The development of this technology has favored the advances noted in recent years in the field of precise positioning. It has also paved the way for a wide range of research into the evaluation of their performance an...The development of this technology has favored the advances noted in recent years in the field of precise positioning. It has also paved the way for a wide range of research into the evaluation of their performance and reliability, their potential use in different fields, the improvement of performance and combined systems, etc. Single-frequency GNSS receivers, which for a long time remained the only category of low-cost GNSS receivers, often limited by their level of accuracy (metric) mainly due to their single-frequency nature, have been joined in the last decade by dual-frequency GNSS receivers developed by certain manufacturers of positioning equipment. These receivers now offer possible alternatives to the relatively expensive conventional (topographic quality) or geodetic receivers and. In this study, the performance of these low-cost dual-frequency receivers was evaluated in static and real-time kinematic GNSS positioning modes. Static positioning was carried out on three points with sessions of 2 h and 4 h over three days with antenna swapping (CHC i50, Leica GS14 and Emlid Reach RS2+). Real-time observations were carried out on eleven (11) points in open, poorly open and not at all open environments, in order to assess not only performance but also receiver sensitivity in environments with a high risk of multipath. The results obtained showed an average agreement of 2 cm in planimetry between the low-cost Emlid RS2+ receiver and the Leica GS14 and CHC i50 receivers. The differences in altimetry are nevertheless greater (sometimes up to decimetres for certain points). Real-time positioning results provided an average convergence of around 1 cm on the E, N and H components with the results from the low-cost Emlid Reach RS2+ and Ublox ZED-F9P receivers and the CHC i50 receiver. Analysis of the results obtained has enabled us to highlight the various issues and challenges associated with this new generation of GNSS receivers, with a view to enhancing their appropriation and optimal integration in the professional and research worlds.展开更多
The numbers of beam positions(BPs)and time slots for beam hopping(BH)dominate the latency of LEO satellite communications.Aiming at minimizing the number of BPs subject to a predefined requirement on the radius of BP,...The numbers of beam positions(BPs)and time slots for beam hopping(BH)dominate the latency of LEO satellite communications.Aiming at minimizing the number of BPs subject to a predefined requirement on the radius of BP,a low-complexity user density-based BP design scheme is proposed,where the original problem is decomposed into two subproblems,with the first one to find the sparsest user and the second one to determine the corresponding best BP.In particular,for the second subproblem,a user selection and smallest BP radius algorithm is proposed,where the nearby users are sequentially selected until the constraint of the given BP radius is no longer satisfied.These two subproblems are iteratively solved until all the users are selected.To further reduce the BP radius,a duplicated user removal algorithm is proposed to decrease the number of the users covered by two or more BPs.Aiming at minimizing the number of time slots subject to the no co-channel interference(CCI)constraint and the traffic demand constraint,a low-complexity CCI-free BH design scheme is proposed,where the BPs having difficulty in satisfying the constraints are considered to be illuminated in priory.Simulation results verify the effectiveness of the proposed schemes.展开更多
Text extraction is the key step in the character recognition;its accuracy highly relies on the location of the text region. In this paper, we propose a new method which can find the text location automatically to solv...Text extraction is the key step in the character recognition;its accuracy highly relies on the location of the text region. In this paper, we propose a new method which can find the text location automatically to solve some regional problems such as incomplete, false position or orientation deviation occurred in the low-contrast image text extraction. Firstly, we make some pre-processing for the original image, including color space transform, contrast-limited adaptive histogram equalization, Sobel edge detector, morphological method and eight neighborhood processing method (ENPM) etc., to provide some results to compare the different methods. Secondly, we use the connected component analysis (CCA) method to get several connected parts and non-connected parts, then use the morphology