Sharif Digital Repository

The burning of fossil fuels such as gasoline, coal, oil, natural gas in combustion reactions results in the production of carbon dioxide. The phase behavior of the carbon dioxide + water system is complex topic. Unlike methane, CO2 exhibits a minimum in the water content. These minima cannot be predicted by existing methods accurately. In this communication, two mathematical-based procedures have been proposed for accurate computation of CO2 water content for tempe-ratures between 273.15 and 348.15 K and the pressure range between 0.5 and 21 MPa. The first is based on least squares support vector machine (LSSVM) algorithm and the second applies multilayer perceptron (MLP) artificial neural... 

Masking effect is the most important problem in Noise Radars. Recently, some waveform design methods to resolve this problem have been developed, however this paper will show an important fact: 'sidelobe suppression increases the Periodicity of signal and, consequently, decreases unpredictability'. Eventually, an appropriate level for sidelobe reduction is introduced  

Inherently safer design is the new approach to maximize the overall safety of a process plant. This approach suggests some risk reduction strategies to be implemented in the early stages of design. In this paper a multi-objective optimization was performed considering economic, exergetic, and environmental aspects besides evaluation of the inherent safety level of a cascade refrigeration system. The capital costs, the processing costs, and the social cost due to CO2 emission were considered to be included in the economic objective function. Exergetic efficiency of the plant was considered as the second objective function. As a measure of inherent safety level, Quantitative Risk Assessment... 

The mean monthly values of sky clearness index, K̄T, were estimated for 36 Iranian cities, utilizing the solar radiation data measured by the Iranian Meteorological Organization. The study shows that the city of Tabas, in the desert regions of Iran, with an annual average K̄T of 0.69 is the sunniest city, followed by the cities of Yazd, Khor, Birjand, Khorramabad, Kerman, and Shiraz. On the other hand, the cities of Babolsar, Gorgan, Ramsar and Rasht, located by the Caspian Sea with average values of K̄T of 0.41, 0.41, 0.39 and 0.39, respectively, are the cloudiest cities in Iran  

The power output of gas turbines reduces greatly with the increase of inlet air temperature. Aquifer thermal energy storage (ATES) is employed for cooling of the inlet air of a gas turbine. Water from a confined aquifer is cooled in winter, and is injected back into the aquifer. The stored chilled water is withdrawn in summer to cool the gas turbine inlet air. The heated water is then injected back into the aquifer. A 20 MW Hitachi gas turbine, along with a two-well aquifer were considered for analysis. It was shown that the minimum power output of the gas turbine on the warmest day of the year could be raised from 16.30 to 20.05 MW, and the mean annual power output could be increased from... 

The coefficient of performance (COP) of a photovoltaic panel or module is defined as the ratio of the total electrical energy produced by the panel during its life to the total energy spent for its manufacture. All processes involved for the manufacture of photovoltaic panels were considered and the energy spent per unit mass of the final product during each process was determined. The total electrical energy spent for the manufacture of a photovoltaic module of 1×0.5 m dimensions, employing 340 micron wafers, with the net wafer area of 0.36 m2, was then determined. Monocrystalline and multicrystalline silicon cells were employed. It was found that for the manufacture of the PV module... 

The quantification of carbon dioxide (CO2) dissolution in oil is crucial in predicting the potential and long-term behavior of CO2 in reservoir during secondary and tertiary oil recovery. Accurate predicting carbon dioxide molecular diffusion coefficient is a key parameter during carbon dioxide injection into oil reservoirs. In this study a new model based on adaptive neuro-fuzzy inference systems (ANFIS) is designed and developed for accurate prediction of carbon dioxide diffusivity in oils at elevated temperature and pressures. Particle Swarm Optimization (PSO) as population based stochastic search algorithms was applied to obtain the optimal ANFIS model parameters. Furthermore, a simple... 

The objective of this study is to develop a general finite element formulation associated with an incremental adaptive procedure which established for thermoviscoelastic stress analysis of orthotropic cylinders made of polymers. This paper concerned with development of a numerical algorithm for the solution of the quasistatic initial/boundary value problems involving the linear viscoelastic media with thermal and mechanical deformations. The viscoelastic constitutive equations, represented in an integral form and involving relaxation functions, are transformed into an incremental algebraic relation. An incremental relaxation is then developed for the finite element formulation to deal with... 

In oil and gas fields, it is a common practice to flow liquid and gas mixtures through choke valves. In general, different types of primary valves are employed to control pressure and flow rate when the producing well directs the natural gas to the processing equipment. In this case, the valve normally is affected by elevated levels of flow (or velocity) as well as solid materials suspended in the gas phase (e.g., fine sand and other debris). Both surface and subsurface chokes may be installed to regulate flow rates and to protect the porous medium and surface facilities from unusual pressure instabilities.In this study a reliable, novel, computer based predictive model using Least-Squares... 

