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Regression Coefficients (regression + coefficient)
Kinds of Regression Coefficients Selected AbstractsGood modeling practice for PAT applications: Propagation of input uncertainty and sensitivity analysisBIOTECHNOLOGY PROGRESS, Issue 4 2009Gürkan Sin Abstract The uncertainty and sensitivity analysis are evaluated for their usefulness as part of the model-building within Process Analytical Technology applications. A mechanistic model describing a batch cultivation of Streptomyces coelicolor for antibiotic production was used as case study. The input uncertainty resulting from assumptions of the model was propagated using the Monte Carlo procedure to estimate the output uncertainty. The results showed that significant uncertainty exists in the model outputs. Moreover the uncertainty in the biomass, glucose, ammonium and base-consumption were found low compared to the large uncertainty observed in the antibiotic and off-gas CO2 predictions. The output uncertainty was observed to be lower during the exponential growth phase, while higher in the stationary and death phases - meaning the model describes some periods better than others. To understand which input parameters are responsible for the output uncertainty, three sensitivity methods (Standardized Regression Coefficients, Morris and differential analysis) were evaluated and compared. The results from these methods were mostly in agreement with each other and revealed that only few parameters (about 10) out of a total 56 were mainly responsible for the output uncertainty. Among these significant parameters, one finds parameters related to fermentation characteristics such as biomass metabolism, chemical equilibria and mass-transfer. Overall the uncertainty and sensitivity analysis are found promising for helping to build reliable mechanistic models and to interpret the model outputs properly. These tools make part of good modeling practice, which can contribute to successful PAT applications for increased process understanding, operation and control purposes. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Multi-block and path modelling proceduresJOURNAL OF CHEMOMETRICS, Issue 11-12 2008Agnar Höskuldsson Abstract The author has developed a unified theory of path and multi-block modelling of data. The data blocks are arranged in a directional path. Each data block can lead to one or more data blocks. It is assumed that there is given a collection of input data blocks. Each of them is supposed to describe one or more intermediate data blocks. The output data blocks are those that are at the ends of the paths and have no succeeding data blocks. The optimisation procedure finds weights for the input data blocks so that the size of the total loadings for the output data blocks are maximised. When the optimal weight vectors have been determined, the score and loading vectors for the data blocks in the path are determined. Appropriate adjustment of the data blocks is carried out at each step. Regression coefficients are computed for each data block that show how the data block is estimated by data blocks that lead to it. Methods of standard regression analysis are extended to this type of modelling. Three types of ,strengths' of relationship are computed for each set of two connected data blocks. First is the strength in the path, second the strength where only the data blocks leading to the last one are used and third if only the two are considered. Cross-validation and other standard methods of linear regression are carried out in a similar manner. In industry, processes are organised in different ways. It can be useful to model the processes in the way they are carried out. By proper alignment of sub-processes, overall model can be specified. There can be several useful path models during the process, where the data blocks in a path are the ones that are actual or important at given stages of the process. Data collection equipments are getting more and more advanced and cheap. Data analysis need to ,catch up' with the challenges that these new technology provides with. Copyright © 2008 John Wiley & Sons, Ltd. [source] PC-Based ECG Waveform Recognition,Validation of Novel Software Against a Reference ECG DatabaseANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2009Corina-Dana Dota M.D. Background: PC-based ECG measurements must cope with normal as well as pathological ECGs in a reliable manner. EClysis, a software for ECG measurements was tested against reference values from the Common Standards for Quantitative Electrocardiography (CSE) database. Methods: Digital ECGs (12 leads, 500 Hz) were recorded by the CSE project. Data Set 3 contains reference values for 125 ECGs (33 normal and 92 pathological). Median values of measurements by 11 computer programs and by five cardiologists, respectively, refer to the earliest P and QRS onsets and to the latest P, QRS, and T offsets in any lead of a selected (index) beat. EClysis automatically measured all ECGs, without user interference. Results: The PQRST points were correctly detected but in two ECGs with AV block II,III. The software was not designed to detect atrial activity in atrial fibrillation (n = 9) and flutter (n = 1). In one case of atrial fibrillation, atrial activity interfered with positioning of QRS and T offsets. Regression coefficients between EClysis© and CSE (software-generated and human) were above 0.95 (P < 0.0001). The confidence intervals were 95% for the slope and the intercept of the regression lines. Conclusions: The PC-based detection and analysis of PQRST points showed a high level of agreement with the CSE database reference values. [source] Impact of substance use on the physical health of patients with bipolar disorderACTA PSYCHIATRICA SCANDINAVICA, Issue 6 2010M. P. Garcia-Portilla Garcia-Portilla MP, Saiz PA, Benabarre A, Florez G, Bascaran MT, Díaz EM, Bousoño M, Bobes J. Impact of substance use on the physical health of patients with bipolar disorder. Objective:, To describe the impact of tobacco, alcohol and cannabis on metabolic profile and cardiovascular risk in bipolar patients. Method:, Naturalistic, cross-sectional, multicenter Spanish study. Current use of tobacco, alcohol and cannabis was determined based on patient self-reports. Metabolic syndrome was defined using the National Health and Nutrition Examination Survey 1999,2000 and the American Heart Association/National Heart, Lung and Blood Institute criteria, and cardiovascular risk using the Framingham and the Systematic Coronary Risk Evaluation functions. Results:, Mean age was 46.6 years, 49% were male. Substance use: 51% tobacco, 13% alcohol and 12.5% cannabis. Patients who reported consuming any substance were significantly younger and a higher proportion was male. After controlling for confounding factors, tobacco was a risk factor for coronary heart disease (CHD) (unstandardized linear regression coefficient 3.47, 95% confidence interval 1.85,5.10). Conclusion:, Substance use, mainly tobacco, was