Reduction of hydroelastic responses of a very-long floating structure by a floating oscillating-water-column breakwater system

The hydroelastic responses of a very-long floating structure (VLFS) placed behind a reverse T-shape freely floating breakwater with a built-in oscillating water column (OWC) chamber are analyzed in two dimensions. The Bernoulli–Euler beam equation is coupled with the equations of rigid and elastic motions of the breakwater and the VLFS. The interaction of waves between the floating rigid breakwater and the elastic VLFS is formulated in a consistent manner. It has been shown numerically that the structural deflections of the VLFS can be reduced significantly by a suitably designed reverse T-shape floating breakwater.     

Factors influencing the oxidation,reduction, methylation and demethylation of mercury species in coastal waters

The objective of this study was to examine the redox reactions and other transformations of mercury (Hg) species in surface waters, and the factors determining the rates of these reactions. For the redox studies completed at the Chesapeake Biological Laboratory (CBL), two isotopes (¹⁹⁹Hg^II and ²⁰²Hg⁰) were added into different types of filtered water (fresh to seawater) to examine the oxidation and reduction reactions. Further studies of both the redox reactions and methylation/demethylation reactions of Hg were conducted with unfiltered water on board research vessels during cruises in May and July 2005 on the Chesapeake Bay and shelf. While CH₃¹⁹⁹Hg^II was added to allow the examination of demethylation, ²⁰¹Hg^II was used to examine both reduction and methylation, and ²⁰²Hg⁰ was used to examine oxidation. Overall, the results showed that both Hg oxidation and reduction were simultaneously occurring and were photochemically mediated in the waters investigated. In contrast to the previously assumed “unreactive” nature of Hg⁰, the studies found that the magnitude of the rate constant for Hg⁰ oxidation was greater than that for reduction, indicating its importance in estuarine and coastal waters. In addition, both experiments at CBL and on board ship showed that Hg^II reduction was similar in magnitude, suggesting that biotic processes were relatively unimportant. While no measurable methylation occurred during the incubation period during the on board studies, concentration of CH₃¹⁹⁹Hg^II decreased over the time during the experiments. It appeared that the demethylation processes were not dominantly photochemically driven, but could be microbially mediated. Further studies are needed in order to help better understand Hg redox and transformations in natural water systems.     

Flood Damage Reduction Program (FDRP) in Québec: Case Study of the Chaudiére River

This study presents the evolution of agreements between the governments of Canadaand Québec on flood damage reduction. In Québec, the implementation of a regulation about building in floodplains came about in 1983–1984. Today, this regulation takes the form of a policy called ``Policy of shores, littoral and floodplain protection'. Municipalities must adopt rules that concur with the principles of this policy.The Chaudiére River basin was selected for analysis of urban developmentduring the period following the application of building rules in flood-risk areas.Despite the ban on building in the strong current zone (0–20 year return periodflood zone), many buildings, essentially residential, have been erected in thiszone. These new constructions generally account for a low percentage of thetotal property value in the 0–100 year flooding area, but are legal since theyare connected to a water and sewage network that existed prior to the officialfloodplain regulation.Flood damage along the Chaudiére River will tend to increase for two reasons.Firstly, while respecting the policy mentioned above, sites are still available infloodplains for future development. Secondly, no structural flood protection workshave been erected in view of the fact they are only marginally profitable from anbenefit-cost point of view.     

开展灾害学研究 保障人类生存与发展

灾害是人类面临的最严重的威胁。本文简要列述了各类灾害对国民经济建设和人类生存的危害性,论述了灾害的分类和体系特征,探讨了灾害形成的科学机理,强调了开展多学科、大体系研究的重要意义。同时结合国土环境遥感调查,提出了开展灾害学研究、监测防御、减灾抗祸的对策和建议,以期发挥现代地球科学理论与遥感技术的潜力,为促进灾害学的研究、保障人类更好地生存与发展作出贡献。     

地震自相似现象初探

依据破裂过程和震源物理参数相似性,给出了自相似震源椭球体三轴之比约为a:b:c=1:0.2:0.2。基于分维理论和方法,讨论了自相似的地震时空分布的分维和强震前的降维现象。由前兆展布范围,大震前区域地震活动特征以及地震空区等可导出近源前兆(红肿)区线性尺度约为震源区的5倍。     

