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The role of Tet2 and Tet3 in the molecular programming of blood cell differentiation during zebrafish development
No full textDNA methylation is an epigenetic mark that regulates gene expression during cellular differentiation. Ten-eleven translocation (Tet) dioxygenase enzymes are involved in active demethylation and are required for hematopoietic stem cell (HSC) differentiation. HSCs arise from haemogenic endothelial cells (HECs) in arterial vessels, which depend on Notch signalling for their specification. Initially, the loss of HSC formation in tet2/tet3 double mutants was attributed to a failure in HEC formation caused by defective Notch signalling, despite normal vascular patterning and arterial specification. This study aimed to reinvestigate Notch signalling and HEC development in the ventral wall of the dorsal aorta (vDA) of tet2/tet3 double mutants to resolve these inconsistencies. Here, the Notch reporter transgene csl:mCherry was expressed in the endothelium of the vDA in the absence of Tet2 and Tet3. Confocal analysis of the gene trap line qmc551, which exhibits GFP expression in primitive red blood cells (prRBCs) and HECs of the vDA, demonstrated normal GFP expression in HECs of the vDA at 2 days post fertilisation (dpf). It also revealed a few GFP+ hematopoietic stem and progenitor cells (HSPCs) in the mesenchyme below the DA in tet2/tet3 double mutants. Whole-mount in situ hybridisation (WISH) experiments using the HEC marker growth factor independence 1aa (gfi1aa) revealed that, at 40 hours post fertilisation (hpf), gfi1aa expression persisted in the HECs of the vDA in tet2/tet3 double mutant embryos, contrasting with its typical downregulation in wild-type (WT) embryos at this stage. These findings suggest a defect in the endothelialto- hematopoietic transition (EHT), likely resulting from disrupted epigenetic programming of HECs in the absence of the two Tet proteins. In tet2/tet3 double mutant embryos, circulation appeared normal without evident shunts; however, blood flow velocity was reduced. To investigate the molecular programming underlying these defects, single-cell transcriptome analysis was performed on a cell population enriched for qmc551:GFP and Gata1a:dsRed single and doublepositive cells isolated from 2dpf WT and tet2/tet3 double mutant embryos. Transcriptomic analyses revealed significant downregulation of key endothelial genes, such as apelin, plvapb, casz1, and pecam1. These data suggest a critical role for Tet2 and Tet3 in endothelial programming and angiogenesis. The analysis also showed significant downregulation of erythroid genes in prRBCs. WISH experiments revealed increased gata1a expression in circulating prRBCs at 2 and 3dpf, indicating a late maturation defect in tet2/tet3 double mutant embryos. Additionally, reduced slc4a1a mRNA expression in mutants at 20hpf, prior to the onset of circulation, suggests delayed early differentiation of prRBCs. These findings indicate that the absence of both Tet2 and Tet3 leads to delayed erythroid development. In summary, this study elucidates the multifaceted roles of Tet2 and Tet3 proteins in regulating both primitive and definitive hematopoietic waves during zebrafish embryogenesis
The bureaucratic governance of China’s public health emergency system: an analysis of one province’s response to COVID-19
Full text linkThis study examines the organisational structure and governance processes of China’s public health emergency system in response to COVID-19, situated within the broader context of China’s bureaucratic governance mechanisms and operational logic. A qualitative research approach was adopted, focusing on a specific province as a case study. Data sources comprise three years of central and provincial policy documents related to COVID-19, alongside interviews conducted with 19 participants from the selected province, all of whom have official backgrounds. Guided by Pierson’s three dynamics framework, the study investigates power distribution, interest representation, and fiscal arrangements to delineate China’s public health emergency system and its governance processes.
The findings reveal dynamic interactions within China’s bureaucratic system, characterised by varying degrees of guidance and leadership across departments, as well as distinct coordination mechanisms between central and provincial governments. These variations are reflected in the governance processes during the pandemic. The study also traces the trajectory of campaign-style governance (yundongshi zhili, 运动式治理) throughout COVID-19, emphasising its initial efficiency followed by subsequent dysfunction. This is evidenced by the limited effectiveness of leadership small groups (lingdao xiaozu, 领导小组) and cadre downshifting. Despite a top-down emphasis on achieving zero-COVID targets, local governance exhibited considerable flexibility, with bureaucrats adopting a muddling through (de guo qie guo, 得过且过) approach. Moreover, amid an increasing centralisation of fiscal power and growing local reliance on central transfers, local officials actively sought alternative financial support.
