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A cumulant-based parameter estimation algorithm for near-field sources

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Progress in Natural Science:Materials International 2007年第8期17卷 900-905页

作者： Liang Junli~(1,2.) Yang Shuyuan~(1,2. Zhang Junying~3 (1.Institute of Acoustics,chinese academy of {2.,beijing 100080,china 2.graduate School,chinese academy of {2.,beijing 100039,china 3.National Laboratory of Radar Signal Processing,Xidian university,Xi'an 710071,china) [a]Institute of Acoustics Chinese Academy of Sciences Beijing China [b]graduate School Chinese Academy of Sciences Beijing China [c]National Laboratary of Radar Signal Processing Xidian University Xi'an China

To efficiently use the array aperture and avoid the complicated parameter pairing computation,this paper proposes a new cumulant-based algorithm for localizing near-field narrowband ***,this algorithm proposes a symmetric uniform linear ar- ray (ULA),and constructs three cumulant matrices by using the fourth-order cumulants of some properly chosen sensor outputs;second- ly,unlike the conventional parallel factor (PARAFAC) analysis models in data or subspace domain,it forms a three-way array (TWA) in the fourth-order cumulant domain using the three matrices,and analyzes the uniqueness of its low-rank decomposition;thirdly,it jointly estimates the frequency,the direction-of-arrival (DOA),and the range of each near-field source from the matrices via the low-rank de- composition of the *** simulation results are presented to validate the performance of our proposed method.

关键词： array signal processing localization cumulant parallel factor (PARAFAC) analysis three-way array (TWA)

Improvement of a 3D radar backscattering model using matrix-doubling method

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Science china Earth sciences 2010年第7期53卷 1029-1035页

作者： NI WenJian1,2. GUO ZhiFeng1 & SUN GuoQing3 1 State Key Laboratory of Remote Sensing Science, jointly sponsored by the Institute of Remote Sensing Applications of chinese academy of {2. and beijing Normal university, beijing 100101, china 2.graduate university of chinese academy of {2.,{12., china 3 Department of Geography, university of Maryland, College Park, MD 2.042. USA 1. State Key Laboratory of Remote Sensing Science jointly sponsored by the Institute of Remote Sensing Applications of Chinese Academy of Sciences and Beijing Normal University Beijing 100101 China2. Graduate University of Chinese Academy of Sciences Beijing 100049 China3. Department of Geography University of Maryland College Park MD 27042 USA

Radiative transfer models have been widely used to simulate the radar backscattering from forested areas. A three-dimensional radar backscatter model of forest canopy developed in previous studies takes full account of spatial position of trees in a forest stand, and the interactions among crown, trunk and ground surface. The model predicted well for the co-polarized backscatter measurements, but underestimated the backscattering for cross-polarization, primarily because only the first-order scattering within tree crowns was considered in the model. The backscattering at cross-polarization depends strongly on multiple scatter- ing within tree crowns. To produce good estimations for cross-polarized component, the matrix-doubling method is employed here to compute multiple-scattering within the crown. The modified model is compared with the original model, and the field forest measurements and AIRSAR data are used for validation of the modified model. The cross-polarization backscattering is improved in different degrees for different crown structures and at different bands.

关键词： remote sensing forestry electromagnetic propagation radar backscattering model matrix-doubling

Constraints of authigenic carbonates on trace elements (Sr,Mg) of lacustrine ostracod shells in paleoenviron-ment reconstruction and its mechanism

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Science china Earth sciences 2008年第5期51卷 654-664页

作者： HU Guang1,2. JIN ZhangDong1 & ZHANG Fei3 1 State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, chinese academy of {2., Xi’an 710075, china 2.graduate university of the chinese academy of {2., beijing 1.0049, china 3 College of Resources and Environmental Science, Nanjing Agricultural university, Nanjing 2.0095, china State Key Laboratory of Loess and Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences Xi’an 710075 China graduate university of the {2. academy of sciences Beijing 100049 China College of Resources and Env

Molar ratios of Mg/Ca and Sr/Ca were measured in two species of ostracod shells preserved in the upper core (15–55 m) of the Hequing Basin in Yunnan Province, southwest china. By correlating the molar ratios between Mg/Ca and Sr/Ca and comparing them with Sr concentrations of the sediments, we suggested that: (1) the molar Mg/Ca and Sr/Ca ratio variations in respective ostracod primo reflected the changes in its ambient water composition and ecology; (2. the molar Sr/Ca ratios responded better to the salinity change linearly than Mg/Ca without aragonite precipitation in the system, and otherwise there was no linear relation between them; and (3) the molar Sr/Ca ratios were mainly controlled by salinity and authigenic carbonate precipitation, whereas the molar Mg/Ca ratios were related to both salinity and temperature. In fact, the rate of ostracod growth owing to temperature controls the fluctuation of Mg/Ca in shells. Here, more attentions should be paid to the constraint of authigenic mineral precipitation processes on the trace elements in ostracod shells and to the correlation between these trace elements in biogenic carbonates and compositions of the sediments in systems and in future in vitro experiments.