黄铁矿与沥青铀矿的共生条件及在沥青铀矿形成过程中所起作用的实验研究

高价铁与高价铀混合溶液在还原场中形成了共生的黄铁矿与沥青铀矿,该过程必须在弱酸性-中性-碱性介质中进行,其中在弱酸性至中性介质中易形成大的黄铁矿单晶。高价铀溶液流经黄铁矿矿区时,若在高温高压条件下,有新生的黄铁矿或白铁矿与沥青铀矿共生。黄铁矿还原六价铀形成沥青铀矿时,起还原作用的是二价硫。赤铁矿常与沥青铀矿共生,但它们是热液演化过程中不同阶段的产物,赤铁矿形成于体系氧逸度高的氧化环境,沥青铀矿形成于体系氧逸度低的还原环境,赤铁矿形成于沥青铀矿之前。     

Performance of surface footing on geocell-reinforced soft clay beds

This paper presents the results of laboratory model tests carried out to develop an understanding of the behaviour of geocell-reinforced soft clay foundations under circular loading. Natural silty clay was used in this study. The geocells were prepared using biaxial polymer grid. The performance of the reinforced bed is quantified using non-dimensional factors i.e., Bearing capacity improvement factor (I_f) and Percentage reduction in footing settlement (PRS). The test results demonstrate that the geocell mattress redistributes the footing load over a wider area thereby improving the performance of the footing. The load carrying capacity of the clay bed is increased by a factor of up to about 4.5 times that of unreinforced bed. From the pressure-settlement responses, it is observed that the geocell-reinforced foundation bed behaves as a much stiffer system compared to the unreinforced case indicating that a substantial reduction in footing settlement can be achieved by providing geocell reinforcement in the soft clay bed. The maximum reduction in footing settlement obtained with the provision of geocell mattress of optimum size placed close to the footing is around 90%. Further improvement in performance is obtained with provision of an additional planar geogrid layer at the base of the geocell mattress.     

Geoid, topography, and the Bouguer plate or shell

 Topography plays an important role in solving many geodetic and geophysical problems. In the evaluation of a topographical effect, a planar model, a spherical model or an even more sophisticated model can be used. In most applications, the planar model is considered appropriate: recall the evaluation of gravity reductions of the free-air, Poincaré–Prey or Bouguer kind. For some applications, such as the evaluation of topographical effects in gravimetric geoid computations, it is preferable or even necessary to use at least the spherical model of topography. In modelling the topographical effect, the bulk of the effect comes from the Bouguer plate, in the case of the planar model, or from the Bouguer shell, in the case of the spherical model. The difference between the effects of the Bouguer plate and the Bouguer shell is studied, while the effect of the rest of topography, the terrain, is discussed elsewhere. It is argued that the classical Bouguer plate gravity reduction should be considered as a mathematical construction with unclear physical meaning. It is shown that if the reduction is understood to be reducing observed gravity onto the geoid through the Bouguer plate/shell then both models give practically identical answers, as associated with Poincaré's and Prey's work. It is shown why only the spherical model should be used in the evaluation of topographical effects in the Stokes–Helmert solution of Stokes' boundary-value problem. The reason for this is that the Bouguer plate model does not allow for a physically acceptable condensation scheme for the topography. Received: 24 December 1999 / Accepted: 11 December 2000     

逐步逼近曲化平方法研究

位场资料的常规处理解释方法是建立在平面数据理论之上的，然而实际的位场数据大多为曲面数据，若把曲面数据当成平面数据进行处理，必然导致很大的误差，因此有必要进行“曲化平”处理. 曲化平目前存在的主要问题是计算精度低、计算量大，因此，研究快速、精度高且适合大数据量处理的曲化平方法具有重要的价值. 本文在已有的泰勒级数曲化平方法基础上提出了逐步逼近技术和平均平面技术，使得曲面位场资料处理的精度得到了很大提高. 最后通过理论模型和实际资料的处理验证了该方法的应用效果.     

Oxidation of copper(I) in seawater at nanomolar levels

The oxidation and reduction of nanomolar levels of copper in air-saturated seawater and NaCl solutions has been measured as a function of pH (7.17–8.49), temperature (5–35 °C) and ionic strength (0.1–0.7 M). The oxidation rates were fitted to an equation valid at different pH and ionic strength conditions in sodium chloride and seawater solutions:

The reduction of Cu(II) was studied in both media for different initial concentrations of copper(II). When the initial Cu(II) concentration was 200 nM, the copper(I) productions were 20% and 9% for NaCl and seawater, respectively. The effect of speciation of copper(I) reduced from Cu(II) on the rates was studied. The Cu(I) speciation is dominated by the CuCl₂⁻ species. On the other hand, the neutral chloride CuCl species dominates the Cu(I) oxidation in the range of 0.1 M to 0.7 M chloride concentrations.