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Linear Relationships (linear + relationships)
Kinds of Linear Relationships Selected AbstractsImpact of climate variability on vegetative cover in the Butana area of SudanAFRICAN JOURNAL OF ECOLOGY, Issue 2009Muna Elhag Abstract Climate variability has an impact on the renewable natural resources. This impact is strong in regions with a delicate balance between climate and ecosystem, like the Sahelian regions. Rainfall is the most important climatic factor influencing livelihoods in Butana, north-eastern part of Sudan. All people and their livestock depend on the amount of rainfall that falls and supports plant growth. Butana area experienced severe drought in 1984, 1990 and 2000. Linear relationships between the long-term rainfall and AVHRR/NDVI data were developed for four separate zones in the Butana area. There is a significant correlation between peak NDVI (beginning of September) and cumulative rainfall for July and August, but weak relationships resulted when annual rainfall and cumulative NDVI were used. This is because the NDVI reached a plateau as the rainfall increased, then it remained constant despite further increases in rainfall. The departure from the long-term average of NDVI for each pixel was calculated using the departure average vegetation method. The area had a high percentage of departure during the drought years and the NDVI recovered during the following year when the rainfall was above the average. It can be noted that the area adjacent to the irrigated scheme showed considerable decrease in NDVI. This may be due to overexploitation by the nomads during the drought year. [source] linear free energy relationships;JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 11 2007UB3LYP/6-31G(d The substituent effect on the reactivity of the CN bond of molecular ions of 4-substituted N -(2-furylmethyl)anilines toward two dissociation pathways was studied. With this aim, six of these compounds were analyzed by mass spectrometry using electron ionization with energies between 7.8 and 69.9 eV. Also, the UB3LYP/6-31G (d,p) and UHF/6-31G (d, p) levels of theory were used to calculate the critical energies (reaction enthalpies at 0 K) of the processes that lead to the complementary ions [C5H5O]+ and [M , C5H5O]+, assuming structures that result from the heterolytic and homolytic CN bond cleavages of the molecular ions, respectively. A kinetic approach proposed in the 1960s was applied to the mass spectral data to obtain the relative rate coefficients for both dissociation channels from ratios of the peak intensities of these ions. Linear relationships were obtained between the logarithms of the relative rate coefficients and the calculated critical energies and other thermochemical properties, whose slopes showed to be conditioned by the energy provided to the compounds within the ion source. Moreover, it was found that the dissociation that leads to [C5H5O]+ is a process strongly dependent upon the electron withdrawing or donating properties of the substituent, favored by those factors that destabilize the molecular ion. On the contrary, the dissociation that leads to [M , C5H5O]+ is indifferent to the polar electronic effects of the substituent. The abundance of both products was governed by the rule of Stevenson,Audier, according to which the major ion is the one of less negative electronic affinity. Copyright © 2007 John Wiley & Sons, Ltd. [source] Pharmacokinetics of liquiritigenin in mice, rats, rabbits, and dogs, and animal scale-upJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2009Hee E. Kang Abstract Pharmacokinetics of liquiritigenin (LQ) and its two glucuronide metabolites, M1 and M2, in mice, rats, rabbits, and dogs and animal scale-up of the pharmacokinetic parameters of LQ were evaluated. After intravenous administration of LQ, the AUC (AUC0,t) values of LQ, M1, and M2 were proportional to LQ doses in all animals studied. Animal scale-up of some pharmacokinetic parameters of LQ was performed based on the parameters after its intravenous administration (20 mg/kg; in the linear pharmacokinetic range) to the four species. Linear relationships were obtained (r,>,0.968) between log CL (or CL/fu) (L/h) and log species body weight (W) (kg) [CL (or CL/fu),=,3.29 (34.0) W0.723 (0.789)] and log,Vss (or Vss/fu) (L) and log,W (kg) [Vss (or Vss/fu),=,0.340 (3.52) W0.882 (0.948)]. Interspecies scale-up of plasma concentration,time data of LQ using apolysichron (complex Dedrick plots) resulted in similar profiles, and plasma concentration,time profile of humans were predicted using the well-fitted four animal data. Our results indicate that the LQ data obtained from laboratory animals could be utilized to generate preliminary estimates of the pharmacokinetic parameters of LQ in humans. These parameters can serve as guidelines for better planning of clinical studies. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4327,4342, 2009 [source] Estimates of basal ileal endogenous losses of amino acids by regression analysis and determination of standardised ileal amino acid digestibilities from casein in newly weaned pigs,JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 4 2008Meike Eklund Abstract BACKGROUND: This study was carried out to estimate basal ileal endogenous crude protein (CP) and amino acid (AA) losses (IAALB) in newly weaned pigs by regression analysis from apparent ileal digestible and the corresponding total dietary contents of CP and AA in order to obtain standardised ileal digestibilities (SID) of CP and AA originating from casein. A total of fourteen 3-week-old barrows were fitted with simple T cannulas at the distal ileum and were fed six diets with two pigs per diet in 4 weekly repeated measurements. Corn starch-based diets containing six graded levels of CP from casein with 90, 155, 220, 285, 350 and 415 g kg,1 CP (as-fed basis) were formulated. RESULTS: Linear relationships (P < 0.001) between apparent ileal digestible and total dietary contents of CP and AA (g kg,1 dry matter intake (DMI)) exist for CP and all AA in the range of 90,220 g kg,1 CP content in the diet. The IAALB extrapolated from the range of 90,220 g kg,1 CP content are different from zero (P < 0.001 to P = 