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    Active brownian particles and run-and-tumble particles separate inside a maze

    , Article Scientific Reports ; Volume 6 , 2016 ; 20452322 (ISSN) Khatami, M ; Wolff, K ; Pohl, O ; Ejtehadi, M. R ; Stark, H ; Sharif University of Technology
    Nature Publishing Group  2016
    A diverse range of natural and artificial self-propelled particles are known and are used nowadays. Among them, active Brownian particles (ABPs) and run-and-tumble particles (RTPs) are two important classes. We numerically study non-interacting ABPs and RTPs strongly confined to different maze geometries in two dimensions. We demonstrate that by means of geometrical confinement alone, ABPs are separable from RTPs. By investigating Matryoshka-like mazes with nested shells, we show that a circular maze has the best filtration efficiency. Results on the mean first-passage time reveal that ABPs escape faster from the center of the maze, while RTPs reach the center from the rim more easily.... 

    Gaseous slip flow mixed convection in vertical microducts of constant but arbitrary geometry

    , Article Journal of Thermophysics and Heat Transfer ; Volume 28, Issue 4 , 1 October , 2014 , Pages 771-784 ; ISSN: 08878722 Sadeghi, M ; Sadeghi A ; Saidi, M. H ; Sharif University of Technology
    Consideration is given to the buoyancy effects on fully developed gaseous slip flow in vertical microducts of constant but arbitrary geometry. The thermal boundary condition is assumed to be the constant wall heat flux of the first kind, H1. The rarefaction effects are treated using the first-order slip velocity and temperature jump boundary conditions. The method of solution being considered, in which the governing equations in cylindrical coordinates and three of the boundary conditions are exactly satisfied, is mainly analytical. The remaining slip boundary conditions on the duct wall are applied to the solution through the least-squares matching method. As an application of the method,... 

    Efficient Observer-Dependent Simplification in Polygonal Domains

    , Article Algorithmica (New York) ; April , 2011 , Pages 1-21 ; 01784617 (ISSN) Zarei, A ; Ghodsi, M ; Sharif University of Technology
    In this paper, we consider a special version of the well-known line-simplification problem for simplifying the boundary of a region illuminated by a point light source q, or its visibility polygon VP(q). In this simplification approach, we should take the position of q as an essential factor into account to determine the quality of the resulting simplification. For this purpose, we redefine the known distance- and area-distortion error criteria as the main simplification criteria to take into account the distance between the observer q and the boundary of VP(q). Based on this, we propose algorithms for simplifying VP(q). More precisely, we propose simplification algorithms of O(n2) and... 

    On a class of degenerate complex manifolds

    , Article Comptes Rendus Mathematique ; Volume 344, Issue 6 , 2007 , Pages 373-376 ; 1631073X (ISSN) Bahraini, A ; Sharif University of Technology
    We study a class of compactifications of open complex analytic surfaces which appear naturally in the study of the singularities of Calabi-Yau metrics. We obtain a new degenerate Hodge theory as well as a degenerate Dolbeault lemma for these surfaces. To cite this article: A. Bahraini, C. R. Acad. Sci. Paris, Ser. I 344 (2007). © 2007 Académie des sciences  

    Interpretation of tensile softening in concrete, using fractal geometry

    , Article Scientia Iranica ; Volume 15, Issue 1 , 2008 , Pages 8-15 ; 10263098 (ISSN) Khezrzadeh, H ; Mofid, M ; Sharif University of Technology
    Sharif University of Technology  2008
    Concrete is a heterogeneous material with a wide variety of usage in structural design. Concrete under tension exhibits strain softening, i.e., a negative slope in the stress-deformation diagrams. Different softening curves have been proposed in the literature to interpret this phenomenon. In current research, a new softening curve for concrete has been proposed by using the newly introduced concept of fractal geometry. This new softening curve is denominated a 'Quasi-fractal' softening curve and consists of two parts, a linear portion at the beginning and an exponential portion in the rest of the curve. A comparison of a "Quasi-fractal" softening curve with a set of proposed experimental... 

