Effect of mixing rate on the morphology of primary Al phase in the controlled diffusion solidification (CDS) process

Controlled diffusion solidification is a novel and promising process wherein near-net-shaped cast product of a desired Al wrought alloy is obtained by mixing two precursor alloys at specific individual composition, mass, and temperature each to obtain a non-dendritic morphology of the primary Al phase in the solidified microstructure. This study is devoted to quantify the effect of the rate of mixing of the two precursor alloys on the morphology of the primary Al phase in the cast component. The results show that the lower mixing rate with a higher mixing velocity is more favorable for the CDS process.     

Eutectic solidification of aluminum-silicon alloys

A mechanism that describes nucleation and growth as well as morphology modification by chemical additives of the eutectic phases in aluminum-silicon hypoeutectic alloys is presented. The mechanism is supported with results of nonequilibrium thermal analyses, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), selected area electron diffraction, and elemental X-ray mapping, as well as results of high-temperature rheological measurements that are performed on alloy samples of precisely controlled chemistry.     

Die soldering: Mechanism of the interface reaction between molten aluminum alloy and tool steel

Die soldering is the result when molten aluminum sticks to the surface of the die material and remains there after the ejection of the part; it results in considerable economic and production losses in the casting industry, and is a major quality detractor. In order to alleviate or mitigate die soldering, one must have a thorough understanding of the mechanism by which the aluminum sticks to the die material. A key question is whether the die soldering reaction is diffusion controlled or interface controlled. A set of diffusion couple experiments between molten aluminum alloy and the ferrous die was carried out. The results of the diffusion couple experiments showed that soldering is a diffusional process. When aluminum comes in contact with the ferrous die material, the iron and the aluminum atoms diffuse into each other resulting in the formation of a series of intermetallic phases over the die material. Initially iron and aluminum react with each other to form binary iron-aluminum intermetallic phases. Subsequently, these phases react with the molten aluminum to further form ternary iron-aluminum-silicon intermetallic phases. Iron and aluminum have a great affinity for each other and the root cause of die soldering is the high reaction kinetics, which exists between iron and aluminum. Once the initial binary and ternary intermetallic phase layers are formed over the die material, the aluminum sticks to the die due to the abnormally low thermal conductivity of the intermetallic phases, and due to favorable interface energies between the intermetallic layers and aluminum. The experimental details, the results of the interface reactions, and the analysis leading to the establishment of the mechanism giving rise to die soldering are reviewed discussed.     

Proofing Direct-Seeded Rice with Better Root Plasticity and Architecture

The underground reserve (root) has been an uncharted research territory with its untapped genetic variation yet to be exploited. Identifying ideal traits and breeding new rice varieties with efficient root system architecture (RSA) has great potential to increase resource-use efficiency and grain yield, especially under direct-seeded rice, by adapting to aerobic soil conditions. In this review, we tried to mine the available research information on the direct-seeded rice (DSR) root system to highlight the requirements of different root traits such as root architecture, length, number, density, thickness, diameter, and angle that play a pivotal role in determining the uptake of nutrients and moisture at different stages of plant growth. RSA also faces several stresses, due to excess or deficiency of moisture and nutrients, low or high temperature, or saline conditions. To counteract these hindrances, adaptation in response to stress becomes essential. Candidate genes such as early root growth enhancer PSTOL1, surface rooting QTL qSOR1, deep rooting gene DRO1, and numerous transporters for their respective nutrients and stress-responsive factors have been identified and validated under different circumstances. Identifying the desired QTLs and transporters underlying these traits and then designing an ideal root architecture can help in developing a suitable DSR cultivar and aid in further advancement in this direction.     

Yielding in Surfactant Suspension Pastes: Effect of Surfactant Type

In this work, we study the rheological properties and the yielding behavior of cleaning pastes containing surfactant and abrasive particles, for three different types of surfactants, namely linear alkyl benzene sulfonate (LAS), alpha olefin sulfonate (AOS) and sodium lauryl ether sulfonate (SLES). All the pastes were observed to have soft solid-like consistency with their elastic modulus significantly greater than the viscous modulus. With around 36 volume percent of particulate matter, the high stiffness of the pastes suggests that particles form a space spanning network. Interestingly, when subjected to oscillatory shear deformation with increasing strain amplitude, the elastic modulus undergoes a decrease in two steps thereby showing a two-step yielding behavior. It is observed that the first yield stress does not show frequency dependence, and for LAS-containing paste was the largest followed by AOS- and SLES-containing pastes, respectively. The second yield stress, on the other hand, for all the three pastes is observed to increase with frequency. Careful assessment of the experimental data suggests that the first yielding event is due to rupture of the network which leads to formation of particulate aggregates. The second yielding event is attributed to breakage of aggregates. In both yielding phenomena, surfactants play an important role. Since, the phase behavior of surfactant in water determines the inter-particle interaction and network density, the nature of surfactant has a pivotal influence on both the yielding phenomena in surfactant suspension pastes used for cleaning purposes.     

