We study two interacting particles in a random potential chain by means of the transfer matrix method. The dependence of the two-particle localization length lampta_2 on disorder and interaction strength is investigated. Our results demonstrate that the recently proposed enhancement of lampta_2 as compared to the results for single particles is entirely due to the finite size of the systems considered. This is shown for a Hubbard-like onsite interaction and also a long-range interaction.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI Company.

The historical method of precise orbit determination is a dynamic approach. However, with the improvement of GPS tracking data and associated tracking networks, two newer methods have been developed: reduced-dynamic and kinematic. In addition to orbit determination, alternative methods of gravity field recovery have been developed using kinematic orbits which do not rely on any force modeling. However, one significant drawback of kinematic orbits is that they lack any velocity or acceleration information. These have to be derived numerically. Based on the results of this thesis, the Savitzky-Golay filter, without using a remove-restore procedure, is recommended for deriving kinematic velocities of the GRACE mission. In addition, the numerical differentiation methods are tested to see how well accurately they represent the satellite's acceleration for all three orbit types. Finally, with the kinematic orbits properly reconstructed, the results can also be compared to dynamic and reduced-dynamic orbits through K-Band Ranging residuals. / text

Research has documented the need for school districts to recruit and retain qualified school leaders capable of navigating the organizational challenges for school improvement, particularly in high-poverty, low-achievement contexts. Recently, scholars have studied principal pipeline structures implemented by school districts to recruit and retain effective principals. A key finding of this research is that clearly-defined standards and performance criteria can inform school districts' strategic identification and development of individuals with the potential to become effective principals. Further research is needed to understand and define potential and readiness for the principalship in assistant principals, commonly the largest candidate group in a principal pipeline. I used a qualitative case study design to investigate veteran principals' perceptions about potential and readiness for the principalship in assistant principals. Six principals in one urban school in Texas were purposefully selected based on their experience with supporting, developing, and/or endorsing former assistant principals for promotion to the principalship while under their supervision. I collected data through questionnaires and in-depth interviews to understand this phenomenon through the informants' lived experience. I found that the principals view professional competence and personal dispositions as indicators of potential and readiness for the principalship. They believe an assistant principal's potential to perform as a principal is evident in the processes and products of their work, but they don't believe all high-potentials are necessarily ready to become principals. Shared leadership was instrumental to developing readiness for the principalship in their assistant principals, and developing capacity by building on strength and targeting weakness worked equally well in their experience. Using these findings and existing research, I identify state and district-level policy implications for the field. I also make recommendations for further study of this topic in the future. / text

Research on multi-agent systems performing cooperative tasks has received considerable attention in recent years. Because multiple agents perform cooperative tasks in close proximity, the coordination control of multiple agents to avoid collisions holds one of the critical keys to mission success. The potential function approach has been extensively employed for collision avoidance, but it has one inherent limitation of local minimum. This dissertation proposes a new avoidance strategy for the issue of local minimum. The primary objective of this research is to construct novel potential-function-based control schemes that drive agents from their initial to the goal configurations while avoiding collision with other agents and obstacles. The control schemes enable agents to avoid being trapped at a local minimum by forcing them to exit from the regions that may contain a local minimum. This dissertation consists of three studies, each of which has different technical assumptions. In the first study, all-to-all communication ability among agents is assumed. In addition, each agent is assumed to a priori know the location of all obstacles. In the second study, all-to-all communication ability is again assumed, but each agent is assumed to determine the location of obstacles using a sensor with a limited sensing range. In the third study, limited communication ability is assumed (i.e., each agent exchanges information only with agents within its limited communication range), and each agent is assumed to determine the location of the obstacles using its sensor with a limited sensing range. Relative to existing solutions, the new control schemes presented here have three distinct advantages. First, our avoidance strategy can provide cost-efficient solutions in applications because agents will never be trapped at a local minimum. Second, our control signals are continuous, which allows agents to change their speed in a realistic manner that is consistent with their natural motion traits. Finally, our control scheme allows for setting the upper bound of the velocity of each agent, which guarantees that the speed of agents will never exceed a maximum speed limit. / text

Creating 3D city models is a hot topic today. Achieving a well-defined 3D representation of urban environments requires large amounts of collected data combined with heavy processing of the data, both manually and automatically. The complexity makes it both expensive and time consuming to create accurate city models. An area which will truly benefit from well-defined city models is solar analysis. There are many tools available today for solar analysis but something all the tools have in common is that radiation calculations are very time consuming. The flexibility of the calculations in time and space domain are also below satisfaction. In this thesis a software was developed and included in a new methodology to go from high resolution elevation data to complete 3D environments. Solar radiation calculations were also implemented to be performed on the finished 3D buildings. The proposed method for radiation calculations is using the fact that the GPU handles some tasks better than the CPU and thereby reducing the calculation times. The results show that the finished 3D models are a relatively accurate representation of the real-life objects and they are well adapted for the purpose of radiation analysis. A validation of radiation calculations were also done using radiation sensors on modelled buildings. According to measured values the model seems to make a good estimation of clear-sky radiation. The calculation times are promising and there’s most probably room for further optimizations.