These governance phenomena during China’s COVID-19 response highlight an inherent tension between decision-making conformity and governance effectiveness within the Chinese bureaucratic system. Informal mechanisms, such as guanxi (关系, meaning social relations), serve to alleviate this tension but do not provide a fundamental solution. Consequently, this study advocates for a reduction in the governance burden on the authoritative government by fostering greater participation from social organisations and private enterprises in future public health emergency governance
The social mobilisation of conservative Malays against the injured Leviathan: a case study of Perkasa and ISMA from 2008 to 2017
Full text linkThis dissertation provides a critical account on how a reactionary Malay-Muslim social movement (SM) emerged and developed in Malaysia between 2008 and 2017. It examines the political opportunity structure (POS) in Malaysia and how two social movement organisations (SMOs) – Perkasa and ISMA – mobilised conservative Malays for collective actions. It is found that the POS is largely determined by state capacity to repress regime opponents. From a previously “robust Leviathan,” the Malaysian state has been reduced to an “injured Leviathan” following the 2008 general election. Using a component of Slater’s (2010) ordering power model, I explain how the decline in repression brought about a cognitive liberation (McAdam, 1999) among conservative Malays and created an opening for a reactionary movement in civil society. To understand the SM development, I have used frame analysis to identify ketuanan Melayu and Islamic populism as collective action frames (CAF) for Perkasa and ISMA respectively (Snow & Benford, 1988). To further elucidate their collective agency, I investigate their “frame alignment strategies” (Snow, et. al., 1986) to mobilise conservative Malays by examining various discourses on the New Economic Model (NEM), the Trans-Pacific Partnership Agreement (TPPA), the Allah row and the Coalition of Malaysian NGOs in the UPR Process (COMANGO). They are found to have employed frame amplification in discourses on globalisation and frame bridging for identity politics. Finally, this dissertation applies the concepts of injured Leviathan, frame amplification and frame bridging to make sense of contemporary Malaysian politics
A data fusion pipeline for registering point clouds with novel characteristics: enabling the computer to recognise a pattern without training dataset
Full text linkData fusion is the technical process which can provide comprehensive information about an object by combining multiple datasets that are collected by different sensors. It has been employed for point cloud registration in the context of optical coordinate measurement, an important subject in metrology. Researchers in this field have proposed numerous methods to improve the performance of data fusion, which can be categorised into user-dependent methods, including Gaussian process (GP) and weighted least-squares (WLS) algorithms, and user-independent methods such as machine learning. Recent research has shown the convenience of deploying GP and WLS and the flexibility and autonomous functionality of machine learning solutions. However, the target scenarios have been focused on point clouds in similar sizes and point densities. This trend leaves room for further innovation in point cloud registration.
In this research project, a new algorithmic pipeline, which is capable of registering two point clouds with the following characteristics contained in a maximum working volume of 500×500×500 mm, is proposed: 1) the two point clouds are collected from an engineered object via two separate optical measurement systems, i.e. they are located in two uncorrelated coordinate frames; 2) the smaller point cloud shows the surface texture on a small area on the engineered object, which is represented by the larger point cloud; 3) the point density of the smaller point cloud is > 10 times the point density of the larger point cloud. The challenge lies in the omission of training data: the variation of surface texture is infinite and the area on the engineered object cannot be rigorously determined by the user. As such, the thesis proposes a statistical method to register two point clouds with aforementioned characteristics, which can be summarised as the “geometrical similarity comparison”. In the step of detecting the target area, the larger point cloud is subdivided into equally sized subsections (sub-clouds); the geometrical similarity between each sub-cloud and the smaller point cloud is measured via principal component analysis (PCA). The comparison based on PCA will result in the smaller point cloud being located in the target area formed by the selected sub-clouds. Afterwards, the space mutually occupied by the target area and the smaller point cloud is voxelised so that the spatial point distributions of both point clouds can be assessed. The orientation of the smaller point cloud which aligns it to the target area is determined as the correct orientation, and hence completes the whole registration process.
