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The existing literature primarily examined the impact of unexpected events on the stock market at a single scale, posing the challenge of a lack of multiscale analysis. This paper investigates the impact of COVID-19 on stock markets (China, the U.S., and Hong Kong) from a multiscale perspective using an improved ensemble empirical mode decomposition (EEMD)-based event analysis method. First, the stock price series is decomposed into several independent intrinsic mode functions (IMFs) and a residue. Second, a novel composition method is proposed to reconstruct the IMFs into three components: high-frequency, low-frequency, and long-term trend. We find that the composition of low-frequency and long-term trend components is dominant, which is used to estimate the strength of COVID-19 impact on the stock markets. In addition, the outbreak of COVID-19 significantly increased the intensity of short-term fluctuations in stock prices. Finally, the high-frequency component is analyzed to capture the volatility spillover effects among the three stock markets by the BEKK(Baba-Engle-Kraft-Kroner)-GARCH model. The results show that before the outbreak, there are two-way volatility spillovers between any two of the three markets. After the outbreak, there is no spillover effect between China and Hong Kong, and Hong Kong has no spillover effect on the U.S. However, volatility in the U.S. market still has a significant spillover effect on the other two markets, implying that a mature market can absorb new information more quickly. [ABSTRACT FROM AUTHOR]

Producing monomeric phenols from lignin biopolymer depolymerization in a detachable and efficient manner comes under the spotlight on the fullest utilization of sustainable lignocellulosic biomass. Here, we report a low-loaded and highly dispersed Ru anchored on a chitosan-derived N-doped carbon catalyst (RuN/ZnO/C), which exhibits outstanding performance in the reductive catalytic fractionation of lignocellulose. Nearly theoretical maximum yields of phenolic monomers from lignin are achieved, corresponding to TON as 431 molphenols molRu−1, 20 times higher than that from commercial Ru/C catalyst; high selectivity toward propyl end-chained guaiacol and syringol allow them to be readily purified. The RCF leave high retention of (hemi)cellulose amenable to enzymatic hydrolysis due to the successful breakdown of biomass recalcitrance. The RuN/ZnO/C catalyst shows good stability in recycling experiments as well as after a harsh hydrothermal treatment, benefiting from the coordination of Ru species with N atoms. Characterizations of the RuN/ZnO/C imply a transformation from Ru single atoms to nanoclusters under current reaction conditions. Time-course experiment, as well as reactivity screening of a series of lignin model compounds, offer insight into the mechanism of current RCF over RuN/ZnO/C. This work opens a new opportunity for achieving the valuable aromatic products from lignin and promoting the industrial economic feasibility of lignocellulosic biomass. Lignin valorization becomes the spotlight on the full utilization of biomass. Here, the authors report a highly dispersed Ru catalyst for reductive catalytic fractionation of lignocellulose, which affords monophenols in theoretical maximum yields, along with high preservation of carbohydrate. [ABSTRACT FROM AUTHOR]

Laser ignition of lean fuels offers a promising route for green combustion with high combustion efficiency and low exhaust emissions. The fundamental limitations which apply to femtosecond laser ignition (fs-LI) of lean fuels are the inferior energy deposition and low thermodynamic temperature. However, it was discovered recently that the fs laser filamentation can induce 100% success rate of fs-LI with ultralow sub-mJ minimum ignition energy, exhibiting distinct contrast to the general understanding that it is hard to achieve fs-LI The present contribution examines the extent to which the minimum ignition energies depend on filamentation formation, and explores the key factors for the success of fs-LI. We perform fs-LI of a lean-fuel CH4/air mixture using a femtosecond near-infrared (~40 fs, 800 nm) pulse at different external focal conditions, and find a Goldilocks focal zone to facilitate fs-LI. In this special zone, a crucial balance between the length of igniting "line" kernel and the plasma density of the fs laser filament is achieved, which determines not only the total amount of resultant OH radicals, but also their distribution along the plasma filament. Our finding provides a viable strategy with clear guidelines for fs-LI, and also opens up an avenue of exploring unprecedented ultrafast ignition dynamics after fs-laser-fuel interactions towards gaining deeper insights into reaction intermediates and combustion processes. [ABSTRACT FROM AUTHOR]

A large-scale shaking table test and a series of numerical simulations were performed to clarify the seismic response of the slope reinforced by frame beam and anchor cable by applying Wenchuan-Qingping and El Centro seismic records. The horizontal acceleration responses and response spectrum characteristics of slope, the axial force of anchor cable, and the displacement of frame beam were mainly studied by shaking table test. The influence of the excitation direction of seismic waves was investigated in numerical simulation. The results show that the amplification effects of acceleration and response spectrum along the slope height are independent of the type of earthquake, while the amplification effects of acceleration and response spectrum with excitation amplitude are related to the type of earthquake. There are obvious differences in the acceleration responses between the lower and upper weak sliding layers, and a stronger nonlinear behavior occurs in the upper weak sliding layer, which is explained by the time-frequency spectrum calculated by synchrosqueezing wavelet transform (SWT). The axial force of anchor cable and the peak displacement of frame beam increase with the increases of slope height and excitation amplitude. The dynamic response and damage range of the slope under bi-directional earthquake excitation are significantly larger than that under one-directional earthquake excitation. [ABSTRACT FROM AUTHOR]

C-lignin is a homo-biopolymer, being made up of caffeyl alcohol exclusively. There is significant interest in developing efficient and selective catalyst for depolymerization of C-lignin, as it represents an ideal feedstock for producing catechol derivatives. Here we report an atomically dispersed Ru catalyst, which can serve as an efficient catalyst for the hydrogenolysis of C-lignin via the cleavage of C−O bonds in benzodioxane linkages, giving catechols in high yields with TONs up to 345. A unique selectivity to propenylcatechol (77%) is obtained, which is otherwise hard to achieve, because this catalyst is capable of hydrogenolysis rather than hydrogenation. This catalyst also demonstrates good reusability in C-lignin depolymerization. Detailed investigations by model compounds concluded that the pathways involving dehydration and/or dehydrogenation reactions are incompatible routes; we deduced that caffeyl alcohol generated via concurrent C−O bonds cleavage of benzodioxane unit may act as an intermediate in the C-lignin hydrogenolysis. Current demonstration validates that atomically dispersed metals can not only catalyze small molecules reactions, but also drive the transformation of abundant and renewable biopolymer. C-lignin represents an ideal feedstock for producing catechol derivatives. Here, the authors engineered an atomically dispersed Ru catalyst, which can cleave C−O bonds efficiently and circumvent C=C bonds hydrogenation selectively, thus leading to propenylcatechol in high yields with high TONs. [ABSTRACT FROM AUTHOR]