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    1 + ϵ approximation of tree edit distance in quadratic time

    , Article 51st Annual ACM SIGACT Symposium on Theory of Computing, STOC 2019, 23 June 2019 through 26 June 2019 ; 2019 , Pages 709-720 ; 07378017 (ISSN); 9781450367059 (ISBN) Boroujeni, M ; Ghodsi, M ; Hajiaghayi, M ; Seddighin, S ; Sharif University of Technology
    Association for Computing Machinery  2019
    Edit distance is one of the most fundamental problems in computer science. Tree edit distance is a natural generalization of edit distance to ordered rooted trees. Such a generalization extends the applications of edit distance to areas such as computational biology, structured data analysis (e.g., XML), image analysis, and compiler optimization. Perhaps the most notable application of tree edit distance is in the analysis of RNA molecules in computational biology where the secondary structure of RNA is typically represented as a rooted tree. The best-known solution for tree edit distance runs in cubic time. Recently, Bringmann et al. show that an O(n2.99) algorithm for weighted tree edit... 

    Fatigue Behavior of Al-SiC Nanocomposite

    , M.Sc. Thesis Sharif University of Technology Ghasemi Yazdabadi, Hassan (Author) ; Simchi, Abdolreza (Supervisor) ; Ekrami, Ali Akbar (Supervisor)
    Recently, mechanical properties of advanced materials such as nanostructured and ultra-fine materials and especially nanocomposites were studied by lots of researcher. In this study, fatigue behavior of Al-SiC nanocomposites is observed. Ultra-fine grains Al matrix nanocomposites reinforced with 50 nm diameter SiC nanoparticles were produced by milling and hot extrusion. For this purpose, pure aluminum powder was mixed with 2, 4 and 6 Vol. % of SiC nanoparticles and then milled by planetary mill. The milled powder then were degased in an Argon atmosphere furnace, cold pressed and then hot extruded. Closed die-hot forging was used with about 18.8% reduction in cross section in order to... 

    Effect of Temperature and Strain Rate on the Nano-Structure Produced by ASB Process in Production of Aluminum CNG Cylinders

    , M.Sc. Thesis Sharif University of Technology Alinaghian, Hossein (Author) ; Akbarzadeh Changiz, Abbas (Supervisor)
    Accumulative spin bonding as a severe plastic deformation process results in a finer microstructure through multi-pass processing. This method consists of successive and repeated preparation of internal and external surfaces of two similar tubes, simultaneous flow forming of two tubes and production of a tube with the same thickness as the primary one. This word was conducted to study the effect of different rotational speeds and different cooling environments on the mechanical properties and microstructure of AA1050 tubes. The samples were prepared with 0.8 mm thickness and 92.8 mm internal diameter through four passes of ASB with 250, 500, 710 rpm under air, water and acetone cooling... 

    A Fine Grained Access Control Mechanism for Hybrid Mobile Applications in Android

    , M.Sc. Thesis Sharif University of Technology Pooryousef, Shahrooz (Author) ; Kharrazi, Mehdi (Supervisor) ; Rabiee, HamidReza (Co-Advisor)
    Hybrid mobile applications combine the features of Web technologies and native mobile apps. Like Web applications, they are implemented in portable, platform independent languages such as HTML and JavaScript. Like native apps, they have direct access to local device resources. In these programs, web contents are loaded into a web component, called WebView, which can render HTML5 pages and execute JavaScript code. In order for the web content to access the system resources, which are isolated from the content inside Web-View due to its sandbox, bridges need to be built between JavaScript and the native code. developers usually use third party plug-ins for native side of application. hybrid... 

    Study of Microstructure and Hot Deformation Behavior of Aluminum Nanocomposites Reinforced with SiC Nanoparticles

    , M.Sc. Thesis Sharif University of Technology Mobarhan Bonab, Mohammad Ali (Author) ; Simchi, Abdolreza (Supervisor)
    Hot deformation behavior of Al-SiC nanocomposites was investigated in this study. Aluminum powders with mean size of 60 micron and SiC nanopowders (mean size of 45nm) in amounts of 1 and 2 volume percents, as reinforced part, were mixed and milled for 40 hours by planetary ball mill. After degassing at 450 oC for 1 hour, milled powders were pressed into Aluminum cans (in Argon atmosphere) and then hot extruded. Extrusion ratio was 1:14. High density billets (with 98% of theoretical density) were produced because of that high extrusion ratio. TEM microstructure studies showed that fine distribution of reinforcements and Aluminum Oxides obtained via this procedure. Hardness and Uniaxial... 

