Investigation of the electrical characteristics of GaAsP light-emitting diodes (LED's) under conditions of mechanical stress

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The main line pursued is the mechanical stressing of light-emitting diodes (LED's) by pressing on the surface with spherically rounded sapphire probes ranging from 100 μm to 500 1m radius of curvature and with forces up to 50 grams weight on the largest probe, care being taken not to exceed the elastic limit of the material, which is estimated to be about 1.4 x 10^9 pascals (14,000 atmospheres) at the central bottom point of the probe. With the diode under forward bias a very wide range of current is covered from 10 mA to about 100 pA in the light-emitting region and from 100 pA to 100 nA in the generation/recombination region - and across the whole range a small decrease in current of about 1 per cent or less is observed. The classical theory of the distribution of stress by a spherical probe has been investigated by a modern computer technique, and by integration of the stress over the whole of the junction interface it is shown that the decrease in current can be ascribed to the increase in band gap of the semiconductor that is brought about by the axial component of pressure stress at right angles to the interface. With the larger currents in the light-emitting region a further decrease in current of the order of 1 per cent or less can be ascribed to heat conduction from the warm surface of the diode to the probe, thereby. lowering the temperature of the interface. Finally, the electrical characteristics of the diode under reverse bias have been investigated, with incident light playing an important role; in the absence of light the extremely small currents (10^-12 to 10^-10 amp) are consistent with thermal generation of carriers similar to the generation/ recombination mechanism for very low currents in the forward direction

Representation of Knowledge for Chess Endgames Towards a Self-Improving System

This thesis describes an investigation of the problems involved in representing knowledge within the task area of elementary Chess endgames. Two major criteria are taken for the choice of a model of & the chessplayer's knowledge : firstly, that algorithms constructed using the model should be natural from the viewpoint of a chessplayer and commensurate with his, view of the complexity of the task, and secondly that the algorithms should be capable of refinement in the light of experience in a manner which preserves the previous property. Elementary chess endgames are studied as a field in which programs based on tree-searching and traditional evaluation functions have achieved poor results and where tree-searching seems to play little or no part for people. It is therefore possible to examine problems of knowledge representation and program refinement largely independently of the tree-searching paradigm. A long term aim of the research is to develop a representation suitable as the basis for a fully automatic system of algorithm refinement, whilst maintaining the criteria given above. A model is proposed and algorithms are given for two endgames, King and Rook against King (KRK) and King and Pawn against King (KPK) using this model. It is argued that both algorithms are reasonably natural and compact representations and experiments in refining these algorithms are described in detail. In both cases, the process of refinement is shown to be a reasonably straightforward one (for people) and one which maintains the properties of naturalness and compactness. The possibility of automating this process is considered

Non-Zero Sum Sport: Pickleball and the Theory of Coopetition

An ethnography of the sport of pickleball was conducted over a span of 7 months in the United States. Findings are partly the result of the author’s journey from playing in the park to playing in the Pros—presented in autoethnographic terms—and partly the result of 11 semi-structured interviews with 13 avid pickleball players. The main contention of this study is that sport is non-zero sum, despite a tendency for sport to be considered in zero sum terms. The non-zero sum aspect of sport is argued to be the result of two main causes: one, sport is coopetive, in that it is simultaneously competitive and cooperative; and two, players’ appraisals of their successes and failures are not strictly tied to wins and losses, but instead indicate a flexibility of potential rewards from competitions. The coopetive element of sport is particularly illuminated through the lens of agential realism. Findings also indicate that pickleball may be more coopetive and less zero sum than most sports

The Lab: Hip Hop and Library Technology

Hip hop is a creative and inspiring tool that you can use to engage library users in a litany of ways. With the appropriate classroom technology (in this case, two turntables and a mixer) as well as knowledge acquired over decades in the culture, we will explore how traditional hip hop production methods can alter our understanding of library technology as well as remix our notion of how libraries can support creativity. Can understanding hip hop literacies - particularly how the culture organizes information and classifies concepts - help inspire innovation? Let’s figure it out together

My Clinging Ivy : My Ivy Green

https://digitalcommons.library.umaine.edu/mmb-vp/2168/thumbnail.jp

Measurements of Free-Space Oscillating Pressures Near Propellers at Flight Mach Numbers to 0.72

In the course of a short flight program initiated to check the theory of Garrick and Watkins (NACA rep. 1198), a series of measurements at three stations were made of the oscillating pressures near a tapered-blade plan-form propeller and rectangular-blade plan form propeller at flight Mach numbers up to 0.72. In contradiction to the results for the propeller studied in NACA rep. 1198, the oscillating pressures in the plane ahead of the propeller were found to be higher than those immediately behind the propeller. Factors such as variation in torque and thrust distribution, since the blades of the present investigation were operating above their design forward speed, may account for this contradiction. The effect of blade plan form shows that a tapered-blade plan-form propeller will produce lower sound-pressure levels than a rectangular-blade plan-form propeller for the low blade-passage harmonics (the frequencies where structural considerations are important) and produce higher sound-pressure levels for the higher blade-passage harmonics (frequencies where passenger comfort is important)

Voltera's Solution of the Wave Equation as Applied to Three-Dimensional Supersonic Airfoil Problems

A surface integral is developed which yields solutions of the linearized partial differential equation for supersonic flow. These solutions satisfy boundary conditions arising in wing theory. Particular applications of this general method are made, using acceleration potentials, to flat surfaces and to uniformly loaded lifting surfaces. Rectangular and trapezoidal plan forms are considered along with triangular forms adaptable to swept-forward and swept-back wings. The case of the triangular plan form in sideslip is also included. Emphasis is placed on the systematic application of the method to the lifting surfaces considered and on the possibility of further application