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Coefficient Measurements (coefficient + measurement)
Selected AbstractsRate coefficients for the reaction of OH with OClO between 242 and 392 K,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2006Tomasz Gierczak Rate coefficients are reported for the gas phase reaction of OH with OClO over the temperature range 242,392 K at 25, 50, and 100 Torr (He). Kinetic measurements were made using pulsed laser photolysis with laser induced fluorescence detection of the OH radical. The measured rate coefficients were independent of pressure and are well represented by k1(T) = (1.43,±,0.3),×,10,12 exp(597,±,36/T) cm3 molecule,1 s,1 (k1(298 K) = 1.06,×,10,11 cm3 molecule,1 s,1). The quoted uncertainties are 2, (95% confidence level) and include estimated systematic errors. Discrepancies with the previous OH + OClO rate coefficient measurement by Poulet et al. (Int J Chem Kinet 1986, 18, 847,859) are discussed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 234,241, 2006 [source] Measurement of mass transfer coefficient in an airlift reactor with internal loop using coalescent and non-coalescent liquid mediaJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2004M Bla Abstract In this work the sulfite oxidation (SOM), dynamic pressure-step (DPM) and gassing-out (GOM) methods were compared for volumetric mass transfer coefficient measurement in an airlift reactor with internal loop. As a liquid phase both, non-coalescent and coalescent media were used. Among the methods discussed here, the mass transfer coefficient (kLa) values obtained by the DPM appear as the most reliable as they were found to be independent of oxygen concentration in the inlet gas, which confirmed the physical correctness of this method. The difference between data measured using air and oxygen was not higher than 10%, which was comparable to the scatter of experimental data. It has been found that the sulfite oxidation method yielded kLa values only a little higher than those obtained by the DPM and the difference did not exceed 10%. Up to an inlet gas velocity (UGC) of ,0.03 m s,1 the GOM using oxygen as a gas medium gave kLa values in fact identical with those obtained by the DPM. At higher flows of the inlet gas, the GOM yielded kLa values as much as 15% lower. The enhancement in oxygen mass transfer rate determined in non-coalescent media was estimated to be up to +15%, when compared with a coalescent batch. The experimental dependence of kLa vs the overall gas hold-up was described by an empirical correlation.1 Copyright © 2004 Society of Chemical Industry [source] Measurement of low-dose active pharmaceutical ingredient in a pharmaceutical blend using frequency-domain photon migrationJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2004Tianshu Pan Abstract Frequency-domain photon migration (FDPM) measurements of time-dependent light propagation are conducted to provide the powder absorbance for quantitative prediction of terazosin as the active pharmaceutical ingredient (API) in a low-dose (0.72 wt %) oral tablet formulation. Calibration of the FDPM-derived powder absorbance at discrete wavelengths of 514, 650, 687, and 785 nm was performed for API contents ranging between 0 and 1.5 wt % in mixtures showing maximum sensitivity at 650 nm. The relative standard deviation (RSD) of FDPM absorption coefficient measurement at 650 nm in a well-mixed 1.08 wt % terazosin blend was <1.6%, of which no more than 0.12% arose from FDPM instrumental error and the remainder was attributable to the complete-random-mixture model. The applicability of FDPM as an on-line sensor for powder-blending operations was further evaluated by analyzing grab samples taken directly from five locations of a 2-cu-ft Gallay blender at intervals of 5 min within the blending process. FDPM results indicate that homogeneity was largely achieved in the first 10 min, during which the RSD of API content across five sampling locations decreased from 27% to 8%, and the RSD decreased to 5% after 25 min of blending. Evolution of homogeneity within the blending process assessed through FDPM measurements was fit to the first-order model of particle blending further evidencing applicability for monitoring powder-blending processes. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:635,645, 2004 [source] Growth and optical characterization of cerium and lead-doped Bi12TiO20 sillenite single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2005J. F. Carvalho Abstract Bi12TiO20 (BTO) single crystals doped with PbO and CeO2 were grown by the Top Seeded Solution Growth (TSSG) technique from the liquid phase with nominal compositions of 10Bi2O3 : (1,x)TiO2 : x PbO and 10Bi2O3 : (1,x)TiO2 : xCeO2 with x = 0.25 and 0.10. No growth-related difficulties were encountered other than those typical of sillenite crystals. Samples with good optical quality were obtained and were characterized by optical absorption, dark current, spectral photocurrent dependence, optical activity and electro-optic coefficient measurements. A comparison is made of the results of the optical measurements of doped and undoped BTO crystals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of semi-insulating InP co-doped with Ti and various acceptors for use in X-ray detectionCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005K. Zdansky Abstract Semi-insulating InP single crystals co-doped with Zn and Ti and co-doped with Ti and Mn were grown by Czochralski technique. Wafers of these crystals were annealed for a long time at a high temperature and cooled slowly. The samples were characterized by temperature dependent resistivity and Hall coefficient measurements. The binding energies of Ti in semi-insulating InP co-doped with Ti and Zn and co-doped with Ti and Mn were found to differ which shows that Ti may occupy different sites in InP. The curves of Hall coefficient vs. reciprocal temperature deviate from straight lines at low temperatures due to electron and hole mixed conductance. The value of resistivity of the annealed semi-insulating InP co-doped with Ti and Mn reaches high resistivity at a reduced temperature easily achievable by thermo-electric devices which could make this material useable in X-ray detection. