Sharif Digital Repository

Compound 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione(3), was prepared and fully characterized. The vibrational modes (FT-IR) and NMR data ( 1H and 13C chemical shifts) were compared with the results of Density Functional Theory (DFT) method at the B3LYP/cc-PVTZ level. The calculated vibrational frequencies and NMR chemical shifts are in good agreement with the experimental results. The electronic (UV-Vis) spectrum was calculated using the TD-DFT method in CH2Cl2 with the Polarizable Continuum Model using the integral equation formalism variant (IEFPCM) and was correlated to the experimental spectra. The assignment and analysis of the frontier HOMO and LUMO orbitals indicate that... 

Like-charge ion pairing is commonly observed in protein structures and plays a significant role in biochemical processes. Density functional calculations combined with the conductor-like polarizable continuum model were employed to study the formation possibilities of doubly charged noncovalently linked complexes of a series of model compounds and amino acids in the gas phase and in solution. Hydrogen bond interactions were found to offset the Coulombic repulsion such that cation-cation clusters are minima on the potential energy surfaces and neither counterions nor solvent molecules are needed to hold them together. In the gas phase the dissociation energies are exothermic, and the... 

By utilizing the fourth-, sixth-, eighth-, and tenth-order elastic moduli tensors of graphene a highly nonlinear constitutive model for it is proposed. Subsequently, an accurate analytical formulation, describing the entire tensile behavior of single-walled carbon nanotubes (SWCNTs) from their initial unloaded states through their ideal strengths, is made possible. The angle of twist which is a critical parameter that varies with the tensile loading is also calculated within the current framework. The estimated value of the theoretical strength of SWCNTs with different chiralities and radii as well as that of graphene ranges from 0.39 to 0.44 TPa. Some peculiarities associated with chirality... 

The reaction pathway (including the transition state) of ethylene addition to permanganate (MnO4-) in the presence of ethylene glycol (EG) has been qualitatively and quantitatively studied by means of B3LYP/6-311++G* theoretical analysis. Interestingly, by cluster formation of the EG with permanganate, oxidation reaction becomes thermodynamically and kinetically more favorable. The influences of electron-withdrawing as well as electron-donating substituents were also explored. Results of the quantum theory of atoms in molecules and natural bond orbital analyses revealed that [3 + 2] addition reaction of alkenes in the presence of EG as hydrogen bonding donor to MnO4- becomes more exothermic.... 

The van der Walls interaction between a carbon nanotube sheet (CNTS) and a rare gas atom, is studied using both atomistic and continuum approaches. We present analytical expressions for the van der Waals energy of continuous nanotubes interacting with a rare gas atom. It is found that the continuum approach does not properly treat the effect of atomistic configurations on the energy surfaces. The energy barriers are small as compared to the thermal energy, which implies the free motion above the CNTS in heights about one nanometer. In contrast to the energy surface of a graphene sheet, the honeycomb lattice structure in the energy surface of a CNTS is imperceivable. Defects alter the energy... 

Carbon nanotubes (CNTs) are viewed as rolled graphene. Thus, an appropriate formulation describing the behavior of CNTs must contain the key information about both their initial configuration as graphene and final configuration as CNT.On this note, to date, somemodels, in particular based on the Cauchy- Born rule, for the description of CNTs behavior exist. A simplifying assumption in some of these models is that the length and perimeter of the CNT equal the corresponding dimensions of the unrolled initial configuration, thus neglecting the induced hoop and longitudinal strains. On the other hand, the present work offers a purely nonlinear continuum model suitable for the description of the... 

In the present paper, a numerical model is developed based on a combination of the extended finite element method and an equivalent continuum model to simulate the two-phase fluid flow through fractured porous media containing fractures with multiple length scales. The governing equations involve the linear momentum balance equation and the flow continuity equation for each fluid phase. The extended finite element method allows for an explicit and accurate representation of cracks by enriching the standard finite element approximation of the field variables with appropriate enrichment functions, and captures the mass transfer between the fracture and the matrix. Due to the high computational... 

In this paper, a micro-polar continuum model is presented based on the Cosserat theory for 3D modeling of localization phenomena. Since the classical continuum model suffers from the pathological mesh-dependence in strain localization problem, the governing equations are regularized by adding the rotational degrees-of-freedom to conventional degrees-of-freedom. The fundamental relations in three-dimensional Cosserat continuum are presented and the internal length parameters are introduced in the elasto-plastic constitutive matrix to control the shear bandwidth. The mesh independency of Cosserat model in strain-softening problem is verified and the effect of internal parameters is... 