    Fine-grained Image Classification

    , M.Sc. Thesis Sharif University of Technology Souri, Yaser (Author) ; Kasaei, Shohreh (Supervisor)
    Fine-grained image classification is image classification where the considered classes are all sub-classes of a certain, more general class. In this setting of the problem, the classes are visually very similar to each other, such that an unskilled human cannot discriminate between them. In this case, proposed methods for the ordinary image classification problem do not obtain good classification accuracy. So proposing new methods for solving this problem is necessary. In this thesis two new methods, based on recent advances in deep learning are proposed for solving the fine-grained image classification problem. First by improving several parts of one of the recent proposed methods for this... 

    Deep relative attributes

    , Article 13th Asian Conference on Computer Vision, ACCV 2016, 20 November 2016 through 24 November 2016 ; Volume 10115 LNCS , 2017 , Pages 118-133 ; 03029743 (ISSN); 9783319541921 (ISBN) Souri, Y ; Noury, E ; Adeli, E ; Sharif University of Technology
    Springer Verlag  2017
    Visual attributes are great means of describing images or scenes, in a way both humans and computers understand. In order to establish a correspondence between images and to be able to compare the strength of each property between images, relative attributes were introduced. However, since their introduction, hand-crafted and engineered features were used to learn increasingly complex models for the problem of relative attributes. This limits the applicability of those methods for more realistic cases. We introduce a deep neural network architecture for the task of relative attribute prediction. A convolutional neural network (ConvNet) is adopted to learn the features by including an... 

    Monthly electricity consumption forecasting: a step-reduction strategy and autoencoder neural network

    , Article IEEE Industry Applications Magazine ; Volume 27, Issue 2 , 2021 , Pages 90-102 ; 10772618 (ISSN) Li, Z ; Li, K ; Wang, F ; Xuan, Z ; Mi, Z ; Li, W ; Dehghanian, P ; Fotuhi Firuzabad, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Accurate monthly electricity consumption forecasting (ECF) can help retailers enhance the profitability in deregulated electricity markets. Most current methods use monthly load data to perform monthly ECF, which usually produces large errors due to insufficient training samples. A few methods try to use fine-grained smart-meter data (e.g., hourly data) to increase training samples. However, such methods still exhibit low accuracy due to the increase in forecasting steps. © 1975-2012 IEEE  

    Resistance spot welding of ultra-fine grained steel sheets produced by constrained groove pressing: Optimization and characterization

    , Article Materials Characterization ; Volume 69 , 2012 , Pages 71-83 ; 10445803 (ISSN) Khodabakhshi, F ; Kazeminezhad, M ; Kokabi, A. H ; Sharif University of Technology
    Constrained groove pressing as a severe plastic deformation method is utilized to produce ultra-fine grained low carbon steel sheets. The ultra-fine grained sheets are joined via resistance spot welding process and the characteristics of spot welds are investigated. Resistance spot welding process is optimized for welding of the sheets with different severe deformations and their results are compared with those of as-received samples. The effects of failure mode and expulsion on the performance of ultra-fine grained sheet spot welds have been investigated in the present paper and the welding current and time of resistance spot welding process according to these subjects are optimized.... 

    Stress relaxation and flow behavior of ultrafine grained AA 1050

    , Article Mechanics of Materials ; Volume 89 , 2015 , Pages 23-34 ; 01676636 (ISSN) Mohebbi, M. S ; Akbarzadeh, A ; Yoon, Y. O ; Kim, S. K ; Sharif University of Technology
    Elsevier  2015
    Abstract Flow behavior of ultrafine grained (UFG) AA 1050 sheets processed by Accumulative Roll-Bonding (ARB) and its viscous nature are investigated by plane strain compression test (PSC) along with stress relaxation. Occurrence of dynamic recovery is validated by TEM observations as the microstructural explanation of the flow softening at the start of deformation of the 8-cycles specimen. Significant recovery of the UFG specimens during the stress relaxation test is also disclosed. It is discussed that neither the internal stress (σi) nor the density of mobile dislocations are constant during the test. The possible effects of these two factors as well as contribution of the... 

