Fabrication and High Temperature Creep Behaviour of Interpenetrated Nickel–Chromium/Alumina Composites

A method to manufacture unique interpenetrating 50 vol% nickel–chromium/alumina composites, namely NiCr8020/Al₂O₃/50_pp, is reported. Key process is a high temperature squeeze casting procedure at temperatures above 1500 °C used to infiltrate alloy NiCr8020 into porous alumina preforms exhibiting a bimodal pore structure. Microstructure and mechanical properties of this new composite material are presented. Bending creep tests at 1000 and 1150 °C are performed. The obtained results are discussed in comparison to a nickel based superalloy. It is shown, that particle preform reinforcement is a promising method to improve creep resistance of nickel based alloys significantly. Due to its outstanding creep resistance, the composite material has a high potential for structural and tribological applications at high temperatures in oxidizing atmospheres.     

Detection of Plaque in Coronary Artery in CMRI Images and 3D Visualization of Blood Flow

Detection of blocks in coronary arteries is becoming crucial interest for early detection of heart attacks. In this paper we propose a framework for detection of plaque in coronary arteries from cardio vascular magnetic resonance imaging(CMRI). It is a quantitative tool for the assessment of cardiovascular diseases. First, select a region of interest and segment the region of coronary artery using enhanced region based active contour (ERAC). Secondly the centreline extraction and lumen segmentation are integrated to extract the artery centreline using geometric moments and the vessel direction using Hessian matrix and segment the vessel lumen in each slice using ERAC. A boundary searching method is adapted to fine tune the segmented surface in each slice of CMRI image. Third, the soft plaques in the coronary artery are extracted by thresholding the segmented region. Finally a 3D visualization of blood flow in coronary artery is presented and the volume of blood flow is calculated. In the experiments we have employed 22 datasets of CMRI images. The experimental results show an average accuracy of 97.6% and with a mean and standard deviation of false discovery rate of 2.48 ± 0.002.

     

Electromyographical indication of muscular fatigue in occupational field studies

Surface electromyography offers a valuable tool for the indication of muscular fatigue in occupational field studies. For this purpose, the time course of the electromyogram (EMG) has to be analysed, in order to detect typical fatigue-induced changes such as an increase in EMG amplitude or a shift in the spectral distribution towards lower frequencies. Such procedures need a detailed knowledge about the actual activity of the person and muscle under test for the total working time. This can be attained by encoding the activity of the person during the work and recording an electrical code signal together with the electrophysiological signals. For the indication of muscle fatigue, EMGs for situations connected with similar muscle load should only be compared, since the EMG amplitude as well as the spectrum do not only depend upon the fatigue state, but also upon the produced muscle force. This demand can be fulfilled by (i) interrupting the work and performing test contractions of known force in a predefined body posture or (ii) by comparing situations connected with a certain reference activity. (iii) In a recently developed approach for the joint analysis of EMG amplitude and spectrum (JASA) changes in the amplitude and the spectrum are considered simultaneously. This method permits the discrimination between fatigue-induced and force-related EMG changes. Using this procedure, changes in the EMG can be attributed to categories like fatigue or recovery as well as increase or decrease in the force production of the muscle under test. Applications from field studies during manual materials handling in a weaving mill, price recording at scanner checkouts in a supermarket and the performance of surgical work using endoscopic operation techniques in urology demonstrate the appropriateness of electromyography for fatigue indication in occupational physiology and ergonomics. Nevertheless, the commonly used measures of muscular fatigue such as increase in EMG amplitude and left shift in EMG spectrum are primarily related to the electrical activation and its propagation along the muscle fibres. Their connection to the fatigue-induced reduction in the force generating capacity of the muscle under test includes complex physiological implications. Therefore, the need for further development of fatigue indicators which are more directly related to muscular force is recognized.

Relevance to industry

In occupational health and ergonomics indication of muscular fatigue is needed, since activities inducing muscular fatigue can be performed for a limited time, only, and the quality of work can be influenced negatively. Electromyography offers valuable tools for the indication of fatigue and the appropriate assessment of ergonomic design measures.     

Three-dimensional numerical simulation of microelectric discharge machining of Ti-6Al-4V

The International Journal of Advanced Manufacturing Technology - The aim of the present work is to develop a predictive thermal model based on heat transfer principle for the simulation of...     

Assessment of Stress Corrosion Cracking Resistance of Activated Tungsten Inert Gas-Welded Duplex Stainless Steel Joints

The stress corrosion cracking behavior of duplex stainless steel (DSS) weld joint largely depends on the ferrite-austenite phase microstructure balance. This phase balance is decided by the welding process used, heat input, welding conditions and the weld metal chemistry. In this investigation, the influence of activated tungsten inert gas (ATIG) and tungsten inert gas (TIG) welding processes on the stress corrosion cracking (SCC) resistance of DSS joints was evaluated and compared. Boiling magnesium chloride (45 wt.%) environment maintained at 155 °C was used. The microstructure and ferrite content of different weld zones are correlated with the outcome of sustained load, SCC test. Irrespective of the welding processes used, SCC resistance of weld joints was inferior to that of the base metal. However, ATIG weld joint exhibited superior resistance to SCC than the TIG weld joint. The crack initiation and final failure were in the weld metal for the ATIG weld joint; they were in the heat-affected zone for the TIG weld joint.     

The synthesis and characterisation of reactive poly(p-phenylene terephthalamide)s: A route towards compression stable aramid fibres

Herein we report on the synthesis of reactive poly(p-phenylene terephthalamide) (PPTA) oligomers and the preparation and characterisation of aramid fibres thereof. Methacrylate and maleimide reactive end-groups were found to be sufficiently stable in H₂SO₄ at 85 °C and they were used to prepare reactive PPTA oligomers. Lyotropic spin-dopes could be prepared with up to 20 wt% of reactive oligomer (M_n = 3900 g mol⁻¹) and this modification did not interfere with the fibre spinning process and had no effect on the fibre tensile properties. The as-spun fibres did indeed show a modest (+0.1 GPa) improvement in compression strength. A high temperature treatment at 380 °C resulted in fibres which all show a significant increase in compressive strength over their as-spun precursors, i.e. from 0.7 to 0.9 GPa. When fibres were treated at 430 °C the compression values of the oligomer-modified fibres dropped somewhat, whereas unmodified PPTA displayed a compressive strength of 1.1 GPa. Other favourable fibre properties such as modulus and tenacity were not compromised.     

Structure-Based Optimization of Inhibitors of the Aspartic Protease Endothiapepsin

Aspartic proteases are a class of enzymes that play a causative role in numerous diseases such as malaria (plasmepsins), Alzheimer’s disease (β-secretase), fungal infections (secreted aspartic proteases), and hypertension (renin). We have chosen endothiapepsin as a model enzyme of this class of enzymes, for the design, preparation and biochemical evaluation of a new series of inhibitors of endothiapepsin. Here, we have optimized a hit, identified by de novo structure-based drug design (SBDD) and DCC, by using structure-based design approaches focusing on the optimization of an amide–π interaction. Biochemical results are in agreement with SBDD. These results will provide useful insights for future structure-based optimization of inhibitors for the real drug targets as well as insights into molecular recognition.