Atomic scale fluctuations govern brittle fracture and cavitation behavior in metallic glasses.

We perform atomistic simulations on the fracture behavior of two typical metallic glasses, one brittle (FeP) and the other ductile (CuZr), and show that brittle fracture in the FeP glass is governed by an intrinsic cavitation mechanism near crack tips in contrast to extensive shear banding in the ductile CuZr glass. We show that a high degree of atomic scale spatial fluctuations in the local properties is the main reason for the observed cavitation behavior in the brittle metallic glass. Our study corroborates with recent experimental observations of nanoscale cavity nucleation found on the brittle fracture surfaces of metallic glasses and provides important insights into the root cause of the ductile versus brittle behavior in such materials.

Building phenotype networks to improve QTL detection: a comparative analysis of fatty acid and fat traits in pigs.

Models in QTL mapping can be improved by considering all potential variables, i.e. we can use remaining traits other than the trait under study as potential predictors. QTL mapping is often conducted by correcting for a few fixed effects or covariates (e.g. sex, age), although many traits with potential causal relationships between them are recorded. In this work, we evaluate by simulation several procedures to identify optimum models in QTL scans: forward selection, undirected dependency graph and QTL-directed dependency graph (QDG). The latter, QDG, performed better in terms of power and false discovery rate and was applied to fatty acid (FA) composition and fat deposition traits in two pig F2 crosses from China and Spain. Compared with the typical QTL mapping, QDG approach revealed several new QTL. To the contrary, several FA QTL on chromosome 4 (e.g. Palmitic, C16:0; Stearic, C18:0) detected by typical mapping vanished after adjusting for phenotypic covariates in QDG mapping. This suggests that the QTL detected in typical mapping could be indirect. When a QTL is supported by both approaches, there is an increased confidence that the QTL have a primary effect on the corresponding trait. An example is a QTL for C16:1 on chromosome 8. In conclusion, mapping QTL based on causal phenotypic networks can increase power and help to make more biologically sound hypothesis on the genetic architecture of complex traits.

Correlations between fat depot traits and fatty acid composition in abdominal subcutaneous adipose tissue and longissimus muscle: results from a White Duroc × Erhualian intercross F2 population.

The aim of this study was to quantify the partial correlation coefficients (r(p)) between fat depot traits (FDT) and the fatty acid composition of abdominal subcutaneous adipose tissue and LM intramuscular fat in 639 F(2) pigs derived from a White Duroc × Chinese Erhualian cross. Fat depot traits are classified into 2 groups: 1 is adipose tissues (abdominal subcutaneous adipose tissue weight, mesenteric adipose tissue weight, perirenal adipose tissue weight, and backfat thickness at 4 locations); the other is LM [intramuscular fat content (IMF) and marbling score]. Correlations of FDT within classification groups were markedly greater (P < 0.001) than those observed between the 2 groups (r(p) = 0.62 vs. 0.26), indicating variability in fat content of muscle is relatively independent of amount of carcass fat. In general, fatter pigs had greater (P < 0.05) proportions of SFA and MUFA, and less PUFA, than leaner pigs. However, the relationships of individual fatty acids with FDT varied. We found that the amounts of some fatty acids regarded as neutral (e.g., stearic acid) or beneficial (e.g., palmitoleic acid and linolenic acid) for human health were associated with smaller amount of adipose tissues, or merely with greater IMF (P < 0.05). Therefore, we conclude that increasing the proportions of these neutral or healthy fatty acids can be achieved without reducing the IMF of LM, which is positively related to eating quality.