bluuebunny/crossref_metadata_2025 huggingface dataset:
Azorellane diterpenoids from Laretia acaulis inhibit nuclear factor‐kappa B activity
Authors: Borquez Jorge , Loyola Luis A. , Morales Glauco , San‐Martín Aurelio , Roldan Raquel , Marquez Nieves , Muñoz Eduardo
Published: July 2007

Transcription factor NF‐κB plays a key role in the inducible expression of genes mediating proinflammatory effects, and is thus an important target for the development of antiinflammatory drugs. Laretia acaulis (Cav.) Gill et Hook (Apiaceae) is a medicinal plant used in the high Andes mountains for different ailments such as diabetes, inflammation and for general pain. In addition to the known azorellanol (2) and 7‐deacetylazorellanol (4), 13‐epiazorellanol (1) was also isolated from the aerial part of this plant. Its structure was based on spectroscopic comparison with azorellanol (2) and by chemical characterization. While compounds 2 and 4 showed potent anti‐NF‐κB activity by targeting the activity of the IκBα kinase, compound 1 was completely inactive highlighting the importance of position 13 in the biological activities of this class of tetracyclic diterpenoids. Copyright © 2007 John Wiley & Sons, Ltd.
Retracted: Tissue culture of some lichens and screening of their antioxidant, antityrosinase and antibacterial properties
Authors: Behera B. C. , Verma Neeraj , Sonone Anjali , Makhija Urmila
Published: July 2007

The article above has been retracted by agreement between the authors, the Editors‐in Chief of Phytotherapy Research (PTR) and John Wiley & Sons, Ltd. The retraction has been agreed due to similarity of data between this article and the following article published in the journal Bioresource Technology (BITE); Antioxidant and antibacterial properties of some cultured lichens by B. C. Behera, Neeraj Verma, Anjali Sonone and Urmila Makhija. Bioresource Technology 99: 776‐784 (2008).
Although the submission to PTR was before that of BITE, the on‐line edition appeared first in BITE.
The Editorial policy of the journal is to publish only original data that has not been submitted elsewhere. Authors are reminded that this is in accordance with the strict guidelines outlined in our Instructions to Authors.

Elizabeth M Williamson
Editor in Chief, Phytotherapy Research.
The feedback view of business policy and strategy
Authors: Morecroft John D. W.
Published: July 2007

A combination of administrative theory and traditional system dynamics modeling promises a flexible model‐based tool to assist businesses in designing policies and programs to support new strategic moves. Administrative theory helps clarify the firm's organization and decision‐making structure. System dynamics highlights feedback loops in the decision‐making structure and shows how structure is related to business behavior. With this dual conceptual framework, a business policy modeling project divides into two distinct phases, each of which has a value in policy analysis. Phase 1 is a descriptive survey of the firm's decision‐making structure, rather like traditional conceptualization but made richer by use of administrative theory. Phase 2 is conventional simulation modeling that builds on the phase 1 survey. Several business cases illustrate the kinds of policy insights that a phase 1 survey can provide. The article also comments on the value that a full‐fledged simulation model adds to the phase 1 analysis.
Notes on the teaching of system dynamics
Authors: Clauset Karl 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. Betriebswirtschaftliches Institut. Universität Stuttgart, Herdweg 23, D‐7000 Stuttgart 1, West Germany.
Generic structures
Authors: Paich Mark
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, Department of Mathematics and Computer Science, Wheaton College, Norton, MA 02766, U.S.A.
Problems with causal‐loop diagrams
Authors: Richardson George P.
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.
Defining sociological concepts as variables for system dynamics modeling
Authors: Jacobsen Chanoch , Bronson Richard
Published: July 2007

Social structures and processes are generally described and analyzed in terms of verbal concepts. To simulate such phenomena in system dynamics models, the concepts must first be transformed into quantifiable variables. Useful intermediate steps in this process are specific but transferable nominal definitions, based on meaning analysis of the concepts. For modeling purposes, a well‐defined variable should be reliable and realistic, and have face validity. The relevance and importance of these criteria, long recognized in sociological research, are documented and illustrated with examples drawn from recently published work on a model of normative systems in industrialized societies.
A model to inform institutional resource allocation procedures
Authors: Galbraith Peter L. , Carss Brian
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, Universität Stuttgart, Herdweg 23, D‐7000 Stuttgart 1, West Germany.
Break the cycle: Poverty causes population growth causes poverty
Authors: Meadows Donella
Published: July 2007

Donella Meadows, who teaches at Dartmouth College, recently won a major award for excellence in journalism. The Champion‐Tuck Awards are given annually in the United States for the best reporting on business and economic issues. She won second prize in the 1986 competition for local or syndicated columnists for her weekly column “The Global Citizen,” which is published in the Valley News of Lebanon, New Hampshire, and appears in a number of newspapers in New England and elsewhere in the United States. The article printed here appeared in the Valley News, June 21, 1986.

