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Investigation of properties of polyethylene/clay nanocomposites prepared by new in situ ziegler-natta catalyst
, Article Materials and Design ; Volume 30, Issue 7 , 2009 , Pages 2309-2315 ; 02641275 (ISSN) ; Ramazani Saadat Abadi, A ; Baniasadi, H ; Tavakolzadeh, F ; Sharif University of Technology
2009
Abstract
This paper is devoted to investigation of morphological and physical-mechanical properties of polyethylene (PE)/clay nanocomposites prepared via in situ polymerization method using bi-supported Ziegler-Natta catalyst. Bentonite type clay and MgCl2 (ethoxide type) were used as the support of TiCl4. Catalyst support and polymerization process have been done in slurry phase using Triisobutylaluminum as the co-catalyst. The microstructure of the nanocomposites was examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM indicated that almost fully exfoliated PE/clay nanocomposites were produced successfully using this method. According to permeability...
Resource Management in Space-Division Multiplexed Elastic Optical Networks
, M.Sc. Thesis Sharif University of Technology ; Pakravan, Mohammad Reza (Supervisor)
Abstract
In recent years, Internet traffic has nearly doubled in the core network every two years, and it is expected to continue to grow in the future. With this growth, there is a need for very high capacity and economically efficient transmission systems, which optical communication is the best choice. Elastic optical network (EON) is one of the best options for achieving this goal in the future. Unlike existing networks, the transmission parameters of EON will be customizable, which will have an essential role in optimizing bandwidth assignment. The problem facing scientists today is to approach the final physical capacity of current optical fibers. The solution proposed for this challenge is...
Development of Computational Fluid Dynamics Model for Spatial Distribution of Greenhouse Temperature and Humidity Considering Plant Evapotranspiration
, M.Sc. Thesis Sharif University of Technology ; Roshandel, Ramin (Supervisor)
Abstract
The purpose of this study is to develop a simulated model of a greenhouse using two different ventilation systems, a fan&pad system and an air-soil converter equipped with a sprinkler in order to compare the cooling performance of these two systems in hot seasons. The main focus of the analysis of the results is on how the temperature and humidity are distributed throughout the greenhouse space. In order to develop a three-dimensional model with computational fluid dynamics method, greenhouse simulation in Ansis software has been used. The development of ventilation model in the greenhouse is done by creating boundary conditions using optimal design. Also, to simulate soil-air conditioning...
Investigation of in situ prepared polypropylene/clay nanocomposites properties and comparing to melt blending method
, Article Materials and Design ; Volume 31, Issue 1 , 2010 , Pages 76-84 ; 02641275 (ISSN) ; Ramazani S. A. A ; Javan Nikkhah, S ; Sharif University of Technology
2010
Abstract
The morphological, physical and mechanical properties of polypropylene/clay nanocomposites (PPCNs) were prepared by in situ polymerization are investigated. Non-modified scmectite type clay (e.g. bentonite) was used to prepare bi-supported Ziegler-Natta catalyst of TiCl4/Mg(OEt)2/clay. Exfoliated PPCNs were obtained by in situ intercalative polymerization of propylene using produced bi-supported catalyst. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) micrograph were used to assess the clay morphology and dispersion of clay. The crystalline structures of PPCNs were characterized by differential scanning calorimetry (DSC). The mechanical properties of PPCNs were...
Effects of obstacles on inertial focusing and separation in sinusoidal channels: An experimental and numerical study
, Article Chemical Engineering Science ; Volume 276 , 2023 ; 00092509 (ISSN) ; Amiri, H. A ; Moshafi, S ; Karimi, A ; Nikkhah, A ; Chen, X ; Ta, H. T ; Nguyen, N. T ; Zhang, J ; Sharif University of Technology
Elsevier Ltd
2023
Abstract
Inertial microfluidics manipulates and separates microparticles based on the finite inertia of the fluid at high flow speed. In inertial microfluidics, modifying the geometry by embedding periodic micro-obstacles into curvilinear channels is emerging as a promising strategy to improve inertial focusing and separation. This work systematically investigated the influence of micro-obstacles on inertial focusing and developed a high-resolution microfluidic device for particle and cell separation. First, we developed numerical modelling to simulate the migration trajectories of particles. Then, we studied the effects of various obstacles on the inertial focusing in the sinusoidal channels. The...
