Abstract
Background
At 10 a.m. on January 23, 2020 Wuhan, China imposed a 76-day travel lockdown on its 11 million residents in order to stop the spread of COVID-19. This lockdown represented the ...largest quarantine in the history of public health and provides us with an opportunity to critically examine the relationship between a city lockdown on human mobility and controlling the spread of a viral epidemic, in this case COVID-19. This study aims to assess the causal impact of the Wuhan lockdown on population movement and the increase of newly confirmed COVID-19 cases.
Methods
Based on the daily panel data from 279 Chinese cities, our research is the first to apply the synthetic control approach to empirically analyze the causal relationship between the Wuhan lockdown of its population mobility and the progression of newly confirmed COVID-19 cases. By using a weighted average of available control cities to reproduce the counterfactual outcome trajectory that the treated city would have experienced in the absence of the lockdown, the synthetic control approach overcomes the sample selection bias and policy endogeneity problems that can arise from previous empirical methods in selecting control units.
Results
In our example, the lockdown of Wuhan reduced mobility inflow by approximately 60 % and outflow by about 50 %. A significant reduction of new cases was observed within four days of the lockdown. The increase in new cases declined by around 50% during this period. However, the suppression effect became less discernible after this initial period of time. A 2.25-fold surge was found for the increase in new cases on the fifth day following the lockdown, after which it died down rapidly.
Conclusions
Our study provided urgently needed and reliable causal evidence that city lockdown can be an effective short-term tool in containing and delaying the spread of a viral epidemic. Further, the city lockdown strategy can buy time during which countries can mobilize an effective response in order to better prepare. Therefore, in spite of initial widespread skepticism, lockdowns are likely to be added to the response toolkit used for any future pandemic outbreak.
The electrochemical CO2 reduction reaction (CO2RR) is a promising strategy to achieve electrical‐to‐chemical energy storage while closing the global carbon cycle. The carbon‐supported single‐atom ...catalysts (SACs) have great potential for electrochemical CO2RR due to their high efficiency and low cost. The metal centers’ performance is related to the local coordination environment and the long‐range electronic intercalation from the carbon substrates. This review summarizes the recent progress on the synthesis of carbon‐supported SACs and their application toward electrocatalytic CO2 reduction to CO and other C1 and C2 products. Several SACs are involved, including MNx catalysts, heterogeneous molecular catalysts, and the covalent organic framework (COF) based SACs. The controllable synthesis methods for anchoring single‐atom sites on different carbon supports are introduced, focusing on the influence that precursors and synthetic conditions have on the final structure of SACs. For the CO2RR performance, the intrinsic activity difference of various metal centers and the corresponding activity enhancement strategies via the modulation of the metal centers’ electronic structure are systematically summarized, which may help promote the rational design of active and selective SACs for CO2 reduction to CO and beyond.
This review summarizes the recent work on the synthesis of carbon‐supported single‐atom catalysts (SACs) and their application in electrochemical CO2 reduction to produce CO and other C1 and C2 products. Several different types of carbon‐supported SACs are involved, including MNx catalysts, heterogeneous molecular catalysts, and the covalent organic frameworks (COFs) based single atoms.
Polygonisation is a common nonuniform wear phenomenon occurring in railway vehicle wheels and has a severe impact on the vehicle–track system, ride comfort, and lineside residents. This paper first ...summarizes periodic defects of the wheels, including wheel polygonisation and wheel corrugation, occurring in railways worldwide. Thereafter, the effects of wheel polygonisation on the wheel–rail interaction, noise and vibration, and fatigue failure of the vehicle and track components are reviewed. Based on the different causes, the formation mechanisms of periodic wheel defects are classified into three categories: (1) initial defects of wheels, (2) natural vibration of the vehicle–track system, and (3) thermoelastic instability. In addition, the simulation methods of wheel polygonisation evolution and countermeasures to mitigate wheel polygonisation are presented. Emphasis is given to the characteristics, effects, causes, and solutions of wheel polygonisation in metro vehicles, locomotives, and high-speed trains in China. Finally, the guidance is provided on further understanding the formation mechanisms, monitoring technology, and maintenance criterion of wheel polygonisation.
Increasing catalytic activity and durability of atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts for the oxygen reduction reaction (ORR) cathode in proton‐exchange‐membrane fuel cells ...remains a grand challenge. Here, a high‐power and durable Co–N–C nanofiber catalyst synthesized through electrospinning cobalt‐doped zeolitic imidazolate frameworks into selected polyacrylonitrile and poly(vinylpyrrolidone) polymers is reported. The distinct porous fibrous morphology and hierarchical structures play a vital role in boosting electrode performance by exposing more accessible active sites, providing facile electron conductivity, and facilitating the mass transport of reactant. The enhanced intrinsic activity is attributed to the extra graphitic N dopants surrounding the CoN4 moieties. The highly graphitized carbon matrix in the catalyst is beneficial for enhancing the carbon corrosion resistance, thereby promoting catalyst stability. The unique nanoscale X‐ray computed tomography verifies the well‐distributed ionomer coverage throughout the fibrous carbon network in the catalyst. The membrane electrode assembly achieves a power density of 0.40 W cm−2 in a practical H2/air cell (1.0 bar) and demonstrates significantly enhanced durability under accelerated stability tests. The combination of the intrinsic activity and stability of single Co sites, along with unique catalyst architecture, provide new insight into designing efficient PGM‐free electrodes with improved performance and durability.
