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Dissolution and conformational behavior of functionalized cellulose chains in the bulk, aqueous and non-aqueous media: A simulation study
, Article Carbohydrate Research ; Volume 496 , October , 2020 ; Moghbeli, M. R ; Rasouli, S ; Gharib Zahedi, M. R ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In the present study, we employ all-atom molecular dynamics simulations to investigate the dynamic behaviors and structural properties of the native and modified cellulose chains in the bulk, aqueous, and organic media. Particular attention has been directed to the role of different hydrophobic and hydrophilic functional groups as linear and branched aliphatic and also cyclic pendent groups on the solubility and packing of the cellulose chain. The various properties related to density profile, mean squared displacement, intramolecular entropy, radius of gyration, and radial distribution function were calculated. The results showed that the chain tendency toward crystallinity decreased when...
Transversal thermal transport in single-walled carbon nanotube bundles: Influence of axial stretching and intertube bonding
, Article Journal of Chemical Physics ; Volume 139, Issue 18 , 2013 ; 00219606 (ISSN) ; Tafazzoli, M ; Böhm, M. C ; Alaghemandi, M ; Sharif University of Technology
2013
Abstract
Using reverse nonequilibrium molecular dynamics simulations the influence of intermolecular bridges on the thermal conductivity (λ) in carbon nanotube (CNT) bundles has been investigated. The chosen cross linkers (CH 2, O, CO) strengthen the transversal energy transport relative to the one in CNT bundles without bridges. The results showed that λ does not increase linearly with the linker density. The efficiency of the heat transport is determined by the number of linkers in the direction of the heat flux, the type of the linker, and their spatial ordering. The influence of a forced axial stress on the transversal λ has been also studied. The observed λ reduction with increasing axial...
Interfacial thermal transport and structural preferences in carbon nanotube-polyamide-6,6 nanocomposites: How important are chemical functionalization effects?
, Article Physical Chemistry Chemical Physics ; Volume 17, Issue 22 , 2015 , Pages 14502-14512 ; 14639076 (ISSN) ; Tafazzoli, M ; Böhm, M. C ; Alaghemandi, M ; Sharif University of Technology
Royal Society of Chemistry
2015
Abstract
We employ reverse nonequilibrium molecular dynamics simulations to investigate the interfacial heat transfer in composites formed by an ungrafted or a grafted carbon nanotube which is surrounded by oligomeric polyamide-6,6 chains. The structural properties of the polymer matrix and the grafted chains are also studied. The influence of the grafting density, the length of the grafted chains as well as their chemical composition on the interfacial thermal conductivity (λi ) are in the focus of our computational study. For the considered grafted polyethylene and polyamide chains we do not find a sizeable difference in the observed λi values. In contrast to this...
Investigation of Carbon Nanotube-Polymer Composites Thermal Conductivity Using Molecular Dynamics Simulations
, Ph.D. Dissertation Sharif University of Technology ; Tafazzoli, Mohsen (Supervisor) ; Alaghemandi, Mohammad (Co-Advisor)
Abstract
In the present research, we have applied reverse non-equilibrium molecular dynamics (RNEMD) to investigate the thermal conductivity (λ) of carbon nanotube (CNT) bundles, CNT-polyamide (PA) nanocomposites, and nanoconfined PA in the vicinity of graphene layers. First, transversal heat transport in CNT bundles with and without intertube chemical bonds are examined. It is found that the transversal λ of samples with cross linkers can surprisingly increase ~9 times than that of neat CNT bundles (0.26 W m-1K-1). According to the simulation results, key parameters are overlapping vibrational density of state (DOS) profiles between the atoms forming the bridging units, cross linker in the direction...
Thermo-mechanical modeling of high speed spindles
, Article Scientia Iranica ; Volume 19, Issue 2 , 2012 , Pages 282-293 ; 10263098 (ISSN) ; Movahhedy, M. R ; Sharif University of Technology
2012
Abstract
Prediction of the thermo-mechanical behavior of machine-tool spindles is essential in the reliable operation of high speed machine tools. In particular, the performance of these high speed spindles is dependent on their thermal behavior. The main source of heat generation in the spindle is the friction torque in angular contact ball bearings. This paper presents an effort to develop a comprehensive model of high speed spindles that includes viable models for the mechanical and thermal behavior of its major components, i.e., bearings, shaft and housing. Spindle housing and shaft are treated as six-degree-of-freedom Timoshenko beam elements. Bearings are modeled as two-node elements with five...
