Two classes of quasi-steady-state model reductions for stochastic kinetics

The quasi-steady-state approximation (QSSA) is a model reduction technique used to remove highly reactive species from deterministic models of reaction mechanisms. In many reaction networks the highly reactive intermediates (QSSA species) have populations small enough to require a stochastic representation. In this work we apply singular perturbation analysis to remove the QSSA species from the chemical master equation for two classes of problems. The first class occurs in reaction networks where all the species have small populations and the QSSA species sample zero the majority of the time. The perturbation analysis provides a reduced master equation in which the highly reactive species can sample only zero, and are effectively removed from the model. The reduced master equation can be sampled with the Gillespie algorithm. This first stochastic QSSA reduction is applied to several example reaction mechanisms (including Michaelis-Menten kinetics) [Biochem. Z. 49, 333 (1913)]. A general framework for applying the first QSSA reduction technique to new reaction mechanisms is derived. The second class of QSSA model reductions is derived for reaction networks where non-QSSA species have large populations and QSSA species numbers are small and stochastic. We derive this second QSSA reduction from a combination of singular perturbation analysis and the Omega expansion. In some cases the reduced mechanisms and reaction rates from these two stochastic QSSA models and the classical deterministic QSSA reduction are equivalent; however, this is not usually the case

The Soviet Union and the Falklands War

The 1982 conflict between Great Britain and Argentina was the first time that a Nato power, other than the United States, tested itself in combat since France had lost the Algerian war twenty years before. The campaign in the South Atlantic involved predominantly sea power-the element of military might in which the Soviet Union had been investing vigorously

Stochastic simulation of catalytic surface reactions in the fast diffusion limit

The master equation of a lattice gas reaction tracks the probability of visiting all spatial configurations. The large number of unique spatial configurations on a lattice renders master equation simulations infeasible for even small lattices. In this work, a reduced master equation is derived for the probability distribution of the coverages in the infinite diffusion limit. This derivation justifies the widely used assumption that the adlayer is in equilibrium for the current coverages and temperature when all reactants are highly mobile. Given the reduced master equation, two novel and efficient simulation methods of lattice gas reactions in the infinite diffusion limit are derived. The first method involves solving the reduced master equation directly for small lattices, which is intractable in configuration space. The second method involves reducing the master equation further in the large lattice limit to a set of differential equations that tracks only the species coverages. Solution of the reduced master equation and differential equations requires information that can be obtained through short, diffusion-only kinetic Monte Carlo simulation runs at each coverage. These simulations need to be run only once because the data can be stored and used for simulations with any set of kinetic parameters, gas-phase concentrations, and initial conditions. An idealized CO oxidation reaction mechanism with strong lateral interactions is used as an example system for demonstrating the reduced master equation and deterministic simulation techniques

Reassuring NATO: Eastern Europe, Russia, and the Western Alliance

Against the background of the changing Russian and East European attitudes toward NATO before and since the end of the Cold War. This Study examines the origins of the alliance's enlargement and the implications for its cohesin and ability to act. The author recommends suspending the enlargement after the admission of Poland, the best qualified candidate

The stochastic quasi-steady-state assumption: Reducing the model but not the noise

Highly reactive species at small copy numbers play an important role in many biological reaction networks. We have described previously how these species can be removed from reaction networks using stochastic quasi-steady-state singular perturbation analysis (sQSPA). In this paper we apply sQSPA to three published biological models: the pap operon regulation, a biochemical oscillator, and an intracellular viral infection. These examples demonstrate three different potential benefits of sQSPA. First, rare state probabilities can be accurately estimated from simulation. Second, the method typically results in fewer and better scaled parameters that can be more readily estimated from experiments. Finally, the simulation time can be significantly reduced without sacrificing the accuracy of the solution

Didaktische Perspektiven des fächerübergreifenden Unterrichts am Beispiel Bewegung und Sport und Physik

