A central result of this thesis is the prediction of short period (transient) GW signatures, using General Relativity. This thesis focused on various LIGO and SKA Gravitational Wave (GW) sources such as collapsing supernovae, rapidly spinning magnetars, the coalescence of compact binary objects and the stochastic Gravitational Wave backgrounds produced by Super Massive Black holes. Upper limits for the GW amplitudes and frequencies were predicted by means of numerical and analytic methods. Finally, the prospects of detecting Gravitational Waves from the galactic center will be discussed.

The recent global research interest in wide band gap semiconductors has been focused on zinc oxide (ZnO) due to its excellent and unique properties as a semiconductor material. The high electron mobility, high thermal conductivity, good transparency, wide and direct band gap (3.37 eV), large exciton binding energy (60 meV) at room temperature and easiness of growing it in the nanostructure form, has made it suitable for wide range of applications in optoelectronics, piezoelectric devices, transparent and spin electronics, lasing and chemical sensing. PbS nanostructures is a narrow energy gap material which have relevance for optical applications in the near-IR region of the electromagnetic spectrum such as telecommunications, photovoltaics and bioimaging. It has similar electron and hole effective masses hence the exciton, can be strongly confined which is not always feasible in other semiconductors. Thus the PbS system provides an ideal platform to investigate the exciton in the strong confinement regime. In this thesis, structural and luminescence properties of undoped and doped ZnO and PbS nanostructures (nanorods, nanoflakes, nanoparticles, and nanoflowers) are investigated by different approaches for possible future application of these nanostructures as solar cells and light emitting diodes. Undoped and doped ZnO and PbS nanostructures were grown by chemical bath deposition process. Still it is a challenge for the researchers to produce a stable, reproducible high quality and homogeneously doped ZnO/PbS materials and this seriously hinders the progress of ZnO and PbS nanostructcures to be utilized in various applications. The first part of the thesis includes synthesis of undoped ZnO nanostructures by controlling the growth parameters such as concentrations of precursors (zinc acetate) and synthesis time. Crystalline zinc oxide (ZnO) flower-like nanostructures were synthesized by the chemical bath deposition (CBD) method. The X-ray diffraction (XRD) pattern for the ZnO flower-like microstructures showed crystalline peaks corresponding to a hexagonal wurtzite ZnO structures. Scanning electron microscopy (SEM) observations showed the presence of microcrystallites forming microflower-like aggregates. In the case where a higher molar concentration of zinc acetate was used in the preparation process the microflower-like structures were larger in size than that of the lower mol% used. The shape however did not change. The absorption edges red shifted slightly with an increase in the molar concentration of the zinc acetate and in synthesizing time. The band gap energies decreased slightly with an increase in the molar concentration of the zinc acetate and again in synthesizing time. PL showed that the maximum luminescence intensity was reached at the ZnO synthesized for 5 minutes, any further increase in the synthesizing time resulted into the luminescence intensity decrease. An increase in zinc acetate mol% resulted only in a decrease in luminescence intensity. Controlling growth parameters is important in the sense of controlling the physical, electronic, and chemical properties of materials. In order to understand how to tune these properties in the nanostructure, it is necessary to have an understanding of the growth mechanism that dictates the morphology, structure, and rate of growth of the nanomaterial. The ZnO nanostructures (flower-like rods) were later doped with rare-earth elements (e.g. Ce3+ and Eu3+) and transition metal (e.g. Cu2+). Flower-like hexagonal ZnO:Ce3+ nanostructures obtained for undoped and low mol% of Ce3+. ZnO changed into mixed structure with emergence of pyramids for higher mol% Ce3+. The absorption edges showed that as the molar concentration of Ce3+ ions increases the optical absorption edge shift to a higher. The band gap energies decreased linearly with Ce Concentration. The luminescence bands of undoped ZnO nanoflower-like was quenched and shifted from the yellow region to the blue region when ZnO flower-like was doped with different molar concentration of Ce3+. Eu3+ doped ZnO flower-like structures were synthesized. The XRD spectra of the undoped and low concentration Eu3+ doped ZnO nanostructures correspond to the various planes of a single hexagonal ZnO phase. In contrast with Ce3+ doping, the morphology of the ZnO flower-like rods totally changed to large blocks shape when doped with Eu3+ ions. The effective band gap energy of the ZnO decayed exponentially with the addition of Eu3+. The maximum luminescence intensity was also measured for the same sample. Although weak luminescence was observed for excitation above the band gap at 300 nm the best results were obtained by exciting the Eu3+ directly through the 7F0 â 5L6 absorption band at 395 nm. Excitation at a wavelength of 395 nm produced the highest Eu3+ luminescence intensity without any noticeable ZnO defect emissions. In this work undoped and Cu2+-doped ZnO nanostructures were prepared by the chemical bath deposition (CBD) method. XRD analysis showed the sample prepared were hexagonal ZnO for undoped and Cu-doped. The presence of Cu2+ ions caused the particle size of ZnO flower-like structures to decrease. In the UV-Visible study the reflectance intensity decreased with an increase in the molar concentration of Cu2+ and there was no shift in the absorption edges. The luminescence intensity was found to be a maximum for the undoped ZnO flower-like structures and quenched after addition of Cu2+ ions. In the last part of the thesis, the influence of synthesis temperature and molar concentration of lead acetate on the structure, morphology and optical properties of PbS nanoparticles were investigated. The X-ray diffraction (XRD) peaks correspond to the various planes of a single phase cubic PbS. The surface morphology study revealed nanorod structures at low synthesis temperatures but a particulate structure at the high synthesis temperatures. It was also observed that an increase in the molar concentration of lead acetate has no significant influence on the morphology of the PbS nanorods and the crystallite sizes. The reflectance spectra showed a shift of the absorption edge to a higher wavelength with an increase in the synthesis temperature and molar concentration of Pb acetate. The luminescence intensity was found to decrease with an increase in the synthesis temperature and molar concentration of Pb acetates. The PbS nanoparticles were later doped with Tb3+ and co-doped with Ce3+ ions. When the Tb3+ concentration was increased to 2 mol%, the morphology of the PbS:Tb3+ changed to a mixture of spherical nanoparticles and nanorods. The absorption edges of these PbS nanoparticles slightly shifted to higher wavelength depending on the ionic strength of the precursors. The PL result show an increase in emission intensity with an increase in Tb3+ ions up to 0.3 mol% Tb3+ and decreased there after most probably due to luminescence concentration quenching. A new band at 433 nm was found to emerge as the Tb3+ ions increases. Co-doping PbS nanostructures with 0.3 mol% and 2 mol% Ce3+, the spherical nanoparticles changed the morphology to the nanorods surrounded by the spherical nanoparticle. It was also observed that the size of the nanorods increased with an increase in the molar concentration of Ce3+ ions. The nanoparticles showed good optical properties with high reflectance in the UV and visible regions. The absorption edges shifted to higher wavelength with the addition of Tb3+ and Ce3+, respectively. The photoluminescence results displayed an optimum increase in luminescence intensity when the ratio of Ce:Tb was 1:10 and further increase in cerium content quenched the luminous intensity. It was observed that as the molar concentration of co-dopant (Ce3+) increased the luminescence band at around 433 nm diminished.

