Kinetic Model For Formation Research Articles

Parameter Dependencies of Early‐Stage Tangential Discontinuity‐Driven Foreshock Bubbles in Local Hybrid Simulations

AbstractForeshock bubbles (FBs) are significant foreshock transients that can accelerate particles and disturb the magnetosphere‐ionosphere system. In the kinetic formation model, foreshock ions interact with the discontinuity by performing partial gyrations to generate currents that change the magnetic field topology around the discontinuity. However, how different foreshock ion properties affect the growth of the field variations is not well understood. Therefore, we use 2‐D local hybrid simulations to study the effects of different foreshock ion distributions and properties on the growth of tangential discontinuity (TD)‐driven FBs. We discover that for a gyrophase‐bunched distribution with an initial phase where the guiding center is on the other side of the TD, the foreshock ions gyrate together across the TD, causing more foreshock ions to cross the TD and leading to a faster expansion of the structure than for a Maxwellian distribution. A ring distribution also yields higher expansion speeds because of the higher projected velocity into the new perpendicular direction. For Maxwellian distributions, there are positive and linear correlations of the FB expansion speeds with the initial foreshock ion densities, thermal speeds, parallel speeds, and sine of the TD magnetic shear angles. These parameter dependencies grow in strength as the structures evolve with time. The foreshock ion distributions and properties that lead to stronger currents produce more significant magnetic field variations and higher expansion speeds. Our study helps quantify the formation and expansion of FBs to forecast their space weather effects and contribution to shock acceleration.

Hybrid Simulations of a Tangential Discontinuity‐Driven Foreshock Bubble Formation in Comparison With a Hot Flow Anomaly Formation

AbstractHot flow anomalies (HFAs) and foreshock bubbles (FBs) are significant foreshock transients that can accelerate particles and disturb the magnetosphere‐ionosphere system. Yet, their early formation mechanisms are still not fully understood. To investigate the formation of tangential discontinuity (TD)‐driven FBs and HFAs, we use 2‐D local hybrid simulations where a reflected or an injected warm foreshock ion beam can interact with a TD whose half‐thickness is comparable to the ion inertial scale. We show that the foreshock ions perform a partial gyration within, or across, the TD. Bulk motion differences between partially‐gyrating foreshock ions and fluid‐electrons lead to the generation of currents. As the trigger, these foreshock‐driven currents change the magnetic field topology around the TD and force the frozen‐in solar wind plasma to redistribute along with the field lines, shaping the foreshock transient. This confirms a recently proposed kinetic formation model. The extent of the magnetic field direction change across the TD within the foreshock ion gyromotion determines the current profile and thus the type of foreshock transient that forms. For a thin TD, the foreshock ions generate a current that is much stronger on the upstream side than the downstream side, forming an FB with one upstream compressional boundary. For the same foreshock ion gyroradius and magnetic shear, a thick TD yields comparable foreshock‐driven currents on the upstream and downstream sides, forming an HFA with two compressional boundaries. Our study suggests that the TD thickness is one of the factors that determine the formation of FBs and HFAs.

Harbingers of dioxins in thermal decomposition of high-energy fuel

Combustion of high-energy chemical fuels containing dioxins in their elemental composition can lead to the formation of super eco toxicants on smoke particles-polychlorinated dioxins and furans. The choice of the method of solving the equations of chemical kinetics is basic in numerical experiment. Calculation and theoretical studies were carried out to solve the problem of determining the parameters of combustion products of chemical fuels taking into account the formation of traces of polychlorinated dioxins. Basic information on the adopted method of determining non-equilibrium composition of combustion products of chlorine-containing chemical fuels is presented. Based on the literary analysis on the mechanisms and rates of chemical reactions of conversion of chlorine-containing compounds, a kinetic model of formation of traces of dioxins was built. Numerical calculations on the assumption of chemical equilibrium have shown that the dioxins formation process is substantially non-equilibrium. The results of kinetic studies on the emission of dioxins precursors showed the nature of the change in time of various components of combustion products of chemical fuels depending on temperature.

