Multi-scale numerical simulations of thermal expansion properties of CNT-reinforced nanocomposites

In this work, the thermal expansion properties of carbon nanotube (CNT)-reinforced nanocomposites with CNT content ranging from 1 to 15 wt% were evaluated using a multi-scale numerical approach, in which the effects of two parameters, i.e., temperature and CNT content, were investigated extensively. For all CNT contents, the obtained results clearly revealed that within a wide low-temperature range (30°C ~ 62°C), thermal contraction is observed, while thermal expansion occurs in a high-temperature range (62°C ~ 120°C). It was found that at any specified CNT content, the thermal expansion properties vary with temperature - as temperature increases, the thermal expansion rate increases linearly. However, at a specified temperature, the absolute value of the thermal expansion rate decreases nonlinearly as the CNT content increases. Moreover, the results provided by the present multi-scale numerical model were in good agreement with those obtained from the corresponding theoretical analyses and experimental measurements in this work, which indicates that this multi-scale numerical approach provides a powerful tool to evaluate the thermal expansion properties of any type of CNT/polymer nanocomposites and therefore promotes the understanding on the thermal behaviors of CNT/polymer nanocomposites for their applications in temperature sensors, nanoelectronics devices, etc.

Effect of the sterilization method on the properties of Bombyx mori silk fibroin films

We have compared the effects of different sterilization techniques on the properties of Bombyx mori silk fibroin thin films with the view to subsequent use for corneal tissue engineering. The transparency, tensile properties, corneal epithelial cell attachment and degradation of the films were used to evaluate the suitability of certain sterilization techniques including gamma-irradiation (in air or nitrogen), steam treatment and immersion in aqueous ethanol. The investigations showed that gamma-irradiation, performed either in air or in a nitrogen atmosphere, did not significantly alter the properties of films. The films sterilized by gamma-irradiation or by immersion in ethanol had a transparency greater than 98% and tensile properties comparable to human cornea and amniotic membrane, the materials of choice in the reconstruction of ocular surface. Although steam-sterilization produced stronger, stiffer films, they were less transparent, and cell attachment was affected by the variable topography of these films. It was concluded that gamma-irradiation should be considered to be the most suitable method for the sterilization of silk fibroin films, however, the treatment with ethanol is also an acceptable method.

Effect of rehydration on structure and surface properties of thermally treated palygorskite

Palygorskite has a fibrous like morphology with a distinctive layered appearance. The simplified formula of palygorskite (Mg5Si8O20(OH)2(OH2)4 nH2O) indicates that two different types of water are present. The dehydration and rehydration of palygorskite have been studied using thermogravimetry and H2O-tem- perature programmed desorption. X-ray diffractograms, NH3 adsorption profiles, and NH3 desorption profiles were obtained for thermally treated palygorskite as a function of temperature. The results proved water molecules were mainly derived from Si–OH units. In addition, five kinds of acid sites were found for palygorskite. The number of acid sites of external surfaces was larger than that of the internal sur- faces. Bonding on the internal surface acid sites was stronger than the bonding of the external surfaces. Rehydration restored the folded structure of palygorskite when thermal treatment temperature was lower than 300 oC.

Comparison of two suspension control strategies for multi-axle heavy truck

Two simple and effective control strategies for a multi-axle heavy truck, modified skyhook damping (MSD) control and proportional-integration-derivative (PID) control, were implemented into functional virtual prototype (FVP) model and compared in terms of road friendliness and ride comfort. A four-axle heavy truck-road coupling system model was established using FVP technology and validated through a ride comfort test. Then appropriate passive air suspensions were chosen to replace the rear tandem suspensions of the original truck model for preliminary optimization. The mechanical properties and time lag of dampers were taken into account in simulations of MSD and PID semi-active dampers implemented using MATLAB/Simulink. Through co-simulations with Adams and MATLAB, the effects of semi-active MSD and PID control were analyzed and compared, and control parameters which afforded the best comprehensive performance for each control strategy were chosen. Simulation results indicate that compared with the passive air suspension truck, semi-active MSD control improves both ride comfort and road-friendliness markedly, with optimization ratios of RMS vertical acceleration and RMS tyre force ranging from 10.1% to 44.8%. However, semi-active PID control only reduces vertical vibration of the driver’s seat by 11.1%, 11.1% and 10.9% on A, B and C level roads respectively. Both strategies are robust to the variation of road level.

