Formation and resettlement of (AuxNi1−x)Sn4 in solder joints of ball-grid-array packages with the Au/Ni surface finish

The interfacial reactions between eutectic PbSn solder and the solder ball pads with the Au/Ni surface finish were studied. Solder joints subjected to up to three repeated reflow-and-aging treatments were examined. For the reflow, the peak reflow temperature was 225°C, and the reflow time was 115 s. Each aging process was performed at 160°C for 500 h. After the first reflow, all the Au would disappear from the interface, and formed many (Au_xNi_1−x)Sn₄ particles inside the solder joints. The value of x was between 0.99 and 0.75. In addition, there was a thin layer of Ni₃Sn₄ (1.4 μm) at the interface. After one reflow and one subsequent aging, most of the (Au_xNi_1−x)Sn₄ would relocate from inside the solder joint to the interface, and the value of x for (Au_xNi_1−x)Sn₄ at the interface decreased to 0.45. This (Au_xNi_1−x)Sn₄ resettlement process repeated itself for additional reflow-aging cycles. More reflow-aging treatments, however, made the microstructure of (Au_0.45Ni_0.55)Sn₄ at the interface become more non-planar. It was shown that gravitational effect was not the driving force for the resettlement of (Au_xNi_1−x)Sn₄. It is proposed that the driving force is for (Au_xNi_1−x)Sn₄ to seek Ni at the interface so that it can become more Ni-rich. In other words, the driving force is lowering the Gibbs energy of (Au_xNi_1−x)Sn₄ by dissolving more Ni. A decomposition-diffusion mechanism is proposed to explain what happened. Kinetic rationales for this rapid resettlement of (Au_xNi_1−x)Sn₄ at such a low temperature were also discussed.     

Anti-Excitotoxic Effects of N-Butylidenephthalide Revealed by Chemically Insulted Purkinje Progenitor Cells Derived from SCA3 iPSCs

Spinocerebellar ataxia type 3 (SCA3) is characterized by the over-repetitive CAG codon in the ataxin-3 gene (ATXN3), which encodes the mutant ATXN3 protein. The pathological defects of SCA3 such as the impaired aggresomes, autophagy, and the proteasome have been reported previously. To date, no effective treatment is available for SCA3 disease. This study aimed to study anti-excitotoxic effects of n-butylidenephthalide by chemically insulted Purkinje progenitor cells derived from SCA3 iPSCs. We successfully generated Purkinje progenitor cells (PPs) from SCA3 patient-derived iPSCs. The PPs, expressing both neural and Purkinje progenitor’s markers, were acquired after 35 days of differentiation. In comparison with the PPs derived from control iPSCs, SCA3 iPSCs-derived PPs were more sensitive to the excitotoxicity induced by quinolinic acid (QA). The observations of QA-treated SCA3 PPs showing neural degeneration including neurite shrinkage and cell number decrease could be used to quickly and efficiently identify drug candidates. Given that the QA-induced neural cell death of SCA3 PPs was established, the activity of calpain in SCA3 PPs was revealed. Furthermore, the expression of cleaved poly (ADP-ribose) polymerase 1 (PARP1), a marker of apoptotic pathway, and the accumulation of ATXN3 proteolytic fragments were observed. When SCA3 PPs were treated with n-butylidenephthalide (n-BP), upregulated expression of calpain 2 and concurrent decreased level of calpastatin could be reversed, and the overall calpain activity was accordingly suppressed. Such findings reveal that n-BP could not only inhibit the cleavage of ATXN3 but also protect the QA-induced excitotoxicity from the Purkinje progenitor loss.     

GaAsSb/InAlAs PA DHBTs Grown by Production MBE

The epi material growth of GaAsSb based DHBTs with InAlAs emitters are investigated using a 4×100mm multi-wafer production Riber 49 MBE reactor fully equipped with real-time in-situ sensors including an absorption band edge spectroscope and an optical-based flux monitor.The state-of-the-art hole mobilities are obtained from 100nm thick carbon-doped GaAsSb.A Sb composition variation of less than ±0.1 atomic percent across a 4×100mm platen configuration has been achieved.The large area InAlAs/GaAsSb/InP DHBT device demonstrates excellent DC characteristics,such as BV_CEO＞6V and a DC current gain of 45 at 1kA/cm2 for an emitter size of 50μm×50μm.The devices have a 40nm thick GaAsSb base with p-doping of 4.5E19cm-3.Devices with an emitter size of 4μm×30μm have a current gain variation less than 2% across the fully processed 100mm wafer.f_t andf_max are over 50GHz,with a power efficiency of 50%,which are comparable to standard power GaAs HBT results.These results demonstrate the potential application of GaAsSb/InP DHBT for power amplifiers and the feasibility of multi-wafer MBE for mass production of GaAsSb-based HBTs.     

Systematic optical and x-ray study of In x Ga1−x As on InP

We present a systematic study of In _x Ga_1−x As on InP grown by molecular beam epitaxy using the characterization techniques of Fourier transform photoluminescence, x-ray diffraction, micro-Raman spectroscopy, and photoreflectance spectroscopy. The four techniques were used to determine and correlate the fundamental parameters of band-gap energy, phonon frequency and composition. Comparing room temperature (293 K) PL and low temperature PL indicate the presence of a partially ionized acceptor with binding energy of about 13 meV in the unintentionally doped material. Double crystal x-ray diffraction (XRD) using a symmetric <400> and asymmetric <224> reflections was also employed. The use of two reflections gives precise lattice constants, composition, and extent of film relaxation. Micro-Raman spectroscopy was used to measure phonon frequencies in the In _x Ga_1−x As films and correlated to XRD composition. Room temperature photoreflectance (PR) was used to determine band-gap energy for both the low and intermediate field cases. Band gap energies determined at room temperature by PL and PR were in agreement within experimental error.     

