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A Self-calibration Bundle Adjustment Algorithm Based on Block Matrix Cholesky Decomposition Technology 被引量:1
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作者 Huasheng SUN Yuan ZHANG 《Journal of Geodesy and Geoinformation Science》 CSCD 2023年第1期11-30,共20页
In this study,the problem of bundle adjustment was revisited,and a novel algorithm based on block matrix Cholesky decomposition was proposed to solve the thorny problem of self-calibration bundle adjustment.The innova... In this study,the problem of bundle adjustment was revisited,and a novel algorithm based on block matrix Cholesky decomposition was proposed to solve the thorny problem of self-calibration bundle adjustment.The innovation points are reflected in the following aspects:①The proposed algorithm is not dependent on the Schur complement,and the calculation process is simple and clear;②The complexities of time and space tend to O(n)in the context of world point number is far greater than that of images and cameras,so the calculation magnitude and memory consumption can be reduced significantly;③The proposed algorithm can carry out self-calibration bundle adjustment in single-camera,multi-camera,and variable-camera modes;④Some measures are employed to improve the optimization effects.Experimental tests showed that the proposed algorithm has the ability to achieve state-of-the-art performance in accuracy and robustness,and it has a strong adaptability as well,because the optimized results are accurate and robust even if the initial values have large deviations from the truth.This study could provide theoretical guidance and technical support for the image-based positioning and 3D reconstruction in the fields of photogrammetry,computer vision and robotics. 展开更多
关键词 bundle adjustment self-calibration block matrix Cholesky decomposition
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A Fractional-N CMOS DPLL with Self-Calibration
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作者 刘素娟 杨维明 +2 位作者 陈建新 蔡黎明 徐东升 《Journal of Semiconductors》 EI CAS CSCD 北大核心 2005年第11期2085-2091,共7页
A digital phase-locked loop (DPLL) based on a new digital phase-frequency detector is presented. The self-calibration technique is employed to acquire wide lock range,low jitter, and fast acquisition. The DPLL works... A digital phase-locked loop (DPLL) based on a new digital phase-frequency detector is presented. The self-calibration technique is employed to acquire wide lock range,low jitter, and fast acquisition. The DPLL works from 60 to 600MHz at a supply voltage of 1.8V. It also features a fraetional-N synthesizer with digital 2nd-order sigma-delta noise shaping, which can achieve a short lock time,a high frequency resolution,and an improved phase-noise spectrum. The DPLL has been implemented in SMIC 0. 18μm 1.8V 1P6M CMOS technology. The peak-to-peak jitter is less than 0. 8% of the output clock period and the lock time is less than 150 times of the reference clock period after the pre-divider. 展开更多
关键词 digital phase-locked loop phase-frequency detector self-calibration voltage controlled oscillator FRACTIONAL-N
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Capacitor self-calibration technique used in time-interleaved successive approximation ADC
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作者 殷勤 戚韬 +1 位作者 吴光林 吴建辉 《Journal of Southeast University(English Edition)》 EI CAS 2006年第2期164-168,共5页
A capacitor self-calibration circuit used in a successive approximation analog-to-digital converter (SA-ADC) is presented. This capacitor self-calibration circuit can calibrate erroneous data and work with the ADC b... A capacitor self-calibration circuit used in a successive approximation analog-to-digital converter (SA-ADC) is presented. This capacitor self-calibration circuit can calibrate erroneous data and work with the ADC by adding an additional clock period. This circuit is used in a 10 bit 32 Msample/s time-interleaved SA- ADC. The chip is implemented with Chart 0. 25 μm 2. 5 V process and totally occupies an area of 1.4 mm× 1.3 mm. After calibration, the simulated signal-to-noise ratio (SNR) is 59. 586 1 dB and the spurious-free dynamic range (SFDR) is 70. 246 dB at 32 MHz. The measured signal-to-noise and distortion ratio (SINAD) is 44. 82 dB and the SFDR is 63. 760 4 dB when the ADC samples a 5.8 MHz sinusoid wave. 展开更多
关键词 capacitor self-calibration analog-to-digital converter successive approximation time-interleaved
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Integration of Tracer Test Data to Refine Geostatistical Hydraulic Conductivity Fields Using Sequential Self-Calibration Method 被引量:5
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作者 胡晓农 蒋小伟 万力 《Journal of China University of Geosciences》 SCIE CSCD 2007年第3期242-256,共15页
