Effect of the TiO2 Nanoparticles on the Growth Behavior of Intermetallics in Sn/Cu Solder Joints

Shengyan Shang,Anil Kunwar,Jinye Yao,Yanfeng Wang,Haitao Ma,Yunpeng Wang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.2

In order to investigate the effect of TiO2 nanoparticles on growth behavior of interfacial Cu6Sn5 intermetallics compounds(IMCs) in Pb-free Sn/Cu system, the solder joints are fabricated by using flux doped with different content (0.0–2.0 wt% offlux) and particle diameter (5 nm and 50 nm) of TiO2 . In context of isothermal reflow soldering at 250 °C and subsequentair cooling, the increase in reflow duration from 10 to 120 s was characterized with an increment in IMC layer thicknessand grain size, due to the enhancement of Cu flux contribution for Ostwald ripening during constant temperature reflow andprecipitation kinetics during cooling. The increased proportion of TiO2 nanoparticles in flux was found to reduce the growthof IMC layer and grain size. The suppression effect on IMC was more pronounced for 5 nm particles as compared to the 50nm TiO2 . The TiO2 nanoparticles, adsorbed on IMC plane can retard the growth of the latter. Presence of sufficient amountof a given sized TiO2 nanoparticles among IMCs, by increasing the effective stress at the localized interfaces, and causingthe breaking of brittle Cu6Sn5 during growth stage; can help in the inhibition of IMC whisker formation. Particle diameterand mass proportion of TiO2 nanoparticles are important for soldering materials design.

Reactive Power Compensation Game Under Prospect-Theoretic Framing Effects

Wang, Yunpeng,Saad, Walid,Sarwat, Arif I.,Hong, Choong Seon IEEE 2018 IEEE transactions on smart grid Vol.9 No.5

<P>Reactive power compensation is an important challenge in smart power systems. However, in the context of reactive power compensation, most existing studies assume that customers can assess their compensation value (their Var unit) objectively. In this paper, customers are assumed to make decisions that pertain to reactive power coordination. In consequence, the way in which those customers evaluate the compensation value resulting from their individual decisions will impact the overall grid performance. In particular, a behavioral framework, based on the framing effect of prospect theory (PT), is developed to study the impact of both objective value and subjective evaluation in a reactive power compensation game. For instance, PT’s framing effect allows customers to optimize a subjective value of their utility which essentially frames the objective utility with respect to a reference point. This game enables customers to coordinate the use of their electrical devices to compensate reactive power. For the proposed game, both the objective case using expected utility theory and the PT consideration are solved via a learning algorithm that converges to a mixed-strategy Nash equilibrium. In addition, several key properties of this game are derived analytically. Simulation results show that, under PT, customers are likely to make decisions that differ from those predicted by classical models. For instance, using an illustrative two-customer case, we show that a PT customer will increase the adoption of a conservative strategy (achieving a high power factor) by 29% compared to a conventional customer. Similar insights are also observed for a case with three customers.</P>

Finite-time Issue of Discrete-time Linear Switched Systems With Partial Finite-time Unstable Modes Based on an Inverse Weighted Switching Scheme

Yunpeng Zhan,Ruihua Wang,Shumin Fei 제어·로봇·시스템학회 2024 International Journal of Control, Automation, and Vol.22 No.2

The work proposes a multiple convex Lyapunov function and an inverse weighted switching scheme to investigate the finite-time stability and finite-time boundedness for a class of discrete-time switched linear systems with partial finite-time unstable modes. A multiple convex Lyapunov function is put forth by constructing a convex combination of positive definite matrices, which can relax the restricted conditions of the Lyapunov function and make it carry more decision variables than traditional Lyapunov function methods. Besides, the inverse weighted switching scheme is devised by summing the reciprocal of each dwell time with weighting coefficients, by which tighter dwell time bounds are ensured. On the basis of the new Lyapunov function and switching scheme, the finitetime control for a class of switched linear systems with partial finite-time unstable modes is addressed. Different from other researches that require all subsystems to be controllable, we only require the existence of one controllable subsystem. In the end, two numerical examples and a tunnel diode circuit example are provided to verify the effectiveness of the developed results.

Two-Dimensional POMDP-Based Opportunistic Spectrum Access in Time-Varying Environment with Fading Channels

Wang, Yumeng,Xu, Yuhua,Shen, Liang,Xu, Chenglong,Cheng, Yunpeng The Korea Institute of Information and Commucation 2014 Journal of communications and networks Vol.16 No.2

In this research, we study the problem of opportunistic spectrum access (OSA) in a time-varying environment with fading channels, where the channel state is characterized by both channel quality and the occupancy of primary users (PUs). First, a finite-state Markov channel model is introduced to represent a fading channel. Second, by probing channel quality and exploring the activities of PUs jointly, a two-dimensional partially observable Markov decision process framework is proposed for OSA. In addition, a greedy strategy is designed, where a secondary user selects a channel that has the best-expected data transmission rate to maximize the instantaneous reward in the current slot. Compared with the optimal strategy that considers future reward, the greedy strategy brings low complexity and relatively ideal performance. Meanwhile, the spectrum sensing error that causes the collision between a PU and a secondary user (SU) is also discussed. Furthermore, we analyze the multiuser situation in which the proposed single-user strategy is adopted by every SU compared with the previous one. By observing the simulation results, the proposed strategy attains a larger throughput than the previous works under various parameter configurations.

