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291.
Photorefractive properties of Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios have been investigated at 488 nm wavelength based on the two-wave coupling experiment. High diffraction efficiency and large recording sensitivity are observed and explained. The decrease in Li vacancies is suggested to be the main contributor to the increase in the photoconductivity and subsequently to the induction of the improvement of recording sensitivity. The saturation diffraction efficiency is measured up to 80.2%, and simultaneously the recording sensitivity of 0.91 cm/J is achieved to in the Hf:Fe:LiNbO3 crystal grown from the melt with the [Li]/[Nb] ratio of 1.20, which is significantly enhanced as compared with those of the Hf:Fe:LiNbO3 crystal with the [Li]/[Nb] ratio of 0.94 in melt under the same experimental conditions. Experimental results definitely show that increasing the [Li]/[Nb] ratio in crystal is an effective method for Hf:Fe:LiNbO3 crystal to improve its photorefractive properties. 相似文献
292.
This paper employs the highly accurate valence internally contracted multireference configuration interaction method to investigate the potential energy curves (PECs) for the ground state (X1Σ+) and two low-lying excited states (A1Π and D1Δ of phosphorus nitride (PN) radical with the correlation-consistent basis set, aug-cc-pV6Z, in the valence range. Relativistic effects are considered in these calculations. The spectroscopic constants of the X1Σ+ and A1Π states are calculated based on the PECs, and the results are in good accord with the available experimental data. The first 30 vibrational states for the A1Π state and the first 40 vibrational states for the A1Π state are determined when J=0. For each vibrational state, molecular constants G(υ), B(υ) and D(υ) are also attained. 相似文献
293.
腾格里沙漠东南缘人工固沙植被区表层土壤有机碳矿化对凋落物添加的响应 总被引:2,自引:2,他引:0
土壤有机碳矿化是调控土壤碳库时空格局、土壤碳收支平衡和植物养分供应的重要过程,植物残体和凋落物分解释放CO2直接影响着土壤有机碳矿化。研究了不同类型凋落物对腾格里沙漠东南缘建植于1956年的人工固沙植被区土壤有机碳矿化过程及其对水分和温度的响应特征。结果表明:凋落物添加显著促进了有机碳矿化,添加柠条锦鸡儿(Caragana korshinskii)、油蒿(Artemisia ordosica)、小画眉草(Eragrostis minor)凋落物后,CO2-C最大矿化速率分别增大了6.94、5.17、3.46倍,0~5 cm层土壤是5~10 cm层土壤的1.09、1.55、1.22倍;CO2-C累积释放量分别增加了3.73、3.38、2.34倍,0~5 cm层土壤是5~10 cm层土壤的1.17、1.30、1.57倍。凋落物对有机碳矿化的促进作用与温度和水分密切相关,25℃时,CO2-C平均释放速率、最大释放速率、累积碳释放量分别是10℃的2.21、3.60、2.21倍,而含水量10%时,CO2-C平均释放速率、最大释放速率和累积碳释放量分别是含水量5%时的1.25、1.20、1.25倍。相关性分析表明,凋落物碳氮含量、碳氮比、木质素比氮和土壤有机碳以及全氮是影响有机碳矿化的主要因子。凋落添加土壤后潜在可矿化碳表现为柠条锦鸡儿>油蒿>小画眉草>对照。凋落物添加显著促进了有机碳矿化过程及碳周转,植被恢复过程中草本植物凋落物的输入更有利于土壤碳固存,凋落物对土壤碳库的调控作用受土壤理化性质和水热等环境因子的共同作用影响。 相似文献
294.
为建立高时空分辨率的福建省复杂地形下气温栅格数据集,利用福建省及其周边33个常规气象站观测资料,基于数字高程模型(DEM)数据,综合考虑海拔、太阳总辐射、地表长波有效辐射对旬平均气温的影响,模拟了福建省复杂地形下旬均温的空间分布。结果表明:1)常规站验证结果显示:各旬气温绝对误差平均值(MAE)最小为0.46℃,最大为2.3℃,全年平均为0.87℃;加密站验证结果显示,MAE最大为2.3℃,最小0.5℃,全年平均为0.96℃。2)模拟结果能反映旬均温的宏观分布规律与局地细节特征。宏观范围内,旬均温受纬度影响较大,由北至南气温逐渐升高,沿海地区旬均温整体高于内陆,山区旬均温明显较低;局地范围内,各坡向上气温差异显著,海拔越高、坡度越大,差异越明显;地形因子对旬平均温的影响具有季节差异,具体表现为冬季时地形因子对旬均温的影响最大,秋季次之,春夏季节中地形因子对旬均温的影响最弱。 相似文献
295.
