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Multiple Correlation Coefficient (multiple + correlation_coefficient)
Selected AbstractsRate and product studies in the solvolyses of methanesulfonic anhydride and a comparison with methanesulfonyl chloride solvolyses,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2007Dennis N. Kevill Abstract The specific rates of solvolysis of methanesulfonic anhydride have been measured conductometrically at ,10,°C in 41 solvents. Use of the extended Grunwald,Winstein equation, with the NT scale of solvent nucleophilicity and the YOTs scale of solvent ionizing power, leads to sensitivity to changes in solvent nucleophilicity (, value) of 0.95 and a sensitivity to changes in solvent ionizing power (m value) of 0.61, with a multiple correlation coefficient (R) of 0.973. Product selectivity values (S) in binary hydroxylic solvents favor alcohol attack in EtOH,H2O (a value of 1.2 in 90% EtOH rising to 4.0 in 40% EtOH) and in MeOH,H2O (a value of 3.7 in 90% MeOH rising to 6.0 in 50% MeOH). In 2,2,2,-trifluoroethanol,H2O, the S values are much lower at about 0.1. Entropy of activation values are appreciably negative. Literature values for the specific rates of solvolysis of methanesulfonyl chloride have been extended to fluoroalcohol-containing solvents (titrimetric method) and, at 45.0,°C, for an overall 43 solvents values are obtained (using NT and YC1 scales) of 1.20 for , and of 0.52 for m (R,=,0.969). It is proposed that both substrates solvolyze by an SN2 pathway. Copyright © 2007 John Wiley & Sons, Ltd. [source] Use of Topological Indices of Organic Sulfur Compounds in Quantitative Structure-Retention Relationship StudyMOLECULAR INFORMATICS, Issue 9 2005F. Safa Abstract Structure-gas chromatographic retention index models were developed for some organic sulfur compounds at four different temperatures (60, 80, 100 and 120,°C) using only topological descriptors. At first, regression models were generated for each temperature separately with high values of multiple correlation coefficient and Fisher-ratio statistics. The results of cross validation test using leave-one-out (Q2,0.956) and leave-two-out (Q2,0.953) methods showed good predictive ability of the models developed. Then, a single combined quantitative structure-retention relationship model, added temperature as a parameter, was also developed for all the temperatures, showing good statistical parameters (R=0.991 and F=728.474). The stability and validity of the combined model were verified by both internal (Q2>0.970) and external validation (Q=0.993) techniques. The results of the study indicated the efficiency of the classical topological descriptors in simultaneous prediction of retention index values of sulfur compounds at different temperatures. The topological descriptors well covered the molecular properties known to be relevant for gas chromatographic retention data, such as molecular size and degree of branching. [source] Noninvasive estimation of bone mass in ancient vertebraeAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2004E. Gonzalez-Reimers Abstract Histomorphometry is useful in the assessment of trabecular bone mass (TBM), and thus, in the estimation of the prevalence and intensity of osteopenia in ancient population groups. However, it is a destructive method. It is therefore necessary to explore the accuracy of nondestructive approaches, such as radiography, bone mineral density (BMD) assessed by double-energy X-ray absorptiometry (DEXA), bone density (BD), or optical density (OD) in the diagnosis of osteopenia. We selected 51 vertebrae out of a total sample composed of 333 T12, L1, and L2 vertebrae belonging to adult pre-Hispanic inhabitants from El Hierro. These vertebrae underwent histomorphometrical analysis, a fine-grained film radiography with assessment of trabecular pattern following standard methods, OD, DEXA-assessed BMD, and BD. The presence of biconcave vertebrae and wedge-shaped vertebrae was also assessed by measuring anterior height (a), posterior height (p), and height at the middle point of the vertebral body (m), and further calculating the indices 2m/(a + p) ("spine score") and a/p. Significant correlations were observed between TBM and BMD (r = 0.43), TBM and BD (r = 0.49), TBM and OD (r = 0.52), BMD and OD (r = 0.51), and BMD and BD (r = 0.36), but not between TBM and the indices 2m/(a + p) and a/p. In the stepwise multiple correlation analysis between TBM and BMD, BD, and OD, OD entered into first place and BD into second place, whereas BMD became displaced; the multiple correlation coefficient was 0.63, with a standard error of 3.78. A BMD greater than 0.60 g/cm2, or a bone density greater than 0.60 g/cm3, excluded osteopenia (TBM <15%) with a specificity greater than 90%, whereas a BMD value less than 0.35 g/cm2, a BD less than 0.35 g/cm3, or optical density >1.6 excluded a normal bone mass (TBM >20%) with a specificity greater than 90%. Based on radiographic criteria on the total sample, we also conclude that the overall prevalence of vertebral fractures in the adult pre-Hispanic population of El Hierro of any age is 7.5%. Am J Phys Anthropol, 2004. © 2004 Wiley-Liss, Inc. [source] Transthyretin levels in the vitreous correlate with change in visual acuity after vitrectomyACTA OPHTHALMOLOGICA, Issue 2009E VAN AKEN Purpose Little is known about biochemical markers related to change in visual acuity after vitrectomy. We investigated the potential use of transthyretin (TTR), a carrier of the retinol/retinol-binding protein, as a biochemical marker protein. Methods We measured TTR using immunonephelometry in a group of patients (n=77) in longstanding (> 1 week) retinal detachment (n=29), fresh (< 1 week) retinal detachment (n=17), macular holes (n=20), or diabetic retinopathy (n=11). Vitreous samples were taken at the start of every vitrectomy procedure. For reference values, cadaver specimens (n=73) were used. Results Reference values for vitreous TTR (median 18 mg/l; IQR 4-24 mg/l) comprised 2.2% of reference values for vitreous protein levels (median 538 mg/l; IQR 269-987 mg/l). Vitreous TTR values of patients were comparable in all disorders. Vitreous TTR values were