No description available.

No description available.

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2005. / Includes bibliographical references (p. 85-86).

No description available.

In this report we give a brief introduction to Item Response Theory models and multilevel models. The general assumptions of two classical Item Response Theory, 1PL and 2PL models are discussed. We follow the discussion by introducing a multilevel level framework for these two Item Response Theory Models. We explain Bock and Aitkin's (1981) work to estimate item parameters for these two models. Finally we illustrate these models with a LSAT exam data and two statistical softwares; R project and Stata. / text

A simple model of surface and sub -surface soil temperature was developed at the watershed scale ( -100 km2) in a semi -arid rangeland environment. The model consisted of a linear combination of air temperature and net radiation and assumed: 1) topography controls the spatial distribution of net radiation, 2) near- surface air temperature and incoming solar radiation are relatively homogeneous at the watershed scale and are available from ground stations and 3) soil moisture dominates transient soil thermal property variability. Multiplicative constants were defined to account for clear sky diffuse radiation, soil thermal inertia, an initially fixed ratio between soil heat flux and net radiation and exponential attenuation of solar radiation through a partial canopy. The surface temperature can optionally be adjusted for temperature and emissivity differences between mixed hare soil and vegetation canopies. Model development stressed physical simplicity and commonly available spatial and temporal data sets. Slowly varying surface characteristics, such as albedo, vegetation density and topography were derived from a series of Landsat TM images and a 7.5" USGS digital elevation model at a spatial resolution of 30 m. Diurnally variable atmospheric parameters were derived from a pair of ground meteorological stations using 30 -60 min averages. One site was used to drive the model, the other served as a control to estimate model error. Data collected as part of the Monsoon '90 and WG '92 field experiments over the ARS Walnut Gulch Experimental. Watershed in SE Arizona were used to validate and test the model. Point, transect and spatially distributed values of modeled surface temperature were compared with synchronous ground, aircraft and satellite thermal measurements. There was little difference between ground and aircraft measurements of surface reflectance and temperature which makes aircraft transects the preferred method to "ground truth" satellite observations. Mid- morning modeled surface temperatures were within 2° C of observed values at all but satellite scales, where atmospheric water vapor corrections complicate the determination of accurate temperatures. The utility of satellite thermal measurements and models to study various ground phenomena (eg. soil thermal inertia and surface energy balance) were investigated. Soil moisture anomalies were detectable, but were more likely associated with average near -surface soil moisture levels than individual storm footprints.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

The purpose of this study is to present the development and application of residual flow procedure for analysis of three-dimensional (3-D) steady-state and transient seepage. The finite element equations are derived using a pseudo-variational principle which leads to a transient residual flow (load) vector that, in turn, is used to correct the position of the free surface iteratively. The procedure involves a fixed mesh which requires no mesh regeneration during transient analysis and during iterations. The procedure is also capable of handling material nonhomogeneities and anisotropy with relative ease. Several applications are made including verification with respect to closed-form solutions, and with results from a laboratory glass bead model simulating three-dimensional situations. For these glass beads, the coefficients of permeability and specific storage are also evaluated experimentally.

Finite difference numerical models based upon the Navier-Stokes equations with the Boussinesq approximation have been utilized to study the dynamics of a rotating liquid with horizontal density gradients. There are two configurations analyzed: a cylindrical annulus of water rotating about a vertical axis (parallel to the body force), and a hemispherical shell of silicone oil with a radial body force, rotating about the polar axis. In both the cylindrical and spherical configurations, the thermal and mechanical forcings (boundary conditions) are symmetric about the axis of rotation. The physical parameters varied are the rotation rate and the amplitude of the horizontal thermal forcing. Two numerical models have been developed for each geometrical configuration: one to calculate axisymmetric flows and another to test the stability of those flows to non-axisymmetric perturbations. The primary purpose of the models is to determine whether axisymmetric or non-axisymmetric flow will be observed in a corresponding laboratory experiment. For the cylindrical annulus, the predictions of axisymmetric and non-axisymmetric flow are in good agreement with laboratory experiments previously performed. In the spherical experiment considered, which has not been performed in the laboratory, there is evidence that if the rotation rate is fixed and the latitudinal thermal forcing is reduced, there exists a transition from non-axisymmetric to axisymmetric flow, but that as the rotation rate is decreased for a fixed latitudinal thermal gradient on the boundaries, the flow does not become axisymmetric. The structures of some of the fastest growing eigenmodes are presented for both cylindrical and spherical cases. Analyses of the energetics indicate that the waves in all cases considered are essentially baroclinic in nature.

Suppose C(x,t) is the concentration at position x in Rᵈ and time t > 0 of a solute which is diffusing in some medium. If on a local scale the dispersion of the solute is governed by a constant dispersion matrix, 1/2(δ²), and a random velocity field, V(x), then C satisfies a convection-diffusion equation with random coefficients, (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) (1). Usually V(x) is taken to be μ + εU(x) where μ ε Rᵈ, U(x) is a given stationary random field with mean zero, and ε > 0 is a dimensionless parameter which measures the variability of V(x). Hydrological experiments suggest that on a regional scale the diffusion is classically Fickian with effective diffusion matrix D(ε) and drift velocity α(ε). Thus for large scales (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) (2) is satisfied by the solute concentration. Here τ and χ are respectively time and space measured on large scales. It is natural to investigate the relation of the large scale coefficients D and α to the statistical properties of V(x). To relate (1) to (2)--and thus to approximate D(ε) and α(ε)--it is necessary to rescale t and x and average over the distribution of V. It can then be shown that the transition form (1) to (2) is equivalent to (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) (3) where A = (∇•δ²∇)/2 + √nμ• ∇ and B(U) = √nU(√nx) • ∇. By expanding each side of (3) estimates of D(ε) and α(ε) can be obtained. The estimates have the form (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) (4). Both D₂ and α₂ depend on the power spectrum of U. Analysis shows that in at least the case of incompressible fluids D₂ is positive definite. In one dimensional transport α₂ < 0, hence α(k) < μ(k) through second order.