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Total 174 records

    Gradient reproducing kernel particle method

    , Article Journal of Mechanics of Materials and Structures ; Volume 3, Issue 1 , 2008 , Pages 127-152 ; 15593959 (ISSN) Hashemian, A ; Shodja, H. M ; Sharif University of Technology
    Mathematical Sciences Publishers  2008
    Abstract
    This paper presents an innovative formulation of the RKPM (reproducing kernel particle method) pioneered by Liu. A major weakness of the conventional RKPM is in dealing with the derivative boundary conditions. The EFGM (element free Galerkin method) pioneered by Belytschko shares the same difficulty. The proposed RKPM referred to as GRKPM (gradient RKPM), incorporates the first gradients of the function in the reproducing equation. Therefore in three-dimensional space GRKPM consists of four independent types of shape functions. It is due to this feature that the corrected collocation method can be readily generalized and combined with GRKPM to enforce the EBCs (essential boundary... 

    Single-replicate longitudinal data analysis in the presence of multiple instrumental measurement errors

    , Article Computers and Industrial Engineering ; Volume 141 , 2020 Moazeni, M ; Behbahani, M ; Khedmati, M ; Akhavan Niaki, S. T ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    In this paper, a novel method as a combination of the expectation–maximization (EM) algorithm and Variogram is proposed to decompose the longitudinal measurement errors in the absence of replications and the presence of multiple instrumental measurement errors. In the proposed method, multiple measurements are considered where the units are observed by several distinct instruments (gauges). The approach decouples the observed variance of the measurement model into the process and measurement system variances. In addition, it decomposes the variance of multiple instruments into the process and instrument variances. In the end, the proposed model is validated and tested based on simulated... 

    ECG denoising using modulus maxima of wavelet transform

    , Article Proceedings of the 31st Annual International Conference of the IEEE Engineering in Medicine and Biology Society: Engineering the Future of Biomedicine, EMBC 2009 ; 2009 , Pages 416-419 ; 1557170X (ISSN) Ayat, M ; Shamsollahi, M. B ; Mozaffari, B ; Kharabian, S ; Sharif University of Technology
    Abstract
    ECG denoising has always been an important issue in medical engineering. The purposes of denoising are reducing noise level and improving signal to noise ratio (SNR) without distorting the signal. This paper proposes a method for removing white Gaussian noise from ECG signals. The concepts of singularity and local maxima of the wavelet transform modulus were used for analyzing singularity and reconstructing the ECG signal. Adaptive thresholding was used to remove white Gaussian noise modulus maximum of wavelet transform and then reconstruct the signal  

    Deep learning for caries detection: A systematic review

    , Article Journal of Dentistry ; Volume 122 , 2022 ; 03005712 (ISSN) Mohammad Rahimi, H ; Motamedian, S. R ; Rohban, M. H ; Krois, J ; Uribe, S. E ; Mahmoudinia, E ; Rokhshad, R ; Nadimi, M ; Schwendicke, F ; Sharif University of Technology
    Elsevier Ltd  2022
    Abstract
    Objectives: Detecting caries lesions is challenging for dentists, and deep learning models may help practitioners to increase accuracy and reliability. We aimed to systematically review deep learning studies on caries detection. Data: We selected diagnostic accuracy studies that used deep learning models on dental imagery (including radiographs, photographs, optical coherence tomography images, near-infrared light transillumination images). The latest version of the quality assessment tool for diagnostic accuracy studies (QUADAS-2) tool was used for risk of bias assessment. Meta-analysis was not performed due to heterogeneity in the studies methods and their performance measurements.... 

    , M.Sc. Thesis Sharif University of Technology Bagherzadeh, Mahsa (Author) ; Mohammadi Shodja, Hossien (Supervisor)
    Abstract
    The present study aims at determining the elastic fields of ultra-small flaws and defects. These defects are often introduced undesirably in elastic solids during fabrication and their sizes are normally in the order of couple of nano-meters. In this work, the elastic fields around a circular nano-void subjected to a uniform farfield uniaxial tension, also the elastic fields of a nano-sized mode I crack under remote uniform loading are studied. In this paper the strain gradient theory developed by Mindlin and co-workers in 1960s is employed. According to this theory, the strain energy density assumes the form of a positive-definite function of the strain components and their first gradient.... 

