bluuebunny/crossref_metadata_2025 huggingface dataset:
Emitter design for high‐efficiency silicon solar cells. Part 2: Space cells
Authors: Wang Aihua , Zhao Jianhua , Green M. A.
Published: July 2007

Over the last decade there have been substantial improvements in the performance of silicon solar cells. This second part of a two‐part paper examines the implications for use in space. High‐efficiency cells, including cells of above 20% Air Mass 0 efficiency were exposed to 1 MeV of electron irradiation. Although the relative performance loss was higher, the cells gave higher performance than conventional silicon space cells even after 5 × 1015cm−21‐MeV electron radiation damage. However, spectral response measurement shows that the rapid degradation mainly came from damage on the emitter surface. This can be accommodated simply by shallow emitter designs. the efficiency of an optimized silicon space cell is expected to be over 14% after 1 × 1015cm−21 MeV electron radiation.
A general battery model for PV system simulation
Authors: Copetti J. B. , Lorenzo E. , Chenlo F.
Published: July 2007

A battery model is proposed as a tool to simulate and optimize photovoltaic (PV) / storage systems. the normalized form of the equations with respect to the battery capacity allows us to generalize its use for any type and size of lead‐acid batteries.

The validity of this model to represent the battery voltage evolution during charge, overcharge and discharge processes and to predict the performance of solar systems under different operational conditions is analysed. Moreover, the battery efficiency losses are presented as a function of the upper regulation thresholds of the charge controllers and the size of the array and storage systems in a domestic application in the climate of Madrid.
Solar cell efficiency tables (version 3)
Authors: Green Martin A. , Emery Keith
Published: July 2007

Tabulations of confirmed efficiencies for a range of photovoltaic cell and module technologies are updated to include recent results (since mid‐1993). Also described are the results of two informal ‘round‐robin’ comparisons of cell and module measurements from a representative sampling of the designated test centres participating in the compilation of these tables.
Fault detection in a photovoltaic plant by time domain reflectometry
Authors: Schirone L. , Califano F. P. , Pastena M.
Published: July 2007

A reflectometric technique has been developed for diagnostic monitoring of a photovoltaic plant. Detailed information on the position and type of fault is inferred from the shape of the voltage waveforms resulting when a pulsed voltage excitation is applied to a string consisting of several series‐connected modules. When an open circuit or a short circuit to ground are occurring, direct reading of the results is obtained by means of a software tool performing numerical analysis of the digitized waveforms. Extensions of this approach to the case of parallel‐connected strings, as well as to the cases of a loaded plant and no illumination, are discussed.
Towards high‐eficiency silicon solar cells by rapid thermal processing
Authors: Hartiti B. , Schindler R. , Slaoui A. , Wagner B. , Muller J. C. , Reis I. , Eyer A. , Siffert P.
Published: July 2007

Rapid thermal processing can offer many advantages, such as small overall thermal budget and low power and time consumption, in a strategy focused on cost‐effective techniques for the preparation of solar cells in a continuous way. We show here that this very short duration (a few tens of seconds) of isothermal heating performed in a lamp furnace can be used for many thermal steps of silicon solar cell processing. Rapid thermal processing was applied to form the p‐n junction from a phosphorus‐doped spin‐on silica film deposted on (100) silicon substrates at typical processing temperatures between 800 and 1100°C. the solar cells showed conversion efficiencies as good as those processed in a conventional way.
7000 high‐eficiency cells for a dream
Authors: Verlinden P. J. , Swanson R. M. , Crane R. A.
Published: July 2007

This paper reports on the fabrication of high‐eficiency back‐side contact silicon solar cells in large volume for the '93 World Solar Challenge. the cells were used exclusively on the winning car, the Dream, made by Honda R&D Company, Ltd. the cell efficiencies were between 20% and 22% (AMI.5G, 25°C) (G = global) and the average cell efficiency was greater than 21%. an important program of quality control was necessary to maintain a tight efficiency distribution and a high fabrication yield.
Thin‐film solar cells
Authors: Bloss W. H. , Pfisterer F. , Schubert M. , Walter T.
Published: July 2007

The R&D status of cells and modules based on hydrogenated amorphous silicon (a‐Si:H) and those based on CdTe and CuInSe2is reviewed.

