Sharif Digital Repository

Response surface methodology (RSM) explores the relationships between several explanatory variables and one or more response variables. The main idea of RSM is to use a set of designed experiments to obtain an optimal response. RSM tries to simplify the original problem through some polynomial estimation over small sections of the feasible area, elaborating on optimum provision through a well known optimization technique, say Gradient Method. As the real world problems are usually very complicated, polynomial estimation may not perform well in providing a good representation of the objective function. Also, the main problem of the Gradient Method, getting trapped in local minimum (maximum),... 

This paper presents sliding mode control and model reference adaptive control strategies for the tape transport mechanism. A nonlinear multivariable MIMO model of the process, consisting of take-up and supply reel servos for tape tension control and capstan servo for speed control is considered. The sliding mode control is applied for the nonlinear dynamic model of the process, while the model reference adaptive control deals with the linearized one. Moreover, in order to associate with the realistic model of system, design of controllers is accomplished with respect to parametric uncertainties. It is shown that both control strategies can guarantee asymptotic stability of the closed-loop... 

In this paper, we study transmission of a memoryless Laplacian source over three types of channels: additive white Laplacian noise (AWLN), additive white Gaussian noise (AWGN), and slow flat-fading Rayleigh channels under both bandwidth compression and bandwidth expansion. For this purpose, we analyze two well-known hybrid digital-analog (HDA) joint source-channel coding schemes for bandwidth compression and one for bandwidth expansion. Then we obtain achievable (absolute-error) distortion regions of the HDA schemes for the matched signal-to-noise ratio (SNR) case as well as the mismatched SNR scenario. Using numerical examples, it is shown that these schemes can achieve a distortion very... 

We study transmission of a memoryless Laplacian source over an average-power limited additive white Laplacian noise (AWLN) channel under bandwidth compression in two cases: 1) matched signal-to-noise ratio (SNR), 2) mismatched SNR. A hybrid digital-analog (HDA) joint source-channel coding (JSCC) scheme is proposed and show that this scheme can achieve a distortion very close to the lower bound on mean-absolute error (MAE) distortion under matched SNR conditions  

Motion capture is a process that movements of living organisms like human or objects are captured and the results are processed for the desired applications. These applications are in rehabilitation, sports, film industry and etc. There are many techniques and instruments for motion capture that optical camera systems are the most accurate ones. But these cameras are high cost and limited to labs. Some sensors like Inertial Measurement Units (IMU) and recently, Kinect cameras have been considered by many researchers because these are low cost and easy to use. But problems like bias, accumulated error and occlusion make them look for improvements. Fusion algorithms are one of the best methods... 

Motion capture is a process that movements of living organisms like human or objects are captured and the results are processed for the desired applications. These applications are in rehabilitation, sports, film industry and etc. There are many techniques and instruments for motion capture that optical camera systems are the most accurate ones. But these cameras are high cost and limited to labs. Some sensors like Inertial Measurement Units (IMU) and recently, Kinect cameras have been considered by many researchers because these are low cost and easy to use. But problems like bias, accumulated error and occlusion make them look for improvements. Fusion algorithms are one of the best methods... 

In the present study the behavior of Ti-Al-C ternary system is investigated during mechanical alloying. The mixture of Ti, Al and C powders was used with initial stoichiometric composition of Ti3AlC2. X-ray diffraction (XRD) was used to characterize the milled powders and a thermodynamic analysis of the process was then carried out using Miedema model. This thermodynamic analysis showed that for all binary Ti-C, Al-C, Ti-Al systems and ternary Ti-Al-C systems, among all compositions, the thermodynamic driving force for intermetallic phase formation is much greater when compared with the formation of solid solutions or amorphous phases. Finally the reactions that are feasible to occur during... 

In this paper, Ti-6Al-4V/TiC composite was fabricated by VIM furnace and graphite crucible. X-ray diffraction analysis and EDS techniques were used to identify the phases in the material. Microstructure characteristics of the Ti-6Al-4V/TiC composite were evaluated by means of optical microscopy. The tensile test was performed at room temperature after hot-rolling of the samples in the beta phase field. The results revealed that at different melting times, three kinds of precipitates are formed in the microstructure including grain boundary, eutectic and transgranular precipitates. The size of transgranular precipitates was significantly larger than that of the other two types of carbides and... 

A metal organic framework-polyaniline (MOF/PANI) nanocomposite was electrodeposited on a stainless steel wire and used as a solid phase microextraction (SPME) fiber coating. The electropolymerization process was carried out under a constant deposition potential and applied to the corresponding aqueous electrolyte containing aniline and MOF particles. The employment of MOFs with their large and small cages and 3-D structures in synthesizing a nanocomposite was assumed to be efficient constitutes to induce more non-smooth and porous structures, approved by scanning electron microscopy (SEM) images. Three different MOFs were incorporated to synthesize the desired nanocomposites and the... 

