Loading...
Search for:
najafi--m
0.006 seconds
Total 32 records
Receptivity of hypersonic flow over blunt-noses to freestream disturbances using spectral methods
, Article Computational Fluid Dynamics 2010 - Proceedings of the 6th International Conference on Computational Fluid Dynamics, ICCFD 2010, 12 July 2010 through 16 July 2010 ; July , 2011 , Pages 357-362 ; 9783642178832 (ISBN) ; Najafi, M ; Esfahanian, V ; Sharif University of Technology
2011
Abstract
The receptivity of supersonic/hypersonic flows over blunt noses to freestream disturbances is performed by means of spectral collocation methods. The unsteady flow computations are made through solving the full Navier-Stokes equations in 2D. A shock-fitting technique is used to compute unsteady shock motion and its interaction with freestream disturbances accurately in the receptivity study. The computational results for receptivity of a semi-cylinder at Mach 8 is presented and validated by comparison with available theoretical and numerical results. The study shows significant effects of the viscosity on the receptivity process
Tribological characteristics of self-lubricating nanostructured aluminum reinforced with multi-wall CNTs processed by flake powder metallurgy and hot pressing method
, Article Diamond and Related Materials ; Volume 90 , 2018 , Pages 93-100 ; 09259635 (ISSN) ; Alipour, S ; Najafi, M ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Ultrafine-grained Al-CNT (2 and 4 vol%) composites were successfully fabricated using the flake powder metallurgy and hot pressing route, and the microstructure and tribological properties of the produced composites were studied. The results showed that the coefficient of friction and the wear rate of Al decrease with the addition of the CNT reinforcement. A carbon-rich film formed on the worn surfaces during wear test, which prevented the Al oxidation and yielded the self-lubricating effect for the composites. This improvement in the wear behavior of the composites can be attributed to the simultaneous effects of the ultrafine-grained matrix and strengthening and self-lubricating properties...
On the outflow conditions for spectral solution of the viscous blunt-body problem
, Article Journal of Computational Physics ; Volume 228, Issue 11 , 2009 , Pages 3936-3972 ; 00219991 (ISSN) ; Esfahanian, V ; Najafi, M ; Sharif University of Technology
2009
Abstract
The purpose of this paper is to study and identify suitable outflow boundary conditions for the numerical simulation of viscous supersonic/hypersonic flow over blunt bodies, governed by the compressible Navier-Stokes equations, with an emphasis motivated primarily by the use of spectral methods without any filtering. The subsonic/supersonic composition of the outflow boundary requires a dual boundary treatment for well-posedness. All compatibility relations, modified to undertake the hyperbolic/parabolic behaviour of the governing equations, are used for the supersonic part of the outflow. Regarding the unknown downstream information in the subsonic region, different subsonic outflow...
Dynamic interdiction networks with applications in illicit supply chains
, Article Omega (United Kingdom) ; 2019 ; 03050483 (ISSN) ; Zolfagharinia, H ; Najafi, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
We study the interdiction of illegal product distribution in a network with multiple sources (origins) and sinks (destinations). This work contributes to the literature of dynamic maximum flow interdiction problems by addressing multiple commodities in a network of relationships. The related distribution network consists of (1) criminals, who are hierarchically connected, and seeking to maximize the total profit flow from origins to destinations, and (2) enforcement officers aiming to minimize criminals’ long-term success by monitoring and arresting them, using the limited resources at their disposal. Considering several real-world operational details, we first propose a mixed-integer...
Dynamic interdiction networks with applications in illicit supply chains
, Article Omega (United Kingdom) ; 2019 ; 03050483 (ISSN) ; Zolfagharinia, H ; Najafi, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
We study the interdiction of illegal product distribution in a network with multiple sources (origins) and sinks (destinations). This work contributes to the literature of dynamic maximum flow interdiction problems by addressing multiple commodities in a network of relationships. The related distribution network consists of (1) criminals, who are hierarchically connected, and seeking to maximize the total profit flow from origins to destinations, and (2) enforcement officers aiming to minimize criminals’ long-term success by monitoring and arresting them, using the limited resources at their disposal. Considering several real-world operational details, we first propose a mixed-integer...