Dr. Rfeadolvs began writing “The Global Citizen” in 1983 on issues ranging from organic farming to causes of economic depression, from political revolution to preservation of tropic ecosystems. The columns are infused with a feedback view of the world and emphasize the endogenous. dynamic. and interconnected nature of the systems within which we live.
Portfolio simulation: A tool to support strategic management
Authors: Merten Peter P. , Löffler Reiner , Wiedmann Klaus‐Peter
Published: July 2007

We show that a quantitative portfolio simulation model can be used effectively in the allocation of investment funds in multibusiness firms. The portfolio simulation model, which is formulated with an extended system dynamics approach, further allows us to show severe limitations of qualitative portfolio approaches, such as that of the Boston Consulting Group (BCG). The simulation experiments demonstrate that it can be extremely dangerous for diversified companies to follow the investment suggestions typically drawn from the BCG portfolio matrix if competitors choose a course of action that is contradictory to normative situations. The simulation runs additionally show that in an economic depression a more flexible positioning strategy can yield much better results than the fixed positioning strategy typically used by the BCG.
System dynamics and heuristic optimisation in defence analysis
Authors: Wolstenholme E. F. , Al‐Alusi Abdul‐Sattar
Published: July 2007

The aim of this paper is to demonstrate the merits of using optimisation for policy design in system dynamics models. The approach has been applied to an existing defence model to design formation change strategies for an attacking force (Red) in response to indirect fire strategies applied by a defending force (Blue). The rationale behind the use of optimisation in system dynamics is presented, followed by a description of the optimisation software used. The model and its basic results are summarised, prior to describing the design and results of optimisation experiments applied to it. It is concluded that the optimisation approach can significantly contribute to the analysis by highlighting new interactions between the Red and Blue strategies. Originally Red's desire to stay in a fast‐moving, highdensity formation was seen primarily as being based on facilitating recovery of lost speed and hence momentum, when Blue's fire ceased. Additionally, however, it is shown here that this strategy is preferable because it also minimises the time over which Red is exposed to Blue's fire.
Lessons from system dynamics modeling
Authors: Forrester Jay W.
Published: July 2007

The power and utility of system dynamics is best achieved by going beyond a model to implications and generalizations that can be drawn from the process of modeling. System dynamics papers too often stop with the description of a model. But models should become part of a more persuasive communications process that interacts with people's mental models, creates new insights, and unifies knowledge. In doing so, modeling uses the full range of available information‐the mental data base and the written data base, as well as the numerical data base. The last century has been devoted to exploring the frontier of physical science. The next century will be the time for exploring the dynamic nature of social systems and using the resulting knowledge for improving institutions and economies.
Empirical and theoretical evidence of economic chaos
Authors: Chen Ping
Published: July 2007

Empirical and theoretical investigations of chaotic phenomena in macroeconomic systems are presented. Basic issues and techniques in testing economic aggregate movements are discussed. Evidence of low‐dimensional strange attractors is found in several empirical monetary aggregates. A continuous‐time deterministic model with delayed feedback is proposed to describe the monetary growth. Phase transition from periodic to chaotic motion occurs in the model. The model offers an explanation of the multiperiodicity and irregularity in business cycles and of the low dimensionality of chaotic monetary attractors. Implications for monetary control policy and a new approach to forecasting business cycles are suggested.
Deterministic chaos in the beer production‐distribution model
Authors: Mosekilde Erik , Larsen Erik Reimer
Published: July 2007

Depending upon the assumed ordering policy, the classical Beer Distribution Model shows a great variety of complex dynamic behaviors, including limit cycle oscillations of different periodicities and deterministic chaos. This article presents an overview of these phenomena. The ordering policy is expressed in terms of two parameters that measure the fraction of the supply line and the fraction of the anticipated shipments accounted for in the placement of orders. Our results indicate that, in certain regions of parameter space, any neighborhood to a given solution will contain qualitatively different solutions. The complexity of the system is revealed in two‐ and three‐dimensional reconstructions of chaotic attractors as well as in Poincaré sections obtained from such reconstructions.
Deterministic chaos in models of human behavior: Methodological issues and experimental results
Authors: Sterman John D.
Published: July 2007

Recent work has shown that several well‐known models in the system dynamics literature contain previously unsuspected regimes of deterministic chaos. Two of the most extensively analyzed are Sterman's model of the economic long wave and the production‐distribution model of the Beer Distribution Game. The significance of these theoretical developments hinges on whether the chaotic regimes lie in the realistic region of parameter space. There are also questions regarding the descriptive accuracy of models of human systems that exhibit chaos. Because of data limitations and the inability to conduct controlled experiments, empirical studies at the aggregate level are not likely to resolve these questions.

