Enhanced carrier confinement in AlInGaN-InGaN quantum wells in near ultraviolet light-emitting diodes

To increase carrier confinement, the GaN barrier layer was substituted with an AlInGaN quaternary barrier layer which was lattice-matched to GaN in the GaN-InGaN multiple quantum wells (MQWs). Photoluminescence (PL) and high-resolution X-ray diffraction measurements showed that the AlInGaN barrier layer has a higher bandgap energy than the originally used GaN barrier layer. The PL intensity of the five periods of AlInGaN-InGaN MQWs was increased by three times compared to that of InGaN-GaN MQWs. The electroluminescence (EL) emission peak of AlInGaN-InGaN MQWs ultraviolet light-emitting diode (UV LED) was blue-shifted, compared to a GaN-InGaN MQWs UV LED and the integrated EL intensity of the AlInGaN-InGaN MQWs UV LED increased linearly up to 100 mA. These results indicated that the AlInGaN-InGaN MQWs UV LED has a stronger carrier confinement than a GaN-InGaN MQWs UV LED due to the larger barrier height of the AlInGaN barrier layer compared to a GaN barrier layer.     

High-performance 94-GHz single balanced mixer using 70-nm MHEMTs and surface micromachined technology

We reported 94-GHz, low conversion loss, and high isolation single balanced active gate mixer based on 70-nm gate length InGaAs/InAlAs metamorphic high-electron mobility transistors (MHEMTs). This mixer showed that the conversion loss and isolation characteristics were 2.5/spl sim/3.5 dB and under -29 dB in the range of 92.95/spl sim/94.5 GHz, respectively. The low conversion loss of the mixer is mainly attributed to the high-performance of the MHEMTs exhibiting a maximum drain current density of 607 mA/mm, an extrinsic transconductance of 1015 mS/mm, a current gain cutoff frequency (f/sub t/) of 330 GHz, and a maximum oscillation frequency (f/sub max/) of 425 GHz. High isolation characteristics are due to hybrid ring coupler which adopted dielectric-supported air-gapped microstrip line structure using surface micromachined technology. To our knowledge, these results are the best performance demonstrated from 94 GHz single balanced mixer utilizing GaAs-based HEMTs in terms of conversion loss as well as isolation characteristics.     

Hybrid accident simulation methodology using artificial neural networks for nuclear power plants

A hybrid accident simulation methodology for nuclear power plants is proposed to enhance the capabilities of compact simulator by introducing artificial neural networks. Two neural networks are trained with the target values obtained from the analyses of detailed computer codes and trained results are combined with the compact simulator to perform the following roles: (i) compensation for inaccuracies of a compact simulator occurring from simplified governing equation and reduced number of physical control volumes, and (ii) prediction of the critical parameter usually calculated from the sophisticated computer code: the autoassociative neural network improves the computational results of the compact simulator up to the accuracy level of detailed best estimate computer code, while the backpropagation neural network predicts the minimum departure from nucleate boiling ratio (DNBR). Simulations are carried out to verify the applicability of the proposed methodology for the loss of flow accidents and the results show that the neural networks can be used as a complementary tool to improve the results of a compact simulator.     

Disturbance attenuation for constrained discrete-time systems via receding horizon controls

In this note, we propose new receding horizon H/sub /spl infin// control (RHHC) schemes for linear input-constrained discrete time-invariant systems with disturbances. The proposed control schemes are based on the dynamic game problem of a finite-horizon cost function with a fixed finite terminal weighting matrix and a one-horizon cost function with time-varying finite terminal weighting matrices, respectively. We show that the resulting RHHCs guarantee closed-loop stability in the absence of disturbances and H/sub /spl infin// norm bound for 2-norm bounded disturbances. We also show that the proposed schemes can easily be implemented via linear matrix inequality optimization. We illustrate the effectiveness of the proposed schemes through simulations.     

Design of receding horizon controls for constrained time-varying systems

In this note, we propose a generalized stabilizing receding horizon control scheme for input/state constrained linear discrete time-varying systems that improves feasibility and on-line computation on the constrained finite-horizon optimization problem, compared with existing schemes. The control scheme is based on a time-varying horizon cost function with time-varying terminal weighting matrices, which can easily be implemented via linear matrix inequality technique. We discuss modifications of the proposed scheme that improve feasibility or on-line computation time. Through simulation examples, we illustrate the results of these schemes.     

In Vitro hydrodynamic evaluation of prosthetic polymer heart valves in steady flow

Hydrodynamic comparison of two polymer valves with two mechanical valves is presented. The valves were perfused in a steady flow system, and comparisons between the valves were made on the transvalvular pressure distribution and drop, opening area, and leakage volume. Particular emphasis was placed on a slit-type bileaflet polymer valve which was newly designed and fabricated in our research group. The results showed that the functional characteristics of a slit-type bileaflet polymer valve compared favorably with that of mechanical valves. This valve may be a viable and inexpensive alternative, especially for short-term use in TAH or VAD systems.     

