The Holomorphic Embedding Load-Flow Method (HELM) solves the power-flow problem to obtain the bus voltages as rational approximants, that is, a ratio of complex-valued polynomials of the embedding ...parameter. The proof of its claims (namely that: 1) it is guaranteed to find a solution if it exists; 2) it is guaranteed to find only a high-voltage (operable) solution; and 3) that it unequivocally signals if no solution exists) are rooted in complex analysis and the theory developed by Antonio Trias and Herbert Stahl. HELM is one variant of the holomorphic embedding method (HEM) for solving nonlinear equations, the details of which may differ from those available in its published patents. In this paper we show that the HEM represents a distinct class of nonlinear equation solvers that are recursive, rather than iterative. As such, for any given problem, there are an infinite number of HEM formulations, each with different numerical properties and precision demands. The objective of this paper is to provide an intuitive understanding of HEM and apply one variant to the power-flow problem. We introduce one possible PV bus model compatible with the HEM and examine some features of different holomorphic embeddings, giving step-by-step details of model building, germ calculation, and the recursive algorithm.
The Keggin‐type polyoxometalates (POMs) are effective catalysts for oxidative desulfurization (ODS) and confining these POMs in metal–organic frameworks (MOFs) is a promising strategy to improve ...their performances. Herein, postsynthetic modification of POMs confined in MOFs by adding thiourea creates more unsaturated metal sites as defects, promoting ODS catalytic activity. Additional modification by confining 1‐butyl‐3‐methyl imidazolium POMs in MOFs is performed to obtain higher ODS activity, owing to the affinity between electron‐rich thiophene‐based compounds and electrophilic imidazolium compounds. The ODS catalytic activities of four Zr‐MOF‐based composites (bottle around ship) including phosphomolybdate acid (PMA)/UiO‐66, Bmim3PMo12O40/UiO‐66, PMA/Thiourea/UiO‐66, and Bmim3PMo12O40/Thiourea/UiO‐66 are therefore investigated in detail. In order to explore the catalytic mechanism of these MOF composites, their microstructures and electronic structures are probed by various techniques such as X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared, Raman, scanning electron microscope, transmission electron microscope, BET, X‐ray photoelectron spectroscopy, EPR, UV–vis, NMR spectra, and H2‐temperature‐programmed reduction. The results reveal that phosphomolybdate blues and imidazolium phosphomolybdate blues with different Mo5+/Mo6+ ratios with the Keggin structure are confined in defected UiO‐66 for all four composites. This approach can be applied to design and synthesize other POMs/MOFs composites as efficient catalysts.
A design strategy aims to form phosphomolybdate blues confined in defected Zr‐metal–organic framework (MOF) by adding thiourea, which can produce oxygen vacancies with electrons trapped in and Mo5+ to promote the catalytic activity. Moreover, 1‐butyl 3‐methyl imidazolium phosphomolybdate blues are confined in Zr‐MOF to obtain higher oxidative desulfurization activity owing to the affinity between electron‐rich thiophene‐based compounds and electrophilic imidazolium compounds.
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Rechargeable lithium batteries (RLBs), including lithium-ion and lithium-metal systems, have recently received considerable attention for electrochemical energy storage (EES) devices due to their low ...cost, sustainability, environmental friendliness, and temporal and spatial transferability. Most RLBs are harnessed only in favourable environments rather than extreme climates/conditions such as ocean exploration, tropical areas, high altitude drones, and polar expeditions. When chronically or periodically exposed to harsh environments, conventional RLBs will fail to work, especially in low- and high-temperature zones (
i.e.
, below 0 °C and above 60 °C). Constructing alternative electrode materials and electrolyte systems with strong temperature tolerance lays the foundation for developing full-climate RLBs. Herein, the key stumbling blocks to realizing wide-temperature RLBs are first comprehensively discussed. Then the latest research progress to address the challenges at extreme temperatures is gradually introduced. And the fundamental operating mechanism and design strategies of electrolyte and electrode materials for RLBs working within a wide-temperature range are reviewed in detail. Finally, insights into and perspectives on energy materials and battery systems are provided to develop wide-temperature-operating range energy storage devices.
