Island Size Research Articles

Mobility of charge carriers in self-assembled monolayers

We present a new approach to study charge transport within 2D layers of organic semi-conductors (OSCs) using atomic force microscopy (AFM)-based lithography applied to self-assembled monolayers (SAMs), fabricated from appropriate organothiols. The extent of lateral charge transport was investigated by insulating pre-defined patches within OSC-based SAMs with regions of insulating SAM made from large band gap alkanethiolates. The new method is demonstrated using a phenyl-linked anthracenethiolate (PAT), 4-(anthracene-2-ylethynyl)benzyl thiolate. I–V characteristics of differently shaped PAT-islands were measured using the AFM tip as a top electrode. We were able to determine a relationship between island size and electrical conductivity, and from this dependence, we could obtain information on the lateral charge transport and charge carrier mobility within the thin OSC layers. Our study demonstrates that AFM nanografting of appropriately functionalized OSC molecules provides a suitable method to determine intrinsic mobilities of charge carriers in OSC thin films. In particular, this method is rather insensitive with regard to influence of grain boundaries and other defects, which hamper the application of conventional methods for the determination of mobilities in macroscopic samples.

Formation and regulation of unoccupied hybridized band with image potential states at perylene/graphite interface.

Occupied and unoccupied electronic structures of submonolayer perylene (C20H12) on a graphite surface have been investigated using two-photon photoemission (2PPE) spectroscopy for two phases at room and low temperatures. Low energy electron diffraction measurements indicated that the molecules are disordered at room temperature and form a well-ordered superstructure below 180 K. In 2PPE, a specific unoccupied peak (Lx) was observed at around room temperature (>180 K) but not at low temperature (<180 K). The temperature-dependence of the excitation probability was attributed to a contribution of a diffuse unoccupied state, which is characterized by the molecular orbital extending outside the perylene molecular framework. At around room temperature, perylene adopts a flat-lying molecular orientation so that the diffuse state can hybridize with a free-electron-like unoccupied surface state, image potential states (IPS). As a result, the hybridized Lx state can be excited from the occupied bulk band through the IPS-mediated process. In contrast, hybridization is not efficient in the low-temperature phase due to the standing molecular orientation, which decouples the molecule away from the image plane of the substrate. The size of molecular islands also affects hybridization between the diffuse states and IPS because the two states encounter each other at the edge part of molecular aggregates. The temperature-dependent 2PPE results indicate that the molecular orientation and island size of perylene are directly linked to the formation of hybridized states, and thus, the excitation probability at the interface can be regulated by the morphology on the surface.

Silver Nanoparticles SERS Sensors Using Rapid Thermal CVD Nanoscale Graphene Islands as Templates

Surface enhanced Raman scattering (SERS) sensors have been fabricated by rapid thermal chemical vapor deposition of high-density nanoscale discrete graphene islands on copper foils followed by electroless chemical plating of discrete, closely spaced, and irregularly shaped silver nanoparticles on the copper surface where it is not covered by graphene islands. By fine tuning of the size and distribution of graphene islands and adjusting the deposition time for silver nanoparticles, nanoscale gaps between silver particles are fabricated. SERS sensors exhibiting Raman scattering signal enhancement factors as high as 1014 in reference to a bare copper have been demonstrated. Raman scattering signal has been measured from as low as 10−16 M of R6G molecules in water. This article reports effects and optimization process of size and distribution of graphene islands on desirable morphology of chemically plated silver nanoparticles. The density of nanoscale gaps of a few nanometers in distance between neighboring silver nanoparticles is optimized, resulting in the demonstration of SERS sensors with very low detection limits for R6G molecules.

Free-energy-based framework for early forecasting of stem cell differentiation.

