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Search Results: 1 - 10 of 495588 matches for " <br>刘文兆 "
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LIU Wen,zhao,<br>
自然资源学报 , 1998,
Abstract: This paper introduces the concepts of marginal water use efficiency (MWUE) and elasticity of water production (EWP),and reveals dynamic interrelations of crop production and water consumption and water use efficiency (WUE) based on the functional relation between water consumption and crop yield ( or photosynthate). Providing the relation of seasonal evapotranspiration (ET) and crop yield (Y) is as Y=f(ET),then WUE=Y/ET,MWUE=dY/dET,and EWP=MWUE/WUE.WUE increases with the rise of ET if EWP>1 and decreases with the rise of ET if EWP<1. Proper construction of the function of crop water production,Y=f(ET),serves as a basis for correct analysis of WUE. If the Y=f(ET) function is linear,the changing trend of WUE with ET is directly affected by the constant term. If the Y=f(ET) function is quadratic parabolic,the maximum WUE comes earlier than the maximum yield with the rise of ET. The ET that makes WUE reach to its maximum value equals the arithmetic square root of a ratio of the constant term to the coefficient of quadratic term(). WUE increases with the rise of ET when ,conversely WUE decreases with the rise of ET when . Field experiment on spring corn yield response to water and fertilizer in the loess tableland of China showed that the form of Y=f(ET) appeared parabolic relationships at both high and low fertility levels,and high fertility plots had higher WUE and ET than low fertility ones under the same level of water supply. At high fertility plots in 1987,WUE increased with the rise of ET when ET< 472mm,reached to the maximum value of 16 3kg/ha.mm when ET =472mm,and decreased with the rise of ET when ET<472mm. The yield reached the maximum of 8 111kg/ha when ET = 524mm. MWUE always decreased with the rise of ET within the experimental range and dropped to zero when ET = 524mm. At low fertility plots,WUE reached the maximum value of 11 6kg/ha.mm when ET =436mm,and the maximum yield of 5 298kg/ha was gained when ET = 485mm; the WUE and the MWUE were similar to the ones of high fertility plots in the aspect of the changing trend.
Electric resistance-capacitance model of water flow through soil-plant system

LIU Wen-Zhao,<br>
生态学报 , 2005,
Abstract: Water flow through a soil-plant system can be simulated by an electric resistance-capacitance circuit when the flow is considered as one-dimensional Darcy-Rechards flow.The hydraulic resistance is a ratio of the water potential difference to the average rate of outflow and inflow,and the water capacitance is a derivative of the water storage with respect to the average water potential because of the nonsteady nature of water transport.Corresponding to the Darcy-Richards equation,hydraulic resistance and resistivity are the reciprocals of conductance and conductivity respectively;time constant is the reciprocal of the diffusance;and time constant per unit squared length is the reciprocal of diffusivity.If the soil-plant system is taken as a catenary series of segments along the water flow path,the hydraulic resistance and water capacitance are connected in parallel with each other in each segment,and all segments are connected in series.The study gave universal formula of water flow through the soil-plant systems,formula of the relationship between the total capacitance and partial capacitances of individual segements,formula of the relationship between the total resistance and partial resistances,and formula of temporal change of leaf water potential under a certain condition.
Investigation and analysis of collapses and landslides on the Loess Plateau of East Gansu Province after the 5.12 Wenchuan Earthquake

生态学报 , 2008,
Abstract: 通过对甘肃省庆阳市、平凉市5.12汶川大地震地质灾害实地调查,发现此次地震造成的崩塌和滑坡,以小型为主,数量众多,主要分布在现代侵蚀沟边缘部位的断崖和陡坡上。地震在塬面、缓坡丘陵和川台地上所造成的崩塌,与窑洞住宅和采矿业的分布基本一致。此次地震虽未造成大中型崩塌和滑坡,但对该地环境的影响不能忽视——可改变微地貌、使未来几年内的土壤流失量有所增加等。认为在黄土高原地区,地震烈度到达Ⅳ度以上,就会引起较为严重的重力侵蚀。对于我国地震高发区之一的黄土高原而言,探讨水土流失的成因时,须要关注地震的影响。