On the basis of local measurements of hydraulic conductivity, geostatistical methods have been found to be useful in heterogeneity characterization of a hydraulic conductivity field on a regional scale. However, the m... On the basis of local measurements of hydraulic conductivity, geostatistical methods have been found to be useful in heterogeneity characterization of a hydraulic conductivity field on a regional scale. However, the methods are not suited to directly integrate dynamic production data, such as, hydraulic head and solute concentration, into the study of conductivity distribution. These data, which record the flow and transport processes in the medium, are closely related to the spatial distribution of hydraulic conductivity. In this study, a three-dimensional gradient-based inverse method--the sequential self-calibration (SSC) method--is developed to calibrate a hydraulic conductivity field, initially generated by a geostatistical simulation method, conditioned on tracer test results. The SSC method can honor both local hydraulic conductivity measurements and tracer test data. The mismatch between the simulated hydraulic conductivity field and the reference true one, measured by its mean square error (MSE), is reduced through the SSC conditional study. In comparison with the unconditional results, the SSC conditional study creates the mean breakthrough curve much closer to the reference true curve, and significantly reduces the prediction uncertainty of the solute transport in the observed locations. Further, the reduction of uncertainty is spatially dependent, which indicates that good locations, geological structure, and boundary conditions will affect the efficiency of the SSC study results. 展开更多
关键词 sequential self-calibration tracer test hydraulic conductivity geostatistical simulation inverse problem
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Self-calibration and Compensation of Setting Errors for Surface Profile Measurement of a Microstructured Roll Workpiece 被引量:3
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作者 GAO Wei XU Bin +2 位作者 TAKEISHI Toshiki SHIMIZU Yuki ITO So 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2014年第1期14-22,共9页
Microstructured roll workpieces have been widely used as functional components in the precision industries. Current researches on quality control have focused on surface profile measurement of microstructured roll wor... Microstructured roll workpieces have been widely used as functional components in the precision industries. Current researches on quality control have focused on surface profile measurement of microstructured roll workpieces, and types of measurement systems and measurement methods have been developed. However, low measurement efficiency and low measurement accuracy caused by setting errors are the common disadvantages for surface profile measurement of microstructured roll workpieces. In order to shorten the measurement time and enhance the measurement accuracy, a method for self-calibration and compensation of setting errors is proposed for surface profile measurement of microstructured roll workpieces. A measurement system is constructed for the measurement, in which a precision spindle is employed to rotate the roll workpiece and an air-bearing displacement sensor with a micro-stylus probe is employed to scan the microstructured surface of the roll workpiece. The resolution of the displacement sensor is 0.14 nm and that of the rotary encoder of the spindle was 0.15r~. Geometrical and mathematical models are established for analyzing the influences of the setting errors of the roll workpiece and the displacement sensor with respect to the axis of the spindle, including the eccentric error of the roll workpiece, the offset error of the sensor axis and the zero point error of the sensor output. Measurement experiments are carded out on a roll workpiece on which periodic microstructures are a period of 133 i^m along the circumferential direction. Experimental results demonstrate the feasibility of the self-compensation method. The proposed method can be used to detect and compensate the setting errors without using any additional accurate artifact. 展开更多
关键词 measurement profile setting error self-calibration COMPENSATION microstructure roll workpiece
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New self-calibration approach to space robots based on hand-eye vision 被引量:3
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作者 刘宇 刘宏 +1 位作者 倪风雷 徐文福 《Journal of Central South University》 SCIE EI CAS 2011年第4期1087-1096,共10页
