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Gas-Phase Radical Reactions Characterised by Mass Spectrometry: Kinetics, Product Detection, and Modelling
No full textOrientated electric fields (OEFs) can influence radical reactivity and exploiting these interactions is a relatively new and rapidly growing field in molecular science. Electrostatic catalysis, however, is difficult to harness in practice as electrostatic interactions are highly directional but molecules are typically unaligned in bulk conditions. Distonic radical ions – species with localised and spatially-separated charge and radical sites – sidestep this challenge as they are comprised of a fixed internal charge site that can be relocated using synthetic strategies to control the orientation and electrostatic field strength induced at the radical site. In this thesis, gas–phase distonic radical ion–molecule reactions are investigated with careful consideration of internal OEFs. Experimental techniques including ion mobility, ion–trap mass spectrometry, and photodissociation action spectroscopy are combined with quantum chemical methods and statistical reaction-rate modelling to study these reactions.In the first study, the reactivity of eighteen distonic radical ions with the simple hydrocarbons ethylene and acetylene are measured at 300 K and 2.5 mTorr using a modified commercial mass spectrometer. The distance between the radical and charged functional group modulates the reactivity of these reactions by three orders of magnitude. Rate coefficients, modelled using 4-point potential energy schemes combined with a RRKM theory master equation model, are in good agreement with the experimental values. This model provides a framework to rationalise and predict the electrostatic effects on the rate of distonic radical ion-molecule reactions.Next, a combination of ion-mobility filtering and laser-equipped quadrupole ion–trap mass spectrometry was used to probe the effect of modifying internal OEFs around the same substrate molecule. The gas-phase reaction kinetics of two seperated quinazoline distonic radical protonation isomers with ethylene are measured with this technique. The protonation site variation drives a 100% increase in the radical reactivity of this system, primarily due to through–space (electrostatic) rather than through-bond effects. Quantum chemical methods specifically designed to calculate long-range interactions, such as double-hybrid density functional theory, was required to rationalize the experimentally measured difference in reactivity.Another study examines the gas-phase ion–molecule reaction of the 2-dehydrobenzonitrileH+ distonic radical cation + propyne. This radical undergoes a rapid primary and secondary propyne reaction to yield two nitrogen-containing tricyclic aromatic hydrocarbon products. Quantum chemical calculations identify four candidates for these major products but this analysis is inconclusive. Thus, a combination of reaction UV photodissociation action spectroscopy and hole burning techniques was deployed to verify these assignments. It is shown that such techniques provide structural information which can assign these ion-molecule reaction products and thus verify complex calculated reaction mechanisms.This thesis extends the study of charge effects by applying similar modelling frameworks to the oxidation of the neutral phenyl radical (c-C6H5). The rapid association of the phenyl radical with oxygen has previously been modelled as a barrierless process with little temperature dependence. However, with double-hybrid density functional methods (DSD-PBEP86-D3(BJ)/aug-cc-pVTZ), a submerged transition state stationary point was located along the entrance pathway of this reaction. Using this potential energy landscape, experimental rate coefficients for the addition of molecular oxygen to the phenyl radical were reproduced with a 4-point RRKM-ME kinetic model. This work highlights that purportedly barrierless radical oxidation reactions may proceed through stationary points.These results join a growing body of evidence that suggest that the reaction rates and product branching ratios of radical reactions can be systematically controlled using the internal OEFs induced by distonic radical ions.</p
The effects of economic policy uncertainty exposure
