Sharif Digital Repository

Chitosan was crosslinked with different amount of glutaraldehyde to prepare appropriate hydrogels to be used as drug delivery system. The swelling behavior of freeze-dried hydrogels in aqueous media at different temperature and pHs has been examined. The swelling, porosity and biocompatibility behavior of samples were investigated to check effects of polymer/polymer and polymer/drug interactions on these system characteristics. Obtained experimental results illustrates that with increasing crosslinking agent from 0.068 to 0.30, swelling of the prepared samples degrees from 1200% to 600% and pore diameters change from 100 to 500 μm. To investigate systems biocompatibility in gastric... 

Five different approaches are presented to assign characteristic ratios for commensurate fractional order systems having order in (0,0.5]. Through the indirect methods, a closed-loop or plant transfer function is converted to a commensurate order one with an order greater than 0.5 so that the previously designed CRA method by the authors is applicable. The first method among the proposed direct ones is based on increasing the order of the desired closed-loop transfer function that allows the employment of positive characteristic ratios. In the second method the closed-loop response is sped up by augmenting an appropriate zero. The final method uses negative characteristic ratios to reach the... 

CFD simulation of cylindrical bubble column including air as dispersed phase and water as continuous phase operating in churn-turbulent flow regime with diameter of 0.49 m, height of 3.6 m and gas superficial velocity of 0.14 m/s have been conducted. All simulations have been carried out in a 2D axisymmetric, unsteady and Euler/Euler framework with the aid of commercial software FLUENT v. 14.5. Simulations were validated by our experimental results through residence time distribution (RTD) data. Effect of bubble size distribution at inlet on column hydrodynamic was investigated and results clearly showed that equilibrium bubble size distribution in most parts of column is independent of... 

One of the major issues related to parallel kinematic machine tools (PKMs) is their structural dependency on their configuration. In this paper, the machine configuration effect on its stability is investigated for the case of a Hexaglide machine tool. An FEM model of the Hexaglide machine tool is developed. The frequency response function (FRF) at the tool tip is obtained by a modal analysis. The numerical results are validated through comparison with those of an experimental modal test. The pose dependency of the PKM stability over its workspace is investigated. It is shown that the machine stability over the workspace is dependent on the spindle/tool/holder system characteristic. For... 

In this paper, we consider a multiple-input single-output (MISO) linear time-varying system whose output is a superposition of scaled and time-frequency shifted versions of inputs. The goal of this paper is to determine system characteristics and input signals from the single output signal. More precisely, we want to recover the continuous time-frequency shift pairs, the corresponding (complex-valued) amplitudes and the input signals from only one output vector. This problem arises in a variety of applications such as radar imaging, microscopy, channel estimation and localization problems. While this problem is naturally ill-posed, by constraining the unknown input waveforms to lie in... 

Iterative methods for modification of vibratory characteristics of dynamic systems have attracted a lot of attention as a convenient and more economical way when compared to the traditional and costly structural dynamic optimization processes. Many complicated structures, such as telecommunication towers, chimneys and tall buildings, may be modeled as simple spring-mass systems. This paper presents an iterative method for modification of the frequencies of simple vibrating system consisting of springs and masses. The proposed algorithm may be used to adjust any of the vibration frequencies of a simple vibrating system to the target values within the desired level of accuracy. The method... 

In this paper, we study and analyze the performance of matched and partially-matched receivers for a typical ultra wide-band Spectrally-Encoded Spread-Time (SE/ST) CDMA in the presence of multiple tone jammers. We investigate a scenario where there is no information about the jammer frequencies in the transmitter side while it is desirable to cancel it in the receiver side. We will demonstrate the performance of the SE/ST system would be improved through partially matched filter at the receiver. In addition, we approximate the two-dimensional RAKE receiver by a simple one-dimensional RAKE for the scenario where there are K asynchronous users. Furthermore, closed form formula for the... 

This paper addresses a low complexity and high efficient cooling system applicable on photovoltaic (PV) system leading to enhance electrical efficiency and provide preheated water. The developed system consists of a photovoltaic panel, a cooling water system establishing a uniform surface temperature, and a solar water heater. According to the proposed system characteristics, the setup is constructed based on a single mono-crystalline solar panel to absorb more solar radiation intensity and generate more electrical energy per area in compare to a poly-crystalline panel. The preheated water produced by absorbed heat from the photovoltaic is conducted to a solar water heater to satisfy... 

This paper presents fractional order multi-input multi-output (MIMO) controllers for the robust performance of airplane longitudinal motion. A novel necessary and sufficient criterion is offered by using the value set concept to analyze the robust performance of fractional order MIMO uncertain systems based on the location of the characteristic equation roots. The criterion is applicable to all linear time-invariant systems of commensurate and incommensurate orders with complex coefficients. The obtained results are applied to an uncertain linear model of a business airplane to improve the robust performance of its longitudinal motion by decentralized MIMO output feedback and MIMO state... 

This paper addresses a low complexity and high efficient cooling system applicable on photovoltaic (PV) system leading to enhance electrical efficiency and provide preheated water. The developed system consists of a photovoltaic panel, a cooling water system establishing a uniform surface temperature, and a solar water heater. According to the proposed system characteristics, the setup is constructed based on a single mono-crystalline solar panel to absorb more solar radiation intensity and generate more electrical energy per area in compare to a poly-crystalline panel. The preheated water produced by absorbed heat from the photovoltaic is conducted to a solar water heater to satisfy... 

This study proposes a modified virtual inertial control (MVIC) scheme for doubly-fed induction generator (DFIG)based wind turbines (WTs), which both improves the frequency response of these renewable resources and enhances the power system oscillation damping capabilities. It is shown that the proposed control structure enables the WT to participate prudentially in system frequency regulation, which means the amount of WT kinetic energy released to the grid and its participation in system frequency support is alleviated as its stored energy decreases. The proposed control strategy is introduced conceptually, and its performance is verified analytically. Effects of wind speed variations on... 

In order to safe design and optimize performance of some industrial systems, it's often needed to categorize two-phase flow into different regimes. In each flow regime, flow conditions have similar geometric and hydrodynamic characteristics. Traditionally, flow regime identification was carried out by flow visualization or instrumental indicators. In this research3 kind of neural networks have been used to predict system characteristic and flow regime, and results of them were compared: radial basis function neural networks, self organized and Multilayer perceptrons (supervised) neural networks. The data bank contains experimental pressure signalfor a wide range of operational conditions in...