• Journal of the Institute of Convergence Signal Processing
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• v.20 no.2
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• pp.91-98
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• 2019

Accidents of worker that occur in isolated places are difficult to rescue, unlike general construction accidents. There is a problem of communication limitation when an accident occurs in an isolated place. Also, it is difficult to search the accident place due to the absence of CCTV. In order to solve these problems, this paper proposes a device that combines IoT technology with a safety helmet, which must be worn in the workplace. The proposed device additionally designs and implements a real-time PPG(Photoplethysmography) sensor, body temperature sensor, accelerometer sensor and a camera sensor on the helmet. The proposed helmet system allows the user and the control center to monitor the state of the worker. In addition, when an abnormal biological signal or fall occurs to the worker, the image is transmitted to the control center. By using the proposed system, it is possible to check the status of the worker in real time, so that it has an advantage that it can cope with the accident quickly.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.254-254
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• 2010

기존의 부유게이트를 이용한 플래시 메모리는 소자의 크기를 줄이는데 한계가 있기 때문에 이를 해결하기 위한 비휘발성 메모리 소자로 CTF가 큰 관심을 받고 있다. CTF 메모리 소자는 기존의 플래쉬 메모리 소자에 비해 쓰고 지우는 속도가 빠르고, 데이터의 저장 기간이 길며, 쓰고 지우는 동작에 의한 전계 스트레스에 잘 견뎌내는 장점을 가지고 있다. 최근 터널 장벽의 두께와 종류를 변화시킨 소자의 전기적 특성을 향상하기 위한 연구들은 많이 있었지만, 터널 장벽의 적층구조 변화에 대한 연구는 비교적 적다. 본 연구에서는 터널 장벽의 적층구조 변화에 따른 CTF 메모리 소자의 프로그램 동작 특성 변화에 대해 관찰하였다. 기존의 단일 산화막 (silicon oxide; O) 대신 산화막과 higk-k 물질인 질화막 (silicon nitride; N)을 조합하여 ON, NON, ONO로 터널 장벽의 여러 가지 적층 구조를 가진 소자를 설계하여 각 소자의 프로그램 동작 특성을 조사하였다. CTF 메모리 소자의 프로그램 동작 특성을 거리와 시간에 따른 연속방정식, Shockley-Read-Hall 유사 트랩 포획 방정식 및 푸아송 방정식을 유한차분법을 사용하여 수치해석으로 분석하였다. WKB 근사를 이용하여 인가된 전계의 크기에 따라 터널링 현상에 의해 트랩층으로 주입하는 전자의 양을 계산하였다. 또한, 터널 장벽의 적층구조 변화에 따른 트랩층의 전도대역과 트랩층 내부에 분포하는 전자의 양을 시간에 따라 계산하였다. 계산 결과에서 터널 장벽의 적층구조 변화가 CTF 메모리 소자의 프로그램 동작 특성에 미치는 영향을 알 수 있었다. 소자의 프로그램 동작 특성을 분석함으로써 CTF 메모리 소자에 적합한 터널 장벽의 구조를 알 수 있었다. 기존의 단일 산화막보다 얇아진 산화막의 두께와 낮은 질화막의 에너지 장벽 높이로 전자의 터널링 현상이 더 쉽게 일어나기 때문에 ON 구조로 터널 장벽을 적층한 CTF 메모리 소자의 프로그램 속도가 가장 빠르게 나타났다. 이러한 결과는 터널 장벽의 구조적 변화가 전자의 터널 효과에 미치는 영향을 이해하고 프로그램 동작 속도가 빠른 CTF 메모리 소자의 최적화에 도움을 줄 수 있다.

• Korean Journal of Remote Sensing
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• v.33 no.5_1
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• pp.507-519
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• 2017

The applications of NDVI (Normalized Difference Vegetation Index) as a vegetation index has been widely used to understand vegetation biomass and physiological activities. However, NDVI is not suitable way for monitoring vegetation stress because it is less sensitive to change in physiological state than biomass. PRI (Photochemical Reflectance Index) is well developed to present physiological activities of vegetation, particularly high-light-stress condition, and it has been adopted in several satellites to be launched in the future. Thus, the understanding of PRI performance and the development of analysis method will be necessary. This study aims to interpret the characteristics of light-stress-sensitive PRI in shadow areas and to evaluate the PRI calculated by other wavelengths (i.e., 488.9 nm, 553.6 nm, 646.9 nm, and 668.4 nm) instead of 570 nm that used in original PRI. Using airborne-based hyperspectral image, we found that PRI values were increased in shadow detection due to the reduction of high light induced physiological stress. However, the qualities of both PRI and NDVI data were dramatically decreased when the shadow index (SI) exceeded the threshold (SI<25). In addition, the PRI calculated using by 553.6 nm had best correlation with original PRI. This relationship was improved by multiple regression analysis including reflectances of RED and NIR. These results will be helpful to the understanding of physiological meaning on the application of PRI.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.149-159
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• 1998

