The Influence of Surface Modification on Friction and Lubrication Mechanism Under a Bovine Serum–Lubricated Condition

Diamond-like carbon (DLC) and microdimples are two potential surface modification techniques that are extensively studied to be utilized in biotribological interfaces in order to reduce the friction coefficient and wear rate. However, in situ observation of bovine serum–lubricated DLC and microdimpled surface contacts are not well understood. In this study, a DLC-coated and a microdimpled steel ball rubbing against a Cr-coated glass disk, where 25% bovine serum was used as a lubricant and the temperature was maintained at 37°C, were investigated. The behaviors of ithe nterface were ca`ptured using optical interferometry and the friction coefficients were simultaneously measured using a torque sensor. The experimental results reveal that DLC/glass sliding is scuffing-free, with a lower friction coefficient; however, the formation of a lubricating film is insignificant. On the other hand, the dimples retained lubrication and, as a result, the wear of the glass disk was minimized; however, the friction coefficient was not reduced. Therefore, DLC and microdimples individually have few improved tribological features, but their combination should be considered to maximize performance.     

An artificial neural network model to characterize porosity defects during solidification of A356 aluminum alloy

In this study, a data-driven multilayer perceptron-based neural network model has been developed to predict the percentage of total porosity and mechanical properties, namely yield strength, ultimate tensile strength and percentage of elongation during the solidification of A356 aluminum alloy. Some of the important processing parameters such as cooling rate, solidus velocity, thermal gradient and initial hydrogen content have been considered as inputs to this model. The network training architecture has been optimized using the gradient-based Broyden–Fletcher–Goldfarb–Shanno training algorithm to minimize the network training error within few training cycles. Parametric sensitivity analysis is carried out to characterize the influence of processing parameters (inputs) on the behavior of porosity formation and simultaneously, the tensile properties of A356 alloy castings. It has been observed that initial hydrogen content in the melt and cooling rate has significant influence on the porosity formation and eventually on the tensile properties of the cast product. There has been an excellent agreement between artificial neural network predictions and the target (measured) values of porosity and the tensile properties as depicted by the regression fit between these values.     

Interaction of Myoglobin with Cationic Gemini Surfactants in Phosphate Buffer at pH 7.4

The interactions between myoglobin, a monomeric water soluble heme protein, and cationic gemini surfactants 14‐3‐14, 14‐4‐14, 14‐5‐14 have been studied in phosphate buffer at pH 7.4 using different techniques such as surface tension, UV–visible spectroscopy, fluorescence spectroscopy and circular dichroism. Myoglobin is a surface active protein and it is bound with surfactant molecules. The spin states of the heme group of myoglobin change depending on the concentration of surfactant. The unfolding process of protein in the presence of surfactant is observed from fluorescence spectra. With increasing surfactant concentration, α‐helicity of myoglobin decreases with the appearance of β‐sheet and random coil. The extent of interaction of myoglobin with gemini surfactant increases with increasing spacer length.     

Adder design using 5-input majority gate in a novel “Multilayer Gate Design Paradigm” for Quantum Dot Cellular Automata Circuits

This paper proposes a novel design paradigm for circuits designed in quantum dot cellular automata (QCA) technology. Previously reported QCA circuits in the literature have generally been designed in a single layer which is the main logical block in which the inverter and majority gate are on the base layer, except for the parts where multilayer wire crossing was used. In this paper the concept of multilayer wire crossing has been extended to design logic gates in multilayers. Using a 5-input majority gate in a multilayer, a 1-bit and 2-bit adder have been designed in the proposed multilayer gate design paradigm. A comparison has been made with some adders reported previously in the literature and it has been shown that circuits designed in the proposed design paradigm are much more efficient in terms of area, the requirement of QCA cells in the design and the input-output delay of the circuit. Over all, the availability of one additional spatial dimension makes the design process much more flexible and there is scope for the customizability of logic gate designs to make the circuit compact.     

Electrical transport properties of polyvinyl alcohol–selenium nanocomposite films at and above room temperature

