Au cours des XIXe et XXe siècles, l’Iran, pays mal connu mais distingué par son histoire, attire l’attention de plusieurs intellectuels occidentaux. Ainsi certains d’entre eux prennent la route et vont à la rencontre de ce pays et ses habitants. Notre étude concerne les récits de voyage de dix écrivains-voyageurs français, suisses et anglais qui ont sillonné les routes de l’Iran entre 1854 (Gobineau) et 1954 (Bouvier) ; parmi eux, la moitié sont des femmes. À travers leurs témoignages écrits et picturaux, chacun de ces écrivains-voyageurs a livré une image de la Perse différente des autres. Mais pourquoi cette divergence d’images ? En effet, sans négliger les spécifiés régionales et culturelles, il est manifeste que la vision du monde de chacun contribue à la naissance de cette image. De plus, en l’espace d’un siècle, secoué d’événements politiques, économiques et sociaux comme les deux Guerres mondiales, l’Europe voit ses rapports modifiés envers ses Autres. Ainsi l’Iran devient tour à tour une terre d’étude, terre d’aventure et terre idéale et spirituelle pour ceux qui ne peuvent plus rester en Europe. En outre, au long de cette période, le genre de la littérature de voyage a notablement évolué. Tous ces facteurs se croisent pour donner de la Perse une image multiple. / During the nineteenth and twentieth centuries, Iran, a country not well known but distinguished by its history, attracted the attention of several Western intellectuals. Thus some of them take the road and go to visit this country and its population. Our study is about the travel stories of ten travel writers from France, Switzerland and Britannia who traveled to Iran between 1854 (Gobineau) and 1954 (Bouvier); Among them, half are women. Through their written and pictorial testimonies, each of these travel writers have delivered an image of Persia different from the others. But why this divergence of images? Indeed, without neglecting the regional and cultural specify, it is clear that the world vision of every one contributed to the appearance of this image. Furthermore, during a century, shaken by political, economical and social events like the two World Wars, Europe sees its relations modified with its “Others”. Thus Iran becomes in turn a land of study, a land of adventure and an ideal and spiritual land for those who can no longer remain in Europe. In addition, during this period, the genre of travel writing has evolved significantly. All these factors intersect to give a multiple images of Persia.

Unmanned aerial vehicles (UAVs) are becoming increasingly popular for surveillance in civil and military applications. Vehicles built for this purpose vary in their sensing capabilities, speed and maneuverability. It is therefore natural to assume that a team of UAVs given the mission of visiting a set of targets would include vehicles with differing capabilities. This paper addresses the problem of assigning each vehicle a sequence of targets to visit such that the mission is completed with the least "cost" possible given that the team of vehicles is heterogeneous. In order to simplify the problem the capabilities of each vehicle are modeled as cost to travel from one target to another. In other words, if a vehicle is particularly suited to visit a certain target, the cost for that vehicle to visit that target is low compared to the other vehicles in the team. After applying this simplification, the problem can be posed as an instance of the combinatorial problem called the Heterogeneous Travelling Salesman Problem (HTSP). This paper presents a transformation of a Heterogenous, Multiple Depot, Multiple Traveling Salesman Problem (HMDMTSP) into a single, Asymmetric, Traveling Salesman Problem (ATSP). As a result, algorithms available for the single salesman problem can be used to solve the HMDMTSP. To show the effectiveness of the transformation, the well known Lin-Kernighan-Helsgaun heuristic was applied to the transformed ATSP. Computational results show that good quality solutions can be obtained for the HMDMTSP relatively fast. Additional complications to the sequencing problem come in the form of precedence constraints which prescribe a partial order in which nodes must be visited. In this context the sequencing problem was studied seperately using the Linear Program (LP) relaxation of a Mixed Integer Linear Program (MILP) formulation of the combinatorial problem known as the "Precedence Constrained Asymmetric Travelling Salesman Problem" (PCATSP).

