An efficient hybrid conventional method to fabricate nacre-like bulk nano-laminar composites

Bulk nano-laminar composites were fabricated by a novel technique called Hot-press Assisted Slip Casting (HASC) which combines hot-pressing and slip-casting to improve alignment and volume fraction of the reinforcement. Alumina flakes were used as filler in an epoxy matrix. Microstructure of composites and alignment of flakes were characterized by Scanning Electron Microscope (SEM). Three point bending test and Vickers hardness test were done for mechanical characterization of composites. Flexural tests on Chevron-notched specimens revealed a high work-of-fracture in the case of the fabricated composites reaching to 254 J/m². Fracture surface of three point bending samples were examined by SEM. Main fracture mechanism is debonding of flakes from the matrix. With its high volume fraction (60%) of reinforcement phase and high degree of flake alignment, a nacre-like microstructure was achieved with a relatively efficient, cost effective and simple hybrid conventional method.     

Formation of nitrogen-containing oligomers by methylglyoxal and amines in simulated evaporating cloud droplets

Reactions of methylglyoxal with amino acids, methylamine, and ammonium sulfate can take place in aqueous aerosol and evaporating cloud droplets. These processes are simulated by drying droplets and bulk solutions of these compounds (at low millimolar and 1 M concentrations, respectively) and analyzing the residuals by scanning mobility particle sizing, nuclear magnetic resonance, aerosol mass spectrometry (AMS), and electrospray ionization MS. The results are consistent with imine (but not diimine) formation on a time scale of seconds, followed by the formation of nitrogen-containing oligomers, methylimidazole, and dimethylimidazole products on a time scale of minutes to hours. Measured elemental ratios are consistent with imidazoles and oligomers being major reaction products, while effective aerosol densities suggest extensive reactions take place within minutes. These reactions may be a source of the light-absorbing, nitrogen-containing oligomers observed in urban and biomass-burning aerosol particles.     

Adhesion of lacquer to phosphated steel — A shear test evaluation

Measurement of the adhesion toughness of a fast cure thermosetting powder coating used for corrosion protection of cold-rolled steel has been attempted in a shear test under uniform plane stress loading conditions at the interface. A specially designed test specimen preparation procedure (by direct crosslinking) and geometry (symmetrical) was developed to enable proper mechanical behaviour under shear initiation of fracture and uniform plane stress loading in the significant section of the specimen — the interface. The shear test was designed to measure the nominal and the net ultimate shear stress values (USS)_n and (USS)_net' as well as the critical stress intensity factor (SIF) of interfaces. From experimentally measured critical load at which the adhesion failed, the ultimate shear stress values (USS_net N mm^–2) were calculated and used as a quantitative information of the bond toughness along the interfaces. The experimental results with a range of specimens revealed that the test can, indeed, discern subtle variations influencing adhesion such as type of cold-rolled steel, an iron phosphate pretreatment before coating or variation in stoving temperatures. Fractographic analysis of shear failed specimens on mating surfaces revealed generation of a microcrack network in most of the fracture pattern tested, indicating fracture mechanism transitions characteristic of pure shear for both iron phosphated free cold-rolled steel-lacquer (SL) as well as for iron phosphated cold-rolled steel-lacquer (SPL) specimens. The fractographs, however, indicate fracture propagation more difficult for SPL specimens and comparatively smooth fracture surface for SL specimens, obviously affected by variations in their respective interface structure and morphology. This behaviour correlates well with measurements of (USS)_net in test.     

A mode II fracture specimen—finite element analysis

A series of studies which demonstrate the potential of a proposed mode II fracture specimen are reported. First, previously obtained photoelastic results[1–3] are reviewed so that this paper will be self-contained. Then, a finite element analysis is presented in order not only to corroborate the experimental results but also to calibrate the specimen for $\text{K}{}_{\mathrm{IIC}}$ measurements. Finally, a preliminary $\text{K}{}_{\mathrm{IIC}}$ test performed on a brittle steel specimen is described.     

Performances of hill-type and neural network muscle models-toward a myosignal-based exoskeleton.

Muscle models are the essential components of any musculoskeletal simulation. In addition, muscle models which are incorporated in neural-based prosthetic and orthotic devices may significantly improve their performance. The aim of the study was to compare the performances of two types of muscle models in terms of predicting the moments developed at the human elbow joint complex based on joint kinematics and neuromuscular activity. The performance evaluation of the muscle models was required to implement them in a powered myosignal-driven exoskeleton (orthotic device). The experimental setup included a passive exoskeleton capable of measuring the joint kinematics and dynamics in addition to the muscle myosignal activity (EMG). Two types of models were developed and analyzed: (i) a Hill-based model and (ii) a neural network. The task, which was selected for evaluating the muscle models performance, was the flexion-extension movement of the forearm with a hand-held weight. For this task the muscle model inputs were the normalized neural activation levels of the four main flexor-extensor muscles of the elbow joint, and the elbow joint angle and angular velocity. Using this inputs, the muscle model predicted the moment applied on the elbow joint during the movement. Results indicated a good performance of the Hill model, although the neural network predictions appeared to be superior. Relative advantages and shortcomings of both approaches were presented and discussed.     

A Unitary Analysis of some Voltage and Current Mode Linear Circuits

This paper presents a systematic and unitary analysis of a large class of current and voltage mode circuits based on a series-shunt-like configuration. Four possible OA types are considered for the basic amplifier. The amplifiers have voltage and current input signals and voltage and current outputs. The analysis method is based on the separation of the circuit signal graph in two different paths, one that controls the gain and the other that controls the bandwidth.     

Antioxidant activity of protein extracts from heat-treated or thermally processed chickpeas and white beans

In this study, antioxidant activities of water-soluble protein extracts from chickpeas and white beans were investigated. The area under the curve (AUC) values of lyophilized crude protein extracts (dialyzed or undialyzed) from thermally processed (121 °C for 20 min) or heat-treated (90 °C for 20 min) chickpeas (73–91 μmol trolox/g) and white beans (39–67 μmol trolox/g) indicated a higher free radical-scavenging capacity and thermostability for chickpea proteins than for white bean proteins. The thermal processing also increased the Fe⁺²-chelating capacity of lyophilized chickpea crude protein extracts 1.8-fold whereas it caused a 2.3-fold reduction in the Fe⁺²-chelating capacity of lyophilized white bean crude protein extracts. Dialysis increased the protein content of lyophilized chickpea extracts 1.5–2-fold but it did not affect the protein content of lyophilized white bean extracts significantly. Ammonium sulfate precipitation was not effective for selective precipitation of antioxidant proteins. However, it improved the free radical-scavenging capacity of lyophilized protein extracts from thermally processed chickpeas and white beans by almost 25% and 100%, respectively. DEAE-cellulose chromatography, indicated the presence of five (A₁–A₅) and three (B₁–B₃) antioxidant protein fractions in heat-treated and thermally processed chickpea protein extracts, respectively, and can be used for the partial purification of antioxidant proteins. The results of this study showed the good potential of chickpea proteins as thermostable natural food antioxidants.