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Dynamic Framework (dynamic + framework)
Selected AbstractsMARSHALL'S CETERIS PARIBUS IN A DYNAMIC FRAMEWORKMETROECONOMICA, Issue 1 2009Fabio Cerina ABSTRACT The paper aims to propose a formalization of the concept of ceteris paribus (CP) by means of a dynamic model. The basic result of the analysis is that the CP clause may assume essentially different meanings according to (1) the kind of variables assumed to be ,frozen' and (2) the length of the time horizon. It is then possible to distinguish, respectively, between an exogenous and an endogenous CP and, within the latter, between a short-run and a long-run CP. This double analytical distinction helps in understanding the role the CP clause plays in Marshall's thought and in economics in general. [source] A structured and dynamic framework to advance traits-based theory and prediction in ecologyECOLOGY LETTERS, Issue 3 2010Colleen T. Webb Ecology Letters (2010) 13: 267,283 Abstract Predicting changes in community composition and ecosystem function in a rapidly changing world is a major research challenge in ecology. Traits-based approaches have elicited much recent interest, yet individual studies are not advancing a more general, predictive ecology. Significant progress will be facilitated by adopting a coherent theoretical framework comprised of three elements: an underlying trait distribution, a performance filter defining the fitness of traits in different environments, and a dynamic projection of the performance filter along some environmental gradient. This framework allows changes in the trait distribution and associated modifications to community composition or ecosystem function to be predicted across time or space. The structure and dynamics of the performance filter specify two key criteria by which we judge appropriate quantitative methods for testing traits-based hypotheses. Bayesian multilevel models, dynamical systems models and hybrid approaches meet both these criteria and have the potential to meaningfully advance traits-based ecology. [source] Some Notes on Institutions in Evolutionary Economic GeographyECONOMIC GEOGRAPHY, Issue 2 2009Ron Boschma abstract Within the evolutionary economic geography framework, the role of institutions deserves more explicit attention. We argue that territorial institutions are to be viewed as orthogonal to organizational routines since each territory is characterized by a variety of routines and a single firm can apply its routines in different territorial contexts. It is therefore meaningful to distinguish between institutional economic geography and evolutionary economic geography as their explanans is different. Yet the two approaches can be combined in a dynamic framework in which institutions coevolve with organizational routines, particularly in emerging industries. Furthermore, integrating the evolutionary and institutional approach allows one to analyze the spatial diffusion of organizational routines that mediate conflicts among social groups, in particular, those between employers and employees. An evolutionary economic geography advocates an empirical research program, both qualitative and quantitative, that can address the relative importance of organizational routines and territorial institutions for regional development. [source] Development of an optimization model for energy systems planning in the Region of WaterlooINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2008Y. P. Cai Abstract In this study, a large-scale dynamic optimization model (University of Regina Energy Model, UREM) has been developed for supporting long-term energy systems planning in the Region of Waterloo. The model can describe energy management systems as networks of a series of energy flows, transferring extracted/imported energy resources to end users through a variety of conversion and transmission technologies over a number of periods. It can successfully incorporate optimization models, scenario development and policy analysis within a general framework. Complexities in energy management systems can be systematically reflected; thus, the applicability of the modeling process can be highly enhanced. Four scenarios (including a reference case) are considered based on different energy management policies and sustainable development strategies for in-depth analysis of interactions existing among energy, socio-economy and environment in the Region. Useful solutions for the planning of energy management systems have been generated, reflecting trade-offs among energy-related, environmental and economic considerations. They are helpful for supporting (a) adjustment or justification of the existing allocation patterns of energy resources and services, (b) allocations of renewable energy resources, (c) formulation of local policies regarding energy consumption, economic development and energy structure, and (d) analysis of interactions among economic cost, system efficiency, emission mitigation and energy-supply security. Results also indicate that UREM can help tackle dynamic and interactive characteristics of the energy management system in the Region of Waterloo and can address issues concerning cost-effective allocation of energy resources and services. Thus, it can be used by decision makers as an effective technique in examining and visualizing impacts of energy and environmental policies, regional/community development strategies and emission reduction measures within an integrated and dynamic framework. Copyright © 2008 John Wiley & Sons, Ltd. [source] Unemployment and liquidity constraintsJOURNAL OF APPLIED ECONOMETRICS, Issue 3 2007Vassilis A. Hajivassiliou We present a dynamic framework for the interaction between borrowing (liquidity) constraints and deviations of actual hours from desired hours, both measured by discrete-valued indicators, and estimate it as a system of dynamic binary and ordered probit models with panel data from the Panel Study of Income Dynamics. We analyze a household's propensity to be liquidity constrained by means of a dynamic binary probit model. We analyze qualitative aspects of the conditions of employment, namely whether the household head is involuntarily overemployed, voluntarily employed, or involuntarily underemployed or unemployed, by means of a dynamic ordered probit model. We focus on the possible interaction between the two types of constraints. We estimate these models jointly using maximum simulated likelihood, where we allow for individual random effects along with an autoregressive process for the general error term in each equation. A novel feature of our method is that it allows for the random effects to be correlated with regressors in a time-invariant fashion. Our results provide strong support for the basic theory of constrained behavior and the interaction between liquidity constraints and exogenous constraints on labor supply. Copyright © 2007 John Wiley & Sons, Ltd. [source] A Comparison of Exit and Voice Relationships Under Common UncertaintyJOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 4 2003Herbert Dawid We consider a repeated interaction between a manufacturing firm and a subcontractor. The relationship between the two parties is characterized (1) by moral hazard, and (2) by the fact that they do not have perfect knowledge about the base cost level of the project, which is carried out by a subcontractor (the parties only have identical a priori