An Optimization Method for Designing LDPC Analog Decoders Based on Frequent Subgraph Mining Algorithm

Yuan Gao,Yujie Lin,Jibo Dai 보안공학연구지원센터 2016 International Journal of Signal Processing, Image Vol.9 No.10

To lower the mapping complexity of designing analog decoders, a method to optimize the design of low-density parity-check (LDPC) analog decoders is proposed in this paper. Based on factor graphs and the sum-product algorithm, the LDPC decoding process on the factor graph and the construction of analog decoders are exploited. Then the frequent subgraph mining algorithm is introduced to search the isomorphic subgraphs in factor graphs. According to the output of the frequent subgraph mining algorithm which enumerates all the subgraphs in factor graphs, the mapping complexity of a LDPC analog decoder can be significantly reduced. Finally, a (40, 16) LDPC analog decoder is constructed using the proposed method. Simulation results show that the need to place gates and connections can be reduced 90% and 23%, respectively, and the ideal performance is obtained by carefully choosing unit currents and decoding time.

Multi-GPU Parallel Computing and Task Scheduling under Virtualization

Yujie Zhang,Jiabin Yuan,Xiangwen Lu,Xingfang Zhao 보안공학연구지원센터 2015 International Journal of Hybrid Information Techno Vol.8 No.7

Numerical study on the internal flow characteristics of an axial-flow pump under stall conditions

Kan Kan,Yuan Zheng,Yujie Chen,Zhanshan Xie,Guang Yang,Chunxia Yang 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.10

When an axial-flow pump works in low flow rate conditions, rotating stall phenomena will probably occur, and the pump will enter hydraulic unsteady conditions. The rotating stall can lead to violent vibration, noise, turbulent flow, and a sharp drop in efficiency. This affects the safety and stability of the pump unit. To study the rotating stall flow characteristics of an axial-flow pump, the steady and unsteady internal flow field in a large vertical axial-flow pump was investigated using 3D computational fluid dynamic (CFD) technology. Numerical calculations were carried out using the Reynolds-averaged Navier–Stokes (RANS) solver and Menter's shear stress transport (SST) k-ω turbulence model. Steady flow characteristics including streamline, velocity vector, pressure and turbulent kinetic energy are presented and analyzed. Unsteady flow characteristics are described using post-processing signals for pressure monitoring points in the time and frequency domains. Using Q-criterion, the locations and evolution rules of the core region of the vortex structure in guide vanes under deep stall conditions were investigated. The reliability of the numerical simulation results was verified using the experimental prototype pressure fluctuation test. In this way, typical flow structure and pressure fluctuation characteristics in an axial-flow pump were analyzed, with contrastive analysis in design condition and stall conditions. Finally, the mechanism of low-frequency pressure fluctuation in a pump unit under the stall condition was revealed.

Property Assessment of High-Performance Concrete Containing Three Types of Fibers

Hua Huang,Yujie Yuan,Wei Zhang,Liang Zhu 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.6

This study investigated the mechanical properties and the effects of the volume fraction for carbon fibers (CF-VF), polypropylene fibers (PPF-VF) and aramid fibers (AF-VF) with a fixed aspect ratio of 650 for the carbon fibers, 400 for the polypropylene fibers and 900 for the aramid fibers in hybrid fiber-reinforced concrete (HFRC). Furthermore, compressive, splitting tensile and flexural tensile tests were carried out to obtain the optimal total volume fraction for the three types of fibers, as well as the optimal ratio between the CF-VF, PPF-VF and AF-VF. In addition, stress-strain curves of normal concrete and HFRC were examined to explore the whole mechanical process. The results indicated the CF-VF, PPF-VF and AF-VF have a significant effect on the tensile and flexural strengths of HFRC. The HFRC with a fiber additional ratio of 25:50:25 had the best hybrid effect. Moreover, a calculation method based on the compressive strength of normal concrete and HFRC and the volume fraction is proposed to calculate the strength of HFRC in engineering as a reference. Besides, a uniaxial compression constitutive mathematical model of normal concrete and HFRC is established.

Frequency-Domain Transformation Approaches to Develop the d-q Synchronous-Frame Models of Three-Phase Symmetrical Networks and Applications in Modeling of PWM Power Converters

Xiaoyu Wang,Jinjun Liu,Yuji Meng,Jinku Hu,Chang Yuan 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

Although state-space averaging small-signal modeling techniques are successfully established in DC-DC converters and three-phase sinusoidal PWM converters, these approaches are limited only to low-order systems, and the modeling process is very complex. This paper proposes two equivalent approaches in frequency domain to develop the d-q synchronous-frame models from stationary-frame models for arbitrary three-phase symmetrical circuits. The first modeling approach is illustrated with frequency transformation, by which the target synchronous-frame models could be easily obtained by frequency transformation of the prototype stationary-frame models. The second modeling approach is based on the reactive elements substitutions. These two approaches can be proven to be equivalent, and the first approach is suitable for input-output models, while the second approach is preferable for state-space models. As illustrative examples, these approaches are applied to develop the synchronous-frame models of large three-phase systems with PWM converters. They are proven valid with the comparison with current published models.