    Accuracy of Kinect's skeleton tracking for upper body rehabilitation applications

    , Article Disability and Rehabilitation: Assistive Technology ; Vol. 9, issue. 4 , 2014 , pp. 344-352 ; ISSN: 17483107 Mobini, A ; Behzadipour, S ; Saadat Foumani, M ; Sharif University of Technology
    Abstract
    Games and their use in rehabilitation have formed a new and rapidly growing area of research. A critical hardware component of rehabilitation programs is the input device that measures the patients' movements. After Microsoft released Kinect, extensive research has been initiated on its applications as an input device for rehabilitation. However, since most of the works in this area rely on a qualitative determination of the joints' movements rather than an accurate quantitative one, detailed analysis of patients' movements is hindered. The aim of this article is to determine the accuracy of the Kinect's joint tracking. To fulfill this task, a model of upper body was fabricated. The... 

    Fetal R-wave detection from multichannel abdominal ECG recordings in low SNR

    , Article Proceedings of the 31st Annual International Conference of the IEEE Engineering in Medicine and Biology Society: Engineering the Future of Biomedicine, EMBC 2009 ; 2009 , Pages 344-347 ; 1557170X (ISSN) Kharabian, S ; Shamsollahi, M. B ; Sameni, R ; Sharif University of Technology
    Abstract
    Abdominal recordings of fetal ECG (fECG) have lower signal-to-noise ratio (SNR) as compared with invasive procedures. In this paper we have combined two previously proposed methods, one for extracting fECG, called piCA and the other, a transformation based on Hilbert transform to enhance the R-peaks. The combination of these methods seems to work well in situations of noisy data and fetal repositioning. Also a comparison is done by using ICA in order to extract the fetal signals. Performance of both methods is studied separately. Results show that applying the transformation on the components extracted with the use of piCA (after maternal ECG cancellation), had a very good performance. Also,... 

    MEG based classification of wrist movement

    , Article Proceedings of the 31st Annual International Conference of the IEEE Engineering in Medicine and Biology Society: Engineering the Future of Biomedicine, EMBC 2009 ; 2009 , Pages 986-989 ; 1557170X (ISSN) ; 978-142443296-7 (ISBN) Montazeri, N ; Shamsollahi, M. B ; Hajipour, S ; Sharif University of Technology
    Abstract
    Neural activity is very important source for data mining and can be used as a control signal for brain-computer interfaces (BCIs). Particularly, Magnetic signals of neurons are enriched with information about the movement of different part of the body such as wrist movement. In this paper, we use MEG (Magneto encephalography) signals of two subjects recorded during wrist movement task in four directions. Data were prepared for BCI competition 2008 for multiclass classification. Our approach for this classification problem consists of PCA as a noise reduction method, ULDA for feature reduction and various linear classifiers such as Bayesian, KNN and SVM. Final results (58%-62% for subject 1... 

    A novel approach to recognize hand movements via sEMG patterns

    , Article 29th Annual International Conference of IEEE-EMBS, Engineering in Medicine and Biology Society, EMBC'07, Lyon, 23 August 2007 through 26 August 2007 ; 2007 , Pages 4907-4910 ; 05891019 (ISSN) ; 1424407885 (ISBN); 9781424407880 (ISBN) Khezri, M ; Jahed, M ; Sharif University of Technology
    2007
    Abstract
    Electromyogram signal (EMG) is an electrical manifestation of contractions of muscles. Surface EMG (sEMG) signal collected form surface of the skin has been used in diverse applications. One of its usages is exploiting it in a pattern recognition system which evaluates and synthesizes hand prosthesis movements. The ability of current prosthesis has been limited in simple opening and closing that decreases the efficacy of these devices in contrary to natural hand. In order to extend the ability and accuracy of prosthesis arm movements and performance, a novel approach for sEMG pattern recognizing system is proposed. In order to have a relevant comparison, present and recent research for... 

    Determination of the Plastic Zone at the Tip of a Crack in Pressure-Sensitive Materials Using RKPM

    , M.Sc. Thesis Sharif University of Technology Malgard, Afsaneh (Author) ; Mohammadi Shoja, Hossein (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    Abstract
    This project presents an outline of the crack tip stress fields in the presence of a plastic enclave around a growing fatigue crack using RKPM and Drucker-Prager criterion for pressure sensitive materials such as concrete and rock. Two distinguished features of RKPM are the arbitrarily high order smoothness and the interpolation property of the shape function which has kronecker delta property at the associated nodes. This method has proved to handle extreme material deformation and moving discontinuities. For the frictional materials such as rock in geotechnical engineering, a non-associated or associated Drucker- Prager plasticity model is appropriate for modeling its constitutive... 

