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In this report we describe simulation of the surface current density on a PEC cylinder and the diffracted field for a line source above a finite PEC ground plane as a means to verify the Nero2D program. The results are compared with the exact solution and give acceptable errors. A terrain model for a communication link is studied in the report and we simulate the wave propagation for terrain with irregular shapes and different materials. The Nero2D program is based on the fast multipole method (FMM) to reduce computation time and memory. Gaussian sources are also studied to make the terrain model more realistic

Communication networks are vulnerable to natural as well as man-made disasters. The geographical layout of the network influences the impact of these disasters. It is therefore, necessary to identify areas that could be most affected by a disaster and redesign those parts of the network so that the impact of a disaster has least effect on them. In this work, we assume that disasters which have a circular impact on the network. The work presents two new algorithms, namely the WHF-PG algorithm and the WHF-NPG algorithm, designed to solve the problem of finding the locations of disasters that would have the maximum disruptive effect on the communication infrastructure in terms of capacity.

The variation of velocity and temperature distribution in arbitrary profile along the centerline in turbulent which encounters non-linearity regular progressive gravity wave and steady uniform flow right in front are investigated analytically and verified by existing experiments. Firstly, the action of periodic waves and current are incorporated into the equation of motion as an external force and applied radiation stress for evaluating the velocity distribution over arbitrary lateral cross section. Based on the momentum exchange after the interaction between turbulent plane jet and oppositive non-linearity wave and uniform flow, the physical characteristics of jet-wave and current are able to be determined theoretically. Secondly, there are critical sections in both velocity and temperature transport processes when the turbulent plane jet influenced by wave and current motion. Fluctuating function will be close to infinity, is the order of wave sharpness; Average velocity for every wave period along the centerline approach to zero, That¡¦s thanks to the momentum of plane jet is extruded by the momentum of wave and current, Beyond the critical section, characteristics of the jet is no longer existing, such phenomena mean that only the wave and current dominating. Velocity and temperature distribution in the zone of flow developed are Gaussian curve, as has been measured in experiment. The momentum extrusion of counter flow in jet is significant in the deep water and small wave; The velocity distribution coefficient is changing with the increasing of counter flow velocity, owing to the entrainment effect, and the potential core will reducing with the increasing of counter flow velocity.

Pure m-plane p-GaN/InGaN/n-GaN on the m-sapphire grown by plasma assisted molecular beam epitaxy (PAMBE) had been achieved. V/III ratio of the first layer m-plane GaN is 20 and growth temperature is 665 ¢XC. ¢½/¢» ratio and the growth temperature are the most important factors in the growth sequence. M-InGaN film with better crystal quality was grown successfully by tuning these two factors. We have obtained a narrow window for epitaxial growth of m-plane InGaN/GaN on m-sapphire at 450 ¢XC. The striated surface is along (1120) a-axis direction of m-InGaN epilayer. As the growth temperature is increased further to 550 ¢XC, there is no InGaN signal from x-ray diffraction (XRD). We study the effect of growth condition on the structural properties and morphology of these films using high-resolution x-ray diffractometer (XRD) and scanning electron microscopy (SEM)

The samples this thesis investigated were m-plane nitrides films grown on m-plane sapphire by plasma-assisted molecular beam epitaxy (PAMBE). Scanning electron microscopy (SEM) images revealed the surface morphologies of the films and thicknesses of the films were measured by cross-sectional scanning electron microscopy. Then we used electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD) to check the growth orientation of the films. The m-plane nitrides films have the anisotropic optical properties were due to the growth orientation of the films. The films are under anisotropic stress since they were grown along m-axis and hence change the electron band structure (EBS), which resulted in anisotropic optical property. We studied the polarization properties of the luminescence at 15 K and 300 K by polarization dependent photoluminescence (PL) and calculated the degree of polarization. And then measured the strain of the m-plane nitrides films by micro-Raman spectroscopy, discussed the degree of polarization and stress. The degree of polarization larger as the anisotropic stress of the film increased.

