A periodic pipe system composed of steel pipes and rubber hoses with the same inner radius is designed based on the theory of phononic crystals. Using the transfer matrix method, the band structure of the periodic pip...A periodic pipe system composed of steel pipes and rubber hoses with the same inner radius is designed based on the theory of phononic crystals. Using the transfer matrix method, the band structure of the periodic pipe is calculated considering the structural-acoustic coupling. The results show that longitudinal vibration band gaps and acoustic band gaps can coexist in the fluid-filled periodic pipe. The formation of the band gap mechanism is further analyzed. The band gaps are validated by the sound transmission loss and vibration-frequency response functions calculated using the finite element method. The effect of the damp on the band gap is analyzed by calculating the complex band structure. The periodic pipe system can be used not only in the field of vibration reduction but also for noise elimination.展开更多
The paper analyses the periodical characteristics of the economic development of Shandong Province by using the mini- mum variation analysis model.The analysis shows that the eco- nomic development process of Shandong...The paper analyses the periodical characteristics of the economic development of Shandong Province by using the mini- mum variation analysis model.The analysis shows that the eco- nomic development process of Shandong Province has short, medium and long cycles respectively for 6,12,19 years,and the fluctuation of the economic development becomes gentler with time passing by.The fluctuation of macro-control policy,invest- ment and consumption are the main reasons of the economic fluc- tuation.展开更多
This paper summarizes the general methods,existing problems and their causes of the period analysis for the monthly mean sea level and points out that it is the key to the analysing period signals and forecasting the ...This paper summarizes the general methods,existing problems and their causes of the period analysis for the monthly mean sea level and points out that it is the key to the analysing period signals and forecasting the change trend of the monthly mean sea level that the periods of the signals are selected reasonably. As there are often many period signals in these series, nonlinear effects exist between pairs of period signals. In order to avoid the false periods that may be introduced due to the effects of side lobes and the periods with statistical phase significance coherence that may be introduced due to the effects of nonlinear effects and their restraint to other period signals, the maximum entropy spectral analysis and the corresponding significance period test may be performed repeatedly on the basis of the bispectrum analysis and meanwhile the most significant period component is filtered out by the least square filtering method, i. e., the method of the significance period analysis with mixed spectra modeled by a nonlinear system is adopted and the signal periods approaching the reality are selected one by one. The examples of the bispectrum analysis, the signal period analysis by mixed spectra and the fitting parameters for combined period components with linear trend in the time series of monthly mean sea level are given in this paper.展开更多
The Tibetan Plateau(TP)is one of the most sensitive areas and is more susceptible to climate change than other regions in China.The TP also experiences extremely frequent light precipitation events compared to precipi...The Tibetan Plateau(TP)is one of the most sensitive areas and is more susceptible to climate change than other regions in China.The TP also experiences extremely frequent light precipitation events compared to precipitation of other intensities.However,the definition,influencing factors,and characteristics of light precipitation in the TP have not been accurately explained.This study investigated the variation characteristics of light precipitation with intensities(Pre)of 0.1-10.0 mm/d based on climate data from 53 meteorological stations over the central and eastern TP from 1961 to 2019.For detailed analysis,light precipitation events were classified into five grades:G1[0.1-2.0 mm/d),G2[2.0-4.0 mm/d),G3[4.0-6.0 mm/d),G4[6.0-8.0 mm/d),and G5[8.0-10.0 mm/d).The results showed that both the amount of precipitation and number of precipitation days had increased significantly at rates of 4.0-6.0 mm/10 yr and 2.0-4.0 d/10 yr,respectively,and most precipitation events were of low intensity(0.1≤Pre<2.0 mm/d).Light precipitation events mainly occurred in the southeast of the study area,and it showed an increasing trend from the northwest to the southeast.Abrupt changes in light precipitation primarily occurred in the 1980 s.A comprehensive time series analysis using the Mann-Kendall test and Morlet wavelet was performed to characterize the abrupt changes and cycles of light precipitation.During the study period,the main periods of light precipitation corresponded to the 6 yr cycle,with obvious periodic oscillation characteristics,and this cycle coexisted with cycles of other scales.Significant correlations were observed between the amount of light precipitation and temperature over the study area.The findings will enhance our understanding of changes in light precipitation in the TP and provide Scientific basis for the definition of light precipitation in the future.展开更多
In this paper, we construct a kind of bivariate real-valued orthogonal periodic wavelets. The corre-sponding decomposition and reconstruction algorithms involve only 8 terms respectively which are very simple in pract...In this paper, we construct a kind of bivariate real-valued orthogonal periodic wavelets. The corre-sponding decomposition and reconstruction algorithms involve only 8 terms respectively which are very simple in practical computation. Moreover, the relation between periodic wavelets and Fourier series is also discussed.展开更多
