bluuebunny/crossref_metadata_2025 huggingface dataset:
The economic long wave: Theory and evidence
Authors: Sterman John D.
Published: July 2007

The economic crisis of the 1980s has revived interest in the economic long wave or Kondratiev cycle. Since 1975 the System Dynamics National Model has been the vehicle for the development of a dynamic, endogenous, integrated theory of the economic long wave. This paper describes the integrated theory that has now emerged from extensive analysis of the full National Model and from simple models. Simulations of the model are presented to show the wide range of empirical evidence accounted for by the model, including many of the symptoms of the present economic crisis. In particular, the theory suggests that the long wave arises from the interaction of two fundamental facets of modern industrial economies. First, firms contain inherently oscillatory structures. Second, self‐reinforcing processes amplify the instability. The relative strengths of these mechanisms and the amplification of the long wave through their interactions are discussed, as are the linkages of the longwave theory of innovation, technological progress, social innovation, and political value change.
The role of credit in a rural economy: The case of Thailand
Authors: Ambali Jayaprakashan , Saeed Khalid
Published: July 2007

Rural credit schemes have formed an essential part of the rural development programs implemented in the developing countries over the past few decades, although a high default rate has made it difficult to continue to support them. This paper analyzes the high loan default rate in the rural areas of Thailand and attributes the problem to the distribution pattern of land ownership. The availability of credit may help to fuel investments into farm inputs which increase land productivity. However, when most of the land is absentee‐owned, a large share of the benefits of improved productivity is siphoned away by the landlords while the farmers are left with the responsibility of servicing the loan. Since the farmers' financial capacity is limited, a high rate of loan repayment default results. The analysis of the paper is based on a system dynamics model of a dual rural economic system, often encountered in the developing countries. It is shown that the lack of credit facilities is not a fundamental impediment to rural development.
A system dynamics model for estimating heroin imports into the United States
Authors: Gardiner L. Keith , Shreckengost Raymond C.
Published: July 2007

A small system dynamics model of the heroin supply in the United States has proved useful in estimating heroin imports and anticipating effects of changes in imports. This paper describes the structure of the model and its application to import data over a ten‐year period. Of particular interest is the way in which the model has been used to flag inconsistencies and fill gaps in federal data.
System dynamics models: A tool for strategic planning of flexible assembly systems
Authors: Zahn Erich , Bunz Andreas , Hopfmann Lienhard
Published: July 2007

Notes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaftliches Institut, Abt. IV, Universität Stuttgart, Keplerstr. 17, 7000 Stuttgart 1, West Germany.
Instabilities and chaos in nonlinear dynamic systems
Authors: Mosekilde Erik , Aracil Javier , Allen Peter M.
Published: July 2007

Increasing computational power in the last decade has led to a breakthrough in the understanding of nonlinear dynamic systems. Deterministic chaos, a distinct mode of behavior qualitatively different from linear modes, can arise in systems with instabilities constrained by nonlinearities.

This article overviews this new field. It is observed that deterministic chaos is associated with the presence of a basic instability, often associated with a negative loop with high‐gain and significant delay, that allows small random fluctuations to be amplified and eventually dominate the behavior of the system.

The mathematical tools of qualitative analysis of nonlinear systems are applied to familiar models of urban dynamics. Spatial disaggregation in an urban migration model is shown to yield a route to chaos through period‐doubling. Alternative routes to chaos are discussed. Examples from the natural and social sciences are used to demonstrate the applicability of the tools and the ubiquity of such complex nonlinear dynamic phenomena.
Qualitative analysis of system dynamics ecological models
Authors: Toro Miguel , Aracil Javier
Published: July 2007

This article deals with the application of qualitative analysis techniques to system dynamics ecological models. Examples include the predator‐prey and the Kaibab plateau models. In the former, we study the appearance of periodic motions. Bifurcation analysis allows us to determine the essential parameter that controls the appearance of the limit cycle through a Hopf bifurcation. We also study the limit case in which the model tends to be of the Lotka‐Volterra type.