关键词： ostracod shell molar Sr/Ca ratio molar Mg/Ca ratio environmental response Heqing Basin

Validating global hydrological models by ground and space gravimetry

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chinese Science Bulletin 2009年第9期54卷 1534-1542页

作者： ZHOU JiangCun1,2.3, SUN HePing1,2.& XU JianQiao1,2.1 Institute of Geodesy and Geophysics, chinese academy of {2., Wuhan 430077, china 2.Key Laboratory of dynamic geodesy, chinese academy of {2., Wuhan 430077, china 3 graduate university of chinese academy of {2., beijing 1.0049, china Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China Key Laboratory of dynamic geodesy Chinese Academy of Sciences Wuhan 430077 China graduate university of {2. academy of sciences Beijing 100049 China

The long-term continuous gravity observations obtained by the superconducting gravimeters (SG) at seven globally-distributed stations are comprehensively analyzed. After removing the signals related to the Earth's tides and variations in the Earth's rotation, the gravity residuals are used to describe the seasonal fluctuations in gravity field. Meanwhile, the gravity changes due to the air pressure loading are theoretically modeled from the measurements of the local air pressure, and those due to land water and nontidal ocean loading are also calculated according to the corresponding numerical models. The numerical results show that the gravity changes due to both the air pressure and land water loading are as large as 100×10-9 m s-2.in magnitude, and about 10×10-9 m s-2.for those due to the nontidal ocean loading in the coastal area. On the other hand, the monthly-averaged gravity variations over the area surrounding the stations are derived from the spherical harmonic coefficients of the GRACE-recovered gravity fields, by using Gaussian smoothing technique in which the radius is set to be 600 km. Com-pared the land water induced gravity variations, the SG observations after removal of tides, polar mo-tion effects, air pressure and nontidal ocean loading effects and the GRACE-derived gravity variations with each other, it is inferred that both the ground- and space-based gravity observations can effec-tively detect the seasonal gravity variations with a magnitude of 100×10-9 m s-2.induced by the land water loading. This implies that high precision gravimetry is an effective technique to validate the re-liabilities of the hydrological models.

关键词：重力测量水文模型模型验证和空间地面重力变化季节性波动空气压力

Analysis of a kind of quantum cryptographic schemes based on secret sharing

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Science china(Physics,Mechanics & Astronomy) 2009年第9期52卷 1313-1316页

作者： ZHANG XingLan1 & JI DongYao2.1 College of Computer Science and Technology, beijing university of Technology, beijing 10012., china 2.State Key Laboratory of Information Security, graduate university of chinese academy of sciences, beijing 1.0049, china College of Computer Science and Technology Beijing University of Technology Beijing 100124 China State Key Laboratory of Information Security Graduate University of Chinese Academy of Sciences Beijing 100049 China

Recently, Yang et al. proposed a kind of quantum cryptographic schemes based on secret sharing. The main idea is drawn from the case, where any n participants who share a secret K can co-operate as K does. This process can be applied to encryption, authentication, signature and so on. Unfortunately, since there is no identity authentication of the share's holder, these schemes inherit the limitation of secret sharing in practice. If some participants do not follow the protocol, the protocol would be a failure at last. Moreover, these schemes encounter another serious attack. Any two participants can co-operate to defeat the schemes by sending different shares to the parties unknown to the distributor of the secret K, such that these parties can execute the protocol as well. The attack proves that it is not enough for quantum cryptographic schemes that only the secret key is secure.

关键词： quantum identity authentication quantum secure direct communication quantum signature secret sharing

Cytotoxicity of carbon nanotubes

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Science china Chemistry 2008年第11期51卷 1021-1029页

作者： ZHU Ying1,2.& LI WenXin1 1 Laboratory of Nano-biology and Medicine, Shanghai Institute of Applied Physics, chinese academy of {2., Shanghai 2.1800, china 2.graduate School of chinese academy of {2., beijing 1.0049, china 1. Laboratory of Nano-biology and Medicine Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai 201800 China 2. graduate School of chinese {2. of sciences Beijing 100049 China

With large-scale production and application at large scale, carbon nanotubes (CNTs) may cause ad-verse response to the environment and human health. Thus, study on bio-effects and safety of CNTs has attracted great attention from scientists and governments worldwide. This report briefly summa-rizes the main results from the in vitro toxicity study of CNTs. The emphasis is placed on the descrip-tion of a variety of factors affecting CNTs cytotoxicity, including species of CNTs, impurities contained, lengths of CNTs, aspect ratios, chemical modification, and assaying methods of cytotoxicity. However, experimental information obtained thus far on CNTs' cytotoxicity is lacking in comparability, and some-times there is controversy about it. In order to assess more accurately the potential risks of CNTs to human health, we suggest that care should be taken for issues such as chemical modification and quantitative characterization of CNTs in cytotoxicity assessment. More importantly, studies on physical and chemical mechanisms of CNTs' cytotoxicity should be strengthened; assaying methods and evaluating criteria characterized by nanotoxicology should be gradually established.

