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Global optimization methods can be classified into two non-overlapping classes with respect to accuracy: those with guaranteed accuracy and those without. The former are called bounding methods, the latter point methods. Bounding methods compute lower and upper bounds of function over a box and give a lower bound and an upper bound for the minimum. Point methods compute function values at points and output as the minimum the function value at a point. R. E. Moore was the first to propose the bounding method using interval arithmetic for unconstrained global optimization. The first bounding method using interval arithmetic for constrained global optimization was due to E. R. Hansen and S. Sengupta. These methods are the well known bounding methods. Since these methods use interval arithmetic, we call them interval arithmetic methods. This dissertation studies the new bounding methods that use interval constraints, which is called interval constraint methods. We prove that interval constraints is a generalization of interval arithmetic, computing an interval function in interval constraints gives the same result as in interval arithmetic. We propose a hypernarrowing algorithm using interval constraints. This algorithm produces a smaller interval result for the range of function f over a given domain than interval arithmetic. We present a generic Branch-and-Bound algorithm for unconstrained global optimization, prove the properties of the algorithm, and propose improvements on the algorithm. From this algorithm, we can obtain its interval arithmetic version and interval constraint version. We investigate the role of interval constraints in global optimization and discuss the performance and characteristics of interval arithmetic methods and interval constraint ones. Based on the Branch-and-Bound algorithm for unconstrained global optimization, we present a generic Branch-and-Bound algorithm for constrained global optimization, study the effect of Fritz-John conditions as redundant constraints and compare the interval arithmetic method for constrained optimization with the interval constraint one. / Graduate

Various authors from countries as diverse as South Africa, the Netherlands, Britain and the United States of America, reported the existence of constraints in corporate communication practitioner career advancement (Moss, 2000:1,6; Moss, Warnaby&Newman, 2000:277,302; Plowman, 1998:243; Spicer, 1997:84; Steyn, 1999:21; Steyn, 2000a:2; Steyn, 2000b:70; Steyn&Puth, 2000:3,7,10,12; Van Ruler, 1997:263; Visagie, 1999:148). Their findings have prompted this exploratory phenomenological research. The primary objective of this research is to explore some corporate communication practitioners’ perceptions of the constraints experienced in advancing to more senior corporate communication roles in the South African banking industry. The research is approached from the excellence and feminist meta-theoretical perspectives. In particular it is based on the strategic contingency theory, organisational structure theory, power-control theory, interpersonal perception theory and corporate communication roles theory. The study focuses on two concepts, namely ‘constraints’ and ‘role’. The research reflected a snapshot in time of the current communication practitioner’s emotional, relational or situational experience of their efforts to advance their careers. The aim was not to support or validate any pre-selected model or theory, but rather to embrace the constraint in a non-assumptive manner as it unfolds from the perspective of the communication practitioner experiencing it (Callahan, 2000:105; Scannell-Desch, 2000). From the findings of the research, one could argue that there are various individual, organisational and professional career constraints that practitioners experience in trying to advance their careers. Over and above the constraints noted in literature, the study identified a few more constraints such as organisational politics, the time spent in the organisation, the practitioner’s lack of networking and relationship building skills, lack of knowledge of overseas practice and the lack of standardisation of communication practitioner deliverables. / Dissertation (MCom)--University of Pretoria, 2006. / Communication Management / MCom / Unrestricted

There are constraints hindering South Africa‘s ICT entrepreneurs form being internationally competitive. The purpose of this research was to explore them through experiential surveying of South African ICT experts who have successfully internationalised. The outcome of the research was an understanding of both internal organisational constraints and external environmental constraints. Six constraints were explored in detail: human resource, strategy and finance from within the enterprise and political/regulatory, economic and socio-cultural within the environment. It was established that internal constraints exert more influence than external constraints. Human resource was the critical constraint followed by financing which could be influenced both externally and internally. Other constraints are also explored including technology constraints and lack of national planning and collaboration. Recommendations are made to stakeholders. Copyright / Dissertation (MBA)--University of Pretoria, 2010. / Gordon Institute of Business Science (GIBS) / unrestricted

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Yes / Research on business growth has blossomed, yet scholars often complain face the difficulty of distililing a clearer pitcure of the business growth phenomenon. This paper attempts to overcome this limitation by reviewing and synthesizing extant research on business growth. First, we begin by examining Penrose’s view of firm growth. Second, we highlight how business growth is measured; these are absolute or relative change and growth as a process. Third, we explore theories of business growth; integrated models-theories that explain the factors that drive business growth and (2) stage models which view business growth as a series of phases or stages of development through which a firm must pass in its life-cycle. Fourth, we examine modes of business growth; these are organic vs. acquisition growth, growth through networks and alliances and growth through internationalization. Fifth, we examine drivers and constraints to business growth. We conclude the review by pointing out areas of harmony and contention in the literature, from which we suggest opportunities for future research.

