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Optimal compensating schemes for the secondary arc current limiting using neutral reactor for 1000 kV ultra-high voltage long parallel transmission lines in maintenance state are investigated in this study. For maintenance safety, the line in maintenance must be electrically isolated from the line in normal operation state. The influential factors such as transposition degree, arc resistance, load current and fault location are studied. Finally, the sensitivity of secondary arc current against the variation of neutral reactor value is investigated. Real-time digital simulator (RTDS) simulation tests have been carried out to verify the correctness and validity of the analysis presented in this study.

The optimal single line compensating model is presented and analysed for short 1000-kV UHV parallel lines, to limit secondary arc current and recovery voltage. According to this study, for perfectly transposed 1000-kV lines shorter than 183 km, 750-kV parallel lines shorter than 280 km and 500-kV parallel lines shorter than 500 km, the secondary arc current can be compensated in single line model, and hence achieving the successful selective pole reclosing. Simulations on real time digital simulator (RTDS) have been carried out to evaluate the compensation scheme proposed in this study.

The solar heating and cooling systems are among the best solutions for the current energy and environment issues. In this chapter, the background and overview of the solar heating and cooling systems are given. In these systems, the energy sources are the solar power, and the consuming components include the heating and cooling devices. In order to ensure the steady operation of solar driven systems, the heat storage systems are also necessary. In this case, the different choices of solar energy, solar heating, solar cooling and heat storage are briefly introduced in this chapter. A technology roadmap is given at last which provides a clear connection between these introduced technologies.

An adsorption cooling system is a heat-activated cooling system based on the solid sorption process. It is also a good choice for solar cooling, just like the absorption cooling system. In this chapter, the working principles of both intermittent and continuous adsorption cooling systems are introduced. The choices of physical adsorption working pair, chemical adsorption working pair, and composite adsorption working pair are introduced. Various adsorption cooling systems are then classified and introduced based on the coupled solar collector, working pair, cooling output, and operating process. This information offers a guideline to solar-driven adsorption cooling systems for various conditions.

This study proposes a fault phase selection scheme for EHV/UHV transmission line protection during unbalanced faults. The scheme utilises the relative phase angle relationship between the negative and zero sequence currents and the fault impedance to identify the fault phase, providing particularly satisfactory tolerance towards high-fault resistance during normal operating situations and power swings. Real time digital simulator (RTDS) simulations demonstrate the outstanding performance of the proposed scheme in varying pre-fault system and fault conditions.

In this paper, the influence of smelting processes on precipitation behaviors and mechanical properties of CLF-1 (China low activation ferrite) steel was investigated. Mechanical properties of CLF-1 steels melted by vacuum induction melting (VIM, CS25 steel) and vacuum induction melting followed by consumable electrode remelting (VIM + ESR, CS350 steel) had been studied. The results indicated that the steels showed similar values of hardness and tensile strength, however, creep properties of CLF-1 steel were obviously improved by VIM + ESR process. M(23)C(6) and M(7)C(3) Carbides were precipitated in the CS25 steel, and M(23)C(6) carbides were precipitated in CS350 steel after high-temperature tempering at 1013 K for 90 min. Creep properties of CS25 steel were shown to be dramatically deteriorated by the existence of rod M(7)C(3) precipitates, which was due to W macrosegregation in the CS25 steel melted by VIM. M(7)C(3) was replaced by M(23)C(6) after ageing at 823 K for 5000 h. (C) 2010 Elsevier B.V. All rights reserved.

Most lithography-based micro-forming technology has the limitations in materials selection, forming efficiency and the complexity of micro-parts etc. It is urgent to develop the efficient low-cost micro-forming method in batch. This paper introduced the state-of-the-art of sheet metal micro-forming technology with laser-induced ultra-high strain rate involving the loading modes, processes and forming fundamental. Then, the application of the micro-forming of ultra-high strain rate induced by laser shock is extended into the bulk forming domain, micro bulk forming. It is pointed out that the further investigation on micro bulk forming method focuses on scale effects, forming mechanism, loading and control modes.

