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61.
Pasquale Crea Concetta De Stefano Demetrio Milea Silvio Sammartano 《Marine Chemistry》2008,112(3-4):142-148
The results of a potentiometric investigation (by ISE-H+, glass electrode) on the speciation of phytate ion (Phy12−) in an ionic medium simulating the major components (Na+, K+, Ca2+, Mg2+, Cl− and SO42−) of natural seawater, at different salinities and t = 25 °C, are reported. The work was particularly aimed at determining the possible formation of mixed Ca2+–Mg2+–phytate ion pairs, and to establish how including the formation of these mixed species would affect the speciation modeling in seawater media. After testing various speciation models, that considering the formation of the MgCaH3Phy5−, MgCaH4Phy4−, Mg2CaH3Phy3− and Mg2CaH4Phy2− species was accepted, and corresponding stability constants were determined at two salinities (S = 5, 10). A discussion is reported both on the choice of the experimental conditions and on the possibility to extend these results to those typical of real seawater. A detailed procedure is also described to demonstrate that the stability of these species is higher than that statistically predicted. As reported in literature, a parameter, namely log X, has been determined in order to quantify this extra stability for the formation of each mixed species at various salinities. For example, at S = 10, log X113 = 2.67 and log X114 = 1.37 for MgCaH3Phy5− and MgCaH4Phy4− (statistical value is log Xstat = 0.60), and log X213 = 6.11 and log X214 = 2.15 for Mg2CaH3Phy3− and Mg2CaH4Phy2− (log Xstat = 1.43), respectively. Results obtained also showed that the formation of these species may occur even in conditions of low salinity (i.e. low concentration of alkaline earth cations) and low pH (i.e., more protonated ligand). 相似文献
62.
We study the stability of motion in the 3-body Sitnikov problem, with the two equal mass primaries (m
1 = m
2 = 0.5) rotating in the x, y plane and vary the mass of the third particle, 0 ≤ m
3 < 10−3, placed initially on the z-axis. We begin by finding for the restricted problem (with m
3 = 0) an apparently infinite sequence of stability intervals on the z-axis, whose width grows and tends to a fixed non-zero value, as we move away from z = 0. We then estimate the extent of “islands” of bounded motion in x, y, z space about these intervals and show that it also increases as |z| grows. Turning to the so-called extended Sitnikov problem, where the third particle moves only along the z-axis, we find that, as m
3 increases, the domain of allowed motion grows significantly and chaotic regions in phase space appear through a series of
saddle-node bifurcations. Finally, we concentrate on the general 3-body problem and demonstrate that, for very small masses, m
3 ≈ 10−6, the “islands” of bounded motion about the z-axis stability intervals are larger than the ones for m
3 = 0. Furthermore, as m
3 increases, it is the regions of bounded motion closest to z = 0 that disappear first, while the ones further away “disperse” at larger m
3 values, thus providing further evidence of an increasing stability of the motion away from the plane of the two primaries,
as observed in the m
3 = 0 case. 相似文献
63.
2008年5月12日汶川发生里氏8.0级大地震,在灾区形成了30多个堰塞湖,严重威胁了下游人民群众的生命财产安全,引起了世人对堰塞湖坝体稳定的高度关注。本文在前人研究的基础上,从地形地貌、诱发原因、寿命三个方面总结了堰塞湖坝体形成及存在的机理。重点分析总结了目前堰塞湖坝体稳定性的研究进展,指出影响坝体稳定性的内因为堰塞坝的形态与规模、物质组成与结构,外因为堰塞湖湖水体积;总结了前人关于影响坝体稳定性的关键因素以及室内模型试验的研究成果。最后分析了目前研究存在的问题,展望了未来的研究方向。 相似文献
64.
ZHOU Ping WEN An-bang YAN Dong-chun SHI Zhong-lin GUO Jin JU Zhan-sheng ZHANG Yi-lan 《山地科学学报》2014,11(2):526-534
Soil erosion becomes a serious environmental problem in the world, especially in western China. An effective management practice called the Grain for Green Program (GGP), which was launched in 1999, aims to reduce soil and water loss and alleviate the ecological environment problem in western China. Two typical counties in western China, the Zhongxian (in Chongqing Municipality) and Ansai (in Shaanxi Province) were chosen to evaluate the dynamic changes of land use and agricultural production structure before and after the implementation of the Program in this paper. The results showed that the cultivated land area was reduced by 7.08% from 1989 to 2003. The cultivated land per person was decreased by 8.42% during 1999-2003. Moreover, the stability index of the secondary sector of the economy was increased from 0.91 in the period 1990-1999 to 0.94 in the following ten years. In addition, the stability index of tertiary economic sector increased from 0.88 to 0.92 in Zhongxian county. Meanwhile, the cultivated land area was reduced by 15.48% from 1990 to 1999. The soil erosion modulus was decreased by 33.33% from 1999 to 2006. Also, the stability index of secondary and tertiary economic sectors was 0.86 in the period 1998-2002. However, it decreased by 77% during 2002 to 2007 in Ansai County. These results imply that the Grain for Green Program had different impact on the two regions. Several effective strategies of soil and water conservation have been carried out to ameliorate the sustainable development of ecological environment and economy in these two counties of western China. 相似文献
65.
