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THE RELATIONSHIP BETWEEN GLOBAL WARMING AND THE VARIATION IN TROPICAL CYCLONE FREQUENCY OVER THE WESTERN NORTH PACIFIC 被引量:8
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作者 马丽萍 陈联寿 《Journal of Tropical Meteorology》 SCIE 2009年第1期38-44,共7页
The relationship between global warming and the variation in tropical cyclone (TC) genesis frequency is analyzed using the data of the Tropical Cyclone Year Book by the China Meteorological Administration and the Nati... The relationship between global warming and the variation in tropical cyclone (TC) genesis frequency is analyzed using the data of the Tropical Cyclone Year Book by the China Meteorological Administration and the National Centers for Environmental Prediction (NCEP) reanalysis data from 1949 to 2007. The observational results indicate that the average sea surface temperature (SST) in the Intertropical Convergence Zone (ITCZ) region (10°N– 20°N, 100°E– 140°E) increases by 0.6°C against the background of global warming, while the frequency of tropical cyclone geneses in this region decreases significantly. Generally, the rise of SSTs is favorable for the genesis of tropical cyclones, but it is now shown to be contrary to the normal effect. Most of the tropical cyclones in the western North Pacific (WNP) are generated in the ITCZ. This is quite different from the case in the Atlantic basin in which the tropical cyclones are mostly generated from the easterly wave. Our research results demonstrate that the ITCZ has a weakening trend in strength, and it has moved much more equatorward in the past 40 years; both are disadvantageous to the formation of tropical cyclones. Furthermore, our study also found that the ridge of the subtropical high tends to shift slightly equatorward, which is another adverse mechanism for the formation of tropical cyclones. 展开更多
关键词 CLIMATOLOGY tropical cyclone frequency long-term variation ITCZ
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Effect of thickness variations of lithium niobate on insulator waveguide on the frequency spectrum of spontaneous parametric down-conversion 被引量:2
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作者 Guang-Tai Xue Xiao-Hui Tian +4 位作者 Chi Zhang Zhenda Xie Ping Xu Yan-Xiao Gong Shi-Ning Zhu 《Chinese Physics B》 SCIE EI CAS CSCD 2021年第11期268-273,共6页
We study the effect of waveguide thickness variations on the frequency spectrum of spontaneous parametric downconversion in the periodically-poled lithium niobate on insulator(LNOI)waveguide.We analyze several variati... We study the effect of waveguide thickness variations on the frequency spectrum of spontaneous parametric downconversion in the periodically-poled lithium niobate on insulator(LNOI)waveguide.We analyze several variation models and our simulation results show that thickness variations in several nanometers can induce distinct effects on the central peak of the spectrum,such as narrowing,broadening,and splitting.We also prove that the effects of positive and negative variations can be canceled and thus lead to a variation-robust feature and an ultra-broad bandwidth.Our study may promote the development of on-chip photon sources in the LNOI platform,as well as opens up a way to engineer photon frequency state. 展开更多
关键词 lithium niobate on insulator spontaneous parametric down-conversion waveguide thickness variation frequency spectrum
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Monitoring the Modal Frequency and Velocity Variations of Bridges under Ambient Excitation 被引量:1
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作者 Chen Haichao Ge Hongkui +2 位作者 Meng Fanbao Wang Xiaoqiong Yang Wei 《Earthquake Research in China》 CSCD 2015年第4期554-566,共13页
We conducted a long-term monitoring experiment on the Lutuanxilu Bridge located in Changping District of Beijing, employing our recently developed real-time bridge monitoring system based on the Guralp CMG-6TD broadba... We conducted a long-term monitoring experiment on the Lutuanxilu Bridge located in Changping District of Beijing, employing our recently developed real-time bridge monitoring system based on the Guralp CMG-6TD broadband seismometer. We identified the modal parameters with the stochastic subspace identification( SSI) algorithm,and continuously monitored the temporal velocity variation with coda wave interferometry.The results show that:( 1) the highly sensitive Guralp CMG-6TD broadband seismometer,which records the three-component vibration signal within broad frequency range,is well suited for long-term bridge health monitoring.( 2) With the continuous vibration signal from ambient excitation,the stochastic subspace algorithm can robustly identify the low-order modal parameters and the coda wave interferometry can accurately monitor the tiny velocity variation.( 3) The elastic modulus of bridge materials changes significantly associated with varying temperature,leading to diurnal velocity variation with amplitude of approximately 1%. The velocity variation shows strong negative correlation with temperature fluctuation. Meanwhile,the modal frequencies remain quite stable,suggesting that the velocity variation may be a more sensitive quantitative damage index.( 4) While the modal frequencies reflect the integrated health status of the bridge,the velocity variation can be utilized to monitor the local elastic modulus. Therefore,it is crucial for bridge health monitoring to continuously monitor the two key damage indexes under ambient excitation. 展开更多
