Kinetic study of carbothermal reduction of zirconia under vacuum condition

Journal of Thermal Analysis and Calorimetry - In this research, formation mechanism and kinetics of vacuum carbothermal synthesis of zirconium carbide using zirconium acetate and sucrose are...     

Identification of the Mass and Stability Interval of Strong Potential in Heavy Mesons

In this paper, we have calculated the masses of mesons containing t-quark and their spins’ coupling coefficients. This was achieved by solving Lippmann-Schwinger equation for the quark-antiquark bound state of heavy mesons in configuration space. Heavy meson masses submitted criteria for the strong nuclear interactive potential between two quarks. We investigated the stability of a few suitable potentials and offered the best of these potentials for heavy mesons.     

Sustained release drug delivery using supramolecular hydrogels of the triblock copolymer PCL–PEG–PCL and α-cyclodextrin

Supramolecular hydrogels (SMGel) have attracted much attention as a drug and gene delivery system in recent years. In this study, SMGels based on the tri-block copolymer of poly-ε-caprolactone–polyethylene glycol–poly-ε-caprolactone (PCL–PEG–PCL) and α-cyclodextrin (α-CD) were prepared and evaluated for the delivery of two model drugs, naltrexone hydrochloride and vitamin B₁₂. Tri-block copolymers were synthesized easily in 15 min by ring-opening polymerization using the microwave irradiation technique, and their structures were determined by gel permeation chromatography and nuclear magnetic resonance methods. SMGels composed of various concentrations of the copolymer and α-CD were prepared and characterized for their rheological behaviour, their gel formation time and in vitro drug release profile. The results indicated that copolymers with a PCL to PEG ratio of 1:4 are suitable for SMGel preparation. The most viscose system with good syringeability was prepared by mixing 12 % wt α-CD and 10 % wt of copolymer. The gelation was found to occur within a minute after mixing. The viscosity of the hydrogel systems was determined as a function of shear rate. Finally, in vitro B₁₂ release through the hydrogel systems was studied. Up to 80 % of Vitamin B₁₂ was released through this system during a period of 20 days. Rheological evaluation revealed that the hydrogel has shear thinning properties, and the system regained its ground rheological state in a time dependent manner. Polymer concentration did not affect the drug release profiles. Finally, it was concluded that such systems are appropriate drug delivery systems due to their ability to provide a controlled drug release profile and their shear thinning thixotropic behaviour, which makes them syringeable and injectable.     

Microwave-Induced Stereoselective Conversion of Dialkyl 2-(Imido-N-yl)-3-(triphenylphosphoranylidene) butanedioates to Electron-Poor ( Z )- N -Vinylimides in the Presence of Potassium Dihydrogen Phosphate and Sodium Dihydrogen Phosphate in Solvent-Free Conditions

Abstract

Potassium dihydrogen phosphate powder and sodium dihydrogen phosphate powder were found to catalyze stereoselective conversion of dialkyl 2-(imido-N-yl)- 3-(triphenylphosphoranylidene)butanedioates to electron-poor (Z)-N-vinylimides in solvent-free conditions under microwave irradiation in 5-6 minutes in high conversions.     

A mixed integer nonlinear programming model for the optimal repair–replacement in the firm

Optimal repair–replacement problem is an important aspect of economic decision making at the firm and aggregate levels. In this paper, we extend the continuous time optimal replacement model in the firm under technological progress by considering the possibility of repairing/replacing the machines during their lifetime period. In our model, two possible decisions can be recognized by the managers in which the machines are repaired under the efficiency condition or replaced under the availability of technological progress in the firm. As a special case, we restrict the model to the more real case in which all the growth, purchase price and repair cost functions are assumed to be in the exponential form. The solvability of the model in this case is also discussed.     

Tjon Lines and Scaling Limit in Four-Body Systems

The fixed-slope correlation between tetramer and trimer binding energies, observed by Tjon in the context of nuclear physics, is mainly a manifestation of the dominance of the two-nucleon force in the nuclear potential, which makes the four-body scale on the order of the three-body one. In a more general four-boson case, the correlation between tetramer and trimer binding energies has a non-fixed slope, which expresses the dependence on the new scale. The associated scaling function generates a family of Tjon lines. This conclusion relies on a recent study with weakly-bound four identical bosons, within a renormalized zero-range Faddeev-Yakubovsky formalism.     

Heavy Mesons Spectroscopy

In this paper, Lippmann-Schwinger equation is solved by using Martin and Cornel potentials to calculate $b\bar{c}$ energy levels. The results for some energy levels which are not observable, such as those of $t\bar{t}$ in its short half-life are also predicted. Our calculated energy levels are in good agreement with results of other groups. The stability interval for Yukawa-Linear potential is also studied by investigating the spectrum of eigenvalues.     

Understanding of the flow behaviour on a Helmholtz resonator excited by grazing flow

In this study, a large eddy simulation of the three-dimensional shear flow over a flow-excited Helmholtz resonator has been implemented. The simulations have been performed over a wide range of flow speeds to analyse the effect of the inlet flow properties on the excitation condition. For validation proposes, the results obtained from the numerical simulations have been compared with published experimental data and show that numerical modelling provides an accurate representation of the pressure fluctuations inside the cavity. The main objective of this paper is to gain an understanding of the flow features over a flow-excited Helmholtz resonator. To this end, using the numerical model, the interaction of a turbulent boundary layer with a Helmholtz resonator has been considered, and the characteristics of the flow inside the resonator and over the orifice for various flow conditions are also analysed.     

Momentum space calculations of the binding energies of argon dimer

The binding energies of argon dimer are calculated by solving the homogeneous Lippmann-Schwinger integral equation in momentum space. Our numerical analysis using two models of argon-argon interaction developed by Patkowski et al. not only confirms the eight argon dimer vibrational levels of the ground state of argon dimer (ie, for j = 0) predicted by other groups but also provides a very precise means for determining the binding energy of the ninth state which its value is a matter of discussion. Our calculations have been also extended to states with higher rotational quantum number j and we have calculated the energy of all 174 bound states for both potential models. Our numerical results for vibrational levels of the ground state of argon dimer are in excellent agreement with other theoretical calculations and available experimental data.