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As further progress in the accurate and efficient computation of coupled partial differential equations (PDEs) becomes increasingly difficult, it is highly desired to develop new methods for such computation. In deviation from traditional approaches, this short communication paper explores a computational paradigm that couples numerical solutions of PDEs via machine-learning (ML) based methods. Particularly, it solves PDEs in subdomains as in a conventional method but develops and trains artificial neural networks (ANN) to couple the PDEs at their interfaces, leading to their solutions in the whole domains. The concepts and algorithms for the ML coupling are discussed via computation of coupled Poisson equations and coupled advection-diffusion equations. Unlike in a conventional method, Schwarz iteration may not be necessary for the ML coupling in computation of the latter. Numerical examples show that the coupling can generate solutions to these equations with acceptable accuracy. They also illustrate that it exhibits predictability; ML algorithms trained with a set of initial and boundary conditions still work in computation when the conditions are modified. Although preliminary, this exploratory study indicates that the ML paradigm is promising in terms of feasibility and performance and deserves further research.

The thermodynamic optimizations of the Nd-Sn and Sn-Tb binary systems were carried out by means of the Calculation of Phase Diagram (CALPHAD) method on the basis of the available experimental data including the thermodynamic properties and phase equilibria. The Gibbs free energies of the liquid, bcc, bct, dhcp and hcp phases were described by the substitutional solution model with the Redlich-Kister equation, while all of the intermetallic compounds (Nd5Sn3, Nd5Sn4, Nd11Sn10, NdSn, Nd3Sn5, NdSn2, Nd3Sn7, Nd2Sn5, NdSn3, Sn3Tb, βSn7Tb3, αSn7Tb3, Sn2Tb, Sn5Tb4, SnTb4, Sn10Tb11, Sn4Tb5 and Sn3Tb5) were described by the sublattice model. A set of self-consistent thermodynamic parameters of each phase in the Nd-Sn and Sn-Tb binary systems has been obtained, and the calculated results are in good agreement with the available experimental data.

Mesoporous thiol-functionalized SBA-15 was investigated as a microcolumn packed material for the on-line preconcentration of trace amounts of Pb(II) and Cd(II) in water samples before their flame AAS determination. The results indicated that the proposed method was tolerant to the coexistence ions, offered good linearity and the achievable enhancement factors were 34 for Pb(II) and 41 for Cd(II), and the detection limits (3σ) of 0.22 μg L−1 and 0.11 μg L−1 and the precision (RSD) for 11 replicate determination of 30 μg L−1 Pb(II) and 20 μg L−1Cd(II) were 0.4% and 0.3%, respectively.

Amino acids are the building blocks of proteins and serve as key molecular components upstream of the signaling pathways that regulate protein synthesis. The objective of this study was to systematically investigate the effect of essential AA ratios on milk protein synthesis in vitro and to elucidate some of the underlying mechanisms. Triplicate cultures of MAC-T cells and bovine mammary tissue explants (MTE) were incubated with the optimal AA ratio (OPAA; Lys:Met, 2.9:1; Thr:Phe, 1.05:1; Lys:Thr, 1.8:1; Lys:His, 2.38:1; and Lys:Val, 1.23:1) in the presence of rapamycin (control), OPAA, a Lys:Thr ratio of 2.1:1, a Lys:Thr ratio of 1.3:1, a Lys:His ratio of 3.05:1, or a Lys:Val ratio of 1.62:1 for 12 h; the other AA concentrations were equal to OPAA. In some experiments, the cells were cultured with OPAA with or without rapamycin (100 ng/mL) or with mammalian target of rapamycin (mTOR) small interference RNA, and the MTE were exposed to OPAA with rapamycin for β-casein expression. Among the treatments, the expression of β-casein was greatest in the MTE cultured with OPAA. In MAC-T cells, the OPAA upregulated the mRNA expression of SLC1A5 and SLC7A5 but downregulated the expression of IRS1, AKT3, EEF1A1, and EEF2 compared with the control. The OPAA had no effect on the mTOR phosphorylation status but increased the phosphorylation of S6K1 and RPS6. When the MTE were treated with rapamycin in the presence of OPAA, the expression of β-casein was markedly decreased. The phosphorylation of RPS6 and 4EBP1 also was reduced in MAC-T cells. A similar negative effect on the expression of RPS6KB1 and EIF4EBP1 was detected when the cells were cultured with either rapamycin or mTOR small interference RNA. The optimal AA ratio stimulated β-casein expression partly by enhancing the transport of AA into the cells, cross-talk with insulin signaling and a subsequent enhancement of mTOR signaling, or translation elongation in both MAC-T cells and bovine MTE.

