首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Land consolidation (LC), as a type of human disturbance, improves land production efficiency and changes landscape distribution through land parcel reallocation. The objective of this study was to comparatively analyze the changes of landscape patches before and after a land consolidation project (LCP) and the effects of land levelling, irrigation and drainage work and road engineering on the landscape structure. FRAGSTAT3.3 and buffer zone analysis were used to investigate those changes. The results suggest that the heterogeneity of landscape depressed, and tended to simplification after LC. Dry land was the most highly variable land use pattern, and the change of forestland was least due to its locations at a gradient larger than 25°. LC resulted in a more rational use of land, and could be an important step in promoting rural development in depressed and fragmented agricultural areas through unused land exploitation, small-patch combination, irrigation and water conservancy, and road construction. Land levelling leveled off the gradient field surface and decreased the slope. The fragmentized patches were much more incorporated with increasing slope. On the other hand, the ridge of a field became longer so that the length of field surface and area of patch were increased. Land levelling regulated, simplified and combined patches, .so that the complexity degree was reduced. It is found that the buffer distance of 35 m was a turning point of human disturbance by irrigation and drainage systems, and patches presented flaky distribution when the buffer distance was smaller than 35 m. Meanwhile, the distance range between 25 m to 50 m was an impressible area for road engineering, which was sensitive to human actions, and the changes of all landscape metrics were larger than those in other buffer zones. In general, LC not only reallocated fragmented parcels, but also improved agricultural conditions.  相似文献   

2.
in order to evaluate the seismic reliability of water distribution system and make rehabilitation decisions correspondingly, it is necessary to assess pipelines damage states and conduct functional analysis based on pipe leak- age model. When an earthquake occurred, the water distribution system kept serving with leakage. By adding a virtual node at the centre of the pipeline with leakage, an efficient approach to pressure-driven analysis was developed for simulating a variety of low relative scenarios, and a hydraulic leakage model was also built to perform hydraulic analy- sis of the water supply network with seismic damage. Then the mean-first-order-second-moment method was used to analyse the seismic serviceability of the water distribution system. According to the assessment analysis, pipes that were destroyed or in heavy leakage were isolated and repaired emergently, which improved the water supply capability of the network and would constitute the basis for enhancing seismic reliability of the system. The proposed approach to seismic reliability and rehabilitation decision analysis on water distribution system is demonstrated effective through a case study.  相似文献   

3.
A water bearer had two large pots, each hung on each end of a pole which he carried across his neck. One of these pots had a crack in it, while the other pot was perfect and always delivered a full portion of water at the end of a long walk from the stream to the master's house, the cracked pot only arrived half-full.  相似文献   

4.
Urban growth represents specific response to economic, demographic and environmental conditions. Rapid urbanization and industrializations have resulted in sharp land cover changes. The present investigation was carried out from Shaoxing City to quantify satellite-derived estimates of urban growth using a three-epoch time series Landsat TM data for the years 1984, 1997 and ETM 2000. The methodology used was based on post classification comparison. The use of GIS allowed spatial analysis of the data derived from remotely sensed images. Results showed that the built-up area surrounding Shaoxing City has expanded at an annual average of 7 km2. Analysis of the classified map showed that the physical growth of urban area is upsetting the other land cover classes such as farming, water resources, etc. The study conclusion mainly emphasized the need for sustainable urban capacity.  相似文献   

5.
Most of us are used to the fact that skirts are basically worn by human females. We do not realize that Scotland is the land that has skirts traditionally worn by men and boys. It is, indeed, a practice of the Scottish male not to be embarrassed when he wears the Scottish kilt , which is actually a beautiful skirt.Long ago, in the land, it was common for Scottish men and boys to use skirts. It was mainly male performers that used them. The practice spread far and wide. Later, it gained favour with the Scottish royalty, especially when kilts were used by the Scottish male bagpipers at court. A bagpipe is a blowing instrument.The Scottish kilt is one of the national of Scotland. Therefore, it is not uncommon to see in Scotland a male using it on himself and feeling proud of it.  相似文献   

