Modelling ternary effects on antiphase boundary energy of Ni3Al

The shearing of ordered gamma' precipitates by matrix dislocations results in the formation of antiphase boundaries (APB) in Ni-base superalloys. The APB energy is an important source of order-strengthening in disk and blade alloys where Ti and Ta substitute for Al in gamma'. While the importance of APB energy is well-acknowledged, the effect of alloying on APB energy is not fully understood. In the present study, the effect of Ti and Ta additions on the {111} and {010} APB energies was probed via electronic structure calculations. Results suggest that at low levels of Ti/Ta, APB energies on either plane increases with alloying. However, at higher Ti/Ta levels, the APB energies decrease with alloying. These trends understood by accounting for nearest neighbour violations about the APB and additionally, invoking the effect of precipitate composition on the energy penalty of the violations. We propose an Environment Dependent Nearest Neighbour Bond (EDNNB) model that predicts APB energies that are in close agreement to calculated values.

Soft-spring wall based non-periodic boundary conditions for non-equilibrium molecular dynamics of dense fluids

Non-equilibrium molecular dynamics (MD) simulations require imposition of non-periodic boundary conditions (NPBCs) that seamlessly account for the effect of the truncated bulk region on the simulated MD region. Standard implementation of specular boundary conditions in such simulations results in spurious density and force fluctuations near the domain boundary and is therefore inappropriate for coupled atomistic-continuum calculations. In this work, we present a novel NPBC model that relies on boundary atoms attached to a simple cubic lattice with soft springs to account for interactions from particles which would have been present in an untruncated full domain treatment. We show that the proposed model suppresses the unphysical fluctuations in the density to less than 1% of the mean while simultaneously eliminating spurious oscillations in both mean and boundary forces. The model allows for an effective coupling of atomistic and continuum solvers as demonstrated through multiscale simulation of boundary driven singular flow in a cavity. The geometric flexibility of the model enables straightforward extension to nonplanar complex domains without any adverse effects on dynamic properties such as the diffusion coefficient. (c) 2015 AIP Publishing LLC.

An estimate of the number of tropical tree species

The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher's alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between similar to 40,000 and similar to 53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of similar to 19,000-25,000 tree species. Continental Africa is relatively depauperate with a minimum of similar to 4,500-6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.

Dynamics of Cricket Sound Production

The clever designs of natural transducers are a great source of inspiration for man-made systems. At small length scales, there are many transducers in nature that we are now beginning to understand and learn from. Here, we present an example of such a transducer that is used by field crickets to produce their characteristic song. This transducer uses two distinct components-a file of discrete teeth and a plectrum that engages intermittently to produce a series of impulses forming the loading, and an approximately triangular membrane, called the harp, that acts as a resonator and vibrates in response to the impulse-train loading. The file-and-plectrum act as a frequency multiplier taking the low wing beat frequency as the input and converting it into an impulse-train of sufficiently high frequency close to the resonant frequency of the harp. The forced vibration response results in beats producing the characteristic sound of the cricket song. With careful measurements of the harp geometry and experimental measurements of its mechanical properties (Young's modulus determined from nanoindentation tests), we construct a finite element (FE) model of the harp and carry out modal analysis to determine its natural frequency. We fine tune the model with appropriate elastic boundary conditions to match the natural frequency of the harp of a particular species-Gryllus bimaculatus. We model impulsive loading based on a loading scheme reported in literature and predict the transient response of the harp. We show that the harp indeed produces beats and its frequency content matches closely that of the recorded song. Subsequently, we use our FE model to show that the natural design is quite robust to perturbations in the file. The characteristic song frequency produced is unaffected by variations in the spacing of file-teeth and even by larger gaps. Based on the understanding of how this natural transducer works, one can design and fabricate efficient microscale acoustic devices such as microelectromechanical systems (MEMS) loudspeakers.

