Sharif Digital Repository

Swampland conjectures are set of conditions that must be satisfied in a quantum field theory in order to be compatible with a theory of quantum gravity. These conditions have been deduced from the features of field theories, which are derived from the compactification of the additional dimensions of the string theory. However, it is thought that the mpatibility of these conditions with the theory of quantum gravity is independent of string theory. One of the important reasons is that the swampland conjectures can be obtained by examining the physics of black holes. Black hole is one of the quantum states of any quantum gravity theory. In this thesis, first we will have an overview of the... 

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,... 

Contraction sections are an integral part of all wind tunnels, whether designed for basic fluid flow research or model testing. The location of the contraction, just upstream of the test section, makes it very important to achieve a high quality contraction design. The effect of a contraction on unsteady velocity variations is significant to increase the mean velocity. Furthermore, contraction has a suitable role on the turbulence reduction in a wind tunnel. The contraction itself further reduces the turbulence in terms of percentage of the wind speed. This is due to the increase of the wind speed by a factor equal to the contraction ratio. In this research, to investigation flow quality in... 

Recently, many studies show that Augmented Reality (AR) and Automatic Speech Recognition (ASR) can help people with disabilities. In this thesis we examine the ability of combining AR and ASR technologies to implement a new system for helping deaf people. This system can instantly take a narrator's speech and convert it into a readable text and show it directly on AR display. Also, with this system, people do not need to learn sign-language to communicate with deaf people. To improve the accuracy of the system, we use Audio-Visual Speech Recognition (AVSR) as a backup for the ASR engine in noisy environments. AVSR is one of the advances in ASR technology that combines audio, video and facial... 

This research focuses on physics-informed neural networks, which are trained to solve supervised machine learning tasks while adhering to physical laws described by general nonlinear partial differential equations. Previous studies utilized Gaussian process regression to develop functional representations designed for a given linear operator. However, despite the flexibility of Gaussian processes, solving nonlinear problems presents two major limitations: first, authors had to linearize each nonlinear term over time, and second, the Bayesian nature of Gaussian process regression requires specific assumptions that may limit the model’s representational capacity. For these reasons, data-driven... 

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... 

the purpose of this research is to construct the facial image of a person from corresponding DNA. In this problem, we have a set of DNAs and facial images and we want to find the relation between the DNA and the features of facial images.using this relation we can find the facial Image of a person using the DNA. for this purpose we should first extract the features of faces that have the most variation among the population. by studying the feature extraction methods in this field, we borrow the deep neural network method that is used in face recognition fields.we found significant relations between DNA and extracted features from this network. finally using this relation we can predict the... 

The effect of alloying elements such as Chrome, Molybdenum and Chrome-Molybdenum on microstructure and mechanical properties of submerged-arc weld of structural St37 and 4135 Chromoly Steel was investigated. Addition of alloying elements was done through flux and slag-weld metal reactions. Bonded flux was used to achieve this purpose. Mechanical properties were studied by means of Longitudinal Tensile, Hardness and Charpy V-notch tests. Microstructure was studied by means of Optical and Scanning Electron Microscope. The results show that chromium increase Ultimate Tensile Strength (UTS) and impairs Impact Toughness (IT), although it increases the percentage of acicular ferrite (AF). In the... 

High mixing efficiency and high liquid-liquid mass transfer rate are two key features of spinning disk contactors. This work presents the experimental investigation of mixing and liquid-liquid mass transfer characteristics in a new double coaxial spinning disks contactor. The micromixing efficiency was investigated using a standard system of competitive parallel reaction known as iodide/iodate test reaction. The influences of various operating conditions such as the rotational speed of the disks, the direction of rotation, the feed radial location, the feed distribution pattern, the distance between the disks, and the feed flow rate on the mixing quality were examined carefully. The obtained... 

Detecting out-of-distribution (OOD) input samples at the inference time is a key element in the trustworthy deployment of intelligent models. While there has been a tremendous improvement in various flavors of OOD detection in recent years, the detection performance under adversarial settings lags far behind the performance in the standard setting. In order to bridge this gap, we introduce RODEO in this paper, a data-centric approach that generates effective outliers for robust OOD detection. More specifically, we first show that targeting the classification of adversarially perturbed in- and out-of-distribution samples through outlier exposure (OE) could be an effective strategy for the... 

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... 

Cancer invasion of tissue is a key aspect of the growth and spread of cancer and is crucial in the process of metastatic spread i.e. the growth of secondary cancers. Invasion consists in cancer cells secreting various matrix degrading enzymes (MDEs) which destroy the surronding tissue or extracellular matrix (ECM). Through a combination of proliferation and migration, the cancer cells then actively spread locally into the surrounding tissue. Thus processes occuring at the level of individual cells eventually give rise to processes occuring at the tissue level. In this thesis we introduce a new type of multiscale model describing the process of cancer invasion of tissue.Our multiscale model... 

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...