Absence Of Constraints Research Articles

Unconstrained receding-horizon control of nonlinear systems

It is well known that unconstrained infinite-horizon optimal control may be used to construct a stabilizing controller for a nonlinear system. We show that similar stabilization results may be achieved using unconstrained finite horizon optimal control. The key idea is to approximate the tail of the infinite horizon cost-to-go using, as terminal cost, an appropriate control Lyapunov function. Roughly speaking, the terminal control Lyapunov function (CLF) should provide an (incremental) upper bound on the cost. In this fashion, important stability characteristics may be retained without the use of terminal constraints such as those employed by a number of other researchers. The absence of constraints allows a significant speedup in computation. Furthermore, it is shown that in order to guarantee stability, it suffices to satisfy an improvement property, thereby relaxing the requirement that truly optimal trajectories be found. We provide a complete analysis of the stability and region of attraction/operation properties of receding horizon control strategies that utilize finite horizon approximations in the proposed class. It is shown that the guaranteed region of operation contains that of the CLF controller and may be made as large as desired by increasing the optimization horizon (restricted, of course, to the infinite horizon domain). Moreover, it is easily seen that both CLF and infinite-horizon optimal control approaches are limiting cases of our receding horizon strategy. The key results are illustrated using a familiar example, the inverted pendulum, where significant improvements in guaranteed region of operation and cost are noted.

Chain dynamics in steady shear flow

Recent experimental measurements of the static and dynamic properties of single fluorescently labeled molecules of DNA in steady shear flow are compared with the predictions of a theoretical model of chain dynamics. The model is based on a set of coupled kinetic equations for the evolution of chain conformations and solvent fluctuations. The polymer is represented as a continuous curve with no excluded volume or hydrodynamic interactions, while the solvent is described by a time and space-varying velocity field. In the absence of constraints that enforce the finite extensibility of the chain at large shear rates, the calculated curves of the normalized dynamic autocorrelation function of the mean extension reproduce the qualitative features of the measured curves, but otherwise deviate significantly from them. We develop an analytically tractable finitely extensible model of the Gaussian chain that is more successful in reproducing the experimental data.

John Milton and the politics of slavery

The argument takes as its point of departure a number of recent studies of the ideologies employed to legitimize the decision by the English Parliament to go to war in 1642. The focus of such studies has generally been on common law theories about the relations between law, prerogative, and the liberty of subjects. As a result, they have arguably paid too little attention to the role played by classical ‐ and especially Roman law — ideas about freedom and unfreedom in the attack on the Stuart monarchy. In Roman law the concept of individual liberty is not defined (as it generally is in modern political theory) in terms of the absence of constraint on action; it is defined by contrast with the condition of slavery, which is viewed in turn as a condition in which someone lives subject to the will of someone else. John Milton is shown to have made use of exactly this analysis of freedom and unfreedom in the tracts he published between 1649 and 1651 in defense of the regicide and the English commonwealth. A new explication is thus offered of the sources as well as the character of Milton's vision of individual liberty.

The 20 K structure of p-amino-p′-nitrobiphenyl in the non-constraining environment of its β-cyclodextrin inclusion complex

Though p-amino-p′-nitrobiphenyl (PANB) is essentially planar in its crystalline form, it takes on a twisted conformation in its 2:2 crystalline inclusion complex with β-cyclodextrin (β-CD); the angles between the two phenyl rings are 40.6(2) and 42.0(1)° for the two molecules respectively, compared with 44.1(1)° for biphenyl in the gas phase, thus indicating the absence of constraints in the β-CD dimer cage.

Les choix de l'âge de la retraite. Aspects incitatifs des règles du régime général et effets de la réforme de 1993

Retirement Age Choices. Incentives under the General Social Security Scheme Rules and Effects of the 1993 reform by Louis-Paul Pelé and Pierre Ralle This paper studies private-sector employees' retirement age choices in the absence of constraints. We start with a brief description of the general social security scheme and the supplementary schemes. We then propose a theoretical modeUng, which shows that it is in employees' best interests not to collect their pensions until it has reached the "full rate". Given this assumption, we study how the generation of individuals bom in 1960 would be affected by the 1993 reform. Relatively few employees would put back their retirement age. The drop in pension, affecting all employees, would depend to a great extent on the length of working Ufe.

