Sharif Digital Repository

Virtualization is one of the widely used technologies which has enhanced the utilization of the hardware resources and made the computer management easier. Cloud computing is one of its appealing application providing various electronic services in the form of virtual machines to users. A common security threat in the virtual machines in cloud services is the vulnerabilities the programs and operating systems have. Attackers can take the advantage of these vulnerable machines and abuse them to carry out attacks. Virtual Machine Introspection (VMI) techniques are proposed and used by the cloud providers utilizing the management capabilities in the hypervisor to intercept hardware accesses and... 

In this study, the revolving door effect on the bank’s performance is investigated through two paths: return on assets as an expression of banks' performance and capital adequacy ratio as a bank financial health indicator and the quality of central bank supervision. We assume these two variables are affected by conflict of interest. The form of conflict of interest used in this research is revolving doors. The board directors of commercial banks, who have previously worked in the central bank, create conflict-of-interest data. Twenty-seven commercial banks were investigated in this research between 2012 and 2022. the conflict-of-interest gap variable was defined in order to separate the... 

Advanced Driver Assistance System (ADAS) is a major area of research in today’s vehicle control and safety. In General ADAS can be seen as a mother system with various subsystems to help the driver from pre-crash to post-crash situations. One of the subsystems for ADAS is the Collision Avoidance System (CAS). Nowadays, many researchers are working on different Aspects of CAS, from perception to decision making. Many challenges exist while developing a CAS, but today the greatest challenge is decision making of CAS and its interaction with driver’s behavior. Driving is a complex task and since driver’s consciousness, gender, age and reflexes can cause different behaviors; it is, therefore,... 

Primary visual cortex plays a paramount role in processing visual information. Visual information after the primitive processing by LGN and Thalamus, will be sent to the primary visual cortex which is called V1 area. According to the fact that V1 neurons have the definitive sensitivity to the edge and contrast of visual stimuli so their behavior are very selective to the certain features, specially contrast, of visual stimuli. These neurons have different response behavior to contrast. In fact most of them have some nonlinear behavior to this feature. Normally we expect that response of them or spiking rate of them grow linearly by the contrast increases but in most many cases they have some... 

The concurrent flow of oil and water is a common occurrence in the field of multiphase flow in different fields including petroleum industry. In oil and gas, production engineers often face a situation in which more than one phase is flowing through the producers. In such conditions an accurate assessment of pressure loss inside the well plays a vital role in efficient and effective production planning. Changes in well orientation, wellbore diameter, reservoir and fluid properties as well as fluid flow rates are among parameters in which will affect the flow patterns that can occur inside a well during its life time. These flow patterns are created as a result of a competition between... 

Casing design is one of the most expensive parts in the drilling of oil wells, and any cost reduction with the basic design of these casing strings will significantly reduce the total cost of the operation. In recent years, occurring scenarios-based casing design has become popular; Because in many cases, it eliminates non-occurring scenarios such as gas kick and saves on drilling costs. In this study, we have tried to investigate all scenarios that may occur during the lifetime of the well, whether drilling or production, and for each well, based on its own field information, possible scenarios for each casing part are selected separately and the applying loads are calculated. For this... 

The electrochemical oxidation behavior of the anti-inflammatory drug piroxicam was investigated. A carbon nanoparticle (CNP)-chitosan (CS) film-coated graphite electrode (PGE) was fabricated and the electrochemical behaviors of piroxicam on its surface was investigated by the means of cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). In comparison to the bare PGE, at the surface of the CNP-CS film modified electrode, the oxidation peak current of piroxicam increased significantly and the peak potential shifted negatively. Consequently, a simple and sensitive electroanalytical method was developed for the determination of piroxicam. The... 

There are high attractions in the development of conducting polymer (CP) coatings to improve the electrochemical properties and biocompatibility of electrodes in the area of biosensors. In the first part of this thesis, a new type of modified electrodes, constructing multi-walled carbon nanotubes (MWCNTs) and polypyrrole is prepared in a layer-by-layer process. In this procedure, the glassy carbon electrode is casted first by a drop suspension of MWCNTs, leading to formation a thin film on its surface. In the second step, electrochemical polymerization of pyrrole in the presence of tiron (used as doping anion) is performed on the surface of the MWCNTs pre-coated electrode. The modification... 