关键词 Ambient excitation Stochastic subspace Identification Coda wave interferometry Modal frequency Velocity variation
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Continuous-cyclic variations in the b-value of the earthquake frequency-magnitude distribution 被引量:3
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作者 Z.H.El-Isa 《Earthquake Science》 2013年第5期301-320,共20页
Seismicity of the Earth (M ≥ 4.5) was compiled from NEIC, IRIS and ISC catalogues and used to compute b-value based on various time windows. It is found that continuous cyclic b-variations occur on both long and sh... Seismicity of the Earth (M ≥ 4.5) was compiled from NEIC, IRIS and ISC catalogues and used to compute b-value based on various time windows. It is found that continuous cyclic b-variations occur on both long and short time scales, the latter being of much higher value and sometimes in excess of 0.7 of the absolute b-value. These variations occur not only yearly or monthly, but also daily. Before the occurrence of large earthquakes, b-values start increasing with variable gradients that are affected by foreshocks. In some cases, the gradient is reduced to zero or to a negative value a few days before the earthquake occurrence. In general, calculated b-values attain maxima 1 day before large earthquakes and minima soon after their occurrence. Both linear regression and maximum likelihood methods give correlatable, but variable results. It is found that an expanding time window technique from a fixed starting point is more effective in the study of b-variations. The calculated b-variations for the whole Earth, its hemispheres, quadrants and the epicentral regions of some large earthquakes are of both local and regional character, which may indicate that in such cases, the geodynamic processes acting within a certain region have a much regional effect within the Earth. The b-variations have long been known to vary with a number of local and regional factors including tectonic stresses. The results reported here indicate that geotectonic stress remains the most significant factor that controls b-variations. It is found that for earthquakes with Mw ≥ 7, an increase of about 0.20 in the b-value implies a stress increase that will result in an earthquake with a magnitude one unit higher. 展开更多
关键词 Earthquake frequency-magnitude B-VALUE Temporal b-variation Spatial b-variation
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Anomalous Variation of Beat Frequency in a Dual Frequency He-Ne Laser
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作者 刘维新 孙明哲 《Chinese Physics Letters》 SCIE CAS CSCD 2016年第2期51-54,共4页
The beat frequency in a dual frequency He-Ne laser varies while the resonant cavity length is tuned. As to the laser with two longitudinal modes, the variation amplitude is commonly less than 500 kHz, proven by experi... The beat frequency in a dual frequency He-Ne laser varies while the resonant cavity length is tuned. As to the laser with two longitudinal modes, the variation amplitude is commonly less than 500 kHz, proven by experiments and theories. This study reveals an anomalous variation of the beat frequency when a piece of element is put into the cavity and is aligned with the laser axis. Consequently the variation amplitude couM reach 22 MHz, several dozen times larger than that without the intra-cavity element. This cannot be explained only by laser mode pulling and pushing effects. Some influencing factors are investigated experimentally, including the tilted angle of the element and the distance between its surface and cavity mirror. The qualitative analysis is discussed, which agrees with the experimental results. 展开更多
关键词 of on AS IT or Anomalous variation of Beat frequency in a Dual frequency He-Ne Laser in IS
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THE CHARACTERISTICS OF THUNDERSTORM FREQUENCY VARIATION AND THEIR POSSIBLE RELATION WITH THE ADJUSTMENT OF CROP DISTRIBUTION IN THE LEIZHOU PENINSULA
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作者 张羽 牛生杰 《Journal of Tropical Meteorology》 SCIE 2009年第1期89-92,共4页