To test the performance of this algorithmic pipeline, three experimental cases were designed with a gradation of geometrical complexity: two cases include synthetic point clouds generated from CAD models and one case in which the point clouds were collected from a coin. The differences of point densities between the pair of point clouds in these cases are in the range of 10 to 10^2. The results indicate that, though manual double-check is needed as the geometries of the test object increases, the algorithmic pipeline is capable of detecting the location in the larger point cloud to register the smaller point cloud. When scanning the point clouds collected from the coin, the most geometrically complex engineered artefact in this research, the pipeline detected the top 0.73% sub-clouds (186 out of 25,459) which potentially formed the target area in the larger point cloud to register the smaller point cloud.
The pipeline is adequate of detecting the most optimised orientation to register the smaller point cloud regardless of the geometrical complexity of both point clouds. With a 10 interval for 360 orientation attempts, the optimal orientation achieves a registration error ranging from 5% to 0.15%, based on the mean point-to-point distance relative to the smaller point cloud’s dimensions.
The directions left for future work are increasing the accuracy of the detection of the target area and renovating the algorithm to reduce the computational cost. Additionally, big-picture topics questioning the empirical methodology of this research are discussed and concluded
Not Dead Yet: High Redshift Recently Quenched Galaxies As Probes Of Galaxy Evolution
Full text linkIn this thesis, we explore the roles that galaxy environment, stellar mass and outflows play in the quenching of star formation, by studying recently quenched galaxies at cosmic noon and beyond (0.5 < z < 4.4). We utilise photometric data from the UKIDSS Ultra Deep Survey (UDS), the deepest NIR survey over ∼1 deg2, which has sufficient volume to enable samples to be split by stellar mass, redshift and environment. Additionally, we use spectroscopic data for galaxies within the UDS field, from deep observations at ESO VLT (UDSz, VANDELS) and JWST NIRSpec (EXCELS), to study galactic scale winds in the interstellar medium.
We conduct the first study of how the relative quenching probability of galaxies depends on environment over the redshift range 0.5 1010.7 M⊙) are on average 1.7 ± 0.2 times more likely to quench per Gyr in the densest third of environments compared to the sparsest third. Finally, we compare the quiescent galaxy growth rate to the rate at which galaxies pass through a PSB phase, finding that the PSB route can explain ∼ half of the growth in the quiescent population at high stellar mass, and potentially all of the growth at lower stellar masses.
We then use optical spectra of galaxies selected from the UDS at z > 1 to explore the transition in outflow properties along a quenching time sequence. To do this, we perform a stacking analysis of Mg II absorption profiles, investigating outflow velocities as a function of time since the last major burst of star formation (tburst). We find evidence for high-velocity outflows (vout ∼ 1000 - 1500 kms−1) in a star-forming progenitor population and for recently quenched galaxies with tburst 1 Gyr) show no evidence for significant outflows. Our samples show no signs of AGN in optical observations, however the presence of significant outflows in the older quenched galaxies (tburst > 0.6 Gyr) is difficult to explain with starburst activity alone, and may indicate energy input from episodic AGN activity as the starburst fades.
Finally, we complement our ground-based stacking analysis using the JWST NIRSpec EXCELS survey. We select a sample of 9 post-starburst galaxies in the redshift range 1.8 < z < 4.4, and utilise the high resolution spectra to establish, for the first time, if outflows are prevalent in post-starburst galaxies at earlier epochs than cosmic noon. The large wavelength coverage and unique sensitivity of JWST allows us to compare outflow properties for both the Mg II and Na D absorption profiles. We first perform a stacking analysis of our sample, finding ∼ 1600 kms−1 and ∼ 290 kms−1 outflows from the magnesium and sodium profiles, respectively. We use these outflow velocities to estimate lower limits on the mass outflow rates, of Mout, MgII ∼ 1 M⊙yr− and Mout, NaD ∼ 3 M⊙yr−1, higher than the average SFR of our sample. We then investigate galactic scale winds for individual objects at z ∼ 3, finding a wide range of outflow velocities, with some galaxies also showing signs of inflowing gas. These results suggest that outflows may play a key role in the quenching of galaxies at these epochs, by removing the gas needed to fuel star formation
A novel fault detection and diagnostic petri net methodology for dynamic systems
No full textFaults in dynamic systems can lead to significant consequences, such as performance degradation, safety hazards, or economic losses. Monitoring, detecting, and diagnosing these faults promptly and accurately is essential. Petri Nets provide a graphical and mathematical tool for modelling and analysing dynamic systems but have limitations in handling feedback control loops, nonlinear dynamics, uncertainties, and multiple faults. This thesis addresses these challenges by proposing an integrated Petri Net methodology for fault detection and diagnosis, combining extended Generalised Stochastic Petri Net (xGSPN) for system operation modelling and modified Bayesian Stochastic Petri Net (mBSPN) for fault diagnosis.
