Monitoring and statistical modelling of sedimentation in gully pots.

Gully pots are essential assets designed to relief the downstream system by trapping solids and attached pollutants suspended in runoff. This study applied a methodology to develop a quantitative gully pot sedimentation and blockage model. To this end, sediment bed level time series from 300 gully pots, spanning 15 months, were collected. A generalised linear mixed modelling (GLMM) approach was applied to model and quantify the accumulation of solids in gully pots and to identify relevant physical and catchment properties that influence the complex trapping processes. Results show that the retaining efficiency decreases as sediment bed levels increase. Two typical silting evolutions were identified. Approximately 5% of all gully pots experienced progressive silting, eventually resulting in a blockage. The other gully pots show stabilising sediment bed levels. The depth of the sand trap, elapsed time since cleaning and the road type were identified to be the main properties discriminating progressive accumulation from stabilising sediment bed levels. Furthermore, sediment bed levels exhibit no residual spatial correlation, indicating that the vulnerability to a blockage is reduced as adjacent gully pots provide a form of redundancy. The findings may aid to improve maintenance strategies in order to safeguard the performance of gully pots.

Settlement as a driver for sewer rehabilitation.

This paper assesses the influence of (differential) settlement on sewer system functioning. Based on historical data of the vertical position of sewer invert levels, tilt measurements and in-sewer inspection videos, settlement and settlement related influences are analyzed for a case study area in Amsterdam. The average settlement rate of this system was 4 mm/year. Given this settlement rate, it is shown that settlement significantly influences sewer system functioning within the lifetime of a sewer (system).

Assessing characteristic time and space scales of in-sewer processes by analysis of one year of continuous in-sewer monitoring data.

Long-term and high-frequency in-sewer monitoring opens up a broad range of possibilities to study (influences on) water quantity and quality variations. Using data from the Eindhoven wastewater system in The Netherlands both dry weather flow and wet weather flow situations have been studied. For approximately 160 dry weather days mean diurnal variations of flow and pollutant concentrations have been derived. For wet weather situations (≈ 40 storm events) peak load factors have been studied. Generally, peak load factors for all considered pollutant parameters are larger than one. Peak load factors for particulate matter are larger than for dissolved constituents. Also, the smallest catchment area consistently shows the largest mean peak factors and vice versa.

Fault tree analysis for data-loss in long-term monitoring networks.

Prevention of data-loss is an important aspect in the design as well as the operational phase of monitoring networks since data-loss can seriously limit intended information yield. In the literature limited attention has been paid to the origin of unreliable or doubtful data from monitoring networks. Better understanding of causes of data-loss points out effective solutions to increase data yield. This paper introduces FTA as a diagnostic tool to systematically deduce causes of data-loss in long-term monitoring networks in urban drainage systems. In order to illustrate the effectiveness of FTA, a fault tree is developed for a monitoring network and FTA is applied to analyze the data yield of a UV/VIS submersible spectrophotometer. Although some of the causes of data-loss cannot be recovered because the historical database of metadata has been updated infrequently, the example points out that FTA still is a powerful tool to analyze the causes of data-loss and provides useful information on effective data-loss prevention.

Probabilistic modeling of sewer deterioration using inspection data.

Accurate prediction of current and future conditions of sewer systems is crucial to manage the sewer system wisely, cost-effectively and efficiently. The application of historical databases of visual inspection data to sewer deterioration modeling seems common sense. However, in The Netherlands, sewer inspection data is only used to determine the direct need for rehabilitation. This paper outlines the possibilities of using inspection data for deterioration modeling and discusses the problems encountered. A case study was performed on the modeling of the condition aspect 'surface damage by corrosion or mechanical action' using a Markov model.

Prediction uncertainty of environmental change effects on temperate European biodiversity.

Observed patterns of species richness at landscape scale (gamma diversity) cannot always be attributed to a specific set of explanatory variables, but rather different alternative explanatory statistical models of similar quality may exist. Therefore predictions of the effects of environmental change (such as in climate or land cover) on biodiversity may differ considerably, depending on the chosen set of explanatory variables. Here we use multimodel prediction to evaluate effects of climate, land-use intensity and landscape structure on species richness in each of seven groups of organisms (plants, birds, spiders, wild bees, ground beetles, true bugs and hoverflies) in temperate Europe. We contrast this approach with traditional best-model predictions, which we show, using cross-validation, to have inferior prediction accuracy. Multimodel inference changed the importance of some environmental variables in comparison with the best model, and accordingly gave deviating predictions for environmental change effects. Overall, prediction uncertainty for the multimodel approach was only slightly higher than that of the best model, and absolute changes in predicted species richness were also comparable. Richness predictions varied generally more for the impact of climate change than for land-use change at the coarse scale of our study. Overall, our study indicates that the uncertainty introduced to environmental change predictions through uncertainty in model selection both qualitatively and quantitatively affects species richness projections.