    A remedy to gradient type constraint dilemma encountered in RKPM

    , Article Advances in Engineering Software ; Volume 38, Issue 4 , 2007 , Pages 229-243 ; 09659978 (ISSN) Shodja, H. M ; Hashemian, A ; Sharif University of Technology
    Elsevier Ltd  2007
    Abstract
    A major disadvantage of conventional meshless methods as compared to finite element method (FEM) is their weak performance in dealing with constraints. To overcome this difficulty, the penalty and Lagrange multiplier methods have been proposed in the literature. In the penalty method, constraints cannot be enforced exactly. On the other hand, the method of Lagrange multiplier leads to an ill-conditioned matrix which is not positive definite. The aim of this paper is to boost the effectiveness of the conventional reproducing kernel particle method (RKPM) in handling those types of constraints which specify the field variable and its gradient(s) conveniently. Insertion of the gradient term(s),... 

    Analysis of a Lamellar Inhomogeneity Via Repordusing Kernel Particle Method

    , M.Sc. Thesis Sharif University of Technology Raeis Hosseiny, Aydin (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    Abstract
    Nowadays, the excellent technological applications of composites have attracted the attentions of industry and numerous scientists. They are advantageous for their high tensile modulus, strength, and promising electrical and thermal properties. In applying the approach of lamellar inhomogeneity to real composites, the micro-geometries of the reinforcement must be considered such that they can be approximated as limiting case of an ellipsoid. In vapor grown carbon nanofiber, the fiber may have a diameter of about 150nm and length of 10-20 µm [1]. The modulus of carbon nanofiber is normally in the range of 100-600 GPa and sometimes even higher, whereas the modulus of some polymers is usually... 

    Buckling Analysis of Nano-Plates in the Context of Modified Couple Stress Theory Using RKPM

    , M.Sc. Thesis Sharif University of Technology Alemi, Bita (Author) ; Mohammadi Shoja, Hossein (Supervisor)
    Abstract
    In this research, a new Kirchhoff plate model based on the modified couple stress theory has been utilized to derive the corresponding closed-form expression for the buckling load. Moreover, a numerical mesh-less method, Reproducing Kernel Particle Method (RKPM), in combination with Corrected Collocation Method (CCM) has been employed to model the nano-plate and calculate its buckling load in the framework of the modified couple stress theory. To this end, two kinds of nano-plates have been modeled, the square nano-plates with all edges simply supported 1) in the presence of the nano-void and 2) without the nano-void. It should be noted that the analytical and numerical solutions for the... 

    Augmented RKPM Modeling of a Glide Edge Dislocation Near a Grain Boundary in the Framework of Surface/Interface Elasticity

    , M.Sc. Thesis Sharif University of Technology (Author) ; Mohammadi Shoja, Hossein (Supervisor)
    Abstract
    Traditional continuum theory of elasticity becomes remarkably inaccurate in the vicinity of singularities, and when the size eect is of concern. For example in the study of ultra-small objects and ultra-thin lms, near defects, near point of application of a concentrated load and as such, the classical solutions are not reliable. This work focuses on determination of the elastic elds of an edge dislocation near the grain boundary of two perfectly bonded nano-size crystals. It is proposed to study this problem in the context of surface/interface elasticity, and incorporate the eect of the grain boundary on the elastic elds. In contrast to the surface/interface elasticity theory, traditional... 

    Elastic Field of an Anticrack Via Reproducing Kernel Particle Method

    , M.Sc. Thesis Sharif University of Technology Sohrabpour, Amir Hossein (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    Abstract
    Meshless Methods using kernel approximation like Reproducing Kernel Particle Method (RKPM) are methods for solving partial differential equations that require only nodal data and a description of the geometry without requiring element connectivity data and mesh producing. An innovative method of nonplanar material partitioning method (NMPM) with implementation of RKPM is employed to calculate the stress intensity factor (SIF) at the tip of an anticrack sited in an isotropic plate under a remote applied loading. Numerical examples in comparison with the exact closed form expressions show that accurate SIF for mode I can be obtained.

