Sharif Digital Repository

An analytic method for prediction of oscillation amplitude and supply current of differential CMOS oscillators is presented. The validity of this method has been verified by designing an LC CMOS oscillator in a 0.24 μm CMOS technology. The predictions are in good agreement with simulation results over a wide range of supply voltage  

This paper first proposes a competitive market structure for reactive power procurement and then develops a methodology for incorporating voltage stability problems into the model. The owners of electric transactions should participate in this competitive framework and submit their own firmness bids in ($/MW) to the Independent/System/Market Operator (ISOIMO). ISO clears the market for reactive energy regarding the value of each transaction and utilization cost of reactive power on one hand, and the impact of transaction amount on the voltage security of the power system on the other hand. Here, the voltage stability margin is incorporated into the power flow equations so that the security... 

The temperature and voltage dependence of spin transport is theoretically investigated in a new type of magnetic tunnel junction, which consists of two ferromagnetic outer electrodes separated by a ferromagnetic barrier and a nonmagnetic (NM) metallic spacer. The effect of spin fluctuation in magnetic barrier, which plays an important role at finite temperature, is included by taking the mean-field approximation. It is found that, the tunnel magnetoresistance (TMR) and the electron-spin polarization depend strongly on the temperature and the applied voltage. The TMR and spin polarization at different temperatures show an oscillatory behavior as a function of the NM spacer thickness. Also,... 

The spin-polarized transport is investigated in a new type of magnetic tunnel junction which consists of two ferromagnetic electrodes separated by a magnetic barrier and a nonmagnetic metallic spacer. Based on the transfer matrix method and the nearly-free-electron approximation the dependence of the tunnel magnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer thickness and the applied bias voltage are studied theoretically. The TMR and spin polarization show an oscillatory behaviour as a function of the spacer thickness and the bias voltage. The oscillations originate from the quantum well states in the spacer, while the existence of the magnetic barrier gives rise... 

An analytic method to predict the oscillation amplitude and supply current values of a differential CMOS oscillator is presented. A simplified model to predict the phase noise performance for this type of oscillator is developed. Using this method, it becomes possible to design an optimised oscillator in terms of a minimum phase noise and low power consumption. The validity of the method has been verified by designing a LC CMOS oscillator using 0.25 μm CMOS technology. The predictions are in good agreement with simulation results over a wide range of the supply voltage  

In this study, an analytical solution is presented for thermo-electro- elastic analysis of piezoelectric semi-infinite bodies. For this purpose, governing equations are derived for a transversely isotropic piezoelectric material under an axisymmetric thermo-electro-mechanical loading condition. A general closed-form analytical solution is presented for the complementary and particular parts of the components of the displacement vector and also for the electric potential function. Then, boundary conditions are imposed and in that case an explicit solution is obtained for piezoelectric semi-infinite bodies. Results show that when a piezoelectric half space is subjected to constant/ramp surface... 

A high speed, high resolution switched-current sample and hold (SI S/H) based on a new class AB transconductance stage is presented. Simulations performed on the SI S/H in standard 0.18um CMOS technology with 1.5v supply voltage indicate low power dissipation, high sampling speed and high SNR. © 2006 IEEE  

Under voltage load shedding is one of the most important tools to avoid voltage instability. In this paper an optimal load shedding algorithm is developed. This approach is based on the concept of the static voltage stability margin and its sensitivity value at the maximum loading point or the collapse point. The traditional load shedding objective is extended to incorporate both technical and economical effects of load shedding. The voltage stability criterion is modeled as a soft constraint into load shedding scheme. The proposed methodology is implemented over the IEEE14 bus system and solved using a mathematical (GAMS/CONOPT) and two heuristic (P.S.O & GA) methods. © 2006 IEEE  

A new family of sampled-data filters in which accuracy is a function of the ratio of the resistors is introduced. It is shown that this structure is suitable for low-voltage high-speed applications. A biquad filter with a quality factor of 10 and a clock frequency of 60MHz consuming only 2mW power is also presented  

The voltammetric performance of edge-plane pyrolytic graphite (EPG) electrode via adsorptive stripping voltammetry was investigated for study of the electrochemical behavior of omeprazole (OMZ) in aqueous solution. The results revealed that the oxidation of OMZ is an irreversible pH-dependent process that proceeds with the transfer of one electron and one proton in an adsorption-controlled mechanism. The determination conditions, such as the pH values of the supporting electrolyte, accumulation time and scan rate were optimized. Simplicity, high reproducibility and low detection limit (3 nM) of the electrode response as well as wide linear range (0.01 to 4.0 µM) can be stated as significant... 