GOP Adaptation Coding of H.264/SVC Based on Precise Positions of Video Cuts

( Yunpeng Liu ),( Renfang Wang ),( Huixia Xu ),( Dechao Sun ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.7

Hierarchical B-frame coding was introduced into H.264/SVC to provide temporal scalability and improve coding performance. A content analysis-based adaptive group of picture structure (AGS) can further improve the coding efficiency, but damages the inter-frame correlation and temporal scalability of hierarchical B-frame to different degrees. In this paper, we propose a group of pictures (GOP) adaptation coding method based on the positions of video cuts. First, the cut positions are accurately detected by the combination of motion coherence (MC) and mutual information (MI); then the GOP is adaptively and proportionately set by the analysis of MC in one scene. In addition, we propose a binary tree algorithm to achieve the temporal scalability of any size of GOP. The results for test sequences and real videos show that the proposed method reduces the bit rate by up to about 15%, achieves a performance gain of about 0.28-1.67 dB over a fixed GOP, and has the advantages of better transmission resilience and video summaries.

Review on Digital Image Watermarking Based on Singular Value Decomposition

Wang, Chengyou,Zhang, Yunpeng,Zhou, Xiao Korea Information Processing Society 2017 Journal of information processing systems Vol.13 No.6

With the rapid development of computer technologies, a number of image modification methods have emerged, which have great impacts on the security of image information. Therefore, it is necessary to protect the integrity and authenticity of digital images, and digital watermarking technique consequently becomes a research hotspot. An effort is made to survey and analyze advancements of image watermarking algorithms based on singular value decomposition (SVD) in recent years. In the first part, an overview of watermarking techniques is presented and then mathematical theory of SVD is given. Besides, SVD watermarking model, features, and evaluation indexes are demonstrated. Various SVD-based watermarking algorithms, as well as hybrid watermarking algorithms based on SVD and other transforms for copyright protection, tamper detection, location, and recovery are reviewed in the last part.

A model to characterize the effect of particle size of fly ash on the mechanical properties of concrete by the grey multiple linear regression

Yunpeng Cui,Jun Liu,Licheng Wang,Runqing Liu,Bo Pang 사단법인 한국계산역학회 2020 Computers and Concrete, An International Journal Vol.26 No.2

Fly ash has become an important component of concrete as supplementary cementitious material with the development of concrete technology. To make use of fly ash efficiently, four types of fly ash with particle size distributions that are in conformity with four functions, namely, S.Tsivilis, Andersen, Normal and F distribution, respectively, were prepared. The four particle size distributions as functions of the strength and pore structure of concrete were thereafter constructed and investigated. The results showed that the compressive and flexural strength of concrete with the fly ash that conforming to S.Tsivilis, Normal, F distribution increased by 5-10 MPa and 1-2 MPa, respectively, compared to the reference sample at 28 d. The pore structure of the concrete was improved, in which the total porosity of concrete decreased by 2-5% at 28 d. With regarding to the fly ash with Andersen distribution, it was however not conducive to the strength development of concrete. Regression model based on the grey multiple linear regression theory was proved to be efficient to predict the strength of concrete, according to the characteristic parameters of particle size and pore structure of the fly ash.

Review on Digital Image Watermarking Based on Singular Value Decomposition

Chengyou Wang,Yunpeng Zhang,Xiao Zhou 한국정보처리학회 2017 Journal of information processing systems Vol.13 No.6

With the rapid development of computer technologies, a number of image modification methods haveemerged, which have great impacts on the security of image information. Therefore, it is necessary to protectthe integrity and authenticity of digital images, and digital watermarking technique consequently becomes aresearch hotspot. An effort is made to survey and analyze advancements of image watermarking algorithmsbased on singular value decomposition (SVD) in recent years. In the first part, an overview of watermarkingtechniques is presented and then mathematical theory of SVD is given. Besides, SVD watermarking model,features, and evaluation indexes are demonstrated. Various SVD-based watermarking algorithms, as well ashybrid watermarking algorithms based on SVD and other transforms for copyright protection, tamperdetection, location, and recovery are reviewed in the last part.

Two-Dimensional POMDP-Based Opportunistic Spectrum Access in Time-Varying Environment with Fading Channels

Yumeng Wang,Yuhua Xu,Liang Shen,Chenglong Xu,Yunpeng Cheng 한국통신학회 2014 Journal of communications and networks Vol.16 No.2

In this research, we study the problem of opportunisticspectrum access (OSA) in a time-varying environment with fadingchannels, where the channel state is characterized by bothchannel quality and the occupancy of primary users (PUs). First,a finite-state Markov channel model is introduced to represent afading channel. Second, by probing channel quality and exploringthe activities of PUs jointly, a two-dimensional partially observableMarkov decision process framework is proposed for OSA. In addition,a greedy strategy is designed, where a secondary user selects achannel that has the best-expected data transmission rate to maximizethe instantaneous reward in the current slot. Compared withthe optimal strategy that considers future reward, the greedy strategybrings low complexity and relatively ideal performance. Meanwhile,the spectrum sensing error that causes the collision betweena PU and a secondary user (SU) is also discussed. Furthermore,we analyze the multiuser situation in which the proposed singleuserstrategy is adopted by every SU compared with the previousone. By observing the simulation results, the proposed strategy attainsa larger throughput than the previous works under variousparameter configurations.

Research on Design Method of Modularized Configuration for Cluster Order Demand

Ge Jianghua,Wang Yaping,Gao Lei,Shi Yunpeng 보안공학연구지원센터(IJUNESST) 2013 International Journal of u- and e- Service, Scienc Vol.6 No.4