The purpose of this paper is to present a comparative study of marine bacteria, molds and actinomycetes in regard to their ability to degrade certain pure and mixed complex compounds possibly occurring in the lagoon waste traps of the Texas Gulf Coast. This comparison was made using a differential oxygen uptake as the index of specific compound utilization.

No description available.

Concentrations of dissolved organic carbon (DOC) measured within water bodies have been increasing on a global scale over the last two decades. Changes in temperature and rainfall have been shown to increase the production and export of DOC from catchments with peat soils in the UK (Freeman et al., 2001). However it is not clear whether increases in DOC concentrations are caused by production increases induced by temperature changes or by a greater incidence of high flows induced by rainfall changes. Increases in both temperature and rainfall have been predicted in Scotland over the next few decades (Kerr et al., 1999) which may further increase current DOC concentrations and exports. The implications of this include both a decrease in water quality and an increase in mobility of metals in upland water bodies. The overall aim of the thesis is to determine if the relationship between dissolved organic carbon (DOC) concentrations and discharge has changed over a 20 year period in small stream catchments in Scotland, in order to better understand the role of hydrology, in driving changes in DOC concentration. To achieve this streams draining two coniferous forest sites and one moorland site were monitored intensively between June 2004 and February 2006. Analysis of the relationship between DOC and discharge, within the catchments, identified the importance of the amount of precipitation falling on the catchment, antecedent precipitation and season, on the concentration of DOC that was measured within the stream. Models were then developed using variables to represent these drivers in terms of both the production (seasonal sine values and 14 day average temperatures) and movement (log of discharge (log Q), days since previous storm event and rising or falling stage) of DOC. In the Ochil Hills catchment, the best predictive model, used 4 hour average discharge and 1 day average 30cm soil temperatures (R2= 0.88). In the Duchray and Elrig catchments, the best predictive models produced used discharge and seasonal sine values; the strength of the model was greater in the Elrig (R2= 0.80) than the Duchray (R2= 0.48) catchment. The strength of the regression models produced highlighted the importance of precipitation in the movement of DOC to the stream and temperature variables representing production in the surrounding catchment. To determine if dissolved organic carbon (DOC) concentrations had changed within the three study catchments, since previous research was conducted at the same sites in the early 1980s and 1990s (Grieve, 1984a; Grieve, 1994), then regression analysis conducted in the previous research was repeated, so changes in the DOC and discharge relationship could be identified. Analysis of the Ochil Hills regression equations identified higher log of discharge and lower temperature and seasonal sine values in the present study (2004-06), when compared to the previous study (1982-83). This suggests that more DOC is now available for movement from the soil, and that the difference between winter and summer DOC production has decreased, potentially because of increasing temperatures. This would explain the limited increase in DOC concentration within the Ochil Hills stream. In the Duchray and Elrig streams, a large increase in DOC was identified at all discharges when all the models produced were compared between the two sampling periods (1989-90 and 2004-06). The increasing trend in DOC concentrations is too large to have been produced by change in temperature alone and it is suggested that the measured reduction in acidic deposition has resulted in the increased DOC concentrations measured in the Duchray and Elrig. The results from this research have identified that concentrations of DOC have increased in Scottish streams over the last 20 years and that the increases in DOC have been induced, potentially by temperature changes in climate. However, changes in temperature are not the only driver of this change as the reduction in acidic deposition is potentially more important, specifically in areas with base poor geology such as the Duchray and Elrig catchments.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / PURPOSE: To assess the long-term effect of a 2% aqueous chlorhexidine (CHX) solution on bond strength to artificially eroded dentin compared to sound dentin. MATERIALS AND METHODS: Flat mid-coronal dentin surfaces of extracted third molars (n = 28) were subjected only to grinding with a 600-grit SiC paper for 1 min (sound dentin S, n = 14) or additionally to erosive pH cycling with a cola-based soft-drink (eroded dentin E, n = 14). After acid etching, rinsing, and air drying, S and E were rehydrated with 1.5 μl of 2% CHX (S2%, n = 7; E2%, n = 7) or of distilled water (control SC, n = 7; EC, n = 7). Composite buildups were incrementally constructed with Filtek Z350 following Adper Single Bond 2 application. Specimens were sectioned into beams, which were subjected to microtensile testing immediately or after 6 or 12 months of aging. Fractured surfaces were observed under a digital microscope (50X magnification). Microtensile bond strength (μTBS) (MPa) was analyzed by three-way ANOVA and Tukey's tests (α = 0.05) and failure mode by the Kruskal-Wallis test (α = 0.05). RESULTS: Compared to sound dentin, eroded dentin was consistently related to lower μTBS. Immediately and after 12-month aging, the effect of CHX was insignificant, but it was significant after 6-month aging, when it conserved the bond strength to both eroded and sound dentin. The percentage of adhesive and mixed failures were equivalent, and significantly more frequent than cohesive failures, whether in dentin or in composite. CONCLUSION: The 2% CHX effect on bond strength conservation to both eroded and sound dentin was not found to be persistent. / Revisión por pares