An experimental, field replaceable travelling wave tube (TWT) with low profile, TEM transitions has been developed with the aim of combining the cost advantages of field replaceable TWTs with the bandwidth advantages of TEM transitions. Field replaceable TWTs are cheaper because their periodic permanent magnet (PPM) stacks (which are expensive) are easier to produce and can be reused. Standard TEM transitions have a high profile and prevent TWTs from being plugged into PPM stacks. The stacks of packaged TWTs are therefore built onto the tubes, using split ring magnets, before the tubes are potted. Upon failure, such tubes are discarded together with their focusing, coupling and cooling structures. Two types of low profile, TEM transitions were investigated: a ring and a plug transition. In the former, the helix was joined to a metal ring that was sandwiched between two ceramic rings in the vacuum envelope. Due to its high shunt capacitance, this transition was narrowband. In the plug transition, the helix was joined to a small metal plug in the wall of a ceramic tube. Plug transitions with a return loss of better than 10 dB over an octave were made but some technological difficulties were encountered. Metal/ceramic joining with active solder is therefore discussed. The development of graphite attenuators was attempted but graphite of high enough resistivity to achieve the attenuation and matching required was not available. Thin film attenuators were therefore used instead. Some good attenuators were made but the molybdenum films were sensitive to processing conditions. An empirical procedure was developed to magnetize PPM stacks to a wanted profile. The stacks that were designed and built resulted in good beam focusing. TWT tests were made using an automated test station that was built. Maximum RF gains and output powers of 20 dB and 43 dBm respectively were measured. The TWT design, construction and testing was a combination of materials science and microwave work. Some simulations were used to solve electromagnetic problems but much of the work was practical, involving trial and error and many measurements. / Thesis (Ph.D.)-University of Natal, Durban, 1994

The Metric Travelling Salesman Problem, henceforth metric TSP, is a fundamental problem in combinatorial optimization which consists of finding a minimum cost Hamiltonian cycle (also called a TSP tour) in a weighted complete graph in which the costs are metric. Metric TSP is known to belong to a class of problems called NP-hard even in the special case of graph-TSP, where the metric costs are based on a given graph. Thus, it is highly unlikely that efficient methods exist for solving large instances of these problems exactly. In this thesis, we develop a new heuristic for metric TSP based on extending ideas successfully used by Mömke and Svensson for the special case of graph-TSP to the more general case of metric TSP. We demonstrate the efficiency and usefulness of our heuristic through empirical testing. Additionally, we turn our attention to graph-TSP. For this special case of metric TSP, there has been much recent progress with regards to improvements on the cost of the solutions. We find the exact value of the ratio between the cost of the optimal TSP tour and the cost of the optimal subtour linear programming relaxation for small instances of graph-TSP, which was previously unknown. We also provide a simplified algorithm for special graph-TSP instances based on the subtour linear programming relaxation.

Σ’ αυτή τη διπλωματική εργασία, παρουσιάζουμε προσεγγιστικούς αλγόριθμους για το Πρόβλημα του Πλανόδιου Πωλητή, μερικές πρακτικές εφαρμογές και κάποιες σχετικές παραλλαγές του κύριου προβλήματος. Ένας πλανόδιος πωλητής θέλει να επισκεφθεί κάθε πόλη ενός συνόλου πόλεων ακριβώς μια φορά ξεκινώντας και επιστρέφοντας στην αρχική πόλη. Το κύριο πρόβλημά του είναι να βρει τη συντομότερη διαδρομή. Παρουσιάζουμε μια αυτόνομη εισαγωγή σε αλγοριθμικές και υπολογιστικές απόψεις του προβλήματος μαζί με τις θεωρητικές απαραίτητες προϋποθέσεις τους από την σκοπιά της Επιχειρησιακής Έρευνας. Η διπλωματική αποσκοπεί να παρουσιάσει τις διαδικασίες επίλυσης του Προβλήματος του Πλανόδιου Πωλητή ανάλογα με το μέγεθος και τη δομή του. Θεωρητικά αποτελέσματα παρουσιάζονται σε μορφή που να καθιστούν σαφή τη σημασία τους στο σχεδιασμό των προσεγγιστικών αλγόριθμων για αποδεδειγμένα καλές ή/και βέλτιστες λύσεις του Προβλήματος. / In this thesis, at short, we present the Travelling Salesman Problem with approximations algorithms, some practical applications and related problems of the main problem. A travelling salesman wants to visit each of a set of towns exactly once starting from and returning to his home town. One of his problems is to find the shortest such trip. We present a self-contained introduction into algorithmic and computational aspects of the TSP along with their theoretical prerequisites as seen from the point of view of an operations researcher who wants to solve practical instances. This thesis is intended to be a guideline of the reader confronted with the question of how to attack a TSP instance depending on its size, its structural properties. Theoretical results are presented in a form which make clear their importance in the design of algorithms for approximate but provably good, and optimal solutions of the TSP.