Sharif Digital Repository

We study wireless sensor network (WSN) node placement in an environment where RF signal losses vary with position. This reflects real-world outdoor environments where vegetation and topography cause nonuniform path loss. Many techniques that solve for a variety of objective functions subject to various constraints have previously been proposed for node placement. However, many of these methods make simplifying assumptions such as all nodes having the same transmission range. Our goal is to take the insights and approaches of this previouswork and extend it to real-world environments. The present work assumes we have a map that quantifies the path loss behaviour of the real environment. Based... 

In this study a multi-objective genetic algorithm is utilized to obtain a Pareto optimal set of solutions for geometrical characteristics of airfoil sections for 10-meter blades of a horizontal axis wind turbine. The performance of the airfoil sections during the process of energy conversion is evaluated deploying a 2D incompressible unsteady CFD solver and the second law analysis. Artificial neural networks are trained employing CFD obtained data sets to represent objective functions in an algorithm which implements exergetic performance and integrity characteristics as optimization objectives. The results show that utilizing the second law approach along with Pareto optimality concept... 

The islanding of a distributed generation (DG)-fed distribution system generally results in frequency drop, which means less power is generated than it is needed. The only way of dealing with this problem is shedding loads as the system cannot generate any more electricity. Load shedding is intended to restore balance between generated and consumed power. This paper proposes a new method for load shedding based on the rate of change of frequency (RoCoF) at the first step and on voltage drop at subsequent steps. For this purpose, three lookup tables were created in order to prioritize loads to be shed according to the willingness of subscribers to pay and the RoCoF. The strength of the... 

This paper presents a new model of call admission control which consists of a few key elements for protecting the network in different conditions of workload in a manner that, calls blocking /dropping are kept under desired level. This model consists of two traffic classes of voice and data. In order to give a priority to handoff call over new call, some parameters in this model are adjusted in a manner that handoff dropping is reduced to the least probability in the target cell and the adjacent cells. Some channels are reserved for voice and data calls in each cell to guarantee the quality of service requirements in the network. Limited fractional guard channel is used to have an optimized... 

In real-time packet-based communication systems, one major problem is misrouted or delayed packets which results in degraded perceived voice quality. If packets are not available on time, the packet is known as lost packet. The easiest task of a network terminal receiver is to replace silence for the duration of lost speech segments. In a high quality communication system, to avoid quality reduction due to packet loss, a suitable method and/or algorithm is needed to replace the missing segments of speech. In this paper, we introduce a low order recursive linear prediction method for replacement of lost speech segment. In this method a normalized least mean square (NLMS) as an adaptive filter... 

This study experimentally investigates the structural performance of full-scale reinforced concrete utility poles fully reinforced with glass fibre reinforced polymer (GFRP) bars. The weak bond strength between GFRP bars and concrete in full-scale structures has been addressed by using an innovative anchorage system. Furthermore, fibre-reinforced concrete (FRC) was successfully used to enhance the crack propagations of GFRP-reinforced concrete poles. Three poles were constructed from FRC, while one was constructed with normal concrete (NC) as a benchmark. Polypropylene (PP) and crimped polyolefin-based macro-synthetic (CPO) fibres were used. An innovative anchorage system was used to... 

A web-based system is designed and implemented as a risk communication tool to incentivize the public to take seismic risk mitigation measures. Risk denotes the expected monetary and social losses herein. The objective of this system is to raise the awareness of two audience groups, the general public and decision makers, about significant seismic risk in Iran. To address the general public, the system employs the notion of risk perception to put the results of sophisticated earthquake engineering risk analyses into perspective. The system also treats the epistemic uncertainty of user input due to the public's lack of technical knowledge through the notion of entropy in information theory.... 

In this paper, a low order recursive linear prediction method and recursive least square as an adaptive filter (LP-RLS) are introduced to predict the speech and the excitation signals. In real-time packet-based communication systems, one major problem is misrouted or delayed packets which results in degraded perceived voice quality. If packets are not available on time, the packet is known as lost packet. The easiest task of a network terminal receiver is to replace silence for the duration of lost speech segments. In a high quality communication system, to avoid quality reduction due to packet loss, a suitable method and/or algorithm is needed to replace the missing segments of speech. The... 

Medical images contain information about vital organic tissues inside of human body and are widely used for diagnoses of disease or for surgical purposes. Image reconstruction is essential for medical images for some applications such as suppression of noise or de-blurring the image to provide images with better quality and contrast. In this paper Kalman filter technique is introduced for medical image reconstruction. This technique is operated in time domain unlike the filtered back projection which operates in frequency domain. Results indicated that as the number of projection increases in both the collected ray sum corrupted by noise and by blurring the quality of reconstructed image... 

Accurate Partial Discharge (PD) measurement requires the expansion of the measurement frequency range to Ultra High Frequency (UHF) band. For this it is needed to implement modern techniques when monitoring an important element of power system, such as power transformer. Different kind of experimental models, such as insulation defect models, and the complete transformer windings models are used to simulate the partial insulation failure situations which occur in a real transformer. However, since in these models, some kind of simplifications are employed which may result in an electromagnetic waves (EM) propagation pattern different from what exists in a real transformer and encounter... 

