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The concepts of chemical reaction engineering are powerful, because the most basic design equations are applicable to a wide range of physical phenomena. For example, the applicability of the ideal continuous-flow stirred tank rea...
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The concepts of chemical reaction engineering are powerful, because the most basic design equations are applicable to a wide range of physical phenomena. For example, the applicability of the ideal continuous-flow stirred tank reactor goes far beyond chemical reactors to include biological, medical and environmental processes. The difficulty in analyz- ing these processes is not in formulating an appropriate reactor equation, but in modeling the chemical kinetics.
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Kinetic aspects of the ion current layer at the center of a reconnection outflow exhaust near the X-type region are investigated by a two-dimensional particle-in-cell (PIC) simulation. The layer consists of magnetized electrons an...
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Kinetic aspects of the ion current layer at the center of a reconnection outflow exhaust near the X-type region are investigated by a two-dimensional particle-in-cell (PIC) simulation. The layer consists of magnetized electrons and unmagnetized ions that carry a perpendicular electric current. The ion fluid appears to be nonideal, sub-Alfvénic, and nondissipative. The ion velocity distribution functions contain multiple populations, such as global Speiser ions, local Speiser ions, and trapped ions. The particle motion of the local Speiser ions in an appropriately rotated coordinate system explains the ion fluid properties very well. The trapped ions are the first demonstration of the regular orbits in the chaotic particle dynamics [Chen and Palmadesso, J. Geophys. Res. 91, 1499 (1986)] in self-consistent PIC simulations. They would be observational signatures in the ion current layer near reconnection sites.
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The first reported examples of kinetic resolution in epoxidation reactions using iminium salt catalysis are described, providing up to 99% ee in the epoxidation of racemic cis-chromenes.
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We propose a model describing the kinetics of accumulation of defects under cyclic loading in metals. Analysis of experimental data on the initial defect distribution and of the role of the free surface of the sample in straining ...
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We propose a model describing the kinetics of accumulation of defects under cyclic loading in metals. Analysis of experimental data on the initial defect distribution and of the role of the free surface of the sample in straining makes it possible to explain the features of generation of fatigue cracks in the bulk, which is typical of the gigacycle fatigue regime at a low stress level. The duality of the Weller curve in the gigacycle fatigue regime is attributed to the emergence of a fine-grain region in the form of a dissipative peaking structure in the defect ensemble.
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This comment illustrates the importance of data analysis in the determination of scale growth kinetics. It proposes a general method permitting to distinguish parabolic kinetics and power-law kinetics and to determine what scale g...
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This comment illustrates the importance of data analysis in the determination of scale growth kinetics. It proposes a general method permitting to distinguish parabolic kinetics and power-law kinetics and to determine what scale growth kinetics is better suited to the analysis of a given data set.
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This paper further develops the connection between Chemical Reaction Network Theory (CRNT) and Biochemical Systems Theory (BST) that we recently introduced [1]. We first use algebraic properties of kinetic sets to study the set of...
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This paper further develops the connection between Chemical Reaction Network Theory (CRNT) and Biochemical Systems Theory (BST) that we recently introduced [1]. We first use algebraic properties of kinetic sets to study the set of complex factorizable kinetics CFK(N) on a CRN, which shares many characteristics with its subset of mass action kinetics. In particular, we extend the Theorem of Feinberg-Horn [9] on the coincidence of the kinetic and stoichiometric subsets of a mass action system to CF kinetics, using the concept of span surjectivity. We also introduce the branching type of a network, which determines the availability of kinetics on it and allows us to characterize the networks for which all kinetics are complex factorizable: A "Kinetics Landscape" provides an overview of kinetics sets, their algebraic properties and containment relationships. We then apply our results and those (of other CRNT researchers) reviewed in [1] to fifteen BST models of complex biological systems and discover novel network and kinetic properties that so far have not been widely studied in CRNT. In our view, these findings show an important benefit of connecting CRNT and BST modeling efforts. (C) 2016 Elsevier Inc. All rights reserved.
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Polyphenol oxidase (PPO) has been extracted from both soluble and particulate fractions of loquat fruit (Eriobotrya-japonica Lindl. cv. Algerie). The soluble PPO (20% of total activity) was partially purified 3.3-fold after ammoni...
