Sharif Digital Repository

For decades Crystal Oscillators (XO) have been the unequaled references for stable and low noise frequency sources. This leadership is due to their high Q-factor. The resonant frequency of such crystal resonator is inversely proportional to the thickness of the quartz disk (the resonant cavity) and is today limited , by physical manufacturing constraints , to about 150 MHz . in order to avoid such limitation , the solution is to start with an oscillator at higher fundamental frequency. SAW technology on quartz offers this opportunity . with SAW the resonant cavity size is not linked to the thickness of the substrate and resonant frequencies up to the GHz range are achievable. In this thesis... 

In order to control accesses in semantic environments, a semantic-based access control and policy specification language should be choosen. Upon to them, some security mechanisms should be designed and implemented. Several access control models and policy specification languages have been arisen, but seldom have focused on designing mechanisms to satisfy their models in any environment. In this thesis, we focus on implementation aspects of access control in semantic environments. We chose semantic web as our studying environment and an extension of the SBAC model named MA(DL)2 as our access control model. To control accesses in the selected environment, we divide semantic web into some... 

In recent decades one neo-Aristotelian school in metaphysics has appeared that with reconstruction on concept of "potency" or "power" try to explain metaphysical problems as: properties ,causation, laws of nature ,modalities and … .this school contradict all classical views in analytic metaphysics ,because they have commitment to Humean metaphysics that all metaphysical categories supervene on distinct particular facts in nature. Dispositional essentialism is one neo-Aristotelian theory saying that some natural properties have dispositional essence. In strong view of this theory, identity of properties supervenes on the structure of a network of properties and therefore properties are... 

The Concept of causation plays a major role in Hume’s philosophy and as yet has been debated between philosophers. This Thesis aims to Consider the main part of Hume’s view about Causation, but it also Ventutes into more recent approaches in this subject. In first chapter, we attend to Consider The project of Hume named "Seience of man" and The associative mechanism of causation is expressed. In Second chapter, We turn to three famous interpretations of Hume’s view and the meaning of two definitions of Causation is discussed. In third chapter, we try to analyse the real nature of necessary Connection. According to fourth chapter, we again attend to three interpretations and recognize the... 

Modern physics and the standard metaphysical point of view, together, result a contradiction which we will explore its roots in this thesis. Be- sides, focusing on various identifications of individuality and the prin- ciple of identity of indiscernibles will made us to choose between to metaphysical and equal pockets, Particles as individuals and particles as non-individuals.Physics alone could not help to choose between these too pockets. Therefore, we will face a metaphysical under-etermination which we have to break in order to save our realistic ontological com-mitments. By a breif study among the possible ways for breaking that underdetermination, structural realism will be the most... 

In Laws and Lawmakers: Science Metaphysics and the laws of nature, Mark Lang has presented an engagingly written, tightly argued, and novel philosophical account of the laws of nature. One of the intuitions behind the notion of a law of nature is, roughly, that of the many regularities we observe in the world there are some which appear to be due to mere happen-stance(“accidental” regularities, in the philosopher’s jargon)while others, which we call “laws,” seem to be possessed of a degree of necessity. although many philosophers, and certainly most scientists, will readily agree that there is a difference between logical, law-like, and accidental regularities, spelling out the nature of... 

Intelligent design theory is based on this idea that Darwinian theory of evolution can not explain Irreducibly complexities in organisms. Intelligent design theory in explaining these complexities conclude the existence of an intelligent designer. It is claimed that by remaining officially agnostic about the nature of the designer, intelligent design theory can be offered as a scientific claim, rather than a religious one, which could make it a viable alternative to Darwinism. In this thesis we study sober's point of view on intelligent design. Sober believes that, initially, we shoud present the strongest formulation of intelligent design theory and then evaluating whether this theory is a... 

The environmental impacts of chemical processes significantly affect the design of these processes and emphasize issues such as changing the reaction path, separation methods, thermal integration, and finally multi-objective optimization. Therefore, it is necessary to investigate the influence of environmental indicators in the design of chemical processes. The background system in this assessment includes two process units, olefin and polyolefin. Environmental impacts assessment has been carried out using the ReCiPe endpoint method (an efficient method for life cycle impact assessment that will be described in chapter 2) and these impacts have been determined in the form of damage to human... 

With the daily increasing demand for energy, we are facing many crises, such as environmental pollution and global warming, etc. Geopolitical issues can also lead to problems for some countries in reaching the energy demand considered in their development plan of them. For this purpose, a part of the global research is focused on removing these obstacles. One of the methods that can be used to produce cleaner fuel, or more precisely "biofuel", is the gaseous fermentation of synthesis gas by microorganisms and algae. A rod-shaped, anaerobic microorganism called Clostridium ljungdahlii uses synthesis gas for its reproduction. In other words, this bacterium can ferment carbon monoxide, carbon... 

The daily growth of cloud computing usage for data based applications and Internet services has caused many challenges in the sense of storage cost, data access performance, QoS provision such as availability, scalability, pay-as-you-go model conformation and etc. Data replication is one of the most important mechanisms for data management in distributed systems. It creates some replicas of data and distributes them to the network. The number of replicas, the time for creating a new replica, the way of their distribution among the nodes and replica replacement strategy in the case of storage unavailability are some important challenges in data replication context. Replication is extensively... 

Extensive growth of the internet has had a profound effect on the business environment and rise to a phenomenon known as electronic commerce.electronic commerce has an important role in improvement of organization performance and likewise,has influence in everyday life.despite its name,e commerce is not fully automated.typically,online transactions require a significant level of human intervention.to achieve high degree of automation,we need a new model of software.this model is based upon the notion of agents.agents can act in different stages of e-commerce.one of the most important of these stages is negotiation.negotiation capabilities are essential for e-commerce systems.the agents...