6.
Forest plays very important roles in global system with about 35% land area producing about 70% of total land net production. It is important to consider both elevated CO2 concentrations and different soil moisture when the possible effects of elevated CO2 concentration on trees are assessed. In this study, we grew Cinnamomum camphora seedlings under two CO2 concentrations (350 μmol/mol and 500μmnol/mol) and three soil moisture levels [80%, 60% and 40% FWC (field water capacity)] to focus on the effects of exposure of trees to elevated CO2 on underground and aboveground plant growth, and its dependence on soil moisture. The results indicated that high CO2 concentration has no significant effects on shoot height but significantly impacts shoot weight and ratio of shoot weight to height under three soil moisture levels. The response of root growth to CO2 enrichment is just reversed, there are obvious effects on root length growth, but no effects on root weight growth and ratio of root weight to length. The CO2 enrichment decreased 20.42%, 32.78%, 20.59% of weight ratio of root to shoot under 40%, 60% and 80% FWC soil water conditions, respectively. And elevated CO2 concentration significantly increased the water content in aboveground and underground parts. Then we concluded that high CO2 concentration favours more tree aboveground biomass growth than underground biomass growth under favorable soil water conditions. And CO2 enrichment enhanced lateral growth of shoot and vertical growth of root. The responses of plants to elevated CO2 depend on soil water availability, and plants may benefit more from CO2 enrichment with sufficient water supply.  相似文献   

7.
The pipe configuration and internal loads along the pipeline during the pipeline laying process have long been the focus of engineers. Most researchers simplify the seabed to be rigid and the water to be calm, ignoring the pipe embedment into the seabed and the influence of ocean currents. In this paper, a novel numerical approach is proposed for the laying of pipelines in the so-called J-lay method, taking into account the importance of both pipe embedment and ocean currents. The pipeline is divided into two parts, one part suspended in water, and the other laid on the seabed. The continuity of the two parts at the touch down point (TDP) is guaranteed to make a whole. The feasibility of the model is proved by the comparison between the present model and an analytical model, which shows good agreement in both pipeline configuration and bending moment distribution. Finally, para- metric study was performed to consider the influence of current velocity, water depth, top inclination angle, and seabed stiffness, and conclusions are drawn.  相似文献   

8.
《辅导员》2009,(4):16-16
A Crow, half-dead with thirst, came upon a pitcher which had once been full of water; but when the Crow put its beak into the mouth of the pitcher he found that only very little water was left in it, and that he could not reach far enough down to get at it. He tried, and he tried, but at last had to give up in despair. Then a thought came to him, and he took a pebble and dropped it into the pitcher.  相似文献   

9.
After the linear analytical method of unsteady flow theory is further improved, an innovative and faster algorithm is introduced. The water storage in a confined aquifer is derived from the water transmissivity coefficient and the water-pressure conductivity coefficient. The water transmissivity coefficient is approximated by a Taylorseries expansion of drawdown, and the water-pressure conductivity coefficient is obtained by the average drawdown. In this algorithm, the distance of the observation points from the pumping well must be short. When the distance is as short as the radius of the main pumping well, the data of the drawdown difference between the sidewall and the center of pumping well are difficult to measure, but the same results can be achieved based on the assumption that the drawdown difference approximates to the drawdown of the observation wells at a radial distance from the pumping well according to the algorithm. Without the help of charts, this algorithm is more concise and efficient, which has been verified by the test of water pumping project in Tianjin Binhai International Airport.  相似文献   