common in bipolar patients. Tobacco use negatively impacted CHD risk. [source] HbA1c levels in non-diabetic Dutch children aged 8,9 years: the PIAMA birth cohort studyDIABETIC MEDICINE, Issue 2 2009H. Jansen Abstract Aim, Glycated haemoglobin (HbA1c) is considered the best index of glycaemic control in established diabetes. It may also be useful in the diagnosis of diabetes and as a screening tool. Little is known about the distribution of HbA1c in healthy children and its predictors. The aim of this study is to describe the distribution of HbA1c in non-diabetic Dutch children aged 8,9 years and to investigate potential associations of HbA1c in this group. Methods HbA1c was measured in 788 non-diabetic children aged 8,9 years participating in the PIAMA birth cohort study. Data on parents and children were collected prospectively by questionnaires. Weight, height and waist and hip circumference of the children were measured when blood samples were taken. Results, Mean (sd) HbA1c was 4.9 ± 0.33%, range 3.5,6.0%. HbA1c was significantly higher in boys (4.9 ± 0.31 vs. 4.9 ± 0.33%) and in children of mothers with gestational diabetes (5.0 ± 0.37 vs. 4.9 ± 0.32%). We found a significant inverse association between HbA1c and haemoglobin (regression coefficient: ,0.169 (95% CI ,0.221 to ,0.118), P < 0.001). HbA1c was not significantly associated with age, body mass index, waist circumference, parental diabetes or maternal body mass index. Conclusions, We found no significant relation between known risk factors for Type 2 diabetes and HbA1c at age 8,9 years. Moreover, there was a significant inverse association between haemoglobin and HbA1c. These results suggest that HbA1c may not only reflect the preceding blood glucose levels, but seems to be determined by other factors as well. [source] Barrel Plating Rhodium Electrode: Application to Flow Injection Analysis of HydrazineELECTROANALYSIS, Issue 14 2005Jun-Wei Sue Abstract We introduce here the application of barrel plating technology for mass production of disposable-type electrodes. Easy for mass production, barrel plating rhodium electrode (Rh-BPE) is for the first time demonstrated for analytical application. Hydrazine was chosen as a model analyte to elucidate the electrocatalytic and analytical ability of the Rh-BPE system in pH,7 phosphate buffer solution. Flow injection analysis (FIA) of hydrazine showed a linear calibration range of 25,1000,ppb with a slope and a regression coefficient of 5,nA/ppb and 0.9946, respectively. Twenty-two replicate injections of 25,ppb hydrazine showed a relative standard deviation of 3.17% indicating a detection limit (S/N=3) of 2.5,ppb. The system can be continuously operated for 1 day without any alteration in the FIA signals and is tolerable to the interference of oxalic acid, gelatine, Triton X-100, and albumin for even up to 100 times excess in concentration with respect to 400,ppb hydrazine. Since the fabrication cost of the electrode is cheap, it is thus disposable in nature. Furthermore, barrel plating technique can be extendable to other transition metals for application in many fields of research interest. [source] Analysis of flavonoids by CE using capacitively coupled contactless conductivity detectionELECTROPHORESIS, Issue 5 2007Stefan Bachmann Abstract A CE method employing capacitively coupled contactless conductivity (C4D) compared to indirect UV-detection was developed for the analysis of phytochemically relevant flavonoids, such as 6-hydroxyflavone, biochanin A, hesperetin and naringenin. To ensure fast separation at highest selectivity, sensitivity and peak symmetry, the pH value and the concentration of the running BGE had to be optimized regarding both co- and counter-EOF mode. Optimum conditions were found to be 1.0 and 5.0,mM chromate BGE (pH,9.50) in the counter- and co-EOF mode, respectively. Validation of the established CE-C4D method pointed out to be approximately seven times more sensitive compared to indirect UV-detection applying the same conditions. The lower LOD defined at an S/N of 3:1 was found between 0.12 and 0.21,µg/mL for the analytes of interest using C4D and between 0.77 and 1.20,µg/mL using indirect UV-detection. Compared to an earlier published CE method employing direct UV-detection, C4D was found to be approximately two times more sensitive. Due to the lower baseline noise, C4D showed an excellent regression coefficient >0.99 compared to 0.93 when using indirect UV detection calibrating within a concentration range between 1 and 10,µg/mL. The influence of the sugar moiety on the conductivity of a flavonoid was studied upon the analysis of the aglycon hesperetin and the rutinosid hesperidin. The sugar moiety in hesperedin shows a higher conductivity compared to hesperetin. Finally, the optimized established CE-C4D method was applied to the determination and quantification of naringenin in Sinupret®. [source] Evaluation of poly(ethylene-co-vinyl acetate-co-carbon monoxide) and polydimethylsiloxane for equilibrium sampling of polar organic contaminants in waterENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2009Jörgen A Magnér Abstract Abstract-The aim of the present study was to develop a passive a bsorptive equilibrium sampler that would enable the determination of the concentrations of polar organic compound (POC) in water more efficiently than existing techniques. To this end, a novel plastic material, poly(ethylene-co-vinyl acetate-co-carbon monoxide) (PEVAC), was evaluated and the results were compared with an existing silicone-based passive absorptive equilibrium device. Seven compounds (imidacloprid, carbendazim, metoprolol, atrazin, carbamazepine, diazinon, and chlorpyrifos), a mixture of pharmaceuticals, and pesticides with a logarithmic octanol-water partition coefficient ranging from 0.2 to 4.77 were selected as model substances for the experiments. The results showed that six of the seven selected POCs reached distribution equilibrium within 4 d in the two materials tested. A linear relation with a regression coefficient of more than 0.8906 between the established logarithmic absorbent-water partition coefficient and the calculated logarithmic dissociation partition coefficient of the selected compounds in the two polymers was observed. The correlation between these two coefficients was within one order of magnitude for the compounds that reached equilibrium in the two polymers, which demonstrates that both materials are suitable for mimicking biological uptake of POCs. The PEVAC material showed an enhanced sorption for all selected compounds compared to the silicone material and up to five times higher enrichment for the most polar compound. Fluorescence analysis of the sampler cross-section, following the uptake of fluoranthene, and proof that the sorption was independent of surface area variations demonstrated that the PEVAC polymer possessed absorptive rather than adsorptive enrichment of organic compounds. [source] Quantifying the effects of aggregation, particle size and components on the