Machines with non-conventional topologies for more electric applications

This thesis investigates the design, performance and fault tolerant capability of electric machines with unconventional topologies used in more electric drive applications. Two different machine topologies are analysed: Flux reversal permanent magnet machine and a field wound flux switching machine. Initially, unconventional flux reversal machine topology in which the volume of the permanent magnet material is minimised to improve the fault tolerance capability and lower the costs whilst achieving significant improvement in the torque is investigated through a simulation and validated through experimental work. It is shown that although the machine belongs to the fault tolerant category, an inter-turn short circuit fault will be a problematic as the magnetic flux from the magnet cannot be neutralised and can cause severe damage to the machine under certain conditions. This however, does not mean that the topologies with permanent magnet material are not suitable for the fault tolerant solutions. If the appropriate design selection in terms of slot and pole numbers is made, the negative influence of the permanent magnet material can be minimised. Therefore, the influence of the slot pole combination on both fault tolerance and performance is investigated and the results are demonstrated on the set of permanent magnet synchronous machines. It is shown that low rotor pole number machines have better fault tolerance capability whilst high rotor pole number machines are lighter and provide higher efficiency. To overcome the challenges related to the short circuit fault, the topology which eliminates the permanent magnet material and works on a basis of the wound excitation is developed. As the short circuit fault cannot be fully eliminated, a solution which prevent the catastrophic failure and minimises the consequences by using wound excitation system on the stator side instead of permanent magnets is proposed. The modification of a permanent magnet synchronous machine towards improvement of the fault tolerance is presented in detail. Different rotor structures are investigated and optimised to maximise the torque performance. It is shown that using stator of existing machine and replacing the current rotor containing permanent magnets not only improves the fault tolerance, but also reduces the manufacturing and material costs

Overview of radiation oncology in the Czech Republic

BackgroundModern radiotherapy (RT) plays a very important role in both curative and palliative treatment of tumours. There are large variations among the EU countries and even regional variations within countries in the provision of RT.AimIn this report we present an overview of the current infrastructure, organisation, education and quality programme of radiotherapy in the Czech Republic.Material and MethodsData from the National Cancer Registry, Institute of Health Information and Statistics of the Czech Republic and from questionnaires and clinical audits of radiotherapy departments were used for evaluation of radiotherapy equipment, numbers of patients treated by radiotherapy and workload of radiotherapy facilities.ResultsRadiotherapy of malignant diseases is provided in 28 facilities in the Czech Republic. There are 35 linear accelerators and 16 cobalt units for the population of 10.3 million inhabitants, which represents one megavoltage unit for 200 000 inhabitants. Fourteen departments are equipped for brachytherapy with high dose rate afterloading machines. Forty-three percent of newly reported cancer patients undergo radiotherapy as part of oncological treatment.ConclusionThe main problem of radiation oncology in the Czech Republic is insufficient centralisation and the persistence of small, under-equipped departments

Modeling and analysis of eddy current losses in permanent magnet machines with multi-stranded bundle conductors

This paper investigates the influence of eddy current losses in multi-stranded bundle conductors employed in out-runner permanent magnet machines, by adopting an analytical model. The analytical model is based on a sub-domain field model that solves the two-dimensional magnetostatic problem using the separation of variables technique for each of the non-magnetically permeable machine sub-domains: PM, airgap and slots. The validity and accuracy of the proposed model is verified using finite element analysis and then used to investigate the eddy current losses. The machine considered for the analysis has 36 slots and 42-poles previously designed for aircraft taxiing. The influence of the number of turns and the conductor cross-sectional area are investigated. It is shown that efficiency can be improved considerably by the choice of multi- stranded bundle conductors

Impact of slot/pole combination on inter-turn short-circuit current in fault-tolerant permanent magnet machines

This paper investigates the influence of the slot/pole (S/P) combination on inter-turn short-circuit (SC) current in fault-tolerant permanent magnet (FT-PM) machines. A 2-D sub-domain field computational model with multi-objective genetic algorithm is used for the design and performance prediction of the considered FT-PM machines. The electromagnetic losses of machines, including iron, magnet, and winding losses are systematically computed using analytical tools. During the postprocessing stage, a 1-D analysis is employed for turn-turn fault analysis. The method calculates self-and mutual inductances of both the faulty and healthy turns under an SC fault condition with respect to the fault locations, and thus SC fault current, considering its location. Eight FT-PM machines with different S/P combinations are analyzed. Both the performance of the machine during normal operation and induced currents during a turn-turn SC fault are investigated. To evaluate the thermal impact of each S/P combination under an inter-turn fault condition, a thermal analysis is performed using finite element computation. It is shown that low-rotor-pole-number machines have a better fault tolerance capability, while high-rotor-pole-number machines are lighter and provide higher efficiency. Results show that the influence of the S/P selection on inter-turn fault SC current needs to be considered during the design process to balance the efficiency and power density against fault-tolerant criteria of the application at hand

Relative importance of climatic variables, soil properties and plant traits to spatial variability in net CO2 exchange across global forests and grasslands

