Low-cycle fatigue in silicon: comparison with fcc metals

Undoped FZ silicon single crystals were cyclically loaded in tension‐compression under plastic strain amplitude control in a temperature and strain rate domain where the glide of dislocations is still controlled by the lattice friction: 1073–1173 K and (1.5–6) × 10⁻⁴s⁻¹; the plastic strain amplitude being varied from 6 × 10⁻⁴ to 10⁻². Cyclic hardening curves display logarithmic then linear hardening and pass through a maximum before the peak stress per cycle stabilizes. The maximum and stabilized stresses decrease when temperature increases. Microscopical observations suggest that strain localization takes place near the maximum cyclic stress and beyond. But, contrary to what is observed in fcc metals, the maximum or saturation stress decreases when the strain amplitude per cycle increases. Several types of dislocation arrangements, rather different from those found in copper, but looking more similar to Ni fatigued at low temperatures, were revealed by transmission electron microscopy. Before mechanical saturation, edge dislocation dipoles gather in thick stripes forming more or less corrugated walls, depending on the amplitude per cycle, when viewed normal to the primary slip plane. Once the maximum stress is reached, it seems that parts of the microstructure cease to participate in the imposed plastic strain, while others concentrate it. In active areas, thick walls condense into much thinner ones, forming chevrons when viewed normal to the slip plane. In areas which seem to be inactive, dipolar walls anneal out leaving a rather homogeneous distribution of prismatic loops. Thin PSBs with a well‐characterized ‘ladder‐structure’ are very rare. Characteristic lengths of the observed patterns are given and briefly discussed using current theories of cyclic deformation.     

Characterization of the flow behaviour of sausage emulsions with a simple tube viscometer

A specially designed tube viscometer was used to measure apparent viscosity during flow of Bologna type sausage emulsions moving through a pipe. Emulsions varied in fat content (from 21.8 to 44.3%) and in moisture/protein ratio (from 3.7 to 5.6), and the effects of added sodium chloride, sodium diphosphate, starch and blood plasma were investigated in a 36% fat, 3.7 moisture/protein emulsion.
The shear stresses determined as a function of shear rate were fitted by a power law. Yield stress of the emulsions was negligible relative to the applied stress. However, inspection of the flow profiles indicated that considerable slip of the sausage emulsion occurred at the pipe wall. Both emulsion flow and slip contribute to overall flow behaviour, so a kind of effective viscosity is determined. Intrinsic rheological properties and wall slip will both be affected by the composition of the sausage emulsion.     

Comments on “Transient stability of an a.c. generator by Lyapunov's direct method”

A matrix method is presented for the determination of the response sequences of discrete time-invariant linear systems for a large range of deterministic input sequences.

Using the z-transform formulation the transfer function of the discrete system is defined and, assuming that the input sequence is a linear combination of a certain set of basic sequences, it is demonstrated that an explicit formulation of the output sequence may be obtained by purely matrix operations. This approach not only simplifies the application of the z-transform technique but can also be used as the basis of a digital computer programme.

Examples are given to illustrate the use of the method including its application to the solution of general nth-order difference equations     

ORIGINAL TITLE: INTERPRETATION OF MICROMIXING EFFECTS ON FAST CONSECUTIVE-COMPETITIVE REACTIONS IN SEMI-BATCH STIRRED TANKS BY A SIMPLE INTERACTION MODEL

Liquid-liquid equilibrium data for two ternary systems were obtained. The experimental data were measured for cyclohexane-toluene-sulfolane at 17, 25 and 50°C, and for hexane-toluene-sulfolane at 18 and 25°C. The NTRL and UNIQUAC models were used to correlate the experimental results and to calculate the phase compositions of the ternary systems. The agreement between the experimental results and the fitted values was equally good with both of the models.     

