Modeling mechanism of oscillating catalytic processes, with application to hydrogenperoxide decomposition

Urađena je detaljna analiza postupaka koje bi trebalo primeniti pri analizi svih složenih procesa, a posebno pri modeliranju oscilatornih katalitičkih reakcija. Sintezom odabranih metoda sačinjen je sopstveni opšti postupak koji je primenjen na polazni model reakcije Braj- Libhavski. Tokom postupka modeliranja, formiran je niz redukovanih modela i utvrđene su njihove osobine. Dobijeni uprošćeni modeli i dalje omogućavaju simulaciju oscilacija, a dovoljno su pojednostavljeni da omoguće i kvantitativnu analizu uslova stabilnosti. Primenjena analitička procedura daje uvid u ulogu pojedinih delova reakcionog mehanizma u celokupnom procesu i naročito u mehanizmu oscilovanja.Detailed analysis was performed of the methods that should be employed in the analysis of complex processes, especially in the modeling of the oscillatory catalytic reactions. By synthesis of selected methods, our own general procedure was made and applied to the initial model of the Bray – Liebhavsky reaction. During the modeling process, a series of reduced models was created and their characteristics defined. The resulting simplified models still allow the simulation of oscillations, but they are sufficiently simplified to allow quantitative analysis of the stability conditions. Applied analytical procedure provides insight into the role of individual components of the reaction mechanism in the whole process and especially in the mechanism of oscillations

Influence of the form of the periodic function that describes the circadian rhythm of the hpa system activity

The influence of the form of the periodic function that describes the circadian rhythm on the hypothalamic-pituitary-adrenal (HPA) system self-regulatory activity in humans is discussed. It was found that the HPA system is very sensitive to the choice of this function since it moderates the concentration of all species that are included in the model, as well as the form of ultradian pulses.Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

The Bray-Liebhafsky oscillatory reaction: Kinetic investigations in reduction and oxidation pathways based on hydrogen peroxide concentration monitoring

By direct monitoring of the hydrogen concentration during its catalytic decomposition into water and oxygen in the presence of potassium iodate and sulfuric acid, that is in the Bray-Liebhafsky system, the pseudo-rate constants of overall reduction and oxidation pathways were determined The dependence of the obtained rate constants on acidity was evaluated. It was found that the pseudo-rate constant of the overall reduction process increases with increasing acidity, whereas the pseudo-rate constant of the overall oxidation process decreases with increasing acidity. The corresponding activation energies were also calculated using values of this constant at two temperatures.Direktnim praćenjem koncentracije vodonik-peroksida u toku njegovog katalitičkog razlaganja na vodu i kiseonik u prisustvu kalijum-jodata i sumporne kiseline, odnosno u Bray-Lievhafsky sistemu, analizirane su konstante brzina celokupnog redukcionog i oksidacionog puta kao konstante brzina pseudo-prvog reda. izvedene su njihove zavisnosti od kiselosti. Nađeno je da pseudo-konstanta brzine celokupnog redukcionog procesa raste sa porastom kiselosti, dok pseudo-konstanta brzine celokupnog oksidacionog procesa opada sa porastom kiselosti. korišćenjem njihovih vrednosti na dve temperature izračunate su odgovarajuće energije aktivacija

Bray-Liebhafsky reaction: From monotonous to chaotic evolution

Many physicochemical processes can exhibit various forms of non-linear dynamics, which have been widely investigated in the oscillatory reaction Bray-Liebhafsky, too. The stoichiometry of this reaction corresponds to the hydrogen peroxide decomposition to water and oxygen in an acidic environment, in the presence of iodate ions as a catalyst. During this reaction an oscillatory change of the intermediate species concentration, along with a cascade change in the hydrogen peroxide concentration and oxygen removal can be obtained. By selecting the experimental conditions, the simple periodic or complex chaotic concentration changes can be generated. Concentration oscillations are a consequence of alternating dominance of different reaction pathways present in the reaction mechanism. Large extent of the phenomena experimentally observed in the oscillatory reaction Bray- Liebhafsky is well explained by the mechanistic model, investigated by the Belgrade group over a many years

Modeling the Non-Linear Dynamics of Information Flows in Neuro-Endocrine Systems

Nonlinear feedback loops inherent to neuroendocrine systems are among the most important information flows at the organism level. They support high sensitivity and responsiveness of the living beings to external perturbations. Moreover, nonlinear feedback loops enable efficient control over dynamic physiological states. Often, they can be recognized through emergence of various dynamic phenomena, such as biological rhythmicity. Typical examples of such neuroendocrine systems are the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic–pituitary–thyroid (HPT) axis. They are characterized by rhythmic dynamics with two characteristic periods, circadian (~ 24 h) and ultradian (20 min – 120 min), which allows living organisms to quickly adjust their neuroendocrine activity to fluctuations in their surroundings and/or their internal physiology. We focus our research on mechanistic modelling of biochemical transformations that underlay complex neuroendocrine networks. Thus far, we have developed several variants of low-dimensional and extended models for the HPA axis, as well as, one medium scale model of the HPT axis. Both of them are assembled by combinations of the pseudo-reaction steps, describing in essence the information flow through the network of chemical transformations. Their role in physiological system is to maintain basal levels of hormone concentrations, and enable their functionally reasonable change when some need emerges. Our models enable one to emulate in numerical simulations changes in blood level of relevant hormones that constitute the HPA or HPT axis (Jelić et al. 2005, Marković et al. 2011, Čupić et al. 2017, Kolar-Anić et al. 2023). The high predictive value of our models paves the way for their use in medical diagnostics of neuroendocrine diseases and for more efficient corticosteroid treatment that is applied in various illnesses, by harnessing the power of the underlying nonlinear feedback loops to the dosage of corticosteroid drugs could be significantly decreased, while preserving their efficacy. We pay special attention to the Stoichiometric Network Analysis of reaction network models to identify conditions ensuring the existence of unstable steady states, and in particular, Hopf bifurcation as a most plausible path leading to the oscillatory dynamics. The simplest way to use this template is to replace the text in this file with your own words using the styles provided as far as possible

