Nanoindentation characterization of intermetallic compounds formed between Sn–Cu (–Ni) ball grid arrays and Cu substrates

The formation of intermetallic compounds (IMCs) at the solder–substrate interface is essential in the manufacturing of solder joints. In this study, the effect of Ni addition into Sn–Cu lead-free solders on mechanical properties of the IMCs formed at the interface between solder ball grid arrays (BGAs) and Cu substrates, which experienced multiple reflows, were investigated. The results from nanoindentation tests showed that elastic modulus and hardness of (Cu,Ni)₆Sn₅ were higher than those of Cu₆Sn₅. The hardnesses of (Cu,Ni)₆Sn₅ were more scattered compared to those of Cu₆Sn₅, which may be attributed to the crystallographic characteristics such as growth texture of the IMCs.     

Effective range of electrical stimulation in brain slice preparations

In order to examine the confines of electrical stimulation in layer 2/3 of the visual cortex in brain slice preparations, we estimated the effective range of stimulation based on the excitatory postsynaptic potential (EPSP) evoked in layer V neurons that receive input from layer 2/3. For this purpose, we recorded and compared ESPS amplitudes evoked by stimulations directly over the site of the recording electrode and at a lateral site in layer 2/3. Since the EPSP increased linearly with stimulus intensity before saturation, it was considered that the EPSP correlates with the number of projecting neurons in an area directly excited by stimulation. Then we formed a region model by which we can obtain the ratios between the neuron numbers in areas excited by different site stimulations against the stimulus effective ranges. In the stimulus intensity for the action potential threshold of layer 5 neurons, we evaluated the effective range for the relative values of EPSP produced by stimulations 250‐μm lateral sites and directly over the site. In the model, the ratio increased monotonically with the effective range and in the case of 250 μm for the effective range, the ratio between these EPSP was less than the value in the model. These results led to the conclusion that the effective range of the intensity for layer 5 neurons to generate an output is confined within 250 μm of a point directly over the site, that is, within layer 2/3. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 56–63, 1999     

Effects of relative humidity and temperature on subcritical crack growth in igneous rock

Effects of relative humidity and temperature on subcritical crack growth in igneous rock have been investigated experimentally on samples of Kumamoto andesite and Oshima granite. Stress intensity factors and crack velocities were measured using the double-torsion technique, and all experiments were conducted in moist air. Our results show that in experiments conducted under the same relative humidity, crack velocity increased with increasing temperature, in agreement with previous studies. Our results also show that, in experiments conducted at the same temperature, crack velocity increased dramatically with increasing relative humidity. A three- to fourfold increase in relative humidity resulted in an increase in crack velocity of between one and four orders of magnitude. Such an increase is larger than that predicted by classical stress corrosion theory. It is suggested that capillary condensation of water vapour close to crack tips of small aperture influences the rate of crack growth. It is concluded that relative humidity needs to be controlled to avoid time-dependent weakening and extend the lifetime of structures in a rock mass.     

Effects of Internet use on self-efficacy: perceived network-changing possibility as a mediator

The effect of Internet use as a mediating variable on self-efficacy as it relates to the cognition of network-changing possibility (i.e., connecting people or groups with different social backgrounds) was examined. The results showed that Internet use (i.e., the frequency of sending e-mail, friends made on the Internet) had a positive effect on the cognition of network-changing possibility. The cognition that it is possible to connect people with different social backgrounds by using the Internet also had a positive effect on self-efficacy. On the other hand, the cognition that it is possible to find people or groups who share beliefs and interests by using the Internet negatively affected self-efficacy. Hence, it was found that the effect of Internet use on self-efficacy was different as a function of cognition of network-changing possibility. Research for this study was supported by grants from the Japan Society for the Promotion of Science, KAKANHI15330137.

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A quantum algorithm using NMR computers to break secret-key cryptosystems

In this paper, we discuss quantum algorithms that, for a given plaintextm _o and a given ciphertextc _o, will find a secret key,k _o, satisfyingc _o=E(k _o,m _o), where an encryption algorithm,E, is publicly available. We propose a new algorithm suitable for an NMR (Nuclear Magnetic Resonance) computer based on the technique used to solve the counting problem. The complexity of, our algorithm decreases as the measurement accuracy of the NMR computer increases. We discuss the possibility that the proposed algorithm is superior to Grover’s algorithm based on initial experimental results. Kazuo Ohta, Dr.S.: He is Professor of Faculty of Electro-Communications at the University of Electro-Communications, Japan. He received B.S., M.S., and Dr. S. degrees from Waseda University, Japan, in 1977, 1979, and 1990, respectively. He was researcher of NTT (Nippon Telegraph and Telephone Corporation) from 1979 to 2001, and was visiting scientist of Laboratory for Computer Science e of MIT (Massachusetts Institute of Technology) in 1991–1992 and visiting Professor of Applied Mathematics of MIT in 2000. He is presently engaged in research on Information Security, and theoretical computer science. Dr. Ohta is a member of IEEE, the International Association for Cryptologic Research, the Institute of Electronics, Information and Communication Engineers and the Information Processing Society of Japan. Tetsuro Nishino,: He received the B.S., M.S. and, D.Sc. degrees in mathematics from Waseda University, in 1982, 1984, and 1991 respectively. From 1984 to 1987, he joined Tokyo Research Laboratory, IBM Japan. From 1987 to 1992, he was a Research Associate of Tokyo Denki University, and from 1992 to 1994, he was an Associate Professor of Japan Advanced Institute of Science and Technology, Hokuriku. He is presently an Associate Professor in the Department of Communications and Systems Engineering, the University of Electro-Communications. His main interests are circuit complexity theory, computational learning theory and quantum complexity theory. Seiya Okubo,: He received the B.Eng. and M.Eng. degrees from the University of Electro-Communications in 2000 and 2002, respectively. He is a student in Graduate School of Electro-Communications, the University of Electro-Communications. His research interests include quantum complexity theory and cryptography. Noboru Kunihiro, Ph.D.: He is Assistant Professor of the University of Electro-Communications. He received his B. E., M. E. and Ph. D. in mathematical engineering and information physics from the University of Tokyo in 1994, 1996 and 2001, respectively. He had been engaged in the research on cryptography and information security at NTT Communication Science Laboratories from 1996 to 2002. Since 2002, he has been working for Department of Information and Communication Engineering of the University of Elector-Communications. His research interests include cryptography, information security and quantum computations. He was awarded the SCIS’97 paper prize.     