The Kaibab plateau model shows a collapse related to the limited availability of resources in a finite habitat. When we combine the structure of the predator‐prey and Kaibab models, we obtain a model representing the chain predator‐prey‐food. Such a model can show a huge variety of behavior modes, including chaos, which we analyze.
A note on migratory dynamics
Authors: Richardson George P. , Sterman John D.
Published: July 2007

Notes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universität Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, F.R.G.
The dynamics of shortening working hours
Authors: Zietemann Ulrich D.
Published: July 2007

Unemployment is at present one of the main economic problems in most Western countries. Shortening working hours and lowering retirement age have both been proposed as useful means of reducing this problem. Discussion of these measures has been conducted mainly at the macroeconomic level, however, and the consequences of such policies on the labor market have been evaluated differently by employers' groups and labor unions. These different evaluations clearly reflect conflicting political viewpoints but may also arise from the fact that little economic research has been performed in this field. To assess the economic implications of shortening working hours, the author has undertaken a microeconomic investigation to identify the dynamic consequences, especially on staff recruitment and on labor‐capital substitution. This article describes the basic structure of the system dynamics model applied in the study.
Synthetic data experiments using system dynamics models: A survey of results and a research agenda
Authors: Crawford Catherine M. , Andersen David F. , Richardson George P.
Published: July 2007

In this section the System Dynamics Review presents problems having the potential to stimulate system dynamics research. Articles may address real‐world dynamic problems that could be approached fruitfully from the system dynamics perspective, or methodological problems affecting the field. A paper submitted to the Research Problems section should concisely motivate and define a problem and start a process of conceptualization or formulation that can open the way for further studies. Manuscripts not exceeding 2,000 words should be sent to George P. Richardson, Milne 308, Rockefeller College, S.U.N.Y., Albany, NY 12222, U.S.A.
Interfuel substitution in OECD‐European electricity production
Authors: Moxnes Erling
Published: July 2007

Fuel substitution in OECD‐European electricity production is described by a putty‐clay formulation. At the time of investment, fuel shares are determined according to a logit model. These fuel shares are maintained throughout the lifetime of the power plants. However, a significant share of capacity is assumed to be flexible. Short‐term fuel switching is described by a logit model. An attempt has been made to formulate the model such that all parameters have a real‐life interpetation. This enables the use of a priori data about all parameters. The model gives a very good fit to historical time series for oil, gas, and coal demand when fuel premiums are calibrated. The most striking finding is that there is a strong preference for the use of coal. Because of the a priori data, the model is not very sample‐dependent. Thus, it should be well suited for policy studies or for predictions. The model should be used with caution if very high fuel prices are expected.
A petroleum life cycle model for the United States with endogenous technology, exploration, recovery, and demand
Authors: Davidsen Pål I. , Sterman John D. , Richardson George P.
Published: July 2007

This article describes a model of the life cycle of the petroleum resource in the United States. Expanding on prior system dynamic models of petroleum resources, the model endogenously generates the complete life cycle of the resource. It treats endogenously petroleum demand; the development of technology for, and investment in, exploration and recovery; discovery and production of petroleum; and the development of petroleum substitutes. With only two exogenous variables, GNP and the international petroleum price, the model portrays the evolution of the U.S. petroleum resource, and the associated industry, starting in 1870. The correspondence between simulated and actual data is examined through a variety of statistical measures. The model is used to show how the interaction between technological progress, depletion, imports, and the development of substitutes creates the life cycle by altering the dominance of the feedback processes in the system.
A system dynamics approach to predator‐prey modeling
Authors: Swart Johan
Published: July 2007

Notes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universität Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, F.R.G.
Computer‐based case studies and learning laboratory projects
Authors: Graham Alan K. , Senge Peter M.
Published: July 2007

In this section the System Dynamics Review presents problems having the potential to stimulate system dynamics research. Articles may address real‐world dynamic problems that could be approached fruitfully from the system dynamics perspective, or methodological problems affecting the field. A paper submitted to the Research Problems section should concisely motivate and define a problem and start a process of conceptualization or formulation that can open the way for further studies. Manuscripts not exceeding 2,000 words should be sent to George P. Richardson, Milne 308, Rockefeller College, S.U.N.Y., Albany, NY 12222, U.S.A.
Methodologia oeconomiae et systematis dynamis
Authors: Radzicki Michael J.
Published: July 2007

After enduring years of criticism from members of the economics profession, many system dynamicists have concluded that economists do not like system dynamics. This article outlines the methodologies of both neoclassical and institutional economics and demonstrates that the system dynamics modeling process is strikingly similar to the latter. Because a majority of economists trained in the West are neoclassicals, system dynamicists should not be surprised if many economists label system dynamics models unscientific. And since the institutional approach and the system dynamics approach are similar, it is argued, system dynamics should be used to strengthen and extend institutional economics.
Philosophical roots of model validation: Two paradigms
Authors: Barlas Yaman , Carpenter Stanley
Published: July 2007

System dynamics models, as causal models, are much like scientific theories. Hence, in evaluating such models, we assume certain norms of scientific inquiry. Most critics hold that the system dynamics approach does not employ formal, objective, quantitative model validation tests. This article argues that this type of criticism presupposes the traditional logical empiricist philosophy of science, which assumes that knowledge is an objective representation of reality and that theory justification can be an objective, formal process. According to the more recent relativist philosophy of science, knowledge is relative to a given society, epoch, and scientific world view. Theory justification is therefore a semiformal, relative social process. We show that relativist philosophy is consistent with the system dynamics paradigm and discuss the practical implications of the two philosophies of science for system dynamics modelers and their critics.
Endogenous safety processes: A model of regulation and safety in industrial firms
Authors: Crawford Catherine M.
Published: July 2007

