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Articoli di riviste sul tema "Chemical reaction"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 1 agosto 2024

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1

DE LACY COSTELLO, B. P. J., I. JAHAN, A. ADAMATZKY e N. M. RATCLIFFE. "CHEMICAL TESSELLATIONS". International Journal of Bifurcation and Chaos 19, n. 02 (febbraio 2009): 619–22. http://dx.doi.org/10.1142/s0218127409023238.

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We report a simple set of chemical reactions based on the reaction of a range of metal salts with potassium ferricyanide loaded gels that spontaneously produce complex and colorful tessellations of the plane. These reactions provide a great resource for scientific demonstrations, whilst also constituting an important class of nonlinear pattern forming reaction.

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2

Blurock, Edward S. "Reaction: System for Modeling Chemical Reactions". Journal of Chemical Information and Modeling 35, n. 3 (1 maggio 1995): 607–16. http://dx.doi.org/10.1021/ci00025a032.

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3

Kikuchi, Shin, Hiroyuki Ohshima e Kenro Hashimoto. "ICONE19-43782 Reaction Path Analysis of Sodium-Water Reaction Phenomena in support of Chemical Reaction Model Development". Proceedings of the International Conference on Nuclear Engineering (ICONE) 2011.19 (2011): _ICONE1943. http://dx.doi.org/10.1299/jsmeicone.2011.19._icone1943_304.

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4

Sieniutycz, Stanisław. "A Fermat-like Principle for Chemical Reactions in Heterogeneous Systems". Open Systems & Information Dynamics 09, n. 03 (settembre 2002): 257–72. http://dx.doi.org/10.1023/a:1019708629128.

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We formulate a variational principle of Fermat type for chemical kinetics in heterogeneous reacting systems. The principle is consistent with the notion of ‘intrinsic reaction coordinate’ (IRC), the idea of ‘chemical resistance’ (CR) and the second law of thermodynamics. The Lagrangian formalism applies a nonlinear functional of entropy production that follows from classical (single-phase) nonequilibrium thermodynamics of chemically reacting systems or its extension for multiphase systems involving interface reactions and transports. For a chemical flux, a “law of bending” is found which implies that — by minimizing the total resistance — the chemical ray spanned between two given points takes the shape assuring its relatively large part in a region of lower chemical resistivity (a ‘rarer’ region of the medium). In effect, the chemical flux bends into the direction that ensures its shape consistent with the longest residence of the chemical complex in regions of lower resistivity. The dynamic programming method quantifies the “chemical rays” and related wavefronts along the reaction coordinate.

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5

Marris, Emma. "Chemical reaction". Nature 437, n. 7060 (ottobre 2005): 807–9. http://dx.doi.org/10.1038/437807a.

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6

Challen, John. "Chemical Reaction". Electric and Hybrid Vehicle Technology International 2021, n. 3 (novembre 2021): 46–50. http://dx.doi.org/10.12968/s1467-5560(22)60257-4.

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7

Schwaller, Philippe, Benjamin Hoover, Jean-Louis Reymond, Hendrik Strobelt e Teodoro Laino. "Extraction of organic chemistry grammar from unsupervised learning of chemical reactions". Science Advances 7, n. 15 (aprile 2021): eabe4166. http://dx.doi.org/10.1126/sciadv.abe4166.

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Humans use different domain languages to represent, explore, and communicate scientific concepts. During the last few hundred years, chemists compiled the language of chemical synthesis inferring a series of “reaction rules” from knowing how atoms rearrange during a chemical transformation, a process called atom-mapping. Atom-mapping is a laborious experimental task and, when tackled with computational methods, requires continuous annotation of chemical reactions and the extension of logically consistent directives. Here, we demonstrate that Transformer Neural Networks learn atom-mapping information between products and reactants without supervision or human labeling. Using the Transformer attention weights, we build a chemically agnostic, attention-guided reaction mapper and extract coherent chemical grammar from unannotated sets of reactions. Our method shows remarkable performance in terms of accuracy and speed, even for strongly imbalanced and chemically complex reactions with nontrivial atom-mapping. It provides the missing link between data-driven and rule-based approaches for numerous chemical reaction tasks.

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8

Wu, Jun-Lin, Zhi-Hui Li, Ao-Ping Peng, Xing-Cai Pi e Xin-Yu Jiang. "Utility computable modeling of a Boltzmann model equation for bimolecular chemical reactions and numerical application". Physics of Fluids 34, n. 4 (aprile 2022): 046111. http://dx.doi.org/10.1063/5.0088440.