Numerical validation of a Eulerian hydrochemical code using a 1D multisolute mass transport system involving heterogeneous kinetically controlled reactions

It is demonstrated that at steady state, the 1D thermo-kinetic hydrochemical Eulerian mass balance equations in pure advective mode are indeed identical to the governing mass balance equations of a single reaction path (or geochemical) code in open system mode. Thus, both calculated reaction paths should be theoretically identical whatever the chemical complexity of the water–rock system (i.e., multicomponent, multireaction zones kinetically and equilibrium-controlled). We propose to use this property to numerically test the thermo-kinetic hydrochemical Eulerian codes and we employ it to verify the algorithm of the 1D finite difference code KIRMAT. Compared to the other methods to perform such numerical tests (i.e., comparisons with analytical, semi-analytical solutions, between two Eulerian hydrochemical codes), the advantage of this new method is the absence of constraints on the chemical complexity of the modelled water–rock systems. Moreover, the same thermo-kinetic databases and geochemical functions can be easily and mechanically used in both calculations, when the numerical reference comes from the Eulerian code with no transport terms ( u and D=0) and modify to be consistent with the definition of the open system mode in geochemical modelling. The ability of KIRMAT to treat multicomponent pure advective transport, subjected to several kinetically equilibrium-controlled dissolution and precipitation reactions, and to track their boundaries has been successfully verified with the property of interest. The required numerical validation of the reference calculations is bypassed in developing the Eulerian code from an already checked single reaction path code. A forward time-upstream weighting scheme (a mixing cell scheme) is used in this study. An appropriate choice of grid spacing allows to calculate within the grid size uncertainty the correct mineral reaction zone boundaries, despite the presence of numerical dispersion. Its correction enables us to improve the convergence and to extend the numerical test to mixed advective–dispersive mass transport. However, the skewness factor involves numerical oscillations that prevent to compute different grid spacing. The use of a different chemically controlled time step constraint in both calculations induces some inconsistencies into the validation tests. This numerical validation method may be applied as well as to check a thermo-kinetic hydrochemical finite element based code, from a 1D heterogeneous systems, and 2D–3D systems provided that they are designed so as to be 1D equivalent. A one-step algorithm and the use of a numerical reference coming from the Eulerian code to be tested ensure the potential success (accuracy) of the numerical validation method.

Electronic Markets and Electronic Governments

:Information technology (IT) has been able to transform the way many business transactions are organized. Mergers, acquisitions, outsourcing, and divestitures are all well-known changes that have resulted from the ability of IT to change the way organizations monitor and coordinate activities. This paper investigates actual and potential changes at the interface between the private and public sectors due to the introduction of IT. Governments, finding themselves with commercially valuable stores of data and software, are beginning to exhibit entrepreneurial characteristics. In other cases, the introduction of IT has created pressures for the privatization of activities previously operated by governments. The introduction of IT has the potential to change the way citizens participate in governments at all levels. This paper surveys these issues and identifies the pressures that would, in the absence of constraints, lead to the conduct of activities in the private or public sector. Finally, the paper examines factors that impede the natural progression toward more desirable organizational forms through the application of IT.

Shortest-Prediction Horizon Nonlinear Model Predictive Control

This article presents a continuous-time formulation of model predictive control. This formulation allows (i) to establish the connections between model predictive control and input-output linearizing control methods and (ii) to address the problems of constraint handling and windup in input-output linearizing control methods. Model predictive control laws with the shortest possible prediction horizon are derived for constrained nonlinear processes with deadtime. They have explicit analytical form, and thus their implementation does not require on-line optimization. Furthermore, in the absence of constraints, they are input-output linearizing.