colour of Mediterranean soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2004M. SÁnchez-Marañón Summary Aggregation, particle size, and chemical composition affect the colour of the soil. We have attempted to quantify and understand these effects in 12 Mediterranean soils. We measured the CIELAB colour variables hab, L*, and C*ab in aggregated and dispersed soil samples, and also in coarse sand, fine sand, silt, and clay samples before and after sequential removal of organic matter, carbonates, and Fe oxides. Grassmann's colour-mixing equations adjusted by regression analysis described the colour of the dispersed soil from its particle-size fractions with an error of 1% for hab, 4% for L*, and 9% for C*ab. This suggests that the contribution of each fraction to the colour of the dispersed soil can be accurately calculated by its colorimetric data weighted by its content and a regression coefficient, which was greatest for clay. We inferred the influence of a component within each fraction by measuring the colour changes after its removal. Iron oxides reduced hab of the silicated substrate by 19%, reduced L* by 12%, and increased C*ab by 64% in all particle-size fractions. Carbonates and organic matter had little influence: the former because they impart little colour to the silicates and the latter because there was little of it. The CIELAB colour-difference between dispersed and aggregated soil (mean ,E*ab = 15.3) was due mainly to ,L* (,14.7). Aggregation contributed to diminishing L* of dispersed soil by 34%. Scanning electron microscopy showed that Fe oxides and organic coatings cover the surface of aggregates thereby influencing soil colour. [source] Estimation of the phosphorus sorption capacity of acidic soils in IrelandEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2001R. O. Maguire Summary The test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be , (Alox + Feox), where Alox and Feox are the amounts of aluminium and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil,1, and a value of 0.5 is commonly used for the scaling factor , in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (Pox) so that DPS = Pox/PSC. The relation between PSC and Alox, Feox and Pox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Alox and Feox extracted, but there was also a negative correlation with Pox. When PSC was calculated as the sum of the measured sorption after 252 days and Pox, the multiple regression of PSC on Alox and Feox gave the equation PSC = 36.6 + 0.61 Alox+,0.31 Feox with a coefficient of determination (R2) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Alox and Feox did not overlap, indicating a significantly larger regression coefficient of P sorption on Alox than on Feox. When loss on ignition was employed as an additional variable in the multiple regression of PSC on Alox and Feox, it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant (P <,0.001), the impact of this variable was small as its inclusion in the multiple regression increased R2 by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0,3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water-soluble P than either the Olsen or Morgan tests for P in soil. [source] AN EXACT FORM OF THE BREEDER'S EQUATION FOR THE EVOLUTION OF A QUANTITATIVE TRAIT UNDER NATURAL SELECTIONEVOLUTION, Issue 11 2005John S. Heywood Abstract Starting with the Price equation, I show that the total evolutionary change in mean phenotype that occurs in the presence of fitness variation can be partitioned exactly into five components representing logically distinct processes. One component is the linear response to selection, as represented by the breeder's equation of quantitative genetics, but with heritability defined as the linear regression coefficient of mean offspring phenotype on parent phenotype. The other components are identified as constitutive transmission bias, two types of induced transmission bias, and a spurious response to selection caused by a covariance between parental fitness and offspring phenotype that cannot be predicted from parental phenotypes. The partitioning can be accomplished in two ways, one with heritability measured before (in the absence of) selection, and the other with heritability measured after (in the presence of) selection. Measuring heritability after selection, though unconventional, yields a representation for the linear response to selection that is most consistent with Darwinian evolution by natural selection because the response to selection is determined by the reproductive features of the selected group, not of the parent population as a whole. The analysis of an explicitly Mendelian model shows that the relative contributions of the five terms to the total evolutionary change depends on the level of organization (gene, individual, or mated pair) at which the parent population is divided into phenotypes, with each frame of reference providing unique insight. It is shown that all five components of phenotypic evolution will generally have nonzero values as a result of various combinations of the normal features of Mendelian populations, including biparental sex, allelic dominance, inbreeding, epistasis, linkage disequilibrium, and environmental covariances between traits. Additive genetic variance can be a poor predictor of the adaptive response to selection in these models. The narrow-sense heritability s,2A/s,2P should be viewed as an approximation to the offspring-parent linear regression rather than the other way around. [source] Surface deformation induced by present-day ice melting in SvalbardGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009H. P. Kierulf SUMMARY The vertical movement of the Earth's surface is the result of a number of internal processes in the solid Earth, tidal forces and mass redistribution in the atmosphere, oceans, terrestrial hydrosphere and cryosphere. Close to ice sheets and glaciers, the changes in the ice loads can induce large vertical motions at intraseasonal to secular timescales. The Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) antennas in Ny-Ålesund, Svalbard that started observations in 1991 and 1995, respectively, observe vertical uplift rates on the order of 8 ± 2 mm yr,1, which are considerably larger than those predicted by postglacial rebound (PGR) models (order 2 mm yr,1). The observations also indicate increased uplift rates starting some time in 2000. A local GPS campaign network that has been reoccupied annually since 1998, reveals a tilting away from the neighbouring glaciers. The Svalbard glaciers have been undergoing melting and retreat during the last century, with increased melting since about 2000. We compared the observed vertical motion to the motion predicted by loading models using a detailed ice model with annual time resolution as forcing. The model predictions correlate well with the observations both with respect to the interannual variations and the spatial pattern of long-term trends. The regression coefficients for predicted and observed interannual