    Walking in streets with minimal sensing

    , Article Journal of Combinatorial Optimization ; Volume 30, Issue 2 , 2014 , Pages 387-401 ; ISSN: 13826905 Tabatabaei, A ; Ghodsi, M ; Sharif University of Technology
    We consider the problem of walking a robot in an unknown polygon called “street”, starting from a point (Formula presented.) to reach a target (Formula presented.). The robot is assumed to have minimal sensing capability in a way that cannot infer any geometric properties of the environment, such as its coordinates, angles or distances; but it is equipped with a sensor that can only detect the discontinuities in the depth information (or gaps). Our robot can also locate the target point (Formula presented.) as soon as it enters in robot’s visibility region. In addition, one pebble is assumed to be available to the robot to be used as an identifiable point and to mark any position of the... 

    On hypercontractivity and a data processing inequality

    , Article IEEE International Symposium on Information Theory - Proceedings ; 29 June through 4 July , 2014 , pp. 3022-3026 Anantharam, V ; Gohari, A ; Kamath, S ; Nair, C ; Sharif University of Technology
    In this paper we provide the correct tight constant to a data-processing inequality claimed by Erkip and Cover. The correct constant turns out to be a particular hypercontractivity parameter of (X,Y), rather than their squared maximal correlation. We also provide alternate geometric characterizations for both maximal correlation as well as the hypercontractivity parameter that characterizes the data-processing inequality  

    Geometry optimization of a fibrous scaffold based on mathematical modelling and CFD simulation of a dynamic cell culture

    , Article Computer Aided Chemical Engineering ; Volume 38 , 2016 , Pages 1413-1418 ; 15707946 (ISSN); 9780444634283 (ISBN) Tajsoleiman, T ; Abdekhodaie, M. J ; Gernaey, K. V ; Krühne, U ; Kravanja, Z ; Bogataj, M ; Sharif University of Technology
    Elsevier B.V  2016
    In tissue engineering, the development of a tissue essentially depends on supply of an adequate amount of nutrients and the design of a proper biophysical micro-environment for cells. The limitation of the available initial number of cells, expensive substances and time consuming experiments are the main bottlenecks in this type of processes. In this regard, mathematical modelling and computational fluid dynamics simulation (CFD) are powerful tools to identify an efficient and optimized design by providing reliable insights of the process. This study presents a mathematical model and CFD simulation of cartilage cell culture under a perfusion flow, which allows not only to characterize the... 

    Failure procedure in epoxy adhesive joining composite plates

    , Article Iranian Journal of Science and Technology - Transactions of Mechanical Engineering ; 2020 Fazel, D ; Kadivar, M. H ; Zohoor, H ; Farid, M ; Hematiyan, M. R ; Sharif University of Technology
    Springer  2020
    In this paper, several numerical simulations are performed to study the failure of epoxy adhesive joining composite plates. Different geometries for the joint and its edge are considered, and the effects of these geometries on the failure load are investigated. Moreover, the joints are subjected to different types of loading in order to determine the failure load. The failure theories of composite materials are implemented into the finite element software ABAQUS, and the failure propagation in the joint is studied. © 2020, Shiraz University  

    Efficient visibility maintenance of a moving segment observer inside a simple polygon

    , Article 19th Annual Canadian Conference on Computational Geometry, CCCG 2007, Ottawa, ON, 20 August 2007 through 22 August 2007 ; 2007 , Pages 249-252 Khosravi, A. A ; Zarei, A ; Ghodsi, M ; Sharif University of Technology
    In this paper we consider maintaining the visibility of a segment observer moving inside a simple polygon. A practical instance of this problem is to identify the regions of a planar scene illuminated by a fluorescent lamp while the lamp moves around. We consider both strong and weak visibility in this paper. Our method is based on the shortest path tree which builds a linear-sized data structure in O(n) time, where n is the number of the vertices of the underlying simple polygon P. We first compute VP(st̄), the initial view of the segment observer st̄. Then, as st̄ moves, each change of VP(st̄) can be computed in O(log2(|V P(st̄)|)) time when the observer is allowed to change its direction,... 