The stability of a‐Si:H solar cells is still a major concern. Improvements have been achieved on an empirical basis by application of multijunction structures, optimization of interfaces, etc. Stabilized efficiencies of close to 10% have been reported. In parallel, the introduction of the ‘defect‐pool model’ led to remarkable progress in understanding; it follows that a‐SiGe:H instead of a‐Si:H should be used for the i‐layer (absorber). Improved cell engineering concepts, however, such as enhancement of the built‐in electric field via reduction of the i‐layer thickness and/or folded structures, are believed to be more promising.

Polycrystalline thin‐film cells based on CdTe and CuInSe2are not affected by inherent degradation mechanisms. the specific properties of these materials demand heterojunctions, and particular problems arise due to the polycrystallinity of the films and to the lattice mismatch and mismatch of the electronic band structures of the materials involved. These are discussed in conjunction with measures currently applied for optimizing solar cell performance. Both cell types exhibit eficiencies in the range 16‐17%.

Estimations of production costs and energy payback times of thin‐film photovoltaic modules are reviewed (even below 1 US$ Wp−1and as low as 4 months, respectively) and environmental concerns, especially for Cd‐containing cells, are summarized.
Coupling of light into mechanically textured silicon solar cells: A ray tracing study
Authors: Brendel R.
Published: July 2007

Light coupling into mechanically textured, encapsulated silicon solar cells is studied by three‐dimensional comprehensive ray tracing with our newly developed programme SUNRAYS. We analyse periodic textures with symmetric and non‐symmetric pyramids and grooves. the facet angles of the textures are varied systematically. the study considers the apparent daily motion of the sun and diffuse illumination. SUNRAYS accounts for the dependence of reflection and transmission on the wavelength, the angle of incidence and the polarization of light. As a result of basic interest, we show that the maximum average path length theoretically possible under isotropic illumination is actually achieved by numerous trapping schemes. As a result of practical interest, we demonstrate the outstanding performance of the simple prism groove texture, which yields a large current density while preserving a small surface when compared to all other textures investigated.
Optimum design of integrated tandem‐type a‐Si solar cell submodule
Authors: Nishiwaki Hidenori , Sakai Souichi , Haku Hisao , Ohnishi Michitoshi
Published: July 2007

A new optimum design, in which the actual daily spectral data under outdoor conditions over a year were considered, was developed for the integrated tandem‐type a‐Si solar cell submodule with a structure of glass/TCO/a‐Si: H(pinpin)/metal. It was found by this design that the optimum cell number connected in series, at which maximum total annual output power was obtained, was small compared with that obtained by the conventional optimum design under standard conditions (AM1.5, 100 mW cm−2). It was also found that when light‐induced degradation was considered, the thickness of the i‐layer for the second pin cell was thinner than that by the conventional optimum design.
Photovoltaic system simulation using a standard electronic circuit simulator
Authors: Castañer Luis , Aloy Raimond , Carles Daniel
Published: July 2007

An approach to photovoltaic (PV) system simulation is presented based on the use of SPICE instead of using a specifically developed software package. SPICE models for PV cells, PV modules, lead‐acid batteries and the rest of the main components of a PV system have been developed. A simulation example of a stand‐alone PV system including measured irradiance data as an input is used to show some of the possibilities inherent in such an approach. Greater flexibility, quick access to all voltages and currents within the system and a simpler way of interfacing with standard electronic components are the main conclusions to be drawn from this work.
Photovoltaic‐powered piston‐type water pump controlled by a linear motor
Authors: Perris Carol , Salameh Ziyad
Published: July 2007

This paper presents a unique technique to control a photovoltaic (PV)‐powered piston‐type water pump. the method uses a linear motor mounted directly onto the piston rod of the pump. This linear motor method replaces the traditional piston‐type water pump, which employs a DC motor with a bulky gear mechanism to convert the rotational motion of the motor to linear motion for the piston.

The electric circuit used to control the linear motor employs a four‐quadrant chopper, which uses four fast MOSFETs and a simple logic circuit for the switching.

