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Measured Values (measured + value)
Selected AbstractsUsing GIS and a digital elevation model to assess the effectiveness of variable grade flow diversion terraces in reducing soil erosion in northwestern New Brunswick, CanadaHYDROLOGICAL PROCESSES, Issue 23 2009Qi Yang Abstract Flow diversion terraces (FDT) are commonly used beneficial management practice (BMP) for soil conservation on sloped terrain susceptible to water erosion. A simple GIS-based soil erosion model was designed to assess the effectiveness of the FDT system under different climatic, topographic, and soil conditions at a sub-basin level. The model was used to estimate the soil conservation support practice factor (P -factor), which inherently considered two major outcomes with its implementation, namely (1) reduced slope length, and (2) sediment deposition in terraced channels. A benchmark site, the agriculture-dominated watershed in northwestern New Brunswick (NB), was selected to test the performance of the model and estimated P -factors. The estimated P -factors ranged from 0·38,1·0 for soil conservation planning objectives and ranged from 0·001 to 0·45 in sediment yield calculations for water-quality assessment. The model estimated that the average annual sediment yield was 773 kg ha,1 yr ,1 compared with a measured value of 641 kg ha,1 yr,1. The P -factors estimated in this study were comparable with predicted values obtained with the revised universal soil loss equation (RUSLE2). The P -factors from this study have the potential to be directly used as input in hydrological models, such as the soil and water assessment tool (SWAT), or in soil conservation planning where only conventional digital elevation models (DEMs) are available. Copyright © 2009 John Wiley & Sons, Ltd. [source] Predicting unit plot soil loss in Sicily, south ItalyHYDROLOGICAL PROCESSES, Issue 5 2008V. Bagarello Abstract Predicting soil loss is necessary to establish soil conservation measures. Variability of soil and hydrological parameters complicates mathematical simulation of soil erosion processes. Methods for predicting unit plot soil loss in Sicily were developed by using 5 years of data from replicated plots. At first, the variability of the soil water content, runoff, and unit plot soil loss values collected at fixed dates or after an erosive event was investigated. The applicability of the Universal Soil Loss Equation (USLE) was then tested. Finally, a method to predict event soil loss was developed. Measurement variability decreased as the mean increased above a threshold value but it was low also for low values of the measured variable. The mean soil loss predicted by the USLE was lower than the measured value by 48%. The annual values of the soil erodibility factor varied by seven times whereas the mean monthly values varied between 1% and 244% of the mean annual value. The event unit plot soil loss was directly proportional to an erosivity index equal to , being QRRe the runoff ratio times the single storm erosion index. It was concluded that a relatively low number of replicates of the variable of interest may be collected to estimate the mean for both high and particularly low values of the variable. The USLE with the mean annual soil erodibility factor may be applied to estimate the order of magnitude of the mean soil loss but it is not usable to estimate soil loss at shorter temporal scales. The relationship for estimating the event soil loss is a modified version of the USLE-M, given that it includes an exponent for the QRRe term. Copyright © 2007 John Wiley & Sons, Ltd. [source] A comparative study of linear regression methods in noisy environmentsJOURNAL OF CHEMOMETRICS, Issue 12 2004Marco S. Reis Abstract With the development of measurement instrumentation methods and metrology, one is very often able to rigorously specify the uncertainty associated with each measured value (e.g. concentrations, spectra, process sensors). The use of this information, along with the corresponding raw measurements, should, in principle, lead to more sound ways of performing data analysis, since the quality of data can be explicitly taken into account. This should be true, in particular, when noise is heteroscedastic and of a large magnitude. In this paper we focus on alternative multivariate linear regression methods conceived to take into account data uncertainties. We critically investigate their prediction and parameter estimation capabilities and suggest some modifications of well-established approaches. All alternatives are tested under simulation scenarios that cover different noise and data structures. The results thus obtained provide guidelines on which methods to use and when. Interestingly enough, some of the methods that explicitly incorporate uncertainty information in their formulations tend to present not as good performances in the examples studied, whereas others that do not do so present an overall good performance. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effect of various estimates of renal function on prediction of vancomycin concentration by the population mean and Bayesian methodsJOURNAL OF CLINICAL PHARMACY & THERAPEUTICS, Issue 4 2009Y. Tsuji BSc Summary Objective:, Renal function was estimated in 129 elderly patients with methicillin-resistant Staphylococcus aureus (MRSA) who were treated with vancomycin (VCM). The estimation was performed by substituting serum creatinine (SCR) measured enzymatically and a value converted using the Jaffe method into the Cockcroft-Gault and Modification of Diet in Renal Disease (MDRD) equations. The serum trough level was predicted from three estimates of renal function by the population mean (PM) and Bayesian methods and the predictability was assessed. Methods:, Two-compartment model-based Japanese population parameters for VCM were used, and the mean prediction error (ME) and root mean squared error (RMSE) were calculated as indices of bias and accuracy, respectively, for predictions by the PM and Bayesian methods. Results:, The PM method gave the highest correlation with the measured value using the estimate of renal function obtained by substituting the Jaffe-converted SCR into the Cockcroft-Gault equation. There was no positive or negative bias in the ME and the value was significantly smaller than for other predicted data (P < 0·05). RMSE was also the smallest, indicating that this method increases the predictability of the serum VCM trough level. While, ME showed a negative bias for all values predicted by the Bayesian method, both the ME and RMSE were very small. Conclusion:, In the application of the PM method for VCM treatment of elderly patients with MRSA, substitution of SCR based on the Jaffe method into the Cockcroft-Gault equation increases the predictability of the serum VCM trough level. The Bayesian method predicted the serum VCM trough level with high accuracy using any of the estimates of renal function. [source] Messunsicherheit in der WerkstoffprüfungMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 5 2007T. Polzin Dr.