0.019) except for tryptophan (P = 0.220). Based on regression analysis in the range of 90,220 g kg,1 CP, estimates of IAALB, expressed as g kg,1 DMI, and SID of CP and AA in casein (in parentheses, %) were as follows: CP 9.3 (98.0); arginine 0.4 (98.9); histidine 0.2 (98.5); isoleucine 0.2 (98.1); leucine 0.5 (99.2); lysine 0.4 (99.0); methionine 0.1 (99.1); phenylalanine 0.4 (99.9); threonine 0.6 (97.8); tryptophan 0.1 (96.2); valine 0.4 (98.5). CONCLUSION: The IAALB and SID of CP and AA originating from casein in newly weaned pigs are in close agreement with values obtained in grower finisher pigs. Copyright © 2007 Society of Chemical Industry [source] Near-infrared photo-excited emission from tissues treated at different temperature levelsLASERS IN SURGERY AND MEDICINE, Issue 1 2001Jing Tang MD Abstract Background and Objective There is a lack of methods to evaluate the extent of thermal treatment of biological tissue. The intensity of the near-infrared (NIR) emission photo-excitation was investigated from tissue undergoing different levels of heat treatment. Study Design/Materials and Methods Chicken muscle was heated in an oven at different temperature levels ranging from 40°C until burn-off. The spectral emission intensity from these heat-treated tissues was measured with a CCD camera and the intensity was calculated. Results The emission intensity increased proportionally with respect to the extent of treatment temperature until burning. Linear relationships between treatment temperature and the emission intensity from tissue samples were found in three temperature ranges: from 40 to 160°C, from 165 to 220°C, and from 225 to 250°C. Conclusions The change in tissue damage after heat treatment could be detected by measuring the NIR emission intensity from the thermally damaged tissues. Lasers Surg. Med. 29:18,22, 2001. © 2001 Wiley-Liss, Inc. [source] Conidial dispersal by Alternaria brassicicola on Chinese cabbage (Brassica pekinensis) in the field and under simulated conditionsPLANT PATHOLOGY, Issue 5 2003L. Y. Chen This study investigated conidial dispersal in the field, and effects of simulated wind and rain on the dispersal of A. brassicicola on Chinese cabbage (Brassica pekinensis). Spores were sampled using a Burkard volumetric spore sampler and rotorod samplers in a Chinese cabbage crop. Disease incidence in the field was well fitted by a Gompertz curve with an adjusted r2 of >0·99. Conidia of A. brassicicola were trapped in the field throughout the growing season. Peaks of high spore concentrations were usually associated with dry days, shortly after rain, high temperature or high wind speed. Diurnal periodicity of spore dispersal showed a peak of conidia trapped around 10·00 h. The number of conidia trapped at a height of 25 cm above ground level was greater than that at 50, 75 and 100 cm. Conidial dispersal was also studied under simulated conditions in a wind tunnel and a rain simulator. Generalized linear models were used to model these data. The number of conidia caught increased significantly at higher wind speeds and at higher rain intensities. Under simulated wind conditions, the number of conidia dispersed from source plants with wet leaves was only 22% of that for plants with dry leaves. Linear relationships were found between the number of conidia caught and the degree of infection of trap plants. [source] Aerodynamics of the Human Larynx During Vocal Fold Vibration,THE LARYNGOSCOPE, Issue 12 2005Randall L. Plant MD Abstract Objectives: The goal of this study was to comprehensively analyze the influence of aerodynamics on laryngeal function. Three specific aspects were considered: 1) a multidimensional comparison of the interaction of subglottic pressure, sound intensity, and fundamental frequency; 2) examination of instantaneous changes in subglottic pressure during each glottic cycle; and 3) determination of the threshold subglottic pressure for vocal fold vibration and its dependence on other aerodynamic factors. Study Design: Prospective study with six healthy individuals without history of voice disorders. Methods: The subjects vocalized the vowel sound /i/ with a variety of different intensities, pitch, and sound intensity. Subglottic air pressure, fundamental frequency, sound intensity, and the electroglottography signal were simultaneously measured. Results: Linear relationships were seen in all subjects between subglottic air pressure and sound intensity, although there were large variations in the slopes of these relationships. Rapid variations in subglottic pressure during each glottic cycle were detected, corresponding to the opening of the vocal folds with each individual vibration. Threshold pressures for vocal fold vibration were dependent primarily on sound intensity and fundamental frequency and tended to be higher at vibration onset than at offset. Conclusion: The larynx responded in a predictable pattern to general aerodynamic forces, but there was tremendous variability in its specific behavior. Fundamental frequency and sound intensity tended to increase with subglottic air pressure, but that relationship was not seen consistently in all subjects. The relationship between subglottic air pressure and sound intensity was usually linear, unlike the exponential relationship seen in previous studies. Subglottic pressure was noted to undergo rapid change with each glottic cycle in some, but not all, subjects and was most strongly affected by average subglottic pressure. Phonation threshold air pressure was influenced by the sound intensity and, to a smaller extent, by the fundamental frequency of the voiced sound. [source] Synthesis of betulin derivatives and the determination of their relative lipophilicities using reversed-phase thin-layer chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 3 2010Jacek Achrem-Achremowicz Abstract A series of superlipophilic or highly lipophilic semisynthetic betulin derivatives was prepared and their relative lipophilicity was measured by reversed-phase thin-layer chromatography (RP-TLC) at different pH values using 1,4-dioxane,acetate buffer mixtures as mobile phases. Cholesterol, 17,-estradiol and pure betulin were used as the reference compounds. Linear relationships were found between RM