The experimental results show that the PV‐powered linear motor system can be used as an alternative to the PV‐powered DC motor gear system.
The individual effects of total quality management on customers, people and society results and quality performance in SMEs
Authors: Claver Enrique , Tarí Juan José
Published: July 2007

The aim of this paper is to test the individual effects of total quality management (TQM) on customer results, people results, society results and quality performance in a small‐ and medium‐sized enterprise (SME) context. The research is based on information from 85 ISO 9000 certified SMEs in Spain. A number of regression analyses are applied in order to examine the impact of TQM on these four results and identify which factors of TQM have the greatest effect. After analysing the survey data, 10 SMEs were randomly selected for individual visits, in order to check the results. The results show that TQM may improve customer results, people results, society results and quality performance. TQM factors related to training and specialist training are showed to be the most significant predictors of quality outcomes. The contribution of this paper is to study this association in SMEs in Spain. Copyright © 2007 John Wiley & Sons, Ltd.
A simple model matching for the stabilization of an inverted pendulum cart system
Authors: Aguilar‐Ibañez Carlos Fernando , Frias Oscar Octavio Gutiérrez
Published: July 2007

We present a simple model matching controller for the stabilization of the inverted pendulum cart system, assuming that the pendulum is initialized above the horizontal plane. The control strategy consists of forcing the closed‐loop system to behave as another nonlinear target system with some stability properties. To this end, we solve two matching conditions that allow us to shape a suitable target system. Having satisfied both matching conditions, the stabilizing controller is directly obtained from the proposed target system. The obtained close‐loop system is locally asymptotically exponentially stable, with a very large domain of attraction. Copyright © 2007 John Wiley & Sons, Ltd.
Efficient routing of multiple vehicles with no explicit communications
Authors: Arsie Alessandro , Frazzoli Emilio
Published: July 2007

In this paper, we consider a class of dynamic vehicle routing problems, in which a number of mobile agents in the plane must visit target points generated over time by a stochastic process. It is desired to design motion coordination strategies in order to minimize the expected time between the appearance of a target point and the time it is visited by one of the agents. We propose control strategies that, while making minimal or no assumptions on communications between agents, provide the same level of steady‐state performance achieved by the best‐known decentralized strategies. In other words, we demonstrate that inter‐agent communication does not improve the efficiency of such systems, but merely affects the rate of convergence to the steady state. Furthermore, the proposed strategies do not rely on the knowledge of the details of the underlying stochastic process. Copyright © 2007 John Wiley & Sons, Ltd.
Synthetic design of policy decisions in system dynamics models: A modal control theoretical approach
Authors: Mohapatra Pratap K. J. , Sharma Sushil K.
Published: July 2007

Researchers and practitioners in system dynamics usually follow a trial‐and‐error process to design new policy decisions. They mainly use influence diagrams for this purpose. However, these diagrams portray the direction of influence but not its strength. Therefore, the process of policy design becomes time‐consuming, especially for beginners and those working with insufficient computer facilities. This paper presents an alternative approach for policy design using modal control theory. Policy variables are treated as control variables by delinking them from other variables. This generally leads to greatly simplified models that are free from many nonlin‐earities. Provided that this reduced system is linear and controllable, it is possible to synthetically generate control policies by modal control theory to ensure any prescribed degree of stability. These theoretical control policies then can be used to design realistic policy decisions. This approach has been used in a test example.
The use of optimization methods for policy design in a system dynamics model
Authors: Coyle R. Geoffrey
Published: July 2007

Optimization methods have the potential to improve the processes of policy analysis and design in system dynamics models. To demonstrate the use of optimization approaches, this article applies routines developed by Keloharju to a simple model of unstable inventory dynamics. Policies derived from the optimization approach are compared with policies obtained in earlier, more intuitive analyses. The results suggest that optimization methods could significantly improve both the speed and power of policy analysis in formal models.
“The” model versus a modeling “process”
Authors: Forrester Jay W.
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, M.I.T. E40–294, Cambridge, MA 02139, U.S.A.
Dominant structure
Authors: 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.
Methods of conceptualization
Authors: Mass Nathaniel J.
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, M.I.T. E40‐294, Cambridge, MA 02139, U.S.A.
Solving economic optimal control problems with system dynamics
Authors: Kivijärvi Hannu , Tuominen Markku
Published: July 2007