Improving blood bank inventory management using double cross-match and hybrid issuance policy
, Article 7th IEEE International Conference on Industrial Engineering and Applications, ICIEA 2020, 16 April 2020 through 21 April 2020 ; 2020 , Pages 819-826 ; Najafi, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2020
Abstract
Blood availability in hospitals is of high humanitarian importance, thus blood shortage is not desired at all. High wastage rate of blood in hospitals is an important issue, which becomes more important as the standards of health care services becomes higher. In order to address blood shortage and wastage issues in a hospital, this paper develops a new inventory management model as a decision making tool to help making tactical and operational level decisions for a Hospital Blood Bank (HBB) inventory management. These decisions include issuance and ordering policy and the aim of the model is to reduce blood wastage and shortage. For this purpose, a multi period, multi-product inventory...
Dynamic interdiction networks with applications in illicit supply chains
, Article Omega (United Kingdom) ; Volume 96 , October , 2020 ; Zolfagharinia, H ; Najafi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
We study the interdiction of illegal product distribution in a network with multiple sources (origins) and sinks (destinations). This work contributes to the literature of dynamic maximum flow interdiction problems by addressing multiple commodities in a network of relationships. The related distribution network consists of (1) criminals, who are hierarchically connected, and seeking to maximize the total profit flow from origins to destinations, and (2) enforcement officers aiming to minimize criminals’ long-term success by monitoring and arresting them, using the limited resources at their disposal. Considering several real-world operational details, we first propose a mixed-integer...
Considering short-term and long-term uncertainties in location and capacity planning of public healthcare facilities
, Article European Journal of Operational Research ; Volume 281, Issue 1 , 16 February , 2020 , Pages 152-173 ; Najafi, M ; Zolfagharinia, H ; Sharif University of Technology
Elsevier B.V
2020
Abstract
This paper addresses a real-world problem faced by the public healthcare sector. The problem consists of both the patients’ and service provider's requirements (i.e., accessibility vs. costs) for locating healthcare facilities, allocating service units to those facilities, and determining the facilities’ capacities. The main contribution of this study is capturing both short-term and long-term uncertainties at the modelling stage. The queuing theory is incorporated to consider stochastic demand and service time as a short-term uncertainty, as well as a service level measurement. The developed nonlinear model is then converted into a linear model after introducing a new set of decision...
Sleep spindles analysis using sparse bump modeling
, Article 2011 1st Middle East Conference on Biomedical Engineering, MECBME 2011, Sharjah, 21 February 2011 through 24 February 2011 ; 2011 , Pages 37-40 ; 9781424470006 (ISBN) ; Najafi, M ; Shamsollahi, M. B ; Sharif University of Technology
Abstract
Sleep Spindle is the hallmark of the second stage of sleep in EEG signal. It had been analyzed using different methods, including Fourier transform, parametric and non-parametric models, higher order statistics and spectra, and also time-frequency methods such as wavelet transform, and matching pursuit. In this study, bump modeling has been used to analyze sleep spindle. Bump modeling is a method which represents the time-frequency map of signals with a number of elementary functions. Results of this work demonstrate that bump modeling is capable of analyzing different sleep spindle patterns in sleep EEG signals successfully
Continuous transforming the BTW to the Manna model
, Article Physica A: Statistical Mechanics and its Applications ; Volume 419 , 2015 , Pages 196-202 ; 03784371 (ISSN) ; Moghimi Araghi, S ; Najafi, M. N ; Sharif University of Technology
Abstract
In this paper we define some stochastic perturbations of the BTW model which make it into Manna model. These models have a continuous parameter p, where p = 0 and 1 correspond to the BTW and Manna models respectively. We have investigated the properties of the statistical observables of the waves of avalanches for various values of p. Our data supports the expectation of a crossover in such systems; at large scales Manna model is dominant. Therefore we find strong evidence in favor of the universality classes being distinct. Also it is observed that the BTW fixed point is unstable when Manna-type perturbation is added to the model
Second law analysis of an infinitely segmented magnetohydrodynamic generator
, Article Journal of Magnetism and Magnetic Materials ; Volume 426 , 2017 , Pages 294-301 ; 03048853 (ISSN) ; Saidi, M. H ; Najafi, M ; Sharif University of Technology
Elsevier B.V
2017
Abstract
The performance of an infinitely segmented magnetohydrodynamic generator is analyzed using the second law of thermodynamics entropy generation criterion. The exact analytical solution of the velocity and temperature fields are provided by applying the modified Hartmann flow model, taking into account the occurrence of the Hall effect in the considered generator. Contributions of heat transfer, fluid friction, and ohmic dissipation to the destruction of useful available work are found, and the nature of irreversibilities in the considered generator is determined. In addition, the electrical isotropic efficiency scheme is used to evaluate the generator performance. Finally, the implication of...