In order to research possible influences of the adjustment of plant distribution on the development frequency of thunderstorms over the Leizhou Peninsula, mathematic statistic methods, including correlation analyses, ... In order to research possible influences of the adjustment of plant distribution on the development frequency of thunderstorms over the Leizhou Peninsula, mathematic statistic methods, including correlation analyses, 11 kinds of fitting models and all-variable regression methods, were used for analyses and research. The results show that the average trend of the number of annual thunderstorm days is descending obviously, and there are thunderstorms in all seasons, in which warm post-midday thunderstorms have taken up the most part, and high frequency is found from May to September, and the starting and ending dates of thunderstorms have a great annual discrepancy. The vegetation structure has been improved along with the reduction of rice fields and the area increment of sugarcane and fruits planting, which results in the decrease of the number of thunderstorm days; the change in the characteristics of winter spare fields, which is caused by the planting of vegetables, limits the formation of thunderstorms in early winter and late spring. Meanwhile, the area adjustment of peanut planting has little influence on the variation of thunderstorm days. The adjustment of principal crop distribution, such as rice, sugarcane, fruits and vegetables, may have obvious influence on the formation of thunderstorms, and sugarcane has the largest effect, followed in turn by rice, vegetables and fruits, and the adjustment of crop distribution has little influence on the starting and ending dates of thunderstorms. 展开更多
关键词 atmospheric physics thunderstorm frequency variation mathematic statistic methods adjustment of crop distribution
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Frequency Variations of Power System Due to Switching of Renewable Energy Sources
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作者 Wendy L. Fuchs Ewald F. Fuehs 《Journal of Energy and Power Engineering》 2013年第1期1-9,共9页
Power systems in Germany mainly containing intermittently operating renewable sources require load/frequency control which is performed up to now at the AC transmissioh and distribution levels. Frequency control can b... Power systems in Germany mainly containing intermittently operating renewable sources require load/frequency control which is performed up to now at the AC transmissioh and distribution levels. Frequency control can be achieved by employing short-and long-term storage plants buffering and complementing renewable energy sources. A representative grid consists of a natural-gas-fired plant serving as frequency leader, long-term storage plant, wind-power farm with associated short-term storage plantfor energy buffering, and photovoltaic farm with associated short-term storage plant interconnected by a long transmission line to two load circuits. Transient analysis is performed with Mathemafica solving the differential equation system for frequency variation. Powerflow through the AC transmission line is limited by its impedance. The long transmission line must be segmented to achieve stability and voltage control over an 800 km distance. The renewable plants must be operated together with the storage plants in order tominimize frequency variations by smoothing the power output of renewable plants, achieving step-wise control of the transmission-line power. Although to date only AC Iransmission lines in Germany exist, it is anticipated that within the next 10 years these will beaugmented by DC high-voltage lines. 展开更多
关键词 Renewable sources frequency variations stability selection of transmission line.
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Variation in allelic frequencies at loci associated with kernel weight and their effects on kernel weight-related traits in winter wheat 被引量:2
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作者 Teng Li Hongwei Liu +8 位作者 Chunyan Mai Guangjun Yu Huili Li Lingzhi Meng Dawei Jian Li Yang Yang Zhou Hongjun Zhang Hongjie Li 《The Crop Journal》 SCIE CAS CSCD 2019年第1期30-37,共8页
Knowledge of allelic frequencies at loci associated with kernel weight and effects on kernel weight-related traits is crucial for yield improvement in wheat. Kernel weight-related traits were evaluated in 200 Chinese ... Knowledge of allelic frequencies at loci associated with kernel weight and effects on kernel weight-related traits is crucial for yield improvement in wheat. Kernel weight-related traits were evaluated in 200 Chinese winter wheat cultivars(lines) grown at the Xinxiang Experimental Station, Chinese Academy of Agricultural Sciences, Xinxiang in Henan Province, for three consecutive years from 2014 to 2016. Alleles associated with kernel weight at nine loci, TaCKX6-D1, TaCwi-A1, TaCWI-4A, TaGS1a, TaGS5-A1, TaGS3-3A, TaGW2-6A, TaSus2-2B, and TaTGW6-A1, were determined for all cultivars(lines). ANOVA showed that genotypes, years and their interactions had