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.

试论朝鲜核武化的逻辑路径——基于冷战后朝鲜半岛核安全 结构变化趋势的思考

Ma, Yunpeng,이성일 부산대학교 중국연구소 2017 Journal of China Studies Vol.20 No.2

After the Cold War, there are two major trends of the nuclear security structure on the Korean Peninsula: Firstly, North Korea has tried to replace the peninsula "one-way nuclear deterrent" structure with "asymmetric nuclear deterrent" structure, and form a "non-balanced nuclear deterrent" structure to strengthen nuclear weapons activities step by step; Secondly, the United States has been vigorously intervened in the Asia-Pacific affairs, implementing the "Asia-Pacific rebalancing" strategy, and taking the DPRK nuclear activities as a reason to strongly promote the missile defense system building in the East Asian region especially in the South Korea. Both of them are the result of the vicious interaction of safety in Korean peninsula, which may eventually change the nuclear security structure of Northeast Asia overall. North Korea's nuclear weaponization services as one of the core security issues of the Korean Peninsula after the Cold War, which is the result of the vicious interaction between the internal and external elements of the Korean Peninsula security structure. After the third nuclear test, the DPRK had taken the nuclear weapons as a strategic issue instead of tactical chips, which had been causing the Korean Peninsula security dilemma around the DPRK nuclear issue increasingly difficult to resolve. The study on the internal logic of the DPRK's nuclear issue may contribute to find negotiating space in a seemingly unexplained security dilemma. There are two basic forces which have been driving North Korea for nuclear power. On the one hand, it’s trying to reduce the possibility of waging "hot war" by the Korea-US alliance to maintain regime and system security through establishing an "asymmetric nuclear deterrent" structure with them. On the other hand, they try to weaken South Korea's dominance of the Korean Peninsula reunification issue and strive for the reciprocity on it. Under the impetus of the two major powers, the DPRK gradually built a prototype structure of the "asymmetric nuclear deterrent" against the ROKUS alliance after five nuclear tests. The structure of "nuclear deterrence without power equilibrium" is concerned with the steady growth of conventional armaments on the basis of steady economic development. This “nuclear deterrent” structure, legally defending the regime and system security, is the ultimate goal of North Korea's nuclear-weapon effort. If the DPRK regime eventually did not "collapse" under the internal and external pressure, it would work towards this ultimate goal. THAAD taken into the ROK may produce an illusion for the North Korea, that the nuclear weapons from the DPRK had formed an "asymmetric nuclear deterrent" structure with the KoreanAmerican alliance at least in the psychological level. THAAD may be taken as an excellent evidence by the North Korea, that the Korean-American alliance began to take strong reaction and hedge measures to deal with the new security structure in Korean Peninsula. When the North Korea believes that the "asymmetric nuclear deterrent" structure had been established and would not be broken in a short term, its nuclear activities will gradually enter into the "Nuclear Deterrence without Power Equilibrium "structural construction period. During the construction phase of the "Nuclear Deterrence without Power Equilibrium ", the nuclear weapons development will gradually give way to the conventional armaments promotion, at the same time, economic development which services as the prerequisite of conventional armaments promotion would become the basis and core work of the DPRK. At this stage, North Korea's demand for economic development is both a subjective desire and an objective necessity. Economic issues will provide a huge space for negotiating space to break the peninsula security dilemma.

冷战后影响韩半岛局势走向的基本变量

馬雲鵬(Yunpeng Ma),朴鍵一(Jianyi Piao) 국제지역연구학회 2014 국제지역학논총 Vol.7 No.2

The basic trend on the Korean Peninsula after the Cold War changes around the reunification issues, and manifested in the North-South relations evolution and the schedule change of the nuclear issue. The North-South relation changes serve as the most fundamental variables affect the situation on the Korean Peninsula situation, as well as, the reunification issue tops in the North-South relations. Furthermore, the uniform policies from the two sides contribute the most to the reunification; especially the Korean policy towards the DPRK plays the core role in the Korean Peninsula situation. In the North-South relations interactions, international influences from China, the US and other big powers around still exists and continues to occupy the structural important position. The North-South relations determine the basic trend on the Korean Peninsula after the Cold War with the influence from the big powers around.

