Island Shape Research Articles

Island shape, size, and isolation affect nest-site selection by Little Terns

Populations of many seabirds and other species that nest along coasts are declining due to habitat degradation and loss. An improved understanding of the species-specific factors that determine nest density across a landscape is therefore critical for conservation efforts. We examined factors that affected the density (number per hectare) and abundance (number at a sampling site) of nests of Little Terns (Sternula albifrons) on the Sinai Peninsula, Egypt. Terns preferred to nest on islands rather than the mainland, with islands constituting 64% of the area surveyed, but containing 99% of the 439 tern nests we found. Nest densities were highest on islands that were small, located at moderate distances from the mainland, and irregularly shaped or elongated. Most nests (69%) were on islands with areas < 3 ha, although these islands represented < 5% of total island area, and islands with the highest nest densities were 80–300 m from the mainland. Terrestrial predators were more likely to occur on larger islands, visiting three of the largest four islands. Most tern nests were within 1 m of shorelines, causing island perimeter to be a strong influence on nest density. Island shape was the only factor that significantly affected nest abundance, with more nests on islands with relatively long perimeters for their size. Our results suggest that protection or creation of relatively small, slender islands at moderate distances from shore may be an effective means of increasing the number of breeding sites for Little Terns. Although not generally considered a potential determinant of nest site preferences for seabirds, island shape is likely to be important for species that prefer sites adjacent to water, including species that nest on beaches and seaside cliffs. RESUMEN Las poblaciones de muchas aves marinas y otras especies que anidan en las costas estan disminuyendo debido a la degradacion y perdida de habitat. Una mejor comprension de los factores especificos a cada especie que determinan la densidad de nidos a traves de un paisaje es de importancia critica para los esfuerzos de conservacion. Examinamos los factores que afectaron la densidad (numero por hectarea) y abundancia (numero en un sitio de muestreo) de nidos de Sternula albifrons en la Peninsula del Sinai, Egipto. S. albifrons prefiere anidar en islas en vez del continente, con las islas constituyendo 64% del area estudiada, pero cual contienen 99% de los 439 nidos de S. albifrons que encontramos. Las densidades de los nidos fueron mas altas en islas pequenas, situadas a distancias moderadas del continente, y que tenian una forma irregular o alargada. La mayoria de los nidos (69%) estaban en islas con areas de < 3 ha, aunque estas islas representaban < 5% de la superficie total de las islas estudiadas, y las islas con las mayores densidades de nidos estaban 80–300 m del continente. Depredadores terrestres tuvieron una probabilidad mas alta de ocurrir en islas grandes, y visitaban tres de las cuatro islas mas grandes. La mayoria de los nidos estaban dentro de 1 m de la costa de la isla, resultando en que el perimetro de la isla sea una fuerte influencia en la densidad de los nidos. La forma de la isla fue el unico factor que afecto significativamente a la abundancia de nidos, con mas nidos en islas que tenian perimetros relativamente largas para su tamano. Nuestros resultados sugieren que la proteccion o creacion de islas relativamente pequenas y delgadas a distancias moderadas de la costa puede ser un medio eficaz para aumentar el numero de sitios de reproduccion de S. albifrons. Aunque la forma de la isla generalmente no se considera como un factor determinante para la preferencia de sitio de anidacion de las aves marinas, probablemente sea importante para especies que prefieren sitios adyacentes al agua, incluyendo especies que anidan en playas y precipicios costeros.

Determination of Bit Patterned Media Noise Based on Island Perimeter Fluctuations

We measured the fluctuation in shape of magnetic islands in bit patterned media fabricated by laser interference lithography. This fluctuation can be accurately described by a model based on a Fourier series expansion of the perimeter of the islands. The model can be easily linked to amplitude and jitter noise. We show that the amplitude and jitter noise are in principle correlated, and the jitter noise increases with increasing island area. The correlation is small for media prepared by laser interference lithography, but expected to gain importance for high density bit patterned media.

