• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.3
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• pp.49-56
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• 2012

Rupture disks are a kind of safety device in high pressure equipment and they are used to control rupture pressure in the solid rocket motor. In this paper, a series of rupture experiments was performed using rupture disks made of AISI 316L and rupture pressure of rupture disks was calculated through various assumptions in relation between elasto-plastic material properties and true stress-strain curve. Experiment and FEA indicated rupture pressure is determined by size of rupture disks. As a result of elasto-plastic analysis, only multi-linear stress-strain curve was able to calculate meaningful estimations. Experimental results also showed rupture location are decided by the size of rupture disks. Experimental and FEA results will be applied to control rupture pressure of disks.

• Electrical & Electronic Materials
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• v.9 no.8
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• pp.789-798
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• 1996

The double nitride layer Metal Nitride Oxide Semiconductor(MNOS) structures were fabricated by variating both gas ratio and nitride thickness, and by duplicating nitride deposited and one nitride layer MNOS structure to improve nonvolatile memory characteristics of MNOS structures by Low Pressure Chemical Vapor Deposition(LPCVD) method. The nonvolatile memory characteristics of write-in, erase, memory retention and degradation of Bias Temperature Stress(BTS) were investigated by the homemade automatic .DELTA. $V_{FB}$ measuring system. In the trap density double nitride layer structures were higher by 0.85*10$^{16}$ $m^{-2}$ than one nitride layer structure, and the AVFB with oxide field was linearly increased. However, one nitride layer structure was linearly increased and saturated above 9.07*10$^{8}$ V/m in oxide field. In the erase behavior, the hole injection from silicon instead of the trapped electron emission was observed, and also it was highly dependent upon the pulse amplitude and the pulse width. In the memory retentivity, double nitrite layer structures were superior to one nitride layer structure, and the decay rate of the trapped electron with increasing temperature was low. At increasing the number on BTS, the variance of AVFB of the double nitride layer structures was smaller than that of one nitride layer structure, and the trapped electron retention rate was high. In this paper, the double nitride layer structures were turned out to be useful in improving the nonvolatile memory characteristics.

• Geomechanics and Engineering
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• v.15 no.1
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• pp.615-620
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• 2018

In order to analyze the healing effectiveness of rock salt cracks affected by the applied stresses and time, we used the ultrasonic technology to monitor the ultrasonic pulse velocity (UPV) variations for different initial stress-damaged rock salts during self-healing experiments. The self-healing experiments were to create different conditions to improve the microcracks closure or recrystallized, which the self-healing effect of damaged salt specimens were analyzed during the recovery period about 30 days. We found that: The ultrasonic pulse velocity of the damaged rock salts increases rapidly during the first 9 days recovery, and the values gradually increase to reach constant values after 30 days. The damaged value and the healed value were identified based on the variation of the wave velocity. The damaged values of the specimens that are subject to higher initial damage stress are still keeping in large after 30 days recovery under the same recovery condition It is interesting that the damage and the healing were not in the linear relationship, and there also existed a damage threshold for salt cracks healing ability. When the damage degree is less than the threshold, the self-healing ratio of rock salt is increased with the increase in damage degree. However, while the damage degree exceeds the threshold, the self-healing ratio is decreased with the increase in damage.

• Structural Engineering and Mechanics
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• v.13 no.5
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• pp.543-556
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• 2002

A dynamic elastic local buckling analysis is presented for a pile subjected to an axial impact load. The pile is assumed to be geometrically perfect. The interactions between the pile and the surrounding soil are taken into account. The interactions include the normal pressure and skin friction on the surface of the pile due to the resistance of the soil. The analysis also includes the influence of the propagation of stress waves through the length of the pile to the distance at which buckling is initiated and the mass of the pile. A perturbation technique is used to determine the critical buckling length and the associated critical time. As a special case, the explicit expression for the buckling length of a pile is obtained without considering soil resistance and compared with the one obtained for a column by means of an alternative method. Numerical results obtained show good agreement with the experimental results. The effects of the normal pressure and the skin friction due to the surrounding soil, self-weight, stiffness and geometric dimension of the cross section on the critical buckling length are discussed. The sudden change of buckling modes is further considered to show the 'snap-through' phenomenon occurring as a result of stress wave propagation.