Predicting 3-D flow in a pier scour hole and the associated bed shear stress τb is important for the safe and economical design of bridge piers. This paper combines layered, hydrostatic hydrodynamic computations with non-hydrostatic pressure corrections, exploring a new modelling approach for efficient and reliable predictions of 3-D flow velocity. The law of the wall method is used for estimating τb. Its suitability for incorporation into layered models for bedload transport and pier scour simulations is also discussed. The predicted flow shows realistic features: strong downward flow adjacent to the upstream nose of a circular pier, vortex motions in the vertical and horizontal direction, and meandering flow wakes. The velocity results compare well with available experimental data. In the approach region, τb is uniform. It attains a local maximum immediately before flow enters the scour hole and then drops non-linearly in the scour-hole region toward the pier. In the wake region, τb has very low values. The τb predictions are consistent with the experimental data. In multi-layer models, when applying the law of wall method, one should use near-bed velocities as opposed to bottom-layer velocities to obtain more reliable τb estimates and avoid noisy results, which can cause a numerical instability problem in bedload transport simulations.

AlGaN/GaN High Electron Mobility Transistors (HEMTs) show great promise for applications such as military radar and satellite-based communications systems. Circular devices, with smaller junction areas and higher effective gate width/gate length, are better suited for high power, high frequency application. Since the circular devices have been shown to improve the device performance, the effect of radiation on their reliability is an important topic. There are many studies characterizing the performance under proton, neutron, and electron irradiations for rectangular AlGaN/GaN HEMTs. However, the studies for circular-shaped devices are limited. In this work, we report the effect of proton irradiation on circular-based AlGaN/GaN HEMT. DC performance, breakdown voltage, and gate lag measurement were done to characterize the devices. AlGaN/GaN HEMT heterostructures were grown on c-plane sapphire by molecular beam epitaxy (MBE). The layer structure included a thin AlGaN nucleation layer followed with a 2 µm thick undoped GaN buffer topped by a 25 nm thick unintentionally doped Al0.28GaN layer. Mesa isolation was achieved by using an inductively coupled plasma system with Ar/Cl2-based discharges. The Ohmic contacts were formed by lifting-off e-beam evaporated Ti (200 Å)/Al (1000 Å)/Ni (400 Å)/Au (800 Å). Gates with the dimension of 1.5 µm × 314 µm were defined by lift-off of e-beam deposited Ni/Au metallization. The contacts were annealed at 850°C for 45 s under a flowing N2 ambient in Heatpulse 610T system. The final step was deposition of e-beam evaporated Ti/Au (300 Å/1200 Å) interconnection contacts. Devices were exposed to protons with 5 MeV and different doses of 2×1014 proton/cm2. The device DC performance was characterized using an HP 4156 parameter analyzer. The breakdown voltage was conducted with a Tektronix 370A curve tracer. FLOODS TCAD finite-element solver was used to simulate the electrical field around the gate edge to confirm the experimental result. As shown in Figure 1, drain current IVs, IDSS, decreased from 454 to 398 mA/mm after irradiation with a proton dose of 2×1014 cm-2. Moreover, resistance between source and drain increased and extrinsic transconductance decreased after irradiation. However, the drain breakdown voltage increased from 150 to 230 V. The improvement of the breakdown voltage was due to the reduction of electric field at the edge of the gate, caused by the defects generated by proton irradiation at AlGaN/GaN interface, which was confirmed with simulation, as shown in Figure 2. Both gate and drain pulse measurements were also performed to verify the introductions of implanted defects into the HMET structure, which will be discussed in the talk.

