森林流域单元水文模型的构建与应用

目前全球缺水、水污染、洪涝灾害以及水土流失仍然非常严重，尤其在我国北方地区。流域水文模型可用来进行不同需水管理的情景分析，为解决我国水问题提供科学依据。分布式水文模型是流域水文模型的发展方向，具有显著特点：1）应用前景广泛，不仅可以模拟流域水文过程，还可以协助模拟泥沙或污染物的运移过程，为水利工程设计、水土保持、环境保护等领域提供技术支持；2）能够预测流域土地利用或气候变化下的流域水文响应过程变化，为管理部门提供决策支持；3）模型所需要的参数全部具有物理意义，可通过实际测量确定，适合模拟实测系列较短或是无观测流域的水文过程；4）对于目前国际水文界的前沿问题—水文尺度转换提供了一种有效的解决途径。 然而分布式水文模型还不完善，如1)真实性问题。对一些水文过程和边界条件还不确定。2)尺度转换问题。目前很少考虑尺度对参数有效性的影响。3)检验问题。还无法判断对有些难以测量的水文状态变量的模拟正确与否。4)计算时间和数据存储的问题。有些分布式水文模型虽然具有很强的水文物理基础和完善的模型结构，但是计算时间过长和(或)数据存储过大，难以应用。上述问题的核心就是对分布式水文模型的核心—单元水文模型的研究不够，需要为进一步完善单元水文模型进行研究。 本文采用饱和入渗理论、Saint-Venant方程、Richards方程、Penman-Monteith方程等等构建了以有限差分法求解的适用于森林流域的单元水文模型，并通过实验室模拟试验和坡地径流场资料进行了验证，主要结论为： 通过不同坡度和不同雨强下的室内坡面产汇流实验模拟，表明：该模型模拟的坡面流和壤中流过程与实测过程基本一致，峰现时间、径流历时、峰值流量、出流总量模拟值与实测值的相对误差均较小，基本小于10%。模型的模拟精度较高，实用性较强，为深入研究壤中流机制和改进流域降雨-径流模型提供了理论依据。 通过坡地径流观测场实测资料的验证，表明：该模型模拟的坡面流过程精度较高，累计流量的精度更高于小时过程的精度，离差系数、效率系数、确定系数均较理想，具有应用价值，有助于改善分布式水文模型在森林流域的模拟效果。

黄土区考虑滞后作用的坡地水量转化模型

建立了考虑滞后作用的坡地水量转化数学模型，并对模型不同情况下的定解条件进行了分析。利用陕西长武王东沟小流域坡地天然降雨－入渗－产流的实测资料对模型进行了系统检验，结果表明该模型具有较高精度，考虑滞后作用时的模拟值更加接近实测值。在降雨入渗过程中，滞后作用对土壤含水率、入渗速率、径流过程、产流量都有相当大的影响。

A theoretical framework of tracer methods for marine sediment dynamics

A new theoretical framework of tracer methods is proposed in the present contribution, on the basis of mass conservation. This model is applicable for both artificial and natural tracers. It can be used to calculate the spatial distribution patterns of sediment transport rate, thus providing independent information and verification for the results derived from empirical formulae. For the procedures of the calculation, first, the tracer concentration and topographic maps of two times are obtained. Then, the spatial and temporal changes in the concentration and seabed elevation are calculated, and the boundary conditions required are determined by field observations (such as flow and bedform migration measurements). Finally, based upon eqs. (1) and (13), the transport rate is calculated and expressed as a function of the position over the study area. Further, appropriate modifications to the model may allow the tracer to have different densities and grain size distributions from the bulk sediment.

Simulation of barotropic and baroclinic tides in the South China Sea

The four leading tidal constituents M-2, S-2, K-1 and O-1 in the South China Sea are simulated by using POM. The model is forced with tide-generating potential and four leading tidal constituents at the open boundary. In order to simulate more exactly, TOPEX/Poseidon altimeter data are assimilated into the model and the open boundary is optimized. The computed co-tidal charts for M-2 and K-1 constituents are generally consistent with previous results in this region. The numerical simulation shows that energetic internal tides are generated over the bottom topography such as the Dongsha Islands, the Xisha Islands, the Zhongsha Islands, the Nansba Islands and the Luzon Strait.

