Sharif Digital Repository

In this paper, we study three types of jammers, namely, pulse-jammer, partial-band jammer, and follower-jammer, in a typical fiber-optic-based spectrally phase-encoded optical code division multiple-access (SPE-OCDMA) system. We analyze, mathematically, the effects of the aforementioned jammers on the performance of an SPE-OCDMA system for two scenarios, namely, ideal noiseless channel with an ideal optimum receiver and an ultrahigh-speed nonlinear receiver based on two-photon-absorption (TPA) in a noisy channel. Also, for each of the above cases, two types of modulation, namely, on-off keying (OOK) and two-code keying (2CK) are investigated and their system performances are compared. It is... 

In this study, the authors perform a complete survey on S-parameter method applications to compensate the coupling effect in circular arrays. The authors illustrate that, despite the simplicity and ease of measurements, the S-parameter algorithm has an adequate performance in comparison with the external calibration techniques in real environments. Based on the simulation and experimental results, for unmatched arrays and low-frequency applications [e.g. high-frequency (HF) radars], the S-parameter method performance is demonstrated to be comparable in accuracy to the external calibration techniques. Despite multipath effect and structural scattering, the direction of arrival can be... 

For direction of arrival (DOA) estimation in compact arrays, a new approach based on time delay and amplitude estimation is presented for a known signal. The DOA can be accurately estimated without any calibration sources since the mutual coupling and multipath effects can be eliminated by the inherent mechanism of the proposed algorithm. The algorithm has significantly lower error and much less computational burden compared with the previous methods in high signal-to-noise ratio (SNR) conditions  

In this paper, we study three types of jammers, namely, pulse-jammer, partial-band jammer, and follower-jammer, in a typical fiber-optic-based spectrally phase-encoded optical code division multiple-access (SPE-OCDMA) system. We analyze, mathematically, the effects of the aforementioned jammers on the performance of an SPE-OCDMA system for two scenarios, namely, ideal noiseless channel with an ideal optimum receiver and an ultrahigh-speed nonlinear receiver based on two-photon-absorption (TPA) in a noisy channel. Also, for each of the above cases, two types of modulation, namely, ON-OFF keying (OOK) and two-code keying (2CK) are investigated and their system performances are compared. It is... 

Landslide events are among natural hazards with many fatalities and financial losses. Studies demonstrate that natural factors such as rainfall and human activities such as deforestation are important causes of triggering a landslide. In this study, an integrated two-dimensional slope stability model, SSHV-2D, is developed that considers various aspects of hydrological effects and vegetation impacts on the stability of slopes. The rainfall infiltration and water uptake of roots change the water content of the unsaturated zone. The temporal and spatial distribution of water content is estimated in the hydrological unit of the developed model. The vegetation unit of the model considers... 

Although, enhanced security is often mentioned as a noticeable benefit of Spectrally Phase Encoded Optical CDMA (SPE-OCDMA) systems, the quantity and degree of security enhancement is not considered deeply in the literature. One of the facts in determining the degree of security is to assess the resistance capability of the system against various jammers attacks. In this paper, we introduce and model three types of jammers, namely (Pulse Jammer, Partialband Jammer, and Follower Jammer). We mathematically analyze the effects of the above jammers on the performance of the SPE-OCDMA systems that use On-Off keying (OOK) modulation scheme. It is demonstrated that under certain conditions, the... 

In this paper, a new software is introduced that is developed to give the most appropriate solution for the component selection and design of a hybrid electric bus. There are several simulation programs that can simulate behavior of a hybrid electric bus, but most of them are not able to suggest the best design and the best choice of the components. Customer requirements are dissimilar and there are several different parameters that they may need. Cost, pollution, driving cycle, battery type, DC link voltage, weight, volume, fuel consumption, and acceleration are some parameters that vary from one customer to the other. The stated software that is developed and presented by this paper will... 

In this paper, sliding-mode control (SMC) is applied to a z-source converter to control output dc voltage of impedance network. The converter is assumed working in continuous conduction mode (CCM). First a comprehensive review of the literature for z-source inverter (ZSI) and use of sliding mode control in switched converters are performed. The procedure of SMC design used in ZSI is presented. The simulations for the application of SMC in z-source inverter are made and the results are illustrated. The results verify the effectiveness and robustness of the controller. © 2008 IEEE  

The flux and torque hysteresis bands are the only gains to be adjusted in direct torque control (DTC). The torque ripple and harmonic loss of motor and switching loss of inverter greatly Influence them. Hence, these variables must be observed in the control process to maximize performance of the system. In this paper, the effects of flux and torque hysteresis bands on inverter switching loss, harmonic loss, and torque ripple of induction motor are investigated. In order to find their optimum values, a cost function consisting motor harmonic losses, torque ripples, and inverter switching losses is defined. Minimizing this cost function leads to the optimum value of the hysteresis bands of... 

In this paper, a flux search controller is proposed to increase the efficiency of a direct torque controlled induction motor with light load. The reference flux value is determined through a two stage minimization algorithm with the amplitude of the stator current as the objective function. In the transient state, a great flux step is used to speed up the convergence. In the steady state, a noise cancellation algorithm is used to let using small flux step and improves the steady state behavior of flux controller. Simulation and experimental confirm the fast dynamics of the proposed method and its superiority compared to the other optimal flux search controllers. © 2005 IEEE  

In this study, a two-user discrete memoryless multiple-access channel with two correlated states known non-causally at the corresponding encoder is considered. Each encoder transmits a message independent of the other encoder's and tries to cooperate with it. To consider cooperative encoders, it is assumed that each encoder strictly-causally receives and finds out the other encoder's transmitted signals and tries to cooperate with the other encoder by transmitting its message. A special case is also studied in which the common part of the states is known at the both encoders, resulting in a larger rate region. For these two scenarios, achievable rate regions are derived using a combination... 

The intrinsic viscosity of very high molecular weight partially hydrolyzed polyacryamide (HPAM), which is mainly used in the EOR processes, was studied in reservoir conditions. The critical concentration that could be helpful in determining the optimized polymer concentration for injection into the reservoir is calculated. The effects of temperature and salt concentration on the parameters are also studied. An experimental model to predict the variations of these parameters with temperature and salt concentration was developed. This is an abstract of a paper presented at the 8th World Congress of Chemical Engineering (Montreal, Quebec, Canada 8/23-27/2009)