significant effects on thousand-kernel weight(TKW), kernel length(KL) and kernel width(KW). The overall mean frequencies of alleles conferring high and low TKW at the nine loci were 65.9% and 33.4%, with the ranges of 37.0%–85.0% and 13.5%–63.0% for single loci. The frequencies of high-TKW alleles were over 50.0% at eight of the loci. Genotypes at each locus with the high-TKW allele had higher TKW than those with the low-TKW allele. The high-TKW allele Hap-H at the TaSus2-2B locus can be preferably used to increase grain yield due to its high TKW(49.32 g). A total of 18 main allelic combinations(ACs) at nine loci were detected. Three ACs(AC1–AC3) had significantly higher TKW than AC6 with high-TKW alleles at all nine loci even though they contained some low-TKW alleles. This indicated that other loci controlling kernel weight were present in the high-TKW cultivars. This work provides important information for parental selection and marker-assisted selection for breeding. 展开更多
关键词 Allelic frequency Allelic variation Functional MARKERS TRITICUM AESTIVUM
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Design and Development of Wind-Solar Hybrid Power System with Compressed Air Energy Storage for Voltage and Frequency Regulations
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作者 Banet Masenga Jean Byiringiro +3 位作者 Charles Kagiri Edwell Tafara Daniel Ngoma Gnoumou Aristid 《Journal of Power and Energy Engineering》 2023年第2期1-24,共24页
The intermittent nature of wind and solar photovoltaic energy systems leads to the fluctuation of power generated due to the fact that the power output is highly dependent upon local weather conditions, which results ... The intermittent nature of wind and solar photovoltaic energy systems leads to the fluctuation of power generated due to the fact that the power output is highly dependent upon local weather conditions, which results to the load shading issue that led to the voltage and frequency instability. In additional to that, the high proportions of erratic renewable energy sources can lead to erratic frequency changes which affect the grid stability. In order to reduce this effect, the energy storage system is commonly used in most wind-solar energy systems to balance the voltage and frequency instability during load variations. One of the innovative energy storage systems is the compressed air energy storage system (CAES) for wind and solar hybrid energy system and this technology is the key focus in this research study. The aim of this research was to examine the system configuration of the CAES system through modelling and experimental approach with PID controller design for regulating the voltage and frequency under different load conditions. The essential elements and the entire system have been presented in this work as thorough modelling in the MATLAB/Simulink environment for different load conditions. The developed model was tested through an experimental workbench using the developed prototype of the compressed air storage in the Siemens Lab at DeKUT and explored the consequence of the working parameters on the system proficiency and the model accuracy. The performance of the system for the developed prototype of CAES system was validated using results from an experimental workbench with MATLAB/Simulink R2022b simulation. The modeling and experimental results, shows that the frequency fluctuation and voltage drop of the developed CAES system during load variations was governed by the I/P converter using a PID_Compact controller programed in the TIA Portal V17 software and downloaded into PLC S7 1200. Based on these results, the model can be applied as a basis for the performance assessment of the compressed air energy storage system so as to be included in current technology of wind and solar hybrid energy systems. 展开更多
关键词 VOLTAGE frequency Compressed Air Energy Storage Load variations PID Control I/P Converter Valve
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Diagnosis of Disc Space Variation Fault Degree of Transformer Winding Based on K-Nearest Neighbor Algorithm
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作者 Song Wang Fei Xie +3 位作者 Fengye Yang Shengxuan Qiu Chuang Liu Tong Li 《Energy Engineering》 EI 2023年第10期2273-2285,共13页
