Extensive Substructure Research Articles

On the capability of grain refinement during selective laser melting of AlSi10Mg alloy

This work focuses on the origin and capability of grain refinement in the microstructure of selective laser-melted AlSi10Mg alloy. The grains in printed microstructure have been oriented in a random manner and there is no sign of preferred micro-texture. In the molten pool, columnar grains have been formed aligned with the building direction, and stretched toward the center of the molten pool. The fraction of refined equiaxed grains by the size of fewer than 10 μm is considerable (∼40%) which have been formed (i) during solidification owing to high solidification rate to thermal gradient ratio, or due to (ii) the occurrence of dynamic recrystallization during the manufacturing process after completion of the solidification. These refined equiaxed grains have been differentiated through plotting Grain Orientation Spread maps. The numerous thermal cycles experienced by each layer cause considerable tensile or compressive micro-plastic strains and give rise to dynamic recrystallization. The presence of incomplete grains can be clearly traced which are ready to be evolved into the recrystallized grains. This, besides the extensive substructure development and sub-grain formation, are main proof for governing of continuous mechanisms of recrystallization mechanisms. Finally, selective laser melting has been approached as a thermomechanical processing route, and the calculated micro-plastic strain has been compared with a critical strain of dynamic recrystallization obtained from the hot compression testing method.

The Extensive Substructure and Long Star-Forming Histories of Young Stellar Populations in the Solar Neighborhood

The Extensive Substructure and Long Star-Forming Histories of Young Stellar Populations in the Solar Neighborhood

Archaeogenomic Distinctiveness of the Isthmo-Colombian Area

The genomic histories of Indigenous groups in the Americas have been recently enriched by modern and ancient data, but the dataset on continental Central America is still meagre. Here, we report ten ancient pre-Hispanic (plus two early colonial) genomes and 84 genome-wide profiles from seven groups presently living in Panama, on the Isthmian land-bridge connecting North and South America. Our analysis reveals extensive sub-structure in the geographic area with pre-colonial Panamanians clustering separately. On a continental scale, the Isthmian populations are distinguished by a previously unknown Indigenous component in the Americas. This component derives from the admixture of different early Indigenous groups that originated from the same northern North American source in the late Pleistocene. The earlier population(s) moved further south, leaving differential footprints in South America, while another group remained restricted to the Isthmo-Colombian area, expanded locally during the early Holocene and left genomic traces up to now.

Examination of high-temperature mechanisms and behavior under compression and processing maps of pure copper

The hot compression behavior of pure copper (commercial grade) was studied in a temperature range between 843 and 993K and in a strain rate range between 10−3 and 10s−1. The activation energy for plastic flow was determined to be 215kJ/mol, which is similar to the activation energy for lattice diffusion in copper (=197kJ/mol). The stress exponent values associated with the plastic flow were 7–9, which are larger than the theoretical values associated with lattice-diffusion controlled dislocation climb creep (4.5–5). A comparison of the current data with the data obtained from the creep tests performed on the pure copper at low strain rates by other investigators in a similar temperature range revealed that the most of the data studied in this study belong to the regime where power-law breakdown occurs. Processing map constructed at a strain where steady-state plastic flow was observed showed that the power dissipation efficiency was low (≤21%) in the entire experimental ranges of strain rate and temperature. Discontinuous dynamic recrystallization (DDRX) associated with a single peak or multiple peaks in the stress-strain curves occurred during the first stage of plastic deformation. Dynamic recovery occurred after the DDRX activity ended, leading to the formation of a subgrains with low-and intermediate angle grain boundaries within the recrystallized grains with high-angle grain boundaries. Due to the formation of extensive substructure within DDRX grains, the fractions of high-angle grain boundaries measured after the compressive deformation were low (≤30%).

Fine-Scale Structure Analysis Shows Epidemic Patterns of Clonal Complex 95, a Cosmopolitan Escherichia coli Lineage Responsible for Extraintestinal Infection.

