3,776 research outputs found
Seismic Illumination Analysis with One-Way Wave Propagators Coupled with Reflection/Transmission Coefficients in 3D Complex Media
Tail dependence structure and extreme risk spillover effects between the international agricultural futures and spot markets
This paper combines the Copula-CoVaR approach with the ARMA-GARCH-skewed
Student-t model to investigate the tail dependence structure and extreme risk
spillover effects between the international agricultural futures and spot
markets, taking four main agricultural commodities, namely soybean, maize,
wheat, and rice as examples. The empirical results indicate that the tail
dependence structures for the four futures-spot pairs are quite different, and
each of them exhibits a certain degree of asymmetry. In addition, the futures
market for each agricultural commodity has significant and robust extreme
downside and upside risk spillover effects on the spot market, and the downside
risk spillover effects for both soybeans and maize are significantly stronger
than their corresponding upside risk spillover effects, while there is no
significant strength difference between the two risk spillover effects for
wheat, and rice. This study provides a theoretical basis for strengthening
global food cooperation and maintaining global food security, and has practical
significance for investors to use agricultural commodities for risk management
and portfolio optimization.Comment: 37 pages, 7 figure
Enantioselective Organocatalytic Four-Atom Ring Expansion of Cyclobutanones: Synthesis of Benzazocinones
International audienceAn enantioselective Michael addition-four-atom ring expansion cascade reaction involving cyclobutanones activated by a N-aryl secondary amide group and ortho-amino nitrostyrenes has been developed for the preparation of functionalized eight-membered benzolactams using bifunc-tional aminocatalysts. Taking advantage of the secondary amide activating group, the eight-membered cyclic products could be further rearranged into their six-membered isomers having a glutarimide core under base catalysis conditions without erosion of optical purity, featuring an overall ring expansion-ring contraction strategy
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Water-Soluble Flexible Organic Frameworks That Include and Deliver Proteins.
Four water-soluble hydrazone-based three-dimensional (3D) flexible organic frameworks FOF-1-4 have been synthesized from a semirigid tetracationic tetraaldehyde and four flexible dihydrazides. 1H NMR spectroscopy indicated the quantitative formation of FOF-1-4 in D2O, while dynamic light scattering experiments revealed that, depending on the concentration, these porous frameworks display hydrodynamic diameters ranging from 50 to 120 nm. The porosity of the frameworks is confirmed by ethanol vapor adsorption experiments of the solid samples as well as the high loading capacity for a 2.3 nm porphyrin guest in water. The new water-soluble frameworks exhibit low cytotoxicity and form inherent pores with diameters of 5.3 or 6.7 nm, allowing rapid inclusion of proteins such as bovine serum albumin and green and orange fluorescent proteins, and efficient delivery of the proteins into normal and cancer cells. Flow cytometric analysis reveals percentages of the delivered cells up to 99.8%
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