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Business processes and information technology are two areas that are very closely related to the sustained competitive advantage in organisations. However, investment in information technology often leads to disappointment, which may in part be due to the non-alignment of the information system domain with the business process domain. Simulation modelling is an established technique often used in business process change projects, as it allows a comparison of different possible scenarios without the expense of physically implementing the system. However business process simulation fails to effectively capture the information systems perspective in the model. This thesis contends that by combining information systems modelling techniques with business process simulation the model will be able to capture all the four perspectives (functional, behavioural, organisational and informational) of an organisation, and the design of the business processes and the information system will be better aligned. Initially, attempts were made to integrate business process simulation with computer network simulation in a simple two- or three-layered simulation model, but this gave rise to significant problems the most significant being the underlying assumptions of the original hypothesis. This led to a refined hypothesis in which the layered models were discarded along with the network domain. The revised hypothesis aimed to capture the informational changes that occur in the information system and therefore combines prototyping with business process simulation. This overcomes the unsafe assumptions of the initial hypothesis about whether the system is 'correct' and provides a method of validating the design of the information system within the context of the business processes. The integrated model allows concurrent design of the information system domain and the business process domain and therefore ensures that the domains are better aligned. The framework is tested on a case study and the results indicate that it is an effective tool in the combined design of business processes and information systems.

by Michael W. Golay and John H. Moinzadeh. / Includes bibliographical references. / Conducted under the sponsorship of Northeast Utilities Service Company.

M.A. Adelman. / "Revision of 86-008WP"--T.p. / Includes bibliographical references. / Research supported by the National Science Foundation. SES-8412971 Research supported by the Center for Energy Policy Research at the M.I.T. Energy Laboratory.

A cable laying ambush game is a two-person zero-sum game in which one player wishes to cross some interval while the other player has n cables that he can lay within the interval to ambush the infiltrator. In the literature solutions have been found for some cases in continuous and discrete cable laying ambush games when n = 2. The culmination of this thesis gives a complete solution for this much studied two cable game. However, prior to this numerous important results are established for the n cable game. It is first shown that the continuous game always possesses a value. This is done by showing that optimal strategies in a new finite game are also optimal in the continuous game. Further to this it is then shown that the discrete game can also be reduced to the same finite game and thus shown that it is equivalent to a finite game. This enables us to find many new results in both games. We also carry out much computational work enabling us to convert games into linear programmes and thus find the game value and optimal strategies. Using these techniques, we produce numerous new results in the three cable ambush game. Analysis of the game value function is then carried out which shows that it is a lower semi-continuous function and enables us to show how the game can be divided into regions which share the same value. By combining these with strategies in special cases for the ambusher, we produce a complete solution for the two cable game without having to calculate strategies for the infiltrator.

No description available.

Nature shows us many organised structures that form through interactions between their components with little external guidance. These self-assembling systems range from simple crystals to considerably more complex biological structures and organisms. Inspired by these systems, the development of programmable self assembling systems could lead to mass manufacturing processes that produce individually unique items. Current artificial self-assembling systems involve small numbers of centimetre-scale components, and have not resulted in structures anywhere near the complexity seen in natural systems. This thesis argues that to advance artificial self-assembling systems towards this complexity, the statistics of the interactions within self-assembling systems need to be empirically examined and understood. However, the pursuit of this involves the resolution of a variety of technical challenges. These are approached in this work through the development of a self-assembly toolkit that allows the collection of these statistics from a physical system with larger numbers of components than in previous works. A novel capacitive communication interface is developed for the components of this toolkit, which allows messaging between neighbouring components that are constrained to the surface of a plane. As self-assembling components reduce in size towards the microscale, the penalty for incorrect activation of a component’s binding mechanism is likely to increase. With this in mind, this capacitive communication interface is optimised to provide spatial alignment sensing, with the aim of allowing informed binding mechanism activation. The toolkit developed in this work uses components that are constrained to two degrees of freedom of motion. In pursuit of the development of programmable self-assembling components for 3D structures, a new design of alignment sensor for use in 3D is created. Simulation of this sensor, which is developed using an evolutionary algorithm, indicates that it is suited for detecting the alignment of components with three degrees of freedom. Approaches using computer vision are developed for the spatial tracking of the components of the toolkit, allowing the collection of empirical data regarding the interaction of components. The technical advances described within this work will allow the progression of data-driven self-assembly process design.

