Physical Investigation into Effective Voltage Balancing by Temporary Clamp Technique for the Series Connection of IGBTs

The series connection of IGBTs is essential for high-voltage applications where fast switching performances need to be maintained. However, unbalanced voltage sharing is a major resistance to the converter application of this structure. There are a number of causes leading to voltage unbalance, such as different signal delays, parasitic parameters, tail currents, and so on. A temporary clamp scheme performed by active voltage control (AVC) has been proven to be effective in solving the unbalanced voltage-sharing issue. However, the basic physics has not been investigated. In this paper, the physical principle of voltage unbalance within IGBTs series operation is discussed. The carrier storage region differences are concluded to be the intrinsic cause of unbalanced voltage sharing. By using an accurate Fourier-series-based IGBT simulation model with appropriate assumptions, a physical explanation for temporary clamp is provided in detail. At the end of the tail current period when the excess carrier concentration becomes close to the intrinsic doping density, the temporary clamp is able to achieve satisfactory equal voltage sharing

The role of thymosin-β4 in kidney disease

Therapies that modulate inflammation and fibrosis have the potential to reduce the morbidity and mortality associated with chronic kidney disease (CKD). A promising avenue may be manipulating thymosin-β4, a naturally occurring peptide, which is the major G-actin sequestering protein in mammalian cells and a regulator of inflammation and fibrosis. Thymosin-β4 is already being tested in clinical trials for heart disease and wound healing. This editorial outlines the evidence that thymosin-β4 may also have therapeutic benefit in CKD

Use of remote sensing to identify suitable breeding habitat for the Kentish Plover and estimate population size along the western coast of Saudi Arabia

he identification of the environmental parameters affecting species’ habitat preferences is a key to understanding the relationships between habitat features and species’ distributions. This understanding provides the evidence base upon which to formulate guidelines for managing populations. We used distribution modelling to quantify habitat relationships and to estimate the population size during the breeding season of the Kentish Plover Charadrius alexandrinus, a poorly known species on the western coast of Saudi Arabia. We used a Generalised Linear Model (GLM) with four habitat variables derived from satellite data: elevation, distance to settlements, vegetation cover and soil moisture to produce a habitat suitability model. Validation of this model using a receiver operating characteristic plot suggests that it is at least 80% accurate in predicting suitable sites. We then used our estimate of total area of suitable habitat above a critical suitability threshold and data on Kentish Plover density, to estimate the total population size to be 9,955±1,388 individuals. Based on our model we recommend sites for potential protected areas to be established. Finally, we believe that our modelling approach can provide inputs for conservation planning and long-term population monitoring of Kentish Plover and other shorebirds in the region. We argue that conservation of Kentish Plover habitat will not only protect this species, but will benefit other species, particularly those with similar habitat requirements

Robust stability analysis of active voltage control for high-power IGBT switching by Kharitonov's theorem

The main idea of active voltage control (AVC) is to employ classic feedback-control methods forcing the IGBT collector voltage transient to follow a predefined trajectory. This feedback control of IGBTs has great advantages in guaranteeing that IGBTs remain in safe operating area (SOA), restricting EMI, mitigating the voltage/current stress, minimizing/predicting their power losses, and balancing voltages of IGBTs in series. Inevitably, however, AVC introduces stability issues. Based on the assumption that accurate IGBT small-signal model parameters are available, an analogue proportional-derivative and multiloop feedback control was proposed to achieve stable performance in previous work. Due to nonlinearities and uncertainties in IGBT parameters, previous stability analysis methods have important limitations. This work uses Kharitonov's theorem during the IGBT controlled turn-off to assess the system's stability and guide the AVC design to account for model uncertainties and varying parameters. We conducted experiments to investigate the system's robust stability due to these uncertainties in the IGBT parameters, which confirm the validity of the proposed theoretical analysis. With the use of wide bandwidth op-amps, it is shown that the feedback design may be simplified

Physics-based Compact Model of Integrated Gate-Commutated Thyristor with Multiple Effects for High Power Application