An alternative approach is based on laboratory experiments in which models provide a simulated environment for the study of human decisionmaking behavior. Recently, laboratory experiments have been conducted to analyze decision‐making behavior in the longwave model and the Beer Distribution Game. This article describes these experiments and shows that the behavior of the subjects is explained well with a simple heuristic long used in system dynamics modeling and well grounded in behavioral decision theory. The parameters of the proposed decision rule are estimated econometrically for each subject. The parameters that characterize a significant minority of the subjects are shown to produce chaos. This direct experimental evidence that chaos can be produced by the decision‐xnaking behavior of real people has important implications for the formulation, analysis, and testing of models of human behavior.
Sustaining economic growth with a nonrenewable natural resource: The case of oil‐dependent Indonesia
Authors: Arif M. Tasrif , Saeed Khalid
Published: July 2007

This study uses a system dynamics model based on an integration of micro‐and macroeconomic theories to understand economic growth with a nonrenewable natural resource. The case of oil‐dependent Indonesia is used as an empirical reference for the study. Long‐run growth patterns resulting from various intuitively appealing development policies are analyzed, and an attempt is made to identify the best policy set for attaining a sustainable growth pattern. The study shows that influencing factor prices to facilitate adoption of capital‐intensive technologies accelerates development and is a key policy for sustaining growth in the long run.
Simplification and understanding of models
Authors: Eberlein Robert L.
Published: July 2007

The theory of model simplification is presented as a means of increasing model understanding. Simplification is based on a selection of the behavior modes defined by the linearized representation of the model and results in a smaller and more easily understood model. To allow understanding, the variables in the simplified model must be easy to interpret relative to those in the original model. This interpretation is complete in an exact simplification, a concept used to derive measures of the importance of different variables in generating selected behavior modes. These measures are used to select which variables to retain and which to omit in forming the simplified model. Issues in the application to nonlinear models are considered, and software that facilitates model simplification is discussed.
System dynamics meets the press
Authors: Meadows Donella H.
Published: July 2007

The shared paradigms of society, the public discourse, the deepest assumptions about how the world works, these are the ultimate sources of system structure and the primary obstacles to structural change. The reigning paradigms of the western world are astonishingly unsystematic, and they give rise to badly structured, difficult‐to‐manage large‐scale social systems with persistent problems, such as pollution, poverty, and war. One way to contribute to the restructuring of those systems is to bring more clear, accurate, and inclusive systems concepts into the public discourse—to communicate systems insights regularly and powerfully through the press.

Even the simplest ideas of system dynamics—stocks, flows, positive and negative feedback, the effect of delays, the importance of nonlinearity—can help to clarify public discussion and improve public policy. They must be communicated without jargon, without mathematics, without loop diagrams. That can be done, and the best partners in doing it are those who are already professionals in the art of public communication—the members of the press.
Projecting the future value of a variable in a system dynamics model
Authors: Clark Rolf , Omholt Clark A.
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.
Software productivity: Potential, actual, and perceived
Authors: Abdel‐Hamid Tarek K. , Madnick Stuart
Published: July 2007

In this article, we investigate the dynamics of software development productivity throughout the software development lifecycle. Our investigation discerns three forms of productivity, namely, potential, actual, and perceived. This conceptual dissection of productivity provides a useful lens for focusing on two distinct sets of managerial concerns: losses in the efficiency of software production, and losses in the effectiveness of managerial control. Losses in production efficiency stem from faulty processes associated with motivation and communication and lead to a gap between potential productivity and actual productivity. Losses in the effectiveness of managerial control arise, particularly in the early stages of a software project, from the discrepancy between what management perceives productivity to be and what it actually is.
Rangelands destruction under population growth: The case of Iran
Authors: Mashayekhi Ali Naghi
Published: July 2007