Winding is one of themost important components in power transformers.Ensuring the health state of the winding is of great importance to the stable operation of the power system.To efficiently and accurately diagnose t... Winding is one of themost important components in power transformers.Ensuring the health state of the winding is of great importance to the stable operation of the power system.To efficiently and accurately diagnose the disc space variation(DSV)fault degree of transformer winding,this paper presents a diagnostic method of winding fault based on the K-Nearest Neighbor(KNN)algorithmand the frequency response analysis(FRA)method.First,a laboratory winding model is used,and DSV faults with four different degrees are achieved by changing disc space of the discs in the winding.Then,a series of FRA tests are conducted to obtain the FRA results and set up the FRA dataset.Second,ten different numerical indices are utilized to obtain features of FRA curves of faulted winding.Third,the 10-fold cross-validation method is employed to determine the optimal k-value of KNN.In addition,to improve the accuracy of the KNN model,a comparative analysis is made between the accuracy of the KNN algorithm and k-value under four distance functions.After getting the most appropriate distance metric and kvalue,the fault classificationmodel based on theKNN and FRA is constructed and it is used to classify the degrees of DSV faults.The identification accuracy rate of the proposed model is up to 98.30%.Finally,the performance of the model is presented by comparing with the support vector machine(SVM),SVM optimized by the particle swarmoptimization(PSO-SVM)method,and randomforest(RF).The results show that the diagnosis accuracy of the proposed model is the highest and the model can be used to accurately diagnose the DSV fault degrees of the winding. 展开更多
关键词 Transformer winding frequency response analysis(FRA)method K-Nearest Neighbor(KNN) disc space variation(DSV)
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A CMOS Fully Integrated Frequency Synthesizer with Stability Compensation 被引量:1
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作者 何捷 唐长文 +1 位作者 闵昊 洪志良 《Journal of Semiconductors》 EI CAS CSCD 北大核心 2005年第8期1524-1531,共8页
A complete closed-loop third order s-domain model is analyzed for a frequency synthesizer. Based on the model and root-locus technique, the procedure for parameters design is described, and the relationship between th... A complete closed-loop third order s-domain model is analyzed for a frequency synthesizer. Based on the model and root-locus technique, the procedure for parameters design is described, and the relationship between the process,voltage,and temperature variation of parameters and the loop stability is quantitatively analyzed. A variation margin is proposed for stability compensation. Furthermore,a simple adjustable current cell in the charge pump is proposed for additional stability compensation and a novel VCO with linear gain is adopted to limit the total variation. A fully integrated frequency synthesizer from 1 to 1.05GHz with 250kHz channel resolution is implemented to verify the methods. 展开更多
关键词 frequency synthesizer closed-loop third-order s-domain loop parameters PVT variation STABILITY variation margin
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ENSO Frequency Asymmetry and the Pacific Decadal Oscillation in Observations and 19 CMIP5 Models 被引量:10
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作者 Renping LIN Fei ZHENG Xiao DONG 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2018年第5期495-506,共12页
Using observational data and the pre-industrial simulations of 19 models from the Coupled Model Intercomparison Project Phase 5(CMIP5), the El Ni o(EN) and La Ni a(LN) events in positive and negative Pacific Dec... Using observational data and the pre-industrial simulations of 19 models from the Coupled Model Intercomparison Project Phase 5(CMIP5), the El Ni o(EN) and La Ni a(LN) events in positive and negative Pacific Decadal Oscillation(PDO) phases are examined. In the observational data, with EN(LN) events the positive(negative) SST anomaly in the equatorial eastern Pacific is much stronger in positive(negative) PDO phases than in negative(positive) phases. Meanwhile,the models cannot reasonably reproduce this difference. Besides, the modulation of ENSO frequency asymmetry by the PDO is explored. Results show that, in the observational data, EN is 300% more(58% less) frequent than LN in positive(negative)PDO phases, which is significant at the 99% confidence level using the Monte Carlo test. Most of the CMIP5 models exhibit results that are consistent with the observational data. 展开更多
关键词 ENSO frequency asymmetry Pacific Decadal Oscillation decadal variation Monte Carlo method CM1P5
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Analysis of the dynamic characteristics and stochastic simulation on variations of beach volumes 被引量:8
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作者 Chen Zishen(Institute of Estuarine and Coastal Research of Zhongshan University, Guangzhou 510275, China) 《Acta Oceanologica Sinica》 SCIE CAS CSCD 1995年第3期393-403,共11页
