Power module stray inductance extraction: Theoretical and experimental analysis

We propose a stray inductance extraction method on power modules of the few-kilovolts/several-hundred-amperes class using only low voltages and low currents. The method incorporates a double-pulse generator, a level shifter, a switching device, and a load inductor. The conventional approach generally requires a high voltage of more than half the power module's rated voltage and a high current of around half the rated current. In contrast, the proposed method requires a low voltage and low current environment regardless of the power module's rated voltage because the module is measured in a turn-off state. Both theoretical and experimental results are provided. A physical circuit board was fabricated, and the method was applied to three commercial power modules with EconoDUAL3 cases. The obtained stray inductance values differed from the manufacturer-provided values by less than 1.65 nH, thus demonstrating the method's accuracy. The greatest advantage of the proposed approach is that high voltages or high currents are not required.     

La-doped SrTiO3 interconnect materials for anode-supported flat-tubular solid oxide fuel cells

An interconnect layer in an anode-supported flat-tubular solid oxide fuel cell connects electrically unit cells and separates fuel from oxidant in the adjoining cells. Nano-sized La-doped SrTiO₃ for the interconnect is synthesized in this study by the Pechini method using citric acid. The materials with stoichiometric and Sr-deficient compositions are prepared and sintered in an oxidizing atmosphere. The synthesized fine powders exhibit high sinterability, leading to near-full densification. The Sr deficiency plays a crucial role in mechanical, electrical and thermal expansion properties. The interconnect is coated using the synthesized powder on a porous flat-tubular anode support by a screen printing process. The thin and dense layer is obtained after co-sintering in air, and the interconnect/anode interface remains intact upon reduction.     

Protective coating based on manganese–copper oxide for solid oxide fuel cell interconnects: Plasma spray coating and performance evaluation

A solid oxide fuel cell (SOFC) stack requires metallic interconnects to electrically connect unit cells, while preventing fuel from mixing with oxidant. During SOFC operations, chromia scales continue to grow on the interconnect surfaces, resulting in a considerable increase of interfacial resistance, and at the same time, gaseous Cr species released from the chromia scales degrades the cathode performance. To address these problems, in this study, protective Mn₂CuO₄ coatings are fabricated on metallic interconnects (Crofer 22 APU) via a plasma spray (PS) process. The PS technique involves direct spray deposition of molten Mn₂CuO₄ onto the interconnect substrate and leads to the formation of high-density Mn₂CuO₄ coatings without the need for post-heat-treatment. The thickness, morphology, and porosity of the PS-Mn₂CuO₄ coating are found to depend on the processing parameters, including plasma arc power, gas flow rate, and substrate temperature. The PS-Mn₂CuO₄ coating fabricated with optimized parameters is completely impermeable to gases and has high adhesion strength on the interconnect substrate. Furthermore, no resistive chromia scales are formed at the coating/substrate interface during the PS process. As a result, the PS-Mn₂CuO₄-coated interconnects show a very low area-specific resistance below 10?mΩ?cm² at 800?°C in air and excellent stability during both continuous operation and repeated thermal cycling. This work suggests that an appropriate combination of the material and coating process provides a highly effective protective layer for SOFC interconnects.     

Low Pt loading,wide area electrospray deposition technique for highly efficient hydrogen evolving electrode in photoelectrochemical cell

Environmental compatibility, high flammability, richest in energy per mass unit, and easy conversion into thermal, mechanical and electrical energy are the key advantages of hydrogen fuel, which makes it an idealized vision for future energy as a promising alternative to the diminishing fossil fuels. Unlike the methods very well known in the literature, we used environmental benign photoelectrochemical (PEC) hydrogen production method. Pt is one of the promising electrode materials for PEC method, but high cost makes it impractical for commercialization. A methodology for low Pt loading (7.22 × 10⁻⁵ g cm⁻²) based on electrospray technique is explained for the preparation of hydrogen evolution electrode. The resulted films are annealed at different temperatures and investigated by different characterization techniques that showed surface morphological and compositional changes with annealing temperature. The pores-type structure is transformed to vertically aligned plate-like structure with annealing temperature. After annealing at 400 °C, Pt film is more oxidized and enriching about ∼30% of film surface area with oxidized Pt. The solar to hydrogen conversion efficiency in water splitting was raised from an initial value of 8.4–10.6% and Pt loading was reduced by approximately 1000-fold (from 0.07 to 7.22 × 10⁻⁵ g cm⁻²). Thus, present high efficient hydrogen electrode preparation method utilized less Pt material than the conventional Pt electrode and the efficiency was increased by 26%. This can be scaled up for becoming a volume production low-cost method.     

