Sharif Digital Repository

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... 

In this paper the dynamic properties of Babolsar dry sand was investigated through one dimensional shaking table tests. 8 models of Babolsar loose dry sand under low confining pressures, were subjected to different harmonic and irregular dynamic loadings. The container was a laminar shear box having 24 layers each moving on the lower one. The dynamic properties including shear wave velocity, maximum shear modulus and damping ratio of the samples were addressed in this project. © 2006 Taylor & Francis Group, London  

After a natural disaster, there is an urgent need to supply critical loads such as hospitals as soon as possible. Microgrid (MG) formation is one of the quickest ways to achieve this goal. However, in MG formation studies, there is a trade-off between maximizing the amount of restored loads and minimizing their risk of interruption due to the following aftershocks. For the former objective, the minimum number of MGs should be formed, whereas, for the latter objective, the maximum number of MGs should be configured. This paper tackles this contradictory situation by considering the failure risk of distribution feeders in its proposed optimization framework. In this paper, at first, a novel... 

Investigating the parameters influencing the behavior of buried pipelines under dynamic loading is of great importance. In this study the soil structure interaction of the pipelines with the surrounding soil was addressed using shaking table tests. Wave propagation along the soil layers was also included in the study. The semi infinite nature of the field was simulated using a laminar shear box. The soil used in the experiments was Babolsar coastal sand (Iran). PVC pipes were used due to their analogy with the field. Eight models were constructed with the first four models having uniform base. In the next models, the non-uniformities of real ground were simulated using a concrete pedestal... 

This paper presents an efficient mixed-integer linear formulation for long term maintenance schedule of overhead lines. The proposed formulation is based on risk management approach and utilizes the model of decoupled risk factors. The proposed methodology yields a significant computational saving comparing to the previously reported dynamic programming. Risk management approach enables the asset managers to consider the actual condition of electrical equipment and expected consequence of their failures. Furthermore, the decoupled risk strategy in conjunction with the mixed-integer linear programming formulation establishes a precise description of time-dependent deterioration failure rate... 

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,... 

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  

Here we report a versatile new method for endfunctionalizing polystyrene. In order to produce polystyrene with an amino end group, 2-(3-bromo-3- phenylpropyl) isoindoline-1,3-dione was synthesized and used as a novel initiator for ATRP. After ATRP polymerization, tri-n-butyltin hydride ((n-Bu) 3SnH) reductively replace existing halogens on polymer chains by hydrogen. Finally, the phthaloyl groups on polymer backbone were cleaved by treatment with hydrazine yielding amino terminated polystyrene. A polymer with M n≈10,350 and M w/M n01.17 was obtained. Therefore, this method allows the preparation of amino end functionalized polystyrene of narrow polydispersity with complete degree of... 

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... 

In this study, residual stress distributions in autofrettaged homogenous spherical pressure vessels subjected to different autofrettage pressures are evaluated. Results are obtained by developing an extension of variable material properties (VMP) method. The modification makes VMP method applicable for analyses of spherical vessels based on actual material behavior both in loading and unloading and considering variable Bauschinger effect. The residual stresses determined by employing finite element method are compared with VMP results and it is demonstrated that the using of simplified material models can cause significant error in estimation of hoop residual stress, especially near the... 

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...