旱地长期定位施肥对冬麦水分利用的影响研究

本文在长期定位施肥试验基础上研究了黄土高原旱地不同施肥条件下冬小麦对水分的利用。结果表明 :旱地不同施肥连续 15年种植冬小麦后对土壤剖面含水量影响显著 ,施N或NP配合处理与CK和单施P处理剖面含水量差异均达显著或极显著水平 ,冬小麦对土壤储水的利用深度超过 2 0 0cm ,最大施肥处理N180kg/hm2 P2 O5180kg/hm2 小麦收获后 0～ 40 0cm剖面储水量比CK少 173 .89mm ,高N肥投入产量与生育年降水量显著相关 ,旱地土壤深层储水利用有很大的抗旱增产潜力

杉木人工林林地土壤呼吸研究

采用CID-301PS光合测定仪,对20年生杉木人工林林地土壤的CO2排放动态进行了观测,结果表明,杉木林地土壤呼吸速率表现出明显的季节和日变化规律。其季节变化规律为:从1~7月份随温度呈上升的趋势,在7月达年呼吸速率(CO2)的最大值,为1.466μmol/(m2.s),8~12月呈逐渐递减的趋势,并且季节变化明显;日变化规律呈现出单峰曲线,最高峰出现在16:00~18:00。分析了林地土壤呼吸速率与环境因子的关系,指出林地土壤呼吸速率与进入土壤呼吸室的CO2浓度呈显著负相关,说明空气中CO2浓度的升高,将在一定程度上抑制土壤呼吸。同时得出杉木林地土壤呼吸速率与地下5cm温度呈显著正相关,建立了土壤呼吸速率与温度的回归方程,计算出杉木林地土壤的年呼吸量(CO2)为10.517t/(hm2.a)。

沈阳市庭院绿地的结构特征与异质性分析

对沈阳城区庭院绿地的景观结构和格局进行了分析.结果表明,沈阳城市庭院绿地景观斑块以居住区最多,占研究区庭院总数的322%,但绿地面积只占195%.各类庭院占地平均为404hm2,庭院绿地面积平均为093hm2,绿地率为23%.研究区内627%的庭院绿地率在15%以下,绿地率达到30%以上的庭院仅占总数的133%.庭院绿地以微型斑块为主,占庭院总数的70%以上.景观多样性指数以居住区绿地最高,而医院和部队绿地最低.在7个城区中不同庭院绿地类型的优势度差异较大,尤其是于洪区的工厂绿地优势度是和平区的3123倍.各区庭院绿地均匀度指数变化幅度较大,其中居住区绿地的均匀度指数最大,部队绿地最小.居住区绿地斑块破碎化程度最大,部队绿地最小;老城区较新城区破碎化程度严重,其中沈河区破碎化程度最重.

生态足迹方法及研究进展

本文介绍了生态足迹的计算方法,回顾了国内外的研究进展,重点介绍了生态足迹计算中能源足迹算法的研究进展。目前,国外对生态足迹的研究集中在对长时间序列计算分析和计算方法的改进上,提出了改进的生态足迹方法“实际土地需求”法;国内研究还多限于生态足迹实例计算分析。探讨了生态足迹方法的优缺点,同时就生态足迹今后的研究重点提出一些看法和展望。

SHACAL-2算法的差分故障攻击

该文采用面向字的随机故障模型,结合差分分析技术,评估了SHACAL-2算法对差分故障攻击的安全性。结果显示:SHACAL-2算法对差分故障攻击是不免疫的。恢复出32 bit子密钥的平均复杂度为8个错误密文,完全恢复出512 bit密钥的复杂度为128个错误密文。

东北地区大豆鼓粒期光合特性的研究

用LI-6400光合测定系统对东北地区大豆鼓粒期叶片光合速率对光合有效辐射通量密度的响应特征和晴天光合速率、光能利用率、水分利用率等特性的日变化规律进行了研究。结果表明,光合速率对光合有效辐射通量密度的响应特征遵循Michaelis-Menten方程,在自然光条件下,上下两层叶片综合考虑,最大光合速率平均为37.25μmolm-2s-1,表观初始量子效率平均为0.0376。在晴天,光合速率、蒸腾速率、气孔导度以及光合有效辐射通量密度、环境温度随时间的变化可以用正弦函数模拟,但其峰值出现的时间不同,光合速率

The regional types of China's floating population: Identification methods and spatial patterns

