Raman spectroscopic studies of carbon nanotube composite fibres

The project has been concerned with structure/property relationships in a series of different carbon nanotube (CNT) composite fibres. Raman spectroscopy has been proved to be a powerful technique to characterise the CNT-containing fibres. Electrospinning has been used to prepare poly(vinyl alcohol) (PVA) nanofibres containing single-wall carbon nanotubes (SWNTs). The effect of the processing conditions including the polymer concentration, electric voltage, tip-to-collector distance, nanotube concentration and the collection method upon the morphology, diameter and the alignment of the fibres have been investigated.Raman spectroscopy of individual SWNTs dispersed in PVA electrospun fibres have been studied systematically in terms of the Raman band frequency, intensity and linewidth. The G'-band shift per unit strain during tensile deformation has been found to be dependent on the nanotube chirality. A detailed study has been undertaken of the efficiency of reinforcement in PVA/SWNT nanocomposites. The stress-induced Raman band shifts in the nanocomposites have been shown to be controlled by both geometric factors such as the angles between the nanotube axis, the stressing direction and the direction of laser polarisation, and by finite length effects and bundling. A theory has been developed that takes into account all of these factors and enables the behavior of the different forms of nanocomposite, both fibres and films, to be compared.The effects of dispersion and orientation of nanotubes and the interfacial adhesion on mechanical properties of poly(p-phenylene terephthalamide) (PPTA)/SWNTs composite fibres have been investigated. It has been shown the change of orientation of the polymer molecules upon incorporating nanotubes had direct effect on mechanical properties of the PPTA fibres. An in-situ Raman spectroscopy study during fibre deformation has revealed good stress transfer from the matrix to nanotubes in low strain range, and the interface failed when the strain exceeded 0.5%.Raman spectroscopy has also been employed to investigate the microstructure and micromechanical process of neat carbon nanotube (CNT) fibres. It has been found the fibres consisted of both SWNTs and MWNTs and varied in composition at different locations. High efficiency of stress transfer both within the fibre and in composites has been observed, suggesting the promising potential of CNT fibres in reinforcing polymers.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Effect of space flight factors on alfalfa seeds

To explore the effect of space flight factors on the early development of alfalfa seedling, dry seeds were placed onboard a satellite for a 15-day flight. After retrieval, the ultra structure of seed coat and the chemical content of seed were tested, followed by tests for germinate ability, seedling growth, and mitotic and chromosome aberrations. Results showed that space flight factors have both positive and negative effects on alfalfa seeds. Positive effects include: (1) A 6.2% increase in germinate potential and (2) an 80% decrease in the number of hard seed in flight seeds. Meanwhile, negative effects included a decrease of 3.0 and 33.2% in the index of germination and vigor of flight seeds, respectively, which may be partly due to the inhibition of cell mitotic (26% less than ground control) and root growth (29.0% less than ground control) after the space flight. Moreover, the DNA and Ca2+ content of alfalfa seeds increased after the space flight, while the reserve energy content of alfalfa seeds, such as saccharine and fatty acid, decreased after the space flight. Conclusively, space flight factors accelerate the germination process of alfalfa seeds but restrain the root from growing due to chromosomal damage and abnormal mitosis induced by cosmic radiation.Key words: Alfalfa, space flight factors, germination, chromosome aberration

Unsupervised domain adaptation semantic segmentation of high-resolution remote sensing imagery with invariant domain-level prototype memory

Semantic segmentation is a key technique involved in automatic interpretation of high-resolution remote sensing (HRS) imagery and has drawn much attention in the remote sensing community. Deep convolutional neural networks (DCNNs) have been successfully applied to the HRS imagery semantic segmentation task due to their hierarchical representation ability. However, the heavy dependency on a large number of training data with dense annotation and the sensitiveness to the variation of data distribution severely restrict the potential application of DCNNs for the semantic segmentation of HRS imagery. This study proposes a novel unsupervised domain adaptation semantic segmentation network (MemoryAdaptNet) for the semantic segmentation of HRS imagery. MemoryAdaptNet constructs an output space adversarial learning scheme to bridge the domain distribution discrepancy between source domain and target domain and to narrow the influence of domain shift. Specifically, we embed an invariant feature memory module to store invariant domain-level context information because the features obtained from adversarial learning only tend to represent the variant feature of current limited inputs. This module is integrated by a category attention-driven invariant domain-level context aggregation module to current pseudo invariant feature for further augmenting the pixel representations. An entropy-based pseudo label filtering strategy is used to update the memory module with high-confident pseudo invariant feature of current target images. Extensive experiments under three cross-domain tasks indicate that our proposed MemoryAdaptNet is remarkably superior to the state-of-the-art methods.Comment: 17 pages, 12 figures and 8 table

Biomass-derived carbons for sodium-ion batteries and sodium-ion capacitors

In the past decade, the rapid development of portable electronic devices, electric vehicles, and electrical devices has stimulated extensive interest in fundamental research and the commercialization of electrochemical energy-storage systems. Biomass-derived carbon has garnered significant research attention as an efficient, inexpensive, and eco-friendly active material for energy-storage systems. Therefore, high-performance carbonaceous materials, derived from renewable sources, have been utilized as electrode materials in sodium-ion batteries and sodium-ion capacitors. Herein, the charge-storage mechanism and utilization of biomass-derived carbon for sodium storage in batteries and capacitors are summarized. In particular, the structure–performance relationship of biomass-derived carbon for sodium storage in the form of batteries and capacitors is discussed. Despite the fact that further research is required to optimize the process and application of biomass-derived carbon in energy-storage devices, the current review demonstrates the potential of carbonaceous materials for next-generation sodium-related energy-storage applications.</p

Potential-Mediated Recycling of Copper From Brackish Water by an Electrochemical Copper Pump.

