Sharif Digital Repository

In this article, the authors introduce and propose an overloaded Synchronous Optical Code Division Multiple Access (SOCDMA) based on Unipolar Walsh Code (UWC) for fiberoptic communication systems. Given μ as the number of chips, it is shown that 2L - 2 active users can be supported by the proposed system. In this system the users of the network are categorized into two groups. Users of each group transmit at the same power level but different from the level of the other group's users. Using the UWC properties we propose a simple receiver that cancels multiple-user interference (MUI) completely. Moreover, we obtain the optimal power level of each group in order to minimize the probability of... 

Cosine similarity and Probabilistic Linear Discriminant Analysis (PLDA) in i-vector space are two state-of-the-art scoring methods in speaker verification field. While PLDA usually gives better accuracy, Cosine Similarity Scoring (CSS) remains a widely used method due to simplicity and acceptable performance. In this domain, several channel compensation and score normalization methods have been proposed to improve the performance. We investigate non-speaker information in cosine similarity metric and propose a new approach to remove it from the decision making process. I-vectors hold a large amount of non-speaker information such as channel effects, language, and phonetic content. This type... 

Satellite remote sensing products of AOD from MODIS along with appropriate meteorological parameters were used to develop statistical models and estimate ground-level PM10. Most of previous studies obtained meteorological data from synoptic weather stations, with rather sparse spatial distribution, and used it along with 10 km AOD product to develop statistical models, applicable for PM variations in regional scale (resolution of ≥10 km). In the current study, meteorological parameters were simulated with 3 km resolution using WRF model and used along with the rather new 3 km AOD product (launched in 2014). The resulting PM statistical models were assessed for a polluted and largely variable... 

In this study, a novel type of LHP is innovated, fabricated, and its performance is assessed by numerous experiments. Compared to conventional LHPs, this novel design has some modifications in its evaporator and reservoir configuration. This particular type has a simpler and less costly fabrication procedure compared to other LHPs and it yields acceptable performance. Additionally, a novel method is introduced to control the temperature distribution in the system. A steel ball is placed in the evaporator to actively control the operating temperature. The ball is moved by two magnets installed outside of the evaporator. Moreover, a steady-state one-dimensional mathematical model of the... 

Using control charts to monitor healthcare systems has gained particular attention. In this paper, a risk-adjusted cumulative sum control chart is designed to monitor surgery outputs. Before undergoing surgery, the patients have some unique risk factors which influence the surgery outputs. Thus, risk-adjustment is carried out with the purpose of taking these risks into account using an accelerated failure time model. But the technical implementation of the chart requires determining the design parameters which should be selected in an optimal way putting the desired statistical and economic considerations into service. To this end, a multi-objective model, considering multiple assignable... 

The overall design of cold gas propulsion systems is pretty complicated when considering the mission requirements, operating constraints and functional limitations imposed by the mechanical components. To address this complication, a precise design process is proposed, which attempts to optimize the cost of operation as well as to minimize the waste volume and weight by using multi-objective trade-off analysis. This analysis is based on a set of ordinary differential equations that are solved iteratively to describe the optimal behavior of the system. Therefore, a numerical code is being developed to give insight on the design sensitivity with respect to uncertainties on the design... 

Long term evolution (LTE)-advanced aims the peak data rates in excess of 3 Gbps for the next generation wireless communication systems. Turbo codes, the specified channel coding scheme in LTE, suffers from a low-decoding throughput due to its iterative decoding algorithm. One efficient approach to achieve a promising throughput is to use multiple Maximum a Posteriori (MAP) cores in parallel, resulting in a large area overhead, a big drawback. The scaled Max-log MAP algorithm is a common approach to implement the MAP algorithm due to its efficient architecture with its acceptable performance. Although many works have been reported to reduce the area of the MAP unit, an efficient VLSI... 

Reference Governor is an important component of Active Fault Tolerant Control. One of the main reasons for using Reference Governor is to adjust/modify the reference trajectories to maintain the stability of the post-fault system, especially when a series of actuator faults occur and the faulty system can not retain the pre-fault performance. Fault estimation error and delay are important properties of Fault Detection and Diagnosis and have destructive effects on the performance of the Active Fault Tolerant Control. It is shown that, if the fault estimation provided by the Fault Detection and Diagnosis (initial “fault estimation”) is assumed to be precise (an ideal assumption), the... 

Cellular learning automata (CLA) is a distributed computational model which was introduced in the last decade. This model combines the computational power of the cellular automata with the learning power of the learning automata. Cellular learning automata is composed from a lattice of cells working together to accomplish their computational task; in which each cell is equipped with some learning automata. Wide range of applications utilizes CLA such as image processing, wireless networks, evolutionary computation and cellular networks. However, the only input to this model is a reinforcement signal and so it cannot receive another input such as the state of the environment. In this paper,... 

Copper slag (CS) is an industrial waste, which is generally disposed of in landfills, posing threats to the environment. Alternatively, it can be used as natural aggregate replacement in concrete/mortar, however, it results in a significant increase in material density, production and handling cost. The use of crumb rubber in combination with CS can overcome these problems, but there was no prior study on effect of such combination on the properties of alkali activated mortars (AAMs). The primary aim of this study is to address the problem stated above by replacing CS with 5, 10, 15% (by volume) crumb rubber in alkali-activated slag mortars. Furthermore, the effect of pre-treatment of crumb... 

Extensive wind-tunnel tests were performed on a Y-shaped diverterless supersonic inlet (DSI). All tests were conducted at a free stream Mach number of M∞ 1.65, the design Mach number for this inlet, and at both zero degrees angle of attack (AOA) and angle of sideslip (AOS). The experiments were performed at various inlet operating conditions comprising supercritical, critical, and subcritical conditions that covered almost all ranges of the engine operating for this DSI. The results showed that the DSI had relatively acceptable performance characteristics when operating at its design condition. A symmetric supersonic flow pattern was observed at both supercritical and critical operating... 

A novel fault-tolerant model predictive control (MPC)-based trajectory tracking approach for an aerial vehicle is presented in this study. A generalised online sequential extreme learning machine is introduced first to identify the corresponding coefficients of actuator faults. Subsequently, a robust trajectory tracking control is developed based on MPC, where the system constraints can be effectively considered in the designed control scheme. Trajectory tracking control is achieved by controlling only the acceleration of the aerial robot in the MPC structure. This leads to less computational burden and faster closed-loop dynamics. In addition, an effective disturbance observer is employed,... 

This study proposes a novel socio-hydrological modeling framework for assessing the performance of complex water resources systems. It employs and integrates agent-based modeling (ABM) and the theory of planned behavior (TPB) into the socio-hydrological modeling framework to account for agents’ behaviors. Due to farmers’ major role in anthropogenic droughts, this paper mainly focuses on farmers’ behavior. The TPB framework and the agents’ behavioral rules in ABM are structured based on the data obtained from field questionnaires and interviews by the farmers in the Zarrineh River Basin as the main river feeding the Urmia Lake. The proposed modeling framework, including the TPB and ABM...