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.

Hydrogen gas sensors based on thermally evaporated nanostructured MoO3 Schottky diode : a comparative study

In this paper, a comparative study of Pt/nanostructured MoO3/SiC Schottky diode based hydrogen gas sensors is presented. MoO3 nanostructured films with three different morphologies (nanoplatelets, nanoplateletsnanowires and nano-flowers) were deposited on SiC by thermal evaporation. We compare the current-voltage characteristics and the dynamic response of these sensors as they are exposed to hydrogen gas at temperatures up to 250°C. Results indicate that the sensor based on MoO3 nanoflowers exhibited the highest sensitivity (in terms of a 5.79V voltage shift) towards 1% hydrogen; while the sensor based on MoO3 nanoplatelets showed the quickest response (t90%- 40s).

Urban agriculture : a growing field of research workshop at INTERACT 2013

Growing food presents diverse challenges and opportunities within the urban environment. As cities develop, population density rises, land prices rise, and the opportunity to use land for traditional farming and gardening diminishes. Counter to this trend there are a growing number of both community gardens, city farms, guerrilla gardening, rooftop and vertical gardens, pot plants, windowsill herbs, and other balcony or backyard gardens cropping up in different cities, all with a purpose to produce food. This workshop brings to-gether practitioners and researchers in the field of urban agriculture and Hu-man-Computer Interaction to explore and opportunities for technology design to support the different forms of growing practice and foster local food production in cities. This 1-day workshop will serve as an active forum for researchers and practi-tioners across various fields including, but not limited to, agriculture and gar-dening, education, urban planning, human-computer interaction, and communi-ty engagement. This workshop has three distinct points of focus: i) Individual and small-scale gardening and food production, and how to connect like minded people who are involved in these practices to share their knowledge ii) Com-munities involved in urban agriculture, either through community gardens, city farms, or grassroots movements, often dependant on volunteer participation, providing the challenge of managing limited resources iii) Environmental and sociocultural sustainability through urban agriculture. The participants will have an opportunity to present their own work. This will be followed by a visit to a nearby city farm, which will provide a local context for a group design exercise. Finally the workshop will conclude with panel dis-cussions to review opportunities for further research and collaborations beyond the conference. For more information, please visit the workshop website, at http://www.urbaninformatics.net/resources/interact2013cfp/

Effect of CT electron density identification on Monte Carlo simulations of radiotherapeutic treatments