• Molecules and Cells
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• v.46 no.8
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• pp.486-495
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• 2023

Lipofuscins are oxidized lipid and protein complexes that accumulate during cellular senescence and tissue aging, regarded as markers for cellular oxidative damage, tissue aging, and certain aging-associated diseases. Therefore, understanding their cellular biological properties is crucial for effective treatment development. Through traditional microscopy, lipofuscins are readily observed as fluorescent granules thought to accumulate in lysosomes. However, lipofuscin granule formation and accumulation in senescent cells are poorly understood. Thus, this study examined lipofuscin accumulation in human fibroblasts exposed to various stressors. Our results substantiate that in glucose-starved or replicative senescence cells, where elevated oxidative stress levels activate autophagy, lipofuscins predominately appear as granules that co-localize with autolysosomes due to lysosomal acidity or impairment. Meanwhile, autophagosome formation is attenuated in cells experiencing oxidative stress induced by a doxorubicin pulse and chase, and lipofuscin fluorescence granules seldom manifest in the cytoplasm. As Torin-1 treatment activates autophagy, granular lipofuscins intensify and dominate, indicating that autophagy activation triggers their accumulation. Our results suggest that high oxidative stress activates autophagy but fails in lipofuscin removal, leaving an abundance of lipofuscin-filled impaired autolysosomes, referred to as residual bodies. Therefore, future endeavors in treating lipofuscin pathology-associated diseases and dysfunctions through autophagy activation demand meticulous consideration.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.660-662
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• 2022

Due to the prolonged aftermath of COVID-19, the number of modern people suffering from stress and mental illness is increasing. Recently, various methods of color therapy are being studied using LED lighting to improve concentration, relieve stress, manage skin, and improve sleep quality. In this paper, pulse waves are measured and heart rate variability is extracted using a PPG (Photoplethysmogram) sensor to analyze a person's mental and physical state. Using RGBLED and Arduino, we propose a mood lighting system that automatically changes colors according to changes in mental and physical conditions by producing color lighting of various wavelengths, which are mainly used to stabilize the mental state.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.4021-4030
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• 2015

Pulse wave is the physiological responses through the autonomic nervous system such as ECG. It is relatively convenient because it can measure the signal just by applying a sensor on a finger. So, it can be usefully employed in the field of U-Healthcare. The objects of this study are acquiring the PPG (Photoplethysmography) one of the way of measuring the pulse waves in non-invasive way using the CMOS image sensor on a smartphone camera, developing the portable system judging stressful or not, and confirming the applicability in the field of u-Healthcare. PPG was acquired by using image data from smartphone camera without separate sensors and analyzed. Also, with that image signal data, HRV (Heart Rate Variability) and stress index were offered users by just using smartphone without separate host equipment. In addition, the reliability and accuracy of acquired data were improved by developing additional hardware device. From these experiments, we can confirm that measuring heart rate through the PPG, and the stress index for analysis the stress degree using the image of a smartphone camera are possible. In this study, we used a smartphone camera, not commercialized product or standardized sensor, so it has low resolution than those of using commercialized external sensor. However, despite this disadvantage, it can be usefully employed as the u-Healthcare device because it can obtain the promising data by developing additional external device for improvement reliability of result and optimization algorithm.

