Sharif Digital Repository

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... 

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 integration of radar and communication functionalities into a unified Joint Radar-Communication (JRC) system offers enhanced spectral efficiency and reduced hardware complexity. Recognized as a key enabler for next-generation wireless networks, JRC systems require a careful balance between radar and communication demands, where waveform design plays a pivotal role in achieving this equilibrium. Although waveform design has been extensively studied separately in radar and communication domains, the requirements of modern networks necessitate a unified approach that simultaneously addresses the needs of both systems. This thesis advances waveform design methodologies for JRC systems,... 

In this research, the numerical simulation of liquid jet ejecting for a series of elliptical orifices into gaseous phase with different aspect ratios, at Rayleigh flow regime and in a range of Weber numbers has been performed.
For simulations, the OpenFoam software was utilized, which its multiphase flow simulation solvers are based on volume of fluid (VOF) method. In order to achieve the most accurate results for axis-switching phenomenon and jet breakup length, the dynamic mesh refinement was used for all the examined cases. The results, which were validated with recent experimental and numerical works, indicate that jet breakup length raises by increasing Weber number from 20 to 300.... 

In this dissertation, the application of frequency and space diversities in radar target parameter estimation are investigated. On this basis, multi-frequency signal is used to improve the range resolution, array structure is used to increase the angle estimation accuracy and the merger of the multi-frequency signal and array structure are used to increase the maximum number of targets that can be uniquely identified.Considering the desirable properties of multi-frequency signals such as high bandwidth efficiency, high range resolution achievement without chip length decrease and …, there has been increased interest in the vast area of research on the design of such signals that has... 

Target recognition techniques based on micro Doppler phenomenon are popular because they are applicable even on low resolution radars, in contrast to other techniques such as High Resolution Range Profile (HRRP) which need high resolution in range or angle. Usually, main purpose of such techniques is generating robust features against target initial state, velocity, aspect angle, etc. rather than features which exactly identify a target. Main approaches in the literature are based on time-frequency transforms (TFT) such as spectrogram in order to generate features to classify targets, but in this thesis, we propose a totally different method using Recurrence Plot for generating features... 

In this research with Finite Element Methods in ABAQUS, numerical modeling has done in three-dimensions, which can be used to determine the effect of different factors on the surface settlement. Also, various factors such as geotechnical conditions, tunnel diameter,tunnel depth, the impact of the thickness of the segments and the amount of eccentricity of the structure relative to the longitudinal axis of the tunnel considered in this study. Face Pressure Supports, and Grout Injection Pressures are taken into account, too.Tunnel drilling causes a change in the displacement area and creates a changing zone around the tunnel. In this regard, not only adjacent buildings will be affected by... 

Proton precession magnetometers are one of the most sensitive scalar magnetic sensors. Their function is based on Zeeman effect and also nuclear magnetic resonance phenomena. In this project we have designed and implemented needed coils, swithching and signal detection circuits. Because of extremely high sensitivity of this sensor to induced noises and also gradient of earth’s magnetic fileld, detection of precession signal needs design of low noise electronic circuits with special EMC considerations. The implemented system in this project contains different blocks, such as switching circuit and its related control unit, amplifier, filter and frequency meter. Using this system, the obtained... 

Effective field theory is a practical method for model building and explaining experimental/observational data. These theories are constructed based on knowing low energy degrees of freedom and symmetries (accidental or fundamental). By construction, these theories are applicable up to a cut-off scale and their predictions beyond that are not reliable. For applications to higher energies a UV completion is needed through which modifications are applied or new heavy degrees of freedom are introduced. In order to complete a theory in a Wilsonian approach, scattering amplitudes must satisfy some constraints. These constraints are derived from basic assumptions like Lorentz invariance,... 

Numerous structures which are involved in seismic soil-pile-structure interaction have been destroyed. Considering complexities which exist in soil-pile interaction problems and lack of precise methods without imperfect bases, it is necessary to use numerical methods for analyzing soil-pile interaction problems. In this research, three-dimensional modeling and studying the effect of changing soil and pile parameters on the behavior of pile under earthquake loading is performed using finite difference software, FLAC3D. The soil in this model has a softening behavior. Real earthquake spectrum has been applied into the model as the acceleration time history at the bedrock level. The results of... 

Present work focuses on the influence of Heteroatom(s) on the bacisity of specific group of amines through the intramolecular hydrogen bonding. This group includes Aza-Crown Ethers specifically. We used Spartan and Gaussian packages to gain optimized structures for all compounds in order to explore the influence of the intramolecular hydrogen bonding on the bacisity of amines. All the gas phase optimizations and energy calculations were performed at the DFT/B3LYP/6-311++G(d,p) level of theory. The Hf/6-31+G(d,p) level was used for all single point calculations in the solution phase. As commonly used solvents in organic and biological reactions, the solution phase calculations were carried... 