Factors influencing the climatological mixed layer depth in the South China Sea: numerical simulations

The mixed layer depth (MLD) in the upper ocean is an important physical parameter for describing the upper ocean mixed layer. We analyzed several major factors influencing the climatological mixed layer depth (CMLD), and established a numerical simulation in the South China Sea (SCS) using the Regional Ocean Model System (ROMS) with a high-resolution (1/12A degrees x1/12A degrees) grid nesting method and 50 vertical layers. Several ideal numerical experiments were tested by modifying the existing sea surface boundary conditions. Especially, we analyzed the sensitivity of the results simulated for the CMLD with factors of sea surface wind stress (SSWS), sea surface net heat flux (SSNHF), and the difference between evaporation and precipitation (DEP). The result shows that of the three factors that change the depth of the CMLD, SSWS is in the first place, when ignoring the impact of SSWS, CMLD will change by 26% on average, and its effect is always to deepen the CMLD; the next comes SSNHF (13%) for deepening the CMLD in October to January and shallowing the CMLD in February to September; and the DEP comes in the third (only 2%). Moreover, we analyzed the temporal and spatial characteristics of CMLD and compared the simulation result with the ARGO observational data. The results indicate that ROMS is applicable for studying CMLD in the SCS area.

潮波模型的优化开边界方法研究

数值模式是潮波研究的一种有利手段，但在研究中会面临各种具体问题，包括开边界条件的确定、底摩擦系数和耗散系数的选取等。数据同化是解决这些问题的一种途径，即利用有限数量的潮汐观测资料对潮波进行最优估计，其根本目的是迫使模型预报值逼近观测值，使模式不要偏离实际情况太远。本文采用了一种优化开边界方法，沿着数值模型的开边界优化潮汐水位信息，目的是设法使数值解在动力约束的意义下接近观测值，获得研究区域的潮汐结果。边界值由指定优化问题的解来定，以提高模拟区域的潮汐精度，最优问题的解是基于通过开边界的能量通量的变化，处理开边界处的观测值与计算值之差的最小化。这里提供了辐射型边界条件，由Reid 和Bodine（本文简称为RB）推导，我们将采用的优化后的RB方法（称为ORB）是优化开边界的特殊情况。 本文对理想矩形海域（ E- E， N- N， 分辨率 ）进行了潮波模拟，有东部开边界，模式采用ECOM3D模式。对数据结果的误差分析采用，振幅平均偏差，平均绝对偏差，平均相对误差和均方根偏差四个值来衡量模拟结果的好坏程度。 需要优化入开边界的解析潮汐值本文采用的解析解由方国洪《海湾的潮汐与潮流》（1966年）方法提供，为验证本文所做的解析解和方文的一致，本文做了其第一个例子的关键值a,b,z,结果与其结果吻合的相当好。但略有差别，分析的可能原因是两法在具体迭代方案和计算机保留小数上有区别造成微小误差。另外，我们取m=20，得到更精确的数值，我们发现对前十项的各项参数值，取m=10,m=20各项参数略有改进。当然我们可以获得m更大的各项参数值。 同时为了检验解析解的正确性讨论m和l变化对边界值的影响，结果指出，增大m，m=20时，u的模最大在本身u1或u2的模的6%；m=100时，u的模最大在本身u1或u2的模的4%；m再增大，m=1000时，u的模最大在本身u1或u2的模的4%，改变不大。当l<1时， =0处u的模最大为2。当l=1时， =0处u的模最大为0.1，当l>1时，l越大，u的模越小，当l=10时，u的模最大为0.001，可以认为为0。 为检验该优化方法的应用情况，我们对理想矩形区域进行模拟，首先将本文所采用的优化开边界方法应用于30m的情况，在开边界优化入开边界得出模式解，所得模拟结果与解析解吻合得相当好，该模式解和解析解在整个区域上，振幅平均绝对偏差为9.9cm,相位平均绝对偏差只有4.0 ，均方根偏差只有13.3cm，说明该优化方法在潮波模型中有效。 为验证该优化方法在各种条件下的模拟结果情况，在下面我们做了三类敏感性试验： 第一类试验：为证明在开边界上使用优化方法相比于没有采用优化方法的模拟解更接近于解析解，我们来比较ORB条件与RB条件的优劣，我们模拟用了两个不同的摩擦系数，k分别为：0,0.00006。 结果显示，针对不同摩擦系数，显示在开边界上使用ORB条件的解比使用RB条件的解无论是振幅还是相位都有显著改善，两个试验均方根偏差优化程度分别为84.3%，83.7%。说明在开边界上使用优化方法相比于没有采用优化方法的模拟解更接近于解析解，大大提高了模拟水平。上述的两个试验得出， k=0.00006优化结果比k=0的好。 第二类试验，使用ORB条件确定优化开边界情况下，在东西边界加入出入流的情况，流考虑线性和非线性情况，结果显示，加入流的情况，潮汐模拟的效果降低不少，流为1Sv的情况要比5Sv的情况均方根偏差相差20cm,而不加流的情况只有0.2cm。线性流和非线性流情况两者模式解相差不大，振幅，相位各项指数都相近, 说明流的线性与否对结果影响不大。 第三类试验，不仅在开边界使用ORB条件，在模式内部也使用ORB条件，比较了内部优化和不优化情况与解析解的偏差。结果显示，选用不同的k,振幅都能得到很好的模拟，而相位相对较差。另外，在内部优化的情况下，考虑不同的k的模式解， 我们选用了与解析解相近的6个模式解的k,结果显示，不同的k,振幅都能得到很好的模拟，而相位较差。 总之，在开边界使用ORB条件比使用RB条件好，振幅相位都有大幅度改进，在加入出入流情况下，流的大小对模拟结果有影响，但线形流和非线性流差别不大。内部优化的结果显示，模式采用不同的k都能很好模拟解析解的振幅。