A method for the analysis of perfluorinated compounds (perfluoroalkyl sulfonates: C4, C6, C8, C10; perfluoroalkyl sulfinates: C6, C8, C10; perfluorooctanesulfonamide, N-ethyl perfluorooctanesulfonamide, N-ethyl perfluorooctanesulfonamidoacetate, perfluorocarboxylates: C4–C14; fluorotelomer carboxylate (7:3, 8:2) in whole blood using acetonitrile and OASIS WAX® solid phase extraction (SPE) cartridge was developed. Separation of target compounds in two HPLC columns (ion exchange JJ50-2D and C18 Betasil columns) was examined. Matrix recoveries of the developed methods ranged from 70% to 120%. Separation of possible inferences such as taurodeoxycholic acid (TDC) was accomplished using an ion exchange JJ50-2D column, and this separation was validated using whole blood of different animals.

The liquid metal and solid ceramic pebble breeder blankets have become the most promising blankets for ITER-TBMs or DEMO reactors in China and the world due to their potential advantages. In recent years the corresponding research work on fusion reactor materials mainly focuses on structural materials, plasma facing materials and the functional materials for the blanket such as breeder, coating and flow channel insert etc. for the successful application of fusion energy in the near future. The R&D on those materials in the two kinds of blankets is being carried out widely in China, including fabrication and manufacturing techniques, physical/mechanical properties assessment before and after irradiation, joining techniques for structural materials, compatibility evaluation, and the development and verification of the criteria for fusion material designs. The progress on main R&D activities of fusion reactor materials in China is introduced and prospected in the paper.

A traditional distance protection relay uses a lumped parameter model of the transmission line. For a long 1000-kV UHV line with large distributed capacitance, such a simplified line model is inadequate and can cause malfunction of the relay due to large errors in the impedance measurement. This paper presents a new line model for a distance relay and the procedure of reliable fault impedance measurement and relay setting. It describes the proposed application of the relay developed to a 645-km 1000-kV UHV transmission line including shunt reactor compensation, which is currently being constructed in China. Tests are carried out on an RTDS (real time dynamic system) to evaluate the relay performance, showing significant improvement compared to a more traditional distance relay. The new distance relay is shown to satisfy the requirement of 1000-kV UHV transmission line protection.

In the EURICA campaign aimed at exploration of the $^{78}\mathrm{Ni}$ region, an isomeric state of $^{76}\mathrm{Co}$ has been observed via $\ensuremath{\gamma}$-ray spectroscopy. The nuclei were produced by in-flight fission of a $^{238}\mathrm{U}$ beam at the Radioactive Isotope-Beam Factory. Two coincident $\ensuremath{\gamma}$ rays of $192.02(30)$ and $446.4(7)$ keV from the decay of a ${t}_{1/2}=2.96{(}_{25}^{29})\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$ isomeric state of $^{76}\mathrm{Co}$ have been observed. The decay of the isomer was assigned to an $E1$ transition with a reduced transition probability of $B(E1;{3}^{+}\ensuremath{\rightarrow}{2}^{\ensuremath{-}})=1.79(16)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ W.u. A $\ensuremath{\beta}$-decaying state with spin-parity ${1}^{\ensuremath{-}}$ and a half-life of $16(4)$ ms was also observed in the data, and the known state with a half-life of $22{(}_{5}^{7})$ ms was assigned to have a spin-parity of ${8}^{\ensuremath{-}}$. Furthermore, the isomer of $^{76}\mathrm{Ni}$ has been remeasured to $547.8(33)$ ns giving a $B(E2;{8}^{+}\ensuremath{\rightarrow}{6}^{+})$ value of $0.786(5)$ W.u. A new excited state at $2994.6(5)$ keV, decaying via a $\ensuremath{\gamma}$ ray of 2004.5(4) keV, has also been observed. This is in agreement with either of the predicted ${0}_{2}^{+}$ or ${2}_{2}^{+}$ states. These results are discussed in terms of the shell model and the interaction of the $\ensuremath{\nu}{p}_{1/2}$ and $\ensuremath{\pi}{f}_{7/2}$ orbitals.

Using V–4Cr–4Ti as structural material in a V–Li blanket offers the blanket to operate at 350–750 °C with high thermal efficiency. This paper investigates ways to strengthen V–4Cr–4Ti and the thermal stability of the strengthening. Results show that the alloy could be greatly strengthened in a proper ageing process, with insignificant loss of ductility or even higher static tensile fracture toughness. Cold rolling is found to be another approach for higher strength. Both strengthening are thermally stable at not more than 500 °C. At higher temperature, the alloy in the sate of complete recrystallization shows better thermal stability than the alloy in solid solution state. For high performance of the V–Li blanket with good economic feature, the design of the blanket should consider to use V–4Cr–4Ti in various thermo-mechanical states in terms of the operation temperature.