-Ing. Uncertainty; tensile test; charpy test; hardness test Abstract Bei der Werkstoffprüfung muss bei jedem Messwert die jeweilige Messunsicherheit angegeben werden. Aus der 1995 erschienenen GUM [1] wurde 2000 der Uncert Report für verschiedenen Messverfahren entwickelt und als Code of Practice (COP) [2,4]. veröffentlicht. Diese sollen in Zusammenhang mit den in den Normen empfohlenen Verfahren und der praktischen Umsetzung dargestellt werden. Measurement uncertainty in testing of materials For the testing of materials the respective uncertainty has to be indicated for each measured value. From the 1995 published GUM [1] 2000 the Uncert report for different measuring methods was developed and published as Code of Practice (COP) [2,4]. These are to be represented in connection with the procedures recommended in the standards and the practical implementation. [source] Two-dimensional phononless VRH conduction in arrays of Ge/Si quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2004A. I. Yakimov Abstract We report measurements of a two-dimensional variable-range hopping conductance in delta-doped Ge/Si heterostructures with a layer of Ge nanometer-scale quantum dots. We found that the conductance , vs. temperature T follows the Efros-Shklovskii behavior , = ,0 exp[,(T0/T )1/2] with the temperatureindependent prefactor ,0 , e2/h. A strong reduction of the measured value of T0 from that calculated for single-particle hopping was observed. All these results provide a manifestation of interaction-driven many-electron correlated hopping in dense arrays of quantum dots. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Variation in barometric pressure in Melbourne does not significantly affect the BTPS correction factorRESPIROLOGY, Issue 3 2004David P. JOHNS Abstract: The conventional BTPS (body temperature and pressure, saturated with water vapour) correction factor varies with ambient barometric pressure (PB) and many lung function laboratories measure PB daily. The aim was to investigate whether a fixed value for PB could replace daily measurements. PB was measured daily over a 12-month period. The highest and lowest values in Melbourne in the last century were also recorded from data published by the Bureau of Meteorology. Using these PB values, the BTPS factor was determined for a range of spirometer temperatures and compared to the BTPS factors obtained using a fixed ambient pressure of 101.3 kPa. The mean (SD) PB measured over the 12-month period was 102.2 kPa (0.64) with a range of 99.9,103.6 kPa. The level of disagreement between the BTPS factor calculated using a PB of 101.3 kPa instead of the measured value was greater at lower temperatures. Over the extremes of PB during the last century (98.0,104.3 kPa) the use of a standard pressure (101.3 kPa) produced an error in the BTPS factor of ,,0.16%. Daily variations in PB do not significantly affect the magnitude of the conventional BTPS correction factor and a fixed value, such as 101.3 kPa at sea level, can be used with little error. [source] A robust approach for assessing misclassification rates under the two-component measurement error modelAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 4 2010Daniela Cocchi Abstract The majority of actions designed to improve processes and quality include the assessment of the capability of a measurement system. The statistical model relating the measured value to the true, but not observable, value of a product characteristic is usually Gaussian and additive. In this paper we propose to extend the said model to a more general formulation by introducing the structure of the two-component error model. An approximated method for evaluating the misclassification rates under the two-component error model is proposed and assessed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Enantioselective [4+2]-Cycloaddition Reaction of a Photochemically Generated o -Quinodimethane: Mechanistic Details, Association Studies, and Pressure EffectsCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2004Benjamin Grosch Dipl. Abstract 1,2,3,4-Tetrahydro-2-oxoquinoline-5-aldehyde (2) was prepared from m -aminobenzoic acid and 3-ethoxyacryloyl chloride (4) in 19,% overall yield. Compound 2 underwent a photochemically induced [4+2]-cycloaddition reaction with various dienophiles upon irradiation in toluene solution. The exo product 10,a was obtained with acrylonitrile (9,a) as the dienophile, whereas methyl acrylate (9,b) and dimethyl fumarate (9,c) furnished the endo products 11,b and 11,c (69,77,% yield). The reactions proceeded at ,60,°C in the presence of the chiral complexing agent 1 (1.2 equiv) with excellent enantioselectivity (91,94,% ee). The enantiomeric excess increases in the course of the photocycloaddition as a result of the lower product association to 1. The intermediate (E)-dienol 8 was spectroscopically detected at ,196,°C in an EPA (diethyl ether/isopentane/ethanol) glass matrix. The association of the substrate 2 to the complexing agent 1 was studied by circular dichroism (CD) titration. The measured association constant (KA) was 589,M,1 at room temperature (25,°C) and normal pressure (0.1 MPa). An increase in pressure led to an increased association. At 400 MPa the measured value of KA was 703,M,1. Despite the stronger association the enantioselectivity of the reaction decreased with increasing pressure. At 25,°C the enantiomeric excess for the enantioselective reaction 2 + 9,a,10,a decreased from 68,% ee at 0.1 MPa to 58,% ee at 350 MPa. This surprising behavior is explained by different activation volumes for the diastereomeric transition states leading to 10,a and ent - 10,a. 1,2,3,4-Tetrahydro-2-oxochinolin-5-aldehyd (2) wurde ausgehend von m -Aminobenzoesäure und 3-Ethoxyacryloylchlorid (4) in fünf Schritten und einer Gesamtausbeute von 19,% hergestellt. Die