Sharif Digital Repository

Equations of state based on the statistical associating fluid theory for potentials of variable range (SAFT-VR) and the perturbed chain statistical associating fluid theory (PC-SAFT) have been used to model the PVT behavior of ionic liquids and the solubility of H2S in six imidazolium-based ionic liquids. The studied systems included [bmim][PF6], [hmim][PF6], [bmim][BF4], [hmim][BF4], [bmim][NTF2] and [hmim][NTF2] at various temperatures and pressures.For pure components, parameters of the models have been obtained by fitting the models to experimental data on liquid densities; the average relative deviation between the calculated and experimental densities for ionic liquids is less than... 

The solubility of hydrogen sulphide in three ionic liquids, viz. 1-hexyl-3-methylilmidazolium hexafluorophosphate ([hmim][PF6]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF4]), and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([hmim][Tf2N]), at temperatures ranging from 303.15 K to 343.15 K and pressures up to 1.1 MPa were determined. The solubility values were correlated using the Krichevsky-Kasarnovsky equation and Henry's constants were obtained at different temperatures. Partial molar thermodynamic functions of solvation such as standard Gibbs free energy, enthalpy, and entropy were calculated from the solubility results. Comparison of the values obtained... 

This paper studies unamped oscillations of fractional-order Duffing system. Stability theorems for fractional order systems are used to determine the characteristic polynomial of the system in order to find the parametric ranges for undamped oscillations in this system. We also derive relations for estimating the frequency and the amplitude of the oscillations in this system using a describing function method. Finally numerical simulation results are provided to justify the analysis  

This paper deals with the existence and the characteristics of the limit cycles in the fractional-order Arneodo system. The analysis is done using the describing function method. Our focus is on a special case where two limit cycles exist. The parametric range for the case of interest is derived, and the frequency and the amplitude of the oscillation are predicted. Numerical simulation results are presented to further demonstrate the reliability of the analysis  

This paper studies undamped oscillations of fractional-order Duffing system. Stability theorems for fractional order systems are used to determine the characteristic polynomial of the system in order to find the parametric ranges for undamped oscillations in this system. We also derive relations for estimating the frequency and the amplitude of the oscillations in this system using a describing function method. Finally numerical simulation results are provided to justify the analysis  

As steel plate shear walls are typically used in the building central cores around the elevators and stairs, introduction of an opening as door seems to be inevitable in steel plate shear wall spans. Due to the weakening of the steel plate shear walls’ performance caused by this particular type of opening, the use of stiffeners around the opening is necessary. Nevertheless, introduction of stiffeners around all sides of the opening, which does continue to boundary elements, is very expensive and inefficient. Therefore, the study on the effect of different arrangements of stiffeners on the behavior of steel plate shear walls is significant. In this research, a number of steel plate shear... 

Land cover classification is one of the most important applications of POLSAR images. In this paper, a hybrid biogeography-based optimization support vector machine (HBBOSVM) has been introduced to classify POLSAR images of RADARSAT 2 in band C acquired from San Francisco, USA. The main purpose of this classification is to minimize the number of features and maximize classification accuracy. The proposed method consists of three main steps: preprocessing, feature selection and classification. As preprocessing, radiometric calibration, speckle reduction and feature extraction have been performed. In the proposed HBBO, the combination of onlooker bee of artificial bee colony (ABC) and... 

Short circuit current is one of the major threats for power system stability. Power system should have the ability to detect and clear these faults within a specified time. The protection system can clear the faults only if the interruption capability of the circuit breakers is higher than the fault level. Expansion of the grid and installation of new power on the scale that is envisaged will require practical solutions to a number of technical challenges. One of the technical challenges is fault level management as system expansion often results in increased fault levels beyond the design limits of the existing switchgears. Replacing the old equipments particularly circuit breakers with the... 

We use the weighted integral form of spherical Bessel functions and introduce a new analytical set of complete and biorthogonal potential-density basis functions. The potential and density functions of the new set have finite central values and they fall off, respectively, similar to r-(1+ l) and r-(4+ l) at large radii, where l is the latitudinal quantum number of spherical harmonics. The lowest order term associated with l = 0 is the perfect sphere of de Zeeuw. Our basis functions are intrinsically suitable for the modelling of three-dimensional, soft-centred stellar systems and they complement the basis sets of Clutton-Brock, Hernquist & Ostriker and Zhao. We test the performance of our... 

One of the shortcomings of photoconductive (PC) antennas in terahertz (THz) generation is low effective radiated power in the desirable direction. In this paper, we propose a defective photonic crystal (DPC) substrate consisting of a customized 2D array of air holes drilled into a solid substrate in order to improve the radiation characteristics of THz PC antennas. The effect of the proposed structure on the performance of a conventional THz PC antenna has been examined from several aspects including radiation efficiency, directivity, and field distribution. By comparing the radiation performance of the THz antenna on the proposed DPC substrate to that of the conventional solid substrate, it... 

