In this paper, a hybrid switch (HyS) consisting of a large current rated Si insulated-gate bipolar transistor (IGBT) device connected in parallel with a small current rated SiC MOSFET device (low ...SiC/Si current ratio below unity) is proposed for high-current high-power converters. A systematic analysis involving a parametric sweep to understand the influence and to derive a boundary line of the parasitic interconnection inductance unbalance between Si and SiC within the HyS is presented. The boundary line prescribes the selection of an appropriate gate sequence control. A comprehensive cost analysis was performed using commercial 1.2 kV devices to demonstrate the cost viability of a 1:4 or 1:6 SiC/Si current ratio HyS compared to a SiC MOSFET. An algorithm using a dynamic junction temperature prediction is presented to select an optimum SiC/Si current ratio, which ensures a reliable HyS operation. Using a design example, the possibility of reliability using a 1:6 SiC/Si HyS is studied. A 650 V Si-IGBT- and SiC-MOSFET-based HyS (1:5 SiC/Si current ratio) was successfully demonstrated in a dc-dc boost converter. Also, electromagnetic interference analysis is presented for the HyS-based converter operation.
Wide bandgap devices enable high power density power converters. Despite the advantages of increased switching frequency, the passive components are still a major bottleneck toward enabling high ...power density. Among the passive components in the converter, the passive electromagnetic interference (EMI) filters are unavoidable to ensure compliance with conducted EMI standards. Active EMI filters (AEFs) help reduce the volume of the passive components and have been around for three decades now. The design and implementation of the AEFs depend upon the type of noise (common-mode or differential-mode) and power converter (ac-dc, dc-dc or inverter). This article presents a comprehensive survey of different AEFs and their implementations for different power converters presented in the literature. A comprehensive survey of noise-sensing, noise-processing, and noise-cancellation circuits is presented. Also, a comparison of attenuation provided by the AEFs for common-mode and differential-mode noises for different converters is carried out. Furthermore, other facets of AEFs such as the auxiliary power supply, power loss, and protection methods for the AEF are also summarized. This article is intended to be a useful reference for power converter designers in both industry and academia.
Single-atom electrocatalysts (SAEs) can realize the target of low-cost by maximum atomic efficiency. However, they usually suffer performance decay due to high energy states, especially in a harsh ...acidic water splitting environment. Here, we conceive and realize a double protecting strategy that ensures robust acidic water splitting on Ir SAEs by dispersing Ir atoms in/onto Fe nanoparticles and embedding IrFe nanoparticles into nitrogen-doped carbon nanotubes (Ir-SA@Fe@NCNT). When Ir-SA@Fe@NCNT acts as a bifunctional electrocatalyst at ultralow Ir loading of 1.14 μg cm–2, the required overpotentials to deliver 10 mA cm–2 are 250 and 26 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 0.5 M H2SO4 electrolyte corresponding to 1370- and 61-fold better mass activities than benchmark IrO2 and Pt/C at an overpotential of 270 mV, respectively, resulting in only 1.51 V to drive overall water splitting. Moreover, remarkable stability is also observed compared to Pt/C-IrO2.
Akebia saponin D (ASD) is derived from the Dipsacus asper Wall. ex Henry, which is a traditional Chinese medicine commonly used to treat rheumatic arthritis (RA). However, the in-depth mechanism of ...the anti-inflammatory effect of ASD is still unclear. This study aimed to preliminarily explore the anti-inflammatory effect of ASD and the underlying mechanisms from the perspective of DNA methylation and inflammation-related pathways. We found that ASD significantly reduced the production of multiple inflammatory mediators, including nitric oxide (NO) and prostaglandin E2 (PGE2), in LPS-induced RAW264.7 cells. The expression of DNA methyltransferase (DNMT) 3b and inducible nitric oxide synthase (iNOS) was also obviously inhibited by the ASD treatment. The protein and mRNA levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were also significantly inhibited by ASD. ASD inhibited the macrophage M1 phenotype, inhibited the high level of DNMT3b, and downregulated the signal transducer and activator of the transcription 3 (STAT3) pathway to exert its anti-inflammatory activity. Furthermore, DNMT3b siRNA and Nrf2 siRNA significantly promoted the anti-inflammatory effect of ASD. Our study demonstrates for the first time that ASD inhibits the IL-6-STAT3-DNMT3b axis and activates the nuclear factor-E2-related factor 2 (Nrf2) signaling pathway to achieve its inhibitory effect on inflammatory reactions.
Patients with obesity are at increased risk of exacerbations from viral respiratory infections. However, the association of obesity with the severity of coronavirus disease 2019 (COVID-19) is ...unclear. We examined this association using data from the only referral hospital in Shenzhen, China.
A total of 383 consecutively hospitalized patients with COVID-19 admitted from 11 January 2020 to 16 February 2020 and followed until 26 March 2020 at the Third People's Hospital of Shenzhen were included. Underweight was defined as a BMI <18.5 kg/m
, normal weight as 18.5-23.9 kg/m
, overweight as 24.0-27.9 kg/m
, and obesity as ≥28 kg/m
.