With the rapid increase of the number and influence of floating population in China, it is urgently needed to understand the regional types of China's floating population and their spatial characteristics. After reviewing the current methods for identifying regional types of floating population, this paper puts forward a new composite-index identification method and its modification version which is consisted of two indexes of the net migration rate and gross migration rate. Then, the traditional single-index and the new composite-index identification methods are empirically tested to explore their spatial patterns and characteristics by using China's 2000 census data at county level. The results show: (1) The composite-index identification method is much better than traditional single-index method because it can measure the migration direction and scale of floating simultaneously, and in particular it can identify the unique regional types of floating population with large scale of immigration and emigration. (2) The modified composite-index identification method, by using the share of a region's certain type of floating population to the total in China as weights, can effectively correct the over- or under-estimated errors due to the rather large or small total population of a region. (3) The spatial patterns of different regional types of China's floating population are closely related to the regional differentiation of their natural environment, population density and socio-economic development level. The three active regional types of floating population are mainly located in the eastern part of China with lower elevation, more than 800 mm precipitation, rather higher population densities and economic development levels.

Effects of cerium on the microstructure and mechanical properties of Mg–20Zn–8Al alloy

Mg-20Zn-8Al-xCe(x=0-2 wt.%) alloys were prepared by metal mould casting method, the effects of Ce on the microstructure and mechanical properties of the alloys were investigated. The results showed that the dendrite as well as gram size were refined by the addition of Ce, and the best refinement was obtained in 1.39% Ce containing alloy.

Reversed micelle formation in a model liquid-liquid extraction system

The formation of reversed micelles and the roles of extractant and extracted complexes were investigated in the Cyanex923/n-heptane/H2SO4 system. Interfacial tension (gamma), electrical conductivity (kappa), and water content measurements showed that Cyanex923 had a tendency to self-assemble, forming reversed micelles. The changes in electrical conductivity with concentration of H2SO4 in the organic phase (CH2SO4,(0)) exhibited an S-type curve: a correlation was found between the change in electrical conductivity and the water content as a function of CH2SO4,(0),.

Thermoluminescence characteristics of NaSr4(BO3)(3):Ce3+ under beta-ray irradiation

The thermoluminescence (TL) properties of Ce3+ doped NaSr4(BO3)(3) phosphor under the beta-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL glow curve of NaSr4(BO3)(3):Ce3+ phosphor was composed of only one peak. TL kinetic parameters of NaSr4(BO3)(3):Ce3+ were deduced by the peak shape method, the activation energy (E) was 0.590 eV and the frequency factor was 1.008x10(6) s(-1). TL dose response was linear in the range of measurement. The 3-dimensional (3D) TL emission spectrum was also recorded, the emission spectrum consisted of two bands located at 441 and 479 nm respectively, corresponding to the characteristic 4f(0)5d(1)-> F-2((5/2,7/2)) transitions of the Ce3+ ion. The fading behavior of the NaSr4(BO3)(3):Ce3+ phosphor over a period of 15 d was also studied.

Effect of yttrium-rich misch metal on the microstructures, mechanical properties and corrosion behavior of die cast AZ91 alloy

Die cast AZ91-xYmm (x = 0-0.8 wt.%) magnesium alloys with excellent tensile properties and corrosion resistance behavior were successfully prepared by a simple addition of yttrium-rich misch metal (Ymm) to AZ91. Influences of Ymm on the microstructure, mechanical properties and corrosion behavior of AZ91 were investigated. The results showed that addition of Ymm to die cast AZ91 alloy could re. ne the microstructure including primary alpha-Mg and eutectic beta-Mg17Al12. When the content of Ymm reached 0.8 wt.% a small quantity of Al2Y phase would form. The tensile properties were improved greatly with addition of Ymm to AZ91. The creep rate of the AZ91-Ymm alloys, tested at 150 degrees C/50MPa, was one order of magnitude lower than that of AZ91. When addition of Ymm was more than 0.3 wt.%, the salt-spray corrosion resistance of AZ91-Ymm alloys could be 30-40 times of that of AZ91. The improvement of corrosion resistance with addition of Ymm was confirmed by the results of electrochemical polarization experiments. Mechanism of the improvement of mechanical properties and corrosion behavior caused by Ymm was also discussed.

Effects of cerium on the microstructure and mechanical properties of Mg-20Zn-8Al alloy

Mg-20Zn-8Al-xCe(x=0-2 wt.%) alloys were prepared by metal mould casting method, the effects of Ce on the microstructure and mechanical properties of the alloys were investigated. The results showed that the dendrite as well as gram size were refined by the addition of Ce, and the best refinement was obtained in 1.39% Ce containing alloy. The main phases in the as cast alloys were alpha-Mg and tau-Mg-32 (Al, Zn)(49), and Al4Ce phase was found in the alloys contained more than 1.39% Ce. The addition of Ce improved the mechanical properties of the alloys. The strengthening mechanism was attributed to grain refinement and compound reinforced.