Sample size effect on the dynamic torsional behaviour of the 2A12 aluminium alloy

In order to investigate the effect of sample size on the dynamic torsional behaviour of the 2A12 aluminium alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample dimensions. It is found that with the decreasing gauge length and thickness, the tested yield strength increases. However, the sample innerlouter diameter has little effect on the dynamic torsional behaviour. Based on the finite element method, the stress states in the alloy with different sample sizes are analysed. Due to the effect of stress concentration zone （SCZ）, the shorter sample has a higher yield stress. Furthermore, the stress distributes more uniformly in the thinner sample, which leads to the higher tested yield stress. According to the experimental and simulation analysis, some suggestions on choosing the sample size are given as well.

Morphological Variation in the Martinican Subspecies White-Breasted Thrasher (<i>Ramphocinclus brachyurus brachyurus</i>)

The White-breasted Thrasher (Ramphocinclus brachyurus) is the smallest passerine bird in the Mimids family. Ranked as “endangered” in the IUCN list, the demographic distribution of this species is spread unevenly across two islands in the Lesser Antilles. The Saint-Lucian subspecies, Ramphocinclus brachyurus sanctaeluciae, was estimated to number between 1200 and 1700 individuals, whereas the Martinique subspecies, Ramphocinclus brachyurus brachyurus, was estimated at between 200 and 400 individuals. As an endemic rare species with a high risk of extinction, the Martinique subspecies should be regarded as a conservation priority. The small size of the Martinique subspecies population, its restricted geographical range, and its narrow habitat tolerance make it quite difficult to study. The variability of morphological traits in this subspecies has not been biostatistically analyzed recently. In order to update knowledge and fill in any gaps, we have used the morphometric approach to study the morphological variability of the Martinique subspecies. The study site is a small peninsula located in the northeast of the island of Martinique (French West Indies) known as “la Caravelle”. We captured 63 White-breasted Thrashers which were marked, measured, and sexed before being released. We did not observe any significant differences between the sexes, signifying an absence of sexual dimorphism. However, we were able to observe a significant variation in morphological traits between individuals measured inside and outside the national protected area of Caravelle. The body mass-tarsus ratio was equal at both sampled sites, something which could potentially be a clue to the bird’s adaptation to different habitats.

Prior-based Bayesian information criterion

We present a new approach to model selection and Bayes factor determination,based on Laplaceexpansions(as in BIC),which we call Prior-based Bayes Information Criterion(PBIC).In thisapproach,the Laplace expansion is only done with the likelihood function,and then a suitableprior distribution is chosen to allow exact computation of the(approximate)marginal likelihoodarising from the Laplace approximation and the prior.The result is a closed-form expression similar to BIC,but now involves a term arising from the prior distribution(which BIC ignores)andalso incorporates the idea that different parameters can have different effective sample sizes(whereas BIC only allows one overall sample size n).We also consider a modification of PBIC whichis more favourable to complex models.

Representative elementary volume analysis of polydisperse granular packings using discrete element method

The representative elementary volume （REV） for three-dimensional polydisperse granular packings was determined using discrete element method simulations. Granular mixtures of various sizes and particle size distributions were poured into a cuboid chamber and subjected to uniaxial compression, Findings showed that the minimum REV for porosity was larger compared with the REV for parameters such as coordination number, effective elastic modulus, and pressure ratio. The minimum REV for porosity and other parameters was found to equal 15,10, and 5 times the average grain diameter, respectively. A study of the influence of sample size on energy dissipation in random packing of spheres has also confirmed that the REV size is about 15 times the average grain diameter. The heterogeneity of systems was found to have no effect on the REV for the parameters of interest for the narrow range of coefficient of uniformity analyzed in this paper. As the REV approach is commonly applied in both experimental and numerical studies, determining minimum REV size for polydisperse granular packings remains a crucial issue.