    Upper bounds for minimum dilation triangulation in two special cases

    , Article Information Processing Letters ; Volume 133 , 2018 , Pages 33-38 ; 00200190 (ISSN) Sattari, S ; Izadi, M ; Sharif University of Technology
    Elsevier B.V  2018
    Give a triangulation of a set of points on the plane, dilation of any two points is defined as the ratio between the length of the shortest path of these points and their Euclidean distance. Minimum dilation triangulation is a triangulation in which the maximum dilation between any pair of the points is minimized. We give upper bounds on the dilation of the minimum dilation triangulation for two kinds of point sets: An upper bound of nsin⁡(π/n)/2 for a centrally symmetric convex point set containing n points, and an upper bound of 1.19098 for a set of points on the boundary of a semicircle. © 2018 Elsevier B.V  

    Jet impact geometry and plunge pool dimensions effects on dynamic pressures at pool sidewalls

    , Article Canadian Journal of Civil Engineering ; Volume 35, Issue 4 , 2008 , Pages 408-417 ; 03151468 (ISSN) Borghei, S.M ; Zarnani, P ; Sharif University of Technology
    A plunge pool is one of the energy dissipater structures for high head dams, which ensures stability of the dam under extreme hydrodynamic pressure, due to falling jet impacts. The excess energy of the jet is dissipated, together with significant impact pressure exerted on the floor and pool walls. Thus, appropriate assessment of jet dynamic characteristics in the plunge pool is essential. This research presents experimental results focusing on. the distribution of mean and extreme pressure fluctuations on the sidewalls, due to circular and rectangular plunging jets, and the effects of pool dimension, especially in narrow valleys. The experimental variables are discharge, geometry of jet,... 

    Firm structure of the separated turbulent shear layer behind modified backward-facing step geometries

    , Article International Journal of Numerical Methods for Heat and Fluid Flow ; Volume 16, Issue 7 , 2006 , Pages 803-826 ; 09615539 (ISSN) Darbandi, M ; Taeibi Rahni, M ; Naderi, A.R ; Sharif University of Technology
    Purpose - One major challenge in turbulent flow applications is to control the recirculation zone behind the backward-facing step (BFS). One simple idea to do so is to modify the original BFS geometry, of course, without causing adverse or undesirable impacts on the original characteristics of the primary stream. The main objective of this work is to examine the solidity of the recirculation zone behind several different geometries which are slightly to moderately different from the original BFS geometry. Design/methodology/approach - The implemented modifications cause complicated irregularities at the boundaries of the domain. The experience shows that the mesh distribution around these... 

    Tensile fracture behavior of heterogeneous materials based on fractal geometry

    , Article Theoretical and Applied Fracture Mechanics ; Volume 46, Issue 1 , 2006 , Pages 46-56 ; 01678442 (ISSN) Khezrzadeh, H ; Mofid, M ; Sharif University of Technology
    Many of heterogeneous structural materials, like concrete, have different behavior under tensile stresses in comparison to their behavior under compressive stresses. The aim of this paper is to interpret behavior of such materials subjected to tensile stresses, by using newly introduced concept of fractal geometry. In the first part of this paper, tensile behavior of granular composites has been studied by using fractal geometry. It is shown that the fractality of the cross section in this kind of composites can be used to interpret the size effect on tensile strength. In fact, this work is a modification with innovations on the previous studies on fractal based size effect. This hypothesis... 

    DOA error estimation in 3D cylindrical dipole array geometries including the mutual coupling effect

    , Article AEU - International Journal of Electronics and Communications ; Volume 84 , February , 2018 , Pages 321-330 ; 14348411 (ISSN) Poormohammad, S ; Sasan Nia, Z ; Farzaneh, F ; Sharif University of Technology
    Elsevier GmbH  2018
    The direction of arrival (DOA) error in dipole 3D arrays is estimated through Monte-Carlo simulations using the standard MUSIC algorithm. Novel 3D geometries are implemented which demonstrate better precision given the same lateral area. The mutual coupling effect is included by changing the search vector in the MUSIC DOA algorithm for the novel 3D geometries. A simple straight forward method is used which does not need complex electromagnetic computations. Simulations show that the proposed method can successfully account for the mutual coupling effects in two dimensional direction finding (both azimuth and elevation angle) with novel 3D array geometries. Reduced DOA estimation error is... 