Preparation and thermal energy storage properties of paraffin/calcined diatomite composites as form-stable phase change materials

A composite paraffin-based phase change material (PCM) was prepared by blending composite paraffin and calcined diatomite through the fusion adsorption method. In this study, raw diatomite was purified by thermal treatment in order to improve the adsorption capacity of diatomite, which acted as a carrier material to prepare shape-stabilized PCMs. Two forms of paraffin (paraffin waxes and liquid paraffin) with different melting points were blended together by the fusion method, and the optimum mixed proportion with a suitable phase-transition temperature was obtained through differential scanning calorimetry (DSC) analysis. Then the prepared composite paraffin was adsorbed in calcined diatomite. The prepared paraffin/calcined diatomite composites were characterized by the scanning electron microscope (SEM) and Fourier transformation infrared (FT-IR) analysis techniques. Thermal energy storage properties of the composite PCMs were determined by DSC method. DSC results showed that there was an optimum adsorption ratio between composite paraffin and calcined diatomite and the phase-transition temperature and the latent heat of the composite PCMs were 33.04 ◦C and 89.54 J/g, respectively. Thermal cycling test of composite PCMs showed that the prepared material is thermally reliable and chemically stable. The obtained paraffin/calcined diatomite composites have proper latent heat and melting temperatures, and show practical significance and good potential application value.

Multifunctional porous graphene for nanoelectronics and hydrogen storage : new properties revealed by first principle calculations

The lack of an obvious “band gap” is a formidable hurdle for making a nanotransistor from graphene. Here, we use density functional calculations to demonstrate for the first time that porosity such as evidenced in recently synthesized porous graphene (http://www.sciencedaily.com/releases/2009/11/091120084337.htm) opens a band gap. The size of the band gap (3.2 eV) is comparable to most popular photocatalytic titania and graphitic C3N4 materials. In addition, the adsorption of hydrogen on Li-decorated porous graphene is much stronger than that in regular Li-doped graphene due to the natural separation of Li cations, leading to a potential hydrogen storage gravimetric capacity of 12 wt %. In light of the most recent experimental progress on controlled synthesis, these results uncover new potential for the practical application of porous graphene in nanoelectronics and clean energy.

Residual Soil Properties of South East Queensland

This project sought to investigate parameters of residual soil materials located in South East Queensland (SEQ), as determined from a large number of historical site investigation records. This was undertaken to quantify material parameter variability and to assess the validity of using commonly adopted correlations to estimate "typical" soil parameters for this region. A dataset of in situ and laboratory derived residual soil parameters was constructed and analysed to identify potential correlations that related either to the entire area considered, or to specific residual soils that were derived from a common parent material. The variability of SEQ soil parameters were generally found to be greater than the results of equivalent studies that analysed transported soil dominant datasets. Noteworthy differences in material properties also became evident when residual soils weathered from different parent materials were considered independently. Large variation between the correlations developed for specific soil types was found, which highligted both heterogeneity of the studied materials and the incompatibility of generic correlations to residual soils present in SEQ. Region and parent material specific correlations that estimate shear strength from in situ penetration tests have been proposed for the various residual soil types considered.

Hydrogen sensing properties of Pt/Lanthanum oxide- molybdenum oxide nanoplatelet/SiC based Schottky diode

An investigation of the electrical and hydrogen sensing properties of a novel Schottky diode based on a nanostructured lanthanum oxide-molybdenum oxide compound is presented herein. Molybdenum oxide (MoO3) nanoplatelets were grown on SiC substrates via thermal evaporation which was then subsequently coated with lanthanum oxide (La2O3) by RF sputtering. The current-voltage characteristics and hydrogen sensing performance (change in barrier height and sensitivity as well as the dynamic response) were examined from 25 to 300°C. At 180°C, a voltage shift of 2.23V was measured from the sensor while exposed to 1% hydrogen gas under a 100 μA constant reverse bias current. The results indicate that the presence of a La2O3 thin layer substantially improves the hydrogen sensitivity of the MoO3 nanoplatelets.

