Sharif Digital Repository

Ring rolling is one of the most significant methods for producing rings with highly precise dimensions and superior qualities such as high strength uniformity, all accomplished without wasting any materials. In this article, we have achieved analytical formulas for calculating the pressure and shear friction over the contact arcs between the rollers and ring in the ring rolling process for the material in general nonlinear hardening property. We have also asserted the best mathematical model to predict friction for rolling processes. The method we use is based on calculating the analytical stress distribution. In other words, by using of Saint-Venan principal the stress components are... 

In this paper, the design of an efficient sparse array, used to reconstruct the image from millimeter-wave signals, is presented. The proposed array takes advantage of the sparsity concept of the image in the spatial Fourier domain to reduce the number of array elements such that the beam pattern of the designed array meets the desired beamwidth and sidelobe level. Simulation and measured results confirm the effectiveness of the proposed design on high-quality reconstruction of the image, while 85% reduction in the number of elements is achieved as well as the reduction in scan time and system complexity  

Real-world image classification, which aims to determine the semantic class of un-labeled images, is a challenging task. In this paper, we focus on two challenges of image classification and propose a method to address both of them simultaneously. The first challenge is that representing images by heterogeneous features, such as color, shape and texture, helps to provide better classification accuracy. The second challenge comes from dissimilarities in the visual appearance of images from the same class (intra class variance) and similarities between images from different classes (inter class relationship). In addition to these two challenges, we should note that the feature space of... 

The goal of this paper is to reduce the antenna count in a millimeter (mm)-wave imaging system by proposing both hardware and software solutions. The concept of image sparsity in the transform domain is utilized to present the compressive sensing (CS) formulation for both mono-static and multistatic imaging at mm-wave frequencies. To reduce the complexity of the imaging system and reconstruction process, we introduce 1.5-D array structure, which is a random sparse array with orthogonal element locations. It is shown that the peak signal-to-noise ratio (PSNR) of the reconstructed image obtained by a 1.5-D array with 65% sparsity is very close to the PSNR of a uniform 2-D array for mono-static... 

In this paper, a new approach based on hybrid Particle Swarm-Based- Simulated Annealing Optimization (PSO-B-SA) for solving thermal unit commitment (UC) problems is proposed. The PSO-B-SA presented in this paper solves the two sub-problems simultaneously and independently; unit-scheduled problem that determines on/off status of units and the economic dispatch problem for production amount of generating units. Problem formulation of UC is defined as minimization of total objective function while satisfying all the associated constraints such as minimum up and down time, production limits and the required demand and spinning reserve. Simulation results show that the proposed approach can... 

We prove that every negatively associated sequence of Bernoulli random variables with “summable covariances” has a trivial tail σ-field. A corollary of this result is the tail triviality of strongly Rayleigh processes. This is a generalization of a result due to Lyons, which establishes tail triviality for discrete determinantal processes. We also study the tail behavior of negatively associated Gaussian and Gaussian threshold processes. We show that these processes are tail trivial though, in general, they do not satisfy the summable covariances property. Furthermore, we construct negatively associated Gaussian threshold vectors that are not strongly Rayleigh. This identifies a natural... 

In this study, free vibration analysis of moderately thick symmetrically laminated general trapezoidal plates with various combinations of boundary conditions is investigated. The governing partial differential equations and boundary conditions for trapezoidal plate are obtained using first order shear deformation theory (FSDT) together with proper transformation from Cartesian system into trapezoidal coordinates. Generalized differential quadrature (GDQ) method is then employed to obtain solutions for the governing equations. Results of the GDQ method are compared and validated with available results in the literature which show accuracy and fast rate of convergence of the method. Effect of... 

An inexpensive silicon rubber-based chip was constructed by fabricating a triangle-shaped microcanal with a 135 μm width and 234 μm depth by laser ablation technique. The fabricated groove was sealed by a thin glass cover while two pieces of stainless-steel tubing were connected to each side of the canal. Then, a thin polyaniline film was synthesized on the walls of the canal by chemical oxidation using a syringe pump to deliver the relevant reagents. The microfluidic system was eventually connected to a gas chromatography-mass spectrometry. To evaluate the capability of the constructed microfluidic system, it was implemented to the analysis of submilliliter volumes of environmental samples... 

The early diagnosis together with an efficient therapy of cancer is essential to treat cancer patients and to enhance their quality of life. The use of nanostructures, as a newer technology, has demonstrated proven benefits as efficient cancer theranostic agents in numerous recent studies. Having a tunable surface plasmon resonance, gold nanostructures have been the subject of many recent studies as excellent imaging and photothermal therapy agents. However, the potential cytotoxicity and weak stability of gold nanostructures necessitate further modifications using biocompatible materials for biological applications. Based on the composition of the final structure, these gold-based hybrid... 

Application of fractional order PID (FOPID) controller to an automatic voltage regulator (AVR) is presented and studied in this paper. An FOPID is a PID whose derivative and integral orders are fractional numbers rather than integers. Design stage of such a controller consists of determining five parameters. This paper employs particle swarm optimization (PSO) algorithm to carry out the aforementioned design procedure. PSO is an advanced search procedure that has proved to have very high efficiency. A novel cost function is defined to facilitate the control strategy over both the time-domain and the frequency-domain specifications. Comparisons are made with a PID controller and it is shown... 