Die Arbeit beschäftigt sich mit einer didaktischen Analyse des fächerübergreifenden Unterrichts am Beispiel Bewegung und Sport – Physik. Nach einer Begriffs- und Standortbestimmung werden 3 Konzepte vorgeschlagen, wie der überfachliche Unterricht didaktisch umgesetzt werden kann. Zunächst erweist sich der mehrperspektivische Unterricht als geeignet, um einen Inhalt vielschichtig und aus mehreren Blickwinkeln zu betrachten. Anschließend wird ein reflexives, problemorientiertes Konzept vorgestellt. Dabei steht anstelle eines Inhalts ein Problem im Zentrum und die Schülerinnen und Schüler sollen selbsttätig auf unterschiedlichen Ebenen Lösungen finden, wobei einer breiten Reflexion der einzelnen Zugänge viel Aufmerksamkeit geschenkt wird. Das dritte Konzept zeichnet sich durch eine starke Handlungsorientierung und eine ganzheitliche Vorgehensweise aus. Gerade zum Unterrichtsfach Bewegung und Sport mit seinen kognitiven, psychologischen und physiologischen Anforderungen scheint dieses Konzept gut zu passen. Aktuelle Erfahrungen und Erkenntnisse von Schulen finden ebenfalls Einzug in diese Arbeit und führen zu folgender Vorgangsweise bei der praktischen Realisierung des fächerübergreifenden Unterrichts. Einer Einführungsphase im Plenumsunterricht folgt ein projektorientierter Blockunterricht, in welchem sich die Schüler/innen in Gruppenarbeiten selbstständig und individuell einem Problem nähren. Abschließend finden eine Präsentation und die Zusammenführung der Ergebnisse statt. Dieses Modell wird in angepasster und modifizierter Form in den insgesamt 5 Unterrichtsbeispielen angewendet, die sich mit folgenden Themen beschäftigen: Physik des Bergwanderns, Physik des Laufens, Splashdiving, Physik des Wintersports und Physik des Krafttrainings. Bei jedem Thema werden der Lehrplanbezug, das Lernziel und die physikalische Grundlagen erläutert, bevor die Möglichkeiten der didaktischen Umsetzung anhand der oberen Konzepte analysiert werden. Beispiele und Möglichkeiten der Durchführung samt Gruppeneinteilung, benötigter Materialien und Zeitplan tragen zur Veranschaulichung bei

Did intelligence matter in the Cold War?

For forty years the superpower conflict between the United States and the Soviet Union dominated the world stage. In popular culture the conflict produced a plethora of “spy” books and films about the daring exploits of intelligence agents. In contrast, the scholarly investigation of the role of intelligence in the Cold War had to await the gradual opening, since 1990, of “Top Secret” archives. It is now time to make a first attempt at assessing the role that intelligence played in the overall development of the conflict. Did intelligence help to avoid the Cold War becoming “hot”? We have invited three prominent intelligence scholars to give their views

Corrosion properties of chromia based eco - friendly coatings on mild steel

Ceramic nanocrystalline coatings of chromium oxide (III) on steel S235JRH-1.0038 (EN 10025-1) were prepared using the liquid precursor plasma spraying (LPPS) method from ammonia dichromate (VI). Their structure and anti – corrosion properties were compared to the standard chromium oxide (III) coating prepared by thermal spraying. The newly prepared coatings had very high adhesion and minimal porosity. Anticorrosion properties were characterized by the means of the electrochemical impedance spectroscopy (EIS), measuring the charge transfer resistance Rct and capacitance of electrical double layer CPEdl in the 0,5 mol/l NaCl. Coatings of Cr2 O3 prepared by the LPPS method showed unambiguously improved anti - corrosion properties

Influence of surface diffusion on catalytic reactivity of spatially inhomogeneous surfaces mean field modeling

Kinetics of model catalytic processes proceeding on inhomogeneous surfaces is studied. We employ an extended mean-field model that takes into account surface inhomogeneities. The influence of surface diffusion of adsorbent on the kinetics of the catalytic process is investigated. It is shown that diffusion is responsible for differences in the reaction rate of systems with different arrangements of active sites. The presence of cooperative effects between inactive and active sites is demonstrated and the conditions when these effects are important are discussed. We show that basic catalytic phenomena on nonuniform surfaces can be studied with mean-field modeling methods.Comment: Submitted to Chemical Physics Letters. Includes supporting material in Appendice

Bond strength of plasma sprayed ceramic coatings on the phosphated steels

In the presented work, results of adhesion measurements for different systems of steel sheet-phosphate interlayer-ceramiccoating are described. The interlayers were produced by zinc phosphating; alumina, olivine and zirconiasilica-alumina (e.g. eucor) coatings were deposited by water stabilized plasma torch WSP®. However, successful application of the WSP technique depends on the choice of correct deposition parameters preserving the hydrated phosphates from thermal destruction by the molten ceramic particles. For the adhesion measurement ISO 4624standardized test was used. Corrosion resistivity was measured by polarisation resistance and free corrosion potential in 3 % NaCl solution. Key words