AC Losses in Superconducting Magnetic Bearings

Since the discovery of high-temperature superconductors, superconducting magnetic bearings have become an icon of applied superconductivity. Their ability to provide passive stable levitation/suspension has attracted much attention for industrial applications such as maglev trains, flywheel energy storage systems, and high speed electrical machines. Paihau-Robinson Research Institute has been working on the design and construction of a 22 kW, 30000 rpm homopolar superconducting motor for a hybrid aircraft propulsion system. Superconducting magnetic bearings seem to be a potential solution to overcome the speed limits imposed by friction and heat in mechanical bearings. Considering the lack of commercial availability of superconducting bearings, the Institute has decided to investigate the challenges involved in developing suitable bearings for ongoing and future projects. The focus of this thesis is to explore the development of suitable low-loss bearings from bulk high-temperature superconductors, and to develop suitable test methodologies that allow the properties and behaviour of high-temperature superconducting bearings to be explored.  In order to accurately predict the behaviour of superconducting magnetic bearings, a precise knowledge about the non-linear voltage-current (E-J) relationshipis required for input to simulations. Unlike coated conductors, this cannot be achieved by transport measurements in superconducting bulks. In this thesis, a convenient non-destructive method based on levitation force decay in superconducting bearings is introduced and evaluated to map the non-linear electrical properties in superconducting bulks. Furthermore, fibre Bragg grating sensors are employed in an actual superconducting bearing environment to monitor temperature at the bearing surface. Accurate cryogenic temperature monitoring with large electromagnetic fields present is of great importance in practical applications, and is problematic with conventional electronic sensors. A barrier to commercial application is suspected to be the effects of inhomogeneous magnet, or superconducting, properties on the efficiency of bearings. The key drivers of this, AC loss mechanisms in superconducting bearings are investigated and a new analytical expression is proposed for hysteresis loss in superconducting bearings which takes magnetic field inhomogeneity, magnetic field periodicity, and loss surface distribution into account. This new expression is tested by performing spin-down experiments, and the results are found to be in good agreement. Lastly, a high-speed superconducting motor/generator demonstration is built, which sets a record for the fastest superconducting bearing made in New Zealand. This will enable applications such as flywheel energy storage systems, direct-drive generators and high speed microfans to be explored whilst also providing the opportunity to demonstrate key technology elements such as flux-pumped hightemperature superconducting field windings and low-loss high-speed bearings. AC loss mechanisms at kHz-rated rotational frequencies are also studied with this prototype. The results show that at high rotational frequencies the superconducting bulks are pushed into a resistive flux-flow regime, where AC losses are createdby an eddy-current-like mechanism. This thesis explores two phenomena of practical importance in superconducting bearings, and proves the principle of the application of superconducting bearings for ongoing and future projects in New Zealand.</p

Comparison of Serum Zinc Levels between Patients with Schizophrenia and Healthy Individuals

Background and objectives: Schizophrenia is a debilitating mental disorder characterized by disruptions in thought processes, perceptions, emotional responsiveness, and social interactions. Zinc is a neuroactive element released in synapses during neuronal activity and is required for proper functioning of the nervous system, particularly the brain. Serum and tissue concentrations of zinc may reflect various physiological and pathophysiological conditions. Evidence suggests a link between zinc level and development of schizophrenia. The aim of this study was to compare serum zinc levels between patients with schizophrenia and healthy individuals. Methods: This case-control study was performed on 55 patients (37 men and 18 women) with schizophrenia who were hospitalized in 5 Azar Hospital in Gorgan (Iran) and 55 healthy individuals. The case subjects were selected based on convenience sampling method using the Positive and Negative Syndrome Scale (PANSS), while the control subjects were enrolled based on the General Health Questionnaire-28 (GHQ-28). The groups were matched in terms of age and gender. Serum concentration of zinc was measured using a commercial colorimetric assay kit (5-Br-PAPS method). Results: Serum zinc concentration did not differ significantly between the patients and the controls (P=0.93). In schizophrenic patients, there was a significant, negative correlation between age and serum zinc concentration (r=-0.298, P=0.027). In both patients and controls, serum zinc level was significantly higher in men than in women (P<0.05). Conclusion: Based on the results, it is recommended to pay more attention to the diet of patients with schizophrenia

Are Fundamental Movement Patterns Affected by Functional Training in Youth Male Soccer Players?

