Sharif Digital Repository

A novel mesoporous silica-functionalized dual Brønsted acidic species has been introduced as an efficient catalyst for solvent-free esterification of fatty acids with ethanol. The structure of the catalyst has been characterized by FT-IR spectroscopy, thermal gravimetric analysis (TGA), TEM and N2 adsorption-desorption. TGA of catalyst 1 showed no weight loss before 200 °C, indicating a high degree of hydrophobicity of the surface of the mesoporous silica. TEM images and nitrogen adsorption-desorption showed no noticeable changes to the structure of the catalyst before and after acid treatment. pH metric analysis was performed for the catalyst to determine the loading of the acidic sites.... 

TiO2 nanorod layers are synthesized by simple chemical oxidation of Ti substrates. Diffuse reflectance spectroscopy measurements show effective light scattering properties originating from nanorods with length scales on the order of one micron. The films are sensitized with CdSe quantum dots (QDs) by successive ionic layer adsorption and reaction (SILAR) and integrated as a photoanode in quantum dot sensitized solar cells (QDSCs). Incorporating nanorods in photoanode structures provided 4- to 8-fold enhancement in light scattering, which leads to a high power conversion efficiency, 3.03% (Voc = 497 mV, Jsc = 11.32 mA/cm2, FF = 0.54), in optimized structures. High efficiency can be obtained... 

This paper presents an improved firefly algorithm (FA) for fast optimization of truss structures with discrete variables. The enhanced accelerated firefly algorithm (AFA) is a simple, but very effective modification of FA. In order to investigate the performance and robustness of the proposed algorithm, some benchmark (structural optimization) problems are solved and the results are compared with FA and other algorithms. The results show that in some test cases, AFA not only finds lighter structures compared to other algorithms, but also converges faster. In the rest test cases, the optimal solutions are found with very less computational effort. The study also shows that the proposed AFA... 

The surface plasmon effect of Au nanostructures placed on the surface of hematite has recently been used to enhance light absorption within its carrier collection distance of 10 nm from the water-hematite interface. Despite significant narrow band absorption enhancements in the visible region, the reported enhancements in the overall performance of the cell under standard AM1.5 sunlight illumination are not significant. We numerically design an array of Au stripes on the surface of an extremely thin layer of hematite to maximize the number of charge carriers that can reach the hematite-water interface and explore the optical processes involved. The lateral dimensions and in particular the... 

-In this paper, a new optimized structure for two-speed, capacitor-run, single-phase axial flux induction motor (AFIM) for direct-drive operation is presented. Although, there are many advantages for direct-drive systems, their axial forces between the stator and rotor increases with reduction in air-gap length and is of serious concern. An increase in the air-gap length will result in the deterioration of performance characteristics of the motor. In this paper, a new construction technique is proposed to fabricate an AFIM with adjustable air-gap length. After presenting a comprehensive design algorithm, all geometrical dimensions and electrical equivalent circuit parameters are analytically... 

In this paper, we present a reconfigurable architecture for networks-on-chip (NoC) on which arbitrary application-specific topologies can be implemented. When a new application starts, the proposed NoC tailors its topology to the application traffic pattern by changing the inter-router connections to some predefined configuration corresponding to the application. It addresses one of the main drawbacks of the existing application-specific NoC optimization methods, i.e., optimization of NoCs based on the traffic pattern of a single application. Supporting multiple applications is a critical feature of an NoC when several different applications are integrated into a single modern and complex... 

The objective of this research is geometrical optimization of half toroidal Continuously Variable Transmission (CVT) in order to achieve high power transmission efficiency. The dynamic analysis of CVT is implemented and contact between the disk and the roller is modeled viaelastohydrodynamic (EHL) lubrication principles. Computer model is created using geometrical, thermal and kinetic parameters to determine the efficiency of CVT. Results are compared by other models to confirm the model validity. Geometrical parameters are obtained by means of Particle Swarm Optimization (PSO) algorithm, while the optimization objective is to maximize the power transmission efficiency. Optimization was... 

Ultrasonic assisted machining (UAM) is an efficient nontraditional machining operation for brittle, hard-to-cut and poor-machinability materials. In UAM, high frequency oscillation in ultrasonic range at low amplitude is imposed on the workpiece or cutting tool. In most cases, the equipments that generates and transfers the vibration, have a complicated structure, and requires significant effort to achieve their optimum function. In this work, a mathematical model is developed and an optimization method is employed for design process. This makes it possible to achieve proper setup and reduce the amount of calculation. For this purpose, the combination of a two level full factorial design is... 

Theoretical study of nitrogen monoxide adsorption on small Six (x = 3-5) clusters has been carried out using the advanced hybrid meta-density functional method of Truhlar (MPW1B95). MG3 semi-diffuse basis sets were employed to improve the results. The geometry, adsorption energy, natural bond orbital charge, natural population analysis (NPA)-derived spin density and vibrational frequency of NO adsorption on all optimized nanoclusters were investigated. Also using the NPA, we have investigated the change of bond orders through adsorption. It has been found that NO is capable of making n-centre bonds (n = 1-4) from the nitrogen side but bonds to one site from the oxygen end. In the later case... 

