Crystallographic and electrochemical characteristics of Ti45Zr35Ni17Cu3 quasicrystalline alloy ball-milled with nickel powder

Crystallographic and electrochemical characteristics of ball-milled Ti45Zr35Ni17Cu3 +xNi (x = 0, 5, 10, 15 and 20 mass%) composite powders have been investigated. The powders are composed of amorphous, I- and Ni-phases when x increases from 5 to 20. With increasing x, the amount of Ni-phase increases but the quasi-lattice constant decreases. The maximum discharge capacity first increases as x increases from 0 to 15 and then decreases when x increases further from 15 to 20. The high-rate dischargeability and cycling stability increase monotonically with increasing x. The improvement of the electrochemical characteristics is ascribed to the metallic nickel particles highly dispersed in the alloys, which improves the electrochemical kinetic properties and prevents the oxidation of the alloy electrodes, as well as to the mixed structure of amorphous and icosahedral quasicrystal line phases, which enhances the hydrogen diffusivity in the bulk of the alloy electrodes and efficiently inhibits the pulverization of the alloy particles.

Crystallographic and electrochemical properties of ball-milled quasicrystalline Ti45Zr35Ni17Cu3 alloy with 20 mass% Ni

Icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy powder was ball-milled with 20 mass% Ni, and the effect of the ball-milling time (t) on crystallographic and electrochemical characteristics were investigated. The amounts of icosahedral quasicrystalline and Ni phases decreased when ball-milling time increased from 30 to 180 min. The powder consisted of amorphous and (Ni and Ti) phases after 360 min of ball-milling. The maximum discharge capacity of the powder electrodes first increased from 89 (t = 0 min) to 192 mAh g(-1) (t = 180 min), and then decreased to 138 mAh g(-1) (t = 360 min). The high-rate dischargeability and the discharge capacity after 15 cycles increased with increasing ball-milling time.

Electrode characteristics and microstructure of AB(2)-AB(5) composite hydrogen storage alloy formed by ball-milling process

For improving the electrode characteristics of the Zr-based AB(2)-type alloy, a new kind of composite hydrogen Zr0.9Ti0.1(Ni0.50Mn0.35V0.15)(2)(represented as AB(2)) with a rare storage alloy was successfully prepared by ball-milling I earth-based AB(5)-type alloy (represented as AB(5)) which worked as a surface modifier. Effects of ball-milling on the electrode characteristics and microstructure of Zr0.9Ti0.1(Ni0.50Mn0.35V0.15)(2) alloy and mixtures of AB(2) with AB(5) alloy were investigated. After milling the mixed AB(2) and AB(5) powders (9: 1 in mass ratio) for 10min, XRD and SEM analysis showed that AB(2) and AB(5) maintained their original crystalline states, respectively, some AB(5) particles were adhered onto the surface of AB(2), and some fresh surfaces were formed. It was found that the activation cycles of AB(2)-AB(5) composite alloy was shortened from 14 to 7 and the maximum discharge capacity was increased from 330mAh . g(-1) to 347mAh . g(-1) as compared with AB(2) alloy. The discharge rate capability of AB(2) alloy was also improved by ball milling AB(2) with AB(5) alloy process. The combined effect of ball-milling and mixing with AB(5) alloy is superior to that of sole treatment. It was believed that AB(5) alloy works not only as a regular hydrogen storage alloy, but also as a surface modifier to catalyze the hydriding/ dehydriding process of AB(2) alloy.

Entrevista a Jordi Dou

Muchos barceloneses lo recuerdan como profesor, miles de matemáticos del mundo conocen la firma “Jordi Dou (Barcelona)” asociada a soluciones de problemas en las publicaciones más prestigiosas: Monthly, Crux, etc.

High electric current density-induced interfacial reactions in micro ball grid array (μBGA) solder joints

The effect of a high electric current density on the interfacial reactions of micro ball grid array solder joints was studied at room temperature and at 150 °C. Four types of phenomena were reported. Along with electromigration-induced interfacial intermetallic compound (IMC) formation, dissolution at the Cu under bump metallization (UBM)/bond pad was also noticed. With a detailed investigation, it was found that the narrow and thin metallization at the component side produced “Joule heating” due to its higher resistance, which in turn was responsible for the rapid dissolution of the Cu UBM/bond pad near to the Cu trace. During an “electromigration test” of a solder joint, the heat generation due to Joule heating and the heat dissipation from the package should be considered carefully. When the heat dissipation fails to compete with the Joule heating, the solder joint melts and molten solder accelerates the interfacial reactions in the solder joint. The presence of a liquid phase was demonstrated from microstructural evidence of solder joints after different current stressing (ranging from 0.3 to 2 A) as well as an in situ observation. Electromigration-induced liquid state diffusion of Cu was found to be responsible for the higher growth rate of the IMC on the anode side.

