The deformation of the chill in experiments to determine the interfacial heat transfer coefficient during casting solidification

Interfacial heat transfer coefficients during casting solidification are often measured in experiments in which unidirectional heat transfer is assumed. Finite element modelling of the chill in these experiments has shown that the chill surface deforms elastically into a convex shape, the extent of which generally decreases with time. Examples from several different unidirectional solidification experiments are given. The deformation of the chill surface was also calculated with the assumption of nonuniform temperature boundary conditions. The deformation of the chill could be such that only in the central region of the casting-chill interface would the two surfaces be in contact, with a localised gap between them at their periphery. The extent of this deformation could be sufficient that heat transfer through the interface may not be unidirectional as assumed in the experiment and, depending on the location of the thermocouples placed close to the interface, the accuracy of the heat transfer coefficients calculated from the data collected at these points may therefore be affected.     

6—THE EFFECT OF ALKALINE AND ACID SWELLING AGENTS ON THE MECHANICAL PROPERTIES OF COTTON FIBRES

A study of the changes in mechanical properties of cotton brought about by sodium hydroxide, an iron tartrate complex in caustic soda (EWNN), cuprammonium hydroxide, and sulphuric, phosphoric, nitric, and perchloric acids has been made. Instead of choosing the normal mercerizing conditions with sodium hydroxide, different temperatures of treatment and of washing were studied to see what effect the condition had on the subsequent mechanical properties of the fibres. The variable studied with the other reagents was that of concentration, so that a distinction between interfibrillar and intrafibrillar swelling could be made. The main effect of swelling is to alter the extensibility of the fibre, and this has been analysed at different stages of loading up to break.     

Statistical analysis of recombination properties of the boron-oxygen defect in p-type Czochralski silicon

This paper presents the application of lifetime spectroscopy to the study of carrier-induced degradation ascribed to the boron-oxygen (BO) defect. Specifically, a large data set of p-type silicon samples is used to investigate two important aspects of carrier lifetime analysis: ①the methods used to extract the recombination lifetime associated with the defect and ② the underlying assumption that carrier injection does not affect lifetime components unrelated to the defect. The results demonstrate that the capture cross section ratio associated with the donor level of the BO defect (k₁) vary widely depending on the specific method used to extract the defect-specific recombination lifetime. For the data set studied here, it was also found that illumination used to form the defect caused minor, but statistically significant changes in the surface passivation used. This violation of the fundamental assumption could be accounted for by applying appropriate curve fitting methods, resulting in an improved estimate of k₁ (11.90±0.45) for the fully formed BO defect when modeled using the donor level alone. Illumination also appeared to cause a minor, apparently injectionindependent change in lifetime that could not be attributed to the donor level of the BO defect alone and is likely related to the acceptor level of the BO defect. While specific to the BO defect, this study has implications for the use of lifetime spectroscopy to study other carrier induced defects. Finally, we demonstrate the use of a unit-less regression goodness-of-fit metric for lifetime data that is easy to interpret and accounts for repeatability error.     

Non-invasive moisture monitoring within an earth embankment — a precursor to failure

An experimental monitoring system is described using electrical resistivity as a proxy for imaging changing moisture content distribution in engineered earthworks. The approach is illustrated using a case history concerning a road embankment constructed of tropical red soil in western Kenya.Tropical red soils have highly variable properties, governed by their soil fabric and mineralogy. As earthworks materials, their geotechnical behaviour is extremely sensitive to changes in moisture content and compaction. The relationship between moisture content and electrical resistivity was established in the laboratory on core obtained using a monitored drilling and sampling technique.The non-invasive nature of electrical resistivity surveys was exploited in the design of a monitoring system placed below the pavement in the topmost layers of compacted soil. Monitoring over a period of 18 months is reported, starting prior to the construction of the pavement following the completion of soil compaction. Initially substantial variability in moisture content was inferred from surface monitoring, and even larger changes were seen in corresponding downhole measurements.The moisture content within the body of the embankment stabilised after six months, while a moist layer ‘trapped’ beneath the pavement dissipated over the following 10 months. Two surveys were undertaken during the ‘December rains’; they showed large changes in moisture content had occurred quickly in the surface layers on one side of the embankment. This area subsequently failed as a small landslip and was remediated by additional drainage.     

CMOS process independent propagation delay macromodelling

An accurate CMOS process independent propagation delay macromodel is presented for inverter and multiple input NAND and NOR gates. A new nonsymmetrical input dependent delay model is shown to improve delay estimation accuracy. CMOS process independence is achieved without the application of recurrent data fitting techniques     

Carbon deposition from a γ-irradiated CO2/CO/CH4/C2H6 gas mixture on the manganese oxides MnO, Mn3O4 and Mn2O3

The composition of oxides formed on steel surfaces within power reactors may influence heat transfer efficiency. Previous studies have indicated that carbon is deposited on spinal-type oxides containing manganese, iron, cobalt, nickel and chromium. In this investigation, characterised manganese oxides have been subjected to γ-irradiation under conditions similar to those experienced in reactors in an effort to understand the catalytic processes involved in deposit initiation and growth. Mn₃O₄ and Mn₂O₃, under the conditions present in the γ-cell, were reduced to MnO during the time of exposure. Relative carbon deposition rates were observed to follow the trend MnO>Mn₃O₄≈Mn₂O₃.     

Sensitivity-based CMOS VLSI circuit performance optimisation

Sensitivity models are presented for propagation delay and average power dissipation which provide low-cost and accurate differential performance information not previously available. A sensitivity-based optimisation technique is compared with a formal mathematical optimisation technique and the results demonstrate that accurate VLSI circuit performance optimisation is now feasible     

Anhydrous fixation of dry plant tissue using non-aqueous fixatives

Non-aqueous preparation techniques such as freeze fracture of the dry tissue, fixation using dimethylsulphoxide as a vehicle for glutaraldehyde, and osmium vapour as a fixative have been used to investigate the fine structure of plant material in the dry state. Fixation using anhydrous glutaraldehyde dissolved in dimethylsulphoxide preserves existing cell structure and cell wall characteristics whereas conventional aqueous fixation methods hydrate the tissue during fixation and this gives a distorted impression of true cell structure.     

Bio-inspired design and movement generation of dung beetle-like legs

African ball-rolling dung beetles can use their front legs for multiple purposes that include walking, manipulating or forming a dung ball, and also transporting it. Their multifunctional legs can be used as inspiration for the design of a multifunctional robot leg. Thus, in this paper, we present the development of real robot legs based on the study of the front legs of the beetle. The leg movements of the beetle, during walking as well as manipulating and transporting a dung ball, were observed and reproduced on the robot leg. Each robot leg consists of three main segments which were built using 3D printing. The segments were combined with four active joints in total (i.e., 4 degrees of freedom) to mimic the leg movements of the beetle for locomotion as well as object manipulation and transportation. Kinematics analysis of the leg was also performed to identify its workspace. The results show that the robot leg is able to perform all the movements with trajectories comparable to the beetle leg. To this end, the study contributes not only to the design of novel multifunctional robot legs but also to the methodology for bio-inspired leg design.