A model of safety and of the impact of the Occupational Safety and Health Administration (OSHA) on safety in industrial firms is described in this article. The model incorporates safety feedback processes in U.S. manufacturing firms, including the relations between safety programs, safety equipment, and accidents. Monte Carlo‐like simulations were produced, with 1,000 firms simulated sequentially. The firms were distributed among the 20 standard industrial sectors and the five size categories that comprise the manufacturing industry. Each firm's safety behavior was simulated for a four‐year period, and each firm was inspected once by OSHA. Injury rates across all firms were measured to determine if OSHA's actions had a measurable effect upon safety in firms. The model captures important underlying assumptions regarding safety regulation that have typically been excluded from evaluations of the impact of safety regulation in the United States. These assumptions may in fact be central to understanding the relations between intervention.
What are we publishing? a view from the editor's desk
Authors: Richardson George P.
Published: July 2007

Notes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universität Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany.
Diagnosing surprise model behavior: A tool for evolving behavioral and policy insights (1981)
Authors: Mass Nathaniel J. , Sterman John D.
Published: July 2007

Founded in the mid‐1950s, the field of system dynamics has intellectual roots reaching much further into the past. The Archives section of the Review seeks to publish material from that past which can contribute to current theory and practice. The section welcomes previously unpublished but deserving system dynamics work, classics from past system dynamics literature that should receive renewed attention, and previously published articles from other disciplines of particular significance to current system dynamicists. Contributions emphasizing the philosophy and theory of model building, validation, implementation, education, and generic structures are particularly encouraged. Submissions may range in length from notes to main articles but may be edited. Send suggested material, together with a brief introduction placing it in historical and current contexts, to John D. Sterman, System Dynamics Group. MIT E40‐294, Cambridge, MA 02139, U.S.A.
Slicing a complex problem for system dynamics modeling
Authors: Saeed Khalid
Published: July 2007

Notes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universitat Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany.

Since formal modeling requires having a model boundary encompassing finite complexity so that deductive logic is possible, complex problems must be partitioned into simpler parts before being analyzed. There are many ways to slice a complex problem but not all create partitions that keep together processes contributing to effective policy design. This paper explores ways in which a complex problem may be appropriately sliced so that the models of partitions can serve as effective tools for policy design.
Benchmarking the system dynamics community
Authors: Scholl Greg J.
Published: July 2007

In this section the System Dynamics Review presents problems having the potential to stimulate system dynamics research. Articles may address real‐world dynamic problems that could be approached fruitfully from the system dynamics perspective, or methodological problems affecting the field. A paper submitted to the Research Problems section should concisely motivate and define a problem and start a process of conceptualization or formulation that can open the way for further studies. Manuscripts not exceeding 2,000 words should be sent to George P. Richardson, Milne 308, Rockefeller College, S.U.N.Y., Albany, NY 12222, U.S.A.
Bringing experimental learning to the social sciences: A simulation laboratory on economic development
Authors: Saeed Khalid
Published: July 2007

This article explores the possibility of introducing experimental learning into the social science disciplines through use of custom‐built experimental media drawing on the system dynamics method. Such learning would essentially require integration of interactive simulation with text materials. A simulation laboratory consisting of a book on issues of economic development and user‐friendly simulation software, developed by the author, is presented as an example of such media. This package may be suitable for use as a graduate text that integrates theory and practicum or as a professional reference tool. The integration of practicum into the teaching of the social sciences would, however, not only require creating new text materials and software suitable for use by students with little computer or mathematics expertise but also modifying teaching formats to accommodate practicum.
Migration on networks and its stability consequences
Authors: Alekseeva Elena I. , Kirzhner Valery M.
Published: July 2007

This article reviews the authors' studies on the behavior of materially coupled dynamic systems. It discusses models of a network of a finite number of localized (pointwise) systems connected through an interaction structure involving migration, diffusion, or other forms of material exchange. On the basis of an analytical criterion for the stabilizing or destabilizing influence of the connecting structure, a classification of possible types of such structures and of the pointwise systems themselves is given.

