Permanent Magnet Machines for High-Speed Applications

This paper overviews high-speed permanent magnet (HSPM) machines, accounting for stator structures, winding configurations, rotor constructions, and parasitic effects. Firstly, single-phase and three-phase PM machines are introduced for high-speed applications. Secondly, for three-phase HSPM machines, applications, advantages, and disadvantages of slotted/slotless stator structures, non-overlapping/overlapping winding configurations, different rotor constructions, i.e., interior PM (IPM), surface-mounted PM (SPM), and solid PM, are summarised in detail. Thirdly, parasitic effects due to high-speed operation are presented, including various loss components, rotor dynamic and vibration, and thermal aspects. Overall, three-phase PM machines have no self-starting issues, and exhibit high power density, high efficiency, high critical speed, together with low vibration and noise, which make them a preferred choice for high-performance, high-speed applications.

Parasitic Effects of PWM-VSI Control Leading to Torque Harmonics in AC Drives

Precise torque control without pulsations is one of the major quality issues in pulse-width modulated voltage-source inverter (PWM-VSI) drives. Theoretically, it could be postulated that at frequencies of some kHz, the machine’s inertia absorbs switching frequency torque harmonics, and the resulting torque becomes smooth; though, in reality, parasitic effects in voltage source inverters may cause additional torque harmonics of low order. In particular, first, second and sixth torque harmonics are observed. Such torque harmonics are especially dangerous for normal drive operation, since they may be amplified by drive train resonances at corresponding rotational velocities. New parasitic effects in PWM-VSI control, leading to torque harmonic of low order, are described in the paper, and recommendations for their compensation are given.

Effectiveness of Azadirachta indica (neem tree) on prevention and treatment of clinical human malaria: A systematic review

Introduction: Neem tree parts such as leaves, stem barks, and roots are known to have some medicinal values in both humans and animals. However, the evidence is scattered and vary with populations and regions. This systematic review sought to explore the effectiveness of neem as a therapeutic and prophylactic agent against malaria. Methodology: The systematic review examined the effectiveness of neem using the pre-registered review protocol and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. The Population Intervention Comparator Outcome (PICO) question was: “What is the effectiveness of neem (Azadirachta indica) when used as a therapeutic and prophylactic agent for malaria infection?” It included all cross-sectional survey studies, qualitative studies, case-control studies, randomised controlled trials, quasi-experimental studies, and cohort studies with or without comparison groups. Studies that had both children and adult patients who were diagnosed with malaria were included in the survey. Malaria patients using traditional medications other than neem as well as those who did not use neem were excluded from this study. The search for articles, screening, and synthesis were conducted using the Rayyan software. Results: Out of the total 1089 articles retrieved, only 3 fitted the inclusion criteria, 1 article could not be retrieved. A narrative synthesis was therefore done on 2 final research articles that were retrievable. The pooled evidence shows that Azadirachta indica is effective against malaria. The medicinal effects are more on symptoms and curbing development to clinical disease than ant parasitic effects. Conclusion: Neem is potential traditional medicine for malaria symptoms’ treatment, but evidence on ant parasitic effects is still not conclusive. The study recommends further primary studies to enhance the power of results to further recommend this plant for the prevention of or treatment of malaria symptoms.

Memristors as Candidates for Replacing Digital Potentiometers in Electric Circuits

Digital potentiometers are substantial components for the design of many mixed-signal electronic circuits and systems. Their capability to program resistance value almost instantly provides hardware designers an additional level of freedom. Unfortunately, this feature is limited to DC and lower frequencies, due to parasitic effects. Nowadays, memristors as continuously tunable resistors are becoming candidates for potentiometer successors. Memristors are two-terminal non-volatile devices which have less significant parasitic effects and a wide resistance range. The memristance value can be changed on the fly. Using nanotechnology, memristor implementation has a nanoscale footprint with nanosecond transition between resistive states. In this paper, we present a comparison between the frequency characteristics of digital potentiometers and the only commercially available memristors. Memristor parasitic effects dominate at higher frequencies which extends the bandwidth. In order to present the advantages of memristive circuits, we have analyzed and implemented tunable circuits such as a voltage divider, an inverting amplifier, a high-pass filter, and a phase shifter. A commercially available memristor by KnowM Inc. is used for this purpose. Experimental results obtained by the measurements verify that a memristor has equal or better characteristics than a digital potentiometer. Memristive realizations of voltage dividers and inverting amplifiers have a wider bandwidth, while filters and phase shifters with a memristor have almost identical frequency characteristics as the corresponding realizations with a digital potentiometer.