Experimental and numerical investigation of fixture time on distortion of welded part
, Article International Journal of Advanced Manufacturing Technology ; Volume 104, Issue 1-4 , 2019 , Pages 1121-1131 ; 02683768 (ISSN) ; Biglari, F. R ; Shafaie, M ; Kokabi, A. H ; Sharif University of Technology
Springer London
2019
Abstract
In this paper, the effect of clamping time on welding distortion is studied. The welding process has been done in austenitic stainless steel 304L butt-welded joint by TIG welding method. The numerical thermo-mechanical analysis is performed using commercial finite element software ABAQUS. The welding simulation is performed using the birth and death of elements technique. The heat source model that used in this study is the Goldak double-ellipsoidal model. At last, for verifying numerical results, a set of experimental tests have been carried out and welding distortion has been measured. The experimental measured data are compared with numerical (FEM) results. The results showed that the...
Secure cloud storage with anonymous deduplication using ID-based key management
, Article Journal of Supercomputing ; Volume 79, Issue 2 , 2023 , Pages 2356-2382 ; 09208542 (ISSN) ; Fazli, M. A ; Sharif University of Technology
Springer
2023
Abstract
Cloud storage systems have been turned into the primary services of Internet users nowadays. While the application of such systems is exponentially increasing, deduplication algorithms help face scalability issues. Although source-side deduplication optimizes both storage and bandwidth, the main concern that deduplication algorithms suffer from is still data confidentiality. Message-locked encryption (MLE) is a well-known key management framework for secure deduplication to provide confidentiality. This framework is the basis of almost all the proposed secure deduplication solutions. Even though there are lots of literature works trying to provide secure deduplication algorithms, to the best...
Enhanced finite difference scheme for the neutron diffusion equation using the importance function
, Article Annals of Nuclear Energy ; Volume 96 , 2016 , Pages 412-421 ; 03064549 (ISSN) ; Vosoughi, N ; Gharib, M ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
Mesh point positions in Finite Difference Method (FDM) of discretization for the neutron diffusion equation can remarkably affect the averaged neutron fluxes as well as the effective multiplication factor. In this study, by aid of improving the mesh point positions, an enhanced finite difference scheme for the neutron diffusion equation is proposed based on the neutron importance function. In order to determine the neutron importance function, the adjoint (backward) neutron diffusion calculations are performed in the same procedure as for the forward calculations. Considering the neutron importance function, the mesh points can be improved through the entire reactor core. Accordingly, in...
SLoPCloud: an efficient solution for locality problem in peer-to-peer cloud systems
, Article Algorithms ; Volume 11, Issue 10 , 2018 ; 19994893 (ISSN) ; Malekimajd, M ; Movaghar, A ; Sharif University of Technology
2018
Abstract
Peer-to-Peer (P2P) cloud systems are becoming more popular due to the high computational capability, scalability, reliability, and efficient data sharing. However, sending and receiving a massive amount of data causes huge network traffic leading to significant communication delays. In P2P systems, a considerable amount of the mentioned traffic and delay is owing to the mismatch between the physical layer and the overlay layer, which is referred to as locality problem. To achieve higher performance and consequently resilience to failures, each peer has to make connections to geographically closer peers. To the best of our knowledge, locality problem is not considered in any well known P2P...
Thermal conductivity of polyamide-6,6 in the vicinity of charged and uncharged graphene layers: A molecular dynamics analysis
, Article Journal of Physical Chemistry C ; Volume 116, Issue 26 , May , 2012 , Pages 14115-14122 ; 19327447 (ISSN) ; Gharib-Zahedi, M. R ; Spohr, E ; Böhm, M. C ; Sharif University of Technology
2012
Abstract
The thermal conductivity (λ) of nanoconfined polyamide-6,6 (PA) oligomers in polymer-graphene nanocomposites has been investigated by reverse nonequilibrium molecular dynamics (RNEMD) simulations. The preferential alignment of the PA chains parallel to the graphene plane as well as their elongation implies that λ of the polymer in nanocomposites is larger than that in the neat polymer system. The ordering of the polymer phase is enhanced in an arrangement of charged graphene surfaces made of one layer with a charge deficit and one with a charge excess. The consequence of the enhanced polymer ordering as well as the denser packing is an increase in λ in the polymer network. Differences in the...