As population and income per capita grow in a developing country like Iran, demand for meat increases but a potential nutrition crisis also arises. Meat production becomes more profitable, and the number of sheep or other meat‐producing animals in the country rises. Growth of the sheep population increases the demand for fodder, which is obtained from two major domestic sources: rangelands and farmlands. However, as a result of population growth in the country, the demand for non‐meat food, which is produced on the farmlands, also rises and increases the demand for the farmlands themselves. Since cultivable land is limited, the price of farmlands increases and makes farm hay production more expensive. As a result, the pressure on the rangelands to feed the growing sheep population rises. The sheep population in the rangelands finally surpasses their carrying capacity, causing rangelands destruction and a collapse in range grass production. Eventually, the domestic food supply falls sharply, producing a serious crisis in meat supply and nutrition of the human population. To prevent such a crisis, different policy alternatives are examined. The key to a successful policy is identified to be balancing the number of sheep in the rangelands with the production capacity of the rangelands. In addition, lower population growth and higher investment in the rangelands can keep domestic meat production per capita at a higher level.
A structured approach to knowledge elicitation in conceptual model building
Authors: Vennix Jac A. M. , Gubbels Jan W. , Post Doeke , Poppen Henk J.
Published: July 2007

Policy‐oriented modeling demands client involvement in the model‐building process. This poses a knowledge elicitation problem, i.e., how to obtain the necessary knowledge from a group of people. Traditionally, interviews and freely interacting groups have been employed most frequently for this purpose. In this article, we present an approach to knowledge elicitation that employs a combination of different techniques to arrive at a conceptual model of a regional health care system. The adopted approach is sufficiently general to be employed in other model development processes as well.
The impact of exchange rate policy on inflation rate in an oil‐exporting economy
Authors: Mashayekhi Ali Naghi
Published: July 2007

Exchange rate policy is one of the most important economic policies to be decided by governments. In countries (like the OPEC countries) where a major part of government revenues is in the form of foreign exchange earned from exports of nationalized products and minerals, the exchange rate influences government finance and budgets directly. This paper describes the structure and behavior of a model formulated to explore fixed and floating exchange rate policies in such an economy. Model‐based policy analyses show that when the government of such an economy faces a decline in foreign exchange revenues, a fixed formal exchange rate intensifies inflationary pressures and leads to a higher market exchange rate. In addition, under a fixed exchange rate policy, a decline in foreign exchange revenues results in a drastic fall of the government budget at fixed prices, while with a floating rate policy, such an erosion of government purchasing power does not occur.
Dynamics of commodity taxation: An example of an energy tax
Authors: Wirl Franz
Published: July 2007

Commodity taxation represents one means of raising public revenues. Recently, this proposal has received considerable support from environmentalists, who argue that commodity taxation, besides raising revenues, will have the positive effect of controlling externalities and limiting negative environmental side‐effects of commodity production. This article considers the dynamics of such taxation when taxpayers must solve a costly and intertemporal adjustment problem. Applying recent data from Austria, the author analytically and quantitatively explores the implications of sluggish consumption on the design of a revenue‐stable tax policy. If demand is elastic, the stability of such a tax regime is questionable for theoretical reasons. In practice, its stability may be questionable even if demand is inelastic.
Qualitative simulation and system dynamics
Authors: Dolado José Javier
Published: July 2007

This article explores some requirements for applying qualitative simulation algorithms to system dynamics models. The field of qualitative simulation lacks a specific procedure for modeling systems (subjects of its models are generally physical systems). Bringing together qualitative simulation techniques and system dynamics modeling techniques could benefit both fields. The structural correctness of system dynamics models is defined using constraint theory. An attempt is made to alleviate some problems of qualitative simulation algorithms by drawing upon system dynamics modeling methods and by establishing the structure for the propagation of constraints in these models.
Food self‐sufficiency in Vietnam: A search for a viable solution
Authors: Bach Nguyen Luong , Saeed Khalid
Published: July 2007

This article attempts to assess the effects on an agricultural resource system of policies to maintain food self‐sufficiency in a centrally planned economy. Vietnam's case serves as an illustration. Experimentation with a system dynamics model of the food production system, incorporating relations concerning soil ecology and agricultural land management policy, serves as a basis for this assessment. Short‐run policies to increase production appear to be detrimental to maintaining food self‐sufficiency in the long run. it appears that a sustainable food production policy must incorporate soil conservation and improvement, and population control. Although difficult to implement in a market system, such a policy agenda may be feasible in a centrally planned economy.
A system dynamics model of aircraft carrier survivability
Authors: Coyle R. G.
Published: July 2007

The use of aircraft carriers in offensive operations in waters where an enemy can deploy strong air forces is the subject of much debate, and it is sometimes asserted that the carriers could not survive long enough to discharge a mission. This article analyzes that proposition and shows that a wide range of possible outcomes exists, depending on the carrier commander's actions.

