Novel zero-voltage and zero-current-switching full bridge PWMconverter using transformer auxiliary winding

A novel zero voltage and zero current switching (ZVZCS) full bridge (FB) pulse width modulation (PWM) converter is proposed to improve the demerits of the previously presented ZVZCS-FB-PWM converters, such as use of lossy components or additional active switches. A simple auxiliary circuit which includes neither lossy components nor active switches provides ZVZCS conditions to primary switches, ZVS for leading-leg switches and ZCS for lagging-leg switches. Many advantages including simple circuit topology, high efficiency, and low cost make the new converter attractive for high power (>2 kW) applications. The operation, analysis, features and design considerations are illustrated and verified on a 2.5 kW, 100 kHz insulated gate bipolar transistor (IGBT) based experimental circuit     

Numerical analysis of SOI LDMOS using a recessed source and a trench drain

A new SOI LDMOS using a recessed source and a trench drain was proposed to improve the on-characteristics at a given breakdown voltage. On-resistance and breakdown voltages of the proposed LDMOS are investigated by the two-dimensional simulator, MEDICI. The simulation results show that the on-resistance of the proposed and the conventional LDMOS are 76.3 and 129.5 mΩ mm², respectively. The on-resistance of the proposed LDMOS decreases by 41% compared to that of the conventional LDMOS at the same breakdown voltage of 36.5 V.     

Room temperature far infrared (8~10 μm) photodetectors usingself-assembled InAs quantum dots with high detectivity

Room temperature operation of far-infrared detectors made of self-assembled quantum dots embedded in the channel region of modulation-doped heterostructures is demonstrated. At room temperature, the detector shows a low dark current ranging in the nano-amperes at a bias voltage of 10 V. After the optimization of the separation between the quantum dot region and the 2DEG, a peak responsivity of 5.3 A/W is obtained at 9.0 μm. The high detectivities of 6×10⁸ and 5×10¹⁰ cmHz^1/2/W are obtained at room temperature and 80 K, respectively     

Vapor–Liquid Equilibria for the 1,1,1-Trifluoroethane (HFC-143a)+1,1,1,2-Tetrafluoroethane (HFC-134a) System

A vapor–liquid equilibrium apparatus has been developed and used to obtain data for the binary HFC-143a+HFC-134a system. Fifty-four equilibrium data are obtained for the HFC-143a+HFC-134a system over the temperature range from 263.15 to 313.15 K at 10 K intervals. The experimental data were correlated with the Carnahan–Starling–De Santis (CSD) and Peng–Robinson (PR) equations of state. Based upon the present data, the binary interaction parameters for the CSD and PR equations of state were calculated for six isotherms for the HFC-143a+HFC-134a system. The binary interaction parameters for both equations of state were fitted by a linear equation as a function of temperature. The present data were in good agreement with the calculated results from the CSD equation of state, and the deviations were less than 1.0% with the exception of two points.     

Stress‐life prediction of 25°C polypropylene materials based on calibration of Zhurkov fatigue life model

In this study, to evaluate the chemical and mechanical properties of polypropylene (PP), activation‐energy and tensile tests were performed at room temperature (25°C) on pure PP and PP reinforced with glass fibre (GF). To improve the prediction accuracy of the fatigue life, three models based on the calibration of the Zhurkov model were proposed: a regression model, modified strain‐rate model and lethargy coefficient‐based model. Based on the experimental data analysis and statistical assessment results, we proposed a modified strain‐rate model that satisfies the dependency of the physical parameters and is congruent with the predicted fatigue life data. The experimental data and modified strain‐rate model were compared with the direct cyclic analysis results. The tendency of the frequency factor as a correction parameter in the modified strain‐rate model corresponded to the experimental activation energy and the increasing GF content.     

Determination of biogenic amines in <Emphasis Type="Italic">Cheonggukjang</Emphasis> using ultra high pressure liquid chromatography coupled with mass spectrometry

A rapid and reliable method for the simultaneous determination of 12 biogenic amines (BAs; agmatine, phenylethylamine, tyramine, putrescine, cadaverine, histamine, serotonin, tryptamine, spermidine, noreinephrine, dopamine, and spermine) in cheonggukjang was optimized and validated using ultra high pressure liquid chromatography-electrospray tandem mass spectrometry (UHPLC-ESI-MS/MS). The BAs were dansylated and separated on a C8 column under LC gradient of 7 min duration, and detected by MS/MS with the multiple reaction monitoring mode (MRM). This method exhibited excellent linearity for all of the analytes with correlation determination (R²) higher than 0.98. The limits of detection (LODs) were 10.8–39.6 μg/kg. The precision results were expressed as relative standard deviation (RSD), ranged from 0.3 to 14.3% for intra-day and from 0.9 to 15.4% for the interday. The proposed method will help to ensure for quality control by monitoring of BAs in cheonggukjang.     

Structure and disorder in MgSiO3 glasses above megabar pressures via nuclear magnetic resonance: DFT calculations

The structural modifications in oxide glasses under extreme compression may account for the pressure-induced increase in their mechanical toughness and rigidity, rendering potential for technological applications of the compressed glasses. High-resolution solid-state nuclear magnetic resonance has provided a structural information regarding glasses by identifying how nuclear spins behave and interact with nearby elements. However, knowledge of nuclear spins resonance in oxide glasses under extreme pressure above 1 million atmospheres has not been available, making the origins of glass densification illusive. In this article, ab initio calculations of prototypical magnesium silicate glasses quantify how structural changes in glasses affect the nature of nuclear spin interactions at high pressure beyond megabars. The calculated results establish novel correlations between pressure-induced evolution of atomic structures, such as oxygen and cation coordination numbers, bond angle and lengths, and structurally relevant nuclear magnetic resonance parameters for Mg, Si, and O in compressed oxide glasses above megabar pressures. The established correlations highlight that the nuclear spins in glasses can serve as a new indicator to the extreme densification paths. Pressure-induced dispersion in nuclear spin parameters also reveals an overall increase in the topological entropy. This entropy gain may weaken glasses at an elevated pressure conditions, accounting for potential softening of the compressed glasses. The proposed relationships open a new window to the evolution of diverse complex glasses under extreme stress and compression with high-resolution solid-state nuclear magnetic resonance.     

Simultaneous determination of trichothecene mycotoxins in cereals by LC-MS/MS

Food Science and Biotechnology - This study was designed to determine the residual trichothecene mycotoxins in cereal samples. The optimal solvent for extraction was 84% (v/v) aqueous acetonitrile...     

Effects of vanadium carbides on hydrogen embrittlement of tempered martensitic steel

Precipitation of V carbides is known to suppress the hydrogen-embrittlement (HE) phenomenon as well as to increase material strength. Despite increasing attention to V carbides, there have been few systematic and quantitative investigations on their effects on HE resistance. This study reveals the role of V carbides on the HE behavior of tempered martensitic steel while eliminating other factors, such as chemical composition of other elements, mechanical strength, and dislocation density. The amount of trapped hydrogen increased with increasing V content, whereas the best HE resistance was attained at 0.2 wt% V and it decreased with further V addition. V carbide was considered as a non-diffusible hydrogen-trapping site in this study. However, excessive V content led to the formation of large undissolved carbides that gave rise to brittle fracture and decreased HE resistance. This study suggests that improved HE resistance can be achieved by minimizing the size and amount of undissolved V carbides.