higher in phakic (median 22.5 mg/l; IQR 10-27 mg/l) than in pseudophakic patients (median 12 mg/l; IQR 8-19 mg/l)(p=0.06). Postoperative change in visual acuity correlated well with vitreous TTR values found peroperatively (rs=0.408; p=0.012). Both change in visual acuity and lens status were the only variables which proved to explain the variance of TTR (multiple correlation coefficient: 0.494; phakic status: t=2.767; p=0.0084; and change in visual acuity t=2.924: p=0.0056). Conclusion Vitreous fluid concentrations of TTR can be regarded as a biochemical marker for retinal function. [source] Effects of atmospheric circulation on ice conditions in the southern Baltic coastal lagoonsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2001Józef Piotr Girjatowicz Abstract Relationships between atmospheric circulation patterns and ice conditions in the southern Baltic coastal lagoons were explored. Ice data consisted of number of ice days (L) and duration of ice season (S) in the Szczecin Lagoon (off Karnin), the Puck Bay (off Puck) and the Vistula Lagoon (off Krasnoflotskoye) from 1950/1951 to 1989/1990. Atmospheric circulation patterns for the period studied were extracted from Lity,ski's ,Calendar of atmospheric circulation types' developed at the Institute of Meteorology and Water Management (IMWM). A circulation pattern was identified by three numerical parameters: the zonal circulation index, the meridional circulation index, both pertaining to a zone delimited by coordinates 40,60°N, 0,35°E, and the surface pressure index for Warsaw. The number of days with individual atmospheric circulation patterns occurring from October to March was calculated. Subsequently, the selected patterns were combined by wind direction sectors and several month-long periods that most closely correlated with ice conditions. The highest linear correlation coefficients (r>0.8) were obtained for the relationship between the number of days with winds from the east from December to February and December to March and the winter number of ice days (L). Somewhat higher were multiple correlation coefficients with winds from the east and west as circulation type predictors. Slightly lower correlation coefficients for the sectors and circulation periods mentioned were obtained for the duration of the ice season (S), although some of the coefficients were significant even at the probability level of ,=0.01. Higher correlation coefficients were obtained for correlations involving ,cold' circulation patterns (sector NE+E+SE winds) and ice conditions than for those involving ,warm' patterns (sector SW+W+NW). Copyright © 2001 Royal Meteorological Society [source] Influence of bone density on the cement fixation of femoral hip resurfacing componentsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 8 2010Rudi G. Bitsch Abstract In clinical outcome studies, small component sizes, female gender, femoral shape, focal bone defects, bad bone quality, and biomechanics have been associated with failures of resurfacing arthroplasties. We used a well-established experimental setup and human bone specimens to analyze the effects of bone density on cement fixation of femoral hip resurfacing components. Thirty-one fresh frozen femora were prepared for resurfacing using the original instruments. ASRÔ resurfacing prostheses were implanted after dual-energy X-ray densitometer scans. Real-time measurements of pressure and temperature during implantation, analyses of cement penetration, and measurements of micro motions under torque application were performed. The associations of bone density and measurement data were examined calculating regression lines and multiple correlation coefficients; acceptability was tested with ANOVA. We found significant relations between bone density and micro motion, cement penetration, cement mantle thickness, cement pressure, and interface temperature. Mean bone density of the femora was 0.82,±,0.13,g/cm2, t- score was ,0.7,±,1.0, and mean micro motion between bone and femoral resurfacing component was 17.5,±,9.1,µm/Nm. The regression line between bone density and micro motion was equal to ,56.7,×, bone density,+,63.8, R,=,0.815 (p,<,0.001). Bone density scans are most helpful for patient selection in hip resurfacing, and a better bone quality leads to higher initial component stability. A sophisticated cementing technique is recommended to avoid vigorous impaction and incomplete seating, since increasing bone density also results in higher cement pressures, lower cement penetration, lower interface temperatures, and thicker cement mantles. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:986,991, 2010 [source] Threshold analysis of selected dose-response data for endocrine active chemicals,APMIS, Issue 3 2001Robert M. Blair Using a biologically relevant mathematical model, the Michaelis-Menten equation, we examined published data from endocrine active chemicals for evidence of no-threshold dose-response curves. Data were fit to a modified Michaelis-Menten equation which accounted for total background response. Subsequently, the data sets were analyzed using non-linear regression in order to estimate the four parameters of interest (non-hormone controlled background (Bnh), maximum response (Rmax), endogenous hormone level (D0), and the dose at which a half-maximal response was observed (ED50)) and to determine the fit to the fully modified Michaelis-Menten equation. Subsequently, response data were adjusted to account for Bnh and then normalized to Rmax, while dose data were adjusted to account for D0 and then normalized to the ED50. This data set was combined into a single, composite data set and fit to the fully modified Michaelis-Menten equation. We examined 31 data sets (24 endpoints) from studies on 9 different chemical/hormone treatments. Twenty-six of the data sets fit the modified Michaelis-Menten equation with high multiple correlation coefficients (r>0.90). The normalized data demonstrated a good fit to the modified Michaelis-Menten equation. These results indicate that a variety of biological responses fit the modified Michaelis-Menten equation, which does not have a threshold dose term. [source] | ||||||||||||||||