Building rechargeable lithium batteries for wide-temperature applications requires us to investigate the battery failure mechanism at low/high temperature, design advanced electrode/electrolyte materials, and optimize the battery management system.
Single-walled carbon nanotubes (SWCNTs) have been attracting tremendous attention owing to their structure (chirality) dependent outstanding properties, which endow them with great potential in a ...wide range of applications. The preparation of chirality-pure SWCNTs is not only a great scientific challenge but also a crucial requirement for many high-end applications. As such, research activities in this area over the last two decades have been very extensive. In this review, we summarize recent achievements and accumulated knowledge thus far and discuss future developments and remaining challenges from three aspects: controlled growth, postsynthesis sorting, and characterization techniques. In the growth part, we focus on the mechanism of chirality-controlled growth and catalyst design. In the sorting part, we organize and analyze existing literature based on sorting targets rather than methods. Since chirality assignment and quantification is essential in the study of selective preparation, we also include in the last part a comprehensive description and discussion of characterization techniques for SWCNTs. It is our view that even though progress made in this area is impressive, more efforts are still needed to develop both methodologies for preparing ultrapure (e.g., >99.99%) SWCNTs in large quantity and nondestructive fast characterization techniques with high spatial resolution for various nanotube samples.
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Colorimetric sensors have attracted considerable attention in many sensing applications because of their specificity, high sensitivity, cost-effectiveness, ease of use, rapid analysis, simplicity of ...operation, and clear visibility to the naked eye ....
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Smart contract, a term which was originally coined to refer to the automation of legal contracts in general, has recently seen much interest due to the advent of blockchain technology. Recently, the ...term is popularly used to refer to low-level code scripts running on a blockchain platform. Our study focuses exclusively on this subset of smart contracts. Such smart contracts have increasingly been gaining ground, finding numerous important applications (e.g., crowdfunding) in the real world. Despite the increasing popularity, smart contract development still remains somewhat a mystery to many developers largely due to its special design and applications. Are there any differences between smart contract development and traditional software development? What kind of challenges are faced by developers during smart contract development? Questions like these are important but have not been explored by researchers yet. In this paper, we performed an exploratory study to understand the current state and potential challenges developers are facing in developing smart contracts on blockchains, with a focus on Ethereum (the most popular public blockchain platform for smart contracts). Toward this end, we conducted this study in two phases. In the first phase, we conducted semi-structured interviews with 20 developers from GitHub and industry professionals who are working on smart contracts. In the second phase, we performed a survey on 232 practitioners to validate the findings from the interviews. Our interview and survey results revealed several major challenges developers are facing during smart contract development: (1) there is no effective way to guarantee the security of smart contract code; (2) existing tools for development are still very basic; (3) the programming languages and the virtual machines still have a number of limitations; (4) performance problems are hard to handle under resource constrained running environment; and (5) online resources (including advanced/updated documents and community support) are still limited. Our study suggests several directions that researchers and practitioners can work on to help improve developers' experience on developing high-quality smart contracts.
