Thermal analysis and mechanical properties of Sn–1.0Ag–0.5Cu solder alloy after modification with SiC nano-sized particles

The size and morphology of intermetallic compounds (IMCs) of Sn–1.0Ag–0.5Cu (SAC105) solder alloys can have a significant influence on the mechanical strength of solder joints. The aim of the present study is to investigate the influence of SiC nano-particles addition on the microstructure, thermal behavior, and corresponding mechanical properties of SAC(105) solder alloys. Results show that the addition of SiC nanoparticles into the SAC(105) alloy melt prompts the formation of primary β-Sn phase with small sub-grain size in the solidified structure. The SiC nanoparticles can offer an additional nucleation sites for the formation of refined Ag₃Sn and Cu₆Sn₅ IMCs. The hard SiC particles and refined IMCs with small spacing could obstruct the dislocation slipping and thus, lead to a strong dispersion strengthening mechanism in the composite solder. As a result, the composite SAC(105)/SiC solder displayed a higher ultimate tensile strength and 0.2 % yield strength (0.2 %YS) than that of plain SAC(105) solder. The addition of SiC nano-sized particles can also effectively reduce the undercooling and pasty range, while the melting temperature is maintained at the SAC(105) level, indicating that the novel composite solder is fit for existing soldering process.     

The advantages of using impact resonance test in dynamic modulus master curve construction through the abbreviated test protocol

Asphalt concrete behavior is heavily dependent on temperature and loading rate. Hence, the material is typically tested at a range of temperatures and loading frequencies to capture its properties. Results are then used to develop a master curve exhibiting material behavior at the full spectrum of loading frequencies. An abbreviated testing protocol, under AASHTO PP 61-13, proposes a practical approach for development of this master curve. In this practice, the low temperature asymptote of the master curve is dominated by the limiting maximum modulus estimated through the Hirsch model. In this study, the dynamic modulus (DM) testing coupled with impact resonance (IR) test was used to evaluate the effect of this limiting maximum modulus on construction of the asphalt concrete master curve. Three different asphalt mixtures prepared with the same gradation and binder content, but different grades of stiffness were tested. The DM testing was performed at multiple temperatures and loading frequencies. The IR tests were conducted on the same specimens at the same temperatures. Two sigmoid functions (MEPDG and Richards models), and three shift factors (Arrhenius, Williams–Landel–Ferry, and polynomial) were utilized in the analysis. Richards sigmoid function coupled with polynomial shift factor provided the best fitting accuracy to the measured data. It was observed that the limiting maximum modulus obtained from experimental data was underpredicted by that obtained from the Hirsch model. The results indicated potential benefits of the IR test as a complementary testing tool to the abbreviated DM testing protocol to reliably characterize asphalt concrete.     

Dynamic security constrained optimal power flow/VAr planning

Traditionally security constrained optimal power flow and VAr planning methods consider static security observing voltage profile and flow constraints under normal and post contingency conditions. Ideally, these formulations should be extended to consider dynamic security. This paper reports on a BC Hydro/CEPEL joint effort establishing a dynamic security constrained OPF/VAr planning tool which considers simultaneously static constraints as well as voltage stability constraints. This paper covers the details of formulation and implementation of the tool together with the test results on a large scale North American utility system and a reduced Brazilian system     

Traveling wave behavior in a two-phase flow model of tumor growth

Tumor growth which undergoes complex bio-mechanical processes has been a significant focus for mathematical modeling, with particular interest in its dynamic behavior. In this paper, we consider a two-phase flow model for describing the dynamics of tumor growth. The model accounts for aggregate cell movement and mechanical interactions between tumor cells as well as cell proliferation. In suitable limits, by using the dynamical systems theory approach, tumor growth in this mechanical model is shown to occur in the form of traveling waves that can propagate either forward or backward, depending on the values of the parameters. Our results, in particular, the wave profiles of tumor cell density are more realistic and explain those obtained in a recently developed simple, experiment-based, model for studying non-spatial dynamics of tumor cells.     

A Modified Particle Swarm Optimizer for the Coordination of Directional Overcurrent Relays

The coordination of directional overcurrent relays (DOCR) is treated in this paper using particle swarm optimization (PSO), a recently proposed optimizer that utilizes the swarm behavior in searching for an optimum. PSO gained a lot of interest for its simplicity, robustness, and easy implementation. The problem of setting DOCR is a highly constrained optimization problem that has been stated and solved as a linear programming (LP) problem. To deal with such constraints a modification to the standard PSO algorithm is introduced. Three case studies are presented, and the results are compared to those of LP technique to demonstrate the effectiveness of the proposed methodology.     

AN EXPERIMENTAL INVESTIGATION OF YIELD STRESS OF WESTERN CANADIAN COAL WATER FUELS

The concept of a yield value is important to many areas of slurry coal water fuel transport such as in predicting its stability or estimating the pressure requirements for pipe-line start-up and turbulent flow. This paper describes techniques to accurately measure coal water fuel yield point. In order to display a wide variation in coal water fuel properties, slurries made from two Western Canadian coals were made available to CRL for yield point study. The proprietory Salzgiter Industrial AG technology (DENSECOAL) was used for a low volatile or bituminous coal (A) and the CARBOGEL process for a medium volatile bituminous (B).     

An approximate analytical solution for the nonlinear inverse axial dispersion model

An analytical solution for diffusion with homogenous n the order nonlinear chemical reaction in laminar flow of a Newtonian fluid through tubular reactor with unknown boundary conditions is presented. The results of the new solution have been compared with previously published numerical solutions and shown to be accurate.     

Synthetic Crystals of Silver with Carbon: 3D Epitaxy of Carbon Nanostructures in the Silver Lattice

Only minimum amounts of carbon can be incorporated into silver, gold, and copper in a thermodynamically stable form. Here, the structure of stable silver carbon alloys is described, which are produced by thermoelectrically charging molten silver with carbon ions. Transmission electron microscopy and Raman scattering are combined to establish that large amount of carbon is accommodated in the form of epitaxial graphene‐like sheets. The carbon bonds covalently to the silver matrix as predicted from density functional theory (DFT) calculations with bond energies in the range 1.1–2.2 eV per atom or vacancy. Graphitic‐like sheets embedded in the crystal lattice of silver form 3D epitaxial structures with the host metal with a strain of ≈13% compared to equilibrium graphene. The carbon nanostructures persist upon remelting and resolidification. A DFT‐based analysis of the phonon density of states confirms the presence of intense vibration modes related to the Ag? C bonds observed in the Raman spectra of the alloy. The solid silver–high carbon alloy, termed “Ag‐covetic,” displays room temperature electrical conductivity of 5.62 × 10⁷ S m^?1 even for carbon concentrations of up to ≈6 wt% (36 at%). This process of incorporation of carbon presents a new paradigm for electrocharging assisted bulk processing.