全球变化不绿洲的演化趋势研究-以塔里木盆地北部渭干河绿洲为例

本文以全球变化对绿洲水文循环影响为主线，分析了地处干旱区的绿洲在全球变化下的演变趋势。以塔里木盆地北部渭干河绿洲为例，探讨了其水量平衡、非灌溉土壤积盐特性、隐域性盐化草甸植被NPP，以及绿洲土地利用／覆被变化对全球变化的响应。从不同时间尺度上分析了全球变化的两大驱动因子，气候变化和人类活动对绿洲演化的影响。运用系统动力学模型模拟了未来30年绿洲土地覆被变化在上述两驱动因子的作用下的动态演变过程。其主要结论如下： 1、从生态学的角度，绿洲可定义为：存在于干旱、半干旱区的依赖于水源而生存的隐域性绿色景观．地质时期，绿洲的演化由气候等自然因子起决定作用;人类历史时期，在气候等自然因素的大背景下，人类活动对绿洲演变的作用越来越大;近百年来，绿洲的演变则主要受人为活动干扰。 2、在不改变绿洲现有土地利用格局和水资源利用率的情况下，当年平均气温升高2.5℃，无论降水增加200%或不增加，绿洲的水资源量都将出现负平衡，全球变化将使绿洲面临更为严重的水资源短缺。 3、绿洲自然土壤0-5 0cm土层积盐速率对全球变化的响应程度依地下水埋深的大小而有所差异。地下水埋深较小，积盐速率随温度的升高增加较明显;地下水埋深较大时，积盐速率变化不明显。当地下水埋深>2m，地表积盐速率不再随气候变化而变化．地下水埋深h=2m为渭干河绿洲非灌溉土壤地表积盐速率对全球变化响应的临界深度。 4、根据绿洲地下水埋深与植被NPP的相关关系，推导出了估算盐化草甸植被NPP的模型： NPP=-O. 991+0. 0005Eo (h-0. 25h^2+0. 021h^3) +5. 276EXP (-0. 651h) 并分别估算了当前及全球变化下的NPP值。盐化草甸植被NPP随地下水埋深的增加呈指数下降。全球变化下，地下水埋深较大时，NPP的增加较明显;地下水埋深较小时，NPP的增加不明显。 5、灵敏度分析表明：NPP对地下水埋深h的变化比对地下水矿化度变化为更敏感。h=3. 3m为渭干河绿洲盐化草甸植被的胁迫深度。 6、系统动力学模型模拟表明，渭干河绿洲耕地面积的增减受水资源利用率和人口数量变化的制约。全球变化下，由于水文状况的改变，未来30年将导致绿洲耕地面积增幅下降4. 5-5.1%。绿洲水文状况和人口数量变化是决定土地利用格局变化的关键驱动因素。 7、绿洲灌溉土地的优化模式为，耕地：林地：改良草地=70: 23:7;种植业（耕地）内部的比例为，粮食作物：经济作物：人工草地=46: 31: 23。

Increasing Critical Sensitivity of the Load/Unload Response Ratio before Large Earthquakes with Identified Stress Acclumulation Pattern

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.

Experimental Study of Surface Deformation and Flow Pattern on Buoyant-Thermocapillary Convection

Free surface deformation is one of the most important physical phenomena in fluids with free surface. In the present paper, convection and surface deformation caused by thermocapillary effect in a rectangular cavity were investigated. In ground experiments, the convection was also affected by gravity. The cavity has a horizontal cross section of 52mm×42mm and the thikkness of the liquid layer is 4mm. Temperature difference between two sides of the liquid layer was increased gradually, and the flow in liquid layer will develop from steady to unstable convection. An optical diagnostic system consisting of a revised Michelson interferometer with image processor was developed to study fluid surface deformation in convection, and the displacements of free surface oscillation were determined. PIV technique was adopted to observe the evolution of flow pattern, and the velocity fields were obtained quantitatively. The present experiments demonstrate that surface deformation is quite distinct in buoyant-thermocapillary convection. in order to understand the mechanism of buoyant-thermocapillary convection, not only the hydrothermal wave instability but also the surface wave instability should be discussed.

Pattern Recognition With Weighted Complex Networks

In this paper we introduce a weighted complex networks model to investigate and recognize structures of patterns. The regular treating in pattern recognition models is to describe each pattern as a high-dimensional vector which however is insufficient to express the structural information. Thus, a number of methods are developed to extract the structural information, such as different feature extraction algorithms used in pre-processing steps, or the local receptive fields in convolutional networks. In our model, each pattern is attributed to a weighted complex network, whose topology represents the structure of that pattern. Based upon the training samples, we get several prototypal complex networks which could stand for the general structural characteristics of patterns in different categories. We use these prototypal networks to recognize the unknown patterns. It is an attempt to use complex networks in pattern recognition, and our result shows the potential for real-world pattern recognition. A spatial parameter is introduced to get the optimal recognition accuracy, and it remains constant insensitive to the amount of training samples. We have discussed the interesting properties of the prototypal networks. An approximate linear relation is found between the strength and color of vertexes, in which we could compare the structural difference between each category. We have visualized these prototypal networks to show that their topology indeed represents the common characteristics of patterns. We have also shown that the asymmetric strength distribution in these prototypal networks brings high robustness for recognition. Our study may cast a light on understanding the mechanism of the biologic neuronal systems in object recognition as well.

