Sharif Digital Repository

We have studied the effect of negative chemical pressure in the RuGd 1.5(Ce 0.5-xPr x)Sr 2Cu 2O 10-δ with Pr content of 0.0 ≤ x ≤ 0.2. This is also investigated using the bond length results obtained from the Rietveld refinement analysis. The c parameter and cell volume increase with x for 0.0 ≤ x ≤ 0.15. The width of the resistivity transition also increases with Pr concentration, indicating higher inhomogeneity and oxygen deficiency. The difference in the ionic valences of Pr 3+,4+ and Ce 4+ causing different hole doping, the difference in the ionic radii, and oxygen stoichiometry affect the superconducting transition. The magnetoresistance shows a cusp around 135 K which lies between the... 

We have compared the electrical and magnetic properties of Ru(Gd 1.5-x Pr x )Ce 0.5Sr 2Cu 2O 10-δ (Pr/Gd samples) with x = 0.0, 0.01, 0.03, 0.033, 0.035, 0.04, 0.05, 0.06, 0.1 and RuGd 1.5(Ce 0.5-x Pr x ) Sr 2 Cu 2O 10-δ (Pr/Ce samples) with x = 0.0, 0.01, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2 prepared by the standard solid-state reaction technique. We obtained the XRD patterns for different samples with various x. The lattice parameters versus x for different substitutions have been obtained from Rietveld analysis. To determine how the magnetic and superconducting properties of these layered cuprate systems can be affected by Pr substitution, the resistivity, and magnetoresistivity, with H ext... 

We have investigated the role of electron-electron correlation in SrRuO 3 and CaRuO 3 bulk structures. At first, the DOS of SrRuO 3 and CaRuO 3 is obtained using the full potential linearized augmented plane wave method by LSDA. We have then calculated the electronic structure, dielectric function, self-energy, and spectral function for the bulk SrRuO 3 and CaRuO 3 by GWA. The shifting of the Ru t 2g orbitals, broadening in Ru valance bands, and also the enhancement in exchange splitting shows better agreement between the GWA many-body correction with the bulk experimental results. But, in spite of the many-body correction, the GWA results is not completely consistent with the PES... 

We have investigated the electronic structure of Sr(Ca)Ru1-xCrxO3 using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr4+-Ru4+ hybridization is responsible for the high Curie temperature TC in SrRu1-xCrxO3, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu1-xCrxO3 clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr-Ru hybridization. The antiferromagnetic coupling of Cr3+ with Ru4+,5+ lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted... 

Local density approximation (LDA) and Green function effective Coulomb (GW) calculations are performed to investigate the effect of electronic correlations on the electronic properties of both graphene and graphane. The size of band gap in graphane increases from 3.7 eV in LDA to 4.9 eV in GW approximation. By calculating maximally localized Wannier wave functions, we evaluate the necessary integrals to get the Hubbard U and the exchange J interaction from first principles for both graphene and graphane. Our ab-initio estimates indicate that in the case of graphene, in addition to the hopping amplitude t ∼ 2.8 eV giving rise to the Dirac nature of low lying excitations, the Hubbard U value... 

We have calculated the electronic structure of SrRu1-xMn xO3 using the full potential linearized augmented plane wave method by LSDA and LSDAU. The antiparallel alignment between the Mn and Ru ions are consistent with the competition between ferromagnetism and antiferromagnetism in the low Mn-doped polycrystalline samples. This is in contrast to the appearance of quantum critical point and FM and AFM transitions in the single crystal measurement. Our results show that the discrepancy between different experimental phase diagrams is related to the conditions of sample preparation and also the difference between the degree of magnetic interactions between the Mn and Ru moments. The DOS and the... 

We have studied the electrical and magnetic properties of RuGd 2-xCexSr2Cu2O10-δ (Ru-1222) with content of Ce = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, prepared by the standard solid-state reaction technique. To determine how the magnetic and superconducting properties of this layered cuprate system can be affected by Ce substitution, the resistivity and magnetoresistivity have been measured at various temperatures. Resistivity curves reveal the presence of four regions for various contents of x. In high temperatures, system is paramagnetic. Magnetic transition from paramagnetic state to antiferromagnetic state occurs at 140 K for x = 0, which varies very slowly with increasing Ce substitution for Gd.... 

In this paper application of Functionally Graded Materials (FGMs) in suspension bridge structures for the purpose of vertical vibration improvement is investigated. Functionally graded materials are inhomogeneous composites, which are usually made from a mixture of metal and ceramic. Initially the classical equation of motion is modified based on the FGM model and natural frequencies of structure are extracted by Galerkin method. The material properties of structure vary continuously in the longitude direction according to power law form. In this regard, combination of materials is structured in such a way that the desired frequencies of the bridge are achieved by designing the proper power... 

