The arrangement in mean elements space of the periodic orbits close to that of the Moon

In a simplified model of the Earth-Moon-Sun system based on the restricted circular 3-dimensional 3-body problem, it is possible to find numerically a set of 8 periodic orbits whose time evolutions closely resemble that of the Moon's orbit. These orbits have a period of 223 synodic months (i.e. the period of the Saros cycle known for more than two millennia as a means of predicting eclipses), and are characterized by a secular rotation of the argument of perigee . Periodic orbits of longer durations exhibiting this last feature are very abundant in Earth-Moon-Sun dynamical models. Their arrangement in the space of the mean orbital elements- for various values of the lunar mean motion is presented.     

黄河影响下开封城市的历史演变

河流对城市的形成和发展起着重要的作用,古人形象地把其比喻为“城市之血脉”。文章从不同的历史时期黄河及其分支对开封城市演变的影响进行分析,得出黄河与开封城市的关系存在着利与害的统一。开封城市的历史发展,即得益于黄河充足的水源,又受害于其频繁的决溢、泛滥、改道。因此,要采用先进的科学技术对黄河进行综合治理开发,使其恢复它应有的美好环境,更好地造福于人民。     

Selenium contamination in the Colorado River Basin, western USA： Remediation by leaching and nanof＇dtration membranes

Selenium （Se） is an essential micronutrient to biota, but can become a potent toxicant at elevated concentrations. The natural sources and chemical properties of Se species make the boundary between deficiency and toxicity narrow for some biota, with both phenomena common around the globe. Large areas of farmland in the Colorado River Basin （CRB） generate salinized drainage water with Se concentrations much higher than 5 μg/L, the U.S. Environmental Protection Agency chronic water-quality criterion for the protection of aquatic life. We have carried out detailed field and laboratory studies to investigate Se geochemistry and remediation in two of these areas： the Middle Green River Basin, Utah and the Salton Sea Basin, California, located respectively in the Upper and Lower CRB. Results from these and other studies show that approximately 90% of the dissolved Se in the Colorado River and its tributaries originally is derived from the Upper Cretaceous Mancos Shale and equivalent pyritic marine units that outcrop in the Upper CRB. Selenium is mobilized commonly by biogeochemical oxidation of this pyritic shale and is concentrated mainly as selenate （SeO4^2-） in soils and agricultural drainage water of dry climates by evaporation. Minor （0%-5%） amounts of Se are present as the selenite species （HSeO3^-） and （SEO3^2-）, but these species and the more reduced species, elemental Se （SeO） and selenide （Se^2-）, have much lower solubility and/or have high sorptive affinity towards organic matter, clay minerals and iron oxyhydroxides. The concentration of dissolved Se （-2.5 μg/L） and salinity in the Lower Colorado River water are among the highest of the world major rivers. Because of low precipitation （7 cm/a） and extreme evapotranspiration （-1.8 m/a） rates in the Salton Sea Basin, California, Se values in irrigation water imported from the Colorado River increase to 〉300 μg/L in drainage wastewater. Removal of Se from contaminated wastewater by nanofiltration membranes was demonstrated in laboratory and pilot-scale field experiments.     

Damage Survey of Water Supply Systems and Fragility Curve of PVC Water Pipelines in the Chi–Chi Taiwan Earthquake

Substantial damage to water supply systems, including water delivery pipelines, water treatment plants, reservoirs, and water storage tanks, was reported after the 1999 Chi–Chi Taiwan Earthquake. This paper first summarizes the damage survey and then presents the results of seismic fragility analysis for underground pipelines. Construction blueprints of the water delivery pipelines and repair work orders of 11 townships and cities in the disastrous area were digitized into a Geographical Information System (GIS) for analysis and assessment. With the aid of the GIS system, we found that PVC pipes made up 86% of water delivery pipelines while steel, cast iron, ductile iron, PE and others took the rest. Therefore, this paper focuses on the fragility analysis of PVC pipes. Three different methods were applied to derive the fragility relations between the PVC water pipes having nominal diameters (approximately inner diameters) greater than or equal to 65 mm and earthquake intensity parameters such as peak ground acceleration and peak ground velocity. The results were then examined with those of other countries. The discrepancy between our results and the empirical equation used by HAZUS, an earthquake loss estimation software developed by the Federal Emergency Management Agency was not significant.     

Karst groundwater protection in the Kupa River catchment area and sustainable development

One of the most significant water resources in the Republic of Croatia is the catchment area of the Kupa River, located in the region bordering the Republic of Slovenia. About 88% of the total amount of water in this catchment originates in Croatia and just 12% from Slovenia; therefore, the largest part of the catchment area (about 1000 km²) is on the Croatian side of the border. It is a typical karst area of the Dinarides with aquifers characterized by a relatively rapid water exchange, high groundwater flow velocities and aquifers open to human impact from the surface. Consequently, the aquifers are highly vulnerable and at risk. Due to the availability of large quantities of high-quality spring water (about 6 m³/s), the entire area has a strategic importance within the context of any future development strategy pertaining to the western part of Croatia. The catchment area on the Croatian side was investigated using a wide range of research methods that included a classical hydrogeological approach, the detailed hydrologic calculation of water balance to the hydrogeochemical analyses and modelling. The objective was to determine protection zones and protection measures for the whole area. The difficulties are increased due to the fact that the karst catchment area is crossed by major traffic corridors, oil pipelines and a railway and that many settlements and a highly developed wood industry are present. The combination of protecting water resources with adequate prevention measures and necessary remedial activities that should satisfy the very strict requirements necessary for the protection of the karst aquifers while still allowing for present and future human activities is difficult – but not impossible – to achieve. One good example is the present highway with a closed dewatering system and waste water treatment before the water passes into the karst underground system.     