Today, the importance of growth and its relation with the survival of the organization is well-known by all managers. However, path selection in this area seems extremely vague and difficult. The present theoretical research, conducted to help further clarify growth dimension characteristics, aims at considering possible growth paths for firms as well as examining required capabilities for each path. In this research, firm growth was studied from three different angles: value chain, product system complexity and the market. A relatively comprehensive categorization was made of organizational capabilities namely technological, managerial and networking and it was examined within dynamic and... 

Time delay generates exponential transcendental terms in characteristic equations. Subsequently, the applied methods are narrow to assess the stability map of delayed fractional-order systems with vanishing fractions. In this case, it is convenient to approximate these equations with its integer-order counterparts to design controllers or investigating features of the systems. But, delay can cause enormous differences between characteristic of these two equations. This study offers a method to survey analytically the stability of fractional-order time delayed linear time invariant systems with infinitesimal fractions. In this method, equations are transferred to an explicit expression which... 

In this project, conceptual and detailed designs of a knee prosthesis constraint testing machine were performed based on ASTM F1223-20 standard. Conceptual and detailed mechanical and electrical design of machine and parts were performed based on common engineering practice and standards. Parts were carefully manufactured and controlled for quality assurance. The machine was then assembled and checked for proof of performance. A plc program was written as machine software. A comprehensive user interface was coded on computer for performing various tests, which can command the machine and view the required data in a graphical environment. Finally, simple experiments were designed and... 

Direct metal deposition (DMD) process is an additive manufacturing technology that is rapidly gaining laser importance due to its various capabilities in applications such as coating, repairing high-value damaged parts, rapid prototyping and even production in small quantities. Among the equipment needed for this process, nozzle is perhaps the most important component because its performance affect the efficiency of powders trapped in the molten pool, and is crucial to the quality of the deposited layer. The existing nozzle designs can be categorized in two groups; lateral and coaxial nozzles; and the coaxial ones are divided into continuous and discontinuous types. Coaxial nozzles have... 

The current global economy challenges and the importance of maintaining a sustainable development strategy has increasingly bolded the importance of construction productivity measures. This research describes the results of a running research that is to find the most critical factors affecting the productivity of high rise concrete building projects in developing countries. To achieve that, we have conducted Delphi method in two phases. In the first phase we had a brainstorming program with construction experts from owner organizations, construction contractors and designing engineers to identify factors that have influenced productivity in recent concrete building construction projects.50... 

Multi-period Value-at-Risk (VaR) forecasting is important for risk management. Financial institutions especially commercial banks according to Basel Committee regulations for capital adequacy in “Internal Approach”, should forecast their VaR for multi-period horizons (longer than one day). The most conventional approach for forecasting multi-period VaR is scaling one-day forecasted VaR that is called “square root of time rule”; therefore most works in this area have been focused on forecasting one-day VaR. In this study, we review performance of a wide range of different methods in forecasting multi-period VaR. The results of our study show that historical simulation performs weakly in... 

Modern communication and space systems such as satellite communication devices, radars, SAR and radio astronomy interferometers are realized with large antenna arrays since this kind of radiating systems are able to generate radiation patterns with high directivity and resolution. In such a framework, conventional arrays with uniform inter-element spacing could be not satisfactory in terms of costs and dimensions. An interesting alternative is to reduce the array elements obtaining the so called ‘ thinned arrays’. Large thinned arrays have been exploited because of their advantages in terms of weight,consumption, hardware complexity, and cost over the... 

A large number of structures subjected to the seismic loading have been damaged or have experienced failure in different parts such as the pile structure or even in the entire structure due to unanticipated effects of the soil-pile-structure interaction.The complexity of problems regarding the soil-pile-structure interaction is an influencing factor in prediction of the behavior of structure during the earthquakes. In this study, the effect of the interaction on the dynamic response of bridges was investigated using the finite element software ABAQUS. The primary purpose of this study, as previously described, is to study the effects of the soil-structure interaction on a bridge located on a... 

After being introduced in 2009, the first fully homomorphic encryption (FHE) scheme has created significant excitement in academia and industry. Despite rapid advances in the last 6 years, FHE schemes are still not ready for deployment due to an efficiency bottleneck. Here we introduce a hardware/software codesign, in fact a hardware accelerator optimized for a class of reconfigurable logic to bring homomorphic encryption schemes one step closer to deployment in real-life applications. The accelerator we present is connected via a fast PCIe interface to a CPU platform to provide homomorphic evaluation services to any application that needs to support blinde computations. Specifically we...