Hydrogen gas sensing properties of Pt/Ta2O5 Schottky diodes based on Si and SiC substrates

We developed Pt/tantalum oxide (Ta2O5) Schottky diodes for hydrogen sensing applications. Thin layer (4 nm) of Ta2O5 was deposited on silicon (Si) and silicon carbide (SiC) substrates using the radio frequency sputtering technique. We compared the performance of these sensors at different temperatures of 100 °C and 150 °C. At these operating temperatures, the sensor based on SiC exhibited a larger sensitivity, whilst the sensor based on Si exhibited a faster response toward hydrogen gas. We discussed herein, the experimental results obtained for these Pt/Ta2O5 based Schottky diodes exhibited that they are promising candidates for hydrogen sensing applications.

Gender-diverse boards and properties of analyst earnings forecasts

Using a sample of 2,200 US listed firm year observations (2001-2007)this study shows a positive (negative) relation between female participation in corporate boards and analysts' earnings forecast accuracy (dispersion), after controlling for earnings quality, corporate governance, audit quality, stock price informativeness and potential endogeneity. Our findings are important as they suggest that board diversity adds to the transparency and accuracy of financial reports such that earnings expectations are likely to be more accurate for these firms.

Influence of fatty acid structure on fuel properties of algae derived biodiesel

Physical and chemical properties of biofuel are influenced by structural features of fatty acid such as chain length, degree of unsaturation and branching of the chain. A simple and reliable calculation method to estimate fuel property is therefore needed to avoid experimental testing which is difficult, costly and time consuming. Typically in commercial biodiesel production such testing is done for every batch of fuel produced. In this study 9 different algae species were selected that were likely to be suitable for subtropical climates. The fatty acid methyl esters (FAMEs) of all algae species were analysed and the fuel properties like cetane number (CN), cold filter plugging point (CFPP), kinematic viscosity (KV), density and higher heating value (HHV) were determined. The relation of each fatty acid with particular fuel property is analysed using multivariate and multi-criteria decision method (MCDM) software. They showed that some fatty acids have major influences on the fuel properties whereas others have minimal influence. Based on the fuel properties and amounts of lipid content rank order is drawn by PROMETHEE-GAIA which helped to select the best algae species for biodiesel production in subtropical climates. Three species had fatty acid profiles that gave the best fuel properties although only one of these (Nannochloropsis oculata) is considered the best choice because of its higher lipid content.

The analytical solution and numerical solution of the fractional diffusion-wave equation with damping

Fractional partial differential equations have been applied to many problems in physics, finance, and engineering. Numerical methods and error estimates of these equations are currently a very active area of research. In this paper we consider a fractional diffusionwave equation with damping. We derive the analytical solution for the equation using the method of separation of variables. An implicit difference approximation is constructed. Stability and convergence are proved by the energy method. Finally, two numerical examples are presented to show the effectiveness of this approximation.

Rapid microwave-assisted synthesis of Mn3O4–graphene nanocomposite and its lithium storage properties

A nanocomposite of Mn3O4 wrapped in graphene sheets (GSs) was successfully synthesized via a facile, effective, energy-saving, and scalable microwave hydrothermal technique. The morphology and microstructures of the fabricated GS–Mn3O4 nanocomposite were characterized using various techniques. The results indicate that the particle size of the Mn3O4 particles in the nanocomposite markedly decreased to nearly 20 nm, significantly smaller than that for the bare Mn3O4. Electrochemical measurements demonstrated a high specific capacity of more than 900 mA h g−1 at 40 mA g−1, and excellent cycling stability with no capacity decay can be observed up to 50 cycles. All of these properties are also interpreted by experimental studies and theoretical calculations.