values and 1,4-dioxane concentrations in the mobile phases. LogP values were also calculated with computer programs ACD/LogP (ChemSketch 11.0, Advanced Chemistry Development Inc.) and ClogP (Daylight Chemical Information Systems Inc.). The empirical and theoretical data were compared, and the RM0 values correlated well with logP. Two of the synthesized betulin derivatives are reported for the first time. Copyright © 2009 John Wiley & Sons, Ltd. [source] An analytical method for cyclosporine using liquid chromatography,mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 2 2010Srividya V. Kanduru Abstract A liquid chromatographic mass spectrometric (LC-MS) assay has been developed for cyclosporine A (CyA) in rat plasma using amiodarone as internal standard (IS). Rat plasma (100,µL) containing drug and IS were extracted using liquid,liquid extraction with 4,mL of 95:5 ether:methanol. After evaporation of the organic layer the residue was reconstituted with 500,µL of water. Then the aqueous layer was transferred to LC-MS sample vials. A 10,µL volume was injected. The analysis was performed on a C8 column 3.5,µm (2.1 × 50,mm) heated to 60°C with a mobile phase consisting of acetonitrile:methanol:0.2% NH4OH (60:20:20) at an isocratic flow-rate of 0.2,mL/min. The ions used for quantitation of CyA and IS were m/z 1202.8 and 645.9, with retention times of 3.35 and 4.72,min, respectively. Linear relationships (r2,>,0.99) were achieved between plasma or blood concentration and peak height ratios (drug:IS) over the concentration range 50,5000,ng/mL. The CV% and mean error were <19%. Based on validation data, the lower limit of quantification for the assay was 50,ng/mL. The reported assay method displayed high measures of linearity, sensitivity, reliability and precision, allowing its applicability in pharmacokinetic studies in rat. Copyright © 2009 John Wiley & Sons, Ltd. [source] Rapid and sensitive determination of ephedrine and pseudoephedrine by micellar electrokinetic chromatography with on-line regenerating covalent coatingBIOMEDICAL CHROMATOGRAPHY, Issue 1 2005Xie Jianping Abstract A rapid, sensitive and reproducible micellar electrokinetic chromatographic method using hexamethyldisilazane as on-line regenerating covalent coating was developed for the quanti,cation of ephedrine (E) and pseudoephedrine (PE). E and PE were derivatized with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol for laser-induced ,uorescence detection. The on-line regenerating covalent coating formed a combinative double coating with the subsequently produced dynamic SDS coating. The total coating can be easily removed and conveniently regenerated on-line. The simple coating procedure was described. By a series of optimization, a running buffer of 20 mm Na2B4O7 + 16 mm SDS was applied for the separation of the derivatives. Linear relationships for E and PE were obtained in the range of 0.044,6.60 µg mL,1 (correlation coef,cients: 0.9975 for E, 0.9981 for PE), and the detection limits for E and PE were 1.71 and 0.67 ng mL,1, respectively. The separation speed, the reproducibility and the sensitivity were much improved over those of other capillary electrophoresis methods more recently reported. The method was applied to the analysis of the two alkaloids in traditional herbal preparations with recoveries in the range 92.8,104.8%. Copyright © 2004 John Wiley & Sons, Ltd. [source] Population pharmacokinetic modelling of gentamicin and vancomycin in patients with unstable renal function following cardiothoracic surgeryBRITISH JOURNAL OF CLINICAL PHARMACOLOGY, Issue 2 2006Christine E. Staatz Aims To describe the population pharmacokinetics of gentamicin and vancomycin in cardiothoracic surgery patients with unstable renal function. Methods Data collected during routine care were analyzed using NONMEM. Linear relationships between creatinine clearance (CLCr) and drug clearance (CL) were identified, and two approaches to modelling changing CLCr were examined. The first included baseline (BCOV) and difference from baseline (DCOV) effects and the second allowed the influence of CLCr to vary between individuals. Final model predictive performance was evaluated using independent data. The data sets were then combined and parameters re-estimated. Results Model building was performed using data from 96 (gentamicin) and 102 (vancomycin) patients, aged 17,87 years. CLCr ranged from 9 to 172 ml min,1 and changes varied from ,76 to 58 ml min,1 (gentamicin) and ,86 to 93 ml min,1 (vancomycin). Inclusion of BCOV and DCOV improved the fit of the gentamicin data but had little effect on that for vancomycin. Inclusion of interindividual variability (IIV) in the influence of CLcr resulted in a poorly characterized model for gentamicin and had no effect on vancomycin modelling. No bias was seen in population compared with individual CL estimates in independent data from 39 (gentamicin) and 37 (vancomycin) patients. Mean (95% CI) differences were 4% (,3, 11%) and 2% (,2, 6%), respectively. Final estimates were: CLGent (l h,1) = 2.81 × (1 + 0.015 × (BCOVCLCr -BCOVCLCr,Median) + 0.0174 × DCOVCLCr); CLVanc (l h,1) = 2.97 × (1 + 0.0205 ×, (CLCr -CLCr,Median)). IIV in CL was 27% for both drugs. Conclusions A parameter describing individual changes in CLcr with time improves population pharmacokinetic modelling of gentamicin but not vancomycin in clinically unstable patients. [source] Spectrally based remote sensing of river bathymetryEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2009Carl J. Legleiter Abstract This paper evaluates the potential for remote mapping of river bathymetry by (1) examining the theoretical basis of a simple, ratio-based technique for retrieving depth information from passive optical image data; (2) performing radiative transfer simulations to quantify the effects of suspended sediment concentration, bottom reflectance, and water surface state; (3) assessing the accuracy of spectrally based depth retrieval under field conditions via ground-based reflectance measurements; and (4) producing bathymetric maps for a pair of gravel-bed rivers from hyperspectral image data. Consideration of the relative magnitudes of various radiance components allowed us to define the range of conditions under which