A study on the improvement of the cam phase control performance of an electric continuous variable valve timing system using a cycloid reducer and BLDC motor

This paper discusses the control performance improvement for an electric-continuous variable valve timing (E-CVVT) system using a brushless direct current (BLDC) motor and cycloid reducer. Each component of the E-CVVT system was implemented with mathematical analysis, and the response performance of the E-CVVT system was determined based on the mathematical model of the cam shaft motion, cam profile, cycloid reducer, BLDC motor, and controller. To control the intake valve timing of the engine, a cycloid speed reducer with a high reduction ratio capable of amplifying the output torque of a small BLDC motor was implemented. The change in valve speed due to the rotation of the cam shaft was represented by the curves described by the vertical movement of the valve using the cam profile. A control performance test apparatus was constructed and the torque of the intake cam shaft was measured and applied to the analysis so that the phase of the cam shaft could be changed using the E-CVVT system. To analyze the operating characteristics of the E-CVVT system, the BLDC motors were modeled using Simulink. The E-CVVT system controls the phase angle of the intake cam shaft. When the E-CVVT system sets the target phase angle, the motor controller generates the optimal motor speed command. The intake cam phase response speed depends on the setting of each PID parameter that changes the phase of the cam shaft. Through analysis and vehicle-based experiments, we confirmed the improvement of the E-CVVT system response performance according to the change of the PID parameter.

     

The effect of steaming on the free amino acid contents and antioxidant activity of Panax ginseng

This study was carried out to investigate changes in the free amino acid contents and antioxidant activity of Panax ginseng induced by steaming at different temperatures. For this purpose, white ginseng (WG), red ginseng (RG, ginseng steamed at 100 °C) and ginseng steamed at 120 °C (SG) were prepared using an autoclave. Most free amino acids were decreased significantly by steam treatment, with the greatest reduction observed in SG. Total content of free amino acids, 17.9 mg/g in WG was reduced to 12.2 mg/g in RG and 2.79 mg/g in SG. As for Arg which is the most predominant amino acid in ginseng, the content, 10.4 mg/g in WG, decreased significantly to 1.38 mg/g in SG. In particular, β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), a well-known neurotoxin, was reduced by 92.9% in SG. In contrast, the level of Maillard reaction products (MRPs) increased with steam treatment, which indicates that the reduction of most amino acids is attributed to the extent of the Maillard reaction. Based on MRPs being useful antioxidants, we assayed the scavenging activity against free radicals produced by 2,2′-azobis-(2-amidinopropane) dihydrochloride (AAPH). The radical scavenging activity of a ginseng extract increased with steam treatment, with the most potent activity in SG. Further, MRPs-rich fraction in SG showed powerful antioxidant activity, which indicates MRPs are major contributors to antioxidant activity enhanced by steam treatment.     

An integral equation model for critical heat flux at subcooled and low quality flow boiling

A new theoretical model of critical heat flux (CHF) is developed for the flow boiling condition from bubble-detached to low quality range. The CHF condition is postulated to occur when the superheated liquid layer on the heated wall, which is formed under the bubbly layer from the point of the onset of significant void generation, is depleted due to the evaporation along the heated length. The model shows a very promising agreement with the uniformly heated round tube data for both water and refrigerants by simply applying well-known constitutive relationships without any tuning constant for the CHF data. The significance of the proposed model in unifying the existing models is also discussed.     

Enhancement of total phenolic and isoflavone-aglycone contents and antioxidant activities during Cheonggukjang fermentation of brown soybeans by the potential probiotic Bacillus subtilis CSY191

Changes in β-glycosidase activity, total phenolic and isoflavone contents, and antioxidant activities during the fermentation of brown soybeans (Galmi) fermented food cheonggukjang by the potential probiotic Bacillus subtilis CSY191 were investigated. The total phenolic and isoflavone-glycoside and -aglycone contents as well as ABTS radical scavenging activity and FRAP assays of extracts increased, but malonylglycoside content decreased after a steaming process. It was found that fermentation enhanced the total phenolic and isoflavone-aglycone and -malonylglycoside contents, corresponding to antioxidant activities increased, but isoflavone-glycoside content decreased. The highest levels of daidzein, glycitein, and gensitein were present at concentrations of 156.5 μg/g, 10.2 μg/g, and 2.5 μg/g after 48 h of fermentation. In addition, ABTS radical scavenging activity and FRAP assay increased significantly during fermentation. We suggest that the high antioxidant activity of cheonggukjang of brown soybeans might be related to the markedly higher levels of total phenolic content and isoflavone-aglycones achieved during fermentation.