A Novel Image Superresolution Reconstruction Algorithm Based on Sparse Representation

Aili Wang,Xinyuan Wang,Yuji Iwahori,Yuan Feng,Na Jiang 보안공학연구지원센터 2015 International Journal of Signal Processing, Image Vol.8 No.6

Superresolution image reconstruction technique uses single or a series of low-resolution images to reconstruct a high resolution image without changing the hardware devices, while improving image quality and the spatial resolution of the image. High resolution means the image with a higher pixel density, can provide more details. In this paper, a novel image superresolution algorithm based on sparse representation is studied. During over-complete dictionary of the training phase, the proposed method improves two aspects including feature extraction and dimension reduction. In the feature extraction process, combining the second derivative with the gradient direction, we construct a new descent direction to improve gradient method. The convergence speed of the new algorithm is faster than the gradient method and can get better results. Then improved two-dimensional Principal Component Analysis (2DPCA) algorithm is used to reduce the dimension, it could eliminate the correlation of the image lines and column. Experiment results show that this method of image reconstruction is better and faster for high resolution image reconstruction.

A Learning-based Power Control Scheme for Edge-based eHealth IoT Systems

( Haoru Su ),( Xiaoming Yuan ),( Yujie Tang ),( Rui Tian ),( Enchang Sun ),( Hairong Yan ) 한국인터넷정보학회 2021 KSII Transactions on Internet and Information Syst Vol.15 No.12

The Internet of Things (IoT) eHealth systems composed by Wireless Body Area Network (WBAN) has emerged recently. Sensor nodes are placed around or in the human body to collect physiological data. WBAN has many different applications, for instance health monitoring. Since the limitation of the size of the battery, besides speed, reliability, and accuracy; design of WBAN protocols should consider the energy efficiency and time delay. To solve these problems, this paper adopt the end-edge-cloud orchestrated network architecture and propose a transmission based on reinforcement algorithm. The priority of sensing data is classified according to certain application. System utility function is modeled according to the channel factors, the energy utility, and successful transmission conditions. The optimization problem is mapped to Q-learning model. Following this online power control protocol, the energy level of both the senor to coordinator, and coordinator to edge server can be modified according to the current channel condition. The network performance is evaluated by simulation. The results show that the proposed power control protocol has higher system energy efficiency, delivery ratio, and throughput.

Frequency Characteristics of the d-q Synchronous-Frame Current Reference Generation Methods for Active Power Filter

Xiaoyu Wang,Jinjun Liu,Jinku Hu,Yuji Meng,Chang Yuan 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

The d-q harmonics detection algorithms are dominant methods to generate current reference for active power filter (APF). They are often processed in synchronous frame and time domain. This paper researches the frequency characteristics of d-q synchronous transformation which are quite related to the design of close loop regulator and analysis of the performance. Intuitively, the synchronous transformation is explained with amplitude modulation (AM) in this paper. Then the synchronous filter is proven as time-invariant linear transformation and modeled with transfer functions in stationary frame and frequency domain. The frequency-domain analytical models imply that the synchronous transformation has an equivalent effect of frequency transformation, with which the synchronous filter achieves a band pass filter from the low pass filter in synchronous frame. To simplify the analytical model, an instantaneous positive/negative sequence frame is proposed as an expansion of symmetrical components theory. Based on these frequency analytical models, the synchronous filter is compared with the traditional filters in stationary frame. Further more, the d-q harmonics detection methods are improved to get rid of the inherent coupling of synchronous transformation. Typical examples are given to verify previous analysis and comparison. Simulation and experimental results are also given.

Frequency Characteristics of the Synchronous-Frame Based D-Q Methods for Active Power Filters

WANG Xiaoyu,LIU Jinjun,HU Jinku,MENG Yuji,YUAN Chang 전력전자학회 2008 JOURNAL OF POWER ELECTRONICS Vol.8 No.1

The d-q harmonic detecting algorithms are dominant methods to generate current references for active power filters (APF). They are often implemented in the synchronous frame and time domain. This paper researches the frequency characteristics of d-q synchronous transformations, which are closely related to the analysis and design issues of control system. Intuitively, the synchronous transformation is explained with amplitude modulation (AM) in this paper. Then, the synchronous filter is proven to be a time-invariant and linear system, and its transfer function matrix is derived in the stationary frames. These frequency-domain models imply that the synchronous transformation has an equivalent effect of frequency transformation. It is because of this feature, the d-q method achieves band-pass characteristics with the low pass filters in the synchronous frame at run time. To simplify these analytical models, an instantaneous positive-negative sequence frame is proposed as expansion of traditional symmetrical components theory. Furthermore, the synchronous filter is compared with the traditional bind-pass filters based on these frequency-domain analytical models. The d-q harmonic detection methods are also improved to eliminate the inherent coupling effect of synchronous transformation. Typical examples are given to verify previous analysis and comparison. Simulation and experimental results are also provided for verification.

Remote estimation of phytoplankton size fractions using the spectral shape of light absorption

Wang, Shengqiang,Ishizaka, Joji,Hirawake, Toru,Watanabe, Yuji,Zhu, Yuanli,Hayashi, Masataka,Yoo, Sinjae The Optical Society 2015 Optics express Vol.23 No.8