Arsenic intake via water and food by a population living in an arsenic-affected area of Bangladesh

More and more people in Bangladesh have recently become aware of the risk of drinking arsenic-contaminated groundwater, and have been trying to obtain drinking water from less arsenic-contaminated sources. In this study, arsenic intakes of 18 families living in one block of a rural village in an arsenic-affected district of Bangladesh were evaluated to investigate their actual arsenic intake via food, including from cooking water, and to estimate the contribution of each food category and of drinking water to the total arsenic intake. Water consumption rates were estimated by the self-reporting method. The mean drinking water intake was estimated as about 3 L/d without gender difference. Arsenic intakes from food were evaluated by the duplicate portion sampling method. The duplicated foods from each family were divided into four categories (cooked rice, solid food, cereals for breakfast, and liquid food), and the arsenic concentrations of each food category and of the drinking water were measured. The mean arsenic intake from water and food by all 18 respondents was 0.15 +/-0.11 mg/d (range, 0.043 - 0.49), that by male subjects was 0.18 +/- 0.13 mg/d (n = 12) and that by female subjects was 0.096 +/- 0.007 mg/d (n = 6). The average contributions to the total arsenic intake were, from drinking water, 13%; liquid food, 4.4%; cooked rice, 56%; solid food, 11%; and cereals, 16%. Arsenic intake via drinking water was not high despite the highly contaminated groundwater in the survey area because many families had changed their drinking water sources to less-contaminated ones. Instead, cooked rice contributed most to the daily arsenic intake. Use of contaminated water for cooking by several families was suspected based on comparisons of arsenic concentrations between drinking water and liquid food, and between rice before and after cooking. Detailed investigation suggested that six households used contaminated water for cooking but not drinking, leading to an increase of arsenic intake via arsenic-contaminated cooking water.     

Assessment of the activities of catalysts for the hydrocracking of coal by means of hydrogen evolution

A close relation has been found between hydrogen evolution from coal-catalyst and pitch-catalyst systems and catalytic activities of liquefaction reactions. A MoO₃?TiO₂ catalyst has the highest activity and the order of activity of the catalysts for hydrogen evolution is: MoO₃?TiO₃> MoO₃?SiO₂>10% $\text{Fe}{}_2\text{O}{}_3\text{TiO}{}_2\text{?AI}{}_2\text{O}{}_3\text{>}\text{coal alone}$. The same trend was observed for benzene-soluble materials for the hydrocracking of Akabira Coal.     

Mechanically controlled domain structure in PZT piezoelectric ceramics

The influence of the mechanically applied load on the piezoelectric properties and domain switching characteristics has been investigated experimentally using a soft lead zirconate titanate (PZT) piezoceramic, which de-poled to make randomly orientated domain structures. Mechanical loads were applied to rectangular PZT ceramics under compressive and tensile stresses. With the applied stress, 90° domain switching occurred in many locations in the PZT ceramics, where the higher stress caused more severe domain switching. The domain switching occurred with different directions, depending on the stress direction. For instance, the (2 0 0) peak increased and the (0 0 2) peak decreased when more severe compressive stress was applied. The opposite trend was detected as more severe tensile stress was applied; the (2 0 0) peak decreased and the (0 0 2) peak increased. With the applied loading process, the domains (long tetragonal c-axis) were orientated regularly in the PZT ceramics. Furthermore, like the electrically poled PZT ceramics, the domain orientations were more aligned when the sample surfaces were constrained during the loading process.     

河姆渡、罗家角两遗址水稻硅酸体形状特征之比较

对长江下游迄今为止发现的最古老的新石器时代遗址———河姆渡遗址、罗家角遗址进行了植物硅酸体分析 ,结果在两遗址出土的陶器碎片中发现了起源于水稻叶片运动细胞硅酸体。硅酸体的形状解析结果表明 :来自两遗址的硅酸体断面形状大致相同 ,而在大小方面存在显著差异。利用硅酸体形状亚种判别函数进行判别 ,结果河姆渡遗址的稻为粳稻 ,罗家角遗址的稻为籼稻。研究结果表明两遗址的栽培稻群体具有不同系统特性 ,为长江下游的水稻系统演化及稻作起源研究提供了有意义的实证数据。