Sharif Digital Repository

This letter adopts an atomistic modeling approach to study free vibrational characteristics of C60, C70, and C80 fullerenes. In this regard, we use the molecular structural mechanics consisting of equivalent structural beams to calculate the nonzero natural frequencies. The simulation results indicate that the first natural frequency of the fullerene is in the order terahertz and decreases nonlinearly with respect to the number of the carbon atoms  

Reliability assessment of phonemes, syllabi, words, concepts or utterances has become the key feature of Automatic Speech Recognition (ASR) engines in order to make a decision to accept or reject a hypothesis. In this paper, we propose utterance-level confidence annotation based on combination of features extracted from multiple knowledge sources in Persian language. The experiment was conducted first to examine the performance of individual features, then to combine them using statistical data analysis and density estimation methods to assign a confidence score to utterances. Using the data collected from a Persian spoken dialogue system, we show that combining features from independent... 

A finite element technique is used to mimic radial deformation of single-walled carbon nanotubes under hydrostatic pressure. The elastic deformation of nanotubes is modeled via elastic beams. Properties of the beam element are evaluated by considering characteristics of the covalent bonds between the carbon atoms in a hexagonal lattice. Applying the beam model in a three dimensional space, the elastic properties of the nanotube in the transverse direction are evaluated. The effects of diameter and wall thickness on the radial and circumferential elastic moduli of zigzag and armchair nanotubes are considered. Results are in good agreement with molecular structural mechanics data in the... 

Vibrational analysis of single-walled carbon nanotubes (SWCNTs) is performed using a finite element method (FEM). To this end, the vibrational behavior of bridge and cantilever SWCNTs with different side lengths and diameters is modeled by three-dimensional elastic beams and point masses. The beam element elastic properties are calculated by considering mechanical characteristics of the covalent bonds between the carbon atoms in the hexagonal lattice. The mass of each beam element is assumed as point masses at nodes coinciding with the carbon atoms. Implementing the atomistic simulation approach, the natural frequencies of zigzag and armchair SWCNTs are computed. It is observed that the... 

A molecular structural mechanics method has been implemented to investigate the vibrational behavior of single-layered graphene sheets. By adopting this approach, mode shapes and natural frequencies are obtained. Vibrational analysis is performed with different chirality and boundary conditions. Numerical results from the atomistic modeling are employed to develop predictive equations via a statistical nonlinear regression model. With the proposed equations, fundamental frequencies of single-layered graphene sheets with considered boundary conditions can be predicted within 3% difference with respect to the atomistic simulation. © IOP Publishing Ltd  

Molecular structural mechanics is implemented to model vibrational behavior of defect free single-layered graphene sheets (SLGSs) at constant temperature. To mimic these two-dimensional layers, zigzag and armchair models with cantilever and bridge boundary conditions are adopted. Fundamental frequencies of these nano structures are calculated, and it is perceived that they are independent of the chirality and aspect ratio. Effects of point mass and atomistic dust on the fundamental frequencies are also considered in order to investigate the possibility of using SLGSs as sensors. Results of exhibit the principle frequencies are highly sensitive to the added mass in the order of 10-6fg.... 

Molecular structural mechanics approach is implemented to investigate vibrational behavior of single-layered graphene sheets. By using the atomistic modeling, mode shapes and natural frequencies are obtained. Vibration analysis is performed under different chirality and boundary conditions. Numerical results from the finite element technique are applied to develop empirical equations via a statistical multiple non-linear regression model. With the proposed empirical equations, fundamental frequencies of single-layered graphene sheets under considered boundary conditions can be predicted within 3 percent accuracy. Copyright © 2007 by ASME  

Finite element (FE) method is used to model radial deformation of single-walled carbon nanotube (SWCNT) under hydrostatic pressure. Elastic deformation of the nanostructure is simulated via elastic beams. Properties of the beam element are calculated by considering the stiffness of the covalent bonds between the carbon atoms in the hexagonal lattice. By applying the beam elements in a three-dimensional space, elastic properties of the SWCNT in transverse direction are obtained. In this regard, influences of diameter and tube wall thickness on the radial and circumferential elastic moduli of zigzag and armchair SWCNTs are considered. It is observed that there is a good agreement between the... 

Molecular structural mechanics is implemented to investigate the vibrational characteristics of defect-free single-layered graphene sheets (SLGSs), which have potential applications as strain sensors. The effect of strain on the fundamental frequencies of the defect-free zigzag and armchair models with clamped-clamped boundary condition is studied. The atomistic modeling results reveal while sensitivities of the strain sensors are not influenced significantly by chirality, they can be slightly increased by decreasing aspect ratios of the sheets. It is further shown that the SLGSs-based strain sensors are more sensitive to the applied stretch than the SWCNTs versions. © 2008 Elsevier Ltd. All... 

Molecular structural mechanics is implemented to model the vibrational behavior of defect-free single-layered graphene sheets (SLGSs) at constant temperature. To mimic these two-dimensional layers, zigzag and armchair models with cantilever and bridge boundary conditions are adopted. Fundamental frequencies of these nanostructures are calculated, and it is perceived that they are independent of the chirality and aspect ratio. The effects of point mass and atomistic dust on the fundamental frequencies are also considered in order to investigate the possibility of using SLGSs as sensors. The results show that the principal frequencies are highly sensitive to an added mass of the order of 1 0-... 

Molecular structural mechanics approach is implemented to investigate vibrational behavior of single-layered graphene sheets. By using the atomistic modeling, mode shapes and natural frequencies are obtained. Vibration analysis is performed under different chirality and boundary conditions. Numerical results from the finite element technique are applied to develop empirical equations via a statistical multiple nonlinear regression model. With the proposed empirical equations, fundamental frequencies of single-layered graphene sheets under considered boundary conditions can be predicted within 3 percent accuracy. Copyright © 2007 by ASME  

Molecular structural mechanics is implemented to model vibrational behavior of defect free single-layered graphene sheets (SLGSs) at constant temperature. To mimic these two-dimensional layers, zigzag and armchair models with cantilever and bridge boundary conditions are adopted. Fundamental frequencies of these nano structures are calculated, and it is perceived that they are independent of the chirality and aspect ratio. Effects of point mass and atomistic dust on the fundamental frequencies are also considered in order to investigate the possibility of using SLGSs as sensors. Results of exhibit the principle frequencies are highly sensitive to the added mass in the order of 10-6 fg.... 

The finite element method has been used to predict the stress intensity factors for cracked annular discs under constant central torque. Linear elastic fracture mechanics finite element analyses have been performed and the results are demonstrated in the form of crack configuration factors. To this end, the extensive ranges of crack configuration factors have been employed while considering the effect of disc stiffness. Then, the finite element results are applied to develop equivalent prediction equations using a statistical multiple nonlinear regression model. The accuracy of this model is measured using a multiple coefficient of determination, R2, where 0 ≤R2 ≤1. This coefficient is found... 

Finite element method has been implemented to predict stress intensity factors (SIFs) for radial cracks in annular discs under constant angular velocity. Effects of internal and external uniform pressure on the SIFs have also been considered. Linear elastic fracture mechanics finite element analyses have been performed and results are presented in the form of crack configuration factors for a wide range of components and crack geometry parameters. These parameters are chosen to be representative of typical practical situations. The extensive range of crack configuration factors obtained from the analyses is then used to develop equivalent prediction equations via a statistical multiple...