The use of artificial potential fields is beneficial in most two dimensional environments but they are bound by limitations. Introduction of the third dimension eradicates some of the limitations and brings about a set of new problems. If the emergent problems are solved then the new approach can give way to smarter helicopters and consequently a new game-play experience or possibly safer flight. This thesis aims to solve the emergent problems and proposes a new solution for guidance of autonomous helicopter agents in 3D games based on artificial potential fields. This new approach is compared to the most used alternative the A* pathfinding algorithm. Our experiments reveal that potential fields is a formidable alternative for navigation of helicopters. It can perform many times faster than the A* alternative and has lower rate of collision. / Neoaxis PFA

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Potential arsenic toxicity in different geologic environments is dependent on total arsenic concentration and arsenic bioavailability. It is important to identify the geologic environments that may sequester arsenic because these systems can act as long-term sources for arsenic as well as retard transport and limit toxicity. Bioavailability is defined as the readiness of a compound or element to be taken up by organisms (Gregorich et al., 2001), while potential bioavailability is possible uptake of a compound or element by organisms. The objective of this research is to quantify the potential bioavailability of arsenic in laboratory microcosms and in different geologic environments in the Nueces and San Antonio River Watersheds, Texas, using a chelating resin as an infinite sink. To assess the applicability of chelating resins to estimate potential arsenic bioavailability in the field, iron-loaded DOWEX M4195 resin was used to extract arsenic from solutions and sediments (pond sediment, river sediment, and ephemeral stream sediment). The average percentage of arsenic sorbed from solution was 66% ± 0.16. Competition studies between arsenate, phosphate, and vanadate suggest there is moderate competition, reducing overall arsenic sorption to the resin in the presence of competing ions. Iron-loaded resin was then exposed to sediment samples spiked with increasing amounts of arsenic over 15, 30, 60 and 90 days. Results of the sediment study showed 1) increased arsenic sorption to the resin over time, 2) small variations of potential bioavailable arsenic among geologically different sediments, and 3) evidence of arsenic sequestration. Field devices that housed iron-loaded resin were used to extract potentially bioavailable arsenic from sediment in six different geologic environments (i.e. lake, river, perennial stream, ephemeral stream, pond, and wetland) in the watersheds over a twenty-eight day period. The wetland (15.7 mmol As/g wet resin) and perennial stream sediments (11.0 mmol As/g wet resin) represented the maximal and minimal calculated potential bioavailability, respectively. However, the potentially bioavailable index calculated from mmol As/g wet resin extracted from field environments and mmol As/ g sediment in digested samples showed sequestration would be high in the wetland environment and high bioavailability in the perennial stream and river environments.

Alla elever i dagens skola, oberoende av inlärningskapacitet, skall ges likvärdiga möjligheter till progressivitet av befintliga kunskaper i det egna lärandet. Iakttagelser under bland annat VFU indikerade en problematik i enskilda lärares förmåga till att förse samtliga elever med kunskapsmässiga utmaningar. En förbigången elevgrupp utgjordes här av klassens snabba inlärare; elever med hög potential. Syftet med undersökningen har varit att ur ett lärarperspektiv, söka reda på fungerande arbetsmetoder för att nå och tillgodose samtliga elevers kunskapsmässiga behov i undervisningen. För att belysa aspekter, specifika ur yrkesverksamma lärares synvinkel, valdes en kvalitativ intervjumetod av semistrukturerad art för undersökningen. Undersökningens resultat baseras på en sammanställning av den information som erhölls under intervjuerna av fyra medverkande lärare. Resultatets utfall pekar på ett aktivt engagemang i arbetet med en individanpassad undervisning. Här framgår elevantalets påverkan på den individuella undervisningen, samt betydelsen av tillgång på aktuella läromedel, elevinflytande, samt alternativa studiemöjligheter och vikten av att utgå från IUP.