Sharif Digital Repository

This study aims to identify the learning orientations and language learning strategies of the students, to determine whether there are any significant differences in the motivational orientations and language learning strategies preferences between male and female learners, and investigate whether there is a relationship between students' motivational orientations and strategy preferences. A total of 206 intermediate level students who studied in English in private language institutes were asked to complete two questionnaires. One was used to identify students' motivational orientations and the other was used to identify students' learning strategies. Statistical analyses demonstrated that... 

In the present study, we aimed to quantify the effects of COVID-19 restrictions and speech treatment approaches during lockdowns on autistic children using CBCL and neuro-fuzzy artificial intelligence method. In this regard, a survey including CBCL questionnaire is prepared using online forms. In total, 87 children with diagnosed Autism spectrum disorders (ASD) participated in the survey. The influences of three treatment approaches of in-person, telehealth and public services along with no-treatment condition during lockdown were the main factors of the investigation. The main output factors were internalized and externalized problems in general and their eight subcategory syndromes. We... 

This research investigates the effect of process parameters on the geometry and properties of In625 parts, manufactured by the direct laser metal deposition (DLMD) process. For this purpose, eight parts, consisting of 5 layers on top of each other, were manufactured, and the effect of laser power, laser focal plane position, and scanning speed on the height, width, and surface smoothness of each of them was investigated using design of experiment (DOE). The experimental results showed that the height of the parts manufactured by 800 W/mm and 200 W/mm of energy density is 3.69 mm and 6.12 mm, respectively. The thickness of the parts manufactured by 80 W/mm and 200 W/mm of energy density is... 

Three ternary copper(II) complexes [Cu(5-bromo-salTyr)(bipy)]·1/ 2CH3OH (1), [Cu(5-bromo-salLue)(bipy)]·CH3OH (2) and [Cu(5-bromo-salTrp)(bipy)]·3CH3OH (3) (where 5-bromo-salTyr, 5-bromo-salLue and 5-bromo-salTrp are tridentate Schiff base ligands derived from the condensation of 5-bromosalicylaldehyde with tyrosine, leucine and tryptophan, respectively, and bipy is 2,2′-bipyridine) have been prepared and characterized by elemental analysis, electronic, IR spectroscopies, magnetic measurement and cyclic voltammetry. The complexes, 1 and 3 have been also structurally characterized by X-ray diffraction technique. Crystal structures of 1 and 3 complexes displayed a distorted square-pyramidal... 

Conditions for an efficient ligand-free Heck C-C coupling reaction of aryl iodides and bromides with terminal olefins under aerobic conditions have been developed. Critical to the success of this new protocol is the use of palladium acetate as an extremely active catalyst for the Heck reaction in water and aqueous media. Both the base and the solvent were found to have a fundamental influence on the efficiency of the reaction, with K2CO3 and a mixture of (2:1) H2O/DMSO being the optimal base and solvent, respectively  

In this study, the existence of a sinusoidal splitter on the formation and distribution of hydrogen and air co-jets are investigated in a dual-combustion ramjet engine. The main scope of this research is to analyze the comprehensive flow structure and flame features directly downstream of the sinusoidal splitter. In this work, shockwave/shear-layer interactions behind the sinusoidal splitter are thoroughly studied through a computational fluid dynamic approach. Two different splitter profiles are compared with a simple splitter to demonstrate the main effects of multi shock wave interactions on fuel distribution and penetrations. To simulate co-air jet, Reynolds Average Navier-Stocks... 

In this study, the artificial neural network (ANN) was used for the prediction of WDT. The inputs to network are molar mass and pressure, and the output is WDT at each input. A two-layer network with different hidden neurons and different learning algorithms such as LM, SCG, GDA and BR were examined. The network with 16 hidden neurons and Levenberg-Marquardt (LM) train function showed the best results in comparison with the other networks. Also, the predicted results of this network were compared with the thermodynamic models and better accordance with experimental data for ANN was concluded  

A new manganese(III) complex [(N-O)2Mn(OAc)] was synthesized using 2-(2'-hydroxyphenyl)-5,6-dihydro-1,3-oxazine (N-O) as a bidentate O, N donor. The complex has been characterized by elemental analysis, IR, UV-vis spectroscopy, and X-ray structure analysis. Oxidation of sulfides and epoxidation of olefins, respectively, to their corresponding sulfoxides and epoxides were conducted by this catalyst using urea hydrogen peroxide as oxidant at room temperature under air. The catalyst is efficient in oxidation reactions giving high yields and selectivities  

In this study, 40% CaO/γ-Al2O3 catalyst was used for biodiesel production from corn oil. A transesterification reaction was done for 5h at a temperature of 65°C in the presence of corn oil, methanol (methanol to oil molar ratio of 12:1), and CaO/γ-Al2O3 catalyst (0.06g/g (6wt%)). Catalyst used in this study was synthesized using the sol-gel method. In this method, two parameters of gelation temperature and nitric acid concentration were used as variables in the catalyst synthesis step, and experiments were designed using central composite design (CCD). The results indicate that the optimal point is achieved at a gelation temperature of 70°C and... 