Theoretical investigation on the adsorption of Ag+ and hydrated Ag+ cations on clean Si(111) surface

In this paper, the adsorption of Ag+ and hydrated Ag+ cations on clean Si(111) surface were investigated by using cluster (Gaussian 03) and periodic (DMol(3)) ab initio calculations. Si(111) surface was described with cluster models (Si14H17 and Si22H21) and a four-silicon layer slab with periodic boundary conditions. The effect of basis set superposition error (BSSE) was taken into account by applying the counterpoise correction. The calculated results indicated that the binding energies between hydrated Ag+ cations and clean Si(111) surface are large, suggesting a strong interaction between hydrated Ag+ cations and the semiconductor surface. With the increase of number, water molecules form hydrogen bond network with one another and only one water molecule binds directly to the Ag+ cation. The Ag+ cation in aqueous solution will safely attach to the clean Si(111) surface.

元谋盆地河湖相沉积记录的上新世印度季风转型事件

The Indian monsoon, an integral part of the global climate system, has been extensively investigated during the past decades. Most of the proxy records are derived from marine sediments and focused on time periods of the late Miocene and Pleistocene. The Pliocene represents a period when Earth’s boundary conditions underwent dramatic changes. However, variations of the Indian monsoon during the Pliocene and its forcing mechanisms have remained unclear. The Yuanmou Basin, located in the region of the Indian monsoon, provides an ideal target for understanding the Pliocene history of Indian monsoon variations. Detailed investigations on the lithostratigraphy, magnetostratigraphy and limnology of a 650-m-thick fluvio-lacustrine sedimentary sequence from the basin are carried out in the present study. The clay and clay-plus-fine-silt fractions of the sediments are referred to the midlake-facies components, and changes in the percentages of both fractions generally reflect changes in the water level of the lakes developed in the basin closely related to variations in the intensity of the Indian monsoon. Whereas the greenish-gray lacustrine mud beds represent the environment of deep-water lakes, and the frequency of individual lacustrine mud beds is considered to indicate the frequency of the deep-water lakes developed in the basin associated with the variability of the Indian monsoon. The proxy data suggest that the Indian monsoon experienced abrupt shifts at 3.53, 3.14, 2.78 and 2.42 Ma, respectivey. 1) Since 3.53 Ma, the midlake-facies components displayed a general trend of increase in the concentrations, accompanied by an increase in the sedimentation rate from an average ~10 to 25 cm ka–1. The data suggest that high stands of the lakes in the basin rose progressively, implying a gradual intensification of the Indian monsoon since that time. This shift occurred coeval with the accelerated uplift of the northern Tibetan Plateau, denoting a close link between the Indian monsoon strengthening and the Tibetan Plateau uplifting. 2) 2.78 Ma ago, the concentrations of the midlake-facies components decreased abruptly and the dominant fraction of the sediments turned to fluvial sands. The data indicate that lakes in the basin disappeared, reflecting a dramatic decline in the intensity of the Indian monsoon at that time. This shift coincided with the formation of extensive Northern Hemisphere ice sheets, implying a quick response of the low-latitude monsoon regime to the high-latitude glaciation. 3) At 3.14 Ma, the initial appearance of blackish-grey mud beds with long durations and occasional occurrences of lacustrine mud beds indicate that the basin was overall dominated by shallow lakes, implying a shift to decreased variability of the Indian monsoon at that time. At 2.42 Ma, an increase in the frequency and a decrease in the duration of the lacustrine mud beds suggest that deep-water lakes were frequently developed in the basin, denoting a shift to increased variability of the Indian monsoon at that time. The former shift coincides with the onset of large-scale glaciation in the circum Atlantic region and the latter corresponds to the inception of predominance of the 41 ka periodicity in Northern Hemisphere ice-sheet cover fluctuations, presumably suggesting a physical link between the Indian monsoon system and the high-latitude ice sheets in the Northern Hemisphere.