A model of a multicentric immunodependent tumor is analyzed. Tumor nodules and white blood cells are regarded as localized systems and migrating agents, respectively. We illustrate the possibility of predicting the behavior of the whole multicentric system from the internal parameters in each nodule and discuss the possibility of regulating multicentric tumor growth by controlling the intensity of migration of cells in the body.
Systems thinking/system dynamics: Let's just get on with it
Authors: Richmond Barry
Published: July 2007

The world has many problems. Many of these problems are approaching crisis proportions. The system dynamics community has something very powerful to contribute to addressing these problems—whether we call that something systems thinking or system dynamics. We have not been very effective in sharing what we have to offer because we have failed to truly appreciate the essence of system dynamics. As a result, we have both consciously and unwittingly diluted this essence, and in the process made more difficult the task of disseminating what we have to offer. We need to better understand and appreciate the essence of our field and then focus our energies on the real task at hand: figuring out why this essence seems to be so difficult for people to grasp, and then fixing that.
Varieties of systems thinking: The case of soft systems methodology
Authors: Checkland Peter B. , Haynes Michael G.
Published: July 2007

A number of ways of intervening rationally in human affairs are based on systems thinking: understanding real‐world complexity via systems ideas. This article reviews the development of systems thinking and focuses on one of the systems approaches: Soft Systems Methodology (SSM). It indicates how SSM embodies systems thinking by giving an account of the crucial steps in the thinking as SSM developed. Issues in current work are reviewed by setting out a number of experientially derived generalizations. These concern: SSM as an ideal‐type process that the user suitably adapts on each occasion of use; the fact that SSM's systemicity lies primarily in the process of inquiry; the fact that its focus is the interaction between theory and practice; the implicit belief behind SSM that learning is axiomatically good; and the belief that SSM is best used participatively.
What is systemic thinking?
Authors: Espejo Raul
Published: July 2007

This article elaborates on the historic roots of management cybernetics and its evolving identity. The nature of this evolution is explained by presenting a theory of action in organizations, which makes visible the interplay between people's autonomous actions and their role as observers of these actions. This interplay is referred to as the process of grounding epistemology in ontology. The article then discusses complexity. The idea of distinctions is central, we make distinctions about our experiences. These distinctions define our individual complexity and also our situational complexity as we ground them in shared tasks (i.e., purposeful action). It is argued that creating situational complexity requires managing our interactions and that this management is effective if it gets the best out of us and provides our actions with direction and purpose.
I keep six honest serving men: They taught me all I knew
Authors: Flood Robert L.
Published: July 2007

This article explores the original holistic intent of systems science, its failure to deliver on this because of a fundamental flaw in the genetics of its conception, and the genetic reengineering that can return systems science to its original holistic intent and enter it into the mainstream of scientific theory and everyday practice. The reengineering is called critical systems thinking, and the form of it employed in practice is called total systems intervention.
Putting systems thinking into practice
Authors: Kim Daniel H. , Senge Peter M.
Published: July 2007

The dynamic systems perspective illuminates some of the core challenges in organizational learning. If learning occurs through experience, there are good reasons why organizations often fail to learn. In particular, large organizations face a class of systemic decision‐making situations in which learning is extremely unlikely. The systems perspective teaches us that cause and effect are often not close in time and space, that obvious interventions do not always produce obvious outcomes, and that long time delays, and systemic effects of actions can make it almost impossible to judge the effectiveness of those actions. This article presents a framework for organizational learning, outlines several breakdowns that thwart the learning process, and discusses how systems thinking can play an important role in helping organizations overcome the learning breakdowns through the design and implementation of managerial practice fields.
Learning in and about complex systems
Authors: Sterman John D.
Published: July 2007

Change is accelerating, and as the complexity of the systems in which we live grows, so do the unanticipated side effects of human actions, further increasing complexity. Many scholars call for the development of systems thinking to improve our ability to manage wisely. But how do people learn in and about complex dynamic systems? Learning is a feedback process in which our decisions alter the real world, we receive information feedback about the world and revise the decisions we make and the mental models that motivate those decisions. Unfortunately, in the world of social action various impediments slow or prevent these learning feedbacks from functioning, allowing erroneous and harmful behaviors and beliefs to persist. The barriers to learning include the dynamic complexity of the systems themselves; inadequate and ambiguous outcome feedback; systematic mispercep‐tions of feedback; inability to simulate mentally the dynamics of our cognitive maps; poor interpersonal and organizational inquiry skills; and poor scientific reasoning skills. To be successful, methods to enhance learning about complex systems must address all these impediments. Effective methods for learning in and about complex dynamic systems must include (1) tools to elicit participant knowledge, articulate and reframe perceptions, and create maps of the feedback structure of a problem from those perceptions; (2) simulation tools and management flight simulators to assess the dynamics of those maps and test new policies; and (3) methods to improve scientific reasoning skills, strengthen group process, and overcome defensive routines for individuals and teams.
Pictorial modeling of dynamic systems
Authors: Camara António S. , Ferreira Francisco C. , Nobre Edmundo , Fialho José E.
Published: July 2007

