Sharif Digital Repository

Model-Driven Development (MDD) has become a familiar software engineering term in recent years, thanks to the profound influence of the Model Driven Architecture (MDA). Yet MDD, like MDA itself, defines a general framework, and as such is a generic approach rather than a concrete development methodology. Methodology support for MDA has been rather slow in coming, yet even though several MDA-based methodologies have emerged, they have not been objectively analyzed yet. The need remains for a critical appraisal of these methodologies, mainly aimed at identifying their achievements, and the shortcomings that should be addressed. We provide a review of several prominent MDA-based methodologies,... 

In analyzing the lifetime properties of a coherent system, the concept of "signature" is a useful tool. Let T be the lifetime of a coherent system having n iid components. The signature of the system is a probability vector s=(s1, s2,., sn), such that s i=P(T=Xi:n), where, Xi:n, i=1, 2,., n denote the ordered lifetimes of the components. In this note, we assume that the system is working at time t>0. We consider the conditional signature of the system as a vector in which the ith element is defined as pi(t)=P(T=Xi: n|T>t) and investigate its properties as a function of time  

Situational Method Engineering (SME) addresses the need for custom-built software development methodologies that are tailored to fit specific project situations. A process pattern is a description of a recurring development process fragment that can be used as a generic model or a building block for engineering development processes. Software development process patterns are extensively used in SME, mainly as process components assembled to form bespoke methodologies; however, the SME field itself has not been scrutinized as to the methodology development process fragments frequently encountered. Situational method engineering knowledge captured in the form of SME process patterns is not... 

Information systems are expected to satisfy increasingly ambitious requirements, while reducing time-to-market has become a primary objective. This trend has necessitated the advent of development approaches that are better equipped and flexible enough to cope with modern challenges. Model-Driven Architecture (MDA) and Situational Method Engineering (SME) are approaches addressing this requirement: MDA provides promising means for automating the software process, and revitalizes the role of modeling in software development; SME focuses on project-specific methodology construction, mainly through assembling reusable method fragments (process patterns) retrieved from a method base. We provide... 

Silver nanoparticles (NPs) stored in pore-arrays (pa) SU-8 photoresist layer were utilized as an antibacterial nanocomposition against E. coli bacteria. The pa-SU-8 matrix was fabricated by an optical interference lithography method resulting in small pores with a diameter of ∼50 nm and a depth of ∼100 nm. The Ag NPs were deposited on the soft polymeric matrix at different drying temperatures of 50 and 90 °C. X-ray photoelectron spectroscopy showed that the deposited silver NPs were substantially in the metallic state, independent from the drying condition. However, the concentration of the immobilized Ag NPs on the film surface increased (by a factor of 2.5) at the higher drying... 

In this paper, we investigate the effect of incorrect disk replacement service on the availability of data storage systems. To this end, we first conduct Monte Carlo simulations to evaluate the availability of disk subsystem by considering disk failures and incorrect disk replacement service. We also propose a Markov model that corroborates the Monte Carlo simulation results. We further extend the proposed model to consider the effect of automatic disk fail-over policy. The results obtained by the proposed model show that overlooking the impact of incorrect disk replacement can result up to three orders of magnitude unavailability underestimation. Moreover, this study suggests that by... 

This investigation employed an interrupted torsion fatigue test using the linear amplitude sweep procedure to assess the intrinsic self-healing potential of unaged, aged, rejuvenated, and re-aged asphalt binders. Continuous oscillatory shear strain loading at different damage levels were interrupted with a single rest period of different durations. An index based on the decrease in crack length following the rest period (Ha) has been defined to accurately reflect the occurrence of healing. The results indicate that Ha is higher at lower damage levels and for longer rest-period durations. The amount of irreversible crack growth increased with an increase in crack propagation and aging level.... 

A procedure based on the linear amplitude sweep (LAS) test has been developed to determine the optimum rejuvenator content for restoring the properties of aged asphalt binders. The LAS test was employed to assess the damage tolerance, fatigue resistance, and fracture behavior of rejuvenated aged binders. In case of fracture analysis, a crack-based indicator to govern the stable crack propagation was defined to characterize fracture resistance of asphalt binders. While rejuvenators improved all of these properties, higher contents were required to restore the cracking behavior of the original binder. The linear relationship between the integrated damage-fatigue-fracture indicator and... 

OMG's Model Driven Architecture (MDA) has deeply influenced modern-day software development, not only by providing promising means for automating the software process, but also through revitalizing the role of modeling in software development, the importance of which had been neglected during the recent euphoria over lightweight development methods. However, MDA's need to remain reasonably abstract means that it is more a software development approach rather than a standalone methodology, and therefore needs methodology support to be practically useful. Several MDA-based methodologies exist today, yet the need remains for the definition of an instantiable MDA-based development process. We... 

Activities conducted in this study can be divided into two general sections: synthesis and analysis and identifies the properties. A geopolymeric cement production process includes two steps of thermal activation and alkaline activation. Geopolymers are cementitious materials synthesized by a polycondensation reaction between an aluminate and silicate. The geopolymeric structures of the products were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). XRD results showed that there are no significant differences between the XRD patterns of geopolymers and metakaolin. The structure of the geopolymer is typically... 

