Enhancement of fracture toughness in bioactive glass-based nanocomposites with nanocrystalline forsterite as advanced biomaterials for bone tissue engineering applications

In this research, the replacement effects of bioactive glass (BG) by nanocrystalline forsterite (NF) on the biomineralization, microstructural and mechanical properties of BG-based nanocomposites were investigated. The hybrid nanocomposites with different NF contents (0, 10, 20, and 30 wt%) were prepared from the nanopowders by means of conventional cold pressing method. Surprisingly, the addition of NF provided redundant mechanisms to improve the toughness of the BG matrix without deteriorating its biomineralization properties. In addition, the resulting enhancement in the fracture toughness, observed for the first time in highly bioactive BG/NF nanocomposites, indicated the potential of the prepared nanocomposites as advanced biomaterials for load-bearing bone tissue engineering applications.     

27—THE NORMAL FORCE BETWEEN TWISTED FILAMENTS: PART II: EXPERIMENTAL VERIFICATION

In a previous paper, the importance of lateral pressure in the tension and bending behaviour of yarns was discussed; a theoretical model, which included the effects of bending and torsional rigidities as well as the tensile, shear, and frictional forces, was proposed, and expressions for the lateral pressures were derived. In this sequel, the experimental verification of the previously derived expressions has been carried out on a very simple twisted structure, consisting of two rubber strands. The results obtained support the theoretical predictions of the lateral pressure for the experimental model and lead to the conclusion that, for filaments with significant torsional and bending rigidities, lateral pressures are obtained in the yarn even when there is no significant tension on the individual filaments. An approximate scheme for estimating the lateral pressures in an idealized, close-packed, multilayered continuous-filament yarn is proposed as an extension of the above results.     

Effect of Reinforcement Volume Fraction on the Wear Behavior of Al-SiC<Subscript><Emphasis Type=Bold>p</Emphasis></Subscript> Composites Prepared by Spark Plasma Sintering

Most investigations on MMCs were carried out using conventional methods. Employing a different approach, this study concentrated on compaction, hardness and wear behavior of Al-SiC composites with different reinforcement volume fractions (5–15%) by spark plasma sintering method. Hardness and density test results of the composite samples used in this study were significantly higher than conventionally produced composites. Such increase in density and hardness resulted in lower wear rate. To study the effect of applied load on samples wear behavior, wear tests were carried out under 1, 3 and 10 N loads with 0.07 m/s sliding rate. Results revealed that in all the applied loads, composite samples had lower wear rates and lower friction coefficients than those of unreinforced aluminum. Conversely, increase in volume fraction of reinforcement particles led to decrease in wear rates and friction coefficients of the composite specimens which were more tangible in Al-15%SiC sample. Obtained data showed that by increasing the applied load, friction coefficient and wear rate increased in all the samples. Also dominant wear mechanism was determined using SEM micrographs of sample surfaces after wear tests.     

Robust Iterative Learning Control Design: Application to a Robot Manipulator

This paper deals with robust iterative learning control design for uncertain single-input-single-output linear time-invariant systems. The design procedure is based upon solving the robust performance condition using the Youla parameterization and the mu-synthesis approach to obtain a feedback controller. Thereafter, a convergent iterative learning law is obtained by using the performance weighting function involved in the robust performance condition. Experimental results, on a CRS465 robot manipulator, are provided to illustrate the effectiveness of the proposed design method.     

Influence of quality assurance on patients dose reduction in some hospitals

The collective effective dose to a population, a-mong man made sources of radiation, is due to a largenumber of medical X-ray examinations performed[1].Nowadays, the use of X-rays is one of the most ef-fective medical techniques for examining and curing p…     

Controlling the degradation rate of bioactive magnesium implants by electrophoretic deposition of akermanite coating

In order to improve the corrosion resistance and the surface bioactivity of biodegradable magnesium alloys, a nanostructured akermanite (Ca₂MgSi₂O₇) coating was grown on AZ91 magnesium alloy through electrophoretic deposition (EPD) assisted with micro arc oxidation (MAO) method. The crystalline structures, morphologies and compositions of samples were characterized by X–ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The in vitro bio–corrosion (biodegradability) and bioactivity behaviors of samples were investigated by electrochemical and immersion tests. The experimental results indicated that the nanostructured akermanite coating could slow down the corrosion rate and improve the in vitro bioactivity of biodegradable magnesium alloy. Thus, magnesium alloy coated with nanostructured akermanite may be a promising candidate to be used as biodegradable bone implants.     

Kinetic Study of Sodium Cocoyl Sarcosinate Synthesis and Factors Affecting the Reaction on Bench and Pilot Scales

Sodium cocoyl sarcosinate is an important surfactant with a particular chemical structure and many practical applications in various industries. The synthesis of sodium cocoyl sarcosinate involves the reaction of cocoyl chloride and N-methyl glycine. The influences of reactant molar ratios, temperature, reaction time, pH, and solvent on the reaction yield were investigated and also the kinetics of the reaction was studied. It was found that the reaction follows second order kinetics and the reaction rate constant is 0.0153?mol^?1?L?s^?1 at 35?°C. Also production of sodium cocoyl sarcosinate was carried out at bench and pilot scales which is described in details.     

Modeling the effect of skewness and kurtosis on the static friction coefficient of rough surfaces

Engineering surfaces possess roughnesses that exhibit asymmetrical height distributions. However, the Gaussian distribution is most often used to characterize the topography of surfaces, and is also used in models to predict contact and friction parameters. In this paper, the effects of kurtosis and skewness on different levels of surface roughness are investigated independently. This is accomplished by adopting the Pearson system of frequency curves and used in conjunction with a static friction model for rough surfaces to calculate the friction force and friction coefficient. This study is the first attempt to independently model the effect of kurtosis and skewness on the static friction and friction coefficient. It is predicted that surfaces with high kurtosis and positive skewness exhibit lower static friction coefficient compared to the Gaussian case. More importantly, it is predicted that, for high kurtosis values, the static friction coefficient decreases with decreasing external force rather than increasing as seen with increasing skewness. This is a very promising result for applications involving smooth lightly loaded contacts such as magnetic storage devices and microelectromechanical systems. The practical significance of the present model is specifically demonstrated on static friction predictions in magnetic storage head–disk interfaces. Such predictions can be used to determine the optimal characteristics of such devices prior to fabrication to achieve lower friction in terms of surface roughness, mechanical properties, apparent contact area, and operational environment.