     

    Study of Size Effect via Strain-gradient Elasticity Based RKPM in Nano-Structures

    , M.Sc. Thesis Sharif University of Technology Arshadi, Amir (Author) ; Mohammadi Shoja, Hossein (Supervisor)
    Abstract
    In this thesis one of the mesh-free methods called RKPM is employed to solve the differential equations of strain-gradient elasticity. To this end the corresponding weak form is laid down. Subsequently the relevant stiffness-matrix is obtained by discretization of the weak form. To be sure about the accuracy of the relations, the problem of a plate weakened by a hole under uniform far-field tension, for which the exact solution is available in the literature, is solved. The obtained numerical result is in good agreement with the solution of Eshel and Rosenfeld. Afterwards, a plate containing a crack of finite length subjected to uniform far-field tension (mode I) is considered. This problem... 

    A comprehensive procedure for characterizing arbitrary azimuthally symmetric photon beams

    , Article Physica Medica ; Vol. 30, Issue. 2 , 2014 , Pages 191-201 ; ISSN: 11201797 Ezzati, A. O ; Sohrabpour, M ; Mahdavi, S. R ; Buzurovic, I ; Studenski, M. T ; Sharif University of Technology
    Abstract
    Purpose: A new Monte Carlo (MC) source model (SM) has been developed for azimuthally symmetric photon beams. Methods: The MC simulation tallied phase space file (PSF) is divided into two categories depending on the relationship of the particle track line to the beam central axis: multiple point source (MPS) and spatial mesh based surface source (SMBSS). To validate this SM, MCNPX2.6 was used to generate two PSFs for a 6MV photon beam from a Varian 2100C/D linear accelerator. Results: PDDs and profiles were calculated using the SM and original PSF for different field sizes from 5×5 to 40×40cm2. Agreement was within 2% of the maximum dose at 100cm SSD and 2.5% of the maximum dose at 200cm SSD... 

    CytoGTA: a cytoscape plugin for identifying discriminative subnetwork markers using a game theoretic approach

    , Article PLoS ONE ; Volume 12, Issue 10 , 2017 ; 19326203 (ISSN) Farahmand, S ; Foroughmand Araabi, M. H ; Goliaei, S ; Razaghi Moghadam, Z ; Sharif University of Technology
    Abstract
    In recent years, analyzing genome-wide expression profiles to find genetic markers has received much attention as a challenging field of research aiming at unveiling biological mechanisms behind complex disorders. The identification of reliable and reproducible markers has lately been achieved by integrating genome-scale functional relationships and transcriptome datasets, and a number of algorithms have been developed to support this strategy. In this paper, we present a promising and easily applicable tool to accomplish this goal, namely CytoGTA, which is a Cytoscape plug-in that relies on an optimistic game theoretic approach (GTA) for identifying subnetwork markers. Given transcriptomic... 

    Graphene based strain sensors: A comparative study on graphene and its derivatives

    , Article Applied Surface Science ; Volume 448 , 2018 , Pages 71-77 ; 01694332 (ISSN) Hosseinzadeh, A ; Bidmeshkipour, S ; Abdi, Y ; Arzi, E ; Mohajerzadeh, S ; Sharif University of Technology
    Elsevier B.V  2018
    Abstract
    In this study, we have experimentally investigated the electrical properties of graphene and its derivatives (Exfoliated graphene, CVD synthesized graphene, graphene oxide and hydrogenated graphene oxide) under uniaxial strain. We have used gauge factor as a common representation of the sensitivity of the strain sensors and found that the hydrogenated graphene oxide shows significantly higher responsivity comparing to other samples under study. Reproducibility, reliability and lack of hysteresis in the responses of the graphene based samples make them a good candidate to be used in the strain sensors. © 2018  

    Model-based Bayesian filtering of cardiac contaminants from biomedical recordings

    , Article Physiological Measurement ; Volume 29, Issue 5 , 2008 , Pages 595-613 ; 09673334 (ISSN) Sameni, R ; Shamsollahi, M. B ; Jutten, C ; Sharif University of Technology
    2008
    Abstract
    Electrocardiogram (ECG) and magnetocardiogram (MCG) signals are among the most considerable sources of noise for other biomedical signals. In some recent works, a Bayesian filtering framework has been proposed for denoising the ECG signals. In this paper, it is shown that this framework may be effectively used for removing cardiac contaminants such as the ECG, MCG and ballistocardiographic artifacts from different biomedical recordings such as the electroencephalogram, electromyogram and also for canceling maternal cardiac signals from fetal ECG/MCG. The proposed method is evaluated on simulated and real signals. © 2008 Institute of Physics and Engineering in Medicine