To overcome the influence of on-orbit extreme temperature environment on the tool pose(position and orientation) accuracy of a space robot,a new self-calibration method based on a measurement camera(hand-eye vision) a... To overcome the influence of on-orbit extreme temperature environment on the tool pose(position and orientation) accuracy of a space robot,a new self-calibration method based on a measurement camera(hand-eye vision) attached to its end-effector was presented.Using the relative pose errors between the two adjacent calibration positions of the space robot,the cost function of the calibration was built,which was different from the conventional calibration method.The particle swarm optimization algorithm(PSO) was used to optimize the function to realize the geometrical parameter identification of the space robot.The above calibration method was carried out through self-calibration simulation of a six-DOF space robot whose end-effector was equipped with hand-eye vision.The results showed that after calibration there was a significant improvement of tool pose accuracy in a set of independent reference positions,which verified the feasibility of the method.At the same time,because it was unnecessary for this method to know the transformation matrix from the robot base to the calibration plate,it reduced the complexity of calibration model and shortened the error propagation chain,which benefited to improve the calibration accuracy. 展开更多
关键词 space robot self-calibration cost function hand-eye vision particle swarm optimization algorithm
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Camera Self-Calibration in Computer Vision with Precise Estimation of Initial Parameters 被引量:1
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作者 裴明涛 于连庆 +1 位作者 刘鹏 贾云得 《Journal of Beijing Institute of Technology》 EI CAS 2004年第2期152-156,共5页
A key problem that plagues camera self-calibration, namely that the classical self-calibration algorithms are very sensitive to the initial values of the camera intrinsic parameters, is analyzed and a practical soluti... A key problem that plagues camera self-calibration, namely that the classical self-calibration algorithms are very sensitive to the initial values of the camera intrinsic parameters, is analyzed and a practical solution is provided. The effect of the camera intrinsic parameters, mainly the principal point and the skew factor is first discussed. Then a practical method via a controlled motion of the camera is introduced so as to obtain an accurate estimation of these parameters. Feasibility of this approach is illustrated by carrying out comprehensive experiments using synthetic data as well as real image sequences. Unreasonable initial values can often make self-calibration impossible, yet a precise initialization guarantees a better and successful reconstruction. Trying to obtain a more reasonable initialization is worthwhile the effort in camera self-calibration. 展开更多
关键词 self-calibration Euclidean reconstruction computer vision
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An improved self-calibration approach based on adaptive genetic algorithm for position-based visual servo 被引量:1
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作者 Ding LIU Xiongjun WU Yanxi YANG 《控制理论与应用(英文版)》 EI 2008年第3期246-252,共7页
An improved self-calibrating algorithm for visual servo based on adaptive genetic algorithm is proposed in this paper. Our approach introduces an extension of Mendonca-Cipolla and G. Chesi's self-calibration for the ... An improved self-calibrating algorithm for visual servo based on adaptive genetic algorithm is proposed in this paper. Our approach introduces an extension of Mendonca-Cipolla and G. Chesi's self-calibration for the positionbased visual servo technique which exploits the singular value property of the essential matrix. Specifically, a suitable dynamic online cost function is generated according to the property of the three singular values. The visual servo process is carried out simultaneous to the dynamic self-calibration, and then the cost function is minimized using the adaptive genetic algorithm instead of the gradient descent method in G. Chesi's approach. Moreover, this method overcomes the limitation that the initial parameters must be selected close to the true value, which is not constant in many cases. It is not necessary to know exactly the camera intrinsic parameters when using our approach, instead, coarse coding bounds of the five parameters are enough for the algorithm, which can be done once and for all off-line. Besides, this algorithm does not require knowledge of the 3D model of the object. Simulation experiments are carried out and the results demonstrate that the proposed approach provides a fast convergence speed and robustness against unpredictable perturbations of camera parameters, and it is an effective and efficient visual servo algorithm. 展开更多
关键词 Dynamic self-calibration Visual servo Adaptive genetic algorithm Parameter optimizing Essential matrix Computer vision
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NOVEL METHOD FOR ERROR ANALYSIS AND SELF-CALIBRATION OF LASER TRACKING MIRROR MECHANISM 被引量:2
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作者 OUYANG Jianfei LIU Wanli +2 位作者 QU Xinghua YAN Yonggang WANG Zhankui 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2008年第4期1-6,共6页
