Molecular dynamics simulation of fracture strength and morphology of defective graphene

Different types of defects can be introduced into graphene during material synthesis, and significantly influence the properties of graphene. In this work, we investigated the effects of structural defects, edge functionalisation and reconstruction on the fracture strength and morphology of graphene by molecular dynamics simulations. The minimum energy path analysis was conducted to investigate the formation of Stone-Wales defects. We also employed out-of-plane perturbation and energy minimization principle to study the possi-ble morphology of graphene nanoribbons with edge-termination. Our numerical results show that the fracture strength of graphene is dependent on defects and environmental temperature. However, pre-existing defects may be healed, resulting in strength recovery. Edge functionalization can induce compressive stress and ripples in the edge areas of gra-phene nanoribbons. On the other hand, edge reconstruction contributed to the tensile stress and curved shape in the graphene nanoribbons.

Composition and morphology of particle emissions from in-use aircraft during takeoff and landing

In order to provide realistic data for air pollution inventories and source apportionment at airports, the morphology and composition of ultrafine particles (UFP) in aircraft engine exhaust were measured and characterized. For this purpose, two independent measurement techniques were employed to collect emissions during normal takeoff and landing operations at Brisbane Airport, Australia. PM1 emissions in the airfield were collected on filters and analyzed using the particle-induced X-ray emission (PIXE) technique. Morphological and compositional analyses of individual ultrafine particles in aircraft plumes were performed on silicon nitride membrane grids using transmission electron microscopy (TEM) combined with energy-dispersive X-ray microanalysis (EDX). TEM results showed that the deposited particles were in the range of 5 to 100 nm in diameter, had semisolid spherical shapes and were dominant in the nucleation mode (18 – 20 nm). The EDX analysis showed the main elements in the nucleation particles were C, O, S and Cl. The PIXE analysis of the airfield samples was generally in agreement with the EDX in detecting S, Cl, K, Fe and Si in the particles. The results of this study provide important scientific information on the toxicity of aircraft exhaust and their impact on local air quality.

Increased plant volatile production affects oviposition, but not larval development, in the moth Helicoverpa armigera

It is well established that herbivorous insects respond to changes in plant odour production, but little attention has been given to whether these responses relate to direct fitness costs of plant volatile production on insect growth and survival. Here, we use transgenic Nicotiana tabacum (tobacco) plants that produce relatively large amounts of the volatile (S)-linalool to study whether the responses of egg-laying herbivorous insects to linalool production relate directly to the growth and survival of offspring. In choice tests, fewer eggs were laid on transgenic plants compared with non-transformed controls, indicating that increased linalool emissions have a deterrent effect on Helicoverpa armigera oviposition. Larval survival and larval mass after feeding on transgenic leaves, however, was comparable to non-transformed controls. (S)-linalool, whether in volatile or sequestered form, does not appear to have a direct effect on offspring fitness in this moth. We discuss how the ecology of this polyphagous moth species may necessitate a high tolerance for certain volatiles and their related non-volatile compounds, and suggest that responses by adult female H. armigera moths towards increased linalool production may be context specific and relate to other indirect effects on fitness.

Molecular dynamics simulation of fracture strength and morphology of defective graphene

Different types of defects can be introduced into graphene during material synthesis, and significantly influence the properties of graphene. In this work, we investigated the effects of structural defects, edge functionalisation and reconstruction on the fracture strength and morphology of graphene by molecular dynamics simulations. The minimum energy path analysis was conducted to investigate the formation of Stone-Wales defects. We also employed out-of-plane perturbation and energy minimization principle to study the possible morphology of graphene nanoribbons with edge-termination. Our numerical results show that the fracture strength of graphene is dependent on defects and environmental temperature. However, pre-existing defects may be healed, resulting in strength recovery. Edge functionalization can induce compressive stress and ripples in the edge areas of graphene nanoribbons. On the other hand, edge reconstruction contributed to the tensile stress and curved shape in the graphene nanoribbons.

