Sharif Digital Repository

The magnetoresistance measurements of single phase polycrystalline Gd(Ba2-xPrx)Cu3O7+δ and (Gd1-xPrx)Ba2Cu3O7-δ samples have been compared and analyzed by the Ambegaokar and Halperin phase slip model. The derived power law dependences of pinning energy to applied magnetic field and temperature have been studied for different amounts of Pr doping. The power factors depend on the Pr doping. Moreover, in both systems, the magnetic field dependence of the pinning energy power factor increases for small amounts of Pr doping, while for larger amount of Pr doping, it decreases. The derived critical magnetic field at zero temperature limit is in good agreement with other model-based and... 

Investigation of nanomachine swarm motion is useful in the design of molecular transportation systems as well as in understanding the assembly process on the surface. Here, we evaluate the motion of the clusters of nanocars on graphene surfaces, using molecular dynamics (MD) simulations. The mechanism of motion of single nanocars is evaluated by considering the rotation of the wheels, direction of the nanocars’ speed and comparing the characteristics of the surface motion of nanocars and similar absorbed molecules. The mentioned analyses reveal that, in the thermally activated surface motion of the nanocars, sliding movements are the dominant mode of motion. A coarse grained (CG) model is... 

In this paper, employing a thermomechanical small strain constitutive model for shape memory polymers (SMP), a beam element made of SMPs is presented based on the kinematic assumptions of Timoshenko beam theory. Considering the low stiffness of SMPs, the necessity for developing a Timoshenko beam element becomes more prominent. This is due to the fact that relatively thicker beams are required in the design procedure of smart structures. Furthermore, in the design and optimization process of these structures which involves a large number of simulations, we cannot rely only on the time consuming 3D finite element analyses. In order to properly validate the developed formulations, the numeric... 

In this study, we designed, engineered and investigated two new thermally activated delayed fluorescence (TADF) dyes obtained from D–A–D′ type, consisted of 2-(9H-carbazol-9-yl)-3-(3-methoxy-9H-carbazol-9-yl)-9H-xanthen and 2-(3,6-di-tert-butyl-9H-carbazol-9-yl)-3-(3-methoxy -9H-carbazol-9-yl)-9H-xanthen. In these dyes, xanthen derivative and carbazole derivatives have played important roles as an acceptor and two unsymmetrical donor units. In addition, the photophysical properties of these dyes were evaluated by the UV–VIS absorption, photoluminescence spectroscopy and photoluminescence decay lifetime analysis in solution, initial dye, non-doped and doped solid state (neat–film) at... 

The rotational and translational motions of nanocars and nanotrucks as well as their motion regimes at different temperatures are investigated. In recent years, few similar types of molecular machines have been simulated. In contrast to previous studies, which have used the Rigid-Body Molecular Dynamics (RBMD) method, an all-atom model and classic atomistic dynamics have been employed in this paper to achieve better accuracy. Our results demonstrated that the exibility of the chassis and its attachment to the gold surface played an important role in the motion of a nanocar. In fact, a heavier and more exible nanocar chassis reduces its speed compared to a nanotruck. In addition, the results... 

We present near-field photothermal heating capability of an aperture SNOM probe by exploiting a bowtie nanostructure on top of the probe aperture, which operates as a nanosource of heat to activate underlying nanoparticle. Heat generation density calculated for the bowtie nanostructure at its absorption resonance wavelength of 694 nm verifies efficient concentration of heating power at the bowtie tips, due to optical near-field effects. Total absorbed power for the nanodisk beneath the probe has the same resonance wavelength at 694 nm, which confirms that the temperature increase produced at the underneath nanoparticle is due to utilizing the bowtie nanostructure on top of the SNOM probe as... 

Compression test was used to study the deformation behaviour of sintered (12% porosity) and powder extruded (1% porosity) Al6061 alloy at high temperatures ranging from 350 to 500°C. The flow curves of the materials were determined at strain rates of 0.001, 0.01 and 0.1 s-1. The extruded alloy exhibited plastic instability in the form of bulging and formation of shear bands. The deformation activation energy of the extruded material was determined to be QI=77±16 kJ mol-1 (T<450°C) and OII=136±12 kJ mol-1 (T≥450°C). The values of activation energy and appearance of strain softening in the stress-strain curves revealed that thermally activated restoration processes, i.e. dynamic recovery and...