Commitment of stem cells to different lineages is inherently stochastic but regulated by a range of environmental bio/chemo/mechanical cues. Here, we develop an integrated stochastic modelling framework for predicting the differentiation of hMSCs in response to a range of environmental cues, including sizes of adhesive islands, stiffness of substrates and treatment with ROCK inhibitors in both growth and mixed media. The statistical framework analyses the fluctuations of cell morphologies over approximately a 24 h period after seeding the cells in the specific environment and uses the cytoskeletal free-energy distribution to forecast the lineage the hMSCs will commit to. The cytoskeletal free energy which succinctly parametrizes the biochemical state of the cell is shown to capture hMSC commitment over a range of environments while simple morphological factors such as cell shape, tractions on their own are unable to correlate with lineages hMSCs adopt.

Microstructure tailoring for property improvements of DP steel via cyclic intercritical annealing

Multi-step intercritical annealing treatment was applied on the quenched and cold rolled martesnitic microstructures to unravel the effects of thermal cycling on dual phase (DP) steel. During intercritical annealing of the quenched microstructure, hardness decreased with increasing holding time and reached a plateau. However, during intercritical annealing of the cold rolled microstructure, there was a rapid fall of hardness due to recrystallization. Afterwards, hardness increased as a result of austenitization, and then reached a plateau. A rapid grain growth was observed during repetition of intercritical annealing cycle for the DP steel originated from the quenched microstructure with adverse effects on the tensile properties. Conversely, decreased size of martensite islands and formation of chain like morphology of martensite around ferrite grains was observed during thermal cycling of the DP steel originated from the cold rolled microstructure with the consequent enhanced work hardening behavior. Accordingly, the combination of cold rolling and cyclic intercritical annealing was recommended in this work to enhance the work hardening behavior and mechanical properties of DP steels.

A global test of the subsidized island biogeography hypothesis

AbstractAimThe decreasing capacity of area to predict species richness on small islands (the small‐island effect; SIE) seems to be one of the few exceptions of the species–area relationship. While most studies have focused on how to detect the SIE, the underlying ecological factors determining this pattern remain largely unexplored. Here, we evaluate one of the few mechanisms proposed to explain the SIE, the subsidized island biogeography hypothesis, which posits that marine productivity around small islands may alter their expected species richness.LocationSeven hundred and ninety islands worldwide, including 420 islands &lt; 1 km2.Time periodPresent.Major taxa studiedAngiosperms.MethodsWe applied iterative partial regression to determine the effects of island area and marine productivity on plant species richness for islands of varying sizes. We also employed geographically weighted regression to account for non‐stationarity in the marine productivity effects. Lastly, we used estimates of ammonia emissions based on nutrient excretion by seabird colonies from a subset of 66 islands to evaluate the effects of marine resources deposition on angiosperm species richness.ResultsWe found no effect of marine productivity on insular species richness, at both regional and global scales. In all models, area emerged as the only predictor of plant species richness. A weak contribution of marine productivity was only detectable in models with a low number of islands, but this effect was independent of island size. Although nutrient deposition significantly contributes to explaining plant diversity, this effect was also independent of island size.Main conclusionsOur study demonstrates that marine productivity has no general effect on plant species richness of small islands worldwide. Although marine‐derived resources may still contribute to species richness variation, this effect does not seem to be restricted to small islands. Overall, our results do not provide support for the subsidized island biogeography hypothesis.

How human activities influence the island ecosystem through damaging the natural ecosystem and supporting the social ecosystem?