On the basis of the analytical results of the period components of monthly mean sea level of 236 stationsin the Pacific, the period components plus linear trend are ed to fit the monthly mean sea level series. The sta...On the basis of the analytical results of the period components of monthly mean sea level of 236 stationsin the Pacific, the period components plus linear trend are ed to fit the monthly mean sea level series. The statisticalresults of linear trend Coefficients of these stations indicate that, if the abnormal values of sea-level rise and fall are neglected, the average rise rate of relative sea level in the Pacific is 1. 16 mm/a. Affected by nonuniformity Of land subsidence and other factors, the regional change of relative sea level rise or fall in the Pacific is greater. In the light of thepositive or negative values of linear trend coefficients as well as the geographical position of the sea area, zoning is madeof the sea level rise or fall in the Pacific including the coastal areas of China and Southeast Asia to obtain the averagerate of rise or fall in each sea area. The rise or fall trends of relative sea level obtained for the entire Pacific Ocean,west coast of North America, the northern and central South America, the greater part of the tropical Pacific and thecoastal Islands of Japan are basically in keeping with the other relevant results. The regional average estimated result ofthe relative sea level in the coast of East Asia is on the rise while the estimated results provided by Barnett tend todrop; the main cause of this nonuniformity is the number of stations selected and the distributional density.展开更多
Fast Fourier Transfer Image Processing was widely applied to the analysis of wood anatomy structure in re-cent years. The cells in the wood transverse section have obviously periodicity and regularity. FFT power spect...Fast Fourier Transfer Image Processing was widely applied to the analysis of wood anatomy structure in re-cent years. The cells in the wood transverse section have obviously periodicity and regularity. FFT power spectral patternscan extract the periodic characteristics so that they can be compared. identified and classified quaytitatively. This paperSummarizes the application of FFT image analysis in wood science and the general way to study wood anatomy by FFT.展开更多
[Objective]The aim was to analyze the first fit of rainstorm in southeast Hubei on June 9,2011.[Method]GFS reanalysis data with resolution 0.5°×0.5°,routine-observational data,the intensive observations...[Objective]The aim was to analyze the first fit of rainstorm in southeast Hubei on June 9,2011.[Method]GFS reanalysis data with resolution 0.5°×0.5°,routine-observational data,the intensive observations of automatic weather station data,satellite image as well as satellite image were used in the analysis for the process of a heavy rain on June 9-10,2011 during Meiyu in Hubei province.[Result]The heavy rainfall occurred under the favorable environmental conditions,but the single-obstruction situation during Meiyu was different from the typical double-obstruction one.The affecting systems were the trough at 45° N on 500 hPa caused the systems moving slowly in the middle and low troposphere.The strong convergence of water vapor and conditional convective instability were provided from the shear line on 700 and 850 hPa,the southwest jet flow and dry lines in the middle and low troposphere for heavy rainfall.Three rain clusters which brought heavy rainfall had the features of meso-scale β system,which came from warm and humid airflow,the tail of shear line on 700 hPa and the head of shear line on 850 hPa.Through convergence and strengthening in southeast region of Hubei Province,the ribbon structure from northeast to southwest was formed to maintain the meso-scale β system.The cloud was the direct producer of precipitation.Heavy rainfall occurred in strengthening phase of strong convection zone on Tongcheng city.[Conclusion]The study provided theoretical reference for the report of rainstorm during Meiyu period.展开更多
Objective To summarize our clinical experience in liver transplantation while considering the background in this filed in China. Methods Ninety-five patients who had received liver transplantation from April 1993 to M...Objective To summarize our clinical experience in liver transplantation while considering the background in this filed in China. Methods Ninety-five patients who had received liver transplantation from April 1993 to March 2002 were analyzed retrospectively. Three periods were defined objectively as period Ⅰ(1993-1997),Ⅱ(1999) and Ⅲ(2000 -2002). Operative techniques, recipients, original diseases, complications and survival rates were compared among the three periods. Results Malignant liver lesions were the main cause for liver transplantation in period Ⅰ and Ⅱ. The ratio of number of malignant disease to total recipients decreased gradually from period Ⅰ to Ⅱ (100%, 53% and 35%, respectively). The 1-year survival rate in patients with benign liver disease was 85 % and the total operative mortality was 5% in period Ⅲ. The incidence of hepatitis B virus reactivation or reinfection was 24% twelve months after liver transplantation. Vascular complication decreased but biliary complications did展开更多
Chaotic maps are widely used to design pseudo-random sequence generators, chaotic ciphers, and secure communication systems. Nevertheless, the dynamic characteristics of digital chaos in finite-precision domain must b...Chaotic maps are widely used to design pseudo-random sequence generators, chaotic ciphers, and secure communication systems. Nevertheless, the dynamic characteristics of digital chaos in finite-precision domain must be degraded in varying degrees due to the limited calculation accuracy of hardware equipment. To assess the dynamic properties of digital chaos, we design a periodic cycle location algorithm(PCLA) from a new perspective to analyze the dynamic degradation of digital chaos. The PCLA can divide the state-mapping graph of digital chaos into several connected subgraphs for the purpose of locating all fixed points and periodic limit cycles contained in a digital chaotic map. To test the versatility and availability of our proposed algorithm, the periodic distribution and security of 1-D logistic maps and 2-D Baker maps are analyzed in detail. Moreover, this algorithm is helpful to the design of anti-degradation algorithms for digital chaotic dynamics. These related studies can promote the application of chaos in engineering practice.展开更多
