Depletion layer recombination effects on the radiation damage hardness of gallium arsenide cells

The significant effect of junction depletion layer recombination on the efficiency of windowed GaAs cells was demonstrated. The effect becomes more pronounced as radiation damage occurs. The depletion is considered for 1 MeV electron fluences up to 10 to the 16th power e/sq m. The cell modeling separates damage in emitter and base or buffer layers using different damage coefficients is reported. The lower coefficient for the emitter predicts less loss of performance at fluences greater than 10 to the 15th power e/sq cm. A method for obtaining information on junction recombination effects as damage proceeds is described; this enables a more complete diagnosis of damage to be made

Alloy composition effects on oxidation products of VIA, B-1900, 713C, and 738X: A high temperature diffractometer study

High temperature X-ray diffraction studies were performed to investigate isothermal and cyclic oxidation at 1000 and 1100 C of the nickel-base superalloys VIA, B-1900, 713C, and 738X. Oxidation was complex. The major oxides, Al2O3, Cr2O3, and the spinels, formed in amounts consistent with alloy chemistry. The alloys VIA and B-1900 (high Al, low Cr alloys) tended to form Al2O3 and NiAl2O4; 738X (high Cr, low Al) formed Cr2O3 and NiCr2O4. A NiTa2O6 type of oxide formed in amounts approximately proportional to the refractory metal content of the alloy. One of the effects of cycling was to increase the amount of spinels formed

A stereographic representation of Knoop hardness anisotropy

Indentation direction parameter for hardness anisotropy representation of single crystal on stereographic triangl

Thermal expansion in the nickel-chromium-aluminum and cobalt-chromium-aluminum systems to 1200 degrees C

Thermal expansion data were obtained on 12 Ni-Cr-Al and 9 Co-Cr-Al alloys by high temperature X-ray diffraction. The data were computer fit to an empirical thermal expansion equation developed in the study. It is shown that the fit is excellent to good, and that the expansion constants depend on phase but not on composition. Phases for the Ni-Cr-Al system and Co-Cr-Al system are given. Results indicate that only alpha Cr has an expansion constant low enough to minimize oxide spalling or coating cracking induced by thermal expansion mismatch

High temperature cyclic oxidation data. Part 1: Turbine alloys

Specific-weight-change-versus-time data and x ray diffraction results are presented derived from high temperature cyclic tests on high temperature, high strength nickel-base gamma/gamma prime and cobalt-base turbine alloys. Each page of data summarizes a complete test on a given alloy sample

High-Temperature Cyclic Oxidation Data, Volume 1

This first in a series of cyclic oxidation handbooks contains specific-weight-change-versus-time data and X-ray diffraction results derived from high-temperature cyclic tests on high-temperature, high-strength nickel-base gamma/gamma' and cobalt-base turbine alloys. Each page of data summarizes a complete test on a given alloy sample

High-temperature cyclic oxidation data. Part 2: Turbine alloys

Specific-weight-change-versus-time data and x ray diffraction results are presented derived from high temperature cyclic tests on high temperature, high strength nickel-base gamma/gamma prime and cobalt-base turbine alloys. Each page of data summarizes a complete test on a given alloy sample

H∞ voltage control of a direct high-frequency converter

Providing a secure power network is a demanding task but as network complexity is expected to grow with the connection of large amounts of distributed generation so the problem of integration, not just connection, of each additional generator becomes more protracted. A fundamental change to contemporary network architectures may eventually become necessary and this will provide new opportunities for power electronic converters to deliver advanced management and new power flow control features. Direct resonant converters (Dang 2005), could be used in novel devices such as the Active Transformers (Garlick 2008). The key to the successful exploitation of these devices will be their versatility, controllability and cost efficiency

Architecture and control of large power networks with distributed generation

The architecture of the UK's passive power network has taken over one hundred years to evolve through a process of demand and technology led development. In the early years of electrical power, distribution systems were islands of distributed generation, often of different voltages and frequencies. Increasing demand for electrical power and the need to reduce distribution costs eventually led to the standardisation of frequency and voltages and to the connection of the island systems into a large network. Today's power networks are characterised by their rigid hierarchical structure and unidirectional power flows. The threat of climate change is driving the demand for the use of more renewable energy. For electricity production, this is achieved through generation using more wind, biomass, tidal and solar energy. This type of generation is often referred to as Distributed Generation (DG) because it is not a centralised facility connected to the high voltage transmission grid but a distributed source connected to the lower voltage distribution network. The connection of DG to the distribution network significantly alters the power flow throughout the network, and costly network reinforcement is often necessary. The advancement in the control of electrical power has largely been facilitated by the development of semiconductor power electronic devices and has led to the application of "Flexible Alternating Current Transmission Systems (FACTS), which include such devices as "Static Var Compensators" (SVC) and Static Compensators (STATCOM), for the control of network voltages and power flows. Providing a secure power network is a demanding task, but as network complexity is expected to grow with the connection of high levels of DG, so the problem of integration, not just connection, of each successive generator becomes more protracted. A fundamental change to the network architecture may eventually become necessary, and a new, more active network architecture, perhaps based on power cells containing local generation, energy storage and loads, has been proposed by some researchers. The results of an historic review of the growth of power networks, largely in the UK, forms the basis of a case to replace the conventional power transformer with an Active Transformer that will provide a more controllable, flexible and robust DG connection and (i) will facilitate greater network management and business opportunities, and new power flow control features. The Active Transformer design is based on an a.c. link system and an a.c.-a.c. highfrequency direct resonant converter. This thesis describes a model of the converter, built in MATLAB and Simulink®, and used to explore control of the converters. The converter model was then used to construct a model of the Active Transformer, consisting of a resonant, supply-side converter, a high frequency transformer and a resonant, load-side converter. This was then used to demonstrate control of bi-directional power flow and power factor control at the Grid and Distribution Network connections. Issues of robustness and sensitivity to parameter change are discussed, both for the uncompensated and compensated converters used in the Active Transformer. The application of robust H∞ control scheme proposed and compared to a current PI control scheme to prove its efficacy.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Stick-slip instability for viscous fingering in a gel

The growth dynamics of an air finger injected in a visco-elastic gel (a PVA/borax aqueous solution) is studied in a linear Hele-Shaw cell. Besides the standard Saffmann-Taylor instability, we observe - with increasing finger velocities - the existence of two new regimes: (a) a stick-slip regime for which the finger tip velocity oscillates between 2 different values, producing local pinching of the finger at regular intervals, (b) a ``tadpole'' regime where a fracture-type propagation is observed. A scaling argument is proposed to interpret the dependence of the stick-slip frequency with the measured rheological properties of the gel.Comment: 7 pages, 4 figures. Submitted to Europhysics Letter