AlGaN/GaN High Electron Mobility Transistors (HEMTs) show great promise for applications such as military radar and satellite-based communications systems. Due to the applications in extreme radiation environments, it is important to characterize the performance after irradiation. There are many studies characterizing the performance under proton, neutron, and electron irradiations for AlGaN/GaN HEMTs. However, the studies for gamma irradiation are limited. Detailed studies are needed to characterize the performance of HEMTs after gamma irradiation. In this study, we characterize the DC performance after irradiation and extract the change of Vth, carrier concentration, mobility and resistance. Also, we use gate lag measurement and drain pulse measurement to characterize the defects generated after irradiation. AlGaN/GaN HEMT heterostructures were grown on c-plane sapphire by molecular beam epitaxy (MBE). The layer structure included a thin AlGaN nucleation layer followed with a 2 µm thick undoped GaN buffer topped by a 25 nm thick unintentionally doped Al0.28GaN layer. Mesa isolation was achieved by using an inductively coupled plasma system with Ar/Cl2-based discharges. The Ohmic contacts were formed by lifting-off e-beam evaporated Ti (200 Å)/Al (1000 Å)/Ni (400 Å)/Au (800 Å). 1-µm gates were defined by lift-off of e-beam deposited Ni/Au metallization. The contacts were annealed at 850°C for 45 s under a flowing nitrogen ambient in Heatpulse 610T system. The final step was deposition of e-beam evaporated Ti/Au (300 Å/1200 Å) interconnection contacts. Devices were exposed to 60Co γ-rays with different doses of 50, 300, 450, or 700 Gy. Irradiations were performed at temperatures As shown in Figure 1, IDSS after irradiation was increased from 293mA/mm to 339mA/mm after irradiation. The increase of IDSSincreases with dose before 450 Gy and saturates after that. From the transmission line method (TLM), there is no significant change in sheet resistance after irradiation. However, the device total resistance, the reciprocal of the current current voltage (I-V) curve slope in the lower drain bias voltage, decreased significantly, as illustrated in Figure 1. The total resistance consisted of the channel resistance and the source resistance as well as the drain resistance. Both The source resistance and the drain resistance determined from the transmission line method change less than 2%. While the channel resistance decreased around 5% as shown in Figure 2. The reduction of the channel resistance was mainly due to the increase of mobility and carrier concentration, which were extracted from the drain IV curve in the low field region and TLM data. Kurakin et. al 1 found a similar effect that mobility increases after irradiation due to the relaxation of strain. Berthet et. al 2 attributed the drain current increases after irradiation to the introduction of donor type defects through the implantation. From gate lag measurement, the dispersion of the drain current measured at 100kHz increased as a function of the gamma irradiation dose indicating additional traps generated between gate and drain electrode and enhanced the current collapse. There was no obvious current dispersion during the drain pulse measurement showing the defects created by the gamma irradiation were less than the original defects through the material growth in the buffer layer. In conclusion, low dose gamma irradiation improved the AlGaN/GaN HEMT dc performance. The effect may be due to the strain relaxation effect and due to the donor type defects generated during the gamma irradiation.

