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VARIATIONS ON A THEME BY EULER

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Journal of Computational Mathematics 1998年第2期16卷 97-106页

作者： Kang Feng Dao-liu Wang (state key {2. of Scientific and Engineering Computing, ICMSEC, Chinese academy of {4., beijing 100080, china) 中科院计算数学与科学工程计算所科学与工程计算国家重点实验室北京

The oldest and simplest difference scheme is the explicit Euler method. Usually, it is not symplectic for general Hamiltonian systems. It is interesting to ask: Under what conditions of Hamiltonians, the explicit Euler method becomes symplectic? In this paper, we give the class of Hamiltonians for which systems the explicit Euler method is symplectic. In fact, in these cases, the explicit Euler method is really the phase how of the systems, therefore symplectic. Most of important Hamiltonian systems can be decomposed as the summation of these simple systems. Then composition of the Euler method acting on these systems yields a symplectic method, also explicit. These systems are called symplectically separable. Classical separable Hamiltonian systems are symplectically separable. Especially, we prove that any polynomial Hamiltonian is symplectically separable.

关键词： Hamiltonian systems symplectic difference schemes explicit Euler method nilpotent symplectically separable

The application of hyperspectral remote sensing to coast environment investigation

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Acta Oceanologica Sinica 2009年第2期28卷 1-13页

作者： ZHANG Liang ZHANG Bin CHEN Zhengchao ZHENG Lanfen TONG Qingxi state key {2. of remote {4. Science Institute of Remote Sensing Applications Chinese Academy of Science Beijing 100101 China Naval institute of Hydrographic Surveying and Charting Tianjin 300061 China Center for Earth Observation and Digital Earth Chinese Academy of Science Beijing 100190 China

Requirements for monitoring the coastal zone environment are first summarized. Then the appli- cation of hyperspectral remote sensing to coast environment investigation is introduced, such as the classification of coast beaches and bottom matter, target recognition, mine detection, oil spill identification and ocean color remote sensing. Finally, what is needed to follow on in application of hyperspectral remote sensing to coast environment is recommended.

关键词： hyperspectral remote sensing coastal zone ocean color remote sensing

Response synchronization: New progress in brain-visual information processing

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Chinese Science Bulletin 1999年第16期44卷 1447-1458页

作者： ZHAO Songnian, XIONG Xiaoyun, YAO Guozheng and GUO Aike1. state key {2. of Atmospheric Boundary Layer Physics and Atmospheric Chemistry , institute of Atmospheric Physics , Chinese {4. of sciences , beijing 10002., china 2. Commission of the National Natural Science Foundation of china , beijing 100083, china 3. The Center of Information Science , Peking University, beijing 100871, china 4. Open {2. of Visual Information Processing , institute of Biophysics , Chinese {4. of sciences , beijing 100101, china state key {2. of Atmospheric Boundary Layer Physics and Atmospheric Chemistry Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China Commission of the National Natural Science Foundation of china Beijing China The Center of Information Science Peking University Beijing China Open laboratory of Visual Information Processing Institute of Biophysics Chinese Academy of Sciences Beijing China

Studies on brain-vision have entered a new stage, after the stimulus-induced y synchronized oscillation of neuron group activities have been discovered in cat primary visual cortex. Naturally, how to understand the visual system became a very important methodological problem. From aspects such as information processing, nonlinear dynamics and neuronal network, some primary problems in vision studies have been deeply discussed, which are

关键词： neuron group (neural population) synchro-oscillation computational theory of vision response synchroniza-tion.

A method for blind separation of components information from mixed pixel

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Progress in Natural Science:Materials International 2006年第7期16卷 760-765页

作者： FAN Wenjie and XU Xiru ( institute of remote {2. and Geographical Information System, Peking University, beijing 100871,{4. Center of remote {2. and GIS of beijing Normal University, beijing 100875,{4.) Peking Univ Inst Remote Sensing & Geog Informat Syst Beijing 100871 Peoples R China beijing Normal Univ Ctr Remote Sensing & GIS Beijing 100875 Peoples R China

In the field of remote sensing, it is important to separate the component information from mixed pixel. If the physical process of remote sensing can be expressed by a set of linear equations, the remote sensing information matrix is equal to the weight matrix multiplied by the component information matrix. Generally speaking, the precondition of retrieval of component information matrix is that the weight matrix is known. However, the blind signal separation (BSS) method can separate the matrix unconditionally, whose basic principle is that the additive information needing separation can be achieved from the statistical characteristics contained in a mass of samples in the remotely sensed information matrix. Therefore, the values of the component information matrix and the weight matrix can be estimated. The wave shape of components can be retrieved by BSS, but the amplitude cannot. In this paper, the plant-soil mixed pixels were chosen as the studying targets in this paper to quantitatively separate the component information and solve the uncertainty of BSS. Simulation and field test verify the reliability of the method. Results show that the BSS can be one of the effective methods of mixed pixel separation, and the foreground of application is very promising.

