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The study presents a mathematical model of Bruk Temkin-Gorodsky Novakovic (BT-GN) reaction system employing palladium-catalyzed oscillatory carbonylation reaction of mono alkyne-terminated poly(ethylene glycol) methyl ether. The proposed model advances simulation capabilities of this particular chemical oscillator but also BT-GN reactions in general. The model was verified using experimental data where good agreement is achieved and existence of complex pH oscillations like burst oscillations was matched. Furthermore, the model was used to predict reaction conditions capable of producing further complexities and initial conditions that would lead to desired period of pH oscillations. Having such a powerful tool, enhances our capabilities to study and further develop BT-GN oscillators with a reduced experimental effort.

The synthesis of thyroid hormones in the hypothalamic-pituitary-thyroid (HPT) axis was studied. For this purpose, a reaction model for HPT axis with stoichiometric relations between the main reaction species was postulated. Using the law of mass action, this model has been transformed into a set of nonlinear ordinary differential equations. This new model has been examined by stoichiometric network analysis (SNA) with the aim to see if it possesses the ability to reproduce oscillatory ultradian dynamics founded on the internal feedback mechanism. In particular, a feedback regulation of TSH production based on the interplay between TRH, TSH, somatostatin and thyroid hormones was proposed. Besides, the ten times larger amount of produced T4 with respect to T3 in the thyroid gland was successfully simulated. The properties of SNA in combination with experimental results, were used to determine the unknown parameters (19 rate constants of particular reaction steps) necessary for numerical investigations. The steady-state concentrations of 15 reactive species were tuned to be consistent with the experimental data. The predictive potential of the proposed model was illustrated on numerical simulations of somatostatin influence on TSH dynamics investigated experimentally by Weeke et al. in 1975. In addition, all programs for SNA analysis were adapted for this kind of a large model. The procedure of calculating rate constants from steady-state reaction rates and very limited available experimental data was developed. For this purpose, a unique numerical method was developed to fine-tune model parameters while preserving the fixed rate ratios and using the magnitude of the experimentally known oscillation period as the only target value. The postulated model was numerically validated by perturbation simulations with somatostatin infusion and the results were compared with experiments available in literature. Finally, as far as we know, this reaction model with 15 variables is the most dimensional one that have been analysed mathematically to obtain instability region and oscillatory dynamic states. Among the existing models of thyroid homeostasis this theory represents a new class that may improve our understanding of basic physiological processes and helps to develop new therapeutic approaches. Additionally, it may pave the way to improved diagnostic methods for pituitary and thyroid disorders.

A kinetic method for the determination of l-tyrosine (Tyr) by analyte pulse perturbation, caused by different amounts of Tyr, in the Bray–Liebhafsky (BL) oscillatory reaction realized in a continuous-flow stirred tank reactor, is proposed. For such purposes, the BL oscillating reaction was kept in a stable non-equilibrium stationary state close to the bifurcation point and was used as the matrix reaction system. Under optimum reaction conditions, the linear relationship between the kinetic parameters, Δτ2 (the period between first two oscillations that appear after applied perturbation) as well as τend (the time elapsed between the perturbation of the BL reaction by Tyr and the termination of the oscillatory phase) and the Tyr concentrations is obtained over the ranges 1.1 × 10− 6 − 9.2 × 10− 6 mol L− 1 and 1.1 × 10− 6 − 1.4 × 10− 5 mol L− 1, with the limit of detections of 6.6 × 10− 7 mol L− 1 and 6.4 × 10− 7 mol L− 1. The described method that relies on a simple instrumental set-up, has been successfully applied to the determination of Tyr in a dietary supplement. Some aspects of the possible mechanism of Tyr action on the BL oscillator are discussed.

The application of alternating current is advantageous in energy transfer over long distances. It is a well-known fact now, but subject of long conflict in the era of pioneering works in electric power production. There are also some processes in physical chemistry, organic and inorganic chemistry, in biochemistry and related sciences, which take place in opposite directions, with consecutive alternations in time. However, the very existence of alternate reactions, now known as the oscillatory or oscillating reactions, has long been disputed because it was thought that it is contrary to the basic principles of thermodynamics. Nevertheless, according to our knowledge, there are no oscillatory reactions without catalytic loop as the essential part of a mechanism. There could be a fundamental rule that catalysis is necessary to generate oscillations in concentrations and reaction rates. Particularly, homogeneous oscillatory reactions are often subject of research as relatively simple systems with good chance to clearly define feedbacks responsible for instability phenomena. However, oscillations can at least equally often be found in heterogeneous catalytic reactions. Recently, changes in product selectivity was proved when Pd catalyzed carbonylation of phenylacetylene was moved to the oscillatory dynamic state. With this simple result, the doors are now open for wide spectrum of research projects and applications.