Introduction: Appropriate movement patterns are important for both injury prevention and athletic performance. Therefore, the use of Functional Movement Screen (FMS), which has been shown to be effective in predicting sport injuries, is recommended by many sports specialists in designing training programs. On the other hand, questions remain regarding its utility as a means to evaluate the effectiveness of training. The purpose of the present study was to investigate whether a functional training program can affect the fundamental movement patterns. Materials and Methods: The study participants consisted of 27 youth male soccer players in the age range of 14 to 16 years and free from pain and previous injury in different layers. The subjects were allocated to experimental and control groups. The experimental group performed functional training for 10 weeks. The total time devoted to training was the same in both groups. Before and after the functional training, FMS was evaluated in both groups. Independent t-test and ANCOVA were used for statistical analysis at the significance level of P < 0.05. Results: A significant difference was observed in FMS score between experimental group (18.07 ± 1.49) and control group (16.07 ± 1.11) (P < 0.001; Effect size = 0.71). Conclusion: This study demonstrated that fundamental movement patterns improved as a result of a functional training intervention in youth male soccer players. Therefore, coaches and sports specialists can be recommended to pay special attention to functional training. The investigation of the effect of functional training on other injury risk factors in future studies seems necessary

Design, Build, and Evaluation of an AC Loss Measurement Rig for High-Speed Superconducting Bearings

Friction and heat generated in conventional bearings impose a limit on maximum design speed in electrical machines. Superconducting bearings offer the potential for low loss, simplified, and passively stable bearings that can overcome the speed limit and operate at high loads. Although such bearings are contactless and seem to be loss free, AC loss mainly caused by magnetic field inhomogeneity gradually slows down the rotating body. This loss, whose mechanism has not been fully explored, is measured through spin-down tests where the rotational speed of the spinning rotor is measured as a function of time. However, there are some challenges in performing a reliable spin-down test. In this paper, we discuss these challenges as well as the engineering of an experimental test rig that enables us to spin-up, release, and recapture the levitated permanent magnet. We also discuss the specifications of the driving mechanism including the self-aligning coupling, which accommodates permanent magnets of different sizes. Initial test results at 6600 rpm are discussed and further technical improvements to the test rig suggested. This rig will be used as a key tool to explore the AC loss mechanism and inform the design of bearings for high-speed superconducting machines

Design, Build, and Evaluation of an AC Loss Measurement Rig for High-Speed Superconducting Bearings

Friction and heat generated in conventional bearings impose a limit on maximum design speed in electrical machines. Superconducting bearings offer the potential for low loss, simplified, and passively stable bearings that can overcome the speed limit and operate at high loads. Although such bearings are contactless and seem to be loss free, AC loss mainly caused by magnetic field inhomogeneity gradually slows down the rotating body. This loss, whose mechanism has not been fully explored, is measured through spin-down tests where the rotational speed of the spinning rotor is measured as a function of time. However, there are some challenges in performing a reliable spin-down test. In this paper, we discuss these challenges as well as the engineering of an experimental test rig that enables us to spin-up, release, and recapture the levitated permanent magnet. We also discuss the specifications of the driving mechanism including the self-aligning coupling, which accommodates permanent magnets of different sizes. Initial test results at 6600 rpm are discussed and further technical improvements to the test rig suggested. This rig will be used as a key tool to explore the AC loss mechanism and inform the design of bearings for high-speed superconducting machines