    The effects of combination of severe plastic deformation and Shot Peening surface treatment on fatigue behavior of 6082 aluminum alloy

    , Article Russian Journal of Non-Ferrous Metals ; Volume 56, Issue 2 , 2015 , Pages 206-211 ; 10678212 (ISSN) Mohammadi, S ; Irani, M ; Karimi Taheri, A ; Sharif University of Technology
    In this paper, the effects of Equal Channel Angular Pressing process (ECAP) followed by Shot Peening process (SP) on the fatigue properties of 6082 aluminum alloy are investigated. Several samples of the alloy are ECAPed and SPed and then their mechanical behavior are characterized using tensile, micro-hardness, and fatigue tests. The results indicate that shot peening and then polishing the specimen after one-pass ECAP is an effective method to improve the fatigue life of the alloy. Moreover, by increasing the number of ECAP passes before shot peening, a local work softening occurs at the subsurface layer, leading to a significant decrease in the fatigue life of the alloy. The results of... 

    Investigation of Structure, Microstructure and Mechanical Properties of Al/AZ31 Composite Produced by ARB

    , M.Sc. Thesis Sharif University of Technology Sabeti, Ali (Author) ; Akbarzadeh Changiz, Abbas (Supervisor)
    Metallic multilayer composites provide remarkable mechanical, electrical and magnetic properties. These kinds of composites are recently processed by severe plastic deformation methods. Accumulative roll bonding (ARB) is one of the SPD processes in which accumulation of strain by repeating cycles, leads to the ultra fine grains structures. The goal of this research is manufacturing of Al/AZ31 composite and investigating the relation between the rolling process parameters and the mechanical and physical properties of the final sheet. The initial composite was carried out by cladding of 1mm thick AZ31 sheet in between two commercially pure aluminum sheets with the same thickness (57%... 

    Physical Modeling of Metal Matrix Composite Sheets With Second Phase Manufactured by Accumulative Roll Bonding (ARB) of Al-Ni Laminations

    , M.Sc. Thesis Sharif University of Technology Rezaei Anvar, Behrouz (Author) ; Akbarzadeh, Abbas (Supervisor)
    Metallic multilayer composites provide remarkable mechanical, electrical and magnetic properties. These kinds of composites have been recently processed by severe plastic deformation (SPD) methods. Accumulative roll bonding (ARB) is one of the SPD processes in which accumulation of strain by repeating cycles, leads to the ultra fine grained materials. The goal of this research is manufacturing of Al/Ni composite sheets by ARB process considering the effects of thickness and number of initial sheets on their mechanical properties and microstructures. The initial composites were produced by commercially pure Al and Ni as the matrix and the reinforcement, respectively. Thickness of the Al... 

    Processing Nano Composite Structure of 1100 and 3004 Al Alloy Sheets Using ARB Technique and Study Influence of Heat Treatment on the Grain Structure

    , M.Sc. Thesis Sharif University of Technology Shishegar, Hamid Reza (Author) ; Asgari, Sirous (Supervisor)
    At this study, nano structure sheet composite produced by1100 and 3004 strips using Accumulative role banding then mechanical and physical properties of the composites were investigated. After surface preparation, primary composite samples produced by putting different layers on each other and then rolling. The rolling was occurred in two steps; thickness reduction at first and second step were about 50% and 34%, respectively. ARB process were done till ninth cycle for Primary composite samples. To investigate mechanical properties of the samples, hardness, micro hardness and tensile strength tests have been done. Furthermore, micro structure of selective samples were studied by light... 

    Production of Nanostructured Composite Sheets of AA1100/St37 Using ARB Technique and Evaluation of Heat Treatment Effect on Grains Structure

    , M.Sc. Thesis Sharif University of Technology Vakili, Hossein (Author) ; Asgari, Sirous (Supervisor)
    In present work, nanostructured multilayer composites produced from AA1100 and St37 alloys and mechanical properties of resulted samples characterized using tension and micro hardness tests. Also dispersion pattern of second phase in matrix studied via optical microscopy. Thickness of second phase layers showed a little reduction after 2 ARB cycles; but their length decrease gradually. With increasing number of ARB cycles up to 6 cycles, sample's tensile strength first decrease rapidly and after that increased, but never reached initial value. In order to evaluation of heat treatment effects on samples grain structure, samples heat treated and tensile test carried on them. Annealing at 300... 