Stress is a physiological reaction of an organism to a demand for change that is imposed by external factors or is coming from within by way of physiological strains or self-perceived mental and/or emotional threats (internal factors). It manifests itself through the sudden release of a flood of hormones, including corticosteroids, into the blood, which rouse the body for action. Normally, stress is beneficial, but when lasting or being very strong, it causes major damage to our mind and body. Despite intense research, we still do not understand fully how the stress response axis, whose main function is to respond to challenges while maintaining the normal physiological balance, loses under prolonged exposure to stressors its capacity to maintain homeostasis. Recent applications of mathematical modelling and dynamical systems theory have enabled us to emulate complex neurochemical transformations that underlie the stress response, and help us to acquire deeper understanding of this dynamical regulatory network.

A model was developed that can be used to study the effect of gradual cholesterol intake by food on the HPA axis dynamics. Namely, well defined oscillatory dynamics of vital neuroendocrine hypothalamic-pituitary-adrenal (HPA) axis has proven to be necessary for maintaining regular basal physiology and formulating appropriate stress response to various types of perturbations. Cholesterol, as a precursor of all steroid HPA axis hormones, can alter the dynamics of HPA axis. To analyse its particular influence on the HPA axis dynamics we used stoichiometric model of HPA axis activity, and simulate cholesterol perturbations in the form of finite duration pulses, with asymmetrically distributed concentration profile. Our numerical simulations showed that there is a complex, nonlinear dependence between the HPA axis responsiveness and different forms of applied cholesterol concentration pulses, indicating the significance of kinetic modelling, and dynamical systems theory for the understanding of large-scale self-regulatory, and homeostatic processes within this neuroendocrine system.

In this paper, we intend to show the importance of the bifurcation analysis in understanding of an oscillatory process. Hence, we use the bifurcation diagram of the Bray-Liebhafsky reaction performed in continuous well-stirred tank reactor under controlled temperature variations for the determination of the activation energies as well as rate constants of particular steps appearing in the kinetic model of oscillatory reaction mechanism. This approach has led us to the development of general procedure for treatment of experimentally obtained data and extracting kinetic parameters from them, which was very important considering that some rate constants of the already proposed model could not be determined experimentally and have to be fitted (or guessed). Also, the proposed approach has the potential to inspire the refinement of already proposed models and the development of a new one that will be able to reproduce experimentally obtained system's dynamical features more successfully. In particular, the dynamic states of the Bray-Liebhafsky oscillatory reaction have been analyzed experimentally and numerically using already proposed model together with qualitative and quantitative analysis of bifurcation diagrams in both cases.

Two hydroxyanthraquinones, alizarin and purpurin, that have been used throughout history as a natural pigment, were extracted from roots of Rubia tinctorum from Serbia. As substances with important chemical activities and, therefore, with wide applications (for example in dyeing textile fabrics as well as in pharmacy because of their anti-inflammatory, anti-cancer, antiviral, antimicrobial and antioxidant activities, etc.) they were analyzed in the kinetically very sensitive Bray–Liebhafsky (BL) oscillatory reaction. However, although they are both, hydroxyanthraquinones it is shown that their interactions with BL nonlinear reaction system differ significantly. Consequently, two different reactions were used to explain the mechanism of their chemical activities. The numerical simulations based on a standard model of the BL oscillatory reaction together with proposed reactions due to alizarin/purpurin interactions with a matrix are correlated with experimental investigations. Moreover, it is shown that very small amounts of alizarin and purpurin (from about 1 × 10–7 M) produce the response of the BL matrix such that micro-quantitative analysis based on the BL oscillatory reaction can be successfully performed in this reaction system. The linear response of the BL matrix on the presence of alizarin and purpurin (necessary for microquantitative determination) is analyzed as a function of two concentration sensitive parameters: pre-oscillatory period τ1 and potential shift after perturbation ΔE.

Stress and alcohol use are interrelated-stress contributes to the initiation and upholding of alcohol use and alcohol use alters the way we perceive and respond to stress. Intricate mechanisms through which ethanol alters the organism's response to stress remain elusive. We have developed a stoichiometric network model to succinctly describe neurochemical transformations underlying the stress response axis and use numerical simulations to model ethanol effects on complex daily changes of blood levels of cholesterol, 6 peptide and 8 steroid hormones. Modelling suggests that ethanol alters the dynamical regulation of hypothalamic-pituitary-adrenal (HPA) axis activity by affecting the amplitude of ultradian oscillations of HPA axis hormones, which defines the threshold with respect to which the response to stress is being set. These effects are complex-low/moderate acute ethanol challenge ( 8 mM) increases instantaneous CORT levels and the amplitude of ultradian CORT oscillations in a dose-dependent manner, affecting the HPA axis activity also during the following day(s). Chronic exposure to ethanol qualitatively changes the HPA axis dynamics, whereas ethanol at intoxicating levels shuts down this dynamic regulation mechanism. Mathematical modelling gives a quantitative biology-based framework that can be used for predicting how the integral HPA axis response is perturbed by alcohol.