地震波模拟：非规则网格离散的数值解法、吸收边界及其实际应用

This dissertation presents a series of irregular-grid based numerical technique for modeling seismic wave propagation in heterogeneous media. The study involves the generation of the irregular numerical mesh corresponding to the irregular grid scheme, the discretized version of motion equations under the unstructured mesh, and irregular-grid absorbing boundary conditions. The resulting numerical technique has been used in generating the synthetic data sets on the realistic complex geologic models that can examine the migration schemes. The motion equation discretization and modeling are based on Grid Method. The key idea is to use the integral equilibrium principle to replace the operator at each grid in Finite Difference scheme and variational formulation in Finite Element Method. The irregular grids of complex geologic model is generated by the Paving Method, which allow varying grid spacing according to meshing constraints. The grids have great quality at domain boundaries and contain equal quantities of nodes at interfaces, which avoids the interpolation of parameters and variables. The irregular grid absorbing boundary conditions is developed by extending the Perfectly Matched Layer method to the rotated local coordinates. The splitted PML equations of the first-order system is derived by using integral equilibrium principle. The proposed scheme can build PML boundary of arbitrary geometry in the computational domain, avoiding the special treatment at corners in a standard PML method and saving considerable memory and computation cost. The numerical implementation demonstrates the desired qualities of irregular grid based modeling technique. In particular, (1) smaller memory requirements and computational time are needed by changing the grid spacing according to local velocity; (2) Arbitrary surfaces and interface topographies are described accurately, thus removing the artificial reflection resulting from the stair approximation of the curved or dipping interfaces; (3) computational domain is significantly reduced by flexibly building the curved artificial boundaries using the irregular-grid absorbing boundary conditions. The proposed irregular grid approach is apply to reverse time migration as the extrapolation algorithm. It can discretize the smoothed velocity model by irregular grid of variable scale, which contributes to reduce the computation cost. The topography. It can also handle data set of arbitrary topography and no field correction is needed.