No full textThis thesis comprises three empirical studies that investigate the effects of exposure to uncertainty surrounding economic policies in listed firms. The main factors tested are firm fundamentals, its stock returns, and its investments into research & development (R&D). Uncertainty exposure is measured at the firm level and is derived from Baker et al.’s (2016) economic policy uncertainty (EPU) index, where high levels of exposure mean that firms are more vulnerable to changes in economic policy.The first study investigates the association between firm fundamentals and exposure to EPU. It offers new insights into how firms statistically exposed to the EPU index differ from those that are not. The evidence revealed emphasises the importance of distinguishing between statistically significant and insignificant exposure to EPU as firms with significant EPU exposure tend to be larger and perform better financially. They are also typically more engaged in the debt market. Among exposed firms, financial performance, market value, and short-term are negatively associated with EPU exposure, while debt-to-equity, market-to-book value, beta, cash holdings, and R&D expenditure are positively associated. High EPU exposure is more common in research-intensive and policy-sensitive industries, such as healthcare and technology, while utilities and real estate are the least exposed. The study contributes to the literature by highlighting the varying impacts of EPU exposure on firm fundamentals, which can help firms with better risk management, financial planning, capital budgeting, and resource allocation. Additionally, investors can benefit by anticipating and managing uncertainty to make better informed investment decisions.The second study examines the impact of both EPU and climate policy uncertainty (CPU) exposures on asset pricing under the risk-return trade-off framework. It notes that uncertainty related to climate policies, which raises the CPU index, also has economic implications that overlap with the EPU index. The study investigates the association between stock returns and policy uncertainty exposures, while controlling for firm size, which has been largely overlooked in previous research. Using a double sorting technique, the study finds that stocks exposed to policy uncertainty – either positively or negatively – generate higher returns than those with zero or near zero exposures. This suggests that these stocks are riskier and, thus, investors require higher returns as compensation. A portfolio analysis reveals that the Fama-French five-factor model does not fully explain the returns on portfolios sorted by EPU and CPU exposures. To address this, two new risk mimicking factors for EPU and CPU exposures are incorporated into the model to enhance the five-factor model’s explanatory power. The presence of these factors supports the argument that EPU and CPU exposures lead to significant abnormal returns. This research therefore not only highlights the importance of considering EPU and CPU exposures in investment strategies and asset pricing models, it also provides robust evidence of their strong association with stock returns even when controlling for size effects.The third study investigates how EPU exposure influences innovation investment, measured by R&D expenditure. Firm-level EPU exposure is expected to be superior in explaining firm decisions, such as innovation investments, because it contains rich firm-level information regarding the varying effects of EPU on individual firms. The results reveal a strong positive association between EPU exposure and investments into R&D, which aligns with the growth options theory. However, this effect is not uniform across industries. It greatly affects sectors like consumer non-cyclicals, basic materials, and energy. Moreover, firms with better growth prospects are more influenced by changes in EPU exposure. These findings remain robust across different model specifications. This study contributes to the literature by emphasising the importance of EPU exposure in firm-level decision-making. As one of the first studies in the field to underscore the significance of considering EPU exposure as a way of explaining firm-level innovation investments, this paper also enriches the literature on the role of policy uncertainty in finance.</p
A material stock and flow analysis for Australian detached residential houses: Insights and challenges
No full textMaterial use within construction dominates resource consumption worldwide. Correspondingly, construction is associated with high rates of waste. Transitioning to a circular economy relies heavily on domestic markets, efficient supply chains, and a clear understanding of current and predicted material flows. Material flow analyses have been used extensively globally to generate insights into materials in use, changes over time and future waste generation. However, existing databases do not hold the necessary information to conduct such an analysis for the Australian residential construction industry. This paper uses a novel qualitative bottom-up approach to complement data gaps in existing databases to establish a material stock and flow analysis of the Australian residential construction industry. This approach has highlighted the dominance and continued growth of concrete by the sector, and has shown the importance of addressing data gaps in the industry as well as employing a location-based approach to move towards the circular economy