Verbindung ließ sich in Toluol als Lösungsmittel mit verschiedenen Dienophilen in einer photochemisch induzierten [4+2]-Cycloaddition umsetzen (69,77,% Ausbeute), wobei als Hauptprodukt mit Acrylnitril (9,a) das exo -Produkt 10,a entstand. Methylacrylat (9,b) und Dimethylfumarat (9,c) lieferten die endo -Produkte 11,b and 11,c. In Gegenwart des chiralen Komplexierungsreagenz, 1 (1.2 Äquiv.) verliefen die Reaktionen mit exzellenter Enantioselektivität (91,94,% ee). Der Enantiomerenüberschuß nahm im Verlauf der photochemischen Umsetzung zu, was man auf die relativ zum Substrat 2 niedrigere Assoziation des Produkts zurückführen kann. Das intermediär gebildete (E)-Dienol 8 wurde spektroskopisch in einer EPA (Ether/i -Pentan/Ethanol) Glasmatrix bei ,196,°C nachgewiesen. Die Assoziation des Substrats 2 an das Komplexierungsreagenz 1 wurde durch CD-Titration genauer untersucht. Die Assoziationskonstante (KA) wurde bei Zimmertemperatur (25,°C) und Normaldruck (0.1 MPa) zu 589,M,1bestimmt. Bei höherem Druck beobachtete man eine verstärkte Assoziation und bei 400 MPa wurde eine Assoziationskonstante von KA=703,M,1bestimmt. Trotz der stärkeren Assoziaion nahm die Enantioselektivität mit wachsendem Druck ab. Bei 25,°C sank der Enantiomerenüberschuß der enantioselektiven Reation 2 + 9,a,10,a von 68,% ee bei 0.1 MPa auf 58,% ee bei 350 MPa. Dieses überraschende Verhalten läßt sich möglicherweise durch die unterschiedlichen Aktivierungsvolumina für die Übergangszustände erklären, die zu 10,a und ent - 10,a führen. [source] Evaluation of the PESERA model in two contrasting environmentsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2009F. Licciardello Abstract The performance of the Pan-European Soil Erosion Risk Assessment (PESERA) model was evaluated by comparison with existing soil erosion data collected in plots under different land uses and climate conditions in Europe. In order to identify the most important sources of error, the PESERA model was evaluated by comparing model output with measured values as well as by assessing the effect of the various model components on prediction accuracy through a multistep approach. First, the performance of the hydrological and erosion components of PESERA was evaluated separately by comparing both runoff and soil loss predictions with measured values. In order to assess the performance of the vegetation growth component of PESERA, the predictions of the model based on observed values of vegetation ground cover were also compared with predictions based on the simulated vegetation cover values. Finally, in order to evaluate the sediment transport model, predicted monthly erosion rates were also calculated using observed values of runoff and vegetation cover instead of simulated values. Moreover, in order to investigate the capability of PESERA to reproduce seasonal trends, the observed and simulated monthly runoff and erosion values were aggregated at different temporal scale and we investigated at what extend the model prediction error could be reduced by output aggregation. PESERA showed promise to predict annual average spatial variability quite well. In its present form, short-term temporal variations are not well captured probably due to various reasons. The multistep approach showed that this is not only due to unrealistic simulation of cover and runoff, being erosion prediction also an important source of error. Although variability between the investigated land uses and climate conditions is well captured, absolute rates are strongly underestimated. A calibration procedure, focused on a soil erodibility factor, is proposed to reduce the significant underestimation of soil erosion rates. Copyright © 2009 John Wiley & Sons, Ltd. [source] Soil detachment and transport on field- and laboratory-scale interrill areas: erosion processes and the size-selectivity of eroded sedimentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2006O. Malam Issa Abstract Field- and laboratory-scale rainfall simulation experiments were carried out in an investigation of the temporal variability of erosion processes on interrill areas, and the effects of such variation upon sediment size characteristics. Poorly aggregated sandy soils from the semi-arid environment of Senegal, West Africa, were used on both a 40 m2 field plot and a 0·25 m2 laboratory plot; rainfall intensity for all experiments was 70 mm h,1 with a duration of 1 to 2 hours. Time-series measurements were made of the quantity and the size distribution of eroded material: these permitted an estimate of the changing temporal balance between the main erosion processes (splash and wash). Results from both spatial scales showed a similar temporal pattern of runoff generation and sediment concentration. For both spatial scales, the dominant erosional process was detachment by raindrops; this resulted in a dynamic evolution of the soil surface under raindrop impact, with the rapid formation of a sieving crust followed by an erosion crust. However, a clear difference was observed between the two scales regarding the size of particles detached by both splash and wash. While all measured values were lower than the mean weight diameter (MWD) value of the original soil (mean 0·32 mm), demonstrating the size-selective nature of wash and splash processes, the MWD values of washed and splashed particles at the field scale ranged from 0·08 to 0·16 mm and from 0·12 to 0·30 mm respectively, whereas the MWD values of washed and splashed particles at the laboratory scale ranged from 0·13 to 0·29 mm and from 0·21 to 0·32 mm respectively. Thus only at the field scale were the soil particles detached by splash notably coarser than those transported by wash. This suggests a transport-limited erosion process at the field scale. Differences were also observed between the dynamics of the soil loss by wash at the two scales, since results showed wider scatter in the field compared to the laboratory experiments. This scatter is probably related to the change in soil surface characteristics due to the size-selectivity of the erosion processes at this spatial scale. Copyright © 2006 John Wiley & Sons, Ltd. [source] Estimation of backward impedance on low-voltage distribution system using measured resonant currentELECTRICAL ENGINEERING IN JAPAN, Issue 3 2010Toru Miki Abstract Two estimation methods for a backward impedance of a power distribution system are proposed in this paper. According to the first method, the backward impedance