Sharif Digital Repository

This paper addresses the midterm preventive maintenance outage scheduling problem of thermal generating units which is becoming increasingly important due to the aging of power generation fleet. In this context, a novel midterm preventive maintenance outage scheduler is proposed based on decision tree and mixed integer linear formation which explicitly considers the thermal units aging momentum in terms of failure rate. This allows the system operators to determine the thermal units' maintenance outage window based on the cost/benefit analysis of preventive maintenance tasks while optimizing the time interval between consecutive maintenance tasks. Additionally, the division of the year-long... 

Dilute Surfactant flooding has been recognized as one of the significant processes in chemical flooding. Many oil reservoirs became appropriate candidates for surfactant/water flooding when screening criteria was developed. Injected surfactant tried to mobilize the residual oil that was trapped in interstice. The main contributing mechanism to enhance oil recovery by surfactant flooding was defined as rock wettability alteration. Wettability is one of the substantial parameters to choose the best approach for a successful surfactant flooding in which tiny change in wettability will lead to improve oil recovery fundamentally. In this experimental study the effect of different aging time and... 

Mechanical properties, microstructural events, residual stresses, and aging behavior of friction stir-welded AA6061-T6 were investigated in this work. Microstructural and mechanical characterizations of the friction stir-welded joints in as-welded and post-welded conditions were made by means of optical metallography, transmission electron microscopy, X-ray diffraction for determination of residual stresses, tensile testing, and hardness measurements. It was found that weld strength and hardness variations after welding are mainly dependent on the imposed heat input per unit length. Besides, the kinetics of natural aging in the welded samples was found to be noticeable within the first 14... 

Aging response of transient liquid phase Nb bearing wrought IN718 nickel base superalloy is studied. The aging behaviour of the joint is influenced by low Nb+Al+Ti content of isothermal solidification zone (ISZ) and formation of Nb-Cr-Mo based boride precipitates in diffusion affected zone (DAZ). It was shown that applying a post-bond heat treatment which was able to eliminate the diffusion induced boride precipitates in DAZ and increase the Nb+Al+Ti content of the ISZ improved the aging response and shear strength of the joint  

In this paper dynamic strain ageing behavior in an Al-Mg-Si alloy related to equal channel angular pressing (ECAP) was investigated. In order to examine the combined plastic deformation and ageing effects on microstructure evolutions and strengthening characteristics, the Al6061 alloy were subjected to φ=90° ECAP die for up to 4 passes via route Bc at high temperatures. For investigating the effects of ageing temperature and strain rate in ECAP, Vickers hardness tests were performed. The combination of the ECAP process with dynamic ageing at higher temperatures resulted in a significant increase in hardness. The microstructural evolution of the samples was studied using electron... 

Intracellular production of recombinant proteins in prokaryotes necessitates subsequent disruption of cells for protein recovery. Since the cell disruption and subsequent purification steps largely contribute to the total production cost, scalable tools for protein release into the extracellular space is of utmost importance. Although there are several ways for enhancing protein release, changing culture conditions is rather a simple and scalable approach compared to, for example, molecular cell design. This contribution aimed at quantitatively studying process technological means to boost protein release of a periplasmatic recombinant protein (alkaline phosphatase) from E. coli.... 

In this study the influence of precipitates on the mechanical properties and plastic anisotropy of an age hardenable aluminum alloy during uniaxial loading was investigated using crystal plasticity modeling. The kinetics model of Myhr et al. was used to obtain the solute and precipitate features after different cycles of aging treatment. The amounts of solute, precipitate size and volume fraction, and dislocation density varying during deformation, were used to calculate the slip system strength. An explicit term was obtained based on the elastic inclusion model for the directional dependency of internal stress developed by non-shearable rod shape precipitates. Also, a dislocation evolution... 

The popularity of self-compacting concrete (SCC), as an innovative construction materials in concrete industry, has increased all over the world in recent decades. SCC offers a safer construction process and durable concrete structure due to its typical fresh concrete behavior which is achieved by SCC's significantly different mixture composition. This modification of mix composition may have significant effect on the hardened mechanical properties of SCC as compared to normal vibrated concrete (NVC). Therefore, it is necessary to know whether the use of all rules and relations that have been formulated for NVC in current design codes based on years of experience are also valid for SCC.... 

Ways to reduce an airline's cost has been studied for years. In fact, in order to achieve this goal, ones need to know different types of airline's costs including; fuel and oil, maintenance, Ticketing, passenger services, etc. and their impact on the total cost of an airline. According to announcement of ICAO [1], "maintenance cost (about 11% of total cost) is the second major cost after fuel and oil". Therefore, this may attract airline owners' attention to find ways to control maintenance cost and eventually the total cost of an airline. Though, there are many systematic approaches to analyze cost reduction and making policies, in this article, SD modeling is applied to develop a... 

Residual stresses, local mechanical properties, and microstructural evolution in terms of grain structures and precipitation distribution have been studied in friction stir welding of AA2017 in T4 and T6 conditions. Microstructural studies including optical and electron microscopy were made to characterize the developed microstructures in different zones of the weldment. Furthermore, X-ray diffraction technique and digital image correlation technique were also utilized to assess residual stress and mechanical properties of the welded alloy. The results show that coarsening of semi-coherent plate-shaped precipitates and formation of incoherent spherical-shaped particles occur in heat affected... 