method and CCA again for the non-connected part to erode some noises, obtain another connected and non-connected parts. Thirdly, we compute the edge feature for all connected areas, combine Support Vector Machine (SVM) to classify the real text region, obtain the text location coordinates. Finally, we use the text region coordinate to extract the block including the text, then binarize, cluster and recognize all text information. At last, we calculate the precision rate and recall rate to evaluate the method for more than 200 images. The experiments show that the method we proposed is robust for low-contrast text images with the variations in font size and font color, different language, gloomy environment, etc.展开更多
In recent years,WiFi indoor positioning technology has become a hot research topic at home and abroad.However,at present,indoor positioning technology still has many problems in terms of practicability and stability,w...In recent years,WiFi indoor positioning technology has become a hot research topic at home and abroad.However,at present,indoor positioning technology still has many problems in terms of practicability and stability,which seriously affects the accuracy of indoor positioning and increases the complexity of the calculation process.Aiming at the instability of RSS and the more complicated data processing,this paper proposes a low-frequency filtering method based on fast data convergence.Low-frequency filtering uses MATLAB for data fitting to filter out low-frequency data;data convergence combines the mean and multi-data parallel analysis process to achieve a good balance between data volume and system performance.At the same time,this paper combines the position fingerprint and the relative position method in the algorithm,which reduces the error on the algorithm system.The test results show that the strategy can meet the requirements of indoor passive positioning and avoid a large amount of data collection and processing,and the average positioning error is below 0.5 meters.展开更多
Given a symmetric matrix X, we consider the problem of finding a low-rank positive approximant of X. That is, a symmetric positive semidefinite matrix, S, whose rank is smaller than a given positive integer, , which i...Given a symmetric matrix X, we consider the problem of finding a low-rank positive approximant of X. That is, a symmetric positive semidefinite matrix, S, whose rank is smaller than a given positive integer, , which is nearest to X in a certain matrix norm. The problem is first solved with regard to four common norms: The Frobenius norm, the Schatten p-norm, the trace norm, and the spectral norm. Then the solution is extended to any unitarily invariant matrix norm. The proof is based on a subtle combination of Ky Fan dominance theorem, a modified pinching principle, and Mirsky minimum-norm theorem.展开更多
叶片覆冰会严重影响风机的安全稳定运行。目前,电热防冰是最高效可靠的风机叶片防冰方法,但存在防冰区域受热不均匀、局部覆冰以及过多分区导致防冰系统过于复杂等问题。为此提出采用正温度系数(positive temperature coefficient,PTC)...叶片覆冰会严重影响风机的安全稳定运行。目前,电热防冰是最高效可靠的风机叶片防冰方法,但存在防冰区域受热不均匀、局部覆冰以及过多分区导致防冰系统过于复杂等问题。为此提出采用正温度系数(positive temperature coefficient,PTC)材料进行风机叶片自适应电加热防冰的创新方法,通过原位聚合法成功制备了一种低居里点PTC材料,其居里温度点为1℃。随后,基于该材料的阻-温特性,建立了风机叶片的电加热防冰模型,并进行数值模拟。研究结果显示,当采用低居里点PTC材料进行风机叶片电加热防冰时,无需进行防冰区域的分区,就能使得防冰区域受热更加均匀。在一定的工作电压下,低居里点PTC材料在不同环境温度和风速下展现出自适应调节加热功率的能力,并且经过100次循环阻-温测试后,材料仍具有极强的自适应调节能力。最后,通过试验验证了材料的这种自适应调节能力。该研究结果为后续基于低居里点PTC材料的风机叶片防冰系统的研究奠定了坚实基础。展开更多
目的探讨极低出生体重儿(very low birth weight,VLBW)中适于胎龄儿(appropriate for gestational age,AGA)和小于胎龄儿(small for gestational age,SGA)身长增长对经外周中心静脉置管(peripherally inserted central catheter,PICC)...目的探讨极低出生体重儿(very low birth weight,VLBW)中适于胎龄儿(appropriate for gestational age,AGA)和小于胎龄儿(small for gestational age,SGA)身长增长对经外周中心静脉置管(peripherally inserted central catheter,PICC)尖端移位的影响,并横向比较影响程度,帮助医护人员更好地把握导管尖端位置监测的时机。方法回顾性分析2021年1月—2022年6月在医院NICU住院并使用PICC的VLBW,按出生体质量和胎龄关系分为AGA组45例和SGA组19例,记录首次置管当日身长(Ht_(1))以及PICC尖端位置、置管期间胸片检查当日身长(Ht_(n))以及PICC尖端位置,并计算相应的身长增长率。身长增长率与PICC尖端移位的相关性用Spearman秩相关分析。将AGA和SGA的身长增长率分别与PICC尖端移位进行简单线性回归分析,构建回归模型,用协方差分析比较两组回归直线。结果VLBW中AGA组97.8%患儿出现移位,SGA组所有的患儿都出现移位,占比最多的均为移位3个椎体。Spearman秩相关分析结果显示,两组患儿身长增长率与PICC尖端移位均具有相关性(AGA组rs=-0.719,P<0.001;SGA组rs=-0.769,P<0.001),随着VLBW身长增长,PICC尖端逐渐移位远离心脏。简单线性回归分析结果显示,AGA组回归模型(R^(2)=0.517,调整后R^(2)=0.513,F=129.487,P<0.001),SGA组回归模型(R^(2)=0.591,调整后R^(2)=0.585,F=95.385,P<0.001)。协方差分析结果显示,由于回归系数检验没有统计学意义,两条直线平行,说明身长增长率对两组患儿位移的影响一致。截距比较有统计学意义(F=9.265,P=0.003),说明两组患儿位移的起点不同(即增长率为零时的位移位置),说明位移与是否为AGA、SGA有关。结论随着VLBW中AGA和SGA身长增长,PICC尖端逐渐移位远离心脏,但相同的身长增长率,SGA引起的导管尖端移位幅度更大。建议AGA身长增长率12.4%、SGA身长增长率9.5%可作为监测导管尖端位置的重要时机,以免导管尖端进一步移位至非中心静脉,导致相关并发症发生。展开更多
