Ultrasonic Vibration Assisted Cutting of Nomex Honeycomb Core Materials

Dao‑Hui Xiang,Bang‑Fu Wu,Yun‑Long Yao,Bo Zhao,Jin‑Yuan Tang 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.1

Nomex honeycomb core materials have been widely used in the aviation industry due to their special structure and performance. Conventional high-speed machining have resulted in the poor machinability of the honeycomb core so that the ultrasonic machining technology was applied. The kinematic characteristics in the ultrasonic vibration assisted cutting process were analyzed according to the movement of the sharp tool. Based on slide effect, a cutting force model was proposed to study the relationship between cutting parameters and cutting force. Ultrasonic vibration assisted cutting and ordinary cutting tests of Nomex honeycomb core material were conducted by considering feed rate, the inclined angle and the deflected angle. Besides, the effects of cutting parameters on machined surface quality of honeycomb core wall were studied. The test results show that slide effect caused by ultrasonic vibrations can reduce cutting resistance compared with ordinary cutting. The developed cutting force model can be applied to evaluated the cutting force in the ultrasonic vibration assisted cutting of Nomex honeycomb core material. The inclined angle has a great influence on the cutting force during ultrasonic vibration assisted cutting. High-speed reciprocating sliding action can effectively cut aramid fibers so that burrs and tearing defects of the incision have been greatly improved under condition of ultrasonic vibration assisted cutting.

Influence of Rain Gauge Density and Temporal Resolution on the Performance of Conditional Merging Method

Dao,Duc Anh,Kim,Soohyun,Kim,Tae-Woong,Kim,Dongkyun 한국방재학회 2019 한국방재학회논문집 Vol.19 No.6

본 연구는 in-situ 강우자료와 레이더자료를 병합하는 조건부 합성(CM)기법의 성능 평가를 목표로 한다. 합성방법은 다음 단계를 통해 처리된다. (1) 정규 크리깅(OK) 기법은 관측소와 레이더 기반 크리깅 강우장을 얻기 위해 적용한다. (2) 보정 강우장은 원래 레이더 강우장에서 레이더기반 크리깅 강우장의 차로 계산한다. (3) 합성강우량은 관측소기반 크리깅 강우장에 보정 강우장을 더하여 도출한다. 분석결과는 CM기반 강우장이 조사된 모든 33개의 10분 강우장 중 22개 사례에 대해 관측소기반 강우장보다 더 정확한 것으로 나타났다. CM 방법과 관측소기반 OK기법의 상관계수는 각각 0.63과 0.83 그리고 0.01과 0.74 사이 값을 보인다. 두 방법의 성능은 관측소 밀도가 높고 시간해상도가 낮을수록 향상되었다. OK기법의 성능은 관측소 밀도에 더 민감하고, CM 기법의 성능은 시간해상도에 더 민감한 것으로 나타났다. 또한, 기존 관측소 밀도가 100 km2 당 1개 일 때, 관측소를 추가하면 두 방법의 성능이 크게 향상되었다. 관측소 증가에 의한 강우량 측정 개선 정도는 관측소 개수가 100 km2 당 4개 이상에 도달할 시 효과가 미미한 것으로 나타났다. This study aims to evaluate the performance of conditional merging (CM) technique to merge radar and in-situ rain gauge data. The merging method contains the following steps: (1) the ordinary kriging(OK) technique is applied to obtain the gauge-only and radar-only kriged rainfall fields; (2) the correction field is calculated by subtracting the radar-only kriged rainfall field from the original radar field; (3) the composite rainfall is derived by adding the correction field to the gauge-only kriged field. We investigated 33 10-min rainfall fields; there were 22 instances where the CM-based rainfall fields were more accurate than the gauge-only fields. The correlation coefficients of the CM and the gauge-only OK methods varied between 0.63 and 0.83, and 0.01 and 0.74 respectively. The performance of both methods improved with greater gauge density and coarser temporal resolution. Furthermore, the OK and CM techniques’performances were more sensitive to gauge density and temporal resolution respectively. We also found that the addition of gauge significantly improved the performance of both methods when the existing gauge density is approximately 1 gauge/100 km2. However, this effect is absent when the density reaches 4 gauges/100 km2.

A Study on Factor that Effect on Consumer’s Behaviour on Cross-Border E-Commerce in Vietnam - Ho Chi Minh City

Dao,Duy Thang,Hyun,In-Gyou 한국유통과학회 2019 KODISA ICBE (International Conference on Business Vol.2019 No.-

Vietnam E-commerce has been used and developed 10 years ago but recently, with removing tariff barriers, Vietnam’s customer can easily buy almost thing in the foreign web-site. However, little research has been done to study how to customer’s using intention on across national borders. This study aims to find the factors that effect to customer’s using intention on foreign direct online shopping. A conceptual model is developed from the perspectives of customer’s trust and value. We also examine the impact of information’s signal, security and safe, country image on customer’s trust, as well as the impact of benefits, innovation, cost on customer’s perceived value. This study use an online survey to make questionnaire about the factor and use the answer to test the research model. Our findings can help researchers and practitioners understand the barriers and behaviour of Ho Chi Minh City’s customers to cross-border e-commerce and devise strategies to make profit.