    Mechanical Property and Structural Changes of Pure Magnesium and AZ91 Alloy Using ECAP Process

    , M.Sc. Thesis Sharif University of Technology Garmroodi, Peiman (Author) ; Assempour, Ahmad (Supervisor)
    In recent years, severe plastic deformation processes have been widely used to correct the grain size of metals. One of these methods is equal channel angular pressing. In this research, the improvement of mechanical property and structural changes of pure magnesium and AZ91 alloy after the ECAP process are investigated. The mold is made of H13 steel with a 90-degree channel crossing angle and a zero-degree external curve angle. The purpose of this study is to find the smallest average grain size at the optimum temperature on these materials. First, pure magnesium and AZ91 are subjected to the ECAP process at temperatures of 250, 300, 350, and 400 °C to calculate the best operating... 

    Microstructure Features and Mechanical Properties Microtubes of WE43 Magnesium Alloys for Biodegradable Vascular Stent Application

    , M.Sc. Thesis Sharif University of Technology Torabi Kafshgari, Mehran (Author) ; Akbarzadeh, Abbas (Supervisor)
    Magnesium and its alloys have gained much attention in medical applications, especially bio-degradable stents. However, they have not been used extensively due to their natural limitations, such as weak mechanical properties. WE43 magnesium alloy has gained attention as a bio-alloy due to its high temperature and good corrosion resistance. The present study aims to use a combination of ECAP and direct tube extrusion to fabricate thin wall tubes with good mechanical properties using WE43 magnesium alloy. In the first phase, the ECAP process at 370°C were conducted up to 4 passes on the homogenized samples to reach ultrafine grain structure. Subsequent to ECAP, direct tube extrusion at 230 °C,... 

    Fabrication and Investigation of the Microscopic Structure and Mechanical Properties of Zx00 Magnesium Alloy by Applying the Multi-Directional Forging Process on Extruded and Homogenized Samples

    , M.Sc. Thesis Sharif University of Technology Dehghan, Ali (Author) ; Akbarzadeh, Abbas (Supervisor)
    Magnesium and its alloys have gained significant attention in medical applications due to their good biocompatibility. However, their widespread use has been limited by some inherent drawbacks, such as poor mechanical properties. The ZX00 magnesium alloy has been used in medical applications, including implants, due to its slow degradation rate and good ossification. However, this alloy lacks sufficient strength and ductility. The severe plastic deformation method can create an ultrafine grain structure and improve mechanical properties. In this study, to improve the mechanical properties and create an ultrafine grain structure, the multi-directional forging process was performed on... 

    Towards dark silicon era in FPGAs using complementary hard logic design

    , Article Conference Digest - 24th International Conference on Field Programmable Logic and Applications, FPL 2014 ; Sept , 2014 , pp. 1 - 6 ; ISBN: 9783000446450 Ahari, A ; Khaleghi, B ; Ebrahimi, Z ; Asadi, H ; Tahoori, M. B ; Sharif University of Technology
    While the transistor density continues to grow exponentially in Field-Programmable Gate Arrays (FPGAs), the increased leakage current of CMOS transistors act as a power wall for the aggressive integration of transistors in a single die. One recently trend to alleviate the power wall in FPGAs is to turn off inactive regions of the silicon die, referred to as dark silicon. This paper presents a reconfigurable architecture to enable effective fine-grained power gating of unused Logic Blocks (LBs) in FPGAs. In the proposed architecture, the traditional soft logic is replaced with Mega Cells (MCs), each consists of a set of complementary Generic Reconfigurable Hard Logic (GRHL) and a conventional... 

    Effects of nucleation agents on the preparation of transparent glass-ceramics

    , Article Journal of the European Ceramic Society ; Volume 32, Issue 11 , August , 2012 , Pages 2989-2994 ; 09552219 (ISSN) Ghasemzadeh, M ; Nemati, A ; Baghshahi, S ; Sharif University of Technology
    Elsevier  2012
    Formation of transparent glass-ceramic in the system MgO-SiO 2-Al 2O 3-K 2O-B 2O 3-F with and without addition of LiF and NaF has been investigated. Crystallization of glass-sample was conducted by controlled thermal heat-treatment, at determined nucleation and crystallization temperatures. In this regard, the effects of addition of LiF and NaF were investigated on the crystallization behavior and transparency of the samples. Low transmission (less than 80% at 600. nm) was observed in the basic composition (K).The addition of NaF and LiF caused more intense phase separation in the system. The results indicated that the glass-ceramic can remain transparent if fine grains with nano size are...