Crystal plasticity simulation of the effect of grain size on the fatigue behavior of polycrystalline Inconel 718

A microstructure-based model that accounts for the effect of grain size has been developed to study the effect of grain size on the fatigue life of Inconel 718 alloys. The fatigue behavior of two alloys with different grain size was determined by means of uniaxial cyclic deformation tests under fully-reversed deformation ($R_\varepsilon$ = -1) at 400$^\circ$C in the low cycle fatigue regime. The model was based in the determination of the fatigue indicator parameter (based on the local crystallographic strain energy dissipated per cycle) by means of computational homogenization of a representative volume element of the microstructure. The mechanical response of the single crystal within the polycrystal was modelled through a phenomenological crystal plasticity model which was modified to account for the effect of grain size on the monotonic and cyclic hardening/softening mechanisms. The microstructure-based crack initiation model parameters were calibrated from the experimental tests of the material with fine grain size. The results of the fatigue simulations were in good agreement with the experimental results in terms of the cyclic stress-strain curves and of the number of cycles for fatigue crack initiation. The model did not show any grain size effect on the fatigue life for the largest cyclic strain ranges while the predicted fatigue life predicted was considerably longer in the case of the microstructure with fine grain size for the lowest strain ranges, in quantitative agreement with experimental data. These differences were attributed to changes in the deformation modes between homogeneous plastic deformation at large cyclic strain ranges and localized plasticity in a few grains at low cyclic strain ranges

Genetic Classification of Populations using Supervised Learning

There are many instances in genetics in which we wish to determine whether two candidate populations are distinguishable on the basis of their genetic structure. Examples include populations which are geographically separated, case--control studies and quality control (when participants in a study have been genotyped at different laboratories). This latter application is of particular importance in the era of large scale genome wide association studies, when collections of individuals genotyped at different locations are being merged to provide increased power. The traditional method for detecting structure within a population is some form of exploratory technique such as principal components analysis. Such methods, which do not utilise our prior knowledge of the membership of the candidate populations. are termed \emph{unsupervised}. Supervised methods, on the other hand are able to utilise this prior knowledge when it is available. In this paper we demonstrate that in such cases modern supervised approaches are a more appropriate tool for detecting genetic differences between populations. We apply two such methods, (neural networks and support vector machines) to the classification of three populations (two from Scotland and one from Bulgaria). The sensitivity exhibited by both these methods is considerably higher than that attained by principal components analysis and in fact comfortably exceeds a recently conjectured theoretical limit on the sensitivity of unsupervised methods. In particular, our methods can distinguish between the two Scottish populations, where principal components analysis cannot. We suggest, on the basis of our results that a supervised learning approach should be the method of choice when classifying individuals into pre-defined populations, particularly in quality control for large scale genome wide association studies.Comment: Accepted PLOS On

Favourable areas for co-occurrence of parapatric species: niche conservatism and niche divergence in Iberian tree frogs and midwife toads

Aim Predicting species responses to global change is one of the most pressing issues in conservation biogeography. A key part of the problem is understanding how organisms have reacted to climatic changes in the past. Here we use species distribution modelling to infer the effects of climate changes since the Last Interglacial (LIG, about 130,000 ybp) on patterns of genetic structure and diversity in the Western Spadefoot toad (Pelobates cultripes) in combination with spatially-explicit phylogeographic analyses. Location Iberian Peninsula and mainland France. Methods 524 individuals from 54 populations across the species range were sampled to document patterns of genetic diversity and infer their evolutionary history based on data from mtDNA and fourteen polymorphic microsatellites. Generalized linear models based on distribution data were used to infer climatic favourability for the species in the present and in paleoclimatic simulations for the LIG, the Mid Holocene and the last glacial maximum (LGM). Results Estimates of genetic diversity show a decreasing trend from south to north, suggesting persistence of high historical population sizes in the southern Iberian Peninsula. Species distribution models show differences in climatic favourability through time, with significant correlations between historically stable favourable areas and current patterns of genetic diversity. These results are corroborated by Bayesian Skyline Plots and continuous diffusion phylogeographic analyses. Main conclusions The results indicate the presence of southern refugia, with moderate recent expansions at the northern end of the species’ range. Toads at the northern range margin exhibit the lowest genetic diversity and occupy areas of high past climate variability, classified as marginal in terms of favourability, rendering these populations most vulnerable to climate-mediated changes in the long term

Simulation guided design of globular single-chain nanoparticles by tuning the solvent quality

The control of primary and further structures of individual folded/collapsed synthetic polymers has received significant attention in recent years. However, the synthesis of single-chain nanoparticles (SCNPs) showing a compact, globular conformation in solution has turned out so far to be highly elusive. By means of simulations, we propose two methods for obtaining globular SCNPs in solution. The first synthesis route is performed in the bad solvent, with the precursor anchored to a surface. In the second route we use a random copolymer precursor with unreactive solvophilic and reactive solvophobic units, which form a single core-shell structure. Both protocols prevent intermolecular cross-linking. After recovering good solvent conditions, the swollen nanoparticles maintain their globular character. The proposed methods are experimentally realizable and do not require specific sequence control of the precursors. Our results pave the way for the synthesis via solvent-assisted design of a new generation of globular soft nanoparticles mimicking global conformations of native proteins in solution.We acknowledge financial support from the Projects MAT2012-31088 (MINECO) and T-654-13 (GV).Peer Reviewe

