Sharif Digital Repository

In the context of controlled release drug delivery approaches, the systems providing zero-order release kinetics have special advantages. Through employing these systems, drug concentration could be maintained within the therapeutic window over release time; thus maximum effectiveness alongside minimized side effects of the drug are achieved. However, obtaining zero-order drug release is extremely challenging. One of the main obstacles is the fact that implemented devices should be designed to overcome the decreasing mass transfer driving force, especially, in polymeric systems in which diffusion mechanism is dominant. In this study, we developed a new configuration of a polymeric matrix... 

Cell lysis is the most important first step for molecular biology and diagnostic testing. Recently, microfluidic systems have attracted considerable attention due to advantages associated with automation, integration and miniaturization, especially in resource-limited settings. In this work, novel centrifugal microfluidic platforms with new configurations for chemical cell lysis are presented. The developed systems employ passive form of pneumatic and inertial forces for effective mixing of lysis reagents and cell samples as well as precise fluidic control. Characterizations of the developed Lab-on-a-Discs (LoaDs) have been conducted with dyed deionized (DI) waters and white blood cells... 

In this paper, the mechanical properties of graphene oxide are obtained using the molecular dynamics analysis, including the ultimate stress, Young modulus, shear modulus and elastic constants, and the results are compared with those of pristine graphene. It is observed that the increase of oxide agents (–O) and (–OH) leads to the increase of C–C bond length at each hexagonal lattice and as a result, alter the mechanical properties of the graphene sheet. It is shown that the elasticity modulus and ultimate tensile strength of graphene oxides (–O) and (–OH) decrease significantly causing the failure behavior of graphene sheet changes from the brittle to ductile. The results of shear loading... 

MEG regeneration and injection unit regenerates aqueous MEG. The main goal of this unit is approaching desired MEG concentration whereas MEG loss via removed water is a big issue. Circulating glycol is polluted with Ca++ and Mg++ which forms carbonate scale and causes plugging of pipe lines, filters, lean/rich exchanger, still column packings and reboiler tube bundle and decreases their efficiency, consequently increases MEG loss via top product. Different alternatives exist according to similar experiences around the world. Using specific criteria and AHP (Analytical Hierarchy Process) method priority of these alternatives has been found. Results are as following: 1. Increasing number of... 

The 1050 aluminum sheets are severely deformed by two passes of the constrained groove pressing (CGP) process to obtain the strain of 2.32. Friction stir processing (FSP) is then performed on these specimens at two conditions of with and without SiC nanoparticles. Microhardness measurements indicate that in the state of FSP without any particle, the microhardness of stir zone is decreased due to the recrystallization and grain growth occurrence because of high stored strain energy in the CGPed specimens. In order to enhance the mechanical properties of the stir zone, SiC nanoparticles are used during FSP. Also, the effect of FSP pass number on the distribution of nanoparticles is... 

The microstructure evolutions of severely deformed aluminum sheets by Constrained Groove Pressing (CGP) after Friction Stir Welding (FSW) are investigated. To do so, the specimens are deformed in three different strains using CGP process which make different the initial microstructures. Then, the specimens are joined at various revolution pitches (traveling speed/rotation speed ratio) of 0.20, 0.25 and 0.33. mm/r. To understand the effect of initial strains on the properties of joints, the microhardness measurements and microstructure investigations of different areas from retreating to advancing sides of the joints are carried out. The results achieved from FSW of CGPed samples are compared... 

The severely deformed aluminum sheets with strain of 2.32 were successfully joined by friction stir welding (FSW) process. Welding was carried out at various rotation speeds of 600, 800, and 1000. rpm at traveling speed of 200. mm/min corresponding to various revolution pitches of 0.33, 0.25, and 0.20. mm/r, respectively. In order to investigate the thermal stability of the joints, annealing was carried out at temperature of 200 °C for 1. h. Microstructure examinations revealed that severely deformed samples were quite unstable upon FSW process. However, during annealing it was found that in contrast to regions of heat affected zone (HAZ) and thermo mechanical affected zone (TMAZ) where... 

The severely plastic deformed aluminum sheets were joined by friction stir welding (FSW). The technique used for imposing the severe strain to the sheets was constrained groove pressing (CGP) process. The specimens with three different imposed strains by CGP, which lead to different initial microstructures, were joined at various rotation (. ω) and traveling (. V) speeds. The microhardness measurements and microstructure investigations were carried out. It was revealed that after FSW process of the specimens strained by CGP process, grain growth and correspondingly hardness reduction were observed at the stir zone. Also, transverse tensile test was performed at all conditions. For the CGPed... 

In this work, 1050 aluminum (Al) sheets were annealed and severely deformed by 1, 2, and 3 passes of constrained groove pressing process to obtain the various initial stored strain values of 0, 1.16, 2.32, and 3.48, respectively. Friction stir processing (FSP) was then applied using SiC nanoparticles to fabricate Al/SiC nanocomposite with approximately 1.5 vol pct reinforced particles. Microstructural examinations revealed that an increase in the initial stored strain of the base metal led to the formation of finer grain structure after 1 pass of FSP. The finer grain structure occurred in the stir zone where a sufficient amount of nanoparticles with a relatively proper distribution existed.... 