Corrosion inhibition properties of some heterocyclic compounds (3-mercapto 1,2,4 triazole, benzotriazole, thiophene, and tetra hydro-thiophene) in Cu/H3PO4 medium were investigated theoretically and experimentally via cluster/polarized continuum and gravimetric approaches. Second-order Møller-Plesset perturbation and density functional theories were applied, and the electronic chemical potential, molecular softness, and extent of charge transfer were determined for inhibitor molecules at the metal/solution interface. Good correlations were observed for both theories between the calculated quantities and experimental data. To reveal the quality of metal-inhibitor interactions, comprehensive... 

Asphalt concrete is a heterogeneous and multi-phase material that consists of aggregates, asphalt binder, and pores. These components create a complex microstructure. There is no consensus on how to quantify the microstructure and the required parameters from two-dimensional images. The load transfer can be managed by aggregate-aggregate or aggregate-mastic interactions that depend on the gradation, aggregate internal structure, and asphalt binder viscoelastic properties. The most important internal structure indices affecting the behavior of HMA are aggregate orientation, contact orientation, contact length, and number of contact points. In this paper, the influence of aggregate structure... 

In this study, we apply a novel numerical technique for modeling the propagation of mechanical wave in the human arteries using the multiscale method. We define a particle region characterized by molecular dynamics (MD) method which is surrounded by a continuous region characterized by a finite element (FE) method. The interface between the two models are defined so as to minimize spurious reflections at the interface. This is a preliminary work for the modeling of the mechanical stability of atherosclerosis plaques using multiscale method. The model offered has extensive application in cell mechanics  

Diversion in heterogeneous carbonate reservoirs plays the most important role to the success of acidizing. Without the use of diversion, more acid preferentially flows into the high-permeability region and leaves the low-permeability region underreacted. But a clear understanding of diverting agents, such as polymer-based in-situ-gelled acids, can help uniformly stimulate the near-wellbore region. In this paper, we correct the rheological model that was developed by Ratnakar et al. (2013) according to experimental data from Gomaa and Nasr-El-Din (2010b) by considering shear-rate effect in a two-scale continuum model. It is found that the rheology parameters and shear rate are influential... 

The structural and conformational behavior of gemcitabine (20; 20-diuoro cytidine) was investigated by advanced NMR experiments and a computational quantum mechanical method (DFT) using Potential Energy Scanning (PES) in gas and solution phases in the Polarizable Continuum Model (PCM). Three stable conformers (G1, G2, and G3) were predicted from minimum points in a potential energy diagram. In order to measure coupling constant values, a set of 2D spectra (H-H COSY, H-C HMQC, and H-C HMBC) was analyzed. Optimized structures and spin-spin coupling constant calculations in gas and solution phases were performed by B3LYP/6-311++G(d,p) method. Both energy and NMR parameters showed that G1-form... 

The Cauchy-Born hypothesis has been used to concurrently bridge atomistic information to continuum model. It has been a prevalent assumption in computational nano-mechanics during the past decade. This kinematic assumption relates the deformation of the continuum to the deformation of its underlying crystalline structure. The main objective of this paper is to investigate the validity of this hypothesis by means of direct atomistic simulations and the continuum mechanic calculations. In fact, we intend to determine under which strain or stress state the crystalline structure undergoes inhomogeneous deformation due to a small perturbation of the homogeneously deformed system. Two failure... 

The Calcium ion Ca2+ plays a critical role as an initiator and preserving agent of the cross-bridge cycle in the force generation of skeletal muscle. A new multi-scale chemo-mechanical model is presented in order to analyze the role of Ca2+ in muscle fatigue and to predict fatigue behavior. To this end, a cross-bridge kinematic model was incorporated in a continuum based mechanical model, considering a thermodynamic compatible framework. The contractile velocity and the generated active force were directly related to the force-bearing states that were considered for the cross-bridge cycle. In order to determine the values of the model parameters, the output results of an isometric simulation... 

In present paper the theory of the micropolar fluid based on a Cosserat continuum model has been applied for analysis of Couette flow and turbulent flow through rough pipes. The obtained results for the velocity field have been compared with known results from experiments done by Reichardt at Max Plank institute for fluids in Gottingen [1,2] and analytical solution of the problem from Gradient theory by alizadeh[3] for couette problem and with known results from experiments done by Nikuradse (1932).the boundary condition used here was the no slip one and Trostel's slip boundary condition[4].a good agreement between experimental results and the results of the problem for Reynolds near 18000...