共查询到19条相似文献，搜索用时 402 毫秒
1.
Chinese urbanization 2050: SD modeling and process simulation 总被引：1，自引：0，他引：1
《中国科学:地球科学(英文版)》2017,(6)
Is Chinese urbanization going to take a long time, or can its development goal be achieved by the government in a short time? What is the highest stable urbanization level that China can reach? When can China complete its urbanization? To answer these questions, this paper presents a system dynamic(SD) model of Chinese urbanization, and its validity and simulation are justified by a stock-flow test and a sensitivity analysis using real data from 1998 to 2013. Setting the initial conditions of the simulation by referring to the real data of 2013, the multi-scenario analysis from 2013 to 2050 reveals that Chinese urbanization will reach a level higher than 70% in 2035 and then proceed to a slow urbanization stage regardless of the population policy and GDP growth rate settings; in 2050, Chinese urbanization levels will reach approximately 75%, which is a stable and equilibrium level for China. Thus, it can be argued that Chinese urbanization is a long social development process that will require approximately20 years to complete and that the ultimate urbanization level will be 75–80%, which means that in the distant future, 20–25% of China's population will still settle in rural regions of China. 相似文献
2.
TANG Shihao ZHU Qijiang WANG Jindi ZHOU Yuyu & ZHAO Feng Research Center for Remote Sensing GIS Department of Geography Beijing Normal University Beijing China National Satellite Meteorological Center China Meteorological Administration Beijing China 《中国科学D辑(英文版)》2005,48(2):241-249
Vegetation index is a simple, effective and experiential measurement of terrestrial vegetation activity, and plays a very important role in qualitative and quantitative remote sensing. Aiming at shortages of current vegetation indices, and starting from the analysis of vegetation spectral characteristics, we put forward a new vegetation index, the three-band gradient difference vegetation index (TGDVI), and established algorithms to inverse crown cover fraction and leaf area index (LAI) from it. Theoretical analysis and model simulation show that TGDVI has high saturation point and the ability to remove the influence of background to some degree, and the explicit functional relation with crown cover fraction and LAI can be established. Moreover, study shows that TGDVI also has the ability to partly remove the influence of thin cloud. Experiment in the Shunyi District, Beijing, China shows that reasonable result can be reached using the vegetation index to retrieve LAI. We also theoretically analyzed the 相似文献
3.
Re-Look to Conventional Techniques for Trapping Efficiency Estimation of a Reservoir 总被引：4，自引：4，他引：0
All reservoirs are subjected to sediment inflow and deposition up to a certain extent leading to reduction in their capacity. Thus, the important practical problem related to the life of reservoir is the estimation of sedimentation quantity in the reservoirs. Large number of methods and models are available for estimation of reservoir sedimentation process. However, each model differs greatly in terms of their complexity, inputs and other requirements. In the simplest way, the fraction of sediment deposit in the reservoir can be determined through the knowledge of its trap efficiency. Trap efficiency （Te） is the proportion of the incoming sediment that is deposited or trapped in a reservoir. Most of the Te estimation methods define a relationship of the T, of the reservoir to their capacity and annual inflow, generally through curves. In this study, the empirical relationships given by Brune and Brown were used and compared for estimating the trap efficiency of Gobindsagar Reservoir （Bhakra Dam） on Satluj River in Bilaspur district of Himachal Pradesh, in the Himalayan region of India. A new set of regression equations has been developed for Brune＇s method and compared with Brown and other available Brune＇s equations. It has been found that Brune＇s equations developed in the present study estimated better than the other Brune＇s equations reported in literature. Later, in the present study it was found that Brown＇s approach was over estimating the T,. Hence it was again modified for Gobindsagar reservoir. It was also identified that sediments coming to this particular reservoir were mainly of coarse nature. 相似文献
4.
