• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.661-669
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• 2021

A mechanical stiffener has been mainly applied on a PCB to secure fatigue life of a solder joint of an electronic components in spaceborne electronics by minimizing bending displacement of the PCB. However, it causes an increase of mass and volume of the electronics. The high damping PCB implemented by multi-layered viscoelastic tapes of a previous research was effective for assuring the fatigue life of the solder joint, but it also has a limitation to decrease accommodation efficiency for the components on the PCB. In this study, we proposed high damping PCB with a multi-layered superelastic shape memory alloy stiffener for spatialminimized, light-weighted, high-integrated structure design of the electronics. To investigate the basic characteristics of the proposed PCB, a static load test, a free vibration test were performed. Then, the high damping characteristic and the design effectiveness of the PCB were validated through a random vibration test.

• Journal of Space Technology and Applications
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• v.1 no.2
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• pp.256-267
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• 2021

In this paper, the New Space characteristics and response of micro & small satellite, and space industrialization strategy using domestic technologies are described. Recently, micro & small satellites are developed worldwide, including Starlink, having the characteristics of low-cost, light-weight and satellite constellation. Therefore, it is necessary to prepare for the constellation operation by considering the use of Commercial Off-The-Shelf (COTS) parts, satellite weight, shape and mass production. In particular, it is necessary to develop Multi Input Multi Output (MIMO) technology in consideration of the frequency interference during constellation operation, and to prepare and make efforts to secure frequencies in the government. Among the commercial-grade memories of Samsung Electronics and SK Hynix, the space-grade memory field using radiation tolerant memory and the high reliable packaging and space environment test technology has potential as a space industrialization strategy.

• Korean journal of communication and information
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• v.71
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• pp.9-32
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• 2015

The media, traditionally, serves to reinforce one's limited memory and transform those personal memories of society's members into collective memories. Notably, the mass media collects countless pieces of personalized memories for the creation of collective memories. Through the process of recollecting as well as recreating the past in the present, mass media exerts influence on the means the public appreciates and understands the history. Although numerous new medias like Internet overflows in today's society, television continues to stand firm as the salient means to construct the memories in daily lives. In this context, the research aims to analyze the televised news as the principal agent of memory producer to determine through which memories it recreates the $5{\cdot}18$ in today's media. The analysis of news values clarifies that every government placed distinctive news values on $5{\cdot}18$ within its historical context. Even so, such values were often fixed based on its relations to the existing political issues. Furthermore, through the discourse analysis, this research concludes that today's coverage of $5{\cdot}18$ is softening and becoming conventional.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.1-7
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• 2022

Recently, satellites equipped with high-performance electronics have required higher power consumption because of the advancement of satellite missions. For this reason, the size of the solar panel is gradually increasing to meet the required power budget. Increasing the size and weight of the solar panel is one of the factors that induce the elastic vibration of the flexible solar panel during the highly agile maneuvering of the satellite or the mode of vibration coupling to the satellite or the mode of vibration coupling to the micro-jitter from the on-board appendages. Previously, an additional damper system was applied to reduce the elastic vibration of the solar panel, but the increase in size and mass of system was inevitable. In this study, to overcome the abovementioned limitations, we proposed a high -damping yoke structure consisting of a superplastic SMA(Shape Memory Alloy) laminating a thin FR4 layer with viscoelastic tape on both sides. Therefore, this advantage contributes to system simplicity by reducing vibrations with small volume and mass without additional system. The effectiveness of the proposed superelastic SMA multilayer solar panel yoke was validated through free vibration testing and temperature testing using a solar panel dummy.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.3
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• pp.78-87
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• 2013

NAND flash memory has been widely used as a storage medium in mobile devices, PCs, and workstations due to its advantages such as low power consumption, high performance, and random accessability compared to a hard disk drive. However, NAND flash cannot support in-place update so that it is mandatory to erase the entire block before overwriting the corresponding page. In order to overcome this drawback, flash storages need a software support, named Flash Translation Layer. However, as the high performance mass NAND flash memory is getting widely used, the size of mapping tables is increasing more than the limited DRAM size. In this paper, we propose an adaptive mapping information caching algorithm based on page mapping to solve this DRAM space shortage problem. Our algorithm uses a mapping information caching scheme which minimize the flash memory access frequency based on the analysis of several workloads. The experimental results show that the proposed algorithm can increase the performance by up to 70% comparing with the previous mapping information caching algorithm.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.361.1-361.1
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• 2016

Due to their high sensitivity, fast response, small energy consumption and ease of integration, nanoelectromechanical systems (NEMS) have attracted much interest in various applications such as high speed memory devices, energy harvesting devices, frequency tunable RF receivers, and ultra sensitive mass sensors. Since the device performance of NEMS is closely related with the mechanical and flexural properties of the material in NEMS, analysis of the mechanical and flexural properties such as intrinsic tensile stress and Young's modulus is a crucial factor for designing the NEMS structures. In the present work, the intrinsic mechanical properties of highly stressed silicon nitride (SiN) beams are investigated as a function of the beam length using two different techniques: (i) dynamic flexural measurement using optical interferometry and (ii) quasi-static flexural measurement using atomic force microscopy. The reliability of the results is analysed by comparing the results from the two different measurement techniques. In addition, the mass density, Young's modulus and internal stress of the SiN beams are estimated by combining the techniques, and the prospect of SiN based NEMS for application in high sensitive mass sensors is discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.350-362
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• 2017

