• Journal of the Korean Geotechnical Society
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• v.40 no.4
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• pp.145-154
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• 2024

This study used the discrete element method (DEM) to model the driving process of open-ended piles and investigate the behavior of soil plug during pile penetration. The developed DEM model was verified by comparing model pile test results and numerical analysis, particularly using a contact model considering rolling resistance between soil particles. The study successfully simulated soil compression inside the pile by adjusting the relative density and penetration velocity, and it was confirmed that the soil plug tended to be more compressed as the initial penetration velocity decreased. Soil plug length measurements, plug length ratio, and incremental filling ratio were analyzed and validated against experimental results. The developed DEM model aims to reduce trial and error in further studies by detailing the modeling and verification process.

• Journal of Korean Orthopaedic Sports Medicine
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• v.3 no.1
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• pp.87-91
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• 2004

Purpose: The purpose of this study is to investigate the incidence and patterns of fractures occurred in Inline skating accident. Materials and Method: We evaluated 20 patients, 20 cases(from september 2002 to August 2003) with fractures occurred during Inline skating. The incidence, sex, age, fracture site, associated injuries, causes of Inline skating injuries were analysed. The cases were male in 18(90$\%$), and female in 2(10$\%$). The most common distribution of age was in twenties and thirties. Result: The patients(12cases 60$\%$) with upper extremity fracture were more common than patients(8cases 40$\%$) with lower extremity fracture. Patients who had fracture in ankle were 35$\%$(7cases), forearm 20$\%$(4cases), wrist 20$\%$(4cases), elbow 15$\%$(3cases), thigh 5$\%$(1cases). According to the The Lauge-Hansen classification in ankle fractures there were four patients of supination-external rotation type, two patients of supination-abduction type, and 1 patient of pronation-external rotation type. In forearm and hand fractures, there were three distal radius fractures, one radio-ulnar shaft fracture, 2 scaphoid fractures, and two meta-carpal fractures. In elbow fractures, there were two supracondyle fractures, and one lateral condyle fracture. There were three epiphyseal plate injuries (Salt-Harris type II) in children, and all of them were treated by conservative method. Six fractures were intra-articular fractures. The most common associated injury was contusion(8cases 42.1$\%$). The number of patients who only rode Inline skating less than 3months(8cases 40$\%$) was the greatest. The number of non-contact injury(14cases, 70$\%$) in Inline skating was more than contact(6cases,30$\%$) injury. 11cases(55$\%$) had operative treatment, and 9cases(45$\%$) had conservative treatment, and there was not any complication. The more detailed study is required since the materials were only limited to fracture patients, and the follow up period was short. Conclusion: The most common age for fracture in Inline skating was in twenties, and thirties, and ankle was the most common fracture site.

• Journal of Bio-Environment Control
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• v.28 no.4
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• pp.322-327
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• 2019

This study was conducted to improve the performance of automatic grafting robot using image recognition technique. The stem diameters of tomatoes and cucumber at the time of grafting were $2.5{\pm}0.3mm$ and $2.2{\pm}0.2mm$ for scions and $3.1{\pm}0.7mm$ and $3.6{\pm}0.3mm$ for rootstocks, respectively. The grafting failure was occurred when the different height between scions and rootstocks were over 4 mm and below 2 mm due to the small contact area of both cutting surface. Therefore, it was found that the height difference at the cutting surface of 3 mm is appropriate. This study also found that grafting failure was occurred when the stem diameters of both scions and rootstocks were thin. Therefore, it was suggested to use at least one stem with thicker than the average stem diameter. Field survey on the cutting angle of stems by hand were ranged from 13 to 55 degree for scions and 15 to 67 degree for rootstocks, respectively, which indicates that this could cause the grafting failure problem. However, the automatic grafting robot developed in this study rotates the seedlings 90 degree and then the stems are cut using a cutting blade. The control part of robot use all images taken from grafting process to determine the distance between a center of both ends of stem and a gripper center and then control the rotation angle of a gripper. Overall, this study found that The performance of automatic grafting robot using image recognition technique was superior with the grafting success rates of cucumber and tomato as $96{\pm}3.2%$ and $95{\pm}4%$, respectively.

