Sharif Digital Repository

Quality of Experience (QoE) indicates the overall quality of one service such as Voice over IP (VoIP) from users' point of view by considering several systems, human, and contextual factors. QoE measurement and prediction are more challenging than Quality of Service (QoS) which is only related to network parameters. There exist various objective and subjective methods for QoE prediction. This research investigates various features affecting QoE by proposing a comprehensive subjective evaluation by employing a large number of users. We show that many unconsidered factors including speaker specifications and signal properties, such as signal-to-noise ratio (SNR), can affect QoE so that the SNR... 

Condition monitoring of machinery is of significant economic importance to mitigate production losses resulting from downtimes. Unforeseen failure of roller element bearings is the most common issue observed in industrial units. However, detecting and tracking the progression of these failures through machine vibration monitoring and predicting the deterioration of these rotating components are viable solutions. Numerous studies have focused on using laboratory accelerated life test data for fault detection and remaining useful life prediction of these components. While online monitoring of all equipment in the industry may not be feasible, and conditions in the field differ from laboratory... 

Intelligent predictive maintenance is recognized as a cornerstone of Industry 4.0, where intelligent software is employed for the early detection of faults and the prevention of unexpected failures. Recent research indicates that the integration of multi-sensor data for fault diagnosis of gearboxes and bearings, using artificial intelligence models, has been successful. However, conventional methods face several challenges. These include an over-reliance on the signal characteristics of a single sensor and the impracticality of applying intelligent learning methods, particularly deep learning, despite their high potential, due to the unavailability of sufficiently large and diverse... 

With altering natural state and increasing impervious surfaces, traditional urbanization leads to deteriorating the environment and water catchments. During the years most efforts in order to control the urban runoff outflow, have been focused on quantity; and awareness about improving water quality has been raised just in the last few years and, which emphasizes on pollution source control. Standard water quality sampling methods are time consuming, expensive and because of sampling in broad geographic areas, difficult; however modeling is a more efficient way in assessing water quality and as worries about non-point source pollution grows, different kinds of models have been used to... 

Cost-effective and reliable damage detection is critical for utilization of composite materials. This research investigates a wavelet-based approach for SHM and detection of through-thickness crack in different lengths and angles in [0/45/-45/90]s CF/EP composite plate utilizing ANSYS finite element method (FEM) software and digital signal processing technique utilizing MATLAB software. To this end, a dual-PZT actuation scheme is applied, aimed at generating the S0 mode at a square composite plate. This study contributes to the damage detection by developing an improved wavelet-based signal processing technique that enhances the visibility and interpretation of the Lamb wave signals related... 

Concrete structures require reinforcement and retrofitting because of possible mistakes in design or calculation, inconformity between plan and implementation, change in occupancy or applied loads, and decay. Development in technology, production of materials, and new methods play important roles in development of structure construction and reinforcement methods. Emerge of new materials creates great demand in studying, surveying, and determining design characteristic and criteria for these materials. One of these materials is FRP composite which is used in concrete structure reinforcement in different ways. In this laboratory research, the effect of external wrapping by GFRP composite... 

Recently many organizations outsource their data to an external server due to easier data maintenance. One of the security issues in data outsourcing scenario is the enforcement of data owner’s access control policies. This includes some challenges; namely, the number of keys needed to access authorized resources, efficient policy updating, write access control enforcement, user and data owner overhead, and preserving confidentiality of data and policies . Most of the existing proposed solutions address only some of these challenges, while they impose high overhead on both the data owner and users. Moreover, most of them address enfrocement of policies in form of access control matrix and... 

Because of the working conditions of semiconductors at ambient temperature and pressure, degradation of organic pollutants through semiconductors photocatalysis has attracted the interest of many researchers. Because of its large exciton binding energy,high chemical and physical stability,high electron and hole mobility, and low cost; zinc oxide, an n-type semiconductor with 3.2 eV direct band gap, is widely used in applications such as photocatalysts, solar cells, and light-emitting diodes. Among various morphologies of ZnO, 1D nanostructures such as nanowires and nanorods have recieved much attention due to their high surface to volume ratio. However, the application of ZnO as a... 

In recent two decades, different anonymous communication systems has been proposed. These systems are interested by journalists, bank employees, military forces, and human rights advocates. Tor is one of the most popular anonymous communication systems. Tor uses onion routing for privacy preserving. Re-cently, many attacks has been introduced against the anonymity of Tor users.In these attacks entry and exit nodes are compromised. One of these malicious nodes, makes the attack on the intented flow and the other one recognizes the flow. All these attacks admit their vulnerability against dummy messages. They state that, because of dynamics of onion’s keys, any dummy injection will dis-turb... 

Nowadays, microgyroscopes are among the most important products of MEMS. The production of small, precise and inexpensive gyroscopes has become possible as the result of recent developments in fabrication technology. In this thesis it is intended to introduce a new method for manufacturing more precise microgyroscopes regarding manufacture facilities. Using this new method, sensitivity and resistance of microgyroscopes are increased against noises which are primarily caused by vibration and rotation about undesirable axes. The rotational movement imposed on the gyro is detected through fluid flow within its torus channel. This transformation facilitates the measurement of the initial motion.... 

In this project Deployment of multi-agent systems was studied. Maximum coverage over a point or curve or area is desired in deployment of multi-agent systems. A facility location optimization function was derived from geometrical concepts such as voronoi, n- geometric median and fermat-weber problem by optimization of which the deployment of multi-agent systems is performed. First, it is assumed that dynamic of agents is first order and second order .Next, it is assumed that agents are in a fluid. In all situations a suitable control algorithm was derived to optimize the facility location function to perform deployment. Next, another facility location function was derived by optimization... 

Massive MIMO systems are systems, where the base station has many number of antenna so each user’s channel is orthogonal to one another.These systems have some valuable advantages such as reduction of energy needed for transmission and significant improvement in spectral efficiency, which makes them be suitable for next generation of wireless communication systems. Another advantage of Massive MIMO systems is inherent resistance against passive eavsdroppers due to having a directed power radiation in direction of the desired user. However another physical layer attack threat these systems: attacking in pilot phase then eavsdropping in downlink phase which must taken care of in physical... 

Recently, to improve the dynamic behavior of Reinforced Concrete (RC) slabs under impact load, the methods of externally bonding Glass Fiber Reinforced Polymer (GFRP) sheets to slab and internally reinforcing concrete by steel fibers have been proposed. Nevertheless, it is required to investigate the comparison between these two methods on response of RC slabs under impact loads. In this study, the influence of volume fraction of steel fibers, the number of GFRP sheet layers (one or two) and the arrangement of GFRP sheets (covering the whole or parts of surface), are examined. Performance of fourteen mm concrete slabs including one plain slab, one steel RC slab, three steel RC slabs... 

Nowadays, multi-agent robotic systems are implemented to perform various operations such as military mission, search and rescue operations, etc. One of the most interested robotic platforms for multi-agent systems is quadrotor aerial robot. In this paper, a team of quadrotors is prepared to perform a formation flight toward a specified target in order to catch and transport it on a desired path. Therefore, at first, trajectory tracking control of the quadrotor has been studied and two types of controllers have been introduced: Hierarchical controller and Non-hierarchical controller. Coordinate free structure of the hierarchical controller provides distinctive properties and guarantees...