A continuous-time formulation of nonlinear model predictive control

A model predictive approach is used to derive a continuous-time, nonlinear feedback control law for open-loop stable, single-input single-output processes with deadtime. The derived model predictive control law minimizes a quadratic performance index in the presence of input constraints and process deadtime. A key feature of the control law is that, for its implementation, one does not need to perform an online optimization. In the absence of constraints, the control law in special cases is identical to the feedback controllers that have already been derived using a geometric approach. The connections between the derived control law and (a) the globally linearizing control and (b) the linear internal model control are established. The model predictive approach provides some insight into the problem of constraint handling in geometric control methods. The application of the theory is illustrated by a chemical reactor example.

McDowell's Direct Realism and Platonic Naturalism

In Mind and World* (Cambridge, Mass.: Harvard Univeristy Press, 1994). Professor McDowell's main concern is to answer the venerable question of the relation of mind and world. He formulates this question in the somewhat quaint Kantian vernacular of spontaneity and receptivity: What's the relation between spontaneity and receptivity? According to McDowell, two opposite and equally unsatisfactory answers to this query have dominated traditional epistemology. First, foundationalists have declared that receptivity provides the Given which furnishes both the content and the grounding for spontaneity's empirical thoughts and judgements. On the other hand, coherentists have declared that the Given, being non-conceptual, is useless for the purpose of providing the content or the grounding for those empirical thoughts and judgements. Foundationalists retort that coherence, in the absence of constraints originating outside of thought, is incapable of explaining how empirical thoughts and judgements bear on the world. McDowell aptly pictures this exchange between advocates of the Given and advocates of uncon-

Truth and Martyrdom: The Structure of Discipleship in Veritatis Splendor

Early in February, I was privileged to participate in a gathering of forty-five predominantly Catholic philosophers and theologians who met to discuss John Paul II’s encyclical Veritatis Splendor. Most of the discussion at the conference focused on the second of the encyclical’s three chapters, which deals with “some trends of theological thinking and certain philosophical affirmations [that] are incompatible with revealed truth.”(§29) Conspicuously absent was any attention to either the first or especially the third chapters of the encyclical. The first chapter investigates the nature of Christian discipleship through the lens of St Matthew’s account of Jesus’ meeting with the rich young man. (Matt 19) The third chapter treats the issue of Christian martyrdom and other sources for Christian renewal. In the course of the discussion, the notion of discipleship was mentioned rarely, and the subject of martyrdom never came up. By concentrating almost exclusively on the second chapter, the conference failed to locate the encyclical’s critique of particular “trends of theological thinking and certain philosophical affirmations” within the context provided by Veritatis Splendor itself, namely that of Christian discipleship. In doing so this group mirrored much of the general response to Veritatis Splendor, which has centred almost exclusively on the second chapter. It is my goal to shift this focus, and to highlight the primacy of discipleship for a right understanding of Veritatis Splendor.Veritatis Splendor has a message about a notion central to our lives: freedom. The Pope argues that the common conception of freedom as merely the absence of constraints is misguided. Christian freedom must be connected with the pursuit of truth.

Modeling the Choice of Telecommuting: Setting the Context

In this paper a conceptual model of the individual decision to telecommute is presented. Key elements of that decision, including constraints, facilitators, and drives, are defined and the relationships among them described. The major types of constraints (if negative) or facilitators (if positive) include external factors related to awareness, the organization, and the job, and internal psychosocial factors. The major types of drives are work, family, leisure, ideology, and travel. It is argued that the absence of constraints is a necessary but not sufficient condition for telecommuting to be adopted by an individual. The presence of one or more drives, assumed to be associated with some dissatisfaction, is necessary to activate the search for a solution to that dissatisfaction. The choice set contains those alternative solutions perceived to be feasible by the individual. It may or may not contain telecommuting (depending on whether all constraints are nonbinding or not), and probably contains other alternatives having nothing to do with telecommuting. Each alternative is evaluated in terms of how effectively it satisfies the drive, and the individual's attitudes toward it. The alternative (or bundle of alternatives) which maximizes individual utility becomes the preferred behavioral pattern. However, short-term constraints may prevent the preferred behavior from being chosen. The process is a dynamic one, in which previous choices affect attitudes and constraints and alter drives. Work directed by the authors is under way to operationalize the conceptual model.

