Sharif Digital Repository

Solar power is expensive, so engineers are encouraged to put effort on increasing efficiency of solar power equipments. Since photovoltaic panels usually output a low voltage, variable direct current electricity, a boost converter and a suitable inverter are required to use this energy for ordinary commercial appliances. In this project, high step up, high efficiency converters are investigated, and the best converter with high efficiency and limited switch stress which achieves high voltage gain by capacitor multipliers and coupled inductors is illustrated. Afterwards, methods for improving efficiency such as modifying the converter structure and its control strategy are suggested. The... 

Earth and rockfill dams are enormous three-dimensional structures constructed from earth and rockfill materials. They are mainly built for water supply, agricultural land irrigation, electricity generation, and flood control. Earthquake is one of the most significant natural hazards affecting the stability of these dams. Nowadays, with the development of computers and software, the seismic behavior of most dams are assessed by dynamic analysis. In a considerable part of technical literature, dynamic analysis of earth and rockfill dams have been performed by applying only the horizontal component of the earthquakes, and the effects of vertical component of the earthquakes have often been... 

This study evaluates hydrogen production from methane cracking driven by the hot products of a rotating detonation combustor. A 2-D axisymmetric, steady, adiabatic Fluent model (ideal gas, no-slip; SST turbulence; species with GRI-3.0) used two inlets: H₂/air detonation products at 100 g/s and 2000 K, and methane at 7.342 g/s and 700 K with steam-to-methane = 3. In the base case, a central recirculation and a shear layer govern mixing and heat transfer: temperature peaks near the reactor inlet and then drops due to mixing and endothermic reactions. The outlet shows 1750 K mean temperature, hydrogen production of 1.4 g/s, and 1.3 g/s residual methane, indicating high conversion. Sensitivity... 

With the increasing development in the field of electronics and information technology, the required dimensions and power of electronic devices and sensors have decreased. The range of applications of these electronic devices is very large, which is the product of technological progress development. There is a problem in the development and application of such devices, the supply of electrical power used in them, especially in the set of wireless sensors, this problem is more significant.The use of piezoelectric materials is one of the methods of converting mechanical energy into electrical energy. The voltage generated by the piezoelectric material can be used to charge the capacitor or... 

In this piece of work, a gravity model is suggested as Iranian non-fuel export model to OIC countries. The most important results out of this model are the acquired coefficients of two variables, namely “ECO membership” and “Economic and Trade Freedom of Importer”. At first, we expected that for importer, being a member of ECO would increase the amount of trade with iran. Surprisingly, this is not what we see in a model. In fact, as ECO has not achieved any tangible success in increasing trade between its members, eastern Asian Muslim countries has become an important trade partner for iranians. This result is compatible with other pieces of researches about ECO. “Economic and Trade Freedom... 

Today’s growing interest to the underwater explorations and navigations demands to design appropriate underwater communication methods and systems. However, radio frequencies which are widely being used in free space communications, can’t be a good candidate for underwater wireless communications, due to their sever attenuation in water. On the other hand, underwater acoustic communication has been widely studied and implemented in the past decades, inspired by suitable propagation of acoustic waves through the underwater medium. Nevertheless, acoustic communication systems have limited bandwidth, lower propagation speed and lower security than optical counterparts, which suggests underwater... 

Visible light communication (VLC) uses huge license-free spectral bandwidth of visible light for high-speed wireless communication. Since each VLC access point covers a small area, handovers of mobile users are inevitable. In order to deal with these handovers, developing fast and effective resource allocation algorithms is a challenge. this paper introduces the problem of mobility-aware optimization of resources in hybrid VLC and 5G radio access technologies networks using the T-step look-ahead policy and employing the notion of handover efficiency. It is shown that the handover efficiency can correlate the overall performance of the network with future actions based on the mobility of... 

In present research, a cohesive based finite element model has been introduced to estimate median crack depth during mechanical machining on optical glasses. Development of the machining numerical model has been initiated by investigating the indentation process. Experimental results of this step have been calibrated primary numerical model which has been used in the scratch process. Due to differences between the scratch mechanism and indentation one, mathematical bases fracture formulas and cohesive relations have been developed. After extracting primary result, using them in the scratch model and developing the primary model, ultimately numerical model has been evolved to an abstract... 

Hydrothermal supercritical method is one of the most suitable methods for metal oxide nano powder, ceramics and mineral catalyst synthesis. Metal oxides nanopowder in its pure or mixed form has wide potential application as chemical industrial catalyst, hot Superconductors, magnetic material, gas sensors and car catalyst convertors. One of the most important metal oxides aspects of application is uranium oxide as nuclear reactor fuel is used. In addition, UO2 is selective catalyst for converting methane to methanol process and Decomposition of organic Chlorine material. In Supercritical hydrothermal method done in high pressure reactor with critical to fluid, is new method for the... 

