Aerodynamic reconstruction of the primitive fossil bat Onychonycteris finneyi (Mammalia: Chiroptera).

We examine the effect of varying roughness-element aspect ratio on the mean velocity distributions of turbulent flow over arrays of rectangular-prism-shaped elements. Large-eddy simulations (LES) in conjunction with a sharp-interface immersed boundary method are used to simulate spatially-growing turbulent boundary layers over these rough surfaces. Arrays of aligned and staggered rectangular roughness elements with aspect ratio >1 are considered. First the temporally- and spatially-averaged velocity profiles are used to illustrate the aspect-ratio effects. For aligned prisms, the roughness length ( $$z_\mathrm{o}$$ ) and the friction velocity ( $$u_*$$ ) increase initially with an increase in the roughness-element aspect ratio, until the values reach a plateau at a particular aspect ratio. The exact value of this aspect ratio depends on the coverage density. Further increase in the aspect ratio changes neither $$z_\mathrm{o}$$ , $$u_*$$ nor the bulk flow above the roughness elements. For the staggered cases, $$z_\mathrm{o}$$ and $$u_*$$ continue to increase for the surface coverage density and the aspect ratios investigated. To model the flow response to variations in roughness aspect ratio, we turn to a previously developed phenomenological volumetric sheltering model (Yang et al., in J Fluid Mech 789:127–165, 2016), which was intended for low to moderate aspect-ratio roughness elements. Here, we extend this model to account for high aspect-ratio roughness elements. We find that for aligned cases, the model predicts strong mutual sheltering among the roughness elements, while the effect is much weaker for staggered cases. The model-predicted $$z_\mathrm{o}$$ and $$u_*$$ agree well with the LES results. Results show that the model, which takes explicit account of the mutual sheltering effects, provides a rapid and reliable prediction method of roughness effects in turbulent boundary-layer flows over arrays of rectangular-prism roughness elements.

Allometric equations on wing dimensions versus body mass are given for eight species of megabats and 76 species of microbats, on forearm length versus mass for 14 species of mega bats and 90 species of microbats, and on lower leg length versus mass for 11 species of megabats and 45 species of microbats. Megabats have, on average, shorter wing span, small wing area, higher wing loading and lower aspect ratio than have frugivorous microbats and the insectivorous vespertilionids of similar mass. Vespertilionids have the longest span, largest wing area and lowest wing loading in relation to body mass of the bat groups for which regression lines were calculated (megabats, frugivorous microbats, vespertilionids, molossids), characteristics that are important for slow flight and manoeuvrability for insect capture. Molossids have the highest wing loading of the groups. There is a weak tendency towards higher aspect ratio for larger bats than for smaller ones (positive slope). The slopes for most characters fit geometric similarity or have confidence intervals including the value for geometric similarity. Only in three cases does the slope lie nearer that for elastic similarity: for the forearm in nycterids and emballonurids and the lower leg length in molossids. Also in these cases the confidence intervals are wide and include the value for elastic similarity and that for geometric similarity as well. In megabats the slope for the lower leg length is much steeper than for geometric similarity. The slope for the forearm length is rather similar to that for wing span in the various groups. Megabats and frugivorous microbats have rather similar slopes for all the characters measured, but differ from the other groups only in wing area, wing loading and aspect ratio. The two frugivorous bat groups also have about the same elevation of the regression lines for aspect ratio and forearm length. Megabats and frugivorous microbats thus show a close convergence in wing area, wing loading, aspect ratio and forearm length. The regression equations provide ‘norms’ for the respective bat groups. Those species that deviate 10% or more from the mean trends for wing measurements are divided into different groups, based on the wing’s aspect ratio and loading. Bats with low aspect ratio wings usually have large pinnae, which improve the ability to discover small objects such as insects on leaves. Families or species of bats with wings of low aspect ratio are, for instance, Megadermatidae, Nycteridae, Rhinolophus ferrumequinum (Rhinolophidae), Chrotopterus auritus (Phyllostomidae) and Plecotus (Vespertilionidae). The group with average aspect ratio wings contains bats with different kinds of flight style and foraging behaviour, for instance many pteropodids, phyllostomids and vespertilionids. Bats with high aspect ratio wings are, for instance, Molossidae, Rhynchonycteris naso (Emballonuridae) and Nyctalus leisleri (Vespertilionidae). The regression lines for wing span, area and loading in megabats lie almost in the region of the lines for Greenewalt’s (1975) passeriform group, whereas the span and area for vespertilionid bats are larger and the wing loading much smaller than for most birds of similar mass. Molossid bats have a larger relative wing span and aspect ratio than have most birds, and a wing area and loading similar to those of small birds of the passeriform group. Vespertilionid bats have about the same aspect ratio as birds of the passeriform group, whereas megabats have somewhat lower ratios. Molossid bats show strong convergence with swifts and swallows in foraging behaviour and in wing form. Similar convergences can be found between various vespertilionid bats, flycatchers and swallows.