The Eulerian nearshore current model is more advantageous than the Lagrangian model in the way that numerical results from the Eulerian model can be directly compared with the measurements by the stationary equipment. It is because the wave mass flux is not included in the computed mass flux of Euleran nearshore current model. In addition, the Eulerian model can simulate the longshore currents with depth varying parabolic profile. However, the numerical models proposed by different researcher have different forms of the wave stress terms. For example, wave stresses in Newberger and Allen's (2007) model is constant over the depth, while those of Chun (2012) are vertically distributed. In the present study, these wave stress terms were compared against Hamilton et al.'s (2001) laboratory experiments to see the effects of different wave stress terms performed on the computation of nearshore currents.

• Journal of the Korean Vacuum Society
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• v.10 no.3
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• pp.328-334
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• 2001

The characteristics of $NO/N_2O$ nitrided oxide and reoxidized nitrided oxide being studied as super thin gate oxide and gate dielectric layers of nonvolatile semiconductor memory(NVSM) was investigated by dynamic secondary ion mass spectrometry(D-SMS), time-of-flight secondary ion mass spectrometry(ToF-SIMS), and x-ray photoelectron spectroscopy (XPS). The specimen was annealed in $NO/N_2O$ ambient after initial oxide process. The result of D-SIMS exhibits that the center of nitrogen exists at the initial oxide interface and the distribution of nitrogen is wider in the annealing process with $N_2O$ than with NO annealing process. For investigating the condition of nitrogen that exists within the nitrided oxide, ToF-SIMS and XPS analysis were carried out. It was shown that the center of nitrogen investigated by D-SIMS was expected the SiON chemical bonds. The nitrogen near the newly formed reoxide/silicon substrate interface was appeared as $Si_2NO$ chemical bonds, and it is agreed with the distribution of SiN and $Si_2NO$ species by ToF-SIMS.

• Journal of People, Plants, and Environment
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• v.21 no.6
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• pp.557-564
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• 2018

Along with the aging society, the prevalence of dementia is also increasing. Dementia causes short-term memory loss as well as difficulties of performing daily activities and gradually causes suffering of the patients and their family. In spite of various programs for prevention of dementia of older people are being implemented, there is a lack of developing natural-based program for physical and mental health promotion. Therefore, it is necessary to develop programs for the elderly living alone who are more vulnerable to dementia because of their social and economic isolation. The purpose of this study was to develop a natural-based program and investigate the effects of 10 weeks forest therapy program for dementia prevention to improve the psychological and physical health of the elderly living alone. The experimental subjects were 30 elderly (aged 65 or older) and 31 elderly participated in control group. The Stress response, depressive symptoms, weight, body mass index (BMI), fat mass and muscle mass were measured for pre and post test. The results showed that the experimental group showed subjective stress relief (t=5.249, p=.000), improvement in symptoms of depression (t=4.152, p=.000), and decreases in weight (t=2.686, p=.012), BMI (t=2.629, p=.014) and fat mass (t=2.918, p=.007) after the forest therapy program. The experimental group showed lower stress reactions(t=-7.185, p=.000) and less depressive symptoms (t=-5.303, p=.000) than control group after participating the program. These results suggest that periodic forest exposure can help having less stressful and depressive status than non-forest exposure and the forest therapy program can reduce participants' psychological and physical risk factors of dementia.

• Smart Structures and Systems
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• v.31 no.1
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• pp.89-100
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• 2023

This paper conducts a parametric study of a new tuned mass damper with pre-strained superelastic SMA helical springs (SMAS-TMD) on the vibration reduction effect. First, a force-displacement relation model of superelastic SMA helical spring is presented based on the multilinear constitutive model of SMA material, and the tension tests of the six SMA springs fabricated are implemented to validate the mechanical model. Then, a dynamic model of a single floor steel frame with the SMAS-TMD damper is set up to simulate the seismic responses of the frame, which are testified by the shaking table tests. The wire diameter, initial coil diameter, number of coils and pre-strain length of SMA springs are extracted to investigate their influences on the seismic response reduction of the frame. The numerical and experimental results show that, under different earthquakes, when the wire diameter, initial coil diameter and number of coils are set to the appropriate values so that the initial elastic stiffness of the SMA spring is between 0.37 and 0.58 times of classic TMD stiffness, the maximum reduction ratios of the proposed damper can reach 40% as the mass ratio is 2.34%. Meanwhile, when the pre-strain length of SMA spring is in a suitable range, the SMAS-TMD damper can also achieve very good vibration reduction performance. The vibration reduction performance of the SMAS-TMD damper is generally equal to or better than that of the classic optimal TMD, and the proposed damper effectively suppresses the detuning phenomena that often occurs in the classic TMD.