beliefs). We consider a two-period model where the players can update their estimate of the base cost level according to incoming information. Exit relationships, where the firm signs one-period contracts with different subcontractors, are compared with voice relationships, where both partners commit to a two-period interaction and (due to information sharing and face-to-face communication between the partners) additional information about the base cost level is generated. It is shown that in such a dynamic framework with common uncertainty the quality of the additional information plays a crucial role in determining the characteristics of the optimal relationship: voice-based strategies governed by long-term contracts are preferable if the precision of the additional information about the base cost level is high. If the precision of the additional signal is low, exit strategies with frequent changes of the subcontractors are optimal for the manufacturer. [source] The Organizational Life of an Idea: Integrating Social Network, Creativity and Decision-Making Perspectives*JOURNAL OF MANAGEMENT STUDIES, Issue 6 2007Bob Kijkuit abstract Existing theories on the influence of social networks on creativity focus on idea generation. Conversely, the new product development literature concentrates more on the selection of ideas and projects. In this paper we bridge this gap by developing a dynamic framework for the role of social networks from idea generation to selection. We apply findings from creativity and behavioural decision-making literature and present an in-depth understanding of the sociological processes in the front-end of the new product development process. Our framework builds on the importance of mutual understanding, sensemaking and consensus formation. The propositions focus on both network structure and content and highlight the need to have strong ties and prior related knowledge, to incorporate decision makers, and to move over time from a large, non-redundant and heterogeneous to a smaller and more cohesive network structure. We conclude with a discussion on empirical validation of the framework and possible extensions. [source] Modelling the adoption of organic horticultural technology in the UK using Duration AnalysisAUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 1 2003Michael Burton Duration Analysis, which allows the timing of an event to be explored in a dynamic framework, is used to model the adoption of organic horticultural technology in the UK. The influence of a range of economic and non-economic determinants is explored using discrete time models. The empirical results highlight the importance of gender, attitudes to the environment and information networks, as well as systematic effects that influence the adoption decision over the lifetime of the producer and over the survey period. [source] Kinetic modeling of cellulosic biomass to ethanol via simultaneous saccharification and fermentation: Part I. Accommodation of intermittent feeding and analysis of staged reactorsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009Xiongjun Shao Abstract The model of South et al. [South et al. (1995) Enzyme Microb Technol 17(9): 797,803] for simultaneous saccharification of fermentation of cellulosic biomass is extended and modified to accommodate intermittent feeding of substrate and enzyme, cascade reactor configurations, and to be more computationally efficient. A dynamic enzyme adsorption model is found to be much more computationally efficient than the equilibrium model used previously, thus increasing the feasibility of incorporating the kinetic model in a computational fluid dynamic framework in the future. For continuous or discretely fed reactors, it is necessary to use particle conversion in conversion-dependent hydrolysis rate laws rather than reactor conversion. Whereas reactor conversion decreases due to both reaction and exit of particles from the reactor, particle conversion decreases due to reaction only. Using the modified models, it is predicted that cellulose conversion increases with decreasing feeding frequency (feedings per residence time, f). A computationally efficient strategy for modeling cascade reactors involving a modified rate constant is shown to give equivalent results relative to an exhaustive approach considering the distribution of particles in each successive fermenter. Biotechnol. Bioeng. 2009;102: 59,65. © 2008 Wiley Periodicals, Inc. [source] A hybrid model of anaerobic E. coli GJT001: Combination of elementary flux modes and cybernetic variablesBIOTECHNOLOGY PROGRESS, Issue 5 2008Jin Il Kim Flux balance analysis (FBA) in combination with the decomposition of metabolic networks into elementary modes has provided a route to modeling cellular metabolism. It is dependent, however, on the availability of external fluxes such as substrate uptake or growth rate before estimates can become available of intracellular fluxes. The framework classically does not allow modeling of metabolic regulation or the formulation of dynamic models except through dynamic measurement of external fluxes. The cybernetic modeling approach of Ramkrishna and coworkers provides a dynamic framework for modeling metabolic systems because of its focus on describing regulatory processes based on cybernetic arguments and hence has the capacity to describe both external and internal fluxes. In this article, we explore the alternative of developing hybrid models combining cybernetic models for the external fluxes with the flux balance approach for estimation of the internal fluxes. The approach has the merit of the simplicity of the early cybernetic models and hence computationally facile while also providing detailed information on intracellular fluxes. The hybrid model of this article is based on elementary mode decomposition of the metabolic network. The uptake rates for the various elementary modes are combined using global cybernetic variables based on maximizing substrate uptake rates. Estimation of intracellular metabolism is based on its stoichiometric coupling with the external fluxes under the assumption of (pseudo-) steady state conditions. The set of parameters of the hybrid model was estimated with the aid of nonlinear optimization routine, by fitting simulations with dynamic experimental data on concentrations of biomass, substrate, and fermentation products. The hybrid model estimations were tested with FBA (based on measured substrate uptake rate) for two different metabolic networks (one is a reduced network which fixes ATP contribution to the biomass and maintenance requirement of ATP, and the other network is a more complex network which has a separate reaction for maintenance.) for the same experiment involving anaerobic growth of E. coli GJT001. The hybrid model estimated glucose consumption and all fermentation byproducts to better than 10%. The FBA makes similar estimations of fermentation products, however, with the exception of succinate. The simulation results show that the global cybernetic variables alone can regulate the metabolic reactions obtaining a very satisfactory fit to the measured fermentation byproducts. In view of the hybrid model's ability to predict biomass growth and fermentation byproducts of anaerobic E. coli GJT001, this reduced order model offers a computationally efficient alternative to more detailed models of metabolism and hence useful for the simulation of bioreactors. [source] | |||||||||||||