Sharif Digital Repository

Abstract: The effect of de-siliconization on the oxidation behavior of AISI 430 stainless steel used for solid oxide fuel cell interconnect application was investigated. De-siliconization treatment was conducted via heating steel parts in an H2 environment. The de-siliconized substrates were then coated with a Mn1.5Co1.5O4 spinel coating, using wet spray method. For comparison, a similar coating process was applied on the as-received AISI 430 stainless steel specimens. Oxidation kinetics of coated interconnects were evaluated at 700, 800 and 900 °C in air. Results showed that the de-siliconization surface treatment decreased oxidation rates, with kinetic rates (g2 cm−4 s−1) of 4.39 × 10−14... 

Investigation of the dynamic characteristics of an existing structure system based on field tests is of practical significance, since it can be employed in the field of examining construction quality, validating or improving analytical finite element structural models, or conducting damage assessment. The main purpose of this study is to investigate the dynamic characteristics of dams using the seismic response data. Whereas, in the process of frequency domain identification of dam properties, frequency response function (FRF) plays the most important role, evaluating the corresponding parameters with better accuracy has always been desirable. Therefore, a comparison was made between some... 

In this study, eggshell (ES) particles as an available and low-cost waste material were used for preparing hydrogel composites as dye biosorbents. For this purpose, hydrogel composites were prepared through free-radical graft copolymerization of wheat starch and sodium methacrylate (NaMA) in the presence of different contents of ES particles with various size ranges. FTIR spectroscopy confirmed graft copolymerization of NaMA moieties onto starch backbone besides the combination of ES particles with the starch-g-PNaMA matrix. The gel content values were high (>99%), which showed proper graft efficiency for hydrogel composites. Incorporation of ES particles into hydrogel matrix resulted in... 

In this paper, a sensitivity-based finite element (FE) model updating method using singular value decomposition (SVD) of frequency response function (FRF) is introduced. An exact sensitivity equation is proposed by incorporating measured responses of a damaged structure in the mathematical formulations. A set of incompletely measured natural frequencies of a damaged structure and mode shapes of the intact structure are used to deal with incomplete measurement without the implementation of FE model reduction or data expansion algorithms. The insights provided from the variation of SVD of transfer functions are used for the selection of proper updating frequency ranges. The appropriate... 

The seismic responses of steel water tanks are unconventional given their complex dynamic behavior and the sources of nonlinearity. Therefore, providing a reliable, finite-element model is instrumental in better understanding their dynamic behavior and improving the design conditions. This paper aims to evaluate the seismic performance of steel water tanks using shaking table tests and provide a finite-element reference model for simulating real-size, semi-anchored water tanks by conducting a series of large-scale tests in the Shaking Table Lab of the Sharif University of Technology (SUT). Since scaling the tank requires a difficult process involving changing the liquid density, this paper... 

Motivated by the bus escape routing problem in printed circuit boards, we revisit the following problem: given a set of n axis-parallel rectangles inside a rectangular region R, find the maximum number of rectangles that can be extended toward the boundary of R, without overlapping each other. We provide an efficient algorithm for solving this problem in O(n2 log3 n log log n) time, improving over the current best O(n3)-time algorithm available for the problem  

Structural reliability methods are employed in this paper for nationwide probabilistic seismic hazard analysis of Iran and in-depth seismic hazard and hazard sensitivity analysis of Downtown Tehran. The companion paper proposes two analysis approaches based on reliability methods and presents the technical framework for such analyses. The first approach was based on Monte Carlo sampling reliability analysis, which is employed here to conduct hazard analysis at a grid comprising 3695 sites throughout Iran. The results are used to produce nationwide hazard maps for the peak ground acceleration, spectral acceleration, and cumulative absolute velocity. The other analysis approach employs the... 

Structural reliability methods are employed in this paper for nationwide probabilistic seismic hazard analysis of Iran and in-depth seismic hazard and hazard sensitivity analysis of Downtown Tehran. The companion paper proposes two analysis approaches based on reliability methods and presents the technical framework for such analyses. The first approach was based on Monte Carlo sampling reliability analysis, which is employed here to conduct hazard analysis at a grid comprising 3695 sites throughout Iran. The results are used to produce nationwide hazard maps for the peak ground acceleration, spectral acceleration, and cumulative absolute velocity. The other analysis approach employs the... 

This paper presents the design and the application of a new self-powered hybrid electromagnetic damper that can harvest energy while mitigating the vibration of a structure. The damper is able to switch between an energy harvesting passive mode and a semi-active mode depending on the amount of energy harvested and stored in the battery. The energy harvested in the passive mode resulting from the suppression of vibration is employed to power up the monitoring and electronic components necessary for the semi-active control. This provides a hybrid control capability that is autonomous in terms of its power requirement. The proposed hybrid circuit design provides two possible options for the... 

Recently it was shown that the differential form of Eringen’s nonlocal elastic theory is unable to model, predict and track the mechanical behaviors of many nano-structures due to their boundary conditions. Therefore, having an accurate model for formulating such structures became an important issue. With respect to this concern, in this study, the influence of having an axially varying elastic environment on vibrational behavior of nanobeams is investigated for the first time. Size-dependent effects are modeled using Eringen’s two-phase local/nonlocal integral model which is well-posed with higher accuracy. The elastic environment is modeled using the Pasternak-Winkler method which could... 