Lifetime estimation of harmonic reducer for manufacturing robot using accelerated life test

We present a calibrated accelerated life test to predict the operational lifetime of newly manufactured harmonic reducers for robots. To this end, a framework based on torque as the accelerating stress is proposed, and a step-stress test is performed to determine the highest stress level. Furthermore, the failure mode and corresponding failure mechanisms of the primary components of the harmonic reducer, and the effect of stress due to the applied load are analyzed. Accordingly, the lifetime of the harmonic reducer under its rated condition is estimated by extrapolating the acceleration test data at three stress levels and analyzing the same using statistical methods. The results obtained include such measures of reliability as the shape and scale parameters of the Weibull distribution, acceleration index for torque, and various estimates of the harmonic reducer’s lifetime.

     

Novel system for detecting SARS coronavirus nucleocapsid protein using an ssDNA aptamer

The outbreak of severe acute respiratory syndrome (SARS) in 2002 affected thousands of people and an efficient diagnostic system is needed for accurate detection of SARS coronavirus (SARS CoV) to prevent or limit future outbreaks. Of the several SARS CoV structural proteins, the nucleocapsid protein has been shown to be a good diagnostic marker. In this study, an ssDNA aptamer that specifically binds to SARS CoV nucleocapsid protein was isolated from a DNA library containing 45-nuceotide random sequences in the middle of an 88mer single-stranded DNA. After twelve cycles of systematic evolution of ligands by exponential enrichment (SELEX) procedure, 15 ssDNA aptamers were identified. Enzyme-linked immunosorbent assay (ELISA) analysis was then used to identify the aptamer with the highest binding affinity to the SARS CoV nucleocapsid protein. Using this approach, an ssDNA aptamer that binds to the nucleocapsid protein with a K_d of 4.93 ± 0.30 nM was identified. Western blot analysis further demonstrated that this ssDNA aptamer could be used to efficiently detect the SARS CoV nucleocapsid protein when compared with a nucleocapsid antibody. Therefore, we believe that the selected ssDNA aptamer may be a good alternative detection probe for the rapid and sensitive detection of SARS.     

Detection of damage locations and damage steps in pile foundations using acoustic emissions with deep learning technology

The aim of this study is to propose a new detection method for determining the damage locations in pile foundations based on deep learning using acoustic emission data. First, the damage location is simulated using a back propagation neural network deep learning model with an acoustic emission data set acquired from pile hit experiments. In particular, the damage location is identified using two parameters: the pile location (P_L) and the distance from the pile cap (D_S). This study investigates the influences of various acoustic emission parameters, numbers of sensors, sensor installation locations, and the time difference on the prediction accuracy of P_L and D_S. In addition, correlations between the damage location and acoustic emission parameters are investigated. Second, the damage step condition is determined using a classification model with an acoustic emission data set acquired from uniaxial compressive strength experiments. Finally, a new damage detection and evaluation method for pile foundations is proposed. This new method is capable of continuously detecting and evaluating the damage of pile foundations in service.     

波形或桁架式钢腹板的预应力钢混组合桥主梁的安全性能和使用性能评估

在许多国家,预应力混凝土箱梁被认为是中等跨径(30～50m)混凝土梁最有效的结构形式。但是当混凝土梁的单跨长度超过50m时,相对钢梁,混凝土箱梁自重问题成为其最大约束。因此,在韩国,中等跨径桥梁主要采用钢箱梁。在20世纪,研究者们多次尝试提高预应力混凝土箱梁结构的有效性,最终采用混凝土-钢混合梁以减轻结构自重。但是,混合桥采用不同类型钢腹板及不同连接形式,会引起结构安全性能和使用性能的变化。为了全面了解钢腹板梁及钢腹板连接形式的性能,对5根带腹板的预应力混凝土梁进行静力荷载试验。这5根试件中,有2根混合梁采用波形钢腹板,而另3根采用桁架式钢腹板。结果显示:通过加强钢腹板与预应力筋的连接节点,可以改善使用性能相关问题(开裂荷载和挠度)及安全性能相关问题(刚度和极限承载力)。     

Superconducting Characteristics of Polycrystalline Magnesium Diboride Ceramics Fabricated by a Spark Plasma Sintering Technique

Highly densified MgB₂ superconductors were successfully fabricated using a spark plasma sintering (SPS) technique, and their superconductivity with respect to microstructural evolution was evaluated. Full densification with final density close to the theoretical density was achieved at a temperature of 1000°C within a total SPS processing time of 40 min. Both an MgB₂ specimen sintered at 1000°C for 30 min and one sintered at 1050°C for 10 min exhibited a high critical transition temperature ( T _c) similar to that of an MgB₂ single crystal (39 K), and a very sharp superconducting transition width (Δ T ) less than 0.5 K. In addition, high critical current densities ( J _c) of 7.7 × 10⁵ A/cm² in a field of 0.6 T at 5 K and of 8.3 × 10⁴ A/cm² in a field of 0.09 T at 35 K were obtained. These excellent superconducting characteristics of the SPS-processed MgB₂ are attributed to uniformly distributed secondary MgO phase nanoparticles and well-developed dislocations in the microstructure that may act effectively as extrinsic flux pinning sites, resulting in the strong pinning force showing a high J _c of 8.7 × 10⁴ A/cm² even in the condition of a field of 4 T at 5 K.