Enhancement of thermal and mechanical properties of microencapsulated phase change materials with graphene oxide
No full textThe low thermal conductivity of microencapsulated phase change materials (MEPCMs) limits the latent heat charging and discharging rates for various applications. To overcome this limitation, we prepared MEPCM by co-surfactants of polyvinyl alcohol and high thermal conductivity graphene oxide (GO) through an emulsion polymerization process. Fourier transformation infrared spectroscopy and Raman spectra results verified that GO was successfully added to the MEPCMs' hybrid polymer shell. The core material content of MEPCM and GO/MEPCM was within the range of 78.4 %−91.8 % according to differential scanning calorimetry testing results. According to the comparison of fabricated microcapsule samples, the dosage of 0–0.5 w.t.% GO can reduce the loss of shell monomers and overcome the supercooling and leakage problem of MEPCM. Thermogravimetric results exhibited that the thermal stability of MEPCM samples increased by 66 °C after encapsulation, and this value further increased by 7–21 °C with the addition of 0.1–0.5 w.t.% GO. The thermal conductivity of MEPCM samples increased from 0.32 W/m∙K to 1.04 W/m∙K with a dosage of 0.5 w.t.% GO. Meanwhile, Young's modulus and the hardness of GO/MEPCM samples with 0.5 w.t.% GO increased by 0.2 GPa and 0.1 GPa, respectively
Enhancing docosahexaenoic acid production in Aurantiochytrium species using atmospheric and room temperature plasma mutagenesis and comprehensive multi-omics analysis
No full textAurantiochytrium sp. belongs to marine heterotrophic single-cell protist, which is an important decomposer in marine ecosystem. Aurantiochytrium sp. has gained notoriety because of its ability to accumulate high-value docosahexaenoic acid (DHA), but the key factors of DHA synthesis were unclear at present. In this study, Atmospheric and Room Temperature Plasma technology was applied to the mutagenic breeding of Aurantiochytrium sp., and transcriptomics and proteomics were adopted to analyze the DHA-biosynthesis mechanism. According to the growth and DHA accumulation profiles, the mutant strain Aurantiochytrium sp. R2A35 was selected. The DHA content in total lipids was greatly improved from 49.39 % of the wild strain R2 to 63.69 % of the mutant strain. Moreover, the DHA content in the biomass of Aurantiochytrium sp. R2A35 as 39.72 % was the highest DHA productivity reported so far. The differentially expressed genes distinguished from transcriptome and the TMT-identified differential proteins distinguished from proteome confirmed that the expression of acetyl-CoA carboxylase and ketoacyl reductase was up-regulated by 4.78-fold and 6.95-fold, respectively and the fatty acid synthase was concurrently down-regulated by 2.79-fold, so that more precursor was transported to the polyketide synthase pathway, thereby increasing the DHA yield in Aurantiochytrium sp. R2A35. This research would provide reference for the DHA metabolism process and contribute to the understanding of the decomposer - Aurantiochytrium sp. in marine ecosystems
Analysis of interface microstructure and element diffusion of WC-Co-Ni-Fe powder and M2 high-speed steel composite
No full textIn this paper, WC-Co-Ni-Fe (powder)/high-speed steel (solid) composites with a diameter of 3 mm were prepared. The microstructure and microhardness of WC-Co-Ni-Fe/HSS composites at different sintering temperatures were studied. The results indicated that with the increase of sintering temperature, the number of micropores in the WC area decreased significantly, and the mutual diffusion trend of Co, Ni and Cr elements increased. In addition, with the increase of sintering temperature, the microhardness of the WC area increased and the microhardness of the HSS area was practically unchanged. The WC zone was more heat-resistant than the high-speed steel region in the heating process of the WC-Co-Ni-Fe/HSS composite. The composite interface began to melt at the temperature of 945.3 °C. When the temperature of the WC-Co-Ni-Fe/HSS composite reached 1341.3 °C, the high-speed steel and WC zone were completely separated
Generation of a gene-edited H9 embryonic stem cell line carrying a DOX-inducible NGN2 expression cassette in the CLYBL locus
No full textThe pro-neural transcription factor neurogenin-2 (NGN2) possesses the ability to rapidly and effectively transform stem cells into fully operational neurons. Here we report the successful generation of a modified H9 human embryonic H9 stem cell line containing a doxycycline (DOX) inducible NGN2 expression construct featuring a floxed Blasticidin/mApple selection module in the safe-harbor locus CLYBL. This cell line retains its pluripotent state in the absence of DOX, yet readily transitions into a neuronal state upon DOX introduction
