Nutrient Limitation of Periphyton in a Spring-Fed, Coastal Stream in Florida, USA.

There is strong evidence to suggest that ground-water nitrate concentrations have increased in recent years and further increases are expected along portions of the central Gulf coast of Florida. Much of the nitrate enriched groundwater is discharged into surface waters through numerous freshwater springs that are characteristic of the area and the potential for eutrophication of their receiving waters is a legitimate concern. To test the potential effects of elevated nutrient concentrations on the periphyton community an in situ nutrient addition experiment was conducted in the spring-fed Chassahowitzka River, FL, USA, during the summer of 1999. Plastic tubes housing arrays of glass microscope slides were suspended in the stream. Periphyton colonizing the microscope slides was subjected to artificial increases in nitrogen, phosphorus or a combination of both. Slides from each tube were collected at 3- to 4- day intervals and the periphyton communities were measured for chlorophyll concentration. The addition of approximately 10 μg/L of phosphate above ambient concentrations significantly increased the amount of periphyton on artificial substrates relative to controls; the addition of approximately 100 μg/L of nitrate above ambient concentrations did not. The findings from this experiment implicated phosphorus, rather than nitrogen, as the nutrient that potentially limits periphyton growth in this system.(PDF contains 4 pages.

High-temperature gas stream filter and method

The present invention relates generally to the removal of solid particulate material from high-temperature gas streams, and more particularly the removal of such particulate material by employing a barrier filter formed of a carbon-carbon composite provided by a porous carbon fiber substrate with open interstitial regions between adjacently disposed carbon fibers selectively restricted by carbon integrally attached to the carbon fibers of the substrate. In a typical utilization of a particulate-bearing hot gas stream, the particulate loading of the gas stream after cleaning is normally less than about 50 ppm and with essentially no particulates larger than about 10 microns. This carbon-carbon filter for removing particulate material of a particle size larger than a preselected particle size from a gas stream at a temperature greater than about 800 F, is produced by the steps which comprise: providing a substrate of carbonaceous fibers with pore-forming open interstitial regions between adjacently disposed fibers; and, sufficiently filling these open interstitial regions with carbon integrally attached to and supported by the fibers for providing the interstitial regions with throughgoing passage-ways of a pore size sufficient to provide for the passage of the gas stream while preventing the passage of particulate material larger than a preselected particle size

Commercial Gasifier for IGCC Applications Study Report

This was a scoping-level study to identify and characterize the design features of fixed-bed gasifiers appearing most important for a gasifier that was to be (1) potentially commercially attractive, and (2) specifically intended for us in integrated coal gasification/combined-cycle (IGCC) applications. It also performed comparative analyses on the impact or value of these design features and on performance characteristics options of the whole IGCC system since cost, efficiency, environmental traits, and operability -- on a system basis -- are what is really important. The study also reviewed and evaluated existing gasifier designs, produced a conceptual-level gasifier design, and generated a moderately advanced system configuration that was utilized as the reference framework for the comparative analyses. In addition, technical issues and knowledge gaps were defined. 70 figs., 31 tabs

Multifunctional photo/thermal catalysts for the reduction of carbon dioxide

The photochemical fixation of CO2 to energy rich products for solar energy storage or feedstock chemicals is an attractive, albeit daunting, challenge. The overall feasibility of CO2 conversion is limited by the availability of efficient photo-active materials that meet the energetic requirements for CO2 reduction and are optically matched to the solar spectrum. Surface modification of TiO2 with earth abundant metal oxides presents one approach to develop visible active photocatalysts through band gap narrowing, while providing catalytic sites to lower the activation energy for CO2 reduction. In this work density functional theory was used to model the effect of surface modification of rutile and anatase using MnOx nanoclusters. The results indicate the formation of inter-band gap states following surface modification with MnOx, but surface water can change this. Oxygen vacancies are predicted to form in supported MnOx and the interaction with CO2 was investigated. MnOx-TiO2 was synthesized and characterised using surface analytical methods and photoelectrochemistry. The interaction of CO2 with the materials under irradiation was probed using in-situ FTIR to interrogate the role of oxygen vacancies in CO2 binding and reaction. These results provide insights into the requirements of a multifunctional catalyst for CO2 conversion