Effect of a mesh on boundary layer transitions induced by free-stream turbulence and an isolated roughness element

Streamwise streaks, their lift-up and streak instability are integral to the bypass transition process. An experimental study has been carried out to find the effect of a mesh placed normal to the flow and at different wall-normal locations in the late stages of two transitional flows induced by free-stream turbulence (FST) and an isolated roughness element. The mesh causes an approximately 30% reduction in the free-stream velocity, and mild acceleration, irrespective of its wall-normal location. Interestingly, when located near the wall, the mesh suppresses several transitional events leading to transition delay over a large downstream distance. The transition delay is found to be mainly caused by suppression of the lift-up of the high-shear layer and its distortion, along with modification of the spanwise streaky structure to an orderly one. However, with the mesh well away from the wall, the lifted-up shear layer remains largely unaffected, and the downstream boundary layer velocity profile develops an overshoot which is found to follow a plane mixing layer type profile up to the free stream. Reynolds stresses, and the size and strength of vortices increase in this mixing layer region. This high-intensity disturbance can possibly enhance transition of the accelerated flow far downstream, although a reduction in streamwise turbulence intensity occurs over a short distance downstream of the mesh. However, the shape of the large-scale streamwise structure in the wall-normal plane is found to be more or less the same as that without the mesh.

Differences in host species relationships and biogeographic influences produce contrasting patterns of prevalence, community composition and genetic structure in two genera of avian malaria parasites in southern Melanesia

1. Host-parasite interactions have the potential to influence broadscale ecological and evolutionary processes, levels of endemism, divergence patterns and distributions in host populations. Understanding the mechanisms involved requires identification of the factors that shape parasite distribution and prevalence. 2. A lack of comparative information on community-level host-parasite associations limits our understanding of the role of parasites in host population divergence processes. Avian malaria (haemosporidian) parasites in bird communities offer a tractable model system to examine the potential for pathogens to influence evolutionary processes in natural host populations. 3. Using cytochrome b variation, we characterized phylogenetic diversity and prevalence of two genera of avian haemosporidian parasites, Plasmodium and Haemoproteus, and analysed biogeographic patterns of lineages across islands and avian hosts, in southern Melanesian bird communities to identify factors that explain patterns of infection. 4. Plasmodium spp. displayed isolation-by-distance effects, a significant amount of genetic variation distributed among islands but insignificant amounts among host species and families, and strong local island effects with respect to prevalence. Haemoproteus spp. did not display isolation-by-distance patterns, showed marked structuring of genetic variation among avian host species and families, and significant host species prevalence patterns. 5. These differences suggest that Plasmodium spp. infection patterns were shaped by geography and the abiotic environment, whereas Haemoproteus spp. infection patterns were shaped predominantly by host associations. Heterogeneity in the complement and prevalence of parasite lineages infecting local bird communities likely exposes host species to a mosaic of spatially divergent disease selection pressures across their naturally fragmented distributions in southern Melanesia. Host associations for Haemoproteus spp. indicate a capacity for the formation of locally co-adapted host-parasite relationships, a feature that may limit intraspecific gene flow or range expansions of closely related host species.

Field induced domain switching as the origin of anomalous lattice strain along non-polar direction in rhombohedral BiScO3-PbTiO3 close to the morphotropic phase boundary

The lattice strain and domain switching behavior of xBiScO(3)-(1-x) PbTiO3 (x = 0.40) was investigated as a function of cyclic field and grain orientation by in situ X-ray diffraction during application of electric fields. The electric field induced 200 lattice strain was measured to be five times larger than the 111 lattice strain in pseudorhombohedral xBiScO(3)-(1-x) PbTiO3 (x = 0.40). It is shown that the anomalous 200 lattice strain is not an intrinsic phenomenon, but arises primarily due to stress associated with the reorientation of the 111 domains in dense polycrystalline ceramic. (C) 2015 AIP Publishing LLC.

Systematic status of Fejervarya ((Amphibia, Anura, Dicroglossidae) from South and SE Asia with the description of a new species from the Western Ghats of Peninsular India