Estimating reservoir connectivity is critical for assessing infill-drilling prospects and initiating fluid injection in enhanced oil recovery operations. Several methods have appeared in the literature over decades to...Estimating reservoir connectivity is critical for assessing infill-drilling prospects and initiating fluid injection in enhanced oil recovery operations. Several methods have appeared in the literature over decades to meet these business needs, given that all tools, including seismic imaging, have limitations. Besides imaging, geochemical fingerprinting constitutes a powerful tool to gauge the compartmentalization question. However, real-time pressure/rate surveillance data allows assessing interwell connectivity vis-à-vis the overall drainage volume.This study presents a simplified approach to using the reciprocal-productivity index (RPI) vs. the total-material-balance time (tTMB) plot. This tool exhibits the same slope for those wells in the same compartment beyond the start of the boundary-dominated flow (BDF) period. The wells showing different slopes imply that they are in separate drainage volumes. The early-time transient period remains muted to minimize confusion on this Cartesian plot. We validated the proposed tool's efficacy with 2D and 3D models with increased degrees of reservoir complexity, followed by the verification phase with four field examples. The use of other analytical tools complemented our findings.展开更多
Periodicity is one of the most common phenomena in the physical world. The problem of periodicity analysis （or period detection） is a research topic in several areas, such as signal processing and data mining. Howev...Periodicity is one of the most common phenomena in the physical world. The problem of periodicity analysis （or period detection） is a research topic in several areas, such as signal processing and data mining. However, period detection is a very challenging problem, due to the sparsity and noisiness of observational datasets of periodic events. This paper focuses on the problem of period detection from sparse and noisy observational datasets. To solve the problem, a novel method based on the approximate greatest common divisor （AGCD） is proposed. The proposed method is robust to sparseness and noise, and is efficient. Moreover, unlike most existing methods, it does not need prior knowledge of the rough range of the period. To evaluate the accuracy and efficiency of the proposed method, comprehensive experiments on synthetic data are conducted. Experimental results show that our method can yield highly accurate results with small datasets, is more robust to sparseness and noise, and is less sensitive to the magnitude of period than compared methods.展开更多
In this paper, we study the properties of periodic multiresolution analysis, and present a complete characterization of the scaling function sequence, which enables us to construct a new scaling function sequence from...In this paper, we study the properties of periodic multiresolution analysis, and present a complete characterization of the scaling function sequence, which enables us to construct a new scaling function sequence from a given one. An application of the main results is given at the end.展开更多
A theoretical method is presented,which analyzes properties of surface acoustic waves propagating on metallic gratings with finite thickness by combining finite element method with variational principle on surface aco...A theoretical method is presented,which analyzes properties of surface acoustic waves propagating on metallic gratings with finite thickness by combining finite element method with variational principle on surface acoustic waves propagating on periodic metal gratings. Based on D.P.Chen and Haus theory,a finite element method is used to investigate the effects of metallic gratings upon the propagation of surface acoustic waves.The coupling-of-modes parameters contributed by mechanical loading are expressed by the matrix derived from the finite element method.Consequently D.P.Chen and Haus theory can also be applied to analyze the properties of surface acoustic waves propagating on metallic gratings with finite thickness and arbitrary shape.Finally,the characteristics of surface acoustic waves propagating under gold and aluminum or silver gratings on a few piezoelectric crystals are studied.Numerical results of the coupling-of-modes parameters of the surface acoustic waves are obtained.展开更多
Typhoons with erratic movement are studied for their annual frequency of occurrence over the South China Sea and Northwest Pacific,based on 102 years of data (1884—1985).It discovers that the years with higher fre- q...Typhoons with erratic movement are studied for their annual frequency of occurrence over the South China Sea and Northwest Pacific,based on 102 years of data (1884—1985).It discovers that the years with higher fre- quency tend to get together.There are well-defined periods of 12 and 30 years,revealed with the maximum entropy method (MEM),the latter of low-frequency oscillation being clearer.展开更多
In this paper we analyze the qualitative behaviour of the equation ε+q(X) +εX=bp(t), where e is a small parameter.We divide the interval of parameter b into four sets of subintervals,A, B,C and D.For bA,B or D,we di...In this paper we analyze the qualitative behaviour of the equation ε+q(X) +εX=bp(t), where e is a small parameter.We divide the interval of parameter b into four sets of subintervals,A, B,C and D.For bA,B or D,we discuss the different structures of the attractors of the equation and their stabilities.When chaotic phenomena appear,we also estimate the entropy.For bC,the set of bifurcation intervals,we analyze the bifurcating type and get a series of consequences from the results of Newhouse and Palis.展开更多