Stupnjevanje invazivnih stanica - pregled

Pathohistologic diagnosis plays a pivotal role in therapeutic modalities for cancer, and acts as a prognostic factor. The histologic grade is a numeric expression of tumor differentiation and is linked to patient outcome. Broders\u27 scoring system is still widely used in scoring squamous cell carcinomas. New data suggest that in the most invasive parts of a malignant tumor, the morphology and biologic behavior differ from the central and superficial areas of the same tumor. A new invasive cell grading system has been proposed as a better prognostic factor in the multifactorial diagnostic and therapeutic approach to the patient with malignant tumor. Numerous studies performed to date have provided sufficient evidence to propose the invasive cell grading system to be introduced instead of the "old" Broders\u27 scoring system.Patohistološka dijagnoza igra ključnu ulogu u terapijskom pristupu raku te djeluje i kao prognostički čimbenik. Histološki stupanj je brojčani izražaj diferencijacije tumora i vezan je uz prognozu tumorske bolesti u pojedinog bolesnika. Danas je u širokoj uporabi Brodersov sustav histološkog stupnjevanja u karcinomima pločastog epitela. Noviji podatci ukazuju na to da se morfologija i biološko ponašanje stanica u invazivnim dubokim dijelovima malignog tumora razlikuju od središnjih i površinskih dijelova istoga tumora. Novi sustav ICG (invasive cell grading . stupnjevanje invazivnih stanica) predložen je kao bolji prognostički čimbenik u složenom dijagnostičkom i terapijskom pristupu bolesniku s malignim tumorom. Brojna su istraživanja potvrdila da se novi sustav ICG može s dovoljnom sigurnošću rabiti u patohistološkom stupnjevanju malignih tumora umjesto "starog" Brodersovog načina

Stoichiometric network analysis as mathematical method for examinations of instability region and oscillatory dynamics

Reaction systems in chemistry, physical chemistry, and biochemistry, which can be described by true or pseudo-stoichiometric relationships between species, and, therefore, represented with stoichiometric models, are usually very complex. For the analysis of the models of these complex nonlinear reaction systems with more than three variables, which can be in different dynamic states like multistability, oscillatority or chaos, some general mathematical methods such as the Stoichiometric network analysis (SNA) must be used. Although the SNA is a powerful method for systematic examination of complex reaction systems, identification of underlying reaction pathways, and stability analysis of dynamic states, this method is practically unknown among mathematicians. Therefore, a simple application of SNA to one five-dimensional model is given here

Doprinosi Beogradske grupe izučavanju oscilatornih reakcija

Oscillatory dynamic states as one form of selforganization of nonlinear systems can be found in almost all sciences, like mechanics, physical chemistry or biomedicine. Although origin of these oscillations is different, computational challenges in modelling oscillatory phenomena remain similar in all fields. Since 1979 researchers from Belgrade's group perform systematic examinations of oscillatory reactions. As stability of steady states is the central point in modelling oscillatory reactions, in last 10 years they have adapted and improved powerful tool of the Stoichiometric Network Analysis for this goal. Moreover, bifurcations of few types were identified in several models of oscillatory reactions. Even very complex chaotic motions in phase space were characterized and quantified by several numerical techniques. Multiple time scale behaviour is found within the core of the complex dynamic behaviour of mixed-mode oscillations. Analytical applications were developed, too.Oscilatorna dinamička stanja, kao oblik samoorganizacije nelinearnih sistema, mogu se naći u gotovo svim naukama, kao što su mehanika, fizička hemija ili biomedicina. Iako je poreklo ovih oscilacija različito, teškoće u modeliranju oscilatornih fenomena su zajedničke na svim poljima. Od 1979. godine istraživači Beogradske grupe sistematski istražuju oscilatorne reakcije. Kako je stabilnost ustaljenih stanja ključni problem u modeliranju oscilatornih reakcija, u poslednjih 10 godina oni su za tu namenu usvojili i unapredili moćnu tehniku Analize stehiometrijskih mreža. Zatim je identifikovano više tipova bifurkacija u nekoliko modela oscilatornih reakcija. Čak su i veoma složena haotična kretanja u koncentracionom faznom prostoru okarakterisana i kvantifikovana različitim numeričkim tehnikama. Ustanovljeno je da izvor oscilacija mešanih modova i drugih uočenih složenih oblika dinamike predstavljaju procesi koji se odigravaju na različitim vremenskim skalama. Takođe su razvijene i analitičke primene oscilatornih reakcija