A heuristic model for potential geomorphic influences on trophic interactions in streams

Whereas certain linkages between stream channel morphology and stream ecology are fairly well-understood, how geomorphology influences trophic interactions remains largely unknown. As a first step, a simple, heuristic model is developed that couples reach-scale geomorphic morphology with trophic dynamics between vegetation, detritus, herbivores, and predators. Predation is assumed to increase with depth beyond a threshold depth, and herbivory is assumed to decrease with velocity beyond a threshold velocity. Results show that the modeled food chain is sensitive to channel geometry, particularly around the threshold conditions for predators and herbivores. Importantly, geomorphic influences are not isolated to a particular trophic level, but rather are transferred through the food chain via top-down and bottom-up effects. The modeled system is particularly sensitive to changes in the end-members of the food chain: vegetation and predators. Results illustrate that geomorphic disturbances, known to affect a single trophic level (e.g., fish), likely impact multiple trophic levels in the stream ecosystem via trophic interactions. Such impacts at the multiple trophic level are poorly understood. While limited by the lack of empirical long-term data for testing and calibration, this simple model provides a structure for generating hypotheses, collecting targeted data, and assessing the potential impacts of stream disturbance or restoration on entire stream ecosystems. Further, the model illustrates the potential for future coupled stream models to explore spatial and temporal linkages.     

Ammonium regeneration in intertidal sediments of the Yangtze estuary during air-exposure

The influences of exposure to the atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with a geochemical approach at a typical station in the Yangtze Estuary during three tidal cycles in September 2003. During an about 8-h emersion period of each diurnal tide, six high-resolution vertical profiles of adsorbed and dissolved ammonium were measured. It was observed that both adsorbed and dissolved ammonium generally had an increasing trend in sediment cores during the exposure. The rate of ammonium regeneration in sediments was estimated using the accumulation amount of ammonium including adsorbed and soluble fractions during the daytime emersion. The calculation result showed that there was relatively high ammonification rate (˜500 nmol N cm⁻³ day⁻¹), which reflected that organic nitrogen in sediments was quickly decomposed with a residence time of ˜52.7 days. Due to the dramatic temperature difference observed in sediment profiles, free convection was considered an important mechanism of regulating the efflux of produced ammonium into overlying waters. The total estimated amount of regenerated ammonium was ˜1.35×10⁵ t N year⁻¹ in the intertidal flat of the Yangtze Estuary, which occupied 7.6% of the total inorganic nitrogen annually transported to the estuarine ecosystem.     

玛纳斯河一级电站引水渠沿线提取地下水进行融冰的可行性研究

通过对向斜洼地含水层水文地质特征的勘探及研究,对研究区的水文地质边界条件进行了概化,并用水均衡法估算了地下水资源量,对拟建一级电站引水渠沿线提取地下水进行融冰的可行性进行了研究,并提出了取水方案.     

Atmospheric Surface-Layer Processes During the Total Solar Eclipse Of 11 August 1999

The central path of the total solar eclipse (TSE) of 11 August 1999 mostly passedthrough a region of active monsoon in India, with the eclipse ending around localsunset. Measurements in the surface layer (SL) were carried out close to the eclipseaxis at Akola (20°42' N, 77°2' E) in central India. The globalradiation flux reaching the surface vanishes around totality at 1803:24 (LT), followedby a small recovery before again dipping to zero at sunset. The temperatures in the SL, and subsoil at 50-mm depth, show a local minimum with a lag of about 10 min after the second contact, whereas the lag appears to vanish when the temperature series is detrended. The SL exhibits near-neutral, though generally stable, conditions from about 1500 hr itself due to heavy cloud cover followed by the eclipse-induced cooling of the surface. The wind component across the eclipse axis vanishes at totality, the wind vector aligning with the azimuth of the traversing moon shadow. The deceleration of the mean flow can be due to the combined effect of the colder surface and downward heat flux, where the locally altered horizontal temperature gradients may cause, as in this instance, the cessation of the cross flow.The oscillations in temperature and wind that show significant peaks, around 90–100 min as well as the semi-period of the eclipse near 60 min, persist for several hours past the eclipse event. A fresh analysis of the published data on the TSE of 7 March 1970 shows spectral peaks in the temperature nearly coincident with those already reported from the surface pressure records. The oscillations in the SL fields during the two TSE events are very similar implying that the source mechanism is also likely to be the same in both the cases.     

长江巨洪前期物理因子的配置

提出了长江巨洪前期物理因子配置的概念，在每一次巨洪发生之前，影响巨洪的主要物理因子之间一般都会表现出相似的特征，即出现一些固有的配置，这些配置正是长江发生巨洪的强信号，对长江巨洪的预测研究具有重要的指示作用。