Sharif Digital Repository

The existence of primordial black holes has been proposed for about half a century, but so far we have not been able to have convincing observations to prove the existence of such black holes. With the discovery of gravitational waves, hopes for finding primordial black holes have increased again; So that in recent years, different ways have been proposed to reveal them. This matter becomes even more important when we know that these black holes can explain all or at least part of the missing matter of the universe known as dark matter. One of the proposed ways is to investigate the 21 cm line of hydrogen in the intergalactic medium. Over time, the temperature of the intergalactic medium is... 

A concern in the production sour oil and gas is the corrosion caused by the acid gas H2S. Even though corrosion resistant alloys (CRA) have long been available as a material selection option that mitigates H2S corrosion, the carbon steel is in general more cost-effective for oil and gas facilities. The aim of this study is to investigate the mechanical properties of 410NiMo cladding on a low alloy steel substrate. In this investigation, two successive layers of ER410NiMo were clad on low alloy steel substrates. To reduce the likelihood of Hydrogen Induced Cracking (HIC) and producing stable hydrogen traps, Post Weld Heat Treatment (PWHT) was used. To characterize the mechanical properties of... 

Nowadays, methods based on deep learning networks are the most effective artificial in­ telligence methods. Although they have achieved success in various fields (such as machine vision and object recognition), practical and experimental cases show the fragility of deep learning networks against perturbations and unwanted changes of the input pattern. All these perturbations must be in a way that the main class of the perturbed input pattern can be rec­ ognized by human, but the network makes a mistake in recognizing its correct class. This thesis seeks a more accurate evaluation by designing adversarial attacks such that the main class of the adversarial pattern is detectable by human... 

Common privacy enhancing technologies fail to effectively hide the certain statistical aspects of encrypted traffic, namely individual packets length, packets direction and, packets timing. Recent researches have shown that using such traffic attributes, an adversary is able to extract various information from the encrypted traffic such as the visited website, used protocol or even spoken language. Such attacks in general are called traffic analysis attacks. Proposed countermeasure try to change the distribution of such features in users traffic but either they fail to effectively reduce the accuracy of that attacker or do so while enforcing a high degree of bandwidth overhead and timing... 

The dispersed phase holdup is one of the important parameters in the design pulsed column and set the column diameter, height and characteristics of flooding and mass transfer. High efficiency and low space requirements of these columns cause is particularly in the nuclear industry, Due to the possible presence of radiation and the need for protection against radiation, considered and used. In this project, the dispersed phase holdup and mean residence time in a pulsed disc and donut column in a semi-industrial scale using radiotracer and shut down methods compared and presented for water-kerosene system. Also axial dispersion coefficient in the column using radiotracer methods is calculated...