Sharif Digital Repository

Unwanted vibrations of vehicles are regarded as harmful threats to human health in biomechanical and psychophysical terms. Road roughness is considered as the main cause of unwanted vibrations of bus vehicles. Vertical seat vibrations were found via simulating a 10-Degree-Of-Freedom (10-DOF) model of an intercity bus vehicle under harmonic and random excitations caused by road roughness. To suppress undesirable vibrations, mass-spring-damper passive absorbers were proposed in a 13-Degree-Of- Freedom (13-DOF) model of the bus. Following the optimization of the characteristics of embedded passive absorbers under each seat and implementation of the designed absorbers, the vertical displacement... 

Reformer gas (syngas) addition to main fuel is a practical solution for combustion timing control in HCCI engines. This study emphasizes the understanding of various effects of reformer gas (RG) addition, with composition of 75%vol H2 and 25%vol CO, in HCCI combustion by developing an artificial inert species method and using a detailed chemical kinetics multi-zone model. Three fuels (iso-octane, n-heptane, and natural gas) with different autoignition characteristics were used in this study. The developed multi-zone model was validated for mentioned fuels at various percentages of RG using six experimental cases of a single-cylinder CFR engine. The results showed that increasing reformer gas... 

This paper presents the results of a series of shake table tests carried out on a half-scale single-story unreinforced masonry building with asymmetric openings. First, the unretrofitted building is subjected to seven increasing steps of bidirectional seismic excitation. The damaged building is then rehabilitated using steel mesh and shotcrete layer with two walls retrofitted from the exterior face and the other two from the interior face. Afterward, the shake table test is again conducted on the retrofitted specimen in nine increasing excitation levels. Three cases of interior-to-interior, interior-to-exterior, and exterior-to-exterior shotcrete connections are considered at the... 

The increase of underground space applications, as a solution for congested urban areas makes it inevitable to cross closely spaced underground structures. The analysis of new TBM EPB-bored tunnel under existing underground station was conducted by 3D finite element method. The influence of new tunneling was investigated on the deformation and moments of final lining of existing underground station. The effectiveness of interaction analysis depends on factors such as station overburden, existing station supporting stiffness and traffic loads. In this paper, a parametric study was conducted to study ground movements and lining moments. It is shown that moment increase is significant when the... 

The increase of underground space applications, as a solution for congested urban areas makes it inevitable to cross closely spaced underground structures. The analysis of new TBM EPB-bored tunnel under existing underground station was conducted by 3D finite element method. The influence of new tunneling was investigated on the deformation and moments of final lining of existing underground station. The effectiveness of interaction analysis depends on factors such as station overburden, existing station supporting stiffness and traffic loads. In this paper, a parametric study was conducted to study ground movements and lining moments. It is shown that moment increase is significant when the... 

The inherent complexities of multi-reservoir flood control systems and their operation conditions along with the improvements of optimization methods have led to a positive trend on better development of these models. This trend tends to provide the operators of these systems with more practical solutions. Although optimization models can provide appropriate solutions for operation of multi-reservoir systems, the exact implementation of these solutions in real world is not guaranteed. This arises mainly due to high level risk of flood situation, real time operation constraints, high level uncertainties of inflows that usually are overlooked in optimization models, and so on. These problems... 

A great number of authentication protocols used in several applications such as payment systems are inherently vulnerable against relay attacks. Distance bounding protocols provide practical solutions against such attacks; some of which are lightweight and implementable on cheap RFID tags. In recent years, numerous lightweight distance bounding protocols have been proposed; however, a few of them appeared to be resistant against the existing attacks up to the present. One of most well-known protocols in this field is the SKI protocol which has a security proof based on a non-standard strong assumption named Circular Keying. In this paper, we demonstrate that without this strong and... 

Power control mechanisms play a critical role in underlay cognitive radio networks where primary users' quality of service should not be degraded by the secondary users transmission. Consequently, the inflicted interference power of the secondary transmitters on the primary receivers should be less than certain threshold levels that is required to be considered in designing power control algorithms for such networks. In this paper, we first propose a power reduction algorithm for the set of secondary transmitting links in order to guarantee that the members of this set do not violate the interference constraints set by primary users while maintaining their specific SINR quality of service... 

This paper addresses the feasibility of applying realtime steganalysis to the Internet data. To reach a practical solution, we have employed offline procedures to minimize the volume of the data to be processed by an online real-time system. Possible offline services that can be provided to an online system then led us to appropriate network designs for the online system. To go into detail of the online systems, we have carefully analyzed some well-known, state-of-the-art steganalysis algorithms and estimated their processing power and memory requirements. Some formulas are derived to relate the network bit rate with the number of the processing units, their processing power, and memory... 

Short circuit current is one of the major threats for power system stability. Power system should have the ability to detect and clear these faults within a specified time. The protection system can clear the faults only if the interruption capability of the circuit breakers is higher than the fault level. Expansion of the grid and installation of new power on the scale that is envisaged will require practical solutions to a number of technical challenges. One of the technical challenges is fault level management as system expansion often results in increased fault levels beyond the design limits of the existing switchgears. Replacing the old equipments particularly circuit breakers with the... 

As a security principle, separation of duty (SoD) is widely considered in computer security. In the role-based access control(RBAC) model, separation of duty constraints enforce conflict of interest policies. There are two main types of separation of duty policies in RBAC, Static SoD (SSoD) and Dynamic SoD (DSoD). In RBAC, Statically Mutually Exclusive Role (SMER) constraints are used to enforce Static Separation of Duty policies. Dynamic Separation of duty policies, like SSoD policies, are intended to limit the permissions that are available to a user. However, DSoD policies differ from SSoD policies by the context in which these limitations are imposed. A DSoD policy limits the... 

Role-Based Access Control (RBAC) model is naturally suitable to organizations where users are assigned organizational roles with well-defined privileges. However, due to the large number of users in nowadays online services of organizations and enterprises, assigning users to roles is a tiresome task and maintaining user-role assignment up- to-date is costly and error-prone. Additionally, with the increasing number of users, RBAC may have problems in prohibiting cheat and changing roles of users. In order to categorize information and formulate security policies, human decision making is required which is naturally fuzzy in the real world. This leads using a fuzzy approach to address the...