The Effect of Lubricant Containing Copper Alloy Nano-Powder on a Diesel Engine

The characteristic of a lubricant is very important when it is used under severe running condition. Especially on diesel engines the better lubrication performance is required because of the extreme condition such as high temperature and pressure by combustion process in a cylinder. Many researches work for improving a boundary lubrication performance have been executed by using solid lubricant but this general lubricant has not been applied to engine due to the extreme condition of high temperature and pressure in a cylinder. Recently, the solid lubricant which contained a copper nickel alloy has been introduced and studied. In this study, the author investigated the effects of lubricant which contains the copper nickel alloy nano-powder on a diesel engine performance. The results were manifested to show the increase of maximum torque, and the decrease of cylinder pressure, exhaust gas temperature, scavenging air temperature, CO emission according to running time lapse at various speed and torque on a diesel engine. It was assured that the lubricant which contains the copper nickel alloy nano-powder decreases friction and wear, and simultaneously increases the sealing effect in a cylinder on diesel engines.목차 Abstract = iii 제1장 서론 = 1 제2장 윤활유 및 첨가제 = 4 2.1 기관의 윤활 = 4 2.1.1 윤활상태 = 5 2.1.2 윤활유의 기능 = 6 2.1.3 윤활유의 조건 = 7 2.2 첨가제의 종류 = 8 2.3 첨가제의 특성 = 10 2.3.1 청정분산제 = 10 2.3.2 산화방지제 및 마모방지제 = 12 2.3.3 점도지수향상제 = 13 2.4 나노구리합금첨가 윤활제 = 15 제3장 실험장치 및 계측장치 = 17 3.1 실험장치 = 17 3.1.1 대상기관 = 17 3.1.2 냉각계통 = 21 3.2 계측장치 = 22 3.2.1 동력측정장치 = 24 3.2.2 배기가스분석기 = 26 3.2.3 실린더내 압력검출장치 = 28 3.2.4 연료소비율 측정장치 = 30 제4장 실험결과 및 고찰 = 31 4.1 최대토크 = 32 4.2 실린더내 연소 최고압력 = 33 4.3 연료소비율 = 38 4.4 배기가스온도 = 42 4.5 급기온도 = 45 4.6 배기배출물 = 48 4.6.1 NOx의 배출농도 = 48 4.6.2 CO의 배출농도 = 51 4.6.3 O₂의 농도 = 55 4.6.4 스모크의 배출농도 = 58 제5장 결론 = 61 참고문헌 = 6