Considering a simple production system, this paper presents an alternative method based on system dynamics for solving economic and managerial optimal control problems. Such an approach can be helpful in cases where the application of the mathematical optimal control theory is impossible or too laborious for planners or decision makers.
Distribution of body fluids, plasma protein, and sodium in dogs: A system dynamics model
Authors: Hansen Jan E. , Bie Peter
Published: July 2007

A whole‐body model of the microvascular and lymphatic transfer of fluid and plasma protein in dogs is presented. The model includes five compartments corresponding to well‐defined fluid spaces in the body: plasma, interstitial, lymphatic, erythrocyte, and cellular compartments. The transcapillary solute and solvent fluxes are computed from the Kedem‐Katchalsky and Patlak‐Bresler equations, respectively. A quantitative application of interstitial volume‐dependent exclusion of macromolecules is also included. Good agreement is found between simulated quantities and experimental data from conscious dogs in steady state and during two protocols of acute hypotonic overhydration. The model is a means of obtaining detailed quantitative descriptions of interactions between capillary and interstitial parameters that cannot be assessed experimentally.
14 “obvious truths”
Authors: Forrester Jay W.
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, M.I.T. E40‐294, Cambridge, MA 02139, U.S.A.
Chaotic structures in generic management models: Pedagogical principles and examples
Authors: Andersen David F. , Sturis Jeppe
Published: July 2007

Recently published evidence suggests that deterministic chaos may be one of the possible modes in a number of commonly occurring structures in ecological, biological, macroeconomic, and managerial systems. Teaching bifurcations and chaos may therefore be an important part of the system dynamics curriculum. In this paper we present a catalog of structures for teaching lessons about chaos in an introductory system dynamics course. The catalog begins with a simple work force inventory oscillator and culminates with a fully chaotic structure. Techniques and principles for presenting chaos in the classroom and for formulating classroom examples are discussed.
Using system dynamics for conservation policy analysis in the Pacific Northwest
Authors: Ford Andrew , Bull Michael
Published: July 2007

The Bonneville Power Administration uses system dynamics to assist in its analysis of conservation policies for the Pacific Northwest electric system. This article describes the system dynamics models—the Conservation Policy Analysis Models—and explains why they are useful. After briefly describing model design and assumptions, the article gives examples of model application. One example involves simulation studies of a hypothetical policy by contractors. The second example involves Bonneville's own study of policies under consideration in the 1986 resource strategy. Key features that have made the models useful at Bonneville are noted.
Control theory heuristics for improving the behavior of economic models
Authors: Özveren Cüneyt M. , Sterman John D.
Published: July 2007

The usefulness of control theory techniques in economic simulations is examined. A model of the capital investment accelerator is used for illustration. It is shown that behavior approaching optimality can be achieved in a highly nonlinear system with simple heuristics based on linearization and constant state feedback with an appropriate choice of desired closed‐loop poles. Applications to real‐life situations are discussed, and suggestions are made for approaching potential problems using similar control theory techniques.
A reference approach for policy optimization in system dynamics models
Authors: Macedo Julio
Published: July 2007

In this article we develop a formal method, the reference approach, that can be used as a tool for policy optimization in a system dynamics model. The obtained policy is expressed in terms of feedback loops, which master the behavior of the system so that it reaches a dynamic according to the objectives of the designer.

The reference approach utilizes three models: a system dynamics model, a reference model, and a control model. The first one is built using Forrester's principles. The second is a large optimization nonlinear model whose solution yields the dynamic desired by the planner. The third is a linear quadratic optimal control model with closed‐loop solution, which minimizes the gap between the observed dynamic (in the system dynamics model) and the desired dynamic expressed by the reference model.