The following is an exploration into the optimal guidance and control of gun-launched guided projectiles. Unlike their early counterparts, modern-day gun-launched projectiles are capable of considerable accuracy. This ability is enabled through the use of control surfaces, such as fins or wings, which allow the projectile to maneuver towards a target. These aerodynamic features are part of a control system which lets the projectile achieve some effect at the target. With the advent of very high velocity guns, such as the Navy's electromagnetic railgun, these systems are a necessary part of the projectile design. This research focuses on a control scheme that uses the projectile's angle of attack as the single control in the development of an optimal control methodology that maximizes impact velocity, which is directly related to the amount of damage in icted on the target. This novel approach, which utilizes a reference trajectory as a seed for an iterative optimization scheme, results in an optimal control history for a projectile. The investigation is geared towards examining how poor an approximation of the true optimal solution that reference trajectory can be and still lead to the determination of an optimal control history. Several different types of trajectories are examined for their applicability as a reference trajectory. Although the use of aerodynamic control surfaces enables control of the projectile, there is a potential down side. With steady development of guns with longer ranges and higher launch velocities, it becomes increasingly likely that a projectile will y into a region of the atmosphere (and beyond) in which there is not sufficient air ow over the control surfaces to maintain projectile control. This research is extended to include a minimum dynamic pressure constraint in the problem; the imposition of such a constraint is not examined in the literature. Several methods of adding the constraint are discussed and a number of cases with varying dynamic pressure limits are evaluated. As a result of this research, a robust methodology exists to quickly obtain an optimal control history, with or without constraints, based on a rough reference trajectory as input. This methodology finds its applicability not only for gun-launched weapons, but also for missiles and hypersonic vehicles. / Doctor of Philosophy / As the name implies, optimal control problems involve determining a control history for a system that optimizes some aspect of the system's behavior. In aerospace applications, optimal control problems often involve finding a control history that minimizes time of ight, uses the least amount of fuel, maximizes final velocity, or meets some constraint imposed by the designer or user. For very simple problems, this optimal control history can be analytically derived; for more practical problems, such as the ones considered here, numerical methods are required to determine a solution. This research focuses on the optimal control problem of a gun-launched guided projectile. Guided projectiles have the potential to be significantly more accurate than their unguided counterparts; this improvement is achieved through the use of a control mechanism. For this research, the projectile is modeled using a single control approach, namely using the angle of attack as the only control for the projectile. The angle of attack is the angle formed between the direction the projectile is pointing and the direction it is moving (i.e., between the main body axis and the velocity vector of the projectile). An approach is then developed to determine an optimal angle of attack history that maximizes the projectile's final impact velocity. While this problem has been extensively examined by other researchers, the current approach results in the analytical determination of the costate estimates that eliminates the need to iterate on their solutions. Subsequently, a minimum dynamic pressure constraint is added to the problem. While extensive investigation has been conducted in the examination of a maximum dynamic pressure constraint for aerospace applications, the imposition of a minimum represents a novel body of work. For an aerodynamically controlled projectile, (i.e., one controlled with movable surfaces that interact with the air stream), dropping below a minimum dynamic pressure may result in loss of sufficient control. As such, developing a control history that accommodates this constraint and prevents the loss of aerodynamic control is critical to the ongoing development of very long range, gun-launched guided projectiles. This new methodology is applied with the minimum dynamic pressure constraint imposed and the resulting optimal control histories are then examined. In addition, the possibility of implementing other constraints is also discussed.

I evaluated possible constraints on the evolution of viviparity in the lizard genus Sceloporus by experimentally extending the length of egg retention past the normal time of oviposition for a number of oviparous species. Observations also included a representative of the genus Urosaurus, the sister genus to Sceloporus. I determined the effects of retention on embryonic development, hatchlings, and gravid females. Results indicated that the proximate constraints on longer retention times and viviparity are 1) embryonic development becomes arrested or severely retarded in utero, and 2) the ability to maintain gravidity past the normal time of oviposition is limited in some species. Observations on Urosaurus further showed that extended egg retention results in hatchlings with traits that are associated with lower fitness. I also tested the hypothesis that reproductive Sceloporus lower their body temperatures during activity because their normal body temperatures are detrimental to embryos. Observations on a viviparous species of Sceloporus indicated that the normal body temperature of the female was detrimental to embryonic development. This result is indicates that viviparity would be constrained in some squamate lineages if maternal body temperatures are too high for successful embryonic development. I also evaluated the hypothesis that the evolutionary transition from oviparity to viviparity involves a "reduction" of the eggshell concurrent with longer durations of egg retention. If this hypothesis is correct, then attributes of eggshells that should enhance exchange of respiratory gases (i.e., thickness, density, permeability to water vapor) would be correlated with the maximal developmental stage that embryos are able to attain in the oviducts (i.e., stage of developmental arrest). The results of this study indicated that these features of shells do not determine the stage at which development becomes arrested. Thus, the results do not support the hypothesis that shell reduction occurs concurrently with longer periods of egg retention. The results are consistent with the alternative hypothesis that reduction of the eggshell occurs after viviparity has evolved. / Ph. D.