ALLOCATION TO ATTRACTIVE STRUCTURES IN ANIMAL-POLLINATED FLOWERS.

An optimal allocation model was developed for the evolutionarily stable size of attractive structures of flowers (ESA) in animal-pollinated plants. It was assumed that a plant can change the sizes of attractive and sexual structures of a flower and the size and the number of flowers. In the absence of constraints on flower size, the ESA should not depend on the frequency of self-fertilization or the sexuality of plants. However, with constraints on flower size, the ESA decreases with increasing self-fertilization, except in special cases, and it is possible that males have a larger or a smaller ESA than females. Thus, differences in self-fertilization and sexuality alone cannot explain the differences in allocation among nondomesticated plants. In addition, attractive structures can contribute more to male or female function depending on the cost of gamete production, pollination efficiency for pollen and ovules, and pollinator availability.

An Inquiry into the Relationship between Economic Freedom and Economic Justice Economic Freedom and Economic Justice

Makes the distinction between negative freedom or liberty, which means the absence of constraint and compulsion, and positive freedom, which always implies the power to make one′s will effective to gain access to a chosen alternative. Argues that positive freedom can be used either creatively or destructively. The creative use of positive freedom enhances and improves the economic freedom and economic justice that accrues to other people. The destructive use of positive freedom damages and diminishes the economic freedom and economic justice of others. It follows that the government should intervene in the political and social economy to encourage and to facilitate the creative use and to discourage or prohibit the destructive use of positive freedom.

Negotiation of leisure constraints

Abstract Virtually all past leisure constraints research has been based on a conception of constraints as insurmountable obstacles to leisure participation. Thus, it has typically been assumed that if an individual encounters a constraint, the outcome will be nonparticipation. This article elaborates an alternative view of constraints that has recently begun to appear in the literature, summarized in the central proposition that leisure participation is dependent not on the absence of constraints but on negotiation through them. Such negotiation may modify participation rather than foreclosing it. Evidence from the existing literature for the negotiation proposition is examined, and five additional propositions are defined concerning relative success in negotiating constraints, interactions between different types of constraints, and balance between constraints and motivations.

La Nature est morte, vive la nature!

In a notorious passage of The Gay Science, Friedrich Nietzsche portrays a madman carrying a lantern in broad daylight and searching for God. Nietzsche's mirthless character then declares that is dead and says that we have murdered Him. Three years ago, Bill McKibben, with dramatic flourish of a contemporary Nietzsche, proclaimed the end of His book by that title was serialized in New Yorker magazine and went on to become a best seller.[1] Once flourishing nature, he argues, has as such come to an end--and we are terminators. The death of God in nineteenth century was death of an idea. The end of nature in twentieth century seems to be a much more literal matter. According to McKibben, one can no longer find any place on earth untrammeled by works of man.[2] The forests, lakes, and streams of Adirondacks, where McKibben lives, famously designated in 1885 by New York state legislature to be forever wild, are ubiquitously affected by acid rain. In addition to such evident works of man as trans-Alaska pipeline, permafrost in erstwhile arctic wilderness is everywhere contaminated with measurable traces of toxic chemicals--everything from DDT to PCBs. There is a hole in ozone over Antarctic created by fugitive chlorofluorocarbons. And once autonomous nature can only become more compromised by human technology as greenhouse effect kicks in, followed by a higher sea level, changed weather patterns, hotter summers, milder winters, desiccated forests, enlarged deserts, irruptions of weedy fauna and flora, and impoverished ecosystems. Nature as Other is over. Everywhere man's works insidiously pervade, if they do not palpably dominate, landscape. Nowhere is earth and its community of life unaffected by man. There are precious few places where man is merely a visitor and not an inhabitant: even South Pole has a permanently occupied research station. The once impenetrable and mysterious Amazon basin is riddled with roads, power plants, gold mines, boom towns, cattle ranches, settlers' swiddens, and coca plantations. Here in United States, man's visitation of designated wilderness areas is so intense that permits are required to limit density, and restrictions on what backpackers can and cannot do make a mockery of Bob Marshall's equation of wilderness with freedom and absence of constraints. Before we all go into mourning, however, let me suggest that what has come to an untimely end is not nature per se, but modern idea of nature. We have no more literally killed nature than we have God. Indeed, we might want to celebrate, rather than mourn, since modern picture of nature is false and its historical tenure has been pernicious. A new dynamic and systemic postmodern concept of nature, which includes rather than excludes human beings, is presently taking shape. From point of view of this new notion of nature, human technologies should be evaluated on their ecological merits, not condemned wholesale. Indeed, there is some hope that a new generation of technology may be not only ecologically benign, but might even help to disseminate broadly an ecological world view and an associated environmental ethics. The Modern Idea of Nature The first and most fundamental feature of modern idea of nature is a sharp dichotomy between man and nature--a dichotomy that is all more radical because it is a feature of both wellsprings of Western intellectual heritage. In first book of Bible, alone among all other creatures, God makes man in His own image, giving him dominion over and charging him to subdue earth and all its denizens. In ancient Greek philosophy, man is set apart from nature because he alone among animals is supposed to be rational. In late medieval and early modern periods, thinkers as different from one another as Thomas Aquinas and Rene Descartes synthesized these two strands of thought, Judeo-Christian and Greco-Roman. …

