Sharif Digital Repository

Change occurrence during project's life cycle and its impact on project's success is common concern of all parties in projects. Hence, predicting and managing them to mitigate their negative outcomes is critical. This study offers categorization of changes types, causes and effects arise in Iranian projects and investigates the most prevalent ones through conducting a survey. Findings demonstrate that schedule, information and time are the most frequent type, cause and impact of changes, respectively  

In this paper, we introduce a model-based Bayesian denoising framework for phonocardiogram (PCG) signals. The denoising framework is founded on a new dynamical model for PCG, which is capable of generating realistic synthetic PCG signals. The introduced dynamical model is based on PCG morphology and is inspired by electrocardiogram (ECG) dynamical model proposed by McSharry et al. and can represent various morphologies of normal PCG signals. The extended Kalman smoother (EKS) is the Bayesian filter that is used in this study. In order to facilitate the adaptation of the denoising framework to each input PCG signal, the parameters are selected automatically from the input signal itself. This... 

In this paper we introduce a dynamical model for Phonocardiogram (PCG) signal which is capable of generating realistic synthetic PCG signals. This model is based on PCG morphology and consists of three ordinary differential equations and can represent various morphologies of normal PCG signals. Beat-to-beat variation in PCG morphology is significant so model parameters vary from beat to beat. This model is inspired of Electrocardiogram (ECG) dynamical model proposed by McSharry et al. and can be employed to assess biomedical signal processing techniques  

Electronic and phonon structures of the BaFe2As2 superconductor in the magnetic-orthorhombic phase have been investigated by the ab-initio density functional theory using the pseudopotential Quantum Espresso code. Density of state and electronic band structure for this phase has been studied, but phonon dispersion has been obtained only for the nonmagnetic-orthorhombic phase. Electronic band structure and density of states are in good agreement with other calculations in the literature. The electronic state near the Fermi energy are essentially made from Fe3d and As4p orbital that indicate in-plane conductivity in FeAs layers in this system. Comparing calculated phonon dispersions with... 

Room temperature gas sensing behavior of arrayed one-dimensional (1D) nickel nanowires (Ni NWs) are investigated using impedance spectroscopy. Ni nanowires synthesized via electrochemical deposition method based on anodic aluminum oxide (AAO) templates. Their structural characterization verified by scanning electron microscopy (SEM), x-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) analysis. Impedance spectroscopy as an essential technique utilized to understand the mechanism of gas interaction with the wires through the changes in their electronic behavior. Bode and Nyquist plots with the real and imaginary impedances are plotted versus frequency range of 500 Hz... 

Investigating the protein adhesion properties of polymeric scaffolds through computational simulations can predict the biocompatibility of scaffolds before an experimental assay is carried out. This prediction can be highly beneficial since it can cut costs and the time it takes for experimental assays. The current study aims to test the hypothesis that there is a correlation between the biocompatibility of a composite scaffold and the molecular dynamics simulations of protein adhesion. To this end, chitosan and gelatin were selected for fabricating a composite skin-tissue wound scaffold with five different polymer ratios. This polymeric blend has not been simulated for protein adhesion. The... 

Inclusion of nano-clays into hydrogels is an efficient approach to produce nanocomposite hydrogels. The introduction of nano-clay into hydrogels causes an increase in water absorbency. In the present work, Nanocomposite hydro-gels based on kappa-carrageenan were synthesized using sodium montmorillonite as nano-clay. Acrylamide and meth-ylenebisacrylamide were used as monomer and crosslinker, respectively. The structure of nanocomposite hydrogels was investigated by XRD and SEM techniques. Swelling behavior of nanocomposite hydrogels was studied by varying clay and carrageenan contents as well as methylenebisacrylamide concentration. An optimum swelling capacity was achieved at 12% of sodium... 

This study presents an electrochemical procedure for synthesizing graphene oxide (GO) nanosheets in a diluted acidic medium (0.05 M), featuring 100% synthesis yield. Characterization results revealed that the synthesized GO in this approach exhibits a low XRD peak position (around 10°) and a C/O ratio of 2.9, offering higher surface functionality than conventional electrochemical methods reported in the literature. We also demonstrated the tunability of the GO's surface functionality by manipulating the synthesis parameters, such as electrolyte concentration and synthesis time, offering flexibility that surpasses the constraints often seen in chemical methods. Additionally, it was observed... 