spectrally based depth retrieval is appropriate: the remotely sensed signal must be dominated by bottom-reflected radiance. We developed a simple algorithm, called optimal band ratio analysis (OBRA), for identifying pairs of wavelengths for which this critical assumption is valid and which yield strong, linear relationships between an image-derived quantity X and flow depth d. OBRA of simulated spectra indicated that water column optical properties were accounted for by a shorter-wavelength numerator band sensitive to scattering by suspended sediment while depth information was provided by a longer-wavelength denominator band subject to strong absorption by pure water. Field spectra suggested that bottom reflectance was fairly homogeneous, isolating the effect of depth, and that radiance measured above the water surface was primarily reflected from the bottom, not the water column. OBRA of these data, 28% of which were collected during a period of high turbidity, yielded strong X versus d relations (R2 from 0·792 to 0·976), demonstrating that accurate depth retrieval is feasible under field conditions. Moreover, application of OBRA to hyperspectral image data resulted in spatially coherent, hydraulically reasonable bathymetric maps, though negative depth estimates occurred along channel margins where pixels were mixed. This study indicates that passive optical remote sensing could become a viable tool for measuring river bathymetry. Copyright © 2009 John Wiley & Sons, Ltd. [source] Modelling and analysing evolution of dispersal in populations at expanding range boundariesECOLOGICAL ENTOMOLOGY, Issue 5 2007CLARE L. HUGHES Abstract 1.,Species would be expected to shift northwards in response to current climate warming, but many are failing to do so because of fragmentation of breeding habitats. Dispersal is important for colonisation and an individual-based spatially explicit model was developed to investigate impacts of habitat availability on the evolution of dispersal in expanding populations. Model output was compared with field data from the speckled wood butterfly Pararge aegeria, which currently is expanding its range in Britain. 2.,During range expansion, models simulated positive linear relationships between dispersal and distance from the seed location. This pattern was observed regardless of quantity (100% to 10% habitat availability) or distribution (random vs. gradient distribution) of habitat, although higher dispersal evolved at expanding range margins in landscapes with greater quantity of habitat and in gradient landscapes. Increased dispersal was no longer evident in any landscape once populations had reached equilibrium; dispersal values returned to those of seed populations. However, in landscapes with the least quantity of habitat, reduced dispersal (below that of seed populations) was observed at equilibrium. 3.,Evolutionary changes in adult flight morphology were examined in six populations of P. aegeria along a transect from the distribution core to an expanding range margin in England (spanning a latitudinal distance of >200 km). Empirical data were in agreement with model output and showed increased dispersal ability (larger and broader thoraxes, smaller abdomens, higher wing aspect ratios) with increasing distance from the distribution core. Increased dispersal ability was evident in populations from areas colonised >30 years previously, although dispersal changes were generally evident only in females. 4.,Evolutionary increases in dispersal ability in expanding populations may help species track future climate changes and counteract impacts of habitat fragmentation by promoting colonisation. However, at the highest levels of habitat loss, increased dispersal was less evident during expansion and reduced dispersal was observed at equilibrium indicating that, for many species, continued habitat fragmentation is likely to outweigh any benefits from dispersal. [source] Acute toxicity of fatty acids to the freshwater green alga Selenastrum capricornutumENVIRONMENTAL TOXICOLOGY, Issue 5 2003Yasushi Kamaya Abstract The acute toxicity of fatty acids (C14 to C18) commonly found in wood was determined by the standard algal growth inhibition test using the freshwater green alga Selenastrum capricornutum. Toxicity, quantified as IC50 values, varied depending on the number of total carbons and double bonds. Of the tested acids, oleic (cis -9-octadecenoic) acid showed the highest toxicity (72-h IC50 = 0.47 mg/L) to the alga, and triolein, a triglyceride of oleic acid, showed no apparent toxicity. Further examination of a series of C18:1 acids with a double bond at the 6, 11, or 12 position revealed that both double-bond position and cis or trans configuration affected toxicity. The 72-h IC50 data for these fatty acids and related compounds seemed to correlate well with the melting point (mp), showing two separate linear relationships: at mp < 35°C toxicity increased with increasing melting point, and at mp > 40°C toxicity decreased with melting point. © 2003 Wiley Periodicals, Inc. Environ Toxicol 18: 289,294, 2003. [source] Characterization of polycyclic aromatic hydrocarbon bioavailability in estuarine sediments using thin-film extractionENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2007Christopher J. Golding Abstract It is well documented that the bioavailability of hydrophobic organic chemicals (HOCs) can vary substantially among sediments. This makes risk assessments based on total sediment concentrations problematic. The present study investigates the application of thin-film solid-phase extraction to measure bioavailable concentrations of phenanthrene in estuarine sediment by comparing concentrations of phenanthrene in the amphipod Corophium colo and in thin ethylene/vinyl acetate films at different concentrations in three geochemically different sediments. For all sediment types, concentrations of phenanthrene in sediments and thin films followed linear relationships, indicating first-order exchange kinetics. Organism/thin-film concentration ratios did not vary systematically among sediment types but dropped significantly with increasing phenanthrene concentration in the sediments. While at low phenanthrene concentrations in the sediment