Sharif Digital Repository

The exponential growth in the semiconductor industry and hence the increase in chip complexity, has led to more power usage and power density in modern processors. On the other hand, most of today's embedded systems are battery-powered, so the power consumption is one of the most critical criteria in these systems. Dynamic Voltage and Frequency Scaling (DVFS) is known as one of the most effective energy-saving methods. In this paper, we propose the optimal DVFS profile to minimize the energy consumption of a battery-based system with uncertain task execution time under deadline constraints using the Calculus of Variations (CoV). The contribution of this work is to analytically calculate the... 

In this paper, a comprehensive study was conducted on the application of various MeAl2O4 spinels (Me = Fe, Co, Ni, Cu, Zn, Mg) as the catalyst support for the preparation of nickel-based catalysts in the combined dry reforming and partial oxidation. These supports were synthesized by a novel facile sol-gel method using propylene oxide as the gelation agent and nickel was deposited on these supports by the deposition-precipitation method. The prepared samples were characterized by N2 adsorption/desorption, XRD, TPR, TPO, CO2-TPD, SEM, and TEM techniques. In addition, the temperature-programmed methane dissociation (TPMD) was performed to evaluate the effect of nickel-support interaction on... 

The appealing advantages of high-temperature superconducting (HTS) power transformers over conventional ones have attracted transformer manufacturing companies, power companies, research institutes, and universities worldwide to conduct research and development in this field. Unfortunately, HTS transformers are more vulnerable to mechanical stresses than conventional transformers. The results of the interaction between current carrying windings and leakage magnetic fluxes are the electromagnetic forces, which act on transformer windings. Under short circuit events, these forces are remarkable, and, therefore, catastrophic failure of transformer may arise. Flux-diverter applications have been... 

Due to the remarkable progress in the field of the manufacturing process, smart composites have become the desired target for high-tech engineering applications. Accordingly, for the first time, thermal buckling, critical voltage and vibration response of a thermally affected graphene nanoplatelet reinforced composite (GPLRC) microdisk in the thermal environment are explored with the aid of generalized differential quadrature method (GDQM). Also, the current microstructure is coupled with a piezoelectric actuator (PIAC). The extended form of Halpin-Tsai micromechanics is used to acquire the elasticity of the structure, whereas, the variation of thermal expansion, Poisson’s ratio, and density... 

The reliability of machinery and automated guided vehicle has been one of the most important challenges to enhance production efficiency in several manufacturing systems. Reliability improvement would result in a simultaneous reduction of both production times and transportation costs of the materials, especially in automated guided vehicles. This article aims to conduct a practical multi-objective reliability optimization model for both automated guided vehicles and the machinery involved in a job-shop manufacturing system, where different machines and the storage area through some parallel automated guided vehicles handle materials, parts, and other production needs. While similar machines... 

This research explored the influences of shielding gases on the appearance of weld beads and the microstructures and mechanical properties of thin-wall samples using conventional gas metal arc welding as the heat source by using 5356 aluminium alloy welding wire as the raw materials and nitrogen (N2) and argon (Ar) as the shielding gases. The results showed that under the same parameters and after mono-layer single-bead welding was performed using N2 as the shielding gas, the bead height was higher, the bead width was narrower, and the penetration depth was shallower. The grain size of the thin-wall sample protected by N2 was 43.5–47.8 % smaller than that obtained under Ar protection.... 

Previously, we have proposed a computational model for decision-making in crisis situations called C-RPD (Computational Recognition Primed Decision). In this paper, a software development process customized for Crisis Situations Decision-Making Systems (CSDMSs) is proposed. Agile processes can skillfully manage uncertainty in software requirements and some of their features like incremental development can solve some problems in developing CSDMSs. However, these processes do not provide comprehensive solutions for issues like the lack of enough knowledge about CSDMSs, very rapid changes, urgent need to overcome security challenges, high development unpredictability, and the performance test.... 

The use of solar-powered reverse osmosis desalination systems is a sustainable and environmentally friendly solution in the desalination industry. However, there are some substantial technical and economic challenges due to the intermittency and fluctuation of solar energy. Recent technological improvement and feed-in tariff policies enable these systems to be competitive with conventional grid-connected reverse osmosis systems. In this paper, a feasibility study of the integration of solar panels with the grid to power small-scale reverse osmosis systems (namely up to 2000 m3/day) is conducted in Iran, as a country with a low price of electricity. For this purpose, a city located on the... 

Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) have been widely applied in fixed partial prostheses as well as dental uses i.e. a substructure for crowns. However, Y-TZP has limited applications, which is due to the presence of defects in its microstructure introduced during the manufacturing process. Accordingly, due to Y-TZP limitations, the novel (X)Y-TZP- 20Al2O3-(80-X) SiO2 (X = 65, 70 and 75) ceramic nanocomposites were successfully fabricated via the powder metallurgy method. X-ray diffraction (XRD) patterns of commercial powders showed the stabilization of monoclinic zirconia (ZM) by increasing the silica content. In order to determine the fracture load and micro-bending... 

Application of composite lattice structures in aerospace application can bring about considerable weight savings, thus allowing for increased payload weight. This study is devoted to reliability analysis of composite anisogrid lattice interstage structure (CALIS) used in typical launch vehicle (LV). CALIS is usually formed in to thin-walled cylindrical or conical shell via helical and circumferential ribs that can act as a lightweight load bearing support structure interfacing any two stages of the LV. Thus, the current study is of practical importance as the interstage structure is acted upon by rather high axial and bending forces emanating from LV external aerodynamics, thrust and... 