미세 물체 수송을 위한 니티놀 마이크로 로봇

학위논문(석사) -- 서울대학교대학원 : 공과대학 기계공학과, 2021.8. 안성훈.A micro-robot is an attractive tool that performs micro-scale tasks within the system by remote control. Most micro-robots are driven by an external force and its characteristic differs according to the type of the external force. Therefore, micro-robots have been developed to utilize the type of external force suitable for their respective application fields. Among various external forces, a light-driven micro-robot has superior controllability in terms of precision and regionality. Recently, lots of studies have been conducted on micro-robot for performing micro-scale tasks in bio-medical fields such as drug transport, surgery and diagnosis. Especially in micro-object transportation, since sophisticated control is required, a light-driven micro-robot which has excellent controllability is advantageous. Micro-robots for transportation so far have focused on force, speed and control, but a few of them have a function of holding objects to avoid object loss. Our micro-object transportation Ni-Ti structure robot(MTNs) not only has sufficient thrust force and speed but also has the capability of holding objects and physically separating them from external systems, thus demonstrating the advantage of excellent transport stability and controllability. It can be fabricated and controlled automatically by a vision-guided laser control system. In consideration of mass production, we designed the micro-robot so that the fabrication process has low cost in terms of time, price and labor, and can be operated by commercial equipment. The newly designed transport micro-robot, which displays holding capability and enhanced control, can be used as an actuator in lab-on-a-chip testing.마이크로 로봇은 원격 제어를 통해 시스템 내에서 미세작업을 수행할 수 있는 도구로써, 약물 수송, 수술, 진단과 같은 생물 의학 분야에서 많 은 연구가 진행되고 있다. 마이크로 로봇은 외력을 통해 에너지를 공급 받고, 제어되므로, 이용하는 외력의 종류에 따라 구동 특성이 달라진다. 여러 외력 중 광 구동형 마이크로 로봇은 정밀하고 국소적인 제어가 가 능하다는 장점을 가지고 있다. 그러므로 정교한 제어가 필요한 마이크로 물체 운반 작업에 광구동형 마이크로 로봇이 적합하다. 지금까지 운송용 마이크로 로봇은 힘, 속도 및 제어에 중점을 두었지만, 물체 유실을 방 지하기 위해 물체를 잡는 기능을 가진 로봇은 거의 없습니다. 우리가 개 발한 미세 물체 수송 Ni-Ti 마이크로 로봇은 충분한 추진력과 속도를 가질 뿐만 아니라 운반 목표 물체를 포획한 상태로 외부 시스템과 격리 한 상태로 운반할 수 있는 능력을 갖추고 있어 우수한 수송 안정성과 제 어 편의성 등 이점을 보인다. 본 로봇은 비전 유도 레이저 제어 시스템에 의해 자동으로 제작이 가능 하다. 양산을 고려하여 상용장비 만으로 제작 공정을 구성하였으며, 시 간, 가격 그리고 노동력 측면에서 저렴하도록 마이크로 로봇을 설계하였 다. 포획 능력과 향상된 제어 기능을 가진 본 로봇은 랩 온어 칩 테스트 에서 액추에이터로 사용될 수 있다.Chapter 1. Introduction 1 1.1. Reviews on micro robots for bio-medical applications 1 1.2. Reviews on micro transportation 3 1.3. Reviews on micro robots using external forces 4 1.4. Reviews on light-driven Ni-Ti micro robots 5 1.5. Purpose of research 7 Chapter 2. Ni-Ti Unit 8 2.1. Actuation mechanism 8 2.2. Fabrication of Ni-Ti unit 10 Chapter 3. Fabrication process 11 3.1. Overview of fabrication process 11 3.2. Formation morphing control 13 3.2.1. Single unit control 13 3.2.2. Vision-guided laser control system 15 3.2.3. Control strategy 17 3.3. Bonding process 19 3.3.1. Adhesion applying using EHD 19 3.3.2. Adhesion applying using microstage 22 Chapter 4. Experiment and Application 23 4.1. Force measurement experiment 23 4.2. Energy efficiency comparison 25 4.3. Functionality of transportation 27 Chapter 5. Conclusion 29 Bibliography 30 Abstract in Korean 35석

Microchannel network hydrogel induced ischemic blood perfusion connection

Angiogenesis induction into damaged sites has long been an unresolved issue. Local treatment with pro-angiogenic molecules has been the most common approach. However, this approach has critical side effects including inflammatory coupling, tumorous vascular activation, and off-target circulation. Here, the concept that a structure can guide desirable biological function is applied to physically engineer three-dimensional channel networks in implant sites, without any therapeutic treatment. Microchannel networks are generated in a gelatin hydrogel to overcome the diffusion limit of nutrients and oxygen three-dimensionally. Hydrogel implantation in mouse and porcine models of hindlimb ischemia rescues severely damaged tissues by the ingrowth of neighboring host vessels with microchannel perfusion. This effect is guided by microchannel size-specific regenerative macrophage polarization with the consequent functional recovery of endothelial cells. Multiple-site implantation reveals hypoxia and neighboring vessels as major causative factors of the beneficial function. This technique may contribute to the development of therapeutics for hypoxia/inflammatory-related diseases.ope

Utility of Diffusion and Magnetization Transfer MRI in Cervical Spondylotic Myelopathy: A Pilot Study

Diffusion tensor imaging (DTI) and magnetization transfer (MT) magnetic resonance imaging (MRI) can help detect spinal cord pathology, and tract-specific analysis of their parameters, such as fractional anisotropy (FA), mean diffusivity, axial diffusivity (AD), radial diffusivity (RD) and MT ratio (MTR), can give microstructural information. We performed the tract-based acquisition of MR parameters of three major motor tracts: the lateral corticospinal (CS), rubrospinal (RuS) tract, and lateral reticulospinal (RS) tract as well as two major sensory tracts, i.e., the fasciculus cuneatus (FC) and spinal lemniscus, to detect pathologic change and find correlations with clinical items. MR parameters were extracted for each tract at three levels: the most compressed lesion level and above and below the lesion. We compared the MR parameters of eight cervical spondylotic myelopathy patients and 12 normal controls and analyzed the correlation between clinical evaluation items and MR parameters in patients. RuS and lateral RS showed worse DTI parameters at the lesion level in patients compared to the controls. Worse DTI parameters in those tracts were correlated with weaker power grasp at the lesion level. FC and lateral CS showed a correlation between higher RD and lower FA and MTR with a weaker lateral pinch below the lesion level.ope

