Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains v, 298 p. Includes abstract. Includes bibliographical references (p. 286-298).

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The Ida B. Wells Homes, the first black-occupied housing project built in Chicago, were completed in 1941. Throughout their construction and inhabitation, the black community in Chicago worked to create a self-contained space which would control the visibility/invisibility of its black inhabitants and, symbolically, the black community as a whole. Taking as theoretical grounding Katherine McKittrick’s work on garreting and Susan Lepselter’s work on license, this essay argues that the Ida B. Wells Homes were a South Side garret for the black community, a space in which freedom became defined by its own boundaries and wherein this freedom could work in tandem with dominant geographies of oppression to construct a “different” geographic story. This “different” geography intended to alter perceptions of black life by working against dominant geographic narratives that were prevalent at the time, such as those put forth by the Chicago School of Sociology. / text

In gas-condensate reservoirs, gas productivity declines due to the increasing accumulation of liquids in the near wellbore region as the bottom-hole pressure declines below the dew point pressure. This phenomenon occurs even in reservoirs containing lean gas-condensate fluid. Various methods were addressed to remediate the productivity decline, for example, fracturing, gas injection, solvent injection and chemical treatment. Among them, gas injection techniques have been used as options to prevent retrograde condensation by vaporizing condensate and/or by enhancing condensate recovery in gas-condensate reservoirs. It is of utmost importance that the behavior of liquid accumulation near the wellbore should be described properly as that provides a better understanding of the productivity decline due to the originated from impaired relative mobility of gas. In this research, several gas injection techniques were assessed by using compositional simulators. The feasibility of different methods such as periodic hot gas injection and gas reinjection using horizontal wells were assessed using different reservoir fluid and injection conditions. It is shown that both the temperature and composition of the injection fluids play a key role in the remediation of productivity and condensate recovery. The combined effect of these parameters were investigated and the resulting impact on gas and condensate production was calculated by numerical simulations in this study. Design parameters pertaining to field development and operations including well configuration and injection/production scheme were also investigated in this study along with the above parameters. Based on the results, guidelines on design issues relating gas injection parameters were suggested. The various simulation cases with different parameters helped with gaining insight into the strategy of gas injection techniques to remediate the gas productivity and condensate recovery. / text

Gas wells suffer a decrease in productivity because of the formation of a liquid hydrocarbon “condensate” in the near wellbore area. This "condensate" forms near producing wells when the flowing pressure is below the reservoir fluid's dew point. Several methods have been shown to temporarily alleviate this problem, but eventually the condensate bank reforms and the productivity again decreases. The use of surfactants to alter the near wellbore wettability to neutral wetting is a potential longer term solution to liquid blocking in these reservoirs. This alteration increases the gas and liquid relative permeabilities and thereby the productivity by reducing the residual liquid saturation. This enhancement allows the accumulated liquid to flow and is durable as long as the wettability alteration is persistent. This solution has been shown to be successful through core flood experiments and field trials in high permeability sandstones, but no improvements had been observed in low permeability cores. As the global demand for energy increases, the petroleum industry has begun to develop unconventional (low permeability) assets, new techniques are needed to maintain and improve their productivity. Liquid blocking in these wells can have a much larger impact on both the gas and condensate production in such low permeability formations. Applying this technique increases both gas and condensate mobility and should increase the economic producing life of these wells. Core flood experiments were conducted to investigate the ability of a chemical treatment to alter the wettability of low permeability sandstones. Previous experimentation did not find any improvement because the increased capillary forces prevented the treatment solution from being easily displaced. This concealed the benefit achieved when the wettability was altered. These experiments recorded smaller relative permeability increases compared to higher permeability core floods, so super critical carbon dioxide was tested as an alternative solvent. While the new treatment was more injectable, it was not as successful at altering wettability. Progress has been made on a solution to liquid blocking in low permeability sandstones, but additional research needs to be completed to further optimize this method. / text