We illustrate the operation of the reference approach by using it to find the optimal policy of a well‐known system dynamics model. For this same model the best policy obtained with a heuristic approach is known. Finally, we compare the performance of these two policies.
Stochastic dynamics of instabilities in evolutionary systems
Authors: Bruckner Eberhard , Ebeling Werner , Scharnhorst Andrea
Published: July 2007

This article develops a modeling framework that allows a formal description of evolutionary processes in social and biological systems. An enumerable set of fields (chemical sorts, biological species, technologies, areas of scientific endeavor, and so on) is considered, each field being characterized by the number and properties of its representatives (occupying elements). By introducing probabilities for the elementary processes of spontaneous generation, identical self‐reproduction, error reproduction, death, and transition to other fields, we define a Markov process in occupation number space. At any time, only a finite set of fields is occupied, and the appearance of a representative of a field with “better” properties produces an instability in the system. The characteristic dynamics of such “innovative instabilities” are investigated by simulation. As a particular example, we consider the nonlinear growth properties associated with the emergence of new areas of scientific research.
Reference modes and the optimal shape parameter
Authors: Radzicki Michael J.
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, D‐7000 Stuttgart 1, F.R.G.
Control theory: A model of organisms
Authors: Powers William T.
Published: July 2007

The concepts of feedback and systems analysis are compatible with a control system model of human behavior. Control theory can contribute a model of the individual for use in larger models of social systems, in which more general feedback phenomena can be found. A review of the properties of control systems shows that they act to make their own input match internal standards or reference signals.

Competent control systems create illusions of stimulus‐response causality. While stimulus‐response theory can approximate the relationship between disturbance and action, it is unable to predict the consequences of behavior. Control theory shows how consequences are maintained despite disturbances.

A control theory view of individual human behavior is applicable in all sciences that deal with social systems—not as a metaphor for social control systems but as a description of the properties of the individuals who generate social phenomena.
Analyzing who gains and who loses: The case of school finance reform in new york state
Authors: Andersen David F.
Published: July 2007

Do better models lead to better decisions? This case study assesses three computer‐based models designed to examine the distributional effects of a single school finance reform in the state of New York. The three models—a tactical simulation model, an econometric model, and a system dynamics simulation model—differ from each other in terms of five classes of assumptions applied to the analysis. Within a political decision‐making environment, the simpler tactical simulation model (essentially a data base management system) produces the most useful results because it requires few assumptions on the part of analysts. However, this class of models also fails to analyze more complex interactions within the school finance system and hence tends to lock decision makers into a myopia defined by one‐year projections. The net effect of introducing computer‐based models into the decision‐making process is to make school finance decision making more myopic. For politically based decisions about distributional impacts, the availability of more sophisticated models does not appear to lead to more sophisticated decision‐making processes.
Learner‐directed systems education: A successful example
Authors: Draper Frank , Swanson Mark
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, D‐7000 Stuttgart 1, F.R.G.
Replication and revision of a classic system dynamics model: Critique of “population control mechanisms in a primitive agricultural society”
Authors: Kampmann Christian
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 dyn‐amicists. 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.
A system dynamics model for national energy policy planning
Authors: Naill Roger F.
Published: July 2007

This article describes the conceptual development of FOSSIL2, an integrated model of U.S. energy supply and demand, which is used to prepare projections for energy policy analysis in the U.S. Department of Energy's Office of Policy, Planning, and Analysis.
On the very idea of a system dynamics model of Kuhnian science
Authors: Wittenberg Jason
Published: July 2007

Validation strategies for models of theories have received scant attention in the system dynamics literature. Yet if system dynamics is to be an effective tool for, evaluating the dynamic consistency of theoretical systems, such strategies will need to be developed. This article illustrates how such validation might take place by analyzing an already published model of Thomas S. Kuhn's theory of scientific revolutions. The results indicate that the model, while capturing many important aspects of Kuhnian science, distorts certain fundamental features of the theory, in particular the process of paradigm change. The article concludes by discussing some of the problems associated with incorporating truly Kuhnian paradigm change into any system dynamics model.
Improving education in public schools: Innovative teachers to the rescue
Authors: Brown Gordon S.
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.
An analysis of the cost effectiveness of U.S. energy policies to mitigate global warming
Authors: Naill Roger F. , Belanger Sharon , Klinger Adam , Petersen Eric
Published: July 2007

The issue of global warming has sparked debate among scientists and policymakers over the past two years. Many studies have been undertaken in the U.S. and other nations to determine the potential severity of global climate change and appropriate policy responses. The U.S. Department of Energy is now conducting one such study of energy technology and policy options to mitigate greenhouse gas emissions. The study attempts to assess the emissions reduction potential and costs of several policies, using the FOSSIL2 integrated energy model. This article focuses on the preliminary results of a subset of eight policy cases. It discusses the modeling methodology, the formulation of these policies, draft results, and some policy insights.
Are we losing one of the best features of system dynamics?
Authors: Machuca José A. 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. Germany.
A system dynamics model of national cocaine prevalence
Authors: Homer Jack B.
Published: July 2007

