No description available.

In programming languages, record types give a universe of discourse (via so-called Σ-types); parameterised record types fix parts of that universe ahead of time (via Π-types), and algebraic datatypes give us first-class syntax (via W-types), which can then be used to program, e.g., evaluators and optimisers. A frequently-encountered issue in library design for statically-typed languages is that, for example, the algebraic datatype implementing the first-class view of the language induced by a record declaration cannot be defined by simple reference to the record type declaration, nor to any common “source”. This leads to unwelcome repetition, and to maintenance burdens. Similarly, the “unbundling problem” concerns similar repetition that arises for variants of record types where some fields are turned into parameters. The goal of this thesis is to show how, in dependently-typed languages (DTLs), algebraic datatypes and parameterised record types can be obtained from a single pragmatic declaration within the dependently-typed language itself, without using a separate “module language”. Besides this practical shared declaration interface, which is extensible in the language, we also find that common data structures correspond to simple theories. Put simply, the thesis is about making tedious and inexpressible patterns of programming in DTLs (dependently typed languages) become mechanical and expressible. The situations described above occur frequently when working in a dependently-typed language, and it is reasonable enough to have the computer handle them. We develop a notion of contexts that serve as common source for definitions of algebraic datatype and of parameterised record types, and demonstrate a “language” of “package operations” that enables us to avoid the above-mentioned replication that pervades current library developments. On the one hand, we demonstrate an implementation of that language as integrated editor functionality — this makes it possible to directly emulate the different solutions that are employed in current library developments, and refactor these into a shape that uses single declaration of contexts, thus avoiding the usual repetition that is otherwise required for provision of record types at different levels of parameterisation and of algebraic datatypes. On the other hand, we will demonstrate that the power of dependently-typed languages is sufficient to implement such package operations in a statically-typed manner within the language; using this approach will require adapting to the accordingly-changed library interfaces. Although our development uses the dependently-typed programming language Agda throughout, we emphasise that the idea is sufficiently generic to be implemented in other DTLs. / Thesis / Doctor of Philosophy (PhD) / There are things we want to use from various perspectives, our tools show that this is possible without any duplication and in a practical and efficient fashion.

A considerable number of Very Long Baseline Interferometry (VLBI) surveys have been conducted in the northern hemisphere and very few in the southern hemisphere mostly because of a lack of telescopes and therefore adequate baseline coverage. Thus there is a deficit of calibrator sources in the southern hemisphere. Further, some of the most interesting astronomical objects eg. the galactic centre and the nearest galaxies (the small and large Magellanic Clouds) lie in the southern hemisphere and these require high resolution studies. With a major expansion of radio astronomy observing capability on its way in the southern hemisphere (with the two SKA (Square Kilometre Array) precursors, meerKAT (Karoo Array Telescope) and ASKAP (Australian SKA Pathfinder), leading to the SKA itself) it is clear that interferometry and VLBI in the southern hemisphere need a dense network of calibration sources at different resolutions and a range of frequencies. This work seeks to help redress this problem by presenting an analysis of 31 southern sources to help fill the gaps in the southern hemisphere calibrator distribution. We have developed a multi-parameter method of classifying these sources as calibrators. From our sample of 31 sources, we have 2 class A sources (Excellent calibrators), 16 class B sources (Good calibrators), 9 class C sources (Poor calibrators) and 4 class D sources (Unsuitable calibrators).

