Sharif Digital Repository

Code-based cryptosystems could be a suitable alternative to the cryptosystems based on number theory. It is shown that cryptosystems based on descrete logarithm and factoring is vulnerable to the Shor’s algorithm running on quantum computers, while code-based cryptosystemsare thought to be secure against this cryptanalysis. Despite its security, large key size and low transmission rate keep thesecryptosystems impractical. Reliability is one of our inevitable desires in communication systems along with security.In order to fulfill these desires, joint encryption-encoding schemes has been released.Using LDPC codes in joint encryption-encoding schemes, as an alternative to classical linear... 

Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to... 

The low female labor force participation rate in the Iranian labor market relative to the global average and even to countries that do not differ significantly from the socio-economic characteristics of our country is one of the important questions of the Iranian labor market. In this study, we seek to answer the question of whether the economic participation rate of married women will increase if the gender gaps in wages, job findings and job losses among women and men are eliminated in the Iranian labor market. To answer this question using household expenditure and income data and labor force data, we show that between the two categories of occupations, in terms of the share of women's... 

Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

Shot peening is a cold-working process commonly used in industry to improve the fatigue performance, stress corrosion resistance and surface nano-crystallization of metallic parts. This process extends fatigue life via two mechanisms: Preventing the crack growth due to compressive residual stresses and, preventing the crack initiation because of increased material hardness. These mechanisms are the results of the bombardment of the component's surface with small spherical particles. In this research, an analytical model is developed for estimating the residual stress distribution induced by shot peening process. The modifications of the developed analytical model are related to... 

Solid-State Drives (SSDs) provide high performance, low power consumption, and hence are widely used in the I/O cache of enterprise storage systems and high performance servers. Although employing high performance SSDs in the I/O cache of storage systems significantly improves system performance, it comes with significant reliability threats for write operations upon power failures. In order to provide high level of reliability, storage architectures employ SSDs in I/O cache with RAID-1 configuration, however, such configuration only partially mitigates the reliability issues of the SSDs. In this thesis, we analyze the reliability of SSD-based I/O caches against power outage and high... 

Network design problem (NDP) is an important problem in transportation planning, in which transit network design is one the most important problems. Public transportation means, however, can not meet urban mobility needs in the developing countries satisfactorily. Bus services are usually unsuitable, insufficient, and unreliable. Bus Rapid Transit (BRT) system, is an emerging public transport alternative designed to provide appropriate, low cost, and effective services, and improve mobility in both developed and developing countries. To design public transportation systems, existing constraints such as resources and budget have to be considered to serve estimated demand properly. Bus Rapid... 

Using magnetic torquers as the sole actuator for attitude control of small satellite despite its benefits has a drawback that is lack of controllability. Mechanical torques can be created only perpendicular to the instantaneous magnetic field vector, thus at each time instant the satellite can be controlled only around two axes out of its three perpendicular axes.
Fortunately because of the satellite motion, the direction of uncontrollable axis changes by time, therefore the sufficient attitude control can be achieved along time. Almost all of the present magnetic attitude control methods need more than one orbital period to control and cause the attitude to converge to the desired... 

Humanoid robots are robots that are similar in appearance and performance to humans. Designing and controlling a humanoid robot to perform such supposedly ordinary tasks as walking, running, writing, talking, driving, riding bikes, and the like is such a difficult task from the control point of view that it seems to be quite ambitious and inaccessible. In this thesis, the previous efforts of scientists and researchers are presented using different intelligent controllers. Additionally, the dynamic analysis of selective biped (seven-link biped robot) is illustrated. In this research, we present a method to control the walking of the biped robot while retaining stability. In this method the... 

An optimal trajectory for flight through Microburst wind shears is designed which minimizes the maximum deviation from desired trajectory With respect to optimal control methods. The suitable performance of airplane retrieval in abort landing and landing phases at microburst encounter is achieved by influence of mentioned design in worse case of wind fluctuation and variation. 3D Vicroy microburst model is selected to investigate its effects on 6 DOF jet engine aircraft EOMs. Above optimal control problem is solved using gradient method of SD . Furthermore, sensitivity of optimal trajectory to lateral and longitudinal location of microburst, microburst parameters, throttle setting and... 

Cosmology is a knowledge that deals with the matter of creation of the world, its current structure and its end. This scientific field that was a subject discussed by the scientific, philosophical and religious groups has nowadays taken the attention of many scientists and researchers. The philosophers of science, also, are not exemptions from theses groups and cosmology, as a topic common between philosophy and science, is one of the points that are under discussion in the field of philosophy of science. On the other hand, the religions, also, have noticed this issue. Koran that is the most complete divine book sent from God, has taken account of the creation and the Creator as the axis of... 

Congestion is the inseparable part of everyday life in large transportation networks. Expansion of road networks especially in downtown area is next to impossible and it is resulting multiplicative congestion problems. Congestion imposes private and public costs. Therefore, restricting policies on road use through cordon-based or area-based pricing is proposed to reduce the negative impacts of traffic, travel demand management and optimal use of transportation systems. This would produce better resource allocation through transportation network optimization. Implementation of congestion pricing policies induces short-term and long-term effects. In this thesis, it is attempted to determine... 

This research deals with pricing private automobiles entering a congested area in urban CBD to reduce auto-related air pollution. There are two factors affecting the pollution level: car volumes, and the weather condition. A Markov decision process is employed to find the optimal tolls and determine the prices for different states of the system, under several weather conditions. The demand for travel is elastic. It is assumed that users change modes in the short run. In longer terms, the part of the demand with shopping, recreation, or similar flexible trip purposes change the respective demand levels according to the price level. The study attempts to estimate elastic demand functions for...