The structural and magnetic properties of one-step mechanochemical route synthesized La0.8Pb0.2MnO3 manganites

Mechanochemical route has been used to produce La_0.8Pb_0.2MnO₃ (LPMO) nanocrystalline samples from oxide precursors. The samples were characterized using X-ray diffraction, scanning electron microscope and AC susceptibility measurements. The results showed that it is possible to produce LPMO perovskite powders after 10 h of ball milling. The crystallite size and microstrain were estimated using Williamson-Hall equation. The results showed that the crystallite size and microstrain increase initially and then decrease by the increase of milling time. By decreasing particle size the dislocation density (strain) increases and reaches to a saturation point at a particular particle size, further particle size reduction takes place through gliding motion along grain boundaries, which leads to a reduction of the strain. The dynamic properties of 15 h ball-milled sample were investigated by AC susceptibility using the Neel-Brown and Vogel-Fulcher law for superparamagnetism. The frequency dependence of blocking temperature is well described by the Vogel-Fulcher law, and fitting the experimental data with Neel-Brown law gives unphysical value for relaxation time.     

In situ generated stabilized phosphorus ylides mediated a mild and efficient method for the preparation of some new sterically congested electron-poor N-vinylated heterocycles

Protonation of the highly reactive 1:1 intermediate produced in the reaction between triphenylphosphine and an acetylenic ester by a N-H acid (4-phenylphthalazin-1(2 H)-one, 5,5-diphenylimidazolidine-2,4-dione) leads to the formation of a vinyltriphenylphosphonium salt. The cation of the salt undergoes an addition reaction with the counter anion in CH₂Cl₂ at room temperature to yield the corresponding stabilized phosphorus ylide. Elimination of triphenylphosphine from the stabilized phosphorus ylides leads to the formation of corresponding electron-poor N-vinylated heterocycles in moderate to high yields (67–95%). The reaction is completely regio- and stereoselective.     

Fabrication and characterization of chitosan-gelatin/single-walled carbon nanotubes electrospun composite scaffolds for cartilage tissue engineering applications

Cartilage is a connective tissue with a slow healing rate due to lack in blood circulation and slow metabolism. Designing tissue engineering scaffolds modified based on its specific features can assist its natural regeneration process. In this study, the chitosan-gelatin/single-walled carbon nanotubes functionalized by COOH (SWNTs-COOH) nanocomposite scaffolds were fabricated through electrospinning. The effect of each component and different duration of cross-linking were assessed in terms of morphology, porosity, chemical structure, thermal behavior, mechanical properties, wettability, biodegradability, and in vitro cell culture study. Adding SWNTs-COOH decreased fiber diameter, water contact angle and degradation rate while increased tensile strength, hydrophilicity, stability and cell viability, due to their high intrinsic electrical conductivity, and mechanical properties and the presence of COOH functional groups in its structure. All the sample presented a porosity percentage of more than 80%, which is essential for tissue engineering scaffolds. The presence SWNTs-COOH did not have any adverse effect on cytocompatibility. The optimal cross-linking time increased the stability of the scaffolds in PBS. It can be concluded that the chitosan-gelatin/1wt% SWNTs-COOH scaffold can be appropriate for cartilage tissue engineering applications.     

Ni(II) and V(IV) Schiff base complexes derived from 2,2′-dimethylpropandiamine: the crystal structure,electrochemical properties and catalytic activities in oxidation of sulfides

Tetradentate Schiff base (H₂L) derived from 2,2′-dimethylpropandiamine and its nickel(II) and oxo-vanadium(IV) complexes (NiL, VOL) have been prepared and characterized. The crystal structure of NiL has been determined. The reported structure contains two molecules of the complex revealing slightly different conformation and the coordination sphere around nickel is distorted square planar. The electrochemical properties of the Ni and oxo-vanadium Schiff base complexes were investigated in CH₃CN by cyclic voltammetry. The catalytic activities of the complexes were studied in the oxidation of sulfides in ethanol. Under the optimized reaction conditions, in the presence of NiL, 89% and VOL, 100% conversion of methyl phenyl sulfide with 100% selectivity for sulfoxide were obtained.     

Sensitive determination of atorvastatin in human plasma by dispersive liquid–liquid microextraction and solidification of floating organic drop followed by high‐performance liquid chromatography

A novel and sensitive dispersive liquid–liquid microextraction method based on the solidification of the floating organic drop combined with high‐performance liquid chromatography and ultraviolet detection was used for the determination of atorvastatine in blood serum samples. The chromatographic separation of atorvastatin was carried out using methanol as the mobile phase organic modifier. Various parameters affecting the extraction efficiency were optimized, such as the kind and volume of extraction solvent (1‐undecanol) and disperser solvent (acetonitrile), pH, and the extraction time. The calibration curve was linear in the range of 0.2–6000 μg/L of atorvastatin (r² = 0.995) with a limit of detection of 0.07 μg/L. The relative standard deviation for 100 μg/L of atorvastatin in human plasma was 8.4% (n = 4). The recoveries of plasma samples spiked with atorvastatin were in the range of 98.8–113.8%. The obtained results showed that the proposed method is fast, simple, and reliable for the determination of very low concentrations of atorvastatin in human plasma samples.     