The world may be considered to consist of interacting objects. An object‐oriented view is missing, however, in traditional system dynamics models. An attempt to develop a simulation methodology based on this view and using extended cellular automata principles is documented in this article. This methodology relies on pictorial entities representing real or abstract objects and a set of intuitive behavior and interaction rules. A simple predator‐prey model shows how such a pictorial simulation approach compares with traditional system dynamics models.
Modeling spatial dynamics of sea‐level rise in a coastal area
Authors: Ruth Matthias , Pieper Frederick
Published: July 2007

This article illustrates the development and functioning of a dynamic spatial model that simulates the effects of gradual sea‐level rise on coastal areas. Emphasis is given to identifying the dynamics of coastal systems and translating them into a spatially explicit dynamic simulation model. The model is designed to be flexible enough to serve as a base model for interdisciplinary research on sea‐level rise and coastal dynamics. An application is provided for a coastal area on Cape Cod, Massachusetts.
Exemplary urban model for Fernbank Museum of Natural History
Authors: Braden Charles H.
Published: July 2007

Notes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universität Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany.
Efficient methods for sensitivity analysis
Authors: Clemson Barry , Tang Yongming , Pyne James , Unal Resit
Published: July 2007

Sensitivity analysis is usually difficult because to test exhaustively too many trials are required for the available time, money, or patience. This article discusses Latin hyper‐cube sampling and Taguchi methods, both of which are methods for experimental design that allow testing of all combinations of parameter values with a manageable number of trials. The procedures for use of the Taguchi methods are presented in some detail.
Benchmarking the system dynamics community: Research results
Authors: Scholl Greg J.
Published: July 2007

This article reports on the findings of a wide‐ranging study designed to ‘benchmark’ the system dynamics community. The study captured information about individual practitioners across a number of dimensions, including background, approach to and practice of model building, use of hardware and software and knowledge of the history and development of the field. Circulated to all members of the System Dynamics Society, the study attracted responses from 163 members (over 35 percent). The following pages present research results and discuss their possible implications. In particular, important conclusions highlight a potential quality gap in the model base, postulate a relationship between pedagogy and practice and begin a dialog concerning the dynamics of supply and demand in the field.
Projecting dynamic behavior in the absence of a model: An experiment
Authors: Dangerfield Brian , Roberts Carole
Published: July 2007

Notes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universitát Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany or to Yaman Barlas, Dept. of Industrial Engineering, Bogazici University, 80815 Bebek, Istanbul, Turkey.
Urban dynamics—the first fifty years
Authors: Alfeld Louis Edward
Published: July 2007

Twenty‐five years have passed since the publication of Jay W. Forrester's Urban Dynamics. Any assessment of the condition of America's cities today raises the question of what might have been had the model and the methodology been accepted as a central urban planning and policy tool. Instead of looking backward at what might have been, however, it seems more useful to look ahead at what still may be. Urban dynamics still has a role to play in our urban future; this article provides a backdrop for how that role might best be shaped.
Designing corporate strategy with system dynamics: A case study in the pulp and paper industry
Authors: Risch Jonathan D. , Sterman John D. , Troyano‐Bermúdez Luis
Published: July 2007

We describe the use of system dynamics tools and processes to assist a major integrated forest products company develop its strategy. The firm had recently acquired a major pulp and paper mill and had entered a new market, the specialty paper business. However, despite substantial investment, the mill was losing money, contrary to expectations. We drew on established strategic frameworks, using system dynamics to integrate the data generated by traditional analyses. Through internal and external interviews, archival data, site visits, and analysis of the market place, we develop a representation of management's collective mental model, showing the feedback processes they believed would lead to success in the specialty market. We then develop a dynamic hypothesis, explicated in the form of causal loop diagrams, to explain the failure of the firm's strategy to yield profitable operation for the mill. We show how management underestimated a variety of side effects of the new strategy, both at the market level and in the mill. These side effect feedbacks undercut the intended effect of the new strategy. We describe the theory, data, and process, including current steps the firm is undertaking to implement the results emerging from the study.
Sensitivity analysis and optimization of system dynamics models: Regression analysis and statistical design of experiments
Authors: Kleijnen Jack P. C.
Published: July 2007

