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Dynamics Theory (dynamics + theory)
Selected AbstractsAn approach to the nonlinear dynamics of Russian wheat aphid population growth with the cusp catastrophe modelENTOMOLOGICAL RESEARCH, Issue 3 2009Z. S. MA Abstract Many insect field populations, especially aphids, often exhibit irregular and even catastrophic fluctuations. The objective of the present study is to explore whether or not the population intrinsic rates of growth (rm) obtained under laboratory conditions can shed some light on the irregular changes of insect field populations. We propose to use the catastrophe theory, one of the earliest nonlinear dynamics theories, to answer the question. To collect the necessary data, we conducted a laboratory experiment to investigate population growth of the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), in growth chambers. The experiment was designed as the factorial combinations of five temperatures and five host plant-growth stages (25 treatments in total): 1800 newly born RWA nymphs arranged in the 25 treatments (each treatment with 72 repetitions) were observed for their development, reproduction and survival through their entire lifetimes. After obtaining the population intrinsic rates of growth (rm) from the experimental data under various environmental conditions, we built a cusp catastrophe model for RWA population growth by utilizing rm as the system state variable, and temperature and host plant-growth stage as control variables. The cusp catastrophe model suggests that RWA population growth is intrinsically catastrophic, and dramatic jumps from one state to another might occur even if the temperature and plant-growth stage change smoothly. Other basic behaviors of the cusp catastrophe model, such as catastrophic jumps, hystersis and divergence, are also expected in RWA populations. These results suggest that the answer to the previously proposed question should be "yes". [source] A modal pushover analysis procedure to estimate seismic demands for unsymmetric-plan buildingsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2004Anil K. Chopra Abstract An Erratum has been published for this article in Earthquake Engng. Struct. Dyn. 2004; 33:1429. Based on structural dynamics theory, the modal pushover analysis (MPA) procedure retains the conceptual simplicity of current procedures with invariant force distribution, now common in structural engineering practice. The MPA procedure for estimating seismic demands is extended to unsymmetric-plan buildings. In the MPA procedure, the seismic demand due to individual terms in the modal expansion of the effective earthquake forces is determined by non-linear static analysis using the inertia force distribution for each mode, which for unsymmetric buildings includes two lateral forces and torque at each floor level. These ,modal' demands due to the first few terms of the modal expansion are then combined by the CQC rule to obtain an estimate of the total seismic demand for inelastic systems. When applied to elastic systems, the MPA procedure is equivalent to standard response spectrum analysis (RSA). The MPA estimates of seismic demand for torsionally-stiff and torsionally-flexible unsymmetric systems are shown to be similarly accurate as they are for the symmetric building; however, the results deteriorate for a torsionally-similarly-stiff unsymmetric-plan system and the ground motion considered because (a) elastic modes are strongly coupled, and (b) roof displacement is underestimated by the CQC modal combination rule (which would also limit accuracy of RSA for linearly elastic systems). Copyright © 2004 John Wiley & Sons, Ltd. [source] Nonadiabatic evolution of electronic states by electron nuclear dynamics theoryINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Frank Hagelberg Abstract The problem of how to determine the nonadiabatic content of any given dynamic process involving molecular motion is addressed in the context of Electron Nuclear Dynamics (END) theory. Specifically, it is proposed to cast the dynamic END wave function into the language of static electronic configurations with time dependent complex-valued amplitudes. This is achieved by adiabatic transport of an electronic basis along the classical nuclear trajectories of the studied molecular system, as yielded by END simulation. Projecting the dynamic wave function on this basis yields a natural distinction between adiabatic and nonadiabatic components of the motion considered. Tracing the evolution of the leading configurations is shown to be a helpful device for clarifying the physical nature of electronic excitation processes. For illustration of these concepts, dynamic configuration analysis is applied to the scattering of a proton by a lithium atom. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Climate mediated exogenous forcing and synchrony in populations of the oak aphid in the UKOIKOS, Issue 2 2009Sergio A. Estay Contemporary population dynamics theory suggests that animal fluctuations in nature are the result of the combined forces of intrinsic and exogenous factors. Weather is the iconic example of an exogenous force. The common approach for analyzing the relationship between population size and climatic variables is by simple correlation or using the climate as an additive covariable in statistical models. Here, we evaluated different functional forms in which climatic variables could influence population dynamics of the oak aphid Tuberculatus annulatus both in each locality and in relation to synchrony between localities. Results indicate that in at least four of eight aphid populations, climate influences population dynamics by modifying the carrying capacity of the system (lateral effect mediated by winter precipitation). Additionally, path analysis showed that synchrony in population dynamics is highly correlated with synchrony in winter precipitation regime, and the spatial scale of both processes is similar, which suggests that this is an example of the Moran effect. Our results show the key effects of precipitation on intra and inter population processes of this aphid. The methods used, mixing population dynamics modelling and test of synchrony, allowed us to connect the direct and indirect effects of exogenous variables into each population with patterns of synchrony inter populations. [source] System Dynamics as a Structural Theory in Operations ManagementPRODUCTION AND OPERATIONS MANAGEMENT, Issue 3 2008Andreas Größler The purpose of the paper is to demonstrate the usefulness of (1) system dynamics as a structural theory for operations management and (2) system dynamics models as content theories in operations management. The key findings are that, although feedback loops, accumulation processes, and delays exist and are widespread in operations management, often these phenomena are ignored completely or not considered appropriately. Hence, it is reasoned why system dynamics is well suited as an approach for many operations management studies, and it is shown how system dynamics theory can be used to explain, analyze, and understand such phenomena in operations management. The discussion is based on a literature review and on conceptual considerations, with examples of operations management studies based on system dynamics. Implications of using this theory include the necessary re-framing of some operations management issues and the extension of empirical studies by dynamic modeling and simulation. The value of the paper lies in the conceptualization of the link between system dynamics and operations management, which is discussed on the level of theory. [source] | |||||||||||||