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A Boltzmann model equation (kinetic model) involving the chemical reaction of a multicomponent gaseous mixture is derived based on Groppi's work [“A Bhatnagar–Gross–Krook-type approach for chemically reacting gas mixtures,” Phys. Fluids 16, 4273 (2004)], in which the relaxation parameters of elastic collision frequency for rigid elastic spheres are obtained based on the collision term, and the pivotal collision frequency of the chemical reaction is deduced from the chemical reaction rate that is determined by the direct simulation Monte Carlo (DSMC) method. This kinetic model is shown to be conservative, and the H theorem for an endothermic reaction is proven. In the framework of the gas-kinetic unified algorithm, the discrete velocity method, finite volume method, and implicit scheme are applied to solve the proposed kinetic model by introducing a suitable boundary condition at the wall surface. For hypersonic flows around a cylinder, the proposed kinetic model and the corresponding numerical methods are verified for both endothermic and exothermic reactions by comparison of the model's results with results from the DSMC method. The different influences of endothermic and exothermic reactions are also given. Finally, the proposed kinetic model is also used to simulate an exothermic reaction-driven flow in a square cavity.

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9

Dunning, Thom H., Elfi Kraka e Robert A. Eades. "Insights into the mechanisms of chemical reactions. Reaction paths for chemical reactions". Faraday Discussions of the Chemical Society 84 (1987): 427. http://dx.doi.org/10.1039/dc9878400427.

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10

Lazaridis, Filippos, Aditya Savara e Panos Argyrakis. "Reaction efficiency effects on binary chemical reactions". Journal of Chemical Physics 141, n. 10 (14 settembre 2014): 104103. http://dx.doi.org/10.1063/1.4894791.

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11

Cerón, María Luisa, Eleonora Echegaray, Soledad Gutiérrez-Oliva, Bárbara Herrera e Alejandro Toro-Labbé. "The reaction electronic flux in chemical reactions". Science China Chemistry 54, n. 12 (23 novembre 2011): 1982–88. http://dx.doi.org/10.1007/s11426-011-4447-z.

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12

Maas, Ulrich. "Coupling of chemical reaction with flow and molecular transport". Applications of Mathematics 40, n. 3 (1995): 249–66. http://dx.doi.org/10.21136/am.1995.134293.

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13

Haddon, R. C., e S. Y. Chow. "Hybridization as a metric for the reaction coordinate of the chemical reaction. Concert in chemical reactions". Pure and Applied Chemistry 71, n. 2 (28 febbraio 1999): 289–94. http://dx.doi.org/10.1351/pac199971020289.

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14

Field, Richard J. "Chaos in the Belousov–Zhabotinsky reaction". Modern Physics Letters B 29, n. 34 (20 dicembre 2015): 1530015. http://dx.doi.org/10.1142/s021798491530015x.

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The dynamics of reacting chemical systems is governed by typically polynomial differential equations that may contain nonlinear terms and/or embedded feedback loops. Thus the dynamics of such systems may exhibit features associated with nonlinear dynamical systems, including (among others): temporal oscillations, excitability, multistability, reaction-diffusion-driven formation of spatial patterns, and deterministic chaos. These behaviors are exhibited in the concentrations of intermediate chemical species. Bifurcations occur between particular dynamic behaviors as system parameters are varied. The governing differential equations of reacting chemical systems have as variables the concentrations of all chemical species involved, as well as controllable parameters, including temperature, the initial concentrations of all chemical species, and fixed reaction-rate constants. A discussion is presented of the kinetics of chemical reactions as well as some thermodynamic considerations important to the appearance of temporal oscillations and other nonlinear dynamic behaviors, e.g., deterministic chaos. The behavior, chemical details, and mechanism of the oscillatory Belousov–Zhabotinsky Reaction (BZR) are described. Furthermore, experimental and mathematical evidence is presented that the BZR does indeed exhibit deterministic chaos when run in a flow reactor. The origin of this chaos seems to be in toroidal dynamics in which flow-driven oscillations in the control species bromomalonic acid couple with the BZR limit cycle.

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15

Mundschau, M., e B. Rausenberger. "Chemical Reaction Fronts on Platinum Surfaces". Platinum Metals Review 35, n. 4 (1 ottobre 1991): 188–95. http://dx.doi.org/10.1595/003214091x354188195.

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In many chemical reactions catalysed on platinum surfaces it is necessary that two reactants be adsorbed simultaneously. Often one reactant is so strongly adsorbed that it blocks the adsorption of the second; such a reaction is said to be self-poisoned. An example is the oxidation of carbon monoxide, where carbon monoxide forms a strongly adsorbed monolayer which effectively blocks the adsorption and decomposition of oxygen. Photoelectron microscopy shows, however, that oxygen can penetrate the carbon monoxide film at special defect sites, typically inclusions or microdust particles, on the platinum. From these special adsorption sites the oxygen rapidly reacts with neighbouring adsorbed carbon monoxide. Reaction fronts initiate at these sites and rapidly propagate across the surface. A second type of self-poisoning occurs in decomposition reactions for which vacant surface sites are necessary; for instance, the decomposition of nitric oxide in the presence of hydrogen. A monolayer film of nitric oxide poisons the reaction not by blocking the adsorption of hydrogen, but rather by preventing the dissociation of nitric oxide which requires a neighbouring unoccupied surface site. Empty sites are provided on impurity particles which weakly adsorb nitric oxide and initiate reaction fronts. Impurity sites also initiate reaction fronts when graphite is removed from platinum by oxidation. In order to avoid self-poisoning in catalytic reactions, these studies suggest that special adsorption sites should be introduced artificially to provide vacant sites by adsorbing only weakly the reactants causing self-poisoning.

