Jo Jan 25, 2024
Some quality indices such as Q, QR, QC and Q0 have been used to evaluate quality level of cast aluminium alloys based on tensile mechanical properties. Quality map has been used to intuitively evaluate the quality level based on quality indices.
They can show quality levels according to tensile properties, but cannot directly show quality levels according to artificial aging heat treatment conditions.
Yang Ji Yon, a student at the Faculty of Materials Science and Technology, has proposed a method to develop a comprehensive quality index and map of cast aluminum alloy according to artificial aging heat treatment conditions by order preference by similarity to ideal solution (TOPSIS) and multiple regression analysis. She has also proposed a method to determine reasonable artificial aging heat treatment conditions by the extremum principle and grid search method. On this basis, she wrote a program for the proposed method by MATLAB.
To illustrate the effectiveness of the proposed methods, she applied them to the cast aluminum alloy A357.
The proposed methods and MATLAB code could be widely used to evaluate the comprehensive quality level of all other cast aluminum alloys, and to select and optimize their reasonable heat treatment conditions.
You can find more information in her paper “Comprehensive quality index and map of cast Al alloys according to artificial aging heat treatment conditions using TOPSIS and multiple regression analysis and determination of reasonable heat treatment condition” in “Proc IMechE Part C: Journal of Mechanical Engineering Science” (SCI).
Jo Jan 24, 2024
A flexible temperature sensor plays an important role in some modern engineering applications such as temperature measurements of curved surfaces or interlayer structures with narrow gaps in industry equipment (e.g. iron cores of generator, motor and transformer).
Platinum is generally used for metallic film temperature sensors owing to its high accuracy and stability, but it is expensive. Several kinds of metallic materials like copper are also occasionally used for special temperature measurement and other temperature measurements that involve not so high accuracy.
Recently, copper film temperature sensors are widely utilized for measurement of temperature in industry instead of platinum sensors because the design of the former based on PCB technology allows cost-efficient fabrication, easy handling, and simple retrofitting and replacement. But, the defects existing on PCB leads lower its performance and stability.
The lethal defects can be divided into two types; one is disconnection and the other is fall. Disconnection leads to reduction in fabrication yield of sensors and fall results in decrease in their stability and lifetime. Therefore, it is important to avoid the defects on PCB leads.
Pak Son Guk, a section head at the Semiconductor Institute, has proposed a new layout design of a sensor to avoid the defects.
The new layout design with addition of detour leads guarantees the yield of almost 98%. The sensor was tested for a long time of 3 000 hours at 150℃. The deviation rate of resistance of the sensor is less than 0.1%, TCR 4.1×10-3℃-1 and the maximum current 10mA.
Jo Jan 23, 2024
Barbell’s trajectory and other kinematic properties such as velocity and acceleration are the most important parameters for weightlifting technique, so they have been investigated by several researchers.
Because weightlifter’s bad motion could cause certain variation in barbell trajectory, studies on optimizing the barbell trajectory have been conducted.
Some optimization algorithms including genetic algorithm and optimal control theory were applied to optimization of barbell trajectory during snatch lift with optimization parameters defined as the sum of actuating torques of all joints. What is more, previous works were limited to 5 segments without considering the head of a lifter’s model and to adoption of statistical data for physical properties of human body.
Jon Min Hyok, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has developed a kinematic model of 6 segments and proposed a method for optimization of barbell’s trajectory based on the kinematic model.
The six segments are shin, thigh, trunk, upper arm, forearm and head which accounts for about 10 percent of body weight and is considered as one segment of one degree of freedom. He obtained the physical properties of the model such as mass, barycenter and inertia moment of every part of body from anthropometry, not statistical data, which were used to make a model by Solidworks and calculated. In addition, for optimization of barbell trajectory, he formulated an optimal control problem so that the actuating torques of joints are minimized and solved it by Pontryagin Maximum Principle (PMP).
The results obtained by the proposed method are in good agreement with ones given by analysis of lifter’s actual performances, so it will give help with weightlifting training.
Jo Jan 20, 2024
Statistical data mixed with qualitative and quantitative indices are usually prepared for object identification. In the medical field, qualitative indices such as pathological complaints and quantitative indices such as laboratory tests are often given together, so it is very important to make a discriminant for diagnosing a patient’s disease properly.
To date, no method has been developed to produce a discriminant in the presence of both qualitative and quantitative indices.
Kim Ju Hyong, a researcher at the Faculty of Biology and Medicine Engineering, has proposed a new method of object identification from statistical data with both qualitative and quantitative indices.
He has applied the method to diagnosis of hundreds of diseases ―cerebral apoplexy, autonomic imbalance, carcinoma in stomach, liver, colon, lungs, women and nose, acute abdomen symptoms, cardiopathy, cryptogenic gangrene, caput external stroke, etc.
The results confirmed that his method has high possibility of producing a more reasonable discriminant by performing iterative calculations considering the degree to which qualitative and quantitative indices contribute to the discrimination, and that it is a simple and widely used method for diagnosis of medical diseases from both indices.
Jo Jan 18, 2024
NTC (Negative Temperature Coefficient) thermistor is widely used in industrial application for temperature measurement, control and compensation. The important problem in using NTC thermistor is to overcome its aging phenomenon.
Yu Nam Chol, a researcher at the Science Engineering Institute, has prepared Fe0.8Mn1.54Ni0.66O4 NTC material by the more convenient nitrate decomposition method, investigated the electrical properties of thermistors sintered at different temperature ranges, and determined the reasonable temperature and time and the effect of N2 annealing atmosphere on the aging behavior.
Observation of the microstructure and phase of this material indicated that it has compact and uniform spinel structure. He also found that the sample sintered at 1 200℃ was suitable for building a thermistor and that the aging behavior drops below 0.7% when it is under N2 heat-treating for 72 hours around 450-550℃.
Jo Jan 17, 2024
Display of works of art such as color photos needs two competing criteria: appearance and color degradation. The more the blue radiant flux of pc-white LED lamps increases, the more color degradation occurs. However, previous studies have focused on the improvement of color rendering property and luminous efficacy, and decreasing the ratio of blue radiant flux while maintaining the needed color rendering property and luminous efficacy has been hardly discussed.
Kim Ju Yong, a researcher at the Faculty of Electronics, has investigated the effect of correlated color temperature (CCT) and spectral power distribution (SPD) of PC-white LED lamps on the color degradation of color samples and the difference between the decolorizing reduction of color samples and that of textiles dyed with natural dyes.
Controlling the SPD by combining the blue LED chip and G-O-R phosphors, he manufactured a test lamp with high color rendering property. The high color rendering property and small blue peak radiant flux of the test lamps lead to the best effect on color appearance and decolorizing reduction.
After color samples for color pictures were decolorized with accelerating degradation method, the color degradation caused by test lamp (TL) was about a half of that of comparison test LED lamp (CL). The test results showed that for the pc-white LED lamps, the decolorizing reduction effect depends on SPD more than CCT.
He also proved that unlike the textiles dyed with natural dyes, green and violet were decolorized most, followed by yellow from samples for color pictures.
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