Influence of the processing conditions and chemical environment on the crystal structures and phonon modes of lanthanide orthotantalates

Lanthanide orthotantalates RETaO(4) (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were synthesized by solid-state reaction in optimized conditions of temperature (1300 °C) and time (up to 14 h) to yield crystalline materials. The crystal structures of the obtained compounds were investigated by X-ray diffraction and Raman scattering. All the samples exhibited monoclinic structures, but with different arrangements as a function of the ionic radius of the rare-earth metal occupying the A-site. For compounds with the largest ionic radii (La-Pr), the ceramics crystallized in the monoclinic structure, P2(1)/c (C(2h)(5), #14, Z = 4), while the compounds with intermediate ionic radii (Nd-Tb) exhibited the fergusonite M-type structure, I2/a (C(2h)(6), #15, Z = 4). Samples with the smallest ionic radii (Dy-Lu) presented the fergusonite M'-type structure, P2/a (C(2h)(4), #13, Z = 2). These last two groups of compounds exhibited phase transitions, which can be related to the processing temperature. The compounds belonging to the M-type structure are stable at high temperatures, whilst materials belonging to the M'-type structure are stable at low temperatures. The results from XRD and Raman scattering allows us to understand the differences between these two structures in terms of the vibrational-active modes assigned to each space group. Also, the Raman patterns in addition to group-theory calculations for this complete lanthanide series were reported for the first time. The experimental results are in perfect agreement with theoretical calculations: samples with P2(1)/c (#14) structure showed 36 Raman-active modes, while both I2/a (#15) and P2/a (#13) structures exhibited 18 Raman modes.     

Synthesis, molecular properties prediction, and anti-staphylococcal activity of N-acylhydrazones and new 1,3,4-oxadiazole derivatives

Five new 1-(2-(5-nitrofuran-2-yl)-5-(aryl)-1,3,4-oxadiazol-3-(2H)-yl) ethanone compounds 5a-e were synthesized by cyclization of N-acylhydrazones 4a-e with acetic anhydride under reflux conditions. Their structures were fully characterized by IR, 1H-NMR, and 13C-NMR. Furthermore, evaluations of the antibacterial activity of the 1,3,4-oxadiazoles 5a-e and N-acylhydrazones 4a-e showed strong activity against several strains of Staphylococcus aureus, with MICs between 4 μg/mL to 32 μg/mL. In silico studies of the parameters of Lipinski's Rule of Five, as well as the topological polar surface area (TPSA), absorption percentage (% ABS), drug likeness and drug score indicate that these compounds, especially 4a and 5d, have potential to be new drug candidates.     

Characterization of the Quasi-Stationary State of an Impurity Driven by Monochromatic Light I: The Effective Theory

We consider an impurity (N-level atom) driven by monochromatic light in a host environment which is a fermionic thermal reservoir. The external light source is a time-periodic perturbation of the atomic Hamiltonian stimulating transitions between two atomic energy levels E ₁ and E _N and thus acts as an optical pump. The purpose of the present work is the analysis of the effective atomic dynamics resulting from the full microscopic time-evolution of the compound system. We prove, in particular, that the atomic dynamics of population relaxes for large times to a quasi-stationary state, that is, a stationary state up to small oscillations driven by the external light source. This state turns out to be uniquely determined by a balance condition. The latter is related to “generalized Einstein relations” of spontaneous/stimulated emission/absorption rates, which are conceptually similar to the phenomenological relations derived by Einstein in 1916. As an application we show from quantum mechanical first principles how an inversion of population of energy levels of an impurity in a crystal can appear. Our results are based on the spectral analysis of the generator of the evolution semigroup related to a non-autonomous Cauchy problem effectively describing the atomic dynamics.     

Okra as a drag reducer for high Reynolds numbers water flows

The capability of a mixture of okra fiber and mucilage as drag reducer in high Reynolds number flows through a pipeline, in which the flux is maintained by a centrifugal pump with controlled rotation, is analyzed. A DR close to the maximum drag reduction asymptote, which is obtained for polymeric additives, was achieved when concentrations around 1600 ppm were used. The loss of efficiency of the solution over the number of passes through the system was almost the same of that observed for rigid materials like Xanthan Gum and Guar Gum, which suggest that the main cause of a decreasing drag reduction is the de-aggregation instead of mechanical degradation, commonly observed in flexible polymers. As expected, the material degrades biologically, but it seems that it is not a great problem for open systems, since such a degradation is perceptible only after 24 h. We strongly believe that this new bio-drag reducer can be an alternative to synthetic polymers or other biopolymers, since it is extremely cheap and easy to be obtained.     