Atomically dispersed single‐Co‐site catalysts, through electrospinning cobalt‐doped ZIF‐8 crystals, and selected dual polyacrylonitrile and poly(vinylpyrrolidone) polymers are reported. The interconnected porous nanofiber networks with hierarchical architecture are essential to facilitate mass and charge transfer within an electrode, along with uniform ionomer dispersion for the oxygen reduction reaction. The catalyst is highly active and durable in proton‐exchange‐membrane fuel cells.
Atomically dispersed and nitrogen coordinated single metal site (MNx, M = Fe, Co, or Mn) moieties embedded in partially graphitized carbon (denoted as M–N–C) are recognized as the most promising ...platinum group metal‐free catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. However, simply regulating their coordination environments and local structures of single metal sites cannot fundamentally change active site structure, which leads to insufficient activity and stability. A second transition metal can be incorporated to design dual‐metal sites, offering a new opportunity to modulate the electronic and geometric structures of M–N–C catalysts. Therefore, exploring optimal atomically dispersed dual‐metal‐site is essential to designing new active sites with enhanced ORR activity, and stability, especially breaking the activity‐stability trade‐off. This review provides a comprehensive analysis of the advances in developing atomically dispersed dual‐metal site catalysts for the ORR, including innovative synthesis methods, primary structural configurations, and the mechanisms to promote catalytic performance. We aim to elucidate the crucial structure–property correlation, emphasizing the inherent electronic and geometric effects of dual metal sites. Finally, we discuss the current challenges of dual‐metal site catalysts concerning rational design, precise synthesis, and high‐fidelity structural characterization.
Designing atomically dispersed dual‐metal site catalysts through the pairing and/or long‐range coupling of two metal sites could provide more opportunities to break catalytic efficiency limitations from the linear relationship and overcome the current problems of single metal‐site catalysts for the oxygen reduction reaction (ORR). Regulating dual‐metal site catalysts concerning atomic/electronic configuration and optimizing coordination environments could accelerate ORR kinetics and address the dilemma of activity‐stability trade‐off. The review summarizes the recent understanding and progress of designing dual‐metal site catalysts for the ORR, emphasizing innovative synthesis methods and mechanistic understanding of promoting catalytic properties.
As a raw material for producing chemical fertilizers, ammonia plays an essential role in human production and life. Due to the severe energy consumption and pollution caused by the industrial ...Haber–Bosch process of NH3 synthesis, developing the NH3 synthesis reaction under ambient conditions is vital. Electrochemical nitrogen reduction reaction (NRR) has recently emerged as a potential method. However, its limited NH3 yield and selectivity are unsatisfactory. NO3
−, as an oxidized form of nitrogen, universally exists in drinking water (<50 mg L−1) and industrial wastewater (2000‐4000 mg L−1). Electrochemical nitrate reduction reaction (NO3
−RR), with higher production and Faradaic efficiency, is a promising strategy for water treatment and NH3 production. In this review, a detailed overview of the recent progress in NO3
−RR for NH3 production with precious group metal (PGM) electrocatalysts, PGM‐free electrocatalysts, and nonmetal electrocatalysts is summarized. In addition, effective design strategies for efficient electrocatalysts, existing challenges, and research prospects for the next stage are also discussed. This review may provide some directions for improving efficient electrocatalysts in electrocatalytic NO3
−RR and offer inspiration for the electrochemical ammonia synthesis process.
A detailed overview of the recent progress in nitrate reduction reaction (NO3
−RR) for NH3 production with noble metal electrocatalysts, non‐noble metal electrocatalysts, and nonmetal electrocatalysts is summarized. The review may provide some inspirations for improving efficient electrocatalysts in electrocatalytic NO3
−RR, based on the discussion of effective design strategies for efficient electrocatalysts, existing challenges, and research prospects for the next stage.
The CRISPR/Cas9 system, composed of a single-guide RNA for target recognition and a Cas9 protein for DNA cleavage, has the potential to revolutionize agriculture as well as medicine. Even though ...extensive work has been done to improve the gene editing activity of CRISPR/Cas9, little is known about the regulation of this bacterial system in eukaryotic host cells, especially at the post-transcriptional level.