Ti6Al4V specimens have been irradiated at different temperatures with 200 keV He ions. Microhardness and elastic modulus of the unirradiated and irradiated specimens were measured by means of the nano-indentation technique and analyzed using the Oliver-Pharr method. The indentation depth of all samples is 700 nm, which is comparable in magnitude to the ion range. The subsurface structure of the Ti6Al4V specimens was investigated by the X-ray diffraction technique. The measurements indicate that the microhardness increased with the irradiation temperature from room temperature to 600 degrees C while the elastic modulus almost monotonically decreased. The Irradiation at 700 degrees C, however, caused softening and slight increase of the elastic modulus within the surface layer of the specimens. The hardening and reduction of the elastic modulus of the Ti6Al4V alloy under irradiation conditions used in this study is tentatively explained by a model based on the presence of point defects and dispersed obstacles of P-precipitates. The softening and slight increase of elastic modulus of helium-irradiated Ti6Al4V at 700 degrees C might be related to the coarsening of beta-precipitates and formation of the hybrid gamma-TiH phase in alpha-phase.

Thermal fatigue is one of the key factors governing the lifetime of the divertor plate. Tungsten is a promising candidate to cover the surface of the divertor plate in the design of the international thermonuclear experimental reactor (ITER). The W/Cr–bronze divertor small scale mock-ups were manufactured by hot isostatic pressing (HIPing) technique. Thermal fatigue tests of W/Cr–bronze divertor mock-ups have been carried out by an electron beam facility. The mock-ups were tested under a cyclic surface heat flux of 9 MW m−2 for 1000 cycles. The electron beam was loaded on the mock-up surface for 20 s and unloaded for 20 s, alternately. The flow rate of water coolant was 0.1 L s−1. The 0.3 mm diameter NiCr–NiSi thermocouples were used to monitor the temperature distribution of the mock-up. It was found that the maximum temperature of the tungsten surface was about 400 °C. The saturated temperature at the joint of tungsten and Cr–bronze was 160 °C. The surface and the W/Cr–bronze joint of the mock-up did not show any damage during the thermal fatigue test up to 1000 cycles. A critical cooling flow rate Lc exists under a certain heat flux for a certain cooling system. The agreement between the experimental results and calculated temperature distributions was good.

Several V-base alloys were exposed to hydrogen gas at 700–800 °C for hydrogen charging. Tensile tests were performed after the exposure to evaluate the hydrogen embrittlement behavior. The results showed that neither the uniform nor the total elongation was significantly affected by the hydrogen before a critical hydrogen concentration ( C CH ) was reached when the alloys were tested at high strain rate of 1.1 × 10 −3 /s. However the total elongation of the V–4Cr–4Ti alloy (NIFS-Heat 2) decreased notably with increasing hydrogen concentration at the strain rate of 4.4 × 10 −4 /s. Hydrogen-induced hardening occurred for all of the alloys, which was thought to be a solid solution hardening. The hardening rate was found to decrease significantly with the addition of Ti/Al to the alloy and the increase of the strain rate. And also, the alloys with Ti or Al were shown to have better properties against the hydrogen embrittlement.

As an alternative choice for fusion application, V alloyed with 6–8 wt%W has been studied. The results showed that W could strengthen the alloy at room temperature, more effectively than Ti or Cr. With both additions of Ti and W, the recovery and recrystallization of the alloys behaved similarly to V–4Cr–4Ti, but the behavior was strongly influenced by the concentration of the interstitial impurities in solid solution. Similar behavior to V–4Cr–4Ti was also found for V–6W–1Ti on hydrogen embrittlement. V–6W–1Ti seemed to have better properties for hydrogen embrittlement due to its low hydrogen absorption rate. Significant differences in oxidation behavior in air were not observed for the alloys investigated.

