Low-threshold proton-implanted 1.3-/spl mu/m vertical-cavity top-surface-emitting lasers with dielectric and wafer-bonded GaAs-AlAs Bragg mirrors

We demonstrate a new structure for long-wavelength (1.3-/spl mu/m) vertical-cavity top-surface-emitting lasers using proton implantation for current confinement. Wafer bonded GaAs-AlAs Bragg mirrors and dielectric mirrors are used for bottom and top mirrors, respectively. The gain medium of the lasers consists of nine strain-compensated AlGaInAs quantum wells. A record low room temperature pulsed threshold current density of 1.13 kA/cm/sup 2/ has been achieved for 15-/spl mu/m diameter devices with a threshold current of 2 mA. The side-mode-suppression-ratio is greater than 35 dB.     

Fatty acid composition of spanish peanut oils as influenced by planting location,soil moisture conditions,variety, and season

Nine varieties or strains of Spanish type peanuts were grown in the National Variety Test in Georgia and Oklahoma with and without irrigation for two growing seasons. The oil of sound kernels was analyzed for fatty acid composition. Although no consistent pattern was found, in general, variation in fatty acid composition due to variety was much less in Oklahoma than in Georgia for both the irrigated and nonirrigated peanuts. Also, location effect and soil moisture conditions gave higher percentages of palmitic and oleic with a lower percentage of linoleic in the Georgia samples and in the nonirrigated samples from both locations. Several significant first and second order interactions with the three major fatty acids involving variety, location, and soil moisture conditions were observed. Presented at the AOCS Meeting, New Orleans, May 1973. Journal paper 2707 of the Oklahoma Agricultural Experiment Station. ARS, USDA.     

Voltage dips due to direct connection of induction generators inlow head hydro electric schemes

This paper analyses phenomena which affect voltage dip due to direct connection of induction generators running close to synchronous speed to electrical distribution systems in low head hydroelectric power schemes. The paper examines transient phenomena on connection of induction generators at close to synchronous speed in determining whether costly system reinforcement may be avoided thus making many uneconomic developments viable while satisfying constraints of permissible voltage dip if the transient phenomena is taken duly into account. More use of renewable energy in electricity supply thus reducing greenhouse gas emissions from fossil plant will therefore result. The analysis is based on a detailed induction generator model with single and double rotor bar simulation using Park's equations with simulation of rotor dynamics on connection of the generator to the electrical supply     

Measurement of torque in steam turbine-generator shafts followingsevere disturbances on the electrical supply system-analysis andimplementation

Phenomena that affects the performance of transducers that measure torque at positions along a turbine-generator shaft are reviewed, and the design of a transducer for precise measurement of torque at positions on a steam turbine-generator shaft that results from severe disturbances of the electrical supply system is discussed. Torque at shaft couplings following severe supply system events predicted using continuum models of turbine-generator shafts are analyzed and compared with that obtained over a section of the shaft by shaft twist and overall stiffness of the section. Algorithms for processing torque deduced from twist over a section to estimate true torque at specific shaft locations are discussed. Studies are performed for severe L-L-L short circuits with clearance. The design of a transient shaft torque transducer which uses disks with slits which are secured to the rotating shaft is described     

Improved second-harmonic generation by selective Yb ion doping in anew nonlinear optical crystal YCa4O(BO3)3

We describe experiments characterizing a new nonlinear optical crystal, YCa₄O(BO₃)₃ (YCOB). This crystal has a number of advantages over other commonly available nonlinear optical crystals. It has a higher nonlinear coefficient than KDP, can be fabricated to large sizes (~3-in diameter, 8-in length), and has a high damage threshold. Moreover, this new nonlinear optical crystal is nonhygroscopic, has good optical quality and mechanical properties, allowing easy optical polishing. This crystal, YCa₄ O(BO₃)₃, commonly termed YCOB, is one of a family of new nonlinear crystals, the oxyborates, that include RECa₄O(BO₃)₃ (RE=La³⁺, La ³⁺, Y³⁺, Sm³⁺, Gd³⁺, Er³⁺, and Nd³⁺). In this paper, we also successfully demonstrate a technique for improving the nonlinear optical properties of this crystal. This technique, ion substitution, has previously had limited success with other crystal hosts. However, the inclusion of yttrium in YCOB provides the opportunity to exploit this technique. Yb³⁺, which has larger mass, but approximately the same atomic size as Y³⁺ can be substituted into the crystal structure without introducing stress and nonuniformities. A systematic investigation of the linear and nonlinear characteristics of several crystals doped with various levels of Yb demonstrate that selective substitution of Yb in YCa₄O(BO₃)₃ improves the second-harmonic conversion efficiency by increasing the optical nonlinearity     