Design and preparation of single-chain nanocarriers mimicking disordered proteins for combined delivery of dermal bioactive cargos

Inspired by the multifunctionality of vitamin D-binding protein and the multiple transient-binding behavior of some intrinsically disordered proteins (IDPs), a polymeric platform is designed, prepared, and characterized for combined delivery of dermal protective and anticancer bioactive cargos on the basis of artificial single-chain nano-objects mimicking IDPs. For the first time ever, simultaneous delivery of folic acid or vitamin B9, and hinokitiol, a relevant natural bioactive compound that exhibits anticancer activity against human malignant melanoma cells, from these multidirectionally self-assembled unimolecular nanocarriers is illustrated.Financial support from the projects MAT2012–31088 (MINECO) and IT-654–13 (GV) is acknowledged. A.S.-S. thanks the PhD grant support of Basque Government.Peer Reviewe

Advantages of orthogonal folding of single polymer chains to soft nanoparticles

We investigate, by means of computer simulations, the formation of soft nanoparticles by irreversible intramolecular cross-linking of homofunctional polymer precursors in good solvent. Simulations reveal that the early and intermediate stages of the cross-linking process are dominated by bonding at short contour distances. Because of the initial self-avoiding character of the precursor, bonding at long contour distances, which is the efficient mechanism for global compactation, is a rare event that essentially occurs in the late stage of cross-linking. Thus, irreversible cross-linking of precursors with identical molecular weight and linker fraction produces both compact and sparse objects. This is confirmed by a detailed analysis of the size and shape distribution of the fully cross-linked nanoparticles. We also investigate intramolecular cross-linking of heterofunctional polymers with two species of orthogonal linkers, bonding between distinct species being forbidden. It is found that simultaneous cross-linking of both species and sequential cross-linking (activation of one species after full cross-linking of the other) lead to the same structural properties for the resulting nanoparticles. The heterofunctional nanoparticles are on average smaller and more spherical than the homofunctional counterparts, though still a significant fraction of sparse objects is found. The simulation results are compared with results from SEC/MALLS and SAXS experiments in real polymeric nanoparticles. © 2013 American Chemical Society.We acknowledge financial support from Projects No. MAT2012-31088 (Spanish Government) and No. IT654-13 (Basque Government). A.S.-S. expresses thanks for the Ph.D. grant support of the Basque Government (Spain).Peer Reviewe

Processing of ultrafine-size particulate metal matrix composites by advanced shear technology

Copyright @ 2009 ASM International. This paper was published in Metallurgical & Materials Transactions A 40A(3) and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.Lack of efficient mixing technology to achieve a uniform distribution of fine-size reinforcement within the matrix and the high cost of producing components have hindered the widespread adaptation of particulate metal matrix composites (PMMCs) for engineering applications. A new rheo-processing method, the melt-conditioning high-pressure die-cast (MC-HPDC) process, has been developed for manufacturing near-net-shape components of high integrity. The MC-HPDC process adapts the well-established high shear dispersive mixing action of a twin-screw mechanism to the task of overcoming the cohesive force of the agglomerates under a high shear rate and high intensity of turbulence. This is followed by direct shaping of the slurry into near-net-shape components using an existing cold-chamber die-casting process. The results indicate that the MC-HPDC samples have a uniform distribution of ultrafine-sized SiC particles throughout the entire sample in the as-cast condition. Compared to those produced by conventional high-pressure die casting (HPDC), MC-HPDC samples have a much improved tensile strength and ductility.EP-SR

Secular trends in reported portion size of food and beverages consumed by Irish adults

The present analysis aimed to investigate the changes in the reported portion sizes (PS) of foods and beverages commonly consumed by Irish adults (18–64 years) from the North South Ireland Food Consumption Survey (NSIFCS) (1997–2001) and the National Adult Nutrition Survey (NANS) (2008–10). Food PS, which are defined as the weight of food (g) consumed per eating occasion, were calculated for comparable foods and beverages in two nationally representative cross-sectional Irish food consumption surveys and were published in NSIFCS and NANS. Repeated measure mixed model analysis compared reported food PS at the total population level as well as subdivided by sex, age, BMI and social class. A total of thirteen commonly consumed foods were examined. The analysis demonstrated that PS significantly increased for five foods (‘white sliced bread’, ‘brown/wholemeal breads’, ‘all meat, cooked’, ‘poultry, roasted’ and ‘milk’), significantly decreased for three (‘potatoes’, ‘chips/wedges’ and ‘ham, sliced’) and did not significantly change for five foods (‘processed potato products’, ‘bacon/ham’, ‘cheese’, ‘yogurt’ and ‘butter/spreads’) between the NSIFCS and the NANS. The present study demonstrates that there was considerable variation in the trends in reported food PS over this period