北京石花洞滴水沉积的季节变化及影响因素

Because of the high resolution, stalagmite laminae can play an important role in the paleoclimate reconstructions. However, few investigations for the formation mechanisms of stalagmite lamilae have been done. Based on two-year observation on calcite growth rate at the drip sites, three-year monitoring of hydrodynamics, physics and chemistry of drip waters at different drip sites and the surrounding environments inside and outside the Beijing Shihua Cave, the seasonal variations of calcite growth rate are revealed and the results can be concluded as follows: 1. The drip waters inside the Cave are mostly sourced from the summer rain, and its minimal response-time to the atmospheric precipitation is less than one day. There are three types of response relationships between the precipitation and the drip rate variations: rapid response type, time-lag response type and stable response type. For rapid response type, the drip discharge is recharged through the flow routes along intensive fractures and interconnectivities; for time-lag response type, the drip discharge is recharged by double-porosity system composed of a high conductivity, low storage capability conduit network and a low-conductivity high-storage capability rock matrix under variable boundary conditions; for stable response type, the drip discharge is mainly recharged by seepage flow and base flow. 2. The observation shows that, inside the Cave, the growth rate of calcite is generally lower in rainy seasons and higher in dry seasons. During the rainy seasons, the drip water is characterized by a lower pH value, higher [Ca2+], [Mg2+], [SO42-] and electrical conductivity (EC) values. According to the calculations of saturation index of calcite (SIc), pCO2 of the drip water, as well as the synthetical analysis of other possible factors, the calcite growth rate is found to be principally influenced by the drip water saturation index of calcite (SIc). And the drip rate and pCO2 in the drip water and in the cave air play the secondly important roles in this process. The recharge mode of heavy rainfall events in the rainy seasons should probably be the main driving force that controls the physicochemical properties and calcite sediment of the drip waters. The abrupt decrease of sedimentary rate and the sharp peak of DOC in drip water in the rainy season probably forms the thin opaque (luminescent under ultraviolet radiation) layers observed in the stalagmites, whereas the relatively higher sedimentary rate in the dry seasons may be responsible for the thicker bright layers. The investigation elucidated here preliminarily reveals the formation mechanism of the stalagmite laminae in Beijing Shihua Cave.

喜马拉雅西构造结区岩石圈演化三维有限元动力学数值模拟

The past three decades have seen numerous attempts to numerically model stress and strain patterns in the lithosphere of the Earth on both global and regional scales. This efforts have been indispensable in identifying the features we need to include in our endeavour to develop better models of our planet’s lithosphere and they have also raised our awareness for the many unresolved issue in the deep geodynamical issues that need to be addressed in the future. Nonetheless, in most models, the lithosphere is treated as a single layer with depth-averaged properties, and as the same distribution in the stress and strain fields, and as deforming under plane strain. All these above make a great hander for its reality and degree of recognition. As the beginning in this paper, some principal numerical models and results on the evolution of Tibetan plateau are reviewed and analyzed. Then, the geological and geophysical expedition on the Western Himalayan Syntaxis is briefly reviewed. Furthermore, we analysis the feature in deep geophysical field studies in this area and adjacent regions. Because, for most continents, stress models driven by plate boundary forces have successfully reproduced the main characteristics of the stress and strain field, we present a set of three-dimensional models of lithosphere system for a simplified geometry of the Western Himalayan Syntaxis area and its adjacent regions, where we try to match the first-order characteristics of the stress and strain fields of lithosphere since 10 Ma, and deformation and geodynamical evolution process in former 2Ma. Of course, the kinematic boundary conditions of the stress models driven by plate boundary forces were applied. The rheology plays a significant role in the lithospheric tectonics, which lead to different rheological parameters were used in different works although the have the same constitutive equations in models. So, in this paper we do not aim to produce all characteristics of the Western Himalayan Syntaxis areas’ stress and strain fields by the choices of various parameters, but rather the dynamic response between various rheological parameters and stress and strain fields. We have chosen to concentrate on the importance of rheology and lateral strength variations for lithospheric stress and strain patterns and use our findings to build a model of the Western Himalayan Syntaxis areas. In doing so, we want to go beyond purely elastic models or purely viscoelastic models. Compared the results of the crust viscosity in the Western Himalayan Syntaxis areas, we believed that, when various viscoelastic models are adopted, the selection of the coefficient of viscosity in the Western Syntaxis area has important influence on the its uplifts and evolutions. A wider uplift ranges and gently elevation was observed at the same time when a lower viscosity was used in our models, and vice versa. Data of stress magnitudes are not available, but it is clear that the stress levels must be at or below the failure threshold of rock under compression. Under these criteria, the calculation results show that the viscosity in the Western Syntaxis area should be smaller than 1023Pa.s When elastic model is adopted in relatively rigid Tarim basin, obvious changes are induced to the stress and strain fields of the whole Western Syntaxis area. We found that rigid block of lithosphere reduced stress levels within its interior and that, at the edges of such regions, stress orientation can change. Furthermore there is no evidence that such rigid regions act as stress barriers in that they shield areas in opposite sides of the structure from the influence of one another. In our models, the upper crustal material of the Western Syntaxis area does not turns to move westward. Whereas, because of the stress and strain fields have been decoupling at the interior of the lithosphere, we can get the results that the deep material must not move westward.