LIU Wenxin,LUAN Zhaokun,TANG Hongxiao,<br>,,汤鸿霄
生态学报 , 1996,
Abstract: Studies on the chemical species of aluminium and its toxic effects have critical importances because of the further serious acid depositions. In this paper, the current approachesof aluminium speciation analysis and related ecologiacal effects on organisms are described.Meanwhile the perspectives of this subject are also discussed.
Soil respiration and carbon fractions in winter wheat cropping system under fertilization practices in arid\|highland of the Loess Plateau

gaohuiyi and,<br>高会议,郭胜利,,车升国
生态学报 , 2009,
Abstract: Based on a long\|term location experiment on Caliche soil in Changwu Station of Chinese Academy of Sciences, Changwu, Shaanxi, China, we monitored diurnal changes and seasonal changes of CO2 flux from soils in a continuous winter wheat (Triticum aestivum L.) cropping system by LI-8100 automated soil CO2 flux system, and soil dissolved organic carbon (DOC), soil microbial biomass carbon (MBC) were also measured during returning green, heading, jointing, filling and mature stages during the wheat growing period Six fertilization practices arranged as a block with 3 replicates from the long\|term experiment were selected, which consists of fallow (F), control (CK), farm yard manure (M, 75 t?hm-2), nitrogen (N, 120 kg?hm-2), nitrogen and phosphorus (NP, 120 kg N?hm-2, 39 kg P?hm-2 ), and nitrogen and phosphorus plus farm yard manure (NPM, 120 kg N?hm-2, 39 kg P?hm-2, 75t ?hm-2 ). The soil CO2 flux showed significant diurnal changes and seasonal changes. For the diurnal changes, the soil CO2 flux rate followed a single peak curve with time, and the maximum of soil respiration appeared about at 12:00 or 14:30, and the minimums between 0:00 to 3:00 or about 6:00. Fertilization significantly increased soil CO2 flux rate, and the order of CO2 flux rate under different fertilizations followed as NPM > M > NP > N > CK > F. For the seasonal changes, the soil CO2 flux rate was highest during the jointing stage, followed by late filling stage, and minimum rate appeared during heading stage. Soil water deficit contributed to most of reduction of soil CO2 flux rate during heading and filling stage. Fertilization significantly affect MBC and DOC, there were significant seasonal changes in DOC and MBC. For DOC, the order was filling stage > heading stage > mature stage> turning green stage > jointing stage in all treatments. For MBC, the order followed as mature stage > heading stage > filling stage > jointing stage > returning green stage, and except manure treatments (M, NPM), MBC in jointing stage was more than in filling stage in all treatments. The relationships between DOC, MBC and soil CO2 flux rate under different growth stages was low under the condition of same fertilization, on contrast, the relationships between DOC, MBC and soil respiration rate were significant under different fertilizations. Soil respiration measurement using the root-exclusion technique indicated that fertilization enhance root respiration. Averaged cross the growing stages, the contribution of the root respiration to soil respiration in CK, N and NP treatment, were 36%, 45% and 54%, respectively.

LIU Wenxin,LUAN Zhaokun,TANG Hongxiao,<br>,,汤鸿霄
生态学报 , 1999,
Abstract: As the quantitative diagnostic tools,the toxic response factor ( E i r ) and the potential ecological risk index ( RI ) were used to evaluate the contamination situation of various heavy metals in sediments of the Le An River.As a result,the distribution of pollutants in the river sediments were divided into four sections with different ecological risk characteristics.On the whole,the assessing results by RI were consistent with that by I geo ,and they could complement each other.
Evapotranspiration of winter wheat field on Loess Plateau tableland

GAN Zhuoting,LIU Wenzhao,<br>甘卓亭,
应用生态学报 , 2006,
Abstract: This paper measured the evapotranspiration (ET) rate of a winter wheat field on the Loess Plateau tableland by using large-scale weighing lysimeter, and analyzed the effects of wheat leaf area index (LAI) , soil water content, air temperature, and rainfall on the ET at the time scales of growth stage, month, day, and hour. The results showed that the mean daily ET rate in different growth stages was in the order of booting-heading > flowering > erecting > jointing > filling > reviving > ripening > overwintering. Air temperature had a larger effect in initial stage, LAI was in mid stage, and soil water content was in last stage in the experimental year. The mean daily ET rate was markedly decreased from 6.25 mmn x d(-1) at booting-heading stage to 2.66 mm x d(-1) at grain-filling stage due to soil water deficit. The monthly ET rate in April, May and June was higher than that in other months, and the ET amount of the three months accounted for 80% of the total during the experimental period. The apices of daily ET curve mainly reflected the effects of rainfall, and the hourly ET process basically reflected the ET changes with weather conditions.
Effect of cutting spring wheat roots on the photosynthesis and the water use efficiency