The low-frequency periodic error of star tracker is one of the most critical problems for high-accuracy satellite attitude determination.In this paper an approach is proposed to identify and compensate the low-frequen...The low-frequency periodic error of star tracker is one of the most critical problems for high-accuracy satellite attitude determination.In this paper an approach is proposed to identify and compensate the low-frequency periodic error for star tracker in attitude measurement.The analytical expression between the estimated gyro drift and the low-frequency periodic error of star tracker is derived firstly.And then the low-frequency periodic error,which can be expressed by Fourier series,is identified by the frequency spectrum of the estimated gyro drift according to the solution of the first step.Furthermore,the compensated model of the low-frequency periodic error is established based on the identified parameters to improve the attitude determination accuracy.Finally,promising simulated experimental results demonstrate the validity and effectiveness of the proposed method.The periodic error for attitude determination is eliminated basically and the estimation precision is improved greatly.展开更多
The Greater Khingan Mountains （Daxinganling） are China＇s important ecological protective screen and also the region most sensitive to climate changes. To gain an in-depth understanding and reveal the climate change...The Greater Khingan Mountains （Daxinganling） are China＇s important ecological protective screen and also the region most sensitive to climate changes. To gain an in-depth understanding and reveal the climate change characteristic in this high-latitude, cold and data-insufficient region is of great importance to maintaining ecological safety and corre- sponding to global climate changes. In this article, the annual average temperature, precipi- tation and sunshine duration series were firstly constructed using tree-ring data and the me- teorological observation data. Then, using the climate tendency rate method, moving-t-testing method, Yamamoto method and wavelet analysis method, we have investigated the climate changes in the region during the past 307 years. Results indicate that, since 1707, the annual average temperature increased significantly, the precipitation increased slightly and the sun- shine duration decreased, with the tendency rates of 0.06~C/10a, 0.79 mm/10a and -5.15 h/10a, respectively （P〈~0.01）. Since the 21 st century, the period with the greatest increase of the annual average temperature （also with the greatest increase of precipitation） corresponds to the period with greatest decrease of sunshine duration. Three sudden changes of the an- nual average temperature and sunshine duration occurred in this period while two sudden changes of precipitation occurred. The strong sudden-change years of precipitation and sunshine duration are basically consistent with the sudden-change years of annual average temperature, suggesting that in the mid-1860s, the climatic sudden change or transition really existed in this region. In the time domain, the climatic series of this region exhibit obvious local variation characteristics. The annual average temperature and sunshine duration exhibit the periodic variations of 25 years while the precipitation exhibits a periodic variation of 20 years. Based on these periodic characteristics, one can infer that in the period from 2013 to 2030, the temperature will be at a high-temperature stage, the precipitation will be at an abundant-precipitation stage and the sunshine duration will be at an less-sunshine stage. In terms of spatial distribution, the leading distribution type of the annual average temperature in this region shows integrity, i.e：, it is easily higher or lower in the whole region; and the second distribution type is more （or less） in the southwest parts and less （or more） in the northeast parts. Precipitation and sunshine duration exhibit complex spatial distribution and include four spatial distribution types. The present study can provide scientific basis for the security in- vestigation of homeland, ecological and water resources as well as economic development programming in China＇s northern borders.展开更多
In order to analyze the stress and strain fields in the fibers and the matrix in composite materials,a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced.Ass...In order to analyze the stress and strain fields in the fibers and the matrix in composite materials,a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced.Assuming matrix cracking as the failure mode of composite materials,an energy-based fatigue damage parameter and a multiaxial fatigue life prediction method are established.This method only needs the material properties of the fibers and the matrix to be known.After the relationship between the fatigue damage parameter and the fatigue life under any arbitrary test condition is established,the multiaxial fatigue life under any other load condition can be predicted.The proposed method has been verified using two different kinds of load forms.One is unidirectional laminates subjected to cyclic off-axis loading,and the other is filament wound composites subjected to cyclic tension-torsion loading.The fatigue lives predicted using the proposed model are in good agreements with the experimental results for both kinds of load forms.展开更多
The 200-hPa wind perturbation(WP) in the subtropical westerly over East Asia(SWEA) has seldom been examined in previous studies, especially in connection with forecast of the summer rainfall in China. Based on the dai...The 200-hPa wind perturbation(WP) in the subtropical westerly over East Asia(SWEA) has seldom been examined in previous studies, especially in connection with forecast of the summer rainfall in China. Based on the daily NCEP/NCAR reanalysis data and precipitation observations in China from 1 June to 31 August of 1960-2015, this study first systematically analyzes the spatiotemporal distribution features of the 200-hPa WP in the SWEA on different scales, especially during the Meiyu season in the Yangtze-Huaihe region and during the rainy period in North China, by using spectral decomposition and period analysis. It is found that in the 56-yr mean fields, the 200-hPa WP in the SWEA is collocated with the East Asian subtropical jet(EASJ), with the centers of the two systems coincidentally overlapped. The WP filed in the subtropical westerly mainly comprises planetary-and synoptic-scale waves. The quasi-stationary planetary-scale wave