AlGaN/GaN HEMTs have high radiation tolerance compared to Si and GaAs transistors. They are also well suited for high power and high frequency applications and thus may be advantageous for satellite-based communication systems. Radiation studies have shown the following DC performance changes: threshold voltage shift (positive), transconductance reduction, and saturation drain current reduction. The basic phenomenon leading to degradation of DC performance is the creation of point defects such as Ga or N vacancies and subsequent ionization of the traps. We have successfully modeled DC degradation due to radiation effects with FLOODS, a TCAD finite-element simulator. The simulation of trapped negative charges in the GaN buffer layer explained experimental results. As Figure 1 shows, there is a positive shift in threshold voltage that increases with the concentration of negatively charged traps. Another phenomenon that occurs in irradiated AlGaN/GaN HEMTs is an increase in breakdown voltage and apparent enhanced reliability. The fundamental mechanism for this phenomenon is unclear. We have shown that the negatively-trapped charges in the GaN buffer are not the primary mechanism and that charging at the AlGaN surface is a plausible reason. This work explores the fundamental mechanisms for charging of the AlGaN surface. We look at the transient effects of electron and hole creation during radiation and subsequent interfacial trapping mechanisms. Figure 1. Positive shift in threshold voltage with respect to trap concentration in GaN buffer layer.

The impedance of the inertance tubes which include the mass flows, pressure amplitudes and phase shifts between them at the inlet of the inertance tubes were measured by correcting the mass flows at the surface of the compressor piston. The experimental results are compared with the theoretical values based on simplified turbulent-flow thermoacoustic model. The wide range of impedance measurements with different inertance tube geometries and operating parameters enable us to summarize the general rules of their effects on impedance respectively, also the differences between the experiments and calculations can be used to modify the theoretical model.

Diamond-like carbon (DLC) films are potential candidates for artificial joint surface modification in biomedical applications, and the influence of the structural features of DLC surfaces on cell functions has attracted attention in recent decades. Here, the biocompatibility of DLC films with different structures was investigated using macrophages, osteoblasts and fibroblasts. The results showed that DLC films with a low ratio of sp 2 /sp 3 , which tend to have a structure similar to that of diamond, led to less inflammatory, excellent osteogenic and fibroblastic reactions, with higher cell viability, better morphology, lower release of TNF-α (tumor necrosis factor-α) and IL-6 (interleukin-6), and higher release of IL-10 (interleukin-10). The results also demonstrated that the high-density diamond structure (low ratio of sp 2 /sp 3 ) of DLC films is beneficial for cell adhesion and growth because of better protein adsorption without electrostatic repulsion. These findings provide valuable insights into the mechanisms underlying inhibition of an inflammatory response and the promotion of osteoblastogenesis and fibrous propagation, and effectively build a system for evaluating the biocompatibility of DLC films.

Phase constitutions, microstructures and room-temperature tensile behavior of Mo-doped Co–9Al–(9 − x)W–2Ta–0.02B–xMo alloys (where x = 0, 2, 4, 6, 9 at.%) are investigated. After aging treatment, the microstructure is composed of γ matrix and nanoscale cuboidal γ′ precipitates, with Mo contents of 0–4 at.%; however, a needle-like cellular κ-Co3Mo phase is additionally found in the γ′/γ microstructure, with Mo contents of 6–9 at.%. The pure γ′/γ microstructure exhibits better room-temperature tensile strength and elongation than the γ/γ′/κ microstructure.

A two-layer analytical function for the vertical distribution of water velocities in ice-covered rivers is obtained from a multi-parameter regression analysis. This analysis uses velocity profiles measured from Canadian rivers covered with ice during the winter. The function contains a coefficient and two exponents. The exponents are associated with the frictional effects of the ice and riverbed, respectively, whereas the coefficient is related to the per-unit-width discharge. The ranges of values for the three parameters have been determined. It is shown that the two-layer function is satisfactory for describing the velocity distribution. Velocity profiles reconstructed using the parameter values are acceptable. Since it is difficult and expensive to obtain field measurements of water velocities from ice-covered rivers, the analytical function is a good alternative for such purposes as estimating winter discharges in such rivers. Also, the function can easily be incorporated into numerical models for sim...

In the future, Evacuated Tube Transportation (ETT) would be built and faster than jets. ETT tube with diameter 2∼4m and length over 1000 km will be the largest scale vacuum equipment on earth. This paper listed some main vacuum technical issues to be solved in ETT as follow. How to build ultra-large-scale vacuum chamber like ETT tube with low cost and high reliability? How to pump gas out off the ETT tube in short time? How to release heat or reduce temperature in the vacuum tube? Hot to avoid vacuum electricity discharge? How to manufacture vehicles with airproof shells and equip the life support system? How to detect leakage and find leakage position efficiently and fast as possible? Some relative solutions and suggestions are put up.