DONG Gui-Ju,LIU Wen-Zhao,<br>董桂菊,
中国生态农业学报 , 2004,
Abstract: The treatment of cutting the spring wheat roots in pot experiment shows that injuring the spring wheat roots moderately in early time can boost the photosynthetic rate and promote the accumulation of the photosynthetic production, improve the water use efficiency (WUE) of spring wheat leaves, and finally increase the grain yield. However, injuring the spring wheat roots in the time of stem elonging mostly restrains the growth of the spring wheat, and the yield is decreased.
Analyzing Variation Trends in Extreme Precipitation Events in the Jing River Watershed during 1965-2005

LI Zhi,LIU Wenzhao,ZHENG Fenli,<br>李 志,,郑粉莉
资源科学 , 2010,
Abstract: Extreme climate events often cause more damages to society and ecosystems than do simple shifts in the mean values, and the impacts of extreme precipitation events are one of the most critical reasons causing severe soil and water loss over the Loess Plateau. Therefore, variations trends in extreme precipitation events need to be reasonably assessed, which can provide meaningful information on regional ecological conservation. The authors performed a study on the Jing River watershed using daily precipitation data from 18 meteorological stations during 1965-2005. Extreme precipitation events were defined in terms of percentile values. Indices, such as amount, frequency, intensity and severe drought frequency, were used to quantify the extreme precipitation events. The Mann-Kendall test and wavelet analysis method were employed to analyze the monotonic trend, abrupt change, interdecadal change and the period of each index. Results showed that the mean annual amount of extreme precipitation events was 143.9 mm/a, accounting for 27% of the total amount of annual precipitation. The mean annual frequency, intensity and maximum daily amount of extreme precipitation events were 3.6 d/a, 39.8 mm/d and 52.3 mm/d, respectively; while the mean annual frequency of severe drought was 7.4 times/a. Most stations in the Jing River watershed had no significant monotonic trend in each selected index of extreme precipitation events; however, the frequency and intensity of extreme precipitation events tended to increase. Furthermore, the variation trends in extreme precipitation events exhibited spatial variability, which might be caused by the integrated effects of terrain, meteorological conditions and global warming. Specifically, there was a positive trend in extreme precipitation events in the middle and lower reaches of the river that was generally in line with the dominant change trends; while a negative trend in extreme precipitation events in the southwestern and northern watershed was detected, which was opposite to the dominant change trend. Each index was fluctuating during 1965-2005; however, they all increased since 1985 and showed several abrupt changes around the year 2000. The oscillating periods of all indices were found to be 2-3 a, 7-8 a, 13 a and 17 a. Though the annual precipitation amount had a slightly downward trend, each index of extreme precipitation events showed an insignificant upward trend. Therefore, the changes in extreme precipitation events should be paid more attention compared with annual precipitation amount due to potential catastrophic damages resulting from extreme precipitation events to water and soil loss. The findings of this study implied that extreme precipitation events in future might cause more severe adverse influences on soil and water conservation in the Jing River watershed. Therefore, some adaption actions should be taken to mitigate the adverse effects of climate change on human and natural systems.
A New Iterative Estimator Method Based on Liu Estimator for Ill-Posed Equations

, 国林, 于胜<br>JIANG Zhaoying, LIU Guolin, YU Shengwen
- , 2017, DOI: 10.13203/j.whugis20150218
Abstract: 当线性回归模型的设计矩阵病态时,最小二乘(least square,LS)估值方差大且不稳定,已不是一种优良估计。为了减弱病态性,许多有偏估计法如岭估计、主成分估计、Liu估计等被提出。基于Liu估计,引入迭代的思想,提出了一种新的有偏估计法—迭代估计法。借助对称正定矩阵的谱分解,将迭代公式转化为便于解算的解析表达式,并证明迭代公式在修正因子d∈[-1,1]是收敛的。基于Liu估计中修正因子d的确定方法,在均方误差最小的情况下给出最优修正因子d的确定公式。最后,分别利用LS估计、岭估计、Liu估计和提出的迭代估计对两个算例进行计算并给出实验结果。在第一个算例中,对观测向量添加不同的扰动,结果表明迭代估计法具有更强的抗干扰能力;第二个算例的结果表明,迭代估计法所得结果更接近于真值,即迭代估计法在均方误差意义下优于LS估计、岭估计和Liu估计
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