is estimated based on information obtained from the frequency response of a transient current flowing into a capacitor connected to a distribution line. The backward impedance is determined from the attenuation constant and the resonant frequency calculated using the capacitance and the impedance of the power distribution system. These parameters can be reliably obtained from a frequency response of the transient current using the least square method. The accuracy of the method strongly depends on the origin on the time axis for Fourier transform. An additional estimate of the time-origin is required for an accurate estimation of the backward impedance. The second method estimates the backward impedance using two transient current waveforms obtained by alternately connecting different capacitors to a distribution line. The backward impedance can be represented as a function of the frequency responses of these currents. Since this method is independent from the time-origin, it is suitable for automatic measurements of the backward impedance. Proposed methods are applicable to the estimation of harmonic currents in distribution systems. In this paper, harmonic currents flowing through a distribution line are calculated based on the estimated backward impedance and on the measured values of voltage harmonics obtained by the instrument developed by the authors. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(3): 28,40, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20900 [source] Electromigration diffusivity spectrometry: A way for simultaneous determination of diffusion coefficients from mixed samplesELECTROPHORESIS, Issue 17 2010Suhua Yang Abstract A novel method was proposed for simultaneous measurement of diffusion coefficients, (D), from mixed samples by electrophoresis and termed electromigration-based diffusivity spectrometry. After theoretical treatment, D- equation for practical use has been deduced. With a modified CE system built in laboratory, electromigration-based diffusivity spectrometry has been realized and validated to suit for fast and accurate determination of diffusivities of mixed aromatic amino acids, phenols and aromatic organic acid, giving diffusivity spectra by peak area versus D, much similar to mass spectra. The precision of the measurement was found to critically depend on pH value of running buffer, which should be so selected that the analytes and internal standards could be charged at above 0.5e. The standards have to be selected at an electric flux far from each other and from analytes. In these cases, sample and running buffer concentrations, voltage and system temperature were found to have only negligible impact on the determination. In our test, the obtained measuring precision was generally kept within 1% for five runs, and the measured values of D agreed well with those from literature, with a deviation of less than 2.2% after the right use of calibration standards. [source] Aqueous films limit bacterial cell motility and colony expansion on partially saturated rough surfacesENVIRONMENTAL MICROBIOLOGY, Issue 5 2010Gang Wang Summary Bacterial motility is a key mechanism for survival in a patchy environment and is important for ecosystem biodiversity maintenance. Quantitative description of bacterial motility in soils is hindered by inherent heterogeneity, pore-space complexity and dynamics of microhydrological conditions. Unsaturated conditions result in fragmented aquatic habitats often too small to support full bacterial immersion thereby forcing strong interactions with mineral and air interfaces that significantly restrict motility. A new hybrid model was developed to study hydration effects on bacterial motility. Simulation results using literature parameter values illustrate sensitivity of colony expansion rates to hydration conditions and are in general agreement with measured values. Under matric potentials greater than ,0.5 kPa (wet), bacterial colonies grew fast at colony expansion rates exceeding 421 ± 94 µm h,1; rates dropped significantly to 31 ± 10 µm h,1 at ,2 kPa; as expected, no significant colony expansion was observed at ,5 kPa because of the dominance of capillary pinning forces in the submicrometric water film. Quantification of hydration-related constraints on bacterial motion provides insights into optimal conditions for bacterial dispersion and spatial ranges of resource accessibility important for bioremediation and biogeochemical cycles. Results define surprisingly narrow range of hydration conditions where motility confers ecological advantage on natural surfaces. [source] Estimating metabolic biotransformation rates in fish from laboratory dataENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008Jon A. Arnot Abstract A method is proposed for estimating metabolic biotransformation rate constants for nonionic organic chemicals from measured laboratory bioconcentration and dietary bioaccumulation data in fish. Data have been selected based on a quality review to reduce uncertainty in the measured values. A kinetic mass balance model is used to estimate rates of chemical uptake and elimination. Biotransformation rate constants are essentially calculated as the difference between two quantities, a measured bio-concentration factor or elimination rate constant, and a model-derived bioconcentration factor or elimination rate constant estimated assuming no biotransformation. Model parameterization exploits key empirical data when they are available and assumes default values when study specific data are unavailable. Uncertainty analyses provide screening level assessments for confidence in the biotransformation rate constant estimates. The uncertainty analyses include the range for 95% of the predicted values and 95% confidence intervals for the calculated biotransformation values. Case studies are provided to illustrate the calculation and uncertainty methods. Biotransformation rate constants calculated by the proposed method are compared with other published estimates for 31 chemicals that range in octanol,water partition coefficients from approximately 101 to 108 and represent over four orders of magnitude in biotransformation potential. The comparison of previously published values with those calculated by the proposed method shows general agreement with 82% of the estimated values falling within a factor of three. [source] Predicting world health organization toxic equivalency factor dioxin and dioxin-like