Maxwell's equations in divergence form for general media with applications to MHD

Maxwell's equations in media with general constitutive relations are reformulated in covariant form as a system of divergence equations without constraints. Our reformulation enables us to express general electro-magneto-fluid problems as hyperbolic systems in divergence form. We illustrate this method on the MHD problem. In the absence of constraints, a general representation is derived for the characteristics form for first-order systems of quasi-linear partial differential equations in vector fields and scalars. Using this covariant formulation of characteristics, we find that the principle of covariance imposes a very rigid structure on the infinitesimally small amplitude waves in MHD. To demonstrate the power of the reformulation, we study numerically ultra-relativistic wave breaking using the divergence formulation of MHD.

Artistic Creativity and the Meaning of Freedom

Despite the fact that today's art world is thought to be a pluralistic one, ostensibly free of many of the constraints inherent in past eras, many artists feel that they are still unable to create meaningful art. Thus we encounter a paradox. Too much freedom somehow leads to too little. It is argued here, however, that because freedom means significantly more than the mere absence of constraints, there is no paradox at all; the illusion of freedom has simply been mistaken for freedom itself. With a more inclusive conception of what freedom means, both in the context of art and in that of society more generally, we may be more likely to see freedom actualized.

Pulse motor control for maximizing average velocity

This paper examines the problem of optimal pulse rocket motor control for minimum time to a specified final range. A complete characterization of the pulsing conditions is derived for the constant altitude case. The results are portrayed in the form of pulse-firing envelopes (one for each pulse) that are range- and velocity-dependent. For the variable altitude case, the problem of optimized guidance and pulse motor control in the vertical plane is treated. One of the major conclusions from this problem analysis is that the use of pulse motors offers little advantage when vertical plane guidance is optimized in the absence of constraints. Special attention is given to the optimality conditions that arise at the junction of boost and coast arcs, and a numerical procedure for computing the junction condition is outlined.

Causes of Polygyny: Ecology, Economy, Kinship, and Warfare

We discuss and test competing explanations for polygyny based on household economics, malecentered kin groups, warfare, and environmental characteristics. Data consist of codes for 142 societies from the Standard Cross‐Cultural Sample, including new codes for polygyny and environmental characteristics. An explanatory model is tested for the worldwide sample using regression analysis, and then replicated with regional samples. We obtain convergent results with two different measures of polygyny, cultural rules for men's marriages and the percentage of women married polygynously. We conclude that the best predictors of polygyny are fraternal interest groups, warfare for capture of women, absence of constraints on expansion into new lands, and environmental quality and homogeneity.