AC-Conductivity Measure from Heat Production of Free Fermions in Disordered Media

We extend (Bru et al. in J Math Phys 56:051901-1-51, 2015) in order to study the linear response of free fermions on the lattice within a (independently and identically distributed) random potential to a macroscopic electric field that is time- and space-dependent. We obtain the notion of a macroscopic AC-conductivity measure which only results from the second principle of thermodynamics. The latter corresponds here to the positivity of the heat production for cyclic processes on equilibrium states. Its Fourier transform is a continuous bounded function which is naturally called (macroscopic) conductivity. We additionally derive Green–Kubo relations involving time-correlations of bosonic fields coming from current fluctuations in the system. This is reminiscent of non-commutative central limit theorems.     

Thermal analysis of salts from 4-nitrophenol and aliphatic amines

In this work, the thermodynamic performance of a single slope solar still with cotton cloth energy storage medium was compared with a simple solar still without energy storage. Two solar stills with similar dimensions (one with cotton cloth energy storage and another without energy storage) were fabricated and investigated its performance under the hot humid climatic conditions of Chennai in India during the summer months of 2017. The performance was evaluated in terms of energy and exergy analysis based on first and second law of thermodynamics, respectively, for 2 mm, 4 mm, 6 mm and 8 mm cotton cloth thickness. The results showed that the maximum energy and exergy efficiency of a solar still was observed to be 23.8% and 2.6%, respectively, for 6 mm cotton cloth thickness. The results confirmed that the cotton cloth regenerative medium has enhanced the still productivity by about 24.1% when compared to the solar still without heat storage.

     

Interface thickness of the incompatible polymer system PS/PnBMA as measured by neutron reflectometry and ellipsometry

The techniques of neutron reflectometry and spectroscopic ellipsometry are compared as methods to measure the interface width between immiscible polymers. The interface thickness of the incompatible polymer system of polystyrene (PS) and polyn-butyl methacrylate) (PnBMA) is determined by neutron reflectrometry to (6.4±0.2) nm and (8.6±0.2) nm at temperatures of 120 and 156°C, respectively. Some emphasis is put on the measurement of those values also by spectroscopic ellipsometry using the same materials. A special sample geometry is chosen for ellipsometric measurements to compensate for thickness changes of films during annealing, and the dispersions of PS and PnBMA films are determined. With respect to the determination of the interface widths, however, it turns out that in the available wavelength range of 280 to 700 nm spectroscopic ellipsometry is not sensitive enough to measure the thin interface width between PS and PnBMA films. Neutron reflectivity results obtained for PS/PnBMA are discussed with respect to the Flory-Huggins segment interaction parameter calculated within the approximations of meanfield theory.     

Haloacetylated enol ethers. 7 . Synthesis of 3-aryl-5-trihalomethylisoxazoles and 3-aryl-5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles

β-Aryl-β-methoxyvinyl trihalomethyl ketones 1a-g, 2a-g [aryl = p-YC₆H₄ where Y= H, Me, OMe, F, Cl, Br, NO₂] are cyclocondensed with hydroxylamine hydrochloride to afford the 3-aryl-5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles 3a-g, 4a-f in good yield. The dehydratation of compounds 3a-g with concentrated sulfuric acid, led the corresponding 3-aryl-5-trichloromethylisoxazoles 5a-g . An alternative one-pot procedure yields 3-aryl-5-trihalomethylisoxazoles 5,6a-g directly by cyclocondesation of 1,2a-g with hydroxylamine hydrochloride in the presence of an excess of concentrated hydrochloric acid.     

Oxazolidine copper complexes: Synthesis,characterization and superoxide dismutase activity of copper(II) complexes with oxazolidine ligands derived from hydroxyquinoline carboxaldehyde

This work describes the synthesis of copper(II) complexes, their identification using spectroscopic and electrochemical methods, structural characterization with X‐ray diffraction and density functional theory calculations (DFT), as well as their catalytic activity mimicking that of superoxide dismutase. Structural analysis revealed the formation of complexes with cyclization of ligands L1 and L2 with the formation of a heterocycle, 1,3‐oxazolidine. The DFT calculations confirmed this trend by stabilizing with lower energy. In addition, evaluations of mimetic enzymatic activity of complexes C1, C2, C3 and C4 revealed promising IC₅₀ values compared to other results seen in the literature (IC₅₀ = 0.22, 0.328, 0.55 and 0.92). Also, calf thymus DNA interactive experiments using UV–visible spectroscopy were conducted in the presence of the copper(II) complexes.