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1.
We describe how positive definite and conditionally negative definite functions on spheres can be used to carry out generalized interpolation on spheres. 相似文献
2.
We study point-distributions over the surface of the unit sphere in unitary space that generate quadrature rules which are
exact for spherical polynomials up to a certain bi-degree. In this first stage, we explore several different characterizations
for this type of point sets using standard tools such as, positive definiteness, reproducing kernel techniques, linearization
formulas, etc. We find bounds on the cardinality of a point-distribution, without discussing the deeper question regarding
best bounds. We include examples, construction methods and explain, via isometric embeddings from real to complex spheres,
the proper connections with the so-called spherical designs. 相似文献
3.
Francesca Loschi Marta Faggian Stefania Sut Irene Ferrarese Erica Maccari Gregorio Peron Stefano DallAcqua 《Molecules (Basel, Switzerland)》2022,27(6)
Products based on plants containing hydroxyanthracene derivatives (HADs)—such as Rheum, Cassia, and Aloe species—are widely used in food supplements or nutraceuticals due to their laxative effects. A more restricted control of HAD contents in food supplements has been implemented by EU Regulation 2021/468, in order to increase the safety of these preparations. Due to their toxicity, aloin A, aloin B, aloe emodin, emodin, and the synthetic derivative danthron have been listed as prohibited substances in food supplements, being tolerated in amounts < 1 mg kg−1 in marketed products. In this work, we report the development of a sensitive and fast LC–DAD–MS-based procedure for the determination of these five compounds in food supplements and plant materials or extracts. The entire procedure includes a simple sample preparation step, where target analytes are concentrated by means of solvent extraction and evaporative concentration (solid samples), or by lyophilisation (liquid samples). The average LOQ of 0.10 mg/L, LOD of 0.03 mg/L, accuracy, and precision with CVs below 12.72 were obtained for the studied analytes. This method is suitable for assessing the compliance of commercial products and raw materials with EU Regulation 2021/468. Furthermore, the proposed method can represent a starting point for the development of a unique and standardised analytical approach for the determination of other HADs under the attention of EU authorities. 相似文献
4.
Positivity - In this paper we consider Positive Definite functions on products $$\Omega _{2q}\times \Omega _{2p}$$ of complex spheres, and we obtain a condition, in terms of the coefficients in... 相似文献
5.
Guilherme F. de Arruda Thomas Kauê Dal’Maso Peron Marinho Gomes de Andrade Jorge Alberto Achcar Francisco Aparecido Rodrigues 《Journal of statistical physics》2013,152(3):519-533
The influence of the network structure on the emergence of collective dynamical behavior is an important topic of research that has not been fully understood yet. In the current work, it is shown how statistical regression analysis can be considered to address this issue. The regression model proposed suggests that the average shortest path length is the network property most influencing the degree of synchronization of Kuramoto oscillators. Moreover, this model revealed to be very accurate, being the predicted and measured values of synchronization highly correlated. Therefore, the regression modeling allows predicting the values of the dynamic variable in terms of network structure. 相似文献
6.
The pericenter shift of a binary system represents a suitable observable to test for possible deviations from the newtonian inverse-square law in favor of new weak interactions between macroscopic objects. We analyzed 13 years of tracking data of the LAGEOS satellites with GEODYN II software but with no models for general relativity. From the fit of LAGEOS II pericenter residuals we have been able to obtain a 99.8% agreement with the predictions of Einstein's theory. This result may be considered as a 99.8% measurement in the field of the Earth of the combination of the γ and β parameters of general relativity, and it may be used to constrain possible deviations from the inverse-square law in favor of new weak interactions parametrized by a Yukawa-like potential with strength α and range λ. We obtained |α| ? 1 × 10(-11), a huge improvement at a range of about 1 Earth radius. 相似文献
7.