Surgical Ligation of Patent Ductus Arteriosus Using the Descending Aortic Approach in Two Dogs

Surgical ligation is the treatment of the choice in patients with patent ductus arteriosus (PDA). This case series presents two cases of PDA, one with and one without persistent left cranial vena cava (PLCVC), treated with surgical ligation through the descending aortic approach with mini-thoracotomy. There were no specific complications during the surgical procedures. The descending aortic approach would be an alternative method for dissection of the PDA.ope

Clinical Characteristics and Risk Factors of First-Ever Stroke in Young Adults: A Multicenter, Prospective Cohort Study

Stroke in young adults has catastrophic consequences and has increased in prevalence, contrary to the trends of most other diseases. This study aimed to determine the major characteristics and risk factors for stroke in younger adults compared with older adults. From the Korean Stroke Cohort for Functioning and Rehabilitation, 10,584 patients with first-ever stroke between August 2012 and March 2015 were enrolled retrospectively and divided into younger (age ≤ 45) and older groups (age > 45). The clinical characteristics and risk factors of stroke were compared between the younger and older groups. The younger group comprised 915 patients (8.6%). The proportion of hemorrhage strokes in the younger group (42.3%) was significantly higher than in the older group (20.0%) (p < 0.001). Obesity, current smoking, and heavy alcohol consumption were significantly more common risk factors in the younger group than in the older group for all stroke types, whereas hypertension, diabetes mellitus, hyperlipidemia, atrial fibrillation, and coronary heart disease were significantly more frequent in the older group (both p < 0.001). The major risk factors in the younger group may be lifestyle-related. Therefore, increasing awareness of lifestyle-related risk factors may be necessary to prevent stroke in young adults.ope

Changes in Bihemispheric Structural Connectivity Following Middle Cerebral Artery Infarction

This study investigated the changes in the structural connectivity of the bilateral hemispheres over time following a middle cerebral artery infarction. Eighteen patients in the subacute group and nine patients in the chronic group with mild upper extremity motor impairment (Fugl-Meyer motor assessment score for the upper limb > 43) following middle cerebral artery infarction were retrospectively evaluated in this study. All the patients underwent T1-weighted and diffusion tensor imaging. Tract-based statistical analyses of fractional anisotropy were used to compare the changes in the bilateral structural connectivity with those of age-matched normal controls. The corticospinal tract pathway of the affected hemisphere, corpus callosum, and corona radiata of the unaffected hemisphere had decreased structural connectivity in the subacute group, while the motor association area and anterior corpus callosum in the bilateral frontal lobes had increased structural connectivity in the chronic group. The bilateral hemispheres were influenced even in patients with mild motor impairment following middle cerebral artery infarction, and the structural connectivity of the bilateral hemispheres changed according to the time following the stroke.ope

Development and accuracy evaluation of field soil temperature prediction model by depth using artificial intelligence and meteorological parameters

