Sharif Digital Repository

In this paper the process of knowledge accumulation for a particular technology is studied. Two countries, say the technology follower and the technology frontier, are considered. The frontier's knowledge growth is determined by its R&D efforts on the technology. The level of knowledge stock for the follower country is augmented by its R&D activities for the technology and absorbing some of the external knowledge through spillover from the frontier. The extent to which the follower is able to exploit the external knowledge depends on technological gap, absorptive capacity, absorption time and degree of spillover. New concepts such as natural and enhanced degree of spillover, background and... 

Falling film heat and mass transfer analysis of a horizontal tube bundle in a generator of absorption chillers have been studied. The film Reynolds number is limited to the laminar flow and the effect of ripple on the free surface has been ignored. Thermal boundary conditions are considered to be constant wall temperature and desorption is considered to be free surface evaporation. Analysis is based on a single column of horizontal tubes, arranged in a vertically spaced configuration. A comprehensive numerical code has been developed to solved the governing equations. The functional relationship of average heat transfer coefficient of tube bundle has been analytically correlated to the first... 

In the recent years, many researchers have been interested in nanoparticles because of their unique properties. In this study, a method for producing ZnO nanoparticle colloids is proposed. The colloids were characterized by spectroscopic analyzer. By absorption spectrum study, we found out that colloids were consisted of nanoparticles with less than 10 nanometer size. The quantum confinement effect in these spectrums was recognized through blue shift of onset absorption wavelengths. These wavelengths shift from 370 nm to 340 nm by decreasing the particles size. Transmittion electron micrographs showed formation of zinc oxide nanoparticles  

The giant Kerr nonlinearity with reduced linear and nonlinear absorption in a four-level quantum dot by employing the tunnel coupling is investigated. It is shown that by enhancement of tunnel coupling value the Kerr nonlinearity increases and at the same time linear and nonlinear absorption reduces at the long wavelength which is very important for communicational applications. Enhanced of Kerr nonlinearity in a double quantum dots is investigated. It is found that the electron tunneling has an essential role to reducing the linear absorption and increasing the Kerr nonlinearity at long wavelength  

In this work, the absorption process of carbon dioxide is performed in a custom designed high pressure experimental setup in which the gas and nanofluid are in direct contact at static state in a closed vessel. The initial condition of the tests are set at 20, 30, and 40 bar and 308 K. Nanoparticles of SiO2, Al2O3, Fe3O4, and carbon nanotubes (CNTs) are dispersed in pure water to form nanofluids at concentrations of 0.02, 0.05, and 0.1 wt %. Also, CNT nanoparticle has been dispersed in methyldiethanolamine and diethanolamine aqueous solutions at the concentration of 0.02 wt %. The absorption performances of different nanofluids are compared with the base solutions and with other nanofluids... 

In this paper, the radiation heat transfer is calculated numerically in a three dimensional enclosure containing non-gray gases. The radiation heat transfer equation is solved using the finite-volume formulation of discrete ordinate method and the SLW model is employed to calculate the radiation absorption coefficients. Three cases are simulated here including the isothermal/homogeneous, isothermal/nonhomogeneous, and the non-isothermal/homogeneous media. The calculated radiation source terms and the wall heat fluxes are compared with the results of SNB method. It is shown that the SLW results are in very good agreement with the SNB in case of isothermal/homogeneous. In the two other cases,... 

In this paper, the radiation heat transfer is calculated numerically in a three dimensional enclosure containing non-gray gases. The radiation heat transfer equation is solved using the finite-volume formulation of discrete ordinate method and the SLW model is employed to calculate the radiation absorption coefficients. Three cases are simulated here including the isothermal/homogeneous, isothermal/nonhomogeneous, and the non-isothermal/homogeneous media. The calculated radiation source terms and the wall heat fluxes are compared with the results of SNB method. It is shown that the SLW results are in very good agreement with the SNB in case of isothermal/homogeneous. In the two other cases,... 

In this work, the optical responses of Fe3O4@Au and Fe3O4@Ag are comprehensively investigated using the discrete dipole approximation. It is found that the resonance wavelength and absorption efficiency strongly depend on the composition of the core and shell, geometry of the nanoparticles, core to particle volume ratio, core radius and shell thickness. The strongest impact is due to the shell material, the shape of the nanoparticles and their combination. When the composition of the shell is changed from gold to silver, instead of one fundamental resonance peak the absorption spectrum shows two, corresponding to the bonding plasmon mode at the nanoparticle-environment interface and... 

The objective of this paper is to provide optimization of falling film LiBr solution on a horizontal single tube based on minimization of entropy generation. Flow regime is considered to be laminar. The effect of boiling has been ignored and wall temperature is constant. Velocity, temperature and concentration distributions are numerically determined and dimensionless correlations are obtained to predict the average heat transfer coefficient and average evaporation factor on the horizontal tube. Thermodynamic imperfection due to passing lithium bromide solution is attributed to nonisothermal heat transfer; fluid flow friction and mass transfer irreversibility. Scale analysis shows that the... 

In this paper, a theoretical analysis of the combined heat and mass transfer over cooled horizontal tubes is presented. The boundary layer assumptions are used for the transport of mass, momentum and energy equations and the finite difference method is employed to solve the governing equations in the absorber tube bundle. The effects of important parameters, such as solution flow rate, absorber pressure and tube radius, are discussed on the overall heat and mass transfer for a tube and tube bundle. © Sharif University of Technology, October 2004  

In this paper, new assumptions are made to determine the energy dissipation capacity of the basic folding mechanism. The basic folding mechanism, introduced by Wierzbicki and Abramowiciz is an intelligent mathematical imitation of the real crumpling process for simple structural sections. A contribution factor for some part of energy absorption and the new concept of varying rolling radios, based on minimizing instantaneously applied load, are utilized to enrich the old analytical solution. A set of finite element analyses on the axial collapse of square boxcolumns with various cross sections and width to thickness ratios, has been performed to verify the proposed analytical solution vs. the... 