AshutoshBagchi 《地震工程与工程振动(英文版)》2004,3(2):223-236
This paper presents a simplified method of evaluating the seismic performance of buildings. The proposed method is based on the transformation of a multiple degree of freedom (MDOF) system to an equivalent single degree of freedom (SDOF) system using a simple and intuitive process. The proposed method is intended for evaluating the seismic performance of the buildings at the intermediate stages in design, while a rigorous method would be applied to the final design. The performance of the method is evaluated using a series of buildings which are assumed to be located in Victoria in western Canada, and designed based on the upcoming version of the National Building Code of Canada which is due to be published in 2005. To resist lateral loads, some of these buildings contain reinforced concrete moment resisting frames,while others contain reinforced concrete shear walls. Each building model has been subjected to a set of site-specific seismic spectrum compatible ground motion records, and the response has been determined using the proposed method and the general method for MDOF systems. The results from the study indicate that the proposed method can serve as a useful tool for evaluation of seismic performance of buildings, and carrying out performance based design. 相似文献
5.
Shuenn-Yih Chang 《地震工程与工程振动(英文版)》2011,10(3):437-451
Although the step degree of nonlinearity has been introduced to conduct basic analysis and error propagation analysis for the pseudodynamic testing of nonlinear systems, it cannot be reliably used to select an appropriate time step before performing a pseudodynamic test. Therefore, a novel parameter of instantaneous degree of nonlinearity is introduced to monitor the stiffness change at the end of a time step, and can thus be used to evaluate numerical and error propagation properties for nonlinear systems. Based on these properties, it is possible to select an appropriate time step to conduct a pseudodynamic test in advance. This possibility is very important in pseudodynamic testing, since the use of an arbitrary time step might lead to unreliable results or even destroy the test specimen. In this paper, guidelines are proposed for choosing an appropriate time step for accurate integration of nonlinear systems. These guidelines require estimation of the maximum instantaneous degree of nonlinearity and the solution of the initial natural frequency. The Newmark explicit method is chosen for this study. All the analytical results and the guidelines proposed are thoroughly confirmed with numerical examples. 相似文献
6.
Gao Wenxue Gao QinhuaState Seismological Bureau Beijing China Institute of Geology SSB Beijing China 《中国地震研究》1995,(2)
This paper is a review on earthquake prediction and forecast research,progress in earthquake prediction work and pre-estimation of earthquake hazard degree in China in recent years.It indicates that China is the first country,the government of which has promoted and organized the state administration department on reduction of seismic hazards and ensured the socialization of earthquake prediction and forecast in the world.A program of earthquake prevention and protection and hazard reduction based on the results of research on earthquake occurrence regularities and prediction of earthquake preparation trend has been completed,and hence the socialization of results of earthquake prediction and forecast research can be expected to be in practice.The practical seismological works in last 20 years indicate that the earthquakes are not considered to be unpredictable,but it is a challenge remaining to be accepted.We are willing to cooperate with all friends who are engaged in earthquake prediction and forecas 相似文献
7.
Effective migration system of coalbed methane(CBM)reservoir,which was controlled by development degree and opening-closing degree of fractures,determines the permeability of coal reservoir and can be characterized by the pore-fracture system in the extrinsic form.In this paper,based on coal matrix elastic self-regulating effect theory and coal reservoir combined elastic energy theory,the fracture opening-closing degree parameterΔand the fracture development degree parameterξare suggested for the quantitative study of the effective migration system of CBM reservoir in southern Qinshui Basin.Further,the control functions ofξandΔto CBM enrichment and high production are discussed.The results show that in present stage the area with highξvalue is located in Anze and Qinyuan,and then Zhengzhuang and Fangzhuang,where fracture development degree is high.The area with highΔvalue is located in Zhengzhuang and Fanzhuang,and then Anze and Qinyuan,indicating where coal matrix elastic self-regulating positive effect dominates and fractures tend to be open.Through the comprehensive analysis onξandΔ,it can be found that their best match area is located in Zhengzhuang and Fanzhuang,with high values for fracture development degree and opening-closing degree probably bringing about high fluid pressure and good permeability of reservoirs,which are advantageous to an abundant CBM production. 相似文献
8.
SCOUR MITIGATION AT BRIDGE PIERS USING SACRIFICIAL PILES 总被引：1，自引：0，他引：1
To mitigate scour around bridge piers, sacrificial piles are economic method where natural processes are involved. The arrangement should be such that scoured materials from the sacrificial piles should have enough volume to fill the scour hole created upstream of the pier in such a way that sediments are trapped inside the scour hole. This concept differs from earlier study made with sacrificial piles that mainly deals to reduce the strength of horseshoe vortex. To determine the effect of sacrificial piles for scour mitigation, alternative arrangements of piles were tested in front of a rectangular pier under clear-water condition and found that when the group of piles is placed at a distance of twice the projected width of the pier, for which percentage of blockage of the pier width is 60%, the scour volume can be reduced upto 61% while the maximum scour depth can be reduced upto 50%. 相似文献
9.
