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Marsusi F.,Organic Solar Cell Research Group | Marsusi F.,Amirkabir University of Technology | Sabbaghzadeh J.,National Center for Laser Science and Technology | Drummond N.D.,Lancaster University
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We compute the absorption and emission energies and hence Stokes shifts of small diamondoids as a function of size using different theoretical approaches, including density-functional theory (DFT) and quantum Monte Carlo (QMC) calculations. The absorption spectra of these molecules are also investigated by time-dependent DFT and compared with experiment. We analyze the structural distortion and formation of a self-trapped exciton in the excited state, and we study the effects of these on the Stokes shift as a function of size. Compared to recent experiments, QMC overestimates the excitation energies by about 0.8(1) eV on average. Benefiting from a cancellation of errors, the optical gaps obtained in DFT calculations with the B3LYP functional are in better agreement with experiment. It is also shown that time-dependent B3LYP calculations can reproduce most of the features found in the experimental spectra. According to our calculations, the structures of diamondoids in the excited state show a distortion which is hardly noticeable compared to that found for methane. As the number of diamond cages is increased, the distortion mechanism abruptly changes character. We have shown that the Stokes shift is size dependent and decreases with the number of diamond cages. If we neglect orbital symmetry effects on the optical excitations, the rate of decrease in the Stokes shift is, on average, 0.1 eV per cage for small diamondoids. © 2011 American Physical Society. Source


Marsusi F.,Organic Solar Cell Research Group | Marsusi F.,Amirkabir University of Technology | Sabbaghzadeh J.,National Center for Laser Science and Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We have developed a theory of charge transport in a system of noninteracting polarons. The theory is conducted to a compact relation through a nonperturbative method based on electron-phonon Hamiltonian. The derived final result represents two different limits of band and phonon-assisted transport, which depends on temperature and electron-phonon coupling strength. © 2012 American Physical Society. Source


Tadjarodi A.,Iran University of Science and Technology | Zabihi F.,Iran University of Science and Technology | Zabihi F.,National Center for Laser Science and Technology
Materials Research Bulletin | Year: 2013

In the present study, the mesoporous structure of silica (mSiO2) nanoparticles as well as hemiaminal grafted mSiO2 decorated by metallic silver (Ag/mSiO2) has been used for the preparation of glycerol based nanofluids. Structural and morphological characterization of the synthesized products have been carried out using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), UV-vis spectroscopy, inductively coupled plasma (ICP) and N2 adsorption-desorption isotherms. The thermal conductivity and viscosity of the nanofluids have been measured as a function of temperature for various weight fractions and silver concentrations of mSiO2 and Ag/mSiO2 nanoparticles, respectively. The results show that the thermal conductivity of the nanofluids increase up to 9.24% as the weight fraction of mSiO2 increases up to 4 wt%. Also, increasing the percent of the silver decorated mSiO2 (Ag/mSiO2) up to 2.98% caused an enhancement in the thermal conductivity of the base fluid up to 10.95%. Furthermore, the results show that the nanofluids have Newtonian behavior in the tested temperature range for various concentrations of nanoparticles. © 2013 Elsevier Ltd. All rights reserved. Source


Gavili A.,National Center for Laser Science and Technology | Isfahani T.D.,National Center for Laser Science and Technology | Sabbaghzadeh J.,National Center for Laser Science and Technology
International Journal for Numerical Methods in Fluids | Year: 2012

The behavior of nanofluids containing cylindrical nanoparticles are investigated numerically inside a two-sided lid-driven differentially heated square cavity to gain insight into the convective recirculation and flow processes induced by a nanofluid. The physical properties of the base fluid such as viscosity, thermal conductivity and thermal expansion coefficient are, respectively, assumed to be temperature independent (taking the mean temperature of the left and right walls) and temperature dependent. A model is developed to analyze the behavior of nanofluids taking into account the nanoparticle volume fraction whereas the transport equations are solved numerically with finite volume approach using SIMPLEC algorithm. The left and right moving walls are maintained at different constant temperatures while the upper and bottom walls are thermally insulated. The directions of the moving walls were considered in a way that the force and natural convections aid each other. The governing parameter Richardson number was 0.1 Source


Tadjarodi A.,Iran University of Science and Technology | Zabihi F.,Iran University of Science and Technology | Zabihi F.,National Center for Laser Science and Technology | Afshar S.,Iran University of Science and Technology
Ceramics International | Year: 2013

This paper presents an experimental investigation of thermophysical properties of platelet mesoporous SBA-15 particles dispersed in 60:40 (v/v) ethylene glycol:water mixture. The effect of weight fraction of particles and temperature is studied on density, viscosity and thermal conductivity of nanofluids. The maximum measured thermal conductivity enhancement reaches up to 22% for the nanofluids containing 5 wt% of SBA-15 at 60° C. The SBA-15 nanofluids show Newtonian behavior in the tested temperature range. Also, the relative density increases between 0.4% and 2.2% when the weight percent of the nanoparticles varies between 1 and 5 at 60° C. Structural and morphological characterization of synthesized SBA-15 have been carried out using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and N2 adsorption-desorption isotherms methods. © 2013 Elsevier Ltd and Techna Group S.r.l. Source

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