This paper analyzes the dynamic characteristics of the variations of the beach volumes for three level zonesof the Yanjing Beach in the Shuidong Bay of the western Guangdong Province by using the methods of dynamic sy... This paper analyzes the dynamic characteristics of the variations of the beach volumes for three level zonesof the Yanjing Beach in the Shuidong Bay of the western Guangdong Province by using the methods of dynamic systemanalysis and the multi-dimensional spectral estimation. The results show that the variations of the beach volume arecharaCterized by the multiband oscillations with a dominant semimonth period. Upwards the low tide level, the beachtends to be stable. The estimates of the partial coherences and the partial phases indicate that the variations of thebeach volumes are mainly the results of the direct actions of the waves which are influenced by the tidal level changesand driven by the wind stress. The simulation results of the beach volume series for different beach heart zones bythreshold mixed regressive models indicate that the influence of the tide on the variations of the beach volumes is weakened and the direct actions of the wave energy and the wind stress are apparently enhanced with the increase of thebeach height.(This project was supported by the National Natural Science Foundation of China.) 展开更多
关键词 Beach volume variations natural frequency damping ratio multi-dimensional spectral estimation stochastic simulation
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The Seasonal Variation of Large Volume Airgun Signals in Hutubi,Xinjiang 被引量:5
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作者 SU Jinbo WANG Qiong +3 位作者 ZHANG Wenxiu WEI Yunyun CHEN Hao WANG Haitao 《Earthquake Research in China》 CSCD 2019年第2期186-194,共9页
In order to study the seasonal variation of large volume airgun signals in Hutubi,Xinjiang,we analyzed 2,936 signals of airgun source excitations during 2015-2016 received by a seismograph on the bank of the excitatio... In order to study the seasonal variation of large volume airgun signals in Hutubi,Xinjiang,we analyzed 2,936 signals of airgun source excitations during 2015-2016 received by a seismograph on the bank of the excitation pool.Firstly,the RMS value of the signal amplitude and the daily average temperature were compared after linearly superimposing the signal in days,to analyze the influence of the surface ice cover on the excitation energy release of the airgun source.The result shows that the ice cover will reduce the excitation energy,and the thicker the ice cover is,the more obvious the excitation energy reduces.Secondly,the time-frequency analysis method was used to analyze the influence of the surface ice cover on the signal frequency.It is concluded that the existence of the ice cover has little effect on the signal frequency,but it will affect the intensity of the signal around 4 Hz between 1-2 s after excitation.The cause of these phenomena is that the ice cover affects the bubble oscillation,which in turn affects the energy conversion.The study shows that when using the cross-correlation delay method to calculate the wave velocity,the signals can be divided into two periods according to the daily average temperature:with or without ice cover on the upper surface of the excitation pool.This can help eliminate the influence of the source variation and improve the accuracy of the monitoring results. 展开更多
关键词 airgun SOURCE SEASONAL variation SIGNAL energy SIGNAL frequency
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Theoretical analysis of ion cyclotron range of frequency antenna array for HT-7U 被引量:2
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作者 张新军 秦成明 赵燕平 《Chinese Physics B》 SCIE EI CAS CSCD 2005年第11期2251-2255,共5页
This paper considers the coupling analysis of phased antenna array designed to excite fast wave in the ion cyclotron range of frequency. The coupling of the antenna is calculated in slab geometry. The coupling code ba... This paper considers the coupling analysis of phased antenna array designed to excite fast wave in the ion cyclotron range of frequency. The coupling of the antenna is calculated in slab geometry. The coupling code based on the variational principle gives the self-consistent current flowing in the antenna, this method has been extended so that it can be applied to a phased antenna array. As an example, this paper analyses the coupling prosperities of a 2 × 2 phased antenna array. It gives the optimum geometry of antenna array. The fields excited at plasma surface are found to more or less correspond to the antenna current phasing. 展开更多
关键词 ion cyclotron range of frequency antenna array variational method
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Variability of the Critical Frequency foF2 for Equatorial Regions during Solar Cycle’s Minima and Maxima at Ouagadougou and Manila Stations 被引量:2
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作者 Kaboré M’Bi Zerbo Jean Louis +1 位作者 Zoundi Christian Ouattara Frédéric 《International Journal of Geosciences》 2019年第10期833-844,共12页