关键词： carbon nanotubes (CNTs) cell bio-security

Representation of microscale ocean wavenumber spectrum correct to the second order

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Science china Earth sciences 2005年第4期48卷 549-554页

作者： YUAN Yeli2.& HUA Feng1,2.3 1. Institute of Oceanology, chinese academy of {2., Qingdao 2.6071, china 2. Key Laboratory of Marine Science and Numerical Modeling, State Oceanic Administration, Qingdao 2.6061, china 3. graduate School of the chinese academy of {2., beijing 100039, china 1. Key Laboratory of Marine Science and Numerical Modeling State Oceanic Administration 266061 Qingdao China 2. Institute of Oceanology Chinese Academy of Sciences 266071 Qingdao China 3. graduate School of the chinese {2. of sciences 100039 Beijing China

In this paper, the analytical representations of four wave source functions in high-frequency spectrum range are given on the basis of ocean wave theory and dimensional analysis, and the perturbation method is used to solve the governing equations of ocean wave high-frequency spectrum on the basis of the temporally stationary and locally homogeneous scale relations of microscale wave. The microscale ocean wavenumber spectrum correct to the second order has an explicit structure, its first order part represents the equilibrium between dif- ferent source functions, and its second order part represents the contribution of microscale wave propagation.

关键词： temporally stationary and locally homogeneous, source function in high-frequency spectrum range, microscale ocean wavenumber spectrum.

Rate of strong consistency of quasi maximum likelihood estimate in generalized linear models

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Science china Mathematics 2004年第6期47卷 882-893页

作者： YUE Li & CHEN Xiru School of Mathematics and Statistics, Wuhan university, Wuhan 430072. china {2. School, chinese academy of sciences, beijing 100039, china 1. School of Mathematics and Statistics Wuhan University 430072 Wuhan China 2. graduate School Chinese Academy of Sciences 100039 Beijing China

Under the assumption that in the generalized linear model (GLM) the expectation of the response variable has a correct specification and some other smooth conditions, it is shown that with probability one the quasi-likelihood equation for the GLM has a solution when the sample size n is sufficiently large. The rate of this solution tending to the true value is determined. In an important special case, this rate is the same as specified in the LIL for iid partial sums and thus cannot be improved anymore.

关键词： quasi-likelihood function generalized linear models strong consistency

Spatial heterogeneity of the driving forces of cropland change in china

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Science china Earth sciences 2005年第12期48卷 2231-2240页

作者： LIU Xuhua1,2. WANG Jinfeng1, LIU Mingliang4,1 & MENG Bin1,2.3 1. Institute of Geographic sciences and Natural Resources Research, chinese {2. of sciences, beijing 100101, china 2. graduate School of the chinese {2. of sciences, beijing 100039, china 3. College of Arts and sciences of beijing Union university, beijing 100083, china 4. School of Forestry and Wildlife sciences, Auburn university, Auburn, Alabama, AL36849, USA 1. Institute of Geographic sciences and Natural Resources Research Chinese Academy of Sciences 100101 Beijing China 2. graduate School of the chinese {2. of sciences 100039 Beijing China 3. School of Forestry and Wildlife sciences Auburn University Auburn AL36849 Alabama USA 4. College of Arts and sciences of beijing Union {2. 100083 Beijing China

By using digital satellite remote sensing data acquired in 1987―1989 and 1999―2.00 and GIS combined with the natural and socio-economic data, this paper drew an integrated zonation of the cropland change and its driving forces in china. The results indicated that the cropland change in the study period was constrained by geographical factors and driven by cli-mate change as well as socio-economic system. Moreover, the regional differences of the drivers for cropland change were significant. In the midwest of china, natural condition changes and geographical background were the main constraints and drivers, while in Eastern china, social and economic changes and economic policies were the main driving forces. The cropland loss was nationwide. The dominant factors to cause this decrease included buildup of developing area to attract foreign capital and technologies, changes of industry structure due to urban in-fluence, the change of employment notions thanks to living standard improvement, rapid ur-banization due to the expansion of cities and towns, the diminished farming net income partly because of the global warming effects, and the rapid economic growth stimulated by the con-venient transportation system. These factors interact and interdepend with each other to cause the cropland loss in china recently. The reasons for the increase of cropland were primarily the cultivation and deforestation by the farmers who want to increase income. This study on the mechnism of LUCC relied on the cropland change integrated classification considering the natural or human factors both inside and outside the region, which provides a new approach to study the integrated regionalization and LUCC mechanism.

关键词： land use change, driving force, integrated classification, spatial statistics, cropland, china.