variations in height is 1.08 ± 0.38, whereas the regression coefficient for the predicted and observed spatial pattern turns out to be 1.26 ± 0.42. Estimates of the predicted secular trend in height due to PGR and present-day melting are on the order of 4.8 ± 0.3 mm yr,1 and thus smaller than the observed secular trend in height. This discrepancy between predictions and observations is likely caused by the sum of errors in the secular rates determined from observations (due to technique-dependent large-scale offsets) and incomplete or erroneous models (unaccounted tectonic vertical motion, errors in the ice load history, scale errors in the viscoelastic PGR models and the elastic models for present-day melting). [source] Factors enabling home death of the elderly in an institution specializing in home medical care: Analysis of apprehension of the bereaved familyGERIATRICS & GERONTOLOGY INTERNATIONAL, Issue 2 2008Akiko Akiyama Aim: To determine the factors enabling home death despite caregiver apprehension about home medical care. Methods: This study was an anonymous mailed survey of bereaved family members (the caregiver) of patients who died in a home medical care setting provided by an institution specializing in home medical care in Japan (home death rate, ,80%). We analyzed the relationships between caregiver apprehension about home medical care, overall satisfaction with home medical care and the place of death. Results: Higher caregiver apprehension about home medical care and lower overall satisfaction with home medical care were significantly associated with dying in a hospital. In addition, the home death group with apprehension about home medical care significantly rated higher overall satisfaction with home medical care than the hospital death group. Meanwhile, there was no difference in the overall satisfaction with home medical care between those with or without apprehension about home medical care in the home death group. Factors influencing overall satisfaction with home medical care in the home death group with apprehension about home medical care were: (i) being free from pain or symptoms (partial regression coefficient: 0.83); and (ii) fulfilled medical care service system (partial regression coefficient: 0.40). Conclusion: These results suggest that caregiver satisfaction with home medical care is an essential factor to enable home death of the patient despite the caregiver apprehension about home medical care. [source] Simulating daily soil water under foothills fescue grazing with the soil and water assessment tool model (Alberta, Canada)HYDROLOGICAL PROCESSES, Issue 15 2004Emmanuel Mapfumo Abstract Grazing is common in the foothills fescue grasslands and may influence the seasonal soil-water patterns, which in turn determine range productivity. Hydrological modelling using the soil and water assessment tool (SWAT) is becoming widely adopted throughout North America especially for simulation of stream flow and runoff in small and large basins. Although applications of the SWAT model have been wide, little attention has been paid to the model's ability to simulate soil-water patterns in small watersheds. Thus a daily profile of soil water was simulated with SWAT using data collected from the Stavely Range Sub-station in the foothills of south-western Alberta, Canada. Three small watersheds were established using a combination of natural and artificial barriers in 1996,97. The watersheds were subjected to no grazing (control), heavy grazing (2·4 animal unit months (AUM) per hectare) or very heavy grazing (4·8 AUM ha,1). Soil-water measurements were conducted at four slope positions within each watershed (upper, middle, lower and 5 m close to the collector drain), every 2 weeks annually from 1998 to 2000 using a downhole CPN 503 neutron moisture meter. Calibration of the model was conducted using 1998 soil-water data and resulted in Nash,Sutcliffe coefficient (EF or R2) and regression coefficient of determination (r2) values of 0·77 and 0·85, respectively. Model graphical and statistical evaluation was conducted using the soil-water data collected in 1999 and 2000. During the evaluation period, soil water was simulated reasonably with an overall EF of 0·70, r2 of 0·72 and a root mean square error (RMSE) of 18·01. The model had a general tendency to overpredict soil water under relatively dry soil conditions, but to underpredict soil water under wet conditions. Sensitivity analysis indicated that absolute relative sensitivity indices of input parameters in soil-water simulation were in the following order; available water capacity > bulk density > runoff curve number > fraction of field capacity (FFCB) > saturated hydraulic conductivity. Thus these data were critical inputs to ensure reasonable simulation of soil-water patterns. Overall, the model performed satisfactorily in simulating soil-water patterns in all three watersheds with a daily time-step and indicates a great potential for monitoring soil-water resources in small watersheds. Copyright © 2004 John Wiley & Sons, Ltd. [source] Estimating the digestibility of Sahelian roughages from faecal crude protein concentration of cattle and small ruminantsJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 9-10 2006E. Schlecht Summary Studies on diet selection and feed intake of ruminants in extensive grazing systems often require the use of simple approaches to determine the organic matter digestibility (OMD) of the ingested feed. Therefore, we evaluated the validity of the one-factorial exponential regression established by Lukas et al. [Journal of Animal Science 83 (2005) 1332], which estimates OMD from the faecal crude protein (FCP) concentration. The equation was applied to two sets of data obtained with free grazing and pen-fed cattle, sheep and goats ingesting low and high amounts of green and dry vegetation of Sahelian pastures as well as millet leaves and cowpea hay. Data analysis showed that the livestock species did not influence the precision of estimation of OMD from FCP. For the linear regression between measured and estimated OMD (%) across n = 431 individual observations, a regression coefficient of r2 = 0.65 and a residual standard deviation (RSD) of 5.87 were obtained. The precision of estimation was influenced by the data set (p = 0.033), the type of feed (p < 0.001) and the feeding level (p = 0.009), and interactions occurred between type of feed and feeding level (p = 0.021). Adjusting the intercept and the slope of the established exponential function to the present data resulted in a compression of the curve; while r2 remained unchanged, the RSD of the regression between measured and estimated OMD was reduced, when compared with the results obtained from the equation of Lukas et al. (2005). Estimating OMD from treatment means of FCP greatly improved the correlation between measured and estimated OMD for both the established function and the newly fit equation. However, if anti-nutritional dietary factors increase the concentration of faecal nitrogen