• Journal of Korean Academy of Nursing
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• v.23 no.3
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• pp.431-452
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• 1993

This study was done to determine the effect of music therapy on stress and quality of life in patients undergoing hemodialysis. The research design was a nonequivalent control group pre -post test design. The subjects consisted of 21 patients who received hemodialysis in two hospitals located in Kwang Ju. The fourteen receiving treatment in one hospital were assigned to the experimental group and the seven in the other hospital to the control group. Data were gathered from December 14, 1992 to January 16, 1993 through questionnaires and physiological measurement. Data were analyzed by the SAS package using frequency, t-test, paired t-test and Pearson Prod uct - Moment Correlation Coefficient. The results of this study are summarized as follows ; 1. There were no significant differences between the two groups on stress scores and quality of life scores before the treatment. 2. The mean score on the psychological stress scale for the patients undergoing hemodialysis was 2.48 out of a maximum mean score of four, the items with high stress scores were “feeling of weakness and annoyed by everything”, “limitation of food”, “limitation of fluid”, “change in skin color” in that order. The psychological category showed the highest stress score followed by developmental, scoioeconomic and physiological stress categories in that order. 3. In the experimental group, post - test diastolic blood pressure decerased significantly(t=3.24, p=0.0064), but in the control group pre and post - test diastolic blood pressure were not different. 4. There was no difference between the two groups on the pre and post -test psychological stress scores or the depression scores. 5. The mean score of quality of life for patients undergoing hemodialysis was 2.75 out of a maxi-mum mean score of five. The category of ‘emtional state’ showed the highest score followed by ‘self - esteem’, ‘physical state and function’, ‘economic life’, ‘relationship with neighbors’ and ‘family relationship’ categories in that order. There was no significant difference in the pre and post - test quality of life scores between the two groups. 6. Hypothesis 1 that patients undergoing hemodialysis who received music therapy would have less stress than patients undergoing hemodialysis who did not receive music therapy is divided into two sub - hypotheses. 1) The first sub-hypothesis that patients undergoing hemodialysis who received music therapy would have less physiological stress than patients undergoing hemodialysis who did not receive music therapy was partly supported. Among three physiological stress indices (pulse, systolic blood pressure, diastolic blood pressure), only diastolic blood pressure decreased significantly after the treatment in the experimental group. 2) The second sub-hypothesis that patients undergoing hemodialysis who received music therapy would have less psychological stress than patients undergoing hemodialysis who did not receive music therapy was not supported. Psychological stress score and depression score were not significantly different before and after the treatment. 7. Hypothesis 2 that patients undergoing hemodialysis who received music therapy would have a higher quality of life score than patients undergoing. hemodialysis who did not received music therapy was not supported. There were no significant changes in the quality of life scores before and after the treatment.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.9
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• pp.1597-1604
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• 2016

The speed at which the SRM (Switched Reluctance Motor) makes a transition from chopping control to single pulse operation. (i.e., low speed to high speed operation). It is unsatisfied with performance at all operational regimes. In this paper, the operational performance of SRM can be improved by using current hysteresis control method. This method maintains a generally flat current waveform. At the high speed, the current chopping capability is lost due to the development of the back-EMF. Therefore SRM operates in single pulse mode. By using zero-current switching and zero-voltage switching technique, the stress of power switches can be reduce in chopping mode. When the commutation from one phase winding to another phase winding, the current can be zero as fast as possible in this period because several times negative voltage of DC-source voltage produce in phase winding. This paper is compared to performance based on energy efficient C-dump converter topology and the proposed resonant C-dump converter topology. Simulation and experimental results are presented to verify the effectiveness of the proposed circuit.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.2
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• pp.315-322
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• 2008

Titanium and its alloys have excellent corrosion resistance, high strength to weight ratios and creep properties in high temperature, which make them using many various fields of application. Especially, pure titanium, which has outstanding resistance for the stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion, brings out to the best material for the heat exchanger, ballast tank, desalination facilities, and so on. Responding to these needs, welding processes for titanium are also being used GTAW, GMAW, PAW, EBW, LBW, resistance welding and diffusion bonding, etc. However, titanium is very active and highly susceptible to embrittlement by oxygen, nitrogen, hydrogen and carbon at high temperature, so it needs to shield the weld metal from the air and these gases during welding by non-active gas. In this study, it was possible to get sound beads without humping and spatter with a decrease of peak power according to increase of pulse width, change of welding speed and overlap rate for heat input control, and shield conditions at pulsed laser welding of titanium plates for Lap welding.