Generation and characterisation of cold atmospheric liquid-containing plasmas

This thesis presents an experimental study of non-thermal atmospheric pressure gas plasmas in presence of liquid as an efficient source of transient and reactive species to initiate chemical reactions necessary for many important applications. Two types of liquid-containing plasmas are considered: discharges formed between a needle electrode and a liquid electrode, and plasma jets formed in a water vapour flow mixed in helium or argon gas. Two plasma modes (the pulsed and the continuous mode) are observed in the needle-to-liquid plasma. A comparative study of the needle-to-liquid plasma in the continuous mode with DC and AC excitations reveals that the plasmas are glow discharges, and AC excited plasmas have the highest energy efficiency. A study of helium/water vapour plasma jet shows that “plasma bullets” are formed even with water vapour in the gas mixture, but become quenched when the moist helium flow rate is above 300sccm (~1800ppm water concentration). Moderate amount of water vapour (~250ppm water concentration) is beneficial for active species production mainly due to the high electron density. Hydrogen peroxide production in saline solution with three different plasma sources is investigated due to the importance of H2O2 in several important applications. Long lifetime of H2O2 in the liquid after plasma treatment indicates an exciting possibility of plasma pharmacy

Chemically bonded phosphate ceramics reinforced with carbon nanotubes

We report herein, a scalable method for the preparation of alumina (Al2O3)-phosphate ceramics reinforced with carbon nanotubes (CNTs). All composites were manufactured by direct on-site growth of CNTs on ceramic particles via catalytic chemical vapour deposition. Introduction of catalyst metals to the substrate was achieved through two simple approaches, drip-coating and vacuum filtration, both of which have been reviewed. Transmission electron microscopy was utilised to investigate the interface between the Al2O3 surface and the in-situ CNTs. Resultant ceramics were produced by impregnating phosphoric acid into the Al2O3+CNT nanocomposite powder followed by die-pressing. In order to maintain the integrity of the CNTs, dehydration/curing was performed at 130-150○C. Scanning electron microscopy was elected to comparatively characterise the microstructure of this type of ceramic nanocomposite against its monolithic equivalent. Possible mechanisms by which specific features have formed are discussed

Manganese Promoted CO Hydrogenation Catalysts: A Study of Metal Promoter Interaction Effects

One of the biggest societal challenges nowadays is the quest for alternative fuels that can provide us sustainable energy, the catalytic conversion of syngas, a mixture of CO and H2, is capable of producing a various kinds of alternative fuels such as Ethanol and long chain hydrocarbons. The aim of my PhD work is to investigate the rational design of promoted metal catalysts for CO hydrogenation reactions. The use of promoters is ubiquitous in CO hydrogenation reactions to increase active metal’s activities as well as the selectivity towards desired products. The main body of my work focuses on the use of simple techniques and common elemental precursors to improve the interactions in between a promoter and active metal. One of the many ways of achieving this is through the use of Strong Electrostatic Adsorption (SEA). Special attention to the surface charging parameters of mixed oxide as a function of solution pH can create a driving force to selectively adsorb a precursor complex onto a single phase of a binary mixture. Although, the precise active site of promoters in reactions and how they interact with active metals to react the reactants require many more studies, it is agreed that a key design objective is to increase the metal-promoter interactions. This work demonstrates a procedure to achieve this with Mn promoted catalysts

Experimental and Numerical Investigation of Membrane Distillation for Desiccant Regeneration in Liquid Desiccant Air Conditioning Systems