seems to determine the shape and intensity of the WP in the SWEA, while the synoptic-scale wave is closely related to the local central intensity of the WP. The daily evolution of the 56-yr mean fields shows that, following the northward(southward) movement of SWEA from 1 June to 31 August, the planetaryscale WP in the SWEA becomes gradually weakened(intensified) whereas the synoptic-scale WP is slightly intensified(weakened).The results also reveal that during the Meiyu season in the Yangtze-Huaihe region, the WP in the SWEA moves northward slowly around 37°-39°N, demonstrating a quasi-biweekly oscillation in its geographic location, which is largely attributed to the strong(weak) planetary-scale(synoptic-scale) component. On the contrast, in the summer rainy season over North China, the WP in the SWEA further strives northward beyond 40°N, showing both quasi-biweekly and weekly oscillations in its position; meanwhile, the planetary-scale wave in the SWEA becomes weakened whereas the synoptic-scale wave is enhanced. These salient variational features of the WP in the SWEA and its scaledependent components may be useful for the medium-range forecast of the rain belt migration in eastern China.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11372346
文摘A periodic pipe system composed of steel pipes and rubber hoses with the same inner radius is designed based on the theory of phononic crystals. Using the transfer matrix method, the band structure of the periodic pipe is calculated considering the structural-acoustic coupling. The results show that longitudinal vibration band gaps and acoustic band gaps can coexist in the fluid-filled periodic pipe. The formation of the band gap mechanism is further analyzed. The band gaps are validated by the sound transmission loss and vibration-frequency response functions calculated using the finite element method. The effect of the damp on the band gap is analyzed by calculating the complex band structure. The periodic pipe system can be used not only in the field of vibration reduction but also for noise elimination.
文摘The paper analyses the periodical characteristics of the economic development of Shandong Province by using the mini- mum variation analysis model.The analysis shows that the eco- nomic development process of Shandong Province has short, medium and long cycles respectively for 6,12,19 years,and the fluctuation of the economic development becomes gentler with time passing by.The fluctuation of macro-control policy,invest- ment and consumption are the main reasons of the economic fluc- tuation.
文摘This paper summarizes the general methods,existing problems and their causes of the period analysis for the monthly mean sea level and points out that it is the key to the analysing period signals and forecasting the change trend of the monthly mean sea level that the periods of the signals are selected reasonably. As there are often many period signals in these series, nonlinear effects exist between pairs of period signals. In order to avoid the false periods that may be introduced due to the effects of side lobes and the periods with statistical phase significance coherence that may be introduced due to the effects of nonlinear effects and their restraint to other period signals, the maximum entropy spectral analysis and the corresponding significance period test may be performed repeatedly on the basis of the bispectrum analysis and meanwhile the most significant period component is filtered out by the least square filtering method, i. e., the method of the significance period analysis with mixed spectra modeled by a nonlinear system is adopted and the signal periods approaching the reality are selected one by one. The examples of the bispectrum analysis, the signal period analysis by mixed spectra and the fitting parameters for combined period components with linear trend in the time series of monthly mean sea level are given in this paper.
基金Under the auspices of the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(No.2019QZKK040)Key Technologies Research and Development Program of Shaanxi Province(No.2021ZDLSF05-02)+2 种基金The National Natural Science Foundation of China(No.42072208,42101100,41901129)The Fundamental Research Funds for the Central Universities(No.GK202001003)Natural Science Foundation of Shaanxi Province(No.2021JQ-313)。
文摘The Tibetan Plateau(TP)is one of the most sensitive areas and is more susceptible to climate change than other regions in China.The TP also experiences extremely frequent light precipitation events compared to precipitation of other intensities.However,the definition,influencing factors,and characteristics of light precipitation in the TP have not been accurately explained.This study investigated the variation characteristics of light precipitation with intensities(Pre)of 0.1-10.0 mm/d based on climate data from 53 meteorological stations over the central and eastern TP from 1961 to 2019.For detailed analysis,light precipitation events were classified into five grades:G1[0.1-2.0 mm/d),G2[2.0-4.0 mm/d),G3[4.0-6.0 mm/d),G4[6.0-8.0 mm/d),and G5[8.0-10.0 mm/d).The results showed that both the amount of precipitation and number of precipitation days had increased significantly at rates of 4.0-6.0 mm/10 yr and 2.0-4.0 d/10 yr,respectively,and most precipitation events were of low intensity(0.1≤Pre<2.0 mm/d).Light precipitation events mainly occurred in the southeast of the study area,and it showed an increasing trend from the northwest to the southeast.Abrupt changes in light precipitation primarily occurred in the 1980 s.A comprehensive time series analysis using the Mann-Kendall test and Morlet wavelet was performed to characterize the abrupt changes and cycles of light precipitation.During the study period,the main periods of light precipitation corresponded to the 6 yr cycle,with obvious periodic oscillation characteristics,and this cycle coexisted with cycles of other scales.Significant correlations were observed between the amount of light precipitation and temperature over the study area.The findings will enhance our understanding of changes in light precipitation in the TP and provide Scientific basis for the definition of light precipitation in the future.