from feed or endogenous origin, the approach might considerably overestimate diet digestibility. [source] Factors affecting abundance and distribution of submerged and floating macrophytes in Lake Naivasha, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2009A. N. Ngari Abstract Macrophytes have been shown to perform important ecological roles in Lake Naivasha. Consequently, various studies regarding the impact of biotic factors on the macrophytes have been advanced but related studies on environmental parameters have lagged behind. In an attempt to address this gap, sampling on floating species and submergents was carried out in eight sampling sites in 2003 to investigate how they were influenced by a set of environmental factors. Soil texture (sandy sediments; P < 0.05, regression coefficient = ,0.749) and wind were the most important environmental parameters influencing the distribution and abundance of floating macrophytes. Combination of soil texture and lake-bed slope explained the most (86.3%) variation encountered in the submergents. Continuous translocation of the floating dominant water hyacinth to the western parts by wind has led to displacement of the submergents from those areas. In view of these findings, the maintenance and preservation of the steep Crescent Lake basin whose substratum is dominated by sand thus hosting most submergents remain important, if the whole functional purpose of the macrophytes is to be sustained. Résumé On a montré que les macrophytes jouent un rôle économique important dans le lac Naivasha. Par conséquent, diverses études ont été réalisées sur l'impact des facteurs biotiques sur les macrophytes, mais les études correspondantes sur les paramètres environnementaux sont à la traîne. Pour essayer de compenser cette lacune, en 2003, on a réalisé un échantillonnage des espèces flottantes et submergées sur huit sites d'échantillonnage pour étudier comment elles étaient influencées par un ensemble de facteurs environnementaux. La texture du sol (sédiments sableux, P < 0,05, coefficient de régression = 0,749) et le vent étaient les paramètres environnementaux les plus important quant à l'influence sur la distribution et l'abondance des macrophytes flottants. La combinaison de la texture du sol et de la pente du fond du lac expliquait la plus grande partie (86,3%) de la variation rencontrée chez les espèces submergées. Le déplacement continuel des jacinthes d'eau, qui est la plante flottante dominante, vers la partie ouest par le vent a entraîné le déménagement des espèces submergées hors de cette partie du lac. Au vu de ces résultats, il est important d'assurer l'entretien et la préservation de la pente raide du bassin du lac en forme de croissant si l'on peut conserver l'ensemble de la fonction des macrophytes. [source] Modeling the Lag Phase and Growth Rate of Listeria monocytogenes in Ground Ham Containing Sodium Lactate and Sodium Diacetate at Various Storage TemperaturesJOURNAL OF FOOD SCIENCE, Issue 7 2007C.-A. Hwang ABSTRACT:, Refrigerated ready-to-eat (RTE) meats contaminated with Listeria monocytogenes were implicated in several listeriosis outbreaks. Lactate and diacetate have been shown to control L. monocytogenes in RTE meats. The objective of this study was to examine and model the effect of lactate (1.0% to 4.2%) and diacetate (0.05% to 0.2%) in ground ham on the lag phase duration (LPD, h) and growth rate (GR, log CFU/h) of L. monocytogenes at a range of temperatures (0 to 45 °C). A 6-strain mixture of L. monocytogenes was inoculated into ground ham containing lactate and diacetate, and stored at various temperatures. The LPD and GR of L. monocytogenes in ham as affected by lactate, diacetate, and storage temperature were analyzed and accurately represented with mathematical equations. Resulting LPD and GR equations for storage temperatures within the range of 0 to 36 °C significantly represented the experimental data with a regression coefficient of 0.97 and 0.96, respectively. Significant factors (P < 0.05) that affected the LPD were temperature, lactate, diacetate, and the interactions of all three, whereas only temperature and the interactions between temperature and lactate and diacetate had a significant effect on GR. At suboptimal growth temperatures (,12 °C) the increase of lactate and diacetate concentrations, individually or in combination, extended the LPD. The effect of higher concentrations of both additives on reducing the GR was observed only at temperatures that were more suitable for growth of L. monocytogenes, that is, 15 to 35 °C. These data may be used to assist in determining concentrations of lactate and diacetate in cooked ham products to control the growth of L. monocytogenes over a wide range of temperatures during manufacturing, distribution, and storage. [source] Correlation between Moisture and Water Activity of Honeys Harvested in Different YearsJOURNAL OF FOOD SCIENCE, Issue 5 2004M.M. Cavia ABSTRACT: For the 1st time, a relationship has been investigated between moisture percentage (M) and water activity (aW) in honeys from 2 different harvesting years and 2 different climatic areas. Moisture was determined by measuring refractive index at 20°C, according to official methods. At the same time, aW of the same samples was assessed at exactly 20°C. Influence on the relationship of the crop's year, aging, and induced fine granulation was evaluated. The results show that, independent of all factors studied, an excellent and statistically significant linear correlation between both parameters [aW = 0.3114 + (0.0170 × M)] was found in all samples with a regression coefficient of 0.8809. The measurement of aW of honey is interesting but time-consuming. This study concludes that this parameter can be easily calculated from the moisture percentage, thus avoiding the use of expensive and slow equipment for aW measurement. [source] Use of mid-infrared spectroscopy in the diffuse-reflectance mode for the prediction of the composition of organic matter in soil and litterJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2008Bernard Ludwig Abstract Mid-infrared spectroscopy (MIRS) is assumed to be superior to near-infrared spectroscopy (NIRS) for the prediction of soil constituents, but its usefulness is still not sufficiently explored. The objective of this study was to evaluate the ability of MIRS to predict the chemical and biological properties of organic matter in soils and litter. Reflectance spectra of the mid-infrared region including part of the near-infrared region (7000,400,cm,1) were recorded for 56 soil and litter samples from agricultural and forest sites. Spectra were used to predict general and biological characteristics of the samples as well as the C composition which was measured by 13C CPMAS-NMR spectroscopy. A partial least-square method and cross-validation were used to develop equations for the different constituents over selected spectra ranges after several mathematical treatments of the spectra. Mid-infrared spectroscopy predicted well the C : N ratio: the modeling efficiency EF was 0.95, the regression coefficient (a) of a linear regression (measured against predicted values) was 1.0, and the correlation coefficient (r) was 0.98. Satisfactorily (EF , 0.70, 0.8 , a , 1.2, r , 0.80) assessed were the contents of C, N, and lignin, the production of dissolved organic carbon, and the contents of carbonyl C, aromatic C, O-alkyl C, and alkyl C. However, the N mineralization rate, the microbial biomass and the alkyl,to,aromatic C ratio were predicted less satisfactorily (EF < 0.70). Limiting the sample set to mineral soils did generally not result in improved predictions. The good and satisfactory predictions reported above indicate a marked usefulness of MIRS in the assessment of chemical characteristics of soils and litter, but the accuracies of the MIRS predictions in the diffuse-reflectance mode were generally not superior to those of NIRS. [source] Use of deltamethrin ,pour-on' insecticide for the control of cattle trypanosomosis in the presence of high tsetse invasionMEDICAL AND VETERINARY ENTOMOLOGY, Issue 1 2001G. J. Rowlands Summary A deltamethrin ,pour-on' insecticide was applied monthly to over 2000 cattle exposed to a high challenge of drug-resistant trypanosomes and high tsetse re-invasion pressure in the Ghibe valley, south-west Ethiopia. Blood samples were taken monthly from an average of 760 cattle for determination of PCV and presence of trypanosomes. The area of the valley is approximately 350 km2 and the cattle grazed in roughly four locations covering about a quarter to half of the area. Two years before the trial commenced, Glossina morsitans submorsitans Newstead (Diptera: Glossinidae) began to invade the valley. Despite the use of the pour-on the mean apparent density of G. m. submorsitans continued to rise, and, during the 4 years of tsetse control, was more than three-fold higher than that recorded during the previous 18 months. Over the same period there was little change in the apparent density of Glossina pallidipes Austen (Diptera: Glossinidae). By contrast, the mean monthly prevalence of trypanosome infections in cattle over 36 months of age decreased from 38.3 to 29.0%, the incidence of new infections decreased from 26.6 to 16.0% (a reduction of 40%), and packed cell volume in cattle increased from 21.7 to 24.1%. Evidence of a change in apparent parasite transmission rate was demonstrated by regression of infection incidence in cattle on the logarithm of apparent density of G. m. submorsitans. Before the trial started the regression coefficient was 45.8 ± 6.3 and this reduced to 9.2 ± 2.5% incidence per loge (flies/trap/day) during the period of tsetse control. It was concluded that this indicated reductions in tsetse numbers in the immediate vicinities of cattle in a way that was not reflected in overall tsetse catches. Nevertheless, the comparatively high levels of trypanosome prevalence that persisted in the cattle demonstrates that, where invasion prevalence is high, treatment of small pockets of cattle will not eradicate tsetse. To achieve more significant reduction in trypanosome prevalence in cattle, integrated methods of control utilizing target barriers in the major routes of invasion will be needed. [source] The effect of differential rater function over time (DRIFT) on objective structured clinical examination ratingsMEDICAL EDUCATION, Issue 10 2009Kevin McLaughlin Context, Despite the impartiality implied in its title, the objective structured clinical examination (OSCE) is vulnerable to systematic biases, particularly those affecting raters' performance. In this study our aim was to examine OSCE ratings for evidence of differential rater function over time (DRIFT), and to explore potential causes of DRIFT. Methods, We studied ratings for 14 internal medicine resident doctors over the course of a single formative OSCE, comprising 10 12-minute stations, each with a single rater. We evaluated the association between time-slot and rating for a station. We also explored a possible interaction between time-slot and station difficulty, which would support the hypothesis that rater fatigue causes DRIFT, and considered ,warm-up' as an alternative explanation for DRIFT by repeating our analysis after excluding the first two OSCE stations. Results, Time-slot was positively associated with rating on a station (regression coefficient 0.88, 95% confidence interval [CI] 0.38,1.38; P = 0.001). There was an interaction between time-slot and station difficulty: for the more difficult stations the regression coefficient for time-slot was 1.24 (95% CI 0.55,1.93; P = 0.001) compared with 0.52 (95% CI , 0.08 to 1.13; P = 0.09) for the less difficult stations. Removing the first two stations from our analyses did not correct DRIFT. Conclusions, Systematic biases, such as DRIFT, may compromise internal validity in an OSCE. Further work is needed to confirm this finding and to explore whether DRIFT also affects ratings on summative OSCEs. If confirmed, the factors contributing to DRIFT, and ways to reduce these, should then be explored. [source] Predictive 3D-Quantitative Structure-Activity Relationship for A1 and A2A Adenosine Receptor LigandsMOLECULAR INFORMATICS, Issue 11-12 2009Olga Yuzlenko Abstract The use of QSAR applications to develop adenosine receptor (AR) antagonists is not so common. A library of all xanthine derivatives, obtained at the Department of Technology and Biotechnology of Drugs, was created. Sixty-three active adenosine A1 receptor ligands and one hundred thirty nine active adenosine A2A receptor ligands were used for 3D-QSAR investigation. The 3D-QSAR equations with a high predictive power in estimating the binding affinity values of potential A1 and A2A ARs ligands were derived. For the first time, hybrid shape-property descriptors were used in 3D-QSAR for xanthine ARs ligands. The obtained models were characterized by a high regression and cross-validation coefficients. Two types of the model validation were tested , dividing the library into the training set for model development and external set for model validation and increasing the number of library components and checking the model by cross-validated regression coefficient. The analysis of the results depicts that for the A1 AR binding activity it is important for ligands to possess R1 -propyl substituents along with the phenyl or benzyl substituents bearing halogen atom and phenethyl moiety. For A2A AR affinity it could be favorable to introduce phenethyl or phenyl substituent connected with the tricyclic ring by the alkoxy chain. The nature of R1 group may not significantly affect the A2A AR affinity. High predictive power of the equations suggests their use for further development of adenosine receptor antagonists within xanthine derivatives. [source] CP-MLR/PLS Directed Structure-Activity Modeling of the HIV-1 RT Inhibitory Activity of 2,3-Diaryl-1,3-thiazolidin-4-onesMOLECULAR INFORMATICS, Issue 4 2004Yenamandra Abstract A detailed structure-activity relationship study of the HIV-1 