Marine Elmaalouf Alexandre Da Silva Silvia Duran Cdric Tard Miguel Comesaa-Hermo Sarra Gam-Derouich Valrie Briois Damien Alloyeau Marion Giraud Jean-Yves Piquemal Jennifer Peron 《Chemical science》2022,13(40):11807
Highly porous iridium oxide structures are particularly well-suited for the preparation of porous catalyst layers needed in proton exchange membrane water electrolyzers. Herein, we report the formation of iridium oxide nanostructured cages, via a water-based process performed at room temperature, using cheap Cu2O cubes as the template. In this synthetic approach, based on Pearson''s hard and soft acid–base theory, the replacement of the Cu2O core by an iridium shell is permitted by the difference in hardness/softness of cations and anions of the two reactants Cu2O and IrCl3. Calcination followed by acid leaching allow the removal of residual copper oxide cores and leave IrO2 hierarchical porous structures with outstanding activity toward the oxygen evolution reaction. Fundamental understanding of the reaction steps and identification of the intermediates are permitted by coupling a set of ex situ and in situ techniques including operando time-resolved X-ray absorption spectroscopy during the synthesis.Hierarchical IrO2 nanocages, easily synthesized in water at room temperature, are extremely active towards the oxygen evolution reaction. The formation mechanism is based on the difference in softness/hardness of the ions involved in the reaction. 相似文献
8.
Irradiation of complexes {PtCl2(olefine)(amine)} leads to the departure of the olefinic ligand forming a dimeric compound {PtCl2(amine)}2 which has a trans configuration. The same behaviour is observed at different irradiation wavelengths, with variation of the nature of the coordinated olefin and with a cis or trans configuration of the starting compound. Experimental results show that the primary photochemical reaction pathway arises probably via a (d → π★ C2H4) charge transfer existed state. A simultaneous cis → trans photoisomerization is observed in the case of the cis complexes. 相似文献
9.
Hong Phong Duong Dr. Jose Guillermo Rivera de la Cruz Dr. Ngoc-Huan Tran Jacques Louis Dr. Sandrine Zanna Dr. David Portehault Dr. Andrea Zitolo Dr. Michael Walls Dr. Deizi Vanessa Peron Dr. Moritz W. Schreiber Prof. Nicolas Menguy Prof. Marc Fontecave 《Angewandte Chemie (International ed. in English)》2023,62(49):e202310788
The need of carbon sources for the chemical industry, alternative to fossil sources, has pointed to CO2 as a possible feedstock. While CO2 electroreduction (CO2R) allows production of interesting organic compounds, it suffers from large carbon losses, mainly due to carbonate formation. This is why, quite recently, tandem CO2R, a two-step process, with first CO2R to CO using a solid oxide electrolysis cell followed by CO electroreduction (COR), has been considered, since no carbon is lost as carbonate in either step. Here we report a novel copper-based catalyst, silver-doped copper nitride, with record selectivity for formation of propanol (Faradaic efficiency: 45 %), an industrially relevant compound, from CO electroreduction in gas-fed flow cells. Selective propanol formation occurs at metallic copper atoms derived from copper nitride and is promoted by silver doping as shown experimentally and computationally. In addition, the selectivity for C2+ liquid products (Faradaic efficiency: 80 %) is among the highest reported so far. These findings open new perspectives regarding the design of catalysts for production of C3 compounds from CO2. 相似文献
10.
Financial markets can be viewed as a highly complex evolving system that is very sensitive to economic instabilities. The complex organization of the market can be represented in a suitable fashion in terms of complex networks, which can be constructed from stock prices such that each pair of stocks is connected by a weighted edge that encodes the distance between them. In this work, we propose an approach to analyze the topological and dynamic evolution of financial networks based on the stock correlation matrices. An entropy-related measurement is adopted to quantify the robustness of the evolving financial market organization. It is verified that the network topological organization suffers strong variation during financial instabilities and the networks in such periods become less robust. A statistical robust regression model is proposed to quantity the relationship between the network structure and resilience. The obtained coefficients of such model indicate that the average shortest path length is the measurement most related to network resilience coefficient. This result indicates that a collective behavior is observed between stocks during financial crisis. More specifically, stocks tend to synchronize their price evolution, leading to a high correlation between pair of stock prices, which contributes to the increase in distance between them and, consequently, decrease the network resilience. 相似文献