A diode end-pumped continuous wave and acoustic-optical Q-switched YVO4/Nd:Y0.9La0.1VO4 crystal lasers are first demonstrated at 1064 nm with a compact planar-planar cavity. The continuous and acoustic-optical Q-switched output characteristics have been investigated with different output couplers. The maximum continuous wave power of 12.26 W is obtained at the incident pump power of 21.7 W, corresponding to optical to optical conversion efficiency of 56.5%. For Q-switching operation, at the incident pump power of 21.7 W, the shortest pulse is 7 ns at 1 kHz and 80% transmission, the maximum average output power is 12.07 W at 100 kHz and 30% transmission, and the highest peak power is 1.076 MW at the 1 kHz repetition rates and 50% output transmission.

In this paper, the application of the finite-difference time-domain (FDTD) algorithm combined with the short-open calibration SOC technique to three-dimensional microstrip discontinuity is presented. This SOC technique is directly accommodated in the FDTD algorithm. It is used to remove the unwanted parasitic errors brought by the approximation of the impressed voltage sources and the feed lines. The FDTD is formulated in such a way that the port voltages and currents are explicitly represented through relevant network matrices. This new method is also used to analyze finite periodic structures. The scattering parameters of the whole periodic structure can be approximately obtained through analyzing only one cell of it. The results for microstrip discontinuities and finite periodic structures are compared with the conventional FDTD method.

High-density AlN ceramics were fabricated without additives under high pressure (3.15–4.95 GPa) at a low temperature (1300 °C), which is 300–500 °C lower than that for conventional liquid-phase sintering, in a cubic anvil high-pressure and high-temperature apparatus. The relative density of pure AlN ceramics is 94.92% at 1300 °C and 4.75 GPa for 50 min. Grain boundary phases were found in the neck area between AlN grains, indicating that grain growth by solution–precipitation must play some role.

We recently indicated that the vascular endothelial growth factor (VEGF) protects neurons against hypoxic death via enhancement of tyrosine phosphorylation of Kv1.2, an isoform of the delayed-rectifier potassium channels through activation of the phosphatidylinositol 3-kinase (PI3-K) signaling pathway. The present study investigated whether VEGF could attenuate ischemia-induced increase of the potassium currents in the hippocampal pyramidal neurons of rats after ischemic injury. Adult male Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion (MCAO) to induce brain ischemia. The whole-cell patch-clamp technique was used to record the potassium currents of hippocampal neurons in brain slices from the ischemically injured brains of the rats 24h after MCAO. We detected that transient MCAO caused a significant increase of voltage-gated potassium currents (Kv) and outward delayed-rectifier potassium currents (IK), but not outward transient potassium currents (IA), in the ipsilateral hippocampus compared with the sham. Moreover, we found that VEGF could acutely, reversibly and voltage-dependently inhibit the ischemia-induced IK increase. This inhibitory effect of VEGF could be completely abolished by wortmannin, an inhibitor of PI3-K. Our data indicate that VEGF attenuates the ischemia-induced increase of IK via activation of the PI3-K signaling pathway.

An outdoor solid-state amplifier chain consists of two separate units, amplifier and power supply, and this amplifier is core of the chain. Tough environment, high heat consumption and complicated EMC requirement are the main difficulties in the structure design. Cold plate, sealed and shielded package are used to solve all these problems, which are proved to be effective by both calculation and tests.

AlGaN/GaN high electron mobility transistors are gaining commercial acceptance for use in high power and high frequency applications, but the degradation mechanisms that drive failure in the devices are not completely understood. Since some of these mechanisms are current or field driven, reliability studies must go beyond the typical Arrhenius accelerated life tests. In this chapter we summarize recent work on electric field or current driven degradation in devices with different gate metallization, device dimensions, electric field mitigation techniques (such as source field plates), and the effect of defects either already present or introduced by exposure to ionizing radiation. Some of the mechanisms now established include gate or Ohmic metal reaction, hot carrier trap generation, stress-induced crack generation and oxidation reactions involving the AlGaN layer.