Increasing risk of meteorological drought in the Lake Urmia basin under climate change: Introducing the precipitation–temperature deciles index
, Article Journal of Hydrology ; 2020 ; Najafi, M. R ; Abrishamchi, A ; Sharif University of Technology
Elsevier B.V
2020
Abstract
Meteorological droughts due to the concurrent occurrence of low-precipitation and high-temperature events can lead to severe negative impacts on agriculture, economy, ecosystem, and society. This study proposes a novel framework to characterize such drought conditions based on the joint variability of precipitation–temperature, particularly under climate change. Generalized hierarchical linear model is used to downscale precipitation and temperature at multiple stations from the outputs of nine General Circulation Models (GCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5. A bivariate drought index called Precipitation–Temperature Deciles Index (PTDI) is developed using...
Stress behaviour across human tooth by temperature gradient resulting of laser irradiation
, Article Journal of Mechanical Engineering and Sciences ; Volume 14, Issue 1 , 2020 , Pages 6218-6228 ; Nouri Borujerdi, A ; Najafi, M ; Sharif University of Technology
Universiti Malaysia Pahang
2020
Abstract
The authors report the simulation of temperature distribution and thermally induced stress in the premolar tooth under ND-YAG pulsed laser beam. The Three-Phase-Lag (TPL) non-Fourier model is proposed to describe the heat conduction in the human tooth with nonhomogeneous inner structures. A premolar tooth comprising enamel, dentin, and pulp with real shapes and thicknesses are considered and a numerical method of finite difference was adopted to solve the time-dependent TPL bio-heat transfer, strain and stress equations. The surface heating scheme is applied for simulation of laser therapy. The aim of this laser therapy is that the temperature of pulp reaches to 47oC. The results are...
Increasing risk of meteorological drought in the Lake Urmia basin under climate change: Introducing the precipitation–temperature deciles index
, Article Journal of Hydrology ; Volume 592 , 2021 ; 00221694 (ISSN) ; Najafi, M. R ; Abrishamchi, A ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Meteorological droughts due to the concurrent occurrence of low-precipitation and high-temperature events can lead to severe negative impacts on agriculture, economy, ecosystem, and society. This study proposes a novel framework to characterize such drought conditions based on the joint variability of precipitation–temperature, particularly under climate change. Generalized hierarchical linear model is used to downscale precipitation and temperature at multiple stations from the outputs of nine General Circulation Models (GCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5. A bivariate drought index called Precipitation–Temperature Deciles Index (PTDI) is developed using...
Increasing risk of meteorological drought in the Lake Urmia basin under climate change: Introducing the precipitation–temperature deciles index
, Article Journal of Hydrology ; Volume 592 , 2021 ; 00221694 (ISSN) ; Najafi, M. R ; Abrishamchi, A ; Sharif University of Technology
Elsevier B.V
2021
Abstract
Meteorological droughts due to the concurrent occurrence of low-precipitation and high-temperature events can lead to severe negative impacts on agriculture, economy, ecosystem, and society. This study proposes a novel framework to characterize such drought conditions based on the joint variability of precipitation–temperature, particularly under climate change. Generalized hierarchical linear model is used to downscale precipitation and temperature at multiple stations from the outputs of nine General Circulation Models (GCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5. A bivariate drought index called Precipitation–Temperature Deciles Index (PTDI) is developed using...