The main objective of this paper is to investigate the stability and stabilization problem of fuzzy large-scale systems in which the system is composed of a number of Takagi-Sugeno fuzzy subsystems with interconnection. Instead of fuzzy parallel distributed compensation (PDC) design, nonlinear state feedback controllers are used in stabilization of the overall large-scale system. Based on Lyapunov stability theory, linear matrix inequalities (LMIs) conditions are derived for asymptotic and exponential stability. Two numerical examples are given to confirm the analytical results and illustrate the effectiveness of the proposed strategy  

An investigation of the possible performance improvements of thin walled composite beams through the use of the variable stiffness concept with curvilinear fiber is presented. The beams are constructed from a single-cell closed cross section and a number of non-classical effects such as material anisotropy, transverse shear, warping inhibition and nonuniform torsional model are considered in the beam model. The governing equations were derived by means of the extended Hamilton's principle. Also the extended Galerkin's method is used to solve governing equations. Composite beams subjected to different loading with given geometry and material properties are optimized for maximum failure load.... 

Because of the complicated buckling characteristics of Y-shaped bracings, calculation of their strength is beyond routine engineering procedures. A method based on slope-deflection equations incorporating stability functions has been used for computation of buckling eigenvalues and effective length factors. Lateral strength is computed based on the least buckling strength of bracing members. This study is limited to bracings with similar sections and fixed end connections resisting out-of-plane rotation. Lateral strengths predicted by the analytical method for two cases are compared with experimental results on full-scale specimens. It is shown that the proposed analytical method predicts... 

This paper proposes a novel method to designing an H∞ PID controller with robust stability and disturbance attenuation. This method uses particle swarm optimization algorithm to minimize a cost function subject to-norm to design robust performance PID controller. We propose two cost functions to design of a multiple-input, multiple-output (MIMO) and single-input, single-output (SISO) robust performance PID controller. We apply this method to a SISO flexible-link manipulator and a MIMO super maneuverable F18/HARV fighter aircraft system as two challenging examples to illustrate the design procedure and to verify performance of the proposed PID controller design methodology. It is shown with... 

In this study, an experimental investigation was conducted from a thermal performance standpoint on closed-loop pulsating heat pipes (CLPHPs) with four different fluids and their water-based binary mixtures as working fluids with volume mixing ratios of 3:1, 1:1, and 1:3. Ethanol and acetone as two types of fluids that are soluble in water and, to unprecedentedly compare the behavior of insoluble mixtures with the soluble ones as the working fluids, toluene and hexane as two types that are insoluble in water were used. Additionally, to predict the thermal performance of the pure, soluble binary, and insoluble binary fluids simultaneously for the first time, a correlation was derived. © 2018,... 

In this study, an experimental investigation was conducted from a thermal performance standpoint on closed-loop pulsating heat pipes (CLPHPs) with four different fluids and their water-based binary mixtures as working fluids with volume mixing ratios of 3:1, 1:1, and 1:3. Ethanol and acetone as two types of fluids that are soluble in water and, to unprecedentedly compare the behavior of insoluble mixtures with the soluble ones as the working fluids, toluene and hexane as two types that are insoluble in water were used. Additionally, to predict the thermal performance of the pure, soluble binary, and insoluble binary fluids simultaneously for the first time, a correlation was derived. © 2018... 

Autologous grafts, as the gold standard for vascular bypass procedures, associated with several problems that limit their usability, so tissue engineered vessels have been the subject of an increasing number of works. Nevertheless, gathering all of the desired characteristics of vascular scaffolds in the same construct has been a big challenge for scientists. Herein, a composite silk-based vascular scaffold (CSVS) was proposed to consider all the mechanical, structural and biological requirements of a small-diameter vascular scaffold. The scaffold's lumen composed of braided silk fiber-reinforced silk fibroin (SF) sponge covalently heparinized (H-CSVS) using Hydroxy-Iron Complexes (HICs) as... 

Kinetic modeling of CO hydrogenation over Fe-Co-Mn catalyst was investigated; a ternary catalyst was prepared using incipient wetness impregnation. The kinetic parameters were determined from experiments carried out in a fixed bed micro-reactor under the following process conditions: T = 523.15-533.15 K, P = 1-10 bar, H2/CO = 1/1-3/1 and space velocity = 4500 h-1. Seventeen rate expressions were derived from five different mechanisms according to Langmuir-Hinshelwood-Hougen-Watson (LHHW) and Eley-Rideal (ER) mechanisms and were tested against the experimental data. Non-linear regression method was used to estimate different kinetic parameters; according to the obtained experimental results... 

The MgO-supported Fe-Co-Mn catalysts, prepared using co-precipitation procedure, were tested for production of light olefins via CO hydrogenation reaction. The effect of a range of drying conditions including drying temperature and drying time on the structure and catalytic performance of Fe-Co-Mn/MgO catalyst for Fischer-Tropsch synthesis was investigated in a fixed bed micro-reactor under the same operational conditions of T = 350 °C, P = 1 bar, H2/CO = 2/1, and GHSV = 4500 h-1. It was found that the catalyst dried at 120 °C for 16 h has shown the best catalytic performance for CO hydrogenation. Furthermore, the effect of drying conditions on different surface reaction rates was also... 

In this brief, an imaging methodology for mono-static millimeter-wave systems is introduced. When the measured object hologram is piece-wise smooth with sharp boundaries, both low-pass and high-pass components are present in a transform domain. Nevertheless, the edges are sparse in transform domain with respect to the image dimensions. It is shown that the down-sampling of the hologram with an appropriate rate determined by the sparsity level, includes the adequate information of all components for image reconstruction. Using random samples, an algorithm is proposed to recover all the sparse components, iteratively. Simulation results illustrate that a high-resolution recovery can be...