Investigation of Production Increasing in In-situ Preparation of Polyolefin/clay Nanocomposites
, M.Sc. Thesis Sharif University of Technology ; Ramazani Saadat Abadi, Ahmad (Supervisor)
Abstract
This project is devoted to experimental investigation of increasing on production of polyethylene/clay nanocomposites (PECNs) and polypropylene/clay nanocomposites (PPCNs) via in-situ polymerization method. First of all we produced bi-supported Ziegler-Natta catalyst to polymerized polyolefins nanocomposites. Bentonite type clay and Magnesiumethoxide (Mg (OEt)2) were used as the support of Tetrachloridetitanium (TiCl4). Catalyst support and polymerization process have been done in slurry phase using Triisobutylaluminum (TiBA) as the co-catalyst. The efficiency of preapared bi-supported Ziegler-Natta was reasonably high (average 200 (gr. Product/mmol Ti. h) for PECNs and 195 (gr. Product/mmol...
The Design and Construction of a Marine Current Turbine and Modeling the Flow Around It
, M.Sc. Thesis Sharif University of Technology ; Seif, Mohammad Saeed (Supervisor) ; Abbaspour, Madjid (Supervisor)
Abstract
Nowadays, science and technology, once again, lead approach to renewable natural resources to access energy due to fossil resources restrictions. Growing need for energy, being concerned about exhaustion of fossil resources, environmental pollution caused by burning fossil materials, climate warming and the greenhouse effect and etc. are obvious evidences of aforesaid fact. On the other hand, oceans and seas are large reservoirs of energy which comes from sunlight, geothermal resources, Earth's rotation and gravity by means of mechanical and hydrothermal processes. During the years, many ideas were conducted to achieve and mine the mentioned enormous energy potential of the oceans and seas....
A comprehensive review on atmospheric water harvesting technologies: From thermodynamic concepts to mechanism and process development
, Article Journal of Water Process Engineering ; Volume 53 , 2023 ; 22147144 (ISSN) ; Azmi, W. M. B. W ; Nikkhah, A ; Najafi, A. M ; Babaei, M. M ; Fen, C. S ; Nouri, A ; Mohammad, A. W ; Lun, A. W ; Yong, N. L ; Mahmoudi, E ; Sharif University of Technology
Elsevier Ltd
2023
Abstract
Water scarcity is one of the most challenging problems that the world has ever faced. There are numerous methods to remedy the water crises. One is using atmospheric water harvesting (AWH) to provide water. So far, there is much research on the subject of AWH. However, there is still a lack of establishing an extensive comparison between different technologies and methods used to harvest atmospheric water. In this review, we provide details on the thermodynamic performance of the AWH system. The systems are categorized into both active and passive systems. Heat pumps, membranes, thermoelectric solar systems, and adsorption systems are some atmospheric harvesting technologies that will be...
A selective chemiresistive sensor for the cancer-related volatile organic compound hexanal by using molecularly imprinted polymers and multiwalled carbon nanotubes
, Article Microchimica Acta ; Volume 186, Issue 3 , 2019 ; 00263672 (ISSN) ; Banan Nojavani, M ; Nikkhah, M ; Alizadeh, T ; Esfandiar, A ; Ganjali, M. R ; Sharif University of Technology
Springer-Verlag Wien
2019
Abstract
A chemiresistive sensor is described for the lung cancer biomarker hexanal. A composite consisting of molecularly imprinted polymer nanoparticles and multiwalled carbon nanotubes was used in the sensor that is typically operated at a voltage of 4 V and is capable of selectively sensing gaseous hexanal at room temperature. It works in the 10 to 200 ppm concentration range and has a 10 ppm detection limit (at S/N = 3). The sensor signal recovers to a value close to its starting value without the need for heating even after exposure to relatively high levels of hexanal
Nonlinear interstory drift contours for idealized forward directivity pulses using "modified fish-bone" models
, Article Advances in Structural Engineering ; Volume 18, Issue 5 , May , 2015 , Pages 603-627 ; 13694332 (ISSN) ; Khosravi, H ; Jamnani, H. H ; Sharif University of Technology
Multi-Science Publishing Co. Ltd
2015
Abstract
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...