By considering the fundamental mechanics of the problem, a number of options for technological improvement are suggested, and it is shown that they have widely differing, and sometimes very unexpected, effects on the outcome.

The model requires a blend of discrete and continuous modeling, the main features of which are discussed in the Appendix.
Complex dynamics in low‐dimensional continuous‐time business cycle models: The Šil nikov case
Authors: Lorenz Hans‐Walter
Published: July 2007

While most examples of complex motion in economic dynamics employ a discrete‐time concept, chaos can also emerge in continuous‐time, nonlinear economic models. It is argued that, (depending on the level of aggregation in the economy) the use of the continuous‐time concept can be mandatory in economic dynamics. The Šil'nikov scenario, based on the existence of homoclinic orbits, is used as a formal means to illustrate the emergence of complex motion in two simple examples from traditional business cycle theory. The consideration of slight nonlinearities in a generalized version of the standard Metzler model with inventories and in Phillips' multiplier‐accelerator model can imply chaotic behavior.
Dynamics of rural development in southern Sudan
Authors: Bontkes Tjark E. Struif
Published: July 2007

This article presents the results of a dynamic simulation study of a rural area in southern Sudan. In order to improve the living conditions of the rural population in this area, three intervention packages were planned: improved veterinary care; improved agricultural practices; and better general facilities like medical care, clean drinking water, schools, and roads. Although these interventions initially seem to benefit the rural population, some worsen the situation after a number of years when compared to the case without interventions, and others are not able to bring about a sustainable development of the area. Especially the improvement of the general infrastructure causes problems in the long run because it accelerates migration from the rural areas to the town. This increases the share of imported sorghum purchased by the town dwellers and diminishes the ability of the rural population to purchase food after a year of a low Productivity. It is concluded that analyzing the dynamics of the system can foster planning of appropriate interventions.
System dynamics as an organizing framework for pre‐college education
Authors: Forrester Jay W.
Published: July 2007

Pre‐college education is under attack for poorly serving the needs of society. Unless a superior concept for improving education emerges, public displeasure is apt to result in still more of what is already not working. But now, a fundamentally new and more effective approach to education is emerging from advances in system dynamics. System dynamics offers a framework for giving cohesion, meaning, and motivation to public school education at all levels. A second important ingredient, learner‐centered learning, imports to pre‐college education die challenge and excitement of a research laboratory. Together, these two innovations harness the creativity, curiosity, and energy of young people. System dynamics improves on the traditional educational sequence, in which years of learning facts precede use of those facts, by introducing synthesis at an early stage in a student's experience. Such synthesis can be based on facts that even elementary school students have already gleaned from life. Learner centered learning relieves teachers from having to lecture facts to resistant students. Learners take charge of their own learning as they explore, gather information, and create unity out of their educational experiences. A teacher in this new setting acts as a guide and participating learner rather than as an authoritarian source of all wisdom.
Systems, science, and schools
Authors: Mandinach Ellen B. , Cline Hugh F.
Published: July 2007

The Systems Thinking and Curriculum innovation Network (STACIN) Project is a multiyear implementation and research effort intended to examine the impact of a systems thinking approach using mulation modeling software. The purpose of the project is test the potential and effects of using are technology‐based oproach in pre‐college curricula as teach problem‐soliving skills as well as content‐specific knowledge.
System dynamics, determinism, and choice: Toward a reconsideration of the image of “systems man”
Authors: Bowen Michael G.
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.
Reality check: A bridge between systems thinking and system dynamics
Authors: Peterson David W. , Eberlein Robert L.
Published: July 2007

System dynamics models are suppose to be more robust than other kinds of simulation models. However, tests of robustness are usually underused and underdocumented. To allow the extensive use of robustness tests, we have included in the Vensim software a language for defining qualitative and quantitative tests, and a facility for automatically executing the tests on a simulation model. Such automatic tests are called Reality Check tests. These tests provide an explicit indication of model quality and an effective way of comparing models.
Causal policy maps of managers: Formal methods for elicitation and analysis
Authors: Hall Roger I. , Aitchison Peter W. , Kocay William L.
Published: July 2007