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Applications of artificial neural networks to RF and microwave measurementsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 1 2002Jeffrey A. Jargon Abstract This article describes how artificial neural networks (ANNs) can be used to benefit a number of RF and microwave measurement areas including vector network analysis (VNA). We apply ANNs to model a variety of on-wafer and coaxial VNA calibrations, including open-short-load-thru (OSLT) and line-reflect-match (LRM), and assess the accuracy of the calibrations using these ANN-modeled standards. We find that the ANN models compare favorably to benchmark calibrations throughout the frequencies they were trained for. We summarize other current applications of ANNs, including the determination of permittivities of liquids from the reflection coefficient measurements of an open-ended coaxial probe and the determination of moisture content of wheat from free-space transmission coefficient measurements. We also discuss some potential applications of ANN models related to power measurements, material characterization, and the comparison of nonlinear vector network analyzers. © 2002 John Wiley & Sons, Inc. Int J RF and Microwave CAE 12: 3,24, 2002. [source] Purification of Fluorous Mitsunobu Reactions by Liquid-Liquid ExtractionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12-13 2006Dennis Abstract Solvent tuning and partition coefficient measurements have identified suitable reagent and solvent combinations for the purification of fluorous Mitsunobu reaction products. The crude reaction mixtures are partitioned between 2/1 HFE-7100/FC-72 and DMF/10,% water to provide reagent (fluorous) and product (organic) fractions. [source] Improving the prediction of liquid back-mixing in trickle-bed reactors using a neural network approachJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2002Simon Piché Abstract Current correlations aimed at estimating the extent of liquid back-mixing, via an axial dispersion coefficient, in trickle-bed reactors continue to draw doubts on their ability to conveniently represent this important macroscopic parameter. A comprehensive database containing 973 liquid axial dispersion coefficient measurements (DAX) for trickle-bed operation reported in 22 publications between 1958 and 2001 was thus used to assess the convenience of the few available correlations. It was shown that none of the literature correlations was efficient at providing satisfactory predictions of the liquid axial dispersion coefficients. In response, artificial neural network modeling is proposed to improve the broadness and accuracy in predicting the DAX, whether the Piston,Dispersion (PD), Piston,Dispersion,Exchange (PDE) or PDE with intra-particle diffusion model is employed to extract the DAX. A combination of six dimensionless groups and a discrimination code input representing the residence-time distribution models are used to predict the Bodenstein number. The inputs are the liquid Reynolds, Galileo and Eötvos numbers, the gas Galileo number, a wall factor and a mixed Reynolds number involving the gas flow rate effect. The correlation yields an absolute average error (AARE) of 22% for the whole database with a standard deviation on the AARE of 24% and remains in accordance with parametric influences reported in the literature. © 2002 Society of Chemical Industry [source] Effect of harvest time and storage conditions on almond kernel oil and sugar compositionJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 4 2003Ioannis Kazantzis Abstract The effect of storage for 6 months at 5,°C (80% RH) versus 20,°C (60% RH) of shelled versus in-shell almonds was studied on early versus late harvested nuts from ,Ferragnes' and ,Texas' trees. Kernel quality characteristics, oil composition and sugar composition were determined initially and after 6 months of storage. Early harvested almonds had similar kernel weight to but higher moisture content than late harvested almonds after 6 months of storage. Early harvested almonds also had similar oil quality (based on ultraviolet absorption coefficient measurements) and oil composition but lower sugar content and modified sugar composition compared with late harvested almonds. Storage of shelled almonds resulted in kernels with higher oil content, better oil quality, similar oil composition, similar sugar content and some modifications in sugar composition compared with in-shell stored almonds. Finally, storage for 6 months at either 5 or 20,°C resulted in lower moisture content, higher oil content, similar oil quality and composition, similar sugar content and some modifications in sugar composition compared with freshly harvested almonds. Almonds stored at 5,°C retained higher kernel weight and moisture content