A hybrid system approach is adopted to study the dynamic behaviour of a controlled reverse flow reactor in which a feedback control law dictates the occurrence of flow inversions. Typical behaviour of hybrid systems (...
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As an example of accidental situations in nuclear power plants, we consider the power oscillations that can occur in a boiling water reactor (BWR) nuclear power plant (NPP) under certain circumstances. An interesting ...
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As an example of accidental situations in nuclear power plants, we consider the power oscillations that can occur in a boiling water reactor (BWR) nuclear power plant (NPP) under certain circumstances. An interesting problem is to study and characterize these instabilities analyzing the neutronic power signals obtained from the local power range monitors (LPRMs) installed in the reactor core. Several techniques exist to detect and classify the possible oscillations in a BWR. The power decomposition method and the singular system analysis methodology are reviewed and the performance of both techniques is compared analyzing points 9 and 10 of cycle 14 of the OECD Ringhals 1 stability benchmark
We discuss a new method of time series data mining using moving approximation (MAP) transform and association measures based on MAP. MAP transform replaces time series values by slope values of lines approximating tim...
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We discuss a new method of time series data mining using moving approximation (MAP) transform and association measures based on MAP. MAP transform replaces time series values by slope values of lines approximating time series data in sliding window. An effective method of MAP transform calculation for time series with fixed time step is proposed. Based on MAP, a measure of local trend associations between time series is introduced. This measure is invariant under independent linear transformations of time series. Measure of local trend associations defines association function depending on the size of sliding window for each pare of considered time series. Based on association function, different association measures may be considered to measure local trend associations or global trend associations between time series. The methods of application of association measure to construction of association network of time series are discussed and illustrated on examples of synthetic and financial time series databases. Association networks give information about relationships between time dynamics of elements of systems given by time series databases.
We examine resonant interactions of optical pulses with nanostructured materials in the case of the electric field interacting with plasmonic oscillations in metallic nanospheres and double resonance including the mag...
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We explore a systematic computational approach to the feedback regulator synthesis problem based on the "equation-free" timestepper methodology [Theodoropoulos, K, et al., 2000], [Makeev, A, et al., 2002], [...
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We explore a systematic computational approach to the feedback regulator synthesis problem based on the "equation-free" timestepper methodology [Theodoropoulos, K, et al., 2000], [Makeev, A, et al., 2002], [Kevrekidis, A. G., et al., 2003], [Siettos, C, et al., 2003], where both the closed-loop dynamics linearization and pole-placement objectives are simultaneously attained in a single design step [Kazantzis, N, 2001]. This is of particular interest in the case of systems/processes modeled via microscopic/stochastic simulations (e.g. kinetic Monte Carlo) for which coarse-grained, macroscopic models at the level we wish to control the behavior are not available in closed form.
In this paper, we consider the problem of dynamically regulating the timing of traffic light controllers in busy cities. We use a Stochastic Fluid Model (SFM) to model the dynamics of the queues formed at an intersect...
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In this paper, we consider the problem of dynamically regulating the timing of traffic light controllers in busy cities. We use a Stochastic Fluid Model (SFM) to model the dynamics of the queues formed at an intersection. Based on this model, we derive gradients of the queue lengths with respect to the green/red light lengths within a signal cycle. We report preliminary numerical results comparing the performance of the estimates with finite-difference and smoothed perturbation analysis estimates. Then all estimators are used to optimize the traffic system via Stochastic Approximation.
Upon oxidation, a silica scale forms on MoSi2, a potential high-temperature coating material for metals. This silica scale protects MoSi2 against high-temperature corrosive gases or liquids. We use periodic density fu...
Upon oxidation, a silica scale forms on MoSi2, a potential high-temperature coating material for metals. This silica scale protects MoSi2 against high-temperature corrosive gases or liquids. We use periodic density functional theory to examine the interface between SiO2 and MoSi2. The interfacial bonding is localized, as evidenced by an adhesion energy that changes only slightly with the thickness of the SiO2 layer. Moreover, the adhesion energy displays a relatively large (0.40J∕m2) variation with the relative lateral position of the SiO2 and MoSi2 lattices due to changes in Si−O bonding across the interface. The most stable interfacial structure yields an ideal work of adhesion of 5.75J∕m2 within the local density approximation (5.02J∕m2 within the generalized-gradient approximation) to electron exchange and correlation, indicating extremely strong adhesion. Local densities of states and electron density difference plots demonstrate that the interfacial Si−O bonds are covalent in character. Mo−O interactions are not found in the SiO2∕MoSi2 interface investigated here. Our work predicts that the SiO2 scale strongly adheres to MoSi2, and further supports the potential of MoSi2 as a high-temperature structural material and coating.
A hybrid system approach is adopted to study the dynamic behaviour of a controlled reverse flow reactor in which a feedback control law dictates the occurrence of flow inversions. Typical behaviour of hybrid systems (...
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A hybrid system approach is adopted to study the dynamic behaviour of a controlled reverse flow reactor in which a feedback control law dictates the occurrence of flow inversions. Typical behaviour of hybrid systems (Zeno phenomena) are found coexisting with other regimes like limit cycles and quasi-periodic regimes. Construction of impact maps, continuation of limit cycles and detection of local bifurcations are employed to understand the influence of Zeno phenomena on bifurcation scenario and on routes to strange attractors.
The chemical mechanisms underlying the growth of cave formations such as stalactites are well known, yet no theory has yet been proposed which successfully accounts for the dynamic evolution of their shapes. Here we c...
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The chemical mechanisms underlying the growth of cave formations such as stalactites are well known, yet no theory has yet been proposed which successfully accounts for the dynamic evolution of their shapes. Here we consider the interplay of thin-film fluid dynamics, calcium carbonate chemistry, and CO2 transport in the cave to show that stalactites evolve according to a novel local geometric growth law which exhibits extreme amplification at the tip as a consequence of the locally-varying fluid layer thickness. Studies of this model show that a broad class of initial conditions is attracted to an ideal shape which is strikingly close to a statistical average of natural stalactites.
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