Introduction: The accurate identification of tissue electron densities is of great importance for Monte Carlo (MC) dose calculations. When converting patient CT data into a voxelised format suitable for MC simulations, however, it is common to simplify the assignment of electron densities so that the complex tissues existing in the human body are categorized into a few basic types. This study examines the effects that the assignment of tissue types and the calculation of densities can have on the results of MC simulations, for the particular case of a Siemen’s Sensation 4 CT scanner located in a radiotherapy centre where QA measurements are routinely made using 11 tissue types (plus air). Methods: DOSXYZnrc phantoms are generated from CT data, using the CTCREATE user code, with the relationship between Hounsfield units (HU) and density determined via linear interpolation between a series of specified points on the ‘CT-density ramp’ (see Figure 1(a)). Tissue types are assigned according to HU ranges. Each voxel in the DOSXYZnrc phantom therefore has an electron density (electrons/cm3) defined by the product of the mass density (from the HU conversion) and the intrinsic electron density (electrons /gram) (from the material assignment), in that voxel. In this study, we consider the problems of density conversion and material identification separately: the CT-density ramp is simplified by decreasing the number of points which define it from 12 down to 8, 3 and 2; and the material-type-assignment is varied by defining the materials which comprise our test phantom (a Supertech head) as two tissues and bone, two plastics and bone, water only and (as an extreme case) lead only. The effect of these parameters on radiological thickness maps derived from simulated portal images is investigated. Results & Discussion: Increasing the degree of simplification of the CT-density ramp results in an increasing effect on the resulting radiological thickness calculated for the Supertech head phantom. For instance, defining the CT-density ramp using 8 points, instead of 12, results in a maximum radiological thickness change of 0.2 cm, whereas defining the CT-density ramp using only 2 points results in a maximum radiological thickness change of 11.2 cm. Changing the definition of the materials comprising the phantom between water and plastic and tissue results in millimetre-scale changes to the resulting radiological thickness. When the entire phantom is defined as lead, this alteration changes the calculated radiological thickness by a maximum of 9.7 cm. Evidently, the simplification of the CT-density ramp has a greater effect on the resulting radiological thickness map than does the alteration of the assignment of tissue types. Conclusions: It is possible to alter the definitions of the tissue types comprising the phantom (or patient) without substantially altering the results of simulated portal images. However, these images are very sensitive to the accurate identification of the HU-density relationship. When converting data from a patient’s CT into a MC simulation phantom, therefore, all possible care should be taken to accurately reproduce the conversion between HU and mass density, for the specific CT scanner used. Acknowledgements: This work is funded by the NHMRC, through a project grant, and supported by the Queensland University of Technology (QUT) and the Royal Brisbane and Women's Hospital (RBWH), Brisbane, Australia. The authors are grateful to the staff of the RBWH, especially Darren Cassidy, for assistance in obtaining the phantom CT data used in this study. The authors also wish to thank Cathy Hargrave, of QUT, for assistance in formatting the CT data, using the Pinnacle TPS. Computational resources and services used in this work were provided by the HPC and Research Support Group, QUT, Brisbane, Australia.

Deformation and failure of graphene sheet and graphene-polymer interface

With a monolayer honeycomb-lattice of sp2-hybridized carbon atoms, graphene has demonstrated exceptional electrical, mechanical and thermal properties. One of its promising applications is to create graphene-polymer nanocomposites with tailored mechanical and physical properties. In general, the mechanical properties of graphene nanofiller as well as graphene-polymer interface govern the overall mechanical performance of graphene-polymer nanocomposites. However, the strengthening and toughening mechanisms in these novel nanocomposites have not been well understood. In this work, the deformation and failure of graphene sheet and graphene-polymer interface were investigated using molecular dynamics (MD) simulations. The effect of structural defects on the mechanical properties of graphene and graphene-polymer interface was investigated as well. The results showed that structural defects in graphene (e.g. Stone-Wales defect and multi-vacancy defect) can significantly deteriorate the fracture strength of graphene but may still make full utilization of corresponding strength of graphene and keep the interfacial strength and the overall mechanical performance of graphene-polymer nanocomposites.

Automatic object segmentation of unstructured scenes using colour and depth maps

This study presents a segmentation pipeline that fuses colour and depth information to automatically separate objects of interest in video sequences captured from a quadcopter. Many approaches assume that cameras are static with known position, a condition which cannot be preserved in most outdoor robotic applications. In this study, the authors compute depth information and camera positions from a monocular video sequence using structure from motion and use this information as an additional cue to colour for accurate segmentation. The authors model the problem similarly to standard segmentation routines as a Markov random field and perform the segmentation using graph cuts optimisation. Manual intervention is minimised and is only required to determine pixel seeds in the first frame which are then automatically reprojected into the remaining frames of the sequence. The authors also describe an automated method to adjust the relative weights for colour and depth according to their discriminative properties in each frame. Experimental results are presented for two video sequences captured using a quadcopter. The quality of the segmentation is compared to a ground truth and other state-of-the-art methods with consistently accurate results.

GrabCutSFM : how 3D information improves unsupervised object segmentation

In this paper, we present an unsupervised graph cut based object segmentation method using 3D information provided by Structure from Motion (SFM), called Grab- CutSFM. Rather than focusing on the segmentation problem using a trained model or human intervention, our approach aims to achieve meaningful segmentation autonomously with direct application to vision based robotics. Generally, object (foreground) and background have certain discriminative geometric information in 3D space. By exploring the 3D information from multiple views, our proposed method can segment potential objects correctly and automatically compared to conventional unsupervised segmentation using only 2D visual cues. Experiments with real video data collected from indoor and outdoor environments verify the proposed approach.

