The effect of hydrostatic pressure on material parameters and electrical transport properties in bulk GaN

Experimental data for temperature dependence of electron transport properties in a bulk, low dislocation density, GaN sample at atmospheric pressure and 7.1 kbar have been presented. The data are representing a weak hydrostatic pressure dependence. Our quantitative analysis on its material parameters including: high and low dielectric constants (ε_∞,εs), longitudinal and transverse optical phonons (ωLO,ωTO), and electronic effective mass show a small fractional change of −0.12,−0.14,0.05,0.058 and 0.089 (percent/kbar), respectively. These results are confirmed by the Hall-effect data analysis on the basis of charge neutrality condition and various scattering mechanisms.     

Plasma coating of nanoparticles in the presence of an external electric field

Film deposition onto nanoparticles by low-pressure plasma in the presence of an external electric field is studied numerically. The plasma discharge fluid model along with surface deposition and heating models for nanoparticles, as well as a dynamics model considering the motion of nanoparticles, are employed for this study. The results of the simulation show that applying external field during the process increases the uniformity of the film deposited onto nanoparticles and leads to that nanoparticles grow in a spherical shape. Increase in film uniformity and particles sphericity is related to particle dynamics that is controlled by parameters of the external field like frequency and amplitude. The results of this work can be helpful to produce spherical core-shell nanoparticles in nanomaterial industry.     

Simulation of nonlinear fractional dynamics arising in the modeling of cognitive decision making using a new fractional neural network

By the rapid growth of available data, providing data-driven solutions for nonlinear (fractional) dynamical systems becomes more important than before. In this paper, a new fractional neural network model that uses fractional order of Jacobi functions as its activation functions for one of the hidden layers is proposed to approximate the solution of fractional differential equations and fractional partial differential equations arising from mathematical modeling of cognitive-decision-making processes and several other scientific subjects. This neural network uses roots of Jacobi polynomials as the training dataset, and the Levenberg-Marquardt algorithm is chosen as the optimizer. The linear and nonlinear fractional dynamics are considered as test examples showing the effectiveness and applicability of the proposed neural network. The numerical results are compared with the obtained results of some other networks and numerical approaches such as meshless methods. Numerical experiments are presented confirming that the proposed model is accurate, fast, and feasible.     

A proposed model to predict thermal conductivity ratio of Al2O3/EG nanofluid by applying least squares support vector machine (LSSVM) and genetic algorithm as a connectionist approach

In this study, a model is proposed by applying the least squares support vector machine (LSSVM). In addition, genetic algorithm is used for selection and optimization of hyperparameters that are embedded in the LSSVM model. In addition to temperature and concentration of nanoparticles, the parameters which are used in most of the modeling procedures for thermal conductivity, the effect of particle size is considered. By considering the size of nanoparticles as one of the input variables, a more comprehensive model is obtained which is applicable for wider ranges of influential factor on the thermal conductivity of the nanofluid. The coefficient of determination (R²) for the introduced model is equal to 0.9902, and the mean squared error is 8.64 × 10^?4 for the thermal conductivity ratio of Al₂O₃/EG.

     

Investigation of Brewster anomalies in one-dimensional disordered media having Lévy-type distribution

In this paper, we calculate the localization length of a TM electromagnetic wave in unitof system length versus incident angle in a disordered layered structure where therefractive index of one of its constituents follows a Lévy-type distribution with a powerexponent α.The incident angle at which the localization length takes the maximum value is called thegeneralized Brewster angle as before. However, in contrast to previous works with a weakdisorder, the wave incident at generalized Brewster angle is not always in the extendedregime. For special values of α and the frequency, the system is in a localizedstate at this angle. But, the localization length at this Brewster angle is always largerthan that at other angles. The effects of α variation on the localization length at thisBrewster angle and its position are investigated for different frequencies. Thelocalization at this angle degrades with increasing α for all frequencies. Atsome working frequencies, the generalized Brewster angle is a decreasing function ofα. However,at other frequencies, the dependence of generalized Brewster angle on α is not monotonic. Forincident angles smaller than a specific angle, the localization length increases withincreasing α.However, for incident angles larger than this specific angle, there are incident angles atwhich any increase of α leads to the decrease of localization length. Inother words, for these incident angles, the improvement of Anderson localizationsurprisingly happens with decrease of disorder strength and the refractive index contrast.     

A theoretical study on the dynamics of the gas phase reaction of NH<Subscript>2</Subscript>(<Superscript>2</Superscript>B<Subscript>1</Subscript>) with HO<Subscript>2</Subscript>(<Superscript>2</Superscript>A″)

Quasi-classical trajectory calculations and stochastic one-dimensional chemical master equation simulation methods are used to study the dynamics of the reaction of amidogen radical [NH₂(²B₁)] with hydroperoxyl radical [HO₂(²A″)] on the lowest singlet electronic state. The title complex reaction takes place on a multi-well multichannel potential energy surface consisting of three deep potential wells and one van der Waals complex. In quasi-classical trajectory calculations a new analytical potential energy surface based on CCSD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) ab initio method was driven and used to study the dynamics of the title reaction. In quasi-classical trajectory calculations, the reactive cross sections and reaction probabilities are determined for 200–2000 K relative translational energies to calculate the rate constants. The same ab initio method was used to have the necessary data for solving the one-dimensional chemical master equation to calculate the rate constants of different channels. In solving the master equation, the Lennard-Jones potential model was used to form the collision between the collider gases. The fractional populations of different intermediates and products in the early stages of the reaction were examined to determine the role of the energized intermediates and the van der Waals complex on the dynamics of the title reaction. Although the calculated total rate constants from both methods are in good agreement with the reported experimental values in the literature, the quasi-classical trajectory simulation predicts the formation of NH₂O + OH as the major channel in the title reaction in accordance with the previous studies (Sumathi and Peyerimhoff, Chem. Phys. Lett., 263:742–748, 1996), while the stochastic master equation simulation predicts the formation of HNO + H₂O as the major products.     

One‐Pot Three‐Component Synthesis of Highly Functionalized 2,3‐Dihydro‐1,3‐dioxo‐1H,5H‐pyrazolo[1,2‐a][1,2,4]triazoles

The reactive 1 : 1 zwitterionic intermediate formed by the addition of isocyanides to dialkyl acetylenedicarboxylates was trapped with 4‐arylurazoles to produce the highly functionalized pyrazolo[1,2‐a][1,2,4]triazoles 5 in good yields (Table). The structures of the products 5a – h were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR), by EI‐MS, and elemental analysis. A possible mechanism for this reaction is proposed (Scheme).     

Copper (II)-supported polyethylenimine-functionalized magnetic graphene oxide as a catalyst for the green synthesis of 2-arylquinazolin-4(3H)-ones

A novel copper (II) catalyst supported on polyethylenimine-functionalized magnetic graphene oxide (denoted Cu@PEI-MGO) has been developed and applied for the cyclization of benzylacetamide with 2-aminobenzamide to afford 2-arylquinazolin-4(3H)-ones in acetonitrile as an inexpensive, non-toxic and reusable solvent medium. Cu@PEI-MGO was characterized by transmission electron microscopy, scanning electron microscopy, thermo-gravimetric analysis, and Fourier-transform infra-red spectroscopy.     

Comparative Study of the Electromagnetic Wave Absorption Properties in (FeNi,CoNi, and FeCo)/ZnS Nanocomposites

Journal of Cluster Science - Three EM wave absorbing (FeNi, CoNi, and FeCo)/ZnS nanocomposites were synthesized by simple and successful process. By comparison, it was demonstrated that the maximum...