Compared to the well-known drivers of spatial variability in gross primary productivity (GPP), the relative importance of climatic variables, soil properties and plant traits to the spatial variability in net ecosystem exchange of CO2 between terrestrial ecosystem and atmosphere (NEE) is poorly understood. We used principal component regression to analyze data from 147 eddy flux sites to disentangle effects of climatic variables, soil properties and plant traits on the spatial variation in annual NEE and its components (GPP and ecosystem respiration (RE)) across global forests and grasslands. Our results showed that the largest unique contribution (proportion of variance only explained by one class of variables) to NEE variance came from climatic variables for forests (24%-30%) and soil properties for grasslands (41%-54%). Specifically, mean annual precipitation and potential evapotranspiration were the most important climatic variables driving forest NEE, whereas available soil water capacity, clay content and cation exchange capacity mainly influenced grassland NEE. Plant traits showed a small unique contribution to NEE in both forests and grasslands. However, leaf phosphorus content strongly interacted with soil total nitrogen density and clay content, and these combined factors represented a major contribution for grassland NEE. For GPP and RE, the majority of spatial variance was attributed to the common contribution of climate, soil and plant traits (50% - 62%, proportion of variance explained by more than one class of variables), rather than their unique contributions. Interestingly, those factors with only minor influences on GPP and RE variability (e.g., soil properties) have significant contributions to the spatial variability in NEE. Such emerging factors and the interactions between climatic variables, soil properties and plant traits are not well represented in current terrestrial biosphere models, which should be considered in future model improvement to accurately predict the spatial pattern of carbon cycling across forests and grasslands globally.Peer reviewe

Detection and attribution of an anomaly in terrestrial photosynthesis in Europe during the COVID-19 lockdown

Carbon dioxide (CO2) uptake by plant photosynthesis, referred to as gross primary production (GPP) at the ecosystem level, is sensitive to environmental factors, including pollutant exposure, pollutant uptake, and changes in the scattering of solar shortwave irradiance (SWin) - the energy source for photosynthesis. The 2020 spring lockdown due to COVID-19 resulted in improved air quality and atmospheric transparency, providing a unique opportunity to assess the impact of air pollutants on terrestrial ecosystem functioning. However, detecting these effects can be challenging as GPP is influenced by other meteorological drivers and management practices. Based on data collected from 44 European ecosystem-scale CO2 flux monitoring stations, we observed significant changes in spring GPP at 34 sites during 2020 compared to 2015-2019. Among these, 14 sites showed an increase in GPP associated with higher SWin, 10 sites had lower GPP linked to atmospheric and soil dryness, and seven sites were subjected to management practices. The remaining three sites exhibited varying dynamics, with one experiencing colder and rainier weather resulting in lower GPP, and two showing higher GPP associated with earlier spring melts. Analysis using the regional atmospheric chemical transport model (LOTOS-EUROS) indicated that the ozone (O-3) concentration remained relatively unchanged at the research sites, making it unlikely that O-3 exposure was the dominant factor driving the primary production anomaly. In contrast, SWin increased by 9.4 % at 36 sites, suggesting enhanced GPP possibly due to reduced aerosol optical depth and cloudiness. Our findings indicate that air pollution and cloudiness may weaken the terrestrial carbon sink by up to 16 %. Accurate and continuous ground-based observations are crucial for detecting and attributing subtle changes in terrestrial ecosystem functioning in response to environmental and anthropogenic drivers

Biomarkers of conversion to alpha-synucleinopathy in isolated rapid-eye-movement sleep behaviour disorder

Patients with isolated rapid-eye-movement sleep behaviour disorder (RBD) are commonly regarded as being in the early stages of a progressive neurodegenerative disease involving \u3b1-synuclein pathology, such as Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy. Abnormal \u3b1-synuclein deposition occurs early in the neurodegenerative process across the central and peripheral nervous systems and might precede the appearance of motor symptoms and cognitive decline by several decades. These findings provide the rationale to develop reliable biomarkers that can better predict conversion to clinically manifest \u3b1-synucleinopathies. In addition, biomarkers of disease progression will be essential to monitor treatment response once disease-modifying therapies become available, and biomarkers of disease subtype will be essential to enable prediction of which subtype of \u3b1-synucleinopathy patients with isolated RBD might develop

Comparison of Gene Expression Profiles in Chromate Transformed BEAS-2B Cells

Hexavalent chromium [Cr(VI)] is a potent human carcinogen. Occupational exposure has been associated with increased risk of respiratory cancer. Multiple mechanisms have been shown to contribute to Cr(VI) induced carcinogenesis, including DNA damage, genomic instability, and epigenetic modulation, however, the molecular mechanism and downstream genes mediating chromium's carcinogenicity remain to be elucidated.We established chromate transformed cell lines by chronic exposure of normal human bronchial epithelial BEAS-2B cells to low doses of Cr(VI) followed by anchorage-independent growth. These transformed cell lines not only exhibited consistent morphological changes but also acquired altered and distinct gene expression patterns compared with normal BEAS-2B cells and control cell lines (untreated) that arose spontaneously in soft agar. Interestingly, the gene expression profiles of six Cr(VI) transformed cell lines were remarkably similar to each other yet differed significantly from that of either control cell lines or normal BEAS-2B cells. A total of 409 differentially expressed genes were identified in Cr(VI) transformed cells compared to control cells. Genes related to cell-to-cell junction were upregulated in all Cr(VI) transformed cells, while genes associated with the interaction between cells and their extracellular matrices were down-regulated. Additionally, expression of genes involved in cell proliferation and apoptosis were also changed.This study is the first to report gene expression profiling of Cr(VI) transformed cells. The gene expression changes across individual chromate exposed clones were remarkably similar to each other but differed significantly from the gene expression found in anchorage-independent clones that arose spontaneously. Our analysis identified many novel gene expression changes that may contribute to chromate induced cell transformation, and collectively this type of information will provide a better understanding of the mechanism underlying chromate carcinogenicity