Sharif Digital Repository

This research aims to study the trade trends of Manufactured goods, classified chiefly by Material, identified under Code 6 in the Standard International Trade Classification, SITC, and its nine divisions. The study scope covered 125 countries throughout Asia, Europe and Africa and 9 distinct years spanning a 40-year time period between 1965 and 2005. By means of this study, determinant factors for modelling and investigation of trade flow characteristics for the mentioned items can come to be better understood. The time-series data were grouped into four categories: bilateral trade value, socio-economic, geographical and transportation variables, obtained from centralized international... 

A new class of design has been introduced in the RF circuits and Frequency Synthesizers, which is based on the digital circuits. Implementation of the digital synthesizers suppresses the need to use loop filter and thus reduces the loop lock time. In this thesis different topologies of digitally controlled oscillators using inductor and capacitor tank and all digital architectures used in high frequency all digital synthesizers in 0.18um CMOS technology has been inspected and simulated. Novel techniques introduced to improve the ring oscillator-based design’s specifications which doesn’t need inductor. Using the introduced techniques, the phase noise has been lessened acceptably with respect... 

Using the general structure of the vacuum polarization tensor П_μν (k_0→0,k) in the infrared (IR) limit, k_0→0 , the ring contribution to the QED effective potential at finite temperature and the nonzero magnetic field is determined beyond the static limit, (k_0→0,k→0). The resulting ring potential is then studied in weak and strong magnetic field limits. In the weak magnetic field limit and at high temperature the improved ring potential consists of a term proportional to T^4 α^(5/2), in addition to the expected term T^4 α^(3/2) arising from the static limit. In the limit of the strong magnetic field, where QED dynamics is dominated by the lowest Landau level, the ring potential includes a... 

Traffic accidents are one of the most important issues of traffic which impose high costs to societies. Regardless of accidents material costs, disabilities and deaths are very considerable. Iran statistics show that death rates caused by driving accidents are two times more than world statistics and each 25 minutes one dies because of driving accidents. Researchers classify factors influencing driving accidents in four categories: human factors, factors related to the environmental conditions, factors related to the vehicles and factors related to the roads. Driver behavior and characteristics are the main human factors that influence his or her behavior. The aim of this study is analyzing... 

Large structures such as dams, long span bridges and piping systems because of an extended interface with the ground as support and the earthquake wave propagation in foundation are subjected to the non-uniform excitations. In such cases, the standard dynamic analysis in which a uniform earthquake is used as an input data is not true and can lead to unrealistic results. In the present study, seismic responses of arch dams subjected to spatial variation of ground motions is investigated and compared with the standard methods. For this purpose the governing equations are implemented into the NSAD-DRI (comprehensive software for Nonlinear Seismic Analysis of Dams) and the seismic responses of... 

The current study is dedicated to free vibration analysis of a thin cylindrical shell with an oblique end. To this end, governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. The differential form of equations is obtained by applying by part integration to the integral form of equations of motion. Equations of motions have been solved by Galerkin method for two different kinds of boundary conditions. Convergence process for different kinds of conditions has been done and results compared with papers. The effect of different parameters such as, length of cylinder, oblique angle, thickness etc. on the fundamental frequencies has been... 

Domino accidents are one types of incidents that lead to irreparable damage to industrial units. Since the consequences of such incidents are far more than the first level incident, consideration of this issue and the provision of appropriate strategies for identifying and evaluating this type of incident is very important. Major efforts have been made in the area of process safety is in risk assessment and identify possible scenarios and their probability of occurrence, and have not addressed the financial consequences of an incident. In this research, an algorithm has been developed to estimate the financial losses incurred with an industrial unit due to a domino incident and various... 

Radio Frequency IDentification (RFID) is an increasingly important area in automatic identification. Low cost RFID tags (labels) are considered as the next generation of barcodes and their purpose is to compensate for shortcomings in computer recognition of objects using cameras. Supply chain management, access control, animal identification,e-passports along with the possibility of having e-health, e-agriculture and smart homes are few examples of RFID application developments. Despite its low cost, ubiquity, and widespread usage, RFID tags suffer from several major drawbacks, particularly information leakage and traceability. In RFID authentication protocols, both information leakage and... 

Failure of mechanical parts in the industry lead to a larger system downtime and even imposing economic losses to the factory. For this Purpose, for many years, researchers have been trying to find ways to predict early failure and to prevent losses from occurring. Creation of new sciences like artificial intelligence, helped researchers in this field.In the current study, using experimental data of a set of bearings that have been tested and recorded in the Intelligent Systems Research Center, A new approach with sufficient accuracy is presented for the prediction algorithm. Among the features extracted, three features of entropy, root mean square and maximum are the most appropriate...