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.

Optimization of OFDMA-Based Cellular Cognitive Radio Networks

Ma, Yao,Kim, Dong In,Wu, Zhiqiang IEEE 2010 IEEE TRANSACTIONS ON COMMUNICATIONS Vol.58 No.8

<P>In this paper, we study the coexistence and optimization of a multicell cognitive radio network (CRN) which is overlaid with a multicell primary radio network (PRN). We propose a PRN-willingness-based design framework for coexistence and subchannel sharing, and a Lagrange duality based technique to optimize the weighted sum rate (WSR) of secondary users (SUs) over multiple cells. First, to avoid unacceptable SU interference to primary users (PUs), the PRN determines its interference margin based on its target performance metric and channel conditions, and broadcasts this information to the CRN. Second, each CRN cell optimizes its WSR and implements intercell iterative waterfilling (IC-IWF) to control the intercell interference. To account for the interference and transmit power limits at SUs, multilevel waterfilling (M-WF) and direct-power truncation (DPT) duality schemes are developed. Third, we develop a serial dual update technique which enables low-complexity and fast-convergence of the proposed duality schemes. Numerical results demonstrate the effects of multiple parameters, such as the number of SUs per cell, subchannel occupancy probability (SOP), and outage probability of the PUs. Our results show that the proposed duality schemes provide a large performance enhancement than the channel-greedy and access-fairness based resource allocation schemes.</P>

Rate-maximization scheduling schemes for uplink OFDMA

Yao Ma,Dong In Kim IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.6

<P>In this paper, we propose and study several sum rate maximization algorithms for uplink orthogonal frequency division multiple access (OFDMA). For uplink scheduling without fairness consideration, we propose two Lagrangian duality optimization-based methods to maximize the weighted sum rate, which include a cyclic dual-update algorithm and a per-stage dual-update algorithm. For a low-complexity alternative, we design and analyze the transmit power and signal-to-noise ratio (SNR) product (PSP) based selective multiuser diversity (SMuD) schemes. Next, for fair scheduling, we propose rate maximization schemes under access proportional fairness (APF) and rate proportional fairness (RPF) constraints, respectively. The APF is achieved using normalized channel SNR (n-SNR) ranking-based SMuD for user selection per carrier, and the RPF is realized using dynamical carrier assignment based on the target rate ratios. Analytical throughput and fairness metrics are derived and verified via simulations. Numerical results illustrate the sum rate loss caused by rate fairness and access fairness constraints compared to the duality approach. Also, we show that unlike the downlink case, for uplink OFDMA the correlated frequency channels (carriers) cause significant ergodic sum rate degradation compared to the independent channels. These results provide new insight into the achievable uplink OFDMA performance with and without fairness constraints.</P>

Review and Prospect of Anti-Americanism in the Middle East

Yao Jide,Ma Run,Ma Yuting 아시아사회과학학회 2021 Jornal of Asia Social Science Vol.3 No.2

Since the end of World War II, Anti-Americanism has emerged and permeated the international community as a kind of social and political ideological trend that negates the American government s foreign policy and its values. After the end of the Cold War, the anti-Americanism has been particularly prominent and presented a trend of continuous escalation in the Middle East. People and parts of the government in the area have strongly criticized the values advocated by the US. This western-style democracy, freedom, and equality are centered around the Anglo-Saxon culture. Anti-Americanism in the Middle East become a social ideological trend and behaviour with hatred to combat and protest against the American political system in hegemonic diplomacy, long-standing partiality for Israel, and double standards on human rights. Thus, a joint of terrorism activities of individuals and institutions has arisen constantly to aim at United States and its overseas relations. Anti-Americanism in the Middle East has a strong Islamic flavor. Religious extremists often distort religious teachings to mobilize society, and blind followers often resort to extremist activities or even terrorist acts. Anti-Americanism in the Middle East has its multidimensional roots. In the new era, after the upheaval of the Arab Spring, the agitation of the Islamic State and the implementation of the Trump administration s policy of America first with one axis and two wings (Liu, 2019) in the Middle East, the anti- Americanism in the Middle East is bound to continue to heat up and many changes may occur.

Storage strategies for containers in container yards

Yao Wen Ma,Su Min Jeon,Kap Hwan Kim 대한산업공학회 2008 대한산업공학회 춘계학술대회논문집 Vol.2008 No.5

Container storage problem is a critical issue for the efficient operation of container terminal. The storage yard in the study is horizontal layout, in which one quay crane is served by several yard cranes and one vessel is served by several blocks during vessel operation. This study addresses various storage strategies for horizontal container lay yard layout. The storage strategies include the strategy for selecting blocks, reserving spaces for a group of containers in advance, and selecting yard stacks. The proposed strategies are tested by a simulation study.

A High Throughput Multiple Transform Architecture for H.264/AVC Fidelity Range Extensions

Ma, Yao,Song, Yang,Ikenaga, Takeshi,Goto, Satoshi The Institute of Electronics and Information Engin 2007 Journal of semiconductor technology and science Vol.7 No.4

In this paper, a high throughput multiple transform architecture for H.264 Fidelity Range Extensions (FRExt) is proposed. New techniques are adopted which (1) regularize the $8{\times}8$ integer forward and inverse DCT transform matrices, (2) divide them into four $4{\times}4$ sub-matrices so that simple fast butterfly algorithm can be used, (3) because of the similarity of the sub-matrices, mixed butterflies are proposed that all the sub-matrices of $8{\times}8$ and matrices of $4{\times}4$ forward DCT (FDCT), inverse DCT (IDCT) and Hadamard transform can be merged together. Based on these techniques, a hardware architecture is realized which can achieve throughput of 1.488Gpixel/s when processing either $4{\times}4\;or\;8{\times}8$ transform. With such high throughput, the design can satisfy the critical requirement of the real-time multi-transform processing of High Definition (HD) applications such as High Definition DVD (HD-DVD) ($1920{\times}1080@60Hz$) in H.264/AVC FRExt. This work has been synthesized using Rohm 0.18um library. The design can work on a frequency of 93MHz and throughput of 1.488Gpixel/s with a cost of 56440 gates.