The Escherichia coli lineage known as clonal complex 95 (CC95) is a cosmopolitan human-associated lineage responsible for a significant fraction of extraintestinal infections of humans. Whole-genome sequence data of 200 CC95 strains from various origins enabled determination of the CC95 pangenome. The pangenome analysis revealed that strains of the complex could be assigned to one of five subgroups that vary in their serotype, extraintestinal virulence, virulence gene content, and antibiotic resistance gene profile. A total of 511 CC95 strains isolated from humans living in France, Australia, and the United States were screened for their subgroup membership using a PCR-based method. The CC95 subgroups are nonrandomly distributed with respect to their geographic origin. The relative frequency of the subgroups was shown to change through time, although the nature of the changes varies with continent. Strains of the subgroups are also nonrandomly distributed with respect to source of isolation (blood, urine, or feces) and host sex. Collectively, the evidence indicates that although strains belonging to CC95 may be cosmopolitan, human movement patterns have been insufficient to homogenize the distribution of the CC95 subgroups. Rather, the manner in which CC95 strains evolve appears to vary both spatially and temporally. Although CC95 strains appeared globally as pandemic, fine-scale structure analysis shows epidemic patterns of the CC95 subgroups. Furthermore, the observation that the relative frequency of CC95 subgroups at a single locality has changed over time indicates that the relative fitness of the subgroups has changed. IMPORTANCEEscherichia coli clonal complex 95 represents a cosmopolitan, genetically diverse lineage, and the extensive substructure observed in this lineage is epidemiologically and clinically relevant. The frequency with which CC95 strains are responsible for extraintestinal infection appears to have been stable over the past 15years. However, the different subgroups identified within this lineage have an epidemic structure depending on the host, sample, continent, and time. Thus, the evolution and spread of strains belonging to CC95 are very different from those of another cosmopolitan human-associated clonal complex, CC131, which has increased significantly in frequency as a cause of extraintestinal infection over the past 15 years due to the evolution and spread of two very closely related, nearly monomorphic lineages.

Holistic processing for bodies and body parts: New evidence from stereoscopic depth manipulations.

Although holistic processing has been documented extensively for upright faces, it is unclear whether it occurs for other visual categories with more extensive substructure, such as body postures. Like faces, body postures have high social relevance, but they differ in having fine-grain organization not only of basic parts (e.g., arm) but also subparts (e.g., elbow, wrist, hand). To compare holistic processing for whole bodies and body parts, we employed a novel stereoscopic depth manipulation that creates either the percept of a whole body occluded by a set of bars, or of segments of a body floating in front of a background. Despite sharing low-level visual properties, only the stimulus perceived as being behind bars should be holistically "filled in" via amodal completion. In two experiments, we tested for better identification of individual body parts within the context of a body versus in isolation. Consistent with previous findings, recognition of body parts was better in the context of a whole body when the body was amodally completed behind occluders. However, when the same bodies were perceived as floating in strips, performance was significantly worse, and not significantly different, from that for amodally completed parts, supporting holistic processing of body postures. Intriguingly, performance was worst for parts in the frontal depth condition, suggesting that these effects may extend from gross body organization to a more local level. These results provide suggestive evidence that holistic representations may not be "all-or-none," but rather also operate on body regions of more limited spatial extent.

Molecular phylogeny reveals extensive ancient and ongoing radiations in a snapping shrimp species complex (Crustacea, Alpheidae, Alpheus armillatus)

Tropical marine habitats often harbor high biodiversity, including many cryptic taxa. Though the prevalence of cryptic marine taxa is well known, the evolutionary histories of these groups remain poorly understood. The snapping shrimp genus Alpheus is a good model for such investigations, as cryptic species complexes are very common, indicating widespread genetic diversification with little or no morphological change. Here, we present an extensive phylogeographic investigation of the diversified amphi-American Alpheus armillatus species complex, with geographic sampling in the Caribbean Sea, Gulf of Mexico, Florida, Brazil, and the tropical Eastern Pacific. Sequence data from two mitochondrial genes (16SrRNA and cytochrome oxidase I) and one nuclear gene (myosin heavy chain) provide strong evidence for division of the species complex into six major clades, with extensive substructure within each clade. Our total data set suggests that the A. armillatus complex includes no less than 19 putative divergent lineages, 11 in the Western Atlantic and 8 in the Eastern Pacific. Estimates of divergence times from Bayesian analyses indicate that the radiation of the species complex began ∼10 MYA with the most recent divergences among subclades dating to within the last 3 MY. Furthermore, individuals from the six major clades had broadly overlapping geographic distributions, which may reflect secondary contact among previously isolated lineages, and have apparently undergone several changes in superficial coloration, which is typically the most pronounced phenotypic character distinguishing lineages. In addition, the extensive substructure within clades indicates a great deal of molecular diversification following the rise of the Isthmus of Panama. In summary, this investigation reflects substantial biodiversity concealed by morphological similarity, and suggests that both ancient and ongoing divergences have contributed to the generation of this biodiversity. It also underlines the necessity to work with the most complete data set possible, which includes comprehensive and wide-ranging sampling of taxa.