This paper presents a physics-based compact model of integrated gate-commutated thyristor (IGCT) with multiple effects for high power application. The proposed model has both acceptable accuracy and computation time requirement, which is suitable for system level circuit simulation and IGCT’s whole wafer modelling work. First, the development of IGCT model is discussed and the one-dimension phenomenon of IGCT is analyzed in the paper. Second, a physics-based compact model of IGCT is proposed. The proposed model of IGCT includes multiple physical effects that are crucial to IGCTs working in high power applications. These physical effects include the impact ionization effect, moving boundary of depletion region during punch-thourgh (PT) and the local lifetime region. The Fourier series solution is applied for the ambipolar diffusion equation in the base region. Third, the proposed model is implemented in Simulink and compared with the model in Silvaco Atlas, a finite-element (FEM) tool. Finally, the proposed compact model of IGCT is validated by experiments

Does consultation improve decision-making?

This paper reports an experiment designed to test whether prior consultation within a group affects subsequent individual decision-making in tasks where demonstrability of correct solutions is low. In our experiment, subjects considered two paintings created by two different artists and were asked to guess which artist made each painting. We observed answers given by individuals under two treatments: In one, subjects were allowed the opportunity to consult with other participants before making their private decisions; in the other, there was no such opportunity. Our primary findings are that subjects in the first treatment evaluate the opportunity to consult positively, but they perform significantly worse and earn significantly less

A multiple spacecraft detection of the 2 April 2022 M-class flare and filament eruption during the first close Solar Orbiter perihelion

CONTEXT: The Solar Orbiter mission completed its first remote-sensing observation windows in the spring of 2022. On 2 April 2022, an M-class flare followed by a filament eruption was seen both by the instruments on board the mission and from several observatories in Earth’s orbit, providing an unprecedented view of a flaring region with a large range of observations. AIMS: We aim to understand the nature of the flaring and filament eruption events via the analysis of the available dataset. The complexity of the observed features is compared with the predictions given by the standard flare model in 3D. METHOD: In this paper, we use the observations from a multi-view dataset, which includes extreme ultraviolet (EUV) imaging to spectroscopy and magnetic field measurements. These data come from the Interface Region Imaging Spectrograph, the Solar Dynamics Observatory, Hinode, as well as several instruments on Solar Orbiter. RESULTS: The large temporal coverage of the region allows us to analyse the whole sequence of the filament eruption starting with its pre-eruptive state. Information given by spectropolarimetry from SDO/HMI and Solar Orbiter PHI/HRT shows that a parasitic polarity emerging underneath the filament is responsible for bringing the flux rope to an unstable state. As the flux rope erupts, Hinode EIS captures blue-shifted emission in the transition region and coronal lines in the northern leg of the flux rope prior to the flare peak. This may be revealing the unwinding of one of the flux rope legs. At the same time, Solar Orbiter SPICE captures the whole region, complementing the Doppler diagnostics of the filament eruption. Analyses of the formation and evolution of a complex set of flare ribbons and loops, of the hard and soft X-ray emissions with STIX, show that the parasitic emerging bipole plays an important role in the evolution of the flaring region. CONCLUSIONS: The extensive dataset covering this M-class flare event demonstrates how important multiple viewpoints and varied observations are in order to understand the complexity of flaring regions. While the analysed data are overall consistent with the standard flare model, the present particular magnetic configuration shows that surrounding magnetic activity such as nearby emergence needs to be taken into account to fully understand the processes at work. This filament eruption is the first to be covered from different angles by spectroscopic instruments, and provides an unprecedented diagnostic of the multi-thermal structures present before and during the flare. This complete dataset of an eruptive event showcases the capabilities of coordinated observations with the Solar Orbiter mission

Treatment Outcomes and Cost-Effectiveness of Shifting Management of Stable ART Patients to Nurses in South Africa: An Observational Cohort

Lawrence Long and colleagues report that “down-referring” stable HIV patients from a doctor-managed, hospital-based ART clinic to a nurse-managed primary health facility provides good health outcomes and cost-effective treatment for patients