This paper summarizes recent achievements in the characterization of candidate vanadium alloys obtained for fusion in the framework of the Japan-China Core University Program. National Institute for Fusion Science (NIFS) has a program of fabricating high-purity V-4Cr-4Ti alloys. The resulting products (NIFS-HEAT-1,2), were characterized by various research groups in the world including Chinese partners. South Western Institute of Physics (SWIP) fabricated a new V-4Cr-4Ti alloy (SWIP-Heat), and carried out a comparative evaluation of hydrogen embrittlement of NIFS-HEATs and SWIP-Heat. The tensile test of hydrogen-doped alloys showed that the NIFS-HEAT maintained the ductility to relatively high hydrogen levels. The comparison of the data with those of previous studies suggested that the reduced oxygen level in the NIFS-HEATs should be responsible for the increased resistance to hydrogen embrittlement. Based on the chemical analysis data of NIFS-HEATs and SWIP-Heats, neutron-induced activation was analyzed in Institute of Plasma Physics (IPP-CAS) as a function of cooling time after the use in the fusion first wall. The results showed that the low level of Co dominates the activity up to 50 years followed by a domination of Nb or Nb and Al in the respective alloys. It was suggested that reduction of Co and Nb, both of which are thought to have been introduced via cross-contamination into the alloys from the molds used should be crucial for reducing further the activation.

This paper reviews recent progress in research on vanadium alloys with emphasis on V–4Cr–4Ti as a reference composition. New high purity V–4Cr–4Ti ingots and products (NIFS-HEATs) were made. The improved purity of the alloys made a practical demonstration of enhanced feasibility of recycling as a method of handling after use in fusion reactors. Significant progress has been made in the understanding of physical metallurgy of V–4Cr–4Ti and effects of O, N and C on the alloy properties such as low and high temperature mechanical properties, welding properties and low temperature irradiation effects, by means of including the comparison of various large heats and model alloys with different impurity levels. The effects of other trace impurities on some of the properties are also discussed. Other current efforts to characterize V–4Cr–4Ti, to improve its properties and to explore advanced vanadium alloys are reviewed. Issues remaining for the future investigations are discussed.

c-axis oriented La2-xSrxCu1-yO4 (x similar to 0.15) films were grown by de magnetron sputtering on Y-stabilized ZrO2, SrTiO3 and LaAlO3 substrates. It was found that the zero resistance temperature, T-c0, and the lattice parameters of the films are strongly dependent on the sputtering O-2:Ar gas ratios. A strong thickness dependence of T-c0 was also found in this kind of film, T-c0 of 22 K was obtained on similar to 2000 Angstrom thickness film grown on LaAlO3 substrate. The O-2:Ar ratios primarily modify the copper content, rather than the oxygen content of the films. The variation of the Cu content of the films strongly dominates the superconductivity of the films. Copyright (C) 1996 Published by Elsevier Science Ltd.

Electrochemical machining plays a prominent role in blisk (bladed integrated disk) construction process. Since blisk channel is narrow and twisted, interference between electrodes may happen during electrochemical machining. Therefore, this paper develops a cathode designing method to avoid interference. Firstly, according to theory of electrochemical machining, machined channel is predicted by calculation. Second, with this channel, interference analysis is carried out and a cathode is designed. Finally, the cathode is employed in experiment and no interference appears. This study was sponsored by the National Natural Science Foundation of China (51205199) and the Natural Science Foundation of Jiangsu Province (BK2012387).

We report optical modulation effects on second harmonic generation (SHG) in C 60 films. It was observed that a large second harmonic response of C 60 films (in a corona poling field of 5.5 kV at a nominal temperature of 140 °C) was almost completely suppressed when the film was illuminated with a second visible-light source (pulsed or steady state). The magnitude of the SHG suppression was measured as a function of the wavelength and intensity of the second source. By scanning the time interval between a “suppression” pulse and the SHG generation pulse we found that the lead time required for the suppression effect is about 250 ps.

The magnetohydrodynamic (MHD) pressure drop of 22 Na 78 K flow in a circular duct was measured under a quickly changing magnetic field. The MHD pressure drop reduced with time as the magnetic field strength decreased. However, the dimensionless pressure drop gradient varied with the interaction parameter and had a higher value in the middle of the range of values of the interaction parameter. Therefore, a quickly changing magnetic field is harmful to the structural material in a liquid metal self-cooled blanket of a fusion reactor, since the greater pressure drop gradient may cause a larger stress in the blanket. This is even more harmful if the magnetic field strength decreases very quickly or its distribution in space is greatly non-uniform.

The HSGS characteristic for secondary arc limitation on UHV parallel lines is investigated versus single- phase to ground faults and cross-country faults, respectively by theoretical analysis and RTDS verification. The influential factors such as electrostatic induction, electromagnetic coupling, line length, HSGS single end closing and the secondary arc resistance are involved. The results show that secondary arc current and recovery voltage of cross-country faults are higher than that of single-phase to ground faults. The secondary arc current and recovery voltage increase with the increasing line length and load level. HSGS single end closing doesn't help extinguishing the arc, while the high secondary arc resistance does. The conclusion shows that HSGS with low resistance and double-end quick closing in middle and short lines could extinguish secondary arc effectively, therefore the single-phase reclosing succeeds. Advice would be provided for the construction of UHV transmission lines in China.