There are many complications associated with abnormally high fluid pressures in overpressured formations. Pore pressure can directly influence all parts of operations including drilling, geological studies, completion, and production. Accurate predictions of pore pressure and fracture pressure are vital aspects to the production and completion of safe, time efficient, and cost efficient projects. Knowledge of pressure distribution in the formation can greatly reduce complexities associated with drilling and completing a well. A three-method pore pressure and fracture pressure study was performed on two prospect deepwater wells located in the Gulf of Mexico. More than thirty offset wells in the greater region were initially analyzed for similarities with the two prospect wells. In the final analysis, only six wells were used to create pore pressure and fracture pressure models due to inconsistencies in similarities or lack of usable data in many of the offset wells. Pore pressure and fracture pressure models were constructed for the offset wells, and then applied and calibrated for the two prospect wells using drilling data such as mud weights, MDTs (Modular Dynamic Testing), and LOTs (Leak-off Test). Three types of pore pressure and fracture pressure models were used in the study: Eaton’s deep resistivity method; Eaton’s acoustic sonic method; and Bower’s interval seismic velocity method. Pore pressure and fracture pressure prediction was complicated by abnormal pressure in the formation due to undercompaction and seals. Both prospects were located in a deep subsalt environment. Low permeability and traps prevents fluid from escaping as rapidly as pore space compacts thus creating overpressure. Drilling through salt in deep water is expensive and risky. Elevated pore pressure and reduced fracture pressure underneath salt seals can create very tight mud weight windows and cause many drilling problems, as seen in the results of the offset wells’ pore pressure and fracture pressure models. Results indicate very small pore pressure and fracture pressure windows, or mud weight windows, because of overpressures in the formation caused by such a deep subsalt environment. Many casing points were needed in the final casing design of prospect wells to accommodate the smaller mud weight windows. Pore pressure has the most significant increase immediately below the salt, while the mud weight window remained constant or decreased with depth. The average mud weight window ranged between 1 to 2 pounds per gallon below the salt. / text

Στη διπλωματική εργασία αυτή μελετάμε αναλυτικά και υπολογιστικά το φαινόμενο της μίξης τεσσάρων κυμάτων σε δια-υποζωνικές μεταβάσεις ενός συστήματος που αποτελείται από δομές συμμετρικών ημιαγώγιμων κβαντικών πηγαδιών. Στο θεωρητικό μοντέλο παίρνουμε υπόψη δύο υποζώνες ενός ημιαγώγιμου κβαντικού πηγαδιού που αλληλεπιδρούν ταυτόχρονα με ένα ισχυρό ηλεκτρομαγνητικό πεδίο (πεδίο σύζευξης) καθορισμένης συχνότητας και ένα ασθενές ηλεκτρομαγνητικό πεδίο (πεδίο ιχνηθέτη) μεταβλητής συχνότητας. Περά από τη σύμφωνη αλληλεπίδραση των ηλεκτρομαγνητικών πεδίων με τα κβαντικά πηγάδια στη θεωρία μας συμπεριλαμβάνουμε και τα φαινόμενα των αλληλεπιδράσεων ηλεκτρονίου-ηλεκτρονίου. Για την περιγραφή της δυναμικής του συστήματος χρησιμοποιούμε τις εξισώσεις του πίνακα πυκνότητας που προκύπτουν, κάτω από κατάλληλες παραδοχές, από τις γενικευμένες μη-γραμμικές εξισώσεις Bloch. Οι εξισώσεις αυτές επιλύονται αριθμητικά για μια συγκεκριμένη δομή διπλού ημιαγώγιμου κβαντικού πηγαδιού GaAs/AlGaAs στην οποία μεταβάλλουμε την επιφανειακή πυκνότητα ηλεκτρονίων. Παρουσιάζουμε αποτελέσματα και για συνεχή και για παλμικά ηλεκτρομαγνητικά πεδία και δείχνουμε ότι τόσο η ένταση όσο και η μορφή του φάσματος της μίξης τεσσάρων κυμάτων εξαρτάται σημαντικά από την επιφανειακή πυκνότητα ηλεκτρονίων, τη συχνότητα και την ένταση του πεδίου σύζευξης, και στην περίπτωση των παλμικών πεδίων από τη σειρά της χρονικής επιβολής των παλμών. / In this diploma thesis we study analytically and numerically the phenomenon of four-wave mixing in intersubband transitions of a symmetric double quantum well structure. In the theoretical model we consider two quantum well subbands that are coupled by a strong coupling electromagnetic field with fixed frequency and a weak probe electromagnetic field with varying frequency. We consider the coherent interaction of the electromagnetic fields with the quantum wells taking into account the effects of electron-electron interactions. For the description of the system dynamics we use the density matrix equations obtained from the generalized nonlinear Bloch equations. These equations are solved numerically for a realistic semiconductor quantum well structure GaAs/AlGaAs with varying electron sheet density. We present results for both continuous and pulsed electromagnetic fields and show that both the intensity and the shape of the four-wave mixing spectrum can be significantly dependent on electron sheet density, on the frequency and the intensity of the coupling field, and in the case of pulsed fields on the delay between the fields.