The use of solid particles as a catalyst in a certain reaction system results in emergence of heterogeneous catalysis. More active catalyst is obtained by resizing the particles up to nanodimension. Nanocatalysts are the most active catalysts considering minimal size which gives maximal activity. Main drawbacks of nanocatalysis will be presented in this chapter through synthesis, characterization, and activity-selectivity relations. Special attention is given to catalysts for application in environmental protection and photocatalytic hydrogen production.

Intermittent oscillations as a chaotic mixture of large amplitude relaxation oscillations, grouped in bursts and small-amplitude sinusoidal ones or even quiescent parts between them known as gaps, were found and examined in the Bray-Liebhafsky (BL) reaction performed in CSTR under controlled temperature variations. They were obtained in a narrow temperature range from 61.0 degrees C to 63.1 degrees C, where 61.0 degrees C is the critical temperature for burst emergence from the stable steady state and 63.1 degrees C is the critical temperature for gap emergence from regular oscillations. Since intermittencies appear gradually from the regular oscillatory state, and no hysteresis was obtained with decreasing/increasing temperature in the vicinity of these two bifurcations, a linear relationship between (tau(B)/tau)(2) and (tau(G)/tau)(2) (where tau(B), tau(G) and tau denotes duration of bursts, gaps, and whole experiment, respectively), as a function of the temperature as the control parameter, was expected and obtained. Although these intermittent oscillations are chaotic with respect to the lengths of individual gaps as well as bursts, their deterministic behavior related to temperature was additionally established. Thus, the number of bursts or gaps per unit of time (N-B/tau and N-G/tau) has the form of a normal distribution function over the temperature range in the region where intermittencies are obtained. Temperature dependence of the Lyapunov exponents was also described by a function of the normal distribution form. Hence, we established some regularities in the chaotic behavior of intermittent oscillations that are common in life but difficult for determinations.

The return maps, as an element of mathematical phenomenology appropriate for general examinations of complex dynamic states of the oscillatory systems were used to detect and explain the evolution of mixed-mode oscillations and chaos in a six-dimensional nonlinear reaction system of the Bray-Liebhafsky (BL) reaction, a well-studied nonlinear chemical reaction system that exhibits complex dynamic behavior. For this purpose principally different Poincar, sections were applied and different transition scenarios between periodic and aperiodic states were examined by numerical simulations. It is shown that emergence of new periodic patterns can be detected by return maps already within chaotic windows. Besides, we also show that the higher dimensionality of manifold gives the impression of having several layers of manifolds.

A brief review of Professor Ljiljana Kolar-AniAc's research on the dynamics and kinetics of complex reaction systems is given, with a special emphasis on contributions in the research of the oscillatory processes of Bray, Belousov and Hypothalamic-pituitary-adrenal system.

The system KSCN-H2O2-CuSO4-NaOH, also known as the OrbA n-Epstein oscillatory reaction, is exposed to external perturbations by several phenolic compounds: catechol, resorcinol, hydroquinone, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 2,3-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, caffeic acid, and ferulic acid. As a result of the performed perturbation in most examined cases, oscillations have been inhibited for some characteristic time, and resumed afterwards. The evaluated inhibition time is typical for each substance and strongly dependent on its concentration. The chemical mechanism of the interaction between the OrbA n-Epstein system and phenolic compounds is briefly discussed. Numerical simulations are performed using the original OrbA n-Epstein model with 30 reactions, extended by three reactions describing the interaction with inhibitory substances. The rate constants of three added reactions are adjusted to fit experimental inhibition times, and compared among used compounds. The observed effects are discussed further in relation with the bond dissociation enthalpy theory. Unlike other tested compounds, 2,5-dihydroxybenzoic acid remains off from predicted order of activity.