Expert key selection impact on the MANETs' performance using probabilistic key management algorithm
, Article SIN 2013 - Proceedings of the 6th International Conference on Security of Information and Networks ; 2013 , Pages 347-351 ; 9781450324984 (ISBN) ; Minaei, M ; Golkari, M ; Movaghar, A ; Sharif University of Technology
2013
Abstract
Mobile ad hoc networks (MANETs) have been turned into very attractive area of research in the duration of recent years, whereas security is the most challenging point that they undergo. Cryptography is an essential solution for providing security within MANETs. However, storing all keys in every node, if practically possible, is inefficient in large scale MANETs due to some limitations such as memory or process capability. This paper extends our previous idea which was a novel probabilistic key management algorithm that stores only a few randomly chosen keys instead of all ones. In this paper, several different scenarios are proposed for key selection in which they are more practical, and...
Optimal control of nonlinear dynamical systems using direct solution of neural network controllers
, Article AIAA Guidance, Navigation, and Control Conference and Exhibit 2002, Monterey, CA, 5 August 2002 through 8 August 2002 ; 2002 ; 9781563479786 (ISBN); 9781624101083 (ISBN) ; Jalali, M. A ; Ghorbani, R ; Zahedi, A ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2002
Abstract
Due to inherent potential of General Regression Neural Network(GRNN) to approximate nonlinear functions, it can be implemented as a nonlinear state-feedback controller. In this paper the methodology of direct collocation and nonlinear programming is utilized in combination with GRNN to determine the optimal control of dynamical systems. Application of this method to the design of an optimal controller for a chaotic flexible beam as a non-autonomous, nonlinear system is investigated. © 2002 The American Institute Aeronautics and Astronautics Inc. All rights reserved
Fully distributed self certified key management for large-scale MANETs
, Article Proceedings - IEEE 10th International Conference on Ubiquitous Intelligence and Computing, UIC 2013 and IEEE 10th International Conference on Autonomic and Trusted Computing, ATC 2013 ; 2013 , Pages 96-102 ; 9781479924813 (ISBN) ; Doostari, M. A ; Gharib, M ; Movaghar, A ; Sharif University of Technology
2013
Abstract
Mobile ad hoc networks (MANETs) have received considerable attention while their special characteristics make them vulnerable against different attacks. Providing security in such networks becomes a challenge and cryptography is an essential solution for it, to implement a cryptosystem, key management is the main challenge. In this paper a new deterministic scheme for key management in MANETs is proposed. Since public and private keys in this algorithm have an unforgeable relationship, there is no need for any certificate. Proposed scheme distributes the role of the key generation center (KGC) among all nodes, therefore the private key is issued by distributed KGCs (DKGCs) and the node...
Network immunization under limited budget using graph spectra
, Article International Journal of Modern Physics C ; Volume 27, Issue 8 , 2016 ; 01291831 (ISSN) ; Khansari, M ; Sharif University of Technology
World Scientific Publishing Co. Pte Ltd
2016
Abstract
In this paper, we propose a new algorithm that minimizes the worst expected growth of an epidemic by reducing the size of the largest connected component (LCC) of the underlying contact network. The proposed algorithm is applicable to any level of available resources and, despite the greedy approaches of most immunization strategies, selects nodes simultaneously. In each iteration, the proposed method partitions the LCC into two groups. These are the best candidates for communities in that component, and the available resources are sufficient to separate them. Using Laplacian spectral partitioning, the proposed method performs community detection inference with a time complexity that rivals...
A new immunization algorithm based on spectral properties for complex networks
, Article 2015 7th Conference on Information and Knowledge Technology, IKT 2015, 26 May 2015 through 28 May 2015 ; May , 2015 , Page(s): 1 - 5 ; 9781467374859 (ISBN) ; Khansari, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
Nowadays, we are facing epidemic spreading in many different areas; examples are infection propagation, rumor spreading and computer viruses in computer networks. Finding a strategy to control and mitigate the spread of these epidemics is gaining much interest in recent researches. Due to limitation of immunization resources, it is important to establish a strategy for selecting nodes which has the most effect in mitigating epidemics. In this paper, we propose a new algorithm that minimizes the worst expected growth of an epidemic by reducing the size of the largest connected component of the underlying contact network. The proposed algorithm is applicable to any level of available resources...