polychlorinated biphenyl levels in farmed atlantic salmon (Salmo salar) based on known levels in feedENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2007Marc H. G. Berntssen Abstract Assimilation and elimination rate constant of dietary polychlorinated dibenzo- p -dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DLPCBs) with a World Health Organization toxic equivalency factor (WHO-TEF) were estimated in market-size Atlantic salmon (Salmo salar) using fish that were previously fed vegetable oil,based (low in PCDD/Fs and DLPCBs) or fish oil,based (high in PCDD/Fs and PCBs) diets. At the start of the kinetic trial, half the fish that were fed fish oils were fed vegetable oil feeds and inverted (cross-over design) for five months. The assimilation efficiencies of the PCDD/F congeners were more variable (3,89%) and, generally, were lower than those of the DLPCBs (70,80%). Among the PCDD/F congeners, the assimilation efficiency of the most toxic tetra- and pentachlorinated PCDD/Fs was greater than that of higher-chlorinated PCDD/Fs. Elimination rates for DLPCBs were higher than those for PCDD/Fs. Lower-chlorinated PCDDs had a lower elimination rate than the higher-chlorinated PCDDs, but no differences were observed among PCDF congeners or DLPCB congeners. Kinetic parameters were used to predict the level of WHO-TEF dioxins and DLPCBs in Atlantic salmon reared in a large-scale facility under commercial conditions. Predictions were based on preanalyzed levels of these organochlorines in feeds with three different replacement levels (0, 30, and 60%) of vegetable oil. A simple one-compartmental, first-order kinetic model was used to predict the level of sum WHO toxic equivalents for PCDD/Fs and DL-PCBs. The predicted values varied by 0 to 11% from the measured values in the commercially reared salmon. [source] Measured partitioning coefficients for parent and alkyl polycyclic aromatic hydrocarbons in 114 historically contaminated sediments: Part 1.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2006KOC values Abstract Polycyclic aromatic hydrocarbon (PAH) partitioning coefficients between sediment organic carbon and water (KOC) values were determined using 114 historically contaminated and background sediments collected from eight different rural and urban waterways in the northeastern United States. More than 2,100 individual KC values were measured in quadruplicate for PAHs ranging from two to six rings, along with the first reported KOC values for alkyl PAHs included in the U.S. Environmental Protection Agency's (U.S. EPA) sediment narcosis model for the prediction of PAH toxicity to benthic organisms. Sediment PAH concentrations ranged from 0.2 to 8,600 ,g/g (U.S. EPA 16 parent PAHs), but no observable trends in KOC values with concentration were observed for any of the individual PAHs. Literature KOC values that are commonly used for environmental modeling are similar to the lowest measured values for a particular PAH, with actual measured values typically ranging up to two orders of magnitude higher for both background and contaminated sediments. For example, the median log KOC values we determined for naphthalene, pyrene, and benzo[a]pyrene were 4.3, 5.8, and 6.7, respectively, compared to typical literature KOC values for the same PAHs of 2.9, 4.8, and 5.8, respectively. Our results clearly demonstrate that the common practice of using PAH KOC values derived from spiked sediments and modeled values based on n -octanol,water coefficients can greatly overestimate the actual partitioning of PAHs into water from field sediments. [source] Inhibition of aquatic toxicity of pyrethroid insecticides by suspended sedimentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2006Weichun Yang Abstract The use of pyrethroid insecticides is increasing in both agricultural and urban environments. Although pyrethroids display very high acute toxicities to water column organisms in laboratory tests, environmental water samples typically contain suspended sediment (SS) that can reduce the freely dissolved concentration of pyrethroids, hence their bioavailability. Consequently, phase distribution could play an important role in pyrethroid aquatic toxicology. In this study, we evaluated the effect of SS on the acute toxicity of four widely used pyrethroid insecticides to Ceriodaphnia dubia. In all assays, median lethal concentrations (LC50s) consistently increased with increasing SS, demonstrating the pronounced inhibitory effects of SS on pyrethroid toxicity. The LC50s in the 200 mg/L SS solutions were 2.5 to 13 times greater than those measured in sediment-free controls. Solid-phase microextraction (SPME) was used to determine the apparent distribution coefficient Kd for the pyrethroids in the water samples. Under the assumption that only the freely dissolved fraction is bioavailable, the measured Kd was used to predict C. dubia LC50s in the water samples. The predicted LC50s were within a factor of two of the measured values for 95% of the treatments. Results from this study suggest that the inhibitory effect of SS can be highly significant and must be considered in estimating exposures to pyrethroids in aquatic systems. The SPME methodology could be used effectively to measure bioavailable concentration and to predict the actual ecotoxicologic effects of pyrethroids. [source] Calibration model of microbial biomass carbon and nitrogen concentrations in soils using ultraviolet absorbance and soil organic matterEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2008X. Xu Summary There is a need for a rapid, simple and reliable method of determining soil microbial biomass (SMB) for all soils because traditional methods are laborious. Earlier studies have reported that SMB-C and -N concentrations in grassland and arable soils can be estimated by measurement of UV absorbance in soil extracts. However, these previous studies focused on soils with small soil organic matter (SOM) contents, and there was no consideration of SOM content as a covariate to improve the estimation. In this study, using tropical and temperate forest soils with a wide range of total C (5,204 mg C g,1 soil) and N (1,12 mg N g,1 soil) contents and pH values (4.1,5.9), it was found that increase in UV absorbance of soil extracts at 280 nm (UV280) after fumigation could account for 92,96% of the variance in estimates of the SMB-C and -N concentrations measured by chloroform fumigation and extraction (P < 0.001). The data were