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Shi D.,Beihang University | Dong C.,Beihang University | Yang X.,Beihang University | Sun Y.,Beihang University | And 2 more authors.
Materials and Design | Year: 2013

Experiments are carried out at elevated temperature to investigate the effect of brazing itself and post-brazing heat treatment on the lifetime of directionally solidified (DS) superalloy. Meanwhile, a new lifetime prediction methodology based on continuum damage mechanics (CDM) is proposed to predict the lifetime of DS superalloy and its brazed joints. After creep and fatigue testing, the fractured specimens are observed by means of Optical Microscope (OM) and Scanning Electron Microscope (SEM) with the Energy Dispersive X-ray Spectrometer (EDXS) to understand their failure mechanisms. The results showed that: (1) under the same test condition, all the brazed joints exhibited a lower creep and fatigue lifetime compared with a typical DS superalloy; (2) the creep and fatigue lifetime of heat treated brazed joint was longer than that of non heat treated one; (3) the developed CDM method can be used to predict the lifetime of all the specimens; (4) all the brazed joints fractured in the brazing seam; and (5) there were many distinctive differences between the failure mechanics of DS superalloy and its brazed joints. © 2012 Elsevier Ltd.


Wang F.N.,Airborne | Wang S.S.,Unit 95868 | Bai Y.,Key Laboratory of Complex Aviation System Simulation | Che W.F.,Key Laboratory of Complex Aviation System Simulation
Applied Mechanics and Materials | Year: 2014

For the complexity and nonlinearity of the input characteristics in network intrusion detection system, a feature extraction method for network intrusion detection based on RS-KPCA is studied. Firstly, the Rough Set (RS) theory is used to select the valuable features, while the unnecessary features are removed. Then, the features of the intrusion detection sample data are extracted by the kernel principal component analysis (KPCA) algorithm. The number of new features is determined by the cumulative contribution rate. Simulation results show that this method can effectively remove the interference features, and has the advantages of obvious principal component feature and concentrated contribution rate, compared with PCA. Overall, the proposed method can effectively integrate the nonlinear features of the original data, reduce the dimension, and improve the intrusion detection performance. © (2014) Trans Tech Publications, Switzerland.


Shi D.Q.,Beihang University | Hu X.A.,Beihang University | Wang J.K.,Key Laboratory of Complex Aviation System Simulation | Yu H.C.,Aerospace Research Institute of Materials And Processing Technology | And 2 more authors.
Fatigue and Fracture of Engineering Materials and Structures | Year: 2013

The effect of notch types and stress concentration factors (Kt) on low cycle fatigue life and cracking of the DZ125 directionally solidified superalloy has been experimentally investigated. Single-edge notched specimens with V and U type geometries were tested at 850 °C with stress ratio R = 0.1. High temperature in situ optical method was used to observe crack initiation and short crack propagation. Scanning electron microscope observation of fracture was used to analyse the failure mechanism. The results reveal that fatigue resistance decreases with Kt increasing from 1.76 to 4.35. The ratcheting is found to be affected by both Kt and the nominal stress from the displacement-force curve. In situ observations indicate that the cracking does not occur at the notch apex but at the location where the max principal stress or Hill's stress is the highest. According to the scanning electron microscope observations, the failure of the notched specimens strongly depends on the anisotropy microstructures. © 2013 Wiley Publishing Ltd.


Zhang S.,Beihang University | Tang Z.,Key Laboratory of Complex Aviation System Simulation | Song X.,Beihang University | Ren Z.,Beihang University | Meng H.,Beihang University
Communications in Computer and Information Science | Year: 2012

A new yet promising technology, Cloud computing, can benefit large-scale simulations by providing on-demand, everywhere simulation services to users. In order to enable multi-task and multi-user simulation tasks with Cloud computing, Cloud Simulation Platform (CSP) is proposed and developed. To promote the running efficiency of HLA systems on CSP, this paper proposes an approach addressing the Virtual Machine task allocation problem, which is divided into two levels of task allocation steps. The first-level uses a heuristic algorithm to optimize the mapping from federates (of HLA system) to virtual machines (of CSP) and aims to achieve load balance on virtual machines in CSP. The second-level dispatches the subtasks of federate to the cores of virtual machines to minimize the makespan (schedule length) of the federate which uses a DAG based list scheduling algorithm: the EST (Earliest-Start-Time) algorithm. Experiments show that the two-level task allocation strategy effectively improves the running efficiency of HLA system on CSP. © 2012 Springer-Verlag.


Wang J.,Beihang University | Wang J.,Key Laboratory of Complex Aviation System Simulation | Yang X.,Beihang University
International Journal of Fatigue | Year: 2012

Generally not only the material but also the notch geometry affects the HCF strength. So, when evaluating the fatigue limit of notched Ti-6Al-4V specimens using the conventional theory of critical distance (TCD), a possible critical distance size effect was identified. In this paper, in order to overcome the critical distance size effect, Kt was introduced. And based on an assumption that the product of critical distance and Kt was constant, the TCD was modified to evaluate the HCF strength of notched Ti-6Al-4V specimens. The prediction results fell into an error interval of about ±15% using the modified TCD. © 2011 Elsevier Ltd. All rights reserved.