This study aimed to determine the levels of health-related behaviours (physical activity, screen exposure and sleep status) among Chinese students from primary, secondary and high schools during the ...pandemic of COVID-19, as well as their changes compared with their status before the pandemic. A cross-sectional online survey of 10,933 students was conducted among 10 schools in Guangzhou, China, between 8th and 15th March, 2020. After getting the informed consent from student's caregivers, an online questionnaire was designed and used to obtain time spending on health-related behaviours during the pandemic of COVID-19, as well as the changes compared with 3 months before the pandemic, which was completed by students themselves or their caregivers. Students were stratified by regions (urban, suburban, exurban), gender (boys and girls), and grades (lower grades of primary school, higher grades of primary schools, secondary schools and high schools). Data were expressed as number and percentages and Chi-square test was used to analyse difference between groups. Overall, the response rate of questionnaire was 95.3% (10,416/10,933). The median age of included students was 13.0 (10.0, 16.0) years and 50.1% (n = 5,219) were boys. 41.4%, 53.6% and 53.7% of total students reported less than 15 min per day in light, moderate and vigorous activities and 58.7% (n = 6,113) reported decreased participation in physical activity compared with the time before pandemic. Over 5 h of screen time spending on online study was reported by 44.6% (n = 4,649) of respondents, particular among high school students (81.0%). 76.9% of students reported increased screen time compared with the time before pandemic. Inadequate sleep was identified among 38.5% of students and the proportion was highest in high school students (56.9%). Our study indicated that, during the COVID-19 pandemic, the school closure exerted tremendous negative effects on school-aged children's health habits, including less physical activity, longer screen exposure and irregular sleeping pattern.
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Incorporation of N,S‐codoped nanotube‐like carbon (N,S‐NTC) can endow electrode materials with superior electrochemical properties owing to the unique nanoarchitecture and improved kinetics. Herein, ...α‐MnS nanoparticles (NPs) are in situ encapsulated into N,S‐NTC, preparing an advanced anode material (α‐MnS@N,S‐NTC) for lithium‐ion/sodium‐ion batteries (LIBs/SIBs). It is for the first time revealed that electrochemical α → β phase transition of MnS NPs during the 1st cycle effectively promotes Li‐storage properties, which is deduced by the studies of ex situ X‐ray diffraction/high‐resolution transmission electron microscopy and electrode kinetics. As a result, the optimized α‐MnS@N,S‐NTC electrode delivers a high Li‐storage capacity (1415 mA h g−1 at 50 mA g−1), excellent rate capability (430 mA h g−1 at 10 A g−1), and long‐term cycling stability (no obvious capacity decay over 5000 cycles at 1 A g−1) with retained morphology. In addition, the N,S‐NTC‐based encapsulation plays the key roles on enhancing the electrochemical properties due to its high conductivity and unique 1D nanoarchitecture with excellent protective effects to active MnS NPs. Furthermore, α‐MnS@N,S‐NTC also delivers high Na‐storage capacity (536 mA h g−1 at 50 mA g−1) without the occurrence of such α → β phase transition and excellent full‐cell performances as coupling with commercial LiFePO4 and LiNi0.6Co0.2Mn0.2O2 cathodes in LIBs as well as Na3V2(PO4)2O2F cathode in SIBs.
α‐MnS nanoparticles are in situ encapsulated into N,S‐codoped nanotube‐like carbon (α‐MnS@N,S‐NTC) as an advanced anode for Li/Na‐ion batteries. The α → β phase transition during the 1st cycle in LIBs is for the first time revealed by ex situ X‐ray diffraction and high‐resolution transmission electron microscopy studies, which improves the electrode kinetics and Li‐storage properties. α‐MnS@N,S‐NTC also exhibits superior performance in Li/Na‐ion half/full cells.
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Pulmonary arterial hypertension (PAH) is clinically characterized by a progressive increase in pulmonary artery pressure, followed by right ventricular hypertrophy and subsequently right heart ...failure. The underlying mechanism of PAH includes endothelial dysfunction and intimal smooth muscle proliferation. Numerous studies have shown that oxidative stress is critical in the pathophysiology of PAH and involves changes in reactive oxygen species (ROS), reactive nitrogen (RNS), and nitric oxide (NO) signaling pathways. Disrupted ROS and NO signaling pathways cause the proliferation of pulmonary arterial endothelial cells (PAECs) and pulmonary vascular smooth muscle cells (PASMCs), resulting in DNA damage, metabolic abnormalities, and vascular remodeling. Antioxidant treatment has become a main area of research for the treatment of PAH. This review mainly introduces oxidative stress in the pathogenesis of PAH and antioxidative therapies and explains why targeting oxidative stress is a valid strategy for PAH treatment.
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