Here, we report the DC and AC electrical properties of polyvinyl alcohol (PVA)–selenium (Se) nanocomposite films in the temperature (T) range 298 K ≤ T ≤ 420 K and in the frequency (f) range 120 Hz ≤ f ≤ 1 MHz. The introduction of selenium nanoparticles into the PVA matrix slightly increases the values of DC conductivity whose temperature dependency obeys Vogel–Fulcher–Tammann law. The AC conductivity follows a power law with frequency in which the temperature dependence of the frequency exponent suggests that the correlated barrier hopping is the dominant charge transport mechanism for the nanocomposite films. Comparative discussions with Dyre’s random free-energy barrier model have also been made in this regard. The increase in AC conductivity with increase in nanoparticles concentration was also observed and attributed to the corresponding increase in conducting channels in the PVA matrix. The real part of the dielectric constant increases either with increase in temperature or with increase in selenium nanoparticles loading into the polymer matrix, which may be attributed to the enhancement of interfacial polarization. The frequency dispersion of the dielectric spectra has been modeled according to the modified Cole–Cole equation. Well-defined peaks were appeared in the plotting of imaginary part of electric modulus with frequency above room temperature, which was fitted with suitable equations to account for the deviations from ideal Debye-type behavior. Though the current–voltage characteristics are linear at smaller voltages, it appreciably becomes nonlinear at higher voltages. This nonlinearity has been accounted in light of Werner’s model and back to back Schottky diode model.     

1D Copper Nanostructures: Progress,Challenges and Opportunities

One‐dimensional noble metal nanostructures are important components in modern nanoscience and nanotechnology due to their unique optical, electrical, mechanical, and thermal properties. However, their cost and scalability may become a major bottleneck for real‐world applications. Copper, being an earth‐abundant metallic element, is an ideal candidate for commercial applications. It is critical to develop technologies to produce 1D copper nanostructures with high monodispersity, stability and oxygen‐resistance for future low‐cost nano‐enabled materials and devices. This article covers comprehensively the current progress in 1D copper nanostructures, most predominantly nanorods and nanowires. First, various synthetic methodologies developed so far to generate 1D copper nanostructures are thoroughly described; the methodologies are in conjunction with the discussion of microscopic, spectrophotometric, crystallographic and morphological characterizations. Next, striking electrical, optical, mechanical and thermal properties of 1D copper nanostructures are highlighted. Additionally, the emerging applications of 1D copper nanostructures in flexible electronics, transparent electrodes, low cost solar cells, field emission devices are covered, amongst others. Finally, there is a brief discussion of the remaining challenges and opportunities.     

Transistor size optimization in digital circuits using ant colony optimization for continuous domain

In this paper, ant colony optimization (ACO) algorithm is presented, as a tool to find transistor sizes in digital circuits. Performance of ACO has been tested on four digital circuits, of different complexity, to find optimum balance between power and delay of circuits. Optimization problem has been set up by first, formulating an objective function, to be minimized, for each circuit and then finding the values of variables of circuits, using optimization algorithm. For the purpose of examining the results, circuits are optimized using genetic algorithm (GA) also. Results show that, ACO performs better than GA, for all the four circuits, in finding optimized transistor sizes. Copyright © 2012 John Wiley & Sons, Ltd.     

New Semifluorinated Siloxane‐Grafted Copolyimides: Synthesis and Comparison with Their Linear Analogs

A siloxane‐grafted new diamino monomer DBPDMS has been prepared and used as a co‐monomer in combination with the fluorinated diamine monomer TFBB to prepare siloxane‐grafted polyimides. The polymers have been characterized by means of GPC, IR, and NMR. Their thermal, mechanical, and surface properties have been evaluated and compared with the homopolyimide and with polyimides where polysiloxane is incorporated in the main chain. DSC revealed melting of the grafted siloxane chain at sub‐ambient temperature and a glass transition corresponding to the main polymer chain at high temperature. Isothermal gravimetric analysis at 350 °C indicated that grafted siloxane moiety can be removed thermally from the polymer chain without affecting the polymer backbone.

     

A comprehensive panel of turn-on caspase biosensors for investigating caspase specificity and caspase activation pathways

Caspases play a central role in apoptosis, differentiation, and proliferation, and represent important therapeutic targets for treating cancer and inflammatory disorders. Toward the goal of developing new tools to probe caspase substrate cleavage specificity as well as to systematically interrogate caspase activation pathways, we have constructed and investigated a comprehensive panel of caspase biosensors with a split-luciferase enabled bioluminescent read out. We first interrogated the panel of caspase biosensors for substrate cleavage specificity of caspase 1-10 in widely utilized in vitro translation systems, namely, rabbit reticulocyte lysate (RRL) and wheat germ extract (WGE). Commercial RRL was found to be unsuitable for investigating caspase specificity, owing to surprising levels of endogenous caspase activity, while specificity profiles of the caspase sensors in WGE agree very well with traditional peptide probes. The full panel of biosensors was utilized for studying caspase activation and inhibition in several mammalian cytosolic extracts, clearly demonstrating that they can be utilized to directly monitor activation or inhibition of procaspase 3/7. Furthermore, the complete panel of caspase biosensors also provided new insights into caspase activation pathways wherein we surprisingly discovered the activation of procaspase 3/7 by caspase 4/5.