文摘The development of this technology has favored the advances noted in recent years in the field of precise positioning. It has also paved the way for a wide range of research into the evaluation of their performance and reliability, their potential use in different fields, the improvement of performance and combined systems, etc. Single-frequency GNSS receivers, which for a long time remained the only category of low-cost GNSS receivers, often limited by their level of accuracy (metric) mainly due to their single-frequency nature, have been joined in the last decade by dual-frequency GNSS receivers developed by certain manufacturers of positioning equipment. These receivers now offer possible alternatives to the relatively expensive conventional (topographic quality) or geodetic receivers and. In this study, the performance of these low-cost dual-frequency receivers was evaluated in static and real-time kinematic GNSS positioning modes. Static positioning was carried out on three points with sessions of 2 h and 4 h over three days with antenna swapping (CHC i50, Leica GS14 and Emlid Reach RS2+). Real-time observations were carried out on eleven (11) points in open, poorly open and not at all open environments, in order to assess not only performance but also receiver sensitivity in environments with a high risk of multipath. The results obtained showed an average agreement of 2 cm in planimetry between the low-cost Emlid RS2+ receiver and the Leica GS14 and CHC i50 receivers. The differences in altimetry are nevertheless greater (sometimes up to decimetres for certain points). Real-time positioning results provided an average convergence of around 1 cm on the E, N and H components with the results from the low-cost Emlid Reach RS2+ and Ublox ZED-F9P receivers and the CHC i50 receiver. Analysis of the results obtained has enabled us to highlight the various issues and challenges associated with this new generation of GNSS receivers, with a view to enhancing their appropriation and optimal integration in the professional and research worlds.
基金supported in part by National Key Research and Development Program of China under Grant 2021YFB2900404。
文摘The numbers of beam positions(BPs)and time slots for beam hopping(BH)dominate the latency of LEO satellite communications.Aiming at minimizing the number of BPs subject to a predefined requirement on the radius of BP,a low-complexity user density-based BP design scheme is proposed,where the original problem is decomposed into two subproblems,with the first one to find the sparsest user and the second one to determine the corresponding best BP.In particular,for the second subproblem,a user selection and smallest BP radius algorithm is proposed,where the nearby users are sequentially selected until the constraint of the given BP radius is no longer satisfied.These two subproblems are iteratively solved until all the users are selected.To further reduce the BP radius,a duplicated user removal algorithm is proposed to decrease the number of the users covered by two or more BPs.Aiming at minimizing the number of time slots subject to the no co-channel interference(CCI)constraint and the traffic demand constraint,a low-complexity CCI-free BH design scheme is proposed,where the BPs having difficulty in satisfying the constraints are considered to be illuminated in priory.Simulation results verify the effectiveness of the proposed schemes.
文摘Text extraction is the key step in the character recognition;its accuracy highly relies on the location of the text region. In this paper, we propose a new method which can find the text location automatically to solve some regional problems such as incomplete, false position or orientation deviation occurred in the low-contrast image text extraction. Firstly, we make some pre-processing for the original image, including color space transform, contrast-limited adaptive histogram equalization, Sobel edge detector, morphological method and eight neighborhood processing method (ENPM) etc., to provide some results to compare the different methods. Secondly, we use the connected component analysis (CCA) method to get several connected parts and non-connected parts, then use the morphology method and CCA again for the non-connected part to erode some noises, obtain another connected and non-connected parts. Thirdly, we compute the edge feature for all connected areas, combine Support Vector Machine (SVM) to classify the real text region, obtain the text location coordinates. Finally, we use the text region coordinate to extract the block including the text, then binarize, cluster and recognize all text information. At last, we calculate the precision rate and recall rate to evaluate the method for more than 200 images. The experiments show that the method we proposed is robust for low-contrast text images with the variations in font size and font color, different language, gloomy environment, etc.
