/library/oar/handle/123456789/11479 2025-11-02T22:50:15Z /library/oar/handle/123456789/101722 Title: Broadband fractal elements phased array antennas for SKA Abstract: This thesis presents instrumentations to measure the abundance of neutral hydrogen gas in the Universe. Particularly, instrumentations for 21-cm intensity mapping telescope. The data acquisition of the Universe's hydrogen measurements enable tracking on how its distribution evolves with time. In correspondence, a comprehensive picture on how galaxies evolve: the nature of dark energy: and how the first cosmic structures formed can be drawn. In these terms and the context of SKA, the work employs phased array technologies functioning at the sub 1 GHz frequency band. The mapping instruments rely on an interferometric aperture arrays telescope subdivided into two bands. Aperture array antennas for the SKA covering the low frequency band at the sub 450 MHz and the high-frequency band (300 MHz to 1 GHz) arrays. A novel class of planar antennas referred to as tightly couple phased arrays (TCPAs) are proposed for SKA. This class of antennas enable a wideband performance utilising the mutual capacitance between the array elements. The requirements of a wide bandwidth performance promoted a key innovation, employing a resistive loading layer. Using this novel technique has translated as an improvement in the bandwidth to a factor of two, while the array when conjugated with a superstrate layer mitigates radiation efficiency degradation. These antenna designs are targeting for low-cost and high sensitivity characteristics. The arrays were devised and validated through measurements of their prototypes. Description: PH.D 2015-01-01T00:00:00Z /library/oar/handle/123456789/100882 Title: Cetaceans and their interactions with coastal fisheries in the Gulf of Kavala, Eastern Mediterranean sea Abstract: Cetacears in the Gulf of Kavala and around Thassos, in the Thracian Sea, were studied as this site has been proposed as a potential cetacean conservation area by ACCOBAMS (Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area. This area is also an important Greek fishing ground, so cetacean-fisheries associations were srtuctured to understand the extent of the reciprocal negative impacts between the two. The research investigated) cetacean abundance and distribution in the study area of the Gulf of Kavala; b) cetacean strandings in the North Aegean Sea and stomach content diet analysis; c) survey of the fisheries catch per gear used in the Thracian Sea and analyses of the extent of fisheries target species overlap with cetacean prey species found through cetacean diet analyses, and J) fishermen questionnaire study on fisheries-cetacean interaction and sightings of cetaceans during fishing activities. Regarding the first task, the presence, abundance and distribution of cetacean species in the study area were investigated between 2005 and 2013 through dedicated scientific marine surveys. Data were collected during a total boat survey effort covering 14,701 km in sea conditions <Beaufort 4, in a study area of 2000 km2 • The survey used the line-transect sampling method to estimate relative abundance, calculated using Distance software 6.0. Six cetacean species v-ere recorded in the study area, estimated at a total of 5,069 individuals (95% C.I. = 3,668 - 7,004; CV = 16.56). Abundance estimates were obtained for bottlenose dolphins (Tursiops truncatus) (2,934 individuals; 95% C.I. = 1,915 - 4,494; CV= 21.91); and common dolphins! Delphinus de/phis) (1,482 individuals; 95% C.I. = 958 -2,295; CV= 22.55). Dolphin sightings were correlated to eight environmental variables using GAM and PCA. Bottlenose dolphins sightings were found to correlate with depth (p = 0.007) and median temperature (p = 0.042). Common dolphin sightings correlated with depth (p = 0.035), temperature (p = 0.022 for median temperature and p = 0.001 for temperature gradient) and salinity (p = 0.001 for median salinity and p = 0.024 for salinity gradient). Apart from, these two species, other visiting cetacean species include: striped dolphins (Stenella coeruleoalba), harbour porpoises (Phocoena phocoena) and Risso's dolphins (Grampus griseus). The Mysticete fin whale (Balaenoptera physalus) and the pinniped Mediterranean monk seal (Monachus monachus) were rarely sighted. Cetacean strandings were recorded and allowed for stomach-content analyses performed on 26 suitable specimen samples. Results from the stomach-content analyses showed that: common dolphins (N = 8) fed mainly on species from the Clupeidae and Myctophidae families and a few cephalopods, bottlenose dolphin (N = 8) fed primarily on snake blenny (Ophidion carbatum), bogue (Boops hoops), species of the Clupeidae family and cephalopods, such as squids of the genus Loligo. Striped dolphins (N = 4) fed on small pelagic fish, such as bogue and especially on Myctophidae, such as Madeira lantern fish (Ceratoscopelus maderensis) and in a smaller proportion on cephalopods. Harbour porpoises (N = 6) fed on fish, with a high preference for species of the Gobiidae family followed by Clupeidae. This present work also contributes first data on harbour porpoises' diet in the Mediterranean Sea. Risso's dolphins (N = 1) fed exclusively on cephalopods, prevalently species from the Teuthida order, and the genus Histiotheutis. In none of the cetacean stomachs investigated, was there a dominant presence of important commercial fisheries species. Trophic levels of the cetacean species were calculated and in all cases showed values higher than 4, indicating a top predator position in the food web; their values ranged from 4.22 for harbour porpoises to 4. 70 for Risso' s dolphins. [...] Description: PHD 2015-01-01T00:00:00Z /library/oar/handle/123456789/93900 Title: Optimizing scheduling in a pharmaceutical company Abstract: Scheduling is very important task which is used on a daily basis. A "good" schedule will increase the company's' profit and customers will be more willing to buy products as they are being satisfied in the shortest period of time. It is also important as it may solve many different objective functions such as minimization of makespan; minimization of delays; and minimization of total completion time. There has been an extensive research about algorithms to solve such problems. An overview of these algorithms both from a deterministic theoretical part and stochastic theoretical part is provided. This dissertation mainly focuses on solving the minimization of makespan on identical parallel machines scheduling problem. A mixed integer linear program (MILP) is built to solve this scheduling problem by using real live data from a local pharmaceutical company. In addition, the Longest Processing Time (LPT) heuristic algorithm which is one of the famous and oldest scheduling algorithms is used to compare its results with the MILP problem results and the original schedule by the company. Description: B.SC.(HONS)STATS.&OP.RESEARCH 2015-01-01T00:00:00Z /library/oar/handle/123456789/93899 Title: Parameter estimation of Lévy processes Abstract: Levy processes have become increasingly popular in mathematical finance because of their ability to capture the leptokurtic shape of stock returns and also the jumps observed in stock prices. In this dissertation we will present some of the theory and major results of Levy processes. In particular we shall focus on the Normal Inverse Gaussian and the Meixner process. Then we shall be looking at different parameter estimation methods for Levy processes, which can be split into two major categories: the parametric approach and nonparametric approach. For the nonparametric approach we shall consider a projection estimator proposed by Comte and Genon-Catalot [14] and also an estimator introduced by Rubin and Tucker [ 44]. In the parametric approach we consider the Integrated Sum of Squared Estimation proposed by Heathcote [28] and a Stochastic Programming method presented by Sant and Caruana [ 45]. Finally these methods of estimation are implemented on the Malta Stock Exchange Index and some results are compared were possible. Description: B.SC.(HONS)STATS.&OP.RESEARCH 2015-01-01T00:00:00Z