LI AiBing ZHANG LiFeng WANG QiuLiang LI Bo LI ZhenZhong WANG YiQing 《中国科学:地球科学(英文版)》2013,(8):1413-1421
In nonlinear error growth dynamics,the initial error cannot be accurately determined,and the forecast error,which is also uncertain,can be considered to be a random variable.Entropy in information theory is a natural measure of the uncertainty of a random variable associated with a probability distribution.This paper effectively combines statistical information theory and nonlinear error growth dynamics,and introduces some fundamental concepts of entropy in information theory for nonlinear error growth dynamics.Entropy based on nonlinear error can be divided into time entropy and space entropy,which are used to estimate the predictabilities of the whole dynamical system and each of its variables.This is not only applicable for investigating the dependence between any two variables of a multivariable system,but also for measuring the influence of each variable on the predictability of the whole system.Taking the Lorenz system as an example,the entropy of nonlinear error is applied to estimate predictability.The time and space entropies are used to investigate the spatial distribution of predictability of the whole Lorenz system.The results show that when moving around two chaotic attractors or near the edge of system space,a Lorenz system with lower sensitivity to the initial field behaves with higher predictability and a longer predictability limit.The example analysis of predictability of the Lorenz system demonstrates that the predictability estimated by the entropy of nonlinear error is feasible and effective,especially for estimation of predictability of the whole system.This provides a theoretical foundation for further work in estimating real atmospheric multivariable joint predictability. 相似文献
10.
Although it has been shown that the implementation of the HHT-α method can result in improved error propagation properties in pseudodynamic testing if the equation of motion is used instead of the difference equation to evaluate the next step acceleration, this paper proves that this method might lead to instability when used to solve a nonlinear system. Its unconditional stability is verified only for linear elastic systems, while for nonlinear systems, instability occurs as the step degree of convergence is less than 1. It is worth noting that the step degree of convergence can frequently be less than 1 in pseudodynamic testing, since a convergent solution is achieved only when the step degree of convergence is close to 1 regardless of whether its value is greater or less than 1. Therefore, the application of this scheme to pseudodynamic testing should be prohibited, since the possibility of instability might incorrectly destroy a specimen. Consequently, the implementation of the HHT-α method by using the difference equation to determine the next step acceleration is recommended for use in pseudodynamic testing. 相似文献
11.
Saleh K. Al Mansoori Stefan IglauerChristopher H. Pentland Martin J. Blunt 《Advances in water resources》2009
We measure the trapped saturations of oil and gas as a function of initial saturation in water-wet sand packs. We start with a water-saturated column and inject octane (oil), while water and oil are produced from the bottom. Once water production has ceased, air (gas) then enters from the top, allowing oil and gas to drain under gravity for different times. Finally water is then injected from the bottom to trap both oil and gas. The columns are sliced and the fluids analyzed using gas chromatography. We find that for high initial gas saturations more gas can be trapped in the presence of oil than in a two-phase (gas/water) system. The residual gas saturation can be over 20% compared to 14% in two-phase flow [Al Mansoori SK, Iglauer S, Pentland CH, Bijeljic B, Blunt MJ. Measurements of non-wetting phase trapping applied to carbon dioxide storage. Energy Procedia 2009;1(1):3173–80]. This is unlike previous measurements on consolidated media, where the trapped gas saturation is either similar or lower to that reached in an equivalent two-phase experiment. For lower initial gas saturation, the amount of trapping follows the initial-residual trend seen in two-phase experiments. The amount of oil trapped is insensitive to initial gas saturation or the amount of gas that is trapped, again in contrast to measurements on consolidated media. More oil is trapped than would be predicted from an equivalent two-phase (oil/water) system, although the trapped saturation is never larger than the maximum reached in two-phase flow (around 11%) [Pentland CH, Al Mansoori SK, Iglauer S, Bijeljic B, Blunt MJ. Measurement of non-wetting phase trapping in sand packs. In: SPE 115697, proceedings of the SPE annual technical conference and exhibition, Denver, Colorado, USA; 21–24 September 2008]. These initially surprising results are explained in the context of oil layer stability and the competition between snap-off and piston-like advance. In two-phase systems, displacement is principally by cooperative piston-like advance with relatively little trapping, whereas in consolidated media snap-off is generally more significant. However, oil layer collapse events during three-phase waterflooding rapidly trap the oil which acts as a barrier to direct water/gas displacement, except by snap-off, leading to enhanced gas trapping. 相似文献
12.