文摘In this paper, we construct a kind of bivariate real-valued orthogonal periodic wavelets. The corre-sponding decomposition and reconstruction algorithms involve only 8 terms respectively which are very simple in practical computation. Moreover, the relation between periodic wavelets and Fourier series is also discussed.
文摘On the basis of the analytical results of the period components of monthly mean sea level of 236 stationsin the Pacific, the period components plus linear trend are ed to fit the monthly mean sea level series. The statisticalresults of linear trend Coefficients of these stations indicate that, if the abnormal values of sea-level rise and fall are neglected, the average rise rate of relative sea level in the Pacific is 1. 16 mm/a. Affected by nonuniformity Of land subsidence and other factors, the regional change of relative sea level rise or fall in the Pacific is greater. In the light of thepositive or negative values of linear trend coefficients as well as the geographical position of the sea area, zoning is madeof the sea level rise or fall in the Pacific including the coastal areas of China and Southeast Asia to obtain the averagerate of rise or fall in each sea area. The rise or fall trends of relative sea level obtained for the entire Pacific Ocean,west coast of North America, the northern and central South America, the greater part of the tropical Pacific and thecoastal Islands of Japan are basically in keeping with the other relevant results. The regional average estimated result ofthe relative sea level in the coast of East Asia is on the rise while the estimated results provided by Barnett tend todrop; the main cause of this nonuniformity is the number of stations selected and the distributional density.
文摘Fast Fourier Transfer Image Processing was widely applied to the analysis of wood anatomy structure in re-cent years. The cells in the wood transverse section have obviously periodicity and regularity. FFT power spectral patternscan extract the periodic characteristics so that they can be compared. identified and classified quaytitatively. This paperSummarizes the application of FFT image analysis in wood science and the general way to study wood anatomy by FFT.
文摘[Objective]The aim was to analyze the first fit of rainstorm in southeast Hubei on June 9,2011.[Method]GFS reanalysis data with resolution 0.5°×0.5°,routine-observational data,the intensive observations of automatic weather station data,satellite image as well as satellite image were used in the analysis for the process of a heavy rain on June 9-10,2011 during Meiyu in Hubei province.[Result]The heavy rainfall occurred under the favorable environmental conditions,but the single-obstruction situation during Meiyu was different from the typical double-obstruction one.The affecting systems were the trough at 45° N on 500 hPa caused the systems moving slowly in the middle and low troposphere.The strong convergence of water vapor and conditional convective instability were provided from the shear line on 700 and 850 hPa,the southwest jet flow and dry lines in the middle and low troposphere for heavy rainfall.Three rain clusters which brought heavy rainfall had the features of meso-scale β system,which came from warm and humid airflow,the tail of shear line on 700 hPa and the head of shear line on 850 hPa.Through convergence and strengthening in southeast region of Hubei Province,the ribbon structure from northeast to southwest was formed to maintain the meso-scale β system.The cloud was the direct producer of precipitation.Heavy rainfall occurred in strengthening phase of strong convection zone on Tongcheng city.[Conclusion]The study provided theoretical reference for the report of rainstorm during Meiyu period.
文摘Objective To summarize our clinical experience in liver transplantation while considering the background in this filed in China. Methods Ninety-five patients who had received liver transplantation from April 1993 to March 2002 were analyzed retrospectively. Three periods were defined objectively as period Ⅰ(1993-1997),Ⅱ(1999) and Ⅲ(2000 -2002). Operative techniques, recipients, original diseases, complications and survival rates were compared among the three periods. Results Malignant liver lesions were the main cause for liver transplantation in period Ⅰ and Ⅱ. The ratio of number of malignant disease to total recipients decreased gradually from period Ⅰ to Ⅱ (100%, 53% and 35%, respectively). The 1-year survival rate in patients with benign liver disease was 85 % and the total operative mortality was 5% in period Ⅲ. The incidence of hepatitis B virus reactivation or reinfection was 24% twelve months after liver transplantation. Vascular complication decreased but biliary complications did
基金Project supported by the National Natural Science Foundation of China (Grant No.62101178)the Fundamental Research Funds for the Higher Institutions in Heilongjiang Province,China (Grant No.2020-KYYWF-1033)。
文摘Chaotic maps are widely used to design pseudo-random sequence generators, chaotic ciphers, and secure communication systems. Nevertheless, the dynamic characteristics of digital chaos in finite-precision domain must be degraded in varying degrees due to the limited calculation accuracy of hardware equipment. To assess the dynamic properties of digital chaos, we design a periodic cycle location algorithm(PCLA) from a new perspective to analyze the dynamic degradation of digital chaos. The PCLA can divide the state-mapping graph of digital chaos into several connected subgraphs for the purpose of locating all fixed points and periodic limit cycles contained in a digital chaotic map. To test the versatility and availability of our proposed algorithm, the periodic distribution and security of 1-D logistic maps and 2-D Baker maps are analyzed in detail. Moreover, this algorithm is helpful to the design of anti-degradation algorithms for digital chaotic dynamics. These related studies can promote the application of chaos in engineering practice.