Epitaxial m-plane (11 ¡Â00) ZnO thin films grown on m-sapphire substrates by atomic layer deposition have been studied. Atomic imaging and electron diffraction conducted in a transmission electron microscope (TEM) and crystallography by X-ray diffractometry all show consistent epitaxial relations with ZnO m-plane // sapphire m-plane, while ZnO [112 ¡Â0] // Al2O3 [0001], and ZnO [0001] // Al2O3 [112 ¡Â0]. The widths (full width at half maximum, or FWHM) of the rocking curves depend on the crystallographic axis of rotation. Dislocations near the interface between the ZnO epi-layers and sapphire substrates can be found from the cross-sectional TEM images when the direction of the incident electron beam, namely, the zone axis, is parallel to ZnO [112 ¡Â0], the a-axis of ZnO. There are stacking faults found in ZnO films away from their interfaces with the substrates. Polarization-dependent photoluminescence by differently polarized incident laser beam have also been investigated. Careful analysis of the spectra via multi-peak fittings revealed optical transitions at 3.32eV for T = 15K, which, however, shifted to 3.28eV at T = 300K. This shift in energy is accounted for by the quadratic temperature dependence of the Fermi level as determined by the positions of the lines of emission corresponding to the band edge transition. The 300K spectrum showed a more distinct peak at 2.48eV when the polarization of the emitted light was along the a-axis of ZnO, as compared to that along the c-axis of ZnO. The origin of this difference remains unaccounted for at the time of writing this thesis. The rest of the peaks have been interpreted in terms of optical transitions involving band gap impurity states, possible exciton formations, and their interactions with phonons.

This experiment use NaCl (001) single crystal as substrate, and the target is zinc oxide, to generate a-plane (112 ¡Â0) zinc oxide nanothim. The nanofilm is used as a buffer layer generating by Ion Beam Sputtering, and then increasing the thickness by Plasma sputtering. Part of specimens to proceed atmospheric heat treatment with different temperature and time, and part of specimens to change the ratio of the gas when the thin film is growth, then use of Transmission electron microscopy (TEM) and Photoluminescence (PL) as the analysis of film properties. The results of experiment, show that (112 ¡Â0) plane have more stringent conditions when generate of thin film, and easy to become the ring of electron diffraction with no-epitaxy .But finally we get a data what can generate a well a-plane ZnO thin film, the substrate temperature of 400 ¢X C, the sputtering time of 1 hour, Ar/O2 = 1.5. From the results of Photoluminescence, we find that there are zinc vacancies in ZnO thin film, probably there are too many oxygen atoms. While the heat treatment in nitrogen, zinc vacancies are reduced rapidly. Indicating that oxygen atoms within the film are reduced by nitrogen atoms or replace the position of the oxygen atoms.

In our research, aluminum (1050) was deformed by plane strain compression (PSC) up to 65% reduction. The total deformation conditions include four temperatures (from 150oC to 300oC) and two strain rates (5¡Ñ10-2s-1 and 5¡Ñ10-4s-1). After the deformation, the specimens were examined by TEM for observing the morphology of the microstructures and measuring various parameters, which includes the sizes and aspect ratios of dislocation cells, as well as the distribution of misorientation angles for dislocation walls. At last, the proportions of GNBs and IDBs were tried to be determined.

In this study, we establish a car body PEC model by using a NEC-2-based numerical software. Based on this model, we then carry out a series of simulations and analysis in the FM band concerning the effects of various car structures on antenna patterns. The results have been compared with those available in open literature in order to verify our model. The simulation results show that the roof support pillars significantly affect the antenna patterns. We investigate the ripples caused by the finite ground plane in the antenna patterns, and propose a new edge treatment technique. Our results indicate that a significant reduction of these unwanted ripples can be obtained, if the proposed technique is applied. The effect of car glasses and human body is also taken into consideration. At last, the issue of studying the effects at higher frequencies is addressed. Two approaches are used, including UTD, and PO. Satisfactory results are obtained.