There is substantial competition among academic institutions. They compete for students, researchers, reputation, and funding. For success, they need not only to excel in teaching, but also their research profile is considered an important factor. Institutions accordingly take actions to improve their research profiles. They encourage researchers to publish frequently and regularly (publish or perish) on the assumption that this generates both more and better research. Collaboration has also been encouraged by institutions and even required by some funding calls. This thesis examines the empirical evidence on the interrelations among institutional research productivity, impact and collaborativity. It studies article publication data across ACM and Web of Science covering five disciplines { Computer Science, Pharmacology, Materials Science, Psychology and Law. Institutions that publish less seek to publish collaboratively with other institutions. Collaboration boosts productivity for all the disciplines investigated excepted Law; however, the amount of productivity increase resulting from the institutions' attempt to collaborate more is small. The world's most productive institutions publish at least 50% of their papers on their own. Institutions doing more collaborative work are not found to correlate strongly with their impact either. The correlation between collaborativity and individual paper impact or institutional impact is small once productivity has been partialled out. In Computer Science, Pharmacology and Materials Science, no correlation is found. The decisive factor appears to be productivity. Partialling out productivity results in the largest reductions in the remaining correlations. It may be that only better equipped and well-funded institutions can publish without having to rely on external collaborators. These institutions have been publishing most of their output non-collaboratively, and are also of high quality and highly reputable, which may have equipped and funded them in the first place.

The attitude and orbit control system of pico- and nano-satellites to date is one of the bottle necks for future scientific and commercial applications. A performance increase while keeping with the satellites’ restrictions will enable new space missions especially for the smallest of the CubeSat classes. This work addresses methods to measure and improve the satellite’s attitude pointing and orbit control performance based on advanced sensor data analysis and optimized on-board software concepts. These methods are applied to spaceborne satellites and future CubeSat missions to demonstrate their validity. An in-orbit calibration procedure for a typical CubeSat attitude sensor suite is developed and applied to the UWE-3 satellite in space. Subsequently, a method to estimate the attitude determination accuracy without the help of an external reference sensor is developed. Using this method, it is shown that the UWE-3 satellite achieves an in-orbit attitude determination accuracy of about 2°. An advanced data analysis of the attitude motion of a miniature satellite is used in order to estimate the main attitude disturbance torque in orbit. It is shown, that the magnetic disturbance is by far the most significant contribution for miniature satellites and a method to estimate the residual magnetic dipole moment of a satellite is developed. Its application to three CubeSats currently in orbit reveals that magnetic disturbances are a common issue for this class of satellites. The dipole moments measured are between 23.1mAm² and 137.2mAm². In order to autonomously estimate and counteract this disturbance in future missions an on-board magnetic dipole estimation algorithm is developed. The autonomous neutralization of such disturbance torques together with the simplification of attitude control for the satellite operator is the focus of a novel on-board attitude control software architecture. It incorporates disturbance torques acting on the satellite and automatically optimizes the control output. Its application is demonstrated