than almonds stored at 20,°C. © 2003 Society of Chemical Industry [source] Increased friction coefficient and superficial zone protein expression in patients with advanced osteoarthritisARTHRITIS & RHEUMATISM, Issue 9 2010C. P. Neu Objective To quantify the concentration of superficial zone protein (SZP) in the articular cartilage and synovial fluid of patients with advanced osteoarthritis (OA) and to further correlate the SZP content with the friction coefficient, OA severity, and levels of proinflammatory cytokines. Methods Samples of articular cartilage and synovial fluid were obtained from patients undergoing elective total knee replacement surgery. Additional normal samples were obtained from donated body program and tissue bank sources. Regional SZP expression in cartilage obtained from the femoral condyles was quantified by enzyme-linked immunosorbent assay (ELISA) and visualized by immunohistochemistry. Friction coefficient measurements of cartilage plugs slid in the boundary lubrication system were obtained. OA severity was graded using histochemical analyses. The concentrations of SZP and proinflammatory cytokines in synovial fluid were determined by ELISA. Results A pattern of SZP localization in knee cartilage was identified, with load-bearing regions exhibiting high SZP expression. SZP expression patterns were correlated with friction coefficient and OA severity; however, SZP expression was observed in all samples at the articular surface, regardless of OA severity. SZP expression and aspirate volume of synovial fluid were higher in OA patients than in normal controls. Expression of cytokines was elevated in the synovial fluid of some patients. Conclusion Our findings indicate a mechanochemical coupling in which physical forces regulate OA severity and joint lubrication. The findings of this study also suggest that SZP may be ineffective in reducing joint friction in the boundary lubrication mode at an advanced stage of OA, where other mechanisms may dominate the observed tribological behavior. [source] In situ effective diffusion coefficient profiles in live biofilms using pulsed-field gradient nuclear magnetic resonanceBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2010Ryan S. Renslow Abstract Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffusion coefficient are currently: (1) invasive to the biofilm, (2) performed under unnatural conditions, (3) lethal to cells, and/or (4) spatially restricted to only certain regions of the biofilm. Invasive measurements can lead to inaccurate results and prohibit further (time-dependent) measurements which are important for the mathematical modeling of biofilms. In this study our goals were to: (1) measure the effective diffusion coefficient for water in live biofilms, (2) monitor how the effective diffusion coefficient changes over time under growth conditions, and (3) correlate the effective diffusion coefficient with depth in the biofilm. We measured in situ two-dimensional effective diffusion coefficient maps within Shewanella oneidensis MR-1 biofilms using pulsed-field gradient nuclear magnetic resonance methods, and used them to calculate surface-averaged relative effective diffusion coefficient (Drs) profiles. We found that (1) Drs decreased from the top of the biofilm to the bottom, (2) Drs profiles differed for biofilms of different ages, (3) Drs profiles changed over time and generally decreased with time, (4) all the biofilms showed very similar Drs profiles near the top of the biofilm, and (5) the Drs profile near the bottom of the biofilm was different for each biofilm. Practically, our results demonstrate that advanced biofilm models should use a variable effective diffusivity which changes with time and location in the biofilm. Biotechnol. Bioeng. 2010;106: 928,937. © 2010 Wiley Periodicals, Inc. [source] Self-Association of Bis-Dendritic Organogelators: The Effect of Dendritic Architecture on Multivalent Cooperative InteractionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2010Myungeun Seo Dr. Abstract A series of bis-dendritic gelators consisting of a benzamide dendron and an alkyl dendron were synthesized to investigate the dendritic effect on self-assembly. The gelators with a first-generation benzamide (benzamide- G1) dendron or a first-generation alkyl (alkyl- G1) dendron formed stable gels in most aromatic solvents, and their self-assembled fibrillar networks were imaged by electron microscopy. The unbranched molecule (G0 - G0) or the molecule possessing a second-generation benzamide (benzamide- G2) dendron did not form gels. Differential scanning calorimetry, powder X-ray diffraction, and Fourier transform IR studies revealed that introduction of a dendritic branch strongly affected the molecular packing as well as the strength of intermolecular interactions. Furthermore, concentration-dependent diffusion coefficient measurements and the evaluation of association constants by 1H NMR spectroscopy indicated that bis-dendritic gelators with a benzamide- G1 dendron possessed high association constants and formed large aggregates, whereas molecules with a single benzamide formed dimers in chloroform. The formation of self-assembled fibrillar networks was driven by the multivalent and cooperative hydrogen bonding observed in the benzamide- G1 dendrons. ,,, stacking of aromatic groups and van der Waals interactions between alkyl chains also played roles in the self-assembly process, thus indicating that a spatial balance between two dendrons is important. [source] | ||||||||||