Nonparametric semantic segmentation for 3D street scenes

In this paper we propose a method to generate a large scale and accurate dense 3D semantic map of street scenes. A dense 3D semantic model of the environment can significantly improve a number of robotic applications such as autonomous driving, navigation or localisation. Instead of using offline trained classifiers for semantic segmentation, our approach employs a data-driven, nonparametric method to parse scenes which easily scale to a large environment and generalise to different scenes. We use stereo image pairs collected from cameras mounted on a moving car to produce dense depth maps which are combined into a global 3D reconstruction using camera poses from stereo visual odometry. Simultaneously, 2D automatic semantic segmentation using a nonparametric scene parsing method is fused into the 3D model. Furthermore, the resultant 3D semantic model is improved with the consideration of moving objects in the scene. We demonstrate our method on the publicly available KITTI dataset and evaluate the performance against manually generated ground truth.

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.

Impact of recent coastal development and human activities on Nha Trang Bay, Vietnam : evidence from a Porites lutea geochemical record

Nha Trang Bay (NTB) is located on the Central Vietnam coast, western South China Sea. Recent coastal development of Nha Trang City has raised public concern over an increasing level of pollution within the bay and degradation of nearby coral reefs. In this study, multiple proxies (e.g., trace metals, rare earth elements (REEs), and Y/Ho) recorded in a massive Porites lutea coral colony were used to reconstruct changes in seawater conditions in the NTB from 1995 to 2009. A 14-year record of REEs and other trace metals revealed that the concentrations of terrestrial trace metals have increased dramatically in response to an increase in coastal development projects such as road, port, and resort constructions, port and river dredging, and dumping activities since 2000. The effects of such developmental processes are also evident in changes in REE patterns and Y/Ho ratios through time, suggesting that both parameters are critical proxies for marine pollution.

Extreme temperatures and emergency department admissions for childhood asthma in Brisbane, Australia

Objectives To examine the effect of extreme temperatures on emergency department admissions (EDAs) for childhood asthma. Methods An ecological design was used in this study. A Poisson linear regression model combined with a distributed lag non-linear model was used to quantify the effect of temperature on EDAs for asthma among children aged 0–14 years in Brisbane, Australia, during January 2003–December 2009, while controlling for air pollution, relative humidity, day of the week, season and long-term trends. The model residuals were checked to identify whether there was an added effect due to heat waves or cold spells. Results There were 13 324 EDAs for childhood asthma during the study period. Both hot and cold temperatures were associated with increases in EDAs for childhood asthma, and their effects both appeared to be acute. An added effect of heat waves on EDAs for childhood asthma was observed, but no added effect of cold spells was found. Male children and children aged 0–4 years were most vulnerable to heat effects, while children aged 10–14 years were most vulnerable to cold effects. Conclusions Both hot and cold temperatures seemed to affect EDAs for childhood asthma. As climate change continues, children aged 0–4 years are at particular risk for asthma.