Diatomite supported NiMgAg catalysts, NiMgAg/D, were prepared by the precipitation-deposition method followed by drying, reduction and passivation. The preparation of the catalysts was performed with different loading of silver ranging from 0.16 to 5.88 wt% and constant molar ratios of SiO2/Ni and Mg/Ni equal to 1.07 and 0.1, respectively. The characterization of the catalysts was performed with N-2-physisorption, mercury intrusion porosimetry, H-2-chemisorption, X-ray diffraction, temperature programmed reduction, and scanning electron microscopy-energy dispersive X-ray analysis. The partial hydrogenation of soybean oil from initial to final iodine value of 90 was carried out at 160 A degrees C and H-2 pressure of 0.16 MPa using stirred semi-batch reactor. Soybean oil was hydrogenated over NiMgAg/D catalysts and NiMg/D catalyst (without silver addition) that was prepared using the same procedure as used for catalysts modified with silver. The selectivity towards trans fatty acid and saturated fatty acid formation was determined for both types of catalysts. By comparing the selectivity of the NiMgAg/D catalysts with the NiMg/D catalyst the promoting effect of silver modifier on the catalyst behavior in the hydrogenation of soybean oil was observed, and correlated with changing of the catalyst surface characteristics caused by the different Ag loading. It was found that the addition of silver to NiMg/D catalyst decreased both the selectivity towards trans fatty acids formation and the selectivity towards saturated fatty acids. For the same iodine value decay, the catalyst with the highest Ag loading (5.88 wt%) had the lowest level of both trans fatty acids and saturated fatty acids in the hydrogenation of soybean oil under studied operating conditions. The hydrogenation activity of NiMgAg/D catalysts is lower than NiMg/D catalyst and decreases with increasing Ag loading. The correlation between adsorption characteristics of the catalysts and their hydrogenation activities was established. The proposed simplified kinetic model to describe the kinetics of soybean oil hydrogenation gave a good description of the experimental data.

The KSCN-H2O2-NaOH-Cu(II)-catalyzed system is one of the few reactions in which chemical oscillations can be observed in batch conditions. In the present paper, this oscillating reaction was revisited in a wide range of initial concentrations of all components in batch. A mixture with a long lasting oscillation time (1 h 34 min) and a great number of oscillations (24) was found and used to investigate the effect of temperature. An Arrhenius-type temperature dependence was observed from which an apparent “average activation energy” Eav = 76 ± 5 kJ for the overall oscillatory reaction was observed. A mechanistic study based on a modified model analyzed by the stoichiometric network analysis approach gave a satisfactory agreement between calculated and experimental oscillating behaviors and temperature dependence. The addition of the three diphenols (catechol, resorcinol, and hydroquinone) causes perturbations similar to those observed in the Briggs-Rauscher oscillating system, i.e., an inhibition of the oscillatory regime. These inhibitory effects were described in detail, and a reasonable qualitative interpretation is given.

A series of silica-supported nickel catalyst precursors was synthesized with different SiO2/Ni mole ratios (0.20, 0.80 and 1.15). Non-isothermal reduction of Ni catalyst precursors was investigated by temperature-programmed reduction at four different heating rates (2, 5, 10 and 20 °C min−1), in a hydrogen atmosphere. Kinetic parameters (E a, A) were determined using Friedman isoconversional method. It was found that for all mole ratios, apparent activation energy is practically constant in conversion range of α = 30–70 %. In considered conversion range, the following values of apparent activation energy were found: E a = 129.5 kJ mol−1 (SiO2/Ni = 0.20), E a = 133.8 kJ mol−1 (SiO2/Ni = 0.80) and E a = 125.0 kJ mol−1 (SiO2/Ni = 1.15). Using two special functions (y(α) and z(α)), the kinetic model was determined. It was established that reduction of Ni catalyst precursors with different SiO2/Ni mole ratios is a complex process and can be described by two-parameter Sestak–Berggren (SB) autocatalytic model. Based on established values of SB parameters for each mole ratio, the possible mechanism was discussed. It was found that for all investigated ratios, the Weibull distribution function fits very well the experimental data, in the wide range of conversions (α = 5–95 %). Based on obtained values of Weibull shape parameter (θ), it was found that experimentally evaluated density distribution functions of the apparent activation energies can be approximated by the unbalanced peaked normal distribution.

The intermittency or intermittent bursting as the type of dynamic state when two qualitatively different behaviors replace one another randomly during the course of the reaction, although all the control parameters remain constant, is found in the BriggsRauscher oscillating system moderated by a very small amount of phenol. Within a range of phenol concentrations, the oscillation amplitude is diminished considerably, and after oscillations cease, they repeat intermittently, giving several bursts of oscillations. For the concentrations used here, the range of phenol concentrations where intermittent bursting oscillations occur in a closed reactor is ca. 1.8 � 10 � 5 to 3.6 � 10 � 5 m. Bursting also occurs in an open reactor and can be sustained indefinitely at 5.53 � 10 � 5 m concentration. The intermittent bursting behavior is robust, and can be achieved at a variety of conditions.

