Extensive development has destroyed and fragmented wildlife habitat in the Lower Florida Keys. The Lower Keys marsh rabbit (LKMR; Sylvilagus palustris hefneri) and the silver rice rat (SRR; Oryzomys argentatus) are listed by the United States Fish and Wildlife Service (USFWS) and the Florida Fish and Wildlife Conservation Commission (FFWCC) as endangered species. Both species depend on coastal prairies, freshwater marshes, and intertidal salt-marsh zones. The objective of this study was to meet specific, species-level recovery goals and to add reliable information that may modify or support current recovery plans. Specifically, I (1) evaluated the use of LKMR reintroduction to suitable habitat, (2) examined characteristics of habitat used by LKMR, and (3) surveyed the Lower Florida Keys for SRRs, documenting current range and examining survey results for the past decade. I reintroduced 7 rabbits (3 males, 4 females) to suitable habitat on Water Key, and monitored their survival and release-site fidelity. All reintroduced rabbits survived and some reproduced, suggesting these translocation techniques are a viable tool for recovery. On Boca Chica Key, I radio-collared 13 LKMRs and compared vegetation characteristics between core-use and avoided areas within home ranges. Binary logistic regression associated rabbit use with high vegetation heights (7–8 dm), low canopy coverage (<=10%), high bunchgrass densities (2.5–3.8/sq m), and forb presence (>5%), supporting the hypothesis that LKMRs may be detrimentally impacted by hardwood encroachment into salt-marsh habitats. For LKMR recovery, I recommend management to resist hardwood encroachment, together with active predator control. I surveyed 36 locations on 18 islands for SRRs, capturing rats on 12 islands, including 2 on which SRRs had not previously been found. Comparisons of my data with historic data suggest SRRs either have increased in abundance over the past decade or that previous trapping efforts were not effective. Abundance of SRRs does not appear to be significantly different from that of populations of rice rats on the mainland. The USFWS and FFWCC should consider revising the conservation status of the SRR; however, it still should be regarded as a unique evolutionary unit with a very limited potential range.

Carbon dioxide (CO2) from energy consumption is a primary source of greenhouse gases. Injection of CO2 from power plants in coalbed reservoirs is a plausible method for reducing atmospheric emissions, and it can have the additional benefit of enhancing methane recovery from coal. Most previous studies have evaluated the merits of CO2 disposal in high-rank coals. Low-rank coals in the Gulf Coastal plain, specifically in Texas, are possible targets for CO2 sequestration and enhanced methane production. This research determines the technical feasibility of CO2 sequestration in Texas low-rank coals in the Wilcox Group in east-central Texas and the potential for enhanced coalbed methane (ECBM) recovery as an added benefit of sequestration. It includes deterministic and probabilistic simulation studies and evaluates both CO2 and flue gas injection scenarios. Probabilistic simulation results of 100% CO2 injection in an 80-acre 5-spot pattern indicate that these coals with average net thickness of 20 ft can store 1.27 to 2.25 Bcf of CO2 at depths of 6,200 ft, with an ECBM recovery of 0.48 to 0.85 Bcf. Simulation results of 50% CO2 - 50% N2 injection in the same 80-acre 5-spot pattern indicate that these coals can store 0.86 to 1.52 Bcf of CO2, with an ECBM recovery of 0.62 to 1.10 Bcf. Simulation results of flue gas injection (87% N2 - 13% CO2) indicate that these same coals can store 0.34 to 0.59 Bcf of CO2, with an ECBM recovery of 0.68 to 1.20 Bcf. Methane resources and CO2 sequestration potential of low-rank coals of the Wilcox Group Lower Calvert Bluff (LCB) formation in east-central Texas are significant. Resources from LCB low-rank coals in the Wilcox Group in east-central Texas are estimated to be between 6.3 and 13.6 Tcf of methane, with a potential sequestration capacity of 1,570 to 2,690 million tons of CO2. Sequestration capacity of the LCB lowrank coals in the Wilcox Group in east-central Texas equates to be between 34 and 59 years of emissions from six power plants in this area. These technical results, combined with attractive economic conditions and close proximity of many CO2 point sources near unmineable coalbeds, could generate significant projects for CO2 sequestration and ECBM production in Texas low-rank coals.