Power links with Ireland-excitation of turbine-generator shafttorsional vibrations by variable frequency currents superimposed on DCcurrents in asynchronous HVDC links

The paper describes an in-depth analysis of excitation of shaft torsional vibrations in steam-turbine-generator-exciter shafts in close proximity to HVDC converter stations by variable-frequency ripple currents superimposed on the DC currents in asynchronous links. It extends earlier work to include an in depth analysis of system scaling factors for harmonic currents impressed on generators in Northern Ireland by an inverter and to investigate the phenomena for possible torsional vibrations in the generators by the link. It is concluded that variable-frequency ripple currents superimposed on the DC current in asynchronous links can excite sympathetic torsional vibrations in turbine-generator-exciter shafts. Subtransient generator reactances may be used to approximately proportion injected harmonic current to each machine of a multi-machine network. Very small noncharacteristic currents could result in serious damage to the machine although possibility of two power systems operating with fixed deviation in system frequencies long enough for the vibrations to build up is remote. Studies should be undertaken as routine on all machines in close proximity to HVDC converter stations to ascertain whether or not the machines are at risk     

Analysis of torques in large steam turbine driven inductiongenerator shafts following disturbances on the system supply

The paper first summarises the advantages of steam turbine-driven induction generators over conventional generators such as low cost, less maintenance, rugged and brushless rotors (squirrel cage type, no need for synchronisation, etc.), together with problems concerning excitation (VAr compensation at loads etc). A mathematical model of the induction generator simulated in direct-phase quantities where saturation of the magnetising reactances is simulated and saturation of stator and rotor leakage reactances is ignored is developed and employed for detailed simulation of the machine. Discrete-mass models of the machine shaft where both steam and electrical viscous damping is simulated are employed in comparing transient shaft torsional response evaluated by time domain simulation and frequency domain analysis following incidence and clearance of severe system faults. The paper then investigates torsional response following incidence and clearance of severe supply system disturbances, when the rotor is stationary and when running at close to synchronous speed unexcited, and following malsynchronisation when excited by a controlled VAr source, together with torsional response following bolted stator-terminal short-circuits at full-load and no-load following switching in of the induction generator onto the system supply. It examines precision of predicting torque in turbine-generator shafts by frequency domain analysis not analyzed for induction generators in the literature heretofore following incidence and clearance of worst-case disturbances on the supply. Effect of steam and electrical damping on maximum shaft torques predicted by frequency domain analysis is also illustrated. The results illustrate there is no tendency for shaft torques to become more onerous as the fault clearing time is increased as is the case for shaft torques in large synchronous machines. Three large two-pole machines of rating of up to a few hundred MWs are analysed     

Metalorganic vapor phase epitaxial growth of all-AlGaAs visible (∼700 nm) vertical-cavity surface-emitting lasers on misoriented substrates

We present a study on the growth of visible (∼700 nm) vertical-cavity surface-emitting lasers (VCSELs) by metalorganic vapor phase epitaxy. The structure was based on AlGaAs for both the quantum well active region and the distributed Bragg reflectors. Photoluminescence intensity from AlGaAs quantum wells was optimized vs the substrate misorientations from the (100) surface. The doping efficiency for n-type by Si and p-type by C was studied as a function of the substrate misorientation and the growth temperature. High-quality VCSEL materials were grown on (311)A substrates. The structure was processed by selective oxidation, and high-performance VCSELs emitting at ∼700 nm were achieved in a continuous-wave mode at room temperature.