Dental professionals are in a unique position to promote smoking cessation among their patients. We evaluated the effects of a brief counselling intervention by a dentist on patients' attitude towards the role of dentists in tobacco cessation programmes. In a semi-experimental study in Tehran, Islamic Republic of Iran, 70 eligible smokers were selected and randomly assigned to intervention and control groups. The initial attitudes of the patients regarding tobacco cessation counselling services provided by the dentist were determined using a validated questionnaire. The intervention group received a brief chair-side counselling by a dentist based on the 5 A's approach, while no intervention... 

Pemphigus vulgaris is an autoimmune disease, in which the role of Th17 cytokines needs to be further explored. This study was performed to assess serum levels of three interleukins (IL) required for Th17 differentiation (IL-β, IL-6 and IL-23) and two specific Th17 cytokines (IL- 17 and IL-22) in a group of patients with pemphigus vulgaris, at baseline, 3 weeks and 6 months after of treatment. Correlations between anti-desmogleins and cytokines with disease severity as well as the influence of therapy on the above factors were assessed. Forty-three first-admitted pemphigus vulgaris patients with the active disease entered the study, but only 31 completed the study. Forty-five healthy... 

In this work, the effects of rolling parameters, cooling media, and deformation path on mechanical properties and aging behavior of hot-rolled AA2017 were studied. First, hot-rolling experiments were conducted under different working conditions, and the rolled strips were then aged at room temperature for up to 57 days during which hardness and tensile tests were carried out to record the changes in the mechanical properties of the alloy. Furthermore, due to the importance of static recrystallization on subsequent aging behavior, the rate of recrystallization was also computed. To this end, a mathematical model was developed to predict thermomechanical responses during hot rolling using the... 

In this paper, distributed electroencephalographic (EEG) sources in the brain have been mapped with the objective of early diagnosis of Alzheimer's disease (AD). To this end, records from a montage of a high-density EEG from 17 early AD patients and 17 matched healthy control subjects were considered. Subjects were in eyes-closed, resting-state condition. Cortical EEG sources were modeled by the standardized low-resolution brain electromagnetic tomography (sLORETA) method. Relative logarithmic power spectral density values were obtained in the four conventional frequency bands (alpha, beta, delta, and theta) and 12 cortical regions. Results show that in the left brain hemisphere, the theta... 

In this paper, dynamic strain aging (DSA) behavior in a temperature range of (25-235°C) and strain rate range of (10-4-5×10-2s-1) was investigated using a supersaturated age hardenable aluminum alloy. It was found that two mechanisms consisted of pinning of solute atoms to mobile dislocations and dynamic precipitation, were responsible for DSA in the testing conditions. The effects of both mechanisms on the macroscopic flow curve were studied using experimental and improved physically based material modeling approaches. It was shown that both phenomena lead to a negative strain rate hardening in the alloy. Dynamic precipitation acting at high temperature results in considerable work... 

Natural aging behavior of the aluminum 6061 alloy after a novel Severe Plastic Deformation process called Tube Channel Pressing (TCP) was studied. For this purpose, Vickers microhardness test was used to investigate the changes of mechanical properties while TEM and XRD observations were utilized in order to characterize microstructural evolution during natural aging. Results show that Si-enriched precipitates appear and coarsen rapidly in the first few days of natural aging of TCPed aluminum 6061 alloy which causes consecutive increase and decrease of Vickers microhardness, respectively. Similarly, other alloying elements such as Cu and Fe lead to formation of coarse precipitates during... 

An investigation was performed on the static strain aging behavior of warm-rolled low carbon steel during a nearly 1-year aging period, from the view point concerning with influence of changing the deformation speed and cooling media. Mechanical response of the examined material during aging period was evaluated through variations occurred in strength and hardness of the warm-deformed steel. It was shown that changing the rolling speed as well as cooling rate, may result in the occurrence of different metallurgical phenomena, consequently altering the aging kinetics of the material. It was also found that by increasing rolling speed, an increase in the value of hardness and UTS takes place,... 

The current study proposes a simple constitutive model that integrates the kinetics of precipitation during static aging and the kinetics of precipitate dissolution during preheating to deformation temperature to predict the hot flow behavior of AA6063 alloy. The model relates the flow behavior of the age-hardenable alloy to the alloy chemistry, thermal history as well as deformation temperature, strain, and strain rate by means of a physically based model. Different aging conditions, including supersaturated solid solution and overaging conditions with different deformation parameters, were assessed. Each part of the model was in good agreement with those of experimental and other model... 

A new integrated physically based constitutive model was developed for an age hardenable Al- Mg-Si alloy. The kinetics of precipitation during various stages of aging was modelled. The precipitate features consisted of particle radius and volume fraction obtained from the kinetics model, which was used to compute the alloy yield strength/hardness. A published multiinternal variable workhardening model was improved to take into account the effects of solute solution and precipitates on the alloy hardening capacity after performing different cycles of aging treatment. The flow curves and hardness predicted by the model were in good agreement with the experimental results. The model is able to... 

Background. Autoimmune process and immunosuppressive therapy of pemphigus vulgaris would predispose the patients to infections. Aim. We aimed to study the prevalence of infection and pathogenic agents in pemphigus vulgaris patients admitted to dermatology service. Material and methods. This retrospective study was conducted on 155 pemphigus vulgaris patients (68 males, 87 females) admitted to dermatology service between 2009 and 2011. In this study, the diagnosis of pemphigus vulgaris was confirmed by light microscopic and direct immunofluorescence findings. Data were collected through a questionnaire. Results. Of 155 pemphigus vulgaris patients, 33 had infection at admission and 9 acquired...