• Journal of the Korean Chemical Society
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• v.37 no.5
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• pp.473-476
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• 1993

Dipropargyldiphenylmetane, $C_{19}H_{16}, crystallizes in a monoclinic space group $C2/_c$$ with a = 11304(3), b = 20.799(5), c = 6.622(2)${\AA}$, ${\beta} = 112.8(3)^{\circ}$, Z = 4, V = 1435.3${\AA}^3,\;F(000)\;=\;520,\;D_c\;=\;1.14g{\cdot}cm^{-3}$ and ${\mu}\;=\;0.32\;cm^{-1}$. The structure was solved by direct methods and all non-H atoms were identified in the E-map. The final refinement gave R = 0.055 from 1328 unique observed reflections with I $\geq$ -1.0 $\sigma(I).$ The molecule belongs to the point group $C_2$ of Symmetry by possessing the 2-fold axis which coincides witeh the crystallographic symmetry axis in the unit cell. The linear propargyl moiety is nearly $perpendicular(94.2)^{\circ}$ to the molecular plane of the benzene ring. The internal angle of methane carbon atoms in $108.1(1)^{\circ}$, bonding to the benzene and the propargyl moiety with the bond lengths of 1.530(2) and $1.560(2)\AA$, respectively. The shortest contant between the molecules is $3.538(2)\AA$ between C(9) and C(9) (-x, y, -1/2-z).

• Journal of Dental Rehabilitation and Applied Science
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• v.27 no.1
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• pp.91-97
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• 2011

The purpose of this study was to evaluate RPM maintenance in X-Smart according to the power supplied by the AC adapter and rechargeable battery. Five new X-Smart were used in this study. A handpiece with rubber disk which has reflective tape was mounted on the vice. To measure the RPM, a non-contact type digital tachometer was used. RPM measurements were recorded every 5 minutes to 180 minutes and repeated 3 times per motor from each power source. To evaluate a difference of the RPM changes, two-way repeated measures were performed using $SPSS^{TM}$ 14.0. All tests were conducted at the 95 percent confidence level. There was no significant difference in the RPM change between the power sources. Continuous use of X-Smart with a rechargeable battery for up to 180 minutes could be safely used as an endodontic wireless motor with a reliable RPM maintenance.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.158-158
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• 2017

비닐포장 하부에 위치한 콩의 생장 초기에 발생한 초엽을 인식하기 위한 연구를 수행중이다. 선행 연구에서 비닐포장에 접촉한 콩 초엽으로 인해 비닐포장 상부 표면의 열 반응 분포에 변화가 있음을 발견하였다. 현장에서 주행 중에 콩 초엽의 위치를 실시간으로 인식하고 연동된 선형 또는 회전형 엑츄에이터를 제어하여 정확한 위치에 천공을 수행하기 위해서는 계측 시스템과 제어 시스템간의 시간적 차이를 최소할 수 있는 실시간 신호 처리 기술이 필수적이다. 선행 연구에서 사용한 다중 IR 센서의 분해능은 $16{\times}4pixel$이며 주파수는 3 Hz로, 폭이 30cm 내외인 비닐포장 상부의 정밀 분석에 한계가 있음을 발견하였다. 이를 해결하기 위하여 분해능과 계측 주기를 개선할 수 있는 초소형 ($1cm{\times}1cm{\times}1cm$) 열화상 센서를 이용하였다. LWIR(Longwave infrared)영역에 해당하는 $8{\mu}m{\sim}14{\mu}m$의 영역에서 $0.05^{\circ}C$의 분해능을 보이는 $ Lepton^{TM}$ (500-0690-00, FLIR, Goleta, CA)모델을 사용하였다. 프레임당 $80{\times}60$ 픽셀의 정보가 2 Byte의 단위로 계측이 되며 9 Hz의 주파수로 대상면의 열 분포를 측정할 수 있다. 이론적으로 초당 정보 전송량은 86,400 Byte ($80{\times}60{\times}2{\times}9$)이며, 1 m를 진행하는 주행형 천공기에 적용할 경우 1 프레임당 10cm 정도의 면적을 측정하므로, 최대 위치 판정 분해능은 약 10 cm / 60 pixel = 0.17 cm/pixel로 상대적으로 정밀한 위치 판별이 가능하다. $80{\times}60{\times}2Byet$의 정보를 0.1초 이내에 분석해야 하는 기술적 과제를 해결하기 위하여 천공 작업기에 적합한 상용 SBC(Single board computer)의 클럭 속도(1 Ghz)로 처리 가능한 공간 분포 분석 알고리즘을 개발하였다. 전체 이미지 도메인을 한 번에 분석하는데 소요되는 시간을 최소화하기 위하여 공간정보 행렬을 균등히 배분하고 별도의 프로세서에서 Feature를 분석한 후 개별 프로세서의 결과를 경합식으로 판정하는 기술을 연구하였다. 오픈 소스인 MPICH(www.mpich.org) 라이브러리를 이용하여 개발한 신호 분석 프로그램을 클러스터링으로 연동된 개별 코어에 설치/수행 하였다. 2D 행렬인 열분포 정보를 공간적으로 균등 분배하여 개별 코어에서 행렬의 Spatial domain analysis를 수행하였다. $20{\times}20$의 클러스터링 단위를 이용할 경우 총 12개의 코어가 필요하였으며, 초당 10회의 연산이 가능함을 확인하였다. 병렬 클러스터링 기술을 이용하여 1m/s 내외의 주행 속도에 대응이 가능한 비닐포장 상부 열 분포 분석 시스템을 구현하였다.