Forecasting of an output of eco toxicants at thermal decomposition of chemical fuel

Combustion of high-energy chemical fuels containing chlorine in the element structure can lead to formation in the particles of smoke of super eco toxicants—the polychlorinated dioxins and furans. The numerical experiment conducted was based on solution of the equations of chemical kinetics. The computational and theoretical researches directed to the solution of a problem of determination of parameters of combustion products of chemical fuels taking into account formation of harbingers of the polychlorinated dioxins were executed. The main data on the accepted method of determination of disequilibrium structures of products of burning the chlorine-containing chemical fuels were represented. Based on the analysis of references about mechanisms and speeds of chemical reactions of transformations of chlorine-containing connections, the kinetic model of formation of predecessors of dioxins is constructed. The carried-out calculations showed (assuming chemical balance) that process of formation of dioxins is significantly disequilibrious. The results of kinetic researches on emission of harbingers of dioxins showed the nature of the influence of different components of combustion products of chemical fuels on time for the different levels of temperatures.

Synthesis of Prebiotic Caramels Catalyzed by Ion-Exchange Resin Particles: Kinetic Model for the Formation of Di-d-fructose Dianhydrides.

Caramel enriched in di-d-fructose dianhydrides (DFAs, a family of prebiotic cyclic fructodisaccharides) is a functional food with beneficial properties for health. The aim of this work was to study the conversion of fructose into DFAs catalyzed by acid ion-exchange resin, in order to establish a simplified mechanism of the caramelization reaction and a kinetic model for DFA formation. Batch reactor experiments were carried out in a 250 mL spherical glass flask and afforded up to 50% DFA yields. The mechanism proposed entails order 2 reactions that describe fructose conversion on DFAs or formation of byproducts such as HMF or melanoidines. A third order 1 reaction defines DFA transformation into fructosyl-DFAs or fructo-oligosaccharides. The influence of fructose concentration, resin loading and temperature was studied to calculate the kinetic parameters necessary to scale up the process.

Kinetic modelling of formation of K+ doped BaTiO3 bones from barium titanyl oxalate via multi stage thermal decomposition

The thermal decomposition kinetics of formation of bone shaped BaTiO3 from barium titanyl oxalate (BTO) and the effect of doping of potassium titanyl oxalate (1×10−4mol%) with BTO upon the reaction pathway and the mechanism were studied at four different heating rates: 2, 5, 7 and 10Kmin−1 under linear non-isothermal heating program using DSC technique in an inert atmosphere (N2). Kinetic deconvolution procedure was applied to perform the overall kinetics of the formation of doped and undoped BaTiO3. The prepared samples and their decomposed products were identified and characterized by means of FT-IR, FT-Raman, XRD, SEM, TEM and SAED pattern. Activation energy needed for each resolved stage of the thermal decomposition was calculated by the KAS method in the temperature range 303–873K. XRD pattern at different stages of thermal decomposition indicates that cubic BaTiO3 is transformed into tetragonal phase. The introduction of K+ −ion into the lattice of BTO enhances the thermal stability of BTO and shows a high energy reaction pathway revealing the complex mechanism.

Monolayer kinetic model of formation of gold nanoparticles by reducing agents hexadecylaniline or bovine serum albumin

In the formation of metal nanoparticles (NPs) in aqueous solution two distinguishable processes take place: the nucleation and the NPs’ growth. In the present paper is proposed an experimental approach which aims to clarify whether the interfacial organization of the reduction reaction plays a role during the growth process. The gold nanoparticles were formed in hexadecylaniline (HDA) or bovine serum albumin (BSA) monolayers spread on aqueous chloroauric acid solution. The kinetics of the NPs formation was followed by measuring of the monolayer properties, namely the change of the surface area with time at constant surface pressure,ΔA(t)π, as well as the NPs’ size and shape by AFM after Langmuir-Blodgett (LB) transfer. The proposed simple monolayer system has few advantage for better control of the physicochemical parameters of the reduction reaction which occurs at the air/water interface, e.g. the surface concentration and the interfacial organization of both components- tetrachloroauric acid (HAuCl4) and HDA (or BSA), the degree of unfolding of BSA molecules, the number of reaction sites involved in interactions etc.A kinetic model of the interfacial reaction of NPs’ formation at the air/water interface was developed and the kinetic constants of the reduction reaction (kr), of nuclei formation (k1), and NPs’ growth (k2) were estimated. It was found that the rate constant of the reduction reaction is many order of magnitude higher than the rate constant of NPs’ formation. The formation of critical nuclei and their subsequent growth under the action of the reducing agent HDA were found to be 100 times faster in comparison with the action of BSA as a reductant.