关键词： mixed pixel component information blind signal separation.

Evolution of desertification in a two-dimensional energy balance model coupled with thermodynamics and dynamics

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Science china Earth sciences 2010年第11期53卷 1726-1733页

作者： CHAO JiPing1,2.& LI YaoKun3,4.1National Marine Environmental Forecasting Center, beijing 100081, china 2.irst {2. of Oceanography, state Oceanic Administration, Qingdao 2.6061, china 3state key laboratory of Numerical Modeling for Atmospheric sciences and Geophysical Fluid Dynamics, {2. of Atmospheric Physics, Chinese academy of sciences, beijing 10002., china 4.raduate University of Chinese academy of sciences, beijing 10004., china National Marine Environmental Forecasting Center Beijing China First institute of Oceanography State Oceanic Administration Qingdao China state key {2. of Numerical Modeling for Atmospheric sciences and Geophysical Fluid Dynamics Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China Graduate University of Chinese academy of sciences Beijing China

The relationship between desert evolution and change in albedo has been investigated quasi-analytically using a zonal mean two-dimensional energy balance model which considers the radiation transmission process due to thermodynamics and bound- ary layer movement caused by kinetics. A climate state including temperature, zonal wind, meridional wind and vertical wind can be simulated according to the current zonal distribution of albedo. Given desert distribution, characterized by the value and distribution of albedo, the response of climate on albedo has been studied to analyze the evolution of desert climate. One significant result is that the simple model can reproduce mean meridional circulation. Another result indicates that climate corresponds to two equilibria. This happens when the junction temperature between vegetation and desert is higher than a certain critical value. As for the first equilibrium, the desert belt is predicted to move southward in the northern hemisphere with the increasing values of albedo, which corresponds to the current trend of climate change. For the second equilibrium, vegetation will expand northward with increasing values of albedo, which would indicate a narrowing of the desert belt. In order to determine if the two equilibria exist, new physical models are needed.

关键词： two-dimensional energy balance model desertification two equilibria

Input function and simulated distributions of tritium in the North Pacific

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Science china Earth sciences 2010年第3期53卷 441-453页

作者： BA Qi1,2.& XU YongFu1 1 state key {2. of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, {4. of Atmospheric Physics, Chinese academy of sciences, beijing 10002., china 2.Graduate University of Chinese academy of sciences, beijing 10004., china state key {2. of Atmospheric Boundary Layer Physics and Atmospheric Chemistry Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China Graduate University of Chinese academy of sciences Beijing China

An ocean general circulation model (OGCM) of the North Pacific with a southern open boundary condition is used to simulate the distribution and transport of tritium in the North Pacific. First, the observed tritium in precipitation dataset of GNIP/ISOHIS is chosen, and used to develop an input function of tritium for the model domain from 1951 to 1997 in terms of the triangulation for interpolation. Then, the input function is used as an upper flux for the tritium model. The OGCM with tritium is integrated for 4. years with the initial condition of zero tritium concentrations. Compared with the observations from GEOSECS and WOCE, the model generates a meridional gradient of surface tritium concentrations and the high tritium concentrations in the subsurface layer, which is consistent with that indicated in the observations. The simulated time series of total tritium fluxes from the atmosphere to the ocean shows a spike in 1963. The total inventory of tritium in the ocean changes slowly with time after 1975. Tritium enters the higher-latitude region, and then is mainly transported by the subsurface process towards the equatorial region, which is well simulated in the model. However, the difference mainly occurs at 30°N–4.°N, which can be seen also in the simulation of CFCs. This difference may partly originate from the insufficient description of physical processes in the OGCM. Nevertheless, some uncertainties exist in the development of the tritium input function, which can also influence the simulated results.

