Sharif Digital Repository

In this thesis, we have tried to study one of the most well known collective behavior phenomena known as the Wisdom of the crowd, from the perspective of statistical physics. In recent decades with the appearance of Social Networks and mass media, collective social phenomena have become a critical topic in the life of every human being. In the Wisdom of crowd phenomenon, the overall process is to ask the crowd’s opinion regarding a special topic and after aggregating the predicted values, the aggregated quantity is declared as the wisdom of the crowd. It has been observed that in some polls and elections, the result of the wisdom of crowd outperforms every individual of the group and in some... 

This paper aims to test an important hypothesis in financial economics: whether equity returns are predictable over various horizons? The variables that we use are dividend yield, dividend-price ratio, price-earning ratio, dividend payout ratio and stock variance. For one month horizon,we compare forecast from predictive regression and forecast from historical mean both in-sample and out-of-sample. Evidence shows that to some extent, stock variance has predictive power and predictive regression model has a better performance than the historical mean model, but fundamental variables don’t have predictive power. The multivariate model has improved the performance, but we don’t see any... 

The hulls of various ships are exposed to the problem of biofoulings on the hull after a period of time due to use in the salt water environment of the sea and the existence of suitable conditions for the growth of marine plants, so that the ship after about one month of stopping in the port, in order to start the activity again, it is necessary to clean the hull from these biofoulings. The ship will be transported to the dry dock for cleaning only when it is heavily involved in biofoulings on the hull, and in the meantime, it must be periodically cleaned in water by other systems, including the diver and robotic systems.Using a robotic system to perform this operation has various... 

Resolvers, due to their robust structure, are widely used in automation systems. Among the types of resolvers, the accuracy of the Wound Rotor (WR) resolver in the occurrence of common mechanical errors is higher than other types of resolvers. therefore, in this thesis, an AFWRR is studied to improve the performance. Increasing the number of poles in WR resolvers is a good solution for increasing the accuracy of these electromagnetic position sensors. However, high-speed WR resolvers due to employing fractional slot windings suffer from rich sub-harmonics in the induced voltages. A common solution for suppressing the undesirable sub-harmonics is using multi-layer winding with appropriate... 

Membrane bioreactors (MBRs) which are commonly understood as the combination of membrane filtration and biological treatment using activated sludge have several advantages, but membrane fouling reduces the membrane efficiency, permeability and lifetime. An alternative is replacing a moving bed biofilm reactor (MBBR) with the activated sludge system which may reduce the effect of membrane fouling. The sludge produced in MBBRs has poor settling characteristics, therefore, their efficiency is limited by the sedimentation tank performance and they require a larger settling surface. The combination of moving bed biofilm reactors and membrane bioreactors can compensate for the drawbacks of both of... 

Control of many mechanical systems such as satellites lies on the control of space robots. Control of space robots has many theoric complexities because of the presence of non-holonomic constraints due to angular momentum conservation. Unlike fixed-base robots, any movement of space robots manipulator has a reaction on the robot base and moves it. Thus manipulator’s movement toward desired configuration rotates the robot base and as a result appropriate attitude may not be attained. Therefore an appropriate path is required to achieve the desired configuration and the base attitude reaches its desired value. In this thesis, first the dynamic of space robots and the interaction between the... 

Washing a dead person’s body and dressing the corpse prior to burial is an act of love and necessity in many religions. Since the deceased loses all bodily functions at time of death, cleaning the body to eliminate odors is generally a hard and unpleasant task for many to perform. It has also been reported that tens of thousands of microbes are present on every square centimeter of a human corpse which is always a health risk to the persons performing the task. Among Islamic nations, preparation of the corpse is usually carried out in washing rooms (Ghassalkhaneh) of cemeteries in large cities. This preparation consists of two important operations namely as washing of the corpse (Ghosl)... 

Inventory control has been always considered important due to its prominent role in managing and better application of resources in the field of operational systems. Ordering system or review stock policy in supply chain management can be mentioned as one of the inventory control study fields of management. A lot of researches have been done in investigating ordering system in supply chain under certainty conditions; however, since the real world is full of uncertainties, parameters such as demand cannot be predicted exactly and we encounter with ambiguity. In this case, using crisp (exact) values can cause to decide wrongly (a wrong decision). On the other hand, due to absence of sufficient... 

Using accelerators inside high speed servers can reduce execution time of applications and total power usage of the system. Sharing accelerator between virtual machines of a server decrease both cost and power, however it won’t provide the gained speedup of using dedicated accelerator for each virtual machines. Creation of an appropriate set of accelerators required for virtual machines, management of accesses to the accelerator, prioritizing and scheduling of requests and reconfiguration type of accelerator are the most important challenges that this project has been dealt with. The main objective of this project is implementing the necessary infrastructure to share an FPGA-based... 

In recent years world countries faced with the ageing aircraft fleet problem which increased the repair and maintenance costs of these aircrafts. The non-destructive inspection methods are common inspection methods of old aircrafts. To do this, the aircraft must test with a certain time scheduled inspection programme in a hangar. This method not only increased the repair and maintenance costs but also affects the flight schedule. To overcome this problem, the structural health monitoring can use to online monitoring the structure and when it needs for repair, the aircraft send to hanger. So, repair and maintenance costs minimize while the flight schedule less affected. One of the structural... 

This thesis proposes two methods for backtesting VaR models. The first is the combination of saddlepoint technique with Berkowitz backtesting and the second is based on maximum loss which uses Fischer-Tippet theorem to backtest VaR models. Monte Carlo simulation studies show that the power of these new backtests, especially the latter which is easy to use, is not less than complex Backtests that are well-known for their accuracy  

Laboratory studies to investigate the effects of different saline concentrations (such as sodium chloride or calcium chloride) on the soil water retention behavior of clayey soils and their volumetric changes have received much attention recently. However, many previous studies have investigated these effects in only one path of the SWRC (wetting or drying path) and the effects of saline concentration on hydraulic hysteresis have not been considered. In addition, researchers have frequently studied these effects on SWRC on clay samples, and little research has been done on collapsible soils. Therefore, the most important purpose of this study is to investigate the effects of increasing... 

Fretting fatigue occurs at the point of contact of two parts that are under dynamic loading. During this phenomenon, due to the force applied at the contact point, deformation occurs and causes slip-stick zones, which intensifies the effect of surface degradation and crack nucleation happens earlier. In this research, the improvement of fretting fatigue life under combined loading by induction of compressive residual stresses by laser pinning process in the sample has been investigated. The laser shock peening process is a method by which residual stress is created in the sample and can improve fatigue life. The material used is 316L stainless steel, which has many industrial applications....