This paper investigates multicomponent gas adsorption at the active surface of plasmonic chemical sensors and shows that there are situations where transients in a single sensor element can be used for simultaneous detection of different gases in multicomponent mixtures. A general master equation set is provided, describing multicomponent adsorption. Analytical expressions for sorption rates are derived and high-accuracy simplified models are proposed. Expressions for adsorption rate constants and rates and for number of binding sites are proposed. The derived analytical model takes into account the adsorbate molecule size, distribution of binding sites as determined by the crystallographic structure of the sensor surface and multi-site adsorption. The model allows for the calculation and optimization of deterministic behavior of the system. It is shown that trace amounts of target gas species can be made detectable by adding controlled amounts of known carrier gas. Besides being applicable in plasmonic sensor design and optimization, the obtained results may be of importance in situations where fast and low-cost detection of trace amounts of gases is needed, including natural gas leakage in residential heating, radon outgassing in dwellings, environmental protection, homeland defense and hazardous materials management, greenhouse footprint investigations, etc. This is the peer-reviewed version of the article: Jaksic, O.M., Randjelovic, D., Jaksic, Z.S., Cupic, Z.D., Kolar-Anic, L.Z., Plasmonic Sensors in Multi-Analyte environment: rate constants and transient analysis, Chemical Engineering Research and Design (2013), [http://dx.doi.org/10.1016/j.cherd.2013.06.033] [http://cer.ihtm.bg.ac.rs/handle/123456789/1543]

The electrochemical oxidation of methanol has been carefully studied due to its application in fuel cells. In this work electrooxidation of methanol was investigated on bare platinum electrode, the platinum electrode covered with Nafion and platinum supported on zeolite 13X. Along with classical electrochemical methods, attractor reconstruction was used to make rough distinction among possible reaction mechanisms on different forms of Pt. The obtained transient voltammogram records were used to calculate apparent rate constants for methanol oxidation limiting steps in transient period. All samples contributed to methanol oxidation by basically same reaction mechanism, but with significantly different apparent rate constants.

The analysis of adsorption kinetics is given, assuming no dissociative adsorption takes place and no multiple binding sites exist. The phenomenological nonlinear model and the simple linear model are considered from the point of view of surface plasmon resonance (SPR) chemical sensors. A simple method for analytical calculation of the necessary rate constants is proposed. A comparative analysis of the described models is performed. Two conditions that affect the validity of the linear model are found. First one, referring to the ratio between the overall number of particles and the number of binding sites, and the second one, that guarantees the validity of linear model in much broader spectrum of practical situations, referring to the ratio of rate constants. A method for avoiding the accumulation of numerical errors in calculus is also proposed. The presented approach is general and can be used in various applications, including other types of chemical sensors, membranes for filtering, different catalytic systems, resonant micro or nano-electro-mechanical structures.

Changes in the hypothalamic-pituitary-adrenal (HPA) axis activity constitute a key component of bipolar mania, but the extent and nature of these alterations are not fully understood. We use here the lateral hypothalamic-kindled (LHK) rat model to deliberately induce an acute manic-like episode and measure serum corticosterone concentrations to assess changes in HPA axis activity. A mathematical model is developed to succinctly describe the entwined biochemical transformations that underlay the HPA axis and emulate by numerical simulations the considerable increase in serum corticosterone concentration induced by LHK. Synergistic combination of the LHK rat model and dynamical systems theory allows us to quantitatively characterize changes in HPA axis activity under controlled induction of acute manic-like states and provides a framework to study in silico how the dynamic integration of neurochemical transformations underlying the HPA axis is disrupted in these states.

Chaotic dynamic states with intermittent oscillations were generated in a Bray-Liebhafsky (BL) oscillatory reaction in an isothermal open reactor i.e., in the continuously-fed well-stirred tank reactor (CSTR) when the inflow concentration of potassium iodate was the control parameter. They are found between periodic oscillations obtained when [KIO3](0) LT 3.00 x 10(-2) M and stable steady states when [KIO3](0) > 4.10 x 10(-2) M. It was shown that the most chaotic states obtained experimentally somewhere in the middle of this region are in high correlation with results obtained by means of largest Lyapunov exponents and phenomenological analysis based on the quantitative characteristics of intermittent oscillations.

Stoichiometric network analysis (SNA) represents a powerful mathematical tool for stability analysis of complex stoichiometric networks. Recently, the important improvement of the method has been made, according to which instability relations can be entirely expressed via reaction rates, instead of thus far used, in general case undefined, current rates. Such an improved SNA methodology was applied to the determination of exact instability conditions of the extended model of the hypothalamic-pituitary-adrenal (HPA) axis, a neuroendocrinological system, whose hormone concentrations exert complex oscillatory evolution. For emergence of oscillations, the Hopf bifurcation condition was utilized. Instability relations predicted by SNA showed good correlation with numerical simulation data of the HPA axis model.