Copper ions (Cu2+ ) disposed to the environment at massive scale pose severe threat to human health and waste of resource. Electrochemical deionization (EDI) which captures ions by electrical field is a promising technique for water purification. However, the removal capacity and selectivity toward Cu2+ are unsatisfying, yet the recycling of the captured copper in EDI systems is yet to be explored. Herein, an efficient electrochemical copper pump (ECP) that can deliver Cu2+ from dilute brackish water into much more concentrated solutions is constructed using carbon nanosheets for the first time, which works based on reversible electrosorption and electrodeposition. The trade-off between the removal capacity and reversibility is mediated by the operation voltage. The ECP exhibits a removal capacity of 702.5 mg g-1 toward Cu2+ and a high selectivity coefficient of 64 for Cu2+ /Na+ in the presence of multiple cations; both are the highest reported to date. The energy consumption of 1.79 Wh g-1 is among the lowest for EDI of copper. More importantly, the Cu species captured can be released into a 20-fold higher concentrated solution. Such a high performance is attributed to the optimal potential distribution between the two electrodes that allows reversible electrodeposition and efficient electrosorption

Compressive performance of fiber reinforced polymer encased recycled concrete with nanoparticles

Nanomaterials have been used in improving the performance of construction materials due to their compacting micro-structure effect and accelerating cement hydration reaction. Considering the brittle characteristic of fiber reinforced polymer (termed as FRP) tube encased concrete and inferior properties of recycled concrete, nanoparticles were used in FRP tube encased recycled aggregate concrete. The axial compressive performance of FRP tube used in recycled concrete treated with nanoparticles strengthening, termed as FRP-NPRC, were investigated by axial compression experiments and theoretical analysis. Five experimental variables were considered including (1) the dosages and (2) varieties of nanoparticles (i.e. 1% and 2% of nanoSiO2, 1% and 2% of nanoCaCO3), (3) replacement ratios of recycled coarse aggregates (termed as RCAs) (0%, 50%, 70% and 100%) the RCAs were mainly produced from the waste cracked bricks, (4) the number of glass FRP (GFRP) tube layers (2, 4 and 6-layer) and (5) the mixing methods of concrete. Results indicate that the combination of FRP confinement and nanoparticle modification in recycled concrete exhibited up to 76.2% increase in compressive strength and 7.62 times ductility improvement. Furthermore, a design-oriented stress–strain model on the basis of the ultimate condition analysis were executed to evaluate the stress–strain property of this strengthened component

The enhancement of electrochemical capacitance of biomass-carbon by pyrolysis of extracted nanofibers

Biomass-derived carbons have been extensively researched as electrode material for energy storage and conversion recently. However, most of the previous works convert crude biomass directly into carbon and the electrochemical capacitances for the resultant carbons are quite often underestimated as well as large variations in capacitances exist in literatures due to the complex nature of biomass, which practically hinder their applications. In this work, polysaccharide nanofibers were extracted from an inexpensive natural fungus using a hydrothermal method and were converted to porous carbon nanofibers (CNFs) by potassium hydroxide activation. The porous carbons were assembled into symmetric supercapacitors using both potassium hydroxide and an ionic liquid (IL) as electrolytes. Solid state nuclear magnetic resonance characterization showed that the micropores of the as-prepared carbons are accessible to the IL electrolyte when uncharged and thus high capacitance is expected. It is found in both electrolytes the electrochemical capacitances of CNFs are significantly higher than those of the porous carbon derived directly from the crude fungus. Furthermore, the CNFs delivered an extraordinary energy density of 92.3 Wh kg−1 in the IL electrolyte, making it a promising candidate for electrode materials for supercapacitors.<br/

High dynamic range photo-detection module using on-chip dual avalanche photodiodes

In this work, a high dynamic range APD-based photo-detection module is designed and developed. In the design, on-chip dual avalanche photodiodes (APDs) are fabricated with one biased to work in linear mode and the other one biased to work in single photon mode. The APD operating in linear mode is connected to a two-stage amplifier I-V conversion circuit and the APD operating in single photon mode is connected to a custom designed active quench and reset integrated circuit. The design enables the two on-chip APDs operate in different modes simultaneously without user intervention. This simplifies the system operation and a wide range of incident light intensities can be easily detected. Experimental results show that a high dynamic range of 164.2 dB is achieved by the module