A system dynamics model reproduces a variety of national Indicator data reflecting cocaine use and supply over a 15‐year period and provides detailed estimates of actual underlying prevalence. Sensitivity testing clarifies the source of observed trends, such as growth in the compulsive use of crack cocaine and decline in the casual use of cocaine powder. Alternative scenarios with possible policy implications are simulated and projected for 12 years, and the results are assessed.
Introducing system dynamics in schools: The Nordic experience
Authors: Davidsen Pal I. , Bjurklo Margaretha , Wikström Hugo
Published: July 2007

This article describes two pilot studies of introducing system dynamics into schools in the Nordic countries. The first study describes the use of system dynamics in a high school economics class. One group of students was taught by the standard economics teaching approach; the other group, by a system dynamics approach. The second study tested the ability of 15‐ and 17‐year‐old students to understand the dynamics of social and ecological systems. The results of these pilot studies suggest that incorporating system dynamics into teaching leads to a better understanding of complex dynamic problems. A list of recommendations for designing educational systems using system dynamics was compiled.
A proposed sequence for developing systems thinking in a grades 4—12 curriculum
Authors: Draper Frank
Published: July 2007

Barry Richmond described seven systems thinking skills needed to become a successful systems thinker. These skills are woven throughout the grades 4‐12 curriculum. The seven systems thinking skills can each be further defined by three distinct levels of competence, with an increase in cognitive capability required at each successive level. A proposed sequence is presented for the skills themselves, and suggestions are given for activities at each level within the skills. Level I activities may begin with ten‐year‐old students, but level II activities are best mastered by the senior students (about 18 years old). More research is needed to justify the proposed developmental sequence.
Using human judgment in system dynamics models of social systems
Authors: Nuthmann Conrad
Published: July 2007

This article addresses concerns about the validity of system dynamics models that rely on the quantification of human judgment. It reviews epistemological and semantic problems associated with scientific discourse, summarizes properties of four levels of scientific discourse (nominal, ordinal, interval, and ratio), and describes the judgmental conditions that must obtain when high‐level (interval and ratio) mathematics are applied to human judgment. Two simple system dynamics models employing continuous and discrete limens are used to illustrate the dynamic consequences of inappropriate uses of human judgment in system dynamics models. The author concludes that unless we have specific evidence that the judgmental phenomena we are modeling behave according to additive, multiplicative, or averaging models, we can not assume we are dealing with anything other than ordinal phenomena.
Skill formation and its impact on the adaptation process of new production systems
Authors: Diawati Lucia , Kawashima Hironao , Hayashi Yoshio
Published: July 2007

A system dynamics model is developed to facilitate the study of a firm's introduction of a new, more technologically sophisticated production facility. The system must adapt in three areas: production facilities, labor, and management. Emphasizing industrial situations commonly encountered by producers in developing countries, this study focuses on the ways management efforts and the learning process influence the development of labor expertise.

The firm's performance is found to move through three phases of adaptation: fluctuations, growth, and adjustment to external change. Three approaches to improving the firm's performance are investigated: better preparation for the new technology, quicker initiatives to develop labor skills, and better‐designed skill training. Comparative simulations show that better skill formation yields better system performance than faster response alone because of its ability to accelerate the development of new skills. However, better preparation can reduce the length of the initial unstable phase in the adaptation process and produce higher system performance when combined with the other skill formation policies.
With a little help from our friends: How system dynamics and soft OR can learn from each other
Authors: Lane David C.
Published: July 2007

At its inception, the paradigm of system dynamics was deliberately made distinct from that of OR. Yet developments in soft OR now have much in common with current system dynamics modeling practice. This article briefly traces the parallel development of system dynamics and soft OR, and argues that a dialogue between the two would be mutually rewarding. To support this claim, examples of soft OR tools are described along with some of the field's philosophical grounding and current issues. Potential benefits resulting from a dialogue are explored, with particular emphasis on the methodological framework of system dynamics and the need for a comple‐mentarist approach. The article closes with some suggestions on how to begin learning from the links between the two fields.
System dynamics, systems thinking, and soft OR
Authors: Forrester Jay W.
Published: July 2007