The xGSPN-mBSPN methodology operates as an integrated model. The xGSPN models operational and failure behaviour, establishing causal relationships between component failures and system behaviour. The mBSPN integrates Bayesian Network diagnostic features, enabling early fault diagnosis through conditional probabilities and inference sampling algorithms. This approach traces the paths leading to observed system failures during operation. The methodology is validated using a water tank level control system, demonstrating effectiveness in detecting and diagnosing single and multiple faults. The diagnostic results align with those obtained from Hugin software.
Additionally, the thesis extends the scope of the methodology by detailing steps for adapting the approach to more complex systems, exemplified by a three-phase separator in the oil and gas industry. While the water tank system demonstrates the methodology’s application to a simple yet dynamic system, the three-phase separator case study showcases its potential to address the complexities of multi-phase flow systems with intricate dependencies. This adaptation framework provides a solid foundation for future implementation and validation in larger-scale industrial systems across sectors such as oil and gas, power generation, and manufacturing.
The key contributions of this thesis include the proposition of an xGSPN formalism incorporating new features like time-varying conditional places and transitions for realistic and flexible modelling of system dynamics. The mBSPN formalism integrates Bayesian Network features with Petri Net constructs to diagnose faults based on observed deviations. Efficient algorithms for automatically generating input Conditional Probability Tables (iCPTs) and the system’s fault diagnostic model reduce manual effort, ensuring consistency and accuracy of the developed model.
The thesis further contributes to the body of knowledge by developing a bespoke C++ programming code to implement the xGSPN-mBSPN method. Its application to the water tank system validated the methodology’s effectiveness for monitoring, early fault detection, and diagnosis of dynamic systems with feedback control loops. The extended case study of a three-phase separator illustrates the potential of the methodology to address complexities in multi-phase flow systems, laying the groundwork for its application in industries like oil and gas, power generation, and manufacturing.
In summary, this research advances fault detection and diagnosis methodologies by introducing a scalable and robust PN-based approach capable of addressing the complexities of dynamic systems. The xGSPN-mBSPN methodology paves the way for reliable and efficient system monitoring, early fault detection, and accurate diagnosis, with promising applications in diverse real-world scenarios
Integrated hybrid ventilative cooling technology for residential buildings in tropical savannah climate
Full text linkThe tropical savannah climate, particularly in Sub-Saharan Africa, is characterised by daytime temperatures as high as 35–37°C and generally low wind speeds of 2–4 m/s. This complicates indoor thermal comfort without mechanical cooling. As a result, energy demand for residential air conditioning and ventilation increases. Meanwhile, residential air conditioning contributes significantly to greenhouse gas emissions.
The study presents the design, validation, and performance analysis of an Encapsulated Phase Change Material Hybrid solar fan assisted Multi-directional Windcatcher system. The study aimed to assess effective cooling, and temperature stabilisation performance without compromising on acceptable ventilation in residential buildings within tropical savannah climates, specifically in Sub-Saharan Africa. The novelty of this research lies in the vertical integration of encapsulated PCM tubes within the windcatcher’s airstreams. The system also combines with hybrid ventilation through fan-assisted airflow during low wind speeds. The fan provides an additional 370L/s airflow. This ensured consistent ventilation and addressed the limitations of passive windcatcher systems, such as inconsistent airflow.
The optimal passive cooling material selected for this study was the RT28HC paraffin PCM, with a melting point of 27–29°C. It was chosen for its efficiency in regulating indoor temperatures without the energy-related costs of air conditioning systems. Encapsulating the PCM in tubes (EPCM-T) ensured consistent heat transfer, which improved the thermal storage capability. The study employed Computational Fluid Dynamics (CFD) simulations to evaluate the system’s performance under different climatic conditions. Simulations explored various EPCM tube configurations and their effects on airflow, cooling, and thermal storage efficiency.