In the present study, the out-of-phase thermomechanical fatigue (OP-TMF) behavior of a cast aluminum-silicon-magnesium alloy, the A356.0 alloy which has been widely used in diesel engine cylinder heads, is compared to room-temperature and high-temperature low cycle fatigue (RT-, HT-LCF) behaviors. For this purpose, strain/temperature-controlled isothermal and non-isothermal fatigue tests were performed based on realistic loading conditions in cylinder heads. Fatigue tests results showed that the plastic strain increased during cycles under constant mechanical strain amplitude, while the specimen failed. Under LCF loadings, the cyclic hardening occurred at low temperatures for the A356.0... 

Machine learning (ML) is generating new opportunities for innovative research in energy economics and finance. We critically review the burgeoning literature dedicated to Energy Economics/Finance applications of ML. Our review identifies applications in areas such as predicting energy prices (e.g. crude oil, natural gas, and power), demand forecasting, risk management, trading strategies, data processing, and analyzing macro/energy trends. We critically review the content (methods and findings) of more than 130 articles published between 2005 and 2018. Our analysis suggests that Support Vector Machine (SVM), Artificial Neural Network (ANN), and Genetic Algorithms (GAs) are among the most... 

The general approach to fault tolerance in uniprocessor systems is to maintain enough time redundancy in the schedule so that any task instance can be re-executed in presence of faults during the execution. In this paper a scheme is presented to add enough and efficient time redundancy to the Earliest-Deadline-First (EDF) scheduling policy for periodic real-time tasks. This scheme can be used to tolerate transient faults during the execution of tasks. We describe a recovery scheme which can be used to re-execute tasks in the event of transient faults and discuss conditions that must be met by any such recovery scheme. For performance evaluation of this idea a tool is developed. © 2007 IEEE  

The reliable transfer in Network on Chips (NoCs) can be threatened by crosstalk fault occurring in wires. Crossstalk fault is due to inter-wire coupling capacitance that based on the patterns of transitions appearing on the wires, significantly limits the reliability of NoCs. Among these transitions, 101 and 010 bit patterns impose the worst crosstalk effects to wires. This work intends to increase the reliability of NoCs against crosstalk faults by applying an improved Fibonacci-based numeral system, called Doubled-Penultimate Fibonacci (DP-Fibo). In the DP-Fibo coding algorithm, code words without ‘101’ and ‘010’ bit patterns are produced to reduce crosstalk faults. Experimental results... 

In the present work, specimens were cut out from St-37 plates with 19 mm thickness. The thickness of plates was reduced to 12.5 mm by milling and grinding operations. Then a standard V-shaped fillet was made on one edge of the plates. Two plates were butt-welded by standard metal arc gas (MAG) welding process. Residual stresses induced by welding were measured on 20 specimens by centre hole drilling. Load controlled axial fatigue tests were carried out to determine the fatigue life of specimens. Crack growth rates were obtained from experiment. Fractography of specimens was performed. Genetic Algorithm (GA) was employed for prediction of residual stress value in weldments using the crack... 

In this work, we implement some analytical techniques such as the Exp-function, Tanh, and extended Tanh methods for solving nonlinear partial differential equation, which contains sine terms, its name Double Sine-Gordon equation. These methods obtain exact solutions of different types of differential equations in engineering mathematics  

The qualitative effects of residual stress parameters on fatigue crack growth are investigated using Monte Carlo probabilistic analysis technique. These parameters include the maximum residual stress,σ0, half-width of the tensile residual stress region, b, and the redistribution of residual stress parameter, β. A normal distribution is assumed for all parameters considered in the investigation and fatigue life is determined using Forman equation. The results indicate that: (i) fatigue life decreases nonlinearly if the mean of random maximum residual stress and the half-width of tensile residual stress region increases; (ii) fatigue life increases nonlinearly if the rate of residual stress...