In this research, 1050 aluminum sheets in the conditions of annealed and severely deformed by 2 passes of constrained groove pressing (CGP) process were used. Two passes of friction stir processing (FSP) were applied on the specimens. Also, another CGPed specimen was processed by 2 passes of FSP using SiC nanoparticles. The samples were then heat treated to study thermal stability of base metal, heat affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and stir zone (SZ). Microstructure examinations revealed that the annealed base metal was relatively stable upon heating even up to 400. °C and a little grain growth was evident. On the other hand, the CGPed base metal was fairly... 

In this work, friction stir soldering (FSS) as a new approach for fabrication of copper/copper lap joints was introduced. This process is principally based on the friction stir processing (FSP) that can be performed using FSP tools with and without pin on the top sheet. In the present study, Pb-Sn foil was used as a solder which would be melted and then extruded in the area between the copper sheets during FSS process. This process was carried out using tools with and without pin at various rotation speeds of 1200, 1400, and 1600 rpm and traverse speed of 32 mm/min. Also, the same joint was fabricated using furnace soldering to compare the mechanical properties obtained with FSS and furnace... 

In this work, examinations on the microstructure and mechanical properties of plain carbon steel and AISI 430 ferritic stainless steel dissimilar welds are carried out. Welding is conducted in both autogenous and using ER309L austenitic filler rod conditions through gas tungsten arc welding process. The results indicate that fully-ferritic and duplex ferritic-martensitic microstructures are formed for autogenous and filler-added welds, respectively. Carbide precipitation and formation of martensite at ferrite grain boundaries (intergranular martensite) as well as grain growth occur in the heat affected zone (HAZ) of AISI 430 steel. It is found that weld heat input can strongly affect grain... 

We introduce two-dimensional space plus time (2D+1) structure and numerically investigate it using a developed multilayer simulation framework, for the first time. The new structure is consisting of crossed grating with time-varying permittivity which is inspired from1D+1. In this regard, we extend FourierModal Method (FMM) in a general approach for spacetime multilayer states. Our proposed framework is fast, robust, and powerful compared to various finite difference methods. We use the scattering matrix technique to develop the proposed spacetime simulation method for multilayer structures using a non-uniform stack of layers. The method is perfectly suitable to investigate the... 

We present an emulation design method for converting asymmetrical transmitters to nonreciprocal isolators equipped with time-varying metasurfaces. To illustrate the model, we design a structure using a combination of the photonic crystal (PhC) and time-varying metasurface. Moreover, we propose a general approach for numerical analysis of the time-modulated proposed structure using the extension of the transfer matrix method (TMM) which consists of working through the device one layer at a time and calculating an overall transfer matrix including the time-variation of the permittivity and permeability in each layer. Also, we use an optimization algorithm that is less used in the field of... 

Method of lines (MoL) is numerically described for analysis of spatial periodic structures based on discrete finite difference hybridization of each transverse plane of multilayer structure. The results show rigorous simulation of the three-dimensional (3D) arbitrary-shaped space grating with the best convergence and high stability for highly conductive metallic layers. We propose our method to be considered for analysis of stacked rotated grating (SRG). Also, we propose time-varying MOL using implementation of the multi-frequency finite difference frequency domain (FDFD) method upon our presented method, so that one can simulate spatiotemporal structures in the hybridization framework... 

We consider a multi-species generalization of the Asymmetric Simple Exclusion Process on an open chain, in which particles hop with their characteristic hopping rates and fast particles can overtake slow ones. The number of species is arbitrary and the hopping rates can be selected from a discrete or continuous distribution. We determine exactly the phase structure of this model and show how the phase diagram of the 1-species ASEP is modified. Depending on the distribution of hopping rates, the system can exist in a three-phase regime or a two-phase regime. In the three-phase regime the phase structure is almost the same as in the one species case, that is, there are the low density, the... 

Redundancy technique is considered as a way to enhance the reliability and availability of a system. This paper models availability of a repairable system with multiple subsystems in which the involved components follow the load sharing strategy. In redundancy allocation problems, the redundancy level is just considered, whereas, in this paper, the number of repair facility (repairman) is added to the decision variables. The goal is to find the optimal number of repairmen and redundant components in each subsystem for optimization of availability subject to weight, cost and volume constraints. The main contribution of this study is to present a straightforward model for availability... 

A novel BiCMOS voltage-to-voltage converter with logarithmic characteristics and very high accuracy is presented. The relationship between the emitter current and the base-emitter voltage in bipolar transistors is used to realize the logarithmic function. With 1.8 supply voltage, the total power consumption is less than 15.75 mW and a Log error of < -36dB is shown in the ADS simulations. Compared to the other method in the literature, very better accuracy in logarithm calculation is achieved. The proposed method can be used in arithmetical operation circuits like analog processors  

A novel semi-active control system for suspension systems of passenger car using Magnetorheological (MR) damper is introduced. The suspension system is considered as a mass-spring model with an eight-degrees-of-freedom, a passive damper and an active damper. The semi-active vibration control is designed to reduce the amplitude of automotive vibration caused by the alteration of road profile. The control mechanism is designed based on the optimal control algorithm, Linear Quadratic Regulator (LQR). In this system, the damping coefficient of the shock absorber changes actively trough inducing magnetic field. It is observed that utilizing the present control algorithm may significantly reduce...