青藏高原壳幔形变与层圈耦合数值模拟

Based on multi-principle (such as structures, tectonics and kinematics) exploratory data and related results of continental dynamics in the Tibetan plateau, the author reconstructed the geological-geophysical model of lithospherical structure and tectonic deformation, and the kinetics boundary conditions for the model. Then, the author used the numerical scheme of Fast Lagrangian Analysis of Continua (FLAC), to stimulate the possible process of the stress field and deformational field in the Tibetan plateau and its adjacent area, since the convergence-collision between the Indian continent and Eurasia continent about 50Ma ago. With the above-mentioned results, the author discussed the relationship between crustal movement in shallow layer and the deformational process in interior layers, and its possible dynamic constraints in deep. At the end of the paper, an integrative model has been put forward to explain the outline images of crust-mantle deformation and coupling in the Tibetan Plateau. (1) The characteristics of crust-mantle structure of the Tibetan plateau have been shown to be very complex, and vertical and horizontal difference is significant. The general characteristics of crust-mantle of the Tibetan plateau may be that it's layering in depth direction, and shows blocking from south to north and belting from east to west, mainly according to the results of about 20 seismic sections, such as wide-angle seismic profiles, CMP, seismic tomography and so on. (2) The crust had shortened about 2200km, while the shortening is different for different block from south to north in the Tibetan plateau. It is about 11.5mm/a in Himalayan block, about 9.0mm/a in Lhas-Gangdese block, about 7.0mm/a in Qiangtang block and Songpan-Ganzi-Kekexili block, about 8.0mm/a in Kunlun-Qaidam, and about ll.Omm/a in Qilian block, since the convergence-collision between the Indian continent and Eurasia continent about 50Ma ago. Which - in demonstrates the shortening rate decreases from south to north, but this rate increases near the north edge of the Tibetan plateau. The crust thickening rate is about 0.4mm/a in the whole Tibetan plateau; and this rate is about 0.5mm/a in Himalayan block, about 0.4mm/a in Lhas-Gangdese block, about 0.3mm/a in Qiangtang block, about 0.2mm/a in Songpan-Ganzi-Kekexili block and about O.lmm/a in Kunlun-Qaidam-Qilian block, since the convergence-collision between the Indian continent and Eurasia continent about 50Ma ago. This implies that the thickening rate decreases in the blocks of the Tibetan plateau. From south to north, the displacement of eastern boundary in the Tibetan plateau is about 37mm/a in Himalayan block, about 45mm/a in Lhas-Gangdese block, about 47mm/a in Qiangtang block, about 43mm/a in Songpan-Ganzi-Kekexili block, and about 35mm/a in Kunlun-Qaidam-Qilian block, since the collision-matching between the Indian continent and Eurasia continent had happened about 50Ma ago. This implies that the rate of eastward displacement is biggest in the middle of plateau, and decreases to both sides. The transition of S-N compression stress field in Tibetan Plateau, since about 28Ma+ ago, may be caused by two reasons: On one hand, the movement direction of Eurasia continent changed from northward to southward about 28Ma± ago in the northern plateau. On the other hand, the front belt that is located between India continent's and Eurasia continent's convergence-collision, had moved southward to high Himalayan from Indus-Brahmaputra suture almost at the same time in southern plateau. Affected by the stress field, the earlier tectonics rotated clockwise, NE and NW conjugate strike-slip faults developed, and the SN rift formed. This indicated that the EW movement started. The ratio between upper crust and lower crust of different blocks from south to north in the Tibetan plateau during the process of deformation are as following: about 3.5~5:1 in Himalayan block, about 1~5: 3-4 (which is about 1:3o--4 in south and about 4~5:3 in north) in Lhas-Gangdese block, about 1:3~447mm/a in these blocks: Which is located to the north of Banggong-nujiang suture.

