This paper investigates the volatility spillover effects and the dynamic relationships among WTI crude oil, gold and the Chinese stock markets of new energy vehicle, environmental protection, new ...energy, coal & consumable fuels, high and new technology, by adopting the method of Diebold and Yilmaz (2012, 2014) based on TVP-VAR model. The results indicate that there exists a high interdependence among all analyzed assets, and the total volatility spillover has a sharp increase under the major crisis events. On average, WTI crude oil and gold are the net receivers of the systemic shocks, while all of the analyzed stock markets are the net transmitters of the systemic shocks. Besides, the Granger causality test shows that the volatility of each asset can Granger cause the total connectedness index. Finally, we also calculate optimal hedge ratios, portfolio weights and the corresponding hedging effectiveness based on DCC-GARCH-t copula model. The empirical results show WTI crude oil and gold are cheap hedging tools. When investing a small part in WTI crude oil and a large part in the analyzed stock markets, high hedging effectiveness could be achieved.
•This paper examines time-varying spillovers among crude oil, gold and new energy vehicle.•The total volatility spillover has a sharp increase under the major crisis events.•New energy vehicle, new energy, new technology enterprises are the net transmitter of systematic shocks.•WTI crude oil futures, coal & consumable fuels and gold futures are the net receiver of systematic shocks.•WTI crude oil and gold futures are cheap hedging tools and gold is also a strong hedge.
A series of diphosphine ligand constructed porous polymers with stable and flexible frameworks have been successfully synthesized under the solvothermal conditions from polymerizing the corresponding ...vinyl-functionalized diphosphine monomers. These insoluble porous polymers can be swollen by a wide range of organic solvents, showing similar behavior to those of soluble analogues. Rather than just as immobilizing homogeneous catalysts, these porous polymers supported with Rh species demonstrate even better catalytic performance in the hydroformylations than the analogue homogeneous catalysts. The sample extraordinary performance could be attributed to the combination of high ligand concentration and flexible framework of the porous polymers. Meanwhile, they can be easily separated and recycled from the reaction systems without losing any activity and selectivity. This excellent catalytic performance and easy recycling heterogeneous catalyst property make them be very attractive. These diphosphine ligand constructed porous polymers may provide new platforms for the hydroformylation of olefins in the future.
The goal of our paper is to improve the accuracy of stock return forecasts by combining new technical indicators and a new two-step economic constraint forecasting model. Empirical results indicate ...the stock return forecasts generated by new technical indicators and new economic constraint forecasting model is statistically and economically significant both in-sample and out-of-sample prediction performance. In addition, the prediction performance of new technical indicators and new economic constraint forecasting model is robust for some extension and robustness analysis.
The goal of this paper is to extend the modified Hestenes-Stiefel method to solve large-scale nonlinear monotone equations. The method is presented by combining the hyperplane projection method ...(Solodov, M.V.; Svaiter, B.F. A globally convergent inexact Newton method for systems of monotone equations, in: M. Fukushima, L. Qi (Eds.)Reformulation: Nonsmooth, Piecewise Smooth, Semismooth and Smoothing Methods, Kluwer Academic Publishers. 1998, 355-369) and the modified Hestenes-Stiefel method in Dai and Wen (Dai, Z.; Wen, F. Global convergence of a modified Hestenes-Stiefel nonlinear conjugate gradient method with Armijo line search. Numer Algor. 2012, 59, 79-93). In addition, we propose a new line search for the derivative-free method. Global convergence of the proposed method is established if the system of nonlinear equations are Lipschitz continuous and monotone. Preliminary numerical results are given to test the effectiveness of the proposed method.
Porous organic polymers (POPs), which feature high surface areas and designable pore walls, have attracted much attention recently as a result of combining the advantages of both heterogeneous and ...homogeneous catalysts. Because of the diversity of chemical reactions, one could design polymer frameworks with unique functionalities used as active sites and ligands in catalysis. In the view of green chemistry, this perspective is focused mainly on rational preparation of the porous organic polymers under metal-free conditions and their applications in heterogeneous catalysis. It is observed that many POP-based heterogeneous catalysts demonstrate superior catalytic properties, even better than the homogeneous counterparts. The strategies for designing highly efficient heterogeneous catalysts are briefly assessed.