Application of effective medium theory with consideration of island shapes to interpret optical properties of discontinuous Pt films

Pt films with mass thicknesses ranging from 0.6 to 3.9 nm were evaporated onto quartz-glass substrates under vacuum conditions (p ~ 10(-4) Pa) with evaporation rate 0.01 to 0.2 mm/s. The transmittance spectra were measured in the wavelength range from 220 to 2500 nm. The microstructures were examined by a transmission electron microscope. The statistical distributions of island areas and the histograms of the fixed ratios of the semiaxes for ellipsoids were determined. It has been found that the transmittance spectra for the films with coverage coefficient 0.2≤p≤0.6 exhibit minima that shift with an increase in the coverage coefficient. To interpret the transmittance spectra of the films, the Maxwell-Garnett theory, which takes into account the island shapes, was used. Measured and calculated spectra were compared. For low coverage coefficients there is a quantitative agreement between the experimental and the calculated results.

Effects on the Hydrodynamics Caused by Artificial Islands of the Hong Kong-Zhuhai-Macao Bridge

Hong Kong-Zhuhai-Macao Bridge will cross Lingding navigation channel in the form of immersed tunnels, with two large artificial islands to provide change-over facilities between bridge and tunnel. In order to predict the effects on the hydrodynamic environment caused by the artificial islands, the physical model for the Bridge is built to analyze the changes of the tidal level and tidal current. The experimental results show that the drag force on flow is increased and the flow section area is decreased by the two large artificial islands built in the sea. Near both ends of the artificial islands, the velocities of tidal currents increase. The opposite side of the artificial islands, there is the recirculation zone with many vortexes in different scales, which have the periodic change from formation to disappearance. Affected by the topography, hydrodynamic conditions, as well as by the position, shape and scale of the artificial islands, the changes of hydrodynamic environment caused by both the west artificial island and the east one is similar in the change rules and different in the forms.

Satellite air temperature estimation for monitoring the canopy layer heat island of Milan

In this work, satellite maps of the urban heat island of Milan are produced using satellite-based infrared sensor data. For this aim, we developed suitable algorithms employing satellite brightness temperatures for the direct air temperature estimation 2 m above the surface (canopy layer), showing accuracies below 2K. The air temperatures measured by ground-based weather stations were properly matched with brightness temperatures observed by the Moderate-resolution Imaging Spectroradiometer (MODIS) on board of both Terra and Aqua satellites. In total, 931 daytime and nighttime scenes taken between 2007 and 2010 were processed. Analysis of the canopy layer heat island (CLHI) maps during summer months reveals an average heat island effect of 3–4K during nighttime (with some peaks around 5K) and a weak CLHI intensity during daytime. In addition, the satellite maps reveal a well defined island shape across the city center from June to September confirming that, in Milan, urban heating is not an occasional phenomenon. Furthermore, this study shows the utility of space missions to monitor the metropolis heat islands if they are able to provide nighttime observations when CLHI peaks are generally significant.

Micropatterning Different Cell Types with Microarray Amplification of Natural Directional Persistence

In vivo, different cell types assemble in specific patterns to form functional tissues. Reproducing this process in vitro by designing scaffold materials to direct cells precisely to the right locations at the right time is important for the next generation of biomaterials. Here, using microarray amplification of natural directional persistence (MANDIP), simultaneous assembly of fibroblasts and endothelial cells is demonstrated by directing their long-range migration. Amplification of the directional persistence occurs through morphology-induced polarity and the asymmetric positioning of individual microsized adhesive islands that restrict lamellipodia attachment, and thus migration, to one preset direction. Quantitative analysis of cell migration on different MANDIP designs yields insight to the relative importance of the asymmetric island shapes and their arrangement. The approach enables spatial patterning of different cell types with micrometer-scale precision over large areas for investigation of cell-cell interactions within complex tissue architectures.

Equilibrium at the edge and atomistic mechanisms of graphene growth

The morphology of graphene is crucial for its applications, yet an adequate theory of its growth is lacking: It is either simplified to a phenomenological-continuum level or is overly detailed in atomistic simulations, which are often intractable. Here we put forward a comprehensive picture dubbed nanoreactor, which draws from ideas of step-flow crystal growth augmented by detailed first-principles calculations. As the carbon atoms migrate from the feedstock to catalyst to final graphene lattice, they go through a sequence of states whose energy levels can be computed and arranged into a step-by-step map. Analysis begins with the structure and energies of arbitrary edges to yield equilibrium island shapes. Then, it elucidates how the atoms dock at the edges and how they avoid forming defects. The sequence of atomic row assembly determines the kinetic anisotropy of growth, and consequently, graphene island morphology, explaining a number of experimental facts and suggesting how the growth product can further be improved. Finally, this analysis adds a useful perspective on the synthesis of carbon nanotubes and its essential distinction from graphene.

