Interpretation of Helioseismic Travel Times - Sensitivity to Sound Speed, Pressure, Density, and Flows

Time-distance helioseismology uses cross-covariances of wave motions on the solar surface to determine the travel times of wave packets moving from one surface location to another. We review the methodology to interpret travel-time measurements in terms of small, localized perturbations to a horizontally homogeneous reference solar model. Using the first Born approximation, we derive and compute 3D travel-time sensitivity (Fr\'echet) kernels for perturbations in sound-speed, density, pressure, and vector flows. While kernels for sound speed and flows had been computed previously, here we extend the calculation to kernels for density and pressure, hence providing a complete description of the effects of solar dynamics and structure on travel times. We treat three thermodynamic quantities as independent and do not assume hydrostatic equilibrium. We present a convenient approach to computing damped Green's functions using a normal-mode summation. The Green's function must be computed on a wavenumber grid that has sufficient resolution to resolve the longest lived modes. The typical kernel calculations used in this paper are computer intensive and require on the order of 600 CPU hours per kernel. Kernels are validated by computing the travel-time perturbation that results from horizontally-invariant perturbations using two independent approaches. At fixed sound-speed, the density and pressure kernels are approximately related through a negative multiplicative factor, therefore implying that perturbations in density and pressure are difficult to disentangle. Mean travel-times are not only sensitive to sound-speed, density and pressure perturbations, but also to flows, especially vertical flows. Accurate sensitivity kernels are needed to interpret complex flow patterns such as convection

Integrating Geographic Information Systems and Remote Sensing with Spatial Economic and Mixed Logit Models for Environmental Valuation

This research focuses on the Emory and Obed Watersheds in the Cumberland Plateau in Central Tennessee and the Lower Hatchie River Watershed in West Tennessee. A framework based on market and nonmarket valuation techniques was used to empirically estimate economic values for environmental amenities and negative externalities in these areas. The specific techniques employed include a variation of hedonic pricing and discrete choice conjoint analysis (i.e., choice modeling), in addition to geographic information systems (GIS) and remote sensing. Microeconomic models of agent behavior, including random utility theory and profit maximization, provide the principal theoretical foundation linking valuation techniques and econometric models. The generalized method of moments estimator for a first order spatial autoregressive function and mixed logit models are the principal econometric methods applied within the framework. The dissertation is subdivided into three separate chapters written in a manuscript format. The first chapter provides the necessary theoretical and mathematical conditions that must be satisfied in order for a forest amenity enhancement program to be implemented. Such a program is possible and would yield an efficient outcome under three conditions: (1) contributors are willing to pay an amount that maximizes the utility they derive from forest amenities; ( 2) an intermediary party sets a compensation price based on contributor aggregate willingness to pay such that the social value of the program is maximized; and (3) a participating landowner maximizes profit given this incentive. The second chapter evaluates the effect of forest land cover and information about future land use change on respondent preferences and willingness to pay for alternative hypothetical forest amenity enhancement options. Land use change information and the amount of forest land cover significantly influenced respondent preferences, choices, and stated willingness to pay. Hicksian welfare estimates for proposed enhancement options ranged from $57.42 to$25.53, depending on the policy specification, information level, and econometric model. The third chapter presents economic values for negative externalities associated with channelization that affect the productivity and overall market value of forested wetlands. Results of robust, generalized moments estimation of a double logarithmic first-order spatial autoregressive error model (inverse distance weights with spatial dependence up to 1500m) indicate that the implicit cost of damages to forested wetlands caused by channelization equaled -$5,438 ha-1. Collectively, the results of this dissertation provide economic measures of the damages to and benefits of environmental assets, help private landowners and policy makers identify the amenity attributes preferred by the public, and improve the management of natural resources

Differentiating a Landscape of Lac Repressor Mediated DNA Loops Using FRET

The variety of DNA loops formed by a protein such as Lac Repressor (LacI), predicted to populate multiple loop topologies and geometries, increases the uncertainty of models that have not been experimentally verified. We created a method for evaluating the multitude of LacI-DNA looped states using FRET with fluorophore position variants (FPVs) on a landscape DNA constructs with dual operator phasing variants bracketing an intrinsically curved DNA sequence. The FRET signature for each FPV corresponds to a specific LacI-DNA loop topology, and when applied to the landscape of constructs we could systematically explore DNA sequence dependent LacI mediated DNA looping. The FRET efficiencies calculated for each FPV landscape revealed the first unambiguous detection of antiparallel (A1 and A2) and distributions among parallel loop (P1) and antiparallel loops. The FRET efficiency maximum of each FPV landscape was used to calculate the loop population distribution for each topology assuming a uniform population at the peaks. The differences in the observed peak FRET among FPV landscapes led to an unavoidable estimate of loop populations with an extended LacI-DNA loop geometry, and also slightly extended LacI-DNA loop in the cases of antiparallel loops. The addition of saturating inducer to the FPV landscape demonstrated that IPTG-LacI-DNA loops have different properties than uninduced loops: they have increased instability, increased competition among previously energetically unfavorable states, and presumably have increased switching between specific and nonspecific LacI-DNA interactions. This multivariate data set confirms that rod mechanics models of DNA looping should also consider protein flexibility, and also demonstrates the importance of protein flexibility in modeling genetic regulatory circuits that are similar to the "hydrogen atom of gene regulation", the lac operon

The Art of Leasing Negotiation in a Frenzied Environment

Let’s face it. The farm economy across much of Nebraska has literally been turned upside down in the past few months by the “Ethanol Gold Rush.” Demand for corn has shot corn prices upward beyond $3.00 per bushel, when only a year earlier the harvest prices hovered around$1.50. Many expect these new price levels to hold, at least for the 2007 crop season

Retail Patterns Across Nebraska, a 10-Year Perspective

Retail activity is very dynamic and highly variable, across both time and space. We have been following total retail activity, using taxable retail sales from the Nebraska Department of Revenue as a proxy for many years. Over time, we have witnessed the continuing trend towards increasing concentration of retail activity in the larger trade centers and urban communities, and away from rural and small trade centers. While state sales tax data provides some clear perspectives on overall changes and trends, even down to town and county levels, details as to the specific type of retail activity is precluded

Mapping quantum-classical Liouville equation: projectors and trajectories

The evolution of a mixed quantum-classical system is expressed in the mapping formalism where discrete quantum states are mapped onto oscillator states, resulting in a phase space description of the quantum degrees of freedom. By defining projection operators onto the mapping states corresponding to the physical quantum states, it is shown that the mapping quantum-classical Liouville operator commutes with the projection operator so that the dynamics is confined to the physical space. It is also shown that a trajectory-based solution of this equation can be constructed that requires the simulation of an ensemble of entangled trajectories. An approximation to this evolution equation which retains only the Poisson bracket contribution to the evolution operator does admit a solution in an ensemble of independent trajectories but it is shown that this operator does not commute with the projection operators and the dynamics may take the system outside the physical space. The dynamical instabilities, utility and domain of validity of this approximate dynamics are discussed. The effects are illustrated by simulations on several quantum systems.Comment: 4 figure