We carried out a large-scale phylogenetic analysis of fejervaryan (dicroglossid frogs with `Fejervaryan lines' on the ventral side of the body) frogs, distributed in South and SE Asia, using published and newly generated sequences of unidentified individuals from the northern Western Ghats. The results corroborate the presence of a larger fejervaryan clade with a sister relationship to a clade composed of Sphaerotheca. Two sister clades could be discerned within the lager fejervaryan clade. The unidentified individuals formed a monophyletic group and showed a strong support for a sister relationship with Minervarya sahyadris. The species was found to be highly divergent (16S rRNA-4% and tyr-1%) from its sister lineage Minervarya sahyadris, and the clade composed of these two lineages were found to be deeply nested within the larger clade of Fejervarya. Based on this, the genus Minervarya Dubois, Ohler and Biju, 2001 is synonymized under the genus Fejervarya Bolkay, 1915. The unidentified lineage is recognized, based on phylogenetic position, genetic divergence and morphological divergence, as a distinct species and named here as Fejervarya gomantaki sp. nov. The presence of rictal glands was observed to be a synapomorphic character shared by the nested clade members, Fejervarya sahyadris and Fejervarya gomantaki sp. nov. Based on the presence of rictal gland and small size, Minervarya chilapata, a species from a lowland region in the Eastern Himalayas, is synonymized under Fejervarya and evidence for morphological separation from the new species, Fejervarya gomantaki sp. nov. is provided. For the fejervaryan frogs, currently three generic names (Frost, 2015) are available for the two phylogenetic subclades; the genus Fejervarya Bolkay, 1915 for the species of fejervaryan frogs having distribution in the South East Asia; the genus Zakerana Howlader, 2011 for the species of fejervaryan frogs having distribution in the South Asia and the genus Minervarya Dubois, Ohler and Biju, 2001 nested within the `Zakerana clade'. In the phylogenetic analysis Minervarya sahyadris, the new species described herein as Fejervarya gomantaki sp. nov. are nested within the `Zakerana clade', if the `Zakerana clade' for the fejervaryan frogs having distribution in the South Asia is provided a generic status the nomen `Minervarya' should be considered as per the principle of priority of the ICZN Code. Taking into consideration the overlapping distribution ranges of members of the sister clades within the larger fejervaryan clade and the absence of distinct morphological characteristics, we also synonymize the genus Zakerana Howlader, 2011, a name assigned to one of the sister clades with members predominantly distributed in South Asia, under the genus Fejervarya Bolkay, 1915. We discuss the need for additional sampling to identify additional taxa and determine the geographical ranges of the members of the sister clades within Fejervarya to resolve taxonomy within this group.

Two new species of Gomphonema (Bacillariophyceae) from Doon Valley, Uttarakhand, India

This paper describes two new Gomphonema species from the lesser Himalayas, India, with their valve morphology using light and scanning electron microscopy. The two species, Gomphonema juettnerii sp. nov. and G. doonensis sp. nov., were found in Nalota stream in Doon Valley of Uttarakhand State. Main features of G. juettnerii are valve outline, shape of the areolae and striae pattern and presence of stigma. Main features of G. doonensis are rounded headpole, striae made by doubly punctate striae and features in central area. A detailed discussion on doubly punctate striae in members of gomphonemoid diatoms is presented.

Morphological and functional characterisation of the burrow systems of six earthworm species (Lumbricidae)

Earthworm burrow systems are generally described based on postulated behaviours associated with the three ecological types. In this study, we used X-ray tomography to obtain 3D information on the burrowing behaviour of six very common anecic (Aporrectodea nocturna and Lumbricus terrestris) and endogeic (Aporrectodea rosea, Allolobophora chlorotica, Aporrectodea caliginosa, Aporrectodea icterica) earthworm species, introduced into repacked soil cores for 6 weeks. A simple water infiltration test, the Beerkan method, was also used to assess some functional properties of these burrow systems. Endogeic worms make larger burrow systems, which are more highly branched, less continuous and of smaller diameter, than those of anecic worms. Among the anecic species, L. terrestris burrow systems are shorter (9.2 vs 21.2 m) with a higher number (14.5 vs 23.5) of less branched burrows (12.2 vs 20.2 branches m(-1)), which are also wider (7.78 vs 5.16 mm) than those of A. nocturna. In comparison, the burrow systems made by endogeic species appeared similar to each other. However, A. rosea burrows were short and narrow, whereas A. icterica had a longer burrow system (15.7 m), more intense bioturbation intensity (refilled macropores or soil lateral compaction around them) and thus a greater number of burrows. Regarding water infiltration, anecic burrow systems were far more efficient due to open burrows linking the top and bottom of the cores. For endogeic species, we observed a linear relationship between burrow length and the water infiltration rate (R (2) = 0.49, p < 0.01). Overall, the three main characteristics significantly influencing water infiltration were burrow length, burrow number and bioturbation volume. This last characteristic highlighted the effect of burrow refilling by casts.