Stoichiometric Network Analysis (SNA) is a powerful method that can be used to examine instabilities in modelling a broad range of reaction systems without knowing the explicit values of reaction rate constants. Due to a lack of understanding, SNA is rarely used and its full potential is not yet fulfilled. Using the oscillatory carbonylation of a polymeric substrate [poly(ethylene glycol) methyl ether acetylene] as a case study, in this work, we consider two mathematical methods for the application of SNA to the reaction models when conservation constraints between species have an important role. The first method takes conservation constraints into account and uses only independent intermediate species, while the second method applies to the full set of intermediate species, without the separation of independent and dependent variables. Both methods are used for examination of steady state stability by means of a characteristic polynomial and related Jacobian matrix. It was shown that both methods give the same results. Therefore, as the second method is simpler, we suggest it as a more straightforward method for the applications. Published by AIP Publishing.

Al,Fe-pillared clay was synthesized from domestic clay from Bogovina according to a common procedure: grinding, sieving, Na exchange, pillaring, drying and calcination. Two synthesized samples differing only in calcining conditions were prepared. Phase composition and textural properties of the starting clay and synthesized pillared clays were characterized using X-ray diffraction and physisorption of nitrogen. Catalytic tests were performed using sample with better textural properties being the one submitted to milder calcining conditions. Catalytic wet peroxide oxidative degradation of aromatic compounds phenol and tartrazine on the synthesized catalyst was confirmed showing better efficiency in the case of tartrazine.

The kinetic investigations of the malonic acid decomposition (8.00 x 10(-3) mol dm(-3) a parts per thousand currency sign [CH(2)(COOH)(2)](0) a parts per thousand currency sign 4.30 x 10(-2) mol dm(-3)) in the Belousov-Zhabotinsky (BZ) system in the presence of bromate, bromide, sulfuric acid and cerium sulfate, were performed in the isothermal closed well stirred reactor at different temperatures (25.0A degrees C a parts per thousand currency sign T a parts per thousand currency sign 45.0A degrees C). The formal kinetics of the overall BZ reaction, and particularly kinetics in characteristic periods of BZ reaction, based on the analyses of the bromide oscillograms, was accomplished. The evolution as well as the rate constants and the apparent activation energies of the reactions, which exist in the preoscillatory and oscillatory periods, are also successfully calculated by numerical simulations. Simulations are based on the model including the Br(2)O species.

Identification of trends and their correspondence with dynamical state transitions are briefly discussed on several reaction network models. The influence of different threshold values on the trend analysis and dynamical state analysis results is examined. Both methods are applied here to the results of the numerical simulation. For this purpose the models of three reaction systems are used: simple model of consecutive, first order, equilibrium reactions, partial oxidation of cyclohexane, and model of the oscillatory reaction Bray Liebhafsky. Detailed kinetic analysis confirmed that transient dynamical states may be identified through the symbolic representation of the sequence of trend episodes in experimentally obtainable time series. Stoichiometric Network Analysis of possible dynamical states was used to identify reaction pathways responsible for the sequences of trend episodes. Some technical problems were also addressed, connected with selection of the threshold value and dynamical state notion.

In this paper, an already published model of the Bray-Liebhafsky reaction was improved by removing the direct autoinhibitory step, which resulted in a new variant of the model with more realistic kinetic scheme than the earlier version. The obtained variant of the model retains all intermediate species (I-, HIO, HIO2 and I-2) that were present in the previous model and has one reaction less. Stability analysis of the improved model was performed by stoichiometric network analysis (SNA). By this method, it was shown that improved model can simulate Andronov-Hopf and saddle-node bifurcations. In order to confirm the results of SNA, bifurcation analysis was performed with the initial concentrations of [H2O2](0) as the control parameter. With selected set of rate constants and constant concentrations of external species, two Andronov-Hopf bifurcations were detected at [H2O2](0) = 5.62 x 10(-2) M and [H2O2](0) = 10.73 M, while the rate constants ought to be changed for a saddle-node to occur. Bifurcation analysis also showed that the interaction between intermediate species I-, HIO and HIO2 has a crucial impact on the emergence of Andronov-Hopf bifurcation.

The mixing of different types of bifurcations, i.e. supercritical Andronov–Hopf (SAH), double loop (DL) and saddle-loop (SL) bifurcations in the vicinity of their total annihilation, is examined on the highly nonlinear six-variable model for the Bray–Liebhafsky (BL) oscillatory reaction under continuously well-stirred tank reactor (CSTR) conditions. For this kind of the reaction system where the law of mass conservation is additional constraint that must be satisfied and where because of that, some simple bifurcations cannot be formed independently to the others, the considered transformations of the bifurcations are particularly important. That is why as the control parameters for bifurcation analysis, the specific flow rate (j0), as well as the inflow hydrogen peroxide concentration (h = [H2O2]in), were used. The complex bifurcations obtained from numerical simulations are compared with some experimental results. It was shown that these complex bifurcations cannot be easily recognized in experimental investigations without knowing their evolution.

