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박동혁,이춘구,박하나,백승환,이중용 한국농업기계학회 2019 바이오시스템공학 Vol.44 No.4
Thediscreteelementmethodcanbeusedtosimulateparticlesystemsandidentifyforcesactingonaparticle,butthesuitabilityof using simulation for the modeling of garlic is undetermined. This study was conducted to evaluate the feasibility of using the EDEM program as a simulation tool for garlic bulbs in a garlic harvester. Simulations were compared with experimental collisions between a bulb and the roller of a garlic harvester. In the collision tests, the behavior and impact of an artificial garlic were observed with a high-speed camera and an accelerometer. The simulated positions and accelerations of the garlic were obtainedinEDEMusingthesameparametersasthoseoftheexperiment.Theimpactsofthegarlicwerecomparedintermsofthe rootmeansquareofacceleration,contactnumber,andaverageforceforrollerspeedsof100–300rpm.Basedonsimilarbehavior observed from photographic images of the experiments, the collision of garlic can be simulated in EDEM. The simulated accelerations were 2.8–7.8 times larger than the measured accelerations, which is attributed to an experimental limitation. The difference was reduced to 1.18 times after applying this limitation to the simulated data. In the simulations, the number of collisions decreased from 185 to 93 as the rotational speed increased, but the average force increased from 3.188 to 6.222 N. EDEM is suitable for simulating the collision of garlic with harvester conveying rollers. Therefore, EDEM can be applied to evaluate the impact forces acting on the garlic and to improve the structure of garlic harvesters.
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유효우량 산정을 위한 NRCS-CN 모형의 초기손실량 산정방법 개선
박동혁,무하마드 아즈말,안재현,김태웅,Park, Dong-Hyeok,Ajmal, Muhammad,Ahn, Jae-Hyun,Kim, Tae-Woong 한국수자원학회 2015 한국수자원학회논문집 Vol.48 No.6
본 연구는 NRCS-CN 방법이 산정하는 유출량의 정확성을 향상시키기 위하여 강우량과 최대잠재보유수량을 초기손실량 계산과정의 주요 기여인자로 고려하였으며, 우리나라 15개 유역에서 관측된 658개의 강우량과 유출량 자료를 이용하여 초기손실량의 수정모형을 제안하였다. 유효우량을 산정하는 방법으로는 NRCS-CN 방법(M1), NRCS-CN 방법에서 초기손실량계수를 감소시킨 방법(M2), 관측 강우-유출 관계를 바탕으로 본 연구에서 제안하는 방법(M3)을 적용하였다. 또한 USDA에서 제시하는 CN값($CN_T$), 관측자료로 부터 계산된 CN값($CN_C$) 그리고 최소자승법으로 추정한 CN값($CN_{LSF}$)을 각각의 방법에 적용하였다. 적용 결과는 RRMSE, NSE 그리고 PBIAS 등을 이용하여 평가되었다. 그 결과 $CN_T$를 M1, M2, M3에 적용한 경우 각 유역에서 평균적으로 [RMSE (23.60, 18.12, 16.04), NSE (0.54, 0.73, 0.79), PBIAS (36.54, 20.25, 12.00)]로 나타났다. 이와 비슷하게 $CN_C$를 M1과 M2에 적용하고, $CN_{LSF}$를 M3에 적용하였을 경우 각 유역에서 평균적으로 [RMSE (17.17, 15.88, 13.82), NSE (0.76, 0.80, 0.85), PBIAS (3.06, 4.47, 0.11)]로 나타났다. 따라서 본 연구에서 제안된 M3 방법을 사용하여 추정한 유효우량이 관측된 직접유출량과 통계학적으로 가장 가까운 값을 제공하는 것으로 나타났다. In order to improve the runoff estimation accuracy of the Natural Resources Conservation Service (NRCS) curve number (CN) model, this study incorporated rainfall and maximum potential retention as contributors for initial abstraction. The modification was proposed based on 658 rank-order data of rainfall and subsequent runoff from 15 watersheds. The NRCS-CN model (M1), one of its inspired modified model (M2), and the proposed model (M3) were analyzed employing different CN approaches. Using tabulated, calculated and least squares fitted CNs ($CN_T$, $CN_C$, $CN_{LSF}$, respectively), the models' performances were evaluated based on Root Mean Square Error (RMSE), Nash-Sutcliffe Efficiency (NSE), and Percent Bias (PBIAS). Applications of model M1, M2, and M3, respectively exhibited watershed cumulative mean [RMSE (23.60, 18.12, 16.04), NSE (0.54, 0.73, 0.79), and PBIAS (36.54, 20.25, 12.00)]. Similarly, using CNC (for M1 and M2 model) and $CN_{LSF}$ (for M3 model), the performance of three models respectively were assessed based on watershed cumulative mean [RMSE (17.17, 15.88, 13.82), NSE (0.76, 0.80, 0.85), and PBIAS (3.06, 4.47, 0.11)]. The proposed model (M3) that linked all of the NRCS-CN variants showed more statistically significant agreement between the observed and estimated data.
