Search

Currently, dozens of empirical frequency formulas have been developed by various countries since the beginning of last century. However, the differences of these empirical frequency formulas directly affect the subsequent analysis, calculation and determination of parameters which have significant impacts on the estimation of design flood. In this paper, by comparing various empirical frequency formulas, analyzing the relative deviation of the empirical frequency formulas, and preliminary verifying the differences of empirical frequency formulas with the measured storm floods series, the conclusion shows that the relative error of the maximum flood recurrence period is the largest, and the relative error of flood recurrence period that less than 20 years is smaller. In order to minimize the theoretical errors of the empirical frequency formulas in the estimation of design flood, and minimize data errors caused by extra-large and extra-small value in short flood series, simple and unbiased empirical frequency formula should be adopted in practice. With regard to relative long flood series, the median formula or mathematical expectation formula are recommended for frequency or recurrence period estimation, and the first order (the second order) and the last order of the frequency or recurrence period are recommended as reference values. [ABSTRACT FROM AUTHOR]

For the problems such as the aliasing phenomenon of signal and noise wavelet packet coefficients, threshold function discontinuity at threshold, and constant deviation between original coefficient and estimation coefficient in traditional threshold denoising, this paper proposed an improved wavelet packet threshold denoising algorithm. The algorithm first calculated the Teager energy operator for the wavelet packet coefficients, making the difference between voice and noise coefficients larger, which was favorable for threshold selection. Then, for the problems of pseudo Gibbs effect and constant deviation, this paper proposed an improved threshold function, which not only overcame the problem of discontinuity and constant deviation of commonly used functions, but also had superior mathematical characteristics. The experimental results show that the improved algorithm has higher signal-to-noise ratio and reduces the mean square error, which demonstrates the algorithm eliminates the noise to the greatest extent and avoids the signal distortion, and has higher practical value. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The energy crisis and environmental pollution have become increasingly prominent, therefore human beings have been exploring and making use of new energy resources. Solar energy, a new energy resource that is clean, renewable, economical, universal, etc., has grown fast worldwide. Taking advantage of solar energy can solve the energy shortage, and solar energy has an important effect on our country's future development. Solar power is considered to be one of the most ideal utilizations of solar energy. The solar thermal power generation is widely concerned. Among dish, groove, and tower solar thermal power generation, dish solar thermal power generation has the highest photoelectric conversion efficiency, and it belongs to point collector generation technology, which makes it worth to develop. The ever-changing solar radiation direction and the instability of the solar radiation energy lead to the inaccuracy of tracking systems and lower utilization. When the incident sunlight parallels the solar collector, the conversion efficiency is higher. Tracking mode can greatly improve the solar utilization rate. Research shows that energy receiving rate improves 37.7% when solar thermal power generation uses tracking mode. Accurate sun tracking can greatly improve the receiver's thermal efficiency. Compared to fixed systems, power output of single-axis and dual axis tracking systems can increase 25% and 41% under the same condition. It is clear that an accurate auto-tracking control system can make solar collectors receive more solar radiation energy to improve the solar energy utilization. Although the tracking system is more complex and costs higher than the fixed system, increasing the annual output power can reduce cost effectively. Program tracking mode, which is not affected by the weather, has high adaptability. When the control software calculates the sun's position, inevitably it would have round-off error. Photoelectric tracking mode has higher tracking accuracy because it can automatically track the sun and is seriously influenced by the weather. Auto-tracking mode of the dish solar tracking system commonly uses hybrid tracking that is a combination of program tracking mode and photoelectric tracking mode. Each tracking mode makes up for the other, so as a result, the precision and stability of the tracking system is further improved and guaranteed. The tracking system works outside, therefore it is easily influenced by environmental factors so tracking accuracy and stabilization is lower. In order to improve tracking accuracy of the dish solar auto-tracking system, this paper chose the more precise transmission mechanism to match the system and mainly focuses on the transmission mechanism error of the dish solar tracking system. Based on a working platform of the existing 1 kW dish solar auto-tracking system, this paper designs a kind of transmission mechanism. The azimuth angle uses double worm single worm wheel; two worms work together to drive the worm wheel. The running speed and direction of the worms are the same, and the screw nut transmission mechanism with self-locking function tracks the altitude angle. Second, deduce the driving equation of the altitude angle and azimuth angle. Thenusesa software named ADAMS is used to do the system's simulation. The simulation focuses on spring equinox, summer solstice, autumn equinox, and winter solstice in 2013 in Lanzhou based on kinematics of the tracking transmission mechanism. The analytical result shows that kinematics errors of the tracking transmission mechanism are nearly +0.021°. Compared to the minimum systematic error, which is ±0.20º, the kinematics errors are just 10%. At the same time, the errors of the dish solar auto-tracking system are analyzed. It lays a theoretical foundation of the study to improve the precision of the dish solar auto-tracking system. Transmission mechanism error is only part of the dish solar auto-tracking system's errors; relevant follow-up studies on other errors of the system are ongoing. [ABSTRACT FROM AUTHOR]