This paper discusses what‐if analysis and optimization of system dynamics models. These problems are solved, using the statistical techniques of regression analysis and Design of Experiments (DOE). These issues are illustrated by applying the statistical techniques to a system dynamics model for coal transportation, taken from Wolstenholme's book System Enquiry: a System Dynamics Approach (1990). The regression analysis uses the least‐squares algorithm. DOE uses classic designs, namely, factorials and central composite designs. Compared with intuitive approaches, DOE is more efficient: DOE gives more accurate estimators of input effects. Moreover DOE is more effective: interactions among inputs are estimable too. The system dynamics model is also optimized, using a heuristic that is inspired by Response Surface Methodology (RSM) but that also accounts for constraints. Conclusions are presented for the case study, and general principles are derived. References are given for further study.
Edutainment, learning and system dynamics
Authors: Langley Paul A. , Larsen Erik R.
Published: July 2007

Notes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaftlic hes Institut, Abt. IV, Universität Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany or to Yaman Barlas, Dept. of Industrial Engineering, Bogazici University, 80815 Bebek, Istanbul, Turkey.
Dietary zinc deficiency lowers the proportions of splenic CD90+(Thy-1+) B-cells and late thymic emigrant T-cells in growing rats
Authors: Hosea Heather J. , Rector Edward S. , Taylor Carla G.
Published: July 2007

Zn-deficient (ZD) rats have a lower proportion of splenic CD90+T-cells which could be due to fewer new T-cells exiting the thymus, defective post-thymic maturation or increased cell death. Post-thymic maturation of splenic lymphocytes and their viability were determined by flow cytometry in weanling rats assigned to ZD ( < 1 mg Zn/kg;ad libitum), diet-restricted (DR; 30 mg Zn/kg; limited to the amount of feed as consumed by ZD rats), marginally Zn-deficient (MZD; 10 mg Zn/kg;ad libitum) or control (30 mg Zn/kg;ad libitum) groups for 3 weeks. ZD rats had a 29 % lower percentage of splenic CD90+T-cells and both ZD and DR rats had a 30 % lower proportion of splenic CD90+B-cells compared with control rats. When the splenic CD90+T-cells were characterised further, there was no difference among the groups in the first two stages of post-thymic development; however, ZD, DR and MZD rats had a 42 % lower proportion of late thymic emigrants (TCRαβ+CD90+CD45RC+RT6.1+) compared with control rats. There was no difference among groups in the proportion of splenic CD90+T-cells in the non-viable region; however, ZD rats had a higher proportion of CD90+B-cells in the non-viable region compared with MZD and control animals, suggesting that this phenotype was more susceptible to cell death during deficiency. The lower proportion of splenic CD90+T-cells in ZD rats does not appear to be due to a defect in thymic production or increased cell death in the spleen. Future studies should determine if late thymic emigrants have homed to other peripheral organs.
Intestinal, hepatic, splanchnic and hindquarter amino acid and metabolite partitioning during an establishedTrichostrongylus colubriformisinfection in the small intestine of lambs fed fresh Sulla (Hedysarum coronarium)
Authors: Bermingham Emma N. , McNabb Warren C. , Sutherland Ian A. , Sinclair Bruce R. , Treloar Bryan P. , Roy Nicole C.
Published: July 2007

Increased partitioning of amino acids (AA) from skeletal muscle to the intestine and immune system during parasitic infection may be the cause of poor growth in parasitised animals. The effect of an establishedTrichostrongylus colubriformisinfection (6000 L3T. colubriformislarvae for 6 d (n5) or kept as parasite-free controls (n6)) on AA fluxes across the mesenteric-drained viscera, portal-drained viscera (PDV), liver, total splanchnic tissues (TSP) and hindquarters were determined in lambs fed fresh Sulla (Hedysarum coronarium; 800 g DM/d) 48 d post-infection. The lambs were infused with ρ-aminohippuric acid (PAH; 723 mg/h) into the mesenteric vein for 8 h to measure TSP plasma flow. Concurrently, indocyanine green (ICG; 14·6 mg/h) was infused into the abdominal aorta to measure plasma flow across the hindquarters. Blood was continuously collected from the mesenteric, portal and hepatic veins, vena cava and the mesenteric artery and plasma harvested. PAH, ICG, AA, metabolite and insulin concentrations were measured. Intestinal worm burdens on day 48 post-infection were higher in the infected lambs (P < 0·05). Plasma flows across the tissue beds were unaffected by parasitic infection (P>0·10). There was a 28 % reduction in the release of AA from the PDV of infected lambs (P < 0·05). The uptakes of most AA were similar in the liver; however, there was increased uptake (P < 0·10) of AA by the TSP of infected lambs. Despite this reduction in AA availability at the liver, there was no effect of parasitic infection on AA uptake across the hindquarters (P < 0·05).
Tectonic significance of Late Triassic post-collisional lamprophyre dykes from the Qinling Mountains (China)
Authors: WANG XIAOXIA , WANG TAO , JAHN BOR-MING , HU NENGGAO , CHEN WEN
Published: July 2007

