Improved imaging and detection of objects through turbid obscurants is a vital problem of current interest to both military and civilian entities. Image quality is severely degraded when obscurant fields such as fog, smoke, dust, etc., lie between an object and the light-collecting optics. Conventional intensity imaging through turbid media suffers from rapid loss of image contrast due to light scattering from particles (e.g. in fog) or random variations of refractive index (e.g. in medical imaging). Intensity imaging does not differentiate between rays scattered off particles in the obscurant field and those reflected off objects within the field. Scattering degrades image quality in all spectral bands (UV, visible, and IR), although the amount of degradation is wavelength dependent. This dissertation features the development of innovative system designs and techniques that utilize scattered radiation's deterministic polarization state evolution to greatly enhance the image contrast of stand-off objects within obscurant fields such as smoke, fog, or dust using active polarized illumination in the visible. The produced sensors acquire and process image data in real time using computationally non-intensive algorithms that differentiate between radiation that scatters or reflects from obscured objects and the radiation from the scattering media, improving image contrast by factors of ten or greater for dense water vapor obscurants.

The design of antenna arrays involves, amongst others, the selection of the array elements and geometry, as well as the element excitations. The feeding network to obtain the desired excitations can become quite complex, and hence expensive. One possible alternative would be to make use of micros trip wire-grid antenna arrays. These arrays are composed of staggered interconnected rectangular loops of dimensions a half¬wavelength by a wavelength (in the presence of the dielectric). It is because the short sides are considered to be discrete elements fed via micros trip transmission lines, that these antennas are viewed as arrays. While considerable success has been achieved in the design of these antennas, published work has been either of an entirely experimental nature or based on approximate (albeit clever) network models which do not allow for fine control of the array element excitations or off-centre-frequency computations generally. It is the purpose of this thesis to perform an almost rigorous numerical analysis of these arrays in order to accurately predict their element excitations. Models used to study microstrip antennas range from simplified ones, such as transmission-line models up to more sophisticated and accurate integral-equation models. The mixed-potential integral equation formulation is one of these accurate models which allows for the analysis of arbitrarily shaped microstrip antennas with any combination of frequency and dielectric thickness. The model treats the antenna as a single entity so that physical effects such as radiation, surface waves, mutual coupling and losses are automatically included. According to this formulation, the microstrip antenna is modelled by an integral equation which is solved using the method of moments. By far the most demanding part of the integral equation analysis is its actual numerical implementation. For this reason a complete description of the numerical implementation of the formulation is given in this thesis. To verify the accuracy of the implementation, rectangular microstrip patch antennas were analysed and surface current distributions were shown to compare favourably with published results. The formulation is then applied to the analysis of micros trip wire-grid antenna arrays which makes it possible to accurately predict surface current distributions on these arrays. Radiation patterns are determined directly from computed current distributions in the presence of the dielectric substrate and groundplane, and are essentially exact except for finite groundplane effects. To verify theoretically predicted results for wire-grid antenna arrays, several arrays were fabricated and actual radiation patterns were measured. Good correspondence between measured and predicted co-polar radiation patterns was found, while the overall cross¬polarization behaviour in cases with large groundplanes could also be predicted. The fact that numerical experimentation can be performed on wire-grid antenna arrays to examine element excitations, means that it is now possible to carefully design for some desired aperture distribution. / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

Wire-grid polarizers (WGPs) offer superior extinction, durability, angle of incidence, and heat resistance when compared to traditional organic polarizers. WGPs are found in applications such as high lumen lighting, laser devices, high lumen digital cinema projectors, LED packaging, and other integrated optical applications and are driving the need for over-coatings. Over-coating a WGP has been found to increase lifetime and durability. This research provides lifetime data on coated and uncoated WGPs. WGPs over-coated with 100nm of SiO2, 300nm of MgF2, and with no over-coating were heated to temperatures of 450 ºC, 500 ºC, and 550 ºC and timed until they reached a predetermined optical failure point. The activation energies were calculated by applying the Arrhenius model to the failure data. WGPs with no over-coating were found to have an activation energy ≥ 1.5329 eV, with silicon dioxide an activation energy ≥ 1.7197 eV, and with magnesium fluoride an activation energy ≥ 2.4577 eV. It has been shown that coating a WGP with an over-coating of silicon dioxide or magnesium fluoride slows the oxidation process of the aluminum nano-wires, thus increasing the lifetime of the WGP by 208% and 27,904%, respectively. Parasitic chemical reactions were not found to exist with silicon dioxide or magnesium fluoride when used as an over-coating.