文摘Estimating reservoir connectivity is critical for assessing infill-drilling prospects and initiating fluid injection in enhanced oil recovery operations. Several methods have appeared in the literature over decades to meet these business needs, given that all tools, including seismic imaging, have limitations. Besides imaging, geochemical fingerprinting constitutes a powerful tool to gauge the compartmentalization question. However, real-time pressure/rate surveillance data allows assessing interwell connectivity vis-à-vis the overall drainage volume.This study presents a simplified approach to using the reciprocal-productivity index (RPI) vs. the total-material-balance time (tTMB) plot. This tool exhibits the same slope for those wells in the same compartment beyond the start of the boundary-dominated flow (BDF) period. The wells showing different slopes imply that they are in separate drainage volumes. The early-time transient period remains muted to minimize confusion on this Cartesian plot. We validated the proposed tool's efficacy with 2D and 3D models with increased degrees of reservoir complexity, followed by the verification phase with four field examples. The use of other analytical tools complemented our findings.
基金Project supported by the National Natural Science Foundation of China （No. 60673082）
文摘Periodicity is one of the most common phenomena in the physical world. The problem of periodicity analysis （or period detection） is a research topic in several areas, such as signal processing and data mining. However, period detection is a very challenging problem, due to the sparsity and noisiness of observational datasets of periodic events. This paper focuses on the problem of period detection from sparse and noisy observational datasets. To solve the problem, a novel method based on the approximate greatest common divisor （AGCD） is proposed. The proposed method is robust to sparseness and noise, and is efficient. Moreover, unlike most existing methods, it does not need prior knowledge of the rough range of the period. To evaluate the accuracy and efficiency of the proposed method, comprehensive experiments on synthetic data are conducted. Experimental results show that our method can yield highly accurate results with small datasets, is more robust to sparseness and noise, and is less sensitive to the magnitude of period than compared methods.
文摘In this paper, we study the properties of periodic multiresolution analysis, and present a complete characterization of the scaling function sequence, which enables us to construct a new scaling function sequence from a given one. An application of the main results is given at the end.
基金supported by the National Nature Science Foundation of China(10974171)Zhejiang Province Nature Science Foundation(LY12A04003)
文摘A theoretical method is presented,which analyzes properties of surface acoustic waves propagating on metallic gratings with finite thickness by combining finite element method with variational principle on surface acoustic waves propagating on periodic metal gratings. Based on D.P.Chen and Haus theory,a finite element method is used to investigate the effects of metallic gratings upon the propagation of surface acoustic waves.The coupling-of-modes parameters contributed by mechanical loading are expressed by the matrix derived from the finite element method.Consequently D.P.Chen and Haus theory can also be applied to analyze the properties of surface acoustic waves propagating on metallic gratings with finite thickness and arbitrary shape.Finally,the characteristics of surface acoustic waves propagating under gold and aluminum or silver gratings on a few piezoelectric crystals are studied.Numerical results of the coupling-of-modes parameters of the surface acoustic waves are obtained.
文摘Typhoons with erratic movement are studied for their annual frequency of occurrence over the South China Sea and Northwest Pacific,based on 102 years of data (1884—1985).It discovers that the years with higher fre- quency tend to get together.There are well-defined periods of 12 and 30 years,revealed with the maximum entropy method (MEM),the latter of low-frequency oscillation being clearer.
文摘In this paper we analyze the qualitative behaviour of the equation ε+q(X) +εX=bp(t), where e is a small parameter.We divide the interval of parameter b into four sets of subintervals,A, B,C and D.For bA,B or D,we discuss the different structures of the attractors of the equation and their stabilities.When chaotic phenomena appear,we also estimate the entropy.For bC,the set of bifurcation intervals,we analyze the bifurcating type and get a series of consequences from the results of Newhouse and Palis.
基金National Natural Science Foundation of China(61004081,11126033)School Advanced Research Foundation of National University of Defense Technology (JC11-02-22)
文摘The low-frequency periodic error of star tracker is one of the most critical problems for high-accuracy satellite attitude determination.In this paper an approach is proposed to identify and compensate the low-frequency periodic error for star tracker in attitude measurement.The analytical expression between the estimated gyro drift and the low-frequency periodic error of star tracker is derived firstly.And then the low-frequency periodic error,which can be expressed by Fourier series,is identified by the frequency spectrum of the estimated gyro drift according to the solution of the first step.Furthermore,the compensated model of the low-frequency periodic error is established based on the identified parameters to improve the attitude determination accuracy.Finally,promising simulated experimental results demonstrate the validity and effectiveness of the proposed method.The periodic error for attitude determination is eliminated basically and the estimation precision is improved greatly.