System dynamics, systems thinking, and soft operations research (soft OR) all aspire to understanding and improvement of systems. In all, the first step interprets the real world into a description used in following stages. In system dynamics, description leads to equations of a model, simulation to understand dynamic behavior, evaluation of alternative policies, education and choice of a better policy, and implementation. Case studies, systems thinking, and soft OR usually lack the discipline of explicit model creation and simulation and so rely on subjective use of unreliable intuition for evaluating the complex structures that emerge from the initial description of the real system. Nevertheless, systems thinking and soft OR, with emphasis on eliciting information from‐real‐world participants, should contribute useful insights to system dynamics. Conversely, the model creation and simulation stages of system dynamics should contribute rigor and clarity to systems thinking and soft OR.
Cognitive mapping and problem structuring for system dynamics model building
Authors: Eden Colin
Published: July 2007

This article discusses an approach to problem structuring that seeks to recognize the significance of multiple perspectives and the richness they provide in generating politically feasible ways of resolving problems. In particular, the method—cognitive mapping and an associated computer‐based group support system—is related to the early stages of modeling situations that are characterized by feedback dynamics. Thus, the method is argued to be particularly suitable as a visual interactive modeling method, which is mutually supportive of visual interactive system dynamics modeling methods.
Competition and complexity in spatially connected networks
Authors: Reggiani Aura , Nijkamp Peter
Published: July 2007

Much attention has recently been paid to the potential of using analytical tools derived from ecology and biology for analyzing competitive (or synergetic) interactions in a complex spatial network.

Defining a network as a complex space‐time system, this article investigates the implications of spatial interconnections when oscillating or chaotic behavior in a certain node of a network is spread in both space and time. The main focus is on stability/ complexity in a network with a view to varying complexity in terms of the number of functional elements (e.g., nodes, competing/growing centers). Some simulation experiments involving simple‐dimensional spatial systems are described.
Teamwork in group model building
Authors: Richardson George P. , Andersen David F.
Published: July 2007

Ongoing research at the Rockefeller College of Public Affairs and Policy is focusing on strategies for efficient and effective model building in groups. The intent is to involve a relatively large client group in the business of model formulation. Recent projects have explored strategies for accelerated group model building in the context of three public policy problem areas: foster care in New York State, Medicaid costs in the state of Vermont, and homelessness policy initiatives in New York City.

Five roles appear to be essential to support effective group model building: the facilitator, the modeler/ reflector, the process coach, the recorder, and the gate keeper. This article identifies the five roles, briefly discusses the problem areas, sketches the design of the group model‐building efforts, and hypothesizes principles and strategies to guide future group model building.
Mode‐locking and entrainment of endogenous economic cycles
Authors: Haxholdt Christian , Kampmann Christian , Mosekilde Erik , Sterman John D.
Published: July 2007

We explore the robustness of aggregation in Sterman's model of the economic long wave. The original model aggregates all capital‐producing firms into a single sector and generates a large‐amplitude self‐sustained oscillation with a period of roughly 50 years. We disaggregate the model into two coupled industries, one representing production of plant and long‐lived infrastructure and the other representing short‐lived equipment and machinery. While holding the aggregate equilibrium characteristics of the model constant, we investigate how mode‐locking occurs as a function of the difference in capital lifetimes and the strength of the coupling between the sectors. Disaggregation allows new modes of behavior to arise: In addition to mode‐locking, we observe cascades of period‐doubling bifurcations, chaos, intermittency, and quasi‐periodic behavior. Despite the introduction of these additional modes, the basic behavior of the model is robust to the aggregation assumption. We consider the likely effects of finer disaggregation, the introduction of additional coupling mechanisms, such as prices, and other avenues for the exploration of aggregation in system dynamics models.
A system dynamics approach to modeling fisheries management issues: Implications for spatial dynamics and resolution
Authors: Ruth Matthias
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 or to Yaman Barlas, Dept. of Industrial Engineering, Bogazici University, 80815 Bebek, Istanbul, Turkey.
Stable insertion of Alzheimer Aβ peptide into the ER membrane strongly correlates with its length
Authors: Lundin Carolina , Johansson Sofia , Johnson Arthur E. , Näslund Jan , von Heijne Gunnar , Nilsson IngMarie
Published: July 2007

