Sharif Digital Repository

The level and character of noise emitted by exhaust system has significant effect on the overall acoustic performance of vehicle powertrain and sound quality which is received by occupants. In addition to meeting aforementioned objective, the exhaust system must meet exterior noise regulation which is ordered by governments. In this study, acoustic performance of the vehicle exhaust system is investigated. Numerical simulation is applied for this aim that is the fastest and the most economical method in early design stages of vehicle development process. Thickness optimum design is performed in order to improve acoustic performance of exhaust system. Robust parameter design, based on Taguchi... 

The wave functions for calculating 13C nuclear magnetic chemical shifts of 22 groups of organic compounds (64 molecules) in chloroform solution have been optimally selected using factorial design as a multivariate technique. Our own N-layered integrated molecular orbital and molecular mechanics approach was applied for molecules with different types of carbons. The results have obtained in very good agreement with the experimental values. An additional series (58 molecules) have been used as test sets and their results confirm the validity and reliability of the approaches. The total root mean square deviation and correlation coefficient of predictions (433 carbons) are 1.88 and .9994,... 

Aseptic loosening is one of the main reasons for the revision of a total knee replacement (TKR). The design of the key component of a TKR, the femoral component, is particularly problematic because its failure can be the result of different causes. This makes the development of new biomaterials for use in the femoral component a challenging task. This paper focuses on the engineering design aspects in order to understand the limitationsof current materials and design deficiencies. The paper describes the introduction of a new biomaterial for a femoral component and justifies the recommendation to use multi-functional materials as a possible solution to aseptic loosening. The potential... 

Economic design of a control chart involves determining its basic parameters such that a cost function is minimized. This design when statistical performance measures are also considered is referred to as the economic-statistical design. In this paper, a simplex-based Nelder-Mead algorithm is used in combination with a particle swarm meta-heuristic procedure to solve both the economic and economic-statistical designs of a MEWMA control chart. The application results on extensive simulation experiments show that the particle swarm can lead the Nelder-Mead algorithm to better results. Furthermore, a comparative study is performed on the performances of three different algorithms of the... 

In the Endurance Time (ET) method, structures are subjected to a calibrated intensifying accelerogram and their performance is assessed based on their response at various equivalent intensity levels. Application of the ET method in performance-based design of structures has been studied by introducing a continuous performance target curve, which expresses the limit of the proper seismic performance of a structure along various times of the ET accelerogram. The correlation between time in the ET method and the return period for different structural periods is investigated. The procedure is based on the coincidence of response spectra obtained from the ET accelerogram at different times and... 

Control charts are the best tools to monitor main process parameters, and the Multivariate Exponentially Weighted Moving Average, MEWMA, type of this tool is used when there are several correlated quality characteristics to be monitored simultaneously where detecting small deviations of the characteristics is desired. In this paper, the models of both the economic and the economic-statistical design problems of MEWMA control charts are solved by a Particle Swarm Optimization (PSO) approach. The comparison study between the economic and the economic-statistical designs shows better statistical performances of the economic-statistical design with negligible increase in cost. Furthermore, in... 

Transportation network design problem (TNDP) aims to choose from among a set of alternatives (e.g., set of new arcs) which minimizes an objective (e.g., total travel time), while keeping consumption of resources (e.g., budget) within their limits. TNDP is formulated as a bilevel programming problem, which is difficult to solve on account of its combinatorial nature. Following a recent, heuristic by ant colony optimization (ACO), a hybridized ACO (HACO) has been devised and tested on the network of Sioux Falls, showing that the hybrid is more effective to solve the problem. In this paper, employing the heuristic of particle swarm optimization (PSO), an algorithm is designed to solve the TNDP.... 

In this study, linear polarization resistance (LPR) of pulse reverse electrodeposited graphene oxide (PREGO) coating is optimized by design of experiments approach (central composite design). Pulse current density (i), cathodic (Tc) and anodic (Ta) pulse durations, and total electrodeposition time (Tt) are selected as the substantial factors. The best prediction model proposes a definitive linear relation without any significant interaction of the LPR by analysis of variance. The desirable value of LPR was predicted equal to 5358 Ω cm2, obtaining at the pulse current density of 235.62 mA cm−2, Ta of 7.75 ms, Tc equal to 3.25 ms (f = 100 Hz), and Tt of approximately 225 s. Appearance of the... 

This paper describes how to find optimal operating conditions of three controlling parameters, i.e. temperature, transmembrane pressure (TMP), and cross-flow velocity (CFV) for maximizing the permeate flux and total organic carbons (TOC) rejection, and minimizing the fouling resistance using Taguchi method in ultrafiltration (UF) treatment of the real produced water. At first, the optimal operating conditions were found at a temperature of 45°C, TMP = 4 bar, and CFV of 2.25 m/s. To determine the most significant parameters affecting the response parameters, an analysis of variance was employed. In the second stage, performance of applied polymeric membrane in the UF system was studied under... 

Delay in communication wires causes design iterations in system-on-chip. Latency-insensitive design copes with this issue by encapsulating each core in a shell wrapper and inserting buffers in the wires to separate the design of core from that of communication wires. Scheduling-based latency-insensitive protocol is a methodology which employs shift registers for periodic clock gating of blocks instead of the shell wrappers. In many cases, the bit sequences inside the shift registers are too long and therefore consume a large area. This study presents a heuristic algorithm that optimises the bit sequences and produces them with shorter lengths compared with the existing method. The algorithm... 

