bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adaptive control vector parameterization for nonlinear model‐predictive control
Authors: Hartwich Arndt , Schlegel Martin , Würth Lynn , Marquardt Wolfgang 
Published: July 2007

AbstractChemical processes are often operated in a dynamic mode. This is always true by definition for the wide class of batch processes and it also holds for the transient phases of continuous processes, caused for example by load or grade changes. Nonlinear model‐predictive control (NMPC) is a powerful approach to deal with the complexity of the related nonlinear control problems aiming for economic optimization. One major element of any NMPC implementation is a dynamic optimization algorithm, which solves the underlying optimization problem efficiently to obtain the optimal control trajectory in real time. Applying nonlinear dynamic optimization to industrial process models results in high calculation times restricting the use of NMPC for most chemical processes. In a previous publication, a method has been presented, which provides the optimizer with a control grid specifically tailored to the problem and therefore facilitates the optimization. In this work, this method is adapted to the on‐line application in NMPC. In contrast to off‐line optimizations, uncertainties and a fixed discrete time sampling have to be taken into account. The approach is applied to a small example and considerable speed‐up is observed. The gain is expected to be even greater for large‐scale industrial problems. Copyright © 2007 John Wiley & Sons, Ltd.
Worker burnout: A dynamic model with implications for prevention and control
Authors: Homer Jack B. 
Published: July 2007

AbstractThis paper explores the dynamics of worker burnout, a process in which a hard‐working individual becomes increasingly exhausted, frustrated, and unproductive. The author's own two‐year experience with repeated cycles of burnout is qualitatively reproduced by a small system dynamics model that portrays the underlying psychology of workaholism. Model tests demonstrate that the limit cycle seen in the base run can be stabilized through techniques that diminish work‐related stress or enhance relaxation. These stabilizing techniques also serve to raise overall productivity, since they support a higher level of energy and more working hours on the average. One important policy lever is the maximum workweek or work limit; an optimal work limit at which overall productivity is at its peak is shown to exist within a region of stability where burnout is avoided. The paper concludes with a strategy for preventing burnout, which emphasizes the individual's responsibility for understanding the self‐inflicted nature of this problem and pursuing an effective course of stability.
Minds over methods
Authors: Saeed Khalid 
Published: July 2007

AbstractNotes 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.
The role of econometric techniques in dynamic modeling: Systematic bias in the estimation of stock adjustment models
Authors: Forrester Nathan B. 
Published: July 2007

AbstractFounded 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.
Dynamic models of evolving systems
Authors: Allen Peter M. 
Published: July 2007

AbstractThe basis of systems modeling has been the Newtonian paradigm that states that the behavior of a system can be understood and anticipated by identifying its components and the causal links between them. This assumption leads to a set of deterministic differential or difference equations that governs the behavior of the system. However, such description is achieved by classifying elements into categories and supposing that only the most probable events in fact occur. But real systems evolve, that is, they add and subtract mechanisms, components, and interactions over time; the deterministic model does not reflect this. Clearly, evolution must therefore result from what has been removed in the reduction process. If we are to understand evolving systems better, to anticipate structural changes, and to explore the real impacts of decisions, we must study the effects on system dynamics of nonaverage behavior. We can then gain new insights into the nature of evolutionary processes and build better models that include the adaptive responses from within the system.
Local and global bifurcations in a model of the economic long wave
Authors: Brøns Morten , Sturis Jeppe 
Published: July 2007

AbstractCombining mathematical analysis with simulations, we obtain a bifurcation diagram for a simple (two state variables) system dynamics model of the economic long wave. Previous linear analysis of the onset of oscillatory behavior (Hopf bifurcation) is extended to include nonlinear effects. It is shown that both sub‐ and supercritical Hopf bifurcation can occur. In the case of subcritical Hopf bifurcation, the system has two coexisting stable solutions, one stationary and one periodic, in a parameter interval below the bifurcation point. The importance of distinguishing between the two types of Hopf bifurcation is discussed. The model also exhibits homoclinic bifurcation to infinity for some parameter combinations: a limit cycle explodes and disappears. Finally, we discuss how the results may apply to other system dynamics models.
Modeling growth strategy in a biotechnology startup firm
Authors: Morecroft John D. W. , Lane David C. , Viita Paul S. 
Published: July 2007