The present study aims at the investigation of free vibration analysis of thin cylindrical shells surrounded by an elastic medium, which is distributed over a particular length of the shell. The Love’s shell theory is utilized along with the Winkler foundation to obtain the governing equations of motion. An exact series expansion method of solution is employed for any arbitrary boundary conditions. The excellent accuracy of the obtained results is validated by comparing to the available literature. Moreover, several case studies are performed to provide an insight into the influence of some practically important parameters on free vibrations of circular cylindrical shells, including... 

Method Engineering (ME) is based on the notion that no two software development projects are identical, and hence, the same development process is never executed twice. The need therefore arises for custom-built software development methodologies that are tailored to fit the specific project situation at hand, thus giving rise to the various Situational Method Engineering (SME) approaches currently in use. A process pattern is a description of a recurring development process fragment that can be used as a building block for engineering development processes. Software development process patterns are extensively used in SME, mainly as process components assembled together to form bespoke... 

In this work, the effect of strain rate on the ductility, intermediate temperature brittleness and fracture surface of Zr-based BMG over a wide range of temperatures from 0.1 Tg to near Tg, has been systematically investigated. The results showed two remarkable ductile to brittle transition at low cryogenic and intermediate temperatures. At low temperatures, below 0.4 Tg, the activation of diffusion mediated phenomena is negligible and the combined effects of strain rate and temperature contribute to the plasticity of material by changing the STZ volume, hence the possibility of forming multiple shear bands. At the temperature range from 0.4 Tg to the temperature at which the intermediate... 

According to previous studies on the fracture surface morphologies of bulk metallic glasses, the stable crack growth region width and vein pattern size increase with the plasticity at room temperature. In the present work, the fracture surface morphologies of Ti- and Zr-based bulk metallic glasses bent over a wide temperature range (0.1–0.8 glass transition temperature) are systematically analyzed. According to our finding, the stable crack growth region width increases while the vein pattern size decreases as the ductility improves by varying temperature. This observation is in contrast to the common thought that the ductility is proportional to the stable crack growth region width and vein... 

In this research, the dynamic behavior of serrated flows observed in the flexural stress-deflection curves during three-point bending (3 PB) tests on Zr-, Ti- and La-based bulk metallic glasses (BMGs) is statistically analyzed. Furthermore, the effect of strain rate on the serrations is studied. Based on the ductility of alloy, two distinct types of dynamics are detected. For more ductile alloys (Zr- and Ti-based BMGs) the stress drop magnitude of serrations obeys a power-law distribution of shear avalanches, which is an indicator of the self-organized critical (SOC) state in dynamics. In this case, the size of avalanches has no characteristic scale. In contrast, the size of serrations... 

In this study, the influence of temperature on serrated flow behavior, strain rate sensitivity (SRS) and effective activation volume in a Ti-based bulk metallic glass (BMG) bent at different strain rates has been investigated. Results reveal that the fundamental origin of shear deformation is related to the time-dependent structural relaxations, which occur during deformation at special temperatures and strain rates. Furthermore, the localized structural relaxation processes at intermediate temperatures cause an inelastic shuffling within cages and mitigate the activation of STZs. The main reason of negative SRS at intermediate temperatures is due to the insufficient time for structural... 

The effect of strain rate on the ductility of a La-based bulk metallic glass (BMG) over a wide temperature range, and the correlation between ductility and relaxation processes within this alloy are investigated in the present work. The three point bending test and dynamic mechanical analysis are employed to study these phenomena. It is found that the activation energies of the nearly constant loss (NCL) relaxation and intermediate temperature brittleness are almost identical. This observation reveals that the NCL relaxation, as a locally confined or caged dynamics, contributes as the main source of intermediate temperature brittleness in La-based BMGs. © 2018 Elsevier B.V  

In recent years, increased I/O demand of Virtual Machines (VMs) in large-scale data centers and cloud computing has encouraged system architects to design high-performance storage systems. One common approach to improving performance is to employ fast storage devices such as Solid-State Drives (SSDs) as an I/O caching layer for slower storage devices. SSDs provide high performance, especially on random requests, but they also have limited endurance: They support only a limited number of write operations and can therefore wear out relatively fast due to write operations. In addition to the write requests generated by the applications, each read miss in the SSD cache is served at the cost of... 

In this study, the influence of temperature on serrated flow behavior, strain rate sensitivity (SRS) and effective activation volume in a Ti-based bulk metallic glass (BMG) bent at different strain rates has been investigated. Results reveal that the fundamental origin of shear deformation is related to the time-dependent structural relaxations, which occur during deformation at special temperatures and strain rates. Furthermore, the localized structural relaxation processes at intermediate temperatures cause an inelastic shuffling within cages and mitigate the activation of STZs. The main reason of negative SRS at intermediate temperatures is due to the insufficient time for structural... 

In recent years, increased I/O demand of Virtual Machines (VMs) in large-scale data centers and cloud computing has encouraged system architects to design high-performance storage systems. One common approach to improving performance is to employ fast storage devices such as Solid-State Drives (SSDs) as an I/O caching layer for slower storage devices. SSDs provide high performance, especially on random requests, but they also have limited endurance: They support only a limited number of write operations and can therefore wear out relatively fast due to write operations. In addition to the write requests generated by the applications, each read miss in the SSD cache is served at the cost of...