Formation of thermal evaporated Ge Nano-Islands by high temperature annealing

High Vacuum thermal evaporation was used to grow germanium islands on the silicon substrate covered by silicon oxide. The Ge nano-islands were formed by thermal annealing at different temperatures from 500 °C to 700 °C. Formation of islands was studied by various analytical techniques. The thickness of Ge layer was determined by rutherford backscattering spectroscopy (RBS). Also, combined with channeling technique, the composition and probable contaminants during synthesis processes were investigated. To explore the islands size and shape, both atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were used. Then the topographical images of surfaces were studied by AFM. The outcome of experimental evaluations of growth mechanism has indicated that with increasing the annealing temperature up to 700 °C, Ge islands were appeared from a uniform layer. Moreover, the statistical assessments of surfaces have shown that the nano-island’s sizes can be varied from several hundred nanometers to 30 nm by growing the annealing temperature. The reduction of the size along with an increase of the number of nano-islands after each thermal treatment is a major factor to prohibit us from seeing their clear images in AFM. The possibility of running statistical estimation on islands, instead, is the powerful tool of extracting and probing the distribution and the shape of Ge island’s peak in AFM images.

Magnetic interactions and reversal of artificial square spin ices

Artificial spin ices are nanoscale geometrically engineered systems that mimic the behavior of bulk spin ices at room temperature. We describe the nanoscale magnetic interactions in a square spin ice lattice by an experimentally verified model that accounts for the correct shape of the magnetic islands. Magnetic force microscopy measurements on lithographically fabricated lattices are compared to Monte Carlo simulations of the reversal process of two lattices with different lattice spacings. Lattice node statistics and correlations show significant differences in the reversal mechanism for lattices with different spacings. The effect of structural variations is also compared for the two lattice reversals.

Strain relief and Pd island shape evolution on the palladium and palladium hydride (100) surface

The mesoscopic relaxation of small Pd islands on Pd(100) and PdH(100) surfaces is investigated on the atomic scale by performing molecular statics calculations. A strong strain and stress inhomogeneity in islands and topmost layers of the substrate is revealed. An unusual size dependence of the shape of islands is discovered.

Kinetic Monte Carlo simulations of heteroepitaxial growth with an atomistic model of elasticity

We have implemented Kinetic Monte Carlo (KMC) simulations of growth of heteroepitaxial thin films. A simple cubic Solid-on-Solid (SOS) model is used to describe the atomic configurations and nearest neighbor bonds are used to describe the energetics. Elastic effects are modeled using harmonic springs between atoms displaced from their lattice positions. The misfit strain is a consequence of different equilibrium spring lengths for the substrate and film. The consistency of this elastic model with continuum theories for strained surfaces has been shown by performing elastic energy calculations for various morphologies. KMC simulations for submonolayer deposition show scaling behavior in the island size distribution. The resulting island shapes are predominantly square and do not show any shape transitions in the physically relevant range of conditions. This method gives a detailed understanding of elastic interactions and their interplay with surface diffusion in heteroepitaxial systems.

InGaN quantum wells and dots on initially shaped GaN islands: Growth and luminescence studies

AbstractDirect growth of InGaN active layers on initially shaped pyramid‐like GaN islands of low dislocation density, realized by enhanced island growth via slightly Si doping in the GaN islands, was investigated in detail. Scanning transmission electron microscopy (STEM) studies reveal the selective growth of relatively thin quantum wells (QWs) on semipolar sidewall facets, whereas In‐rich InGaN quantum dots (QDs) form on the island apex. Spatially resolved scanning electron microscopy (SEM) and cathodoluminescence (CL) studies show strong emission from the island sites, whereas very weak emission arises from the nonisland sites, suggesting the preferential growth of InGaN active layers on the GaN islands rather than on the SiNx‐treated nonisland sites. Polychromatic emissions from the InGaN QWs on island sidewall and top facets, and the In‐rich InGaN QDs on the island apex were observed. Studies on the growth mechanism and properties of InGaN/GaN QWs on nanoscale faceted islands may serve as a nanoscale investigating tool for further studies of GaN island shaping and shape variations during heteroepitaxy in the early growth stages.