당송(唐宋)시기 도통(道統)내용의 전환 -당말(唐末)에서 북송(北宋)시기 도의 전승 내용에 관한 담론을 중심으로-

임명희 ( Myung Hee Lim ) 한국철학사연구회 2013 한국 철학논집 Vol.0 No.36

住居移動의 理念的 모델 定立

韓大鉉 강릉대학교 영동산업문제연구소 1985 産經論叢 Vol.4 No.-

Stewardship Theory and Information on Family Firm Performance in Vietnam

Thi Thanh Binh DAO(Thi Thanh Binh DAO ),Linh Chi HOANG(Linh Chi HOANG ) 한국유통과학회 2022 유통과학연구 Vol.20 No.12

Purpose: The paper contributes to the existing literature on Vietnamese corporate governance and firm performance with a focus on listed family firms and the use of a more suitable econometric framework to analyze firm performance. The study investigates how family firm performance is affected by corporate governance under the standpoint of stewardship theory in Vietnam. Research design, data and methodology: With the use of different measures for firm performance (Tobin’s Q, ROA, and ROE), regression models were estimated using Generalized Least Square (GLS) method on a panel data of a total of 113 listed companies during the five-year period from 2015 to 2019. Results: We found that family ownership as the main characteristic of the stewardship theory affects family firms positively. In addition, several other characteristics in corporate governance as board composition (board independence, board audits, and board committees), CEO (age and tenure) and firm characteristics (size, age, expansion, and annual sales) showed significant impacts on firm performance. Our findings also suggest that family firm performance can be either positively or negatively affected based on the characteristics of corporate governance. The findings can help companies evaluate the significance of corporate governance through deciding board structure and the selection of CEOs to match family firm characteristics. It also gives insights for investors, rating agencies, and policymakers for relevant purposes.

Passive control of railway vehicle car body flexural vibration by means of underframe dampers

Dao Gong,Jinsong Zhou,Wenjing Sun 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.2

To suppress vertical flexural vibration of a railway vehicle car body, a new passive control method by mounting dampers on the longitudinal beams of the car body underframe is proposed. The method is firstly studied by an Euler-Bernoulli beam model using Green’s functions, then it is further verified by a nonlinear dynamic model of the vehicle. Results show that the car body flexural vibration can be noticeably reduced by this method. It is better to mount the damper near the car body centre. The higher damping coefficient of the damper, the more effective in decreasing the car body first vertical bending vibration. The higher the rigidity of the damper bracket and rubber bush, the better performance of the damper. It is found that when mounting six dampers at proper positions, the damping coefficient of each damper is 1.33×10 7 N·s/m, even if the first vertical bending frequency of the studied car body is only 7.2 Hz, a very good ride quality will be achieved when the vehicle runs at 250 km/h.

Adaptive Grey Predictor-based Controller for Force Control of EHA System

Dao Thanh Liem,Bui Ngoc Minh Truong,Kyoung Kwan Ahn 제어로봇시스템학회 2016 제어로봇시스템학회 국제학술대회 논문집 Vol.2016 No.10

This study aims to develop an effective control approach for force control of a typical EHA system. This control scheme is considered as an advanced combination of a feedforward neural network – based PID (FNNPID) controller and a fuzzy grey predictor (FGP), shortened as feedforward neural network fuzzy grey predictor (FNNFGP). Here, the FNNPID controller is used to drive the system to desired targets. Meanwhile, the FGP predictor with self-tuning ability of the predictor step size takes part in, first, estimating the system output in the near future to optimize the controller parameters in advance and, second, creating a compensating control signal accordingly to the system perturbations and, consequently, improving the control performance. Real-time experiments have been carried out to investigate the effectiveness of the proposed control approach.

Terpenylated coumarins as SIRT1 activators isolated from Ailanthus altissima.

Dao, Trong-Tuan,Tran, Tien-Lam,Kim, Jayeon,Nguyen, Phi-Hung,Lee, Eun-Hee,Park, Junsoo,Jang, Ik-Soon,Oh, Won-Keun American Society of Pharmacognosy ; American Chemi 2012 Journal of natural products Vol.75 No.7

<P>Four new terpenylated coumarins (1-4) were isolated from the stem bark of Ailanthus altissima by bioactivity-guided fractionation using an in vitro SIRT1 deacetylation assay. Their structures were identified as (2'R,3'R)-7-(2',3'-dihydroxy-3',7'-dimethylocta-6'-enyloxy)-6,8-dimethoxycoumarin (1), 6,8-dimethoxy-7-(3',7'-dimethylocta-2',6'-dienyloxy)coumarin (2), (2'R,3'R,6'R)-7-(2',3'-dihydroxy-6',7'-epoxy-3',7'-dimethyloctaoxy)-6,8-dimethoxycoumarin (3), and (2'R,3'R,4'S,5'S)-6,8-dimethoxy-7-(3',7'-dimethyl-4',5'-epoxy-2'-hydroxyocta-6'-enyloxy)coumarin (4). Compounds 1-4 strongly enhanced SIRT1 activity in an in vitro SIRT1-NAD/NADH assay and an in vivo SIRT1-p53 luciferase assay. These compounds also increased the NAD-to-NADH ratio in HEK293 cells. The present results suggest that terpenylated coumarins from A. altissima have a direct stimulatory effect on SIRT1 deacetylation activity and may serve as lead molecules for the treatment of some age-related disorders.</P>

Estimating People's Position Using Matrix Decomposition

Dao, Thi-Nga,Yoon, Seokhoon The Institute of Internet 2019 International journal of advanced smart convergenc Vol.8 No.2

Human mobility estimation plays a key factor in a lot of promising applications including location-based recommendation systems, urban planning, and disease outbreak control. We study the human mobility estimation problem in the case where recent locations of a person-of-interest are unknown. Since matrix decomposition is used to perform latent semantic analysis of multi-dimensional data, we propose a human location estimation algorithm based on matrix factorization to reconstruct the human movement patterns through the use of information of persons with correlated movements. Specifically, the optimization problem which minimizes the difference between the reconstructed and actual movement data is first formulated. Then, the gradient descent algorithm is applied to adjust parameters which contribute to reconstructed mobility data. The experiment results show that the proposed framework can be used for the prediction of human location and achieves higher predictive accuracy than a baseline model.