No description available.

The development of hydrogen as an energy transfer mechanism is of great importance to alleviate environmental damage and economic destabilisation caused by over-reliance on oil, as long as the hydrogen can be generated renewably. To be suitable for road transport applications, safe and compact hydrogen storage systems need to be developed, the primary technological motivation for this PhD project which investigates hydrogen absorbed into graphite intercalation compounds (GICs), to gain a fundamental physical understanding of the sorption processes to improve such materials' capacity for hydrogen storage. Literature searching has led to a principal investigation, primarily using neutron scattering and thermogravimetry, of potassium and calcium-GICs with hydrogen. Inelastic neutron scattering on hydrogenated KC24 has shown hydrogen sorption in this system to be quantitatively different from its analogues RbC24 and CsC24. A consistent model of the H2 sites and dynamics has been proposed. Time-resolved structural data on the hydriding phase transition in KC8Hx have been obtained. A calcium-ammonia intercalate has shown most promise for hydrogen storage, with uptake of 3.2 wt.% H2 at 77 K and 2 bar, a signifcant amount of the 6 wt.% target set by the US DoE. It is concluded that available internal volume and donor charge in GICs are critical parameters for optimising hydrogen uptake.

Thesis (Ph.D.)--Michigan Technological University, 2007. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph.D.)--Michigan Technological University, 2007. / Includes bibliographical references. Also available on the World Wide Web.

Predation is one of many factors that form the structure of the macroinvertebrate community in lakes, wetlands and watercourses. Earlier studies lack an examination concerning how fish- and waterfowl predation affect macroinvertebrates during shorter periods in the spring. I performed an exclosure study in the shallow eutrophic Lake Tåkern which is located in the western part of Östergötland County, Sweden. The experiment was performed during a three week period (1-21 April 2012) when the water temperature was low and the density of migrating diving ducks was high. The experimental cages used included three out of four different treatments; general predation (open cages), bird exclusion (net with mesh size 90*45mm) and no predation (net with mesh size 1*1mm). In the fourth treatment, which was used to control for cage effects, samples were collected outside the cages. The cages where placed in blocks three and three, one for each the three treatments, on eight different locations in the experiment area. No significant difference was detected between the different treatments concerning diversity (Shannon diversity index: F3,25=1,39; P=0,27 and Simpson diversity index: F3,25=1,47; P=0,25), taxonomic richness (F3,25=1,74; P=0,19) nor density (F2,25=0.41; P=0,75) of the macroinvertebrate fauna. The lack of effect from predation of fish is most likely explained by the low water temperature during the experiment period. The lack of effect from waterfowl predation is most likely due to a low density of diving ducks, despite the season. / Predation är en av flera faktorer som styr makroevertebratfaunans sammansättning i sjöar, våtmarker och vattendrag. Jag genomförde ett utestängningsexperiment i den grunda näringsrika sjön Tåkern i västra Östergötland. Experimentet genomfördes under en treveckorsperiod (1april-21-april) på året då densiteten flyttande dykänder är hög och vattentemperaturen är låg, vilket saknas från tidigare studier. Experimentet innefattade fyra behandlingar; kontrollpunkter utan burar, generell predation (öppna burar), fågelexkludering (nät 45*90mm) samt ingen predation (stängda burar, nät, 1,1mm). Burarna bestod av plastlådor med en volym på 130 liter (Längd*höjd*bredd: 79cm*57cm*42cm). Burarna placerades i block om tre, en för varje behandling, på botten av sjön vid åtta olika provpunkter. Resultatet visade ingen signifikant skillnad mellan de olika behandlingarna gällande makroevertebratfaunans sammansättning, varken i fråga om diversitet (Shannons diversitetsindex: F3,25=1,39; P=0,27 och Simpsons diversitetsindex: F3,25=1,47; P=0,25 ANOVA) eller densitet (F2,25=0.41; P=0,75). Avsaknaden av effekt från fiskpredation förklaras troligen av låg vattentemperatur under experimentperioden vilken påverkar fiskarnas födosökshastighet negativt. Som förväntat såg vi ingen effekt av fågelpredation vilket troligen beror på att densiteten dykänder inte var tillräckligt hög.