PREDICTION OF TRANSITIONAL AND SEPARATED BOUNDARY LAYERS IN A COMPRESSOR CASCADE

Numerical simulations were performed of experiments from a cascade of stator blades at three low Reynolds numbers representative of flight conditions. Solutions were assessed by comparing blade surface pressures, velocity and turbulence intensity along blade normals at several stations along the suction surface and in the wake. At Re = 210,000 and 380,000 the laminar boundary layer over the suction surface separates and reattaches with significant turbulence fluctuations. A new 3-equation transition model, the k-k(L)-omega model, was used to simulate this flow. Predicted locations of the separation bubble, and profiles of velocity and turbulence fluctuations on blade-normal lines at various stations along the blade were found to be quite close to measurements. Suction surface pressure distributions were not as close at the lower Re. The solution with the standard k-omega SST model showed significant differences in all quantities. At Re = 640,000 transition occurs earlier and it is a turbulent boundary layer that separates near the trailing edge. The solution with the Reynolds stress model was found to be quite close to the experiment in the separated region also, unlike the k-omega SST solution. Three-dimensional computations were performed at Re = 380,000 and 640,000. In both cases there were no significant differences between the midspan solution from 3D computations and the 2D solutions. However, the 3D solutions exhibited flow features observed in the experiments the nearly 2D structure of the flow over most of the span at 380,000 and the spanwise growth of corner vortices from the endwall at 640,000.

A rapid method to assess reactive oxygen species in yeast using H2DCF-DA

A protocol to efficiently assess Reactive Oxygen Species (ROS) levels in yeast cells using H2DCF-DA is described here. This method employs lithium acetate to permeate the cell wall, and thus, augments the release of the fluorescent product, dichlorofluorescein from the cells. This protocol obviates the need for both physical and enzymatic lysis methods that are arduous and time consuming. This method is simple, less time consuming and reproducible, especially while dealing with a large sample size. The lithium acetate method gave significantly reproducible and linear results (P < 0.0001), as compared with direct measurement (P = 0.0005), sonication (P = 0.1466) and bead beating (P = 0.0028).

The Asian elephant is amongst the top three frugivores of two tree species with easily edible fruit

Large animal species are prone to local extirpation, but ecologists cannot yet predict how the loss of megaherbivores affects ecosystem processes such as seed dispersal. Few studies have compared the quantity and quality of seed dispersal by megaherbivores versus alternative frugivores in the wild, particularly for plant species with fruit easily consumed by many frugivorous species. In a disturbed tropical moist forest in India, we examine whether megaherbivores are a major frugivore of two tree species with easily edible, mammal-dispersed fruit. We quantify the relative fruit removal rates of Artocarpus chaplasha and Careya arborea, by the Asian elephant (Elephas maximus) and alternative dispersers. Through focal watches and camera trapping, we found the elephant to be amongst the top three frugivores for each tree species. Furthermore, seed transects under A. chaplasha show that arboreal frugivores discard seeds only a short distance from the parental tree, underscoring the elephant's role as a long-distance disperser. Our data provide unprecedented support for an old notion: megaherbivores may be key dispersers for a broad set of mammal-dispersed fruiting species, and not just fruit inaccessible to smaller frugivores. As such, the elephant may be particularly important for the functional ecology of the disturbed forests it still inhabits across tropical Asia.

Supersymmetry: Boundary conditions and edge states

When spatial boundaries are inserted, supersymmetry (SUSY) can be broken. We have shown that in an N = 2 supersymmetric theory, all local boundary conditions allowed by self-adjointness of the Hamiltonian break N = 2 SUSY, while only a few of these boundary conditions preserve N = 1 SUSY. We have also shown that for a subset of the boundary conditions compatible with N = 1 SUSY, there exist fermionic ground states which are localized near the boundary. We also show that only very few nonlocal boundary conditions like periodic boundary conditions preserve full N = 2 supersymmetry, but none of them exhibits edge states.

Local structure of boundary layer transition in experiments with a single streamwise vortex

Transition induced by an isolated streamwise vortex embedded in a flat plate boundary layer was studied experimentally. The vortex was created by a gentle hill with a Gaussian profile that spanned on half of the width of a flat plate mounted in a low turbulence wind tunnel. PIV and hot-wire anemometry data were taken. Transition occurs as a non-inclined shear layer breaks up into a sequence of vortices, close to the boundary layer edge. The passing frequency of these vortices scales with square of the freestream velocity, similar to that in single-roughness induced transition. Quadrant analysis of streamwise and wall-normal velocity fluctuations show large ejection events in the outer layer. (C) 2015 Elsevier Inc. All rights reserved.