文摘In recent years,WiFi indoor positioning technology has become a hot research topic at home and abroad.However,at present,indoor positioning technology still has many problems in terms of practicability and stability,which seriously affects the accuracy of indoor positioning and increases the complexity of the calculation process.Aiming at the instability of RSS and the more complicated data processing,this paper proposes a low-frequency filtering method based on fast data convergence.Low-frequency filtering uses MATLAB for data fitting to filter out low-frequency data;data convergence combines the mean and multi-data parallel analysis process to achieve a good balance between data volume and system performance.At the same time,this paper combines the position fingerprint and the relative position method in the algorithm,which reduces the error on the algorithm system.The test results show that the strategy can meet the requirements of indoor passive positioning and avoid a large amount of data collection and processing,and the average positioning error is below 0.5 meters.
文摘Given a symmetric matrix X, we consider the problem of finding a low-rank positive approximant of X. That is, a symmetric positive semidefinite matrix, S, whose rank is smaller than a given positive integer, , which is nearest to X in a certain matrix norm. The problem is first solved with regard to four common norms: The Frobenius norm, the Schatten p-norm, the trace norm, and the spectral norm. Then the solution is extended to any unitarily invariant matrix norm. The proof is based on a subtle combination of Ky Fan dominance theorem, a modified pinching principle, and Mirsky minimum-norm theorem.
文摘叶片覆冰会严重影响风机的安全稳定运行。目前,电热防冰是最高效可靠的风机叶片防冰方法,但存在防冰区域受热不均匀、局部覆冰以及过多分区导致防冰系统过于复杂等问题。为此提出采用正温度系数(positive temperature coefficient,PTC)材料进行风机叶片自适应电加热防冰的创新方法,通过原位聚合法成功制备了一种低居里点PTC材料,其居里温度点为1℃。随后,基于该材料的阻-温特性,建立了风机叶片的电加热防冰模型,并进行数值模拟。研究结果显示,当采用低居里点PTC材料进行风机叶片电加热防冰时,无需进行防冰区域的分区,就能使得防冰区域受热更加均匀。在一定的工作电压下,低居里点PTC材料在不同环境温度和风速下展现出自适应调节加热功率的能力,并且经过100次循环阻-温测试后,材料仍具有极强的自适应调节能力。最后,通过试验验证了材料的这种自适应调节能力。该研究结果为后续基于低居里点PTC材料的风机叶片防冰系统的研究奠定了坚实基础。
文摘目的探讨极低出生体重儿(very low birth weight,VLBW)中适于胎龄儿(appropriate for gestational age,AGA)和小于胎龄儿(small for gestational age,SGA)身长增长对经外周中心静脉置管(peripherally inserted central catheter,PICC)尖端移位的影响,并横向比较影响程度,帮助医护人员更好地把握导管尖端位置监测的时机。方法回顾性分析2021年1月—2022年6月在医院NICU住院并使用PICC的VLBW,按出生体质量和胎龄关系分为AGA组45例和SGA组19例,记录首次置管当日身长(Ht_(1))以及PICC尖端位置、置管期间胸片检查当日身长(Ht_(n))以及PICC尖端位置,并计算相应的身长增长率。身长增长率与PICC尖端移位的相关性用Spearman秩相关分析。将AGA和SGA的身长增长率分别与PICC尖端移位进行简单线性回归分析,构建回归模型,用协方差分析比较两组回归直线。结果VLBW中AGA组97.8%患儿出现移位,SGA组所有的患儿都出现移位,占比最多的均为移位3个椎体。Spearman秩相关分析结果显示,两组患儿身长增长率与PICC尖端移位均具有相关性(AGA组rs=-0.719,P<0.001;SGA组rs=-0.769,P<0.001),随着VLBW身长增长,PICC尖端逐渐移位远离心脏。简单线性回归分析结果显示,AGA组回归模型(R^(2)=0.517,调整后R^(2)=0.513,F=129.487,P<0.001),SGA组回归模型(R^(2)=0.591,调整后R^(2)=0.585,F=95.385,P<0.001)。协方差分析结果显示,由于回归系数检验没有统计学意义,两条直线平行,说明身长增长率对两组患儿位移的影响一致。截距比较有统计学意义(F=9.265,P=0.003),说明两组患儿位移的起点不同(即增长率为零时的位移位置),说明位移与是否为AGA、SGA有关。结论随着VLBW中AGA和SGA身长增长,PICC尖端逐渐移位远离心脏,但相同的身长增长率,SGA引起的导管尖端移位幅度更大。建议AGA身长增长率12.4%、SGA身长增长率9.5%可作为监测导管尖端位置的重要时机,以免导管尖端进一步移位至非中心静脉,导致相关并发症发生。