The Qinling–Dabie orogen in central China is one of the major orogenic belts in East Asia. In the eastern Dabie–Sulu region, mafic lamprophyres show the enriched signatures of old sub-continental lithospheric mantle. However, little is known about the mafic igneous rocks and their lithospheric mantle sources in the western Qinling Range. New 40Ar–39Ar age dating, major- and trace-element data, and isotopic analyses of Qinling lamprophyres reveal their differences from the Dabie Sulu lamprophyres. Biotite 40Ar–39Ar dating yielded a plateau age of 219±2 Ma, identical to the ages of rapakivi-textured granitoids in the area. The association of lamprophyre dykes and rapakivi-textured granitoids indicates that the Qinling region was a post-collisional setting at c. 220 Ma. The Qinling lamprophyres are calc-alkaline, and rich in large ion lithophile elements (e.g. Ba, K), but depleted in Nb, Ta and Ti. They show highly fractionated REE patterns with LaN>100 and HREE <10 times chondrite abundances. εNd (219 Ma) values range from −0.5 to −3.3 and initial Sr isotope values from 0.7036 to 0.7058. These features suggest generation of the lamprophyre by partial melting of a metasomatized, garnet peridotite mantle source. The Qinling lamprophyres are distinct from the Dabie–Sulu lamprophyres in emplacement age (c. 135 Ma for Dabie–Sulu) and isotopic composition, suggesting that the nature of the lithospheric mantle and geodynamic evolution of the Qinling region contrasts with that of the Dabie–Sulu region.
Effectiveness of transmeatal low power laser irradiation for chronic tinnitus
Authors: Gungor A , Dogru S , Cincik H , Erkul E , Poyrazoglu E
Published: July 2007

Objective:

To evaluate effectiveness of 5 mW laser irradiation in the treatment of chronic tinnitus.

Study design:

Prospective, randomised, double-blind study.

Methods:

This investigation included 66 ears in 45 patients with chronic unilateral or bilateral tinnitus. A 5 mW laser with a wavelength of 650 nm, or placebo laser, was applied transmeatally for 15 minutes, once daily for a week. A questionnaire was administered which asked patients to score their symptoms on a five-point scale, before and two weeks after laser irradiation. A decrease of one scale point, regarding the loudness, duration and degree of annoyance of tinnitus, was accepted to represent an improvement.

Results:

The loudness, duration and degree of annoyance of tinnitus were improved, respectively, in up to 48.8, 57.7 and 55.5 per cent of the patients in the active laser group. No significant improvement was observed in the placebo laser group.

Conclusion:

Transmeatal, low power (5 mW) laser irradiation was found to be useful for the treatment of chronic tinnitus.
Serum leptin levels in patients with nasal polyposis
Authors: Guven M , Bulut Y , Aladag I , Yelken K , Erdoğan H
Published: July 2007

Background:

Nasal polyposis is one of the most common inflammatory pathologies of the nasal cavity. The aetiopathogenetic mechanisms of nasal polyp formation are still unclear.

Objectives:

The aim of this study was to investigate the serum leptin levels in patients with nasal polyposis.

Design:

A randomised, prospective study was performed of 28 adult patients with nasal polyposis and 22 control subjects of a similar age, sex and body mass index.

Results:

Serum leptin levels were 12.10 ± 9.39 ng/ml in the nasal polyposis patients and 6.17 ± 7.68 ng/ml in the controls. A significant difference (p = 0.021) was observed in the mean serum leptin levels between nasal polyposis patients and controls.

Conclusion:

Serum leptin levels were found to be significantly higher in patients with nasal polyposis. Leptin, apart from its primary role in the regulation of body weight and energy expenditure, may have a role in the inflammatory response of nasal polyposis.
Global structure of solutions for equations of Brezis–Nirenberg type on the unit ball
Authors: Kabeya Yoshitsugu , Yanagida Eiji , Yotsutani Shoji
Published: July 2007

The Brezis–Nirenberg equation and the scalar field equation on the three-dimensional unit ball are studied. Under the Robin condition, we show the existence and uniqueness of radial solutions in a unified way. In particular, it is shown that the global structure of solutions changes qualitatively when a parameter in the boundary condition exceeds a certain critical value.
Bifurcation for some quasilinear operators
Authors: Arcoya David , Carmona José , Pellacci Benedetta
Published: July 2007

This paper deals with existence, uniqueness and multiplicity results of positive solutions for the quasilinear elliptic boundary-value problem
,
where Ω is a bounded open domain in RN with smooth boundary. Under suitable assumptions on the matrix A(x, s), and depending on the behaviour of the function f near u = 0 and near u = +∞, we can use bifurcation theory in order to give a quite complete analysis on the set of positive solutions. We will generalize in different directions some of the results in the papers by Ambrosetti et al., Ambrosetti and Hess, and Artola and Boccardo.
The spectral boundary of complemented invariant subspaces in Lp(R)
Authors: Buczolich Zoltán , Olevskiĭ Alexander
Published: July 2007