A connection is traced from the informal policy maps of managers, to some formal methods that have been reported for eliciting causal policy maps from the minds of managers, to commercially available computer‐driven methods for storing, displaying, and analyzing policy maps in a group setting. A gap in available techniques for analyzing policy maps is identified, and a path‐finding algorithm built into an artificial intelligence program is put forward as a step toward closing this gap. It is used to demonstrate a causal‐map analysis as an aid to a group policy meeting.
Simulating the controllability of feebates
Authors: Ford Andrew
Published: July 2007

System dynamics is used to simulate the impact of feebates to encourage the sale of cleaner vehicles in southern California. With a feebate system, fees would be imposed on dirty vehicles to finance rebates for clean vehicles. The model is used to learn whether the State of California could operate a feebate system in a financially prudent manner. I consider an example in which fees are imposed on conventional vehicles, and rebates are used to encourage the sale of electric vehicles. The simulations show that feebates can be controlled despite the many uncertainties in predicting the future sales of both conventional and electric vehicles.
Loop polarity, loop dominance, and the concept of dominant polarity (1984)
Authors: Richardson George P.
Published: July 2007

Founded in the mid‐1950s, the field of system dynamics has intellectual roots reaching much further into the past. This section seeks to publish material from that past that can contribute to current theory and practice. It 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 material, 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.
The dynamics of resource sharing: A metaphorical model
Authors: Morecroft John D. W. , Larsen Erik R. , Lomi Alessandro , Ginsberg Ari
Published: July 2007

Most system dynamicists have used the example of a simple shower to explain feedback and to introduce the cyclical dynamic behaviour characteristic of a balancing loop. The damped system's temperature is relatively easy to manage. But with two showers sharing the same limited supply of hot water it is much harder to control the water temperature, because a person “managing” one shower is unaware of the other, yet must react to the aggregate temperature outcome resulting from “joint management” effort. A system dynamics model of a two shower system is presented and is simulated to illustrate the causes and consequences of interdependence in resource allocation, and to explore changes that can improve the coordination of decision‐makers. Insights from the two shower model are then applied to understanding coordination in multinational subsidiaries with overlapping geographical markets. The article ends with some reflections on the value and limits of a metaphorical model.
Non‐participation and system dynamics
Authors: Romme A. Georges L.
Published: July 2007

Non‐participation is currently one of the most pertinent problems confronting large organizations. The non‐participation problem is related to two untested assumptions made by the conventional wisdom of participative management: first, power is assumed to flow from top to bottom rather than the other way around and, second, participation schemes provide sufficient opportunities for worker participation. The sociocratic organization provides a participative management model derived from system dynamics concepts which challenges both assumptions. Sociocratic organizations are based on a circle structure, decision making by consent, and double linking between circules. The circular and reflexive nature of these organizations appears to open up real opportunities for participation at all levels.
The system biology of thiol redox system in Escherichia coli and yeast: Differential functions in oxidative stress, iron metabolism and DNA synthesis
Authors: Toledano Michel B. , Kumar Chitranshu , Le Moan Natacha , Spector Dan , Tacnet Frédérique
Published: July 2007

By its ability to engage in a variety of redox reactions and coordinating metals, cysteine serves as a key residue in mediating enzymatic catalysis, protein oxidative folding and trafficking, and redox signaling. The thiol redox system, which consists of the glutathione and thioredoxin pathways, uses the cysteine residue to catalyze thiol‐disulfide exchange reactions, thereby controlling the redox state of cytoplasmic cysteine residues and regulating the biological functions it subserves. Here, we consider the thiol redox systems of Escherichia coli and Saccharomyces cerevisiae, emphasizing the role of genetic approaches in the understanding of the cellular functions of these systems. We show that although prokaryotic and eukaryotic systems have a similar architecture, they profoundly differ in their overall cellular functions.
Towards sustainable grassland and livestock management
Authors: KEMP D. R. , MICHALK D. L.
Published: July 2007