Influence of oxidation and reduction conditions upon the morphology of silica-supported polycrystalline silver catalysts

The effect of oxidation and reduction conditions upon the morphology of polycrystalline silver catalysts has been investigated by means of in situ Fourier-transform infrared (FTIR) spectroscopy. Characterization of the sample was achieved by inspection of the νas(COO) band profile of adsorbed formate, recorded after dosing with formic acid at ambient temperature. Evidence was obtained for the existence of a silver surface reconstructed by the presence of subsurface oxygen in addition to the conventional family of Ag(111) and Ag(110) crystal faces. Oxidation at 773 K facilitated the reconstruction of silver planes due to the formation of subsurface oxygen species. Prolonged oxygen treatment at 773 K also caused particle fragmentation as a consequence of excessive oxygen penetration of the silver catalyst at defect sites. It was also deduced that the presence of oxygen in the gas phase stabilized the growth of silver planes which could form stronger bonds with oxygen. In contrast, high-temperature thermal treatment in vacuum induced significant sintering of the silver catalyst. Reduction at 773 K resulted in substantial quantities of dissolved hydrogen (and probably hydroxy species) in the bulk silver structure. Furthermore, enhanced defect formation in the catalyst was also noted, as evidenced by the increased concentration of formate species associated with oxygen-reconstructed silver faces.

Morphology of osteocyte cells in normal and hyper-gravity

Osteocyte cells are the most abundant cells in human bone tissue. Due to their unique morphology and location, osteocyte cells are thought to act as regulators in the bone remodelling process, and are believed to play an important role in astronauts’ bone mass loss after long-term space missions. There is increasing evidence showing that an osteocyte’s functions are highly affected by its morphology. However, changes in an osteocyte’s morphology under an altered gravity environment are still not well documented. Several in vitro studies have been recently conducted to investigate the morphological response of osteocyte cells to the microgravity environment, where osteocyte cells were cultured on a two-dimensional flat surface for at least 24 hours before microgravity experiments. Morphology changes of osteocyte cells in microgravity were then studied by comparing the cell area to 1g control cells. However, osteocyte cells found in vivo are with a more 3D morphology, and both cell body and dendritic processes are found sensitive to mechanical loadings. A round shape osteocyte’s cells support a less stiff cytoskeleton and are more sensitive to mechanical stimulations compared with flat cellular morphology. Thus, the relative flat and spread shape of isolated osteocytes in 2D culture may greatly hamper their sensitivity to a mechanical stimulus, and the lack of knowledge on the osteocyte’s morphological characteristics in culture may lead to subjective and noncomprehensive conclusions of how altered gravity impacts on an osteocyte’s morphology. Through this work empirical models were developed to quantitatively predicate the changes of morphology in osteocyte cell lines (MLO-Y4) in culture, and the response of osteocyte cells, which are relatively round in shape, to hyper-gravity stimulation has also been investigated. The morphology changes of MLO-Y4 cells in culture were quantified by measuring cell area and three dimensionless shape features including aspect ratio, circularity and solidity by using widely accepted image analysis software (ImageJTM). MLO-Y4 cells were cultured at low density (5×103 per well) and the changes in morphology were recorded over 10 hours. Based on the data obtained from the imaging analysis, empirical models were developed using the non-linear regression method. The developed empirical models accurately predict the morphology of MLO-Y4 cells for different culture times and can, therefore, be used as a reference model for analysing MLO-Y4 cell morphology changes within various biological/mechanical studies, as necessary. The morphological response of MLO-Y4 cells with a relatively round morphology to hyper-gravity environment has been investigated using a centrifuge. After 2 hours culture, MLO-Y4 cells were exposed to 20g for 30mins. Changes in the morphology of MLO-Y4 cells are quantitatively analysed by measuring the average value of cell area and dimensionless shape factors such as aspect ratio, solidity and circularity. In this study, no significant morphology changes were detected in MLO-Y4 cells under a hyper-gravity environment (20g for 30 mins) compared with 1g control cells.

Variation in leaf morphology of the invasive cat's claw creeper Dolichandra unguis-cati (Bignoniaceae)

The invasive liana cat’s claw creeper Dolichandra unguis-cati (L.) L.G. Lohmann (syn. Macfadyena unguis-cati (L.) A.H. Gentry) exhibits intraspecific variation in leaf morphology, but this is rarely noted in the published literature. The present study documents variation in leaf morphology in two forms of the species that occur in Australia (long pod and short pod). Leaf morphology is compared between the two forms and the position of the shoots (trunk and ground) at the only two sites in which they co-occur. Leaves were categorised on the basis of leaflet number and the presence or absence of tendrils. Simple leaves were produced mainly on shoots growing along the ground and were more abundant in the short-pod form. Long-pod plants were dominated by bifoliate leaves with tendrils. Cat’s claw creeper exhibits considerably wider variation in leaf morphology than recorded previously. Variations in leaf morphology may be linked to differences in the genotype, developmental stage and plastic responses of the plants. Understanding these variations may have implications for taxonomic delimitation and improved management, particularly biological control involving leaf-feeding insects.