296.
潍坊市耕地资源动态变化及驱动力分析 总被引:1,自引:0,他引:1
潍坊市是国家重要的农副产品生产基地。近几年来,随着经济的发展,耕地资源迅速退化和流失,使得人口与耕地的矛盾日渐突出。通过对相关数据的分析,揭示了潍坊市自改革开放以来耕地资源的变化趋势。运用定性和定量的方法对耕地数量变化的驱动因子进行了分析;并结合潍坊市耕地资源利用的具体情况,提出保护耕地的对策与建议。 相似文献
297.
298.
Masahiko Fujii Fei Chai Lei Shi Hisayuki Y. Inoue Masao Ishii 《Journal of Oceanography》2009,65(5):689-701
The oceanic carbon cycle in the tropical-subtropical Pacific is strongly affected by various physical processes with different
temporal and spatial scales, yet the mechanisms that regulate air-sea CO2 flux are not fully understood due to the paucity of both measurement and modeling. Using a 3-D physical-biogeochemical model,
we simulate the partial pressure of CO2 in surface water (pCO2sea) and air-sea CO2 flux in the tropical and subtropical regions from 1990 to 2004. The model reproduces well the observed spatial differences
in physical and biogeochemical processes, such as: (1) relatively higher sea surface temperature (SST), and lower dissolved
inorganic carbon (DIC) and pCO2sea in the western than in the central tropical-subtropical Pacific, and (2) predominantly seasonal and interannual variations
in the subtropical and tropical Pacific, respectively. Our model results suggest a non-negligible contribution of the wind
variability to that of the air-sea CO2 flux in the central tropical Pacific, but the modeled contribution of 7% is much less than that from a previous modeling
study (30%; McKinley et al., 2004). While DIC increases in the entire region SST increases in the subtropical and western tropical Pacific but decreases
in the central tropical Pacific from 1990 to 2004. As a result, the interannual pCO2sea variability is different in different regions. The pCO2sea temporal variation is found to be primarily controlled by SST and DIC, although the role of salinity and total alkalinity,
both of which also control pCO2sea, need to be elucidated by long-term observations and eddy-permitting models for better estimation of the interannual variability
of air-sea CO2 flux. 相似文献
299.
The Luzon Strait is the only deep channel that connects the South China Sea(SCS) with the Pacific.The transport through the Luzon Strait is an important process influencing the circulation,heat and water budgets of the SCS.Early observations have suggested that water enters the SCS in winter but water inflow or outflow in summer is quite controversial.On the basis of hydrographic measurements from CTD along 120° E in the Luzon Strait during the period from September 18 to 20 in 2006,the characteristics of t... 相似文献
300.
Urban three-dimensional expansion and its driving forces —A case study of Shanghai, China 总被引:4,自引:1,他引:3
Longyu Shi Guofan Shao Shenghui Cui Xuanqi Li Tao Lin Kai Yin Jingzhu Zhao 《中国地理科学(英文版)》2009,19(4):291-298
Urban expansion is a phenomenon of urban space increase, and an important measuring index of the process of urbanization.
Taking Shanghai as an example, the changes of urban average height and built-up area were studied to represent city’s vertical
and horizontal increases respectively, and statistical methods were used to analyze the driving forces of urban expansion.
The research drew following conclusions: 1) The urban expansion process of Shanghai from 1985 to 2006 had a clear periodic
feature, and could be divided into three stages: vertical expansion in dominance, coordinated vertical and horizontal expansion,
and horizontal expansion in dominance. 2) The average height and quantity of buildings in core city were significantly bigger
than those in suburbs, but the changing speed of the latter was faster. And 3) urbanization process was the major driving
force for the city’s horizontal expansion, while industrial structure improvement was the key driving factor for the vertical
expansion. Those two driving forces were simultaneously affected by city’s political factors. 相似文献