Sharif Digital Repository

Continuum-based modeling of nanostructures is an efficient and suitable method to study the behavior of these structures when the deformation can be considered homogeneous. This paper is concerned about multiscale nonlinear tensorial constitutive modeling of carbon nanostructures based on the interatomic potentials. The proposed constitutive model is a tensorial equation relating the second Piola-Kirchhoff stress tensor to Green-Lagrange strain tensor. For carbon nanotubes, some modifications are made on the planar representative volume element (RVE) to account for the curved atomic structure resulting a non-planar RVE. Using the proposed constitutive model, the elastic behavior of the... 

We have used a hierarchical multiscale modeling scheme for the analysis of cortical bone considering it as a nanocomposite. This scheme consists of definition of two boundary value problems, one for macroscale, and another for microscale. The coupling between these scales is done by using the homogenization technique. At every material point in which the constitutive model is needed, a microscale boundary value problem is defined using a macroscopic kinematical quantity and solved. Using the described scheme, we have studied elastic properties of cortical bone considering its nanoscale microstructural constituents with various mineral volume fractions. Since the microstructure of bone... 

A finite element-based hierarchical multiscale modeling scheme is presented and used for the analysis of nanotube-reinforced polymer composites. The scheme presented here consists of micro- and macroscale boundary value problems linked together using a computational homogenization scheme. Using the presented hierarchical multiscale scheme, we have studied nanotube-reinforced polymer composites, and the elastic properties are determined. Using different representative volume elements (RVEs) representing different volume fractions of aligned nanotubes, the effect of the nanotube volume fraction and the existence of an interphase layer on the effective elastic modulus of the nanocomposite are... 

We have used a hierarchical multiscale modeling scheme for the analysis of carbon nanotube reinforced nanocomposites. This scheme consists of definition of two boundary value problems, one for macroscale (the scale in which the material exists homogeneously and we are interested in modeling the material behavior on that scale), and another for microscale (the scale in which the material becomes heterogeneous and microstructural constituents emerge). The coupling between these scales is done by using homogenization techniques. Using the presented scheme, we have studied carbon nanotube (CNT) reinforced composites behavior and the effects of an interphase layer between CNT and matrix material.... 

Packet loss recovery is an important part of P2P video streaming networks due to inevitable packet loss in today's internet and interdependency of data units in compressed video streams. In addition, the architecture of P2P streaming networks, in which the data delivered to the receivers through chain of peers, can intensify the impact of the internet packet loss on the quality of perceived video at the receivers. FEC and ARQ are the two most important techniques that can be used to overcome the side effect of the internet packet loss in P2P video streaming networks. Based on these two techniques, different packet loss recovery strategies can be applied in different overlay hops of a given... 

Co(salen)-type [where salen = di-(salicylal)-ethylenediimine] complexes were shown to be efficient catalysts in the oxidation of 2-phenylpropane (cumene) by dioxygen primarily to 2-phenyl-2-propanol (cumyl alcohol), 2-phe-nylpropene (a-methylstyrene), and 1-phenylethanone (acetophenone) applying 1H NMR spectroscopy and gas chromatography-mass spectrometry (GC-MS). The effect of substitution on the ligand was also monitored in both oxygen-absorption and the catalytic reaction. Based on these results, the trend observed for the production of a-methylstyrene and cumyl alcohol were parallel to dioxygen uptake by the catalyst in neat cumene, while acetophenone productions obeyed a non-linear... 

In this paper joint optimization of layers in the layered video coding is investigated. Through theoretical analysis and simulations, it is shown that, due to higher interactions between the layers in a SNR scalable codec, this type of layering technique benefits most from joint optimization of the layers. A method for joint optimization is then proposed, and its compression efficiency is contrasted against the separate optimization and an optimized single layer coder. It is shown that, in joint optimization of SNR scalable coders when the quantization step size of the enhancement layer is larger than half the step size of the base layer, an additional improvement is gained by not sending... 

We present a methodology for characterization and an approach for computing the solutions of fuzzy linear systems with LR fuzzy variables. As solutions, notions of exact and approximate solutions are considered. We transform the fuzzy linear system into a corresponding linear crisp system and a constrained least squares problem. If the corresponding crisp system is incompatible, then the fuzzy LR system lacks exact solutions. We show that the fuzzy LR system has an exact solution if and only if the corresponding crisp system is compatible (has a solution) and the solution of the corresponding least squares problem is equal to zero. In this case, the exact solution is determined by the... 

Peer-to-peer streaming has recently gained attention as an effective solution to support large scale media streaming applications over the Internet. One of the main challenges of peer-to-peer video streaming is the cumulative impact of the Internet packet loss due to the decoding dependency of the compressed video frames. In this paper we study the impact of the Internet packet loss on the performance of peer-to-peer video streaming systems, and analyze the efficiency of various packet loss recovery policies in such systems. Our analytical and simulation results show how the Internet packet loss can affect the performance of peer- to-peer video streaming systems and how different packet loss... 

One of the man concerns of peer-to-peer video streaming over the internet is the cumulative impact of the Internet packet loss due to the decoding dependency of the compressed video frames. In this paper we study the efficiency of various packet loss recovery policies that can be used in peer-to-peer streaming. Our analytical and simulation results show how different packet loss recovery policies can be effective for peer-to-peer video streaming. © 2007 IEEE  

In recent years, the demand for video transmission over wireless communication networks is growing very fast. The H.264 video compression standard which offers high quality at low bit rates, is a suitable codec for applications that require efficient video transmission over wireless networks. While the compressed videos are transmitted through error-prone networks, error robustness becomes an important issue. In this paper, a joint source-channel Lagrange optimization method in which the distortion of the decoder is estimated without using feedback which can be used for both multicast and point-to-point applications is proposed. The experimental results show that the new algorithm has a good... 