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / Although mass minimisation is an important application within structural optimisation, other applications include: (1) concept generation, (2) concept evaluation, (3) design for structural feasibility and (4) data matching. These applications, except data matching, are discussed and illustrated on a prototype design of the Karoo Array Telescope (KAT) antenna. The KAT passed through the design process and a full scale prototype was built, but was found to be too expensive. A detailed finite element model of the finalised design was considered as a test bed for reducing costs. Size-, shape- and topology optimisation are applied to three KAT components, while considering wind, temperature and gravity loads. Structural- and nonstructural constraints are introduced. Coupling of the structural optimisation code with an external analysis program to include non-structural responses and the parallelisation of the sensitivity calculations are presented. It is shown that if a finite element model is available, it is generally possible to apply structural optimisation to improve an existing design. A reduction of 2673 kg steel was accomplished for the existing KAT components. The total cost saving for the project will be significant, when considering that a large amount of antennas will be manufactured.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The world's astronomy community is working together to build the largest and most sensitive radio telescope in the world namely: the SKA (Square Kilometre Array). It will consist of approximately three thousand dishes which will each require accurate positioning. The Square Kilometer Array has a testbed called the Phased Experimental Demonstrator (PED) in Observatory, Cape Town. A hexapod positioning mechanism is required to position a 3.7 m radio telescope which forms part of an array of seven radio telescopes. This thesis details the design process of the hexapod system. The design consists of the mechanical design of the joints and linear actuators, a kinematic and dynamic model, a controller and a user interface. In order to verify the design for the PED hexapod a scaled prototype was designed, built and tested. The hexapod's repeatability as well as ability to track a path was tested using an inclinometer. The tests confirmed the design feasibility of the PED hexapod and also highlight issues that require care when constructing the full scale hexapod, such as the amount of play in the platform joints. The designed full scale hexapod will have an error angle less than 0.13°, a payload capacity of 45 kg, withstand wind speeds of 110 km/h and cost R160 000. / AFRIKAANSE OPSOMMING: Die wêreld se sterrekundige gemeenskap is besig om saam te werk om die grootste en mees sensitiewe radioteleskoop in die wêreld te bou, naamlik: die SKA (Square Kilometre Array). Dit sal uit ongeveer drie duisend skottels bestaan wat elkeen akkurate posisionering benodig. Die SKA het 'n toetssentrum, genaamd die “Phased Experimental Demonstrator” in Observatory, Kaapstad. 'n Sespoot posisionering meganisme word benodig om die 3.7 m radioteleskoop te posisioneer, wat deel vorm van 'n stelsel van sewe radioteleskope. Hierdie tesis beskryf die proses om die sespoot stelsel te ontwerp. Die ontwerp bestaan uit die meganiese komponent van die koppelings en lineêre aktueerders, 'n kinematiese en dinamiese model, 'n beheerder, asook 'n gebruikersintervlak. 'n Geskaleerde prototipe is ontwerp, gebou en getoets om die ontwerp te verifieer. Die platform se herhaalbaarheid sowel as akkuraatheid om 'n pad te volg was getoets met 'n oriëntasie sensor. Die toetse het probleme uitgelig wat versigtig hanteer moet word gedurende die konstruksie van die volskaalse sespoot, veral die hoeveelheid speling in die koppelings. Die volskaalse sespoot ontwerp het 'n hoek fout van minder as 0.13°, 'n ladingsvermoë van 45 kg en kan 'n windspoed van 110 km/h weerstaan en kos R160 000.

Thesis (DPhil (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Karoo Array Telescope (KAT) will be used by South Africa in its bid to host the international Square Kilometre Array (SKA). As the SKA will have orders of magnitude greater sensitivity than existing radio telescopes, it will also be concomitantly more sensitive to radio frequency interference (RFI). The influence of RFI on a differential mode (DM) KAT conductive system is an unavoidable phenomenon. In this context, the conductive or galvanic system can, in its most basic form, consist of a source, a load, and connecting conductors. It can also, in the case of the KAT-7 seven-dish interferometer, consist of each telescope, its functional cabling, and the main correlator connecting the telescopes together. However, additional connections between the system and the environment exist. These might be an intentional connection made to the earthing layout, or unintentional connections due to parasitic capacitances and inductive connections. As a result of this, additional conductive systems are created which carry common mode (CM) currents. Interference present in such CM paths enters the DM system through the transfer impedance (Zt) between them. To reduce or eliminate this interference in the DM system, Zt has to be minimised. The use of an earthed parallel conductor (EPC as commonly referred to) in the form of a cable tray is considered to be one of the principal methods to reduce Zt. The properties of cable trays as EPCs at wavelengths which are greater than the tray length are well documented. One main focus in this dissertation is on cable tray mid-span and end connections. They are not well described in the literature over the wide range of frequencies that is expected for KAT developments. The influence of the most common connections on the measured and computed Zt of the cable tray is determined. Computer