Laser tracking system (LTS) is an advanced device for large size 3D coordinates measuring with the advantages of broad range, high speed and high accuracy. However, its measuring accuracy is highly dominated by the ... Laser tracking system (LTS) is an advanced device for large size 3D coordinates measuring with the advantages of broad range, high speed and high accuracy. However, its measuring accuracy is highly dominated by the geometric errors of the tracking mirror mechanism. Proper calibration of LTS is essential prior to the use of it for metrology. A kinematics model that describes not only the motion but also the geometric variations of LTS is developed. Through error analysis of the proposed model, it is claimed that gimbals axis misalignments and tracking mirror center off-set are the key contributors to measuring errors of LTS. A self-calibration method is presented of calibrating LTS with planar constraints. Various calibration strategies utilizing single-plane and multiple-plane constraints are proposed for different situations. For each calibration strategy, issues about the error parameter estimation of LTS are exploded to find out in which conditions these parameters can be uniquely estimated. Moreover, these conditions reveal the applicability of the planar constraints to LTS self-calibration. Intensive studies have been made to check validity of the theoretical results. The results show that the measuring accuracy of LTS has increased by 5 times since this technique for calibration is used. 展开更多
关键词 Laser tracking Error analysis self-calibration Planar constraints Tracking mirror
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Self-calibration Applied in Converting Simulation Surveying
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作者 WANG Ren ZHU Xinhui 《Geo-Spatial Information Science》 2007年第1期57-60,共4页
In the field of converting simulation surveying and traditional close range photogrammetry, it has been developed so far to survey objects by commercial digital camera and this technique is applied widely in every par... In the field of converting simulation surveying and traditional close range photogrammetry, it has been developed so far to survey objects by commercial digital camera and this technique is applied widely in every part of production. In order to get three-dimensional information of objects, commercial digital camera must be examined. For a long time, digital camera has been examined by DLT. Then there must be a high-precision control field. For realizing surveying without control points, a method for self-calibration is proposed. 展开更多
关键词 absolute conic absolute quadric self-calibration
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Self-calibration and algorithm of sample set of piezoresistive pressure sensors
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作者 黄晓因 晋芳伟 周平 《Journal of Shanghai University(English Edition)》 CAS 2007年第2期178-181,共4页
Aiming at piezoresistive pressure sensors, this paper studies simulation of standard pressure by using benchmark current source and self-calibration of the sampling data characteristics. A data fusion algorithm for sa... Aiming at piezoresistive pressure sensors, this paper studies simulation of standard pressure by using benchmark current source and self-calibration of the sampling data characteristics. A data fusion algorithm for sample set is presented which transforms a surface problem into a curve fitting and interpolation problem. The simulation result shows that benchmark current source simulating pressure is successful and data fusion algorithm is effective. The maximum measurement error is only 0.098 kPa and maximum relative error is 0.92% at 0-45 kPa and -10-45~C. 展开更多
关键词 pressure sensor constant current source SAMPLE data fusion self-calibration.
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Long-term outcomes of urethral balloon dilation for anterior urethral stricture: A prospective cohort study
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作者 Ahmed M.Abdel Gawad Abhijit Patil +3 位作者 Abhishek Singh Arvind P.Ganpule Ravindra B.Sabnis Mahesh R.Desai 《Asian Journal of Urology》 CSCD 2024年第3期480-485,共6页
Objective:To prospectively follow up a cohort of anterior urethral stricture disease patients managed with balloon dilation(BD)for 3 years to evaluate the long-term outcomes and to study factors that contribute to rec... Objective:To prospectively follow up a cohort of anterior urethral stricture disease patients managed with balloon dilation(BD)for 3 years to evaluate the long-term outcomes and to study factors that contribute to recurrence.Methods:This study included men who had urethral BD for significant anterior urethral stricture disease between January 2017 and March 2019.Data about the patient age,stricture characteristics,and recurrence date were recorded,along with information on postoperative indwelling catheter use and operative complications.Furthermore,information