Due to the uncertainties introduced by the propagation channel, and RF and mixed signal circuits imperfections, digital communication receivers require efficient and robust signal acquisition algorithms for timing and carrier recovery, and interfer- ence rejection. The main theme of this work is the development of efficient and robust signal synchronization and interference rejection schemes for narrowband, wideband and ultra wideband communications systems. A series of novel signal acquisition schemes together with their performance analysis and comparisons with existing state-of-the- art results are introduced. The design effort is first focused on narrowband systems, and then on wideband and ultra wideband systems. For single carrier modulated narrowband systems, it is found that conventional timing recovery schemes present low efficiency, e.g., certain feedback timing recov- ery schemes exhibit the so-called hang-up phenomenon, while another class of blind feedforward timing recovery schemes presents large self-noise. Based on a general re- search framework, we propose new anti-hangup algorithms and prefiltering techniques to speed up the feedback timing recovery and reduce the self-noise of feedforward tim- ing estimators, respectively. Orthogonal frequency division multiplexing (OFDM) technique is well suited for wideband wireless systems. However, OFDM receivers require high performance car-rier and timing synchronization. A new coarse synchronization scheme is proposed for efficient carrier frequency offset and timing acquisition. Also, a novel highly accurate decision-directed algorithm is proposed to track and compensate the residual phase and timing errors after the coarse synchronization step. Both theoretical analysis and computer simulations indicate that the proposed algorithms greatly improve the performance of OFDM receivers. The results of an in-depth study show that a narrowband interference (NBI) could cause serious performance loss in multiband OFDMbased ultra-wideband (UWB) sys- tems. A novel NBI mitigation scheme, based on a digital NBI detector and adaptive analog notch filter bank, is proposed to reduce the effects of NBI in UWB systems. Simulation results show that the proposed NBI mitigation scheme improves signifi- cantly the performance of a standard UWB receiver (this improvement manifests as a signal-to-noise ratio (SNR) gain of 9 dB).

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Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 139-148). Available also in a digital version from Dissertation Abstracts.

Thesis (M. Sc.)--University of Hong Kong, 1982.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

In this thesis we develop a new model that explains the overall grief recovery process for abusiness failure on a family group level. The model builds on, and expands the theories ofanticipatory grief as presented by Shepherd, Wiklund, and Haynie (2009) and the dual processof coping presented by Shepherd (2003). The qualitative method used for this thesiswas a multiple case study approach, with an in-depth focus. Our main findings was the importanceof aligning the entrepreneurs anticipatory grief stage with the family’s coping process,by maintaining transparent and open relationships where information could easily beexchanged. In addition we found that maintaining this transparency was often difficult forthe entrepreneur due to a series of factors, which we refer to as a “barrier to informationflow”, which include everything from stress to societal interference. Finally we proposehow our model can be applied and used to generate further knowledge and additional researchon the emotional aspects of a business failure.

