Sharif Digital Repository

A new optimal waveform for Ultra-wideband (UWB) radios is proposed in this paper. This new waveform extracted through mathematical analysis for achieving high spectral utilization under the restrictions imposed by the U.S. Federal Communications Commission (FCC) spectral masks. Exploiting Inverse Fourier Transform (IFT) of FCC mask, the required analog signals are extracted through robust calculation and the optimum realizable analog signal for FCC mask is constructed while the simulations confirmed the analytical approach. Normalized effective signal power (NESP) of the proposed method is 95.27% which shows better efficiency compared to the other methods in the literature  

An efficient low-complexity VLSI architecture for timing synchronization of a real-time intensity modulation direct detection optical OFDM (IMDD-OOFDM) system is proposed, which results in a significant area reduction. This architecture calculates the correlation among cyclic prefix (CP) regions to estimate the beginning of the OFDM symbol. The proposed architecture utilizes only one functional unit for this purpose, while the throughput is devised for high data-rate optical OFDM systems. Synthesis results of this architecture proves an area saving of 31% compared to the previous work. Moreover, the performance of the correlation method is significantly improved due to a modification applied... 

Condensate and water blockage are known as the most prevalent causes of well productivity decline in gas condensate reservoirs. The methodology of wettability alteration of near wellbore region to gas wetting condition, is a novel and permanent technique to address the aforementioned problem. In this work, we report the introduction of a hydrocarbon based polymer solution to change the wettability of reservoir rocks from liquid wetting to intermediate- to gas wetting condition. Both air-n-decane and air-water contact angles changed from liquid wetting condition to intermediate and gas wetting condition, respectively, after treatment of calcite and laminated glass thin sections with chemical... 

Redundancy technique is considered as a way to enhance the reliability and availability of a system. This paper models availability of a repairable system with multiple subsystems in which the involved components follow the load sharing strategy. In redundancy allocation problems, the redundancy level is just considered, whereas, in this paper, the number of repair facility (repairman) is added to the decision variables. The goal is to find the optimal number of repairmen and redundant components in each subsystem for optimization of availability subject to weight, cost and volume constraints. The main contribution of this study is to present a straightforward model for availability... 

A novel BiCMOS voltage-to-voltage converter with logarithmic characteristics and very high accuracy is presented. The relationship between the emitter current and the base-emitter voltage in bipolar transistors is used to realize the logarithmic function. With 1.8 supply voltage, the total power consumption is less than 15.75 mW and a Log error of < -36dB is shown in the ADS simulations. Compared to the other method in the literature, very better accuracy in logarithm calculation is achieved. The proposed method can be used in arithmetical operation circuits like analog processors  

A novel semi-active control system for suspension systems of passenger car using Magnetorheological (MR) damper is introduced. The suspension system is considered as a mass-spring model with an eight-degrees-of-freedom, a passive damper and an active damper. The semi-active vibration control is designed to reduce the amplitude of automotive vibration caused by the alteration of road profile. The control mechanism is designed based on the optimal control algorithm, Linear Quadratic Regulator (LQR). In this system, the damping coefficient of the shock absorber changes actively trough inducing magnetic field. It is observed that utilizing the present control algorithm may significantly reduce... 

We use the topological entanglement entropy (TEE) as an efficient tool to fully characterize the Abelian phase of a Z2 ×Z2 spin liquid emerging as the ground state of topological color code (TCC), which is a class of stabilizer states on the honeycomb lattice. We provide the fusion rules of the quasiparticle (QP) excitations of the model by introducing single- or two-body operators on physical spins for each fusion process which justify the corresponding fusion outcome. Besides this, we extract the TEE from Renyi entanglement entropy (EE) of the TCC, analytically and numerically by finite size exact diagonalization on the disk shape regions with contractible boundaries. We obtain that the EE... 

In discussions related to reliability optimization using redundancy allocation, one of the structures that has attracted the attention of many researchers, is series-parallel structure. In models previously presented for reliability optimization of series-parallel systems, there is a restricting assumption based on which all components of a subsystem must be homogeneous. This constraint limits system designers in selecting components and prevents achieving higher levels of reliability. In this paper, a new model is proposed for reliability optimization of series-parallel systems, which makes possible the use of non-homogeneous components in each subsystem. As a result of this flexibility,... 

An electric power supply is the backbone of development in advanced as well as in developing economies. An integral part of ensuring a secure power supply system is a power communication system. Due to the high and sustained performance requirements of power communication systems, electric companies prefer to construct their own communication networks privately rather than relying solely on a public communication system. The focus of this paper is on the optimal topological design of a power communication network. Based on advanced optimization models in public communication networks, and taking into account the specific Quality of Service, as demanded by various applications, such as... 

