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Mobile Sensor Network Navigation Using Gaussian Processes With Truncated Observations
Yunfei Xu,Jongeun Choi,Songhwai Oh IEEE 2011 IEEE transactions on robotics Vol.27 No.6
<P>In this paper, we consider mobile sensor networks that use spatiotemporal Gaussian processes to predict a wide range of spatiotemporal physical phenomena. Nonparametric Gaussian process regression that is based on truncated observations is proposed for mobile sensor networks with limited memory and computational power. We first provide a theoretical foundation of Gaussian process regression with truncated observations. In particular, we demonstrate that prediction using all observations can be well approximated by prediction using truncated observations under certain conditions. Inspired by the analysis, we then propose a centralized navigation strategy for mobile sensor networks to move in order to reduce prediction error variances at points of interest. For the case in which each agent has a limited communication range, we propose a distributed navigation strategy. Particularly, we demonstrate that mobile sensing agents with the distributed navigation strategy produce an emergent, swarming-like, collective behavior for communication connectivity and are coordinated to improve the quality of the collective prediction capability.</P>
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DETECTION AND RESTORATION OF NON-RADIAL VARIATION OVER FULL-DISK SOLAR IMAGES
Yunfei Yang,Jiaben Lin,Song Feng,Hui Deng,Feng Wang,Kai-fan Ji 한국천문학회 2013 Journal of The Korean Astronomical Society Vol.46 No.5
Full-disk solar images are provided by many solar telescopes around the world. However, the observed images show Non-Radial Variation (NRV) over the disk. In this paper, we propose algorithms for detecting distortions and restoring these images. For detecting NRV, the cross-correlation coefficients matrix of radial profiles is calculated and the minimum value in the matrix is defined as the Index of Non-radial Variation (INV). This index has been utilized to evaluate the H$\alpha$ images of GONG, and systemic variations of different instruments are obtained. For obtaining the NRV's image, a Multi-level Morphological Filter (MMF) is designed to eliminate structures produced by solar activities over the solar surface. Comparing with the median filter, the proposed filter is a better choice. The experimental results show that the effect of our automatic detection and restoration methods is significant for getting a flat and high contrast full-disk image. For investigating the effect of our method on solar features, structural similarity (SSIM) index is utilized. The high SSIM indices (close to 1) of solar features show that the details of the structures remain after NRV restoring.
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Yunfei Zha,Maojin Li,Jianyong Yang 대한영상의학회 2010 Korean Journal of Radiology Vol.11 No.2
Objective: To investigate the significance of the dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) parameters of diffuse spinal bone marrow infiltration in patients with hematological malignancies. Materials and Methods: Dynamic gadolinium-enhanced MR imaging of the lumbar spine was performed in 26 patients with histologically proven diffuse bone marrow infiltration, including multiple myeloma (n = 6), acute lymphoblastic leukemia (n = 6), acute myeloid leukemia (n = 5), chronic myeloid leukemia (n = 7), and non-Hodgkin lymphoma (n = 2). Twenty subjects whose spinal MRI was normal, made up the control group. Peak enhancement percentage (Emax), enhancement slope (ES), and time to peak (TTP) were determined from a timeintensity curve (TIC) of lumbar vertebral bone marrow. A comparison between baseline and follow-up MR images and its histological correlation were evaluated in 10 patients. The infiltration grade of hematopoietic marrow with plasma cells was evaluated by a histological assessment of bone marrow. Results: Differences in Emax, ES, and TTP values between the control group and the patients with diffuse bone marrow infiltration were significant (t = -11.51, -9.81 and 3.91, respectively, p < 0.01). Emax, ES, and TTP values were significantly different between bone marrow infiltration groups Grade 1 and Grade 2 (Z = -2.72, -2.24 and -2.89 respectively, p < 0.05). Emax, ES and TTP values were not significantly different between bone marrow infiltration groups Grade 2 and Grade 3 (Z = -1.57, -1.82 and -1.58 respectively, p > 0.05). A positive correlation was found between Emax, ES values and the histological grade of bone marrow infiltration (r = 0.86 and 0.84 respectively, p < 0.01). A negative correlation was found between the TTP values and bone marrow infiltration histological grade (r = -0.54, p < 0.01). A decrease in the Emax and ES values was observed with increased TTP values after treatment in all of the 10 patients who responded to treatment (t = -7.92, -4.55, and 5.12, respectively, p < 0.01). Conclusion: DCE-MRI of spine can be a useful tool in detecting diffuse marrow infiltration of hematological malignancies, while its parameters including Emax, ES, and TTP can reflect the malignancies’ histological grade. Objective: To investigate the significance of the dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) parameters of diffuse spinal bone marrow infiltration in patients with hematological malignancies. Materials and Methods: Dynamic gadolinium-enhanced MR imaging of the lumbar spine was performed in 26 patients with histologically proven diffuse bone marrow infiltration, including multiple myeloma (n = 6), acute lymphoblastic leukemia (n = 6), acute myeloid leukemia (n = 5), chronic myeloid leukemia (n = 7), and non-Hodgkin lymphoma (n = 2). Twenty subjects whose spinal MRI was normal, made up the control group. Peak enhancement percentage (Emax), enhancement slope (ES), and time to peak (TTP) were determined from a timeintensity curve (TIC) of lumbar vertebral bone marrow. A comparison between baseline and follow-up