The seismic behaviour of a 4-story building is investigated under horizontal excitation of simulated earthquakes. The model has been constructed with a 3D sandwich panel system without any conventional frame system in four storeys on a shaking table. The building has been modelled before construction. Due to the table limit, the scale factor of the model is chosen as 1: 2.35 of a prototype. The shaking table test of the scaled model of the building is carried out under several ground motions to verify the safety of the system. The simulated motions were applied to the model in two-perpendicular directions, simultaneously. The failure mechanism and dynamic behaviour of the model, as a... 

In this paper, the characteristics of a hybrid regenerative electromagnetic (EM) damper are first determined and experimentally examined. The main idea is to have two modes of operation for the EM damper, namely passive energy harvesting and semi-active modes. In the passive mode, the vibrational energy of an underlying structure is harvested and stored in a rechargeable battery. The harvested energy can then be employed in the semi-active control mode to supply the power demand for the required sensors and microcontroller. This hybrid damper would thus be capable of realizing the characteristics of a self-powered EM damper. A prototype of the damper was designed and tested under different... 

The Gnutella protocol requires peers to broadcast messages to their neighbors when they search files. The message passing generates a lot of traffic in the network, which degrades the quality of service. We propose the new method to optimize the speed of search and to improve the quality of service in a Gnutella based peer-to-peer environment with using semantic routing and priority of nodes. Once peers generate their "friends lists", they use these lists to route queries in the network. This helps to reduce the search time and to decrease the network traffic by minimizing the number of messages circulating in the system as compared to standard Gnutella  

By increasing the penetration level of the combined heat and power systems and demand response programs between energy consumers in the distribution network, the interaction between electricity and the natural gas network becomes more complicated. This paper proposes a peer-to-peer (P2P) energy sharing scheme for energy trading among Smart Energy Hubs (S.E. Hubs) which can trade both electrical and thermal energy with each other to reduce their cost and, reduce their dependency to gas and electricity utility companies. A two-stage energy strategy is presented. In the first stage, the S.E. Hubs total social cost is reduced by finding the optimal energy sharing profiles. And, in the second... 

The Iranian government has started and performed several Information Technology (IT) development plans and projects during recent years with the aim of taking advantage of IT in developing governmental services and increasing their efficiency. This case study intends to investigate the overall effectiveness of the implemented plans according to viewpoints of experts. A survey was conducted in The 1st International Conference on Information and Communication Technology Management in which the attendants were experts from academia and public sector. The questions were designed to obtain their views and standpoints about various issues concerning the success of IT plans in different segments... 

Production optimization is defined as the process of maximizing oil production over the long term while minimizing total production costs. The overall goal is to achieve the optimum profitability from the well or field. In this process, the reservoir system can be considered as a multiple input–output system. In this complex system injection and production wells are known as inputs and outputs. The output of the system is often affected by various parameters consisting reservoir conditions, petrophysics, and PVT data. The optimization of the injector rates and number and installation of submersible pumps are the main issues which have been studied in this paper. Determining the factor with... 

We revisit the problem of finding (Formula presented.) paths with a minimum number of shared edges between two vertices of a graph. An edge is called shared if it is used in more than one of the (Formula presented.) paths. We provide a (Formula presented.)-approximation algorithm for this problem, improving the best previous approximation factor of (Formula presented.). We also provide the first approximation algorithm for the problem with a sublinear approximation factor of (Formula presented.), where (Formula presented.) is the number of vertices in the input graph. For sparse graphs, such as bounded-degree and planar graphs, we show that the approximation factor of our algorithm can be... 

We revisit the problem of finding k paths with a minimum number of shared edges between two vertices of a graph. An edge is called shared if it is used in more than one of the k paths. We provide a ⌊k/2⌋-approximation algorithm for this problem, improving the best previous approximation factor of k - 1. We also provide the first approximation algorithm for the problem with a sublinear approximation factor of O(n3/4), where n is the number of vertices in the input graph. For sparse graphs, such as bounded-degree and planar graphs, we show that the approximation factor of our algorithm can be improved to O(√n). While the problem is NP-hard, and even hard to approximate to within an O(log n)... 

Integrating high spatial resolution of functional magnetic resonance imaging (fMRI) and high temporal resolution of electroencephalogram (EEG) is promising in simultaneous EEG and fMRI analysis, especially for epileptic patients. The EEG recorded inside an MR scanner is interfered with MR artifacts. In this article, we propose new artifact reduction approaches and compare them with the conventional artifact reduction methods. Our proposed approaches are based on generalized eigenvalue decomposition (GEVD) and median filtering. The proposed methods are applied on experimental simultaneous EEG and fMRI recordings of an epileptic patient. The results show significant improvement over... 

In this paper, different aspects of the behavior of 2×2 pile groups under liquefaction-induced lateral spreading in a 3-layer soil profile is investigated using large scale 1g shake table test. Different parameters of the response of soil and piles including time-histories of accelerations, pore water pressures, displacements and bending moments are presented and discussed in the paper. In addition, distribution of lateral forces due to lateral spreading on individual piles of the groups is investigated in detail. The results show that total lateral forces on the piles are influenced by the shadow effect as well as the superstructure mass attached to the pile cap. It was also found that...