Monolayer kinetic model of formation of β-cyclodextrin–β-carotene inclusion complex

The carotenoids are sensitive molecules and their chemical integrity must be preserved from pro-oxidant elements which could affect and decrease their physiological benefits. The encapsulation based on the inclusion of the carotenoids into cage molecules is a promising approach for preserving over time of the intrinsic properties of the carotenoids. It is well known that cyclic oligosaccharide β-cyclodextrin (CD) as a cage molecule possesses strong inclusion ability to β-carotene (C) and as a result of the hydrophobic interactions forms an inclusion complex.In the present paper a monolayer kinetic model was established with the notion to extract more information about the influence of the molecular structure and organization to the interfacial interactions between the interacting species as well as about the role of the specific areas, which are often underestimated in previously studied dispersed systems. We developed the monolayer kinetic model for the formation of the inclusion CD–C complex by applying an experimental approach for following the kinetics by means of measuring the decrease of the surface area (ΔA) versus time (t) at constant surface pressure (π) and the decrease of surface pressure (π) versus time (t) at constant surface area (A). We also visualized by AFM the state of the monolayers at the initial and end points of the kinetic process. The values for the degree (d) and constant (Ka) of the association were estimated and compared with those from the studies of dispersed systems.

A dislocation kinetic model of the dislocation structure formation in a nanocrystalline material under intense shock wave propagation

A dislocation kinetic model of the formation and propagation of plastic shock waves in nanocrystalline materials (with a grain size of 1–100 nm) at pressures ranging from 1 to 50 GPa has been discussed theoretically. The model is based on a nonlinear equation of the reaction-diffusion type for the dislocation density, which includes the processes of multiplication, annihilation, and diffusion of dislocations with a strong absorption of the dislocations by nanograin boundaries. The solution of this equation is obtained in the form of a traveling dislocation density wave propagating with a constant velocity. The dependences of the dislocation density and dislocation front width on the nanograin size and pressure in the wave are determined. A comparison of the obtained dependences with the available results of the experiments and molecular dynamics simulations of shock-deformed nanocrystalline materials demonstrates their good quantitative agreement.

Low-Temperature Spectroscopic Properties of the Peridinin–Chlorophyll a–Protein (PCP) Complex from the Coral Symbiotic Dinoflagellate Symbiodinium

The spectroscopic properties of the peridinin-chlorophyll a-protein (PCP) from the coral symbiotic dinoflagellate Symbiodinium have been characterized by application of various ultrafast optical spectroscopies including femto- and nanosecond time-resolved absorption and picosecond time-resolved fluorescence (TRF) at 77 K. Excited state properties of peridinin and Chl a and their intramolecular interaction characteristics have been obtained from global fitting analysis and directed kinetic modeling of the data sets and compared to their counterparts known for the PCP from Amphidinium carterae. The lifetimes of the excited state of peridinin show close agreement with those known for the counterpart PCP, demonstrating that molecular interactions have the same characteristics in both complexes. More variances have been recorded for the excited state properties of Chl a including elongation of both the intramolecular energy transfer time between Chl's within the pair in the protein monomer and the excited state lifetime of the long wavelength form of Chl a (terminal acceptor). Kinetic modeling of formation of the peridinin triplet state has shown that the PCP is protected from potential photodamage due to an extremely fast peridinin triplet state formation of kTT = (14.4 ± 2.3) × 10(9) s(-1) ((70 ± 12)(-1) (ps)(-1)) that guarantees instantaneous depletion of Chl a triplets and prevents formation of harmful singlet oxygen ((1)ΔgO2).