Approved for public release; distribution is unlimited / The Numerical Electromagnetics Code (NEC) was used to evaluate the admittance, average power gain, and the electric near and far field of a monopole antenna mounted on a cubical box over a perfectly conducting ground plane. Two models of the box, employing surface patches and wire grids, were evaluated. The monopole was positioned at the center, the edge, and at a corner of the box's top surface. Admittance and average power gain of the antenna were calculated. NEC results were examined and compared with experimental data and with results from "PATCH", another independent electromagnetic modeling code. The near electric field was calculated for both models. Computer graphics techniques were presented for plotting NEC near field results using DISSPLA (Display Integrated Software System and Plotting Language), a commercial graphics package. Contour and 3-D amplitude, and phase plots of the near electric fields were presented. Radiation patterns were calculated to relate far field and near field behavior of the antenna. Surface patch and wire grid models are compared and conclusions were presented. / Naval Ocean Systems Center / http://archive.org/details/investigationofn00elli / O&MN, Direct Funding / Lieutenant, Hellenic Navy

Yes / Microstrip patch antennas with harmonic suppression are designed and optimised, using a genetic algorithm and applying a novel adaptive meshing program to generate a wire-grid simulation. A coaxially-fed air-dielectric patch antenna design with a folded patch was investigated. It was confirmed that antennas with excellent performances could be designed by this method. / MSCRC

Amyotrophic lateral sclerosis (ALS) is a progressive neurological disorder of the central nervous system characterized by loss of motor neurons and voluntary muscle degeneration. Astrocytes play a major role in regulation of the disease onset and progression due to their intimate association with neurons. Regulation of ionic homeostasis is one of their key functions and its failure has been linked to several neurological diseases. The aim of this thesis was to explore differences in membrane properties of astrocytes in ALS. To fulfill this aim, a double transgenic mouse strain with ALS-like phenotype and a specific expression of enhanced green fluorescent protein in astrocytes was generated. To phenotype this strain, two sensorimotor tests, wire grid hang test and rotarod test, were conducted. Immunohistochemistry was used to characterize the strain on a cellular level and to explore changes of specific ion channels. Functional properties of astrocytes were explored using the patch clamp technique. The double transgenic strain has the characteristic ALS-like phenotype and is comparable to the original strain with differences in symptom onset and progression between models and sexes. On the cellular level, there are characteristic ALS features, specifically loss of motor neurons and astrogliosis....

No description available.

The necessity to incorporate renewable energy systems into existing electric power grid and need of efficient utilization of electrical energy are growing every day. A shunt connected Voltage Source Inverter(VSI) capable of bidirectional power flow and fast control has become one of the building block to address such requirements. However with growing number of grid connected VSI, new requirements related to harmonic injection, higher overall efficiency and better performances during short term grid disturbances have emerged as challenges. For this purpose a grid connected three phase four wire VSI with LCL filter can be considered as a general module to study different control approaches and system behavior under ideal and non-ideal grid conditions. This work focuses on achieving enhanced performance by analyzing effect of non-ideal conditions on system level and relating it to individual control blocks. In this work a phase locked loop structure has been proposed which is capable of extracting positive sequence fundamental phase information under non-ideal grid conditions. It can also be used in a single phase system without any structural modification. The current control for the three phase four wire VSI system has been implemented using Proportional Resonant (PR) controller in a per phase basis in stationary reference frame. A simplified controller design procedure based on asymptotic representation of the system transfer function is proposed. Using this method expressions for controller gains can be derived. A common mode model of the inverter system has been derived for low frequencies. Using this model a controller is designed to mitigate DC bus imbalance caused by sensor and ADC channel offsets. A multi-rate approach for digital implementation of PR controller with low resource consumption, that is suitable for an FPGA like digital controller ,is proposed. This multi-rate method can maintain resonance frequency accuracy even at low sampling frequency and can easily be frequency adaptive. Anti-wind up methods for PI controller have been studied to find suitable anti-wind up methods for PR controller. The tracking anti-wind up method is shown to be suitable for use with a PR controller. The effectiveness of this method under sudden disconnection and reconnection of VSI from grid is experimentally verified. A resonant integrator based second order filter is shown to be useful for active damping of LCL filter resonance with a wide range of grid inductance variation. The proposed method utilizes the LCL filter capacitor voltage to estimate resonance frequency current. Suitability of fundamental current PR controller for active damping alone, and with the proposed method show the superiority of the proposed method especially for low switching frequencies. Design oriented analysis of the above topics are included in the thesis. The theoretical understandings developed have been verified through experiments in the laboratory and can be readily implemented in industrial power electronic systems.