Lattice Boltzmann simulation of double diffusive natural convection in a square cavity with a hot square obstacle

Double diffusion convection in a cavity with a hot square obstacle inside is simulated using the lattice Boltzmann method. The results are presented for the Rayleigh numbers 104,105 and 106, the Lewis numbers 0.1, 2 and 10 and aspect ratio A(obstacle height/cavity height) of 0.2, 0.4 and 0.6 for a range of buoyancy number N = 0 to- 4 with the effect of opposing flow. The results indicate that for |N| b 1, the Nusselt and Sherwood numbers decrease as buoyancy ratio increases, while for |N| N 1, they increase with |N|. As the Lewis number increases, higher buoyancy ratio is required to overcome the thermal effects and the minimum value of the Nusselt and Sherwood numbers occur at higher buoyancy ratios. The increase in the Rayleigh or Lewis number results in the formation of the multi-cell flow in the enclosure and the vortices will vanish as |N| increases.

The Effect of Intraband Transitions on the Optical Spectra of Metallic Carbon Nanotubes

First-principles calculations of the electronic structure and linear optical properties of metallic carbon nanotubes are carried out using the full-potential linear-augmented plane-wave method.The effect of intraband transition and electric-field polarization on the optical spectra of(5,2)chiral,(15,0)zigzag,and(8,8)armchair metallic carbon nanotubes are investigated.The optical spectra are calculated for both electric-field polarizations,parallel and perpendicular to the axis of the tube.It is revealed that the optical spectra are anisotropic along these two polarizations.For the parallel polarization to the tube axis,adding the intraband transition contributions shows that the dielectric function has singularity at zero frequency due to the screening effect in metallic carbon nanotubes.

Motion of a Nonrelativistic Quantum Particle in Non-commutative Phase Space

The equation governing the motion of a quantum particle is considered in nonrelativistic non-commutative phase space. For this aim, we first study new Poisson brackets in non-commutative phase space and obtain the modified equations of motion. Next, using novel transformations, we solve the equation of motion and report the exact analytical solutions.

Calculating Binding Energy for Odd Isotopes of Beryllium （7 ≤ A ≤ 13）

In this article, we present exact solution of the Schr6dinger equation （for an N-identical body-force） for odd-A isotopes of Beryllium in the presence of Yukawa potential by Nikiforov-Uvarov （NU） method. The NU method can be used to solve second order differential equation. By this method, we find the wave equation and binding energy. Numerical results of binding energy are presented and show that these results are in good agreement with experimental values.

Differentiated Use of the Cross-Lingual Strategy in Foreign Language Teaching： A Grounded Theory

Despite its potential in foreign language education, the cross-lingual strategy has been marginalized and stigmatized in many EFL contexts including language education in private language schools of Iran. This study aims to uncover the facilitative role of the cross-lingual strategy in foreign language instruction by theorizing experienced language teachers＇ practice. To this end, some experienced teachers were selected in line with the sampling procedures of Grounded Theory from famous English language institutes of Tehran, the capital city of lran. Iterative data collection and analysis revealed that first language use can be differentiated based on learners＇ level of proficiency. For the beginners, it can be used to present classroom management rules, provide learners with the necessary classroom language and establish rapport. Similarly, at intermediate level LI can be used to check mastery over the teaching points, give vocabulary equivalents, and explain writing rules. As for advanced learners, it can be used to explain the subtleties of grammar and provide learners with ideas to participate in classroom discussion and text processing.

Investigating the first-order flotation kinetics models for Sarcheshmeh copper sulfide ore

This study was performed in two phases of work.In the first stage,four conventional first-order flotation kinetics models were fitted to the measured recoveries data and the best model were selected.In the second stage,influence of pH,solid concentration,water chemistry and the amount of collector dosage were investigated on kinetics parameters including flotation rate constant and ultimate recovery.The results indicated that that perfectly mixed reactor model and Kelsall model gave the best and the weakest fit to the experimental data,respectively.It was observed that flotation rate constant and ultimate recovery were strongly affected by chemical factors investigated especially water quality.The flotation rate constant decreased with increasing the solids content,while ultimate recovery increased to certain value and thereafter reduced.It was also found that the most values of flotation rate constant and ultimate recovery obtained in dosage of collector are 30 and 40 g/t,respectively.

Nonrelativistic Shannon information entropy for Kratzer potential

The Shannon information entropy is investigated within the nonrelativistic framework. The Kratzer potential is con- sidered as the interaction and the problem is solved in a quasi-exact analytical manner to discuss the ground and first excited states. Some interesting features of the information entropy densities as well as the probability densities are demonstrated. The Bialynicki-Birula-Mycielski inequality is also tested and found to hold for these cases.