Predicate encryption with various properties

Predicate encryption (PE) is a new primitive which supports exible control over access to encrypted data. In PE schemes, users' decryption keys are associated with predicates f and ciphertexts encode attributes a that are specified during the encryption procedure. A user can successfully decrypt if and only if f(a) = 1. In this thesis, we will investigate several properties that are crucial to PE. We focus on expressiveness of PE, Revocable PE and Hierarchical PE (HPE) with forward security. For all proposed systems, we provide a security model and analysis using the widely accepted computational complexity approach. Our first contribution is to explore the expressiveness of PE. Existing PE supports a wide class of predicates such as conjunctions of equality, comparison and subset queries, disjunctions of equality queries, and more generally, arbitrary combinations of conjunctive and disjunctive equality queries. We advance PE to evaluate more expressive predicates, e.g., disjunctive comparison or disjunctive subset queries. Such expressiveness is achieved at the cost of computational and space overhead. To improve the performance, we appropriately revise the PE to reduce the computational and space cost. Furthermore, we propose a heuristic method to reduce disjunctions in the predicates. Our schemes are proved in the standard model. We then introduce the concept of Revocable Predicate Encryption (RPE), which extends the previous PE setting with revocation support: private keys can be used to decrypt an RPE ciphertext only if they match the decryption policy (defined via attributes encoded into the ciphertext and predicates associated with private keys) and were not revoked by the time the ciphertext was created. We propose two RPE schemes. Our first scheme, termed Attribute- Hiding RPE (AH-RPE), offers attribute-hiding, which is the standard PE property. Our second scheme, termed Full-Hiding RPE (FH-RPE), offers even stronger privacy guarantees, i.e., apart from possessing the Attribute-Hiding property, the scheme also ensures that no information about revoked users is leaked from a given ciphertext. The proposed schemes are also proved to be secure under well established assumptions in the standard model. Secrecy of decryption keys is an important pre-requisite for security of (H)PE and compromised private keys must be immediately replaced. The notion of Forward Security (FS) reduces damage from compromised keys by guaranteeing confidentiality of messages that were encrypted prior to the compromise event. We present the first Forward-Secure Hierarchical Predicate Encryption (FS-HPE) that is proved secure in the standard model. Our FS-HPE scheme offers some desirable properties: time-independent delegation of predicates (to support dynamic behavior for delegation of decrypting rights to new users), local update for users' private keys (i.e., no master authority needs to be contacted), forward security, and the scheme's encryption process does not require knowledge of predicates at any level including when those predicates join the hierarchy.

Static and dynamic performance of lightweight hybrid composite floor plate system

In the modern built environment, building construction and demolition consume a large amount of energy and emits greenhouse gasses due to widely used conventional construction materials such as reinforced and composite concrete. These materials consume high amount of natural resources and possess high embodied energy. More energy is required to recycle or reuse such materials at the cessation of use. Therefore, it is very important to use recyclable or reusable new materials in building construction in order to conserve natural resources and reduce the energy and emissions associated with conventional materials. Advancements in materials technology have resulted in the introduction of new composite and hybrid materials in infrastructure construction as alternatives to the conventional materials. This research project has developed a lightweight and prefabricatable Hybrid Composite Floor Plate System (HCFPS) as an alternative to conventional floor system, with desirable properties, easy to construct, economical, demountable, recyclable and reusable. Component materials of HCFPS include a central Polyurethane (PU) core, outer layers of Glass-fiber Reinforced Cement (GRC) and steel laminates at tensile regions. This research work explored the structural adequacy and performance characteristics of hybridised GRC, PU and steel laminate for the development of HCFPS. Performance characteristics of HCFPS were investigated using Finite Element (FE) method simulations supported by experimental testing. Parametric studies were conducted to develop the HCFPS to satisfy static performance using sectional configurations, spans, loading and material properties as the parameters. Dynamic response of HCFPS floors was investigated by conducting parametric studies using material properties, walking frequency and damping as the parameters. Research findings show that HCFPS can be used in office and residential buildings to provide acceptable static and dynamic performance. Design guidelines were developed for this new floor system. HCFPS is easy to construct and economical compared to conventional floor systems as it is lightweight and prefabricatable floor system. This floor system can also be demounted and reused or recycled at the cessation of use due to its component materials.