in space on board of the UWE-3 satellite through various attitude control experiments of which the results are presented here. The integration of a miniaturized electric propulsion system will enable CubeSats to perform orbit control and, thus, open up new application scenarios. The in-orbit characterization, however, poses the problem of precisely measuring very low thrust levels in the order of µN. A method to measure this thrust based on the attitude dynamics of the satellite is developed and evaluated in simulation. It is shown, that the demonstrator mission UWE-4 will be able to measure these thrust levels with a high accuracy of 1% for thrust levels higher than 1µN. The orbit control capabilities of UWE-4 using its electric propulsion system are evaluated and a hybrid attitude control system making use of the satellite’s magnetorquers and the electric propulsion system is developed. It is based on the flexible attitude control architecture mentioned before and thrust vector pointing accuracies of better than 2° can be achieved. This results in a thrust delivery of more than 99% of the desired acceleration in the target direction. / Eine präzise Lage- und Orbitregelung stellt derzeit eine der größten Limitierungen der Einsatzmöglichkeiten von Kleinstsatelliten dar. Um zukünftige wissenschaftliche und kommerzielle Missionen auch mit dieser Klasse von Satelliten erfolgreich durchführen zu können, ist eine Leistungssteigerung bei gleichbleibender Größe und Masse nötig. Die vorliegende Arbeit beschäftigt sich mit der Verbesserung des Lageregelungssystems, der Vermessung der Ausrichtgenauigkeit im Orbit und der Herstellung von Orbitregelungskapazitäten mithilfe von fortschrittlicher Sensordatenanalyse und optimierter on-board Software. Die hier entwickelten Methoden wurden an im Orbit befindlichen Satelliten demonstriert und deren Gültigkeit gezeigt. Neben einer Methode um die typische CubeSat Lageerkennungssensorik im Orbit zu kalibrieren wurde ein Verfahren entwickelt, um die Ausrichtgenauigkeit ohne die Zuhilfenahme eines externen Referenzsensors zu bestimmen. Beide Verfahren wurden mithilfe des UWE-3 Satelliten im Orbit demonstriert. Die genaue Analyse der Dynamik eines Satelliten gibt Aufschluss über die vorwiegend herrschenden Störmomente. Für Kleinstsatelliten im erdnahen Orbit kann gezeigt werden, dass Störungen aufgrund von statischen magnetischen Verunreinigungen bei Weitem am meisten Einfluss auf die Dynamik des Satelliten haben. In dieser Arbeit wird eine Methode präsentiert, die Daten der Lageerkennung nutzt um das magnetische Dipolmoment eines Kleinstsatelliten zu bestimmen. Mithilfe dieses Verfahrens konnte das Dipolmoment von drei unterschiedlichen CubeSats im Bereicht von 23.1mAm² bis 137.2mAm² präzise bestimmt werden. Um die Lageregelungsgenauigkeit zu steigern wird ein Software Konzept präsentiert, welches die bekannten Störungen der Satellitendynamik inherent und energieoptimiert kompensiert. Die Anwendung dieser on-board Software wurde mit UWE-3 in einer Vielzahl von Lageregelungsexperimenten im Orbit demonstriert. Die Integration von elektrischen Antrieben wird zukünftigen Kleinstsatelliten die Möglichkeit zur Orbitkontrolle geben und damit viele neue Anwendungsszenarien eröffnen. Die Qualifizierung und Vermessung der Triebwerke im Orbit stellt jedoch eine technische Schwierigkeit dar, da Schübe im Bereich von µN gemessen werden müssen. Ein Verfahren zur genauen Bestimmung des Schubs eines solchen Triebwerks basierend auf dessen Auswirkung auf die Satellitendynamik wurde entwickelt und wird hier mit Hilfe von Simulationen für die UWE-4 Mission demonstriert. Es wird gezeigt, dass mit Hilfe von UWE-4 der Schub der Triebwerke mit einer hohen Genauigkeit von 1% Fehler für Schübe größer 1µN gemessen werden können. Eine magnetische Lageregelung unter Zuhilfenahme der elektischen Antriebe stellt das Konzept der hybriden Lage- und Orbitregelung für UWE-4 dar. Die damit erzielbare Leistung hinsichtlich der Ausrichtgenauigkeit sowie Orbitregelung wurde untersucht und ist hier für verschiedene Szenarien gezeigt.

