Sharif Digital Repository

In order to engage students in higher-level thinking, cognitive activation (CA) strategies have been advanced and utilized in mathematics. CA develops when learners are challenged, confronted with conflicts, asked to think and explain clearly on their learning, and realize connections between new and previous content. Extending the theme to English language teaching (ELT), this study investigated Iranian English language teachers‟ knowledge and practice of cognitive activation writing strategies (CAWS). In so doing, a model was proposed based on a questionnaire that was developed and validated in the present study. Through this scale, knowledge and practice of CAWS by 213 English as a... 

In this paper, we study the differences between the Centralized and Decentralized approaches in a two-echelon stochastic inventory system under the lost sale policy. We formulate the condition in which the retailer applies (r, Q) inventory policy, and his relation with the upper echelon who acts as a manufacturer. This situation has not been considered in the literature before. The Centralized approach results in optimal solution of the system and the Decentralized one is based on Stackelberg game in which the manufacturer is the leader. The demand arrives according to the stationary Poisson process. We drive the long-run average cost functions, then a set of computational steps are... 

A comprehensive analysis on flow stress of a wrought Al-Mg alloy is performed to examine the effect of strain. For this study, hot compression tests were carried at different temperatures and strain rates. Corrections of friction and adiabatic heating effects lead to the true stress-true strain curves in the form of dynamic recovery, which reach to a steady-state condition. After correction, constitutive analysis at a constant strain is carried out using hyperbolic-sine equation. The effect of strain on each constitutive parameter is studied to derive a strain-dependent constitutive equation based on hyperbolic-sine equation. Some of constitutive parameters reach to the constant values at... 

The behavior of hot extruded Al-6Mg during hot deformation has been studied using hot compression test. The tests were performed at temperatures of 350, 450, and 550°C and strain rates of 0.001, 0.1, and 1s -1. Due to the effects of friction and adiabatic heating generated during compression, the attained true stress-true strain curves have been corrected. After correction of friction effect, the virtual work hardening has been removed from stress-strain curves. The flow stress increases and reaches a steady state after correction of adiabatic heating effect. Corrected curves and microstructural examinations exhibit the occurrence of dynamic recovery during hot compression of the alloy. The... 

A novel method is proposed in order to find the kinetics of dynamic recovery in the form of Avrami relation using hot flow curves. The relation is derived on the basis of variation of dislocation density with strain. The model is applied on an Al-Mg alloy  

In this research, low-carbon steel sheets with two different microstructures containing carbides (as-received steel) and pearlites (austenitized steel) are subjected to severe plastic deformation (SPD), and ultra-rapid annealing (URA) is applied with the heating rate of 200 °C s−1 up to the intercritical temperature near Ac1. Microstructure of SPDed as-received steel after URA is consisted of fully refined ferrite grains surrounded by fine pearlites; but for SPDed austenitized steel, grain refinement is not observed, and microstructure is consisted of martensite and high fraction of coarse non-recrystallized ferrite. Presence of carbides for SPDed as-received steel leads to strong... 

An interaction between ferrite recrystallization and austenite transformation in low-carbon steel occurs when recrystallization is delayed until the intercritical temperature range by employing high heating rate. The kinetics of recrystallization and transformation is affected by high heating rate and such an interaction. In this study, different levels of strain are applied to low-carbon steel using a severe plastic deformation method. Then, ultra-rapid annealing is performed at different heating rates of 200–1100°C/s and peak temperatures of near critical temperature. Five regimes are proposed to investigate the effects of heating rate, strain, and temperature on the interaction between... 

Ultra-rapid annealing (URA) of deformed low-carbon steel can provide refined microstructure. In this research, severely deformed low-carbon steel is ultra-rapidly annealed to subcritical and intercritical temperature ranges at the heating rates of 75-1800°C/s and then rapidly cooled. Also, conventional annealing by the heating rate of 0.3°C/s is performed at the same temperature ranges. The results show that conventional and subcritical ultra-rapid annealing cannot lead to a fully refined microstructure. High heating rate causes the interaction between recrystallization and transformation as the temperature exceed Ac1 (intercritical temperature range). High kinetics of transformation during... 

To study the grain-refinement ability of ultra-rapid annealing (URA), heating rates from 0.3 °C/s up to 1200 °C/s with conventional annealing and URA in the intercritical temperature range were performed on severely deformed low-carbon steel. The results show that recrystallization in conventional annealing is completed below the critical temperature of Ac1 without grain refinement. URA up to 730 °C at a heating rate of 200 °C/s causes grain refinement due to full interaction between the recrystallization and phase transformation. URAs up to 730 °C with heating rates of 600 °C/s and 1000 °C/s lead to partial grain refinement and no grain refinement, respectively. During annealing with a... 