In this paper we report on the foF2 variabilities for two equatorial regions (Ouagadougou: Lat. 12.4°N;Long. 358.5°E, Dip. 1.43°S;and Manila: Lat. 14°36'15.12''N;Long. 120°58'5... In this paper we report on the foF2 variabilities for two equatorial regions (Ouagadougou: Lat. 12.4°N;Long. 358.5°E, Dip. 1.43°S;and Manila: Lat. 14°36'15.12''N;Long. 120°58'55.92''E;Dip. 0.6°S) during solar cycles 20 and 21 minima and maxima phases. Many previous works have argued on the diurnal and seasonal variation of foF2 for different solar events conditions for latitudinal position. But there are few investigations for Africa equatorial region longitudinal variation. The present paper’s goal is to outline possible similarity in foF2 behavior between variations for better understanding of physical process lead to some observed phenomenon in Asia-Africa equatorial sector. The F-layer critical frequency (foF2) data observed from the two equatorial ionosonde stations have been used for the present comparative study. The results show significant similarity between the critical frequency (foF2) seasonal variations over the time intervals 1976-1996. During day-time measured data from Manila station are higher than those from Ouagadougou station. That may lie in that Manila is closer to equatorial ionization crest region. During solar minimum phase, the longitudinal variation of foF2 shows two crossing points (11:00 UT and 22:00 UT) between the foF2 profiles form the two stations for all seasons regardless of the solar cycle. However during intense solar activity condition, the number of crossing-point between measured data from Manila and Ouagadougou stations varies by seasons and solar cycle. This phenomenon may be due to the compilations of severe activities (storms, coronal mass ejection, heliosheet fluctuations) during the solar maximum phases. 展开更多
关键词 Critical frequency (foF2) Longitudinal variation Seasonal Solar Cycle
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The Background Variation of Natural Source ELF and Its EM Abnormal Phenomena in Yunnan Earthquakes 被引量:2
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作者 Fan Ye Tang Ji +2 位作者 Han Bing Cui Tengfa Xu Qin 《Earthquake Research in China》 CSCD 2018年第1期130-140,共11页
In order to add earthquake monitoring methods and develop new method research,the ELF Network for Earthquake Monitoring selected 30 stations in the Capital Circle and the Sichuan-Yunnan region. Finding electromagnetic... In order to add earthquake monitoring methods and develop new method research,the ELF Network for Earthquake Monitoring selected 30 stations in the Capital Circle and the Sichuan-Yunnan region. Finding electromagnetic field background variation is the basis of distinguishing the seismic electromagnetic anomalies. This paper introduces the data acquisition and selection of the Shexian,Anqiu,Lijiang and Dali stations which have recorded for longer time with better data and are located on the similar latitude. Then we use the natural source electromagnetic field's auto-power spectrum to express the intensity of the electromagnetic field. By using power spectral data of many frequencies in the observation frequency band,after the data pre-processing and sliding average noising,the background variation of extremely low frequency stations and the range ability were acquired.Taking the Baoshan M5. 1 earthquake on October 30,2015 and Dali M5. 0 earthquake on May 18,2016 as examples,the authors analyzed the earthquake electromagnetic anomaly characteristic of ELF stations around the earthquakes. 展开更多
关键词 NATURAL SOURCE Extremely low frequency(ELF) Electric and magnetic fields auto-power spectrum BACKGROUND variation Earthquake electromagnetic anomaly(EM)
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IMPACT OF LARGE-SCALE CIRCULATION ON THE INTERDECADAL VARIATIONS OF THE WESTERN NORTH PACIFIC TROPICAL CYCLONE 被引量:1
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作者 卢秋珍 胡邦辉 +1 位作者 王举 张勇 《Journal of Tropical Meteorology》 SCIE 2008年第1期81-84,共4页
Based on the annual frequency data of tropical cyclones from 1960 to 2005 and by the polynomial fit and statistical analysis, this work has discovered that TC activity in the 46a exhibits significant decadal-scale var... Based on the annual frequency data of tropical cyclones from 1960 to 2005 and by the polynomial fit and statistical analysis, this work has discovered that TC activity in the 46a exhibits significant decadal-scale variability. It has two high frequency periods (HFP) and two low frequency periods (LFP). Significant differences in the number of TCs between HFP and LFP are found in active TC seasons from July to October. Differences of large-scale circulation during HFP and LFP have been investigated with NCEP/NOAA data for the season. In HFP, the condition includes not only higher sea surface temperature, lower sea level pressure, larger divergence of upper air, larger relative vorticity at low levels and smaller vertical shear, but also 500-hPa wind vector being more available for TC activity and moving to western North Pacific, the position of the subtropical anticyclone over the western Pacific shifting more northward, and South Asian Anticyclone at 100-hPa being much smaller than that in LFP. The precipitation of western North Pacific has no clear influence on TC activity. 展开更多