Regional cerebral blood flow in schizophrenics. Tests using the xenon Xe 133 inhalation method.

Measurements of intrahemispheric and bilateral regional cerebral blood flow (CBF) for gray and white matter were compared in 29 schizophrenic patients and 22 normal controls, using the xenon Xe 133 inhalation method. Results showed significantly lower CBF values for all brain regions in the schizophrenic group, and post hoc comparisons showed relatively greater reduced gray-matter CBF values in the anterior areas of the brain. There was also a left-hemisphere frontal loss similar to that reported previously, although it was in the context of a generalized loss in anterior functioning. Interhemispheric comparison within both groups showed no differences between homologous regions for gray matter, and greater white-matter CBF values in the right hemisphere than in the left hemisphere. The findings support a hypothesis of a bilateral anterior deficit in schizophrenia.

Red blood cell volume in preterm neonates.

In the high-risk neonate, the direct determination of the red cell volume by radionuclide dilution technique appears to be the singularly definitive method of defining treatment efficacy, and is thus a useful evaluation and management tool for the pediatrician. For effective patient management, the red blood cell(RBC) volume of 69 preterm and term neonates was determined. The method utilized, Tc-99m-labeled RBCs, provided a fast and accurate answer with a large reduction in the absorbed radiation dose. In the population studied within a high-risk newborn ICU, the mean RBC volumes between the preterm and term neonates were without significant difference. Grouping and analysis of the RBC volume data with respect to birth weight, gestational ages, and 1- and 5-minute Apgar scores revealed on statistical difference. The mean value found in our population, 32.2 +/- 9.2 ml/kg, however, does differ from those previously reported in which the determinations were made using an indirect estimation from the plasma compartment.

Evaluation and testing of in vitro labeled technetium Tc-99m red blood cells in two animal models for neonatal RBC volume determinations.

The present study was designed to evaluate the red blood cell (RBC) radiolabeling technique utilizing the short half-lived radionuclide technetium-99m and to compare the results with the well-recognized standard chromium-51 method. The procedure was evaluated in a canine and a newborn lamb model utilizing dual radionuclide labeling and counting techniques. With the express purpose of providing a significant radiation dose reduction, the procedure presented was adapted for utilization in a neonatal patient population. Statistical analysis of the data revealed that there was no significant difference in the radiolabeling efficiency for the two methods (Cr-51, 86.6%; Tc-99m, 92.4%). Assessment of the in vitro stability for technetium-99m RBCs showed that less than a 4% loss of radiolabel from the RBC was seen in a 4-hr time span in the canine model (15 min, 90.5%; 2 hr, 88.9%; 4 hr, 86.6%) when compared to the 15 min equilibrium sample. Evaluation of newborn lamb RBC volumes showed that the technetium-99m RBC volume did not significantly differ from the chromium-51 labeling technique (Cr-51, 24.0 ml/kg; Tc-99m, 23.2 ml/kg). Summarization of the whole-body radiation dose showed that greater than a 30-fold reduction in absorbed dose was achieved in the newborn (Cr-51, 30.0 mrad; Tc-99m, 0.9 mrad). The modified procedure presented for the radiolabeling of the RBC with the short half-lived radionuclide technetium-99m provides a technique comparable to the utilized standard chromium-51 RBC method, yet with a large reduction in absorbed radiation dose. This procedure is presented as a superior technique for the determination of pediatric RBC volumes.

Effect of heparin on radioimmunoassay of gentamicin.

The effect of various heparin concentrations on the radioimmunoassay of gentamicin was studied in vitro and in rats. Heparainized test tubes were prepared, and whole blood was added followed by a gentamicin sulfate solution. Eight Sprague-Dawley rats were given heparin or gentamicin or both via infusion, and blood samples were drawn and tested. A radioimmunoassay for gentamicin was used in both the in vitro and in vivo tests. When 0-1000 units/ml of heparin were added to a constant amount of gentamicin (12 micro grams) in vitro, no difference was found in the assayed gentamicin concentration (p greater than 0.01). Similarly, when gentamicin concentrations of 0-16 micro grams /ml were added to a constant amount of heparin (20 units), the assays yielded results similar to the known gentamicin concentrations added. No significant difference was found in the clearance rate (p greater than 0.05) or terminal half-lives (p greater than 0.05) of gentamicin in treated and nontreated rats. The results suggest that variable heparin concentrations do not affect gentamicin concentrations as determined by radioimmunoassay.

Filling vials aseptically while monitoring for bacterial contamination.

An aseptic system for prefilling radiopharmaceutical kit vials or syringes is described. The system combines ultrafiltration with a method for monitoring for bacterial contamination. It could be used in any vial or syringe prefilling operation and is not restricted to radiopharmaceuticals.