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Study of Graphene-based 2D-Heterostructure Device Fabricated by All-Dry Transfer Process
Tien, Dung Hoang,Park, Jun-Young,Kim, Ki Buem,Lee, Naesung,Choi, Taekjib,Kim, Philip,Taniguchi, Takashi,Watanabe, Kenji,Seo, Yongho American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.5
<P>We developed a technique for transferring graphene and hexagonal boron nitride (hBN) in dry conditions for fabrication of van der Waals heterostructures. The graphene layer was encapsulated between two hBN layers so that it was kept intact during fabrication of the device. For comparison, we also. fabricated the devices containing graphene on SiO2/Si wafer and graphene on hBN. Electrical properties of the devices were investigated at room temperature. The mobility of the graphene on SiO2 devices and graphene on hBN devices were 15 000 and 37 000 cm(2) V-1 s(-1), respectively, while the mobility of the sandwich structure device reached the highest value of similar to 1.00 000 cm(2) V-1 s(-1), at room temperature. The electrical measurements of the samples were carried out in air and vacuum environments. We found that the electrical properties of the encapsulated graphene devices remained at a similar level both in a vacuum and in air, whereas the properties of the graphene without encapsulation were influenced by the external environment.</P>
Self-adjusting on-line cutting condition for high-speed milling process
Tien-Dung Hoang,Quang-Vinh Nguyen,Van-Cuong Nguyen,Ngoc-Hien Tran 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.8
The paper presents an intelligent control system for self-adjusting on-line cutting condition for high speed machining (self-HSM) with considering the tool-wear amount to keep the machined product’s quality in allowable limit. For realizing the self-HSM, the empirical analysis of variance (ANOVA) and artifical neural network (ANN) are used. The ANOVA is used for generating the empirical functions which are used as the boundary condition as well as constraint evaluation. The ANN is used for generating the new optimal cutting condition. Then, the self-HSM updates this cutting condition on the real machine - HS Super MC500. The new optimal cutting parameter is sent to the controller for updating the new machining condition to keep the machined part’s quality. The integration of the empirical analysis and ANN enables generating the optimal cutting parameters correctly and efficiently for high-speed milling.
An Energy Harvester Based on a Bistable Origami Mechanism
Tien-Hoang Ngo,I-Ting Chi,Minh-Quang Chau,Dung-An Wang 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.2
This paper describes a vibration energy harvester based on an origami mechanism through piezoelectric energy conversion. The device is capable of broadband energy harvesting from low frequency ambient vibrations. This design utilizes bistability inherent in the waterbomb base origami structure to increase the bandwidth of its frequency response. The folding along the crease pattern of the origami mechanism can facilitate large bending deformations of piezoelectric films to generate high electric power output. The compact size and light weight of the origami mechanism render it convenient for integration into various hosts subjected to vibrations. Performance of the origami mechanism is investigated under external excitations with various vibration magnitudes and acceleration levels. This work demonstrates a scheme of broadband vibration energy harvesting by integration of an origami structure with piezoelectric materials. A high fractional bandwidth of 40% is attained under a sinusoidal excitation with a peak acceleration of 0.1 g.
Tien Ngoc DAO,Ha Thi Thu LE,Phuong Thi Mai CHU,Ngan Hoang PHAM,Trang Thi Dai LUONG,Dung Tri TRAN 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.12
Guided by a resource-based theory, this study is the first one that takes a quantitative approach to identify determinants of competitiveness of women-owned small and medium enterprises (SMEs) in Vietnam. The study employs time series data of Vietnamese SMEs extracted from the Vietnam Small and Medium Enterprises Survey conducted biennially from 2005 to 2015 in ten Vietnamese provinces. Firm competitiveness hereby is indicated by revenue, market share, profitability, and export volume. The research reveals a number of determining factors, of all, research and development, labor skills, business environment, technology investment are the most important factors, followed by capital and headcount. It is indicated that the determining factors have different influences on competitiveness obtained by different measurements. Therefore, it is based on specific targets and situations to make wise business decisions. The authors also make comparisons among groups of women-owned enterprises divided by their firm age, location, ownership, export, age, and educational background of business owners. The findings serve as critical empirical evidence and provide policy recommendations for improving the competitiveness of women-owned SMEs in Vietnam. The recommendations range from technology support, education and professional support for female entrepreneurs, access to capital and human resources to business environment improvement.