Island human activities damage the natural ecosystem with unique functions and support the social ecosystem for human survival and living. Identifying, quantifying, and spatially exhibiting the damage and support generated by human activities are of great significance for comprehensively revealing the anthropogenic influences on the island ecosystem and reasonably providing references for island development strategy. In this study, an evaluation model was established in perspectives of damage to the natural ecosystem and support for the social ecosystem. The damage involved geomorphology, landscape, habitat, and pollution, and the support included provision, accommodation, transportation, and recreation. The evaluation model was realized on the basis of the island use types, size effects, utilization levels, and change processes. Two new indices, namely, natural ecosystem damaged index (NEDI) and social ecosystem supported index (SESI), were proposed to represent the damage and support, respectively. Thereafter, scenario analysis was adopted to simulate the variations of NEDI and SESI in different scenarios of human activities and to provide references for the island development strategy. A total of ten islands in the Dongtou Archipelago in South China were used as the study area to demonstrate the model. Results indicated that the high NEDI and SESI areas were distributed in building, industrial, road, and reclamation areas, whereas the low NEDI and SESI areas were mainly located in vegetation areas and bare land. In different scenarios, the expansions of the road and building land generated much more damage than support, and the improvement of the utilization level produced more support than damage. The prohibition and limitation of island use types with low efficiency, the enhancement of vegetation restoration, the adequate use of reclamation area, the control of disordered exploitation expansion, and the improvement of utilization levels should be the strategies used by the Dongtou Archipelago for sustainable development. The application of the model validated its effectiveness and applicability in revealing the overall and spatial characteristics of the damage and support for islands and other coastal areas with intensive human activities.

Heisenberg pseudo-exchange and emergent anisotropies in field-driven pinwheel artificial spin ice

Rotating all islands in square artificial spin ice (ASI) uniformly about their centres gives rise to the recently reported pinwheel ASI. At angles around 45$^\mathrm{o}$, the antiferromagnetic ordering changes to ferromagnetic and the magnetic configurations of the system exhibit near-degeneracy, making it particularly sensitive to small perturbations. We investigate through micromagnetic modelling the influence of dipolar fields produced by physically extended islands in field-driven magnetisation processes in pinwheel arrays, and compare the results to hysteresis experiments performed in-situ using Lorentz transmission electron microscopy. We find that magnetisation end-states induce a Heisenberg pseudo-exchange interaction that governs both the inter-island coupling and the resultant array reversal process. Symmetry reduction gives rise to anisotropies and array-corner mediated avalanche reversals through a cascade of nearest-neighbour (NN) islands. The symmetries of the anisotropy axes are related to those of the geometrical array but are misaligned to the array axes as a result of the correlated interactions between neighbouring islands. The NN dipolar coupling is reduced by decreasing the island size and, using this property, we track the transition from the strongly coupled regime towards the pure point dipole one and observe modification of the ferromagnetic array reversal process. Our results shed light on important aspects of the interactions in pinwheel ASI, and demonstrate a mechanism by which their properties may be tuned for use in a range of fundamental research and spintronic applications.

One-dimensional island size distribution: From non-equilibrium to equilibrium

We present a critical view of the analysis of experimental one-dimensional island size distribution as a function of time. We study the processes of island growth using large-scale kinetic Monte Carlo simulations with diffusion barriers calculated within the framework of the density functional theory. We have shown that one-dimensional island size distribution depends significantly on the time of the experiment. Our model predicts that during annealing or cooling, the transition from one state of thermodynamical equilibrium to another occurs through a non-equilibrium state. This transition consists of Ostwald ripening and decay of one-dimensional islands. The results of our work demonstrate that considering experimental one-dimensional island size distribution as an equilibrium is a big misconception.

Bird assemblages on Amazonian river islands: Patterns of species diversity and composition

AbstractThe principles of island biogeography are rarely applied to the animal assemblages of Amazonian river islands. Here, we compare bird assemblages of Amazonian river islands with a variety of mainland habitats. We also examine how bird species diversity and composition are related to island physical attributes. Birds were sampled with mist nets and qualitative censuses on 11 river islands and 24 mainland sites on the lower reaches of the Rio Negro in the Brazilian Amazon. Island bird assemblages were characterized by lower species richness and a higher abundance of a few dominant species. Additionally, the species composition of the islands was distinct from that of the mainland, including the nearby floodplain habitats. The number of bird species increased with island size and habitat diversity, and decreased with degree of isolation. In addition, small islands tended to harbor an impoverished subset of the species present on larger ones. Bird species diversity and composition on Amazonian river islands are likely influenced by the ecological succession and historical events affecting island formation. Considering their small total area across the Amazon basin, these insular fluvial communities could be disproportionately threatened by river channel disturbances related to climate change or hydroelectric dam development.Abstract in Portughese is available with online material.