Of the 383 patients, 53.1% were normal weight, 4.2% were underweight, 32.0% were overweight, and 10.7% were obese at admission. Obese patients tended to have symptoms of cough (
= 0.03) and fever (
= 0.06) compared with patients who were not obese. Compared with normal weight patients, those who were overweight had 1.84-fold odds of developing severe COVID-19 (odds ratio OR 1.84, 95% CI 0.99-3.43,
= 0.05), while those who were obese were at 3.40-fold odds of developing severe disease (OR 3.40, 95% CI 1.40-2.86,
= 0.007), after adjusting for age, sex, epidemiological characteristics, days from disease onset to hospitalization, presence of hypertension, diabetes, cardiovascular disease, chronic obstructive pulmonary disease, liver disease, and cancer, and drug used for treatment. Additionally, after similar adjustment, men who were obese versus those who were normal weight were at increased odds of developing severe COVID-19 (OR 5.66, 95% CI 1.80-17.75,
= 0.003).
In this study, obese patients had increased odds of progressing to severe COVID-19. As the severe acute respiratory syndrome coronavirus 2 may continue to spread worldwide, clinicians should pay close attention to obese patients, who should be carefully managed with prompt and aggressive treatment.
DC/AC inversion technology is of vital importance for industrial applications, including electrical vehicles and renewable energy systems, which require a large number of inverters. In recent years, ...inversion technology has developed rapidly, with new topologies improving the power factor and increasing power efficiency. Proposing many novel approaches, this book describes advanced DC/AC inverters that can be used for renewable energy systems. The book introduces more than 100 topologies of advanced inverters originally developed by the authors, including more than 50 new circuits. It also discusses recently published cutting-edge topologies. A key topic for multilevel inverters is the need to manage the switching angles to obtain the lowest total harmonic distortion (THD). The authors outline four methods for finding the best switching angles and use simulation waveforms to verify the design. The optimum switching angles for multilevel DC/AC inverters are also listed in tables for quick reference. Highlighting the importance of inverters in improving energy saving and power-supply quality, the final chapter of the book supplies design examples for applications in wind turbine and solar panel energy systems. Written by pioneers in advanced conversion and inversion technology, this book guides readers in designing more effective DC/AC inverters for use in renewable energy systems.
Abstract
Proton exchange membrane fuel cells have been recently developed at an increasing pace as clean energy conversion devices for stationary and transport sector applications. High platinum ...cathode loadings contribute significantly to costs. This is why improved catalyst and support materials as well as catalyst layer design are critically needed. Recent advances in nanotechnologies and material sciences have led to the discoveries of several highly promising families of materials. These include platinum-based alloys with shape-selected nanostructures, platinum-group-metal-free catalysts such as metal-nitrogen-doped carbon materials and modification of the carbon support to control surface properties and ionomer/catalyst interactions. Furthermore, the development of advanced characterization techniques allows a deeper understanding of the catalyst evolution under different conditions. This review focuses on all these recent developments and it closes with a discussion of future research directions in the field.
We report on a non-precious, two-phase bifunctional oxygen reduction and evolution (ORR and OER) electrocatalyst with previously unachieved combined roundtrip catalytic reactivity and stability for ...use in oxygen electrodes of unitized reversible fuel cell/electrolyzers or rechargeable metal–air batteries. The combined OER and ORR overpotential, total, at 10 mA cm
−2
was a record low value of 0.747 V. Rotating Ring Disk Electrode (RRDE) measurements revealed a high faradaic selectivity for the 4 electron pathways, while subsequent continuous MEA tests in reversible electrolyzer cells confirmed the excellent catalyst reactivity rivaling the state-of-the-art combination of iridium (OER) and platinum (ORR).
Miniaturized electrochemical (MEC) sensors have been broadly applied to point-of-care testing (POCT) in various fields, including health care, food safety, and environmental monitoring, due to their ...easy operation, portability, high sensitivity, as well as their short analysis time. This review summarizes the state-of-the-art advancements on various types of MEC sensors, applications in POCT, and the future perspectives, opportunities, and challenges in this field.
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Most of the current analytical methods depend largely on laboratory-based analytical techniques that require expensive and bulky equipment, potentially incur costly testing, and involve lengthy detection processes. With increasing requirements for point-of-care testing (POCT), more attention has been paid to miniaturized analytical devices. Miniaturized electrochemical (MEC) sensors, including different material-based MEC sensors (such as DNA-, paper-, and screen electrode-based), have been in strong demand in analytical science due to their easy operation, portability, high sensitivity, as well as their short analysis time. They have been applied for the detection of trace amounts of target through measuring changes in electrochemical signal, such as current, voltage, potential, or impedance, due to the oxidation/reduction of chemical/biological molecules with the help of electrodes and electrochemical units. MEC sensors present great potential for the detection of targets including small organic molecules, metal ions, and biomolecules. In recent years, MEC sensors have been broadly applied to POCT in various fields, including health care, food safety, and environmental monitoring, owing to the excellent advantages of electrochemical (EC) technologies. This review summarized the state-of-the-art advancements on various types of MEC sensors and their applications in POCT. Furthermore, the future perspectives, opportunities, and challenges in this field are also discussed.
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