Polythiophene encapsulated inside(13, 0) CNT: A nano-hybrid system

We present a first-principles calculation on the electronic and optical properties of a hybrid nanotube system consisting of a （13, 0） single-walled carbon nanotube encapsulated by polythiophene. This hybrid-system represents a complete new type of matter and is known as the peapod system. We analyze bow the polythiophene changes the electronic and optical properties of the nanotube. In particular, we examine new features in the dielectric function due to the transitions between the states of the polymer and the nanotube. The electronic structure of the combined system appears to be a simple superposition of the individual constituents. The density functional theory calculations demonstrate van der Waals interaction as the bonding mechanism between the tube and the encapsulated molecule.

Some Generalization for an Operator Which Preserving Inequalities Between Polynomials

For a polynomial p（z） of degree n which has no zeros in ｜z｜ 〈 1, Dewan et al., （K. K. Dewan and Sunil Hans, Generalization of certain well known polynomial inequalities, J. Math. Anal. Appl., 363 （2010）, 38-41） establishedfor any complex number β with ｜β｜≤ and｜z｜ = 1. In this paper we consider the operator B, which carries a polynomial p（z） into

Foreign Language Teacher Recruitment： Theoretical Perspectives and Empirical Findings

In some contexts such as private language schools of Iran language teachers are recruited mainly on the basis of their speaking fluency and in other EFL contexts they are recruited simply because they are native speakers. Moreover, previous studies mainly focus on comparing the effectiveness of native and non-native language teachers by exploring learners＇ and teachers＇ perceptions of native and non-native language teachers. Since recruitment criteria are theoretically unjustified and the results of previous studies are subjective and inconclusive, this study aims at making a case in the opposite direction. That is, the researchers argue that there should be： （1） a shift away from recruiting language teachers on the basis of their speaking fluency and native language background towards hiring language teachers on the basis of their professional performance in the language classroom; （2） a shift away from exploring learners＇ and teachers＇ perceptions of native and non-native teachers towards studying the effect of teachers＇ native language on learners＇ proficiency, accuracy, fluency, and achievement. To pave the way for these shifts, this study first reviews the theoretical perspectives and empirical findings concerning effective language teachers and then draws conclusions and implications which help interested stakeholders, i.e., supervisors, make informed decisions when they recruit language teachers.

Mineral Chemistry and Magmatic Differentiation Evidences in the Neshveh Intrusion (NW Saveh, Central Iran)

Neshveh intrusion which is located in the NW of Saveh City is a part of Sahand-Bazman magmatic arc within the Central Iranian zone. This intrusion consists of quartz-monzogabbro, quartz-monzodiorite, granodiorite and granite that have intruded into the Eocene volcano-sedimentary rocks. This intrusion is medium to high-K calc alkaline, metaluminous, and I-type granitoid. All phases of the Neshveh granitoid are characterized by LREE-rich patterns with high LREE/HREE ratio and negative Eu anomalies. Similarity of patterns suggests a comagmatic source for these rocks and demonstrates the role of magmatic differentiation in their evolution. Clinopyroxene classified as calcic type with varying from clinoenstatite-clinofferosillite to diopside and augite from quartz-monzogabbros to quartz-monzodiorite and granodiorite. Plagioclase composition varies from bytownite and labradorite in quartz-monzogabbros to andesine in quartz-monzodiorites and oligoclase in granodiorites and granites. Core of some plagioclases in granodiorites and granites shows the calcic composition which is labradorite and andesine in granodiorite and andesine in granites. Field investigations along with petrographic and geochemical studies indicate that all phases of the Neshveh intrusion derived from a common magma source as a result of mineral differentiation. Geochemical evidences show smooth differentiation trends in which most of major elements (except Al2O3, K2O and Na2O) are negatively correlated with SiO2?and K2O, Ba, Rb, Ce, Nb, and Zr are positively correlated with SiO2. Some elements such as Na2O, Sr, Eu and Y follow curves that reflect crystal fractionation of clinopyroxene, plagioc1ase and hornblende. Furthermore, large volumes of quartz-monzogabbros compared to granites, as well as the lack of mafic enclaves in more evolved rocks, are also indicative of crystal fractionation. Clinopyroxene fractionation was the main control in the evolution of the magmas up to 55 wt% SiO2. Hornblende took over from 55 wt% SiO2, resulting in decreasing Dy/Yb with increasing silica content in the most siliceous rocks. Fractionation of opaque minerals and apatite throughout the sequence, and the continuous increase in K2O and Ba vs. SiO2?reflect the absence of significant fractionation of biotite and K-feldspar.