Stability analysis of descriptor systems with multiple commensurate time-delays
, Article Journal of the Franklin Institute ; Volume 356, Issue 15 , 2019 , Pages 8690-8705 ; 00160032 (ISSN) ; Haeri, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
A new method is proposed to analyze stability of descriptor systems with multiple commensurate time-delays. In this method, purely imaginary roots of the system are calculated, asymptotic behavior of root path at these roots is studied, and unstable regions of the system in the space of delays are determined. Moreover, the number of roots in each unstable region is calculated. Also necessary and sufficient conditions for τ-stabilizability of these systems are presented. Examples are provided to illustrate the effectiveness and validity of the proposed method. © 2019 The Franklin Institute
Decomposition and robust non-fragile stabilisation of singular time-delay systems
, Article IET Control Theory and Applications ; Volume 12, Issue 13 , 2018 , Pages 1882-1888 ; 17518644 (ISSN) ; Haeri, M ; Sharif University of Technology
2018
Abstract
This study presents a new approach to decompose singular time-delay systems (STDSs) in a way that they can be transformable to normal time-delay systems (TDSs) with a lower order. Necessary and sufficient conditions are provided to determine which STDSs can be transformed to TDSs. Also, a stabilisation method is provided to stabilise the system, while the time delay in the system can belong to several distinct intervals or even everywhere. The proposed method is non-fragile towards controller parameters. This method also reveals one of the many applicable situations of the proposed decomposition. The effectiveness of the proposed method is illustrated through some examples. © 2018 The...
Asymptotic stability of linear descriptor systems with time-delay by designing delay margin
, Article 5th International Conference on Control, Instrumentation, and Automation, ICCIA 2017 ; Volume 2018-January , 2018 , Pages 23-29 ; 9781538621349 (ISBN) ; Haeri, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
In this paper a new approach is developed to stabilize descriptor systems with time-delay, while time-delay can belong to a given interval. This approach takes the advantages of system's singularity to simplify the model and uses the so-called Rekasius substitution to compute the controller parameters in a way that the asymptotic stability of the closed-loop system in the given interval of the delay can be guaranteed. Finally, a numerical example is provided to evaluate the proposed method's effectiveness. © 2017 IEEE
Investigating the effect of geometric parameters on hydrodynamic and hydro-acoustic performances of submerged propellers
, Article Applied Ocean Research ; Volume 114 , 2021 ; 01411187 (ISSN) ; Ebrahimi, A ; Zahedi, F ; Javanmardi, M. R ; Seif, M. S ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The hydro-acoustic analysis of submerged propellers is an important issue in marine industries, which is examined to reduce the vibrations and noise level of vessels alongside reducing fuel consumption and improving hydrodynamic efficiency. B-series propellers are common propellers whose hydrodynamic and acoustic investigation through applying suitable rake, and skew angle can offer proper results to designers for enhancing the hydrodynamic performance and reducing noise. In this study, a model of the five-bladed B-series propeller with the normal skew angle is chosen. The effects of geometric parameters, including the rake angle, skew angle, geometric pitch ratio, and the number of blades...
Non-invasive techniques for assessing the endothelial dysfunction: ultrasound versus photoplethysmography
, Article IFMBE Proceedings, 3 December 2008 through 6 December 2008 ; Volume 23 , 2009 , Pages 65-68 ; 16800737 (ISSN) ; 9783540928409 (ISBN) ; Jaafar, R ; Zahedi, E ; Sharif University of Technology
2009
Abstract
Endothelial dysfunction, which can be noninvasively assessed by flow mediated vasodilation (FMD), predicts an increased rate of adverse cardiovascular events. The endothelial dysfunction is considered as a leading cause of development and progression of the atherosclerotic process. The main aim of this study is to review different non-invasive methods to assess the endothelial dysfunction and to propose enhancements to a new method based on photoplethysmography (PPG). First, non-invasive techniques developed for the evaluation of peripheral endothelial function (including the Doppler ultrasound (US)) will be reviewed. Although noninvasive, US -based techniques present a few disadvantages. To...