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한국 노인의 안정시심박수, 상대 악력 및 당뇨병 유병률의 연관성: 2015-2018 국민건강영양조사 자료를 기반으로
박동혁,홍성현,조원희,전용관 한국운동생리학회 2020 운동과학 Vol.29 No.4
PURPOSE: The purpose of this study was to examine the association of resting heart rate (RHR) and relative hand grip strength (RHGS) with diabetes among Korean adult over 65 years old. METHODS: Cross-sectional analyses were performed using the 2015-2018 Korea National Health and Nutrition Examination Survey (KNHANES). Among 31,649, a total of 4,814 adults over 65 years old were included in this study. Participants were divided into tertile according to their RHR and RHGS. Statistical methods included frequency analysis, ANCOVA (Analysis of covariance) and logistic regression. RESULTS: Participants in the 3rd tertile of RHR (RHR over 73 bpm in men, 74 bpm in women) had 2.00 times [95% Confidence Interval (CI): 1.58-2.54] and 1.80 times (95% CI: 1.44-2.26) higher odds of having diabetes in men and women, respectively, compared with participants in the 1st tertile (RHR below 64 bpm in male, 65 bpm in female). Participants in the 1st tertile of RHGS (RHGS below 0.46 in men, 0.31 in women) had 2.51 times (95% CI: 1.76-3.58) and 1.86 times (95% CI: 1.48-2.35) higher odds of having diabetes in men and women, respectively, compared to participants with 3rd tertile (RHGS over 0.54 in men, 0.38 in women). When a joint association of RHR and RHGS with risks of diabetes were analyzed, participants with the highest RHR and the lowest RHGS had 4.23 times (95% CI: 2.74-6.54) and 2.90 times (95% CI: 1.98-4.23) higher odds of having diabetes compared to participants with the lowest RHR and the highest RHGS in men and women, respectively. CONCLUSIONS: The current study showed that higher RHR and lower RHGS were associated with increased risk of diabetes in Korean elderly population.
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박동혁,김관래 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.6
Intensive research has been conducted to develop flexible piezoelectric pressure sensors, since selfpowering devices are advantageous for wearable electronic applications. Recently, two types of piezoelectric devices, ceramic-PDMS composite film and PVDF nanofiber mats, have drawn attention in the research community. Piezoelectric ceramics such as BaTiO3 (BTO) and PZT exhibit outstanding piezoelectric coefficients, while PDMS provides flexibility. In contrast, a PVDF nanofiber mat simultaneously exhibits piezoelectricity and flexibility. In the present study, a comparative analysis of BTO-PDMS composite film and a PVDF nanofiber mat for application to flexible pressure sensors was carried out. First, step-wise electric poling was conducted on these two types of pressure sensors, after which the open-circuit voltage (Voc) was measured under compressive force. The 1.8 V peak-to-peak Voc was measured in a BTO-PDMS composite with a 30 wt.% BTO content that was poled by 10 kV/mm electric field for 15 min. This peak-to-peak Voc of the BTO-PDMS composite increased further to ~ 4 V when it was poled for 24 hr. Unlike the BTO-PDMS composite films, the maximum Voc (1.1 V) was measured in a PVDF nanofiber mat that did not undergo subsequent electric poling. A BTO-PDMS composite film and a PVDF nanofiber mat were fabricated, and the compressive force and strain-rate dependencies of Voc and the short-circuit current (Isc) were investigated. Overall, the Voc and Isc of the BTO-PDMS composite film exceeded those of the PVDF nanofiber mat in a force range of 1 − 25 N and frequency range of 0.5 − 2.0 Hz. However, the Voc and Isc signals from the PVDF nanofiber mat were more stable than those from the BTO-PDMS composite film due to the longer lifetime of the signals.
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박동혁 한국카운슬러협회 2011 相談과 指導 Vol.46 No.-
개인적 측면에서 학업성취는 청소년기에 중요한 발달과업의 하나이며, 자아존중감의 형성에도 영향을 미치고(Hater, 1990b), 자아개념과도 의미 있는 상관을 가지고 있다(Purkey, 1970).
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