The utilization of patients’ information to improve the performance of radiotherapy centers: A data-driven approach
, Article Computers and Industrial Engineering ; Volume 172 , 2022 ; 03608352 (ISSN) ; Najafi, M ; Mesgari, S ; Zolfagharinia, H ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
The high demand for radiotherapy services, combined with the limited capacity of available resources, patient unpunctuality, and series of appointments, makes Patient Appointment Scheduling (PAS) in radiotherapy centers very challenging. Although most centers use a First-Come-First-Serve (FCFS) policy for appointment scheduling, this approach does not consider patients’ behaviors, and consequently, it performs poorly. This type of inappropriate scheduling usually leads to inefficiency at the center and/or patient dissatisfaction. This study provides a data-driven approach to patient appointment scheduling to deal with the challenges mentioned above, and it considers patients’ histories of...
Applicability of lattice Boltzmann method in simulation of drops and bubbles formation and transport
, Article AIP Conference Proceedings, 22 September 2014 through 28 September 2014 ; Volume 1648 , 2015 ; 0094243X (ISSN) ; 9780735412873 (ISBN) ; Alizadeh, M ; Haghshenas, M ; Salimi, H ; Najafi, M ; Miller, R ; Sharif University of Technology
Abstract
Multiphase flows appear in many scientific and engineering applications. On the other hand, there has been a tremendous experimental and numerical investigation trying to understand complex fluid-fluid interfaces better. However, conventional CFD have certain limitations in complicated situations. Fortunately in the past two decades, new approaches, namely SPH and LBM (sometimes called meshless methods) have been developed. Since they are mesoscopic, they have been able to perform much better than conventional CFD. Especially, LBM is becoming more and more popular and has already been divided to many branches
Numerical solution of non-fourier heat transfer during laser irradiation on tooth layers
, Article Journal of Mechanical Science and Technology ; Volume 31, Issue 12 , 2017 , Pages 6085-6092 ; 1738494X (ISSN) ; Nouri Borujerdi, A ; Najafi, M ; Mohammadzadeh, A ; Sharif University of Technology
Abstract
This study reports on the simulation of temperature distribution of human tooth under a laser beam based on non-Fourier models. The temperature in the tooth depth that directly results from the conduction heat transfer process is caused by the lengthy thermal relaxation time in the tooth layers. A detailed tooth composed of enamel, dentin, and pulp with unstructured shape, uneven boundaries, and realistic thicknesses was considered. A finite difference scheme was separately adopted to solve time-dependent equations in solid layers and soft tissue of the tooth. In this study, a dual-phase-lag non-Fourier heat conduction model was applied to evaluate temperature distribution induced by laser...
Evaluation of heat conduction in a laser irradiated tooth with the three-phase-lag bio-heat transfer model
, Article Thermal Science and Engineering Progress ; Volume 7 , 2018 , Pages 203-212 ; 24519049 (ISSN) ; Nouri-Borujerdi, A ; Mohammadzadeh, A ; Najafi, M ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
In this study, a dental short pulse laser with a Gaussian beam profile was applied normally to the top surface of a mineral organ i.e. the human tooth for a root canal therapy. A numerical method of finite difference is adopted to solve the time-dependent heat transfer equation. The real boundary conditions of thermal insulation on the sharp segment of the root canal and periodic heat flux on the top boundary of the tooth were applied. The comparison of a three-phase-lag (TPL) bio-heat transfer model with other heat transfer studies has shown that this new bio-heat model (TPL) could accurately predict the thermal behaviour of a non-homogeneous structure such as the human tooth. It was...
Drop formation in cross-junction micro-channel using lattice Boltzmann method
, Article Thermal Science ; Volume 22, Issue 2 , 2018 , Pages 909-919 ; 03549836 (ISSN) ; Taeibi Rahni, M ; Mohammadzadeh, A ; Najafi, M ; Sharif University of Technology
Serbian Society of Heat Transfer Engineers
2018
Abstract
Drop formation in cross-junction micro-channels is numerically studied using the lattice Boltzmann method with pseudo-potential model. To verify the simulation, the results are compared to previous numerical and experimental data. Furthermore, the effects of capillary number, flow rate ratio, contact angle, and viscosity ratio on the flow patterns, drop length, and interval between drops are investigated and highlighted. The results show that the drop forming process has different regimes, namely, jetting, drop, and squeezing regimes. Also, it is shown that increasing in the flow rate ratio in the squeezing regime causes increment in drop length and decrement in drops interval distance. On...