Sharif Digital Repository

Three dimensional calculation of control dynamics for finding the optimized laser filed is formulated using an iterative method and time-dependent density functional approach. An appropriate laser pulse is designed to control the desired products in the dissociation of methane molecule. The tailored laser pulse profile, eigenstate distributions and evolution of the efficient occupation numbers are predicted and exact energy levels of this five-atomic molecule is obtained. Dissociation rates of up to 78%, 80%, 90%, and 82% for CH2 +, CH+, C+ and C++ are achieved. Based on the present approach one can reduce the controlling costs. © 2016 Elsevier B.V  

Three magneto-plasmonic nanohybrids were synthesized using Au- and Ag-coated Fe3O4 nanoparticles (NPs)-modified dual pH- and temperature-responsive triblock copolymer of poly (butyl methacrylate-co-acrylamide-co-methacrylic acid) to serve as drug carriers with potential of using in both photothermal and controlled/targeted chemotherapies. The internal superparamagnetic core gives the carriers targeted-delivery characteristics, and surface plasmon resonance–based noble metallic Au/Ag shells give them on-demand photothermal and photo-triggering release properties. To investigate the effect of coating method on the targeting property of synthesized carriers, Au NPs were attached to the magnetic... 

The main effects of liquid compressibility on the dynamics of single bubble sonoluminescence are investigated via three different radial dynamics models. In order to precise description of the interior gas thermodynamics, a hydrochemical model is used. In the case of an argon gas bubble in water, the results obtained with the Gilmore model and the Lezzi and Prosperetti model are compared with those resulting from the Keller and Miksis model. It is shown that the variation of liquid density at bubble surface in a very short time interval around the end of the bubble collapse, which has been incorporated into the first two models, strongly influences the bubble cavitation dynamics at higher... 

The effects of liquid density variation at the bubble surface on the dynamics of a single acoustic cavitation bubble are numerically studied. The Gilmore model together with a comprehensive hydrochemical model is used. The evaporation and condensation of water vapor are included in the hydrochemical model. The simulation results are compared to those resulting from the widely known Keller-Miksis model, which assumes a constant liquid density at the bubble surface. The numerical results for a single argon bubble in water reveal that the pressure and the temperature inside the bubble in collapse phase significantly increase, when the non-constant liquid density is used. These differences... 

In this work, the 3D proton dose profile is calculated in a homogenous water phantom using a Monte Carlo application developed with the Geant4 toolkit. The effect of the ridge filter material (for SOBP widths of 6, 9 and 12 cm) on the homogeneity of the dose distribution, secondary neutron production and beam efficiency are investigated in a single ring wobbling irradiation system. The energy spectrum of secondary neutrons per primary proton at various locations around the phantom surface is calculated. The simulation revealed that most of the produced neutrons are released at slight angles which enable them to reach the patient and consequently to be hazardous. Also, the homogeneity of the... 

Abstract The effect of the produced light flashes from sonoluminescence (SL) on the fat tissue and water is studied. By using KZK equation as an essential equation for calculating the thermal source in bio-liquids, the effective bubble parameters in quasi-adiabatic model are calculated and compared in these systems. It is noticed that the temperature and the intensity for fat tissue are about 30% and 38% less than the ones for water respectively. These results are almost in good agreement with the only experimental measurement denoting less SL temperature in bio-liquids which present more suitable condition for using SL in such applications  

(GraphPresented) The quantum optimal control theory in conjunction with time dependent density functional theory is used to optimize the laser pulse shape for dissociation of nitrogen molecule. For several initial peak intensities and frequency ranges, the optimum shapes are produced and compared to determine the most efficient pulse. Ehrenfest molecular dynamics model is also used to test the dissociation process. The corresponding snapshots of density and time dependent electron localization function are presented. It is noticed that when the frequency ranges of laser pulses are doubled, it leads to 60% faster dissociation of N2 molecule  

The effect of strong femto-second laser pulses on the dissociation probability of methane has been investigated analytically in various arrangements. The ellipticity dependence of the dissociation probability at intensities from 1014 W cm-2 to 1016 W cm-2 for Ti:Sapphire laser is presented. A reliable calculation of the dissociation probability based on 3D time-dependent Schrodinger equation with an improved model of time-dependent density-functional theory is presented. These calculations are carried out for three different cases of elliptically polarized laser pulse, optimum convolution of dual short pulses, and two-color mixed nonresonant laser pulses. It is found that the rescattering... 

High order harmonic generation is investigated for N2 and CO molecules under ten-cycle sin-squared laser pulse at 800 nm wavelength and I = 2 × 1014 W cm−2 intensity. In order to study effects of the asymptotic behavior of the exchange-correlation (XC) potentials, the time-dependent Kohn-Sham equations are numerically solved in the non-linear non-perturbative regime with four different XC potentials. Time-dependent electron localization function is used to get imaging on the temporal dependence of the electron density. Time-profile analysis was also utilized for studying long and short electron trajectories. It is found that the ionization energy values both molecules calculated by using... 