全波形反演可以为叠前深度偏移成像提供更高精度的速度模型,但该方法具有较强的非线性,对初始速度模型的依赖性较强,尤其是在实际应用中,地质条件复杂多变,速度变化不连续,增加了反演非线性程度,常常使反演陷入局部极小值,影响反演的精度.全变差约束在图像去噪领域应用广泛,属于非光滑约束,在去噪过程中能有效的保留图像的不连续界面和边缘信息.本文提出基于Hinge损失函数的垂向全变差约束全波形反演方法,在全变差约束的基础上,利用Hinge损失函数控制模型的更新方向,并使用原-对偶混合梯度算法进行求解,给出这一优化问题的迭代格式,有效提高了对地下不连续界面的重构精度,同时也降低反演对初始速度模型的依赖程度.数值算例证明：与常规全波形反演方法相比,基于全变差约束的全波形反演方法可以有效的重构速度模型中的不连续界面,尤其对高速体边缘的重构效果更明显,但该方法对初始速度模型的依赖性仍然较强;基于Hinge损失函数的垂向全变差约束全波形反演方法降低了对初始速度模型的依赖程度,可以从一个较差的初始模型通过循环迭代的方式最终得到同样精确的速度模型,较好的重构了高速体边缘和不连续界面. 相似文献
13.
Formation of Artefacts and its Suppression during the Determination of Volatile Halogenated Hydrocarbons in Water by Means of Headspace Gas Chromatography under the Standard Conditions of DIN 38407-F5. Part II: Increased Trihalomethane Formation in Chlorinated Swimming-pool Water A comparison of two analytical standard procedures for the determination of trihalomethanes (THM) in water (headspace gas chromatography and pentane extraction/gas chromatography) yielded strongly differing results. Under the conditions recommended by the German Standard Method DIN 38407-F5 (60…80°C for at least 60 min) degradation of thermo-labile chlorination products occurs resulting in elevated THM concentrations. The reactions involved are partly pH-dependant, and these can be suppressed by sample acidification. The degradation of trihalogen acetic acids, however, can only be influenced by minimizing the equilibration time and temperature. Other intermediate chlorination products (haloacetonitriles) are also degraded to THM after preceding hydrolysis to the corresponding carboxylic acids. Comparative results obtained with a purge and trap method at ambient temperature, i.e. without thermal stress during the enrichtment step, are lower than with static headspace GC but still high in comparison to the pentane extraction method. Presumably volatile THM-precursors are also trapped and subsequently decomposed upon thermal desorption from the trap. As the static headspace GC is the most rational method of LHKW determination available, the recommended experimental sample handling conditions should be modified in a way that deterioration reactions are reduced as far as possible. 相似文献
14.
We use a three-dimensional mixed-wet random network model representing Berea sandstone to extend our previous work on relative permeability hysteresis during water-alternating-gas (WAG) injection cycles [Suicmez, VS, Piri, M, Blunt, MJ, 2007, Pore-scale simulation of water alternate gas injection, Transport Porous Med 66(3), 259–86]. We compute the trapped hydrocarbon saturation for tertiary water-flooding, which is water injection into different initial gas saturations, Sgi, established by secondary gas injection after primary drainage. Tertiary water-flooding is continued until all the gas and oil is trapped. We study four different wettability conditions: water-wet, weakly water-wet, weakly oil-wet and oil-wet. We demonstrate that the amounts of oil and gas that are trapped show surprising trends with wettability that cannot be captured using previously developed empirical trapping models. We show that the amount of oil that is trapped by water in the presence of gas increases as the medium becomes more oil-wet, which is opposite from that seen for two-phase flow. It is only through a careful analysis of displacement statistics and fluid configurations that these results can be explained. This illustrates the need to have detailed models of the displacement processes that represent the three-phase displacement physics as carefully as possible. Further work is needed to explore the full range of behavior as a function of wettability and displacement path. 相似文献
15.