Multiple reflow study of ball grid array (BGA) solder joints on Au/Ni metallization

This paper evaluates the shearing behavior of ball grid array (BGA) solder joints on Au/Ni/Cu pads of FR4 substrates after multiple reflow soldering. A new Pb-free solder, Sn–3Ag–0.5Cu–8In (SACI), has been compared with Sn–3Ag–0.5Cu (SAC) and Sn–37Pb (SP) solders, in terms of fracture surfaces, shearing forces and microstructures. Three failure modes, ball cut, a combination of solder shear and solder/pad bond separation, and pad lift, are assessed for the different solders and reflow cycles. It is found that the shearing forces of the SP and SAC solder joints tend to increase slightly with an increase in the number of reflow cycles due to diffusion-induced solid solution strengthening of the bulk solder and augmentation of the shearing area. However, the shearing forces of the SACI solder joints decrease slightly after four cycles of reflow, which is ascribed to the thermal degradation of both the solder/intermetallic compound (IMC) and IMC/Ni interfaces. The SACI solder joints yield the highest strengths, whereas the SP solder joints give the smallest values, irrespective of the number of reflow cycles. Thickening of the interfacial IMC layer and coarsening of the dispersing IMC particles within the bulk solders were also observed. Nevertheless, the variation of shearing forces and IMC thickness with different numbers of reflow cycles was not so significant since the Ni under layer acted as an effective diffusion barrier. In addition, the initially-formed IMC layer retarded the further extensive dissolution of the pad material and its interaction with the solder

Shear strength analysis of ball grid array (BGA) solder interfaces

Ball shear test is the most common test method used to assess the reliability of bond strength for ball grid array (BGA) packages. In this work, a combined experimental and numerical study was carried out to realize of BGA solder interface strength. Solder mask defined bond pads on the BGA substrate were used for BGA ball bonding. Different bond pad metallizations and solder alloys were used. Solid state aging at 150degC up to 1000 h has been carried out to change the interfacial microstructure. Cross-sectional studies of the solder-to-bond pad interfaces was conducted by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray (EDX) analyzer to investigate the interfacial reaction phenomena. Ball shear tests have been carried out to obtain the mechanical strength of the solder joints and to correlate shear behaviour with the interfacial reaction products. An attempt has been taken to realize experimental findings by Finite Element Analysis (FEA). It was found that intermetallic compound (IMC) formation at the solder interface plays an important role in the BGA solder bond strength. By changing the morphology and the microchemistry of IMCs, the fracture propagation path could be changed and hence, reliability could be improved

Judging where a ball will go: the case of curved free kicks in football

This study examined whether adding spin to a ball in the free kick situation in football affects a professional footballer's perception of the ball's future arrival position. Using a virtual reality set-up, participants observed the flight paths of aerodynamically realistic free kicks with (+/- 600 rpm) and without sidespin. With the viewpoint being fixed in the centre of the goal, participants had to judge whether the ball would have ended up in the goal or not. Results show that trajectories influenced by the Magnus force caused by sidespin gave rise to a significant shift in the percentage of goal responses. The resulting acceleration that causes the ball to continually change its heading direction as the trajectory unfolds does not seem to be taken into account by the participants when making goal judgments. We conclude that the visual system is not attuned to such accelerated motion, which may explain why goalkeepers appear to misjudge the future arrival point of such curved free kicks.

Support vector machine classification for large data sets via minimum enclosing ball clustering

Support vector machine (SVM) is a powerful technique for data classification. Despite of its good theoretic foundations and high classification accuracy, normal SVM is not suitable for classification of large data sets, because the training complexity of SVM is highly dependent on the size of data set. This paper presents a novel SVM classification approach for large data sets by using minimum enclosing ball clustering. After the training data are partitioned by the proposed clustering method, the centers of the clusters are used for the first time SVM classification. Then we use the clusters whose centers are support vectors or those clusters which have different classes to perform the second time SVM classification. In this stage most data are removed. Several experimental results show that the approach proposed in this paper has good classification accuracy compared with classic SVM while the training is significantly faster than several other SVM classifiers.

Cinderella comes to the Ball: Article 14 and the right to non-discrimination in the ECHR

Article 14 ECHR has often been derided as a Cinderella provision, but during the last few years, this has started to change. This article examines how Article 14 has developed, and may live up to its potential as a powerful non-discrimination principle. The case law developments in relation to the “ambit” requirement in Article 14, the development of indirect discrimination case law, and the approval of positive action, all point to a more substantive conception of equality, which offers protection to disadvantaged and vulnerable groups.

The unit ball of the complex P(3H)

Let H be a two-dimensional complex Hilbert space and P(3H) the space of 3-homogeneous polynomials on H. We give a characterization of the extreme points of its unit ball, P(3H), from which we deduce that the unit sphere of P(3H) is the disjoint union of the sets of its extreme and smooth points. We also show that an extreme point of P(3H) remains extreme as considered as an element of L(3H). Finally we make a few remarks about the geometry of the unit ball of the predual of P(3H) and give a characterization of its smooth points.

Optic variables used to judge future ball arrival position in expert and novice soccer players

Although many studies have looked at the perceptual-cognitive strategies used to make anticipatory judgments in sport, few have examined the informational invariants that our visual system may be attuned to. Using immersive interactive virtual reality to simulate the aerodynamics of the trajectory of a ball with and without sidespin, the present study examined the ability of expert and novice soccer players to make judgments about the ball's future arrival position. An analysis of their judgment responses showed how participants were strongly influenced by the ball's trajectory. The changes in trajectory caused by sidespin led to erroneous predictions about the ball's future arrival position. An analysis of potential informational variables that could explain these results points to the use of a first-order compound variable combining optical expansion and optical displacement.