In this paper a reliability, emission, and network security constrained unit commitment (UC) with the focus on wind power integration is formulated. It is shown that clearing both energy and spinning reserve markets taking into account network constraints provides a reliable and economic solution for day-ahead operation planning of a power system with a significant amount of thermal and wind power in the generation portfolio. The developed UC is formulated and implemented in MATLAB. The IEEE 24-Bus Reliability Test System (RTS) is used to verify the UC method by simulation. © 2017 IEEE  

Implementation of metal-organic frameworks (MOFs) in the separation science is attractive for many researchers, nowadays. In this study, three MOFs were synthesized and employed as extractive coating fibers. The MIL-101-NH2-based coatings were implemented in immersed solid phase microextraction (ISPME) of organophosphorus pesticides (OPPs) from real-life samples. The three different kinds of fiber coatings included MIL-101-NH2 and its acyl and ethyl modified structures as particles and 3-aminopropyl triethoxysilane (APTES) sol-gel precursor as binder. Each single MOF was coated on a stainless steel substrate via sol-gel technique. The uniform and tunable pore structure, high surface area,... 

In this article, ferrohydrodynamic forced-convection heat transfer from a heated sphere embedded in a ferrofluid in the presence of the uniform external magnetic field has been studied numerically for the first time over a wide range of Reynolds number value, nanoparticle diameter, particle volume fraction, and magnetic field intensity. Despite the uniform external magnetic field applied, the internal magnetic field near the sphere could be nonuniform due to the considerable difference between the relative magnetic permeability of the sphere and the surrounding medium. Kelvin body force arises from this nonuniformity and induces vortexes near the sphere. These vortexes disturb the boundary... 

In this paper, an in-situ powder metallurgy technique of fabricating near net shape particulate Al3Ti-Al composite is developed. Titanium tri-aluminide particles were generated in aluminum matrix by solid state reactive diffusion of homogenous blended pure Ti and Al powders. Effects of titanium particle size, temperature and time of sintering on microstructure and mechanical properties of the composite were studied by X-ray diffraction analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy and tensile testing. After 5 h sintering at 600 °C, Al3Ti intermetallic particles were formed as the major second phase. By decreasing the titanium particle size or increasing the... 

The objective of the research is to determine the effect of friction stir processing (FSP) parameters and vibration on the machining behavior of AZ91 alloy. The article displays the state of the art of AZ91 alloy machinability including chip formation, chip morphology, and cutting forces. In this method, the vibration was applied to the process line through the fixture under the workpiece during the FSP. The three-dimensional finite element (FE) modeling was applied for simulating the small-hole drilling process of AZ91 alloy. The large deformation of work and the chip formation in drilling process is realized by incorporating Johnson-Cook material constitutive model and material failure... 

A numerical analysis is improved to study the effect of vibration on temperature history, heat generation, and mechanical properties during the friction stir welding process with different welding speeds. In this investigation, smoothed particle hydrodynamics (SPH) was applied to improve the 3D numerical analysis for simulation of the friction stir welding (FSW) process and friction stir vibration welding (FSVW) under different welding speeds. According to the experimental analysis, the grain size of the FSVW-ed sample is finer compared with that of the FSW-ed sample. The analysis was validated through a comparison of the simulated thermal cycles with the experimental results. There was a... 

In the present study, a ratiometric fluorescent sensor array as an artificial tongue has been developed on a nanopaper platform for chemical discrimination applications. The bacterial cellulose (BC) nanopaper was utilized for the first time as a novel, flexible, and transparent substrate in the optical sensor arrays for developing high-performance artificial tongues. To fabricate this platform, the hydrophobic walls on the BC nanopaper substrates were successfully created using a laser printing technology. In addition, we have used the interesting photoluminescence (PL) properties of an immobilized ratiometric probe (carbon dot-Rhodamine B (CD-RhB) nanohybrids) on the nanopaper platform to... 

The objective of the research is to determine the effect of friction stir processing (FSP) parameters and vibration on the machining behavior of AZ91 alloy. The article displays the state of the art of AZ91 alloy machinability including chip formation, chip morphology, and cutting forces. In this method, the vibration was applied to the process line through the fixture under the workpiece during the FSP. The three-dimensional finite element (FE) modeling was applied for simulating the small-hole drilling process of AZ91 alloy. The large deformation of work and the chip formation in drilling process is realized by incorporating Johnson-Cook material constitutive model and material failure... 

A method for joining metals in the semisolid state is presented. A model alloy Sn-15%Pb was used to demonstrate the concept. By presented process, dendritic microstructure of the weld zone can be avoided. Moreover, near-weld zone of the cold worked substrates which is affected by heat would have a globular structure due to a thermomechanical treatment. The two substrates were heated up locally in the joint line to the semisolid temperature range. At this point a stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. Localized mechanical properties of different zones were examined using Shear Punch Test (SPT), showing a good strength in the weld... 

The influence of different parameters such as welding pressure, rotational speed, and traverse speed on the weld properties has been evaluated earlier but there are some important parameters yet to be thoroughly investigated. In this study, an effort has been made to determine the influence of different ratios of rotational speed/traverse speed on mechanical properties of different zones of friction stir welded AZ31 magnesium alloy. Mechanical properties of different zones were determined by a shear punch test. It was found out that increasing the aforementioned ratio leads to a slight decrease in yield and ultimate strength of the stir zone and the transitional zone. It was also observed... 

The effectiveness of the application of CFD to vapour cloud explosion (VCE) modelling depends on the accuracy with which geometrical details of the obstacles likely to be encountered by the vapour cloud are represented and the correctness with which turbulence is predicted. This is because the severity of a VCE strongly depends on the types of obstacles encountered by the cloud undergoing combustion; the turbulence generated by the obstacles influences flame speed and feeds the process of explosion through enhanced mixing of fuel and oxidant. In this paper a CFD-based method is proposed on the basis of the author's finding that among the various models available for assessing turbulence, the...