Direct Visualization of Independent Ta Centers Supported on Two-Dimensional TiO2 Nanosheets

Highly-dispersed, supported oxides are ubiquitous solid catalysts, but they can be challenging to characterize with atomic precision. Here it is shown that crystalline anatase TiO2 nanosheets (~5 nm thick) are ideal supports for imaging highly-dispersed active sites. Ta cations are deposited by several routes, and high-resolution high angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) is used to determine the location of Ta with respect to the TiO2 lattice and to quantify Ta-Ta distances. In the best case, it is shown that >80% of Ta atoms are isolated from one another, whereas other techniques are blind to this critical catalytic property or give only qualitative estimates. TiO2 nanosheets may prove to be a useful platform for other types of catalysis studies

Role of surface reconstruction on Cu/TiO2 nanotubes for CO2 conversion

Carbon dioxide hydrogenation to CO via the reverse water gas shift (RWGS) reaction is one route to integrate CO2 utilization into the chemical industry. TiO2 supported Cu catalysts are known to be active for RWGS, but Cu is shown here to behave differently on TiO2 nanotubes (TiNT) vs TiO2 nanoparticles (TiNP). Whereas nanoparticle supports give low rates that are hardly changed by added Cu, the nanotube supports yield much higher activity and three distinct behaviors as the Cu surface density increases. At low surface densities (0.3 Cu/nm2), active Cu-O-Ti sites are created that have low apparent activation energies. At high surface densities (6 Cu/nm2), Cu nanoparticles on TiNT are formed, and reaction barriers are lowered when both Cu and TiNT surfaces are accessible. At intermediate surface densities, metallic Cu domains are engulfed by a TiOx overlayer formed during H2 pretreatment, akin to those formed by classical strong metal support interactions (SMSI). These reduced layers are markedly more active for RWGS than the initial TiNT surfaces, but have similar activation barriers, which are higher than those for which both Cu and TiNP surfaces are exposed. These catalytic findings are supported by computational modeling, in situ IR, UV–vis, and X-ray absorption spectroscopies, and they provide insight into an important reaction for CO2 utilization

Dimensions of global population projections: what do we know about future population trends and structures?

The total size of the world population is likely to increase from its current 7 billion to 8–10 billion by 2050. This uncertainty is because of unknown future fertility and mortality trends in different parts of the world. But the young age structure of the population and the fact that in much of Africa and Western Asia, fertility is still very high makes an increase by at least one more billion almost certain. Virtually, all the increase will happen in the developing world. For the second half of the century, population stabilization and the onset of a decline are likely. In addition to the future size of the population, its distribution by age, sex, level of educational attainment and place of residence are of specific importance for studying future food security. The paper provides a detailed discussion of different relevant dimensions in population projections and an evaluation of the methods and assumptions used in current global population projections and in particular those produced by the United Nations and by IIASA

Socioeconomic fertility differentials in a late transition setting: A micro-level analysis of the Saguenay region in Quebec

Background: Historically, the French Canadian population of Quebec, Canada, is known for its high fertility, which lasted well into the 20th century, and for its late fertility transition. Within Quebec, regions such as Saguenay are known for having experienced an even more delayed fertility transition. Objective: In Quebec, as elsewhere, various factors modulated the transition, and differential behaviors and timing can be observed across socioeconomic groups. These factors are studied here in the context of the Saguenay region, where particularly rich data are available. The region was mostly rural at first, but industrialization and urbanization occurring since the beginning of the 20th century allow us to study socioeconomic reproductive differentials before and during the transition. Methods: To do so, we rely on the BALSAC database, which contains all church and civil records from the onset of colonization around 1840 up to 1971. In addition to the usual descriptive statistics, we use Cox models to analyze the probability of having a first birth and higher order births among four socioeconomic groups defined with HISCLASS coding. Results: The results demonstrate the late timing of the transition and a clear progression from the non-manual and skilled workers, who show the first signs of declining fertility during the 1930s, to the farmers, who do the same only at the end of the 1950s. As a result, socioeconomic fertility differentials widened during the transition period. Conclusions: Even in a context where the transition was significantly delayed compared to most other regions studied in this issue, some socioeconomic differentials were observed prior to the transition, and they widened during the transition due to the differential progression of contraceptive practices among couples