Co Solubility in Sn and Interfacial Reactions in Sn-Co/Ni Couples

It has been reported that minute Co additions to Sn-based solders are very effective for reducing undercooling, probably due to low Co solubility in Sn. In this study, Co solubility in molten Sn was determined experimentally. According to results of metallographic analysis, Co solubility in molten Sn is as low as 0.04 wt.% at 250°C. Interfacial reactions in Sn-Co/Ni couples at 250°C were examined for Co contents from 0.01 wt.% to 0.4 wt.%. The Ni₃Sn₄ phase was the only interfacial reaction phase in almost the entire Sn-0.01 wt.%Co/Ni couple. For Sn-Co/Ni couples with a Co content higher than 0.01 wt.%, a thin, continuous Ni₃Sn₄ layer and a discontinuous decahedron (Ni,Co)Sn₄ phase were formed in the initial stage of reaction. The reaction products evolved with time. With longer reaction time, the Sn content in the decahedron (Ni,Co)Sn₄ phase decreased, and the (Ni,Co)Sn₄ phase transformed into the (Ni,Co)Sn₂ phase and cleaved into a sheet, which then detached from the interface, after which Ni₃Sn₄ began to grow significantly with longer reaction times.     

Kinetics of Intermetallic Compound Formation at the Interface Between Sn-3.0Ag-0.5Cu Solder and Cu-Zn Alloy Substrates

The growth kinetics of an intermetallic compound (IMC) layer formed between Sn-3.5Ag-0.5Cu (SAC) solders and Cu-Zn alloy substrates was investigated for samples aged at different temperatures. Scallop-shaped Cu₆Sn₅ formed after soldering by dipping Cu or Cu-10 wt.%Zn wires into the molten solder at 260°C. Isothermal aging was performed at 120°C, 150°C, and 180°C for up to 2000 h. During the aging process, the morphology of Cu₆Sn₅ changed to a planar type in both specimens. Typical bilayer of Cu₆Sn₅ and Cu₃Sn and numerous microvoids were formed at the SAC/Cu interfaces after aging, while Cu₃Sn and microvoids were not observed at the SAC/Cu-Zn interfaces. IMC growth on the Cu substrate was controlled by volume diffusion in all conditions. In contrast, IMC growth on Cu-Zn specimens was controlled by interfacial reaction for a short aging time and volume diffusion kinetics for a long aging time. The growth rate of IMCs on Cu-Zn substrates was much slower due to the larger activation energy and the lower layer growth coefficient for the growth of Cu-Sn IMCs. This effect was more prominent at higher aging temperatures.     

A Novel FRFT Beamformer for Rayleigh Faded Channels

A method of optimal beamforming for flat Rayleigh faded channels using the Fractional Fourier Transform (FRFT) is considered in this paper. It has been demonstrated through simulations that optimal beamforming with FRFT allows smaller mean-square errors in restoring signals degraded with linear time-or frequency variant distortions and Additive White Gaussian Noise. This is made possible by the additional flexibility that comes with free parameter ‘a’ of the fractional Fourier transform as oppose to the classical Fourier transform (FT). The method is especially useful in moving source problems, where Doppler Effect produces frequency shift when the source is moving, as in mobile and wireless communication where user produces the frequency shift while moving. In this paper it is shown through simulations that beamforming in fractional domain reduces BER as compared to time or frequency domain.     

Advances In Peer-To-Peer Content Search

Peer-to-peer (P2P) computer networks have recently received tremendous attention due to their inherent scalability and flexibility, which facilitates a broad spectrum of innovative multimedia applications. Such networks rely on the power of participant nodes of the network (called peers) for communications and computation. Traditional applications of P2P multimedia include decentralized file sharing and content distribution. Yet, the value of the virtually unlimited amount of data distributed in the P2P network will be sacrificed if effective and efficient ways to locate the content are missing. This challenge has stimulated extensive research in recent years, and many new P2P content search methods have been proposed. This paper provides a timely review of influential work in the area of peer-to-peer (P2P) content search. We begin with a survey of text-based P2P search mechanisms and continue with an exposition of content-based and semantic-based approaches followed by a discussion of future directions.     

A novel Ultra WideBand monopole antenna with band-notched characteristics

A simple and compact microstrip-fed Ultra WideBand(UWB) printed monopole antenna with band-notched characteristic is proposed in this paper.The antenna is composed of a square ring with a small strip bar,so that the antenna occupies about 7.69 GHz bandwidth covering 3.11～10.8 GHz with expected band rejection from 5.12 GHz to 5.87 GHz.A quasi-omnidirectional and quasi-sym-metrical radiation pattern is also obtained.This kind of band-notched UWB antenna requires no ex-ternal filters and thus greatly simplifie...     

Clustering validity based on the improved S_Dbw* index

For many clustering algorithms, it is very important to determine an appropriate number of clusters, which is called cluster validity problem. In this paper, a new clustering validity assessment index is proposed based on a novel method to select the margin point between two clusters for inter-cluster similarity more accurately, and provides an improved scatter function for intra-cluster similarity. Simulation results show the effectiveness of the proposed index on the data sets under consideration regardless of the choice of a clustering algorithm.     

