Sharif Digital Repository

Quantum-dot cellular automata (QCA) which is a suitable alternative to conventional CMOS technology is susceptible to some defects in chemical synthesis and deposition phases of circuit fabrication. Besides, the majority gate is one of the most important primary gates for designing digital circuits in this emerging technology. Designing a fault-tolerant majority gate is one of the hot topics in QCA technology. Most previous works tried to improve the majority gate reliability by increasing the number of QCA cells which resulted in occupying more area. In this paper we propose a novel area-efficient three-input majority gate which can tolerate the single-cell omission and extra-cell... 

Recent developments in the space industry and the great tendency to define efficient, precise and low cost missions are the main reasons for the growing interest in satellites formation flight. Regarding the aforementioned, the study of multiple satellites control methods is the subject of the present paper. In this paper, two linear robust control strategies are applied to position control system of certain satellites in the virtual structure formation flight. The proposed controllers are designed considering different parametric uncertainties such as semimajor axis and eccentricity changes as well as some disturbances like second term of gravitational acceleration function (j2) and drag... 

In this paper, we propose a new modeling approach for analytical evaluation of normalized throughput and average backoff time for IEEE 802.11 MAC standard in non-saturation mode and with Poisson arrivals. To this end, we map different stages of distributed coordinated function (DCF) onto different components of a closed multi-class BCMP queueing network with arbitrary service time distribution. At the last part of the paper, we illustrate the applicability of the proposed approach by some numerical results in both saturation and non-saturation modes and obtain average backoff time for different arrival rates. © 2007 IEEE  

In this paper, we propose a new model to evaluate the behavior of cognitive radios (CRs). In this model, we consider a specific number of primary users having independent probabilistic on-off behavior. In addition, a specific number of opportunistic cognitive radios in saturation mode is assumed. We consider contention for CRs in order to occupy an inactive primary channel independently according to a simple MAC scheme. Our model is based on a closed BCMP state-dependent queueing network. We map contention of the CRs and the behavior of primary users on suitable parameters of the queueing network. By solving the network, we obtain the steady state behavior of CRs, then we find the efficient... 

During the last two decades, energy production has been directed towards renewable resources, one of the most important of which is geothermal energy. Despite the reliability of geothermal energy as a resource, its effects on the surrounding environment have not been investigated in detail. This study focuses on reservoir deformation as one of the environmental concerns of geothermal energy extraction. A coupled thermo-hydro-mechanical (THM) model is employed for simulating the reservoir deformations. The validity of the model results is examined by comparing the numerical results with the analytical solution of a benchmark THM problem. The model is then utilised to study the behaviour of a... 

Nerve repositioning surgery is one of the treatments chosen for the patients with edentulous posterior atrophic mandible. Like any other treatments, this therapy has its advantages and disadvantages, indications and contraindications. The most important complication of this procedure is neurosensory disturbance. This problem may occur at different stages of the treatment. One common time when nerve damage happens is when the nerve is located outside the canal and drilling and insertion of the implant are performed. Accordingly, this report describes a simple and feasible method to retract and protect nerves outside the canal during the treatment of nerve transposition. This will reduce the... 

Nerve repositioning surgery is one of the treatments chosen for the patients with edentulous posterior atrophic mandible. Like any other treatments, this therapy has its advantages and disadvantages, indications and contraindications. The most important complication of this procedure is neurosensory disturbance. This problem may occur at different stages of the treatment. One common time when nerve damage happens is when the nerve is located outside the canal and drilling and insertion of the implant are performed. Accordingly, this report describes a simple and feasible method to retract and protect nerves outside the canal during the treatment of nerve transposition. This will reduce the... 

Knowing the rate of evaporation from surface water resources such as channels and reservoirs is essential for precise management of the water balance. Few detailed evaporation studies exist for small lakes or reservoirs in arid regions of the world. In this study, monthly evaporation was determined by Bowen Ratio Energy Budget technique (BREB) for Alghadir reservoir (Saveh, Iran) from 1995-2007 and compared with class-A pan. Daily data were obtained from IMO (Iran Meteorological Organization) weather station, located near the reservoir, for all of these years. Some variations have been observed on the estimated evaporation of the energy budget at different years, ranging from 151 cm for 1997... 

In non-linear scales, the matter density distribution is not Gaussian. Consequently, the widely used two-point correlation function is not adequate anymore to capture the matter density field's entire behaviour. Among all statistics beyond correlation functions, the spherical contact (or equivalently void function), and nearest neighbour distribution function seem promising tools to probe matter distribution in non-linear regime. In this work, we use haloes from cosmological N-body simulations, galaxy groups from the volume-limited galaxy group and central galaxies from mock galaxy catalogues, to compare the spherical contact with the nearest neighbour distribution functions. We also... 

Motorcycles are the third most common means of transportation in the megacity of Tehran. Hence, measurements of emission factors are essential for Tehran motorcycle fleets. In this study, 60 carburetor motorcycles of various mileages and engine displacement volumes were tested in a chassis dynamometer laboratory according to cold start Euro-3 emissions certification test procedures. For almost all of the tested samples, the average carbon monoxide (CO) emission factors were about seven times higher than the limits for Euro-3 certification. No motorcycle fell within the Euro-3 certification limit on CO emissions. 125 cc engine displacement volume motorcycles, which are dominant in Tehran,... 

Passenger cars (PCs) not only are a major contributor to greenhouse gas (GHG) emissions in Iran but also pose severe energy security challenges due to their dependence on gasoline. This study aimed to understand the future trends of the gasoline demand and GHG emissions from PCs in Iran and assess the effectiveness of mitigation policies. The data were collected from multiple sources and used to develop the survival rate function of PCs. The study used back-calculation to compensate for the short period of stock data availability. The use intensity of PCs was estimated based on the gasoline consumption statistics. Econometric models were developed to project the future PC stock and use... 

Passenger cars (PCs) are a major contributor to urban air pollution, greenhouse gas emissions, and energy security challenges in megacities in developing countries because of their high growth potential. Since the PC fleet changes through time, the projection of air pollutant emissions from PCs is essential for effective emission reduction policymaking. However, the extensive amount of data and proper models are required for this purpose that are not available in many developing countries. Hence, this study develops multiple econometric and emission models and integrate them into a framework to simulate the future stock and activity of PCs and projects PCs’ air pollutants and CO2 emissions... 

As an essential step of product design, tolerance design plays a critical role in reducing manufacturing costs while ensuring mechanical assemblies’ quality and reliability. However, existing tolerance allocation approaches only are concentrated on design specification constraints during the design stage, although component degradation caused by environmental and operating conditions increases the probability of product failure during the service life. To deal with the degradation effect arising over the service life of mechanical assemblies, this paper proposes a reliability-based tolerance design approach to allocate optimal, reliable tolerances to mechanical systems. The proposed approach...