Effects of the lateral ordering of self-assembled SiGe nanoislands grown on strained Si1 − x Ge x buffer layers

Atomic-force microscopy, micro-Raman spectroscopy, and high resolution X-ray diffraction are applied to study the spatial ordering in single layers of SiGe nanoislands grown on a strained Si1 − xGex buffer sublayer. It is shown that, apart from stimulating the spatial ordering of nanoislands, the introduction of a Si1 − xGex sublayer leads to an enhanced role for interdiffusion processes. An unusually high increase in the volume of nanoislands in the process of the epitaxy is related to the anomalously strong diffusion from the buffer sublayer into the islands that is induced by nonuniform fields of elastic strains. The anisotropy of the islands shape and spatial ordering is discussed in terms of the anisotropy of the diffusion processes in spatially nonuniform fields of elastic strains.

Structure of Co-2 × 2 nanoislands grown on Ag/Ge(111)-√3 × √3 surface studied by scanning tunneling microscopy

We have found that Co-2 × 2 islands grown on an Ag/Ge(111)-√3 × √3 surface have hcp structure with the (11-20) orientation. The island evolution involves transformation of the unit cell shape from parallelogram into rectangular, which is accompanied by the island shape transformation from hexagonal into stripe-like. Identified are two crystallographic directions for the island growth, the pseudo-[0001] and the pseudo-[1-100]. We have observed the occurrence of a lateral shift between the topmost and the underlying bilayers in the case of the island growth along the pseudo-[0001] direction. In contrast, the topmost and the underlying bilayers are unshifted for the growth along the pseudo-[1-100] direction.

Influence of rare earth nanoparticles and inoculants on performance and microstructure of high chromium cast iron

The high chromium cast irons (HCCIs) with rare earth (RE) nanoparticles or inoculants were fabricated in the casting process. The phase compositions and microstructure were analyzed by X-ray diffraction (XRD) and optical microscopy (OM), respectively. The hardness and impact toughness were tested by Rockwel-hardmeter and impacting test enginery. And then, the morphology of fracture was researched by scanning electron microscopy (SEM). The results demonstrated that the phase compositions of HCCIs with addition of RE nanoparticles or inoculants which were M7C3 carbides + a-Fe did not change obviously. However, the prime M7C3 carbides morphology had great changes with the increase of RE nanoparticles, which changed from long lath to granular or island shape. When the content of RE nanoparticles was 0.4 wt.%, the microstructure of high chromium cast iron was refined greatly. The microstructure of carbides was coarser when the addition of RE nanoparticles was higher than 0.4 wt.%. The hardness and impact toughness of HCCIs were improved by addition of RE nanoparticles or inoculants. The impact toughness of HCCIs was increased 36.4% with RE nanoparticles of 0.4 wt.%, but the hardness changed slightly. In addition, the adding of RE nanoparticles or inoculants could reduce the degree of the brittle fracture. Fracture never seemed regular, instead, containing lots of laminates and dimples with the increase of the RE nanoparticles. The results also indicated that the optimal addition amount of the RE nanoparticles was 0.4%, under this composition, the microstructure and mechanical property achieved the best cooperation. In addition, through the study of erosion wear rate, when adding 0.4% RE nanoparticles into the HCCIs, the erosion wear rate got the minimum 0.32×10−3 g/mm2, which could increase 51.5% compared with that without any RE nanoparticles.

Strain inhomogeneity in copper islands probed by coherent X-ray diffraction

The strain field of individual epitaxial sub-micrometric copper islands is studied using coherent X-ray diffraction and finite element modelling. The strain inhomogeneity in each island is so large that the characteristic features of the island shape tend to disappear in the diffraction pattern, which is dominated by strain effects. The model confirms the tensile strain imposed to the island by the thermal mismatch occurring during the preparation of the samples. An evaluation of the residual strain is obtained by qualitatively fitting the diffraction data.