Production of Tween 80-inducing Esterase by Acinetobacter sp. B1 Using Response Surface Methodology

Ma, Peiyu,Li, Yuqi,Miao, Chensi,Sun, Yunpeng,Liu, Chunhui,Li, Huijuan The Korean Society for Microbiology and Biotechnol 2019 한국미생물·생명공학회지 Vol.47 No.1

Esterase produced by Acinetobacter sp. B1 (strain B1) was optimized by means of one-variable-at-a-time and response surface methodologies. Results of the one-variable-at-a-time experiment showed that Tween 80 significantly increased esterase production of strain B1. The addition of Tween 80 to the culture medium increased the biomass and esterase activity of strain B1, stimulated content of total extracellular protein, and enhanced the oleic acid (C18:1) composition in the cell membrane of strain B1. The influence of eight culture variables on esterase production was evaluated by Plackett-Burman design. Results showed that Tween 80, pH, and $K_2HPO_4$ significantly affected the esterase production of strain B1. Tween 80, pH, and $K_2HPO_4$ were further optimized by central composite design. Under the optimized conditions (w/v, soluble starch 2.5%, tryptone 1.5%, Tween 80 0.8%, $K_2HPO_4$ 0.5%, NaCl 0.5%, pH 8.0, inoculum size 1%, and inoculum age 24 h), the maximum esterase activity of strain B1 was 152.13 U/ml, which was 10-fold higher than that of non-optimization after 36 h cultivation.

Automatic Test Case Generation for BPEL Using Stream X-Machine

Chunyan Ma,Junsheng Wu,Tao Zhang,Yunpeng Zhang,Xiaobin Cai 보안공학연구지원센터(IJUNESST) 2008 International Journal of u- and e- Service, Scienc Vol.1 No.1

Production of Tween 80-inducing Esterase by Acinetobacter sp. B1 Using Response Surface Methodology

Peiyu Ma,Chensi Miao,Yunpeng Sun,Chunhui Liu,Hui-Juan Li 한국미생물·생명공학회 2019 한국미생물·생명공학회지 Vol.47 No.1

Esterase produced by Acinetobacter sp. B1 (strain B1) was optimized by means of one-variable-at-a-time and response surface methodologies. Results of the one-variable-at-a-time experiment showed that Tween 80 significantly increased esterase production of strain B1. The addition of Tween 80 to the culture medium increased the biomass and esterase activity of strain B1, stimulated content of total extracellular protein, and enhanced the oleic acid (C18:1) composition in the cell membrane of strain B1. The influence of eight culture variables on esterase production was evaluated by Plackett-Burman design. Results showed that Tween 80, pH, and K2HPO4 significantly affected the esterase production of strain B1. Tween 80, pH, and K2HPO4 were further optimized by central composite design. Under the optimized conditions (w/v, soluble starch 2.5%, tryptone 1.5%, Tween 80 0.8%, K2HPO4 0.5%, NaCl 0.5%, pH 8.0, inoculum size 1%, and inoculum age 24 h), the maximum esterase activity of strain B1 was 152.13 U/ml, which was 10-fold higher than that of non-optimization after 36 h cultivation.

The Concept Definition of “Northeast Asia” and the Analysis from Cultural Perspective