combined with those of earlier workers to calibrate UV-based regression models for all the soils, by taking into account their varying SOM content. The validation analysis of the calibration models indicated that the SMB-C and -N concentrations in the 0,5 cm forest soils simulated by using the increase in UV280 and SOM could account for 86,93% of the variance in concentrations determined by chloroform fumigation and extraction (P < 0.001). The slope values of linear regression equations between measured and simulated values were 0.94 ± 0.03 and 0.94 ± 0.04, respectively, for the SMB-C and -N. However, simulation using the regression equations obtained by using only the data for forest profile soils gave less good agreement with measured values. Hence, the calibration models obtained by using the increase in UV280 and SOM can give a rapid, simple and reliable method of determining SMB for all soils. [source] A model incorporating the diffuse double layer to predict the electrical conductivity of bulk soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007M. A. Mojid Summary A model has been developed to predict the electrical conductivity of bulk soil. The total soil-water content is divided into free water and water in the diffuse double layer (DDL) around clay particles. These two fractions of soil water conduct electrical current through the soil and are assumed to act in parallel with the soil solid. The volume of water in the DDL is evaluated from the surface area of the clay and the thickness of the DDL. The surface area of the clay is estimated from its cation exchange capacity (CEC) and surface charge density. A transmission coefficient correcting for the effect of the tortuous flow path of current through the soil, and a proportionality constant relating the electrical conductivity of water in the DDL to that of free water, are included in the model. The transmission coefficient is a function of the contents of water and clay and has been modelled in terms of these factors. The values of the proportionality constant and those relating to the transmission coefficient were optimized for five different soils. The electrical conductivities of the five soils estimated by the model compare well with the measured values, which, however, deviate systematically from predictions by the three-component model of Rhoades et al. [source] Predicting HCl concentrations in fire enclosures using an HCl decay model coupled to a CFD-based fire field modelFIRE AND MATERIALS, Issue 7 2007Z. Wang Abstract The amount of atmospheric hydrogen chloride (HCl) within fire enclosures produced from the combustion of chloride-based materials tends to decay as the fire effluent is transported through the enclosure due to mixing with fresh air and absorption by solids. This paper describes an HCl decay model, typically used in zone models, which has been modified and applied to a computational fluid dynamics (CFD)-based fire field model. While the modified model still makes use of some empirical formulations to represent the deposition mechanisms, these have been reduced from the original three to two through the use of the CFD framework. Furthermore, the effect of HCl flow to the wall surfaces on the time to reach equilibrium between HCl in the boundary layer and on wall surfaces is addressed by the modified model. Simulation results using the modified HCl decay model are compared with data from three experiments. The model is found to be able to reproduce the experimental trends and the predicted HCl levels are in good agreement with measured values. Copyright © 2006 John Wiley & Sons, Ltd. [source] Oligotrophication outweighs effects of global warming in a large, deep, stratified lake ecosystemGLOBAL CHANGE BIOLOGY, Issue 2 2010H. B. STICH Abstract Between 1951 and 1979, total phosphorous concentrations in Lake Constance increased from 7 to 87 ,g L,1. Following wastewater treatment, phosphorus levels were brought under control, returning to 7.6 ,g L,1 by spring 2007. The biological and chemical data from 1980 to 2004 were first modelled by seasonal time series analyses and then used to create a general model. Excluding collinear variables allowed the data set to be condensed to six variables that could be fitted into a general linear model that explained ,75% of the observed annual variation in chlorophyll a. A clear seasonal influence was apparent, with chlorophyll a tracking trends in temperature and the progress of spring. A nonseasonal influence was also observed in the interaction of two biological components, the proportion of phytoplankton biomass available to Daphnia (i.e. the percentage of ingestible size <30 ,m) and the grazing intensity. In combination, these biotic variables had a negative impact on chlorophyll a levels. In contrast, the concentration of soluble reactive phosphorus (SRP) correlated positively with chlorophyll a. The effect of SRP showed a significant seasonal component, as it was more abundant in spring than at other times of year. In general, the model predicts a negative exponential response of chlorophyll a to further depletion of SRP in Lake Constance, while the temperature trends predicted by current global warming scenarios will result in a moderate increase in productivity. Data from 2005 to 2007 were used to verify the model. The modelled chlorophyll a values were nonbiased and showed a close match to the measured values (r2: 75%). Thus the applicability, reliability, and informative value of the model for pelagic Lake Constance was confirmed. The approach might easily be applied to other waters. [source] Runoff and suspended sediment yields from an unpaved road segment, St John, US Virgin IslandsHYDROLOGICAL PROCESSES, Issue 1 2007Carlos E. Ramos-Scharrón Abstract Unpaved roads are believed to be the primary source of terrigenous sediments being delivered to marine ecosystems around the island of St John in the eastern Caribbean. The objectives of this study were to: (1) measure runoff and suspended sediment yields from a road segment; (2) develop and test two event-based runoff and sediment prediction models; and (3) compare the predicted sediment yields against measured values from an empirical road erosion model and from a sediment trap. The runoff models use the Green,Ampt infiltration equation to predict excess precipitation and then use either an empirically derived unit hydrograph or a kinematic wave to generate runoff hydrographs. Precipitation, runoff, and suspended