Theory for the Load Relaxation Technique in Fracture Studies Using Four-Point-Bend Chevron-Notched Specimens

The load-relaxation technique is reviewed using the energy approach for four-point-bend chevron-notched samples. The influence of the sample and bending geometry and the stiffness of the testing system on the strain-energy release rate is considered. Proper experimental design allows the study of fracture initiation, propagation, and arrest, Special attention is paid to the effect of overload at fracture initiation on crack propagation. It is concluded that the chevron–notched sample offers great flexibility for gaining information on the fracture properties of ceramic materials.     

Factors that affect the aggregation of rennet-altered casein micelles at low temperatures

The effects of temperature, CaCl₂ concentration, pH and ionic strength of milk on the aggregation of casein micelles in milk renneted at 15ºC were studied using particle size analysis determined by laser-light scattering. The rate of aggregation of rennet-altered casein micelles became significantly slower on reducing the temperature of renneting from 30 to 10ºC. At 15ºC, the rate of aggregation of rennet-altered casein micelles increased significantly on adding CaCl₂, on reducing the pH of renneted milk or on adding NaCl (up to 50 m m ). These results indicate that particle size analysis can be used successfully to study the aggregation of rennet-altered casein micelles.     

A new approach for the design of multivariable feedback systems

A new design technique for multivariable feedback systems is presented. In this approach, n —1 open-loop transfer functions at different inputs of the plant, with all other feedback paths closed, are specified in advance, and are achieved exactly. The nth open-loop transfer function is a by-product of the design process, such that the overall feedback system is stabilized. The design approach is fitted to solve problems in which the plant elements can have non-stable poles and non-minimum phase zeros. The design process is straightforward, no iterations are necessary, and the achieved design copes exactly with the design specifications. The gainbandwidths of the different lis and the overall loop gain l* might be constrained due to non-stable poles and zeros of the plant elements. Based on the obtained different loop gains, any input output matrix T can bo achieved with the aid of an appropriate prefilter matrix F.     

Thermal-Shock Structures in a Partially Stabilized ZrO2 in the System CaO-ZrO2

The stress-relieving mechanisms in two batches of thermal-shock-resistant ZrO₂ partially stabilized by CaO were investigated by electron-optical replication techniques. In one batch of material, thermal shock produces a high density of micro-cracks; this behavior is interpreted as resulting from the brittle nature of the matrix cubic phase. In the other batch of material, thermal shock produces coherent "bumps," suggesting that the material acts in a ductile fashion.     

Modified atmosphere packaging of common mushroom

Until recently, the films used for packaging fresh fruits and vegetables were not permeable enough to balance the high respiration rate of mushrooms. Consequently, modified atmosphere packaging (MAP) in sealed pouches or punnets was not appropriate for this commodity. Four microporous films in oriented polypropylene (OPP) and one film currently used to overwrap mushroom punnets (stretchable PVC) were tested. Mushroom punnets placed into pouches were stored at 4 and 10°C for 8 days. the influence of the modified atmosphere on the marketing quality of pre-packed mushrooms was assessed by measuring the external and internal colour, development stage, firmness and microbial growth. A mathematical model was used to predict the gas composition within the pouches at steady state as a function of the film properties and the characteristics of the plant tissues. the equation calculated from the simplified model shows a linear relationship between the reciprocal of O₂ concentration at steady state, (1/x) at 10 and 4°C and the reciprocal of the film permeability, (1/PmO₂).     

Inhomogeneous Dehydroxylation of Talc

Dehydroxylation and enstatite development during the decomposition of talc were investigated by transmission electron microscopy using in situ heating. Bubbles and voids are produced during dehydroxylation, and enstatite then precipitates near the voids. Evidence of preferential bubble nucleation at dislocations was obtained. Enstatite crystallites of random orientation were observed initially but on further heating the product phase was formed topotactically.     

Influence of Anisotropy and Water Vapor on the Solid-State Reaction of CaO and Beta Quartz

The kinetics of the solid-state reaction of CaO and β-quartz were studied between 1000° and 1200°C in wet and dry N₂. Parabolic kinetics were observed in all cases; Ca₂SiO₄ was the only reaction product. The reaction was faster on the basal plane of the β-quartz than on the prism plane, and although moisture enhanced the reaction rates on both planes, the enhancement of the basal-plane reaction was significantly higher. Activation energies and results of marker experiments indicated that Ca²⁺ diffusion in the product was rate-controlling and that α-Ca₂SiO₄ possibly formed on the basal plane of the β-quartz and α'-Ca₂SiO₄ on the prism plane. A model for the observed kinetic enhancement in the presence of moisture is proposed on the basis of creation of interstitial Ca²⁺ sites in the products.