Zeta-potential and morphology of electrospun nano- and microfibers from biopolymers and their blends used as scaffolds in tissue engineering

Electrostatic spinning or electrospinning is a fiber spinning technique driven by a high-voltage electric field that produces fibers with diameters in a submicrometer to nanometer range.1 Nanofibers are typical one-dimensional colloidal objects with an increased tensile strength, whose length can achieve a few kilometers and the specific surface area can be 100 m2 g–1 or higher.2 Nano- and microfibers from biocompatible polymers and biopolymers have received much attention in medical applications3 including biomedical structural elements (scaffolding used in tissue engineering,2,4–6 wound dressing,7 artificial organs and vascular grafts8), drug and vaccine delivery,9–11 protective shields in speciality fabrics, multifunctional membranes, etc. Other applications concern superhydrophobic coatings,12 encapsulation of solid materials,13 filter media for submicron particles in separation industry, composite reinforcement and structures for nano-electronic machines.

YBa2Cu3O7-x films on yttria-stabilized ZrO2 substrates : influence of the substrate morphology

c-axis-oriented YBa2Cu3O7-x (YBCO) thin films were laser deposited on (001) yttria-stabilized ZrO2 (YSZ) substrates with different surface morphologies. The in-plane orientation of the films on smooth substrates was sensitive to the deposition conditions, often resulting in mixed orientations. However, a strongly dominating [110] YBCO//[110]YSZ orientation was obtained at a deposition temperature of 770°C. Films on substrates with surface steps, induced by depositing a homoepitaxial buffer layer or by thermally annealing the substrate, had a [110]YBCO//[100]YSZ orientation when deposited at the same temperature. It was concluded that the [110]YBCO//[100] YSZ orientation was promoted by a graphoepitaxial mechanism. Films prepared under identical conditions on smooth and stepped substrates grew with extended c axes on the former. It is proposed that the extension can be induced by disorder, invoked by a low oxygen pressure and a low density of adsorption sites. The disorder may be eliminated by either an increase of the oxygen pressure or an increase of the density of adsorption sites in the form of steps. The film microstructure influenced the microwave surface resistance, which was similar for films with one exclusive in-plane orientation and higher for films with mixed orientations. The films on the stepped surfaces had superior superconducting properties; inductive measurements gave a Tc onset of 88 K, a ΔT(90%-10%) c of 0.2 K, and the transport jc was 1.5×106 A/cm2 at 83 K, for films on substrates with homoepitaxial buffer layers.

Morphology changes and mechanistic aspects of the electrochemically-induced reversible solid-solid transformation of microcrystalline TCNQ into Co TCNQ 2-based materials (TCNQ= 7, 7, 8, 8-Tetracyanoquinodimethane)

The chemically reversible solid−solid phase transformation of a TCNQ-modified glassy carbon, indium tin oxide, or metal electrode into Co\[TCNQ]2(H2O)2 material in the presence of Co2+(aq) containing electrolytes has been induced and monitored electrochemically. Voltammetric data reveal that the TCNQ/Co\[TCNQ]2(H2O)2 interconversion process is independent of electrode material and identity of cobalt electrolyte anion. However, a marked dependence on electrolyte concentration, scan rate, and method of electrode modification (drop casting or mechanical attachment) is found. Cyclic voltammetric and double potential step chronoamperometric measurements confirm that formation of Co\[TCNQ]2(H2O)2 occurs through a rate-determining nucleation and growth process that initially involves incorporation of Co2+(aq) ions into the reduced TCNQ crystal lattice at the TCNQ|electrode|electrolyte interface. Similarly, the reverse (oxidation) process, which involves transformation of solid Co\[TCNQ]2(H2O)2 back to parent TCNQ crystals, also is controlled by nucleation−growth kinetics. The overall chemically reversible process that represents this transformation is described by the reaction:  2TCNQ0(s) + 2e- + Co2+(aq) + 2H2O \[Co(TCNQ)2(H2O)2](s). Ex situ SEM images illustrated that this reversible TCNQ/Co\[TCNQ]2(H2O)2 conversion process is accompanied by drastic size and morphology changes in the parent solid TCNQ. In addition, different sizes of needle-shaped nanorod/nanowire crystals of Co\[TCNQ]2(H2O)2 are formed depending on the method of surface immobilization.

