International Journal of Fatigue 24 (2002) 1047--1062

There have been few studies to date describing fatigue-crack propagation thresholds under mixed-mode loading conditions in the presence of cracks, that are small as compared to the characteristic microstructural dimensions. To address this need, the variation in mixed-mode, high-cycle fatigue-crack growth thresholds with crack size is reported for a Ti-6Al-4V turbine blade alloy with a fine-grained bimodal microstructure. Specifically, threshold behavior is examined for large through-thickness cracks #4mmin length), short through-thickness cracks (~200 m in length), and microstructurally-small surface cracks (10--50 m in diameter) under combined mode I and mode II loading at load ratios (ratio of minimum to maximum load) ranging from 0.1 to 0.8. For mode-mixities ranging from pure mode I to predominantly mode II, large crack, mode I #K I,TH thresholds were found to decrease substantially with increasing phase angle. However, by characterizing in terms of the range in strain energy release rate, #G TH , incorporating both mode I and mode II contributions, it was observed that the pure mode I threshold could be regarded as a `worst case' under mixed-mode loading in this alloy. By estimating the effective crack-driving force actually experienced at the crack tip, the observed increase in the mixed-mode #G TH threshold with mode-mixity was attributed to an increasing influence of crack-tip shielding due to crack closure and crack-surface interference. Equivalent thresholds for through-thickness short cracks, where the crack wake and hence the effect of such shielding is minimized, were consequently far less sensitive to mode-mixity and corresponded in magnitude to the shielding-corrected large-crack thresholds. This effect was accentuated for the measured thresholds of mic..

Livestock Production Science 65 (2000) 19--38

Weights of beef cows recorded on a monthly basis were analysed using a random regression model. Data originated from a selection experiment in Western Australia, involving two herds of about 300 cows, Polled Herefords and a four breed synthetic, the so-called Wokalups. Weights were subject to large seasonal effects. Short mating periods and thus tight calving seasons led to substantial confounding between age and season at weighing. Records between 19 and 84 months were considered, up to 62 per cow, yielding 27 728 and 29 033 records for 922 and 1020 cows, respectively. Only phenotypic random regressions for animal effects, ignoring relationships, were considered. Covariances between regression coefficients and error variances were estimated by restricted maximum likelihood. A variety of models, involving random regressions on orthogonal polynomials of age, on segmented polynomials and on sine and cosine functions and different assumptions about the structure of error variances, were considered. Analyses identified a distinct cyclic, seasonal pattern of variation, both between animals and for temporary environmental effects. This could only partially be attributed to scale effects. Orthogonal polynomials proved well capable of modelling such sinuousity but required a high order of fit and thus a large number of parameters. Alternative curves utilising the known periodicity (12 months) provided more parsimonious parameterisations. Due to the high degree of confounding between age and season of recording their contributions to the total variance could not be separated. 2000 Elsevier Science B.V. All rights reserved

Planetary andSdgR SdgRTT 50 (2002) 601 -- 612

Large (from tens of percent up to several times) ion #ux (or density) and magnetic #eld magnitude variations are typical magnetosheath features. Case and statistical comparisons of simultaneous solar wind observations, magnetosheath observations, and the gasdynamic model for the magnetosheath #ow ofSgD4#LR et al

Physica A 288 (2000) 31-- 48

The protein folding problem has attracted an increasing attention from physicists. The problem has a #avor of statistical mechanics, but possesses the most common feature of most biological problems -- the profound e#ects of evolution. I will give an introduction to the problem, and then focus on some recent work concerning the so-called "designability principle". The designability of a structure is measured by the number of sequences that have that structure as their unique ground state. Structures di#er drastically in terms of their designability; highly designable structures emerge with a number of associated sequences much larger than the average. These highly designable structures (1) possess "protein-like" secondary structures and motifs, (2) are thermodynamically more stable, (3) fold faster than other structures. These results suggest that protein structures are selected in nature because they are readily designed and stable against mutations, and that such selection simultaneously leads to thermodynamic stability and foldability. According to this picture, a key to the protein folding problem is to understand the emergence and the properties of the highly desginable structures. c 2000 Elsevier Science B.V. All rights reserved