Sharif Digital Repository

Protecting sensitive data stored in database systems, especially in outsourced ones, has become a major concern in many organizations. One of the main possible solutions is to encrypt data before storing them on databases. Bucket-based encryption is among different approaches proposed to accomplish this goal which besides its various benefits, suffers from generating false-positive results. Multi-join queries are one of the most important operations in database systems and their usage grows rapidly in comparison to other types of queries by increasing the size of stored information. While using the decision support systems and data mining solutions are growing continuously, executing... 

This research investigates the presence of banana shaped crack in transversely isotropic media under internal pressure and calculates the stress intensity coefficients. In the beginning, the equations of equilibrium, along with the constitutive equations governing the transversely isotropic media and the boundary conditions of the problem, are determined. Then, by using a three-dimensional mapping, the non-centered banana shaped crack is turned into a centered crack. In the following, we solve the problem analytically by using the Fabrikant's potential functions for transversely isotropic environment, and by the method provided by Fabrikant rewriting the boundary conditions in terms of these... 

The role of a mathematical model is to explain a set of experiments, and to make predictions. In setting up a mathematical model of a biological process, by a set of differential equations, it is very important to determine the numerical value of the parameters. For biological processes are typically valid only within a limited range of parameters. In the last decades, various cancer models have been developed in which the evolution of the densities of cells (abnormal, normal, or dead) and the concentrations of biochemical species are described in terms of differential equations. Some of these models use only ordinary differential equations (ODEs), ignoring the spatial effects of tumor... 

Today, smart devices have become an integral part of everyday life. The Android operating system is also the most popular operating system of these devices, and as a result, various malwares are produced and distributed for this operating system every day. This makes it especially important to investigate these malwares. This includes finding people involved in the development and distribution of malware, as well as discovering other malwares created by them. Discovering other involved entities, such as social media accounts, websites, Android store accounts, and taking steps to prevent malware from being distributed by them is another aspect of this story. In order to deal with organized... 

A typical problem in applied mathematics and science is to estimate the future state of a dynamical system given its current state. One approach aimed at understanding one or more aspects determining the behavior of the system is mathematical modeling. This method frequently entails formulation of a set of equations, usually a system of partial or ordinary differential equations. Model parameters are then measured from experimental data or estimated from computer simulation or other methods. Solutions to the model are then studied through mathematical analysis and numerical simulation usually for qualitative fit to the dynamical system of interest and any relative time-series data that is... 

In recent years, one of the research interests is ensuring the integrity of computations done on data received from multiple data sources. Limited research has been done to ensure the integrity of computations that the output depends on data generated by different data sources. However, there are many solutions for systems that the input data is generated by a single data source. In this thesis, ensuring the integrity of multi-source aggregate functions and general functions are investigated in an untrusted server. To verify the integrity of aggregate functions, first of all, we present a construction for verifying the results of linear functions using the RSA signature. It should be noted... 

Platinum is one of the most used catalysts in refining and petrochemical industries. Also, Platinum uses in other industries like automobile catalytic convertor. As respect to importance of Platinum in these industries, growth of its consumption in recent decades and its very high price, recovery of Platinum is essential. Hence, many of various methods including hydro-metallurgy are applied. In despite of these wide spreading experimental investigations, due to low information about the reactions and the nature of reaction products, a few investigations were done on kinetics of Platinum recovery. A new method that used iodine solution to extract Platinum from spent reforming catalysts was... 

The controllability problem may be formulated roughly as follows. Consider an evolution system (either described in terms of partial or ordinary differential equations) on which we are allowed to act by means of a suitable choice of the control (the right-hand side of the system, the boundary conditions, etc.). Given a time interval 0 < t < T, and initial and final states, the goal is to determine whether there exists a control driving the given initial data to the given final ones in time T. Now, consider the simplest parabolic equation, namely heat equation and suppose that one could act by appropraite controls on this system. The null controllability problem which is one of the very... 

In this thesis,we consider aperiodic predator–ysystem with mutualinter ference andimpulses. By constructing a suitable Lyapunov function and using the compar-ison the orem of impulsive differential equation, sufficient conditions which ensure the permanence and global attractivity of the system are obtained. We also present some examples to verify our main results  

In this thesis, first, the modeling method of neural fields is precisely presented. Then, Existence and Stability of different solutions of one dimensional neural fields like Standing Pulses, Traveling Waves and ... are investigated in three different models of neural fields. In order for proving Existence and Stability of the solutions the mathematical tools like Fourier transform and Evans function are applied. All the models which analysed in this thesis have the following Integro-Differential Equation form:
τ
∂u(x, t)
∂t
= −u(x, t) +
∫ +∞
−∞
w(x, y)f[u(y, t)]dy + I(x, t) + s(x, t)
and also in some models the parameters might be changed  

Surface tension is the most important interfacial parameter of a liquid. This quantity plays a key role in many processes such as extraction, distillation, absorption and chemical reactions. Various methods are proposed for measuring this quantity among which, the laser based methods are the most accurate ones. Unlike most of the mechanical methods, laser based methods remotely measure the surface tension. The aim of the current thesis is to measure the surface tension using laser beam, more specifically using homodyne detection system. This method implemented in both reflected and transmitted modes. In each of the mentioned methods, first the laser beam was incident to the liquid-air... 

One of the applications of Internet of things (IoT) is its usage in the eHealth area. Various types of sensors (e.g., sensor to measure heart health, blood sugar levels, and respiratory) exist that not only provide required information for patients, but also send the health information to hospital staff through the network. Leveraging this technology in various intensive care units of hospital facilitate nurses and medical staff in monitoring of patients. However, moving towards these environments leads to new security challenges. One of the most important challenges is controlling access to sensors’ data and preserving patients privacy so that doctor and nurses should access patients’... 

The propagation of love waves in a one-layered piezoelectric medium with slightly curved boundaries of sinusoidal type have been investigated in this study. Because of the widespread use of piezoelectric materials as surface acoustic wave (SAW) devices, sensors, actuators and in vibration control, the study of Love wave propagation in this Medias has been in the forefront of present studies in this era. But there always will be imperfection on surfaces. By employing the Taylor expansion up to the first order and using perturbation technic on the case with no irregularity and solving the problem, it has been found that along with the usual displacement components for stratified boundaries,... 

In this study, flexural vibration of a functionally graded nanotube under an initial stress is investigated. The small scale effect is taken into consideration based on Eringen’s nonlocal elasticity theory. The material properties are assumed to vary exponentially along the depth direction. The complete effect of the initial stress is taken into account in the problem formulation. The governing equations of motion are derived by using the Hamilton’s principle on the basis of the nonlocal Timoshenko beam theory. An analytical solution of the governing equations, for free vibration of a simply-supported nanotube is presented. Numerical results are presented to investigate the effect of the... 

Advanced Persistent Threats (APTs), use hybrid, slow, and low-level patterns to leak and exfiltrate information, manipulate data, or prevent progression of a program or mission. Since current intrusion detection systems (IDSs) and alert correlation systems do not correlate low-level operating system events with network events and use alert correlation instead of event correlation, the intruders use low and hybrid events in order to make detection difficult for such detection systems. In addition, these attacks use low and slow patterns to bypass intrusion detection and alert correlation systems. Since most of the attack detection approaches use a short time-window, the slow APTs abuse this...