Preconcentration and Determination of Chromium Species Using Octadecyl Silica Membrane Disks and Flame Atomic Absorption Spectrometry

A novel and selective method for the fast determination of trace amounts of chromium species in water samples has been developed. The procedure is based on the selective formation of chromium diethyldithiocarbamate complexes at different pH in the presence of Mn（Ⅱ） as an enhancement agent of chromium signals followed by elution with organic eluents and determination by atomic flame absorption spectrometry. The maximum capacity of the employed disks was found to be （396±3） pg and （376±2） pg for Cr（Ⅲ） and Cr（Ⅵ）, respectively. The detection limit of the proposed method is 49 and 43 ng·L^-1 for Cr（Ⅲ） and Cr（Ⅵ）, respectively. The proposed method was successfully applied for determination of chromium species Cr（Ⅲ） and Cr（Ⅵ） in different water samples.

Spin and Pseudospin Symmetries of Hellmann Potential with Three Tensor Interactions Using Nikiforov–Uvarov Method

The Dirac equation with Hellmann potential is presented in the presence of Coulomb-like tensor(CLT),Yukawa-like tensor(YLT),and Hulthen-type tensor(HLT) interactions by using Nikiforov–Uvarov method. The bound state energy spectra and the radial wave functions are obtained approximately within the framework of spin and pseudospin symmetries limit. We have also reported some numerical results and figures to show the effects of the tensor interactions. Special cases of the potential are also discussed.

Two-Dimensional Linear Dependencies on the Coordinate Time-Dependent Interaction in Relativistic Non-Commutative Phase Space

In this paper, the Non-Commutative phase space and Dirac equation, time-dependent Dirac oscillator are introduced. After presenting the desire general form of a two-dimensional linear dependency on the coordinate timedependent potential, the Dirac equation is written in terms of Non-Commutative phase space parameters and solved in a general form by using Lewis–Riesenfield invariant method and the time-dependent invariant of Dirac equation with two-dimensional linear dependency on the coordinate time-dependent potential in Non-Commutative phase space has been constructed, then such latter operations are done for time-dependent Dirac oscillator. In order to solve the differential equation of wave function time evolution for Dirac equation and time-dependent Dirac oscillator which are partial differential equation some appropriate ordinary physical problems have been studied and at the end the interesting result has been achieved.

Discrete-time indirect adaptive fuzzy control for robot manipulators

Purpose–The purpose of this paper is to design a discrete indirect adaptive fuzzy controller for a robotic manipulator.This paper addresses how to overcome the approximation error of the fuzzy system and uncertainties for asymptotic tracking control of robotic manipulators.The uncertainties include parametric uncertainty,un-modeled dynamics,discretization error and external disturbances.Design/methodology/approach–The proposed controller is model-free and voltage-based in the form of discrete-time Mamdani fuzzy controller.The parameters of fuzzy controller are adaptively tuned for asymptotic tracking of a desired trajectory.A robust control term is used to compensate the approximation error of the fuzzy system.An adaptive mechanism is derived based on the stability analysis.Findings–The proposed model-free discrete control is robust against all uncertainties associated with the robot manipulator and actuators.The approximation error of the fuzzy system is well compensated to achieve asymptotic tracking of the desired trajectories.Stability analysis and simulation results show its efficiency in the tracking control.Originality/value–A novel discrete indirect adaptive fuzzy controller is designed for electrically driven robot manipulators using the voltage control strategy.The novelty of this paper is compensating the approximation error of the fuzzy system and discretizing error for asymptotic tracking of the desired trajectory.

Voltage control strategy for an uncertain mobile robot

Purpose–The uncertainty and nonlinearity are the challenging problems for the control of a nonholonomic wheeled mobile robot.To overcome these problems,many valuable methods have been proposed by using two control loops namely the kinematic control and the torque control so far.In majority of the proposed approaches the dynamics of actuators is omitted for simplicity in the control design.This drawback degrades the control performance in high-velocity tracking control.On the other hand,to guarantee stability and overcome uncertainties,the control methods become computationally extensive and may be impractical due to using all states.The purpose of this paper is to design a simple controller with guaranteed stability for overcoming the nonlinearity,uncertainty and actuator dynamics.Design/methodology/approach–The control design includes two control loops,the kinematic control loop and the novel dynamic control loop.The dynamic control loop uses the voltage control strategy instead of the torque control strategy.Feedbacks of the robot orientation,robot position,robot linear and angular velocity,and motor currents are given to the control system.Findings–To improve the precision,the dynamics of motors are taken into account.The most important advantages of the proposed control law is that it is free from the robot dynamics,thereby the controller is simple,fast response and robust with ignorable tracking error.The control approach is verified by stability analysis.Simulation results show the effectiveness of the proposed control applied on an uncertain nonholonomic wheeled mobile robot driven by permanent magnet dc motors.A comparison with an adaptive sliding-mode dynamic control approach confirms the superiority of the proposed approach in terms of precision,simplicity of design and computations.Originality/value–The originality of the paper is to present a new control design for an uncertain nonholonomic wheeled mobile robot by using voltage control strategy in replace of the torque control strategy.In addition,a novel state-space model of electrically driven nonholonomic wheeled mobile robot in the workspace is presented.