A study of the temperature sensitivity of GaAs-(Al,Ga)As multiplequantum-well GRINSCH lasers

We have measured the temperature sensitivity, T₀, of GaAs-(Al,Ga)As, GRINSCH, multiple quantum-well (MQW) lasers with different numbers of quantum wells ranging from one to ten. Our data suggests that there is an optimum number of wells, namely five, where T ₀ is highest. Using a temperature-dependent model based on drift-diffusion equations, we have systematically analyzed the temperature sensitivity of a MQW GaAs-(Al, Ga)As laser. The T₀ versus well-number behavior observed experimentally is verified, and the important temperature-dependent factors are identified     

A theoretical investigation of the characteristic temperature T/sub 0/ for semiconductor lasers

The temperature dependence of the characteristic temperature T/sub 0/ of semiconductor quantum-well lasers is investigated using detailed simulations. The critical-temperature-dependent processes are the optical gain and the nonradiative recombination. The gain model is based on k /spl middot/ p theory with the multiple quantum wells in the active layer represented by a superlattice. The Auger process is assumed to be thermally activated. It is shown that, with inclusion of the continuum state filling and interband mixing, the most important features experimentally observed in the temperature dependence of the T/sub 0/ value can be explained. The continuum state filling and band nonparabolicity cause a significant deviation from the ideal linear carrier density versus temperature relation for quantum wells. The results are compared to experiment for broad area devices lasing at 980 nm and 1.3, and 1.55 /spl mu/m, and show good agreement over a broad range of temperature.     

Photothermal-induced temperature changes in a model inner ear: acomparison of visible, infrared, and ultraviolet lasers

The temperature change in a model cylindrical vestibule (90 mm³) was measured following irradiation by argon (488-514 nm), CO₂ (10.6 μm), KTP (Nd:YAG) (532 nm), Er:YAG (2.9 μm), and XeCl (308 nm) lasers. Otic capsule bone was used to simulate the otosclerotic stapes footplate, and the thickness of each specimen was machined to variable thicknesses (0.20-0.90 mm). Thermocouples were used to measure the temperature below the air-bone surface at depths of 1.0, 3.0, and 5.0 mm. The time-dependent temperature change, thermocouple position, and bone thickness were measured following single pulse application from argon, CO₂, and KTP (Nd-YAG) lasers. The effect of infrared and ultraviolet lasers on vestibule fluid temperature changes were studied with several fluence and pulse sequences. The temperature change in the vestibule following pulsed laser irradiation decreased with increasing bone thickness and thermocouple depth. Laser irradiation from CO₂, argon, KTP-532, XeCl, and Er:YAG lasers produced minimal (less than 5°) vestibule temperature changes. Measured temperatures were in good agreement with an analytic model, based on a solution to the bio-heat equation in semi-infinite media. The results are discussed with relevance to ear surgery     

An investigation into the use of adaptive setting techniques forimproved distance back-up protection

Changes in power system operating conditions adversely affect the reach point accuracy of distance relays. This paper discusses adaptation of the settings of distance relays within an integrated digital hierarchical protection system for the optimisation of relay performance. Specific reference is made to adaptation of the zone 3 setting to ensure optimal relay performance over a wide variety of operating conditions. Results illustrating the performance of adaptive methods compared to conventional fixed setting are presented for an application study of the North Wales 400 kV transmission network, UK     

Estimation of the sensitivity of the electrical energy demand to variations in meteorological conditions: History of methods and development of new approaches at EDF

The development of electrical heating makes French consumption of electrical energy increasingly sensitive to climatic random variations, and this considerably complicates the a posteriori analysis of realizations, not only for itself, but also as a help in forecasting. The necessity of having homogenous realizations as far as meteorological conditions are concerned, has led, for many years, to diverse reseacch and development projects at Electricité de France. A comprehensive survey is given of EDF activities in this area until the end of 1981. The results obtained by various techniques (linear or nonlinear regression methods, ARIMA models with transfer function and adaptive filtering techniques) are described.     