Use of near infrared spectroscopy to evaluate the intensity of extrusion-cooking processing of pea flour

Twenty-five different pea extrudates were produced using a Clextral BC45 twinscrew extruder. Near infrared reflectance (NIR) spectra of the extrudates were recorded between 1100 and 2500 nm. the application of principal component analysis (PCA) on these spectral data permitted discrimination between the extrudates produced under moderate, intermediate or severe conditions of extrusion-cooking. the study of protein quality through solubility experiments, polyacrylamide gel electrophoresis, determination of available basic amino acids and brown colour measurement showed that, under moderate conditions of extrusion-cooking, protein was only slightly affected. All protein subunits could be restored after solubilization in phosphate buffer containing a detergent and a reducer of disulphide bonds. However, under severe conditions of extrusion-cooking, the extrudates exhibited a relatively intense brown colour and all protein fractions were implicated in non-disulphide covalent bonds and underwent some macromolecular degradation. Therefore, the spectral discrimination between pea extrudates which was related to the processing parameters, could also be related to the degree of transformation of these extrudates. Thus, the method may be used to classify an extrudate produced under unknown conditions by projecting its spectrum on the similarity maps obtained by PCA on a known collection of extrudates.     

Two Lipoxygenases from Germinated Barley-Heat and Kilning Stability

Using ammonium sulfate precipitation followed by hydrophobic and ion exchange chromatography, two lipoxygenase isoenzymes, LOX 1 and LOX 2, were 18.3- and 44.5-fold purified from germinated barley, with 18 and 24% recovery of activity respectively. LOX 1 and LOX 2 were characterized by isoelectric points 4.9 and 6.4, and molecular weights of 90 kd and 110 kd, respectively. Apparent Km values for linoleic acid were 0.06 mM for LOX 1 and 0.18 mM for LOX 2. LOX 1 converted linoleic acid to 9 and 13 hydroperoxides at about 4:1, whereas the 13 hydroperoxide was the major product formed by LOX 2 (ratio 3:7). For both isoforms, thermal inactivation data indicated first order kinetics with activation energies influenced by ionic strength and pH. Isoenzymes composition was analyzed for three kilning schemes: the 1:3 ratio between LOX 1 and LOX 2 observed in germinated barley increased during the course of kilning.     

Inhibition of Horse Bean and Germinated Barley Lipoxygenases by Some Phenolic Compounds

Phenolic compounds have been repeatedly implicated as potent antioxidants. Efficiency has been frequently estimated by radical scavenging activity and few reports have considered lipoxygenase (LOX) inhibition. Horse bean LOX was inhibited by a range of phenolic acids, gallates and flavonoids. All compounds tested were uncompetitive inhibitors with the exception of flavonol aglycons which were non competitive type. In each class of compounds, inhibition constants were strongly affected by structures. Inhibition patterns of (-)-epicatechin on germinated barley LOXs were detailed: (-)-epicatechin acted as an uncompetitive inhibitor while (-)-epicatechin reduced hydroperoxide formation by its radical scavenging activity and thus limited enzyme activation.     

C(B) materials as interphases in SiC/SiC model microcomposites

A specific test procedure has been developed to compare the high temperature lifetimes of SiC/SiC microcomposites with various interphases in air and under mechanical loading. The interphases, namely pure pyrocarbon (PyC) or C(B) materials with uniform or variable boron contents in the thickness, were prepared by chemical vapour deposition (CVD). Uniform addition of boron in PyC interphases improved their oxidation resistance and consequently the lifetimes of the microcomposites. However, room temperature tensile tests have shown that this improvement occurs to the detriment of the mechanical properties even when a non-brittle behaviour is maintained. In the case of variable boron contents, compositional gradient interphases (CGI) in which boron content increases from the fibre interface to the matrix interface allow the mechanical fuse properties of PyC to be combined with the oxidation resistance of a C(B) material. This revised version was published online in November 2006 with corrections to the Cover Date.     

Hollow Fiber Ultrafiltration of Maple Sap: A Performance Study

In an attempt to develop new products from maple sap, membrane technology was used to fractionate and concentrate macromolecular components (10,000 daltons or larger). Permeate fluxes increased with transmembrane pressure, reaching a maximum at 190–200 kPa, at 8–10°C. The flux profiles were similar to those of protein solutions and fruit juices. This method of clarification was successfully applied to obtain a clear “cold sterilized” sap. Application of ultrafiltration to maple farms or industries are discussed.