Lithium has 9 isotopes which two isotopes are stable and remaining isotopes are unstable and have half-life. Lithium stable isotopes include 6Li and 7Li that their abundance is 7.53% and 92.47% respectively. Importance of lighter lithium isotope appears for its small cross section against thermal neutron and producing fusion reactors fuel in nuclear industries. Thermal neutron absorption cross section for 6Li and 7Li are 950 barn and 37 mbarn respectively. Interesting of these isotopes in nuclear industry is due to the large difference in the absorption cross section.6Li compounds implied for tritium producing in coat of nuclear fusion reactor with DT fuel. Following tritium is used in... 

Foil gas bearings are compliant surface, self-acting hydrodynamic bearings that use ambient gas as their working fluid. They do not require external pressurization and are typically constructed from several layers of sheet metal foils. In high-speed, high-temperature applications the GFB’s have the advantage of developing higher load capacities than with fixed geometry gas bearings. Since GFB’s have a complex structure consisting of a spring-like substructure with an overlying flexible surface, there exists a great variety of permutations on any given design. At current work presents a 1D model for GFB with couple solving Reynolds and Euler-Bernoulli beam equation. This mean top foil assume to... 

Lameness in dairy cattle is a crucial welfare issue in dairy industry, and over the years scientists are attempting to present a detection method. In recent years it is attracting more attention to make the identification and discrimination of sounds and lames systematic and automatic. Right now, the most hopeful results have been obtained through the measurement of Ground Reaction Forces (GRF) of hooves, and analysis of load distribution between four legs, which seems applicable for wide use in dairy industry. However, the accuracy, validity, and reliability of discrimination is still far from an acceptable point, that is because of a great lack in understanding quantitative effects of the... 

Natural boron consists of two stable isotopes, mass 10 (19.3%) and mass 11 (80.7%). 10B isotope has a large thermal neutron capture cross-section and it therefore, used widely in such aspects as modern industry, military equipment, medical science and so on. specially the demand of atomic energy industry for the boron isotope is increased severely. So the separation of 10B from natural boron has received very wide attention at present. There are many kinds of methods on the boron isotopes separation, such as chemical exchange reaction and distillation in boron trifluoride method, ion exchange in boric acid solution method, counter current recycle membrane cascades in boron trifluoride... 

In this study the feasibility of xenon separation from xenon-krypton mixture was investigated by utilizing of the chromatographic column filled with nano and micron sized NaY zeolite. For this purpose the nano NaY with the yield of 100% related to Al2O3 and the average size of 98.6 nm was synthesized through the clear solution method with the mid-adding of NaOH. Furthermore, a novel method for granulation of nano zeolite was developed by utilizing sodium alginate as an external template. In this method the production of uniform spherical granules with the different sizes in the range of several milimiteres to 100 µm was easily performed. Moreover, the results showed that the adding of... 

Natural boron includes two stable isotopes 10B and 11B with 19.3 and 80.7 weight percent respectivley.10B isotope has a high thermal neutron absorption cross section. So isotope 10B material is suitable for making atomic reactor control rods. Other and even more important applications of 10B are in disclosing neutrons in order to measure neutron reactors fluxes and also are in nuclear physics laboratories and medical radiation. This isotope also is used in the pharmaceutical and the military industries. There are several methods for separating boron isotopes. Among the distillation methods, thermal diffusion of BF3, distillation of BF3, distillation of methyl borate, boric acid distillation... 

Due to both dynamic and opportunistic spectrum access, Cognitive radio networks is a promising solution for spectrum scarcity problem. In cognitive radio networks, users need to have a control channels in order to cooperate for sharing the sensing information, channel sharing and etc. In Ad-hoc cognitive radio networks because of the absence of infrastructure and central nodes, every user runs a distributed algorithm to create a common control channel. If the control channel gets jammed, network’s performance degrades dramatically, therefore the jammer’s target in cognitive radio networks is the control channels to disturb the networks’ performance. The traditional solution to confront... 

In this work, graphene oxide (GO) and Amino ethyl phosphonic acid (AEPA) functionalized graphene were synthesized using chemical method. In addition, reduced graphene was prepared by chemical and supercritical methods. Physical, chemical, morphological properties of as-synthesized materials were investigate using XRD, FTIR, RAMAN, UV, TEM, TGA, and BET. Thickness of monolayer GO which synthesized using Hummer’s method was evaluated 1 nm using AFM. FTIR and CHN results were affirmed the presence of AMPA onto graphene nanosheets. Adsorption properties of functionalized graphene for Th ions from aqueous solution was examined. Isotherm adsorption results demonstrated that maximum adsorption... 

Technology, especially in recent centuries, has changed human form of life. Case studies show that there is a mutual relationship between human being and technology; Human is a technological being and technology is also a social entity. Therefore, trying to develop a conceptual framework to describe the important role of technical artifacts in our life can be regarded as a legitimate philosophical concern. Peter Paul Verbeek is one of the contemporary philosophers who take this concern seriously. He, by using the doctrines of The Empirical Turn in the philosophy of technology, has developed a lexical system, called post-phenomenology, to describe the role of Technology in human’s perception...