To explore the effect of aspect ratio (AR) of carbon nanotubes (CNT) on the piezoresistive behavior of the composites, four kinds of multiwalled carbon nanotubes (MWNT) with different nominal aspect ratios (AR = 62, 133, 433, and 833) were well dispersed in a thermoplastic elastomer (TPE) via melt blending. The piezoresistivity of the MWNT/TPE nanocomposites was found to be dependent on the nominal MWNT aspect ratios. However, their relationship is non-linear and non-monotonic. By introducing the effective MWNT aspect ratios which are length-dependent and diameter-dependent, it has been demonstrated that the piezoresistivity will decrease with the increase of effective aspect ratios. The length-dependent increase of aspect ratio results in one hundred-fold or more decrease of piezoresistivity, but the diameter-dependent increase of aspect ratios only leads to a slight marginal change of the piezoresistivity. The proper selection of MWNT aspect ratios could enable their utilization to tailor as well as finely tune the piezoresistivity of the MWNT/TPE nanocomposites.

In this study, the effects of aspect ratio and loading of multiwalled carbon nanotubes (MWCNTs) on the dynamic mechanical, thermal, and flammability properties of low-density polyethylene (LDPE)/MWCNT nanocomposites prepared by the melt blending technique were investigated. At low CNT loading, CNT with low aspect ratio acted as a plasticizer in LDPE. The storage modulus of the nanocomposites increased with the increase in aspect ratio and CNT loading. The increase in scan rate for the composites results in the decrease in total crystallinity, crystallization peak temperature, and a late onset of crystallization. The flammability properties like heat release capacity, peak heat release rate, and total heat release decrease with the increase in both aspect ratio and loading of CNTs in the composites.

Modulation of field emission properties of vertically aligned ZnO nanorods with aspect ratio and number density

Background Posterior communicating artery aneurysms are often associated with a high rupture risk. This study compares the differences in the rate of growth and morphological characteristics between growing posterior communicating artery aneurysms and other types of growing aneurysms. Materials and methods Thirteen patients with growing internal carotid artery aneurysms were scanned using Siemens 64 slice computed tomography scanners. Three patients had ophthalmic aneurysms, three had superior hypophyseal aneurysms and seven had posterior communicating artery aneurysms. Each aneurysm case had three distinct time points, with an average separation time of 1.3 ± 0.6 years. Annual aneurysm dimensional growth, annual volume growth, annual increase in surface area, size ratio, aspect ratio, and non-sphericity index were analysed. Results Posterior communicating artery aneurysms demonstrated significantly higher annual increases in dimensional growth, volume and surface area when compared to other internal carotid artery aneurysms. Posterior communicating artery aneurysms also demonstrated a significantly higher increase in aspect ratio, size ratio and lower non-sphericity index. Discussion Posterior communicating artery aneurysms had significantly greater growth per year when compared to other types of internal carotid artery aneurysms, and had different morphological characteristics.