关键词 western North Pacific TC frequency interdecadal variation large scale circulation
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On Frequency Sensitivity and Mode Orthogonality of Flexible Robotic Manipulators 被引量:5
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作者 Fei-Yue Wang Yanqing Gao 《IEEE/CAA Journal of Automatica Sinica》 SCIE EI 2016年第4期394-397,共4页
This paper presents sensitivity analysis of vibration frequencies of flexible manipulators with respect to variations of systems parameters such as rotational inertia of hub, and mass, moment, and side of tip load. Bo... This paper presents sensitivity analysis of vibration frequencies of flexible manipulators with respect to variations of systems parameters such as rotational inertia of hub, and mass, moment, and side of tip load. Both Euler-Bernoulli and Timoshenko dynamical models of flexible manipulators are discussed. By using variational method, sensitivity indices are obtained with explicit expressions for measuring the sensitivity of frequencies. Based on variational formulations, a novel method for deriving the orthogonal relations among vibration modal shape functions of flexible manipulators is introduced. With this method, the orthogonal relations can be derived easily without invoking the tedious process of differentiation and integration by part, as commonly used in their derivation. © 2014 Chinese Association of Automation. 展开更多
关键词 Dielectric waveguides Flexible manipulators MANIPULATORS Orthogonal functions Vibration analysis
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Annual and interannual variations of sea-level anomaly in the Bay of Bengal and the Andaman Sea 被引量:2
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作者 QIU Yun LI Li +1 位作者 YU Weidong HU Jianyu 《Acta Oceanologica Sinica》 SCIE CAS CSCD 2007年第6期13-29,共17页
Annual and interannual variations of sea-level anomaly (SLA) in the Bay of Bengal and the Andaman Sea are investigated using altimeter - derived SLA data from 1993 to 2003. It is found that the SLA annual variation ... Annual and interannual variations of sea-level anomaly (SLA) in the Bay of Bengal and the Andaman Sea are investigated using altimeter - derived SLA data from 1993 to 2003. It is found that the SLA annual variation in the study area can be divided into three phases with distinctive patterns. During the southwest monsoon (May -September), positive SLA presents in the equatorial region and extends northward along the eastern boundary of the bay, and the SLA distribution in the interior bay appears to be high in the east and low in the west with two cyclonic ceils developing in the north and south of the western bay respectively, between which an anticyclonic cell exists. During the early northeast monsoon ( October - December) , the whole bay is dominated by a large cyclonic cell with the pattern of high SLA in the east and low in the west still retained, and the SLA distribution outside the bay is changed in response to the reversal of the Indian Monsoon Current (IMC) in November. During the late northeast monsoon (January -April) , a large anticyclonic cell of SLA develops in the bay with negative SLA prevailing in the equatorial region and extending northward along the eastern boundary of bay. Therefore, the SLA distribution in the interior bay reverses to be high in the west and low in the east. It is suggested that the SLA annual variation in the bay is primarily driven by the local wind stress curl, involving Sverdrup balance while the abrupt SLA variation during the peak of northeast monsoon may be partly caused by the semiannual fluctuation of wind in the equatorial region. This fast adjustment in the interior bay is induced by the upwelling coastal Kelvin wave excited by the decay of Wyrtki jet during December through January. Besides the annual variation, in the bay, there are obvious SLA fluctuations with the periods of 2 and 3 - 7 a, which are driven by the interannual variability of large - scale wind field in the equatorial region. The coastal Kelvin wave also provides an important link for the SLA interannual variation between the equatorial region and the interior bay. It is found that the E1 Nino -Southern Oscillation (ENSO) -induced influence on the SLA interannual variation in the interior bay is stronger than the Indian Ocean dipole (IOD) with the associated pattern of low sea-level presenting along the periphery of the bay and high sea-level in the northeast of Sri Lanka. 展开更多
关键词 Bay of Bengal sea-level anomaly low-frequency variation satellite altimeter
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