Fractal Pattern Formation In Anodic Bonding Of Pyrex Glass/Al/Si

Anodic bonding of Pyrex glass/Al/Si is an important bonding technique in micro/nanoelectromechanical systems (MEMS/NEMS) industry. The anodic bonding of Pyrex 7740 glass/Aluminum film/Silicon is completed at the temperature from 300 degrees C to 375 degrees C with a bonding voltage between 150 V and 450 V. The fractal patterns are formed in the intermediate Al thin film. This pattern has the fractal dimension of the typical two-dimensional diffusion-limited aggregation (2D DLA) process, and the fractal dimension is around 1.7. The fractal patterns consist of Al and Si crystalline grains, and their occurrences are due to the limited diffusion, aggregation, and crystallization of Si and Al atoms in the intermediate Al layers. The formation of the fractal pattern is helpful to enhance the bonding strength between the Pyrex 7740 glass and the aluminum thin film coated on the crystal silicon substrates.

Role Of Convection Flow On The Pattern Formation In The Drying Process Of Colloidal Suspension

We study the macroscopic drying patterns of aqueous suspensions of colloidal silica spheres. It was found that convection strength can influence pattern formation. Uniformed films are obtained at weaker convection strength. In addition, we make clear that it is not reasonable to discuss individually the effect of temperature and humidity on the colloid self-assembly. The physical mechanism is that these factors have relationship with the evaporation rate, which can affect the convection strength.

圆柱振荡绕流中涡旋运动模式(pattern)的数值模拟

提出并发展的一种基于区域分解思想,综合了解 N—S方程的有限差分法及涡法各自优点的新数值方法,计算了各种 Keulegan-Carpenter 数下(Kc=2～24)振荡流绕圆柱的流动。系统地研究了振荡流中涡旋运动模式随 Kc 数变化的规律,模拟了不对称区、单对涡区(或模向区)、双对涡区(或对角区)和三对涡区四种不同的涡旋运动模式。将计算所得的阻力系数 C_D、惯性系数 C_M与国外近期发表的计算结果进行了比较。

Laser-induced wavy pattern formation in metal thin films

Laser-induced well-ordered and controllable wavy patterns are constructed in the deposited metal thin film. The micrometer-sized structure and orientation of the wavy patterns can be controlled via scanning a different size of rectangle laser spot on the films. Ordered patterns such as aligned, crossed, and whirled wave structures were designed over large areas. This patterning technique may find applications in both exploring the reliability and mechanical properties of thin films, and fabricating microfluidic devices. (C) 2004 American Institute of Physics.

Wave pattern characteristics of a two-phase nozzle flow by shock propagation

In this paper, the wave pattern characteristics of shock-induced two-phase nozzle Hows with the quiescent or moving dusty gas ahead of the incident-shock front has been investigated by using high-resolution numerical method. As compared with the corresponding results in single-phase nozzle flows of the pure gas, obvious differences between these two kinds of flows can be obtained.

A new dynamic model for study of dislocation pattern formation

Based on the principle given in nonlinear diffusion-reaction dynamics, a new dynamic model for dislocation patterning is proposed by introducing a relaxation time to the relation between dislocation density and dislocation flux. The so-called chemical potential like quantities, which appear in the model can be derived from variation principle for free energy functional of dislocated media, where the free energy density function is expressed in terms of not only the dislocation density itself but also their spatial gradients. The Linear stability analysis on the governing equations of a simple dislocation density shows that there exists an intrinsic wave number leading to bifurcation of space structure of dislocation density. At the same time, the numerical results also demonstrate the coexistence and transition between different dislocation patterns.

Statistical description of pattern evolution in damage-fracture

A model of dynamical process and stochastic jump has been put forward to study the pattern evolution in damage-fracture. According to the final states of evolution processes, the evolution modes can be classified as globally stable modes (GS modes) and evolution induced catastrophic modes (ElC modes); the latter are responsible for fracture. A statistical description is introduced to clarify the pattern evolution in this paper. It is indicated that the appearance of fracture in disordered materials should be depicted by probability distribution function.

The mechanism of pattern selection in coupled map lattices

The pattern selection of one-dimensional coupled map lattices is studied in this paper. It is shown by spatiotemporal variable separation that there exists a threshold wavelength in pattern selection which possesses wave-like structures in space and periodic chaotic motion in time.

Flow pattern in chandler loop - the artificial thrombus formation

In this paper a hydrodynamic approach is used to analyse carefully the flow field inChandler loop--the artificial thrombus formation. The results obtained show that near thelower meniscus where the thrombus is formed, there is a back flow accompanied with asecondary flow and its mainflow is toward the meniscus, thus providing a favourable condi-tion for corpuscle aggregation. Our finding is valuable for studying the mechanism ofthrombus formation in artificial organ and in vivo.

Effect of Pipe Diameter on Flow Pattern Transition in Vertical Oil Water Flows

This paper investiges the effect of pipe diameter on flow pattern transition boundary in oil water vertical flows, and proposes a model to determine the maximum inner diameter (D_{infty s}) of a pipe in which the slug flow would not occur When pipe inner diameter D>D_{infty s}, only bubble flow exists, while D

Experimental Study the Flow Pattern in Thermal Capillary Convection

In the present research work, the thermal capillary convection has been investigated and measured by particle image velocimetry (PIV) technique. There is one liquid layer in a rectangular cavity with different temperature’s sidewalls. The cavity is 52mm,42mm,20mm, 4mm in height of the silicon oil liquid layer. A sidewall of the cavity is heated by electro-thermal film, another sidewall is cooled by the semiconductor cooling sheet. The velocity field and the stream lines in cross section in liquid layer have been obtained at different temperature difference. The present experiment demonstrates that the pattern of the convection mainly relates with temperature difference.