Reverse Transcriptase (RT) inhibitory activity of two series of compounds, 2-(2,6-dihalo phenyl)-3-(substituted pyridin-2-yl)-thiazolidin-4-ones and 2-(2,6-Dihalophenyl)-3-(substituted phenyl)-thiazolidin-4-ones, belonging to 2,3-diaryl-thiazolidin-4-ones in terms of physicochemical and structural descriptors have been carried out using combinatorial protocol interfaced multiple linear regression (CP-MLR) and partial least squares (PLS) analysis. The models developed in the study indicate a preference for hydrophobic compounds for better inhibitory activity. Also, a positive regression coefficient of I2,3, an indicator descriptor meant for the joint disposition of substituents of 2,3-diaryl moieties of thiazolidinones to address their ability in taking a butterfly like conformation, is in agreement with all earlier observations that compounds having the ability to take butterfly like conformation will be showing better inhibitory activity. The identified models suggest that the meta-positions of 3-aryl moiety has the ability to accommodate hydrophobic/ steric groups. The replacement of C2, of 3-phenyl by nitrogen resulted in 3-pyridyl variants of these analogues. Even though from geometry point of view, the phenyls and pyridyls span almost the same structural space and steric features, presence of nitrogen in pyridyls gave them a blend of polarity, electronic features and a different hydrophobicity profile when compared to corresponding phenyl analogue. Furthermore the PLS models, developed from those descriptors took part in CP-MLR models, indicate that most of the descriptors have almost equal influence in accounting for the variation in the activity of these compounds. This suggests that the factors responsible for the variation in the activity have been uniformly distributed across the varying centers of the molecule. The study suggests that thiazolidinones with 3-(pyridin-2-yl) moiety provide scope for further substituent variation to modulate the HIV-1 RT inhibitory activity. [source] Non-therapeutic risk factors for onset of tardive dyskinesia in schizophrenia: A meta-analysis,,MOVEMENT DISORDERS, Issue 16 2009Diederik E. Tenback MD Abstract A meta-analysis of prospective studies with schizophrenia patients was conducted to examine whether the evidence exists for risk factors for the emergence of Tardive Dyskinesia (TD) in schizophrenia. A computer assisted Medline/PubMed and Embase search was conducted in January 2008 for the years 1985,2007. Selected were truly prospective studies of incident cases of TD in a population with at least 80% patients with schizophrenia. Measures of relative risk were collected from the individual studies, either directly or by calculating the relative risk from the cox- or logistic regression coefficient provided in the article. Hazard Ratio's and Odds Ratio's were pooled using fixed and random effect models in case of multiple studies using the same measure of risk and outcome. Only eight studies satisfied the inclusion criteria reporting on 25 different single estimate risk factors. Of 25 risk factors, six concerned replicated estimates suitable for meta-analysis. Of these, non-white ethnic group and early extrapyramidal symptoms qualified as risk factors for the emergence of TD in schizophrenia. The association with older age was suggestive but inconclusive. Despite many reported risk factors for TD in schizophrenia, little conclusive evidence exists to corroborate this. However, the fact that early EPS predicts onset of TD has important clinical and research implications. © 2009 Movement Disorder Society [source] The Role of Central Hypersensitivity in the Determination of Intradiscal Mechanical Hyperalgesia in Discogenic PainPAIN MEDICINE, Issue 5 2010Juerg Schliessbach PhD Abstract Objective., The primary aim of the present study was to investigate whether there is a relationship between central hypersensitivity (assessed by pressure pain thresholds of uninjured tissues) and intradiscal pain threshold during discography. The secondary aim was to test the hypothesis that peripheral noxious stimulation dynamically modulates central hypersensitivity. Patients., Twenty-four patients with positive provocation discography were tested for central hypersensitivity by pressure algometry before and after the intervention with assessments of pressure pain detection and tolerance thresholds. Intradiscal pain threshold was assessed by measuring intradiscal pressure at the moment of pain provocation during discography. Correlation analyses between intradiscal pain threshold and pressure algometry were made. For the secondary aim, pressure algometry data before and after discography were compared. Results., Significant correlation with intradiscal pain threshold was found for pressure pain detection threshold at the toe (regression coefficient: 0.03, P = 0.05) and pressure pain tolerance thresholds at the nonpainful point at the back (0.02, P = 0.024). Tolerance threshold at the toe was a significant predictor for intradiscal pain threshold only in multiple linear regression (0.036, P = 0.027). Detection as well as tolerance thresholds significantly decreased after discography at the painful and the nonpainful point at the back, but not at the toe. Conclusions., Central hypersensitivity may influence intradiscal pain threshold, but with a modest quantitative impact. The diagnostic value of provocation discography is therefore not substantially impaired. Regional, but not generalized central hypersensitivity is dynamically modulated by ongoing peripheral nociceptive input. [source] Low PAPP-A in the first trimester is associated with reduced fetal growth rate prior to gestational week 20PRENATAL DIAGNOSIS, Issue 6 2010J. D. Salvig Abstract Objective To evaluate the association between maternal pregnancy-associated plasma protein-A (PAPP-A) and fetal growth from the first to the second trimester. Methods A prospective cohort study including 8347 pregnant women attending prenatal care at Aarhus University Hospital were conducted. PAPP-A was measured during 8 to 14 gestational weeks. Fetal growth between the two scans in the first and second trimesters was estimated by (GA20, GA12)/Dayscalendar, where GA12 reflects gestational age in days calculated from crown-rump length at a 12-week scan, GA20 reflects gestational age in days calculated from biparietal diameter at a 20-week scan, and Dayscalendar reflects the number of calendar days between the two scans. Results Fetal growth rate from the first to the second trimester was correlated with PAPP-A, with a regression coefficient of 0.009 (95% CI, 0.007,0.012, P < 0.001). PAPP-A below 0.30 MoM was associated with a fetal growth rate below the tenth centile, with an adjusted OR of 2.05 (95% CI, 1.24,3.38). Conclusion Low levels of PAPP-A are associated not only with low birth weight at term but also with slower fetal growth prior to 20 weeks of gestation. Copyright © 2010 John Wiley & Sons, Ltd. [source] Validation of multi-detector computed tomography as a non-invasive