Here, we evaluate the expression levels of the two CRISPR/Cas9 components and the gene editing efficiency in a set of Arabidopsis mutants involved in RNA silencing. We find that mutants defective in the post-transcriptional gene-silencing pathway display significantly higher Cas9 and sgRNA transcript levels, resulting in higher mutagenesis frequencies than wild-type controls. Accordingly, silencing of AGO1 by introduction of an AGO1-RNAi cassette into the CRISPR/Cas9 vector provides an increase in gene editing efficiency. Co-expression of the viral suppressor p19 from the tomato bushy stunt virus to suppress the plant RNA-silencing pathway shows a strong correlation between the severity of the phenotypic effects caused by p19 and the gene editing efficiency of the CRISPR/Cas9 system for two different target genes, AP1 and TT4.
This system has useful practical applications in facilitating the detection of CRISPR/Cas9-induced mutations in T1 plants as well as the identification of transgene-free T2 plants by simple visual observation of the symptom severity caused by p19. Our study shows that CRISPR/Cas9 gene editing efficiency can be improved by reducing RNA silencing in plants.
Summary
The widely used Streptococcus pyogenes Cas9 (SpCas9) requires NGG as a protospacer adjacent motif (PAM) for genome editing. Although SpCas9 is a powerful genome‐editing tool, its use has been ...limited on the targetable genomic locus lacking NGG PAM. The SpCas9 variants xCas9 and Cas9‐NG have been developed to recognize NG, GAA, and GAT PAMs in human cells. Here, we show that xCas9 cannot recognize NG PAMs in tomato, and Cas9‐NG can recognize some of our tested NG PAMs in the tomato and Arabidopsis genomes. In addition, we engineered SpCas9 (XNG‐Cas9) based on mutations from both xCas9 and Cas9‐NG, and found that XNG‐Cas9 can efficiently mutagenize endogenous target sites with NG, GAG, GAA, and GAT PAMs in the tomato or Arabidopsis genomes. The PAM compatibility of XNG‐Cas9 is the broadest reported to date among Cas9s (SpCas9 and Cas9‐NG) active in plant.
In this study, we engineered SpCas9 (XNGCas9) based on mutations from both xCas9 and Cas9‐NG, and found that Cas9‐NG can efficiently mutagenize endogenous target sites with NG, GAG GAA and GAT PAMs in tomato or Arabidopsis genomes. The PAM compatibility of XNG‐Cas9 is the broadest reported to date among Cas9s.
Social security systems were successively established in most developing countries in the 1980s and 1990s. To ensure the long-term sustainability of these newly established systems it is essential to ...carefully monitor the economic impact. Based on the panel data of 21 developing countries from 2000 to 2016, this paper is the first to apply the panel threshold model to empirically analyze the relationship between national health expenditures and economic growth under different levels of human capital. The results show that health expenditure and economic growth have significant interval effects because of the different levels of human capital. Specifically, when human capital levels are low, health expenditure is significantly negatively correlated with economic growth. When human capital is at a medium level, health expenditure has a positive but not significant impact on economic growth. When the level of human capital is high, the positive economic impact of the health expenditure is significantly enhanced. In addition, subgroup analyses indicate that population aging and low fertility aggravate the negative impact of health expenditures on economic growth. This study provides reliable analysis and can be used by developing countries to maintain a long-term sustainable social security system.
As one of the most important chemicals and carbon‐free energy carriers, ammonia (NH3) has significant energy‐related applications in industry and agriculture. Ninety percent of NH3 is produced by the ...Haber–Bosch process using high‐purity N2 and H2 at high temperatures and pressures, which consumes about 1% of the total energy production and causes 1.4% of global CO2 emissions. The environmentally friendly electrochemical nitrogen reduction reaction (NRR) with low energy consumption is a promising alternative to the conventional Haber–Bosch process. However, the main issue is the low Faradaic efficiency and NH3 selectivity of electrochemical NRR, caused by inert nitrogen molecules and competitive hydrogen evolution reaction. As one of the cheapest and most abundant transition metals widely utilized in the Haber–Bosch process, the Fe element has presented the potential high performance for the electrochemical NRR. This article summarizes recent advances and research progress in non‐noble Fe‐based catalysts used for NH3 electrosynthesis. Various synthetic protocols, structure/morphology modification, performance improvement, and reaction mechanisms are comprehensively presented. Based on recent experimental and theoretical studies, we aim to illuminate the structure–property relationship and offer an excellent opportunity for engineering advanced Fe‐based catalysts for nitrogen fixation. The most critical challenges and opportunities for Fe‐based catalysts are also provided. This review would open up a promising avenue toward developing platinum‐group‐metal‐free catalysts for electrochemical NRR applications in the future.
Emerging Fe‐based catalysts have been demonstrated to be promising substitutes for platinum‐group‐metal‐based catalysts for the electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions. However, breakthroughs in current Fe‐based catalyst improvement are needed to enable efficient ammonia (NH3) synthesis. This review focuses on the development of Fe‐based catalysts, with the tailored architecture and compositional design for the NRR discussed, focusing on the role of various active Fe sites in improving high Faradaic efficiency and NH3 yields. The key challenges and future opportunities in this exciting field are also highlighted.
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