西北太平洋海域风浪、涌浪、混合浪波浪能资源特征 总被引:1,自引:0,他引:1
用ECMWF的ERA-40海浪再分析资料,应用波浪能流密度计算方法,对西北太平洋海域的风浪能、涌浪能、混合浪能展开研究。结果表明:(1)波浪能流密度呈现出显著季节性差异。混合浪能流密度表现为冬高夏低;春、夏、秋季的涌浪能流密度明显大于风浪能流密度,冬季相反;(2)混合浪能流密度的大值区主要分布于阿留申群岛附近海域,高值中心可达60 kW/m以上;近海的大值区主要分布于琉球群岛—巴士海峡—传统的南海大风区一带,年平均值在4 kW/m以上,南海北部可达12 kW/m以上;(3)黄渤海的涌浪和混合浪能流密度峰值出现在8—9月,波谷出现在6月。风浪能流密度峰值出现在11月—次年3月,波谷出现在6—8月,均呈现双峰型月变化特征。东海、南海北部、南海中南部海域能流密度的月变化特征相似,都为双峰型,12月—次年4月的能流密度整体较高,波峰出现在12月,波谷出现在5—7月;(4)2 kW/m以上混合浪能流密度出现的频率较高,近海低于大洋;(5)0.5 m以上有效波高出现的频率都非常高,中国近海稍低于大洋;(6)涌浪能流密度的稳定性明显好于风浪能流密度;大洋的能流密度稳定性明显强于近岸。1月份能流密度的稳定性最好,4月和7月次之,10月的稳定性最差。 相似文献
66.
南京南郊大气湍流统计特征的实验研究 总被引:2,自引:1,他引:1
利用2011年8月南京南郊溧水大气边界层加强实验站的大气湍流观测资料,分析了城市郊区自然状态下垫面大气湍流宏观统计规律,以及湍流动量、热量、水汽和CO2的湍流输送特征。结果表明:不稳定层结下,3方向风速归一化标准差σu/u*,σv/u*,σw/u*,随稳定度参数ζ呈1/3幂次关系;稳定层结下也呈现类似规律;近中性条件下,分别趋近于常数。不稳定层结下,温度、比湿、CO2质量浓度归一化标准差σT/|T*|,σq/|q*|,σρCO2/|ρCO2*|,随ζ呈1/3幂次负相关关系,但结果相对离散,并且相对离散的数据对应着较小的|T*|、|q*|、|ρCO2*|值;稳定层结下,三者ζ之间的关系没有明显变化规律。实验期间相对于感热通量,潜热通量在热量平衡中所占比例较大;CO2通量平均值为负,整体表现为碳汇。水汽、热量和CO2均存在水平输送。 相似文献
67.
地下采煤通常会引起地表严重开裂,甚至发生滑坡、崩塌等地质灾害,采动坡体的稳定性研究一直是工程实际关心的问题。本文以贵州省都匀市煤洞坡采动坡体为例,在斜坡破坏机制分析基础上,采用组合楔形块体原理构建了采动坡体稳定性系数计算方程,并从实验、经验类比、采空率等方面对采动坡体的强度指标进行了综合取值,计算了采动坡体在天然、饱水及裂隙水作用下的安全系数。结果表明:煤洞坡山体是处于稳定状态的,这与坡体上的裂缝位移监测成果是相符的。但在长时间降雨或暴雨情况下,煤洞坡山体稳定性就会逐渐变差,甚至发生滑动; 坡体稳定性安全系数随内摩擦角的降低而降低,随裂隙水充水高度的增加而降低; 一旦后缘块体挤压前缘块体时,就会存在一个安全系数急剧降低的阀值。从裂缝水柱高度与降雨渗入裂缝的雨水量关系出发,建立了裂缝水柱高与降雨量之间关系式。经计算当降雨量(短时间内)超过192mm,斜坡就会失稳。 相似文献
68.
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
69.
E. A. Perdios 《Celestial Mechanics and Dynamical Astronomy》2007,99(2):85-104
This paper deals with the Sitnikov family of straight-line motions of the circular restricted three-body problem, viewed as
generator of families of three-dimensional periodic orbits. We study the linear stability of the family, determine several
new critical orbits at which families of three dimensional periodic orbits of the same or double period bifurcate and present
an extensive numerical exploration of the bifurcating families. In the case of the same period bifurcations, 44 families are
determined. All these families are computed for equal as well as for nearly equal primaries (μ = 0.5, μ = 0.4995). Some of the bifurcating families are determined for all values of the mass parameter μ for which they exist. Examples of families of three dimensional periodic orbits bifurcating from the Sitnikov family at double
period bifurcations are also given. These are the only families of three-dimensional periodic orbits presented in the paper
which do not terminate with coplanar orbits and some of them contain stable parts. By contrast, all families bifurcating at
single-period bifurcations consist entirely of unstable orbits and terminate with coplanar orbits. 相似文献
70.
陈以良 《广东海洋大学学报》1991,(2)
溶胶的电动电位是溶胶发生电动现象的主要原因,它的大小直接影响溶胶的稳定性。本文采用界面移动法研究了溶胶的浓度,电极的种类以及不同的辅助液和硫化锑溶胶的电动电位之间的关系。 相似文献