method for measuring ovarian volume in macaques (Macaca fascicularis)AMERICAN JOURNAL OF PRIMATOLOGY, Issue 6 2010Jeryl C. Jones Abstract The purpose of this study was to validate low radiation dose, contrast-enhanced, multi-detector computed tomography (MDCT) as a non-invasive method for measuring ovarian volume in macaques. Computed tomography scans of four known-volume phantoms and nine mature female cynomolgus macaques were acquired using a previously described, low radiation dose scanning protocol, intravenous contrast enhancement, and a 32-slice MDCT scanner. Immediately following MDCT, ovaries were surgically removed and the ovarian weights were measured. The ovarian volumes were determined using water displacement. A veterinary radiologist who was unaware of actual volumes measured ovarian CT volumes three times, using a laptop computer, pen display tablet, hand-traced regions of interest, and free image analysis software. A statistician selected and performed all tests comparing the actual and CT data. Ovaries were successfully located in all MDCT scans. The iliac arteries and veins, uterus, fallopian tubes, cervix, ureters, urinary bladder, rectum, and colon were also consistently visualized. Large antral follicles were detected in six ovaries. Phantom mean CT volume was 0.702±SD 0.504,cc and the mean actual volume was 0.743±SD 0.526,cc. Ovary mean CT volume was 0.258±SD 0.159,cc and mean water displacement volume was 0.257±SD 0.145,cc. For phantoms, the mean coefficient of variation for CT volumes was 2.5%. For ovaries, the least squares mean coefficient of variation for CT volumes was 5.4%. The ovarian CT volume was significantly associated with actual ovarian volume (ICC coefficient 0.79, regression coefficient 0.5, P=0.0006) and the actual ovarian weight (ICC coefficient 0.62, regression coefficient 0.6, P=0.015). There was no association between the CT volume accuracy and mean ovarian CT density (degree of intravenous contrast enhancement), and there was no proportional or fixed bias in the CT volume measurements. Findings from this study indicate that MDCT is a valid non-invasive technique for measuring the ovarian volume in macaques. Am. J. Primatol. 72:530,538, 2010. © 2010 Wiley-Liss, Inc. [source] ORIGINAL RESEARCH,EPIDEMIOLOGY: Effect of Sexual Function on Health-Related Quality of Life Mediated by Depressive Symptoms in Cardiac Rehabilitation.THE JOURNAL OF SEXUAL MEDICINE, Issue 6 2010Findings of the SPARK Project in 493 Patients ABSTRACT Introduction., Empirical evidence suggests associations between cardiovascular diseases, sexual functioning, depressive symptoms, and quality of life. However, to date, the interrelation of these constructs has not been examined simultaneously in a structural analysis. Aim., To estimate the prevalence of sexual disorders and depressive symptoms and to examine the association between sexual disorders, depressive symptoms, and quality of life in patients in the rehabilitation of cardiovascular disorders. Aim., A postal survey in five German inpatient rehabilitation centers for cardiovascular diseases was conducted. Prevalence of sexual disorders and depressive symptoms were assessed using psychometrically sound instruments. To analyze complex associations, structural equation modeling was used. Main Outcome Measures., For epidemiological questions, proportions with 95% confidence intervals were calculated. The strength of association in structural equation models was expressed as a standardized regression coefficient. Results., Data from 493 patients were analyzed (response rate 22.7%). At least moderate erectile dysfunction proved to be present in 20.3% of men. The prevalence of female sexual dysfunction lay at 43.1%. At least moderate depressive symptoms were present in 14.4% of men and 16.5% of women. A considerable association between sexual functioning and quality of life was found in both sexes, which was largely mediated by depressive symptoms. Major drawbacks of the study are imprecision of the estimates due to limited sample size and questionable generalizability of the findings due to possible self-selection bias. Conclusions., Considering the high prevalence of depressive symptoms and their role as a mediating factor between sexual functioning and quality of life, it is recommended to routinely screen for depression in men and women with cardiac disease. Kriston L, Günzler C, Agyemang A, Bengel J, and Berner MM. Effect of sexual function on health-related quality of life mediated by depressive symptoms in cardiac rehabilitation. Findings of the SPARK project in 493 patients. J Sex Med 2010;7:2044,2055. [source] Adjustment for Missingness Using Auxiliary Information in Semiparametric RegressionBIOMETRICS, Issue 1 2010Donglin Zeng Summary In this article, we study the estimation of mean response and regression coefficient in semiparametric regression problems when response variable is subject to nonrandom missingness. When the missingness is independent of the response conditional on high-dimensional auxiliary information, the parametric approach may misspecify the relationship between covariates and response while the nonparametric approach is infeasible because of the curse of dimensionality. To overcome this, we study a model-based approach to condense the auxiliary information and estimate the parameters of interest nonparametrically on the condensed covariate space. Our estimators possess the double robustness property, i.e., they are consistent whenever the model for the response given auxiliary covariates or the model for the missingness given auxiliary covariate is correct. We conduct a number of simulations to compare the numerical performance between our estimators and other existing estimators in the current missing data literature, including the propensity score approach and the inverse probability weighted estimating equation. A set of real data is used to illustrate our approach. [source] A Multiple Imputation Approach to Cox Regression with Interval-Censored DataBIOMETRICS, Issue 1 2000Wei Pan Summary. We propose a general semiparametric method based on multiple imputation for Cox regression with interval-censored data. The method consists of iterating the following two steps. First, from finite-interval-censored (but not right-censored) data, exact failure times are imputed using Tanner and Wei's poor man's or asymptotic normal data augmentation scheme based on the current estimates of the regression coefficient and the baseline survival curve. Second, a standard statistical procedure for right-censored data, such as the Cox partial likelihood method, is applied to imputed data to update the estimates. Through simulation, we demonstrate that the resulting estimate of the regression coefficient and its associated standard error provide a promising alternative to the nonparametric maximum likelihood estimate. Our proposal is easily implemented by taking advantage of existing computer programs for right,censored data. [source] | ||||||||||||||||||||||||||||||||||||||||