Shape Transitions in Strained Cu Islands on Ni(100): Kinetics versus Energetics

We examine the ramified islands observed in submonolayer Cu/Ni(100) growth. Our results indicate that the strain-energy contribution to the dependence of island energy on shape is surprisingly weak. In contrast, our accelerated dynamics simulations indicate that unexpected concerted popout processes occurring at step edges may be responsible. Kinetic Monte Carlo (KMC) simulations which include these processes produce island shapes which are very similar to those observed in experiment. These results suggest that the shape transition is of kinetic origin but is strongly mediated by strain.

Bistability of bilayer islands under anisotropic misfit stress

The equilibrium shapes of bilayer islands under anisotropic misfit stress have been theoretically characterized from a thermodynamics point of view. Based on an energy variation calculation, it is found that when the ratio σ between the components of the misfit stress is such that σ=−1, both square and rectangular shaped bilayer islands may coexist depending on the island volume and stress level. When σ≠−1 and σ<0, the possibility of formation rectangular islands along both perpendicular directions is also discussed.

Patterning silver nanocubes in monolayers using phase separated lipids as templates

Strategies for assembling silver nanocubes (NCs) into distinct 2D patterns on Langmuir–Blodgett (LB) films are demonstrated using two different lipid mixtures as vehicles: (1) raft mixtures containing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), sphingomyelin (SPM), and cholesterol in different mole ratios (2:2:1 and 1:1:1) and (2) 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) at a 1:3 mol ratio. Atomic force microscopy was employed to unveil the mechanisms of such pattern formation in the LB film. The results demonstrate that aggregation of NCs into round-like pattern is governed by preferential localization of NCs within the liquid condensed (LC) domains of DOPC/SPM/Cholesterol mixture. Cholesterol was found to govern the size and shape of the rounded islands. On the other hand, incorporation of NCs within the liquid expanded (LE) phase of DPPC/DLPC mixture produced linear-branched chains, oriented normal to the Langmuir film transfer direction. The as engineered patterns of silver NCs exhibited characteristic plasmonic signatures. Our results reveal the potential in assembling plasmonic metal nanoparticles into diverse patterns on solid substrates by exploiting their preferential localization either in LC or LE phase of appropriate lipid mixture in Langmuir film.

Richness and composition of plants and birds on land‐bridge islands: effects of island attributes and differential responses of species groups

AbstractAim To test relationships between the richness and composition of vascular plants and birds and attributes of habitat fragments using a model land‐bridge island system, and to investigate whether the effects of fragmentation differ depending on species natural history traits.Location Thousand Island Lake, China.Methods We compiled presence/absence data of vascular plant and bird species through exhaustive surveys of 41 islands. Plant species were assigned to two categories: shade‐intolerant and shade‐tolerant species; bird species were assigned to three categories: edge, interior, and generalist species. We analysed the relationships between island attributes (area, isolation, elevation, shape complexity, and perimeter to area ratio) and species richness using generalized linear models (GLMs). We also investigated patterns of composition in relation to island attributes using ordination (redundancy analysis).Results We found that island area explained a high degree of variation in the species richness of all species groups. The slope of the species–area relationship (z) was 0.16 for all plant species and 0.11 for all bird species. The lowest z‐value was for generalist birds (0.04). The species richness of the three plant species groups was associated with island area per se, while that of all, generalist, and interior birds was explained mainly by elevation, and that of edge bird species was associated primarily with island shape. Patterns of species composition were most strongly related to elevation, island shape complexity, and perimeter to area ratio rather than to island area per se. Species richness had no significant relationship with isolation, but species composition did. We also found differential responses among the species groups to changes in island attributes.Main conclusions Within the Thousand Island Lake system, the effects of fragmentation on both bird and plant species appear to be scale‐dependent and taxon‐specific. The number of plant species occurring on an island is strongly correlated with island area, and the richness of birds and the species composition of plants and birds are associated with variables related to habitat heterogeneity. We conclude that the effects of fragmentation on species diversity and composition depend not only on the degree of habitat loss but also on the specific patterns of habitat fragmentation.