Miniaturized satellites on a nanosatellite scale below 10kg of total mass contribute most to the number of launched satellites into Low Earth Orbit today. This results from the potential to design, integrate and launch these space missions within months at very low costs. In the past decade, the reliability in the fields of system design, communication, and attitude control have matured to allow for competitive applications in Earth observation, communication services, and science missions. The capability of orbit control is an important next step in this development, enabling operators to adjust orbits according to current mission needs and small satellite formation flight, which promotes new measurements in various fields of space science. Moreover, this ability makes missions with altitudes above the ISS comply with planned regulations regarding collision avoidance maneuvering. This dissertation presents the successful implementation of orbit control capabilities on the pico-satellite class for the first time. This pioneering achievement is demonstrated on the 1U CubeSat UWE–4. A focus is on the integration and operation of an electric propulsion system on miniaturized satellites. Besides limitations in size, mass, and power of a pico-satellite, the choice of a suitable electric propulsion system was driven by electromagnetic cleanliness and the use as a combined attitude and orbit control system. Moreover, the integration of the propulsion system leaves the valuable space at the outer faces of the CubeSat structure unoccupied for future use by payloads. The used NanoFEEP propulsion system consists of four thruster heads, two neutralizers and two Power Processing Units (PPUs). The thrusters can be used continuously for 50 minutes per orbit after the liquefaction of the propellant by dedicated heaters. The power consumption of a PPU with one activated thruster, its heater and a neutralizer at emitter current levels of 30-60μA or thrust levels of 2.6-5.5μN, respectively, is in the range of 430-1050mW. Two thruster heads were activated within the scope of in-orbit experiments. The thrust direction was determined using a novel algorithm within 15.7° and 13.2° of the mounting direction. Despite limited controllability of the remaining thrusters, thrust vector pointing was achieved using the magnetic actuators of the Attitude and Orbit Control System. In mid 2020, several orbit control maneuvers changed the altitude of UWE–4, a first for pico-satellites. During the orbit lowering scenario with a duration of ten days, a single thruster head was activated in 78 orbits for 5:40 minutes per orbit. This resulted in a reduction of the orbit altitude by about 98.3m and applied a Delta v of 5.4cm/s to UWE–4. The same thruster was activated in another experiment during 44 orbits within five days for an average duration of 7:00 minutes per orbit. The altitude of UWE–4 was increased by about 81.2m and a Delta v of 4.4cm/s was applied. Additionally, a collision avoidance maneuver was executed in July 2020, which increased the distance of closest approach to the object by more than 5000m. / Heutzutage werden überwiegend Kleinstsatelliten in niedrige Erdumlaufbahnen befördert, da dies schnell und sehr kostengünstig möglich ist. Von der Planung bis zum Raketenstart vergehen oft nur wenige Monate. Im vergangenen Jahrzehnt haben sich Kleinstsatelliten bezüglich Systemgestaltung, Kommunikation und Lageregelung dahingehend weiterentwickelt, dass diese in den Anwendungsbereichen Erdbeobachtung, Kommunikationsdienstleistungen und wissenschaftlichen Missionen mit herkömmlichen Satelliten konkurrieren können. Ein weiterer wichtiger Entwicklungsschritt für Kleinstsatelliten wäre die Möglichkeit der Orbitkontrolle. Diese würde die Betreiber befähigen, die Flugbahn der Satelliten entsprechend den aktuellen Zielen der Mission anzupassen und Formationsflug von Kleinstsatelliten durchzuführen, um neue wissenschaftliche Erkenntnisse in vielen Bereichen der Weltraumforschung zu fördern. Gleichzeitig würden Kleinstsatelliten den aktuell geplanten Vorschriften Rechnung tragen, nach denen Satelliten mit Flughöhen oberhalb der ISS manövrierfähig sein müssen, um Kollisionen zu vermeiden. Die vorliegende Dissertation präsentiert die erste erfolgreiche Orbitkontrolle auf einem Piko-Satelliten. Diese Pionierleistung wird auf dem 1U CubeSat UWE–4 demonstriert. Ein Schwerpunkt dieser Arbeit liegt dabei auf der Integration und dem Betrieb eines elektrischen Antriebssystems auf Kleinstsatelliten. Diese Integration des Antriebssystems hält den wertvollen Platz an den Außenflächen des CubeSats für zukünftige Nutzlasten frei und ermöglicht dessen Anwendung als Lage- und Orbitregelungsaktuator. Das verwendete NanoFEEP Antriebssystem beinhaltet vier Triebwerke, zwei Neutralisatoren und zwei Platinen zur Steuerung. Nach der Verflüssigung des Treibstoffs durch dedizierte Heizer können die Triebwerke pro Erdumrundung für 50 Minuten kontinuierlich genutzt werden. Der Stromverbrauch einer Steuerplatine mit einem aktiven Triebwerk, seinem Heizer und einem Neutralisator bei Emitterströmen von 30-60μA bzw. Schüben von 2.6-5.5μN liegt im Bereich von 430-1050mW. Im Rahmen von In- Orbit Experimenten wurden zwei Triebwerke aktiviert. Die Schubrichtungen der aktiven Triebwerke konnten mit einem neuartigen Algorithmus in einem Winkel von 15.7° bzw. 13.2° bezüglich ihrer Einbaurichtung bestimmt werden. Trotz mangelnder Steuerbarkeit der verbleibenden Triebwerke konnte eine Ausrichtung des Schubvektors unter Zuhilfenahme der magnetischen Aktuatoren des Lageregelungssystems erreicht werden. Mehrere Orbitregelungsexperimente zur Veränderung der Flughöhe konnten Mitte 2020 zum ersten Mal auf einem Piko-Satelliten gezeigt werden. Um die Flughöhe zu verringern, wurde ein Triebwerk über einen Zeitraum von zehn Tagen während 78 Orbits gefeuert, wobei dieses pro Erdumrundung für durchschnittlich 5:40 Minuten aktiviert wurde. Hierdurch wurde die Flughöhe von UWE–4 um 98m reduziert und seine Geschwindigkeit um ein Delta v von 7.2cm/s erhöht. In einem anderen Experiment wurde dasselbe Triebwerk während 44 Orbits in einem Zeitraum von fünf Tagen für durchschnittlich 7:00 Minuten aktiviert, wodurch die Flughöhe des Kleinstsatelliten um 74.2m angehoben und seine Geschwindigkeit um ein Delta v von 4.0cm/s verringert wurde. Zudem wurde ein Manöver zur Kollisionsvermeidung durchgeführt, das den Abstand zwischen UWE–4 und dem Objekt auf Kollisionskurs zum Zeitpunkt der kleinsten Annäherung um mehr als 5000m vergrößert hat.