fugacities of phenanthrene in the amphipods approached the fugacities in the thin films, they were significantly lower than those in the sediments at higher concentrations. While phenanthrene concentrations in the three sediment types were identical, biota sediment accumulation factors and concentrations in amphipods and thin films were consistently lower in sediments enriched with black carbon than in sediments with sedimentary organic matter bearing a more diagenetic organic signature. It is concluded that, for the range of concentrations tested, thin-film solid-phase extraction can be a useful tool in the characterization of differences in bioavailability of HOCs among sediment types. [source] Development and field validation of a predictive copper toxicity model for the green alga Pseudokirchneriella subcapitataENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2003Karel A. C. De Schamphelaere Abstract In this sudy, the combined effects of pH, water hardness, and dissolved organic carbon(DO) concentration and type on the chronic (72-h) effect of copper on growth inhibition of the green alga Pseudokirchneriella subcapitata were investigated. Natural dissolved organic matter (DOM) was collected at three sites in Belgium and The Netherlands using reverse osmosis. A full central composite test design was used for one DOM and a subset of the full design for the two other DOMs. For a total number of 35 toxicity tests performed, 72-h effect concentration resulting in 10% growth inhibition (EbC10s) ranged from 14.2 to 175.9 ,g Cu/L (factor 12) and 72-h EbC50s from 26.9 to 506.8 ,g Cu/L (factor 20). Statistical analysis demonstrated that DOC concentration, DOM type, and pH had a significant effect on copper toxicity; hardness did not affect toxicity at the levels tested. In general, an increase in pH resulted in increased toxicity, whereas an increase of the DOC concentration resulted in decreased copper toxicity. When expressed as dissolved copper, significant differences of toxicity reduction capacity were noted across the three DOM types tested (up to factor 2.5). When expressed as Cu2+ activity, effect levels were only significantly affected by pH; linear relationships were observed between pH and the logarithm of the effect concentrations expressed as free copper ion activity, that is, log(EbC50) and log(EbC10): (1) log(EbC50) = ,1.431 pH + 2.050 (r2 = 0.95), and (2) log(EbC10) = ,1.140 pH , 0.812 (r2 = 0.91). A copper toxicity model was developed by linking these equations to the WHAM V geochemical speciation model. This model predicted 97% of the EbC50dissolved and EbC10dissolved values within a factor of two of the observed values. Further validation using toxicity test results that were obtained previously with copper-spiked European surface waters demonstrated that for 81% of tested waters, effect concentrations were predicted within a factor of two of the observed. The developed model is considered to be an important step forward in accounting for copper bioavailability in natural systems. [source] Evaluating and expressing the propagation of uncertainty in chemical fate and bioaccumulation modelsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2002Matthew MacLeod Abstract First-order analytical sensitivity and uncertainty analysis for environmental chemical fate models is described and applied to a regional contaminant fate model and a food web bioaccumulation model. By assuming linear relationships between inputs and outputs, independence, and log-normal distributions of input variables, a relationship between uncertainty in input parameters and uncertainty in output parameters can be derived, yielding results that are consistent with a Monte Carlo analysis with similar input assumptions. A graphical technique is devised for interpreting and communicating uncertainty propagation as a function of variance in input parameters and model sensitivity. The suggested approach is less calculationally intensive than Monte Carlo analysis and is appropriate for preliminary assessment of uncertainty when models are applied to generic environments or to large geographic areas or when detailed parameterization of input uncertainties is unwarranted or impossible. This approach is particularly useful as a starting point for identification of sensitive model inputs at the early stages of applying a generic contaminant fate model to a specific environmental scenario, as a tool to support refinements of the model and the uncertainty analysis for site-specific scenarios, or for examining defined end points. The analysis identifies those input parameters that contribute significantly to uncertainty in outputs, enabling attention to be focused on defining median values and more appropriate distributions to describe these variables. [source] Semiparametric approaches to flow normalization and source apportionment of substance transport in riversENVIRONMETRICS, Issue 3 2001Per Stålnacke Abstract Statistical analysis of relationships between time series of data exhibiting seasonal variation is often of great interest in environmental monitoring and assessment. The present study focused on regression models with time-varying intercept and slope parameters. In particular, we derived and tested semiparametric models in which rapid interannual and interseasonal variation in the intercept were penalized in the search for a model that combined a good fit to data with smoothly varying parameters. Furthermore, we developed a software package for efficient estimation of the parameters of such models. Test runs on time series of runoff data and riverine loads of nutrients and chloride in the Rhine River showed that the proposed smoothing methods were particularly useful for analysis of time-varying linear relationships between time series of data with both seasonal variation and temporal trends. The predictivity of the semiparametric models was superior to that of conventional parametric models. In addition, normalization of observed annual loads to mean or minimum runoff produced smooth curves that provided convincing evidence of human impact on water quality. Copyright © 2001 John Wiley & Sons, Ltd. [source] Rapid Organocatalytic Aldehyde-Aldehyde Condensation ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2007Anniina Erkkilä Abstract We report the results of the systematic optimization of the ,-methylenation of aldehydes with aqueous formaldehyde. A simple combination of a secondary amine catalyst and a weak acid co-catalyst has been identified, allowing access to ,-substituted acroleins in a matter of minutes. In the absence of formaldehyde, the catalytic system promoted the self-condensation reaction of ,,,-unsaturated aldehydes. Both of these reactions exhibited linear relationships between co-catalyst acidities and reaction rates. A second-order dependence of catalyst concentration was observed, pointing to the involvement of two molecules of the ammonium catalyst in the rate-determining step. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Sediment Loss from a Waste Rock Dump, ERA Ranger Mine, Northern AustraliaGEOGRAPHICAL RESEARCH, Issue 1 2001Michael J. Saynor During the 1994/95 wet season, runoff, suspended load and bedload loss from large scale erosion plots under natural rainfall events were measured at three sites with different treatments on the Energy Resources of Australia Ranger waste rock dump (cap, soil, fire). The fire site has well established trees, the soil site smaller shrubs and the cap site minimal vegetation. All three sites are located on the flat areas of the waste rock dump with similar slopes and cap, fire and soil are local names for the sites. The quantity of bedload eroded from the soil and fire sites decreased during the monitoring period, however, the same trend was not observed on the cap site. Bedload loss from the fire and soil sites is significantly log-linear with time and reduces at a decreasing rate until becoming statistically constant toward the later part of the first half of the wet season. For corresponding storms at each site, bedload erosion was highest from the unvegetated and unripped cap site and lowest from the well vegetated fire site. Site specific linear relationships between bedload and total sediment load have been derived and can be used to derive total sediment load in the absence of measured suspended load. [source] Leaf litter nitrogen concentration as related to climatic factors in Eurasian forestsGLOBAL ECOLOGY, Issue 5 2006Chunjiang Liu ABSTRACT Aim, The aim of this study is to determine the patterns of nitrogen (N) concentrations in leaf litter of forest trees as functions of climatic factors, annual average temperature (Temp, °C) and annual precipitation (Precip, dm) and of forest type (coniferous vs. broadleaf, deciduous vs. evergreen, Pinus, etc.). Location, The review was conducted using data from studies across the Eurasian continent. Methods, Leaf litter N concentration was compiled from 204 sets of published data (81 sets from coniferous and 123 from broadleaf forests in Eurasia). We explored the relationships between leaf litter N concentration and Temp and Precip by means of regression analysis. Leaf litter data from N2 -fixing species were excluded from the analysis. Results, Over the Eurasian continent, leaf litter N concentration increased with increasing Temp and Precip within functional groups such as conifers, broadleaf, deciduous, evergreen and the genus Pinus. There were highly significant linear relationships between ln(N) and Temp and Precip (P < 0.001) for all available data combined, as well as for coniferous trees, broadleaf trees, deciduous trees, evergreen trees and Pinus separately. With both Temp and Precip as independent variables in multiple regression equations, the adjusted coefficient of determination () was evidently higher than in simple regressions with either Temp or Precip as independent variable. Standardized regression coefficients showed that Temp had a larger impact than Precip on litter N concentration for all groups except evergreens. The impact of temperature was particularly strong for Pinus. Conclusions, The relationship between leaf litter N concentration and temperature and precipitation can be well described with simple or multiple linear regression equations for forests over Eurasia. In the context of global warming, these regression equations are useful for a better understanding and modelling of the effects of geographical and climatic factors on leaf litter N at a regional and continental scale. [source] Rainfall-discharge relationships for a monsoonal climate in the Ethiopian highlandsHYDROLOGICAL PROCESSES, Issue 7 2008Ben M. Liu Abstract This study presents a simple rainfall-discharge analysis for the Andit Tid, Anjeni, and Maybar watersheds of northern Ethiopia. The Soil Conservation Research Programme (SCRP) established monitoring stations in each of these sites during the 1980s, with climate and stream flow measurements being recorded up to the present. To show how these data could be used to provide insight into catchment-level runoff mechanisms, simple linear relationships between effective precipitation and runoff are developed for each watershed, with the conclusion that all three watersheds exhibit consistent hydrologic behaviour after approximately 500 mm of cumulative effective seasonal rainfall has fallen since the beginning of season. After the 500 mm rainfall threshold is reached, approximately 50% of any further precipitation on these watersheds will directly contribute to catchment runoff. Copyright © 2008 John Wiley & Sons, Ltd. [source] Use of turbidometry to characterize suspended sediment and phosphorus fluxes in the Lake Tahoe basin, California, USAHYDROLOGICAL PROCESSES, Issue 3 2007Andrew P. Stubblefield Abstract The efficacy of in-stream nephelometric turbidometry as a surrogate for total suspended solids (TSS) and total phosphorus (TP) concentrations was evaluated for use in low turbidity (<50 NTU) subalpine watersheds at Lake Tahoe, California,Nevada, USA. Continuous turbidity records for the 1999, 2000 and 2001 snowmelt seasons and data from water quality samples (1982,2000) were examined to determine watershed sediment delivery dynamics. Strong correlations were found between turbidity and both TSS and TP concentration. The strong correlation indicates that turbidity can serve as a good surrogate for direct measurement in these watersheds. The watersheds displayed clockwise hysteresis: sediment flushing