MR images and its histological correlation were evaluated in 10 patients. The infiltration grade of hematopoietic marrow with plasma cells was evaluated by a histological assessment of bone marrow. Results: Differences in Emax, ES, and TTP values between the control group and the patients with diffuse bone marrow infiltration were significant (t = -11.51, -9.81 and 3.91, respectively, p < 0.01). Emax, ES, and TTP values were significantly different between bone marrow infiltration groups Grade 1 and Grade 2 (Z = -2.72, -2.24 and -2.89 respectively, p < 0.05). Emax, ES and TTP values were not significantly different between bone marrow infiltration groups Grade 2 and Grade 3 (Z = -1.57, -1.82 and -1.58 respectively, p > 0.05). A positive correlation was found between Emax, ES values and the histological grade of bone marrow infiltration (r = 0.86 and 0.84 respectively, p < 0.01). A negative correlation was found between the TTP values and bone marrow infiltration histological grade (r = -0.54, p < 0.01). A decrease in the Emax and ES values was observed with increased TTP values after treatment in all of the 10 patients who responded to treatment (t = -7.92, -4.55, and 5.12, respectively, p < 0.01). Conclusion: DCE-MRI of spine can be a useful tool in detecting diffuse marrow infiltration of hematological malignancies, while its parameters including Emax, ES, and TTP can reflect the malignancies’ histological grade.
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Design and optimization of coil structure based on the uniformity of core temperature field
Yunfei Gu,Jiazhong Xu,Tianyu Fu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.6
Coil structure size parameters during electromagnetic induction heating affect the temperature field and heating rate of a carbon fiber-reinforced polymer (CFRP) shell. In this study, a finite element analysis model is established on the basis of a single-screw coil structure, and the influence of coil diameter, length, turns, and position relationship on the temperature field distribution and heating rate of the CFRP shell is studied. According to image entropy theory, the influence of coil structure size parameters on the uniformity of a temperature field distribution is analyzed. Furthermore, the accuracy of the coil structure size parameters with respect to temperature field variation is verified with a CFRP induction heating experiment. This study provides theoretical support and a verification method for the selection, design, and optimization of the coil structure size parameters of CFRP shells during induction heating.
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SIFT-Based Low-Quality Fingerprint LSH Retrieval and Recognition Method
Yunfei Zhong,Xiaoqi Peng 보안공학연구지원센터 2015 International Journal of Signal Processing, Image Vol.8 No.8
Most of the existing fingerprint retrieval systems are based on the overall characteristics and detailed features of fingerprints, and their performance is poor in the cases of low-quality fingerprint images, such as incomplete fingerprint images. In order to improve the recognition speed, accuracy, and robustness of automated fingerprint recognition systems based on large-scale fingerprint databases, in this paper, we propose a fast fingerprint classification retrieval and identification method based on Scale Invariant Feature Transform (SIFT) and Local Sensitive Hash (LSH) algorithms. A method based on scale space theory extracts SIFT feature point descriptors of relatively high-quality fingerprint images in accordance with the principle of a greater matching contribution rate, uses multi-template image feature fusion technology to build a stable fingerprint feature template database, achieves the storage and retrieval of high-dimensional SIFT features using the LSH algorithm, and carries out matching progressively by level on the basis of SIFT’s matching principle of close neighboring priority scale. Experimental results show that the proposed method has strong penetration, high retrieval efficiency, good recognition accuracy, and strong robustness, thereby providing a fast and efficient retrieval and matching mechanism for the automated recognition of the large-scale fingerprint database, with strong practicality.
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Dynamic analysis of metro vehicle traveling on a high-pier viaduct under crosswind in Chongqing
Yunfei Zhang,Jun Li,Zhaowei Chen,Xiangyang Xu 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.29 No.5
Due to the rugged terrain, metro lines in mountain city across numerous wide rivers and deep valleys, resulting in instability of high-pier bridge and insecurity of metro train under crosswind. Compared with the conditions of no-wind, crosswind triggers severer vibration of the dynamic system; compared with the short-pier viaduct, the high-pier viaduct has worse stability under crosswind. For these reasons, the running safety of the metro vehicle traveling on a high-pier viaduct under crosswind is analyzed to ensure the safe operation in metro lines in mountain cities. In this paper, a dynamic model of the metro vehicle-track-bridge system under crosswind is established, in which crosswind loads model considering the condition of wind zone are built. After that, the evaluation indices and the calculation parameters have been selected, moreover, the basic characteristics of the dynamic system with high-pier under crosswind are analyzed. On this basis, the response varies with vehicle speed and wind speed are calculated, then the corresponding safety zone is determined. The results indicate that, crosswind triggers drastic vibration to the metro vehicle and high-pier viaduct, which in turn causes running instability of the vehicle. The corresponding safety zone for metro vehicle traveling on the high-pier is proposed, and the metro traffic on the high-pier bridge under crosswind should not exceed the corresponding limited vehicle speed to ensure the running safety.
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