基金National Natural Science Foundation of China,No.41165005,No.40865005
文摘The Greater Khingan Mountains （Daxinganling） are China＇s important ecological protective screen and also the region most sensitive to climate changes. To gain an in-depth understanding and reveal the climate change characteristic in this high-latitude, cold and data-insufficient region is of great importance to maintaining ecological safety and corre- sponding to global climate changes. In this article, the annual average temperature, precipi- tation and sunshine duration series were firstly constructed using tree-ring data and the me- teorological observation data. Then, using the climate tendency rate method, moving-t-testing method, Yamamoto method and wavelet analysis method, we have investigated the climate changes in the region during the past 307 years. Results indicate that, since 1707, the annual average temperature increased significantly, the precipitation increased slightly and the sun- shine duration decreased, with the tendency rates of 0.06~C/10a, 0.79 mm/10a and -5.15 h/10a, respectively （P〈~0.01）. Since the 21 st century, the period with the greatest increase of the annual average temperature （also with the greatest increase of precipitation） corresponds to the period with greatest decrease of sunshine duration. Three sudden changes of the an- nual average temperature and sunshine duration occurred in this period while two sudden changes of precipitation occurred. The strong sudden-change years of precipitation and sunshine duration are basically consistent with the sudden-change years of annual average temperature, suggesting that in the mid-1860s, the climatic sudden change or transition really existed in this region. In the time domain, the climatic series of this region exhibit obvious local variation characteristics. The annual average temperature and sunshine duration exhibit the periodic variations of 25 years while the precipitation exhibits a periodic variation of 20 years. Based on these periodic characteristics, one can infer that in the period from 2013 to 2030, the temperature will be at a high-temperature stage, the precipitation will be at an abundant-precipitation stage and the sunshine duration will be at an less-sunshine stage. In terms of spatial distribution, the leading distribution type of the annual average temperature in this region shows integrity, i.e：, it is easily higher or lower in the whole region; and the second distribution type is more （or less） in the southwest parts and less （or more） in the northeast parts. Precipitation and sunshine duration exhibit complex spatial distribution and include four spatial distribution types. The present study can provide scientific basis for the security in- vestigation of homeland, ecological and water resources as well as economic development programming in China＇s northern borders.
基金the supports from the Jiangsu Province Key Laboratory of Aerospace Power System of China(No.NJ20140019)the National Natural Science Foundation of China(No.51205190)
文摘In order to analyze the stress and strain fields in the fibers and the matrix in composite materials,a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced.Assuming matrix cracking as the failure mode of composite materials,an energy-based fatigue damage parameter and a multiaxial fatigue life prediction method are established.This method only needs the material properties of the fibers and the matrix to be known.After the relationship between the fatigue damage parameter and the fatigue life under any arbitrary test condition is established,the multiaxial fatigue life under any other load condition can be predicted.The proposed method has been verified using two different kinds of load forms.One is unidirectional laminates subjected to cyclic off-axis loading,and the other is filament wound composites subjected to cyclic tension-torsion loading.The fatigue lives predicted using the proposed model are in good agreements with the experimental results for both kinds of load forms.
基金Supported by the National Natural Science Foundation of China(41575066)National Science and Technology Support Program of China(2015BAC03B04)
文摘The 200-hPa wind perturbation(WP) in the subtropical westerly over East Asia(SWEA) has seldom been examined in previous studies, especially in connection with forecast of the summer rainfall in China. Based on the daily NCEP/NCAR reanalysis data and precipitation observations in China from 1 June to 31 August of 1960-2015, this study first systematically analyzes the spatiotemporal distribution features of the 200-hPa WP in the SWEA on different scales, especially during the Meiyu season in the Yangtze-Huaihe region and during the rainy period in North China, by using spectral decomposition and period analysis. It is found that in the 56-yr mean fields, the 200-hPa WP in the SWEA is collocated with the East Asian subtropical jet(EASJ), with the centers of the two systems coincidentally overlapped. The WP filed in the subtropical westerly mainly comprises planetary-and synoptic-scale waves. The quasi-stationary planetary-scale wave seems to determine the shape and intensity of the WP in the SWEA, while the synoptic-scale wave is closely related to the local central intensity of the WP. The daily evolution of the 56-yr mean fields shows that, following the northward(southward) movement of SWEA from 1 June to 31 August, the planetaryscale WP in the SWEA becomes gradually weakened(intensified) whereas the synoptic-scale WP is slightly intensified(weakened).The results also reveal that during the Meiyu season in the Yangtze-Huaihe region, the WP in the SWEA moves northward slowly around 37°-39°N, demonstrating a quasi-biweekly oscillation in its geographic location, which is largely attributed to the strong(weak) planetary-scale(synoptic-scale) component. On the contrast, in the summer rainy season over North China, the WP in the SWEA further strives northward beyond 40°N, showing both quasi-biweekly and weekly oscillations in its position; meanwhile, the planetary-scale wave in the SWEA becomes weakened whereas the synoptic-scale wave is enhanced. These salient variational features of the WP in the SWEA and its scaledependent components may be useful for the medium-range forecast of the rain belt migration in eastern China.
