Sharif Digital Repository

Solvent extraction of rare earths from nitrate leach liquor of apatite using mixtures of tributyl phosphate (TBP) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) was studied. The effects of nitrate and hydrogen ion concentration of the aqueous phase as well as the composition and concentration of extractants in the organic phase on the extraction behavior of lanthanum, cerium, neodymium, and yttrium were investigated. The distribution ratio of REEs increases by increasing the nitrate concentration in aqueous phase and concentration of extractants in organic phase, but the hydrogen ion concentration in aqueous phase has a decreasing effect. Yttrium as a heavy rare earth is more sensitive to... 

The leaching of rare earth elements (REEs) including cerium, lanthanum and neodymium from apatite concentrate obtained from iron ore wastes by nitric acid was studied. The effects of nitric acid concentration, solid to liquid ratio and leaching time on the recoveries of Ce, La and Nd were investigated using response surface methodology. The results showed that the acid concentration and solid to liquid ratio have significant effect on the leaching recoveries while the time has a little effect. The maximum REE leaching recoveries of 66.1%, 56.8% and 51.7% for Ce, La and Nd, respectively were achieved at the optimum leaching condition with 18% nitric acid concentration, 0.06 solid to liquid... 

In this paper, a modified space-time method is presented for the simulation of convection-diffusion equations. The new method differs from the original space-time method in the sense that the weight functions for space and time are different. The performance of the proposed algorithm is studied for numerical simulation of incompressible immiscible two-phase flow in porous media. The governing equations consist of one conservation of mass equation for each phase, the Darcy law and one capillary-saturation correlation for the flow. By defining a global pressure, the governing equations lead to a system of nonlinear equations in terms of this global pressure, the velocity components and the... 

In this paper a novel soft switching three-phase pulse width modulation (PWM) rectifier is proposed. Various switching state sequences of a three-phase three-switch buck-type unity power factor rectifier are reviewed and the operation modes of the converter are explained and analyzed. The converter operates under zero current switching (ZCS) condition. By using an auxiliary circuit with a simple method of energy recovery, the current is diverted away from the main power switches before they are to be turned off; so, switching losses in the converter are reduced. The auxiliary circuit consists of two auxiliary switches and a resonant inductance-capacitance circuit connected to the auxiliary... 

A novel control method is proposed for single-stage three-phase isolated buck+boost rectifier. The control method is based on the conventional cascade two-loop control structure and is modified to achieve constant instantaneous input power. Input voltages, output voltage, and DC-link inductor current are measured to control the power switches to achieve output voltage regulation as well as input power factor correction. In the proposed method, input currents are controlled such that input power is constant even for unbalanced mains. Thus for balanced mains converter behaves like an ideal rectifier, and for unbalanced mains, low-frequency harmonics of the output voltage are suppressed. The... 

Biofiltration is a commonlypracticed biological technique to remove volatile compounds from waste gas streams. From an industrial view-point, biofilter (BF) operation should be flexible to handle temperatures and inlet load (IL) variations. A compost BF was operated at different temperatures (30-45°C) and at various inlet loading rates (ILR; 8-598gm -3h -1) under intermittent loading conditions. Complete removal of n-hexane was observed at 30 and 35°C at ILRs up to 330gm -3h -1. Besides, 20-75% of the pollutant was removed at 40°C, corresponding to the different ILs applied to the BF. Increasing the temperature to 45°C decreased the removal efficiency (RE) significantly. A feed forward... 

In this paper, a dual-frame hybrid vector control (DFHVC) of vector-modulated VIENNA I rectifier is proposed. The purpose of this novel vector control system is not only to reduce second-order harmonic pulsation on the dc-side and consequently, to reduce odd-order harmonics on the ac side of VIENNA I rectifier under unbalanced mains, but also to ensure a near unity power factor operation of the rectifier under such circumstances. To serve this purpose, at first, a mathematical model of the VIENNA I rectifier under unbalanced condition is derived. In this model, besides demonstrating the nonlinear nature of the DC-link voltage dynamic, a new set of equations for current reference generation... 

Two major structures for rotor core of superconducting synchronous machine are air-cored and magnetic-cored structures. Magnetic-cored structure can be divided into two categories including salient and non-salient magnetic core. In this paper, three different structures of superconducting synchronous machine comprising air-cored, non-salient magnetic-cored and salient magnetic-cored, have been studied and compared considering required superconducting wire and machine weight. Required superconducting wire determines the capital cost and the weight of the machine determines the running cost in the case of portable applications such as ships and aircrafts  

The Cúk converter operating in discontinuous capacitor voltage mode (DCVM) inherently benefits from PFC features as unity power factor can be achieved by using a constant duty cycle and switching frequency. In this paper, the switch network modeling technique is applied to the Cúk converter operating in DCVM in order to develop its small-signal model under the assumption that it is fed by a dc voltage source. Afterwards, the model is extended to derive the small-signal behavior of the converter while operating as a PFC converter. The validity of the proposed model is confirmed by both simulation and experimental results  

Local educational institutions produce in-house English for Specific Purpose (ESP) materials according to the curriculum policies designated and developed by the Ministry of Higher Education In Iran. To this end, this book aims to be used in the Iranian setting at the tertiary level for undergraduate students majoring in Mechanical Engineering. Moreover, the style of English usage in this ESP textbook is American.
Regarding the content of the textbook, it has both thematic organizations in which the topics are relevant and includes sufficient treatment of the target language areas necessary for the students. The principle organizing approach of this textbook is theme-based. In addition,... 

The aim of this study is to employ feedback control loops to provide a stable forward dynamics simulation of human movement under repeated position constraint conditions in the environment, particularly during stair climbing. A ten-degrees-of-freedom skeletal model containing 18 Hill-type musculotendon actuators per leg was employed to simulate the model in the sagittal plane. The postural tracking and obstacle avoidance were provided by the proportional—integral—derivative controller according to the modulation of the time rate change of the joint kinematics. The stability of the model was maintained by controlling the velocity of the body's centre of mass according to the desired centre of... 

A combination of silica chloride and wet SiO2 was used as an effective deacetalizating agent for the conversion of acetals to their corresponding carbonyl derivatives under mild and heterogeneous condition  

Free Content Selective synthesis of conjugated enynes from α-arylalkynols using LiCl-Acidic Al2O3 under solvent-free conditions