Grasslands are one of the world's major ecosystems groups and over the last century their use has changed from being volunteer leys, or a resource on non-arable land, to a productive resource equal to any crop and managed as such. Many grasslands are now being acknowledged as having a multifunctional role in producing food and rehabilitating crop lands, in environmental management and cultural heritage. However, grasslands across the globe are under increasing pressure from increasing human populations, reduced areas with increasing livestock numbers, and declining terms of trade for livestock production, and they are managed to varying degrees of effectiveness. The complexity of grassland uses and the many aspects of grassy ecosystems require a framework wherein solutions for better management can be developed. The present paper discusses a generic approach to grassland management to satisfy these multiple objectives. A focus on ecosystem functionality, i.e. on water, nutrient and energy cycling and on the biodiversity required to sustain those functions, provides a means of resolving the dilemmas faced, through the intermediary, management-related, criteria of herbage mass, which also relates directly to animal production. Emphasis is placed on the opportunities to satisfy multiple objectives. A consideration of the basic relationships between stocking rate and animal production shows that the longer-term, economically optimal stocking rate is associated with improved environmental outcomes. There may be environmental objectives that go beyond economically sustainable limits for livestock producers and in those cases direct payments from the government or others will be needed. These are likely to be where degradation is clearly apparent. The achievement of desirable outcomes in grassland management that satisfy multiple objectives will require new areas of research that seek viable solutions for farmers and society.
Chronic facial pain following injection of sodium tetradecyl sulphate into an intraparotid haemolymphangioma
Authors: Crampsey D P , Cochrane L , Roebuck D , Hartley B E
Published: July 2007

Objective:

We report a rare case of chronic facial pain following sclerotherapy for intraparotid haemolymphangioma, thereby highlighting an important clinical consideration when advising this treatment option as an alternative to surgery in the head and neck.

Method:

Case report, with a review of relevant literature.

Results:

Sclerotherapy of lymphangiomata is well reported in the literature. Unusually, our young patient with an intraparotid haemolymphangioma experienced severe, chronic pain following intralesional injection of sodium tetradecyl sulphate, which required management by a specialist pain service. We discuss the technique of sclerotherapy for such lesions, and also discuss the potential side effects of two agents commonly used in our centre: OK 432 and sodium tetradecyl sulphate.

Conclusion:

Non-surgical treatments of lymphangiomata and venous vascular malformations are not without complication. Both patient and clinician should be aware of this, and of the other potential side effects of sclerotherapy, prior to its use in the head and neck.
Modified Mitchellson endoscope holder
Authors: Raman R , Dahalil M B , Prepageran N
Published: July 2007

Mitchellson's ear speculum holder has been modified to act as an endoscope holder, in order to be used in endoscopic surgery of the nose or ear.
Dynamic dexterity of a planar 2-DOF parallel manipulator in a hybrid machine tool
Authors: Wu Jun , Wang Jinsong , Li Tiemin , Wang Liping , Guan Liwen
Published: July 2007

This paper addresses the dynamic dexterity of a planar 2-degree of freedom (DOF) parallel manipulator with virtual constraint. Without simplification, the dynamic formulation is derived by using the virtual work principle. The condition number of the inertia matrix of the dynamic equation is presented as a criterion to evaluate the dynamic dexterity of a manipulator. In order to obtain the best isotropic configuration of the dynamic dexterity in the whole workspace, two global performance indices, which consider the mean value and standard deviation of the condition number of the inertia matrix, respectively, are proposed as the objective function. For a given set of geometrical and inertial parameters, the dynamic dexterity of the parallel manipulator is more isotropic in the center than at the boundaries of the workspace.
Mobile robot localization using the Hausdorff distance
Authors: Donoso-Aguirre F. , Bustos-Salas J.-P. , Torres-Torriti M. , Guesalaga A.
Published: July 2007

This paper presents a novel method for localization of mobile robots in structured environments. The estimation of the position and orientation of the robot relies on the minimisation of the partial Hausdorff distance between ladar range measurements and a floor plan image of the building. The approach is employed in combination with an extended Kalman filter to obtain accurate estimates of the robot's position, heading and velocity. Good estimates of these variables were obtained during tests performed using a differential drive robot, thus demonstrating that the approach provides an accurate, reliable and computationally feasible alternative for indoor robot localization and autonomous navigation.
Imbeddings of Brezis–Wainger type. The case of missing derivatives
Authors: Krbec M. , Schmeisser Hans-Jürgen
Published: July 2007

We prove limiting imbeddings of spaces with dominating mixed derivatives into the spaces of almost Lipschitz continuous functions.
The classifying space of the gauge group of an SO(3)-bundle over S2
Authors: Bauer S. , Crabb M. C. , Spreafico M.
Published: July 2007

Stable homotopy decompositions of the classifying spaces of the gauge groups of principal SO(3) and U(2)-bundles over the sphere S2 are obtained using a fibrewise stable splitting theorem for the loop space of an unreduced suspension. The stable decomposition is related to a description of the integral cohomology ring.
An L–A pair for the Hess–Apel'rot system and a new integrable case for the Euler–Poisson equations on so(4) × so(4)
Authors: Dragović Vladimir , Gajić Borislav
Published: July 2007