In this paper, we consider the problem of transmit code design to optimize the detection probability of an extended target embedded in Gaussian signal-dependent interference. We model the target with a priori known target impulse response (TIR) structure along with an unknown reflection factor. As is known, the performance of the generalized likelihood ratio test (GLRT) detector, for the case at hand, monotonically increases with the signal-to-interference-plus-noise ratio (SINR). Hence, we deal with the code design problem via maximizing the SINR. We also enforce a peak-to-average power ratio (PAR) constraint on the sought code. We devise a cyclic method to tackle the highly non-convex... 

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.... 

Featuring a nonlinear novel design, Gimbal transmission, is a replacement for traditional robotic joints like gearboxes and revolute joints. This mechanism is one of the most recent types of nonlinear direct transmission (DT) methods in robots. As an alternative for traditional drive methodologies - herein called direct drive transmission (DD) methods, DT provides dynamic coupling and joint interaction attenuation while its capability to be adjusted for a desired task space point, smooth input-output characteristic, and varying reduction ratio lead to a desired force and motion behavior for the whole manipulator. In this paper, design optimization of a gimbal mechanism used as a replacement... 

The wave functions for calculating gas phase 19F chemical shifts were optimally selected using the factorial design as a multivariate technique. The effects of electron correlation, triple-ξ valance shell, diffuse function, and polarization function on calculated 19F chemical shifts were discussed. It is shown that of the four factors, electron correlation and the polarization functions affect the results significantly. B3LYP/6-31 + G(df,p) wave functions have been proposed as the best and the most efficient level of theory for calculating 19F chemical shifts. An additional series of fluoro compounds were used as a test set and their predicted 19F chemical shifts values confirmed the... 

Employing profiles using variable sample size (VSS) may improve its effectiveness and hence is investigated in this paper. Besides, the implementation cost of a profile is an important factor in determining the main parameters. In this paper, the Lorenzen-Vance function is first extended to model implementation cost of VSS linear profiles. Then, the resulted economic model is solved using a genetic algorithm (GA). The average run length criterion when process is in control, ARL0 and the average run length measure when process goes out of control, ARL1 , is used to evaluate statistical properties of the designed profile. Moreover, a sensitivity analysis on the main parameters of the... 

A three-step method for the deposition of CH3NH3PbI3 perovskite films with a high crystalline structure and large cuboid overlayer morphology is reported. The method includes PbI2 deposition, which is followed by dipping into a solution of C4H9NH3I (BAI) and (BA)2PbI4 perovskite formation. In the final step, the poorly thermodynamically stable (BA)2PbI4 phase converts into the more stable CH3NH3PbI3 perovskite by dipping into a solution of CH3NH3I. The final product is characterized by XRD, SEM, UV/Vis, and photoluminescence analysis methods. The experimental results indicate that the prepared perovskite has cuboids with high crystallinity and large sizes (up to 1 μm), as confirmed by XRD... 

Successful design and implementation of knowledge management systems have been the main concern of many researchers. It has been reported that more than 50% of knowledge management systems have failed, therefore, it is required to seek for a new and comprehensive scientific approach to design and implement it. In the design and implementation of a knowledge management system, it is required to know 'what we want to achieve' and 'how and by what processes we will achieve it'. A literature review conducted and axiomatic design theory selected for this purpose. For the first time, this paper develops a conceptual design of knowledge management systems by means of a hierarchical structure,... 

The current study is an attempt to contribute for efficient and cost-effective substrates for xanthan gum production. In this context, the sugar cane molasses wastes can be used as a cheap substrate for xanthan gum production. Xanthan biopolymer production by a novel Xanthomonas campestris strain IBRC-M 10644 was optimized with statistical approaches. Based on the results of Response Surface Methodology (RSM) with Central Composite Design (CCD) technique, a second-order polynomial model was developed and evaluated the effects of variables on the maximum xanthan production. Agitation rate (X1: 200-500 rpm), sugar cane molasses concentration (X2: 30-90 g/L) and operation temperature (X3: 25-35... 

Due to substantial impacts of nanoparticles on mass and heat transfer, having knowledge about different types of nanoparticles can contribute to access high efficiencies. As an investigation, in the present study, a number of liquid-liquid extraction experiments were designed by the use of Taguchi design model in order to study the impacts of SiO2 and MgO nanoparticles on mass transfer, in the batch systems. Acetic acid was considered as solute in some organic phases (i.e., n-butanol, n-butyl acetate, toluene, and chloroform), and pure water was applied as solvent. Taguchi experiment design method made more precision and convenience in the work. Final results showed reduction of mass... 

Background: The researches regarding the influence of microthread design variables on the stress distribution in bone and a biomechanically optimal design for implant neck are limited. The aim of the present study is to compare the effect of different microthread designs on crestal bone stress. Materials and Methods: Six implant models were constructed for three-dimensional finite element analysis including two thread profile (coarse and fine) with three different lengths of microthreaded neck (1 mm, 2 mm, and 3 mm). A load of 200 N was applied in two angulations (0° and 30°) relative to the long axis of the implant and the resultant maximum von Mises equivalent (EQV), compressive, tensile,...