Experience in using a guide vane design with a “floating” lower bearing

Conclusion The use of the floating bearing of the vanes in the lower ring of the gate apparatus makes it possible to reduce the cycle and labor expenditures of manufacture at the plant and on assembly of the gate apparatus with a substantial improvement of the quality of assembly.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 4, pp. 45–47, April, 1984.     

Automated image analysis of Euglena gracilis Klebs (Euglenophyta) for measuring sublethal effects of three model contaminants

The short-term impacts of atrazine (herbicide), tributyltin (organometal) and copper on the behaviour of Euglena gracilis Klebs (Euglenophyta) were assessed. First, the ECOTOX automated image analysis system was used, which measured swimming velocity, cell shape, percentage of cells swimming upwards, and randomness of swimming. Next, visual observation by microscopy was used to measure percentage of cell motility and cell shape. Behavioural changes can be used as an indicator of stress in less than 24 h, potentially making them suitable for inclusion in early-warning systems for water quality. Findings indicate that E. gracilis is a very sensitive organism to copper, showing inhibition of motility with visual observation at 0.8 μmol/L within 1 h. The image analysis system was in general less sensitive than visual observation for detecting behavioural changes after incubation in copper. In contrast, after exposure to organic contaminants atrazine and tributyltin, the ECOTOX system detected small changes in the number of cells swimming upwards (antigravitactic behaviour) at higher concentrations.     

The use of NDVI and its Derivatives for Monitoring Lake Victoria’s Water Level and Drought Conditions

Normalized Difference Vegetation Index (NDVI), which is a measure of vegetation vigour, and lake water levels respond variably to precipitation and its deficiency. For a given lake catchment, NDVI may have the ability to depict localized natural variability in water levels in response to weather patterns. This information may be used to decipher natural from unnatural variations of a given lake’s surface. This study evaluates the potential of using NDVI and its associated derivatives (VCI (vegetation condition index), SVI (standardised vegetation index), AINDVI (annually integrated NDVI), green vegetation function (F _g ), and NDVIA (NDVI anomaly)) to depict Lake Victoria’s water levels. Thirty years of monthly mean water levels and a portion of the Global Inventory Modelling and Mapping Studies (GIMMS) AVHRR (Advanced Very High Resolution Radiometer) NDVI datasets were used. Their aggregate data structures and temporal co-variabilities were analysed using GIS/spatial analysis tools. Locally, NDVI was found to be more sensitive to drought (i.e., responded more strongly to reduced precipitation) than to water levels. It showed a good ability to depict water levels one-month in advance, especially in moderate to low precipitation years. SVI and SWL (standardized water levels) used in association with AINDVI and AMWLA (annual mean water levels anomaly) readily identified high precipitation years, which are also when NDVI has a low ability to depict water levels. NDVI also appears to be able to highlight unnatural variations in water levels. We propose an iterative approach for the better use of NDVI, which may be useful in developing an early warning mechanisms for the management of lake Victoria and other Lakes with similar characteristics.     

Effect of the outlet angle β2 on the characteristics of low specific-speed centrifugal pumps

Conclusions An experimental check of various low specific-speed pumps showed that on changing the geometry of the vaning of the impeller, in conformity with the recommendations [1], the main feature of which is an increase of the outlet angles of the vanes to values 90°₂130° and installation of short intermediate vanes in the passages between the main vanes, the head increases considerably without a decrease of pump efficiency.For centrifugal pumps with a volute and diffuser whose impellers have a different number of main vanes, the most rational is the installation of three intermediate vanes in each vane passage with a change in the direction of the flow by the main vane toward an increase of the outlet angle on diameter D₂=0.5–0.65D₃ for fecal pumps and pumps with short vanes.The use of the new impeller design is especially effective for high rotative-speed pumps. For multistage submersible pumps with a guide-vane apparatus at the inlet and axial outlet, the optimal variant is the installation of one intermediate vane with a start of the change in the flow direction D₃=0.63D₂.In conclusion, it is necessary to note that all tests were conducted without modifying the casing and branch pipes, which leaves room for a further increase of the head developed by pumps with the new type of impeller.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 5, pp. 21–25, May, 1982.     

Frictions, Heterogeneity and Optimality in Mortgage Modeling

The purpose of this article is to provide a unified framework for incorporating frictions into a theoretical options-pricing model (OPM) for mortgages. This article presents formulation for a frictions-adjustable mortgage model that integrates borrower heterogeneity while simultaneously preserving prepayment and default financial decisions. Our model demonstrates the flexibility of the OPM by simulating separate and concurrent effects of three categories of frictions on the mortgage and mortgage components. Researchers can use our example formulation to determine the effects of specific borrower characteristics on mortgage values without destroying the options theoretic framework.