对马尼拉俯冲带中段高精度地形数据编辑后绘制成图,联合之前所获取的地震剖面数据,对俯冲带增生楔的精细构造地貌特征及发育模式进行了深入探讨.在增生楔下构造区发现了大量狭长的微型圈闭盆地,经过对其平面断裂特点与深部应力状态的分析,发现增生楔从俯冲前缘到脊顶区其构造特点的转变对应着微型圈闭盆地4个完整的发育阶段,即初期的加积断裂阶段、中期的圈闭成盆阶段、后期的挤压消亡阶段乃至最终的隆升推覆阶段,揭示出一种新型的俯冲带增生楔发育模式,并推断其本质是深部板片俯冲活动所产生的压应力在海底面的表现. 相似文献
16.
对于迭代方式的参数化反演方法,如何使反演结果稳定地收敛到整体极小仍是目前大地电磁（MT）反演中急需解决的问题．本文利用小波变换理论中的多尺度分析方法将大地电磁反问题分解为依赖于尺度变量的反问题序列,然后按尺度从大到小的次序依次求解,求解过程中前一个尺度反问题的解作为下一个尺度反问题的初始模型,直到来出对应于尺度为0的原反问题的解为止．该方法称为多尺度反演方法．数值试验和实际资料的反演结果表明,该方法可有效改善传统广义逆反演方法易陷入局部极小的弊端． 相似文献
17.
The transport and sedimentation of copper in the Glomma estuary, SE Norway during a period of 90% reduction in the industrial input of Cu, was studied from sediment trap material and compared to samples of the bottom sediments. Traps were deployed at four stations for several monthly periods during 1990, 1994 and 1995. Trapped material was analysed for suspended particulate matter (SPM), total organic carbon (TOC) and nitrogen (TN), Cu, and Al. Only about 10% of the Cu from the river is trapped in the estuary. Still there was a moderate but significant reduction in Cu concentration in the trap SPM from 1990 to 1994, reflecting the industrial reductions, but only if excluding summer samples apparently influenced by antifouling Cu from boat paint. Settling matter therefore seems appropriate and sensitive for monitoring changes in the Cu load. The results supported the view that TOC is the main carrier of Cu to the sediments. 相似文献
18.
Rivers are known to carry sediment loads. Many rivers in Asia including Kosi, Brahmaputra, Bagmati rivers in India and Yellow and Yarlung Tsangpo rivers in China are well known for their carriage of excessive sediment loads. In India, many water abstraction units are located along river banks. Their success depends on how the sediment load is trapped as the sediment laden water flows towards the pumping wells located few hundred meters away from river bank. In this work, based on the analysis of a data of one year on suspended load variations in a canal, located at Haridwar, India, trap efficiency variations are studied during the passage of source water to the abstraction well. Considering the subsurface basin, located within the source water and the abstraction well, as a hypothetical settling basin, variation of trap efficiency is related with the influent concentration. It is observed that the trap efficiency depends on the influent concentration. Appropriate functional forms for the variation of trap efficiency with the influent concentrations are also identified. 相似文献
19.
Robert S. White 《Earth and Planetary Science Letters》1979,42(1):114-120
It has been postulated that the sediments of the Gulf of Oman, in the northwest Indian Ocean contain a number of localised accumulations of free gas which are apparent on continuous seismic reflection profiles as horizons with anomalously high amplitude reflections. We suggest that the gas is trapped beneath a relatively impermeable gas hydrate layer which is stable within the uppermost 350–700 m of sediment. The depth beneath the sea floor of all the observed highly reflective horizons varies with water depth in a manner similar to that predicted from theoretical estimates of the depth at which the phase change occurs from gas hydrate to free gas. Further evidence that the gas is trapped by a hydrate layer is provided by the detailed shape of gas layers within the cores of gentle anticlines. The curvature of the gas reflector mirrors that of the sea floor above it, but transgresses the local bedding, suggesting that the gas is trapped by a hydrate phase change governed by the pressure and temperature conditions rather than by a stratigraphic trap. 相似文献