Reinforced cast metals: Part II Evolution of the interface

Interface evolution in metal-matrix composites is a thermodynamic necessity and interface design a kinetics challenge. The synergistic interaction between processing science and surface engineering has led to considerable progress in understanding, modelling and tailoring the fibre–matrix interface at the microstructural, crystallographic and atomic levels. The chemical, morphological, crystallographic and thermoelastic compatibilities between the fibre and the matrix influence the interfacial adhesion strength. This article examines the role of material properties and fabrication conditions in chemical interactions between the fibre and the matrix in metal-matrix composites synthesized using the solidification and casting techniques. © 1998 Chapman & Hall     

Effect of doping concentration on normal state resistivity of La2 −x (Ba,Sr) x CuO4 superconductors

Based on free electron layered electron gas model of quasi two dimensional CuO₂ layers in La(Ba/Sr)CuO superconductors a model potentialV(q) is developed earlier with the electron-electron and electron-phonon interactions. The model approach facilitates the dielectric functions and the dispersion relations of 2D acoustic phonon and plasmon modes. We have then worked out the coupling strength (γ) linking electrons to the 2D acoustic phonon mode (ħω_) from the residue at the pole ofV(q). Furthermore, the scattering time (τ _e−ph) during electron-phonon interaction (EPI) for this simplified system is also estimated. The contribution to the normal state in plane resistivity due to EPI is then evaluated. Finally, the variations ofτ andρ is studied with the doping concentration (x) and temperature (T) and the results obtained by us show reasonably good agreement with the available experimental data.     

Interface- and diffusion-limited capillary rise of reactive melts with a transient contact angle

The kinetics of unidirectional capillary penetration by a reactive fluid under the limiting cases of diffusion control and interface control has been derived for the reactive infiltration phenomenon characterized by a shrinking capillary radius due to interphase formation and an exponentially decaying contact angle. The computational outcomes for the reactive penetration of Si₃N₄ capillaries by AgCuTi brazes and of carbon capillaries by Si show that greater lengths are attained at lower values of the parabolic rate constant (under diffusion control), and the limiting length is reached earlier at larger values of the linear rate constant (under interface control). A capillary-driven flow analysis (Washburn equation) overestimates the infiltration kinetics, whereas an analysis that considers pore shrinkage but assumes the contact angle and the capillary pressure to be constant during flow underestimates the kinetics. The penetration lengths predicted by the analysis at pore closure due to reaction choking exhibit a slightly better agreement with the recent measurements in the Si/C system than the models of reactive flows currently in vogue.     

Interpretation of Resistivity of Nd1.85Ce0.15CuO4: Electron–Phonon Mechanism

The temperature-dependent normal state resistivity of single crystal Nd_1.85Ce_0.15CuO_{4 ? δ} is theoretically analyzed within the framework of classical electron–phonon i.e., Bloch-Gruneisen model of resistivity. For the reason of inherent acoustic (low frequency) phonons (ω_ac) as well as high-frequency optical phonons (ω_op), the contributions to the resistivity were first derived. The optical phonons of the oxygen breathing mode yields a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons. Estimated contribution to in-plane resistivity by considering both phonons, i.e., ω_ac and ω_op, along with the zero-temperature-limited resistivity, when subtracted from single crystal data infers a quadratic temperature dependence over most of the temperature range [25 ≤ T ≤ 300]. Quadratic temperature dependence of ρ_diff. = [ρ_exp. ? {ρ₀ + ρ_e–ph (=ρ_ac + ρ_op)}] is understood in terms of 3D electron–electron inelastic scattering. The comparison of single crystal experimental data appears favorable with the present analysis.     

A discussion of yield modeling with defect clustering, circuitrepair, and circuit redundancy

The mathematical foundation of common integrated--circuit yield models based on the assumption that the yield is dominated by random point defects is discussed. Various mathematical models which are commonly used to account for defect clustering are given a physical interpretation and are compared mathematically and graphically. A yield model applicable when the repair of some defects in a chip is possible is developed and discussed. Simple yield models for systems with two-fold block redundancy and triple modular redundancy in the presence of defect clustering are developed. and the implications for overall system yield are discussed. It is shown that the yield of systems with circuit redundancy can be substantially affected by defect clustering and, hence, that a correct understanding of defects and yield is essential to predict the yields and costs of wafer-scale products     

Mobile Commerce: Framework,Applications and Networking Support

Advances in e-commerce have resulted in significant progress towards strategies, requirements, and development of e-commerce applications. However, nearly all e-commerce applications envisioned and developed so far assume fixed or stationary users with wired infrastructure. We envision many new e-commerce applications that will be possible and significantly benefit from emerging wireless and mobile networks. To allow designers, developers, and researchers to strategize and create mobile commerce applications, we propose a four-level integrated framework for mobile commerce. Since there are potentially an unlimited number of mobile commerce applications, we attempt to identify several important classes of applications such as mobile financial applications, mobile inventory management, proactive service management, product location and search, and wireless re-engineering. We discuss how to successfully define, architect, and implement the necessary hardware/software infrastructure in support of mobile commerce. Also, to make mobile commerce applications a reality, we address networking requirements, discuss support from wireless carriers, and present some open research problems.     

The solidification of metal-matrix particulate composites

The simplicity, economy and flexibility of solidification processes make them attractive methods for the production of particle-reinforced metal-matrix composites. At present, however, there is limited understanding of the phenomena occurring during solidification of these advanced materials. Nucleation and refinement of crystalline phases, physical and chemical interactions between dispersed particles and solidifying interfaces, and buoyancy-driven movement of the particles are areas where a knowledge base is beginning to be formed. Ultimately, the understanding of solidification processes in metal-matrix composites must become complete enough that microstructures can be tailored for specific applications.