Dynamic internal gradients control and direct electric currents within nanostructured materials

Switchable nanomaterials--materials that can change their properties and/or function in response to external stimuli-have potential applications in electronics, sensing and catalysis. Previous efforts to develop such materials have predominately used molecular switches that can modulate their properties by means of conformational changes. Here, we show that electrical conductance through films of gold nanoparticles coated with a monolayer of charged ligands can be controlled by dynamic, long-range gradients of both mobile counterions surrounding the nanoparticles and conduction electrons on the nanoparticle cores. The internal gradients and the electric fields they create are easily reconfigurable, and can be set up in such a way that electric currents through the nanoparticles can be modulated, blocked or even deflected so that they only pass through select regions of the material. The nanoion/counterion hybrids combine the properties of electronic conductors with those of ionic gels/polymers, are easy to process by solution-casting and, by controlling the internal gradients, can be reconfigured into different electronic elements (current rectifiers, switches and diodes).     

Mission possible? The performance of prosocially motivated employees depends on manager trustworthiness.

The authors propose that in mission-driven organizations, prosocially motivated employees are more likely to perform effectively when trust cues enhance their perceptions of task significance. The authors develop and test a model linking prosocial motivation, trust cues, task significance, and performance across 3 studies of fundraisers using 3 different objective performance measures. In Study 1, perceiving managers as trustworthy strengthened the relationship between employees’ prosocial motivation and performance, measured in terms of calls made. This moderated relationship was mediated by employees’ perceptions of task significance. Study 2 replicated the interaction of manager trustworthiness and prosocial motivation in predicting a new measure of performance: dollars raised. It also revealed 3-way interactions between prosocial motivation, manager trustworthiness, and dispositional trust propensity, such that high trust propensity compensated for low manager trustworthiness to strengthen the association between employees’ prosocial motivation and performance. Study 3 replicated all of the previous mediation and moderation findings in predicting initiative taken by professional fundraisers. Implications for work motivation, work design, and trust in organizations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Two-dimensional-numerical investigation on the influence of first rib distance from the entrance of channel on Nusselt number and pressure drop

Enhancing the heat transfer coefficient in heat sinks can be achieved by surface modification techniques. Although the addition of ribs increases heat transfer capacity, it also increases pressure drop, lowering the channel's thermohydraulic performance (THP) factor. Rib research began a decade ago, with the majority of studies focusing on new rib designs or factors such as relative roughness pitch, relative roughness height, channel width, and channel height (geometric optimization) to improve THP. The goal of this study is to investigate the influence of the positioning of the first rib from the channel entrance on the Nusselt number, pressure drop, and THP factor with a simple design that could be manufactured easily. Three distinct rib designs are evaluated with rib positioning from the channel entrance, rib thickness, pitch, and Reynolds number as the parameters. It was found that the fluid starts settling up at the ribs as the ribs are moved closer to the channel entry point, thus increasing the pressure drop and reducing the fluid velocity. For the proposed design and dimensions, the Nusselt number increases by 3%–5%, and the pressure drop lowers by 4%–14% when the first rib is placed away from the channel entrance.     

Model for self-polarization and motility of keratocyte fragments

Computational modelling of cell motility on substrates is a formidable challenge; regulatory pathways are intertwined and forces that influence cell motion are not fully quantified. Additional challenges arise from the need to describe a moving deformable cell boundary. Here, we present a simple mathematical model coupling cell shape dynamics, treated by the phase-field approach, to a vector field describing the mean orientation (polarization) of the actin filament network. The model successfully reproduces the primary phenomenology of cell motility: discontinuous onset of motion, diversity of cell shapes and shape oscillations. The results are in qualitative agreement with recent experiments on motility of keratocyte cells and cell fragments. The asymmetry of the shapes is captured to a large extent in this simple model, which may prove useful for the interpretation of experiments.     

Effect of carboxyl graphene nanofluid on automobile radiator performance

Nanofluid is a promising solution for the improvement of the radiator performance. In the current research work, the effect of the nanofluid carboxyl graphene on the performance of a radiator is studied. Carboxyl graphene nanoplatelets are added to 50:50 ethylene glycol–distilled water at three concentrations of 0.02, 0.03, and 0.04 vol%. The liquid flow rate is varied from 3 liters per minute (LPM) to 6 LPM, and the inlet liquid to the radiator has been maintained at constant temperatures of 40 °C and 50 °C. The inlet air Reynolds number is varied between 1200 and 2500. The effects of these on performance parameters such as Nusselt number, effectiveness, and friction factor are investigated. It is observed that addition of carboxyl graphene nanoplatelets increases the Nusselt number and effectiveness of radiator while friction factor is unaltered. The effectiveness of radiator increases by 27.38% and 23.41% for inlet temperatures of 40 °C and 50 °C respectively at 0.02 vol% and 5 LPM flow rate.