By numerically simulated Bray-Liebhafsky (BL) reaction under a continuously fed well stirred tank reactor (CSTR) conditions, we discussed the attractors and Poincar, 1D maps with respect to flow rate as the control parameter. The new technique of the return maps from transient trajectories over the slow manifold is developed and applied in order to explore its multilayered structure related to dynamical states (periodic and aperiodic -chaotic oscillating modes) of the system. Kinetic relations underlying the slow manifold structure are briefly discussed.

A series of silica-supported nickel catalyst precursors was synthesized with different SiO2/Ni molar ratios. Reduction of Ni catalyst precursors with different SiO2/Ni molar ratios under a hydrogen atmosphere was investigated at different heating rates. Kinetic parameters were determined using Kissinger-Akahira-Sunose isoconversional and invariant kinetic parameter methods. It was found that for all molar ratios, the apparent activation energy (E-a) is practically constant in the conversion range of 0.20 LT = alpha LT = 0.80. In the considered conversion range, following values of E-a were found: 134.5 kJ mol(-1) (SiO2/Ni = 0.20), 139.6 kJ mol(-1) (SiO2 /Ni = 0.80), and 128.3 kJ mol(-1) (SiO2/Ni = 1.15). It was established that the reduction of Ni catalyst precursors with different SiO2/Ni molar ratios is a complex process and can be described by the Sestak-Berggren autocatalytic model. It was found that the reaction is more Langmuir-Hinshelwood type, as hydrogen dissociates rapidly on surface nuclei and the dissociated hydrogen reacts with the Ni-O active system. It was concluded that the reduction process proceeds through bulk nucleation, which is a dominant mechanism, where three-dimensional growth of crystals with polyhedron-like morphology exists. It was found that the Ni/Si ratio decreases after the reduction process. This has been explained by low Ni and higher Si surface concentrations. It has been disclosed that Ni dispersion decreases. This is the peer reviewed version of the following article: Janković, B., Čupić, Ž., Jovanović, D., Stanković, M., 2016. Kinetic Analysis of Nonisothermal Reduction of Silica-Supported Nickel Catalyst Precursors in a Hydrogen Atmosphere. Chemical Engineering Communications 203, 182–199. [https://doi.org/10.1080/00986445.2014.983268] [http://cer.ihtm.bg.ac.rs/handle/123456789/1980]

The mathematical analogy between properties of simple and complex models of non-linear reactions was used to determine reaction steps in the complex model, necessary to generate instability region and appropriate type of bifurcations on the border between stable and unstable non-equilibrium stationary state. The autocatalator was recognized as the simple prototype two-variable non-linear model practical for examination of the complex four-variable non-linear neuroendocrine system known as the Hypothalamic-Pituitary-Adrenal (HPA) axis. In both cases, we derived the instability criteria by stoichiometric network analysis (SNA), determine conditions under which dynamic transitions, i.e. bifurcations occur, and identify the type of bifurcation. The supercritical Andronov–Hopf bifurcation was found in both cases whereas saddle-node bifurcation was detected only in the model for HPA axis. Thus, by stoichiometric network analysis, the mathematical analogy is found between two different models with same autocatalytic steps, that is, between two models with easily recognizable qualitative analogy.

Cyclic voltammetry (CV) on rotating Pt disc electrode was used for electrocatalytic oxidation of OH−. Hydroxide ion oxidation is followed by oxygen evolution with gas bubble formation. The image analysis was performed in situ in order to find correlation between bubbles related phenomena and the current of OH− oxidation. Bubble formation was tested in four different regimes having different scan rate and/or electrode rotation rate. The videometry using high speed camera was applied to observe the bubble related phenomena. The integral effect of presence of bubbles was analyzed. The fast Fourier transformation and normalized power spectra were used for advanced image analysis. Using this type of analysis, two different characteristic periodical behaviors were reported for the first time. The obtained periods were in accordance with scan rate and electrode rotation rate. The former periodic component of bubble formation process was correlated with well defined CV cycles, and hence, related to electrocatalytic oxidation–reduction of OH−. The other periodic component of bubble behavior induced by rotation rate (600 rpm) was shifted from 0.01 s toward slightly higher values probably due to hydrodynamic conditions in the investigated system.

In stoichiometric network analysis (SNA) the instability condition is calculated by the current rates. Recently, we have shown that in the final result the current rates can be substituted by reaction rates, which is a more appropriate value for the examination of instability from experimental point of view. Here, we elaborate the problem of whether the current rates are necessary parameters in the calculation, with the aim of obtaining the region of instability. All calculations are performed on a model for Belousov-Zhabotinsky (BZ) reaction, which has not been examined by SNA.