The reasonable prediction of time-dependent deformation of prestressed concrete(PSC) box girder bridges is very important for accurate construction as well as good serviceability. The long-term behavior is mostly influenced by the probabilistic characteristic of creep and shrinkage. This paper presents a method of statistical analysis and sensitivity analysis of creep and shrinkage effects in PSC box been taken into account - model uncertainty, parameter variation and environmental condition. The statistical and sensitivity analyses are performed by using the numerical simulation of Latin Hypercube sampling. For each sample, the time-dependent structural analysis is performed to produce response data, which are then statistically analyzed. The probabilistic prediction of the confidence limits on long-term effects of creep and shrinkage is then expressed. Three measure are examined to quantify the sensitivity of the outputs of each of the input variables. These are rank correlation coefficient(RCC), partical rank correlation coefficient(PRCC) and standardiozed rank regression coefficient(SRRC) computed on the ranks of the observations. Three creep and shrinkage models - i. e., ACI model. CEB-FIP model and the model in Korea Highway Bridge Specification - are studied. The creep model uncertainy factor and the relative humidity appear to be the most dominant factors with regard to the model output uncertainty.

• Korean Journal of Remote Sensing
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• v.36 no.5_1
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• pp.667-677
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• 2020

Crop water stress can be detected based on soil moisture content, crop physiological characteristics and remote-sensing technology. The detection of crop water stress is an important issue for the accurate assessment of yield decline. The crop water stress index (CWSI) has been introduced based on the difference between leaf and air temperature. In this paper, drone-based thermal infrared image was used to map of crop water stress in water control plot (WCP) and water deficit plot (WDP) over spring chinese cabbage fields. The spatial distribution map of CWSI was in strong agreement with the abnormal growth response factors (plant height, plant diameter, and measured value by chlorophyll meter). From these results, CWSI can be used as a good method for evaluation of crop abnormal growth monitoring.

• Korean Security Journal
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• no.35
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• pp.125-149
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• 2013

In this study changes in biorhythm are observed by measuring heart rate variabilities in order to verify, compare, and evaluate stresses in guard duties of guards and CCTV monitoring works of staffs serviced in practical guard sites. Guard duties and CCTV monitoring works similar to a practical situation are implemented for nine students in the department of security at K University over 150 minutes. In the results of observing heart rate variabilities and autonomic function tests for six times with an interval of 30 minutes, the heart rate variability (HRV) in CCTV monitoring works represents lower levels than that of guard duties. Also, in a stable condition the guard duties for 30 and 60 minutes exhibit lower levels than that of 90, 120, and 150 minutes. Regarding SDNN, CCTV monitoring works show higher levels that guard duties and the guard duties for 30 and 60 minutes represent lower levels than that of 150 minutes. In autonomic function tests, there are no differences in TP between groups according to guard duties and CCTV monitoring works. Also, the guard duties for 150 minutes represent more differences in TP compared to that of 30 minutes. The interaction between the duty type and the duty duration is presented. In the case of LF, guard duties for 150 minutes show large differences in duty duration compared to that of 60 minutes. In the case of HF, the CCTV monitoring work group shows higher levels than the guard duty group in which the guard duties for 120 and 150 minutes represent higher levels than that of 30 minutes. The interaction between the duty type and the duty duration is presented. In the case of the LF/HF ratio, the guard duty group exhibits higher levels than the CCTV monitoring group. Also, there is an interaction between the duty type and the duty duration including the difference in durations. The CCTV monitoring works represent lower heart function activities than the guard duties according to increases in parasympathetic nervous activities. It shows that the long-term CCTV monitoring duty repeated everyday shows a high possibility of increasing the exposures of VDT syndrome and nervous breakdown.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.3
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• pp.677-684
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• 2018