sediment data were collected from a 230 m long, mostly unpaved road segment over an 8-month period. Only 3,5 mm of rainfall was sufficient to initiate runoff from the road surface. Both models simulated similar hydrographs. Model performance was poor for storms with less than 1 cm of rainfall, but improved for larger events. The largest source of error was the inability to predict initial infiltration rates. The two runoff models were coupled with empirical sediment rating curves, and the predicted sediment yields were approximately 0·11 kg per square meter of road surface per centimetre of precipitation. The sediment trap data indicated a road erosion rate of 0·27 kg m,2 cm,1. The difference in sediment production between these two methods can be attributed to the fact that the suspended sediment samples were predominantly sand and silt, whereas the sediment trap yielded mostly sand and gravel. The combination of these data sets yields a road surface erosion rate of 0·31 kg m,2 cm,1, or approximately 36 kg m,2 year,1. This is four orders of magnitude higher than the measured erosion rate from undisturbed hillslopes. The results confirm the importance of unpaved roads in altering runoff and erosion rates in a tropical setting, provide insights into the controlling processes, and provide guidance for predicting runoff and sediment yields at the road-segment scale. Copyright © 2006 John Wiley & Sons, Ltd. [source] The modelling of anchors using the material point methodINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2005C. J. Coetzee Abstract The ultimate capacity of anchors is determined using the material point method (MPM). MPM is a so-called meshless method capable of modelling large displacements, deformations and contact between different bodies. A short introduction to MPM is given and the derivation of the discrete governing equations. The analysis of a vertically loaded anchor and one loaded at 45° is presented. The load,displacement curves are compared to that obtained from experiments and the effect of soil stiffness and anchor roughness is investigated. The results of the vertically loaded anchor are also compared to an analytical solution. The displacement of the soil surface above the anchor was measured and compared to the numerical predictions. Convergence with mesh refinement is demonstrated and the effect of mesh size and dilatancy angle on the shear band width and orientation is indicated. The results show that MPM can model anchor pull out successfully. No special interface elements are needed to model the anchor,soil interface and the predicted ultimate capacities were within 10% of the measured values. Copyright © 2005 John Wiley & Sons, Ltd. [source] Missing data estimation for 1,6,h gaps in energy use and weather data using different statistical methodsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2006David E. Claridge Abstract Analysing hourly energy use to determine retrofit savings or diagnose system problems frequently requires rehabilitation of short periods of missing data. This paper evaluates four methods for rehabilitating short periods of missing data. Single variable regression, polynomial models, Lagrange interpolation, and linear interpolation models are developed, demonstrated, and used to fill 1,6,h gaps in weather data, heating data and cooling data for commercial buildings. The methodology for comparing the performance of the four different methods for filling data gaps uses 11 1-year data sets to develop different models and fill over 500 000 ,pseudo-gaps' 1,6,h in length for each model. These pseudo-gaps are created within each data set by assuming data is missing, then these gaps are filled and the ,filled' values compared with the measured values. Comparisons are made using four statistical parameters: mean bias error (MBE), root mean square error, sum of the absolute errors, and coefficient of variation of the sum of the absolute errors. Comparison based on frequency within specified error limits is also used. A linear interpolation model or a polynomial model with hour-of-day as the independent variable both fill 1,6 missing hours of cooling data, heating data or weather data, with accuracy clearly superior to the single variable linear regression model and to the Lagrange model. The linear interpolation model is the simplest and most convenient method, and generally showed superior performance to the polynomial model when evaluated using root mean square error, sum of the absolute errors, or frequency of filling within set error limits as criteria. The eighth-order polynomial model using time as the independent variable is a relatively simple, yet powerful approach that provided somewhat superior performance for filling heating data and cooling data if MBE is the criterion as is often the case when evaluating retrofit savings. Likewise, a tenth-order polynomial model provided the best performance when filling dew-point temperature data when MBE is the criterion. It is possible that the results would differ somewhat for other data sets, but the strength of the linear and polynomial models relative to the other models evaluated seems quite robust. Copyright © 2006 John Wiley & Sons, Ltd. [source] Predicting abundance from occupancy: a test for an aggregated insect assemblageJOURNAL OF ANIMAL ECOLOGY, Issue 3 2003M. Warren Summary 1The ubiquitous, positive abundance-occupancy relationship is of potential value to conservation and pest management because of the possibility of using it to predict species abundance from occupancy measures. 2He & Gaston (2000a) developed a model, and a parameterization method, for the prediction of abundance from occupancy based on the negative binomial distribution. There are to date few empirical tests of either the estimation method or model. Here we conduct such a test in a field-based mesocosm experiment using a Drosophilidae assemblage associated with decaying fruit. 3With individual (and groups of) fruit as minimum mapping units, abundance estimates derived using the parameterization method of the He-Gaston model differed significantly from measured values, and were least accurate for the most abundant species. 4Substitution of k -values corrected for species density in the model did not improve abundance predictions significantly. However, substitution of k -values calculated directly from the negative binomial distribution yielded highly accurate abundance predictions. 