Effect of nanosecond lasers on the methane dissociation is experimentally studied by using three different laser wavelengths at 248 nm, 355 nm and 532 nm. C2H2 generation is measured as a major reaction product in experiments and the energy consumptions in production of this component are measured as 5.8 MJ/mol, 3.1 MJ/mol and 69.0 MJ/mol, for 355 nm, 532 nm and 248 nm wavelengths, respectively. The mechanism of conversion and production of new stable hydrocarbons is also theoretically investigated. It is found that in theoretical calculations, the ion-molecule reactions should be included and this leads to a unique approach in proper explanation of the experimental measurements  

Effect of thermal conduction on radiation from a single cavitating bubble has been studied in a hydrochemical framework including variation of heat conductivity of noble gases up to 2500 K. Results of numerical simulation show that thermal conductivity plays an important role in determining ultimate cavitation temperature. Higher thermal conductivity of lighter noble gases causes to more thermal dissipation during the bubble collapse, leading to a lower peak temperature. Moreover, at the same driving conditions, radius of light emitting region is greater for heavier noble bubbles. Therefore, sonoluminescence radiation is more intensive from heavier noble gases. Phase diagrams of... 

Propagation of Gaussian X-ray laser beam is presented in collisional quantum plasma and the beam width oscillation is studied along the propagation direction. It is noticed that due to energy absorption in collisional plasma, the laser energy drops to an amount less than the critical value of the self-focusing effect and consequently, the laser beam defocuses. It is found that the oscillation amplitude of the laser spot size enhances while passing through collisional plasma. For the greater values of collision frequency, the beam width oscillates with higher amplitude and defocuses in a shallower plasma depth. Also, it is realized that in a dense plasma environment, the laser self-focusing... 

Propagation of a Gaussian x-ray laser beam has been analyzed in collisionless thermal quantum plasma with considering a ramped density profile. In this density profile due to the increase in the plasma density, an earlier and stronger self-focusing effect is noticed where the beam width oscillates with higher frequency and less amplitude. Moreover, the effect of the density profile slope and the initial plasma density on the laser propagation has been studied. It is found that, by increasing the initial density and the ramp slope, the laser beam focuses faster with less oscillation amplitude, smaller laser spot size and more oscillations. Furthermore, a comparison is made among the laser... 

Excitation and propagation of the surface polaritonic rogue waves and breathers are investigated by proposing a coupler free optical waveguide that consists of a transparent layer, middle negative index metamaterial layer, and bottom layer of the cold four level atomic medium. In this planar optical waveguide, a giant controllable Kerr nonlinearity is achieved by sufficient field concentration and a proper set of intensities and detunings of the driven laser fields. As a result, various kinds of temporal surface polaritonic solitons, rogue waves, and breathers can be propagated in the narrow window for electromagnetically induced transparency. We find that the giant intensity and extreme... 

The fragmentation dynamics of CH4 and H2CO molecules have been studied with ultra-short pulses at laser intensityof up to 1015Wcm-2. Three dimensional molecular dynamics calculations for finding the optimized laser pulses are presented based on time-dependent density functional theory and quantum optimal control theory. A comparison of the results for orientation dependence in the ionization process shows that the electron distribution for CH4 is more isotropic than H2CO molecule. Total conversion yields of up to 70% at an orientation angle of 30o for CH4 and 65% at 900 for H2CO are achieved which lead to enhancement of dissociation probability  

The interaction of the sub-picosecond UV laser in sub-relativistic intensities with deuterium is investigated. At high plasma temperatures, based on the quantum correction in the collision frequency, the electron heating and the ion block generation in plasma are studied. It is found that due to the quantum correction, the electron heating increases considerably and the electron temperature uniformly reaches up to the maximum value of 4.91-×-107-K. Considering the quantum correction, the electron temperature at the laser initial coupling stage is improved more than 66.55% of the amount achieved in the classical model. As a consequence, by the modified collision frequency, the ion block is... 

In this study, high harmonic generation from a multi-atomic nitrous oxide molecule was investigated. A comprehensive three-dimensional calculation of the molecular dynamics and electron trajectories through an accurate time-dependent density functional theory was conducted to efficiently explore a broad harmonic plateau. The effects of multi-electron and inner orbitals on the harmonic spectrum and generated coherent attosecond pulses were analyzed. The role of the valence electrons in controlling the process and extending the harmonic plateau was investigated. The main issue of producing a super-continuum harmonic spectrum via a frequency shift was considered. The time-frequency... 

The effect of pulse shaping on the intense laser-driven proton beam produced through radiation pressure acceleration as a highly efficient mechanism is investigated. In this regard, the interaction of pulses with modified frequencies, including positive and negative chirped pulses with plasma, is simulated using particle-in-cell code. The simulation results indicate that the proton acceleration could be significantly enhanced for both negative and positive chirped pulses. As a consequence of the acceleration time extension as well as the electron heating suppression, a sharper and narrower proton beam could be achieved for negative chirped pulses. The same trend is observed for all negative... 

Shear stress effect has been often neglected in calculation of the Weibel instability growth rate in laser-plasma interactions. In the present work, the role of the shear stress in the Weibel instability growth rate in the dense plasma with density gradient is explored. By increasing the density gradient, the shear stress threshold is increasing and the range of the propagation angles of growing modes is limited. Therefore, by increasing steps of the density gradient plasma near the relativistic electron beam-emitting region, the Weibel instability occurs at a higher stress flow. Calculations show that the minimum value of the stress rate threshold for linear polarization is greater than... 

In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a...