Storage strategies for containers in container yards

Yao Wen Ma,Su Min Jeon,Kap Hwan Kim 한국경영과학회 2008 한국경영과학회 학술대회논문집 Vol.2008 No.5

Container storage problem is a critical issue for the efficient operation of container terminal. The storage yard in the study is horizontal layout, in which one quay crane is served by several yard cranes and one vessel is served by several blocks during vessel operation. This study addresses various storage strategies for horizontal container lay yard layout. The storage strategies include the strategy for selecting blocks, reserving spaces for a group of containers in advance, and selecting yard stacks. The proposed strategies are tested by a simulation study.

A High Throughput Multiple Transform Architecture for H.264/AVC Fidelity Range Extensions

Yao Ma,Yang Song,Takeshi Ikenaga,Satoshi Goto 대한전자공학회 2007 Journal of semiconductor technology and science Vol.7 No.4

In this paper, a high throughput multiple transform architecture for H.264 Fidelity Range Extensions (FRExt) is proposed. New techniques are adopted which (1) regularize the 8×8 integer forward and inverse DCT transform matrices, (2) divide them into four 4 × 4 sub-matrices so that simple fast butterfly algorithm can be used, (3) because of the similarity of the sub-matrices, mixed butterflies are proposed that all the sub-matrices of 8 × 8 and matrices of 4×4 forward DCT (FDCT), inverse DCT (IDCT) and Hadamard transform can be merged together. Based on these techniques, a hardware architecture is realized which can achieve throughput of 1.488Gpixel/s when processing either 4×4 or 8×8 transform. With such high throughput, the design can satisfy the critical requirement of the real-time multi-transform processing of High Definition (HD) applications such as High Definition DVD (HD-DVD) (1920x1080@60Hz) in H.264/AVC FRExt. This work has been synthesized using Rohm 0.18um library. The design can work on a frequency of 93MHz and throughput of 1.488Gpixel/s with a cost of 56440 gates.

Simulating Strength Parameters and Size Effect of Stochastic Jointed Rock Mass using DEM Method

Chong Ma,Wenmin Yao,Yuan Yao,Jun Li 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.12

The strength parameters and the size effect of stochastic jointed limestone rock mass is investigated in this paper. Based on extensive statistics of joint parameters of rock mass in the research region, the probable distribution of geometric characteristic parameters of discontinuities are obtained by the probability graph method. Then the Monte-Carlo method is used for discontinuities network modeling. In addition, 3DEC software and its built-in FISH programming language are used to establish the stochastic jointed rock mass network model based on discrete element method. Triaxial numerical simulation tests under variable confining pressure are conducted with different model sizes and dip angles of bedding planes. The numerical simulation results indicate that the jointed rock mass exhibits weak anisotropy property and significant size effect when it is cut by stochastic discontinuities; the mechanical strength parameters of rock mass begins to fluctuate distinctly as the model size increases, and tend to be stable once the model size reaches or exceeds 4 m × 4 m × 8 m. Besides, the comprehensive mechanical parameters of rock mass in the research region are determined and failure modes of rock mass are analyzed as well based on the numerical simulation results.

On The Way of Becoming Expert-SSU Student Journalist`s Self-Directed Learning

( Jie Yao Ma ),( Tsung Jen Shih ) 한국체육학회 2015 국제스포츠과학 학술대회 Vol.2015 No.1

Purpose: It is important to equip our students with the requisite skills they need to become professional. However, currently there is a discrepancy between what journalism education provides and what the industry needs. The crux of this problem lies in the missing of strategic procedural knowledge in journalism education. Upon realizing this hiatus in journalism education, the researcher develops this study, to examining the Self-Directed Leaning (SDL) mechanism adopted by the Student Sports Union (SSU). From the result of this study, the researcher gather already graduated SSU journalists` SDL experience, and to convert these tacit knowledge into documentation for future generations of young journalism graduates to refer to. Method: To discover extra knowledge regarding to SSU journalists` learning experience, and to understand their SDL process comprehensively, the researcher employed semi-structured in-depth interview in this study. The selection of interviewees focus on gradated SSUs` actual performance while they were in the organization, and their career performance after they graduated. Result: Through constantly accessing authentic sports events, SSU student journalists are better able to combine theory and practice together. The SDL journey allows students to proceduralize their knowledge from "knowing what" (declarative knowledge) to "knowing how" (procedural knowledge), and move towards the path of becoming expert. According to the result of the study, SSU`s SDL matches with Spear`s interactive model. This means (1). Opportunities people find in their own environments. (2). Past or new knowledge. And (3). Chance occurrences are three important elements for SSU journalists to form their SDL. Conclusion: To survive in the dynamic environment of journalism, it is important to provide students more practical trainings for them to bridge the gap between theory and practice. In this case, SDL is a useful method for students to gain the knowledge, skill and experience they need to become professional.