Recently, negative emotional responses by drivers are a growing problem, which leads to not only a traffic accident but a crime so called 'road rage' in countries with heavy traffics including South Korea. Under such a circumstance, measuring stress- and fatigue-induced emotional responses by means of wireless communication and a wearable system would be useful. The purpose of this study is to implement a system that measures various signals from a driver, derives and monitors his emotional responses from the measurements and verify its derivations with reliability. This paper, as a first part of the research, describes how the system has been implemented with experimental methods.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.24 no.3
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• pp.271-279
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• 2006

Acoustic Emission (AE) technology is an effective nondestructive testing for continuous monitoring of defect formation and failures in structural materials. This paper presents a source location model using Acoustic Emission (AE) sensors in a Pre-Stressed Concrete (PSC) beam and the evaluation of the model was performed through lab experiments. 54 AE events were made on the surface of the 5m-PSC beam using a Schmidt Hammer and arrival times were measured with 7AE sensors. The source location f3r each event was estimated using least squares. The results were compared with actual positions and the RMSE (Root Mean Square Errors) was about 2cm.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.194-194
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• 2010

Charge trap flash (CTF) 구조를 가진 플래시 메모리 소자는 기존의 플래시 메모리 소자에 비해 쓰고 지우는 속도가 빠르고, 데이터의 저장 기간이 길며, 쓰고 지우는 동작에 의한 전계 스트레스에 잘 견디는 장점을 가지고 있다. 이러한 장점에도 불구하고 CTF 플래시 메모리에서도 수십 나노 이하로 소자의 셀 사이즈가 감소함에 따라 단 채널 효과, 펀치스루 현상 및 셀 사이의 간섭현상이 발생함에 따라 이러한 문제들을 해결해야 한다. 인접한 셀 사이에 발생하는 간섭 현상에 대해선 플로팅 게이트를 사용한 플래시 메모리 소자에 대하여 많은 연구가 진행되었으나, CTF 플래시 메모리 소자에서 나타나는 셀 사이의 간섭현상에 대한 연구는 만히 진행되어 있지 않다. 본 연구에서는 CTF 플래시 메모리 소자의 셀 사이의 간격이 작아짐에 따라 발생하는 인접한 셀 간의 간섭 현상에 대해 관찰하였다. CTF 플래시 메모리 소자의 셀 사이의 간격에 따른 비교를 위하여 각 소자의 셀을 구성하는 터널링 산화막, 질화막 및 블로킹 산화막의 두께를 동일하게 하였다. 각 셀 사이의 간격이 감소함에 따라 발생하는 소자의 전기적 특성을 TCAD 시뮬레이션 툴인 Sentaurus를 사용하여 계산하였다. 인접한 셀의 상태에 따라 발생하는 간섭 효과를 확인하기 위해 word line (WL)과 bit line (BL) 방향에 있는 주변 셀의 프로그램 상태에 따른 선택한 셀의 문턱전압이 변화 정도를 관찰하였다. 시뮬레이션 결과는 셀 사이의 간섭효과가 WL 방향에 의한 간섭 현상보다 BL 방향에 의한 간섭 현상보다 크다. 시뮬레이션한 전류-전압 특성 결과는 CTF 플래시 메모리 소자가 비례 축소할 때 인접하는 셀 사이에 간격이 15 nm 이하로 줄어들 경우에 간섭 현상이 급격히 증가하였다.

• Journal of Sensor Science and Technology
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• v.20 no.2
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• pp.118-123
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• 2011

Heart related diseases mainly caused by heavy work load and increasing stress in human daily life. Therefore, researches on mobile healthcare monitoring for daily life has been carried out. Notably, wearable healthcare monitoring system which has least restriction has been tried to provide an emergency alert of abnormal heart rate. In this study, we developed chair type unconstrained BCG measurement system which able to perform continuous heart status monitoring at the office and daily life in the unconstrained way. Furthermore, adaptive threshold is used to detect the heart rate from BCG signals. The HRV(heart rate variability) is calculated from heart rate interval. ECG signal measured using conventional method and BCG signal measured using unconstraint system are carried out simultaneously for the purpose of performance evaluation. From the comparison result, BCG signal shows a similar heart beat characteristic as ECG signal. This proves the possibility of practical implementation of unconstraint healthcare monitoring system. In addition, medical examination like valsalva maneuver is performed to observe the changes in HRV due to stress. By performing valsalva maneuver, heart is said to be placed under an artificial physical stress condition. Under this artificial physical stress condition, the time and frequency domain of HRV parameters are evaluated.