Intra-generational social mobility and mortality among older men in the Concord Health and Ageing in Men Project: A cohort study
No full textObjectives: We examined associations between intra-generational social mobility (reflected in life-course socioeconomic trajectories) and mortality, among older men. Methods: Data came from a prospective Australian community-based cohort of older men. Social mobility was defined by socioeconomic indicators from three points in the life-course: educational attainment (late adolescence-early adulthood), occupation (mid-life), and current sources of income (older age). We defined indicators of social mobility trajectory (6 categories; reflecting the direction of social mobility) and social mobility status (2 categories; mobile or non-mobile). We used Cox regression to examine associations with mortality, adjusting for age, country of birth, and living arrangement. Results: We followed 1568 men (mean age 76.8, SD 5.4) for a mean duration of 9.1 years, with 797 deaths recorded. Moving upward was the predominant social mobility trajectory (36.0%), followed by mixed trajectories (25.1%), downward (15.1%), stable low (12.2%), stable high (7.6%), and stable middle (4.0%). Men with downward (Hazard ratio 1.58, 95% CI 1.13 to 2.19) and stable low socioeconomic trajectories (1.77, 1.25 to 2.50) had higher mortality risks than men with stable high socioeconomic trajectories, while men with upward trajectories had similar risks to those with stable high trajectories. 76.2% of the participants were classified as having mobile status; no associations were evident between binary social mobility status and mortality. Discussions: These findings suggest cumulative and persistent exposure to disadvantaged socioeconomic conditions across the life-course, rather than social mobility, is associated with increased mortality. For each stage of the life-course, addressing socioeconomic disadvantage may reduce inequities in mortality
Metal-organic framework-based nanoarchitectonics: A promising material platform for electrochemical detection of organophosphorus pesticides
No full textOver recent decades, the widespread use of pesticides has been instrumental in securing a global food supply. However, this has led to significant environmental pollution concerns. Given the prevalent use of organophosphorus pesticides (OPs), there is an urgent need to develop sensors that can detect OPs with high selectivity and sensitivity. Electrochemical sensors offer an affordable and highly efficient solution for this challenge. Particularly, there have been remarkable advancements in creating metal–organic framework (MOF)-based electrochemical sensors. This review delves into the current advancements of MOF-based electrochemical sensors, emphasizing their use in detecting OPs. We investigate prevalent MOF modifications, detail methods for affixing MOF materials to various electrodes, and compare the electrochemical performance and stability of these methods. We also provide insights into the design principles of MOFs used in the electrochemical detection of OPs, breaking down the core detection mechanism. We hope our insights will guide researchers in developing sustainable, effective, and robust MOF-based portable electrochemical sensors
A self-sensing approach for estimating suspension displacement and velocity in semi-active electromagnetic dampers
No full textElectromagnetic damper (EMD) suspension systems have gained significant recognition for their fast response and precise control capabilities. Nonetheless, the necessity of sensor-based control escalates system costs too high and limits its application. This paper introduces an innovative self-sensing approach for semi-active EMD that aims to autonomously acquire vehicle suspension state information without external sensors. The goal is to improve the performance of vibration damping while remaining cost-efficiency. Initially, the EMD is designed and modelled, followed by an analysis of the variable damping principle of the permanent magnet synchronous motor (PMSM). The variable damping EMD model is formulated using the machine-electric coupling equation. Subsequently, a detailed explanation of the principle behind the proposed self-sensing approach is presented. Simulation results confirm its precise capability to estimate the suspension displacement and velocity even in the absence of external sensor input. Moreover, bench experiments for the EMD are conducted to validate the effectiveness of the variable damping and self-sensing approach. Experimental results indicate that the damping characteristic of the EMD can be controlled by manipulating external resistance value. In addition, accurate estimation of suspension displacement and velocity can be achieved under varying excitation conditions, even with changes in damper damping