Transesterification of leather tanning waste to biodiesel at supercritical condition: Kinetics and thermodynamics studies

Catalyst-free transesterification of leather tanning waste with high free fatty acid (FFA) content at supercritical condition was reported in this work. The experiments were performed in batch system at various temperatures (250–325°C) under constant pressure of 12MPa and methanol/fatty oil molar ratio of 40:1 for reaction time of 2–10min. Kinetic modeling of formation of fatty acid methyl esters (FAMEs) that incorporate reversible esterification and non-reversible transesterification simultaneously was verified. The proposed semi-empirical model was fitted against kinetic experimental data over temperature range studied. The kinetic parameters (i.e. k′TE, k′E, and kE′) were determined by nonlinear regression fitting. Thermodynamic activation parameters of the reactions were evaluated based on activation complex theory (ACT) and the following results are obtained: ΔG‡>0, ΔH‡>0, and ΔS‡<0. The activation energy (Ea) of transesterification, forward and reverse esterification reactions was 36.01kJ/mol, 28.38kJ/mol, and 5.66kJ/mol, respectively.

Kinetic model for formation of DMPO-OH in water under ultrasonic irradiation using EPR spin trapping method

The rate of the formation of the 2-hydroxy-5,5-dimethyl-1-pyrrolidinyloxy (DMPO-OH) radical in water during ultrasonic irradiation was evaluated both experimentally and theoretically. The hydroxyl radical (OH radical) was indirectly detected using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the spin trapping compound, and the generated DMPO-OH by the reaction between the OH radical and DMPO was measured by an electron paramagnetic resonance. The rate of change in the concentration of the DMPO-OH decreased with time, suggesting that not only the formation reaction of DMPO-OH but also the degradation reaction would take place by ultrasonic irradiation. The formation rate of the DMPO-OH was higher with ultrasonic power intensity and lower with reaction temperature. Based on the experimental results, a kinetic model for the formation of the DMPO-OH was proposed by considering the formation reaction, the ultrasonic degradation, and spontaneous degradation of DMPO-OH. The model well described the effect of the ultrasonic power intensity and the reaction temperature on the formation rate of DMPO-OH. The rate of the formation of the DMPO-OH was evaluated with the aid of the kinetic model.

A kinetic model for formation of nanodisperse matter in the gas phase

Taking CsI aerosol as an example, it was shown that growth of primary aerosol particles can be described in terms of both discrete and continuum models. This conclusion is based on the results of experiments carried out using a method that makes it possible to distinguish primary particles against the background of their aggregates, to provide a complete transfer of the primary particles from aerosol bulk to a collector, and to determine the particle sizes by transmission electron microscopy. Under the conditions studied, the size distribution of the primary particles is described by a Fokker—Planck type equation.

Analytic model of nanoparticle formation and growth in a SiH4-Ar plasma

A kinetic model of formation and growth of nanoparticles in a low-pressure plasma-chemical reactor with an rf capacitive discharge in a SiH4-Ar mixture is presented. Analytic formulas are derived for calculating the concentration of monomers, as well as the concentration and average size of nanoparticles. The results are compared with the results of numerical calculations and experimental data for nanoparticles in a SiH4-Ar plasma.

Experimental study and global model of PAH formation from coal combustion

Measurements of polycyclic aromatic hydrocarbons (PAHs) resulting from coal combustion under different ambient gas properties are presented and a global kinetic model of formation is proposed. This model has been implemented into a numerical code based on the KIVA II approach and the computed results are compared with experimental data. The numerical code was also assessed using experimental results obtained by Godoy and Lockwood using the combustion of a turbulent coal–air jet.