5Although the distribution of fly species did not deviate significantly from the negative binomial distribution, and the finest possible minimum mapping units were used (individual fruit), the parameterization method in the He-Gaston model consistently underestimated the abundance of species in the assemblage because individuals were very highly aggregated within fruit. 6Because of its potential importance, this model and parameterization method require further exploration at fine scales, commonly represented by individual habitat units, for highly aggregated species. The incorporation of spatially explicit information may provide a means of improving abundance predictions in this regard. [source] Elastic deformations in a perfect bulk Si crystal studied by high-energy X-raysJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2009Alexander Gröschel Long-range strain fields induced in highly perfect bulk crystals during the manufacturing process significantly affect the quality and may even lead to spontaneous fracturing. Obviously a quantitative assessment of these deformations is crucial. A possible means is to examine the diffraction of X-rays by strained crystals, as the deformations bear on the diffraction characteristics of such crystals. In this report a quantitative examination of the diffraction characteristics of a perfect silicon bulk crystal with long-range strain fields in a well defined geometry is presented. The experiments were carried out using a high-energy X-ray laboratory source. By simulating the elastic deformation of the crystal by a finite element program the strain fields of the diffracting crystal are accessed. From these, simulated data values for integrated intensities can be derived on the basis of the dynamical diffraction theory for slightly distorted crystals. The theoretical calculations show good agreement with the experimental measured values. The smallest deformation yielding a noticeable change of the integrated intensity can be associated with a bending radius of the diffracting lattice planes of 16,km. [source] Novel adamantane-containing epoxy resinJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2007Xiaoming Su Abstract A novel adamantane-containing epoxy resin diglycidyl ether of bisphenol-adamantane (DGEBAda) was successfully synthesized from 1,3-bis(4-hydroxyphenyl)adamantane by a one-step method. The proposed structure of the epoxy resin was confirmed with Fourier transform infrared, 1H-NMR, gel permeation chromatography, and epoxy equivalent weight titration. The synthesized adamantane-containing epoxy resin was cured with 4,4,-diaminodiphenyl sulfone (DDS) and dicyandiamide (DICY). The thermal properties of the DDS-cured epoxy were investigated with differential scanning calorimetry and thermogravimetric analysis (TGA). The dielectric properties of the DICY-cured epoxy were determined from its dielectric spectrum. The obtained results were compared with those of commercially available diglycidyl ether of bisphenol A (DGEBA), a tetramethyl biphenol (TMBP)/epoxy system, and some other associated epoxy resins. According to the measured values, the glass-transition temperature of the DGEBAda/DDS system (223°C) was higher than that of the DGEBA/DDS system and close to that of the TMBP/DDS system. TGA results showed that the DGEBAda/DDS system had a higher char yield (25.02%) and integral procedure decomposition temperature (850.7°C); however, the 5 wt % degradation temperature was lower than that of DDS-cured DGEBA and TMBP. Moreover, DGEBAda/DDS had reduced moisture absorption and lower dielectric properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Force field-dependant structural divergence revealed during long time simulations of Calbindin d9kJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2010Elad Project Abstract The structural and the dynamic features of the Calbindin (CaB) protein in its holo and apo states are compared using molecular dynamics simulations under nine different force fields (FFs) (G43a1, G53a6, Opls-AA, Amber94, Amber99, Amber99p, AmberGS, AmberGSs, and Amber99sb). The results show that most FFs reproduce reasonably well the majority of the experimentally derived features of the CaB protein. However, in several cases, there are significant differences in secondary structure properties, root mean square deviations (RMSDs), root mean square fluctuations (RMSFs), and S2 order parameters among the various FFs. What is more, in certain cases, these parameters differed from the experimentally derived values. Some of these deviations became noticeable only after 50 ns. A comparison with experimental data indicates that, for CaB, the Amber94 shows overall best agreement with the measured values, whereas several others seem to deviate from both crystal and nuclear magnetic resonance data. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] HEAT TRANSFER TO CANNED PARTICULATES IN HIGH-VISCOSITY NEWTONIAN FLUIDS DURING AGITATION PROCESSINGJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 6 2006YANG MENG ABSTRACT Heat transfer to canned particulate-laden Newtonian high-viscous fluids (Nylon particles suspended in aqueous glycerin solution [40, 60, 80, 90 and 100%, v/v] and motor oil [85W140]) during end-over-end rotation was studied in a pilot-scale, full water-immersion single-cage rotary retort. Computations of conventional fluid-to-particle heat transfer coefficient (hfp) and overall heat transfer coefficient (U) were successful with multiple particles for an entire range of viscosity, but the predicted particle lethality was underestimated. With a single particle in the can, hfpand U calculations were successful only for low-viscosity fluids (40 and 60% glycerin solutions), but again resulted in underestimation of particle lethality. Apparent heat transfer coefficients (hap) between retort and particle surface and apparent overall heat transfer coefficient (Ua) were also evaluated, and this methodology worked well for all cases. Further, the particle lethality predicted using hap better matched the measured values. With a single particle in the can, the associated hap was significantly (P < 0.05) influenced by rotation speed, retort temperature, liquid viscosity, particle material and can size. Ua was significantly (P < 0.05) influenced by rotation speed and liquid viscosity. The effects of headspace, radius of rotation and particle size were not significant (P > 0.05) on hap and Ua values. [source] | ||||||||||||||||||||||||||||