AbstractThe top managers of a biotechnology startup firm agreed to participate in a system dynamics modeling project to help them think about the firm's growth strategy. The article describes how the model was created and used to stimulate debate and discussion about growth management. The paper highlights several novel features about the process used for capturing management team knowledge. A heavy emphasis was placed on mapping the operating structure of the factory and distribution channels. Qualitative modeling methods (structural diagrams, descriptive variable names, and “friendly” algebra) were used to capture the management team's descriptions of the business. Simulation scenarios were crafted to stimulate debate about strategic issues such as capacity allocation, capacity expansion, customer recruitment, customer retention, and market growth, and to engage the management team in using the computer to design strategic scenarios. The article concludes with comments on the impact of the project.
Using system dynamics to measure the value of information in a business firm
Authors: Clark Thomas D. , Augustine Fred K. 
Published: July 2007

AbstractThe primary focus of the research reported in this article was on measuring the value of information in a business firm. A five‐sector system dynamics model was developed and calibrated to an average firm in the U.S. metal‐can production industry. The model was used to test several propositions about the economic value of information. A framework in which to assess information value was developed, and the performance of the firm was assessed using cost, profitability, and efficiency measures for the information attributes of accuracy, timeliness, relevance, and reliability at the strategic, managerial, and operational decision‐making levels of the firm.
Transition in the New York State solid waste system: A dynamic analysis
Authors: Mashayekhi Ali N. 
Published: July 2007

AbstractThis article presents a system model to analyze the solid waste disposal problem in New York State. The model shows that the solid waste system will go through a costly transition from a landfill‐dominated mode of disposal to other disposal alternatives. The solid waste budget has to rise sharply during the transition. Solid waste expenses are financed by local taxes and state financial aid. If local and state governments do not respond rapidly to higher budget requirements, illegal disposal will increase and the total cost of transition will rise. Rapid response of the local authorities to increase the solid waste budget and to lower solid waste generation per capita is necessary to manage the transition with a lower total cost and less illegal disposal.
New technologies in simulation games
Authors: Simons Kenneth L. 
Published: July 2007

AbstractNew computer software allows modelers to create sophisticated educational tools based on models. Such computerized simulation games have generally failed as standalone educational tools. Effective learning requires that computerized simulation games not only simulate models but also give an understanding of structure and dynamics. Feedback during the game may be able to teach this systems understanding without textbook readings. Computerized feedback requires new methods of “expert” computer analysis; some methods are suggested in this article. Simulation games also offer the opportunity to integrate learning of structure and dynamics with learning of facts. Other tools need to be developed to help create simulation games and to give the games abilities that they do not yet have, such as access to data bases of models, pictures, and text, and connections between simulation games.
Complete representation of some functionals showing the Lavrentieff phenomenon
Authors: Esposito A. Corbo , Durante T. 
Published: July 2007

The functional F(u) = ∫Bf(x, Du) is considered, where B is the unit ball in R2, u varies in the set of the locally Lipschitz functions on R2 and f belongs to a family containing, as model case, the following integrand:
The computation of the relaxed functional F̄ is provided yielding an explicit representation formula.This formula nevertheless is not integral, because F̄ is not a measure and does not coincide with the obvious extension of F over all W1,p(B).This phenomenon is essentially due to the non-standard growth behaviour of f(x, z) in the variable z.
On the Dirichlet problem with several volume constraints on the level sets
Authors: Stepanov Eugene , Tilli Paolo 
Published: July 2007

We consider minimization problems involving the Dirichlet integral under an arbitrary number of volume constraints on the level sets and a generalized boundary condition. More precisely, given a bounded open domain Ω ⊂ Rn with smooth boundary, we study the problem of minimizing ∫Ω |∇u|2 among all those functions u ∈ H1 that simultaneously satisfy n-dimensional measure constraints on the level sets of the kind |{u = li}| = αi, i = 1,…, k, and a generalized boundary condition u ∈ K. Here, K is a closed convex subset of H1 such that ; the invariance of K under provides that the condition u ∈ K actually depends only on the trace of u along ∂Ω.By a penalization approach, we prove the existence of minimizers and their Hölder continuity, generalizing previous results that are not applicable when a boundary condition is prescribed.Finally, in the case of just two volume constraints, we investigate the Γ-convergence of the above (rescaled) functionals when the total measure of the two prescribed level sets tends to saturate the whole domain Ω. It turns out that the resulting Γ-limit functional can be split into two distinct parts: the perimeter of the interface due to the Dirichlet energy that concentrates along the jump, and a boundary integral term due to the constraint u ∈ K. In the particular case where K = H1 (i.e. when no boundary condition is prescribed), the boundary term vanishes and we recover a previous result due to Ambrosio et al.
Hyperbolic inverse boundary-value problem and time-continuation of the non-stationary Dirichlet-to-Neumann map
Authors: Kurylev Yaroslav , Lassas Matti 
Published: July 2007