Iran has been experiencing slow growth for the past ten years. Using plant-level information, we show that on average firm-specific productivity in manufacturing sectors declined at the rate of 2.6 percent annually, while large top decile firms experienced a modest growth in productivity between 2005 and 2011. We decompose this trend and find that within-plant variation is its main driving force while the between firms and industries component is insignificant. We test several alternative explanations that may contribute to these negative trends. We show that the subsidy reform had a negative effect, while privatization seems to have had no effect. Private management not affected on... 

In this paper, arrays of two different terahertz (THz) antennas based on defective photonic crystal (DPC) substrates are proposed and their radiation characteristics are investigated by using full-wave simulation. We show that employing DPC substrates in THz photoconductive antenna (PCA) arrays reduces the amount of power coupled to the substrate surface waves and, as a result, decreases the mutual coupling between the elements of the antenna array and increases the directivity in the boresight direction. By studying 1 × 2 arrays of bowtie and four-leaf-clover-shaped antennas, we show that either the improvement of directivity in a broad bandwidth or the enhancement of photomixer antenna... 

Using plant level panel data of manufacturing firms in Iran from 2003 to 2013, we test the Dutch disease predictions, including the impact of a rise in oil prices on intensive and extensive margins of trade. Our findings indicate that during periods of high oil prices domestic currency appreciates, but contrary to resource curse theories, domestic firms export more, and new firms enter foreign markets. We reconcile this paradox by proposing a new channel, which we call “subsidy disease.” Despite rising oil prices, the government of Iran kept domestic energy prices at low levels, which increased the implicit subsidy accruing to energy intensive firms. In effect, these firms gain a competitive... 

A set of bi-orthogonal potential-density basis functions is introduced to model the density and its associated gravitational field of three dimensional stellar systems. Radial components of our basis functions are weighted integral forms of spherical Bessel functions. We discuss on the properties of our basis functions and demonstrate their shapes for the latitudinal Fourier number l = 2. © 2008 Copyright International Astronomical Union 2008  

At least four source impedances are required to characterize the noise parameters of a two-port network. The accuracy of the noise parameters depends on the configuration of the employed source impedances (pattern). The configuration of a specified pattern, generated generally by an impedance tuner, changes with frequency, and as such, the accuracy is usually degraded in a wideband characterization. To realize a low-error wideband noise characterization, the present article thoroughly investigates the method of choosing a four-source impedance pattern. A Monte Carlo simulation-based approach is proposed to obtain the desired impedance patterns. The measurement and simulation results show... 

Low scalability and power efficiency of the shared bus in SoCs is a motivation to use on chip networks instead of traditional buses. In this paper we have modified the Orion power model to reach an analytical model to estimate the average message energy in K-Ary n-Cubes with focus on the number of virtual channels. Afterward by using the power model and also the performance model proposed in [11] the effect of number of virtual channels on Energy-Delay product have been analyzed. In addition a cycle accurate power and performance simulator have been implemented in VHDL to verify the results. ©2008 IEEE  

This paper aims to develop a numerical methodology to investigate the penetration process of nanoneedles into cells and the corresponding force and indentation length. The finite element approach via the explicit dynamic method handles convergence difficulties in the nonlinear phenomenon. The cell is modeled as an isotropic elastic hemiellipsoidal shell with a thickness of 200 nm, which represents the lipid membrane and actin cortex, encapsulating cytoplasm that is regarded as an Eulerian body because of its fluid-type behavior. Nanoneedles with diameters 400, 200, and 50 nm are considered for model development based on available experimental data. The Von Mises strain failure criterion is... 

Aims and objectives: This research aims to develop a kinetic model that accurately captures the dynamics of nanoparticle impact and penetration into cell membranes, specifically in magnetically-driven drug delivery. The primary objective is to determine the minimum initial kinetic energy and constant external magnetic force necessary for successful penetration of the cell membrane. Model Development: Built upon our previous research on quasi-static nanoneedle penetration, the current model development is based on continuum mechanics. The modeling approach incorporates a finite element method and explicit dynamic solver to accurately represent the rapid dynamics involved in the phenomenon.... 

This paper presents a small open economy, dynamic general equilibrium model with cash-in advance constraint and a currency attack to explain the dynamic effects of changes in trade barriers in the short and long run. The model is calibrated using data on macroeconomic variables in Iran's economy from 1990 to 2013 to identify and analyze the effects of barriers imposed on trade. We analyze the effects of counterfactual fiscal, monetary and exchange rate policies in response to trade barriers and show how the economy would respond in different time horizons. We also evaluate the effects of eliminating each of the factors causing this stagflation. Our findings show that the short-term drop in... 

Thermodynamic and kinetic studies have been carried out on the adsorption of uranium(VI) by Amberlite IRA-910 resin. The adsorption process has been investigated as a function of adsorbate concentration, solution acidity, contact time, adsorbent dosage, and temperature. The experiments were preformed in batch mode, where uranium initial concentration on the solution samples were 185.5, 277.6 and 456.8 (mg/lit), sulfuric acid concentration range was 0.02-9 (mol/lit) and sorbent dosages were 0.2, 0.3 and 0.5 g. Equilibrium isotherm data were analyzed using Freundlich and Dubinin-Radushkevich isotherm models. The results showed that the adsorption process was well described by Freundlich...