We present an L–A pair for the Hess–Apel'rot case of a heavy rigid three-dimensional body. Using it, we give an algebro-geometric integration procedure. Generalizing this L–A pair, we obtain a new completely integrable case of the Euler–Poisson equations in dimension four. Explicit formulae for integrals that are in involution are given. This system is a counterexample to one of Ratiu's theorems. A corrected version of this classification theorem is proved.
KP description of unidirectional long waves. The model case
Authors: Gallay Thierry , Schneider Guido
Published: July 2007

The Kadomtsev–Petviashvili (KP) equation can be formally derived as an envelope equation for three-dimensional unidirectional water waves in the limit of long waves. As a first step towards a mathematical justification, we consider here a two-dimensional Boussinesq equation, which is a realistic model for three-dimensional water waves. Using rigorous estimates, we show that part of the dynamics of the KP equation can be found approximately in the two-dimensional Boussinesq equation. On the other hand, there exist initial data for the KP equation such that the corresponding solutions of the two-dimensional Boussinesq equation behave in no way according to the KP prediction. We expect that similar results hold for the three-dimensional water wave problem too.
On a theorem of Ambarzumian
Authors: Horváth Miklós
Published: July 2007

We consider the eigenvalue problem for the one-dimensional (stationary) Dirac operator with some boundary conditions. We prove that if the spectrum is the same as the spectrum belonging to the zero potential, then the potential is actually zero. The analogous statement for the Schrödinger operator is due to Ambarzumian. The proof is based on the fact that the (generalized) moments of a function cannot have alternating signs unless the moments are zero (see §2).
Oscillation theory for Sturm–Liouville problems with indefinite coefficients
Authors: Binding P. A. , Volkmer H.
Published: July 2007

Oscillation and related results are given for the problem

under separated end conditions, assuming 1/p, q and r ∈ L1(I). Attention focuses on the two cases (i) p > 0 with r indefinite, and (ii) p indefinite with r > 0.
The deformation multiplicity of a map germ with respect to a Boardman symbol
Authors: Bivià-Ausina C. , Nuño-Ballesteros J. J.
Published: July 2007

We define the deformation multiplicity of a map germ f: (Cn, 0) → (Cp, 0) with respect to a Boardman symbol i of codimension less than or equal to n and establish a geometrical interpretation of this number in terms of the set of Σi points that appear in a generic deformation of f. Moreover, this number is equal to the algebraic multiplicity of f with respect to i when the corresponding associated ring is Cohen-Macaulay. Finally, we study how algebraic multiplicity behaves with weighted homogeneous map germs.
Existence of positive solutions of some semilinear elliptic equations with singular coefficients
Authors: Chaudhuri Nirmalendu , Ramaswamy Mythily
Published: July 2007

In this paper we consider the semilinear elliptic problem in a bounded domain Ω ⊆ Rn,

where μ ≥ 0, 0 ≤ α ≤ 2, 2α* := 2(n − α)/(n − 2), f : Ω → R+ is measurable, f > 0 a.e, having a lower-order singularity than |x|-2 at the origin, and g : R → R is either linear or superlinear. For 1 < p < n, we characterize a class of singular functions Ip for which the embedding is compact. When p = 2, α = 2, f ∈ I2 and 0 ≤ μ < (½(n − 2))2, we prove that the linear problem has -discrete spectrum. By improving the Hardy inequality we show that for f belonging to a certain subclass of I2, the first eigenvalue goes to a positive number as μ approaches (½(n − 2))2. Furthermore, when g is superlinear, we show that for the same subclass of I2, the functional corresponding to the differential equation satisfies the Palais-Smale condition if α = 2 and a Brezis-Nirenberg type of phenomenon occurs for the case 0 ≤ α < 2.
An existence and uniqueness result for a phase-field model of diffusion-induced grain-boundary motion
Authors: Deckelnick Klaus , Elliott Charles M.
Published: July 2007

We consider a phase-field model for diffusion-induced grain boundary motion. The model couples a parabolic variational inequality to a degenerate diffusion equation. Using a regularization technique, we prove an existence theorem for the resulting system. We also obtain a uniqueness result, provided the solution has some additional regularity.
Asymptotic problems for a kinetic model of two-phase flow
Authors: Goudon T.
Published: July 2007

We consider asymptotic problems for coupled equations modelling interactions between particles and a viscous fluid. The particles are driven by a Vlasov-like equation, involving the velocity of the fluid. We obtain, as certain parameters tend to 0, hydrodynamic equations for the macroscopic density and the velocity.