Simulation Technology’s Microwave Studio (CST MWS) is employed to validate the measured results and also to enable visualisation of the fields and currents. Recommendations for the best connection to use for any cable tray installation is given. The overall shielding ability of optimally-connected cable trays has been evaluated using a physical and computational model. In both cases the induced voltage on a victim conductor, and far-field gain functions for varying angles of incidence onto the model, are determined. The results also show that for certain scenarios, most of the coupling to the victim conductor, takes place inside the end enclosure and not the cable tray. In general, properly-connected cable trays do provide protection to their enclosed conductors, even at frequencies were the wavelength is much shorter than the width of the tray. The second main focus arises from an on-site radio frequency (RF) current audit undertaken on two of the seven KAT-7 telescopes. Shielding measures, such as interface barriers at the floor and roof of the lower telescope pedestal, are studied. The investigation is facilitated by the development of an accurate physical and computational scale model of the dish. Direct current injection and plane wave illumination methods are used to excite the system. The measured CM current distributions are compared and comments made regarding the validity of the measurement procedure. The CM currents, measured around the outside of the lower pedestal show higher levels when a direct current path to ground is established, as opposed to when no clear path exists. This finding suggests at least two methods of preventing CM interference entering or leaving the pedestal: harden the floor and roof barriers, or manage current paths outside the telescope. Related to this, CM currents measured either side of the telescope interface barriers, are used to determine the level of shielding the interface provides. When compared to the common definition of shielding effectiveness, the current measurement provides more conservative shielding estimates. The research in this dissertation has influenced, and will continue to influence, the layout of galvanic systems for the present KAT-7 structures and the anticipated developments to MeerKAT. / AFRIKAANSE OPSOMMING: Die Karoo Array Telescop (KAT) sal gebruik word deur Suid-Afrika in sy poging om die bod te kry om die internasionale Square Kilometre Array (SKA) te huisves. Aangesien die SKA ordes meer sensitief sal wees as bestaande radioteleskope, sal dit terselfdertyd ook meer sensitief wees vir radio frekwensie steurnisse. Die invloed van radio frekwensie steurnisse op die differentiëlemodus KAT geleidende netwerk is iets onvermydeliks. Binne hierdie konteks kan die geleidende netwerk, in sy mees basiese vorm, bestaan uit ʼn bron, ʼn las, en verbindingsgeleiers. Dit kan ook, in die geval van die KAT-7 sewe-teleskoop interferometer, bestaan uit elke teleskoop, sy funksionele bekabeling, en die korrelator wat die verbinding is tussen al die teleskope. Daar is egter, addisionele verbindings tussen die netwerk en die onmiddellike omgewing rondom dit. Hierdie verbindings kan opsetlik gemaak word deur byvoorbeeld, verbinding van die netwerk se aardkabel aan die res van die beaarding, of onopsetlik deur parasitiese kapasitansies en induktiewe verbindings. As gevolg hiervan word addisionele geledende netwerke geskep waarin gemenemodus strome kan vloei. Indien daar wel strome in die gemenemodus netwerk vloei, word dit oorgedra aan die differentiëlemodus netwerk deur ʼn oordragimpedansie (Zt) wat teenwoordig is tussen die twee. Om dus die steurnisse in die differentiëlemodus netwerk te verminder of te elimineer, moet Zt tot ʼn minimum beperk word. Die gebruik van ʼn geaarde parallelle geleier in die vorm van ʼn kabelkanaal, word beskou as een van die mees doeltreffendste metodes om Zt te verminder. Die eienskappe van kabelkanale as geaarde parallelle geleiers by frekwensies waar die golflengtes langer is as die van die kabelkanaal, is volledig gedokumenteer. Een van die belangrikste fokuspunte in hierdie verhandeling is rakende die kabelkanale se middel en eindpuntverbindings. Hulle word nie goed beskryf in die beskikbare literatuur nie, en weliswaar vir wyeband doeleindes wat vir KAT ontwikkelinge verwag word. Die invloed van die mees algemeenste kabelkanaal verbindings op gemete en berekende Zt word bepaal. Computer Simulation Technology’s Microwave Studio (CST MWS) word eerstens, gebruik om die akkuraatheid van die gemete resultate te bewys en tweedens, deur visualisering van E-veld en gemenemodus oppervlak strome. Aanbevelings vir die beste verbindings vir enige kabelkanaal opstelling word gegee. Die algemene afskerminsvermoeë van ʼn idiaal-verbinde kabelkanaal word bepaal deur middel van metings en simulasies. In beide gevalle word die geïnduseerde spanning op ʼn slagoffer kabel, en die verveld aanwins funksie bepaal vir verskillende invalshoeke op die model. Die resultate toon verder dat vir spesifieke gevalle wat beskou word, die meeste koppeling binne die kabinet aan die einde van die kabelkanaal plaasvind. Oor die algemeen verskaf goed verbinde kabelkanale wel ʼn sekere vlak van beskerming aan kabels binne die kabelkanaal, selfs by frekwensies waar die golflengte baie korter is as die breedte van die kabelkanaal. Die tweede belangrike fokuspunt spruit voort uit ʼn radio frekwensie stroomoudit, wat twee van die KAT-7 teleskope evalueer het. Afskermingsmatreëls soos die kabelhindernisse op die vloer en dak van die onderste teleskoop voetstuk, word bestudeer. Tesame met die metings op die werklike teleskoop wat geneem is, word ʼn akkurate fisiese en simulasie skaalmodel geskep om die metings beter te analiseer. Direkte stroominspuitings metode en platvlakgolf beligting word gebruik om gemenemodus strome op die teleskoop se struktuur te induseer. Die