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16

Von Korff, Modest, e Thomas Sander. "Molecular Complexity for Chemical Reactions". CHIMIA 77, n. 4 (26 aprile 2023): 258. http://dx.doi.org/10.2533/chimia.2023.258.

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A new method is presented on how to calculate molecular complexity for chemical reactions by the fractal dimension of educts and products. Two pathways for the total synthesis of strychnine were compared. Significant differences in the two synthesis pathways were reflected by reaction complexity. These results demonstrate that reaction complexity is a powerful measure to group chemical reactions beyond substructural changes.

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17

Guo, Jeff, Bojana Ranković e Philippe Schwaller. "Bayesian Optimization for Chemical Reactions". CHIMIA 77, n. 1/2 (22 febbraio 2023): 31. http://dx.doi.org/10.2533/chimia.2023.31.

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Reaction optimization is challenging and traditionally delegated to domain experts who iteratively propose increasingly optimal experiments. Problematically, the reaction landscape is complex and often requires hundreds of experiments to reach convergence, representing an enormous resource sink. Bayesian optimization (BO) is an optimization algorithm that recommends the next experiment based on previous observations and has recently gained considerable interest in the general chemistry community. The application of BO for chemical reactions has been demonstrated to increase efficiency in optimization campaigns and can recommend favorable reaction conditions amidst many possibilities. Moreover, its ability to jointly optimize desired objectives such as yield and stereoselectivity makes it an attractive alternative or at least complementary to domain expert-guided optimization. With the democratization of BO software, the barrier of entry to applying BO for chemical reactions has drastically lowered. The intersection between the paradigms will see advancements at an ever-rapid pace. In this review, we discuss how chemical reactions can be transformed into machine-readable formats which can be learned by machine learning (ML) models. We present a foundation for BO and how it has already been applied to optimize chemical reaction outcomes. The important message we convey is that realizing the full potential of ML-augmented reaction optimization will require close collaboration between experimentalists and computational scientists.

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18

Yang, Xueming, David C. Clary e Daniel M. Neumark. "Chemical reaction dynamics". Chemical Society Reviews 46, n. 24 (2017): 7481–82. http://dx.doi.org/10.1039/c7cs90121f.

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19

Crim, F. F. "Chemical reaction dynamics". Proceedings of the National Academy of Sciences 105, n. 35 (27 agosto 2008): 12647–48. http://dx.doi.org/10.1073/pnas.0805363105.

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20

Levenspiel, Octave. "Chemical Reaction Engineering". Industrial & Engineering Chemistry Research 38, n. 11 (novembre 1999): 4140–43. http://dx.doi.org/10.1021/ie990488g.

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21

Field, Richard. "Chemical reaction kinetics". Scholarpedia 3, n. 10 (2008): 4051. http://dx.doi.org/10.4249/scholarpedia.4051.

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22

Bro, Per. "Chemical reaction automata". Complexity 2, n. 3 (gennaio 1997): 38–44. http://dx.doi.org/10.1002/(sici)1099-0526(199701/02)2:3<38::aid-cplx7>3.0.co;2-j.

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23

Hinrichsen, Kai-Olaf, e Elias Klemm. "Chemical Reaction Engineering". Chemical Engineering & Technology 39, n. 11 (21 ottobre 2016): 1992. http://dx.doi.org/10.1002/ceat.201690063.

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24

Zhang, Xiaolong, e Zheng Zhong. "Thermo-Chemo-Elasticity Considering Solid State Reaction and the Displacement Potential Approach to Quasi-Static Chemo-Mechanical Problems". International Journal of Applied Mechanics 10, n. 10 (dicembre 2018): 1850112. http://dx.doi.org/10.1142/s1758825118501120.

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Engineering materials and structures represent complex behaviors when reacting to superposed influences of mechanical forces, high temperature, diffusion and reaction of chemicals, which could cause large internal stresses and further induce cracks or failure. To determine the material reliability and integrity, the multi-field interactions and stresses/strains evolutions need to be identified at first. We proposed a theory of thermo-chemo-elasticity considering solid state reactions between the solid phase and absorbed chemicals in a stressed-solid. Both diffusion–reaction induced chemical strains and thermal dilations are taken into account as functions of species concentration, reaction extent and temperature. The fully coupled conservation laws, constitutive equations and chemical kinetics are formulated for the initial-boundary problem. For isotropic solids, we developed a displacement potential approach for steady-state 3D problems of thermo-chemo-elasticity. Solutions can be found from particular solutions of displacement potential and homogeneous solution of thermo-chemo Lamé equation. This approach is also available for transient chemo-mechanical problems in thermal equilibrium providing that quasi-static conditions are introduced. We exemplified the model with a reaction-dominated problem of a core–shell structure subjected to chemo-mechanical loading and the results demonstrate the capability of the model in dealing with comprehensive influences of solid state reaction and species diffusion on solids.

