Effect Of Rate Constants Research Articles

Dynamic magnetic hysteresis loop features of a mixed spin (1/2, 1) Ising system on a hexagonal lattice using path probability method

Batı and Ertaş [Physica B 513 (2017) 40] presented a study of dynamic magnetic hysteresis loop properties (DMHLFs) of a mixed spin (1/2, 1) Ising system (IS) on a hexagonal lattice within the mean-field theory based on the Glauber dynamics approach. They observed a number of interesting DMHLFs. We extended the investigation of DMHLFs of a mixed spin (1/2, 1) IS on a hexagonal lattice using the path probability method. We also examined the influences of the rate constants on DMHLFs as well as magnetic coercive fields and remanent magnetizations. We observed that some of our results are in quantitatively good agreement with some theoretical works on various ISs and experimental reported works on some magnetic materials as well as works within the melt-spinning method. We also found that the effects of rate constants are more effective on DMHLFs of the magnetization of spin-1 particles than loops of the magnetization of spin-1/2 particles.

Modeling and Simulation of Crystallization of Metal–Organic Frameworks

Metal–organic frameworks (MOFs) are the porous, crystalline structures made of metal–ligands and organic linkers that have applications in gas storage, gas separation, and catalysis. Several experimental and computational tools have been developed over the past decade to investigate the performance of MOFs for such applications. However, the experimental synthesis of MOFs is still empirical and requires trial and error to produce desired structures, which is due to a limited understanding of the mechanism and factors affecting the crystallization of MOFs. Here, we show for the first time a comprehensive kinetic model coupled with population balance model to elucidate the mechanism of MOF synthesis and to estimate size distribution of MOFs growing in a solution of metal–ligand and organic linker. The oligomerization reactions involving metal–ligand and organic linker produce secondary building units (SBUs), which then aggregate slowly to yield MOFs. The formation of secondary building units (SBUs) and their evolution into MOFs are modeled using detailed kinetic rate equations and population balance equations, respectively. The effect of rate constants, aggregation frequency, the concentration of organic linkers, and concurrent crystallization of organic linkers are studied on the dynamics of SBU and MOF formation. The results qualitatively explain the longer timescales involved in the synthesis of MOF. The fundamental insights gained from modeling and simulation analysis can be used to optimize the operating conditions for a higher yield of MOF crystals.

Prediction of Chain Propagation Rate Constants of Polymerization Reactions in Aqueous NIPAM/BIS and VCL/BIS Systems.

Microgels have a wide range of possible applications and are therefore studied with increasing interest. Nonetheless, the microgel synthesis process and some of the resulting properties of the microgels, such as the cross-linker distribution within the microgels, are not yet fully understood. An in-depth understanding of the synthesis process is crucial for designing tailored microgels with desired properties. In this work, rate constants and reaction enthalpies of chain propagation reactions in aqueous N-isopropylacrylamide/N,N'-methylenebisacrylamide and aqueous N-vinylcaprolactam/N,N'-methylenebisacrylamide systems are calculated to identify the possible sources of an inhomogeneous cross-linker distribution in the resulting microgels. Gas-phase reaction rate constants are calculated from B2PLYPD3/aug-cc-pVTZ energies and B3LYPD3/tzvp geometries and frequencies. Then, solvation effects based on COSMO-RS are incorporated into the rate constants to obtain the desired liquid-phase reaction rate constants. The rate constants agree with experiments within a factor of 2-10, and the reaction enthalpies deviate less than 5 kJ/mol. Further, the effect of rate constants on the microgel growth process is analyzed, and it is shown that differences in the magnitude of the reaction rate constants are a source of an inhomogeneous cross-linker distribution within the resulting microgel.

Effect of Rate Constants in TF Regulated Gene Expression

Simple mathematical model of gene expression has been studied thoroughly in this paper. We assume that protein synthesis and protein decay are deterministic in nature whereas transition from active to inactive state is totally stochastic. The probability distribution function of transcript number is calculated and evidence of binary and graded response has been observed for different reaction rates. Slow and fast kinetics have been studied explicitly. Different rate constants play a significant role in calculating distribution function (PDF) and mean value of TF regulated gene expression. It is seen that rate constants control the variance as well. A small change in the value of the rate constant gives a significant change in average protein value. The randomness of gene expression is reduced with increasing value of one of the rate constants. The main focus of this paper is to observe the effect of rate constants in transcription factor regulated gene expression.

Phase portrait of the dynamic system of parallel chemical reactions: An analysis of the effect of the rate constants

The rate constant effect on the reaction path pattern, conversion, and selectivity is analyzed using the dynamic system for consecutive reversible chemical reactions. In some cases, it is impossible to simultaneously attain large values of conversion and selectivity by using a catalyst or varying the temperature.