about the self-calibration procedure was collected and where available,free flow(FF)measurements during the follow-up period were recorded and analyzed.Success was defined as a lack of symptoms and acceptable FF rates(maximum flow rate>12 mL/s).Results:The final analysis was conducted on 187 patients.The mean follow-up period was 37 months.The long-term overall success rate at the end of our study was 66.8%.Our recurrence rate was 7.4%at 12 months,24.7%at 24 months,and reached 33.2%at the end of our study.The time to recurrence ranged from 91 days to 1635 days,with a mean of 670 days.The stricture-free survival was significantly shorter with lengthy peno-bulbar(p=0.031)and multiple strictures(p=0.015),and in the group of patients who were not committed to self-calibration protocol(p<0.011).However,post-procedural self-calibration was the most important factor that may have decreased the incidence of recurrence(odds ratioZ5.85).Adjuvant self-calibration after BD not only reduced the recurrence rate from 85.4%in the non-self-calibration group to 15.1%in the self-calibration one(p<0.001),but also improved the overall stricture-free survival and FF parameters. 展开更多
关键词 Balloon dilation Internal urethrotomy RECURRENCE self-calibration Urethral stricture
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Three-step self-calibrating generalized phase-shifting interferometry
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作者 Yu Zhang 《Chinese Physics B》 SCIE EI CAS CSCD 2022年第3期234-240,共7页
An accurate and fast three-step self-calibrating generalized phase-shifting interferomertry(SGPSI) is proposed. In this approach, two new phase-shifting signals are constructed by the difference interferograms normali... An accurate and fast three-step self-calibrating generalized phase-shifting interferomertry(SGPSI) is proposed. In this approach, two new phase-shifting signals are constructed by the difference interferograms normalization and noise suppressing, then the unknown phase shift between the two difference phase-shifting signals is estimated quickly through searching the minimum coefficient of variation of the modulation amplitude, a limited number of pixels are selected to participate in the search process to further save time, and finally the phase is reconstructed through the searched phase shift. Through the reconstruction of phase map by the simulation and experiment, and the comparison with several mature algorithms, the good performance of the proposed algorithm is proved, and it eliminates the limitation of requiring more than three phase-shifting interferograms for high-precision SGPSI. We expect this method to be widely used in the future. 展开更多
关键词 self-calibrating generalized phase-shifting interferomertry phase shift difference interferograms modulation amplitude
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Multi-rater Prism:Learning self-calibrated medical image segmentation from multiple raters
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作者 Junde Wu Huihui Fang +14 位作者 Jiayuan Zhu Yu Zhang Xiang Li Yuanpei Liu Huiying Liu Yueming Jin Weimin Huang Qi Liu Cen Chen Yanfei Liu Lixin Duan Yanwu Xu Li Xiao Weihua Yang Yue Liu 《Science Bulletin》 SCIE EI CAS CSCD 2024年第18期2906-2919,共14页
In medical image segmentation,it is often necessary to collect opinions from multiple experts to make the final decision.This clinical routine helps to mitigate individual bias.However,when data is annotated by multip... In medical image segmentation,it is often necessary to collect opinions from multiple experts to make the final decision.This clinical routine helps to mitigate individual bias.However,when data is annotated by multiple experts,standard deep learning models are often not applicable.In this paper,we propose a novel neural network framework called Multi-rater Prism(MrPrism)to learn medical image segmentation from multiple labels.Inspired by iterative half-quadratic optimization,MrPrism combines the task of assigning multi-rater confidences and calibrated segmentation in a recurrent manner.During this process,MrPrism learns inter-observer variability while taking into account the image's semantic properties and finally converges to a self-calibrated segmentation result reflecting inter-observer agreement.Specifically,we propose Converging Prism(ConP)and Diverging Prism(DivP)to iteratively process the two tasks.ConP learns calibrated segmentation based on multi-rater confidence maps estimated by DivP,and DivP generates multi-rater confidence maps based on segmentation masks estimated by ConP.Experimental results show that the two tasks can mutually improve each other through this recurrent process.The final converged segmentation result of MrPrism outperforms state-of-the-art(SOTA)methods for a wide range of medical image segmentation tasks.The code is available at https://github.-com/WuJunde/MrPrism. 展开更多