Toward a Kinetic Model for Acrylamide Formation in a Glucose−Asparagine Reaction System

A kinetic model for the formation of acrylamide in a glucose-asparagine reaction system is pro-posed. Equimolar solutions (0.2 M) of glucose and asparagine were heated at different temperatures (120-200 degrees C) at pH 6.8. Besides the reactants, acrylamide, fructose, and melanoidins were quantified after predetermined heating times (0-45 min). Multiresponse modeling by use of nonlinear regression with the determinant criterion was used to estimate model parameters. The proposed model resulted in a reasonable estimation for the formation of acrylamide in an aqueous model system, although the behavior of glucose, fructose, and asparagine was slightly underestimated. The formation of acrylamide reached its maximum when the concentration of sugars was reduced to about 0. This supported previous research, showing that a carbonyl source is needed for the formation of acrylamide from asparagine. Furthermore, it is observed that acrylamide is an intermediate of the Maillard reaction rather than an end product, which implies that it is also subject to a degradation reaction.

Kinetic formation of J/ψ at RHIC

Centrality dependence of J/ψ production in Au–Au collisions at is studied using the Glauber model plus the kinetic formation model. Initial J/ψ production and destruction by incoming nucleons are described by the Glauber model. J/ψ-charm equilibration in the gluon plasma is described by the kinetic formation model. We explore the possibility of J/ψ suppression suggested by the recent PHENIX data. We show that the J/ψ yield monotonically decreases with increasing centrality in the kinetic formation model when the charm mass is smaller than a critical mass. The final J/ψ yield is between the value after the Glauber suppression and the dynamical equilibrium value. This underscores the importance of both J/ψ production from d–Au collisions, which is essential in determining the Glauber suppression, and high-statistics Au–Au data, which can further constrain final-state J/ψ-charm equilibration.

Suppression of dome-shaped clusters during molecular beam epitaxy of Ge on Si(100)

Morphological properties of Ge nanoscale island arrays formed on the Si(100) surface during molecular beam epitaxy are studied using reflection high-energy electron diffraction and atomic-force microscopy. It is shown that codeposition of Sb and Ge significantly increases the density of final island arrays and suppresses the formation of dome-shaped clusters at substrate temperatures of 550–600°C. The results are discussed in the context of the kinetic model of formation of elastically strained islands in heteroepitaxial systems with a lattice mismatch.

The kinetic model of formation of nanofibrous carbon from CH 4–H 2 mixture over a high-loaded nickel catalyst with consideration for the catalyst deactivation

A mathematical model is suggested for the process of formation of nanofibrous carbon from the mixture of methane and hydrogen over a high-loaded nickel catalyst (90 wt.% Ni–Al 2O 3) to describe the observed process kinetics involving the catalyst deactivation. The experimental kinetic data obtained at hydrogen volume fraction of 0–40%, 490–590 °C and atmospheric pressure are analyzed to suggest the formula for calculation of the maximal rate of the carbon formation and the equation of the catalyst deactivation. The suggested kinetic model relates to the mechanism when the cleavage of the first hydrogen atom from a methane molecule adsorbed on the catalyst surface is the rate-limiting stage. The model is appropriate for the qualitative and quantitative description of the process under consideration. The calculations in terms of the model are exemplified with synthesis of nanofibrous carbon in an isothermal perfect-mixing reactor at a constant methane consumption. The calculated results agree well with the experimental data.

J/ ψ production in a gluon plasma produced in Au–Au collisions at [formula omitted

Centrality dependence of J/ ψ production in Au–Au collisions at s NN =200 GeV is studied using the Glauber model plus the kinetic formation model. Initial J/ ψ production and destruction by incoming nucleons are described by the Glauber model. J/ ψ-charm equilibration in the gluon plasma is described by the kinetic formation model. We explore the possibility of J/ ψ suppression suggested by the recent PHENIX data. We show that the J/ ψ yield monotonically decreases with increasing centrality in the kinetic formation model when the charm mass is smaller than a critical mass. The final J/ ψ yield is between the value after the Glauber suppression and the dynamical equilibrium value. This underscores the importance of both J/ ψ production from d–Au collisions, which is essential in determining the Glauber suppression, and high statistics Au–Au data, which can further constrain final state J/ ψ-charm equilibration.