Metastable Kitaev Magnets

Nearly two decades ago, Alexei Kitaev proposed a model for spin-1/2 particles with bond-directional interactions on a two-dimensional honeycomb lattice which had the potential to host a quantum spin-liquid ground state. This work initiated numerous investigations to design and synthesize materials that would physically realize the Kitaev Hamiltonian. The first generation of such materials, such as Na2IrO3, α-Li2IrO3, and α-RuCl3, revealed the presence of non-Kitaev interactions such as the Heisenberg and off-diagonal exchange. Both physical pressure and chemical doping were used to tune the relative strength of the Kitaev and competing interactions; however, little progress was made towards achieving a purely Kitaev system. Here, we review the recent breakthrough in modifying Kitaev magnets via topochemical methods that has led to the second generation of Kitaev materials. We show how structural modifications due to the topotactic exchange reactions can alter the magnetic interactions in favor of a quantum spin-liquid phase.     

Thermal Analysis of Flow in a Porous Medium Over a Permeable Stretching Wall

This work presents a similarity solution for boundary layer flow through a porous medium over a stretching porous wall. Two considered wall boundary conditions are power-law distribution of either wall temperature or heat flux which are general enough to cover the isothermal and isoflux cases. In addition to momentum, both first and second laws of thermodynamics analyses of the problem are investigated. Independent numerical simulations are also performed for verification of the proposed analytical solution. The results, from the two independent approaches, are found to be in complete agreement. A comprehensive parametric study is presented and it is shown that heat transfer and entropy generation rates increase with Reynolds number, Prandtl number, and suction to the surface.     

Diminishing vortex intensity and improving heat transfer by applying magnetic field on an injectable slip microchannel containing FMWNT/water nanofluid

In this study, heat transfer and entropy generation were investigated in a microchannel containing FMWNT/water nanofluids given the slip condition. The main focus was on utilizing injection technique in the presence of the magnetic field. The injection from the upper high-temperature wall was incorporated into the flow field. Injection at high Reynolds number causes vortex formation, which ultimately reduces local heat transfer in the adjacent injection zone. By applying the magnetic field, the vortex intensity as well as boundary layer thickness was diminished which in turn improved the heat transfer. Based on numerical results, at higher nanoparticle volume fraction, the effect of the magnetic field on heat transfer enhancement was amplified. Moreover, at higher Reynolds numbers, the magnetic field efficacy is more obvious. The highest heat transfer occurred at the highest values of the Hartmann and Reynolds numbers and eventually the nanoparticle volume fraction. Owing to applying the magnetic field on the injectable microchannel containing nanofluid, heat transfer improvement can reach up to 79%. From the second law prospective, the entropy generation intensified by 82.8%.

     

Numerical investigation of the effects of inlet valve closing temperature and exhaust gas recirculation on the performance and emissions of an RCCI engine

Journal of Thermal Analysis and Calorimetry - In this paper, the effects of inlet valve closing temperature (TIVC) and exhaust gas recirculation (EGR) on the emissions and the performance of a...     

Determination of urinary methylhippuric acids using MIL-53-NH2 (Al) metal–organic framework in microextraction by packed sorbent followed by HPLC–UV analysis

For the analysis of methylhippuric acids (MHAs) in human urine samples, in this study, a new method based on the metal–organic framework (MOF) of MIL-53-NH₂ (Al) in microextraction by packed sorbent (MEPS) was developed. The synthesis of MIL-53-NH₂ (Al) was characterized by Fourier transform infrared spectra, field emission-scanning electron microscopy and X-ray diffraction. Response surface methodology was used to investigate the influences of several parameters including type and volume of elution, type of conditional solvent, sample volume and extraction cycle on MEPS efficiency. The results showed good recoveries (>94%) and excellent extraction efficiencies (>96%) at three different concentrations of 50, 500 and 1500 μg ml⁻¹ (as low, mid and high concentrations, respectively) of MHA isomers. Calibration curves of MHAs were linear over the concentration range of 1–1500 μg ml⁻¹, with high correlation coefficients (r ≥ 0.998). The reproducibility of the proposed MIL-53-MEPS for determination of three isomers of MHA was found to be in the range of 3.5–11.1%. After optimization of the proposed technique, it was used to analyze MHAs in urine samples of workers exposed to xylenes in a petrochemical plant in Asalouyah, Iran. The results indicated that the MOF–MEPS method was selective, sensitive, rapid and efficient for the extraction of urinary MHAs. The technique is also environmentally friendly and inexpensive, and the MOF sorbent is reusable.