Different heating rates of 200-1200 deg;C/s were utilized during ultra-rapid annealing (URA) up to the temperatures of 730 and 760 °C on the severely deformed low carbon steel. Higher hardness, strength and ductility achieved for the sample heated at 730 °C with 600 °C/s due to formation of bimodal grain size (BGS) microstructure than them for non-BGS samples. The BGS enhancement for the hardness, strength and ductility with respect to those of as received sample was 67%, 80% and 7%, respectively, and, with respect to those of severely deformed one was 16%, 44% and 24%, respectively. URA with the heating rate of 200 °C/s and 1000 °C/s leads to fully recrystallized and non-recrystallized... 

Production of high-Mg content Al–Mg alloys in the form of sheet from cast condition, should be performed with some pre- and post-deforming treatments to achieve desirable mechanical properties. In this research, to find the necessity and influence of pre- and post-rolling homogenisation process on Al–6Mg alloy properties, series of experimental investigations were carried out on direct chill (DC) cast Al–6Mg. Hot extrusion at the temperature of 350°C has been selected as a pre-rolling homogenisation process, which leads to homogenisation by formation of partially recrystallised grains. Cold rolling performed on both DC cast and hot extruded samples up to 80%. Post-rolling homogenisation... 

This paper presents a new balanced, distributed data structure for storing data with multidimensional keys in a peer-to-peer network. It supports range queries as well as single point queries which are routed in O (log n) hops. Our structure, called SkipTree, is fully decentralized with each node being connected to O (log n) other nodes. We propose modifications to the structures, so that the memory usage for maintaining the link structure at each node is reduced from the worst case of O (n) to O (log n log log n) on the average and O (log2 n) in the worst case. It is also shown that the load balancing is guaranteed to be within a constant factor. Our experimental results verify our... 

This paper presents the SkipTree, a new balanced, distributed data structure for storing data with multidimensional keys in a peer-to-peer network. The SkipTree supports range queries as well as single point queries which are routed in O(log n) hops. SkipTree is fully decentralized with each node being connected to O(logn) other nodes. The memory usage for maintaining the links at each node is O(log n log log n) on average and O(log2 n) in the worst case. Load balance is also guaranteed to be within a constant factor. © Springer-Verlag Berlin Heidelberg 2005  

In order to engage students in higher-level thinking, cognitive activation (CA) strategies have been advanced and utilized in mathematics. CA develops when learners are challenged, confronted with conflicts, asked to think and explain clearly on their learning, and realize connections between new and previous content. Extending the theme to English language teaching (ELT), this study investigated Iranian English language teachers‟ knowledge and practice of cognitive activation writing strategies (CAWS). In so doing, a model was proposed based on a questionnaire that was developed and validated in the present study. Through this scale, knowledge and practice of CAWS by 213 English as a... 

Abutments of concrete arch dams are usually crossed by several joints, which may create some rock wedges. Abutment stability analysis and controlling the probable wedge movements is one of the main concerns in the design procedure of arch dams that should be investigated. For decades, the quasi-static method, due to its simple approach, has been used by most of dam designers. In this study, the dynamic method is presented and the obtained time history of sliding safety factors is compared with the quasi-static results. For this purpose, all three components of Kobe (1979) and Imperial Valley (1940) earthquakes are applied to the wedge, simultaneously, and the magnitude and direction of wedge... 

This paper discusses the interaction between one manufacturer and a single retailer in a channel in which both are willing to optimize their profit by adjusting pricing and advertising decisions. The manufacturer produces and sells a product at wholesale price to the retailer who in turn distributes it to consumers with retail price. The market demand is simultaneously affected by retail price, brand advertising of the manufacturer, and local advertising of the retailer. A Cobb-Douglas demand function is used to demonstrate the relationship between the parameters. Decision variables are two firms’ prices and their advertising investments. The problem is modelled under integrated policy and... 

The sharing economy, defined by peer-to-peer interactions through a platform, has been gaining ground in recent years. In this study, we discuss the relative importance of customers' perceived motives to participate in the two most common models of the sharing economy: access-based consumption and ownership-transfer. We focus on taxi-hailing and post-delivery as examples of access-based consumption and second-hand trade as an example of the ownership-transfer. While these two contain heterogeneous business model patterns that can motivate customers differently, common motives are significant in both models. We study common motives and motives aligned with the business model patterns, which... 

Modal identification is a type of system identification, which studies on the modal parameters of systems by using modal test. In the case of using operational or ambient modal analysis, there is no need to measure excitation, and the system output data are adequate for identification purposes. These modal parameters of system are of great importance from the engineering point of view particularly in the area of system identification, damage detection, and condition monitoring. In a fully-automated identification approach, the modal parameters are extracted without intervention of a specialized user. In this study, a Fully Automated Operational Modal Identification algorithm is developed to...