Constructions of children's needs in informal kinship care in rural China

Kinship care is the oldest form of alternative child care in the world. Recent years have witnessed a significant increase in the number of children being placed in kinship care across Western countries. However, in contrast to rapid knowledge advances about formal kinship care, far less is known about the needs of children in informal kinship care, especially in Asian contexts. This thesis and the study upon which it is formed sought to redress this knowledge gap. Qualitative approach was adopted to explore social constructions of children in informal kinship care in rural China. Parents in China seeking work in cities have left behind around 58 million rural children, mostly with relatives and without the involvement of the state. The present study examined caregivers’ and school personnel’s understandings of these school-age children’s needs through semi-structured interviews with 23 kin caregivers and five school personnel in Shijiapu Town, Jilin Province, China. The central question that guided the whole study is: What are the needs of children in informal kinship care in rural Jilin Province, China? Interpretative Phenomenological Analysis was used to categorise and interpret the qualitative data. Based on participants’ constructions, this study developed a need model with eight themes. They are: (1) emotional needs and mental health, (2) relationships, (3) empowerment and agency, (4) safety, (5) education, (6) basic care, (7) physical health, and (8) personal development. These needs are grounded in the Chinese context, and therefore a good understanding of Chinese culture is essential to address them. The first four needs particularly capture children’s separations from their parents, and the rest are more general, and can be applied to most Chinese children. To meet the most important need for children left behind, namely education, these caregivers determined that others needs sometimes have to be compromised. Children left behind are a vulnerable group in contemporary rural China, and their diverse needs are attended to by several groups. This study found that as children’s closest kin while their parents are away, caregivers play a vital role in salving the children’s emotional loss. Caregivers’ love and familial obligations strongly motivate them to care for these children, and sensitivity to social stigma makes them strive to show their love and care to compensate for perceived differences between these children and their peers. Caregivers’ efforts to make children happy, however, were sometimes criticised by some school personnel, who see this as spoiling. The conflicting viewpoint between caregivers and school personnel indicate their different roles and perceptions in children’s lives, and the latter influence these children in a more authoritative way. Informal kinship care has several advantages of addressing children’s needs, especially their needs for emotional bonds with family. Community-based kin networks provide children with both emotional and material support. However, these advantages sometimes are restricted by caregivers’ child rearing capacity. Having developed a model of the needs of children left behind in China, this study suggests that caregivers, school personnel and government social services work in harmony to be child-centred and meet these children’s diverse needs. The unmet needs of children left behind mainly result from unbalanced development between urban and rural China, therefore, it is imperative to enhance state policies and programs that improve wellbeing for this growing part of China’s people.

Monocular vision based autonomous navigation for a cost-effective MAV in GPS-denied environments

In this paper, we present a monocular vision based autonomous navigation system for Micro Aerial Vehicles (MAVs) in GPS-denied environments. The major drawback of monocular systems is that the depth scale of the scene can not be determined without prior knowledge or other sensors. To address this problem, we minimize a cost function consisting of a drift-free altitude measurement and up-to-scale position estimate obtained using the visual sensor. We evaluate the scale estimator, state estimator and controller performance by comparing with ground truth data acquired using a motion capture system. All resources including source code, tutorial documentation and system models are available online.

Electropolishing of polycrystalline YBa2Cu3O7-δ to meet the need for sharp needle geometry

An electropolishing method has been developed for preparing sharp needles from polycrystalline YBa2Cu3O7-δ by modifying a recipe for TEM specimen preparation. The method is characterized by a polishing temperature of below 0°C, a non-acidic electrolyt and an even removal of the constituent phases. An approach was employed of combining I-V measurements for polishing process and microscopical observation of surface morphology in finding optimum polishing conditions. TEM evidenced that no preferential attack appeared to grain boundaries. X-ray diffractometry and electron diffraction implied that no change in oxygen content occurred during electropolishing. The sharpness of the tip was examined by field-ion microscopy.

A meshfree-based local Galerkin method with condensation of degree of freedom

Condensation technique of degree of freedom is firstly proposed to improve the computational efficiency of meshfree method with Galerkin weak form. In present method, scattered nodes without connectivity are divided into several subsets by cells with arbitrary shape. The local discrete equations are established over each cell by using moving kriging interpolation, in which the nodes that located in the cell are used for approximation. Then, the condensation technique can be introduced into the local discrete equations by transferring equations of inner nodes to equations of boundary nodes based on cell. In the scheme of present method, the calculation of each cell is carried out by meshfree method with Galerkin weak form, and local search is implemented in interpolation. Numerical examples show that the present method has high computational efficiency and convergence, and good accuracy is also obtained.