X-ray fluorescence in some rare earth and high Z elements excited by 661.6 keV γ-rays

The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm, Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of ¹³⁷Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other measured values.     

Generalized interpolation on spheres using positive definite and related functions

We describe how positive definite and conditionally negative definite functions on spheres can be used to carry out generalized interpolation on spheres.     

Exact point-distributions over the complex sphere

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.     

Characterization of Strict Positive Definiteness on products of complex spheres

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...     

The Influence of Network Properties on the Synchronization of Kuramoto Oscillators Quantified by a Bayesian Regression Analysis

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.     

Accurate measurement in the field of the earth of the general-relativistic precession of the LAGEOS II pericenter and new constraints on non-newtonian gravity

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.     

Development of an LC–DAD–MS-Based Method for the Analysis of Hydroxyanthracene Derivatives in Food Supplements and Plant Materials

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.     

Etude du comportement photochimique de complexes {PtCl2(oléfine)(amine)}, influence de la nature de l'olefine et de la configuration du complexe

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.     

Silver and Copper Nitride Cooperate for CO Electroreduction to Propanol

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.     

The structure and resilience of financial market networks

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.