Many QTLs for fatness traits have been mapped on pig chromosome 7q1.1-1.4 in various pig resource populations. Eight novel markers, including seven SNPs and one insertion or deletion within BTNL1, COL21A1, PPARD, GLP1R, MDFI, GNMT, ABCC10, and PLA2G7 genes, as well as two previously reported SNPs in SLC39A7 and HMGA1 genes, were genotyped in Large White and Meishan pig breeds. Except for two SNPs in HMGA1 and ABCC10 genes, allele frequencies of the other eight markers are highly significant different between Chinese indigenous Meishan breeds and Large White pig breeds. Eight polymorphic sites were then used for linkage and QTL mapping to refine the fatness QTL in a Large White × Meishan F(2) resource population. Five chromosome-wise significant QTLs were detected, of which the QTLs for leaf fat weight, backfat thickness at 6-7th rib and rump, and mean backfat thickness were narrowed to the interval between PPARD and GLP1R genes and the QTL for backfat thickness at thorax-waist between GNMT and PLA2G7 genes on SSC7p1.1-q1.4.

A liquid metal experimental loop for magnetohydrodynamic (MHD) pressure drop and compatibility studies has been built up in China recently. It is operating in two phases: phase I, using 22Na78K, the loop operates at Room Temperature (RT) for MHD experiments; phase II, liquid lithium will be employed and the loop operates at elevated temperatures for compatibility experiments. The gap of the electromagnet is 8 cm and the magnetic strength within it, where the MHD test section is installed, is 1.9 T. The maximum values of the Hartmann number M and interaction parameter N for MHD experiments are 7500 and 25 000, respectively. The minimum value of the pressure drop which can be reliably measured by the pressure transducer is 3000 Pa, and the maximum flow velocity in the present MHD test section is 0.9 m/s. The operation temperature for compatibility experiments is up to 520° C and the maximum flow velocity in the compatibility test section is not less than 1.7 m/s.

We have used several different photoluminescence techniques to study exciton localisation in In x Ga 1- x As/GaAs quantum wells. The experimental techniques involved temperature modulated photoluminescence, photoluminescence excitation and photoluminescence spectroscopy. The combination of these methods allowed us to determine the average exciton localisation energies in several single- and multi-quantum well samples. The localisation energies for the different samples varied between 0 and 3 meV. We also show evidence for the potential application of temperature modulated photoluminescence to resolve fine structure due to well width fluctuations and alloy disorder in multiple quantum wells.

In order to obtain good OFF-characteristics, we have proposed a novel method to depress the OFF-current by inserting a buffer layer at the n/i interface in a-Si TFTs. The results showed that the OFF-current can approach the magnitude of 10 −13 A when the thickness is about 50A, whereas the ON-current is the constant of magnitude of 10 −6 A. Theoretical analysis upon the “intrinsic”, “electron”, and “hole” electric field suggested the contribution of n/i buffer layer to the OFF-characteristics of a-Si TFTs.

Compared with optical-wave, millimeter-wave has the advantage of penetration through fog, smoke, clothing etc, which can detect weapons concealed underneath clothing. Unfortunately, the images obtained by millimeter-wave imaging systems have very low resolution. Thus image processing methods to improve image quality is necessary. In the paper, a new image algorithm combining Projection onto Convex Sets algorithm (POCS) and nonlinear extrapolation algorithm for improving millimeter-wave images is proposed and the experimental results show it is efficient.

A model of endochronic constitutive theory is applied to the analysis of stress-strain behavior of sintered high purity aluminum powder-based material (P/M) under uniaxial strain-controlled cyclic test conditions. Different strain amplitudes were used on specimens which during fabrication were subjected to cold isostatic pressure of 25 ksi. It was found that mean strain does not significantly affect the fatigue life. It was also discovered that Poisson's ratio at the peak tensile strain decreases gradually with the number of loading cycles, while it reaches a constant value at the peak compressive strain as the number of cycles increases. Results provide a comparison between theory and experiment for both hydrostatic and deviatoric stress-strain behavior for several cases of peak strains in the strain-controlled test. Reasonable agreement has been achieved. The changing trends of the peak volumetric strain, deviatoric stress, hydrostatic stress and Poisson's ratio versus loading cycles are also reported for each case.