关键词 Medical image segmentation Multiple raters self-calibration Half-quadratic algorithm
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Tb(Ⅲ)functionalized MOF based self-calibrating sensor integrated with logic gate operation for efficient epinephrine detection in serum
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作者 Dongsheng Zhao Wenqian Li +4 位作者 Rongmei Wen Wencui Li Xin Liu Xiutang Zhang Liming Fan 《Journal of Rare Earths》 SCIE EI CAS CSCD 2024年第5期987-994,I0006,共9页
By anchoring Tb^(3+)ions on its free carboxyl groups of the nanocaged NiMOF,a dual-emission self-calibrating sensor of Tb^(3+)@NiMOF was fabricated through coordination post-synthetic modification(PSM)strategy.With Tb... By anchoring Tb^(3+)ions on its free carboxyl groups of the nanocaged NiMOF,a dual-emission self-calibrating sensor of Tb^(3+)@NiMOF was fabricated through coordination post-synthetic modification(PSM)strategy.With Tb^(3+)ions as the secondary fluorescent signal and sensing active sites,Tb^(3+)@NiMOF presents great potentials in visually and efficiently monitoring EPI in serum,with high sensitivity and selectivity,fast response,excellent recyclable,and the low detection limit(LOD,3.06 ng/mL).Furthermore,a tandem combinational logic gate based intelligent detection system was constructed to improve the practicability and convenience of epinephrine(EPI)detection in serum by comparing the light emitted colour with the series standard colour cards preset in the smartphone.This work provides a promising approach of developing metal-organic frameworks(MOFs)based self-calibrating sensors for intelligent detection of bioactive molecules. 展开更多
关键词 Metal-organic framework Post-synthetic modification self-calibrating sensor Logic gate operation Epinephrine detection Rare earths
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Mismatch Calibration Techniques in Successive Approximation Analog-to-Digital Converters
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作者 王沛 龙善丽 吴建辉 《Journal of Semiconductors》 EI CAS CSCD 北大核心 2007年第9期1369-1374,共6页
Comparator offset cancellation and capacitor self-calibration techniques used in a successive approximation analog-to-digital converter (SA-ADC) are described. The calibration circuit works in parallel with the SAAD... Comparator offset cancellation and capacitor self-calibration techniques used in a successive approximation analog-to-digital converter (SA-ADC) are described. The calibration circuit works in parallel with the SAADC by adding additional calibration clock cycles to pursue high accuracy and low power consumption, and the calibrated resolution can be up to 14bit. This circuit is used in a 10bit 3Msps successive approximation ADC. This chip is realized with an SMIC 0. 18μm 1.8V process and occupies 0.25mm^2 . It consumes 3. 1mW when operating at 1.8MHz. The measured SINAD is 55. 9068dB, SFDR is 64. 5767dB, and THD is - 74. 8889dB when sampling a 320kHz sine wave. 展开更多
关键词 analog-to-digital converter successive approximation self-calibration techniques
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The design of adaptive sigma-delta A/D converter 被引量:1
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作者 冯晖 Lin Zhenghui 《High Technology Letters》 EI CAS 2005年第4期367-370,共4页
The signal to noise ratio (SNR) of conventional sigma delta analog to digital converter (∑△ADC) reduces with input signal strength. The existing concept of adaptive quantization is applied to the design of ∑△A... The signal to noise ratio (SNR) of conventional sigma delta analog to digital converter (∑△ADC) reduces with input signal strength. The existing concept of adaptive quantization is applied to the design of ∑△ADC to improve SNR with high dynamic range. An adaptive algorithm and its circuit implementation is proposed. Because of the error due to the circuit implementation, an error self-calibration circuit is also designed. Simulation results indicate that SNR can he nearly independent of the signal strength. 展开更多
关键词 SIGMA-DELTA A/D ADAPTIVE ERROR self-calibration
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Analysis of spatio-temporal evolution of droughts in Luanhe River Basin using different drought indices 被引量:4
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作者 Kai-yan Wang Qiong-fang Li +3 位作者 Yong Yang Ming Zeng Peng-cheng Li Jie-xiang Zhang 《Water Science and Engineering》 EI CAS CSCD 2015年第4期282-290,共9页