Copyright of Control Theory & Applications / Kongzhi Lilun Yu Yinyong is the property of Editorial Department of Control Theory & Applications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Mountain Research (10082786) is the property of Mountain Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper aims to assess the latest 1 km-grid Analysis Real Time (ART_1 km) precipitation product developed by the National Meteorological Information Center of China Meteorological Administration (CMA), which can provide great support for disaster weather monitoring and warning, intelligent grid forecasting and weather services. Observed precipitation data from the independent stations (including non-uploaded regional meteorological stations and hydrometric stations) that were not integrated into the ART_1 km precipitation product as well as precipitation classification inspection are used to assess the quality of this product during twenty disastrous rainstorm cases from May to August during 2019-2022 in Guangdong. The results show that the ART_1 km precipitation product successfully reproduces the precipitation location, strength, and trends in these cases, with the best performance in the Pearl River Delta, the east of eastern Guangdong, and the north of northern Guangdong. The stronger the precipitation, the greater the correlation as well as the root mean square error (RMSE) and mean error (ME) between the ART_1 km precipitation and the observed precipitation. When the hourly precipitation is not classified, about 60% of these independent stations present a correlation efficient ≥ 0.8, more than 90% of the stations present an RMSE within the range of [1.0, 5.0) mm, and more than 60% of the stations present a ME within ±0.1 mm. When the hourly precipitation is < 5 mm, most of the stations have a correlation efficient < 0.5, an RMSE within the range of [1.0, 5.0) mm, and a ME within [0.0, 0.5] mm. When the hourly precipitation is ≥ 20 mm, 42%~56% of the stations have a correlation efficient ≥ 0.5, and most of the stations have an RMSE ≥ 10 mm and a ME < 0 mm, even when the hourly precipitation is ≥ 50 mm, most of the stations have a ME < -10 mm. Overall, ART_1 km precipitation is usually underestimated at the independent stations, and integrating observations from more sites into producing ART_1 km precipitation is helpful to improve the quality of the products.

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper proposed a twice channel estimation algorithm, in which used weighted coefficient to cancel ICI caused by Doppler frequency shift in high speed mobile environment. The algorithm achieved twice channel estimation. The first estimation provided channel state information to cancel the ICI under the premise of ensuring the symbol rate. In the case of ICI cancellation, the second estimation enhanced the channel estimation accuracy. Then the algorithm improved the simplified PIC algorithm, and introduced the weighting coefficient to make the residual error smallest after ICI cancellation based on the minimum mean square error criterion. The simulation results are in good agreement with the theoretical analysis. The proposed algorithm improves the estimation accuracy of rapidly time-varying channels. The maximum value of NMSE performance gain is0. 071 4, when the SNR is 0 dB. [ABSTRACT FROM AUTHOR]

Due to the impact of the surrounding environment, the stability of Wi-Fi fingerprint positioning was very poor. And the PDR couldn’t independently give positioning result without the initial position of the target and had serious cumulative error. To address this issue, the paper presented a Wi-Fi indoor positioning algorithm based on PDR feedback. The scheme consisted of three processes. The first was to get the initial position based on relevance vector regression (RVR) methods, and the second was the feedback correction process which based on PDR. The third was the fingerprint positioning process based on Knearest neighbor (KNN) algorithm. Experimental results show that the proposed algorithm can well improve the accuracy and stability of the final positioning result. And the proposed method can greatly reduce the time complexity which improves real time performance. [ABSTRACT FROM AUTHOR]

Test cost and misclassification cost are commonly considered in cost-sensitive learning. In real applications, the test cost of a feature is often related to the granularity of attribute values, and the misclassification cost of an object with multiple attributes is usually influenced by the total test cost of attributes. Based on this consideration, the paper studies the selection of attribute and granularity of data in the case where the total test cost is restrained. Aiming at minimizing the average total cost of data processing, a method is proposed to choose the optimal attribute subset and the optimal data granularity simultaneously. We first construct the theoretical model of the proposed method, and then design an efficient algorithm. Experimental results show that the proposed algorithm can effectively select the attributes and the granularity of data under different test cost constraints. [ABSTRACT FROM AUTHOR]

The rotation precision of rotator is an important factor affecting the performance of mechanical equipment. It is a meaningful task to measure the rotation precision of rotator and analyze its effect factors. Based on the data acquisition principle of universal serial bus (USB) and the circle image method, an experimental test system for the rotation precision of rotator was set up in the paper. The software environment which is suitable for testing and evaluating the rotation precision was also developed by using VC + +. Depending on the high-performance computer with multichannel data acquisition instrument and the rotary accuracy testing software, the offline demonstration and online measurement and evaluation for the rotation precision can be realized efficiently. With the experimental system for the rotation precision, four kinds of methods for evaluating the rotation precision were discussed and the rotation precision was analyzed and evaluated by using least square circle (LSC) method. The results verified the validation of the developed system. Moreover, a good teaching demonstration and excellent experimental effect have been achieved by the developed system after many times of experimental teaching. [ABSTRACT FROM AUTHOR]

In the parameter identification of inverse problems, it was well-known that the information quantity contained in measurement information influences the reconstruction precision of parameter directly. How to describe the information quantity in measurement information plays an important role in the selection of the number of measurement points. According to the Bayesian method, it calculated the probability of the parameter sample to be identified by combining the priori probability reflecting prior information and the likelihood probability reflecting measurement information. It calculated the evaluation factors by the maximum entropy and information entropy of the parameter. This paper introduced the information entropy to describe the information quantity of measurement information with error before parameter identification. Numerical tests show that this proposed method can describe the measured information with error effectively and determine the measured information in practice. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Deformation of North China Region is very small, there is little discussion about whether GPS long-term crustal tectonic deformation can reflect the deformation of North China Region or not. In this paper the GPS velocity field of COMNOC-I was used to calculate the strain rate and its accuracy for North China using multiquadric-biharmonic method. Analysis of standard deviation, calculated by the law of error propagation, shows that these strain rate results are highly accuracy. And that the reliable results distribution was consistent with the measured data. The more measured point the higher the accuracy of the strain rate. [ABSTRACT FROM AUTHOR]