gemenemodus stroomverspreiding vir beide tegnieke word vergelyk in ʼn poging om kommentaar te lewer rakende die geldigheid van die meettegniek. Die gemenemodus strome wat aan die buitekant van die teleskoop voetstuk gemeet word, is hoër wanneer ʼn direkte stroompad na grond op die voetstuk geskep word in vergelyking met ʼn ongedefinieerde pad. Hierdie verskynsel dui daarop dat ten minste twee metodes bestaan om die ongevraagde gemenemodus strome te verhoed om aan die binnekant van die teleskoop voetstuk te vloei. Die een is die verbetering van die vloer en dak kabelhindernisse, en die ander is verbetering van die stroompad (stroompaaie) aan die buitekant van die voetstuk sodat ʼn meer direkte pad na grond geskep word. Die gemiddelde gemenemodus strome weerskante van die kabelhindernis, kan gebruik word op te bepaal hoeveel afskerming die hindernis bied. Indien die berekende waardes by verskillende frekwensies vergelyk word met die tradisionele filter doeltreffendheid (Zt), word ʼn meer konserwatiewe beraming verkry. Die navorsing in hierdie verhandeling het alreeds, maar sal ook die toekomstige uitleg van galvaniese stelsels vir KAT-7 asook die verwagte MeerKAT beïnvloed.

QC 351 A7 no. 07 / The Meinel Reducing Camera for the U. S. Naval Observatory's 60-inch telescope, Flagstaff, Arizona, comprises an f /10 collimator designed by Meinel and Wilkerson, and a Leica 50-mm f/2 Summicron camera lens. The collimator consists of a thick, 5-inch field lens located close to the focal plane of the telescope, plus four additional elements extending toward the camera. The collimator has an efl of 10 inches, yielding a 1-inch exit pupil that coincides with the camera's entrance pupil, 1.558 inches beyond the final surface of the collimator. There is room between the facing lenses of the collimator and camera to place filters and a grating. The collimated light here is the best possible situation for interference filters. Problems of the collimator design work included astigmatism due to the stop's being so far outside the collimator, and field curvature. Two computer programs were used in development of the collimator design. Initial work, begun in 1964, was with the University of Rochester's ORDEALS program (this was the first time the authors had used such a program) and was continued through July, 1965. Development subsequently was continued and completed on the Los Alamos Scientific Laboratory's program, LASL. The final design, completed January 24, 1966, was evaluated with ORDEALS. This project gave a good opportunity to compare ORDEALS, an "aberration" program, with LASL, a "ray deviation" program. It was felt that LASL was the superior program in this case, and some experimental runs beginning with flat slabs of glass indicated that it could have been used for the entire development of the collimator. Calculated optical performance of the design indicated that the reducing camera should be "seeing limited" for most work. Some astigmatism was apparent, but the amount did not turn out to be harmful in actual astronomical use. After the final design was arrived at, minor changes were made to accommodate actual glass indices of the final melt, and later to accommodate slight changes of radii and thicknesses of the elements as fabricated. An additional small change in spacing between two of the elements was made at the observatory after the reducing camera had been in use for a short time. The fabricated camera is working according to expectations. Some photographs are included in the report to illustrate its performance and utility.

QC 351 A7 no. 16 / This document has been prepared to form the basis for the operational specifications for the Cassegrain instrumentation for the 90-inch telescope of the Steward Observatory. The publication of this document is for the purpose of providing guidance to other astronomical groups who may have use for the considerations recorded herein.

Há várias evidências experimentais da existência de matéria escura no universo. Apesar destas evidências, pouco se sabe sobre sua constituição, sabendo-se apenas que interage gravitacionalmente, mas não eletromagneticamente. Neste projeto, investigamos a possibilidade da matéria escura ser composta por partículas supermassivas e fortemente interagentes (Simpzillas). Para isto determinamos o sinal que deve ser deixado no telescópio IceCube por neutrinos resultantes de aniquilações de matéria escura no Sol. Após determinarmos o espectro de neutrinos no centro do Sol, simulamos sua propagação até a superfície, depois até a Terra e através da Terra até o detector. Comparamos então estes resultados com os fornecidos pelo IceCube. Esta comparação permite testar uma região do espaço de fase massa versus seção de choque previamente não-excluída por outros tipos de experiência que não telescópios de neutrinos. Como resultado, concluímos que partículas supermassivas e fortemente interagentes não podem constituir a matéria escura. / There are many experimental evidences for the existence of dark matter in the universe. Despite these evidences, there is no knowledge about its constitution other than the fact that it interacts gravitationally but not electromagnetically. In this project, we investigate the possibility that dark matter is composed of strongly interacting massive particles (Simpzillas). We determine the expected signal in the IceCube telescope from Simpzilla annihilation in the center of the Sun. We first determine the neutrino spectrum in the core of the Sun. We then simulate its propagation through both the Sun and Earth, and finally the rate of neutrinos at the detector. A comparison of these results to the ones published by the IceCube collaboration covers a large region of the yet not excluded regions of the mass versus cross-section phase space. As a result, the possibility of Simpzillas composing the dark matter is ruled out.