Theoretical study of NH3(H2O) n=0,1,2,3 adsorption on (8, 0) carbon nanotube was performed at the X3LYP/6-31G* level of density functional theory (DFT). The tube-NH3 interaction was discussed in the terms of binding energy (EB), coupling energy (EC), charge density, molecular orbitals, and dipole moments. The results reveal that addition of water molecules to tube-NH3 system increases the interaction between tube and ammonia molecule  

Histidine rich protein II derived peptide (HRP II 169-182) was investigated by molecular dynamics, MD, simulation and 17O electric field gradient, EFG, tensor calculations. MD simulation was performed in water at 300 K with α-helix initial structure. It was found that peptide loses its initial α-helix structure rapidly and is converted to random coil and bent secondary structures. To understand how peptide structure affects EFG tensors, initial structure and final conformations resulting from MD simulations were used to calculate 17O EFG tensors of backbone carbonyl oxygens. Calculations were performed using B3LYP method and 6-31 + G* basis set. Calculated 17O EFG tensors were used to... 

Insula is considered an important region of the brain in the generation and maintenance of a wide range of psychiatric symptoms, possibly due to being key in fundamental functions such as interoception and cognition in general. Investigating the possibility of targeting this area using non-invasive brain stimulation techniques can open new possibilities to probe the normal and abnormal functioning of the brain and potentially new treatment protocols to alleviate symptoms of different psychiatric disorders. In the current study, COMETS2, a MATLAB based toolbox was used to simulate the magnitude of the current density and electric field in the brain caused by different transcranial direct... 

Theoretical calculations of structural parameters, 57Fe, 14N and 17O electric field gradient (EFG) tensors for full size-hemin group have been carried out using density functional theory. These calculations are intended to shed light on the difference between the geometry parameters, nuclear quadrupole coupling constants (QCC), and asymmetry parameters (ηQ) found in three spin states of hemin; doublet, quartet and sextet. The optimization results reveal a significant change for propionic groups and porphyrin plane in different spin states. It is found that all principal components of EFG tensor at the iron site are sensitive to electronic and geometry structures. A relationship between the... 

The surface of nanoparticles (NPs) get coated by a wide range of biomolecules, upon exposure to biological fluids. It is now being increasingly accepted that NPs with particular physiochemical properties have a capacity to induce conformational changes to proteins and therefore influence their biological fates, we hypothesized that the gold NP’s metal surface may also be involved in the observed Fg unfolding and inflammatory response. To mechanistically test this hypothesis, we probed the interaction of Fg with gold surfaces using molecular dynamic simulation (MD) and revealed that the gold surface has a capacity to induce Fg conformational changes in favor of inflammation response. As the... 

Four 5-, 10-, 20- and 30-story moment frames, representing low-, mid-, and two high-rise structures, were subjected to a great number of idealized directivity pulses. The amplitudes and periods of pulses vary from 0.02 g to 1.0 g and 0.5 to 12 sec, respectively. Over 1400 nonlinear dynamic analyses of low- to high-rise moment frames were performed which were feasible through using modified fish-bone model. The distribution of interstory drift along the height was studied and two applied contours were proposed: (i) the maximum interstory drift contour, and (ii) the critical story contour. These contours were demonstrated versus the ratio of natural period of the structure to the pulse period... 

In this article singular points of a parallel manipulator are obtained based on a novel geometrical method. Here we introduce the constrained plain method (CPM) and some of its application in parallel mechanism. Given the definition of constraint plane (CP) and infinite constraint plane (ICP) the dependency conditions of constraints is achieved with the use of a new theorem based on the Ceva geometrical theorem. The direction of angular velocity of a body is achieved by having three ICPs with the use of another theorem. Finally, with the use of the above two novel theorems singularities of the 3UPF_PU mechanism are obtained. It should be emphasized that this method is completely geometrical,... 

An analytical model is proposed to study the effect of particle size on melting enthalpy and entropy of metallic nanoparticles (NPs). The Mott's and Regel's equations for melting entropy in the combination of core average coordination number (CAC) and surface average coordination number (SAC) of freestanding NPs are considered. Clusters of icosahedral (IC), body centered cubic (BCC), and body centered tetragonal (BCT) structure without any vacancies and defects are modeled. Using the variable coordination number made this model to be in good agreement with experimental and molecular dynamic (MD) results of different crystal structures. The model predicts melting entropy and enthalpy of...