Browsing by Subject "isolation"
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Item Biodegradation of triclosan by a triclosan-degrading isolate and an ammonia-oxidizing bacterium(Texas A&M University, 2007-09-17) Zhao, FumanTriclosan is incorporated in a wide array of medical and consumer products as an antimicrobial agent or preservative. Disposal of these products transport triclosan into wastewater and later into soils and surface waters. Due to incomplete removal of triclosan in wastewater treatment plants, contamination of triclosan in the environment has raised several concerns, including: (i) an aid to the development of cross-resistance to antibiotics, (ii) the toxicity to ecological health, (iii) the formation of chlorodioxins from triclosan and its metabolites. By using 14C-labeled triclosan, 14CO2 was observed in activated sludge samples, suggesting that triclosan was biodegraded. However, little is known about the microorganisms responsible for triclosan biodegradation in activated sludge. The goal of this study is to better understand biodegradation of triclosan in activated sludge. Two specific objectives are: (i) isolating and characterizing triclosan-degrading bacteria from activated sludge, (ii) characterizing the cometabolic degradation of triclosan through an ammonia-oxidizing bacterium Nitrosomonas europaea. A triclosan-degrading strain, KCY1, was successfully isolated from the activated sludge. The strain KCY1 completely degraded triclosan in three days when OD600 was 0.4. Based on 16S rRNA analysis, the strain KCY1 has 97% similarity with Phingomonas or Phingopyxis. Negative results of oxygenase activity assays suggested that other enzymes rather than oxygenases might be responsible for the triclosan biodegradation. Experiments using N. europaea showed that triclosan could be cometabolized. In the presence of inhibitor for ammonia monooxygenase (AMO), N. europaea was unable to degrade triclosan, suggesting that AMO might be responsible for triclosan degradation. Triclosan appeared to competitively inhibit ammonia oxidation by N. europaea. Results of this study showed that triclosan might be effectively biodegraded by triclosan-degrading cultures, strain KCY1 and N. europaea.Item Spatial attainment trends of racial and ethnic groups in Houston, Texas, 1970 to 2000(2009-05-15) Waren, WarrenPrevious research in the spatial assimilation of racial and ethnic groups has not assessed trends over time due to methodological difficulties and data limitations. I use an innovative method to assess the intercensal changes in neighborhood spatial attainment for African Americans, Hispanics, and non-Hispanic whites in Houston, Texas, between 1970 and 2000. I extend the current literature by showing that an accepted and commonly used method for assessing longitudinal change in spatial attainment is flawed and yields incorrect results. I highlight an alternative approach which makes use of data readily available in Census Summary Files to estimate individual-level spatial attainment regressions. I also show that the choice of neighborhood size affects estimates of spatial attainment effects. Although the influence of spatial scale has been demonstrated in the segregation literature, its consequences for spatial attainment research have not. I investigate and report findings from four geographic scales useful to and commonly used by spatial attainment researchers: the block group, the Census tract, the Zip Code Tabulated Area, and the Public Use Micro Data Area. I compare the benefits and drawbacks of estimating spatial attainment at each level of geography.Item Subsurface conductive isolation of refraction correlative magnetic signals (SCIRCMS)(Texas A&M University, 2004-11-15) Erck, Eric StephensonIsolation of terrestrially-observed magnetic signals by restoring their diffusive loss due to subsurface electrical conductivity sufficiently correlates these signals with those derived from the Alfven ionospheric electron movement of refraction variation. Temporary magnetic observatories were established on a conductive sedimentary basin (with a sampling interval of 5 s) and on a resistive large igneous intrusion (with a sampling interval of 10 s). Conventional modeling techniques estimate and remove the effects of the magnetometer, geomagnetic diurnal changes, whorls (solar quiet current vortices), and some bays from the acquired signals. Conventional one-dimensional skin depth modeling estimates the diffusive attenuation. The residual magnetic signal and the diffusive filter (as applied to the topography) become quantities in the linear system estimation of the geoelectric subsurface. Angular frequency domain least squares solution of the equations yields an isolated magnetic anomaly spectrum. Interpretive refinement, by selection of the zero or near zero curvature onset of either the spectrum's real or imaginary component, critically prepares the signal solution for correlation to a pseudomagnetic anomaly signal. This is an independently-derived sequence of anomalous values derived from Global Positioning System (GPS) refracted ranges. Detailed application of the Biot-Savart law provides independent anomaly signals to which the magnetic anomalies correlations show great correlation improvement by the isolation. These correlation improvements are from 2% to 83% and 9% to 91% for the sedimentary basin and from 2% to 96% and 24% to 78% for the igneous intrusion.