10.
The objective of this study was to investigate the tempo-spatial distribution of paddy rice in Northeast China using moderate resolution imaging spectroradiometer(MODIS) data.We developed an algorithm for detection and estimation of the transplanting and flooding periods of paddy rice with a combination of enhanced vegetation index(EVI) and land surface water index with a central wavelength at 2130 nm(LSWI2130).In two intensive sites in Northeast China,fine resolution satellite imagery was used to validate the performance of the algorithm at pixel and 3×3 pixel window levels,respectively.The commission and omission errors in both of the intensive sites were approximately less than 20%.Based on the algorithm,annual distribution of paddy rice in Northeast China from 2001 to 2009 was mapped and analyzed.The results demonstrated that the MODIS-derived area was highly correlated with published agricultural statistical data with a coefficient of determination(R2) value of 0.847.It also revealed a sharp decline in 2003,especially in the Sanjiang Plain located in the northeast of Heilongjiang Province,due to the oversupply and price decline of rice in 2002.These results suggest that the approaches are available for accurate and reliable monitoring of rice cultivated areas and variation on a large scale.  相似文献   

11.
The mechanical dewatering of activated sludge is difficult due to its high compressibility, which can be improved by electroosmosis. In electroosmosis, direct electric field is applied to sludge cake. Based on the conductivity modes of different sludge beds, a model is presented in which sludge cake consists of two series parts in the circuit: a dewatered bed and an undewatered one. The dewatered bed called solid conductor is mainly made up of immovable water and sludge particles. The undewatered bed includes movable water and solid conductor, which are connected in parallel in the circuit. The model describes the variation of water content with time and electric power consumption as a function of water content in sludge cake, and interprets the reason for the variation of electroosmotic dewatering rate. Comparison with the experimental data for electroosmotic dewatering under constant voltage supports the validity of the model.  相似文献   

12.
Effectiveness of urban construction boundaries in Beijing: an assessment   总被引:6,自引:0,他引:6  
Based on the remote sensing (RS) and geographic information system (GIS) analysis of the Landsat multispectral scanner (MSS) and thematic mapper (TM) satellite images of 1983, 1993, and 2005, the present research examined the effectiveness of the urban construction boundaries (UCBs) in containing urban growth within the 6th Ring Road of Beijing Municipality. Three indicators on boundary control were proposed, through which the effectiveness of boundary containment, land inventory sufficiency and illegal adjacent development to the UCBs were explored. The results suggested that, first, the UCBs were limited in effectiveness in containing urban growth; second, the area encompassed by the UCBs might not be designed large enough to accommodate new development. The frustration of the urban growth control through the UCBs mainly resulted from the lack of a transparent system for urban land use planning and control to provide sufficient information, the limitation of the traditional land use prediction method to consider contingencies, and the absence of a mechanism to monitor and adjust the UCBs to respond just in time to urban change.  相似文献   

13.
Vertical distribution of sediment concentration   总被引:1,自引:0,他引:1  
A simple formula is proposed to predict the vertical distribution of a suspended load concentration in a 2D steady turbulent flow. The proposed formula significantly improves the well-known Rouse formula where sediment concentration has an infinitely large value at the channel bottom and a zero value at the water surface. Based on this formula and the logarithmic velocity profile, a theoretical elementary function for the transport rate of a suspended load is developed. This equation improves the Einstein equation in which the unit-width suspended sediment discharge must be solved by numerical integration and a contradiction between the lower limit of the integral and that of velocity distribution exists.  相似文献   

14.
The influences of Mn and Ni contents on the impact toughness and microstructure in the weld metals of high strength low alloy steels were studied. The objective of this study was to determine the optimum composition ranges of Mn and Ni to develop welding consumables with better resistance to cold cracking. The results indicated that Mn and Ni had considerable effect on the microstructure of weld metal, and both Mn and Ni promoted acicular ferrite at the expense of proeutectoid ferrite and ferrite side plates. Varying Ni content influenced the Charpy impact energy, the extent of which depended on Mn content. Based on the properties and impact resistance, the optimum levels of Mn and Ni were suggested to be 0.6%—0.9%,, and 2.5%—3.5%, respectively. Additions beyond this limit promoted the formation of segregation structures and other microstructural features, which may be detrimental to weld metal toughness.  相似文献   

15.
As a trend of thought in literature and art,aestheticism rose suddenly at the end of the 19th century and withered away soon.It was just like a flash in the world of literature and art.One of the initiators,Oscar Wilde,has been noticed with great attention by the critics.Wilde earnestly practiced the aestheticism he advocated.Some of his acts were cast aside by the moral in his time,which at last led to his death in a strange land.  相似文献   

