Efficiency and Optimality of Two-Period Limit Cycle Walking

This paper investigates the efficiency of a two-period gait from the kinetic energy viewpoint. First, we formulate a steady two-period gait for a compass-like bipedal robot by using a simple recurrence formula for the kinetic energy of an asymmetric rimless wheel. Then, we theoretically show that, in the case where the mean value of the hip angle is constant, the generated two-period steady gait is less efficient than a one-period symmetric gait in terms of kinetic energy. We also show that the symmetric gait is not always optimal from another viewpoint. We then extend the analysis to biped walking and investigate the validity of the derived method through numerical simulations of virtual passive dynamic walking.     

Mechanochemical synthesis of alumina–zirconia nanocomposite powder

Abstract

The alumina–zirconia nanocomposite powder has been synthesised by mechanical activation of a dry powder mixture of AlCl₃, ZrCl₄ and CaO. Mechanical milling of the above raw materials with the conditions adopted in this study resulted in the formation of a mixture consisting of crystalline CaO and amorphous aluminium and zirconium chlorides phases. There was no sign of chemical reaction occurring during milling stage as evidenced by X-ray diffraction (XRD) studies. Subsequent heat treatment of the milled powder at 350°C resulted in the occurrence of displacement reaction and the formation of ZrO₂ and Al₂O₃ particles within a water soluble CaCl₂ matrix. The effect of higher temperature calcination on the phase development in this powder mixture was followed by XRD analysis. Scanning electron microscopy and differential thermal analysis were also used in the characterisation of the powders. Perhaps the most important observation in this study was the formation of α-Al₂O₃ phase at a very low temperature of 400°C.     

Synthesis of mullite aggregates from fly ash: effect on thermomechanical behaviour of low cement castables

Abstract

Refractory aggregates were synthesised from beneficiated fly ash by reaction sintering with calcined alumina at 1600°C, and 83% mullite yield was achieved. The aggregates had low porosity, low thermal expansion and good refractoriness. To study compatibility in castable refractories, the aggregates were used in high alumina cement based low cement castables and their thermomechanical behaviour was studied. Microstructural characterisation revealed that the emergence of new bond phases such as mullite and calcium hexa-aluminate had a beneficial effect on the hot modulus of rupture and creep resistance of castables. An attempt was made to establish a structure–property relationship.     

Change of phase composition and morphology of sonochemically synthesised hydroxyapatite nanoparticles with glycosaminoglycans during thermal treatment

Abstract

Based on the preparation of glycosaminoglycans (GAGs) stabilised hydroxyapatite (HAP) nanoparticle suspension via sonochemical synthesis, the change of phase composition and morphology of freeze dried HAP nanoparticles with GAGs was investigated from 500 to 1200°C by TEM, X-ray diffraction, Fourier transform infrared spectroscopy and SEM. Results show that thermal treatment brought the phase transformation and the morphology change of HAP nanoparticles. In the low temperature stage (～650°C), the samples were mainly composed of HAP as main crystalline phase and β-NaCaPO₄ as minor crystalline phase. This phase transformation was mainly attributed to the residues containing sodium derived from combustion of GAGs. The particles were near spherical, and the nanocrystalline nature was retained. In the high temperature stage (650–1200°C), the samples were glass ceramic powders composed of HAP, β-tricalcium phosphate, Na₃Ca₆(PO₄)₅, β-NaCaPO₄ and Na–Ca–P–O glass phase. The grains rapidly grew into larger particles with morphology transformation from rodlike shape to irregular shape and the size increase from (0·1–0·15) × (0·3–0·5) μm to 1·5–10 μm.     

Combustion synthesis and characterisation of lanthanum hexa-aluminate

Abstract

Lanthanum hexa-aluminate (LHA) is considered a promising material for thermal barrier coatings for gas turbine applications as well as oxidation resistant coatings for fibres in oxide based ceramic composites. Combustion synthesis has attractive advantages such as simple experimental setup, low cost, short reaction time, energy savings due to exothermic reaction, better control of stoichiometry and fine powder size. The present study involves combustion synthesis of LHA using lanthanum and aluminium nitrates as oxidising precursors, and urea as fuel. The precursor salts were dissolved in a minimum amount of deionised water and the solution was heated in a mantle heater to temperatures of around 300–350°C, at which combustion takes place with rapid evolution of gas. The LHA powder was also prepared by a precipitation route for comparative study. The as synthesised powders were calcined at up to 1450°C and subjected to X-ray diffraction for phase evolution studies. Product powders were then characterised. The influence of the lanthanum/aluminium molar ratio in the starting composition and the effect of temperature on the formation sequences of lanthanum monoaluminate (LMA) and LHA and on the conversion of LMA to LHA are discussed.     

