Sharif Digital Repository

A low voltage current mode sample and hold (S/H) in 0.18μm technology with 1.5v supply voltage is presented. This S/H has 12-bit linearity, i.e., gain and nonlinearity errors of S/H are less than 0.02μA for 100uA input current. Maximum sampling rate for this structure is 100 MHz (using double sampling technique). © 2005 IEEE  

The deposition behavior of fine sediment is an important phenomenon, and yet unclear to engineers concerned about reservoir sedimentation. An elliptic relaxation turbulence model (v2̄ - f model) has been used to simulate the motion of turbid density currents laden whit fine solid particles. During the last few years, the v2̄ - f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proved that the v2̄ - f model to be superior to other RANS methods in many fluid flows where complex flow features are present. Due to low Reynolds number turbulence of turbidity current,(its critical Reynolds... 

In this paper, we present the room temperature current-voltage characteristics of large (100×100 μ m2) and a nanoscale (100×100 nm2) metal-oxide-semiconductor (MOS) capacitor containing few silicon nanocrystals. The layer of silicon crystals is synthesized within the oxide of this capacitor by ultralow energy ion implantation and annealing. Current fluctuations in the form of discrete current steps and sharp peaks are apparent in the static and dynamic I (V) characteristics of the capacitor. These features have been associated to quantized charging and discharging of the nanoparticles and the resulting Coulomb interaction to the tunneling current. © 2005 American Vacuum Society  

Detecting high impedance faults is one of the challenging issues for electrical engineers. Over-current relays can only detect some of the high impedance faults. Distance relays are unable to detect faults with impedance over 100Ω. In this paper, by using an accurate model for high impedance faults, a new wavelet-based method is presented. The proposed method, which employs a 3 level neural network system, can successfully differentiate high impedance faults from other transients. The paper also thoroughly analyzes the effect of choice of mother wavelet on the detection performance. Simulation results which are carried out using PSCAD/EMTDC software are summarized  

An index for characterizing wettability of reservoir rocks is presented using slope analysis of spontaneous imbibition recovery data. The slope analysis is performed using the known exact analytical solution to infinite acting period of counter-current spontaneous imbibition. The proposed theoretically based wettability index offers some advantages over existing methods: (1) it is a better measure of the spontaneous imbibition potential of rock (because the magnitude is directly proportional to the imbibition rate); (2) there is no need for forced displacement data; (3) there is no need for waiting until the spontaneous imbibition process ceases completely; and (4) the data needed to run the... 

This paper aims at investigating the resonance frequencies and stability of a long Graphene Nano-Ribbon (GNR) carrying electric current. The governing equation of motion is obtained based on the Euler-Bernoulli beam model along with Hamilton's principle. The transverse force distribution on the GNR due to the interaction of the electric current with its own magnetic field is determined by the Biot-Savart and Lorentz force laws. Using Galerkin's method, the governing equation is solved and the effect of current strength and dimensions of the GNR on the stability and resonance frequencies are investigated  

An index for characterizing wettability of reservoir rocks is presented using slope analysis of spontaneous imbibition recovery data. The slope analysis is performed using the known exact analytical solution to infinite acting period of counter-current spontaneous imbibition. The proposed theoretically based wettability index offers some advantages over existing methods: (1) it is a better measure of the spontaneous imbibition potential of rock (because the magnitude is directly proportional to the imbibition rate); (2) there is no need for forced displacement data; (3) there is no need for waiting until the spontaneous imbibition process ceases completely; and (4) the data needed to run the... 

Time-variant axial and radial electromagnetic for ces under inrush current and short-circuit current are calculated (by finite element method; FEM) and compared. A simplified analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this method are compared with the measured values. A compact three-phase, core-type 132/20 KV, 30 MVA, power transformer is modeled, employing two-dimensional (2D) FEM, the different forces under short-circuit and inrush current conditions are evaluated as a function of time. The simulation results for this sample transformer show that the inrush current axial force is larger than clamping force (which is... 

Distributed power generation and the ever-growing load demand have caused fault current levels to exceed the nominal rating of the power system devices, and fault current limiters are more needed. Superconducting fault current limiter (SFCL) forms an important category of current limiters. In this paper, a novel flux-based model for the inductive shield-type high-temperature SFCL is developed based on the Bean model. This model is employed to simulate the SFCL performance in a sample circuit. Utilizing the model, the signal characterization of the limited current is determined. A prototype laboratory scale SFCL has been fabricated with superconducting rings. Yttrium barium copper oxide... 

This paper gives the design and analysis approaches for the class-E power amplifier with a shunt inductor under the nominal conditions, i.e., zero-current switching (ZCS) and zero-current derivative switching (ZCDS), with taking into account the MOSFET nonlinear output parasitic capacitance at any duty ratio. Although, the class-E ZCS/ZCDS conditions obtained high-efficiency, but the switch-current waveform affected by the slope of the voltage across the MOSFET nonlinear drain-to-source parasitic capacitance during the switch-off state, which restricted the operating frequency. On the other hand, the duty ratio is an adjustment parameter to obtain high-frequency operation. Therefore, the... 

Gas metal arc welding (GMAW) process was used to weld plates of strain-hardened Al-6.7Mg alloy. It was observed that HAZ softening issue occurred extensively for the current material using the GMAW process. So, as a solution, pulsed current was employed and the plates were welded by pulsed GMAW (PGMAW) process. The effects of peak current (93, 120, 140, and 160 A) and pulse frequency (0.5, 2.0, and 5.0 Hz) on the strength of the weldments were investigated. For high peak currents (160 A), catastrophic defects were formed in the weld metal. It was observed that for the lowest pulse frequency (0.5 Hz), increasing the peak current increased the weld strength. The peak current did not change the... 

In this paper, design and analysis using analytical expressions for the inverse class-E power amplifier (PA) operating at the outside nominal operation, i.e., class-En PA, is presented. This operation is defined as non-zero current switch (n-ZCS) and non-zero derivative current switch (n-ZDCS) conditions. The generalized design equations as a function of design specifications, load-resistance and a given dc-supply voltage are derived. Two degrees of the design freedom achieved thanks to n-ZCS and n-ZDCS that are utilized for the simultaneous satisfaction of design specifications, such as peakswitch- voltage and peak-switch-current along with a given loadresistance. The output power... 

Modular multilevel converter (MMC) is among the promising topologies used in high-voltage/power purposes, especially for high-voltage direct-current (HVDC) transmission systems. In this paper, a modified model predictive control (MPC) strategy for an MMC-HVDC system is presented. In the proposed MPC strategy, output current, circulating current and capacitors voltage are controlled separately. In order to reduce the computational burden of the controller, the output current is controlled directly without any optimization. For suppression of the circulating current, capacitors voltage variations are employed to settle the converter arms voltages to their reference values. In addition, the...