and depletion, on daily, seasonal and decadal time-scales. The hysteresis curves had strong concave shapes, indicating a sensitive response to peak flow. A pronounced seasonal trend was observed for the ratio of suspended sediment concentration (SSC)/discharge over time, indicating early season flushing of available sediment. Significant linear relationships (p < 0·05) were found for 12 of 17 years. Comparison of annual sediment rating curve coefficients indicated smaller coefficients during high sediment loading years and in the years following. The smaller coefficients are evidence of sediment depletion during high flow years. The effect of hysteresis on monitoring methods was illustrated by comparing turbidity estimates of TSS load with sediment rating curve estimates of SSC. After accounting for differences in SSC/TSS methods of analysis, daily loads calculated with turbidity methods were 58,98% of rating curve estimates for the spring snowmelt seasons of 1999,2001. Copyright © 2006 John Wiley & Sons, Ltd. [source] Relationship of topography to surface water chemistry with particular focus on nitrogen and organic carbon solutes within a forested watershed in Hokkaido, JapanHYDROLOGICAL PROCESSES, Issue 2 2006Akiko Ogawa Abstract We studied the relationships between streamwater chemistry and the topography of subcatchments in the Dorokawa watershed in Hokkaido Island, northern Japan, to examine the use of topography as a predictor of streamwater chemistry in a watershed with relatively moderate terrain compared with other regions of Japan. Topographic characteristics of the Dorokawa watershed and its subcatchments were expressed as topographic index (TI) values, which ranged from 4·5 to 20·4 for individual grid cells (50 × 50 m2), but averaged from 6·4 to 7·4 for the 20 subcatchments. Streamwater samples for chemical analyses were collected four times between June and October 2002 from 20 locations in the watershed. The pH of water that passed through the watershed increased from ,5·0 to 7·0, with major increases in Na+ and Ca2+ and marked decreases in NO3, and SO. Distinctive spatial patterns were observed for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and NO3, concentrations of streamwater across the watershed. Statistical analyses indicated significant linear relationships between the average TI values of subcatchments and DOC, DON, and NO3, concentrations. Furthermore, the proportion of DOC in streamwaters in the wet season increased with TI values relative to other nitrogen species, whereas NO3, concentrations decreased with TI. The gradients of soil wetness and the presence of wetlands explained many of the observed spatial and temporal patterns of DOC, DON, and NO3, concentrations in the surface waters of the Dorokawa watershed. Our results suggest that the TI is especially useful for predicting the spatial distribution of DOC, DON and NO3, in the surface waters of Hokkaido, where topographical relief is moderate and wetlands more common than in other regions of Japan. Copyright © 2006 John Wiley & Sons, Ltd. [source] A theoretical investigation on the structures, densities, detonation properties, and pyrolysis mechanism of the nitro derivatives of phenolsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2010Guixiang Wang Abstract The nitro derivatives of phenols are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G* level. Detonation properties are evaluated using the modified Kamlet,Jacobs equations based on the calculated densities and heats of formation. It is found that there are good linear relationships between density, detonation velocity, detonation pressure, and the number of nitro and hydroxy groups. Thermal stability and pyrolysis mechanism of the title compounds are investigated by calculating the bond dissociation energies (BDEs) at the unrestricted B3LYP/6-31G* level. The activation energies of H-transfer reaction is smaller than the BDEs of all bonds and this illustrates that the pyrolysis of the title compounds may be started from breaking OH bond followed by the isomerization reaction of H transfer. Moreover, the CNO2 bond with the smaller bond overlap population and the smaller BDE will also overlap may be before homolysis. According to the quantitative standard of energetics and stability as a high-energy density compound, pentanitrophenol essentially satisfies this requirement. In addition, we have discussed the effect of the nitro and hydroxy groups on the static electronic structural parameters and the kinetic parameter. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] U.S. Perceptions of Nuclear Security in the Wake of the Cold War: Comparing Public and Elite Belief SystemsINTERNATIONAL STUDIES QUARTERLY, Issue 4 2002Kerry G. Herron Our research adds new evidence to the continuing debate about capacities of mass publics to contribute to foreign and security policy processes. Focusing on U.S. beliefs and preferences about nuclear security in the post,Cold War era, we examine not only linear relationships among elite and mass belief structures, but also combinations of beliefs that may be precursors to policy coalitions. We examine attitudes and preferences about nuclear issues among two elite publics,scientists and legislators,surveyed in 1997, and among two samples of the U.S. general public surveyed in 1997 and 1999. We compare elite and mass belief structures using three different methods: descriptive comparisons of central tendencies, relational analyses using bivariate and multivariate regressions, and coalitional analyses using cluster analytical techniques. With each method of analysis we find evidence of similar belief structures and similar relationships between beliefs and nuclear policy preferences among our elite and mass samples. [source] Mineral absorption in tapirs (Tapirus spp.) as compared to the domestic horseJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 6 2009M. Clauss Summary To test whether mineral recommendations for horses are likely to guarantee adequate mineral provision for tapirs (Tapirus spp.), we investigated the apparent absorption (aA) of macro and micro-minerals in 18 tapirs from five zoological institutions in a total of 24 feeding trials with total faecal collection. Samples