Soybean oil has been partially hydrogenated in the presence of a synthesized nickel catalyst, in an industrial reactor, under the standard industrial working conditions. The GC measurements of fatty acids in the investigated oil and hydrogenated products have been performed. The total trans isomers content has been determined by the IR spectroscopy. The model is established, which could be useful for the characterization of hydrogenation and isomerization reactions of poly-unsaturated acids. Iteration procedure, incorporating numerical simulation in each step is used to calculate rate constants of the proposed model from the comparison of the experimental and calculated kinetic runs. By the simultaneous treatment of the kinetic runs for the fatty acids composition and trans -isomer content, the 12 rate constants of individual hydrogenation and isomerization reaction steps are obtained.

The existing model for the Bray–Liebhafsky reaction aimed at simulating the largest possible number of various self-organization phenomena observed experimentally, is reduced herewith with the purpose of removing the intermediate I2O preserving the main characteristics of the parent model. The stoichiometric network analysis is applied.

a b s t r a c t The basic parameters of a sensor element defining its ultimate performance are sensitivity and intrinsic noise. In plasmonic gas sensors both are determined by refractive index changes due to adsorption and desorption (a-d) of target analyte particles to the sensor active area. In this paper we present a general model that can be simultaneously used to determine sensitivity and intrinsic noise of a plasmonic sensor both during transients and in steady-state and is valid for multi-analyte environments. The model util- izes the conventional probabilistic approach. It is derived without any assumptions about the stochastic nature of the fundamental (a-d) process. It reveals how all stochastic properties of the processes with (pseudo) first order kinetics with the initial number of particles equal to zero can be fully determined from the deterministic solution, without any previous stochastic analysis. Based on the proposed model it is possible to establish the optimum moment for readout when fluctuations are minimal. Transients last longer and fluctuations are lower at lower temperatures. The insight into the transient dynamics opens the possibility to use a single element sensor for multiple analyte sensing. Another result is that a-d noise is higher for smaller adsorption areas, which may be important for micro and nanosystems generally, since each of them has to be kept immersed in some kind of environment and thus be subject to contamination by adsorption that can significantly influence their behavior. Besides being applicable for plasmonic sensors of trace amounts of gases and other nanoplasmonic devices used in sensing, the model is applicable for other adsorption-based sensors, as well as for the investigations of stochastic phenomena in micro and nanostructures.

Perturbation of the BrayLiebhafsky non-oscillating subsystem (mixture of KIO3 and H2SO4), i.e., Dushman reaction (DR), by piroxicam (PX), was observed in an open reactor, i.e., in the continuously fed well-stirred tank reactor (CSTR). Monitoring the response of DR to perturbations by different concentrations of PX allows developing a simple procedure for quantitative determination of this analyte in both bulk drug and pharmaceutical preparation (injection). A tentative perturbation mechanism of PX action on the DR matrix, based on a kinetic scheme that was suggested by Agreda et al., is proposed. The PX reactivity in DR has been generally related to the reaction of PX with hypoiodous acid (HIO) present in the matrix.

The investigation represented here is focused on fundamental intrinsic fluctuations caused by the adsorption and desorption (a–d) of surrounding particles on the active surface in plasmonic metamaterial devices. The variance and relative fluctuations in adsorption–desorption dynamics are studied based on two different kinetic models (pseudo-first order kinetics and second order kinetics). The limits of the applicability of the pseudo-first order model are determined, thus ensuring the use of the vast mathematical heritage developed for linear systems in calculation of a–d noise, while at the same time speeding up and simplifying calculations. An approach is proposed to assess adsorption in a metamaterial sensor using an effective parameter dependent on the properties of the metamaterial unit cell.

The main pseudo-steady states in the process of catalytic hydrogen peroxide decomposition are analysed. The dominant steady states during the monotonic and oscillatory evolution, well known experimentally, are defined by stoichiometric network analysis of the model for this process. The trajectories for the evolution of the system in the phase space in the vicinity of the unstable pseudo-steady state where oscillatory behaviour is obtained, are also calculated. The adjustment of the phase trajectory to the corresponding oscillation is proposed as an additional criterion for the selection of the kinetic parameters necessary for numerical simulation. The calculation procedure is general, independent of the model under consideration.

A mathematical model of the hypothalamic-pituitary-adrenal (HPA) axis with cholesterol as a dynamical variable was derived to investigate the effects of cholesterol, the primary precursor of all steroid hormones, on the ultradian and circadian HPA axis activity. To develop the model, the parameter space was systematically examined by stoichiometric network analysis to identify conditions for ultradian oscillations, determine conditions under which dynamic transitions, i.e. bifurcations occur and identify bifurcation types. The bifurcations were further characterized using numerical simulations. Model predictions agree well with empirical findings reported in the literature, indicating that cholesterol levels may critically affect the global dynamics of the HPA axis. The proposed model provides a base for better understanding of experimental observations, it may be used as a tool for designing experiments and offers useful insights into the characteristics of basic dynamic regulatory mechanisms that, when impaired, may lead to the development of some modern-lifestyle-associated diseases.