Transesterification reaction was performed in the presence of soybean oil, methanol, and Demineralized water plant sedimentation catalyst at 60°C for 8 h in this study. Central composite design method was used to study the effect of catalyst concentration and methanol to oil molar ratio on purity and yield of produced biodiesel. The results showed catalyst concentration of 9.08 wt% and methanol to oil molar ratio of 22.49 as the optimum condition in which the values of purity and yield of the produced biodiesel in the second-order models were 99.89% and 81.83%, respectively. Experiments are in good agreement with the mentioned values as corresponded values are 99.95% and 86.68%,... 

Cancer is a deadly disease that has long plagued humans and has become more prevalent in recent years. The common treatment modalities for this disease have always faced many problems and complications, and this has led to the discovery of strategies for cancer diagnosis and treatment. The use of magnetic nanoparticles in the past two decades has had a significant impact on this. One of the objectives of the present study is to introduce the special properties of these nanoparticles and how they are structured to load and transport drugs to tumors. In this study, iron oxide (Fe3O4) nanoparticles with 6 nm sizes were coated with hyperbranched polyglycerol (HPG) and folic acid (FA). The... 

Under different loading conditions, the over-head cranes may experience a wide range of model parameters variation. A robust control strategy is developed to achieve the high positioning accuracy, short transportation time and suppression of swing angle for an uncertain over-head crane system. Over-head crane is modeled as a three degrees of freedom system and control problem is investigated for two cases: a system with a single control input (the force on trolley) and a system with two control inputs (the force on trolley and the torque on lifter). Regulator and observer systems are designed. To achieve the tracking objectives, an optimal robust controller is designed based on μ-synthesis... 

Due to international competition and strict limitations of standards regarding the noise level, investigation of gear vibration is of great importance. In this paper, nonlinear oscillations of spur gear pairs including the backlash nonlinearity is studied. Dynamic system is described through the classical single degree of freedom (SDOF) model in terms of dynamic transmission error (DTE). Using multiple scale method, forced vibration responses of the gear system including primary, super-harmonic and sub-harmonic resonances are investigated. In each case, the jump phenomenon and stability analysis are studied. In addition, the effect of dynamic and manufacturing parameters of the gear system... 

In this paper, nonlinear oscillation of the automobile gear system is studied. The backlash dynamic parameter is included in the nonlinear mathematical modeling of the problem. Using multiple scale method, forced vibration responses of the gear system including Primary, Subharmonic and Super-harmonic resonances are investigated. In each case, the jump phenomenon and stability analysis are studied. In addition, the effect of dynamic and manufacturing parameters of the gear system on the time responses are analyzed. Simulation and nonlinear analysis of the problem are developed in MAPLE and MATLAB environments  

Under different loading conditions, the over-head cranes may experience a wide range of model parameters variation. A robust control strategy is developed to achieve the high positioning accuracy, short transportation time and suppression of swing angle for an uncertain over-head crane system. Over-head crane is modeled as a three degrees of freedom system and control problem is investigated for two cases: a system with a single control input (the force on trolley) and a system with two control inputs (the force on trolley and the torque on lifter). Regulator and observer systems are designed. To achieve the tracking objectives, an optimal robust controller is designed based on μ-synthesis... 

To achieve a cost-effective and reliable use of wind power generation, advanced control techniques are required. In this paper, the application of two control strategies for the improvement of wind turbine power output is investigated in the presence of model/environmental uncertainties. Rotational speed of the wind turbine and consequently its power output are controlled via manipulation of blades pitch angle (at a constant generator torque). First, the classical PID controller is designed based on root locus analysis while in the second scheme, an H∞-robust controller is designed via μ-synthesis based on DKiteration algorithm. Performance of the two controllers in tracking of the desired... 

Performance control of a boiler–turbine unit is of great importance due to demands for the economical operations of power plants and environmental awareness. In this paper, an optimal control strategy is designed to achieve the desired performance of a boiler–turbine unit. A multivariable nonlinear model of a utility boiler–turbine unit is considered. By manipulation of valves position for the fuel, steam and feed-water flows; output variables including the drum pressure, electric output and fluid density (and consequently drum water level) are controlled. Performance measure of the problem is defined such that the control efforts are minimized while the tracking objectives are obtained. In...