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25

Domingos, Mariana G., e Silvana S. S. Cardoso. "Turbulent thermals with chemical reaction". Journal of Fluid Mechanics 784 (28 ottobre 2015): 5–29. http://dx.doi.org/10.1017/jfm.2015.583.

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This study investigates the behaviour of a turbulent thermal undergoing a second-order chemical reaction with the fluid entrained from the environment. Environments with uniform and stratified density are considered. We show that the dynamics of such a reactive thermal is fully determined by three dimensionless groups, $N/E$, $G/R$ and $R/E$, where $N$ is the buoyancy frequency of the environment, $G$ measures the ability of the reaction to change buoyancy, $R$ reflects the rate of consumption of the chemical species and $E$ is the rate of entrainment of reactive species from the environment. Exact analytical solutions are found for the limiting cases of slow and instantaneous chemical reaction. The effect of each governing group on the time for neutral buoyancy and depletion of the source chemical is assessed numerically. Our theoretical predictions compare well with new experimental results for the limits of a moderately slow chemical reaction and an instantaneous reaction. It is shown that fast reactions, with $R/E\gg 1$, occur only in a fraction of the total volume of the thermal due to incomplete mixing. Finally, our model is applied to study the dynamics of a radioactive cloud formed after a nuclear accident.

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26

Zhong, Wei, e Zhou Tian. "The Chemical Kinetic Numerical Computation and Kinetic Model Parameters Estimating of Parallel Reactions with Different Reaction Orders". Advanced Materials Research 560-561 (agosto 2012): 1126–32. http://dx.doi.org/10.4028/www.scientific.net/amr.560-561.1126.

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Abstract. Parallel reaction is a common reaction of chemical kinetics, and there are two types of parallel reactions according to the reaction orders equivalence: parallel reactions with same reaction orders and parallel reactions with different reaction orders. For the reason that the reaction orders are different, the chemical kinetic numerical computation and kinetic model parameters estimating of parallel reactions with different reaction orders is more complicated than parallel reactions with same reaction orders. In this paper, the 4th order Runge-Kutta method was employed to solve the numerical computation problems of complex ordinary differential equations, which was the chemical kinetic governing equations of parallel reactions with different reaction orders, and also, the Richardson extrapolation and Least Square Estimate were employed to estimate the kinetic model parameters of parallel reactions with different reaction orders. A C++ program has been processed to solve the problem and has been tested by an example of parallel reactions with different reaction orders.

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27

Melissas, Vasilios S., Donald G. Truhlar e Bruce C. Garrett. "Optimized calculations of reaction paths and reaction‐path functions for chemical reactions". Journal of Chemical Physics 96, n. 8 (15 aprile 1992): 5758–72. http://dx.doi.org/10.1063/1.462674.

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28

Maiti, Shyantani, Sanjay Ram e Somnath Pal. "Extension of Ugi's Scheme for Model-Driven Classification of Chemical Reactions". International Journal of Chemoinformatics and Chemical Engineering 4, n. 1 (gennaio 2015): 26–51. http://dx.doi.org/10.4018/ijcce.2015010103.

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The first step to predict the outcome of a chemical reaction is to classify existing chemical reactions, on the basis of which possible outcome of unknown reaction can be predicted. There are two approaches for classification of chemical reactions: Model-Driven and Data-Driven. In model-driven approach, chemical structures are usually stored in a computer as molecular graphs. Such graphs can also be represented as matrices. The most preferred matrix representation to store molecular graph is Bond-Electron matrix (BE-matrix). The Reaction matrix (R-matrix) of a chemical reaction can be obtained from the BE-matrices of educts and products was shown by Ugi and his co-workers. Ugi's Scheme comprises of 30 reaction classes according to which reactions can be classified, but in spite of such reaction classes there were several reactions which could not be classified. About 4000 reactions were studied in this work from The Chemical Thesaurus (a chemical reaction database) and accordingly 24 new classes have emerged which led to the extension of Ugi's Scheme. An efficient algorithm based on the extended Ugi's scheme have been developed for classification of chemical reactions. Reaction matrices being symmetric, matrix implementation of extended Ugi's scheme using conventional upper/lower tri-angular matrix is of O(n2) in terms of space complexity. Time complexity of similar matrix implementation is O(n2) in worst case. The authors' proposed algorithm uses two fixed size look-up tables in a novel way and requires constant space complexity. Worst case time complexity of their algorithm although still O(n2) but it outperforms conventional matrix implementation when number of atoms or components in the chemical reaction is 4 or more.

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29

Peng, Zhen, Jeff Linderoth e David A. Baum. "The hierarchical organization of autocatalytic reaction networks and its relevance to the origin of life". PLOS Computational Biology 18, n. 9 (9 settembre 2022): e1010498. http://dx.doi.org/10.1371/journal.pcbi.1010498.