Polymer flooding is a commercially proven technology to enhance oil recovery from mature reservoirs. The main mechanism for improving oil recovery is to increase the viscosity of injection water by adding polymer, thereby creating a favorable mobility ratio for improved volumetric sweep efficiency. However, polymer injection brings on several potential problems: a) a high injection pressure with associated pumping cost; b) creation of unwanted injection well fractures; and c) mechanical degradation of polymers due to high shear near wellbore. The high viscosity of polymer solutions and permeability reduction by polymer retention reduce mobility, and simultaneously increase the pressure drop required for the propagation of the polymer bank. The objective of this dissertation is to develop an improved polymer injection process that can minimize the impact of those potential problems in the polymer flooding process, and to extend this application to conformance control. This objective is accomplished by utilizing the pH sensitivity of partially hydrolyzed polyacrylamide (HPAM), which is the most commonly used EOR polymer. The idea of the “low-pH polymer process” is to inject HPAM solution at low-pH conditions into the reservoir. The polymer viscosity is low in that condition, which enables the polymer solution to pass through the near wellbore region with a relatively low pressure drop. This process can save a considerable amount of pump horse power required during injection, and also enables the use of large-molecular-weight polymers without danger of mechanical degradation while injecting below the fracture gradient. Away from the near wellbore region, the polymer solution becomes thickened with an increase in pH, which occurs naturally by a spontaneous reaction between the acid solution and rock minerals. The viscosity increase lowers the brine mobility and increases oil displacement efficiency, as intended. Another potential application of the low-pH polymer injection process is conformance control in a highly heterogeneous reservoir. As a secondary recovery method, water flooding can sweep most oil from the high-permeability zones, but not from the low-permeability zones. The polymer solution under low-pH conditions can be placed deep into such high-permeability sands preferentially, because of its low viscosity. It is then viscosified by a pH increase, caused by geochemical reactions with the rock minerals in the reservoir. With the thickened polymer solution in the high permeability sands, the subsequently injected water is diverted to the low permeability zone, so that the bypassed oil trapped in that zone can be efficiently recovered. To evaluate the low-pH polymer process, extensive laboratory experiments were systematically conducted. As the first step, the rheological properties of HPAM solutions, such as steady-shear viscosity and viscoelastic behavior, were measured as functions of pH. The effects of various process variables, such as polymer concentrations, salinity, polymer molecular weight, and degree of hydrolysis on rheological properties, were investigated for a wide range of pH. A comprehensive rheological model for HPAM solutions was also developed in order to provide polymer viscosity in terms of the above process variables. As the second step, weak acid (citric acid) and strong acid (hydrochloric acid) were evaluated as pH control agents. Citric acid was shown to clearly perform better than hydrochloric acid. A series of acid coreflood experiments for different process variables (injection pH, core length, flow rate, and the presence of shut-ins) were carried out. The effluent pH and five cations (total Ca, Mg, Fe, Al, and K) were measured for qualitative evaluation of the geochemical reactions between the injected acid and the rock minerals; these measurements also provide data for future history matching simulations to accurately characterize these geochemical reactions. Finally, polymer coreflood experiments were carried out with different process variables: injection pH, polymer concentration, polymer molecular weight, salinity, degree of hydrolysis, and flow rate. The transport characteristics of HPAM solutions in Berea sandstone cores were evaluated in terms of permeability reduction and mobility reduction. Adsorption and inaccessible/excluded pore volume were also measured in order to accurately characterize the transport of HPAM solutions under low-pH conditions. The results show that the proposed “low-pH polymer process” can substantially increase injectivity (lower injection pressures) and allow deeper transport of polymer solutions in the reservoir due to the low solution viscosity. The peak pH’s observed in several shut-ins guarantee that spontaneous geochemical reactions can return the polymer solution to its original high viscosity. However, low-pH conditions increase adsorption (polymer-loss) and require additional chemical cost (for citric acid). The optimum injection formulation (polymer concentration, injection pH) will depend on the specific reservoir mineralogy, permeability, salinity and injection conditions. / text

High oil-viscosity is a major concern for the recovery of oil from heavy-oil reservoirs. Introducing energy to the formation has proven to be an effective way of lowering the oil viscosity by raising the temperature in the formation. The application of low-frequency heating, also known as electrical resistance heating, is limited by water vaporization near the wellbore which breaks the conductive path to the reservoir, and limits the heating rate as well as the resulting production rates. Electromagnetic (EM) heating, also called high-frequency heating, can be used instead. Although its potential was recognized during the late 70’s, no simulation results or detailed modeling studies have yet been published that completely model the complex interactions of EM energy and multiphase flow. One of the main drawbacks of proposed models is the use of the EM adsorption coefficient as a constant regardless of the properties of the medium, which can obscure the important effect of this parameter on the extension of the reservoir area heated. This dissertation presents a multiphase, two-dimensional radial model that describes the three-phase flow of water, oil, and steam and heat flow in a reservoir within confining conductive formations. The model accounts for the appearance and/or disappearance of a phase, and uses the variation in temperature and water saturation to update the EM absorption coefficient. This model allows determining the temperature distribution and the productivity improvement from EM heating when multiple phases are present. For the numerical simulations of EM heating, I used COMSOL Multiphysics, a Lagrange-quadratic finite element simulator, and its partial differential equations (PDE) application. Several simulations were made for hypothetical reservoirs with different fluid and rock properties. Also, analytical solutions for a single-phase EM heating model were developed and used to validate the numerical solutions. Special attention is focused on reservoirs with characteristics for which steam injection is not attractive or feasible such as low permeability, thin-zone, and extra-heavy oil reservoirs. Results showed that EM heating is feasible based on the power source and frequency used to maintain an optimum absorption coefficient and to obtain higher production rates. Comparisons showed that cumulative oil production and recovery factor obtained by EM heating are better than what is achieved by cyclic steam stimulation (CSS) for reservoirs with the above mentioned characteristics. / text