Free-volume changes at nanoscale in doped polyacrylic acid studied by positron annihilation spectroscopy

Polyacrylic acid (PAA) doped with carbon black (CB), chromium oxide (Cr₂O₃) and cupferron with different wt% (0.25%, 0.50%, 0.75%, and 1%) was studied using positron annihilation lifetime (PAL) technique and Doppler broadening of annihilation radiation (DBAR). Ortho-positronium lifetime components (τ₃ and I₃) were used to estimate the nanoscale free-volume hole sizes (V_f) and its fractions (f). It was found that the hole size V_f and its fractions f as well as S-parameters decreased at high value of doping concentration due to dopants-polymer formation. These results are supported by a significant narrowing in the nanoscale free-volume hole size distributions.

The correlation between positron annihilation parameters and electric conductivity are discussed.     

Numerical investigation of corner angle and wing number effects on fluid flow characteristics of a turbulent stellar jet

In this research the fluid dynamics characteristics of a stellar turbulent jet flow is studied numerically and the results of three dimensional jet issued from a stellar nozzle are presented. A numerical method based on control volume approach with collocated grid arrangement is employed. The turbulent stresses are approximated using k–ε and k–ω models with four different inlet conditions. The velocity field is presented and the rate of decay at jet centerline is noted. Special attention is drawn on the influence of corner angle and number of wings on mixing in stellar cross section jets. Stellar jets with three; four and five wings and 15–65° corner angles are studied. Also the effect of Reynolds number (based on hydraulic diameter) as well as the inflow conditions on the evolution of the stellar jet is studied. The Numerical results show that the jet entrains more with corner angle 65° and five wings number. The jet is close to a converged state for high Reynolds numbers. Also the influence of the inflow conditions on the jet characteristics is so strong.     

How Does Tempering Affect the Local and Global Properties of Fractional Brownian Motion?

Journal of Theoretical Probability - The present paper investigates the effects of tempering the power law kernel of the moving average representation of a fractional Brownian motion (fBm) on some...     

二氧化钛纳米粒子催化合成Hantzsch酯和多氢喹啉衍生物(英文)

1,4-Dihydropyridine and polyhydroquinoline derivatives have been prepared efficiently in a one-pot synthesis via Hantzsch condensation using nanosized titanium dioxide as a heterogeneous catalyst.The present methodology offers several advantages such as excellent yields,short reaction times (30-120 min),environmentally benign,and mild reaction conditions.The catalyst can be readily separated from the reaction products and recovered in excellent purity for direct reuse.     

Tris(tetraceno)triquinacenes: Synthesis and Photophysical Properties of Threefold Linearly Extended Tribenzotriquinacenes

The linear extension of the rigid, C_3v‐symmetrical carbon framework of tribenzotriquinacene (TBTQ) along its three wings is reported. The key step of the extension procedure consists of a Diels–Alder reaction of three ortho‐quinodimethane units generated in situ at the triquinacene core. The use of 1,4‐naphthoquinone provides a facile and particularly efficient access to tris(tetraceno)‐annellated triquinacenes. The steady‐state photophysical properties of these new oligotetracenes bearing three mutually orthogonal chomophores are determined and analyzed by DFT calculations.     

Investigation of keto–enol tautomerism in tetraketonate ligands

Molecular structure, vibration analysis, and natural bond orbital study of four derivatives of tetraketonate ligand were investigated in three different solvents using density functional theory B3LYP/6-31++G** method. The solution phase studies were carried out using an Onsager model. According to the obtained results the enol form of the ligands is more stable than keto form, even in solvents with high dielectric constant such as DMSO. This result is also confirmed experimentally using NMR studies for tetraacetylethane. Their stabilities are due to the presence of hydrogen bonding in the enol tautomers. A comparison among different possible enol forms of the substituted tetraketonate ligands demonstrated that three factors control the stability of the compounds as hydrogen bonding, steric hindrance, and charge distribution. The effectiveness of each of these factors on the stability of ligands depends on the nature of the substituent attached to the ligand.     

Exact three-dimensional interface stress and electrode-effect analysis of multilayer piezoelectric transducers under torsion

In this paper, exact three-dimensional analysis for torsion of multilayer piezoelectric transducers is presented to highlight the remarkable effects of electrode and size effects on interface stresses and deformation. A generalized formulation is introduced for torsion of an arbitrarily layered cross section. In order to reach an advanced and better device, multilayer piezoelectric materials with different properties are formulated while axis of torsion and the polarization axes of each layer make different orientations with respect to each other. An exact formulation for n-layer piezoelectric device with rectangular cross section is presented to compensate considerable deviation of previous studies’ results from exact solution due to the assumption of linear distribution for the electric potential. In order to improve the performance of the transducers, being utilized in industry, several case studies are presented in order to investigate the influence of different parameters, e.g. thickness and material properties of electrodes over shear and peel stresses. Besides, a correction factor is introduced to completely compensate the effect of ignoring electrodes.     

An accurate empirical correlation for predicting natural gas compressibility factors

The compressibility factor of natural gas is an important parameter in many gas and petroleum engineering calculations. This study presents a new empirical model for quick calculation of natural gas compressibility factors. The model was derived from 5844 experimental data of compressibility factors for a range of pseudo reduced pressures from 0.01 to 15 and pseudo reduced temperatures from 1 to 3. The accuracy of the new empirical correlation has been compared with commonly used existing methods. The comparison indicates the superiority of the new empirical model over the other methods used to calculate compressibility factor of natural gas with average absolute relative deviation percent (AARD%) of 0.6535.     

Encapsulation of Pd(II) into superparamagnetic nanoparticles grafted with EDTA and their catalytic activity towards reduction of nitroarenes and Suzuki–Miyaura coupling

A robust, safe and magnetically recoverable palladium catalyst was synthesized by anchoring Pd(II) onto ethylenediaminetetraacetic acid‐coated Fe₃O₄ (Fe₃O₄@EDTA) magnetic nanoparticles. The Fe₃O₄ magnetic nanoparticle‐supported Pd(II)–EDTA complex catalyst thus obtained was characterized using scanning and transmission electron microscopies, thermogravimetric analysis, vibrating sample magnetometry, X‐ray diffraction, and inductively coupled plasma atomic emission and Fourier transform infrared spectroscopies. Fe₃O₄@EDTA–Pd(II) was screened for the Suzuki reaction and reduction of nitro compounds in water. The Pd content of the catalyst was measured to be 0.28 mmol Pd g^?1. In addition, the Fe₃O₄@EDTA–Pd catalyst can be easily separated and recovered with an external permanent magnet. The anchored solid catalyst can be recycled efficiently and reused five times with only a very slight loss of catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

A study of quasi-Gorenstein rings

This paper is devoted to study certain quasi-Gorenstein counterparts to some known properties of Gorenstein rings.