Looming perception, the ability to sense approaching objects, is crucial for the survival of humans and animals. After hundreds of millions of years of evolutionary development, biological entities ...have evolved efficient and robust looming perception visual systems. However, current artificial vision systems fall short of such capabilities. In this study, we propose a novel spiking neural network for looming perception that mimics biological vision to communicate motion information through action potentials or spikes, providing a more realistic approach than previous artificial neural networks based on sum-then-activate operations. The proposed spiking looming perception network (SLoN) comprises three core components. Neural encoding, known as phase coding, transforms video signals into spike trains, introducing the concept of phase delay to depict the spatial-temporal competition between phasic excitatory and inhibitory signals shaping looming selectivity. To align with biological substrates where visual signals are bifurcated into parallel ON/OFF channels encoding brightness increments and decrements separately to achieve specific selectivity to ON/OFF-contrast stimuli, we implement eccentric down-sampling at the entrance of ON/OFF channels, mimicking the foveal region of the mammalian receptive field with higher acuity to motion, computationally modeled with a leaky integrate-and-fire (LIF) neuronal network. The SLoN model is deliberately tested under various visual collision scenarios, ranging from synthetic to real-world stimuli. A notable achievement is that the SLoN selectively spikes for looming features concealed in visual streams against other categories of movements, including translating, receding, grating, and near misses, demonstrating robust selectivity in line with biological principles. Additionally, the efficacy of the ON/OFF channels, the phase coding with delay, and the eccentric visual processing are further investigated to demonstrate their effectiveness in looming perception. The cornerstone of this study rests upon showcasing a new paradigm for looming perception that is more biologically plausible in light of biological motion perception.
The sophisticated control of surface wettability for target-specific applications has attracted widespread interest for use in a plethora of applications. Despite the recent advances in modification ...of non-porous materials, surface wettability control of porous materials, particularly single crystalline, remains undeveloped. Here we contribute a general method to impart amphiphobicity on single-crystalline porous materials as demonstrated by chemically coating the exterior of metal-organic framework (MOF) crystals with an amphiphobic surface. As amphiphobic porous materials, the resultant MOF crystals exhibit both superhydrophobicity and oleophobicity in addition to retaining high crystallinity and intact porosity. The chemical shielding effect resulting from the amphiphobicity of the MOFs is illustrated by their performances in water/organic vapour adsorption, as well as long-term ultrastability under highly humidified CO
environments and exceptional chemical stability in acid/base aqueous solutions. Our work thereby pioneers a perspective to protect crystalline porous materials under various chemical environments for numerous applications.
Hepatitis B can cause acute or chronic liver damage due to hepatitis B virus (HBV) infection. Cirrhosis or hepatocellular carcinoma (HCC) caused by chronic HBV infection often leads to increased ...mortality. However, the gut and liver have the same embryonic origin; therefore, a close relationship must exist in terms of anatomy and function, and the gut microbiota plays an important role in host metabolic and immune modulation. It is believed that structural changes in the gut microbiota, bacterial translocation, and the resulting immune injury may affect the occurrence and development of liver inflammation caused by chronic HBV infection based on the in-depth cognition of the concept of the “gut-liver axis” and the progress in intestinal microecology. This review aims to summarize and discuss the immunologic role of the gut microbiota in chronic HBV infection.
Self-quenching and vulnerability of active sites are major issues posed for practical applications of highly efficient chiral organometallic catalysts. Here, we demonstrate an effective strategy to ...address these challenges by constructing them into homochiral porous frameworks, which renders them with extraordinary resistance against deactivation yet fully retains the intrinsic catalytic activities and selectivities under heterogeneous systems. Representatively, after partial metalation of the porous chiral phosphoramidite ligand-based frameworks (Phos-HPFs) with Rh species, the afforded catalysts exhibit dramatically enhanced durability while maintaining the activity and selectivity of the homogeneous counterparts in asymmetric hydrogenation of olefins. The rigid framework of Phos-HPFs can isolate the active sites, thus preventing the self-quenching from forming coordinatively saturated complexes, while the active sites surrounded by dense free chiral ligands in Phos-HPFs can inhibit them from decomposing into metallic particles. Our work thereby highlights the advantages of HPFs for the deployment of catalysts, which offers an opportunity for enhancing the utilization efficiency rather than merely having the benefits of easy separation and recycling of the chiral catalysts.
Abstract
Access to sustainable energy is paramount in today’s world, with a significant emphasis on solar and water-based energy sources. Herein, we develop photo-responsive ionic dye-sensitized ...covalent organic framework membranes. These innovative membranes are designed to significantly enhance selective ion transport by exploiting the intricate interplay between photons, electrons, and ions. The nanofluidic devices engineered in our study showcase exceptional cation conductivity. Additionally, they can adeptly convert light into electrical signals due to photoexcitation-triggered ion movement. Combining the effects of salinity gradients with photo-induced ion movement, the efficiency of these devices is notably amplified. Specifically, under a salinity differential of 0.5/0.01 M NaCl and light exposure, the device reaches a peak power density of 129 W m
−2
, outperforming the current market standard by approximately 26-fold. Beyond introducing the idea of photoelectric activity in ionic membranes, our research highlights a potential pathway to cater to the escalating global energy needs.
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