In the present work, edge-functionalaized graphene was used as electrode material and its electrochemical properties were systematically characterized by electrochemical impedance spectroscopy and cyclic voltammetry. Two methods were applied to modify the gold electrode surface. First method was the self assembling process of graphene nanosheets on gold electrode surface. Second method was simply casting specific amounts of graphene suspension on the gold electrode surface. Nyquist plots show decrease of the charge transfer resistance on the electrode surface at both cases. In cyclic voltammetry studies, first electrode shows no significant changes while the second electrode exhibits... 

Graph Theory and Combinatorial Analysis like the other branches of science use the probability for solving their problems. At the first , we will introduce the most common tools from probability used in Discrete Mathematics, such as “The Lovasz Local Lemma”. Most of them are based on Linearity of Expectation, Concentration Theorems and some other innovative methods such as Deletation Method. We will present different examples for these techniques. Also we will introduce “Random Graphs” and their importance. Specially we will explain how to use “Threshold Functions” to obtain different properties about the majority of graphs. Rainbow Connection, is a natural and interesting quantifiable way... 

At the first part of this thesis, a pyrolitic graphite electrode (PGE) modified with new coccine/multi-walled carbon nanotubes film (NC/MWCNT) was applied as a sensitive electrochemical sensor for determination and study of electrochemical behavior of tyrosine (Tyr) in aqueous solutions. The results showed that NC/MWCNT caused a remarkable increase in the peak current so the NC/MWCNT/PGE electrode surface was far more sensitive to the concentration of Tyr than the PGE surface. The determination of Tyr was investigated by linear sweep voltammetry (LSV). Experimental parameters, such as scan rate, pH and amount of the modifier used on the PGE surface were optimized by monitoring the LSV... 

There are many papers in which some graphs are assigned to algebraic structures such as rings groupsThe concept of regular graph related to a ring was rst investigated by DF Anderson and A Badawi in Assume that R is a commutative ring and Z??R denotes the set of zerodivisors of R and Reg??R R n Z??R The regular graph of R which is denoted by Reg????R is a graph whose vertex set is Reg??R and two vertices x and y are adjacent if and only if x y ?? Z??R This can be generalized to a non commutative ring For the vertex set we consider the set of left ??right zerodivisors and join two elements if their sum is a left ??right zerodivisor Let R be the ring of n n matrices over a eld F with... 

For an undirected graph G, a zero-sum flow is an assignment of non-zero real numbers on the edges of G such that the total sum of all edges incident with any vertex of G is zero. A zero-sum k-flow for a graph G is a zero-sum flow with labels from the set {±1, . . . , ±(k ? 1)}. In this thesis for a graph G, a necessary and sufficient condition forthe existence of zero-sum flow is given. It has been conjectured that if a graph G has azero-sumflow, then it has a zero-sum 6-flow. Also, it has been proved that this conjectureand Bouchet’s Conjecture for bidirected graphs are equivalent. It is shown that the con-jecture is true for 2-edge connected bipartite graphs, and every r-regular graph... 

One of the most important issues in modeling and simulation of reservoirs is determination of different rock types or Rock Typing. In this study, after a brief review of some conventional methods for rock typing, their capabilities have been investigated. In this way, for the first time, pore network modeling is used as a tool for validating the rock typing methods. By using flow simulation in porous medium with pore network modeling approach, similar rock types data have been generated and these artificially data have been used for validating of rock typing methods. To form more realistic pore networks, both regular and irregular pore network have been modeled and analyzed. Pore size... 

Let G be a graph. A labeling f : V (G) ! f0; 1; 2g is called a Roman dominating function, if every vertex u with f(u) = 0 has at least a neighbor v with f(v) = 2. Define the weight of a Roman dominating function f to be w(f) =Σv2V (G) f(v). The Roman domination number of G is R(G) = minfw(f) : f is a Roman dominating functiong. Some other parameters are defined based on Roman domination number. A Roman bondage number bR(G) of G is the minimum cardinality of all sets E E(G) for which R(G E) > R(G). The edge Roman domination number of G, LR(G), is defined as R(L(G)), where L(G) is the line graph of G. In this thesis, after determining the exact value of the Roman bondage number for some... 

Feyerabend was a philosopher of science that became famous for his purportedly anarchistic view of science and his rejection of the existence of universal methodological rules and rationality of science. Feyerabend’s view of science can be summarize in a few points; 1. On the issue of falsifiability, Feyerabend argues that no theory is ever consistent with all the relevant facts. He sees the use of ad-hoc postulates to save the dominant paradigm as an essential to the progress of science. He claims that scientists frequently depart completely from the scientific method when they use ad-hoc ideas to explain observations that are only later justified by theory. To Feyerabend, ad-hoc...