Ladder Climbing Method for the Limb Mechanism Robot ASTERISK

A ladder climbing method for the limb mechanism robot ASTERISK is proposed. This robot has six legs. The upper three legs hold on to the upper rung from both sides alternately, just like pinching it. The lower three legs hold on to the lower rung in the same way. Hence, the robot can take hold of the ladder stably. First, the robot releases the left upper and lower legs from the current rungs, and hangs them on the next rungs while supporting itself with the other four legs. Then, the mid two legs and the right two legs are moved to the next rungs in sequence. Finally, the robot lifts up its body using the six legs. Depending on the relative pose of the robot to the ladder, the robot automatically selects the legs that can support vertical and/or horizontal forces applied by the rungs. The robot then distributes its weight to the legs supporting the vertical force based on their force margins. The legs that cannot support forces are controlled to always touch the rungs slightly in order to pinch the rungs with the other legs. The advantages of the proposed gait and control method are verified by analysis of the leg workspace for generating the ladder climb gait, analysis of the range of force direction that the legs can support, analysis of the joint torques required for ladder climbing and an experiment on force distribution. Finally, the range of ladder pitch variation that ASTERISK can climb is clarified.     

Plenary Address Traditional whitewares industries

Abstract

The technical and engineering developments that have taken place in the whitewares sector over the past century have focused on improving quality and productivity. Now, however, demand is for more individualised products, customer rather than mass oriented production, a trend that will be accelerated by e-commerce. The life cycle of goods will continue to shorten, placing greater emphasis on product development, marketing, and distribution functions.     

Effect of solution treatment under load on microstructure and fabrication of porous NiTi shape memory alloy by self-propagating high temperature synthesis

Abstract

Porous NiTi shape memory alloy was fabricated by self-propagating high temperature synthesis. Effects of solution treatment under load applied on the microstructure were investigated. The densities of the phases changed insignificantly with solution treatment but the intermetallic phases such as Ti₂Ni, Ni₄Ti₃ and Ni₃Ti₂ disappeared and the density of B2(NiTi) phase increased with the load applied during solution treatment. Consequently, porous NiTi SMA with ideal pore characteristics, high chemical homogeneity and high strength for hard tissue implants was obtained.     

Microstructural evolution in bone china

Abstract

Phase and microstructural evolution in model bone china bodies was determined by XRD and electron microscopy of quenched samples fired for 3 h at 600–1500°C. Unfired but shaped bone china comprised bone ash and clay agglomerates (≤70 μm) in a matrix of smaller (from submicron to 10 μm) mixed clay, feldspar, and bone ash particles. The unfired microstructure and subsequent phase evolution is believed to be strongly dependent on the extent of prior mixing. On firing, the clay component dehydroxylated to metakaolin at ～550°C. Metastable sanidine formed from decomposition of the feldspar component above 600°C and dissolved at 1100°C. The bone ash com ponent decomposed into β-TCP and lime (and/or Ca²⁺ and O^2- ions) beginning at ～800°C. CaO from the bone ash reacts with the clay decomposition products forming liquid and anorthite at ～900°C. Liquid formation is due to reaction of CaO with feldspar and clay relict grains and is discussed in terms of the CaO–P₂O₅–Al₂O₃ ternary phase diagram. Above 1200°C pure bone ash relicts contained small (5–10 μm) β-TCP crystals, CaO penetrated clay relicts contained anorthite, and mixed clay–bone–feldspar regions contained both anorthite and larger (>50 μm) β-TCP crystals in calcium aluminosilicate glass. The major phase in the clay relicts was anorthite although a few elongated (～100 nm) needles resembling mullite in composition and morphology also crystallised in samples fired to 1100°C and grew to ～30 μm in length at 1300°C.     

Informational Performance In Radiography

An “information index” as a measure of informational performance of a radiographic system is derived, taking into account visual threshold concepts of the human eye. Theoretically, this information index is related to the Wiener spectrum, describing the noise power spectrum in a detection system as a function of spatial frequency, and to the informational sensitivity. It is found that the “spread” (unsharpness or blur) in a radiographic system determines the smallest image size for which the information index may be found whereas the maximum scan of the eye (~02 inch) determines the largest image size. The information index depends on quantum-statistical fluctuations and varies with the speed of the radiographic film, its gradient and the optical density to which It is developed. These conclusions are borne out in experiments. Practically, the information index is a useful tool to judge the adequacy of different photographic materials for radiographic applications. A procedure for routine evaluation of the informational performance of radiographic systems is described.