Research report on the dynamics of nitric compounds in different water levels of shallow wells, located in Pypliai, Kaunas District, is given in the thesis. Subject of research – water quality indicators: nitrates (NO3-), nitrites (NO2-) and ammonium (NH3). Aim of research – to define variation of nitrates concentrations in different water levels of shallow wells. Methodology: analysis of scientific literature; chemical water quality analyzes methods: spectral and electrochemical methods; statistical analysis using EXCEL, STATISTICA programs. Results of research: the results of scientific research showed, that nitrates concentrations in deeper levels of shallow wells vary differently; the tendencies of these variations depend on seasons. Seasons make no impact to nitrites and ammonium concentrations in deeper levels of shallow wells. The following statistically relevant water indicators were determined to influence nitrate concentration in shallow well water: oxygen quantity and electrical conductivity. Nitrite concentrations are inversely proportional to oxygen amount. Ammonium concentrations depend on organic compound quantity. Statistically relevant links between nitrites and ammonium were estimated.

Disertacija skirta krūvininkų rekombinacijos tyrimams plačiatarpiuose nitridiniuose puslaidininkiuose bei jų dariniuose. Kompleksiniai eksperimentiniai tyrimai buvo atlikti naudojant kelias skirtingas metodikas. Atlikti krūvininkų dinamikos GaN sluoksniuose tyrimai labai žemų ir aukštų sužadinimų sąlygomis. Pasiūlytas naujas liuminescencijos gesimo kinetikų interpretavimo metodas, siejant liuminescencijos ir šviesa indukuotų dinaminių gardelių kinetikas. Naujas požiūris į geltonosios liuminescencijos juostą GaN sluoksniuose leido susieti geltonosios liuminescencijos intensyvumą su krūvininkų gyvavimo trukme. Skirtingomis technologijomis augintų AlGaN sluoksnių palyginimas suteikė informacijos apie juostos potencialo fliuktuacijas bei krūvininkų gyvavimo trukmę ribojančius veiksnius AlGaN medžiagose. Atskleista naujų krūvininkų dinamikos daugialakštėse AlGaN/AlGaN kvantinėse duobėse ypatumų – vidinio elektrinio lauko bei kvantinės duobės pločio fliuktuacijų sąlygotos lokalizacijos įtaka krūvininkų dinamikai. Dauguma tirtų bandinių buvo auginti naudojant MEMOCVDTM technologiją ir tyrimai patvirtino šios technologijos potencialą siekiant pagerinti medžiagų kokybę. / The thesis is dedicated to carrier recombination investigations in wide-band-gap semiconductors and their structures. The complex experimental studies were performed by combining several different techniques. Carrier dynamics in GaN epilayers were investigated under extremely low and high excitation conditions. A new method for interpreting photoluminescence decay kinetics was suggested by interrelating luminescence and light-induced grating decay transients. The new approach for studies of yellow band in GaN was shown by linking the carrier lifetime with yellow band intensity. Two AlGaN epilayers grown by different novel growth techniques were compared and the factors limiting carrier lifetime were identified. Moreover, more evidence on alloy mixing and band potential fluctuations in AlGaN was provided by our study. Essential knowledge was attained about carrier dynamics in high-Al-content AlGaN/AlGaN multiple quantum well structures: the influence of built-in electric field and carrier localization on carrier dynamics. Most of the samples under study were grown by MEMOCVDTM growth technique, and our study confirmed the high potential of this innovative growth technique for improving material quality.