A learning style classification mechanism for e-learning

With the growing demand in e-learning, numerous research works have been done to enhance teaching quality in e-learning environments. Among these studies, researchers have indicated that adaptive learning is a critical requirement for promoting the learning performance of students. Adaptive learning provides adaptive learning materials, learning strategies and/or courses according to a student’s learning style. Hence, the first step for achieving adaptive learning environments is to identify students’ learning styles. This paper proposes a learning style classification mechanism to classify and then identify students’ learning styles. The proposed mechanism improves k-nearest neighbor (k-NN) classification and combines it with genetic algorithms (GA). To demonstrate the viability of the proposed mechanism, the proposed mechanism is implemented on an open-learning management system. The learning behavioral features of 117 elementary school students are collected and then classified by the proposed mechanism. The experimental results indicate that the proposed classification mechanism can effectively classify and identify students’ learning styles.     

IEEE802．15．4的MAC协议实现

IEEE802.15.4协议是无线传感网中多采用的一种低速率、低功耗、低成本的无线通信协议.Imote2是Intel公司推出的高集成度的无线传感器平台.文中介绍了Imote2平台以及IEEE802.15.4协议,及网络驱动程序的体系结构,给出了实现IEEE802.15.4的MAC协议过程中的关键函数,还对MAC协议实现中的中断服务响应以及时钟等关键问题进行了描述.并分别对节点的工作性能及组网时节点的性能及损耗进行了测试,给出了系统的性能.结果显示,该种实现方法有效地保证了系统的性能并且可以达到无线传感网组网需求.     

Application of persulfate to remediate petroleum hydrocarbon-contaminated soil: feasibility and comparison with common oxidants

In this study, batch experiments were conducted to evaluate the feasibility of petroleum-hydrocarbon contaminated soil remediation using persulfate oxidation. Various controlling factors including different persulfate and ferrous ion concentrations, different oxidants (persulfate, hydrogen peroxide, and permanganate), and different contaminants (diesel and fuel oil) were considered. Results show that persulfate oxidation is capable of treating diesel and fuel oil contaminated soil. Higher persulfate and ferrous ion concentrations resulted in higher diesel degrading rates within the applied persulfate/ferrous ion molar ratios. A two-stage diesel degradation was observed in the batch experiments. In addition, treatment of diesel-contaminated soil using in situ metal mineral activation under ambient temperature (e.g., 25°C) may be a feasible option for site remediation. Results also reveal that persulfate anions could persist in the system for more than five months. Thus, sequential injections of ferrous ion to generate sulfate free radicals might be a feasible way to enhance contaminant oxidation. Diesel oxidation efficiency and rates by the three oxidants followed the sequence of hydrogen peroxide>permanganate>persulfate in the limited timeframes. Results of this study indicate that the application of persulfate oxidation is a feasible method to treat soil contaminated by diesel and fuel oil.     

Microstructure and Optical Properties of Tantalum Modified TiO<Subscript>2</Subscript> Thin Films Prepared by the Sol–Gel Process

Tantalum doped TiO₂ thin films ((TiO₂)_1−x (Ta₂O₅) _x , x=0, 0.1%, 0.3%, 0.5%, 0.8%) were prepared on ITO-coated substrates by means of the sol–gel method and spin coating technology followed by rapid thermal annealing treatment (RTA). The effects of various processing parameters, including Ta content (x=0–0.8%) and annealing temperature, on the growth and properties of thin films were investigated. Structural characteristics by X-ray diffraction analysis indicated that the doping of Ta₂O₅ in the TiO₂ without change the anatase structure of TiO₂ thin films. The optical transmittance of (TiO₂)_1−x (Ta₂O₅) _x thin films decrease from 50% down to 20% with increasing the Ta₂O₅ concentrations from x=0.00 to x=0.8%. The absorption coefficient shows energy gap were decreased with increasing Ta₂O₅ content from 2.932 eV for x=0.00 to 2.717 eV for x=0.8%. Doping TiO₂ with Ta₂O₅ can lower its band gap and shift its optical response to the visible region.     

The Development of a Distributed Surface Machining System

1 Introduction Owing to the drastically continuous performance enhancement on the information technology such as com-puter ,communication,and network technology,the resources sharing and in-ti me information integration fornetwork-based automationin manufacturing industry has become an extremely i mportant focus . Furthermore ,withthe growing trend of the transnational enterprise number towards globalization, promotion of the globalcompetitiveness has also been increasingly paid more attention…     

数字矿井及其相关技术分析

结合数字地球和数字中国战略的提出 ,对未来的数字矿井进行了构想 ,给出了数字矿井的基本框架 ,全面、系统地论述了数字矿井的相关技术———矿井空间数据的获取与分析技术、网络数据库与分布式计算技术、数据仓库及数据挖掘技术、多种数据整合及虚拟现实技术 ,最后指出数字矿井的作用和意义