Yin X.,Department of National Defence | Han L.,Beijing Institute of Radiation Medicine | Bai H.,Beijing Institute of Radiation Medicine | Bo X.,Beijing Institute of Radiation Medicine | And 4 more authors.
Proceedings of the International Joint Conference on Neural Networks | Year: 2015

Modern understanding of microbiology largely lays foundation in the biological characterization of microorganisms. However, the landscape relationships of host transcriptional response (HTR) to different bacterial pathogens have not yet been systematically explored. Here, we established the first generation of HTR network (HTRN) according to the HTR similarities among 21 different human pathogenic bacterial species by integrating 258 pairs of host cellular gene expression profiles upon infections. Further, the network was dissected into five bacterial communities of more consensus internal HTR. Interestingly, analysis of signature genes across different communities revealed that distinct community signatures (CS) present differential gene expression patterns. Functional annotation suggested a common feature of host cell response to bacterial infections that specific functional gene clusters (BPs and/or signaling pathways) were preferentially elicited or subverted by community bacterial pathogens. Notably, community signatures (especially key associators participating dissimilar functional profiles) were highly enriched of GWAS disease-related genes, which associated bacterial infections with common and specific non-infectious human disease(s). About 40% of the associations were confirmed by literature investigation that further indicated possible/potential association directionality. Our characterization and analysis were the first to feature differential community HTRs upon bacterial pathogen infections and suggested new perspective of understanding infection-disease associations and underlying pathogenesis. © 2015 IEEE.


Zhao G.,Beijing Institute of Technology | Zhang K.,Key Laboratory of Complex Aviation System Simulation | Wang W.,Beijing Institute of Technology | Huang S.,Science and Technology on Information Systems Engineering Laboratory | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

This paper presents a new image enhancement method based on self-adaptive piecewise linear transformation. It is most important to select division points during the processing course of piecewise linear transformation because these division points can decide the quality and efficiency of image enhancement. In this paper, division points are automatically and self-adaptive selected based on the gray grade and histogram feature of images. In order to increase the contrast of the image, it is necessary to extend the object section, maintain the transition section and compress the background section. Our method is easy to use, and the experiment results show that the technique can produce good results on a variety of images. © 2013 SPIE.


Bai Y.,Key Laboratory of Complex Aviation System Simulation | Bai Y.,PLA Air Force Aviation University | Zhang F.M.,PLA Air Force Aviation University | Che W.F.,Key Laboratory of Complex Aviation System Simulation | And 2 more authors.
Applied Mechanics and Materials | Year: 2014

Most of the research on the relationship between Artificial Intelligence(AI) and Complexity argued the possibility and reality from a philosophical point of view. Recently A few papers popped up to explored AI Science through Complex System Theory. In fact, Dr. Bai's conception of the Top Machine(TM), which was firstly proposed in his dissertation "Generalized Symbolism and Knowledge Presentation of Hyper Topology Structure" in 1999, may comprise the following three fundamental points. He proposed this idea, defined it, and established the Wave and High Jump Principles. This paper intended to explore the scientific features of the TM Model in relation to the three concerned points, and drew the conclusion that TM model is worth in-depth study not only because it visualized the complexity of AI Science, but also it could be an abstract conceptual model of Intelligent System(IS). © (2014) Trans Tech Publications, Switzerland.


Wang F.N.,Airborne | Wang S.S.,Key Laboratory of Complex Aviation System Simulation | Che W.F.,Key Laboratory of Complex Aviation System Simulation | Bai Y.,Key Laboratory of Complex Aviation System Simulation
Applied Mechanics and Materials | Year: 2014

An intrusion detection method based on RS-LSSVM is studied in this paper. Firstly, attribute reduction algorithm based on the generalized decision table is proposed to remove the interference features and reduce the dimension of input feature space. Then the classification method based on least square support vector machine (LSSVM) is analyzed. The sample data after dimension reduction is used for LSSVM training, and the LSSVM classification model is obtained, which forms the ability of detecting unknown intrusion. Simulation results show that the proposed method can effectively remove the unnecessary features and improve the performance of network intrusion detection. © (2014) Trans Tech Publications, Switzerland.


Cheng J.,Key Laboratory of Complex Aviation System Simulation | Cheng J.,National University of Defense Technology | Cheng J.,Australian National University | Kim J.,Australian National University | And 2 more authors.
Robotics and Autonomous Systems | Year: 2016

This paper presents a new parameterization approach for the graph-based SLAM problem and reveals the differences of two popular over-parameterized ways in the optimization procedure. In the SALM problem, constraints or relative transformations between any two poses are generally separated into translations plus 3D rotations, which are then described in a homogeneous transformation matrix (HTM) to simplify computational operations. This however introduces added complexities in frequent conversions between the HTM and state variables, due to their different representations. This new approach, unit dual quaternion (UDQ), describes a spatial transformation as a screw with only 8 elements. We show that state variables can be directly represented by UDQs, and how their relative transformations can be written with the UDQ product, without the trivial computations of HTM. Then, we explore the performances of the unit quaternion and the axis-angle representations in the graph-based SLAM problem, which have been successfully applied to over parameterize perturbations under the assumption of small errors. Based on public synthetic and real-world datasets in 2D and 3D environments, experimental results show that the proposed approach reduces greatly the computational complexity while obtaining the same optimization accuracies as the HTM-based algorithm, and the axis-angle representation is superior to be the quaternion in the case of poor initial estimations. © 2015 Elsevier B.V. All rights reserved.

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