In this paper we construct a compact set K of zero Hausdorff dimension that satisfies certain ‘arithmetic-type’ thickness properties. The concept of ‘arithmetic thickness’ has its origins in applications to harmonic analysis, introduced in a paper by Lebedev and Olevskiĭ. For example, there are no spectral sets whose ‘essential boundary’ can contain the above set K.
Bifurcation from the essential spectrum without sign condition on the nonlinearity
Authors: Kunze M.
Published: July 2007

We study a problem from nonlinear optics that leads to an integro-differential equation which can be written as the abstract bifurcation problem Au = λLu + ∇φ(u). For such a type of equation, a general theorem on the bifurcation of solutions from the essential spectrum is proved. The hypothesis that φ is non-negative (as is usually assumed) could be omitted and replaced by other conditions that allow us to use the results for the particular example. We also indicate applications to semilinear elliptic equations.
On the Yosida approximation of operators
Authors: Penot Jean-Paul , Ratsimahalo Robert
Published: July 2007

A generalized Yosida approximation of monotone (and non-monotone) operators in Banach space is introduced. It uses a general potential that is not necessarily the square of the norm. It is therefore advisable to use it in cases where some other more convenient potentials are available, such as in Lp-spaces. As an illustration, the case of Nemyckii operators is considered.
On a theorem of Cohen and Montgomery for graded rings
Authors: Kelarev A. V.
Published: July 2007

Giving as answer to Bergman's question, Cohen and Montgomery proved that, for every finite group G with identity e and each G-graded ring R = ⊕g∈GRg, the Jacobson radical J(Re) of the initial component Re is equal to Re ∩ J(R). We describe all semigroups S, which satisfy the following natural analogue of this property: J(Re) = Re ∩ J(R) for each S-graded ring R = ⊕s∈SRs and every idempotent e ∈ S.
Minimal blow-up asymptotics of quasilinear heat equations
Authors: Chaves M. , Galaktionov Victor A.
Published: July 2007

We study the asymptotic properties of blow-up solutions u = u(x, t) ≥ 0 of the quasilinear heat equation
,
where k(u) is a smooth non-negative function, with a given blowing up regime on the boundary u(0, t) = ψ(t) > 0 for t ∈ (0, 1), where ψ(t) → ∞ as t → 1−, and bounded initial data u(x, 0) ≥ 0. We classify the asymptotic properties of the solutions near the blow-up time, t → 1−, in terms of the heat conductivity coefficient k(u) and of boundary data ψ(t); both are assumed to be monotone. We describe a domain, denoted by , of minimal asymptotics corresponding to the data ψ(t) with a slow growth as t → 1− and a class of nonlinear coefficients k(u).

We prove that for any problem in S11−, such a blow-up singularity is asymptotically structurally equivalent to a singularity of the heat equation ut = uxx described by its self-similar solution of the form u*(x, t) = −ln(1 − t) + g(ξ), ξ = x/(1 − t)1/2, where g solves a linear ordinary differential equation. This particular self-similar solution is structurally stable upon perturbations of the boundary function and also upon nonlinear perturbations of the heat equation with the basin of attraction .
A new approach to analyticity of Dirichlet-Neumann operators
Authors: Nicholls David P. , Reitich Fernando
Published: July 2007

This paper outlines the theoretical background of a new approach towards an accurate and well-conditioned perturbative calculation of Dirichlet-Neumann operators (DNOs) on domains that are perturbations of simple geometries. Previous work on the analyticity of DNOs has produced formulae that, as we have found, are very ill-conditioned. We show how a simple change of variables can lead to recursions that satisfy analyticity estimates without relying on subtle cancellation properties at the heart of previous formulae.
Some interpolation results that are the exclusive property of compact operators
Authors: Cobos Fernando , Fernández-Cabrera Luz M. , Martínez Antón , Pustylnik Evgeniy
Published: July 2007

We show that certain interpolation results for compact operators established by Cobos and co-workers cannot be extended to general closed operator ideals. We shall also characterize compactness of an embedding in terms of functions related to the classical K- and J-functionals of interpolation theory.
Convergence of diffusive BGK approximations for nonlinear strongly parabolic systems
Authors: Lattanzio Corrado , Natalini Roberto
Published: July 2007

We study a class of BGK approximations of parabolic systems in one space dimension. We prove stability and existence of global solutions for this model. Moreover, under certain conditions, we prove a rigorous result of convergence toward the formal limit, by using compensated compactness techniques.