Nature of the structural transformations in B2O3 glass under high pressure

We study high-pressure polyamorphism of B2O3 glass using x-ray diffraction up to 10 GPa in the 300-700 K temperature range, in situ volumetric measurements up to 9 GPa, and first-principles simulations. Under pressure, glass undergoes two-stage transformations including a gradual increase of the first B-O (O-B) coordination numbers above 5 GPa. The fraction of boron atoms in the fourfold-coordinated state at P<10 GPa is smaller than was assumed from inelastic x-ray scattering spectroscopy data, but is considerably larger than was previously suggested by the classical molecular dynamics simulations. The observed transformations under both compression and decompression are broad in hydrostatic conditions. On the basis of ab initio results, we also predict one more transformation to a superdense phase, in which B atoms are sixfold coordinated.     

The effect of electric vehicles on urban noise maps

The electric vehicle is the best-positioned alternative to the ICE conventional vehicle become of, among other reasons, its environment friendly properties. One of its most significant properties is its quiet electric engine which can be a good tool for decreasing noise pollution in cities.     

Measurement of relaxation times in extensional flow of weakly viscoelastic polymer solutions

The characterization of the extensional rheology of polymeric solutions is important in several applications and industrial processes. Filament stretching and capillary breakup rheometers have been developed to characterize the extensional properties of polymeric solutions, mostly for high-viscosity fluids. However, for low concentration polymer solutions, the measurements are difficult using available devices, in terms of the minimum viscosity and relaxation times that can be measured accurately. In addition, when the slow retraction method is used, solvent evaporation can affect the measurements for volatile solvents. In this work, a new setup was tested for filament breakup experiments using the slow retraction method, high-speed imaging techniques, and an immiscible oil bath to reduce solvent evaporation and facilitate particle tracking in the thinning filament. Extensional relaxation times above around 100 μs were measured with the device for dilute and semi-dilute polymer solutions. Particle tracking velocimetry was also used to measure the velocity in the filament and the corresponding elongation rate, and to compare with the values obtained from the measured exponential decay of the filament diameter.     

Particle Size Distribution of Nanospheres by Monte Carlo Fitting of Small Angle X‐Ray Scattering Curves

A method for recovering the size distribution of spherical particles from small angle scattering data by using a Monte Carlo interference function fitting algorithm is presented. The method is based on the direct simulation of the small angle scattering data upon the assumption of non‐interacting hard sphere ensembles (“dilute” solution approximation). The algorithm for retrieving the particle size distribution does not require any additional parameters apart from the input of the scattering data. The fitting strategy necessarily implies positive particle size distributions, while preserving the advantage of the indirect transformation method for data desmearing. Furthermore, the present approach does not use any regularisation procedures of the best fit solution and favours smooth particle size distributions. The Monte Carlo procedure has been tested against several simulated cases with various types of mono‐ and bi‐modal size distributions and different noise levels. In the special case of non‐interacting spheres, the Monte Carlo fitting algorithm had the same retrieving ability as the well assessed indirect transformation, structure interference and maximum entropy methods. Finally, the algorithm was applied to retrieve the distribution of spherical nanopowders produced by gas‐to‐particle conversion both as free powder and as reinforcing second‐phase agent in polymer nanocomposites.     

New Models to Predict the Acute and Chronic Toxicities of Representative Species of the Main Trophic Levels of Aquatic Environments

To assess the impact of chemicals on an aquatic environment, toxicological data for three trophic levels are needed to address the chronic and acute toxicities. The use of non-testing methods, such as predictive computational models, was proposed to avoid or reduce the need for animal models and speed up the process when there are many substances to be tested. We developed predictive models for Raphidocelis subcapitata, Daphnia magna, and fish for acute and chronic toxicities. The random forest machine learning approach gave the best results. The models gave good statistical quality for all endpoints. These models are freely available for use as individual models in the VEGA platform and for prioritization in JANUS software.     

Analytical solution for a class of learning by doing models with multiplicative uncertainty

We find the closed form optimal solution for a class of learning by doing models, where multiplicative uncertainty is introduced in a piecewise linear cost reduction function. Previous literature does not find the closed form optimal solution for these models. We consider a monopolist, facing a linear demand function. The optimal policy for the resulting problem is shown to be piecewise linear and continuous. The optimal output increases with unit cost for certain values of the latter. Numerical examples are provided.     

Experimental and theoretical structural study of 2‐pyridyl‐ and 4‐hydroxyphenyl‐1,4‐dihydropyridine derivatives

A series of substituted 1,4‐dihydropyridines (1,4‐DHPs) has been synthesised following the well‐known Hantzsch's procedure for symmetrical 1,4‐DHP. The structures of these compounds have been thoroughly studied by X‐ray crystallographic analysis and semiempirical (AMI) calculations. A good agreement is found between the theoretical and experimental results. In all cases, the most stable conformation fulfils all the requirements needed for exhibiting an antagonist calcium effect.     

Icosahedral hybrid orbitals

A set of twelve equivalent icosahedral hybrid orbitals pointing from the centre to the corners of a regular icosahedron has been obtained. Such hybrids can be used to explain the geometry of twelve-coordinate complexes of a rare-earth atom. Using group theoretical considerations, it is shown that these hybrids can be constructed by linear combination of one s, three p, five d and three f-orbitals. Bearing in mind that the twelve hybrids have identical shape but are oriented differently in space, their mathematical expressions have been obtained by applying geometrical transformations to the sp³d⁵f³ hybrid pointing along the positive z-axis. In order to obtain elegant mathematical expressions, the x, y and z axes have been chosen to be coincident with three orthogonal binary axes of the icosahedron.     

Exothermal Process in Miscible Polylactide/Poly(vinyl phenol) Blends: Mixing Enthalpy or Chemical Reaction?

Summary: In a previous paper (Macromolecules, 2005 , 38, 9221), the enthalpy of mixing in poly(DL ‐lactide) /poly(vinyl phenol) blends was directly measured by DSC. The first DSC scan for solution/precipitation blends showed phase separation, but miscibility was observed in the second DSC scan. Hence, miscibility was achieved after thermal treatment, an unusual behavior in polymer blend current research. However, the exothermal event observed during the first heating scan could also be the result of a chemical reaction. In this work, a new research study conducted to elucidate the nature of the exothermal heat observed in PDLA/PVPh during the first DSC heating scan. Since the single‐phase PDLLA/PVPh blend obtained after thermal treatment can be redissolved and reprecipitated, results obtained in the consecutive DSC scan prove that the process is completely reversible. Furthermore, GPC and ¹³C NMR results provide evidence that there is no change in the chemical structure of the studied polymers before and after the thermal treatment, which evidences the absence of transesterification reactions. Therefore, it can be concluded that the exothermal heat is the result of a mixing process, and miscibility is a consequence of specific interactions.

New structure expected for transesterfication reactions.     

Systematic optimization of the analysis of wine bouquet components by solid-phase microextraction

The extraction, identification, and quantification of wine aroma compounds are preliminary steps required for further investigation of wine quality, i.e. determination of the varieties of grapes used, the production process, and the origin and age of the wine. This paper deals with the optimization of solid-phase microextraction for the determination of compounds which produce wine bouquet. Optimum operating conditions have been determined to obtain high reproducibility at low cost and with low time-consumption. Several factors influencing the equilibrium of the aroma compounds between the sample and the fiber must be taken into account, including length of contact time between the two phases involved, speed of agitation of the sample, the matrix in which the process takes place, and, furthermore, the place, duration, and temperature of desorption in the injector of the chromatograph.