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Prior work on abiogenesis, the emergence of life from non-life, suggests that it requires chemical reaction networks that contain self-amplifying motifs, namely, autocatalytic cores. However, little is known about how the presence of multiple autocatalytic cores might allow for the gradual accretion of complexity on the path to life. To explore this problem, we develop the concept of a seed-dependent autocatalytic system (SDAS), which is a subnetwork that can autocatalytically self-maintain given a flux of food, but cannot be initiated by food alone. Rather, initiation of SDASs requires the transient introduction of chemical “seeds”. We show that, depending on the topological relationship of SDASs in a chemical reaction network, a food-driven system can accrete complexity in a historically contingent manner, governed by rare seeding events. We develop new algorithms for detecting and analyzing SDASs in chemical reaction databases and describe parallels between multi-SDAS networks and biological ecosystems. Applying our algorithms to both an abiotic reaction network and a biochemical one, each driven by a set of simple food chemicals, we detect SDASs that are organized as trophic tiers, of which the higher tier can be seeded by relatively simple chemicals if the lower tier is already activated. This indicates that sequential activation of trophically organized SDASs by seed chemicals that are not much more complex than what already exist could be a mechanism of gradual complexification from relatively simple abiotic reactions to more complex life-like systems. Interestingly, in both reaction networks, higher-tier SDASs include chemicals that might alter emergent features of chemical systems and could serve as early targets of selection. Our analysis provides computational tools for analyzing very large chemical/biochemical reaction networks and suggests new approaches to studying abiogenesis in the lab.

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30

Kol'tsov, Nikolay I. "CHAOTIC OSCILLATIONS IN SIMPLEST CHEMICAL REACTION". IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 61, n. 4-5 (17 aprile 2018): 133. http://dx.doi.org/10.6060/tcct.20186104-05.5654.

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It is known that chaotic oscillations for chemical reactions can be described by non-stationary kinetic models consisting of three ordinary differential equations. Rossler established the first examples of chemical reactions, including the two-route five-stage reaction of the Villamovski-Rossler, with three intermediate substances, containing three autocatalytic on intermediates stages, the dynamic model of which describes chaotic oscillations. In given article presents a simple one-route four-stages reaction A+E=D involving two autocatalytic and one linear on intermediate stage, the non-stationary kinetic model of which describes chaotic oscillations. The non-stationary kinetic model under the assumption of quasistationarity with respect to the main substances within the framework of the law of acting masses is a system of three ordinary differential equations. The presence of chaos is confirmed by numerical calculations of the kinetic model and Lyapunov exponentials. The Lyapunov exponents satisfy the condition L1+L2+L3<0, which proves the existence of chaotic oscillations.Forcitation:Kol'tsov N.I. Chaotic oscillations in simplest chemical reaction. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 4-5. P. 133-135

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Carpenter, K. J. "Chemical reaction engineering aspects of fine chemicals manufacture". Chemical Engineering Science 56, n. 2 (gennaio 2001): 305–22. http://dx.doi.org/10.1016/s0009-2509(00)00231-1.

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32

Kitamura, Shin-ya. "Kinetics of Metal Smelting ReactionⅡ ―Chemical Reaction Rate―". Materia Japan 60, n. 3 (1 marzo 2021): 181–85. http://dx.doi.org/10.2320/materia.60.181.

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Hartke, B., e J. Manz. "Do chemical reactions react along the reaction path?" Journal of the American Chemical Society 110, n. 10 (maggio 1988): 3063–68. http://dx.doi.org/10.1021/ja00218a011.

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Bernhard Grob e Rudolf Riesen. "Reaction calorimetry for the development of chemical reactions". Thermochimica Acta 114, n. 1 (aprile 1987): 83–90. http://dx.doi.org/10.1016/0040-6031(87)80244-7.

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35

Mukbaniani, Omar, Tamara Tatrishvili, Zurab Pachulia, Levan Londaridze e Nana Pirtskheliani. "Quantum-Chemical Modeling of Hydrosilylation Reaction of Triethoxysilane to Divinylbenzene". Chemistry & Chemical Technology 16, n. 4 (22 dicembre 2022): 499–506. http://dx.doi.org/10.23939/chcht16.04.499.

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Hydrosilylation of triethoxysilane with the mixture of ortho- and para-divinylbenzene in the presen¬ce of Karstedt’s catalyst has been carried out and the corresponding product triethoxy(vinylphenethyl)silane have been obtained. The structure and composition of the obtained product were proved by means of determining molecular mass, molecular refraction, and 1H and 13C NMR spectra data. It was found that the addition reaction proceeds both in ortho-position as well as in para-position. Hydrosilylation proceeds both Markovnikov and anti-Markovnikov rule. Via quantum-chemical calculations using the non-empirical density functional theory (DFT) method, the possible direction of the reaction has been considered.