Das Energiespektrum der kosmischen Strahlung bietet wichtige Hinweise auf ihren Ursprung und ihre Ausbreitung. Verschiedene Messtechniken müssen kombiniert werden, um den ganzen Energiebereich abdecken zu können: Direkte Messungen mit Teilchendetektoren bei niedrigen Energien sowie indirekte Messungen von Luftschauern bei hohen Energien. Dazu kommt die Messung von Photonen, hauptsächlich im GeV- und TeV-Bereich, die bei der Wechselwirkung von kosmischer Strahlung mit Materie oder elektromagnetischen Feldern entstehen. Im Folgenden werde ich zwei Studien dazu vorstellen, die beide auf Daten des abbildenden Tscherenkow-Teleskopes VERITAS beruhen. Erstens stelle ich eine Messung das Energiespektrums von Eisenkernen in der kosmischen Strahlung vor. Für die Bestimmung der Energie und Ankunftsrichtung der Primärteilchen benutze ich eine neuartige Template-Likelihood-Methode, die hier erstmals auf Eisenschauer angewendet wird. Zur Identifizierung der Eisenschauer benutze ich unter anderem das sogenannte direkte Tscherenkow-Licht, welches von geladenen Teilchen vor der ersten Wechselwirkung ausgestrahlt wird. Dazu kommt eine multivariate Klassifizierungsmethode, um den Verbleibenden Untergrund zu charakterisieren. Das so gemessene Energiespektrum von Eisen wird im Bereich von 20 TeV bis 500 TeV gut durch ein Potenzgesetz beschrieben. Zweitens beschreibe ich eine Suche nach Gammastrahlung oberhalb von 100 GeV von den drei Galaxien Arp 220, IRAS 17208-0014 und IC 342. Diese drei Galaxien haben hohe Sternentstehungsraten und daher viele Supernova-Überreste, welche kosmische Strahlung erzeugen. Diese wechselwirkt erwartungshalber mit den dichten Staubwolken in den Sternentstehungsgebieten und erzeugt Gammastrahlung. VERITAS konnte keine solche Gammastrahlung messen. Die daraus abgeleitete Höchstgrenze für die Luminosität schränkt theoretische Modelle der Erzeugung und Propagation von kosmischer Strahlung in der Galaxie Arp 220 ein. / The energy spectrum of cosmic rays can provide important clues as to their origin and propagation. Different experimental techniques have to be combined to cover the full energy range: Direct detection experiments at lower energies and indirect detection via air showers at higher energies. In addition to detecting cosmic rays at Earth, we can also study them via the electromagnetic radiation, in particular gamma rays, that they emit in interactions with gas, dust, and electromagnetic fields near the acceleration regions or in interstellar space. In the following I will present two studies, both using data taken by the imaging air Cherenkov telescope (IACT) VERITAS. First, I present a measurement of the cosmic ray iron energy spectrum. I use a novel template likelihood method to reconstruct the primary energy and arrival direction, which is for the first time adapted for the use with iron-induced showers. I further use the presence of direct Cherenkov light emitted by charged primary particles before the first interaction to identify iron-induced showers, and a multi-variate classifier to measure the remaining background contribution. The energy spectrum of iron nuclei is well described by a power law in the energy range of 20 to 500 TeV. Second, I present a search for gamma-ray emission above 100 GeV from the three star-forming galaxies Arp 220, IRAS 17208-0014, and IC342. Galaxies with high star formation rates contain many young and middle-aged supernova remnants, which accelerate cosmic rays. These cosmic rays are expected to interact with the dense interstellar medium in the star-forming regions to emit gamma-ray photons up to very high energies. No gamma-ray emission is detected from the studied objects and the resulting limits begin to constrain theoretical models of the cosmic ray acceleration and propagation in Arp 220.