Many recent studies show that Augmented Reality (AR) and Automatic Speech Recognition (ASR) technologies can be used to help people with disabilities. Many of these studies have been performed only in their specialized field. Audio-Visual Speech Recognition (AVSR) is one of the advances in ASR technology that combines audio, video, and facial expressions to capture a narrator's voice. In this paper, we combine AR and AVSR technologies to make a new system to help deaf and hard-of-hearing people. Our proposed system can take a narrator's speech instantly and convert it into a readable text and show the text directly on an AR display. Therefore, in this system, deaf people can read the... 

Recently, many researches show Augmented Reality (AR) and Automatic Speech Recognition (ASR) can help people with disabilities. In this paper we implement an innovative system for helping deaf people by combining AR, ASR, and AVSR technologies. This system can instantly take narrator's speech and converts it into readable text and shows it directly on AR display. We show that our system's accuracy becomes over 85 percent on average, by using different ASR engines near using an AVSR engine in different noisy environments. We also show in a survey that more than 90 percent of deaf people on average need such system as assistant in portable devices, near using only text or only sign-language... 

Augmented Reality (AR), Automatic Speech Recognition (ASR) and Text-to-Speech Synthesis (TTS) can be used to help people with disabilities. In this paper, we combine these technologies to make a new system for helping deaf people. This system can take the narrator's speech and convert it into a readable text and show it directly on AR display. To improve the accuracy of the system, we use Audio-Visual Speech Recognition (AVSR) as a backup for the ASR engine in noisy environments. In addition, we use the TTS system to make our system more usable for deaf people. The results of testing the system show that its accuracy is over 85 percent on average in different places. Also, the result of a... 

We used a method to evaluate angular accuracy for air showers direction recorded by a pentagon array of scintillation detectors. This is achieved by using the coincidences between the air showers recorded by the two sub-arrays. Also, using the CORSIKA code the angular precision of this array and the effect of inherent error on it is obtained at different energies of the primary particles and at different zenith angles. © 2020 Elsevier B.V  

In this article, we consider an energy harvesting cooperative network comprised of two data sources and one relay. All nodes transmit based on a predefined slotted Aloha protocol in a random access environment. The main challenge we study is to find how the relay node must share its energy between two sources to optimize their QoS metrics, i.e., throughput and average transmission delay (ATD), separately. Thus, according to our multi-source scenario, we encounter a multi-objective optimization problem (MOOP). Since the relay does not prioritize between two sources, in order to solve the MOOP, we optimize equal-weight linear aggregation of the QoS metrics of two sources. Interestingly, we... 

Catalytic ozonation has recently been used as a new means of contaminant removal from water and wastewater. In this study, bone charcoal (BC), a new catalyst prepared under laboratory conditions, was used to catalyze the ozonation of humic substances (HS) in aqueous solutions. The catalytic effect of bone charcoal and the relevant parameters of this ozonation process (solution pH, temperature, scavenger effect, humic acids concentration and BC dosage) were investigated. In the catalytic ozonation experiments, the degradation kinetics was investigated. The reaction rate and the rate constant were determined. The results showed that using a BC catalyst in the ozonation of HS produced a 1.43-... 

The main challenge in many applications of acetic acid is acid dehydration and its recovery from wastewater streams. Therefore, the performance of polyamide thin film composite is evaluated to separate acetic acid from water. To reach this goal, the formation of polyamide layer on polysulfone support membrane was investigated via interfacial polymerization (IP) of meta-phenylenediamine (MPD) in water with trimesoyl chloride (TMC) in hexane. Also, the effect of synthesis conditions, such as concentration of monomers and curing temperature on separation of acetic acid from water were investigated by reverse osmosis process. Moreover, the separation mechanism was discussed. The solute... 

Pitch detection is the process of determining the period of the vocal cords closure or in another word the time duration of one glottal closed, open and returning phase. Dyadic wavelets transform (DyWT) and modified higher order moment, are two pitch detection methods. DyWT is an accurate pitch detection method, however it has less accuracy compared to modified higher order moment. On the other hand modified higher order moment has high computational complexity and is time consuming. The DyWT pitch period detection is based on a two pass dyadic wavelet transform over a signal. Modified higher order moment is based on autocorrelation function (ACF) and in this method the speech signal has... 

This paper proposes an efficient many-to-many group key management protocol in distributed group communication. In this protocol, group members are managed in the hierarchical manner logically. Two kinds of keys are used, asymmetric and symmetric keys. The leaf nodes in the key tree are the asymmetric keys of the corresponding group members and all the intermediate node keys are symmetric keys assigned to each intermediate node. For asymmetric key, Diffie-Hellman key agreement is introduced. To calculate intermediate node keys, members use codes assigned to each intermediate node key tree. Group members calculate intermediate node keys rather than distributed by a sponsor member. The... 

Pitch detection is the process of determining the period of the vocal cords closure or in another word the time duration of one glottal closed, open and returning phase. Dyadic wavelets transform (DyWT) and modified higher order moment, which is based on the autocorrelation function, are two pitch detection methods. DyWT is an accurate pitch detection method, however it has less accuracy compared to modified higher order moment. On the other hand modified higher order moment has high computational complexity and is time consuming. In this paper, we propose a pitch detection method based on DyWT which has use modified higher order moment. Modified higher order moment is applied only in some...