Sharif Digital Repository

Invariant manifolds are important objects in the theory of dynamical systems. The stable manifold theorem is a very important theorem about this concept which proves the existence of stable and unstable manifolds in a wide range of dynamical systems. The importance of invariant manifolds encourages us to view their pictures. It helps us to understand their bahavior. For this purpose, at first we need to approximate the invariant manifold we want to visualize. There are several algorithms designed to approximate invariant manifolds. Those algorithms approximate a set of points on an invariant manifold and then provide an approximation of the manifold by the calculated points. Visualizing an... 

Wireless sensor network (WSN) multimedia applications impose new challenges in the design of algorithms and communication protocols for sensor networks. Indeed, wireless multimedia sensor networks (WMSNs) must provide relatively high throughput and low end-to-end delay and jitter while being energy-efficient. In view of these challenges, error control is an important mechanism which enables us to provide robust and high quality multimedia communication in WSNs. In this thesis, we first perform a comprehensive performance evaluation of different error control schemes for multimedia communication over WSNs. The results of our analysis show how wireless channel errors can affect the performance... 

Reciprocating Machinery are one of the key components of chemical and petrochemical plants and their down time cause loss of production. Therefore condition monitoring in these machinery is of special interest and high value. In this thesis first, different methods of condition monitoring for reciprocating compressors are introduced then the main cause of high vibrations of three compressors in a refinery is investigated. Finally by using the foundation model prepared, it would be shown that insufficient strength of foundation block has lead cracks initiation and development in these foundations. Therefore high vibration is consequence of weak design  

Studies show that Pedestrians are at fault in 59% of the vehicle-pedestrian accidents. The traffic crash statistics show the importance of understanding factors of pedestrian errors. If pedestrians terminate their waiting behavior during the red light period and cross the street, they would put themselves in danger. Pedestrians’ red-light violation is a type of highly dangerous behavior occurring at intersections. A total of 1130 pedestrians approaching the intersections during red light periods were observed from the videotapes data collected at 6 intersections in Tehran, Iran. Pedestrian crossing behaviors are classified into immediate crossing behavior and waiting behavior. A logit model... 

Among the xenobiotic compounds, chlorophenols are considered to be as the most dangerous compounds for the environment and living organisms. These compounds are abundantly found in the wastewater of many chemical industry factories. In this research, by using Gaussian software and density functional theory at the level of B3LYP / 6-31G (d, p),the adsorption of molecules such as phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol over graphene, nitrogen and boron doped graphene sheet are studied. The most stable configurations were determined and adsorption energies were calculated. In addition, to understand the adsorption mechanism, electron properties such as state density and... 

Multicore platforms prepare a great opportunity to implement fault-tolerance techniques. Task replication is a well-established technique to obtain high reliability against transient faults. However, replicated executions can increase power consumption more than Thermal Design Power (TDP) constraint. TDP is considered as the highest sustainable power that a chip can dissipate before being forced to exploit a performance throttling mechanism, e.g. Dynamic Thermal Management (DTM). If the chip violates its TDP constraint, it automatically restarts or significantly reduces its performance to prevent a permanent damage. Therefore, due to the unwanted system restarts, DTM techniques may not be... 

Particuale matters, as a criterion for evaluationg the air quality, have been one of the most important air pollutants through the last decade. Considering the adverse health effects of particulate matters, the importance of monitoring pollutant’s concentration is inevitable. While there are monitoring stations for evaluating the air quality, our knowledge is so limtted since there are few stations working, so there is a spatial and temporal gap. On the other hand, chemical transport models and remote sensing provide us a better chance to track the air quality thoroughly. Since chemical transport models are our only way of filling the gaps, they should be rigorous and accurate. In this study... 

Bathymetric maps are used for monitoring water bodies such as lakes, wetlands, and coastal areas, providing valuable information regarding changes in water storage volumes in these environments. For lakes prone to drying and salinity issues, where the lakebed elevation is constantly changing, the importance of these maps becomes even more pronounced as they play a crucial role in monitoring these lakes' conditions and assessing restoration efforts. Various methods exist for generating bathymetric maps, one of which is satellite remote sensing, which is more time- and cost-effective than traditional methods. One of the most common and accessible types of remote sensing data used for...