Effect of size distribution on mixing of a polydisperse wet granular material in a belt-driven enclosure

We use a recently developed coupled fluid–particle discrete element model to study mixing of a wet granular material in a two dimensional setting. The particles are modeled as linearly elastic disks and are considered to be immersed in a Newtonian fluid. The fluid–particle interaction is modeled using a linear drag model under the assumption that the fluid inertia is small compared to particle inertia. The granular slurry is driven by a belt moving at constant velocity in a square cavity. In the simulations, we consider three types of size distributions: monodisperse, bidisperse with several particle size ratios, and polydisperse Gaussian distributions with several different standard deviations. Mixing is characterized using both strong and weak measures. Size segregation is observed only in the bidisperse simulations. The energy required for mixing polydisperse slurries decreases with increasing standard deviation of the particle sizes. Finally, we show the benefits of engineering certain polydisperse particle size distributions towards minimizing energy consumption.     

Effect of Powder Mixed Dielectric on Material Removal and Surface Modification in Microelectric Discharge Machining of Ti-6Al-4V

Microelectric discharge milling is one of the variants of microelectric discharge machining process which acquire the attention of researchers due to its unique ability to produce microchannels and three-dimensional structures in difficult-to-machine materials like titanium. In the present work, an experimental investigation has been performed in order to study the effect of SiC microparticle suspended dielectric on machining Ti-6Al-4V with tungsten carbide electrode. The effects of major electric discharge milling process parameters—voltage, capacitance, and powder concentration in dielectric—on responses—viz., material removal rate (MRR) and tool wear rate (TWR)—were studied. Experiments were designed and performed based on response surface methodology (RSM)-Box–Behnken statistical design and the significance of in put parameters were identified with the help of analysis of variance. From the results, it is recommended to use powder concentration of 5 g/L, capacitance of 0.1 µF, and voltage of 115 V for achieving high material removal and low tool wear rate. Finally, the studies were conducted to analyze the surface modification and the quality of machined surface.     

High-throughput dry drilling of titanium aluminide

There is always an increasing interest in and demand for materials with superior properties, particularly in aerospace and automobile industries. Intermetallic titanium aluminides have been recognized as the possible material that could be used in high-performance applications. The understanding of the machinability during various machining processes is very much essential in order to widen the usage of these materials over various fields of application. Drilling, particularly with high aspect ratio, is a complex machining process that has to be explored. In the present work, machinability of titanium aluminide has been evaluated during high-throughput dry drilling, based on thrust, torque, surface integrity, and chip morphology.     

An assessment of mechanical properties of P92 steel weld joint and simulated heat affected zones by ball indentation technique

Mechanical properties of P92 steel weld joint fabricated by shielded metal arc welding were evaluated using ball indentation (BI) technique. Microstructure of the P92 weld joint consisted of the weld metal, coarse grain region, fine grain region, intercritical region and base metal. The individual microstructural regions of the heat affected zones (HAZs) were separately prepared by heat treating the steel at particular temperatures. Ball indentation and uniaxial tensile tests were carried out across the weld joint and on the simulated HAZ microstructures at temperatures of 300 K (27 °C) and 623 K (350 °C). The tensile strengths gradually decreased from weld metal to the base metal with trough in the intercritical region (ICR) of the joint and simulated at 1173 K (900 °C) steel. The formation of coarser M₂₃C₆ precipitates and sub-grain formation with reduced dislocation density led to soften the ICR/simulated at 1173 K (900 °C) steel than the other regions of the joint. The variation of mechanical properties across the joint was comparable with variation of hardness and microstructural constituents across the joint.     

Confidence limits for compliance testing using mixed acceptance criteria

For manufactured items sold by weight or volume, this article considers mixed acceptance criteria that put limits on the sample mean or on an upper confidence limit based on the sample mean and on the number of individual sample units that are nonconforming. For a normally distributed quality characteristic of interest, this article develops lower confidence limits for the mixed acceptance criteria applying the concept of a generalized pivotal quantity and applying a bias-corrected and accelerated parametric bootstrap. The accuracy of the confidence limits is assessed using estimated coverage probabilities, and the results are illustrated with an example.     

Designing quantum rods for optimized energy transfer with firefly luciferase enzymes

The bioluminescence resonance energy transfer (BRET) between firefly luciferase from Photinus pyralis (Ppy) with core/shell semiconductive quantum rods (QRs) has been studied as a function of QR aspect ratio and internal microstructure. The QRs were found to be ideal energy acceptors, and Ppy-to-core distances were optimized using rod-in-rod microstructures that were achieved by the synthetic control of rod morphology, surface chemistry, and Ppy:QR loading. The BRET ratios of >44 measured are the highest efficiencies to date.     

New simulated corrugated scattering surface giving wideband characteristics

Simultaneous elimination of specular reflection and backscattered power from a plane metallic surface by simulated corrugated surfaces of constant period and variable strip width for TM polarisation is reported. This new configuration offers almost a ten-fold frequency bandwidth compared with a regularly spaced strip grating of the same size.<>     

Infrared study of free carriers in X/ZnO (X = semiconductor, metal) nanocomposites

The infrared (IR) reflectance spectroscopy technique was used for the qualitative determination of free carrier density in metal and semiconductor nanocluster embedded ZnO films. The effects of incorporation of metal and semiconductor nanoclusters on the evolution of the free carrier absorption band in the nanocomposites were studied. Our results reveal that the concentration of free carriers in the composite films depends strongly on the nature of incorporated clusters in the matrix and the annealing temperature. It is demonstrated that just by monitoring the position of a single IR reflectance band, the extent of oxidation of any incorporated species in ZnO can be monitored qualitatively.     

Detection techniques for high-density magnetic recording

In this paper, we present techniques for improving the performance of Viterbi detector in the presence of channel nonlinearities and media noise, which are the dominant source of errors in high density magnetic recording channels. Instead of treating these distortions separately, we combine them into a "high-density (HD) noise", which is signal dependent and correlated in nature. To compensate for signal-dependent mean and correlation of HD noise, we modify the branch metrics by subtracting an estimate of the mean from the signals on each branch and optimize the equalization target by minimizing the dominant error event probability, respectively. Simulation results show that these modifications yield significant performance gains.