This paper presents stability analysis of a distributed generation (DG) controller [1], in an islanded mode, based on the Mapping Theorem and the Zero Exclusion Condition, and validates the results based on a laboratory scale experimental setup. The DG unit is interfaced to the host system through a voltage-sourced converter (VSC). The control strategy regulates the load voltage at the desired value in the islanded mode, despite uncertainties in the load parameters. The frequency of the island is controlled in an open loop manner by an internal oscillator. The experimental results show that the controller provides robust voltage control for a wide range of load parameters, and even maintains... 

Infinite series solutions are obtained for electrical potential, electroosmotic velocity, ionic conductance, and surface physicochemical properties of long pH-regulated rectangular nanochannels of low surface potential utilizing the double finite Fourier transform method. Closed form expressions are also obtained for channels of large height to width ratio for which the depthwise variations vanish. Neglecting the Stern layer impact, the effects of EDL (Electric Double Layer) overlap, multiple ionic species, and association/dissociation reactions on the surface are all taken into account. Moreover, finite-element-based numerical simulations are conducted to account for the end effects as well... 

In this study a more precise formulation of electrical capacitance for a cylindrical capacitive sensor is reported. By using different theoretical models such as Coulomb law, Gauss law and Laplace equation the electrical capacitance is calculated. Based on the given models the relation between the capacitance and the geometrical parameters (e.g., cylindrical length) is formulated and by using suitable software capacitance variation is computed and compared for different methods. In Coulomb method, the electrical potential is first solved numerically by using Mathematica and then the electrical capacitance is computed. It is found that the active capacitor length is crucial parameter in the... 

A novel approach for particles size separation based on dielectrophoresis (DEP) method is introduced and analyzed both computationally and experimentally. The proposed technique has been utilized for the separation of polystyrene (PS) particles with 8, 6 and 2 μm diameters passing through microchannels with planar electrodes. The performance of the technique has been computationally analyzed using the finite element method (FEM). Considering the structure of the planar electrodes, we propose an approach based on applying an electric potential between one of the global electrodes, and a needle touched the top of the cell suspension. Results of both simulation and experiment show that by... 

We present the results on the correlation between the flux to voltage transfer function, Vspp, of the rf-SQUID and the rf-bias frequency as well as rf-bias power. Measurements were performed for different SQUID gradiometer samples chosen from the same batch or different batches. In order to have full control on the electronics parameters, an experimental rf-SQUID circuit was designed and implemented with an operation frequency of 600 MHz to 900 MHz. According to our findings, It has been observed that at any particular rf-bias power, Vspp vs. rf-bias frequency shows Sine-like behavior. We observed that the main lobe maxima exist close to the resonance frequency of the LC tank circuit and by... 

The design of a copper chloride laser is described, and the laser is optimised by studying the dependence of its output power on the buffer gas type. The voltage and current of the laser discharge at the optimum buffer gas pressure are measured. The influence of the diaphragm diameter on the specific output power is studied after optimisation of switch parameters. When an diaphragm producing the optimal temperature gradient in the laser gas-discharge tube, the record specific output power of 123 W L-1 is obtained without any admixtures. ©2007 Kvantovaya Elektronika and Turpion Ltd  

We have investigated the rf SQUID (radio-frequency superconducting quantum interference device) and its coupling to tank circuit configurations to achieve an optimal front-end assembly for sensitive and high spatial resolution magnetic imaging systems. The investigation of the YBCO rf SQUID coupling to the conventional LC tank circuits revealed that coupling from the back of the SQUID substrate enhances the SQUID signal while facilitating the front-end assembly configuration. The optimal thickness of the substrate material between the SQUID and the tank circuit is 0.4 mm for LaAlO3 resulting in an increase of the SQUID flux-voltage transfer function signal, Vspp, of 1.5 times, and 0.5 mm for... 

In this investigation, the effect of coloring voltage and thickness on optical and also electrochromical properties of W O3 thin films has been studied. The W O3 thin films were grown on glass and indium tin oxide coated conducting glass substrates by e-beam evaporation at different thicknesses of 200, 400, and 700 nm. Optical properties of the deposited samples were characterized in the ultraviolet-visible range (300-1100 nm). The optical bandgap energy of the W O3 was obtained in a range of 3.3-3.5 eV showing its increase by decreasing the film thickness. The refractive index of the W O3 films was measured around 2 in the visible range. Surface chemical states of the films were studied by... 

Detection and location of any partial discharge signal requires an accurate frequency dependent cable model to correctly simulate the P.D. signal attenuation during its propagation in the cable. This model should be capable of simulating the semiconducting layers which have significant effects on P.D. signal attenuation and its propagation velocity. There is a substantial need for improvements in the flexibility of transient cable model through direct introduction of the two semiconducting layers in the cable model. This can be employed, in the next step to develop a 3 phase cable model for ATP. This paper has derived an impedance formula for the semiconducting layers. The propagation...