Behaviour of plastic-fibre-reinforced sand

Influence of grain shape and intergranular friction on material behavior in uniaxial compression: Experimental and DEM modeling

Novel, non-toxic antifouling technologies are focused on the manipulation of surface topography to deter settlement of the dispersal stages of fouling organisms. This study investigated the effect of the aspect ratio (feature height/feature width) of topographical features engineered in polydimethylsiloxane, on the settlement of cyprids of Balanus amphitrite and zoospores of Ulva linza. The correlation of relative aspect ratios to antifouling efficacy was proven to be significant. An increase in aspect ratio resulted in an increase of fouling deterrence for both zoospores and cyprids. The spore density of Ulva was reduced 42% with each unit increase in aspect ratio of the Ulva-specific Sharklet AF™ topography. Similarly, the number of settled cyprids was reduced 45% with each unit increase in aspect ratio. The newly described barnacle-specific Sharklet AF™ topography (40 μm feature height, aspect ratio of 2) reduced cyprid settled by 97%. Techniques have been developed to superimpose the smaller Ulva-specific topographies onto the barnacle-specific surfaces into a hierarchical structure to repel both organisms simultaneously. The results for spore settlement on first-generation hierarchical surfaces provide insight for the efficacious design of such structures when targeting multiple settling species.

Due to heavy traffic emissions within an urban environment, air quality during the last decade becomes worse year by year and hazard to public health. In the present work, numerical modeling of flow and dispersion of gaseous emissions from vehicle exhaust in a street canyon were investigated under changes of the aspect ratio and wind direction. The three-dimensional flow and dispersion of gaseous pollutants were modeled using a computational fluid dynamics (CFD) model which was numerically solved using Reynolds-averaged Navier-Stokes (RANS) equations. The diffusion flow field in the atmospheric boundary layer within the street canyon was studied for different aspect ratios (W/H=1/2, 3/4, and 1) and wind directions (θ=90°, 112.5°, 135°, and 157.5°). The numerical models were validated against wind tunnel results to optimize the turbulence model. The numerical results agreed well with the wind tunnel results. The simulation demonstrated that the minimum concentration at the human respiration height within the street canyon was on the windward side for aspect ratios W/H=1/2 and 1 and wind directions θ=112.5°, 135°, and 157.5°. The pollutant concentration level decreases as the wind direction and aspect ratio increase. The wind velocity and turbulence intensity increase as the aspect ratio and wind direction increase.

LES analysis of fire source aspect ratio effects on fire-wind enhancement

Mathematical modelling of conjugate laminar and turbulent heat transfer in a cavity: Effect of a vertical glazed wall

A grain texture model to investigate effects of grain shape and orientation on macro-mechanical behavior of crystalline rock

A sensitivity analysis on thermal and pumping power for the flow of nanofluid inside a wavy channel

A coin always floats in stable equilibrium with its longitudinal axis normal to the air–liquid interface. In contrast, a long thin cylindrical pin floats with its longitudinal axis parallel to the air–liquid interface. In this context, we present a theoretical investigation of the stability of small-scale hydrophobic cylinders floating in vertical and horizontal orientations at various aspect ratios (length/diameter). The study is limited to cylinders denser than water floating at the air–water interface. Our analysis shows that, unlike large-scale vertically floating cylinders, the stability of vertically orientated small-scale cylinders increases with an increase in aspect ratio. A similar trend is observed in the stability of small-scale horizontal cylinders. We also explain the underlying mechanics that leads to a rise in the stability of floating cylinders with an increase in aspect ratio. Unlike large-scale floating cylinders with uniform density, we show that the effect of governing forces (weight, buoyancy and surface tension) in small-scale cylinders changes from a stabilising to a destabilising force with a change in the aspect ratio. For example, in the case of a vertically floating cylinder, the buoyancy force acts as a stabilising force at a small aspect ratio whereas, at large aspect ratios, the buoyancy force has a destabilising influence. Likewise, the body's weight has a destabilising influence at a small aspect ratio and stabilising effect at a large aspect ratio. The reason behind this transformation is that, above a particular aspect ratio, the centre of gravity of small-scale floating cylinders lies below the centre of buoyancy.