Transmission of video over error prone and still bandwidth limited wireless channels demand high compression efficiency and resilience to packet losses and errors. Scalable or layered video coding applied to highly compression efficient codecs is an ideal solution to the problem. However, scalability reduces compression efficiency of the coders. In this paper we show how compression efficiency of two-layer SNR scalable video coders can be retained via joint base-enhancement layer optimization. Simulation results show that joint base-enhancement layer optimization significantly outperforms separate optimization of the layers, and it closely follows the compression performance of the... 

In this paper we propose a rate-efficient peer-to-peer architecture for video multicasting over the Internet. The limited capacity of the Internet hosts and the heterogeneous property of their access links are the main challenges of the peer-to-peer video multicasting over the Internet. Although, the rate-optimized overlay tree construction is a NP-hard problem, we propose a number of distributed and efficient protocols for rate-efficient overlay tree construction. Our proposed protocols include efficient join, improvement, overlay tree refinement and an optimum rate allocation protocol. The simulation results show the efficiency of the proposed protocols in rate-efficient overlay tree... 

In this paper, a new dynamic proxy solution based on overlay multicasting network for layered video streaming is presented. In our proposed approach, all clients in an Internet service provider network interested in receiving a video stream, provided by a media server in the Internet, organize themselves into an overlay tree. The root of the overlay tree acts as a proxy and receives video stream from original server and distributes it in the local overlay tree. In addition to introducing a new architecture, our main contribution in this paper is proposing a number of distributed protocols for construction and improvement of local overlay tree in video streaming applications. The experimental... 

The depth of anesthesia quantification has been one of the most research interests in the field of EEG signal processing and nonlinear dynamical analysis has emerged as a novel method for the study of complex systems in the past few decades. In this investigation we use the concept of nonlinear time series analysis techniques to reconstruct the attractor of anesthesia from EEG signal which have been obtained from different hypnotic states during surgery to give a characterization of the dimensional complexity of EEG by Correlation Dimension estimation. The dimension of the anesthesia strange attractor can be thought of as a measure of the degrees of freedom or the 'complexity' of the... 

Herein, we describe for the first time synthesis, characterization, chemosenor behavior, and mechanism of metal ion-ligand interaction of two novel side-armed naphthodiaza-crown macrocycles (L1 and L2) by employing of IR, 1H and 13C NMR, UV–vis, fluorescence spectroscopy, CHN microanalysis and single crystal X-ray diffraction. Preliminary fluorescence studies in ethanol as solvent revealed that the metal ion recognition by L1 was strongly different from L2 suggesting the importance of the number of benzylic side-arms on the extent of the interaction with Mn+. For instance employing fluorescence titration in ethanol showed binding constant values 105 M−1 and 2.6×106 M−1 for L1/Al3+ and... 

The reaction of 15-18 membered benzodiazacrown ethers with salicylaldehyde afforded n-membered O2N2-donor macrocyclic ligands mounted with 1,3-diazacyclohexane subrings (1-4) in high yields. The products were characterized by FT-IR, 1H, 13C NMR spectroscopy, elemental analyses, and single crystal X-ray studies. The solid state structures revealed strong intramolecular hydrogen bonding between the pendant phenolic group and the tertiary nitrogen of the corresponding macroring  

Let G be a graph and f: V (G) → ℕ be a function. An f-coloring of a graph G is an edge coloring such that each color appears at each vertex v ∈ V (G) at most f(v) times. The minimum number of colors needed to f-color G is called the f-chromatic index of G and is denoted by χʹf(G). It was shown that for every graph G, Δf(G) ≤ χʹf(G) ≤ Δf(G) + 1, where Δf(G) = maxv ∈V (G)(formula presented). A graph G is said to be f-Class 1 if χʹf(G) = Δf(G), and f-Class 2, otherwise. Also, GΔfis the induced subgraph of G on (formula presented). In this paper, we show that if G is a connected graph with Δ(GΔf) ≤ 2 and G has an edge cut of size at most Δf(G) − 2 which is a star, then G is f-Class 1. Also, we... 

A new non-enzymatic sensor for glucose is prepared by using of Ni(II)-one dimensional coordination polymer (Ni(II)-Cp) and C 60 . The Ni(II)-Cp prepared by slow diffusion and evaporation of two solution layers of NiCl 2 and diaza-macrocycle bearing two pyridine side arms (as the reported tecton) in DMF. The Ni(II)-Cp was characterized by powder x-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) as well as Fourier transform infrared spectroscopy (FT-IR). C 60 as modified was added to Ni(II)-Cp for improving the electrical and chemical stability of the composite. The newly assembled Ni(II)-Cp/C 60 also coated on glassy carbon electrode (GC) to... 

The in vitro endothelial response of human umbilical vein endothelial cells was investigated on a poly (caprolactone)-based polyurethane surface vs an in situ TiO2-polyurethane nanocomposite surface, which has been produced as scaffolds for artificial vascular graft. The in situ synthesis of TiO2 nanoparticles in polyurethane provided surface properties that facilitated cellular adhesion, cell sensing, cell probing and especially cell migration. Cells on the nanocomposite surface have elongated morphology and were able to produce more extracellular matrix. All of these advantages led to an increase in the rate of endothelialization of the nanocomposite scaffold surface vs pure polyurethane....