Capture Properties of the Generalized CMA in Alpha-Stable Noise Environment

Constant modulus algorithm (CMA) is an adaptive technique for correcting multipath and interference-induced degradations in constant envelope waveforms. The algorithm exploits the fact that both multipath and additive interference can disrupt the constant envelope of the received signal. By detecting the received envelope variations, the adaptive algorithm has the ability to reset the coefficients vector so as to remove the variations, and in the process, reject the various interference components from the desired signal. If both the interferer and the signal of interest have constant envelope and are spectrally non-overlapped, it is possible to find two different solutions for the coefficient vector, in which one suppresses the interferer and the other “captures” the interferer. The problem of how “capture” can occur and how it may be prevented in Gaussian noise environment has been perfectly developed in the previous work (Treichler, Larimore, IEEE Trans Acoust Speech Signal Process, 33:946–958, 1985). However, recent investigation on the physical channels in wireless communication shows that there is aggregate noise component exhibiting high amplitudes for small duration time interval. This paper proposes a GCMA (Generalized CMA) which generalizes the CMA by introducing the α-stable distribution as the noise model. Here the original CMA is only a special case of the GCMA. In order to describe the average behavior of the GCMA, a simple model consisting of only two sinusoids is presented. As assuming slow adaptation, the adaptive weight recursion is shown to compress into a two-by-two recursion in the tone output amplitudes. The simplified recursion is analyzed to determine what combination of signals power and initialization on coefficient vectors leads to “lock” and what leads to the capture of the interferer. The method to determine lock and capture zone boundaries is analyzed. These convergence properties of the GCMA are studied by computer simulations.

A Cross-Layer Approach to Enhance QoS for Multimedia Applications Over Satellite

The need for on-demand QoS support for communications over satellite is of primary importance for distributed multimedia applications. This is particularly true for the return link which is often a bottleneck due to the large set of end-users accessing a very limited uplink resource. Facing this need, Demand Assignment Multiple Access (DAMA) is a classical technique that allows satellite operators to offer various types of services, while managing the resources of the satellite system efficiently. Tackling the quality degradation and delay accumulation issues that can result from the use of these techniques, this paper proposes an instantiation of the Application Layer Framing (ALF) approach, using a cross-layer interpreter (xQoS-Interpreter). The information provided by this interpreter is used to manage the resource provided to a terminal by the satellite system in order to improve the quality of multimedia presentations from the end user’s point of view. Several experiments are carried out for different loads on the return link. Their impact on QoS is measured through different application as well as network level metrics.

Effect of Electromigration on the Mechanical Performance of Sn-3.5Ag Solder Joints with Ni and Ni-P Metallizations

The effect of moderate electric current density (1 × 10³ to 3 × 10³ A/cm²) on the mechanical properties of Ni-P/Sn-3.5Ag/Ni-P and Ni/Sn-3.5Ag/Ni solder joints was investigated using a microtensile test. Thermal aging was carried out at 160°C for 100 h while the current was passed. The interfacial microstructure and intermetallic compound (IMC) growth were analyzed. It was found that, at these levels of current density, there were no observable voids or hillocks. Samples aged at 160°C without current stressing failed mostly inside the bulk solder with significant prior plastic deformation. The passage of current was found to cause brittle failure of the solder joints and this tendency for brittle failure increased with increasing current density. Fractographic analysis showed that, in most of the electrically stressed samples, fracture occurred at the interface region between the solder and the joining metals. The critical current density that caused brittle fracture was about 2 × 10³ A/cm². Once brittle fracture occurred, the tensile toughness, defined as the energy per unit fractured area, was usually lower than ~5 kJ/m², compared with the case of ductile fracture where this value was typically greater than ~9 kJ/m². When comparing the two types of joint, the brittle failure was found to be more severe with the Ni than with the Ni-P joint. This work also found that the passage of electric current affects the IMC growth rate more significantly in the Ni than in the Ni-P joint. In the case of the Ni joint, the Ni₃Sn₄ IMC at the anode side was appreciably thicker than that formed at the cathode side. However, in the case of electroless Ni-P metallization, this difference was much smaller.     

Combining Coarse-Grained Software Pipelining with DVS for Scheduling Real-Time Periodic Dependent Tasks on Multi-Core Embedded Systems

In this paper, we combine coarse-grained software pipelining with DVS (Dynamic Voltage/Frequency Scaling) for optimizing energy consumption of stream-based multimedia applications on multi-core embedded systems. By exploiting the potential of multi-core architecture and the characteristic of streaming applications, we propose a two-phase approach to solve the energy minimization problem for periodic dependent tasks on multi-core processors with discrete voltage levels. With our approach, in the first phase, we propose a coarse-grained task-level software pipelining algorithm called RDAG to transform the periodic dependent tasks into a set of independent tasks based on the retiming technique (Leiserson and Saxe, Algorithmica 6:5–35, 1991). In the second phase, we propose two DVS scheduling algorithms for energy minimization. For single-core processors, we propose a pseudo-polynomial algorithm based on dynamic programming that can achieve optimal solution. For multi-core processors, we propose a novel scheduling algorithm called SpringS which works like a spring and can effectively reduce energy consumption by iteratively adjusting task scheduling and voltage selection. We conduct experiments with a set of benchmarks from E3S (Dick 2008) and TGFF () based on the power model of the AMD Mobile Athlon4 DVS processor. The experimental results show that our technique can achieve 12.7% energy saving compared with the algorithms in Zhang et al. (2002) on average.