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.

An Auto-Tuner for OpenCL Work-Group Size on GPUs

Dao, Thanh Tuan,Lee, Jaejin IEEE 2018 IEEE transactions on parallel and distributed syst Vol.29 No.2

<P>Tuning the kernel work-group size for GPUs is a challenging problem. In this paper, using the performance counters provided by GPUs, we characterize a large body of OpenCL kernels to identify the performance factors that affect the choice of a good work-group size. Based on the characterization, we realize that the most influential performance factors with regard to the work-group size include occupancy, coalesced global memory accesses, cache contention, and variation in the amount of workload in the kernel. By tackling the performance factors one by one, we propose auto-tuning techniques that selects the best work-group size and shape for GPU kernels. We show the effectiveness of our auto-tuner by evaluating it with a set of 54 OpenCL kernels on three different NVIDIA GPUs and one AMD GPU. On average, the auto-tuner needs to spend no more than 8 percent of the time required by an exhaustive search to find an optimal work-group size. The execution time of the selected sub-optimal work-group size is at most 1.14x slower than that of the optimal work-group size found by the exhaustive search, on average.</P>

N-tetradecane/Water Emulsion as a Low-cost Phase Change Material for Efficient Packaging and Shipping of Vaccines

Dao, Van-Duong,Choi, Ho-Suk The Korean Society of Clean Technology 2017 청정기술 Vol.23 No.3

This study presents the preparation of n-tetradecane-in-water emulsions with different weight ratios of n-tetradecane and water, and their potential application in packaging and shipping vaccines. The size and distribution of the n-tetradecane droplets are characterized using optical microscopy and light scattering methods, respectively. The thermal properties of the emulsions are determined using the T-history method. In the results, the emulsions, which are comprised of 17 ~ 30 wt% oil, 3 wt% surfactant, and 67 ~ 80 wt% water, are stable and have droplet sizes in the range of 100 to 800 nm. The thermal properties demonstrate that subcooling is prevented through increasing the droplet size. The results indicate that the n-tetradecane/water emulsions containing 25 ~ 35 wt% n-tetradecane, with a melting point of $2{\sim}8^{\circ}C$ and a latent heat of $227.0{\sim}250.8kJ\;kg^{-1}$, are good candidate materials for packaging and shipping vaccines.

Bank Capital Adequacy Ratio and Bank Performance in Vietnam: A Simultaneous Equations Framework

DAO, Binh Thi Thanh,NGUYEN, Kieu Anh Korea Distribution Science Association 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.6

Playing an important role in developing the economy and overall developments of the country, commercial banks have to be aware of their crucial presence in order to perform well and contribute significantly. At the same time, as a place to receive deposits, banks are required to be in safe situations to avoid bankruptcy or deal with financial crises. This research seeks to identify the determinants of Capital Adequacy Ratio and Banks' performance as well as the relationship between these two dependent variables. The paper uses 128 observations of 16 Vietnamese commercial banks during the period from 2010 to 2017, with two simultaneous dependent variables CAR and ROE, and independent variables including Return on Assets, Tobin Q, Credit growth, GDP growth, Equity to Deposits, Loans to Deposits, Bank size, Cost to Income, Liquidity risk, Provision for Loan loss ratio, Non-performing loans and Inflation. The results reveal that Capital Adequacy Ratio and Banks' Performance have statistically significant relationship and Credit growth, GDP growth, Equity-to-Deposit ratio and Cost-to-Income ratio all have significant effects on two dependent variables. The findings of this study suggest that commercial banks should control the respective elements in order to maintain adequate level of capital and also create effective performance.

Pilot power allocation for maximising the sum rate in massive MIMO systems

Dao, Hieu Trong,Kim, Sunghwan Institution of Electrical Engineers 2018 IET communications Vol.12 No.11

<P>In this study, the authors investigate the issue of pilot power allocation in multi-cell multi-user massive multiple-inputmultiple-output (MIMO) systems to maximize the sum rate. In contrast to conventional scheme that assigns equal pilot power for all users in the system, they assume that different users can be assigned different pilot powers while the total pilot power per cell is fixed. They show that when the number of BS antennas goes to infinity, the signal-to-interference-and-noise ratio of a user only depends on the large-scale fading and pilot power of users who have the same pilot sequence. From that they derive an optimization problem to maximize the total uplink achievable rate of a target cell and prove that this problem is convex, which can be solved by the well-known Lagrange multiplier method. They also propose an extended optimization problem that solves the issue of zero-pilot power in the original problem. Eventually, two algorithms corresponding to the original and extended optimization problems are proposed to obtain the optimized pilot power set for all users in the systems. Numerical results show that the proposed algorithms outperform the existing methods relating to pilot power allocation problem as well as conventional scheme.</P>