of feeds and faeces were analysed for Ca, P, Mg, Na, K, Fe, Cu and Zn. The resulting aA coefficients and the linear relationships of apparently absorbable dietary mineral content to total dietary mineral content (per 100 g dry matter) were compared with data for domestic horses. While there were no apparent differences in the absorption patterns for P, K, Na, Fe, Cu or Zn, the absorption of both Ca and Mg was distinctively higher in tapirs than in horses. Tapirs are browsers that are adapted to a diet of higher Ca content and higher Ca:P ratio than equids, and high absorptive efficiency for Ca might have evolved to ensure that high dietary Ca concentrations do not lead to the binding of dietary P in the intestine, making it unavailable for hindgut microbes. Similar to other hindgut fermenters, in tapirs, absorption coefficients for Ca increased with dietary Ca:P ratio, and urinary Ca:creatinine ratios increased with dietary Ca. Several zoo diets used were deficient in one or more minerals. When compared with faeces of free-ranging animals, faeces of zoo animals had higher concentrations of most minerals, probably indicating a lesser diluting effect of indigestible fibre in zoo animals. [source] Linear and threshold forecasts of output and inflation using stock and housing pricesJOURNAL OF FORECASTING, Issue 2 2008Greg Tkacz Abstract This study examines whether simple measures of Canadian equity and housing price misalignments contain leading information about output growth and inflation. Previous authors have generally found that the information content of asset prices in general, and equity and housing prices in particular, are unreliable in that they do not systematically predict future economic activity or inflation. However, earlier studies relied on simple linear relationships that would fail to pick up the potential nonlinear effects of asset price misalignments. Our results suggest that housing prices are useful for predicting GDP growth, even within a linear context. Meanwhile, both stock and housing prices can improve inflation forecasts, especially when using a threshold specification. These improvements in forecast performance are relative to the information contained in Phillips-curve type indicators for inflation and IS-curve type indicators for GDP growth. Copyright © 2008 John Wiley & Sons, Ltd. [source] Predicting the phase equilibria of petroleum fluids with the SAFT-VR approachAICHE JOURNAL, Issue 3 2007Lixin Sun Abstract The SAFT-VR equation of state is combined with a semi-continuous thermodynamic approach to model several synthetic and crude oil systems. In our approach, the oil fractions are defined by a continuous distribution that is then represented as discrete pseudo-components using the Gaussian quadrature method. The SAFT-VR parameters for the pseudo-components are obtained from simple linear relationships that were defined in earlier work, which allows the approach to be easily applied to undefined oil systems. Good agreement between the theoretical predictions and experimental data is obtained for bubble point pressure calculations of several gas condensates and the solubility of gases such as methane, ethane, and carbon dioxide in several crude oils. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] THE APPLICATION OF ELECTRON SPIN RESONANCE AS A GUIDE TO THE MATURATION AND TYPING OF ORGANIC MATTER IN THE NORTH SEAJOURNAL OF PETROLEUM GEOLOGY, Issue 1 2003R. A. McTavish In early electron spin resonance (ESR) analysis of North Sea wells, maturation of organic matter (OM) was expressed in terms of maximum palaeotemperature (MPT) based on North American calibrations that did not consider the influences of kerogen composition or overpressure. In the North Sea, the MPTs were anomalous in overpressured sequences and relative to other indices of OM maturation such as vitrinite reflectance, so the ESR method was abandoned there in geochemical studies. However, early empirical study of North Sea ESR data indicated that, in relation to functions that linked temperature and pore pressure, some ESR parameters were predictable without reference to MPTs. In order to re-evaluate ESR parameters as indices of OM maturation, the physical factors (temperature and pressure) which affect OM maturation are related in the present paper to the ESR parameters "g" (spectral position) and Ng (spin density) at six well locations in the northern North Sea. A third ESR parameter, W (line width), is not an effective guide to maturation levels due to its complex relationship to the physical factors and kerogen types. However, cross-plots of W versus "g" and Ng appear to be as effective as pyrolysis for kerogen typing. Levels of maturation investigated in the North Sea wells range through the equivalent vitrinite reflectance values of about 0.50,1.50%. The values of "g" and Ng have been differentiated for kerogen type, but undifferentiated values of "g" have also been studied. Regression analysis has shown that there are linear relationships between the ESR parameters "g" and Ng, and the physical factors present-day temperature (To), "effective" temperature (Te), and differential pressure (Pd). Correlation coefficients for both "g" (undifferentiated and differentiated) and Ng (differentiated) relative to the physical factors are high; the highest values are for "g" and Ng relative to Te and Pd (r =,0.950 for "g" differentiated or undifferentiated, r = 0.944,0.976 for Ng differentiated, respectively). However, correlation coefficients were lower for "g" and Ng relative to To. More frequent high correlation coefficients and larger sample populations suggest that "g" (undifferentiated) is a more reliable index of OM maturation than Ng(differentiated). However, the estimation of levels of OM maturation is improved if both indices are used together. The ESR method appears to be effective both for estimating levels of OM maturation and for kerogen typing. It has a number of potential advantages over other geochemical methods: firstly, it is more sensitive for estimating OM maturation than most other methods; secondly, it can be used to analyze organic matter which is as old as Proterozoic; thirdly, it does not destroy the samples analyzed. [source] | |||||||||||||||||||||||||