We present a new block adaptive algorithm as a variant of the Toeplitz-preconditioned block conjugate gradient (TBCG) algorithm. The proposed algorithm is formulated by combining TBCG algorithm with a data-reusing scheme that is realized by processing blocks of data in an overlapping manner, as in the optimum block adaptive shifting (OBAS) algorithm. Simulation results show that the proposed algorithm is superior to the block conjugate gradient shifting (BCGS), TBCG and Toeplitz-OBAS (TOBAS) algorithms in both convergence rate and tracking property of input signal conditioning.

Aims: To develop an immunocapture universal primer PCR (iUPPCR) combined with denaturing gradient gel electrophoresis (DGGE) and evaluate it as a method permitting rapid detection of Shigella species and their serotypes. Methods and Results: This method amplifying the conserved regions of bacterial 16S rRNA genes of different species or serotypes of Shigella dysentery bacilli captured and enriched by polyvalent antibodies can detect and distinguish causative pathogens rapidly. Four serotypes from three Shigella species including Shigella dysenteriae serotype 1, Shigella boydii serotype 1, Shigella flexneri serotypes 1a and 3a were examined. Conclusion: Our approach could be adopted for not only axenic bacterial population but also mixed communities and achieve rapid detection of various bacteria from the same genus or species in one sample. Significance and Impact of the Study: The iUPPCR–DGGE method was shown to be more convenient than serotype-specific-antibody-based method of iUPPCR for Shigella species detection and it could be also applied to the quick detection for other kinds of pathogens with many serotypes.

The reaction pathway and kinetics of a-CuInSe2 formation from a glass/In2Se3/CuSe polycrystalline bilayer precursor film were investigated using time-resolved, in situ high-temperature X-ray diffraction. Bilayer glass/In2Se3/CuSe precursor films were deposited on thin glass substrates in a migration enhanced molecular beam epitaxial deposition system. These films were then temperature ramp annealed or isothermally soaked while monitoring the phase evolution. The initial In2Se3 and CuSe reactant phases were directly transformed to a-CuInSe2 without any detectable intermediate phase. Kinetic parameters were estimated using the Avrami and parabolic diffusion controlled reaction models. The parabolic reaction model fitted the experimental data better than the Avrami model over the entire temperature range (230‐290 8C) of the set of isothermal experiments, with an estimated activation energy of 162 (G5) kJ/mol. q 2005 Elsevier Ltd. All rights reserved.

The effect of a secondary copper selenide phase that appears during epitaxial growth of CuInSe2 (CIS) films on (1 0 0) GaAs substrates was investigated. CIS films with different copper to indium molar ratios were deposited on (1 0 0) GaAs substrates at 3601C by migration-enhanced epitaxy. Films grown under In-rich conditions were polycrystalline, whereas films grown with a Cu-rich composition were epitaxial, as evidenced by pole figure analysis, even when the copper composition was only slightly higher than the 1:1 Cu:In molar ratio. The epitaxial film growth followed a Stranski–Krastanov mode and contained both matrixand island regions. Grazing incidence XRD revealed a small amount of CIS with the Cu–Au-like structure near the surface of the island regions. A binary Cu–Se secondary phase aggregated near the surface in the island regions of the film, as determined by electron probe microanalysis (EPMA) before and after etching in 10% KCN. It is proposed that a Cu–Se phase present during the growth of Cu-rich CIS films enhances the mobility of adatoms on the substrate surface, allowing the film to grow epitaxially to a critical thickness. After that critical thickness is attained, the Cu–Se phase segregates at dislocation sites to nucleate the island regions. TEM-EDX scans of cross-sections also suggested a small amount of the Cu–Se secondary phase segregates on the film surface.

