Sharif Digital Repository

Cryogenic is the study of physical phenomena at temperatures below 123 Kelvin. One of the applications of cryogenic science is the liquefaction of gases. In the liquefaction cycles of gases, such as helium liquefaction, fluidization occurs in the pressure reducing valve but temperature of the gas should be greatly reduced before it enters the pressure reducing valve. For this purpose, high-performance heat exchangers should be used. Spiral Wound is one of the heat exchangers that has ability to achieve over 90% efficiency due to its structure. Researchs in the field of design and simulation of spiral heat exchangers are limited and are done with a lot of simple assumptions such as constant... 

Providing low-power fault tolerance is usually an important requirement in real-time embedded systems. A faulty result in safety-critical systems and a failure to meet a deadline in hard real-time systems can cause catastrophic consequences for the system or environment. Therefore, these systems must be highly reliable and meet real-time constraints. Slack time in time redundancy techniques (e.g. roll-back recovery) can be used to increase system reliability and to save energy. Time redundancy techniques are suitable from an energy consumption point of view but may not be sufficiently reliable for tight real-time constraints. In the condition of tight timing constraints, the hardware... 

Financing is an important barrier in growth path of small and medium-sized technology-based firms. Using guarantee letters to ease access of such firms to credit, is one way to encounter this barrier. In this study, the pioneer research and technology fund in offering this service to technology-based firms in Iran have been considered. Credit guarantee issuance records of this fund illustrates that none of credit guarantee letters certified by this fund has been defaulted yet. Comparison of fund’s credit scoring model with Chandler’s framework for organizational capabilities reveals that the fund does not investigate marketing and managerial capabilities in its credit scoring model. So, the... 

With the significant advances in software engineering and developing complicated systems, it’s important to investigate the interaction between systems. Agentoriented software engineering is a new paradigm for developing distributed intelligent systems. Agent technology currently plays an important role in complex software development. The underlying paradigm offers a large repertoire of original concepts, architectures, interaction protocols, and methodologies for the analysis and the specification of complex systems built as Multi-Agent Systems (MAS). Several efforts, originating from academia, industry, and several standardisation consortium, have been made in order to provide new tools,... 

The need to protect the key in cryptosystems has been a motivation of studying secret sharing schemes. A secret sharing scheme is a method for sharing a secret data (key) by distributing some values, called shares, to a number of participants in such a way that only some authorized subset of them can recover the secret. In a threshold secret sharing scheme, authorized subsets are those whose size are at least a given value called threshold of the scheme. Increasing the attacker capabilities in achieving the participants’ shares, requires an increase in the threshold parameter. In a changeable threshold secret sharing scheme, participants ate able to compute new shares from their old shares... 

Environmental contamination is one most important concern that human has encountered currently the increasing demand of power production has been lead to environmental problem, therefore it is crucial to find appropriate methods managing these sources. Carbon dioxide forming from usage of fossil fuel as the main source of energy play a central role in environmental issues of climate change in atmosphere, so more attention in its emission reduction seems vital. CCS has been used as a recent attractive in order to reduce the greenhouse gases emission for large industrial units releasing carbon dioxide. The aim of this paper is environmental and economical assessment using ccs for power plants... 

In this project, the forced vibrations of a pair of strips carrying electric current inside the fluid have been analyzed. Euler-Bernoulli theory is used to model the structure and von-Karman strain is included in the structural equations. In terms of the degrees of freedom of the structure, the bending motion along with the twisting is defined for the current-carrying strips. In this way, the system has 4 degrees of freedom, whose equations are coupled to each other due to the mentioned assumptions. In order to model hydrodynamics and the forces corresponding to it, with the help of numerical simulation of the movement of the strip section inside the fluid (CFD analysis), the corresponding... 

As demand for floght has been incrased, a critical questin to pose is that is it economic to use larger Ailplanes or smaller Airplanes with higher flight frequency should be use. It is self evident that in a large Airplane the whole seats can not be accupied in all cases. Conversly, in small Airplanes, in most cases the seats are accupied but for aqual demand there most be more flights.In order to increase the number of flights, new methods should be used in such a way that smaller Airplanes live the Runway as soon as possible.In this project with modelling all effective factor regarding to Landing of a commercial FAR_23 Airplane, the Landing distance and thr erquired time for living the... 

As a connective tissue devoid of blood vessels, lymphatics, and nerves, articular cartilage has limited self-repair capabilities. This is because essential nutrients and signals necessary for cell proliferation are restricted. Despite advances in therapeutic approaches, complete repair of damaged cartilage remains a major challenge in medicine. Tissue engineering has attracted considerable attention as a novel approach for the repair of damaged tissues, including cartilage. In this study, a temperature-sensitive and injectable hydrogel based on chitosan-bacterial nanocellulose and silk fibroin was designed and optimized for controlled release of quercetin. After selecting a constant ratio of...