We present a combined trust region-line search structured algorithm for solving constrained nonlinear least-squares problems. The approach is based on adaptive structured scheme due to Mahdavi-Amiri and Bartels of the exact penalty method of Coleman and Conn for nonlinearly constrained optimization problems. The structured adaptation also makes use of the ideas of Nocedal and Overton for handling quasi-Newton updates of projected Hessians. For robustness, we propose a new penalty parameter updating strategy and a specific line search strategy within the trust region, taking account of the least-squares objective and special structured considerations for the approximate projected... 

During design, microsatellites are subject to different changes like the changes in weight, location and dimension of parts and elements of subsystems and the payload. These changes should be accumulated by the structure subsystem in a way that some key structural parameters like the center of gravity (CG) and inertia moments remain unchanged. This subject is also important regarding the design of a modular structure of a satellite. In the present study it is tried to accommodate any changes in weight and location of any part(s) and element(s) of a microsatellite by optimum (minimum) rearrangement of other parts on their plane of rest in order to keep the CG and inertia moments unchanged.... 

It has been well documented that multivariate systems will benefit from application of advanced control strategies. The application of these methods has thus far been hindered for a variety of reasons which range from complexity of the design methodologies to the cost associated with implementation of these solutions. This paper shows that there exist alternative means by which existing control strategies of a multivariate system could be extended, thereby leading to increased efficiency, without the need to remove and implement a new control system installation. A realistic model of an entire pulping mill is used in this paper to show that by careful selection of only a few additional... 

This article explores the main tradeoffs in design of power and area efficient bandgap voltage reference (BGR) circuits. A structural design methodology for optimizing the silicon area and power dissipation of CMOS BGRs will be introduced. For this purpose, basic equations of the bandgap circuit have been adapted such that can simply be applied in the optimization process. To improve the reliability of the designed circuit, the effect of amplifier offset has been also included in the optimization process. It is also shown that the minimum achievable power consumption and area are highly depending on the fabrication process parameters especially sheet resistivity of the available resistors in... 

Theoretical study of carbon monoxide adsorption on SixGe4 - x(x = 0-4) nano-clusters has been carried out using advanced hybrid meta density functional method of Truhlar (MPW1B95). MG3 semi-diffuse (MG3S) and correlation consistent valence basis sets with relativistic core potential were employed to improve the results. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. The geometry, adsorption energy, charge distribution, and vibrational frequency of CO adsorption on all possible structures were investigated. The maximum vibrational... 

Radial flux variable reluctance resolvers (RFVR2s) are widely used in variety of applications. However, they suffer from an intrinsic error which is called static eccentricity (SE). Although most of the errors in the resolvers can be suppressed using electronic methods in resolver to digital (R/D) converters, static misalignment is an exception. In this paper an axial flux configuration is proposed for variable reluctance (VR) resolvers with concentric windings. Then the proposed structure is optimized to achieve the minimum sensitivity of accuracy against SE. The performance of the presented structure, so called axial flux variable reluctance resolver (AFVR2), is validated using 3-D time... 

We propose a nano-plasmonic thin-film solar cell (TFSC) as a receiver for the visible light communication (VLC). The presented design is a novel and optimized structure that can be used instead of photodetectors and power supplies in the VLC. The plasmonic TFSC that described in this work is capable of increasing the light absorption in comparison with the conventional thick Si solar cell without plasmonic nanostructures. However, plasmonic nanoparticles can improve the absorption of Si solar cell in a visible range of solar spectra. In this paper, different situations for inserting nanoparticles in an active layer are considered and the absorption is calculated as a function of particle... 

The study develops a methodology for the aero-structural design including consideration of the starting of a small wind turbine blade. To design a fast-starting blade, starting time was combined with output power in an objective function and the blade allowable stress was considered as a constraint. The output power and the starting time were calculated by the blade-element momentum theory and the simple beam theory was employed to compute the stress and deflection along the blade. A genetic algorithm was employed to solve the constrained objective function, finding an optimal blade for which the starting time was small and output power was high while the stress limitation was also met.... 

Conventional lateral resisting systems can provide sufficient strength and ductility for design based earthquakes, although the considerable residual deformation remaining in the plasticized regions undermines the resiliency of the structures. In order to resolve this problem, various self-centering systems have been proposed and tested in recent years, most of which are specified for new buildings and are not simply suitable for retrofitting applications. Moreover, the available self-centering systems are costly and complex to assemble, which can be considered as a serious barrier for practical application. To address these drawbacks, an innovative Core-Less Self-Centering (CLSC) brace is... 

Three-dimensional reduced graphene oxide (3D-rGO) structures decorated with CuO particles (GCu) are synthesized through a simple and scalable method for detection of hydrogen sulfide (H2S) gas. For characterization and investigation of porous structure various techniques were employed. Decorated 3D structures demonstrated higher sensitivity and selectivity in comparison to pure structure. Optimized structure for sensing was obtained through introducing different amounts of CuO. The GCu heterostructures containing 35 μmol of CuO powder demonstrated reproducible response of about 30% to the concentration of 10 ppm at room temperature, while complete recovery was obtained through heating to 150... 

In this paper, an attempt is made to examine a new method for designing and applying the active vibration control system to improve building performance under mainshock–aftershock sequences. In this regard, three different structures are considered; 5-, 10-, and 15-story buildings. Seven mainshock–aftershock sequences are selected from the Iranian accelerogram database for analyzing the structures. By implementing an advanced two-step optimization method, buildings equipped with the active vibration control system (linear–quadratic regulator (LQR) algorithm) are designed to withstand all events of mainshock–aftershock sequences. In the first optimization step, a multi-objective optimization...