Analysis of singularities of a 3DOF parallel manipulator based on a novel geometrical method
, Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) ; Sadeghian, H ; Roozbehani, H ; Zohoor, H ; Sharif University of Technology
2006
Abstract
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,...
Melting enthalpy and entropy of freestanding metallic nanoparticles based on cohesive energy and average coordination number
, Article Journal of Physical Chemistry C ; Volume 115, Issue 35 , August , 2011 , Pages 17310-17313 ; 19327447 (ISSN) ; Delavari H., H ; Madaah Hosseini, H. R ; Sharif University of Technology
2011
Abstract
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...
On the temperature and residual stress field during grinding
, Article WCE 2010 - World Congress on Engineering 2010, 30 June 2010 through 2 July 2010 ; Volume 2 , 2010 , Pages 1196-1200 ; 9789881821072 (ISBN) ; Farrahi, G. H ; Ghadbeigi, H ; Sharif University of Technology
2010
Abstract
Grinding is widely used for manufacturing of components that require fine surface finish and good dimensional accuracy. In this study a thermo-mechanical finite element analysis is conducted to find out how grinding parameters can affect temperature and residual stress distribution in the workpiece. Results of parametric study presented in this work indicate, by carefully selecting the grinding parameters, minimum thermal and mechanical damage can be achieved. Higher workpiece velocities produce higher surface residual stress. By increasing depths of cut, depth of tensile residual stresses increases. Convection heat coefficient does not have any considerable effect on surface residual stress...
A new lattic LP-based post filter for adaptive noise cancellers in mobile and vehicular applications
, Article Proceedings of the 8th IEEE International Symposium on Signal Processing and Information Technology, ISSPIT 2008, 16 December 2008 through 19 December 2008, Sarajevo ; 2008 , Pages 407-412 ; 9781424435555 (ISBN) ; Sameti, H ; Veisi, H ; Abutalebi, H. R ; Sharif University of Technology
2008
Abstract
Adaptive Noise Cancellation (ANC) is a well-known technique for background noise reduction in automobile and vehicular environments. The noise fields in automobile and other vehicle interior obey the diffuse noise field model closely. On the other hand, the ANC does not provide sufficient noise reduction in the diffuse noise fields. In this paper, a new multistage post-filter is designed for ANC as a solution to diffuse noise conditions. The designed post-filter is a single channel Linear Prediction (LP) based speech enhancement system. The LP is performed by an adaptive lattice filter and attempts to extract speech components by using intermediate ANC signals. The post-filter has no...
Finite element analysis of shot-peening effect on fretting fatigue parameters
, Article Tribology International ; Volume 44, Issue 11 , 2011 , Pages 1583-1588 ; 0301679X (ISSN) ; Alvandi Tabrizi, Y ; Farrahi, G. H ; Majzoobi, G. H ; Ghadbeigi, H ; Sharif University of Technology
2011
Abstract
Shot peening is widely used to improve the fretting fatigue strength of critical surfaces. Fretting fatigue occurs in contacting parts that are subjected to fluctuating loads and sliding movements at the same time. This paper presents a sequential finite element simulation to investigate the shot peening effects on normal stress, shear stress, bulk stress and slip amplitude, which are considered to be the controlling parameters of fretting damage. The results demonstrated that among the modifications related to shot peening, compressive residual stress has a dominant effect on the fretting parameters
Mechanically activated synthesis of single crystalline MgO nanostructures
, Article Journal of Alloys and Compounds ; Volume 506, Issue 2 , September , 2010 , Pages 715-720 ; 09258388 (ISSN) ; Yoozbashizadeh, H ; Askari, M ; Kobatake, H ; Fukuyama, H ; Sharif University of Technology
2010
Abstract
One-dimensional (1D) MgO structures were successfully synthesized via carbothermic reduction of mechanically activated mixture of MgO and graphite. Mechanical activation of source materials before carbothermic reduction can substantially enhance the formation of MgO products at a temperature (1000 °C) relatively lower than that required in previous approaches (≥1200 °C). However, the morphology of MgO formed is dependent on the degree of mechanical activation and the condition of the subsequent carbothermic reduction. Two distinctive morphologies were found for MgO products synthesized using our method: single crystalline nanorods with rectangular cross-sections whose diameters range from 50...