New aspects of unsaturated polyester resin synthesis. Part I: modelling and simulation of reactant sequence length distributions in stepwise polymerization

The quantification of the relationship between physical properties of polymeric products and the sequence distribution of comonomer units in a polymer chain is not an easy task. In this work, detailed consideration is given to the sequence lengths and sequence length distributions to be expected in unsaturated polyesters formed by the reaction of maleic anhydride, phthalic anhydride and a diol, a reaction which gives rise to the low molecular weight precursors used in unsaturated polyester resins. Monte Carlo methods are used to explore the effects of rate constants, reactant stoichiometry and extent of reaction on the microstructure of the chain. Attention is also given to structural asymmetry of the diol component and the influence of the dynamics of the ring opening of the anhydride coreactants on the products. The approach is generic and can be readily adapted for any copolymerization which proceeds by a stepwise kinetic mechanism. © 2003 Society of Chemical Industry

Subnetwork Analysis for the Determination of Multiple Steady States in Complex Reaction Networks

A new version of subnetwork analysis is developed to determine multiple steady states in family members of complex reaction networks. In the analysis, one of its subnetworks admits a zero-eigenvalue steady state and its eigenvector is in the stoichiometric subspace. The new version can be used to determine the capacity of multiple steady states in more general family networks than the old one. Without the simplification of the complex network by the quasi-steady-state manipulation, this method improves the study of a large family of networks, instead of the case-by-case study. These advantages are demonstrated by an enzyme kinetic involving two substrates operating in an isothermal CSTR. The hysteresis and bifurcation diagrams of the studied reaction network are presented. The effects of rate constants on the steady-state multiplicity are discussed.

Characteristics of methods for the simultaneous determination of catalysts by first-order inhibition kinetics.

Factors that affect the simultaneous kinetic determination of catalysts based on differences in rates of inhibition by a common inhibitor are investigated by computer simulation. Both derivative and integral models for the kinetic responses are studied. Nonlinear regression is used to fit data with a fixed level of noise for the combined responses due to the first-order inhibition of two catalysts. Effects of rate constants, ratios of rate constants, fitting ranges, data density, and number of replicate determinations on reliability, useful activity range, sensitivity, scatter, limits of detection, and measurement/data-processing times are considered. It is found that values for rate constants, ratios of rate constants, and fitting ranges which provide results with desired reliability are restricted. Small ratios of rate constants and short fitting ranges were observed to produce the largest useful activity ranges and shortest measurement times but also gave the worst accuracy and most dependence on initial estimates of fitting parameters. Values of the coefficients of correlation between the individual first-order responses can aid in the selection of the smallest ratio of rate constants and fitting range which will yield suitable results.

Biochemical switching device: Monocyclic enzyme system

The switching characteristics of a monocyclic enzyme system, in which two enzymes share substrates or co-factors in a cyclic manner, such as, --> X(1) + B + E(1) right arrow over left arrow A + E(1) + X(2) -->, --> X(3) + A + E(2) right arrow over left arrow B + E(2) + X(4) --> (E(1), E(2) are enzymes, X(1), X(3) are substrates, X(2), X(4) are products, A, B are cofactors), were demonstrated using computer simulations. The detailed mathematical models of biochemically possible cyclic enzyme systems were built up and the effects of rate constants and the effects of initial concentrations of enzymes and cofactors on switching characteristics were discussed. The cyclic enzyme system could function as a switching circuit when the initial concentrations of enzymes or cofactors are over a certain threshold value. Based on the present results, we further discuss the dynamic characteristics of a biochemical reactor system (bioreactor) involving this cyclic enzyme system as a switching controller.

The reaction characteristics of parallel consecutive reactions in a fluidized bed.

The reaction characteristics (the reactant conversion and the yield of the intermediate product) of a parallel consecutive reaction in a fluidized bed were analyzed on the basis of the Bubble Assemblage Model. The effects of rate constants, particle size and bed diameter upon the reaction characteristics were investigated theoretically. When the rate constants and the size of particles were small, the reaction characteristics for a fluidized-bed reactor closely approached those for a plug-flow reactor and scale-up of the fluidized bed reactor became easy.

Reaction Rates of Electrons in Picosecond Pulse Radiolysis

HUNT and co-workers have used pulse radiolysis to study the reaction rate constants of hydrated electrons with solutes in the time range 20–350 ps (for review see ref. 1). Using various solutes over a range of solute concentrations (mainly Cs≥ 0.4 M), they obtained Open image in new window reaction rate constants which differed by a factor of 2–3 in most cases from those obtained in dilute solutions, as determined by pulse radiolysis with ∼ 0.1–1.0 µs pulses of electrons. Furthermore, from the observed decrease in the initial yield of hydrated electrons, it was concluded that a precursor of the hydrated electron was scavenged by high concentrations of solutes and e− rate constants were derived. This provided experimental evidence for the postulated2,3 reactions of the “dry electron” e−. Schwarz4 has indicated that the time-dependent rate constant effect for nearly diffusion-controlled reactions could explain some of the results obtained in the picosecond time region.