Based on the monthly precipitation and air temperature from 1960 to 1989 in the Luanhe River Basin, the standardized precipitation evapotranspiration index (SPEI) and standardized precipitation index (SPI) at thre... Based on the monthly precipitation and air temperature from 1960 to 1989 in the Luanhe River Basin, the standardized precipitation evapotranspiration index (SPEI) and standardized precipitation index (SPI) at three- and six-month time scales and the self-calibrating Palmer drought severity index (sc-PDSI) were calculated to evaluate droughts in the study area. Temporal variations of the drought severity from 1960 to 1989 were analyzed and compared based on the results of different drought indices, and some typical drought events were identified. Spatial distributions of the drought severity according to the indices were also plotted and investigated. The results reveal the following: the performances of different drought indices are closely associated with the drought duration and the dominant factors of droughts; the SPEI is more accurate than the SPI when both evaporation and precipitation play important roles in drought events; the drought severity shown by the sc-PDSI is generally milder than the actual drought severity from 1960 to 1989; and the evolution of the droughts is usually delayed according to the scPDSI. This study provides valuable references for building drought early warning and mitigation systems in the Luanhe River Basin. 展开更多
关键词 Drought index Drought assessment self-calibrating Palmer drought severity index (sc-PDSI) Standardized precipitation evapotranspiration index(SPEI) Standardized precipitation index (SPI) Luanhe River Basin
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Drought fluctuations based on dendrochronology since 1786 for the Lenglongling Mountains at the northwestern fringe of the East Asian summer monsoon region 被引量:1
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作者 HOU Ying NIU Zhenmin +5 位作者 ZHENG Fang WANG Nai'ang WANG Jianyu LI Zhuolun CHEN Hongxiang ZHANG Xuemin 《Journal of Arid Land》 SCIE CSCD 2016年第4期492-505,共14页
The Lenglongling Mountains (LLM) located in northeastern part of the Tibet Plateau, belong to a marginal area of the East Asian summer monsoon (EASM) and are sensitive to monsoon dynamics. Two tree-ring width chro... The Lenglongling Mountains (LLM) located in northeastern part of the Tibet Plateau, belong to a marginal area of the East Asian summer monsoon (EASM) and are sensitive to monsoon dynamics. Two tree-ring width chronologies developed from six sites of Picea crassifolia in the LLM were employed to study the regional drought variability. Correlation and temporal correlation analyses showed that relationships between the two chronologies and self-calibrated Palmer Drought Severity Index (sc_PDSI) were significant and stable across time, demonstrating the strength of sc_PDSI in modeling drought conditions in this region. Based on the relationships, the mean sc_PDSI was reconstructed for the period from 1786 to 2013. Dry conditions prevailed during 1817-1819, 1829-1831, 1928-1931 and 1999-2001. Relatively wet periods were identified for 1792-1795 and 1954-1956. Spatial correlations with other fourteen precipitation/drought reconstructed series in previous studies revealed that in arid regions of Northwest China, long-term variability of moisture conditions was synchronous before the 1950s at a decadal scale (1791-1954). In northwestern margin of the EASM, most of all selected reconstructions had better consistency in low-frequency variation, especially during dry periods, indicating similar regional moisture variations and analogous modes of climate forcing on tree growth in the region. 展开更多
关键词 dendrochronology East Asian summer monsoon region self-calibrated Palmer Drought Severity Index Lenglongling Mountains
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New design of high-precision oven controlled crystal oscillator 被引量:1
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作者 董绍锋 杜保强 周渭 《Journal of Beijing Institute of Technology》 EI CAS 2012年第3期362-369,共8页
Combining oven controlled technique,digital compensation,high-resolution frequency difference measurement and self-calibration technique,a new design method of precise oven controlled crystal oscillator(OCXO) is pro... Combining oven controlled technique,digital compensation,high-resolution frequency difference measurement and self-calibration technique,a new design method of precise oven controlled crystal oscillator(OCXO) is proposed.Fine compensation is made in the vicinity of the crystal temperature inflection point by using the non-real-time temperature compensation strategy,and self-calibration system is integrated in the crystal.The method improves the digital compensated phase noise,simplifies the traditional OCXO development system,reduces the cost and shortens the developing cycle.Experiment results show that with a standard reference signal and self-calibration updated data,the oscillator can work stable and achieve its best performence.The performance index of crystal oscillator had an improvement with one to two orders of magnitude on the basis of original technical index.The method is widely used in the improvement of high-end crystal oscillator and atomic clock. 展开更多
关键词 crystal oscillator temperature compensation non-real-time control frequency difference measurement self-calibration
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