Sharif Digital Repository

Molecular dynamics simulations were employed to both estimate the solubility of nonelectrolyte solids, such as acetanilide, acetaminophen, phenacetin, methylparaben, and lidocaine, in supercritical carbon dioxide and understand the underlying molecular-level driving forces. The solubility calculations involve the estimation of the solute's limiting activity coefficient, which may be computed using conventional staged free-energy calculations. For the case of lidocaine, wherein the infinite dilution approximation is not appropriate, we demonstrate how the activity coefficient at finite concentrations may be estimated without additional effort using the dilute solution approximation and how... 

In this letter, the problem of source localization using time difference of arrival (TDOA) is investigated. Then, a closedform two-stage solution is proposed based on estimation of the range nuisance parameter in the first stage and refinement of initial solution in the next stage. The proposed solution is shown analytically and verified by simulations to be an efficient estimate, which can attain the CRLB performance under mild Gaussian noise assumption. This method is able to locate the source with the minimum number of sensors required for N-dimensional localization. Numerical simulations demonstrate significant performance improvement of the proposed method compared with the... 

In this study, an algebraic closed-form method for jointly locating the target and refining the antenna positions in multiple-input-multiple-output radar systems is proposed. First, a set of linear equations is formed by non-linear transformation and nuisance parameters elimination, and then, an estimate of the target position is obtained by employing a weighted least-squares estimator. To jointly refine the target and antenna positions, the associated error terms are estimated in the sequence. The proposed method is shown analytically and confirmed by simulations to attain the Cramér-Rao lower bound performance under small-error conditions. Numerical simulations are given to support the... 

In this paper, a novel solution for the problem of joint moving target and antenna localization in the distributed multiple-input multiple-output (MIMO) radar systems is proposed. The localization problem in the presence of antenna location uncertainty is formulated as a maximum likelihood (ML) estimation problem, which is then recast into convex form by defining some auxiliary variables and applying semidefinite relation (SDR) technique. Next, an algebraic closed-form estimator is proposed to jointly estimate the target and the antennas error terms and refine their uncertain values. The proposed method is shown analytically and verified by the numerical simulations to be an efficient... 

New advances in technology of mobile computers along with advent of wireless and mobile networking bring new capabilities, applications and concerns to the computer world. In this paper, we discussed on file sharing requirements in a mobile environment. Then, we proposed an architecture that supports mobility of hardware, data and software over the environment. Finally a sample implementation of the suggested architecture is presented. © 2005 by Knowledge Systems Institute Graduate School  

In this paper, the problem of locating a target in a distributed multiple-input multiple-output radar system using bistatic range measurements is addressed. An algebraic closed-form two-stage weighted least squares solution for the considered problem is developed and analyzed. In the first stage, we establish a set of linear equations by eliminating the nuisance parameters first and then we apply a weighted least squares estimator to determine the target position estimate. In the second stage, in order to improve the localization performance and refine the solution of the first stage, an estimate of the target position estimation error is obtained. The final solution is obtained by... 

In this paper, a fundamental investigation on the performance of localization problem in a distributed multiple-input multiple-output radar system using bistatic range (BR) and angle of arrival (AOA) measurements is conducted. The study is based on the Cramer-Rao lower bound (CRLB) for the target position under Gaussian measurement noise. We attempt to approximately compute the CRLB separately in the cases of BR-only and joint BRlAOA localization schemes and determine which factors can affect the CRLB values. The three factors the transmitter/receiver placement, the number of transmitters and receivers, and noise power levels are shown to be effective on the localization performance.... 

In this paper, an algebraic solution for elliptic localization in multiple-input multiple-output (MIMO) radar systems is proposed by taking the uncertainties in antenna positions and their clock parameters into account. Through nonlinear transformation and multi-stage processing, the target position is estimated in closed-form by successively utilizing the weighted least squares estimator. Theoretical analysis demonstrates that the proposed method is able to attain the Cramer-Rao lower bound (CRLB) performance under mild Gaussian error. The conditions for achieving the CRLB are derived as well. The numerical simulations confirm the analytical results and demonstrate significant performance... 

