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Haifeng Chang,Lele Zhang,Weiyuan Dou,Haifeng Zhang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.2
For high-speed trains (HSTs), interface failures often occur in their aluminumPVC foam sandwich floor, the service life of which can affect the maintenance economy significantly. In this study, a floor model considering crushable foam layer and cohesive element was implemented to validate its bending behavior, with which the load-bearing capacity of actual floor structures under different loading conditions was analyzed. Accordingly, two strategies were presented for improving the load-bearing capacity of the floor: adding grid stiffened ribs on the aluminum layer and adjusting the layout of the supporting seats appropriately. The numerical simulation results indicated that the position of the maximum stress concentration was on the edge of the floor foam layer, and the limits of the load-bearing capacity were 50 and 575 kPa with respect to two operation conditions. By varying the supporting seats with different layouts or adding reinforced structures, the maximum stress and deflection in the critical zones were reduced significantly compared with those of the original design.
Design of Slot Structure and Pilot Pattern for Underwater Acoustic Downlink Channel below 10kHz
Jinhui Liu,Haifeng Yu,KyungHi Chang 한국통신학회 2016 한국통신학회 학술대회논문집 Vol.2016 No.1
Though underwater acoustic (UWA) channel is the most challenging due to its time varying and frequency selective characteristics, UWA communications draw lots of attention to satisfy the increasing demand of the various applications. In this paper, for the purpose of providing high data rate and reliable services for UWA communications, slot structure as well as the pilot pattern is designed based on the UWA channel characteristics below 10 kHz. MCS level for the downlink application is also optimized by the system performance evaluation at link-level.
A Survey on the Underwater Communication Network Projects
Woon Kim,Haifeng Yu,KyungHi Chang 한국통신학회 2014 한국통신학회 학술대회논문집 Vol.2014 No.1
The development on the underwater (UW) communication network for sea observation is on the rise due to increasing importance of its applications such as oceanography, marine commercial operation and military surveillance. This paper gives overview of several underwater communication network projects conducted by active member for the ocean studies such as U.S.A., Canada, Erope, and Japan. The UW projects for shallow sea observation include SEAWEB and PLUSNet, and deep sea observation project includes GEOSTAR. The network architecture and communication method for each project mentioned above are described in this paper. As introducing various kinds of projects, this paper can be a guidance for future research on underwater network project.
Case Study for Ship Ad-hoc Networks under a Maritime Channel Model in Coastline Areas
( Xin Su ),( Haifeng Yu ),( Kyunghi Chang ),( Seung-geun Kim ),( Yong-kon Lim ) 한국인터넷정보학회 2015 KSII Transactions on Internet and Information Syst Vol.9 No.10
ITU-R M.1842-1, as a well-known specification dedicated to maritime mobile applications, has standardized wireless transmission protocols according to the particular characteristics of a maritime communications scenario. A time division multiple access (TDMA) frame structure, along with modulation schemes to achieve a high data rate, has been described clearly in ITU-R M.1842-1. However, several specification items are still under “to be decided” status, which brings ambiguity to research works. In addition, the current version of ITU-R M.1842-1 is focused mainly on maritime transmissions in open-sea areas, where the cyclic prefix (CP) is set to zero and only 16-QAM is used in the multi-carrier (MC) system. System performance might be dramatically degraded in coastline areas due to the inter-symbol interference (ISI) caused by selective fading. This is because there is a higher probability that the signal will be reflected by obstacles in coastline areas. In this paper, we introduce the transmission resource block (TRB) dedicated to ITU-R M.1842-1 for a ship ad-hoc network (SANET), where the pilot pattern of TRB is based on the terrestrial trunked radio (TETRA). After that, we evaluated SANET performance under the maritime channel model in a coastline area. In order to avoid noise amplification and to overcome the ISI caused by selective fading, several strategies are suggested and compared in the channel estimation and equalization procedures, where the link-level simulation results finally validate our proposals.
Interference cancellation for non-orthogonal multiple access used in future wireless mobile networks
Su, Xin,Yu, HaiFeng,Kim, Wansoo,Choi, Chang,Choi, Dongmin Springer (Biomed Central Ltd.) 2016 Eurasip Journal on Wireless Communications and Net Vol.2016 No.-
<P>Non-orthogonal multiple access (NOMA) is suggested as a radio access candidate for future wireless mobile networks. It utilizes the power domain for user multiplexing on the transmitter side and adopts a successive interference cancellation (SIC) as the baseline receiver scheme, considering the expected mobile device evolution in the near future. However, recent research focuses more on the performance evaluation of NOMA in context of assuming the perfect SIC at receiver side. In order to clarify the performance gap between the perfect and the practical SIC in NOMA schemes, and to examine the possibility of applying NOMA with practical SIC, this paper investigates the performance of NOMA applying multi-input multi-output (MIMO) technology with zero-forcing (ZF) and minimum mean square error (MMSE) SIC schemes. We propose an analysis on error effects of the practical SIC schemes for NOMA and in addition propose an interference-predicted minimum mean square error (IPMMSE) IC by modifying the MMSE weight factor using interference signals. According to the IPMMSE IC and analysis of IC error effect, we further suggest the remaining interference-predicted MMSE (RIPMMSE) IC to cancel the remaining interference. The simulation results show that by considering practical IC schemes, the bit error rate (BER) is degraded compared with conventional orthogonal multiple access (OMA). This validates that the proposed IC schemes, which can predict the interference signals, provide better performance compared to NOMA with conventional ZF and MMSE IC schemes.</P>
Strategy for Fabricating Wafer-Scale Platinum Disulfide
Xu, Hongjun,Huang, Hsin-Pan,Fei, HaiFeng,Feng, Jiafeng,Fuh, Huei-Ru,Cho, Jiung,Choi, Miri,Chen, Yanhui,Zhang, Lei,Chen, Dengyun,Zhang, Duan,Coileá,in, Cormac Ó,Han, Xiufeng,Chang, Ching-Ra American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.8
<P>PtS<SUB>2</SUB> is a newly developed group 10 2D layered material with high carrier mobility, wide band gap tunability, strongly bound excitons, symmetrical metallic and magnetic edge states, and ambient stability, making it attractive in nanoelectronic, optoelectronic, and spintronic fields. To the aim of application, a large-scale synthesis is necessary. For transition-metal dichalcogenide (TMD) compounds, a thermally assisted conversion method has been widely used to fabricate wafer-scale thin films. However, PtS<SUB>2</SUB> cannot be easily synthesized using the method, as the tetragonal PtS phase is more stable. Here, we use a specified quartz part to locally increase the vapor pressure of sulfur in a chemical vapor deposition furnace and successfully extend this method for the synthesis of PtS<SUB>2</SUB> thin films in a scalable and controllable manner. Moreover, the PtS and PtS<SUB>2</SUB> phases can be interchangeably converted through a proposed strategy. Field-effect transistor characterization and photocurrent measurements suggest that PtS<SUB>2</SUB> is an ambipolar semiconductor with a narrow band gap. Moreover, PtS<SUB>2</SUB> also shows excellent gas-sensing performance with a detection limit of ∼0.4 ppb for NO<SUB>2</SUB>. Our work presents a relatively simple way of synthesizing PtS<SUB>2</SUB> thin films and demonstrates their promise for high-performance ultrasensitive gas sensing, broadband optoelectronics, and nanoelectronics in a scalable manner. Furthermore, the proposed strategy is applicable for making other PtX<SUB>2</SUB> compounds and TMDs which are compatible with modern silicon technologies.</P> [FIG OMISSION]</BR>