• Journal of Korea Game Society
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• v.12 no.5
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• pp.79-88
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• 2012

In this paper, we present a real-time hand pose recognition method to provide an intuitive user interface through hand poses or movements without a keyboard and a mouse. For this, the areas of right and left hands are segmented from the depth camera image, and noise removal is performed. Then, the rotation angle and the centroid point of each hand area are calculated. Subsequently, a circle is expanded at regular intervals from a centroid point of the hand to detect joint points and end points of the finger by obtaining the midway points of the hand boundary crossing. Lastly, the matching between the hand information calculated previously and the hand model of previous frame is performed, and the hand model is recognized to update the hand model for the next frame. This method enables users to predict the hidden fingers through the hand model information of the previous frame using temporal coherence in consecutive frames. As a result of the experiment on various hand poses with the hidden fingers using both hands, the accuracy showed over 95% and the performance indicated over 32 fps. The proposed method can be used as a contactless input interface in presentation, advertisement, education, and game applications.

• Applied Chemistry for Engineering
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• v.26 no.5
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• pp.615-620
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• 2015

Polypropylene (PP)/bamboo fiber (BF) composites were fabricated by twin screw extruder in order to investigate effects of the compatibilizer on physical properties of PP/BF composites. The content of BF changed from 10 to 25 wt% and that of the compatibilizer was fixed at 3 wt%. Maleic anhydride grafted PP (PP-g-MAH) was used to increase the compatibility between PP and BF as a compatibilizer. Chemical structures of the composites were confirmed by the existence of carbonyl group (C=O) stretching peak at $1,700cm^{-1}$ in FT-IR spectrum. Considering the degradation and mechanical properties, the optimum extrusion conditions were selected to be $210^{\circ}C$ and 100 rpm, respectively. There was no distinct changes in melting temperature of the composites, but the crystallization temperature increased by $10-20^{\circ}C$ owing to the heterogeneous nuclei of BF. It was checked that the optimum BF content was in the range of 15-20 wt% from the results of tensile and flexural properties of the composites. The effect of the compatibilizer on mechanical properties was confirmed by SEM images of fractured surface and contact angles.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1807-1811
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• 2009