中新世秦安黄土一古土壤序列记录的古气候变化周期

Analysis of periodic oscillations of climate is very important in understanding the behavior of the climate system. Milankovitch hypothesis, which holds that the glacial-interglacial climatic cycles during the Quaternary were primarily driven by variations in orbital parameters, has been supported by substantial geological evidence. Continuous long-term and high-resolution records are crucial to detect how variations of Earth's orbital parameters affected climate before the Quaternary when the boundary conditions were significantly different. Qinan loess formed in the Miocene is nearly continuous aeolian deposit in northern China. Previous study has established a constrained chronology, which provides a basis to examine long-term climatic variations. One of important issues to untangle the mechanisms behind major climate changes is the investigation of climate cycles recorded in Qinan loess. In this paper, two climatic proxies, magnetic susceptibility and redness, are analyzed for QA-I section to evaluate climate cycles using Maximum entropy spectral analysis and Blackman-Tuckey method. Main conclusions are presented as following: Results exhibit significant peaks at periods of 100 ka, 64 ka, 41 ka, 30 ka and 23 ka, but also 1000 ka, 600 ka and 400 ka. These peaks correspond to the dominant periods of the Earth's orbit parameters, which indicates that the formation of the aeolian sediment in northern China might be primarily driven by variations in orbital parameters. Fluctuations with different cycles respectively dominated in different periods. Major shifts in the dominant cycles occurred at 20.3, 19.0, 17.9, 15.2, 12.5 and 11.3 Myr ago. The transition that happened at 17.9 Myr ago was synchronous with the uplift of the Tibetan Plateau, while others at 15.2, 12.5 and 11.3 Myr ago were in good agreement with the timing of the development of Antarctic ice sheet. Therefore we inferred that these shifts might be related to changes in global ice volume and/or the Tibetan uplift. 3. The strong period of 100 ka is observed between 17.9 and 15.2, and 12.5 and 11.3 Myr ago. Ice sheet-climate models that have been used to explain the cause of the 100 ka period since the middle Pleistocene couldn't be responsible for driving the 100 ka climate cycle in the Miocene in Northern China because of the different boundary of climatic conditions between the Quaternary and Miocene. Further investigation is needed to understand how this cycle became dominant in Qinan loess records during these two time segments.

高斯束射线追踪

Using the approximate high-frequency asymptotic methods to solve the scalar wave equation, we can get the eikonal equation and transport equation. Solving the eikonal equation by the method of characteristics provides a mathematical derivation of ray tracing equations. So, the ray tracing system is folly based on the approximate high-frequency asymptotic methods. If the eikonal is complex, more strictly, the eikonal is real value at the rays and complex outside rays, we can derive the Gaussian beam. This article mainly concentrates on the theory of Gaussian beam. To classical ray tracing theory, the Gaussina beam method (GBM) has many advantages. First, rays are no longer required to stop at the exact position of the receivers; thus time-consuming two-point ray tracing can be avoided. Second, the GBM yields stable results in regions of the wavefield where the standard ray theory fails (e.g., caustics, shadows zones and critical distance). Third, unlike seismograms computed by conventional ray tracing techniques, the GBM synthetic data are less influenced by minor details in the model representation. Here, I realize kinematical and dynamical system, and based on this, realize the GBM. Also, I give some mathematical examples. From these examples, we can find the importance and feasibility of the ray tracing system. Besides, I've studied about the reflection coefficient of inhomogeneous S-electromagnetic wave at the interface of conductive media. Basing on the difference of directions of phase shift constant and attenuation constant when the electromagnetic wave propagates in conductive medium, and using the boundary conditions of electromagnetic wave at the interface of conductive media, we derive the reflection coefficient of inhomogeneous S-electromagnetic wave, and draw the curves of it. The curves show that the quasi total reflection will occur when the electromagnetic wave incident from the medium with greater conductivity to the medium with smaller conductivity. There are two peak, values at the points of the critical angles of phase shift constant and attenuation constant, and the reflection coefficient is smaller than 1. This conclusion is different from that of total reflection light obviously.

Perceptual Organization, Figure-Ground, Attention and Saliency

Notions of figure-ground, inside-outside are difficult to define in a computational sense, yet seem intuitively meaningful. We propose that "figure" is an attention-directed region of visual information processing, and has a non-discrete boundary. Associated with "figure" is a coordinate frame and a "frame curve" which helps initiate the shape recognition process by selecting and grouping convex image chunks for later matching- to-model. We show that human perception is biased to see chunks outside the frame as more salient than those inside. Specific tasks, however, can reverse this bias. Near/far, top/bottom and expansion/contraction also behave similarly.