Let M be a compact Riemannian manifold with non-empty boundary M. In this paper we consider an inverse problem for the second-order hyperbolic initial-boundary-value problem utt + but + a(x, D)u = 0 in M R+, u|MR+ = f, u|t=0 = ut|t=0 = 0. Our goal is to determine (M, g), b and a(x, D) from the knowledge of the non-stationary Dirichlet-to-Neumann map (the hyperbolic response operator) RT, with sufficiently large T 0. The response operator RT is the map , where is the normal derivative of the solution of the initial-boundary-value problem.More specifically, we show the following.
(i)It is possible to determine Rt for any t 0 if we know RT for sufficiently large T and some geometric condition upon the geodesic behaviour on (M, g) is satisfied.(ii)It is then possible to determine (M, g) and b uniquely and the elliptic operator a(x, D) modulo generalized gauge transformations.
The New Era of Eclipsing Binary Research with Large Telescopes
Authors: Ribas Ignasi 
Published: July 2007

AbstractThe advent of larger telescopes and powerful instrumentation enables the exploration of new aspects of faint eclipsing binaries that are just now becoming accessible. An example of this are eclipsing binaries in Local Group galaxies such as the LMC, SMC, M31 and M33, whose study yields not only stellar properties of stars formed in different chemical environments (thus providing useful model tests) but also direct distance determinations to the host galaxies. In general this is also applicable to eclipsing binaries belonging to any stellar ensemble. Another example is the observation and study of eclipsing very-low mass stars, brown dwarfs and planets. Besides the need for large telescopes because of their faintness, these also benefit from improved observational capabilities in the infrared spectral windows. Here we discuss the prospects for eclipsing binary research using photometry and spectroscopy from large telescopes.
Classical Observations of Visual Binary and Multiple Stars
Authors: Mason Brian D. 
Published: July 2007

AbstractChanges in the double star database are highlighted, describing various methods of observation (both historically and those of the past few years) and their effectiveness in different regimes of separation space. The various niches for wide- and narrow-field work as they apply to double and multiple stars are examined and the different types of information which each can provide are described. Despite the significant growth of the double star database, much can still be done, such as finding lost pairs, filling in missing parameters so that observing programs can select all stars appropriate to their capabilities, or providing at least gross kinematic descriptions. After more than 20 years of successful work, speckle interferometry and conventional CCD astrometry have replaced filar micrometry and photography as preferred classical techniques. Indeed, most work in filar micrometry is now being done by amateurs. Work on pairs described as neglected in the last major WDS data release (2001) is given as a specific example. Finally, the continued need to publish data in classical double star parameters is also discussed.
Bipolar Jets, Hot Interaction Regions, and Colliding Winds in OB Interacting Binaries
Authors: Peters Geraldine J. 
Published: July 2007

AbstractContemporary information on the nature of the circumstellar environment in early-type interacting binaries derived from observation is discussed. Emphasis is placed on results from FUV spectroscopy. New spectra from the FUSE spacecraft and earlier FUV observations with IUE have revealed the presence of hot interaction regions, bipolar outflows, splash outflows, and accretion hot spots in Algol-type systems with B-type mass gainers. In addition, close O-type pairs and systems containing O + W stars show a shock-heated region generated from their colliding winds. Recent FUSE observations of an apparent hot accretion spot and associated splash plasma in the direct-impact system U Cephei are presented.
Close Binary Star Observables: Modeling Innovations 2003-06
Authors: Wilson R. E. 
Published: July 2007