Liquid desiccant air conditioning (LDAC) systems, which can independently deal with sensible and latent heat loads, have attracted increasing attention. In LDAC systems, regeneration is a key process for maintaining the dehumidification function of the liquid desiccant solution, which consumes a large part of the system energy demand. Most previous studies have been focused on direct contact regeneration, whilst this regeneration method has a major challenge of liquid desiccant droplets carryover. Membrane distillation has been recently recognised as an attractive alternative to regeneration as it can nearly eliminate the carryover issue in the regeneration process by using a microporous membrane and can generate dual products, i.e. concentrated liquid desiccant solutions and freshwater. However, the research development of membrane distillation for liquid desiccant regeneration is still in the early stage and further investigations are needed. This thesis aims to investigate and optimise membrane distillation for liquid desiccant regeneration and develop a membrane distillation regeneration-assisted LDAC system driven by solar energy for air dehumidification, cooling, and freshwater production. The novelties of this work include evaluating the membrane distillation performance by considering concentration polarisation and membrane fouling and, for the first time, analysing the feasibility of integrating membrane distillation into an LDAC system. This study first experimentally investigated the performance of a flat plate direct contact membrane distillation (DCMD) module for regenerating a 25-30 wt.% lithium chloride (LiCl) solution. The results showed that the DCMD regenerator can provide stable regeneration capacity and water flux, and over 99.99% of LiCl salt rejection rate with low thermal efficiency due to the high feed concentration. The temperature difference between the feed and distillate sides should be higher than a threshold to avoid negative flux in the DCMD regenerator. The interactive effects of key operating parameters, i.e. initial feed concentration, feed inlet temperature, distillate inlet temperature, and volumetric flow rate, were studied by means of the response surface method (RSM). The RSM models showed good model fitness with R2 of 0.9820, 0.9787 and 0.9689 for the regeneration capacity, water flux and thermal efficiency, respectively. The predicted regeneration capacity showed a similar trend to that of water flux. In terms of regeneration capacity, the feed inlet temperature was the most significant influencing variable, whilst an interaction between the initial feed concentration and the volumetric flow rate was observed. In terms of thermal efficiency, the feed inlet temperature and distillate inlet temperature showed a significant interactive effect, whilst increasing the volumetric flow rate had a negative effect on thermal efficiency.</p

Quantification of Thiazolidine-4-carboxylic Acid in Toxicant-Exposed Cells by Isotope-Dilution Liquid Chromatography–Mass Spectrometry Reveals an Intrinsic Antagonistic Response to Oxidative Stress-Induced Toxicity

Carcinogenic formaldehyde is produced by endogenous protein oxidation and various exogenous sources. With formaldehyde being both ubiquitous in the ambient environment and one of the most common reactive carbonyls produced from endogenous metabolism, quantifying formaldehyde exposure is an essential step in risk assessments. We present in this study an approach to assess the risk of exposure to oxidative stress by quantifying thiazolidine-4-carboxylic acid (TA), a cysteine-conjugated metabolite of formaldehyde in toxicant-exposed Escherichia coli. The method entails TA derivatization with ethyl chloroformate, addition of isotope-labeled TA derivatives as internal standards, solid-phase extraction of the derivatives, and quantification by liquid chromatography–mass spectrometry (LC–MS). After validating for accuracy and precision, the developed method was used to detect TA in oxidizing agent-exposed E. coli samples. Dose-dependent TA formation was observed in E. coli exposed to hydroxyl radical mediators Fe²⁺-EDTA, H₂O₂, and NaOCl, indicating the potential use of TA as a biomarker of exposure to oxidative stress and disease risk

Visualization results of VGGT-Count in different scenarios.

Visualization results of VGGT-Count in different scenarios.</p

Comparison with the state-of-the-art methods on ShanghaiTech A, ShanghaiTech B, and UCF-QNRF.

The top performance is highlighted in bold, while the second best is underlined.</p

Analysis of loss variation in different epoch for a VGGT-Count network.

A crowd image is first fed into VGG-19 network for convolution. Then the flatten output feature map is transmitted into the transformer encoder with Multi-Head Attention. Finally, a regression decoder predicts the density map. The Optimal Transport (OT) and Total Variation (TV) loss function is optimized during the training process.</p

Optimizing performance by using different components and structures on ShanghaiTech B datasets.

Optimizing performance by using different components and structures on ShanghaiTech B datasets.</p

Comparison of real-time performance in different models with size, frames and inference time.

Comparison of real-time performance in different models with size, frames and inference time.</p