16.
李佳蔚 《海外英语》2014,(18):290-293
The paper presents an analytical study on the American society through a popular American drama series "the Desperate House Wives". Typical American values can be found everywhere on the show as they have been ingrained in the soul of the American people. As a nation with not very long history but great achievements, its people are the one that should be highlighted. Unlike China, the nation of which have formed since thousands of years ago, so has its culture, America’s history is an immigration history. People started migrating from other parts of the world since the 17 thcentury and gathered at the land of America to build up their new homes and realize their dreams. They influence each other and fuse with each other. America is one of the countries in the world that plural cultures successfully mix together.The paper focuses on the American people’s daily life to explain to the readers the American traits and values prevailing in their society. Except the Foreword which is the general introduction to the paper, this paper is presented in five parts. The first part to the forth part are the emphasis of the paper which respectively analyze the American traits and values. A series of vivid examples are provided with a wide range of study objects, man and woman, kids to elders, in hope of making the paper understandable and persuasive. It is expected that the study can offer a general idea to the people who are interested in the American society and its people.  相似文献   

17.
Mercury pollution in the Three Gorges Reservoir area of P. R. China merits special attention. We investigated into the current situation in the Chongqing part of the Reservoir area, identified the pollution sources and proposed some suggestions for the remediation and prevention of mercury pollution in this area. Atmospheric mercury in Chongqing was mainly from coal burning and releases of mercury-containing products such as various types of lights and fever thermometers. Urban drainage in Chongqing and Changshou, and runoffs from the high mercury background area in the lower reaches of the Wujiang River contributed most of the mercury in the water of the Yangtze River. A majority of the blame should be laid on mercury and gold mining in the Wujiang valley. We suggested foresting sloping lands to relieve soil erosion and prevent mercury-bearing soil from running into rivers, educational activities to discourage use of mercury-containing products and improved infrastructure to collect mercury-containing wastes for reducing mercury releases, more facilities for treating wastewater and solid waste to accommodate increased requirements of discharge, and growing selected perennial plants in mercury-contaminated land to absorb the mercury in soil. We also suggested concerted operation of a dedicated water-quality monitoring system, reinforced legislation and an effective administrative mechanism to ensure lasting efforts are invested in curbing mercury releases and restoring mercury contaminated land and water in the Reservoir area.  相似文献   

18.
A new approach to coastal water quality assessment was put forward through study on self-organizing map ( SOM ). Firstly, the water quality data of Bohai Bay from 1999 to 2002 were prepared. Then, a set of software for coastal water quality assessment was developed based on the batch version algorithm of SOM and SOM toolbox in MATLAB environment. Furthermore. the training results of SOM could be analyzed with single water quality indexes, the value of N : PC atomic ratio) and the eutrophication index E so that the data were clustered into five different pollution types using k-means clustering method. Finally, it was realized that the monitoring data serial trajectory could be tracked and the new data be classified and assessed automatically. Through application it is found that this study helps to analyze and assess the coastal water quality by several kinds of graphics, which offers an easy decision support for recognizing pollution status and taking corresponding measures.  相似文献   

19.
The deep, unconsolidated sedimentary aquifersof eastern coastal China have been heavily over-exploited, which caused aquifer compaction and re-sulted in the highest rates of land subsidence in Chinaduring the past50 years. As the government and gen-eral public paid more attention to land subsidence is-sues, land subsidence monitoring networks have beenset up since the mid-1980s. However, due to lack ofgeological data as well as practical simulation meth-ods, current work focuses on routine obs…  相似文献   

20.
The famine began in 1983.As of November 1984,at least 300,000people had died because of drought and famine.Perhaps eight millionmore face starvation—just in Ethiopia alone.People have left theirhomes and villages to look for help.Most Africans live off the land.As their numbers grow,more andmore people have to try to raise food on land that cannot quickly renew  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号