Influences of land use/cover on water quality in the upper and middle reaches of River Njoro, Kenya

Data from 10 sampling sites along the River Njoro are used to examine the contribution of nutrients from upstream land uses draining each of the sampling sites. The data also are used to assess whether both the proportion of land uses and the size of the subwatersheds account for the variability in water quality in the River Njoro watershed. Geographical Information System analysis was used to determine the spatial distribution of land‐cover types and subwatersheds contributing run‐off to the sampling sites in the River Njoro. Standard Digital Elevation Model‐based routines were used to establish the watershed area contributing run‐off to each sampling site. Water and sediment samples were collected for chemical analysis, and the nutrient levels were related to the upstream land‐use types and the size of the subwatersheds. The mid‐stream portion of the River Njoro (near Egerton University) accounts for the highest nutrient contributions. The percentage contribution is magnified by additions from industrial, human settlements and agricultural land uses around the University. There is a significant decrease in nutrient levels downstream, however, indicating natural purification as the river flows through an area of large‐scale farming with intense, well‐preserved riparian and in‐stream vegetation. Steep slopes of the land upstream of Egerton University enhance erosion and nutrient losses from those subwatersheds. Mixed small‐scale agricultural and bare lands contribute over 55% of the phosphorus load to the upper and mid‐reaches of the River Njoro. The size of the subwatershed accounts for about 53% of the variability in the soluble phosphorus in the river. The land‐use subwatershed proportions are important for characterizing and modelling water quality in the River Njoro watershed. Upland land uses are as important as near‐stream land uses. We suggest that conservation of intact riparian corridor along the river and its tributaries contributes significantly to natural purification processes and recovery of the ecological integrity of the River Njoro ecosystem.     

Differential absorption lidar sensing of ozone

The differential absorption lidar (DIAL) technique for deriving O/sub 3/ profiles from lidar measurements is discussed. The US National Aeronautics and Space Administration's airborne DIAL system is described, and examples of a broad range of O/sub 3/ and aerosol measurements are presented from a number of field experiments. The airborne and ground-based DIAL measurements discussed demonstrate the outstanding capability of lidar for conducting O/sub 3/ investigations throughout the troposphere and lower stratosphere under widely different atmospheric conditions.<>     

Numerical investigation of DQMoM-IEM as a turbulent reaction closure

This paper investigates a mean reaction rate closure for turbulent reacting flows called the Direct Quadrature Method of Moments using the Interaction by Exchange with the Mean micromixing model (DQMoM-IEM). The method was first introduced for reacting flows by Fox (Computational Models for Turbulent Reacting Flows, Cambridge University Press, 2003). We present a systematic study that considers several important new aspects of the method. In particular we introduce a new analytic expression for the DQMoM-IEM source terms. We present a rigourous numerical investigation and discuss problems of boundedness and singularity in detail. We introduce a filter function to overcome these issues in the general case and present analytic integrals for special cases of specific terms. We extend the methodology to take advantage of these developments and show details of the implementation in a commercial computational fluid dynamics (CFD) code. We present an extensive set of numerical experiments and validation. The method is proven for a problem known from the literature which includes an isothermal dimerisation process. Experimental and transported probability density function (PDF) data compare reasonably well. The method is discussed critically and areas for further research are suggested to make the method more practical.     

生态景观设计40年

本文简要总结了英国生态景观设计的历史,阐述了在景观设计中如何纳入生态设计原则。通过对位于爱丁堡郊区里卡顿的一所新大学校园的规划与建设的案例研究,阐明了生态景观理论在景观设计中的实践。     

Torsion und Querbiegung in Plattenbrücken,gegebenenfalls mit einbetonierten Stahlträgern (WIB‐Bauweise)

Torsion und transverse bending in plate bridges, also those containing cast‐in steel beams (WIB‐construction). In usual reinforced‐concrete plate bridges, torsion and transverse bending are superfluous for equilibrium. These secondary moments depend on the assumed stiffness and will be unnecessarily overestimated in a homogeneous elastic analysis without consideration of cracking. This results in excessive transvers reinforcement, particularly for railroad bridges containing cast‐in steel beams. Apparently paradoxical aspects of the plate twisting moment are clarified. This facilitates insight into modeling plates by gridworks. Procedures to determine the strain‐induced stress in the transverse reinforcement are described.     

Manuelle Vordimensionierung von Stahlbetonbrücken

Manual predesign of reinforced‐concrete bridges. Despite the extensive requirements of the “DIN ‐Fachberichte” 101 and 102 it is possible to predesign a common reinforced‐concrete bridge in almost all its details via simple manual calculations and then to verify its sufficiency subsequently with a minimum of electronic analysis. A few rules of thumb serve to fulfil implicitly many computationally‐involved norm criteria and to take into account temperature strain in statically indeterminate cases.     

NASA multipurpose airborne DIAL system and measurements of ozone and aerosol profiles

An airborne differential absorption lidar (DIAL) system has been developed for the remote measurement of gas and aerosol profiles in the troposphere and lower stratosphere. The multipurpose DIAL system can operate from 280 to 1064 nm for measurements of ozone, sulfur dioxide, nitrogen dioxide, water vapor, temperature,pressure, and aerosol backscattering. The laser transmitter consists of two narrow linewidth Nd: YAG pumped dye lasers with automatic wavelength control. The DIAL wavelengths are transmitted with a 00-,usec temporal separation to reduce receiver system complexity. A coaxial receiver system is used to collect and optically separate the DIAL and aerosol lidar returns. Photomultiplier tubes detect the backscattered laser returns after optical filtering, and the analog signals from three tubes are digitized and stored on high-speed magnetic tape. Real-time gas concentration profiles or aerosol backscatter distributions are calculated and displayed for experiment control. Operational parameters for the airborne DIAL system are presented for measurements of ozone, water vapor, and aerosols in the 290-, 720-, and 600-nm wavelength regions, respectively. The first ozone profile measurements from an aircraft using the DIAL technique are discussed in this paper. Comparisons between DIAL and in situ ozone measurements show agreement to within +/-5 ppbv in the lower troposphere. Lidar aerosol data obtained simultaneously with DIAL ozone measurements are presented for a flight over Virginia and the Chesapeake Bay. DIAL system performance for profiling ozone in a tropopause folding experiment is evaluated, and the applications of the DIAL system to regional and global-scale tropospheric investigations are discussed.     

A coupled CFD-population balance approach for nanoparticle synthesis in turbulent reacting flows

This paper investigates the first part of a two-stage methodology for the detailed fully coupled modelling of nanoparticle formation in turbulent reacting flows. We use a projected fields (PF) method to approximate the joint composition probability density function (PDF) transport equation that describes the evolution of the nanoparticles. The method combines detailed chemistry and the method of moments with interpolative closure (MoMIC) population balance model in a commercial computational fluid dynamics (CFD) code. We show details of the implementation and present an extensive set of numerical experiments and validation. We consider the example of the chloride process for the industrial synthesis of titania. We show good agreement with experimental data and present fully coupled detailed chemistry CFD simulations of nanoparticle formation in a representative ‘slot’ reactor geometry. The simulations show that inception occurs in a mixing zone near the reactor inlets. Most of the nanoparticle mass is due to surface growth downstream of the mixing zone with a narrower size distribution occurring in the regions of higher surface growth. The predicted temperature and particle properties are compared to a perfect mixing case. The implications for the second part of the methodology, where it is proposed to post-process the data using a more detailed particle model, are discussed critically.