Speciation and mitochondrial DNA diversification of the diving beetles Agabus bipustulatus and A. wollastoni (Coleoptera, Dytiscidae) within Macaronesia

Diversification of populations of two morphologically similar diving beetles within the Agabus tristis group, A. wollastoni and A. bipustulatus, was investigated, with partial mtDNA cytochrome b (Cyt b) sequences, allozymes and landmark-based morphometrics. The Madeiran endemic A. wollastoni was collected from 11 localities. Population genetic and morphological variation was compared to Scandinavian localities of the widespread west Palearctic A. bipustulatus, recorded also from the Azores. Agabus wollastoni and European A. bipustulatus specimens representing eight and 13 localities respectively, were used in evaluating their phylogenetic relationship. Maximum parsimony analysis of the Cyt b sequences showed that both the A. bipustulatus and A. wollastoni specimens form well-supported monophyletic groups. Three lines of evidence suggest that Agabus wollastoni has speciated through a few founders: (1) a well-supported mtDNA line; (2) the mean heterozygosity of A. wollastoni is lower when compared to A. bipustulatus on the mainland; and (3) several uncommon alleles of A. bipustulatus are missing in A. wollastoni. The Azorean A. bipustulatus population was drastically affected by the colonization event, since several loci have become fixed with a resulting lower mean heterozygosity. The colonization was relatively recent, as the mtDNA lineage represented in the Azores is deeply nested within the A. bipustulatus clade. Population structure shows moderate inbreeding of A. wollastoni, and extensive substructuring at all localities with moderate gene-flow between them. Morphological variation in A. wollastoni showed significant differentiation among several populations. Island colonizations, population structure of A. wollastoni, and an observed pattern of variation of the α-glycerophosphate dehydrogenase locus are discussed. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 653–666.

Fluorescence-dip IR spectra of jet-cooled benzoic acid dimer in its ground and first excited singlet states.

The IR spectra of three isotopomers of the benzoic acid dimer have been recorded under jet-cooled conditions using the double resonance method of fluorescence-dip IR spectroscopy. In so doing, the spectra are assuredly due exclusively to dimers in the ground-state zero-point level at a rotational temperature of 3-5 K. Even under these conditions, the three isotopomers have remarkably broad spectra, extending from 2600 to almost 3150 cm-1. The spectra show extensive substructure consisting of some 15-20 transitions where only a single OH stretch fundamental should appear in the harmonic limit. The comparison of the undeuterated d0-d0 dimer with the ring-deuterated d5-d5 dimer tests the effect of mixing with the C-H stretches and overtones of the C-H bends. The mixed OH/OD ring-deuterated d6-d5 dimer shifts the frequency and changes the form of the OH stretch normal mode. The analogous OH stretch IR spectrum of the d0-d0 dimer out of the S1 excited-state zero-point level has also been recorded. In this case, much of the closely-spaced substructure is not apparent. What remains is a set of three bands separated from one another by about 180 cm-1. Preliminary results of model calculations of the anharmonic coupling, responsible for the broadening and substructure, are presented. These calculations indicate that it is OH stretch-OH bend coupling, rather than coupling with the intermolecular stretch, that is responsible for much of the observed structure and breadth.

Multi‐domain general axisymmetric stress analysis by BEM

AbstractIt is well known that there are many benefits in solving axisymmetric solids subjected to non‐axisymmetric loading by using Fourier series expansion of field variables. Although many researchers have utilized this technique to solve problems of cooling towers and rocket nozzles, etc. by the Finite Element Method, the BEM formulation and implementation of such a method have been available only recently, mainly due to the efforts of Rizzo and Shippy3 and Mayr et al.4 In this paper these early developments have been generalized further by including more expansion terms, an efficient decomposition of kernels into symmetric and antisymmetric forms, improved evaluation of matrix coefficients and developing more general computer implementation to include surface stress calculations, effects of body forces and extensive substructuring facilities to analyse multi‐zone problems.

Tandem-repetitive noncoding DNA: forms and forces.

A model of sequence-dependent, unequal crossing-over and gene amplification (slippage replication) has been stimulated in order to account for various structural features of tandemly repeated DNA sequences. It is shown that DNA whose sequence is not maintained by natural selection will exhibit repetitive patterns over a wide range of recombination rates as a result of the interaction of unequal crossing-over and slippage replication, processes that depend on sequence similarity. At high crossing-over frequencies, the nucleotide patterns generated in the simulations are simple and highly regular, with short, nearly identical sequences repeated in tandem. Decreasing recombination rates increase the tendency to longer and more-complex repeat units. Periodicities have been observed down to very low recombination rates (one or more orders of magnitude lower than mutation rate). At such low rates, most of the sequences contain repeats which have an extensive substructure and a high degree of heterogeneity among each other; often higher-order structures are superimposed on a tandem array. These results are compared with various structural properties of tandemly repeated DNAs known from eukaryotes, the spectrum ranging from simple-sequence DNAs, particularly the hypervariable mini-satellites, to the classical satellite DNAs, located in chromosomal regions of low recombination, e.g., heterochromatin.