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Versteeg, G. F., J. A. M. Kuipers, F. P. H. Van Beckum e W. P. M. Van Swaaij. "Mass transfer with complex reversible chemical reactions—I. Single reversible chemical reaction". Chemical Engineering Science 44, n. 10 (1989): 2295–310. http://dx.doi.org/10.1016/0009-2509(89)85163-2.

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Hiraoka, K., T. Sato e T. Takayama. "Laboratory Simulation of Chemical Reactions in Interstellar Ices". Symposium - International Astronomical Union 197 (2000): 283–92. http://dx.doi.org/10.1017/s0074180900164873.

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The reactions of H atoms with solid thin films at 10 K were studied by using thermal desorption mass spectrometry and FT-IR spectroscopy. The N, C, and O atoms trapped in solid matrices were converted efficiently to fully hydrogenated compounds. In the reaction of H atoms with a solid CO film, the formation of formaldehyde and methanol were confirmed. The relatively low yield of the reaction products suggests either the smaller rate constants of the H atom addition reactions to CO and/or the occurrence of the hydrogen abstraction reaction H + HCO → H2+ CO. The reactions of H atoms with thin films of acetone and 2-propanol were also studied. The major products from acetone were found to be methane and alcohols but 2-propanol was not detected as a reaction product. The reaction of H with 2-propanol led to the formation of methane, alcohols, and acetone as major products.In the reaction of H with C2H2, C2H6was found to be the major product but C2H4could not be detected. This is due to the fact that the first-step addition reaction H + C2H2→ C2H3is the rate-controlling process and the following reactions to form the final product C2H6proceed much faster than the initial one. This finding is in accord with the observation of comets Hyakutake and Hale-Bopp, i.e., C2H2and C2H6but not C2H4were detected in the coma of these comets. In the reactions of H with C2H2and C2H4, the C2H6product yields increased drastically with decrease of temperature from 50 to 10 K. This is most likely due to the increase of the sticking probability of H atoms on the solid films at lower temperature. These findings led us to conclude that the chemical evolution taking place on the dust grains via H-atom tunneling reactions becomes efficient only at cryogenic temperatures, i.e., ~ 10 K.

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Horno, José, e Carlos F. González-Fernández. "Analysis of chemical reaction systems by means of network thermodynamics". Collection of Czechoslovak Chemical Communications 54, n. 9 (1989): 2335–44. http://dx.doi.org/10.1135/cccc19892335.

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The simple network thermodynamics approach is applied to chemical reaction systems, whereby chemical reactions can be studied avoiding complex mathematical treatment. Steady state reaction rates are obtained for two chemical reaction systems, viz. the decomposition of ozone and the reaction of hydrogen with bromine. The rate equations so obtained agree with those derived from the chemical kinetics concept.

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De Corato, Marco, e Ignacio Pagonabarraga. "Onsager reciprocal relations and chemo-mechanical coupling for chemically active colloids". Journal of Chemical Physics 157, n. 8 (28 agosto 2022): 084901. http://dx.doi.org/10.1063/5.0098425.

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Similar to cells, bacteria, and other micro-organisms, synthetic chemically active colloids can harness the energy from their environment through a surface chemical reaction and use the energy to self-propel in fluidic environments. In this paper, we study the chemo-mechanical coupling that leads to the self-propulsion of chemically active colloids. The coupling between chemical reactions and momentum transport is a consequence of Onsager reciprocal relations. They state that the velocity and the surface reaction rate are related to mechanical and chemical affinities through a symmetric matrix. A consequence of Onsager reciprocal relations is that if a chemical reaction drives the motion of the colloid, then an external force generates a reaction rate. Here, we investigate Onsager reciprocal relations for a spherical active colloid that catalyzes a reversible surface chemical reaction between two species. We solve the relevant transport equations using a perturbation expansion and numerical simulations to demonstrate the validity of reciprocal relations around the equilibrium. Our results are consistent with previous studies and highlight the key role of solute advection in preserving the symmetry of the Onsager matrix. Finally, we show that Onsager reciprocal relations break down around a nonequilibrium steady state, which has implications for the thermal fluctuations of the active colloids used in experiments.

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Cheng, Maurice M. W. "Students' visualisation of chemical reactions – insights into the particle model and the atomic model". Chemistry Education Research and Practice 19, n. 1 (2018): 227–39. http://dx.doi.org/10.1039/c6rp00235h.

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This paper reports on an interview study of 18 Grade 10–12 students’ model-based reasoning of a chemical reaction: the reaction of magnesium and oxygen at the submicro level. It has been proposed that chemical reactions can be conceptualised using two models: (i) theparticle model, in which a reaction is regarded as the simple combination and rearrangement of reactant particles and does not involve any change in the identity of the reactants, and (ii) theatomic model, wherein a reaction involves the transformation of one chemical species into another. This paper suggests that although theparticle modellooks simpler than theatomic model, it can help to support the learning of some advanced chemical concepts such as energetics and collision theory. Therefore, it is postulated that students who reason using theparticle modelare able to demonstrate some advanced ideas about chemical reactions. The conceptualisation of reactions in terms of theatomic modeland theparticle modelallows a flexible understanding of students’ learning. Students’ representations of the reaction between magnesium and oxygen were analysed with reference to the two models. The models were found to be useful in assessing the students’ understanding of the reaction and revealing the novel ways that the students reasoned the chemical reaction. In addition, a student who used theparticle modelto represent the reaction was found to explain the reaction in terms of some energetics and kinetics concepts. The study offers insights for curriculum planners and teachers into the potential of these two models to help students understand chemical reactions.

