using the Lien Hua Chih (LHC) measurements conducted in Taiwan and HAPEX-Mobilhy (HAPEX) measurements in France. The results show that stemâroot flow generally caused a decrease in the moisture content at the top soil layer and moistened the deeper soil layers. Such soil moisture redistribution results in significant changes in heat flux exchange between land and atmosphere. In the humid environment at LHC, the stemâroot flow effect on transpiration was minimal, and the main influence on energy flux was through reduced soil evaporation that led to higher soil temperature and greater sensible heat flux. In the Mediterranean environment of HAPEX, the stemâroot flow significantly affected plant transpiration and soil evaporation, as well as associated changes in canopy and soil temperatures. However, the effect on transpiration could either be positive or negative depending on the relative changes in the moisture content of the top soil vs. deeper soil layers due to stemâroot flow and soil moisture diffusion processes
Fast QMC matrix-vector multiplication
Quasi-Monte Carlo (QMC) rules
can be used to approximate integrals of the form , where is a matrix and
is row vector. This type of integral arises for example from
the simulation of a normal distribution with a general covariance matrix, from
the approximation of the expectation value of solutions of PDEs with random
coefficients, or from applications from statistics. In this paper we design QMC
quadrature points
such that for the matrix whose rows are the quadrature points, one can
use the fast Fourier transform to compute the matrix-vector product , , in operations and at most extra additions. The proposed method can be
applied to lattice rules, polynomial lattice rules and a certain type of
Korobov -set.
The approach is illustrated computationally by three numerical experiments.
The first test considers the generation of points with normal distribution and
general covariance matrix, the second test applies QMC to high-dimensional,
affine-parametric, elliptic partial differential equations with uniformly
distributed random coefficients, and the third test addresses Finite-Element
discretizations of elliptic partial differential equations with
high-dimensional, log-normal random input data. All numerical tests show a
significant speed-up of the computation times of the fast QMC matrix method
compared to a conventional implementation as the dimension becomes large
Combustion: Structural interaction in a viscoelastic material
The effect of interaction between combustion processes and structural deformation of solid propellant was considered. The combustion analysis was performed on the basis of deformed crack geometry, which was determined from the structural analysis. On the other hand, input data for the structural analysis, such as pressure distribution along the crack boundary and ablation velocity of the crack, were determined from the combustion analysis. The interaction analysis was conducted by combining two computer codes, a combustion analysis code and a general purpose finite element structural analysis code
Suppression of core polarization in halo nuclei
We present a microscopic study of halo nuclei, starting from the Paris and
Bonn potentials and employing a two-frequency shell model approach. It is found
that the core-polarization effect is dramatically suppressed in such nuclei.
Consequently the effective interaction for halo nucleons is almost entirely
given by the bare G-matrix alone, which presently can be evaluated with a high
degree of accuracy. The experimental pairing energies between the two halo
neutrons in He and Li nuclei are satisfactorily reproduced by our
calculation. It is suggested that the fundamental nucleon-nucleon interaction
can be probed in a clearer and more direct way in halo nuclei than in ordinary
nuclei.Comment: 11 pages, RevTex, 2 postscript figures; major revisions, matches
version to appear in Phys. Rev. Letter
Mass Hierarchies and the Seesaw Neutrino Mixing
We give a general analysis of neutrino mixing in the seesaw mechanism with
three flavors. Assuming that the Dirac and u-quark mass matrices are similar,
we establish simple relations between the neutrino parameters and individual
Majorana masses. They are shown to depend rather strongly on the physical
neutrino mixing angles. We calculate explicitly the implied Majorana mass
hierarchies for parameter sets corresponding to different solutions to the
solar neutrino problem.Comment: 11 pages, no figures, replaced with final version. Minor corrections
and one typo corrected. Added one referenc
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