Jianyi Piao,Yunpeng Ma 국제지역연구학회 2014 국제지역학논총 Vol.7 No.1

동북아국제관계 연구 중에는 오랫동안 한가지 문제가 존재해오고 있다. 이는 바로 동북아의 개념과 그 지역 범위의 정의가 확실하지 않다는 것이다. 엄격한 지리학적 견해로는 이른바 “동북아” 지역이 존재하지 않지만, “동북아” 지역은 국제관계연구 중에서는 이미 지정학 개념으로 자리잡고 있다. 기존의 연구에서는 “동북아”의 내재적 의미, 즉, 동북아의 중심지역이 비교적 명확했지만, 그 경계는 매우 불분명했다. 본 논문에서는 “동북아”의 범위를 확정한 기초 위에서 이 지역의 지리적 분포 및 지정학적 특징에 대하여 연구 결론을 제시하였다. 또한 “동북아”는 하나의 지정학적 개념으로서 발전, 변화의 중요한 특징을 가지고 있다. 현재 동북아 지역의 각종 요소들의 상호 작용의 결과는 동북아의 지역 범위 및 문화형태 등 특징을 결정할 것이다. A problem long existing in the research of international relations in northeast Asia is the ambiguous definition of the concept of northeast Asia and its area limits. In the strict sense of geo-related science, there is no so-called “northeast Asia”. Rather, “northeast Asia” is a geo-concept that has been gradually developed in the research of international relations. Current research has basically defined the connotation of “northeast Asia”, namely, its central area, but not its denotation. Based on the longtime research, the relatively clear area limits of northeast Asia have been defined in this paper-the north, west and south boundaries are spherical lines, while the east is characterized by northeast-to-southwest spherical diagonal, which contributed to its overall appearance as a spherical trapezoid. This paper further generalizes the geo-related distributive characteristics of “Northeast Asia”, based on which the paper put forward the thesis―the geo-features and the geo-related distributive characteristics is one of the most stable and constant factors that determine the regional security of northeast Asia. As a geo-related concept, one of the most important features of “northeast Asia” is its character with development and changes, further explained, the current elements interactive results in Northeast Asia region would determine the scope, culture form and other features in the next stage of Northeast Asia.

Endothelial Progenitor Cells Correlated with Oxidative Stress after Mild Traumatic Brain Injury

Xintao Huang,Dahai Wan,Yunpeng Lin,Naizhao Xue,Jiehe Hao,Ning Ma,Xile Pei,Ruilong Li,Wenju Zhang 연세대학교의과대학 2017 Yonsei medical journal Vol.58 No.5

Purpose: Endothelial progenitor cells (EPCs) play a key role in tissue repair and regeneration. Previous studies have shown that infusion of human umbilical cord blood-derived endothelial colony-forming cells improves outcomes in mice subjected to experimentaltraumatic brain injury (TBI). However, the efficiency of cell transplantation is not satisfactory. Oxidative stress plays a significant role in the survival of transplanted cells following ischemic reperfusion injury. This observational clinical study investigatedthe correlation between the number of circulating EPCs and plasma levels of superoxide dismutase (SOD) and malonyldialdehyde(MDA). Materials and Methods: Peripheral blood samples were collected from 20 patients with mild TBI at day-1, day-2, day-3, day-4, and day-7 post TBI. The number of circulating EPCs and the plasma levels of SOD and MDA were measured. Results: The average of circulating EPCs in TBI patients decreased initially, but increased thereafter, compared with healthy controls. Plasma levels of SOD in TBI patients were significantly lower than those in healthy controls at day-4 post-TBI. MDA levels showed no difference between the two groups. Furthermore, when assessed on day-7 post-TBI, the circulating EPC number were correlated with the plasma levels of SOD and MDA. Conclusion: These results suggest that the number of circulating EPCs is weakly to moderately correlated with plasma levels of SOD and MDA at day-7 post-TBI, which may offer a novel antioxidant strategy for EPCs transplantation after TBI.

Geometrical Effects of Cu@Ag Core–Shell Nanoparticles Treated Flux on the Growth Behaviour of Intermetallics in Sn/Cu Solder Joints

Shengyan Shang,Anil Kunwar,Yanfeng Wang,Jinye Yao,Yingchao Wu,Haitao Ma,Yunpeng Wang 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.2

Solder ball of initial diameter 1.4 mm, was refl ow soldered with Cu substrate at 523.15 K using fl ux doped with Cu@Agcore–shell nanoparticles (NPs) in the proportion 0–2 wt%. The solders were then air cooled to room temperature. The use ofNPs, by reducing the base height (H) of the solder and enhanced the diameter (W) of the solder, caused an overall increase inthe spread ratio of the solder. The altered magnitudes of heat and mass transfer in these geometrically diff erent but constantvolume specimens were analyzed using fi nite element method. The occurrence of diff erential concentration gradient, radialthermal gradient and velocity magnitudes, in solders with diff ering geometry were numerically elaborated. The Cu6Sn5 intermetalliccompound (IMC) formed at the Cu/Sn interface, was obtained to be the thickest for the specimen using undopedfl ux, whereas it was found to be smallest for the sample processed with fl ux containing 0.5% NPs. From the growth kineticsstudy, it has been inferred that IMC thickness is linearly proportional to the geometrical parameter H and Wb , with b < 1.