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41

Sato e Nakamura. "Protein Chemical Labeling Using Biomimetic Radical Chemistry". Molecules 24, n. 21 (3 novembre 2019): 3980. http://dx.doi.org/10.3390/molecules24213980.

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Chemical labeling of proteins with synthetic low-molecular-weight probes is an important technique in chemical biology. To achieve this, it is necessary to use chemical reactions that proceed rapidly under physiological conditions (i.e., aqueous solvent, pH, low concentration, and low temperature) so that protein denaturation does not occur. The radical reaction satisfies such demands of protein labeling, and protein labeling using the biomimetic radical reaction has recently attracted attention. The biomimetic radical reaction enables selective labeling of the C-terminus, tyrosine, and tryptophan, which is difficult to achieve with conventional electrophilic protein labeling. In addition, as the radical reaction proceeds selectively in close proximity to the catalyst, it can be applied to the analysis of protein–protein interactions. In this review, recent trends in protein labeling using biomimetic radical reactions are discussed.

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Fuji, Taiki, Shiori Nakazawa e Kiyoto Ito. "Feasible-metabolic-pathway-exploration technique using chemical latent space". Bioinformatics 36, Supplement_2 (dicembre 2020): i770—i778. http://dx.doi.org/10.1093/bioinformatics/btaa809.

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Abstract Motivation Exploring metabolic pathways is one of the key techniques for developing highly productive microbes for the bioproduction of chemical compounds. To explore feasible pathways, not only examining a combination of well-known enzymatic reactions but also finding potential enzymatic reactions that can catalyze the desired structural changes are necessary. To achieve this, most conventional techniques use manually predefined-reaction rules, however, they cannot sufficiently find potential reactions because the conventional rules cannot comprehensively express structural changes before and after enzymatic reactions. Evaluating the feasibility of the explored pathways is another challenge because there is no way to validate the reaction possibility of unknown enzymatic reactions by these rules. Therefore, a technique for comprehensively capturing the structural changes in enzymatic reactions and a technique for evaluating the pathway feasibility are still necessary to explore feasible metabolic pathways. Results We developed a feasible-pathway-exploration technique using chemical latent space obtained from a deep generative model for compound structures. With this technique, an enzymatic reaction is regarded as a difference vector between the main substrate and the main product in chemical latent space acquired from the generative model. Features of the enzymatic reaction are embedded into the fixed-dimensional vector, and it is possible to express structural changes of enzymatic reactions comprehensively. The technique also involves differential-evolution-based reaction selection to design feasible candidate pathways and pathway scoring using neural-network-based reaction-possibility prediction. The proposed technique was applied to the non-registered pathways relevant to the production of 2-butanone, and successfully explored feasible pathways that include such reactions.

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Aggarwal, Sudhanshu. "Rishi Transform for Determining the Concentrations of the Chemical Compounds in First Order Successive Chemical Reaction". Journal of Advanced Research in Applied Mathematics and Statistics 8, n. 1&2 (29 agosto 2023): 10–17. http://dx.doi.org/10.24321/2455.7021.202303.

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Козлова, М. А., e В. А. Шаманский. "SEARCHING FOR AN EXTREME COMPONENT CONTENT IN A REACTING SYSTEM USING GRAPH OF CHEMICAL REACTIONS". Proceedings in Cybernetics 22, n. 1 (2023): 21–28. http://dx.doi.org/10.35266/1999-7604-2023-1-21-28.

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The article presents a technique for calculating a maximum amount of a substance in a closed system using a step-by-step graph of chemical reactions. A list of probable one- and two-particle reversible reactions is generated based on the substances that may be a part of the reacting system. The list is narrowed down according to the research objectives and conditions of the reacting system. The obtained list corresponds to the incidence matrix, which is suitable for analyzing the graph via a computer. The search for the maximum amount of the component in question is conducted through the comparison of weights of the graph’s edges at each stage of its intermediate reactions. The graph’s weights are calculated based on the kinetic coefficients of reactions. They also determine the dominant reaction. The amount is calculated under the premise that the dominant reaction is equilibrium. The maximum amount of hydroperoxyl radical HO2 in a hydrogen H and oxygen O reacting system is calculated.

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45

Kim, Jinsu, e German Enciso. "Absolutely robust controllers for chemical reaction networks". Journal of The Royal Society Interface 17, n. 166 (maggio 2020): 20200031. http://dx.doi.org/10.1098/rsif.2020.0031.