The Ag-sheathed (Bi,Pb)-2223 multifilamentary tapes with different filament distribution and resistive barriers have been fabricated by powder-in-tube (PIT) method. A rectangular deformation process by using a four-roller machine was applied to fabricate the multifilamentary wires. Bi-2201 and Ag-Cu alloy sheets were introduced into the tape as resistive layers to decrease the coupling between filaments. The transport AC losses were measured on these tapes at 77 K with power frequency between 50 Hz and 1000 Hz The results indicated that the behaviors of transport AC losses are influenced by both filament distribution and resistive barrier. The introduction of resistive barriers to divide the tape into several thin strips is effective to reduce the transport AC losses. For the prepared 39 filament tapes, when the resistive layers are configured parallel to the tape surface, the transport AC losses at 50 Hz measured at 77 K are greatly reduced compared to those of 37 filament tape without barriers fabricated by a conventional PIT method.

A genetic-algorithm (GA)-based fuzzy proportional-plus-integral-proportional-plus-derivative (PI/PD) controller is proposed for an automotive active suspension system (AASS). The fuzzy PI- and PD-type controllers are combined to cope with the different road conditions. By using the merit of GAs, the optimal decision-making rules for both types of controllers are constructed. The real-time simulation results demonstrate that the fusion of GAs and fuzzy controller for an AASS can provide passengers much more ride comfort.

We have studied two Si-doped p-type quantum well infrared photodetectors (QWIPs) using AlGaAs GaAs and AlGaAs InGaAs grown on (3 1 1)A GaAs. The Si-doped AlGaAs GaAs p-QWIP exhibits a symmetrical dark I–V characteristic at all the measured temperatures from 40 to 120 K. The strained p-type AlGaAs InGaAs QWIP exhibits a slightly asymmetrical dark I–V characteristic, but is markedly less asymmetrical than that doped with beryllium. The slight asymmetry in dark I–V characteristic and the large blue-shift in responsivity spectra may be due to the thickness modulation observed from TEM and the red-shift of PL peak energy, where PL peak energies from (3 1 1)A AlGaAs InGaAs multiple quantum wells are red-shifts of 7 and 22 meV to the side-by-side grown (1 0 0).

The fabrication of long silver-sheathed oxide superconducting tapes by the powder-in-tube technique tends to lead to non-uniformity in the core thickness during mechanical deformation and densification. This non-uniformity restricts current flow and reduces the critical current density. Using a simple model, the detrimental effects of various types of core thickness non-uniformity on the critical current density are investigated. Also the degree to which such non-uniformity needs to be controlled, based on the temperature of application of these conductors, is qualitatively inferred.

A GaAs Schottky-barrier with high quantum efficiency-bandwidth product has been developed by using a GaAs/Al/sub 0.25/Ga/sub 0.75/As multilayer reflector. The multilayer reflector structure wa designed by using the scattering matrix method. By growing four pairs of Al/sub 0.25/Ga/sub 0.75/As (825 AA)/GaAs (330 AA) multilayer reflectors between the undoped GaAs active layer and the buffer layer, a responsivity of 0.6 A/W at lambda =0.84 mu m was obtained for this device. This represents a 30% improvement over the device without a multilayer reflector. The response speed of the photodiode was measured by the impulse response method, and the results yielded a rise time of 38.45 ps, corresponding to a bandwidth of 9 GHz for this detector. >

For pt.I see ibid., vol.39, no.7, p.1740-46 (1992). A bias-scan deep-level transient spectroscopy (DLTS) method for measuring interface states in a semiconductor-insulator-semiconductor (SIS) capacitor structure is described. Introducing a charge coupling factor between the film/oxide (F/O) and the substrate/oxide (S/O) interfaces made it possible to extract interface trap densities from the measured transient signals. This technique was used to determine the interface trap densities and capture cross sections at both the F/O and S/O interfaces of SIMOX (separation by implantation of oxygen) based SIS capacitors. >