    An investigation of fracture geometry in hydraulic fracturing on a gas reservoir well production enhancement

    , Article Petroleum Science and Technology ; Vol. 32, issue. 2 , 2014 , pp. 150-157 ; ISSN: 10916466 Baghbanan, A. R ; Parvazdavani, M ; Abbasi, S ; Rahnama, A. R ; Sharif University of Technology
    Utilizing improved production methods have been always challenging in upstream industries. Nowadays, hydraulic fracturing is one of the most prestigious mechanical methods. Application of this method is in wells with low productivity index. Hydraulic fracturing efficiency depends on various factors, such as fracture geometry, fluid composition, and stress distribution. But some of them would be ignored, such as fracture geometry, which is neglected due to nongravity and lack of investigation of DFN statistical population assumption. The authors develop a more comprehensive methodology based on fracture geometry and aim to model one of the gas reservoirs in Iran that is naturally fractured by... 

    A polygonal finite element method for modeling arbitrary interfaces in large deformation problems

    , Article Computational Mechanics ; Volume 50, Issue 1 , 2012 , Pages 19-33 ; 01787675 (ISSN) Biabanaki, S. O. R ; Khoei, A. R ; Sharif University of Technology
    In this paper, a polygonal-FEM technique is presented in modeling of arbitrary interfaces in large deformations. The method is used to model the internal interfaces and arbitrary geometries using a uniform non-conformal mesh. The technique is applied to capture discontinuous deformations in the non-conformal elements, which are cut by the interface in a uniform regular mesh. In this approach, a uniform non-conformal mesh is decomposed into sub-elements that conform to the internal interfaces. The geometry of interface is used to produce various triangular, quadrilateral and pentagonal elements at the intersection of interface with regular FE mesh, in which the extra degrees-of-freedom are... 

    Design and application of a new tapered superelement for analysis of revolving geometries

    , Article Finite Elements in Analysis and Design ; Volume 47, Issue 11 , November , 2011 , Pages 1242-1252 ; 0168874X (ISSN) Ahmadian, M. T ; Movahhedy, M. R ; Rezaei, M. M ; Sharif University of Technology
    Structures of tapered geometry are customarily used in a variety of applications. The analysis of such structures is usually made through finite element method using traditional beam, shell or brick elements. In this paper, a new tapered superelement is presented that lends itself to modeling revolving geometries under lateral, axial and torsional loads. The presented tapered superelement has 16 nodes. The performance of this element under static and dynamic loading and in rotating condition is examined. It is shown that this element yields accurate results with higher computational efficiency compared to conventional elements. Furthermore, it is verified that a single tapered superelement... 

    A finite element approach to develop track geometrical irregularity thresholds from the safety aspect

    , Article Journal of Theoretical and Applied Mechanics (Poland) ; Volume 55, Issue 2 , 2017 , Pages 695-705 ; 14292955 (ISSN) Miri, A ; Mohammadzadeh, S ; Salek, H ; Sharif University of Technology
    Polish Society of Theoretical and Allied Mechanics  2017
    Riding quality and safety of rail tracks are directly influenced by track geometry; hence, their degradation along time could reduce safety and cause serious accidents. Standards propose thresholds for track geometrical parameters to keep track safety and riding comfort at an acceptable level. In this study, a method is proposed to select or define a set of proper thresholds for geometrical parameter irregularities according to desirable to safety level. The impact of track geometry irregularities on the derailment index has been investigated through the finite element model. The results suggest that twist and gauge shortage have a greater effect on the derailment index compared to the... 

    Exploring contraction–expansion inertial microfluidic-based particle separation devices integrated with curved channels

    , Article AIChE Journal ; Volume 65, Issue 11 , 2019 ; 00011541 (ISSN) Shamloo, A ; Abdorahimzadeh, S ; Nasiri, R ; Sharif University of Technology
    John Wiley and Sons Inc  2019
    Separation of particles or cells has various applications in biotechnology, pharmaceutical and chemical industry. Inertial cell separation, in particular, has been gaining a great attention in the recent years since it has exhibited a label-free, high-throughput and efficient performance. In this work, first, an inertial contraction–expansion array microchannel device, capable of passively separating two particles with diameters of 4 and 10 μm, was numerically studied. Then, the validated model was combined with curved geometries in order to investigate the effect of curve features on the separation process. The overall purpose was to investigate the interaction between the two different...