As a low-energy effective theory on non-symmorphic lattices, we consider a generic triple point fermion Hamiltonian, which is parameterized by an angular parameter λ. We find strong λ dependence in both Drude and interband optical absorption of these systems. The deviation of the T2 coefficient of the Drude weight from Dirac/Weyl fermions can be used as a quick way to optically distinguish the triple point degeneracies from the Dirac/Weyl degeneracies. At the particular λ = π/6 point, we find that the 'helicity' reversal optical transition matrix element is identically zero. Nevertheless, deviating from this point, the helicity reversal emerges as an absorption channel. © 2021 IOP Publishing... 

The infrared range optical absorption mechanism of carbon-copper composite thin layer coated on the diamond-like carbon buffer layer has been investigated. By consideration of weak interactions between copper nanoparticles in their network, optical absorption is modelled using their coherent dipole behaviour induced by the electromagnetic radiation. The copper nanoparticles in the bulk of carbon are assumed as a chain of plasmonic dipoles, which have coupling resonance. Considering nearest neighbour interactions for this metallic nanoparticles, surface plasmon resonance frequency (ω 0) and coupled plasmon resonance frequency (ω 1) have been computed. The damping rate against wavelength is... 

In this article, a comprehensive 2D mathematical model has been developed to simulate process intensification of carbon dioxide absorption in the presence of nanoparticles in hollow fiber membrane contactors (HFMCs). The influences of nanoparticle were taken into account considering Brownian motion and Grazing effect as dominant phenomena of mass-transfer enhancement in nanofluids. The obtained simulation results were validated against experimental data reported in the literature and excellent agreement was obtained. It was found that by adding 0.05 wt % silica nanoparticles, the absorption rate could be enhanced by 16%, while the corresponding value is 32% for CNT nanoparticles. High... 

Semiconductor photoelectrodes for water oxidation that absorb visible light usually have poor electronic transport properties and small optical absorption coefficients near their absorption edge. Therefore, innovative designs that lead to significant optical absorption in relatively thin layers of these compounds are highly desirable. Here, using full-field electromagnetic optical simulations, we demonstrate that a monolayer of resonant-size BiVO4 spheres can provide enhancement up to a factor of two in solar light absorption relative to dense planar layers. In this monolayer, BiVO4 spheres do not need to be interconnected; therefore, such monolayers are flexible and their fabrication... 

Novel class of polyelectrolyte gels based on the copolymer of vinylimidazolium-typed ionic liquid monomer and Dodecyl methacrylate was prepared by free radical polymerization. A small amount of 3-n-Dodecyl-1- vinylimidazolium tetrafluoroborate is incorporated into crosslinked polyacrylates to provide new lipophilic polyelectrolyte gels that evaluated for swelling in less-polar and nonpolar organic solvents. Their swelling degree becomes more than 50 times as much as their dried weights in some organic solvents. By varying the polarity of the neutral monomer in these polyelectrolyte gels, the design of gels that can absorb solvents of nearly any polarity is demonstrated. The present... 

Total site integration offers energy conservation opportunities across different individual processes. It also helps for design as well as optimization of the central utility system. It gives massive energy-saving opportunities. The large industrial CHP sites generate heat and power simultaneously. These sites have different steam levels at different pressures which are used for power generation via steam turbines and also directly for satisfying process heat demand. There are many sites requiring cooling demand in hot seasons. In this article, integration of a LiBr/water absorption chiller in a CHP site has been investigated until its cooling demand is satisfied. Low pressure steam at 3 bar... 

Metallic nanoparticles (NPs) have not been effective in improving the overall performance of the cells with micrometer-thick absorbing layers mainly due to the parasitic optical dissipation in the metal. Here, using both experiment and theory, we demonstrate that aggregates of metallic NPs enhance the light absorption of dye-sensitized solar cells of a few micrometer-thick light absorbing layers. The composite electrode containing the optimal concentration of 5 wt% Au@SiO2 aggregates shows the enhancement of 80% and 52% in external quantum efficiency and photocurrent density, respectively. The superior performance of the aggregates relative to NP is attributed to their larger scattering... 

The behavior of Alsteel bilayer sheets produced by cold roll welding is investigated through the wedge tearing process. It is observed that through tearing the energy absorbed by cold roll welded bilayer sheets is larger than that of non-welded ones, even though all parameters are identical. Also bilayer sheets with low bond strength have the same energy absorbed by non-welded bilayer sheets. By investigating all contributing mechanisms in tearing and mechanical properties of composite layers and developing theoretical equations, it is concluded that bending of sheets through wedge tearing plays a major role in difference of energy absorbed by welded and non-welded bilayer sheets. Moreover,... 

Embedded dielectric scatterers comprise an important approach for light trapping in dye-sensitized solar cells (DSCs) due to their simple fabrication process. The challenge in applying these scatterers lies in finding the optimal dimensions and concentration of the scatterers. This requires many experiments and it is often quite difficult to have a starting point for optimizing the concentration. Based on theories of light propagation in random media, we propose a simple model for DSCs with embedded silica spherical particles. Then, by full-wave optical calculations, we determine a narrow range for the concentration of silica particles that leads to the largest optical absorption in the...