Island area, body size and demographic history shape genomic diversity in Darwin's finches and related tanagers.

Genomic diversity is the evolutionary foundation for adaptation to environmental change and thus is essential to consider in conservation planning. Island species are ideal for investigating the evolutionary drivers of genomic diversity, in part because of the potential for biological replicates. Here, we use genome data from 180 individuals spread among 27 island populations from 17 avian species to study the effects of island area, body size, demographic history and conservation status on contemporary genomic diversity. Our study expands earlier work on a small number of neutral loci to the entire genome and from a few species to many. We find significant positive correlation between island size and genomic diversity, a significant negative correlation between body size and genomic diversity, and that historical population declines significantly reduced contemporary genomic diversity. Our study shows that island size is the key factor in determining genomic diversity, indicating that habitat conservation is key to maintaining adaptive potential in the face of global environmental change. We found that threatened species generally had a significantly smaller values of Watterson's theta (θW =4Ne μ) compared to nonthreatened species, suggesting that θW may be useful as a conservation indicator for at-risk species. Overall, these findings (a) provide biological insights into how genomic diversity scales with ecological, morphological and demographic factors; and (b) illustrate how population genomic data can be leveraged to better inform conservation efforts.

Sampling design may obscure species–area relationships in landscape‐scale field studies

We investigated 1) the role of area per se in explaining anuran species richness on reservoir forest islands, after controlling for several confounding factors. We also assessed 2) how sampling design affects the inferential power of island species–area relationships (ISARs) aiming to 3) provide guidelines to yield reliable estimates of area‐induced species losses in patchy systems. We surveyed anurans with autonomous recording units at 151 plots located on 74 islands and four continuous forest sites at the Balbina Hydroelectric Reservoir landscape, central Brazilian Amazonia. We applied semi‐log ISAR models to assess the effect of sampling design on the fit and slope of species–area curves. To do so, we subsampled our surveyed islands following both a 1) stratified and 2) non‐stratified random selection of 5, 10, 15, 20 and 25 islands covering 1) the full range in island size (0.45–1699 ha) and 2) only islands smaller than 100 ha, respectively. We also compiled 25 datasets from the literature to assess the generality of our findings. Island size explained ca half of the variation in species richness. The fit and slope of species–area curves were affected mainly by the range in island size considered, and to a very small extent by the number of islands surveyed. In our literature review, all datasets covering a range of patch sizes larger than 300 ha yielded a positive ISAR, whereas the number of patches alone did not affect the detection of ISARs. We conclude that 1) area per se plays a major role in explaining anuran species richness on forest islands within an Amazonian anthropogenic archipelago; 2) the inferential power of island species–area relationships is severely degraded by sub‐optimal sampling designs; 3) at least 10 habitat patches spanning three orders of magnitude in size should be surveyed to yield reliable species–area estimates in patchy systems.

Detecting inter- and intra-island genetic diversity: population structure of the endangered crocodile newt, Echinotriton andersoni, in the Ryukyus

The endangered crocodile newt, Echinotriton andersoni, is a relatively large species of the family Salamandridae and is distributed on six islands in the central part of the Ryukyu Archipelago, Japan. Because of an originally small distribution range and recent habitat loss, this species has been steadily declining in number. To elucidate fine-scale population structure, which is essential for effective conservation management, we analyzed genetic diversity and gene flow based on nine microsatellite loci. Our results identified three different island groups (Amamioshima, Tokunoshima, and Okinawajima) and multiple genetic assemblages within the Amami and Okinawa island groups. The gross genetic variation within each island was positively correlated with island size. Population structure followed a latitudinal cline and isolation by distance, even among geographically isolated islands. In northern Okinawajima, relatively complex genetic structure was observed. This unexpected population structure seems to reflect historical migration and distribution expansion through the formation of land bridges and shifted coastlines in the Pleistocene. We also found that small islands showed little genetic variation (Ukeshima, Sesokojima, and Tokashikijima). In particular, our findings revealed that the Tokashikijima population is at greater risk for extinction than the other populations because it has the smallest effective population size.