An investigation into the effectiveness of simulated annealing as a solution approach for the generator maintenance scheduling problem

The generator maintenance scheduling (GMS) problem is the difficult combinatorial optimisation problem of finding a schedule for the planned maintenance outages of generating units in a power system. The GMS model considered in this paper is formulated as a mixed integer program, with a reliability optimality criterion, subject to a number of constraints. A new version of the simulated annealing (SA) method for solving the GMS problem is presented. Four cooling schedules (the geometric and three adaptive schedules), two neighbourhood move operators (an elementary move and an ejection chain move operator), and a hybrid local search heuristic/SA algorithm are compared. To our knowledge, this is the first study considering a different SA cooling schedule and move operator in a GMS context. A new 32-unit GMS test system is established and used in conjunction with a benchmark test system from the literature in this investigation. It is found that choosing a different cooling schedule and an ejection chain move operator yield improved results to that of the SA algorithm currently employed in the GMS literature. The hybrid SA algorithm performs very well compared to other methods on the benchmark test system from the literature, and an improved lower bound on the objective function value is presented for this test system.     

Preparation of organic semiconductive thin films by laser ablation: Control of structure and electric properties by selecting wavelength,fluence, and substrate temperature

Amorphous organic semiconductive thin films with electric conductivities ranging between 10⁻⁵ and 10¹ Scm⁻¹ are prepared on several temperature-controlled substrates by excimer laser ablation (ELA) of 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) with 193 nm (ArF), 248 nm (KrF) and 308 nm (XeCl) beams. The structure, electric conductivity, and carrier species of the prepared films depend strongly on the ablation wavelength, fluence, and substrate temperature. Thermoelectromotive force measurements demonstrate conversion of carrier species from n-type to p-type with increasing fluence of a 308-nm beam from 0.2 to 4.0 Jcm⁻²pulse⁻¹. A film prepared on a substrate at 300 °C by ELA with a 308-nm beam partially contains a polyperinaphthalene (PPN) structure with electric conductivity of 10⁻² to 10⁻¹ Scm⁻¹. © 1998 Scripta Technica, Electr Eng Jpn, 125(2): 19–26, 1998     

Impact of gate sidewall angle on the electrical characteristics of V-shaped gate III-nitride HEMTs: An investigation into self-heating and geometrical effects

Journal of Computational Electronics - Variation of gate sidewall angle in V-shaped gate HEMTs impacts the device electrical performance, including self-heating effects, high-frequency operation...     

The costs and benefits of real-time pricing: An empirical investigation into consumer bills using hourly energy data and prices

This study analyzed smart meter data to compare how residential consumers would have fared in 2016 under traditional, flat-rate electricity pricing versus the ‘real-time pricing’ program offered by Illinois utility Commonwealth Edison. Although further study is needed with more customers and multiple years, 97% of households in the study would have saved with real-time pricing. The average savings would have been $86.63, or 13.2%, annually. Total savings would have been $29.8 million.     

An investigation into a method of detecting the fault induced highfrequency voltage signals of EHV transmission lines for protectionapplications

A method is investigated for detecting the fault-induced high-frequency voltage signals of the EHV transmission lines for protection applications. The method is based on the principle of a power line carrier communication system using a stack tuner for detecting the high-frequency voltage signals in a particular frequency bandwidth. The digitally simulated fault responses of different frequency bandwidths in the kilohertz range and at different fault inception angles of the voltage waveform are studied     

An experimental investigation into expedient enhancement of convective heat transfer in the rectangular ducts of tubular-plate heat-transfer surfaces having transverse projections and grooves

Results are presented from systematic experimental investigations into enhancement of convective heat transfer in air in short rectangular channels having transverse projections and grooves [with the Re numbers varying in the range (0.6–10) × 10³; the relative length of the channel’s smooth section, from 0.183 to 2.003; and the channel cross-section contracton ratio, from 0.748 to 0.953]. Conditions are determined under which convective heat transfer can be efficiently enhanced through artificially turbulizing the flow of coolant by means of periodical throttling, and the degree of this enhancement is evaluated.     

Preparation, characterization and dielectric study of new ferroelectric relaxors crystallizing with the tetragonal tungsten bronze structural type

The replacement of sodium and niobium by lanthanum and iron in Pb₂NaNb₅O₁₅, have allowed to prepare the new solid state solution Pb₂Na_1−x La _x Nb_5−x Fe _x 0₁₅ (0 ≤ x ≤ 1), crystallising with the tungsten bronze structure. The latter synthesized, in air, by solid state reaction, has been studied by means of X-ray and dielectric measurements. The composition dependencies of ferroelectric—paraelectric transition temperature and the lattice parameters are reported. The dielectric constants ɛ′_r and ɛ″_r have been also investigated as a function of temperature in the range 20°–700°C, and as a function of frequency in the range 1 k–13 MHz. In the composition range 0 ≤ x ≤ 0.35, the materials exhibit a typical ferroelectric–paraelectric transition while, in the composition range 0.35 < x ≤ 1, a relaxor effect has been evidenced.     