In today’s emerging information systems, it is natural to have data distributed across multiple sites. We define a System of Databases (SyDb) as a collection of autonomous and heterogeneous databases. R-SyDb (System of Relational Databases) is a restricted form of SyDb, referring to a collection of relational databases, which are independent. Similarly, X-SyDb (System of XML Databases) refers to a collection of XML databases. Global integrity constraints ensure integrity and consistency of data spanning multiple databases. In this dissertation, we present (i) Constraint Checker, a general framework of a mobile agent based approach for checking global constraints on R-SyDb, and (ii) XConstraint Checker, a general framework for checking global XML constraints on X-SyDb. Furthermore, we formalize multiple efficient algorithms for varying semantic integrity constraints involving both arithmetic and aggregate predicates. The algorithms take as input an update statement, list of all global semantic integrity constraints with arithmetic predicates or aggregate predicates and outputs sub-constraints to be executed on remote sites. The algorithms are efficient since (i) constraint check is carried out at compile time, i.e. before executing update statement; hence we save time and resources by avoiding rollbacks, and (ii) the implementation exploits parallelism. We have also implemented a prototype of systems and algorithms for both R-SyDb and X-SyDb. We also present performance evaluations of the system.

Constraints allow developers to specify desired properties of systems in a number of domains, and have those properties be maintained automatically. This results in compact, declarative code, avoiding scattered code to check and imperatively re-satisfy invariants. Despite these advantages, constraint programming is not yet widespread, with standard imperative programming still the norm. There is a long history of research on integrating constraint programming with the imperative paradigm. However, this integration typically does not unify the constructs for encapsulation and abstraction from both paradigms. This impedes re-use of modules, as client code written in one paradigm can only use modules written to support that paradigm. Modules require redundant definitions if they are to be used in both paradigms. We present a language – Babelsberg – that unifies the constructs for en- capsulation and abstraction by using only object-oriented method definitions for both declarative and imperative code. Our prototype – Babelsberg/R – is an extension to Ruby, and continues to support Ruby’s object-oriented se- mantics. It allows programmers to add constraints to existing Ruby programs in incremental steps by placing them on the results of normal object-oriented message sends. It is implemented by modifying a state-of-the-art Ruby virtual machine. The performance of standard object-oriented code without con- straints is only modestly impacted, with typically less than 10% overhead compared with the unmodified virtual machine. Furthermore, our architec- ture for adding multiple constraint solvers allows Babelsberg to deal with constraints in a variety of domains. We argue that our approach provides a useful step toward making con- straint solving a generic tool for object-oriented programmers. We also provide example applications, written in our Ruby-based implementation, which use constraints in a variety of application domains, including interactive graphics, circuit simulations, data streaming with both hard and soft constraints on performance, and configuration file Management. / Constraints – Beschränkungen und Abhängigkeiten zwischen Systemteilen – erlauben es Entwicklern, erwünschte Eigenschaften von Systemen zu spezifizieren, sodass diese automatisch sichergestellt werden. Das führt zu kompaktem, deklarativem Quelltext, und vermeidet verstreute Anweisungen, die wiederholt Invarianten prüfen und wiederherstellen müssen. Trotz dieser Vorteile ist Programmieren mit Constraints nicht verbreitet, sondern imperatives Programmieren die Norm. Es gibt eine lange Forschungsgeschichte zur Integration von Constraints mit imperativem Programmieren. Jedoch vereinheitlicht diese Integration nicht die Programmierkonstrukte zur Abstraktion und Kapselung beider Paradigmen. Das verhindert die Wiederverwendung von Modulen, da Quelltext, der in einem Paradigma geschrieben wurde, nur Module verwenden kann, die so geschrieben sind, dass sie dieses Paradigma unterstützen. Module benötigen daher redundante Definitionen, wenn sie in beiden Paradigmen zur Verfügung stehen sollen. Wir präsentieren hier eine Sprache – Babelsberg – welche die Konstrukte zur Abstraktion und Kapselung vereinheitlicht, indem sie bekannte objektorientierte Methodendefinitionen sowohl für deklarativen, als auch für imperativen Code verwendet. Unser Prototyp –Babelsberg/R – ist eine Erweiterung von Ruby, und unterstützt Rubys objektorientierte Semantik. Dieser erlaubt es Programmieren, Constraints schrittweise zu existierenden Ruby Programmen hinzuzufügen, indem diese auf den Ergebnissen von Methodenaufrufen deklariert werden. Der Prototyp ist auf Basis einer virtuellen Maschine für Ruby implementiert, wobei die Ausführungsgeschwindigkeit von objektorienterten Programmteilen ohne Constraints nur minimal – typischerweise weniger als 10% – beeinträchtigt wird. Weiterhin erlaubt es unsere Architektur, je nach Anwendungsfall, mehrere Lösungsalgorithmen für Constraints zu verwenden. Wir argumentieren, dass unser Ansatz einen nützlichen Schritt darstellt, um Programmieren mit Constraints zu einem allgemeinen Werkzeug für objektorientierte Programmierer zu machen. Wir zeigen Beispielanwendungen, die unserer Ruby-basierten Implementierung geschrieben sind, welche Constraints in einer Reihe von Anwendungen verwenden: Für interaktive Grafik, Schaltkreissimulation, Datenströme mit sowohl harten, als auch weichen Constraints bezüglich ihrer Geschwindigkeit, und Konfigurationsverwaltung.