학위논문(석사) -- 서울대학교대학원 : 농업생명과학대학 바이오시스템공학과, 2022.2. 이중용.Precise agricultural technology that analyzes weather, soil environment and crop information using various advanced technologies, minimizes resource use, and maximizes productivity, needs to be applied in the field, but it is difficult to control the environment due to the influence of external weather. In the case of this, the efficiency is low compared to the cost of the equipment, so there are few cases where it is applied to the actual agricultural environment. Of these, soil is directly involved in crop growth, so it is essential to acquire soil environment data for the normal growth of crops. Because it is important information, it is necessary to acquire data according to depth. In this study, as a way to acquire soil temperature data by depth without the cost of measuring equipment, we made a model that predicts soil temperature by depth over time using artificial intelligence, and compares the predicted value derived through the model with the actual value. and, it was reviewed whether it can be applied to actual agriculture. Time unit geothermal data at three depths of 10 cm, 20 cm, and 30 cm using three machine learning models, RNN, LSTM, and GRU, and five meteorological factors: temperature, humidity, wind direction, wind speed, and insolation, which were judged to have an influence on the geothermal temperature. The optimal combination of parameters and models to accurately predict Confirmed. And, the applicability to actual agricultural activities was judged by confirming the similarity of the predicted values ​​made from the two combinations evaluated as having the best performance through pattern analysis and residual analysis with the actual values. Evaluation was made through the values ​​of three indicators: Root Mean Square Error (RMSE), Nash - Sutcliffe Efficiency (NSE), and Determination Coefficient (). As a result of the experiment, the combination of parameters and models using temperature, humidity, wind speed, solar radiation, average monthly temperature data and LSTM model showed the highest performance. and temperature, humidity, wind speed, insolation, soil temperature data by depth in other regions, and the parameter and model combination using the RNN model showed the second highest performance. In addition, as a result of residual analysis with the measured values, it was confirmed that the residuals were normal and the outlier rate at all depths was around 1%. Both the predicted values ​​of the two datasets and model combinations selected through the experimental process were judged to show high agreement with the actual values ​​through evaluation index, pattern analysis, and residual analysis, and were evaluated as applicable to actual agricultural activities.각종 첨단 기술을 활용하여 기상, 토양 환경 및 작물 정보를 분석하고 자원의 사용을 최소화하며 생산성을 극대화하는 정밀농업 기술이 노지에서도 적용되어야 할 필요가 있지만 외부 기상의 영향을 많이 받아 환경제어가 어려운 노지의 경우 발생되는 장비의 비용에 비해 효율성이 낮아 실제 농업환경에 적용되는 사례가 적다. 이 중 토양은 농작물 생장에 직접적으로 관여하므로 작물의 정상적 생장을 위해 토양 환경 데이터를 습득하는 것은 필수적이며, 토양온도 데이터의 경우 비료 시비, 관수, 농작업 일정 등 농업활동의 여러 의사결정을 하는데 필요한 중요한 정보이기 때문에 깊이에 따른 데이터를 습득하는 것이 필요하다. 본 연구에서는 계측장치에 발생되는 비용 없이 깊이별 토양온도 데이터를 습득하기 위한 방편으로 인공지능을 활용하여 시간에 따른 깊이별 토양온도를 예측하는 모델을 만들고 모델을 통해 도출된 예측값을 실측값과 비교하여 실제 농업에 적용이 가능한지 검토하였다. RNN, LSTM, GRU 세 개의 머신러닝 모델과 지온에 영향력을 미칠 것이라 판단되었던 기온, 습도, 풍향, 풍속, 일사량 다섯 가지 기상인자를 활용하여 10cm, 20cm, 30cm 세 곳의 깊이에서의 시간 단위 지온 데이터를 정확하게 예측하는 최적의 매개변수와 모델 조합을 선정하였고, 시간에 따라 주기성을 갖는 월평균기온, 실시간 태양고도, 타지역 깊이별 토양온도 데이터 세 가지 주기성 인자를 추가하여 정확도 상승에 기여하는지 그 여부를 확인하였다. 그리고 가장 성능이 좋다고 평가된 두 개 조합으로부터 만들어진 예측값을 실측값과의 패턴분석과 잔차분석을 통해 유사성을 확인하여 실제 농업활동에 적용 가능성을 판단하였다. 평가는 Root Mean Square Error(RMSE), Nash - Sutcliffe Efficiency(NSE), Determination Coefficient() 세 가지 지표의 값을 통해 이루어졌다. 실험 결과 기온, 습도, 풍속, 일사량, 월평균기온 데이터와 LSTM 모델을 활용한 매개변수와 모델 조합이 가장 높은 성능을 보였고, 기온, 습도, 풍속, 일사량, 타지역의 깊이별 토양온도 데이터와 RNN 모델을 활용한 매개변수와 모델 조합이 다음으로 높은 성능을 보였으며, 실측값과의 잔차분석 결과 잔차의 정규성이 있으며 모든 깊이에서의 이상치율이 1% 내외로 나타나는 것을 확인하였다. 실험 과정을 통해 선별된 두 데이터세트, 모델 조합의 예측값 모두 평가 지표, 패턴분석, 잔차분석을 통해 실측값과 높은 일치성을 보인다고 판단되며, 실제 농업활동에 적용 가능하다고 평가하였다.1. 서론 1 1.1. 연구배경 1 1.2. 문제점과 필요성 4 1.3. 연구목적 5 2. 문헌조사 6 2.1. 용어와 관련 이론 6 2.1.1 기상인자 매개변수 6 2.1.1.1. 기온 6 2.1.1.2. 습도 6 2.1.1.3. 풍향 및 풍속 7 2.1.1.4. 일사량 8 2.1.2. 주기성을 나타내는 매개변수 8 2.1.2.1. 전국 월평균기온 9 2.1.2.2. 태양고도 10 2.2. 지온의 특성 11 2.3. 지온이 작물생육 미치는 영향 16 2.4. 노지 스마트팜에서의 환경모니터링 연구 18 2.5. 노지에서 깊이별 지온데이터 예측 연구 21 2.6. 시계열데이터 예측을 위한 연구 24 3. 재료 및 방법 26 3.1. 공공기상자료 확보 28 3.1.1. 공공기상대 데이터 28 3.1.2. 학습용 데이터의 전처리 29 3.2. 지온예측 평가용 지온데이터 30 3.2.1. 외부기상대 및 토양센서 30 3.3. 매개변수 선정 33 3.4. 인공지능 모델 선정과 학습 34 3.5. 깊이별 지온 예측 절차 및 평가 방법 37 4. 결과 38 4.1. 기상인자 데이터를 이용한 최적의 매개변수 선택 38 4.1.1. 소거를 이용한 기상인자 영향력 순서 평가 38 4.1.2. 전진 선택법을 통한 기상인자 최적의 매개변수 조합 선택 51 4.2. 주기성변수 62 4.3. 데이터 비교 및 분석 74 4.3.1. 추세 비교 74 4.3.1.1. 10cm 75 4.3.1.2. 20cm 80 4.3.1.3. 30cm 85 4.3.2. 잔차 분석 90 4.3.2.1. Q-Q Plot을 이용한 정규성 진단 90 4.3.2.2. 표준화 잔차를 이용한 이상치 검출 91 4.3.2.2.1. 예측값A 92 4.3.2.2.2. 예측값B 95 5. 결론 97 6. 참고문헌 100석