An experimental investigation into the heat transfer developed along a uniformly heated tube carrying a flow of liquid metal and placed in transverse magnetic field

We present results from an experimental investigation into heat transfer for liquid-metal coolant flowing through a horizontal heated tube (at q _w = constant on its wall) placed in transverse magnetic field. Three-dimensional fields of averaged temperature are measured, and heat-transfer coefficients along the tube length are calculated in a wide range of Reynolds numbers and Hartman numbers for different values of heat flux density.     

An improved method to approximate closest saddle node bifurcation based on multiple load flow solutions: A new method of voltage stability monitoring and control

Although a closest bifurcation point (CBP) is known to be a superior security measure against voltage collapse, no fast computation methods exist presently. In such a circumstance, the authors proposed an approximation method for CBP in Ref. 11 where two major problems were left unsolved: (1) the method cannot take into Q limits of generators and (2) it utilizes a low‐voltage power flow solution, which is not easily obtained unless a suitable initial estimate is available. This paper presents a series of techniques to solve these problems. It is shown that the proposed method can provide fairly accurate CBP without suffering any major problems. The total computation time is not more than that of ten power flows even when no information of low‐voltage solution is available in advance. The proposed method will make possible a reliable on‐line monitoring and control of voltage stability. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 19–30, 2000     

An investigation of the quality of the output voltage,current, and energy relationships of independent inverters with transformers with a rotating magnetic field

It is analyzed how commutator circuits of independent inverters with transformers with rotating magnetic fields influence the quality of the output voltage and current. Based on a harmonic analysis of curve forms under different types of loads, the dependences of the coefficients of voltage and current harmonics on the number of power-key pairs involved in commutators of independent inverters with transformers with rotating magnetic fields have been determined.     

MULTITEST II: a program for the generation, correction, andanalysis of multiple choice tests

Multitest II is a program for the generation, correction, and analysis of multiple-choice examinations. The program is written in Pascal and has been implemented for the IBM-PC and compatible microcomputers, and for the VAX minicomputer. The program allows the random generation of tests from a master test, and supports several types of multiple-choice tests. The tests are graded by means of a user-definable numerical grading system. Certain statistical analyses can be performed on the tests results. A special effort was made when designing the program to make it highly error-proof. This was achieved by using menus included in the program. The prompts were designed to elicit very specific and simple answers. As a result, the program can be handled by personnel without special computer training     

Ancient Science, Current Problems: Insight into the Vitality of Electrostatics Research Today

Electrostatics, though one of the oldest sciences, is also nowadays a dynamical and very wide research area. Static charge, well known for its destructive power when accumulating in storms and causing lightning, is now used in many systems as a mastered force to produce acoustic waves, to control aerodynamics, to filter pollution. Its control still remains a very important challenge in many systems, from spacecrafts, high voltage cables, to petro chemistry, and agriculture. We intend here only to highlight some aspects of this very rich and multiform science, without forgetting the great pioneers, Gilbert and Faraday.     

群策群力做好仪器仪表行业、企业"十五"规划跨入新世纪

论述了新世纪仪器仪表行业的定位问题和仪器仪表在信息工业中的重要地位,提出了为适应新世纪仪器仪表市场的变化我国可以开拓的仪器仪表领域.针对我国仪器仪表行业的实际情况,提出了我国"十五"仪器仪表规划和发展的一些建设性的建议.     

The Public Health, Safety and Welfare: An Analysis of the Social Responsibilities of Engineers

What obligations does an engineer have to protect the public interest in the creation and use of new technologies? How can the engineer best act so as to fulfill his or her responsibilities to the public? This paper considers these questions from the point of view of social ethics, by means of case studies of engineers in the nuclear power industry. An ethical framework is presented that allows us to define the social responsibilities of engineers. The modes of action generally available to engineers for fulfilling those responsibilities are then analyzed. All of these are judged to be inadequate, leading to the conclusion that unless the decision-making structures for the use of technology are changed, engineers will continue to be frustrated in their ability to ensure the responsible use of technology.