MICROWAVE ENERGY CONVERSION

Plasma Diode. Operating conditions for the microwave absorber are set forth. A tapered coaxial load is proposed in which the outside of the load is also the cathode of the plasma diode which should operate at temperatures of 2000 - 2500° K, The load and cathode temperature must be raised from about 300°K to operating temperature by microwave power. A test set up is proposed for making the necessary measurements of conductivity, thermal and mechanical properties of the more promising absorber-cathode materials. Some of the test equipment is not yet available but tests at room temperature on conductivity at microwave frequencies are now in progress on carbon, zirconium carbide and silicon carbide. The thermodynamic problems of the microwave absorber- cathode are discussed. Direct Rectification by Semi-conductor Diodes. Test have been made on a considerable number of diodes at 60 cycles, 600 Mc, and 2500-3000 Mc, with resistance loads, with and without capacitance filters, and at power levels of 370 milliwatts at 600 Mc, and 200 milliwatts per diode at microwave frequencies. The best measured efficiencies obtained with resistance-capacitance loads were between 40 and 63% at microwave frequencies. When storage batteries were used as the load at microwave frequencies maximum efficiency with a two volt load was 72% and with a four volt load it was 65%. Higher efficiencies are anticipated with full-wave and bridge type rectifiers using a new higher power source. Conversion by Acceleration of Electron Beams Klystron Converter. A theoretical model is described and the equations presented. The computer results are not complete but it appears that for high power the klystron converter is not much better than the closed spaced diode which may reach actual efficiencies of 65 to 70%. Inverted Magnetron. Theoretical equations are presented, for a parallel plane type of magnetron, and some results have been obtained on a computer. At 3000 Mc. efficiencies of 25 - 35% were computed. The work is still in progress. Vacuum Diode. The vacuum diode has been investigated theoretically and the results presented in curve form. From the curve efficiencies for a close space diode of 65 - 70% appear\u27 to be feasible. Experimental results are described which would indicate reasonably high efficiencies at microwave frequencies

The Muqarnas in contemporary art and epigraphic design: developing technical vision in the design of the muqarnas

This thesis is about muqarnas, a type of three-dimensional decorative finishing strip using concave elements. It is a kind of corbel used in Islamic architecture both as a decorative motif and as an enriched block or horizontal bracket. It is generally found under the cornice and above the bed -mould of the Corinthian entablature, and at the same time, it hides the transitional zones between various surfaces (e.g. arches, domes, capitals, windows, ceilings, minarets, mihrabs, minbar, façade). It can take a number of forms and in some circumstances resembles stalactites. It has been applied, artistically, to different materials (e.g. stucco, stone, marble, wood, faience and polychrome) in unique, regularly spaced, geometric arrangements.The muqarnas is an important feature in Islamic architecture because of its social, cultural and symbolic meanings. The research aim is to critically analyse the muqarnas and to shed light on its genesis, nature and evolution. This will be followed by an attempt to transform the muqarnas to suit modern use without losing its meaning. This study will highlight the importance of providing a simple software program for modelling the muqarnas, relevant to the field of Islamic architecture, epigraphic design and art such that it can be appreciated by contemporary practitioners, especially contemporary viewers, who will find different options in the model (muqarnas blocks) that will allow them to assess alternative designs and have them ready for use in the form of computerised two -dimensional and three-dimensional drawings.The thesis begins with a first chapter comprising an introduction to the background, aim, objectives, methodology and the significance of the research. The second chapter is a review of the history of muqarnas and offers an interpretation of all the figures that combine to make the muqarnas types, spatial compositions in interlocking values. The chapter also explores the cultural and compositional units (cube, sphere, wall, columns and arches) and the properties of the organic rules of the muqarnas. The third chapter is an analysis of the proportional order and harmony of each element of the muqarnas units in Islamic architecture. The fourth chapter puts an intellectual and subjective perspective on the properties of the muqarnas, concentrating on structural transformation in Islamic art and architecture using structuralism and associated theories. The fifth chapter reviews the performance of the muqarnas design processing program `Generator of Mugarnas'. This program can be used to visualise data generated from the blocks of muqarnas, to create a user interface and to convert two-dimensional plans into three- dimensional muqarnas data. The program is based on the original muqarnas types and allows for efficiency of working with materials, textures, colours and light. The final chapter concludes with a brief overview of the significance of the study.This innovative approach to the modern world will introduce the aesthetics of the muqarnas to a new audience, and rekindle the interest of designers, artists and architects. Using the program they will find alternatives ready for use in the form of computer -generated muqarnas drawings which will help them, as they are easy to use, saving time and effort. The author has made contact with professionals who are interested in using muqamas and those who are looking to invest and publish the software program when it has been fully developed and tested