Brain Connectivity Affecting Gait Function After Unilateral Supratentorial Stroke

Gait dysfunction is a leading cause of long-term disability after stroke. The mechanisms underlying recovery of gait function are unknown. We retrospectively evaluated the association between structural connectivity and gait function in 127 patients with unilateral supratentorial stroke (>1 month after stroke). All patients underwent T1-weighted, diffusion tensor imaging and functional ambulation categorization. Voxel-wise linear regression analyses of the images were conducted using fractional anisotropy, mean diffusivity, and mode of anisotropy mapping as dependent variables, while the functional ambulation category was used as an independent variable with age and days after stroke as covariates. The functional ambulation category was positively associated with increased fractional anisotropy in the lesioned cortico-ponto-cerebellar system, corona radiata of the non-lesioned corticospinal tract pathway, bilateral medial lemniscus in the brainstem, and the corpus callosum. The functional ambulation category was also positively associated with increased mode of anisotropy in the lesioned posterior corpus callosum. In conclusion, structural connectivity associated with motor coordination and feedback affects gait function after stroke. Diffusion tensor imaging for evaluating structural connectivity can help to predict gait recovery and target rehabilitation goals after stroke.ope

3D Bioprinted Artificial Trachea with Epithelial Cells and Chondrogenic-Differentiated Bone Marrow-Derived Mesenchymal Stem Cells

Tracheal resection has limited applicability. Although various tracheal replacement strategies were performed using artificial prosthesis, synthetic stents and tissue transplantation, the best method in tracheal reconstruction remains to be identified. Recent advances in tissue engineering enabled 3D bioprinting using various biocompatible materials including living cells, thereby making the product clinically applicable. Moreover, clinical interest in mesenchymal stem cell has dramatically increased. Here, rabbit bone marrow-derived mesenchymal stem cells (bMSC) and rabbit respiratory epithelial cells were cultured. The chondrogenic differentiation level of bMSC cultured in regular media (MSC) and that in chondrogenic media (d-MSC) were compared. Dual cell-containing artificial trachea were manufactured using a 3D bioprinting method with epithelial cells and undifferentiated bMSC (MSC group, n = 6) or with epithelial cells and chondrogenic-differentiated bMSC (d-MSC group, n = 6). d-MSC showed a relatively higher level of glycosaminoglycan (GAG) accumulation and chondrogenic marker gene expression than MSC in vitro. Neo-epithelialization and neo-vascularization were observed in all groups in vivo but neo-cartilage formation was only noted in d-MSC. The epithelial cells in the 3D bioprinted artificial trachea were effective in respiratory epithelium regeneration. Chondrogenic-differentiated bMSC had more neo-cartilage formation potential in a short period. Nevertheless, the cartilage formation was observed only in a localized area.ope