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Remote Sensing and GIS for Nonpoint Source Pollution Analysis in the City of Dallas' Western Watersheds

Description: This report describes the findings of a study conducted on the watersheds of "Lake Lewisville, Lake Ray Roberts, Lake Grapevine and the Elm Fork of the Trinity River between Lake Lewisville and Frazier Dam," which are all part of the upper Trinity drainage basin (p. 31). The study examines the potential benefit of "remote sensing and geographic information systems (GIS) for watershed management" in and around Dallas, Texas (p. i).
Date: August 1988
Creator: University of North Texas. Department of Biological Sciences.
Partner: UNT College of Arts and Sciences

Remote Sensing and GIS for Nonpoint Source Pollution Analysis in the City of Dallas' Eastern Watersheds

Description: This report describes the findings of a study conducted on the Eastern Watersheds of Lake Lavon, Lake Ray Hubbard, Lake Tawakoni, Lake Palestine and Lake Fork, which are located within the Blackland Prairie, Post Oak Savannah and Pineywoods provinces. These watersheds are among nine that provide drinking water to Dallas, Texas. The study examines the potential benefit of "remote sensing and geographic information systems (GIS) for watershed management" in these five watersheds (p. iii).
Date: June 1989
Creator: University of North Texas. Department of Biological Sciences.
Partner: UNT College of Arts and Sciences

Structural study of Sr{sub 2}CuO{sub 3+delta} by neutron powder diffraction

Description: Average crystal structures of superconducting Sr{sub 2}CuO{sub 3+{delta}} synthesized at ambient pressure from a hydroxometallate precursor were refined from neutron powder diffraction data. A simplified model was used to fit the modulated superstructures. Both compounds have an oxygen deficient La{sub 2}CuO{sub 4}-type tetragonal T structure with O vacancies located in the CuO{sub 2} planes, not in the Sr{sub 2}O{sub 2} layers. This raises important questions about the superconductivity in Sr{sub 2}CuO{sub 3+{delta}} reported to be a 70 K superconductor.
Date: November 1, 1996
Creator: Shimakawa, Y.; Jorgensen, J.D.; Mitchell, J.F.; Hunter, B.A.; Shaked, S.; Hinks, D.G. et al.
Partner: UNT Libraries Government Documents Department

Suppression of superconductivity in orthorhombic La{sub 2-x}M{sub x}CuO{sub 4} (M = Ca,Sr)

Description: We have extended the calcium solid-solubility limit in La{sub 2{minus}x} Ca{sub x}CuO{sub 4} to x = 0.2 using synthesis at high oxygen pressure. The superconducting transition temperature increases with doping to 34 K at x = 0.15 and is suppressed for x > 0.15, similar to the Sr-substituted material. At a fixed doping level, the optimum superconducting properties (the highest {Tc}) are found for flat and square CuO{sub 2}planes.
Date: May 1, 1994
Creator: Dabrowski, B.; Wang, Z.; Jorgensen, J. D.; Hitterman, R. L.; Wagner, J. L.; Hunter, B. A. et al.
Partner: UNT Libraries Government Documents Department

Roles of oxygen defects in copper-oxide superconductors

Description: Oxygen vacancy and interstitial defects can have a profound effect on the superconducting compounds. Recent work on compounds such as La{sub 2}CuO{sub 4+x} new insight into the role of interstitial oxygen defects as a doping mechanism. Studies of (La,Sr,Ca){sub 3}Cu{sub 2}O{sub 6+x} with various metal compositions and metal-site ordering show that interstitial oxygen defects that form between the CuO{sub 2} layers in this structure systematically lower {Tc} and eventually destroy superconductivity. However, oxygen vacancies in the CuO{sub 2} planes have surprisingly little effect at concentrations below 3%. The infinite-layer compounds, ACuO{sub 2} where A=La, Sr, Ca, Nd, etc., in solid-solution combinations, offer a very environment for the formation of interstitial oxygen defects between the CuO{sub 2} planes. However, neutron diffraction experiments on Sr{sub 0.9}La{sub 0.1}CuO{sub 2} ({Tc}=42K) have not found any interstitial oxygen.
Date: April 1, 1993
Creator: Jorgensen, J. D.; Radaelli, P. G.; Shaked, H.; Wagner, J. L.; Hunter, B. A.; Mitchell, J. F. et al.
Partner: UNT Libraries Government Documents Department