AbstractInnovative work on close binary models in 2003-06 improved upon synthesized line spectra, line profiles, and polarimetry; developed new ways of parameter estimation; and increased solution effectiveness and efficiency. Recent applications demonstrate the analytic power of binary system line spectrum models that pre-date the triennium. X-ray binary line profiles and radial velocity curves were refined by solution of the radiative transfer problem with specific inclusion of X-irradiation. Model polarization curves were generated by Monte Carlo experiments with multiple Thomson scattering in thin and thick binary system disks. In the parameter estimation area, independent developments by two groups now allow measurement of ephemerides, apsidal motion, and third body parameters from whole light and velocity curves, to supplement the traditional way of eclipse timings. Although the new route to those parameters is not well known within the ephemeris community, there are accuracy advantages and the number of applications is increasing. Numerical solution experiments on photometric mass ratios have checked two views of their intuitive basis, and show that mass ratios are well determined where star radii and limiting lobe radii are both well determined, which is for semi-detached or over-contact binaries with total-annular eclipses. Solution efficiency and automatic operation is needed for processing of light curves from large surveys, and will also be valuable for preliminary solutions of individually observed binaries. Neural networks have mainly been used for classification, and now a neural network program reliably finds preliminary solutions for W UMa binaries. Archived model light curves and Fourier fitting also are being pursued for classification and for preliminary solutions. Light curves in physical units such as erg·sec−1·cm−3 now allow direct distance estimation by combining the absolute accuracy of model stellar atmospheres with the astrophysical detail of a physical close binary model, by means of rigorous scaling between surface emission and observable flux. A Temperature-distance (T-d) theorem specifies conditions under which temperatures of both stars and distance can be found from light and velocity curves.
Evaluating the Gaia Contribution to the Field of Eclipsing Binaries with Ground-Based Spectroscopy and Hipparcos Photometry
Authors: Niarchos P. G. , Munari U. , Zwitter T. 
Published: July 2007

AbstractDuring its definition phase, ESA's Cornerstone mission Gaia was designed to perform extremely accurate photometry in 10 medium plus 5 broad bands and to collect about 90 epoch spectra with a resolving power of 11500 and a wavelength range 8480–8740Å (centered on the CaII triplet in the far red). Combining epoch photometry from the ground and the Hipparcos mission with ground-based spectra strictly simulating Gaia ones, we have investigated in a series of papers the performance expected from Gaia on SB2 EBs. We review here the results we obtained. The Gaia design is now under major revision, and its impact on EBs will be briefly addressed.
Fragile Binaries: Observational Leverage on Difficult Astrophysical Problems
Authors: Oswalt T.D. , Johnston K.B. , Rudkin M. , Vaccaro T. , Valls-Gabaud D. 
Published: July 2007

AbstractLoosely bound,fragilebinary stars, whose separations may reach ∼ 0.1 pc, are like open clusters with two coeval components. They provide a largely overlooked avenue for the investigation of many astrophysical questions. For example, the orbital distribution of fragile binaries with two long-lived main-sequence components provides a sensitive test of the cumulative effects of the Galactic environment. In pairs where one component is evolved, the orbits have been amplified by post-main-sequence mass loss, potentially providing useful constraints on the initial-to-final mass relation for white dwarfs. The nearly featureless spectra of cool white dwarfs usually provide little information about intrinsic radial velocity, full space motion, population membership, metallicity, etc. However, distant main sequence companions provide benchmarks against which those properties can be determined. In addition, the cooling ages of white dwarf components provide useful limits on the ages of their main sequence companions, independent of other stellar age determination methods. This paper summarizes some of the ways fragile binaries provide useful leverage on these and other problems of interest.
The Ejection of Runaway Massive Binaries
Authors: McSwain M. Virginia , Ransom Scott M. , Boyajian Tabetha S. , Grundstrom Erika D. , Roberts Mallory S.E. 
Published: July 2007

AbstractThe runaway O-type stars HD 14633 and HD 15137 are both SB1 systems that were probably ejected from the open cluster NGC 654. Were these stars dynamically ejected by close gravitational encounters in the dense cluster, or did the binaries each receive a kick from a supernova in one member? We present new results from our investigation of the optical, X-ray, and radio properties of these binary systems to discuss the probable ejection scenarios. We argue that these binaries may have been ejected via dynamical interactions in the dense cluster environment.
Catalogs of Wide Binaries: Impact on Galactic Astronomy
Authors: Chanamé Julio 
Published: July 2007

AbstractWide binaries, particularly in large numbers and as free from selection biases as possible, constitute a largely overlooked tool for studying the Galaxy. The goal of this review is to highlight the potential inherent to large samples of field wide binaries for research on problems as varied as star formation in the early Galaxy, the nature of halo dark matter, the evolution of the stellar halo, new geometric distances, metallicities, masses, and ages of field stars and white dwarfs, and much more. Using the Revised NLTT as an illustrative example, I review the main steps in the assembly of a large catalog of wide binaries useful for multiple applications. The capability of cleanly separating between the Galactic disk and halo populations using good colors and proper motions is emphasized. The critical role of large surveys for research on wide binaries as well as for the better understanding of the Galaxy in general is stressed throughout. Finally, I point out the potential for assembling new samples of wide binaries from available proper-motion surveys, and report on current efforts of using the SDSS towards this goal.