Interaction of the DNA thymine base with Cu+ and Zn3+ was studied to explore: a) The metal binding energy (MIA) of thymine with Cu+ and Zn2+ and b) The possible correlation between charge transfer and MIAs. The gas-phase Cu+ and Zn2+ affinities of thymine, as well as the Mulliken charges, on the complexed metal cations were both determined at the same computational level, including the density functional level and employing the hybrid B3LYP exchange correlation potential in connection with the 6-311++G (d,p) basis set. All the molecular complexes were obtained by interaction between the most stable tautomer of thymine and two transition mono and divalent (Cu+, Zn2+) metal ions. To probe all... 

A new approach is presented in this paper to determine the degree of system well-being in the form of healthy, marginal and at risk state indices using the fuzzy logic concepts. Conventional well-being method uses a crisp deterministic criterion to divide power system comfort zone into the healthy and marginal states. In this regard, the main drawback is associated with categorising the system performance in the comfort zone into the healthy and marginal states. To overcome this problem, a new approach is developed that categorises the states as healthy or marginal using fuzzy logic. The technique together with the effects on the system risk and the system health and margin probabilities of... 

A novel semi active control system for eleven Degrees of Freedom passenger car's suspension system using Magneto rheological damper is presented. The considered suspension system is modeled using mass spring damper model. The semi active vibration control is designed to reduce the amplitude of vehicle's vibration due to by road profile. The applied control strategies are based on a Linear Quadratic Gaussian optimal control algorithm to obtain desired damping forces of MR dampers. In considered system, the damping coefficient of the shock absorber changes actively through inducing magnetic field. The necessary input voltage to MR dampers to generate desired damping forces are derived using... 

Deep wells suffer from the instability and disintegration of natural polymers and other commonly used additives under high pressure and high temperature condition. As a result, serious problems such as hydraulic loss, stuck pipe, and high torque and drag are expected to take place which leads to a dramatic increase in cost and time. This study presents the functionality of a novel synthetic based acrylamide-styrene copolymer (SBASC) as a supersede additive for water-based drilling mud. First, the SBASC was synthesized using an emulsion polymerization process and its particle morphological and polymer chain structural properties were determined by Field Emission Scanning Electron Microscopy... 

This paper considers a repair-replacement strategy for a special class of discretely degrading and repairable products under renewing free replacement warranty. Each product may experience N different working states with different exponential hazard functions, before the warranty contract expires. Once the item enters working state i (i = 1,2, ⋯ ,N), it can either fail or move to any of the subsequent working states with different probabilities, given that a transition has been made. In the former case, the best rectification action, replacement or minimal repair, regarding the failure status, i.e., the product degradation level at the failure time and the remaining warranty time, should be... 

We develop a replacement-repair model to study a renewing free replacement warranty (RFRW) for a class of multi-state deteriorating repairable products. Each product may experience N different working states with different hazard functions, before the warranty contract expires. Once the item enters working state j(j = 1, 2, . . . , N), it can either fail or move t any of the subsequent states. In the former case, the best rectification action, replacement or minimal repair, regarding the failure status, should be done to put the item into operation. In each working state there is a determined probability for transition to each of the subsequent working states. After a replacement the product... 

Due to complicated implementation of IP multicast, application layer multicast has attracted the attention of researchers. Tree overlay has some challenges such as resiliency problems caused by peer churns and also network resources may not be efficiently used. Mesh overlay doesn't have such problems, but has a high delivery latency and overhead caused by pull mechanism. Using a hybrid mesh/tree overlay offers push pull approach and leads to use the advantages of both overlays simultaneously. Also in p2p networks a significant problem is heterogeneity of peers. In this paper we propose a hybrid mesh/tree overlay that by means of streaming layered coded video, addresses these challenges. This... 

The Legendre polynomial expansion method (LPEM), which has been successfully applied to homogenous and longitudinally inhomogeneous gratings [J. Opt. Soc. Am. B 24, 2676 (2007)], is now generalized for the efficient analysis of arbitrary-shaped surface relief gratings. The modulated region is cut into a few sufficiently thin arbitrary-shaped subgratings of equal spatial period, where electromagnetic field dependence is now smooth enough to be approximated by keeping fewer Legendre basis functions. The R-matrix propagation algorithm is then employed to match the Legendre polynomial expansions of the transverse electric and magnetic fields across the upper and lower interfaces of every slice.... 

In this article a novel method has been developed to improve the ride comfort of a passenger car by optimum choice of shock absorbers. The objective is to minimize the fatigue provided in the body due to transmitted vibrations. A comprehensive ADAMS model of the car was constructed for perfect simulation of car motions in different maneuvers. This model was validated by further construction of a car and test rig model, and comparing hydro-pulse test data on the real car with simulation results of ADAMS model. The real road profile was adopted as stimulus for the model. Copyright © 2005 SAE International  

In this paper, a new method for the calculation of electromagnetic fields around a transmission line subjected to a lightning strike is described and discussed. The electric fields and magnetic fields are presented graphically as a function of spatial coordinate, as a function of time and as a function of both. It is believed that this exact solution have not been published before. First, a double exponential lightning surge current is injected into a transmission line. Once The temporal variations of current is known, then electric and magnetic fields can be calculated by using the field expressions for electric dipoles over infinitely conducting ground. As the calculation was done for each...