An investigation of silver electrodeposition from ionic liquids : influence of atmospheric water uptake on the silver electrodeposition mechanism and film morphology

The electrodeposition of silver from two ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) and N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ([C4mPyr][TFSI]), and an aqueous KNO3 solution on a glassy carbon electrode was undertaken. It was found by cyclic voltammetry that the electrodeposition of silver proceeds through nucleation–growth kinetics. Analysis of chronoamperometric data indicated that the nucleation–growth mechanism is instantaneous at all potentials in the case of [BMIm][BF4] and [C4mPyr][TFSI], and instantaneous at low overpotentials tending to progressive at high overpotentials for KNO3. Significantly, under ambient conditions, the silver electrodeposition mechanism changes to progressive nucleation and growth in [C4mPyr][TFSI], which is attributed to the uptake of atmospheric water in the IL. It was found that these differences in the growth mechanism impact significantly on the morphology of the resultant electrodeposit which is characterised ex situ by scanning electron microscopy and X-ray diffraction.

Effect of Imidazolium-based Ionic Liquids on the nanoscale morphology of CuTCNQ (TCNQ= 7, 7, 8, 8-tetracyanoquinodimethane) metal-organic semiconductors

We demonstrate for the first time the ionic-liquid-mediated synthesis of nanostructured CuTCNQ by the simple immersion of copper in a solution of TCNQ where the viscosity of the medium significantly impacts the corrosion–crystallization process and the final morphology of the material.

Cyclic mechanical strain guides capillary-like morphology in vitro

Introduction Stretching of tissue stimulates angiogenesis but increased motion at a fracture site hinders revascularisation. In vitro studies have indicated that mechanical stimuli promote angiogenic responses in endothelial cells, but can either inhibit or enhance responses when applied directly to angiogenesis assays. We anticipated that cyclic tension applied during endothelial network assembly would increase vascular structure formation up to a certain threshold. Methods Fibroblast/HUVEC co-cultures were subjected to cyclic equibiaxial strain (1 Hz; 6 h/day; 7 days) using the FlexerCell FX-4000T system and limiting rings for simultaneous application of multiple strain magnitudes (0–13%). Cells were labelled using anti-PECAM-1, and image analysis provided measures of endothelial network length and numbers of junctions. Results Cyclic stretching had no significant effect on the total length of endothelial networks (P > 0.2) but resulted in a strain-dependent decrease in branching and localised alignments of endothelial structures, which were in turn aligned with the supporting fibroblastic construct. Conclusion The organisation of endothelial networks under cyclic strain is dominated by structural adaptation to the supporting construct. It may be that, in fracture healing, the formation and integrity of the granulation tissue and callus is ultimately critical in revascularisation and its failure under severe strain conditions.

Cell adhesion molecule uvomorulin expression in human breast cancer cell lines : relationship to morphology and invasive capacities

Loss of cell-cell adhesion in carcinoma cells may be an important step in the acquisition of an invasive, metastatic phenotype. We have examined the expression of the epithelial-specific cell adhesion molecule uvomorulin (E-cadherin, cell-CAM 120/80, L-CAM) in human breast cancer cell lines. We find that fibroblastoid, highly invasive, vimentin-expressing breast cancer cell lines do not express uvomorulin. Of the more epithelial-appearing, less invasive, keratin-expressing breast cancer cell lines, some express uvomorulin, and some do not. We examined the morphologies of the cell lines in the reconstituted basement membrane matrix Matrigel and measured the ability of the cells to traverse a Matrigel-coated filter as in vitro models for detachment of carcinoma cells from neighboring cells and invasion through basement membrane into surrounding tissue. Colonies of uvomorulin-positive cells have a characteristic fused appearance in Matrigel, whereas uvomorulin-negative cells appear detached. Cells which are uvomorulin negative and vimentin positive have a stellate morphology in Matrigel. We show that uvomorulin is responsible for the fused colony morphology in Matrigel since treatment of uvomorulin-positive MCF-7 cells with an antibody to uvomorulin caused the cells to detach from one another but did not induce invasiveness in these cells, as measured by their ability to cross a Matrigel-coated polycarbonate filter in a modified Boyden chamber assay. Two uvomorulin-negative, vimentin-negative cell lines are also not highly invasive as measured by this assay. We suggest that loss of uvomorulin-mediated cell-cell adhesion may be one of many changes involved in the progression of a carcinoma cell to an invasive phenotype.