The bending performance of standard nanoplasmonic slot waveguides is substantially improved by reducing the leakage loss and reflection in a systematic way. The out-of-plane power leakage is suppressed by using square metallic patches above and below the bend. The in-plane power leakage is reduced by elimination of the asymmetry between the electrical length of the inner and outer corners of the bend. The unwanted reflection is decreased by changing the shape of the outer corner of the bend. The partial reflections caused by the indentations of the modified shape destructively interfere with each other and thereby decrease the unwanted back reflection  

Two new designs of wind towers were tested side by side with a conventional wind tower in the city of Yazd, Iran. All the towers were of identical dimensions. The two new designs were one with wetted column, consisting of wetted curtains hung in the tower column, and the other one with wetted surfaces, consisting of wetted evaporative cooling pads mounted at its entrance. The air temperature leaving the wind towers with evaporative cooling provisions were much lower than the air temperature leaving the conventional design, and its relative humidity much higher. The air-flow rate was reduced slightly in these new towers. It was found that the wind tower with wetted column performs better with... 

An easy-to-design single-stub nano-coupler is proposed to increase the direct coupling efficiency between metal-insulator-metal (MIM) plasmonic and high-index dielectric waveguides. The modal reflection and transmission from the junction are exploited to provide a circuit description for the structure. The return loss of direct coupling is then minimized by loading the MIM waveguide with a single stub. Numerical examples are given, and the accuracy of the model is examined via finite-difference time-domain method  

One of the most promising methods for transporting natural gas and overcoming its low energy density is adsorbed natural gas (ANG) technology. ANG technology is highly dependent on the perfect conception of adsorption isotherms in different operational conditions and on different adsorbents. In this study, the utilization of a novel mathematical model of least squares support vector machine (LSSVM) for accurate prediction of adsorption isotherm has been examined. The considered variables were temperature, pressure and type of adsorbents. A data set containing 670 experimental data points of methane adsorption on 10 different adsorbents in a broad range of temperature and pressure were used... 

In recent years, the role of optically sensitive nanomaterials has become powerful moieties in therapeutic techniques and has become particularly emphasized. Currently, by the extraordinary development of nanomaterials in different fields of medicine, they have found new applications. Phototherapy modalities, such as photothermal therapy (PTT) by toxic heat generation and photodynamic therapy (PDT) by reactive oxygen species, are known as promising phototherapeutic techniques, which can overcome the limitations of conventional protocols. Moreover, nanomaterial-based PDT and PTT match the simultaneous immune therapy and increase the immune system stimulation resulting from the denaturation of... 

In this study, effects of replacing cement with colloidal amorphous silica nano-particles have been experimentally investigated on the physical and mechanical properties, durability and microstructure of concrete. Experimental results include workability, fresh concrete density, and hardened concrete properties like compressive strength at different ages of 3, 7, and 28-days, and also 28-days splitting tensile strength. Furthermore, influence of silica nano-particles on durability and microstructure of concrete for 28-days specimens was tested by conducting water absorption test, Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Analysis (EDAX), respectively. In order to study... 

A coupled transmission line model whose parameters are analytically given is provided for fast and accurate analysis of miscellaneous plasmonic structures with metal-dielectric-metal (MDM) arrangement. The coupling of surface plasmons supported by the planar metal-dielectric interfaces is included in the proposed model and thereby the effects of the first non-principal mode of the MDM waveguide are considered. In particular, MDM bends, junctions, and stubs are studied. Using rigorous numerical solutions, e.g., the finite-element method and the finite-difference time-domain, it is shown that the proposed model is accurate in all those cases  

A simple yet accurate model for the analysis of coupling between arrayed plasmonic slot cavities and bus/drop metal-dielectric-metal waveguides is presented. The evanescent coupling region is replaced by a transmission line section whose propagation constant and characteristic impedance are given in closed form. The side coupling between the bus waveguide and the slot cavity is modeled together with the direct coupling between the slot cavity and the drop channel. The proposed model is validated by using rigorous numerical method, and is used to design a typical demultiplexer  

RSA based SmartCards have been widely used in security services such as secure data transmission in many applications over the past few years. Generation of a secure key pair which is based on finding a pair of large prime numbers is an indispensable part of creating a secure channel. This paper describes a novel approach for secure and fast key generation of the public key cryptographic algorithm of RSA. This method has been implemented on a typical SmartCard equipped with a crypto-coprocessor and a true random number generator. An efficient method for generating the large random prime numbers is proposed that considerably reduces the total time required for generating a key pair. The key...