This paper deals with the moving target localization problem from time delay and Doppler shift measurements in a distributed multiple-input multiple-output radar system. An algebraic closed-form two-stage weighted least squares solution is presented to locate the target position and velocity. In the first stage, a set of pseudo-linear equations is established by introducing and decreasing the nuisance parameters. Then, two quadratic equations are obtained in terms of the nuisance parameters by considering relationships among them and the target position and velocity. By applying the elimination method that gives the nuisance parameters and substituting them into the localization problem, the... 

In a transformerless grid-connected photovoltaic system, many issues arise from the leakage current flow into the ground, as EMI problems. The leakage current is originated from the common-mode voltage fluctuations. In this paper, the common-mode voltage harmonics in a three-phase quasi-Z-source inverter are analyzed using Fourier transform and a closed-loop formulation is presented for the harmonics value. The shoot-through mode in a quasi-Z-source inverter causes extra fluctuations in the common-mode voltage comparing to a classic inverter. The proposed harmonic analysis method provides a systematic way to figure out how shoot-through mode and also other parameters affect the common-mode... 

In this paper a single stage structure is proposed for realizing a three-phase unity power factor rectifier. This topology utilizes a forward/flyback transformer to allow the high-frequency isolation. The principle of the operation and the applied control concept is discussed. Space vector modulation is used in order to achieve unity power factor and to have the output voltage be regulated. Furthermore, the system transient is analyzed during turn-on and a novel method is applied to the control system in order to limit inrush current during startup. The proper operation of the soft-start method is confirmed by numerical simulation of a 6KW, 380V/48Vdc. The stability of the closed-loop as... 

In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through (SH) states in a quasi-Z-source inverter (q-ZSI), increase the amplitude of high order harmonics of CMV. In this paper, by using the modulation technique based on odd PWM (OPWM) and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. IEEE  

In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through states in a quasi-Z-source inverter (q-ZSI) increase the amplitude of high-order harmonics of CMV. In this paper, by using the modulation technique based on odd pulse width modulation and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. ©... 

In this paper a novel soft switching isolated buck rectifier is proposed. Various switching state sequences of a three-phase three-switch buck-type unity power factor rectifier are reviewed and the value of switching power loss in each state transition is investigated. The switching power loss of the converter is decreased by using zero current switching (ZCS) method. The operation modes of the converter are explained and analyzed. 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 turned off; so, switching losses in the converter are reduced. In this topology, the power transformer has only the... 

The leakage current originated from the fluctuations of the common-mode voltage (CMV) is an issue in a transformerless grid-connected photovoltaic (PV) system. In this paper, a modified space vector modulation based on the Fourier transform analysis is proposed to reduce the leakage current in a three-phase quasi-Z-source inverter (qZSI). The CMV harmonic content in a qZSI contains low and high-frequency harmonics which cause safety and EMI problems respectively. By implementing the proposed modulation in a three-phase qZSI, the low-frequency harmonics of the CMV are mainly reduced. The distribution of the high-frequency harmonics is also modified in a way they can be simply filtered.... 

Classical molecular dynamics simulations are used to compute the solvation free energy of two pharmaceutical solids, namely ibuprofen and acetaminophen in carbon dioxide (CO2), over the density range of interest in supercritical processes. In order to examine the influence of the solvent model on the resulting free energies, three popular CO2 models (Zhang, EPM2, and TraPPE) are studied. Relatively large discrepancies for the solvation free energy exist between these CO2 models, suggesting that the former is sensitive to the different balances between dispersive and electrostatic forces used in these models. In particular, for the solvation of the highly polar (dipole moment of ∼5.2 Debye)... 

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... 

In this paper a novel T type scheme for 1-phase direct ac/ac converters is proposed. In this topology, frequency changing takes place directly (without common DC voltage bus) through three converters that are connected in a T structure. Unity power factor and precise output voltage regulation is achieved through appropriate control of these three converters. H-bridge converters are implemented, as the basic unit, in each branches of T to make the proposed converter. The converter is controlled such that the average active power of each H-bridges remains zero. So capacitors are implemented in DC links of H-bridges. In comparison to conventional back-to-back converters, life time of each...