Light effective hole mass in undoped Ge/SiGe quantum wells

We report density-dependent effective hole mass measurements in undoped germanium quantum wells. We are able to span a large range of densities ($2.0-11\times10^{11}$ cm$^{-2}$) in top-gated field effect transistors by positioning the strained buried Ge channel at different depths of 12 and 44 nm from the surface. From the thermal damping of the amplitude of Shubnikov-de Haas oscillations, we measure a light mass of $0.061m_e$ at a density of $2.2\times10^{11}$ cm$^{-2}$. We confirm the theoretically predicted dependence of increasing mass with density and by extrapolation we find an effective mass of $\sim0.05m_e$ at zero density, the lightest effective mass for a planar platform that demonstrated spin qubits in quantum dots

Intelligent hybrid cheapest cost and mobility optimization RAT selection approaches for heterogeneous wireless networks

The evolution of wireless networks has led to the deployment of different Radio Access Technologies (RATs) such as UMTS Terrestrial Radio Access Network (UTRAN), Long Term Evolution (LTE), Wireless Local Area Network (WLAN) and Mobile Worldwide Interoperability for Microwave Access (WiMAX) which are integrated through a common platform. Common Radio Resource Management (CRRM) was proposed to manage radio resource utilization in heterogeneous wireless networks and to provide the required Quality of Service (QoS) for allocated calls. RAT selection algorithms are an integral part of the CRRM algorithms. Their role is to decide, when a new or Vertical Handover (VHO) call is requested, which of the available RATs is most suitable to fit the need of the incoming call and when to admit them. This paper extends our earlier work on the proposed intelligent mobility optimization and proposes an intelligent hybrid cheapest cost RAT selection approach which aims to increase users' satisfaction by allocation users that are looking for cheapest cost connections to a RAT that offers the cheapest cost of service. A comparison for the performance of centralized load-balancing, proposed and distributed cheapest cost and mobility optimization algorithms is presented. Simulation results show that the proposed intelligent algorithms perform better than the centralized load-balancing and the distributed algorithms. © 2014 Academy Publisher

Performance analysis of the intelligent mobility optimization CRRM approach using a markovian chain model

Due to the increasing demand of wireless services, mobile technology has rapidly progressed towards the fourth generation (4G) networking paradigm. This generation will be heterogeneous in nature and it can be achieved through the integration of different Radio Access Technologies (RATs) over a common platform. Common Radio Resource Management (CRRM) was proposed to manage radio resource utilization in heterogeneous wireless networks and to provide required Quality of Service (QoS) for allocated calls. RAT selection algorithms are an integral part of the CRRM algorithms. Their role is to decide, when a new or Vertical Handover (VHO) call is requested, which of the available RATs is most suitable to fit the need of the incoming call and when to admit them. This paper extends our earlier work on the proposed intelligent hybrid mobility optimization RAT selection approach which allocates users in high mobility to the most suitable RAT and proposes an analytical presentation of the proposed approach in a multidimensional Markov chain model. A comparison for the performance of centralized load-balancing, distributed and the proposed intelligent mobility optimization algorithms is presented in terms of new calls blocking probability, VHO calls dropping probability, users' satisfactions probability, average networks load and average system throughput. Simulation and analytical results show that the proposed algorithm performs better than the centralized loadbalancing and distributed algorithms. © 2014 ACADEMY PUBLISHER

Symmetric Boundary Condition Technique in NASIR Galerkin Finite Volume Solver for 3D Temperature Field

In order to solve a typical three-dimensional temperature problem numerically, the three-dimensional temperature diffusion equation is chosen as the mathematical model. The finite volume formulation is derived using Galerkin approach for the mesh of tetrahedral elements, which facilitates solving temperature problems with complicated geometries. In this approach, the Poisson equation is multiplied by the piece wise linear shape function of tetrahedral element and integrated over the control volumes which are formed by gathering all the elements meeting every computational node. The linear shape functions of the elements vanish by some mathematical manipulations and the resulting formulation can be solved explicitly for each computational node. The algorithm is not only able to handle the essential boundary conditions but also the natural boundary conditions using a novel technique. Accuracy and efficiency of the algorithm are assessed by comparison of the numerical results for a bench mark problem of heat generation and transfer in a block with its analytical solution. Then, the introduced technique for imposing natural boundary conditions on unstructured tetrahedral mesh is examined for cases with inclined symmetric boundaries

Symmetric Conditions for Strain Analysis in a Long Thick Cylinder under Internal Pressure Using NASIR Unstructured GFVM Solver

Utilization of symmetric condition in NASIR Galerkin Finite Volume Method for linear triangular element unstructured meshes is introduced for numerical solution of two dimensional strain and stress fields in a long thick cylinder section. The developed shape function free Galerkin Finite Volume structural solver explicitly computes stresses and displacements in Cartesian coordinate directions for the two- dimensional solid mechanic problems under either static or dynamic loads. The accuracy of the introduced algorithm is assessed by comparison of computed results of a thick cylinder under internal fluid pressure load with analytical solutions. The performance of the solver for taking advantage of symmetric conditions is presented by computation of stress and strain contours on a half and a quarter of the cylinder section