홍수기 유량측정에 있어서 가장 큰 어려움이었던 유속측정의 정확성을 확보하고 실무자의 안전성을 보장하기 위한 기본 취지에서 1993년 시작된 "대하천 유량 자동측정 설비개발"이라는 연구 주제하에 비접촉식 유속측정 기법에 대한 연구를 수년간 연구개발을 거듭한 결과물인 전자파표면유속계를 1999년도에 상품화하여 현재 국내에서 홍수유속측정 설비로 이용되어지고 있다. 현장에서 유량측정업무에 종사하는 실무자들은 홍수유량측정에 비하여 훨씬 간편함을 몸소 느끼게 되었고, 상품화보급이 시작된지 수년이 지난 상태에서는 더욱 성능이 개선된 전자파표면유속계가 개발되기를 기대하였다. 무엇보다도 홍수기에 유량측정시 기존의 유속측정 방법과 같은 방식으로 각 측선마다 전자파표면유속계를 설치해야하는 번거로움을 피력하였다. 기존의 전자파표면유속계는 하천을 가로지르는 교량위에서 흐름방향에 나란히 측정하는 조건을 고려하였기 때문에 이와 같은 편각인 상태의 유속측정은 검토하지 않았다. 이와 같은 사용자의 요구에 대하여 한국수자원공사에서는 홍수기 유량측정시의 사용자 편의성을 증대하기 위하여 성능개선 작업에 착수하여 편각측정용 전자파표면유속계를 개발하였다. 편각측정의 주된 목적은 전자파표면유속계를 모든 측선에 설치하지 않고 한 지점에서 편각(oblique angle)으로 여러 측선의 유속을 측정함으로써 유속측정의 효율성을 증대시키는 것이다. 전자파표면 유속계에서의 편각 측정은 하천의 유속 방향을 기준으로 정면에서 측정하면 수평 편각이 0도가 되며 좌우로 안테나를 회전하여 움직인 각도가 측정 편각으로 결정된다. 전자파의 물리적 특성 때문에 편각이 증가하면 반사된 신호의 수신 크기가 감소하여 측정이 불가능하게 된다. 이러한 문제를 최대한 극복하는 것이 본 연구의 중점 개선사항이다. 이를 통하여 전자파표면유속계를 교량의 임의 지점에 설치하여 좌우로 편각 $20^{\circ}$에 이르는 범위의 유속을 측정하고자 목표로 하였다. 홍수시의 현장 측정 환경은 열악하기 때문에 정확한 측정을 조건으로 측정자에게 최대한의 편리함과 신속한 측정 환경을 제공해야 효과적인 업무수행이 가능하다. 이러한 편각 측정을 가능토록 하기 위해서는 유속측정시 송신되는 전자파의 출력을 기존의 시스템보다 보다 높게 발사하여야 하며 안테나의 수신감도 및 지향성이 개선되어야 한다. 이를 위해서 안테나 형태에 있어 기존 전자파표면유속계와의 차이점은 기존안테나는 파라볼릭 형상이었으나 신규 제작된 안테나는 평면안테나로 이러한 형태의 개선를 통해 안테나 특성 및 구조적인 차이를 유도하였다. 두 가지 안테나 사양 각각 장단점이 있으나 가장 큰 차이점은 빔폭 특성에서 평면 안테나가 우수하며 수신 감도를 향상시킬 수 있다는 강점이 있다. 특히 Tx/Rx 분리의 평면안테나 구조는 파라볼릭 안테나에서 불가능한 기능으로서 편각측정으로 인한 수신감도의 저하의 문제를 해결하기 위한 개선조치이었다. 성능개선 제작된 편각측정용 전자파표면유속계를 이용하여 일반하천의 홍수유속에 대한 편각측정 실험을 안성천에서 실시한 결과 유속 약 1.7 m/s 인 상황에서 편각 $20\;^{\circ}$ 까지 편각 $0\;^{\circ}$일때와 유사한 측정 성능을 보였다.

• Tunnel and Underground Space
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• v.30 no.5
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• pp.484-495
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• 2020

To numerically simulate the advance of EPB TBM, various type of numerical analysis methods have been adopted including discrete element method (DEM), finite element method (FEM), and finite difference method (FDM). In this paper, an EPB TBM driving model was proposed by using coupled DEM-FDM. In the numerical model, DEM was applied in the TBM excavation area, and contact properties of particles were calibrated by a series of triaxial tests. Since the ground around the excavation area was coupled with FDM, the horizontal stress considering the coefficient of earth pressure at rest could be applied. Also, the number of required particles was reduced and the efficiency of the analysis was increased. The proposed model can control the advance rate and rotational speed of the cutter head and screw conveyor, and derive the torque, thrust force, chamber pressure, and discharging during TBM tunnelling.