Polymer sintering is not only a well-established procedure for producing functional polymeric parts, but it is also the basis for the relatively new additive manufacturing technique, selective laser sintering. Although studying the impact of thermo-oxidative degradation during sintering has significant practical importance, few studies have focused on this aspect of the sintering process. In the present work, we have investigated the active thermo-oxidative degradation mechanisms during sintering of high-density polyethylene (HDPE) particles, the conditions that promote them, and their respective impact on the morphological evolution of the polyethylene particles. To perform a comprehensive... 

Introduction of digital solutions has made dentistry more efficient and effective in response to patients’ demands. Moreover, digital solution helps participants to manage daily workflow simpler than traditional practices. Scanners, CAD/CAM software, CNC machines and 3D printers are components of digital solutions in current dentistry. Responding to patients as quickly as possible is essential in medical fields and dentistry has similar situations. On the other hand, demands in dentistry are highly customized that it makes managing orders more difficult because each order needs special design and production. Thus, this paper assesses orders in digital dentistry and develops a mathematical... 

Maximizing the value of resources and producing less waste are strategic decisions affecting sustainability and competitive advantage. Sustainable closed-loop supply chains (CLSCs) are designed to minimize waste by circling back (repairing, reselling, or dismantling for parts) previously discarded products into the value chain. This study presents a novel two-stage fuzzy supplier selection and order allocation model in a CLSC. In Stage 1, we use the fuzzy best-worst method (BWM) to select the most suitable suppliers according to economic, environmental, social, and circular criteria. In Stage 2, we use a multi-objective mixed-integer linear programming (MOMILP) model to design a... 

Because of several vulnerabilities in software products and high amount of damage caused by them, software developers are enforced to produce more secure systems. Software grows up through its life cycle, so software development methodologies should pay special attention to security aspects of the product. This paper focuses on agile methodologies in order to equip them with security activities. We can restrain reduction of agile nature of organization's current process by means of agility measurement and applying an efficient activity integration algorithm with a tunable parameter named agility reduction tolerance (ART). Using this approach, method engineer of the project can enhance his... 

New Advances in mobile computer technology and the rapid growth of wireless networks in quality and quantity has introduced new applications and concerns in computer science and industry. The unique requirements and constraints associated with mobile systems have brought new challenges to software development for such environments, as it demands extensive improvements to traditional systems development methodologies in order to fulfill the special needs of this field. We examine the challenges of developing software for mobile systems, starting by reviewing mobile systems' characteristics and investigating the status quo of mobile software development methods. It has been shown that Agile... 

In recent years there have been many efforts to develop a hydrogen energy system in Iran. For instance, the Iranian fuel cell steering committee conducted a project and determined some targets to implement hydrogen in different sectors, especially transportation. In this paper, the costs of building stations and the levelized cost of hydrogen for two types of stations, SMR and electrolysis, with various sizes and capacity factors have been investigated. Also, in the case of electrolysis, hydrogen cost sensitivity to the price of electricity has been examined. According to the cost analysis conducted here, it is understandable that hydrogen costs ($/kg) vary considerably based on station... 

In this paper we study and present an in-depth analysis on the operability and the viability of a typical wireless optical CDMA (OCDMA) local area network. Three receiver structures for OCDMA systems, using optical orthogonal codes (OOC) with minimum auto and cross-correlations as signature sequence, namely, correlation, correlation with hard-limiter, and chip-level detection are studied and proposed for such a network. For the synchronization circuit design the performance of two algorithms for OOC based OCDMA networks, namely, simple serial-search and multiple-shift in the context of wireless OCDMA LAN are studied. Furthermore, we study a synchronization method based on matched filtering... 

It is widely recognized that knowledge is an essential strategic resource for a firm to achieve sustainable competitive advantage and Knowledge Management (KM) is a fundamental concept for those interested in the ever changing business world. However, KM has received little attention in Small and Medium sized Enterprises (SMEs). Unique characteristics of SMEs affect their approach in knowledge management, so different KM processes should be applied in these firms. SMEs have very simple structures, so they have less difficulty in managing their internal knowledge than large organizations. But this is not the case for external knowledge management, especially external knowledge acquisition... 

A new low voltage bandgap reference (BGR) in CMOS technology, with high power supply rejection ratio (PSRR) is presented. The proposed circuit uses a regulated current mode structure and some feedback loops to reach a low voltage, low power and high PSRR voltage reference. The circuit was designed and simulated in 0.18um CMOS technology, with a power supply of 1.4 volt. The results show PSRR is 65dB at 1MHz and the output voltage variation versus temperature (-40 to 140) is less than 0.1%. This circuit shows robustness against process variation. ©2008 IEEE  

Cartesian Genetic Programming (CGP) has an unusual genotype representation which makes it more efficient than Genetic programming (GP) in digital circuit design problem. However, to the best of our knowledge, all methods used in evolutionary design of digital circuits deal with rugged, complex search space, which results in long running time to obtain successful evolution. Therefore, employing a method to guide evolution in these spaces can facilitate achieving more reasonable results. It has been claimed that a two-step evolutionary scenario caused by benefit and cost of learning called Baldwin effect can guide evolution in the biology and artificial life. Therefore, we have been motivated...