The findings have indicated that the EPCM-HMW system can reduce supply air temperature by up to 3.15°C (9% temperature reduction) compared to conventional windcatcher systems without PCM. Supply air dropped to 305 K (31.85 oC) in the best-case scenario. This occurred when outdoor air temperature was as high as 308 K (35 oC). This temperature drop was essential for maintaining indoor comfort without mechanical cooling, particularly during peak heat when outdoor air is or exceeds 308 K (35 oC). The study findings also showed that the air supply offered by the system achieved temperature stabilisation for approximately 5 hours. However, cooling (indoor temperature reduction) continued for 7 hours. The ventilation performance, although lower than that of a conventional windcatcher, was still within acceptable thermal comfort limits of 140.86 L/s air flow rate, sufficient for 14 to 17 occupants.
The EPCM-HMW system consumed 95% less energy than a ductless split AC unit, equating to 20 times lower energy consumption. Annual energy savings were estimated at 23,690.71 (£19,070.81). The system achieved a payback period of approximately 8.24 years and an ROI of 106.2%.
This research demonstrates the significant long-term financial benefits of adopting the EPCM-HMW system. It also advances windcatcher technology by integrating thermal energy storage to enhance cooling efficiency and temperature stabilisation. The outcomes of this research would be beneficial to broader applications of PCM-based hybrid cooling systems in tropical savannah climates. The study offers a practical, low-energy solution for residential ventilative cooling in high-temperature and low wind regions with limited energy infrastructure. The research also suggests future work in optimising PCM encapsulation techniques and conducting further field testing to further validate the system’s real-world performance
Modelling and design of a synchronous homopolar machine for aircraft DC power generation
No full textDriven by stringent regulations and the net-zero emission target essential for limiting global temperature rise and mitigating the effects of climate change, the aerospace industry views aircraft electrification as a potential solution for sustaining its business. The More-Electric Aircraft concept is gradually advancing towards hybrid and turbo-electric drivetrain configurations with DC primary power distribution, serving as an intermediate step towards fully electrified aircraft. In this context, onboard electric power generation has to satisfy increased propulsive power demands, reaching the multi-megawatt scale, while maintaining strict aerospace standards for reliability, power density, and efficiency.
Independent power generation and propulsion channels are often implemented to ensure sufficient redundancy and reliability. However, when using permanent magnet synchronous generators, full-rated active power electronic converters are necessary, often introducing complexity, cost, and potential reliability concerns in multi-phase and redundant architectures. Solutions based on front-end diode rectifiers represent valid alternatives thanks to their simplicity, cost-effectiveness, compactness, and higher efficiency.
In this scenario, synchronous homopolar machines present a compelling option as a robust electro-mechanical conversion system, characterised by their stationary DC excitation and simple rotor design- free from permanent magnets and brush-slip systems- enabling high-speed operation. The controllable excitation field provides full voltage-control capability, reliable de-excitation, and ease of integration with advanced thermal management systems or superconductive technologies.
Despite these advantages, their diffusion is hindered by their complex three-dimensional magnetic behaviour which requires time-consuming 3D finite-element analysis for performance prediction, limiting its utilisation in the design optimisation process. While analytical methods offer a favourable trade-off between accuracy and computational burden, a significant gap in the literature remains regarding the electromagnetic modelling and design of this machine topology.
This thesis proposes a novel generation unit concept based on synchronous homopolar generators with a dual DC-link configuration, where each power bus is supplied through two series-connected rectifiers and a direct oil-cooled excitation coil provides the DC-link voltage regulation. The manuscript tackles the challenges of sizing and analytically modelling this machine topology, filling the existing gap in the literature. The developed analytical tools are incorporated into a genetic design optimisation algorithm to determine the optimal set of input parameters. The design, prototyping, and testing of a proof-of-concept generation unit delivering 1.2kW at 6000rpm are detailed, with the ultimate goal of validating the proposed modelling and design approaches through a comprehensive electromagnetic and thermal testing campaign. Although the design exercise and experimental validation are performed on a small-scale prototype, this work may provide a foundation for designing an active power electronic-free electric generation unit for future aerospace electric power generation
Design, fabrication and modelling of soft robots with novel actuation and materials
No full textSoft robots are gaining attention due to their potential for safe human-robot interactions and delicate operations while maintaining low commercial costs. However, challenges remain in promoting the use of electroactive polymers (EAPs), particularly in improving product quality (particularly in behaviour consistency and product lifetime) and developing dynamic models that enable coordination between multiple actuators.