Alzheimer's disease is characterized by the deposition of amyloid β‐peptide (Aβ) plaques in the brain. Full‐length amyloid‐β precursor protein (APP) is processed by α‐ and β‐secretases to yield soluble APP derivatives and membrane‐bound C‐terminal fragments, which are further processed by γ‐secretase to a non‐amyloidogenic 3 kDa product or to Aβ fragments. As different Aβ fragments contain different parts of the APP transmembrane helix, one may speculate that they are retained more or less efficiently in the membrane. Here, we use the translocon‐mediated insertion of different APP‐derived polypeptide segments into the endoplasmic reticulum membrane to assess the propensities for membrane retention of Aβ fragments. Our results show a strong correlation between the length of an Aβ‐derived segment and its ability to integrate into the microsomal membrane.
Association of fast food consumption with energy intake, diet quality, body mass index and the risk of obesity in a representative Mediterranean population
Authors: Schröder Helmut , Fïto Montserrat , Covas Maria Isabel
Published: July 2007

The aim of the present study was to describe the association of fast food consumption with BMI, energy intake and diet quality in a Mediterranean population. The subjects were Spanish men (n 1491) and women (n 1563) aged 25–74 years who were examined in 1999–2000, in a population-based cross-sectional survey in northeast Spain (Girona). Dietary intake was assessed using a FFQ that included four typical fast food items. Two dietary-quality indices, the Mediterranean diet score and the healthy eating index, were created. Height and weight were measured. Within the population studied, 10·1 % reported eating fast food at least once per month. Dietary energy intake and energy density were directly associated with frequency of fast food consumption. Multivariate logistic regression analysis adjusted for lifestyle and educational level showed an inverse association of frequency of fast food consumption with meeting the dietary reference intake (DRI) for energy (P = 0·001). The consumption of fast food more than once per week increased the risk of overall low diet quality (P < 0·001). BMI was directly associated with fast food consumption expressed in g/d (P = 0·025) and in kJ/d (P = 0·017). The risk of being obese increased with the frequency of fast food consumption (P = 0·046). Fast food consumption was associated with higher energy intakes, poor diet quality and higher BMI. The likelihood of not meeting the DRI for energy, and of being obese, increased with the frequency of fast food consumption.
Tubercular and chronic pyogenic osteomyelitis of cranio-facial bones: a retrospective analysis
Authors: Sethi A , Sethi D , Agarwal A K , Nigam S , Gupta A
Published: July 2007

Aim:

To analyse current trends in our population with respect to the presentation, diagnosis and management of tubercular and chronic pyogenic osteomyelitis of the cranio-facial bones.

Design:

Retrospective study.

Setting:

Tertiary healthcare centre.

Patients and methods:

The study population comprised 14 patients with tubercular and chronic pyogenic osteomyelitis who were managed in the otorhinolaryngology department between May 2002 and December 2005.

Results:

Odontogenic infections, sinus infections and aural infections were the most commonly identified aetiological factors. Most of the patients presented with swelling, pain and discharging sinus. The diagnosis was established on the basis of clinical evaluation, radiological investigations and histopathological analysis, with six cases diagnosed with tubercular osteomyelitis and eight cases with chronic pyogenic osteomyelitis. All the patients were initially commenced on oral antibiotics, which were continued for two weeks in all cases with chronic pyogenic osteomyelitis. All the patients with pyogenic osteomyelitis underwent surgical management, with one patient requiring repeated surgical interventions. All the patients with tubercular osteomyelitis received anti-tubercular chemotherapy, with complete cure.

Conclusions:

Osteomyelitis of the cranio-facial bones is an uncommon entity which requires a high index of clinical suspicion along with radiological and histopathological investigations in order to establish the diagnosis. Tubercular osteomyelitis is clinically and radiologically indistinguishable from pyogenic osteomyelitis, and the two conditions can be differentiated only on the basis of histopathological evaluation of involved tissue.