The Centaurus cluster of galaxies - III. Its structure and the distribution of the different galaxy types

We have previously shown that the Centaurus cluster (⁠|$\alpha=12^\text h47^\text m,\enspace \delta=-41$|°) is composed of two velocity components, Cen 30 (mean velocity 3000kms−1) and Cen 45 (mean velocity 4500kms−1), which very probably lie within one cluster. In this paper we describe the internal structure of the cluster and discuss the spatial and velocity distributions of the different galaxy types within the cluster. Centaurus possesses extensive substructure, with several recognizable features within the Cen 30 and Cen 45 components. In the outer parts of the cluster, groups of galaxies have been identified. The most prominent, the ‘Western Branch’, is a flattened structure that extends westwards and slightly northwards of the cluster centre. This feature is made up of equal contributions from the two velocity systems. Another notable group, the NGC 4930 group, lies 2.°5 to the east of the cluster. It is a loose aggregate consisting almost entirely of spiral galaxies, with a small velocity dispersion and a mean velocity |$\sim490\text {kms}^{-1}$| lower than the mean velocity of the dominant Cen 30 component. Other recognized groups are more compact and are often dominated by a large elliptical galaxy, e.g. the NGC 4373 group and the NGC 4767 group. We discuss the substructure in clusters generally and support the view that it is a common feature of most galaxy clusters. The morphology–density relationship is very striking within the cluster, with the early-type galaxies dominating the cluster core. Although the spiral galaxy distribution shows little central concentration, several distinct groups, e.g. the NGC 4930 group, are apparent. Unlike the Virgo cluster, we find that for Centaurus the velocity dispersions of the different galaxy types are similar. However, the spiral galaxies have a more clumpy velocity distribution which we interpret as additional evidence that spiral-dominated groups of galaxies exist within Centaurus. The presence of these spiral-dominated groups ensures that the infall rate of spirals into the cluster core will be very irregular. This guarantees that at some epoch the spirals would be observed to possess a larger velocity dispersion than the elliptical and S0 galaxies. It is concluded that a cluster's population mix depends on the epoch at which the main body of the cluster was formed.

Substructure and Perfection in UO2 Single Crystals

The quality of UO2 single crystals grown by arc‐melting, by a modified floating‐zone technique (ICZG), and by vapor deposition was studied using etch‐pit patterns, electron microscopy, and X‐ray topography. These techniques complemented each other and indicated significant variations between the crystals grown by the different techniques. Both types of melt‐grown crystals contained extensive substructure and approximately 106 etch pits/cm2; finely dispersed inhomogeneities were found in the vapor‐grown crystals. Stoichiometry control during growth permitted a major improvement in the perfection of the ICZG crystals.

Diffraction Effects from Irradiated Aluminum Single Crystals*

AbstractThe effect of substructural perfection on the accumulation of irradiation damage in aluminum was examined. Large single crystals with extensive substructure and crystals essentially free of substructure, all with faces cut parallel to crystal planes, were subjected to neutron irradiation. Subsequent examination by X-ray diffraction revealed pronounced changes in integrated intensity and Debye-Waller temperature factor for the substructure-free crystals; these effects disappeared upon re-etching of the surface. Laue photographs showed that the normal single-crystal pattern was partially obscured by a polycrystalline effect which also disappeared upon etching. Crystals with extensive substructure showed no such effects.This diffraction evidence supports the view that irradiation-induced defects in aluminum migrate to and collect at the crystal surface if no internal trapping sites exist.

Microscopic studies on deformed ZnS-crystals

Synopsis An optical and interferometric study was made of (111) faces of ZnS crystals grown at relatively high temperature. Next to triangular growth terraces and not much developed growth spirals, an extensive substructure, covering the whole of the faces was found. This substructure was proved by multiple beam interferometry to consist of steps. Evidence for movement of dislocations is also given. The substructure itself is devided into a fine-structure by lines of lower visibility, some of which are rows of etchpits. They are interpreted as polygonisation lines (rows of Taylor dislocations), or very small steps.