GaAs/sub 1-x/N/sub x/ alloys with small N composition (x

Carrier recombination dynamics in AlInGaN alloy has been studied by photoluminescence (PL) and time-resolved photoluminescence (TRPL). The fast redshift of PL peak energy is observed and well fitted by a physical model considering the thermal activation and transfer processes. This result provides evidence for the exciton localization in the quantum dot (QD)-like potentials in our AlInGaN alloy. The TRPL signals are found to be described by a stretched exponential function of exp[(-t//spl tau/)/sup /spl beta//], indicating the presence of a significant disorder in the material. The disorder is attributed to a randomly distributed quantum dots or clusters caused by indium fluctuations. By studying the dependence of the dispersive exponent /spl beta/ on the temperature and emission energy, we suggest that the exciton hopping dominate the diffusion of carriers localized in the disordered quantum dots. Furthermore, the localized states are found to have 0D density of states up to 250 K, since the radiative lifetime remains almost unchanged with increasing temperature.

This paper is to preview the future of LSI business in China by reviewing the history, present market and the events happening in IC industry in China. With some statistics data from central government and practical investigation on site, the author believes that the international collaboration will become More and more important for LSI business in China for next century.

This paper presents a novel power network protection scheme during power swing blocking. The blocked protective relays will be released when the system restores to its normal operating conditions. The protection scheme is based on symmetrical components. EMTP simulation results show the proposed scheme in this paper are quite suitable for modern digital-based protective relays. Examples are shown for unbalanced fault cases.

This study proposes a new fault impedance estimation algorithm of phase-ground fault for ground distance relaying based on the negative-, zero- and comprehensive negative-zero-sequence current component. The principle is based on the assumption that fault path is purely resistive, and the phase angle of fault point voltage and fault path current is equal to construct the fault impedance estimating equations for ground distance relay, which can eliminate the effect of fault path resistance, load current and power swing. PSCAD software simulations show the accuracy of proposed algorithm.

This study presents a new fault impedance estimation algorithm for inter-phase faults for the purpose of phase distance relaying of extra high voltage (EHV) and ultra high voltage (UHV) transmission lines. The principle is based on the assumption that the fault arc path is predominantly resistive, and the phase angles of the unmeasured fault point voltage and fault arc path current are equal. This is used to construct the fault impedance estimation equation, which naturally prevents the effects of fault arc path resistance, load current, power swing and load encroachment. PSCAD (simulation software) simulation shows the validity of the proposed algorithm.

Magnetization measurements were performed on Cu-, Sr-doped and undoped La2CuO4+δ samples before and after electrochemical oxidation. Experimental results showed that different samples exhibited different behaviors at various phase separation stages. Possible explanation is presented.

Cu-doped and undoped La2CuO4+δ samples prepared under the same conditions have been investigated. It is distinctly shown that phase separation only exists in Cu-doped one, in which a stripe structure was observed at room temperature. This leads to a suggestion as that Cu doping may promote phase separation and the stripe structure is directly related to the phase separation.

Based on a new gap DOS model, the effect of the gap DOS in a-Si on the properties of the N a-Si/P c-Si heterojunction is studied. The peak value of acceptor-like deep states make electrostatic potential profile shift, and the low frequency C-V curve has a single minimum value. The multitunneling capture-emission model is used and a multi-tunneling recombination model is proposed to explain the forward J-V characteristics.

Both the extrinsic luminescence related to the impurities near the well center and that related to the impurities at the GaAs-GaAlAs interfaces have been observed from all our samples with well widths ranging from 78 to 145 A. This identification has been confirmed by the dependence of the extrinsic photoluminescence on the excitation intensities and temperature. Relatively strong interface-related luminescence is believed to be due to the presence of more trapped impurities at the interfaces.

This paper describes a closed-loop controlled arc welding power source using a microcomputer as controller. The system possesses two advantages: (1) possibility of obtaining arbitrary type of output characteristics without changing hardware; (2) excellent transient performance. A nonlinear control mode applied in the system by software is developed for the purpose. The actual system is of a complicated discrete-sampling type, but for ease of studying and improving the performance of the system, a simplified mathematical model has been set up through synthetical study of the practical test results and theoretical analysis.