Direct Growth of Highly Strained Pt Islands on Branched Ni Nanoparticles for Improved Hydrogen Evolution Reaction Activity.

The direct growth of Pt islands on lattice mismatched Ni nanoparticles is a major synthetic challenge and a promising strategy to create highly strained Pt atoms for electrocatalysis. By using very mild reaction conditions, Pt islands with tunable strain were formed directly on Ni branched particles. The highly strained 1.9 nm Pt-island on branched Ni nanoparticles exhibited high specific activity and the highest mass activity for hydrogen evolution (HER) in a pH 13 electrolyte. These results show the ability to synthetically tune the size of the Pt islands to control the strain to give higher HER activity.

Coalescence of Islands of Different Thicknesses in Smectic Nanofilms

In smectic nanofilms, the coalescence of islands (areas thicker than the smectic nanofilm) of different thicknesses and radial dimensions is studied. The initial stage of coalescence (fusion of islands) has a dislocation nature and is associated with changes in the energy of dislocation loops. The second stage of coalescence with the collapse of one of the islands occurs with the increase in the size of the other island. The estimates obtained show that the change in the energy of dislocation loops and the interaction of the surfaces of the smectic nanofilm play the decisive role at this stage. An unexpected effect of displacement of the center of mass of two islands in the process of their coalescence is also discovered. The effect is related to the collective dynamics of the material flows of the islands and the smectic nanofilm.

Diet variability among insular populations of Podarcis lizards reveals diverse strategies to face resource-limited environments.

Access to resources is a dynamic and multicausal process that determines the success and survival of a population. It is therefore often challenging to disentangle the factors affecting ecological traits like diet. Insular habitats provide a good opportunity to study how variation in diet originates, in particular in populations of mesopredators such as lizards. Indeed, high levels of population density associated with low food abundance and low predation are selection pressures typically observed on islands. In the present study, the diet of eighteen insular populations of two closely related species of lacertid lizards (Podarcis sicula and Podarcis melisellensis) was assessed. Our results reveal that despite dietary variability among populations, diet taxonomic diversity is not impacted by island area. In contrast, however, diet disparity metrics, based on the variability in the physical (hardness) and behavioral (evasiveness) properties of ingested food items, are correlated with island size. These findings suggest that an increase in intraspecific competition for access to resources may induce shifts in functional components of the diet. Additionally, the two species differed in the relation between diet disparity and island area suggesting that different strategies exist to deal with low food abundance in these two species. Finally, sexual dimorphism in diet and head dimensions is not greater on smaller islands, in contrast to our predictions.

Identification of important error fields in stellarators using the Hessian matrix method

Error fields are predominantly attributed to inevitable coil imperfections. Controlling error fields during coil fabrication and assembly is crucial for stellarators. Excessively tight coil tolerance increases time and cost, and, in part, led to the cancellation of the National Compact Stellarator Experiment and delay of W7-X. In this paper, we improve the recently proposed Hessian matrix method to rapidly identify important coil deviations. Two of the most common figures of merit, magnetic island size and quasi-symmetry, are analytically differentiated over coil parameters. By extracting the eigenvectors of the Hessian matrix, we can directly identify sensitive coil deviations in the order of the eigenvalues. The new method is applied to the upcoming Chinese First Quasi-axisymmetric Stellarator configuration. Important perturbations that enlarge n/m = 4/11 islands and deteriorate quasi-axisymmetry of the magnetic field are successfully determined. The results suggest each modular coil should have separate tolerance and some certain perturbation combinations will produce significant error fields. By relaxing unnecessary coil tolerance, this method will hopefully lead to a substantial reduction in time and cost.