To address these issues, we designed a robot incorporating an angular stroke amplification mechanism to optimise the balance between actuation force and stroke. The frame’s weight was significantly reduced by employing 3D puzzle-like strip structures. A novel method for constructing a stable conductive paint on a silicone-based dielectric film was developed, using laser engraving to pattern the film and applying a sandwich-type electrode made from conductive particles (carbon black) and photosensitive resin (Formlab elastic 30A). Compared to conventional carbon grease electrodes, this approach fully cures the resin and prevents the dehydration-caused electro resistance and stiffness increment, demonstrating greater consistency in dynamic performance, especially after extended periods of use.
A key contribution of this work is the development of an dynamic model that incorporates an expanded Bergstrom-Boyce model to capture the constitutive behaviour of the dielectric film, addressing the effects of hyper-elasticity, hysteresis, and viscoelasticity. Experimental validation showed that the model accurately modeled the robot’s output force with a root mean square error (RMSE) of 12.4% in stationary phases and achieved path tracking with an RMSE of less than 2.5%. Furthermore, the hysteresis-considered model was applied to a planar, ultrathin robot with high viscoelasticity for forward control, demonstrating the versatility of the model across different applications
Development of in-service monitoring based models for remaining life management of thermally loaded ageing structures
Full text linkThe primary aim of this thesis is to propose and develop a novel and practical life assessment methodology for power plant applications that uses more proactively both periodic and routine inspection data in conjunction with online operational data. This methodology facilitates the computation of the remaining life of high temperature components and essentially links the plant data routinely collected during outage inspections, via online monitoring or by testing of material samples to the life prediction models. High temperature pipework will be used as an example of the proposed approach and deployable creep life prediction models are reviewed that could function with these plant datasets. Of critical importance is that the output from the life prediction is used to inform plant operations on any necessary changes in order to mitigate damage accumulation.
A holistic empirical lifing approach, which accommodates the on-site information of replica, hardness and strain, is established. The approach is based on an extensive review and analysis of a large amount of outage inspection data on ageing high temperature parent ½Cr½Mo¼V (CrMoV) material and has been used to illustrate how such routinely collected inspection data can be better utilised to provide the plant operator with predictions of residual creep life. The model differentiates between long term and persistent thermal softening behaviour revealed by change in hardness over time and short-term creep cavitation that accelerates material damage. Importantly, the models developed are designed to be used iteratively with surface replica and hardness data available from an outage inspection. The study shows that the availability of more data will enable further refinements, but more importantly, it emphasises the importance of systematically capturing these data and processing them at the time of inspection to forecast residual life and then updating and tuning the model periodically at future inspections. The capture of strain data from pipe diametral measurements is also a routine outage activity and this data is included in a case study to demonstrate the capabilities in the residual life forecast by the new methods.
An integrated life assessment procedure for structures operating under thermomechanical loading is also developed. The methodology uses a viscoplasticity based framework combined with the R5 life assessment code. The viscoplastic
constitutive model used for the stress-strain analysis is derived from the Chaboche-Lemaitre formulation from which can be directly obtained the required parameters for the R5 assessment as stress relaxation per cycle and the elastic follow-up factor. The R5 procedure is therefore significantly simplified. The proposed life assessment procedure is demonstrated on a martensitic steel (FV566) industrial gas turbine rotor under a typical start up – shut down operation. The effect of creep-fatigue interaction at different locations within the rotor structure is assessed and the remaining life at each location is calculated. A sensitivity study is performed at half load, which shows an increase in lifetime of the rotor compared to the full load condition.
The developed lifing model techniques are backed up with a physical explanation by investigating the softening behaviour of a P91 steel due to its microstructural changes under creep testing. The creep degradation behaviour of ex-service-exposed P91 steel is investigated during interrupted creep tests at 660°C and 80 MPa using a number of material characterization techniques including TEM, SEM, EBSD, EDS and optical microscopy to identify the microstructural evolution and the associated deformation mechanisms during creep at temperature. Microhardness has also been measured in order to evaluate the softening mechanism. Under the creep conditions examined, microstructural degradation is found to be governed by the disappearance of the lath sub-structure, lath widening and recrystallization, dislocation density reduction, coarsening of M23C6 and creep cavitation while MX and Laves phases are stable. Hardness evolution, extrapolated from hardness data obtained from uniaxial creep tests, is used to characterize the softening of the material. On this basis, hardness decrease is justified in term of the aforementioned microstructural changes. Implications of the findings for specific in-service life management in thermal plant piping systems are finally addressed
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