关键词： North Pacific basin-wide ocean general circulation model tritium input function tritium distributions

Three-dimensional thermal structure of the Chinese continental crust and upper mantle

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Science china Earth sciences 2007年第10期50卷 1441-1451页

作者： AN MeiJian1,2. & SHI YaoLin1 1 laboratory of Computational Geodynamics, Graduate University of Chinese academy of {2., {4. 10004., china 2.key laboratory of Crust Deformation and Processes and institute of Geomechanics, Chinese academy of Geological {2., {4. 100081, china laboratory of Computational Geodynamics Graduate University of Chinese Academy of Sciences Beijing China key laboratory of Crust Deformation and Processes and {2. of Geomechanics Chinese Academy of Geological Sciences Beijing China

We invert S-wave velocities for the 3D upper-mantle temperatures, in which the position with a temperature crossing the 1300℃ adiabat is corresponding to the top of the seismic low velocity zone. The temperatures down to the depth of 80 km are then calculated by solving steady-state thermal conduction equation with the constraints of the inverted upper-mantle temperatures and the surface temperatures, and then surface heat flows are calculated from the crustal temperatures. The misfit between the calculated and observed surface heat flow is smaller than 2.% for most regions. The result shows that, at a depth of 2. km, the crustal temperature of eastern china (500―600℃) is higher than that of western china ( china are higher than the adiabatic temperature of 1300℃, while that beneath west china is lower. The Tarim craton and the Sichuan basin show generally low temperature. At a depth of 150 km, temperatures beneath south china, eastern Yangtze craton, North china craton and around the Qiangtang terrane are higher than the adiabatic temperature of 1300℃, but is the lowest beneath the Sichuan basin and the regions near the Indian-Eurasian collision zone. At a depth of 2.0 km, very low temperature occurs beneath the Qinghai-Tibet Plateau and the south to the Tarim craton.

关键词： crust, upper mantle, temperature, seismic velocity, china

Role of gallium wetting layer in high-quality ZnO growth on sapphire (0001) substrates

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Science china(Physics,Mechanics & Astronomy) 2004年第5期47卷 612-620页

作者： ZENG Zhaoquan1,3, WANG Yong2. DU Xiaolong1, MEI Zengxia1, KONG Xianghe3, JIA Jinfeng1, XUE Qikun1 & ZHANG Ze2. 4.1. state key {2. for Surface Physics, institute of Physics, Chinese academy of sciences, beijing 100080, china 2. {2. of Electron Microscopy, institute of Physics, Chinese academy of sciences, beijing 100080, china 3. College of Physics and Engineering, Qufu Normal University, Qufu 2.3165, china 4. beijing University of Technology, beijing 10002., china state key {2. for Surface Physics Institute of Physics Chinese Academy of Sciences Beijing China College of Physics and Engineering Qufu Normal University Qufu China laboratory of Electron Microscopy Institute of Physics Chinese Academy of Sciences Beijing China beijing University of Technology Beijing China

A Ga wetting layer was used to modify the surface structure of sapphire (0001) substrate to prepare high-quality ZnO film by radio frequency plasma-assisted molecule beam epitaxy. We found that this Ga layer plays a crucial role in eliminating 30 rotation domains, controlling polarity and decreasing defect density in ZnO epilayers, as demonstrated by in situ reflection high energy electron diffraction, ex situ high resolution X-ray diffraction and high resolution cross-sectional transmission electron microscopy. Zn-polar film of ZnO was determined by convergent beam electron diffraction. A Ga bilayer model is proposed to understand the effects of the Ga wetting layer on high-quality ZnO growth.

关键词： Ga wetting layer, sapphire, polarity, defect density, zinc oxide, rf-MBE, RHEED, HRXRD, TEM, CBED.

Interdecadal trend turning of global terrestrial temperature and precipitation during 1951-2.02

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Progress in Natural Science:Materials International 2008年第11期18卷 1383-1393页

作者： Xiaohui Shi Xiangde Xu state key {2. of Severe Weather,Chinese academy of Meteorological {4.,beijing 100081,china state key {2. of Severe Weather Chinese Academy of Meteorological Sciences Beijing 100081 China

A grid-by-grid counting of interdecadal trend turning(ITT)of annual mean surface air temperature(SAT)and total precipitation at 67,359 terrestrial grids in the period 1951-2.02.is *** analysis of the last ITTs of SAT and total precipitation in the period,in the context of both occurrence time and linear trends after the breakpoint,indicates that a warming trend has become highly significant across most reagent of the world in the late 2.th *** terrestrial grids have recorded an ITT of total precipitation in either the 1970s or 1980s,and 4..7% of the terrestrial grids in the study have seen a decreasing trend in total annual precipitation after the break- point,with the remaining 54.3% having experienced an increasing ***,global terrestrial regions have experienced either an increasingly warm and dry climate or an increasingly warm and wet *** analysis of ITT of regional mean SAT and total pre- cipitation in 2. regions shows that the Northern American continent has become increasingly warm and dry after the last interdecadal ***,the African continent has become increasingly warm and wet,with both Europe and most of Asia having the same *** South America and the West of Australia have experienced an opposite trend in climate,becoming increasingly cold and wet.

关键词： Global terrene Surface air temperature Precipitation Interdecadal trend turning