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In this work, we design a type of controller that consists of adding a specific set of reactions to an existing mass-action chemical reaction network in order to control a target species. This set of reactions is effective for both deterministic and stochastic networks, in the latter case controlling the mean as well as the variance of the target species. We employ a type of network property called absolute concentration robustness (ACR). We provide applications to the control of a multisite phosphorylation model as well as a receptor–ligand signalling system. For this framework, we use the so-called deficiency zero theorem from chemical reaction network theory as well as multiscaling model reduction methods. We show that the target species has approximately Poisson distribution with the desired mean. We further show that ACR controllers can bring robust perfect adaptation to a target species and are complementary to a recently introduced antithetic feedback controller used for stochastic chemical reactions.

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Kvasnička, Vladimír, Jiří Pospíchal e Vladimír Baláž. "Reaction and chemical distances and reaction graphs". Theoretica Chimica Acta 79, n. 1 (gennaio 1991): 65–79. http://dx.doi.org/10.1007/bf01113330.

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47

Pastore, Christopher, e Moishe Garfinkle. "The expected time to attain chemical equilibrium from a thermodynamic probabilistic analysis". Canadian Journal of Chemistry 90, n. 3 (marzo 2012): 243–55. http://dx.doi.org/10.1139/v11-154.

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Abstract (sommario):

Employing a stochastic model, both Planck and Fokker proposed almost a century ago that stoichiometric chemical reactions proceed by a chain mechanism involving discrete reaction steps. To determine whether such a chain mechanism was in fact a valid mechanism for chemical reactions was the subject of a recent study (Garfinkle, M. 2002. J. Phys. Chem. 106A: 490). Using a thermodynamic–probabilistic algorithm the stochastic reaction paths were found to be in excellent agreement with the observed reaction paths plotted from experimental data. This study was then extended to test the conclusions of Ehrenfest and Prigogine that a chain mechanism dictates that the number of discrete reaction steps required for a chemical reaction to attain equilibrium must be finite. The stochastic and empirical reaction paths were compared using experimental data for first-, second-, and third-order reactions as well as fractional order reactions. The empirical verification was excellent.

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Vaida, Veronica, Karl J. Feierabend, Nabilah Rontu e Kaito Takahashi. "Sunlight-Initiated Photochemistry: Excited Vibrational States of Atmospheric Chromophores". International Journal of Photoenergy 2008 (2008): 1–13. http://dx.doi.org/10.1155/2008/138091.

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Atmospheric chemical reactions are often initiated by ultraviolet (UV) solar radiation since absorption in that wavelength range coincides to typical chemical bond energies. In this review, we present an alternative process by which chemical reactions occur with the excitation of vibrational levels in the ground electronic state by red solar photons. We focus on the O–H vibrational manifold which can be an atmospheric chromophore for driving vibrationally mediated overtone-induced chemical reactions. Experimental and theoretical O–H intensities of several carboxylic acids, alcohols, and peroxides are presented. The importance of combination bands in spectra at chemically relevant energies is examined in the context of atmospheric photochemistry. Candidate systems for overtone-initiated chemistry are provided, and their lowest energy barrier for reaction and the minimum quanta of O–H stretch required for reaction are calculated. We conclude with a discussion of the major pathways available for overtone-induced reactions in the atmosphere.

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Park, Seong Jun, e M. Y. Choi. "Product molecule numbers and reaction rate fluctuations in elementary reactions". AIP Advances 12, n. 6 (1 giugno 2022): 065308. http://dx.doi.org/10.1063/5.0091597.

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In many chemical reactions, reaction rate fluctuations are inevitable. Whenever chemical reactions occur, reaction rates vary due to their dependence on the number of reaction events or products. Accordingly, understanding the impact of rate fluctuations on the product number counting statistics is of the utmost importance when developing a quantitative explanation of chemical reactions. In this work, we examine the relationship between the reaction rate and product number fluctuations. Product number counting statistics uncover stochastic properties of the product number; the latter directly manipulates the reaction rate. Specifically, we find that the product number displays super-Poisson characteristics as the reaction rate increases with the product number. On the other hand, when the product number shows sub-Poisson behavior, a decrease in the reaction rate follows. Furthermore, our analysis, dealing with reaction rate fluctuations, allows for quantifying the deviations of an elementary reaction process from a renewal process.

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Fu, Zunyun, Xutong Li, Zhaohui Wang, Zhaojun Li, Xiaohong Liu, Xiaolong Wu, Jihui Zhao et al. "Optimizing chemical reaction conditions using deep learning: a case study for the Suzuki–Miyaura cross-coupling reaction". Organic Chemistry Frontiers 7, n. 16 (2020): 2269–77. http://dx.doi.org/10.1039/d0qo00544d.

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Deep learning was used to optimize chemical reactions with the quantum mechanical properties of chemical contexts and reaction conditions as inputs. The trained deep learning model determines optimal reaction conditions by in silico exploration of accessible reaction space.

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