Chemically Enhanced Treatment Wetland to Improve Water Quality and Mitigate Land Subsidence in the Sacramento‒San Joaquin Delta: Cost and Design Considerations

Water quality impairment and land surface subsidence threaten the viability of the Sacramento–San Joaquin Delta (Delta), a critical component of California’s water conveyance system. Current-day irrigation drainage through Delta island peat soils affects drinking water treatment and is linked to mercury transport, potentially posing both ecological and public health concerns. To cost-effectively treat agricultural drainage water from subsided Delta islands to reduce the export of drinking Water Quality Constituents of Concern and mitigate land subsidence through accretion, we studied hybrid coagulation-treatment wetland systems, termed Chemically Enhanced Treatment Wetlands (CETWs). We provide cost estimates and design recommendations to aid broader implementation of this technology. Over a 20-year horizon using a Total Annualized Cost analysis, we estimate treatment costs of $602 to $747 per acre-foot (ac‑ft) water treated, and $36 to $70 per kg dissolved organic carbon (DOC) removed, depending upon source water DOC concentrations for a small 3-acre CETW system. For larger CETW systems scaled for island sizes of 3,500 to 14,000 acres, costs decrease to $108 to $239 per ac-ft water treated, and $11 to $14 per kg DOC removed. We estimated the footprints of CETW systems to be approximately 3% of the area being treated for 4-day hydraulic retention time (HRT) systems, but they would decrease to less than 1% for 1-day HRT systems. CETWs ultimately address several of the Delta’s key internal issues while keeping water treatment costs competitive with other currently available treatment technologies at similar scales on a per-carbon-removed basis. CETWs offer a reliable system to reduce out-going DOC and mercury loads, and they provide the additional benefit of sediment accretion. System costs and treatment efficacy depend significantly on inflow source water conditions, land availability, and other practical matters. To keep costs low and removal efficacy high, wetland design features will need site-specific evaluation.

Morphological diversity of channel patterns of braided rivers

The paper presents the description of main channel types of braided rivers distinguished in the channel pattern classification produced in the Moscow State University. It is shown that the diversity of braided channels is determined by various conditions of their formation, different degree of channel stability and other factors. This diversity is defined by the number, size and shape of islands, formation of islands in channel arms, composing bifurcations of the 2nd and 3rd orders, presence of floodplain branches (floodplain multi-channel), symmetry or asymmetry of braided reaches themselves, development of the bends of the branches, water discharge of the branches and distribution of runoff over them in different phases of water regime, high- and low-water years, etc. Also braided channel reaches occur when cut-off meanders are formed (incomplete meandering). On the largest rivers there are braided reaches which are characterized by the development of branches in different parts of the river valley bottom and differing in their channel and even water regime. Certain features are typical for braided reaches of wide-floodplain or incised channels, for rivers with a one-sided floodplain. As a result single, conjugated, floodplain, parallel branches, one-sided, alternate one-sided braided reaches can be either simple (for example, single or parts of conjugated formed by one island) or complex, and the latter are represented by several varieties. The identification of various morphological types, subtypes and varieties of braided channel reaches is directly connected and determines the methods of channel processes management in water economy and water transport development of rivers, construction of communications through rivers, etc.

Evolution of Morphology in the Process of Growth of Island Poly(p-xylylene) Films Obtained by Vapor Deposition Polymerization

Using atomic force microscopy, the evolution of the morphology of island poly(p-xylene) films formed on silicon substrates by vapor deposition polymerization at two deposition temperatures of +23 and 0°C and a fixed monomer flow is studied. The dependences of the surface coverage, the effective thickness of the island coating, and the density and average size of the polymer islands on the deposition time are investigated. Within the framework of the dynamic scaling theory, the size distribution of islands and the size distribution of their capture zones are analyzed. It is shown that the observed features of the evolution of the morphology of island poly(p-xylylene) films cannot be fully described in the framework of classical models based on diffusion-limited aggregation. However, they can be explained by the reversibility of aggregation, which is a specific feature of the polymeric nature of the island coatings being formed.