Dinh, To Xuan,Thuy, Le Khac,Tien, Nguyen Thanh,Dang, Tri Dung,Ho, Cong Minh,Truong, Hoai Vu Anh,Dao, Hoang Vu,Do, Tri Cuong,Ahn, Kyoung Kwan The Korean Society for Fluid Power and Constructio 2019 드라이브·컨트롤 Vol.16 No.2
Fuel cell hybrid electric vehicle is an attractive solution to reduce pollutants, such as noise and carbon dioxide emission. This study presents an approach for energy management and control algorithm based on energetic macroscopic representation for a fuel cell hybrid electric vehicle that is powered by proton exchange membrane fuel cell, battery and supercapacitor. First, the detailed model of the fuel cell hybrid electric vehicle, including fuel cell, battery, supercapacitor, DC-DC converters and powertrain system, are built on the energetic macroscopic representation. Next, the power management strategy was applied to manage the energy among the three power sources. Moreover, the control scheme that was based on back-stepping sliding mode control and inversed-model control techniques were deduced. Simulation tests that used a worldwide harmonized light vehicle test procedure standard driving cycle showed the effectiveness of the proposed control method.
TOXUAN DINH,Le Khac Thuy,Nguyen Thanh Tien,Tri Dung Dang,Cong Minh Ho,Hoai Vu Anh Truong,Hoang Vu Dao,Tri Cuong Do,안경관 사단법인 유공압건설기계학회 2019 드라이브·컨트롤 Vol.16 No.2
Fuel cell hybrid electric vehicle is an attractive solution to reduce pollutants, such as noise and carbon dioxide emission. This study presents an approach for energy management and control algorithm based on energetic macroscopic representation for a fuel cell hybrid electric vehicle that is powered by proton exchange membrane fuel cell, battery and supercapacitor. First, the detailed model of the fuel cell hybrid electric vehicle, including fuel cell, battery, supercapacitor, DC-DC converters and powertrain system, are built on the energetic macroscopic representation. Next, the power management strategy was applied to manage the energy among the three power sources. Moreover, the control scheme that was based on back-stepping sliding mode control and inversed-model control techniques were deduced. Simulation tests that used a worldwide harmonized light vehicle test procedure standard driving cycle showed the effectiveness of the proposed control method.
Hong Khanh Dieu Nguyen,Toan Dang Nguyen,Dung Ngoc Hoang,Duc Sy Dao,Thao Tien Nguyen,Limphirat Wanwisa,Lan Linh Hoang 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.2
Hydrotalcite-like compound containing metal cations such as Mg2+, Al3+ and Ni2+ was characterized using Ni K-edge EXAFS and in situ Ni K-edge XANES techniques for clarifying its bonding environment around Ni2+ sites and structure changes during calcination from room temperature to 550 oC, respectively. At the fixed molar ratio of Mg/Ni/Al of 2/1/1, the results obtained from EXAFS analysis showed a slight blue shift before and after the calcination at 550 oC and a reduction in white line peak; the best fits of the two samples revealed tiny change in coordination number about 7 for Ni-O path but considerable difference for Ni-Mg(Al) path from about 4.5 to 9.5, confirming a modification from brucite like to mixed oxide structure. On the other hand, bond distances of the Ni-O and Ni-Mg paths nearly fixed at about 2.06 Å to 3.0 Å reflected stability of the cationic bond order on each plane, but partial collapse and decomposition of the interlayer formed by water molecules and anion CO3 2− after the calcination. Linear combination fit extracted from the in situ Ni K-edge XANES also confirmed the changes along with the calcination such as slow and fast decreases of brucite fraction at 150 oC and 330 oC, respectively, in corresponding to the mixed oxide fraction increases. The achieved bonding structures were also applied to explain acid-base occurrence of the hydrotalcite-like material, especially the acid sites generated by different static charges along with the bonds. The explanation was illustrated by NH3-TPD method.
P122강 열화재의 소형펀치 크리프 평가 및 미세조직 분석
김범준 ( Bum Joon Kim ),김문기 ( Moon K Kim ),임병수 ( Byeong Soo Lim ),Hoang Tien Dung 대한금속·재료학회 2010 대한금속·재료학회지 Vol.48 No.1
This paper investigates the influence of aging time on creep properties via a small punch creep test and evaluates the microstructural change of P122 steel at 600℃. The area fraction of precipitates was quantitatively analyzed to identify the relationship between the creep rupture life and precipitates. The coarsening behavior of precipitates along the grain boundaries was also investigated for various aging times. It is found that this coarsening behavior led to a loss of solution hardening and resulted in a hardness drop and a reduction of creep life.