Boundary control design for vibration suppression and attitude control of flexible satellites with multi-section appendages
, Article Acta Astronautica ; Volume 173 , 2020 , Pages 22-30 ; Salarieh, H ; Nejat Pishkenari, H ; Jalili, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Attitude and vibration control of a general form of flexible satellites is addressed in this paper. Partial differential dynamic equations are derived considering new details such as multi sectioned solar panels and elastic connections between main hub and solar panels. Boundary control approach is adopted to eliminate simplification errors of discrete models, using just one actuator in the hub. Asymptotic stability of attitude dynamics is proved for a group of boundary controllers and necessary conditions for asymptotic stability of vibrations are discussed. Being independent of modeling accuracy and using easily measurable feedbacks are among advantages of the proposed class of...
Characterization and calcination behavior of a low-grade manganese ore
, Article Materials Today Communications ; Volume 25 , 2020 ; Becker, H ; Eftekhari, H ; Yoozbashizadeh, H ; Safarian, J ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Characterization and calcination behavior of a low-grade manganese ore, as a part of Mn ferroalloys production, was studied by XRF, ex-situ XRD, in-situ XRD, and SEM-EDS techniques. Calcination experiments were carried out at and up to 900 °C (1173 K) in air and argon atmospheres. The samples were in particles and powder forms. The results indicated that both quartz and calcite phases in the ore exhibit a bimodal spatial distribution; as relatively large regions and finely distributed in the Mn- and Fe-containing phases. By Rietveld analysis of the in-situ XRD data, the reactions occurring upon heating during the calcination process were deduced. Thermal decomposition and reactive diffusion...
Minimizing the error of time difference of arrival method in mobile networks
, Article 2005 International Conference on Wirelessand Optical Communications Networks, Dubai, 6 March 2005 through 8 March 2005 ; 2005 , Pages 328-332 ; 0780390199 (ISBN); 9780780390195 (ISBN) ; Aghababa, H ; Radfar, M. H ; Khalaj, B. H ; Sharif University of Technology
2005
Abstract
Estimating the position of a mobile set is of great importance in new mobile services. However, in most cases, the accuracy should be less than 100 meters. This accuracy is hard to reach especially in urban areas. The main problem is that there are a lot of obstacles like buildings between the BTS and the mobile set. Thus the time measured between BTS and the mobile set is somehow greater than the time it takes the wave to travel directly between two points. This paper introduces an optimized solution for TDOA as one of the most efficient ways for finding the location of a mobile phone. Considering the standards and limitations of both GSM and UMTS, the Authors present a solution for...
A fast and novel method of pattern synthesis for non-uniform phased array antennas
, Article Proceedings International Radar Symposium, 24 June 2015 through 26 June 2015 ; Volume 2015-August , 2015 , Pages 924-929 ; 21555753 (ISSN) ; 9783954048533 (ISBN); 9783954048533 (ISBN); 9783954048533 (ISBN) ; Sebt, M. A ; Nayebi, M. M ; Behroozi, H ; Rohling, H ; Rohling, H ; Rohling, H ; Sharif University of Technology
IEEE Computer Society
2015
Abstract
Weighting elements to achieve radiation patterns with desired characteristics is a classical work in phased array antennas. These characteristics can be low sidelobe level, narrow beamwidth, high directivity, pattern nulling in special angle and etc. For each of these characteristics, different methods have been introduced. Most of methods have been presented for uniform arrays, however there are lots of methods to obtain a desired pattern for antennas with non-uniform element distances. The problem with these methods is complexity or not very good results. In this paper, fast and easy methods based on Least Square Error that leads to good results are presented. In addition, weighting of...