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Polyphenol oxidase (PPO) has been extracted from both soluble and particulate fractions of loquat fruit (Eriobotrya-japonica Lindl. cv. Algerie). The soluble PPO (20% of total activity) was partially purified 3.3-fold after ammonium sulfate fractionation being in its active state. The particulate PPO fraction (80% of total activity) was purified to homogeneity in a latent form being activable by sodium dodecyl sulfate (SDS). The enzyme was purified 40.0-fold with a total yield of 15.3% after extraction by phase partitioning in Triton X-114 followed by three chromatographic steps. The molecular weight was estimated to be about 59.2 and 61.2 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration chromatography, respectively, indicating that latent PPO is a monomer. Latent PPO catalyzed the oxidation of chlorogenic acid (CA) at a rate 50-fold faster than that of 4-tert-butylcatechol (TBC) but the soluble active counterpart only twice. Both PPOs exhibited similar K-m values for TBC but K-m for CA was 5-fold higher for the latent than for the active soluble PPO. Other kinetic characteristics, including sensitivity to inhibitors, substrate specificity, thermal stability, temperature, and pH profiles, were quite different between both PPOs. These results provide strong evidences that the Soluble active and the particulate latent are different forms of PPO in loquat fruit flesh. The results suggest that the major PPO form for the oxidation of CA, leading to enzymatic browning under physiological conditions, is the latent one. (c) 2006 Elsevier Inc. All rights reserved.
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Dr. Marek Maciejewski reported in 1999 in an excellent work the second part of a series of papers dealing with the results of the International Confederation for Thermal Analysis and Calorimetry (ICTAC) Kinetic Analysis Project [M...
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Dr. Marek Maciejewski reported in 1999 in an excellent work the second part of a series of papers dealing with the results of the International Confederation for Thermal Analysis and Calorimetry (ICTAC) Kinetic Analysis Project [M.E. Brown, M. Maciejewski, S. Vyazovkin, R. Nomen, J. Sempere, A. Burnham, J. Opfermann, R. Strey, H.L. Anderson, A. Kemmler, R. Keuleers, J. Janssens, H.O. Desseyn, C.-R. Li, T.B. Tang, B. Roduit, J. Malek, T. Mitsuhashi, Thennochim. Acta 355 (2000) 125-143; M. Maciejewski, Thermochim. Acta 355 (2000) 145-154; S. Vyazovkin, Thermochim. Acta 355 (2000) 155-163; A.K. Burnham, Thennochim. Acta 355 (2000) 165-170; B. Roduit, Thermochim. Acta 355 (2000) 171-180]. In this work Dr. Maciejewski emphasized the very limited applicability of the kinetic methods that use single-heating rate data and stated that to obtain reliable kinetic descriptions, computational methods that employ multi-heating rate data should be used for treating multistep processes. The reasons supporting this argument are presented in his "Fact 2", where it was stated that two different models represent very similar alpha-T curves at one heating rate (5 degrees C/min), but at other two different heating rates (2 and 10 degrees'C/min) the same kinetic parameters used at 5 degrees C/min illustrate very different curves. In this letter to the editor, we show different examples where we intend to illustrate that interactions among parameters are even higher than this author described, since there is a possibility that different models, could be able to reproduce the same conversion curves at different heating rates simultaneously. (c) 2006 Elsevier B.V. All rights reserved.
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Xanthation reaction in viscose process is heterogeneous reaction (gaseous CS2-wet alkaline cellulose) complicated with side reactions. Commercial requirement of CS2 in viscose process is 32-34%, which is significantly higher than ...
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Xanthation reaction in viscose process is heterogeneous reaction (gaseous CS2-wet alkaline cellulose) complicated with side reactions. Commercial requirement of CS2 in viscose process is 32-34%, which is significantly higher than the stoichiometric requirement (23.5% w/w of the cellulose) due to formation of byproducts. Detailed xanthation reaction kinetics study was performed to understand the xanthate and by-products formation mechanism along with effect of mass transfer and its possible impact on CS2 consumption. Heterogeneous nature of the xanthation reaction offers significant mass transfer resistance and was hypothesized to be driven by CS2 partitioning into wet alkali cellulose and its unstable complex (DTCdithiocarbonate) formation with alkali. Xanthation reaction mechanism in the form of physico-chemical process steps has been proposed with experimental justification.
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An integrated model was developed by associating separate degradation kinetics for an array of degradations during a decomposition process, which was considered as a novelty of this study. The raw composting material was divided i...
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An integrated model was developed by associating separate degradation kinetics for an array of degradations during a decomposition process, which was considered as a novelty of this study. The raw composting material was divided into soluble, hemi-/cellulose, lignin, NBVS, ash, water, and free air-space. Considering their specific capabilities of expressing certain degradation phenomenon, Contois, Tessier ( an extension to Monod kinetic), and first-order kinetics were employed to calculate the biochemical rates. It was found that the degradation of soluble substrate was relatively faster which could reach a maximum rate of about 0.4 per hour. The hydrolysis of lignin was rate-limiting with a maximum rate of about 0.04 per hour. The dry-based peak concentrations of soluble, hemi-/cellulose and lignin degraders were about 0.9, 0.2 and 0.3 kg m(-3), respectively. Model developed, as a platform, allows degradation simulation of composting material that could be separated into the different components used in this study. (C) 2016 Elsevier Ltd. All rights reserved.
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