Assessing vegetation dynamics and their relationships with climatic variability in Heilongjiang province, northeast China

In this study, the vegetation dynamics in Heilongjiang province and their relationships with climate variability were assessed using normalized difference vegetation index (NDVI) and meteorological datasets from 1981 to 2003. The conclusions from our results are as follows: (1) After 1981, vegetation cover, as indicated by the NDVI, exhibited an insignificant increasing tendency. However, the inter-annual variations of the NDVI showed apparent spatial differentiations. (2) The inter-annual changes of the NDVI were different from season to season. The spring and autumn NDVI values increased, while the summer and winter NDVI decreased. (3) The annual NDVI was significantly correlated with precipitation. Thus, as compared to temperature, precipitation was the dominant climatic factor affecting the vegetation dynamics in Heilongjiang province. (4) The trend in the NDVI showed a marked homogeneity corresponding to regional and seasonal variations in climate. Additionally, land use changes also play an important role in influencing the NDVI trends over some regions. All of these findings will enrich our knowledge of the natural forces that impact the stability of boreal ecosystems and provide a scientific basis for the environmental management in Heilongjiang province in response to climate change and human activities.     

Prediction of Floor Water Inrush: The Application of GIS-Based AHP Vulnerable Index Method to Donghuantuo Coal Mine,China

Floor water inrush represents a geohazard that can pose significant threat to safe operations for instance in coal mines in China and elsewhere. Its occurrence is controlled by many factors, and the processes are often not amenable to mathematical expressions. To evaluate the water inrush risk, the paper proposes the vulnerability index approach by coupling the analytic hierarchy process (AHP) and geographic information system (GIS). The detailed procedures of using this innovative approach are shown in a case study in China (Donghuantuo Coal Mine). The powerful spatial data analysis functions of GIS was used to establish the thematic layer of each of the six factors that control the water inrush, and the contribution weights of each factor was determined with the AHP method. The established AHP evaluation model was used to determine the threshold value for each risk level with a histogram of the water inrush vulnerability index. As a result, the mine area was divided into five regions with different vulnerability levels which served as general guidelines for the mine operations. The prediction results were further corroborated with the actual mining data, and the evaluation result is satisfactory.     

中天山天湖东铁钼矿含矿片麻状花岗岩年代学、地球化学和锆石Hf同位素-对于中天山早古生代构造演化的启示

以中天山东段的天湖东铁钼矿含矿花岗岩为例,在LA-ICP-MS锆石U-Pb年代学测定其为早古生代花岗岩（（445.3±4.6） Ma）基础上,通过岩相学、地球化学及锆石原位Hf同位素组成等多方面研究,探讨该岩体的成岩作用及其构造背景。天湖东含矿片麻状花岗岩的主要矿物为斜长石、石英、钾长石,并含少量黑云母和角闪石等。全岩地球化学分析结果表明,该片麻状花岗岩高硅、弱富铝、富钙、富钠而贫钾,ASI值为0.68~0.82,属于准铝质钙碱性花岗岩,总体上富集大离子亲石元素（LILE）Rb、Ba等和轻稀土元素La、Ce、Nd等,而亏损高场强元素Nb、Ta、Ti、Yb等,轻重稀土分异明显,轻稀土分异较为明显,而重稀土分异不明显,表现出典型岛弧岩浆岩的地球化学特征。锆石的ε_Hf(445 Ma)值为-6.31~-1.77,二阶段Hf模式年龄（T_DM2）为1.538~1.825 Ga,表明该花岗岩的源区主要为壳源物质。综合分析上述资料,认为天湖东铁钼矿片麻状花岗岩是由俯冲过程中地壳物质重熔的产物。结合前人的研究和本课题组的新近研究成果认为,在早古生代时,中天山为岩浆弧构造环境,形成一系列的钙碱性岩浆岩,而该岩浆弧的形成可能是受到介于吐哈陆块和塔里木板块之间的古天山大洋在早古生代时期向南俯冲而形成的。     

基于粒子群优化神经网络算法的深基坑变形预测方法

深基坑变形预测是进行施工参数调整和确保深基坑施工安全的重要手段,而如何对其变形进行有效、准确的预测是一个有待解决的技术难题。采用粒子群优化算法对神经网络模型的初始权值和阈值进行优化,并将已有的变形监测数据作为神经网络的输入参数,建立了基于粒子群优化神经网络算法的深基坑变形预测方法。将形成的方法应用于长春市火车站北广场深基坑开挖监测工程中。结果表明：8号水平位移测点预测结果的均方根误差为3.78%,平均百分比误差为5.48%;9号地面沉降点预测结果的均方根误差为5.62%,平均百分比误差为3.23%。经验证,本文方法预测深基坑开挖过程中的变形具有较高的可信度。     

Experimental evidence for eukaryotic fossil preservation: Onion skin cells in silica solution

Research on the origin of eukaryotes often focuses on the exceptional preservation found in silicified Precambrian fossils. Nuclei like subcellular structures in well-preserved fossil becomes confusion and arguments, which focus on whether the partial degradation of prokaryotes produces artifacts that resemble a ‘nucleus’, or fossilized nuclei of eukaryotes. In order to understand the mechanisms of silicification and identify the fossilized subcellular and microstructures in rocks, a series of laboratory controlled experiments were performed for simulating the silicification process. The effects of different silica solutions in eukaryote fossilization were studied in our experiments by exposing onion skin cells (epidermis) to silica solutions. Onion skin provides a good experimental model because of its well characterized cellular structures which are easily observed. The designed experiments revealed that the possibility of onion cell preserved as a “fossil” with nuclear structures, the first week fossilization, or mineralization as rapid as 1 week is important. And the experiment also revealed interactions between silica and the onion skin cell wall surface functional groups were weak. The preservation of nuclei in the onion skin model was due to precipitation in highly supersaturated silica solutions rather than simply the high silica concentration. When the silica gel precipitates slowly at low supersaturation states, the nuclei were not well preserved, but the rapid precipitation at high supersaturated silica conditions preserved nuclear structures. A better understanding of the processes involved in onion skin fossilization will further contribute to issues concerning the silicification of other eukaryotic materials.     

A laboratory study on groundwater quality and mass movement occurrence

In this study, soil samples collected from the sides of two streams with high debris flow potential at Shenmu and Fengchiou village in Nantou County, Taiwan, were used for seepage tank tests in the laboratory. While the tests were being conducted, observations were made to investigate the relationships among displacement of the slope, quality of the seepage water and occurrence of mass movement. The results showed that according to the change rate, displacement could be divided into two stages, namely, the initial failure displacement stage and primary failure displacement stage. While the displacement of the slope was in primary failure displacement stages, the probability of slope failure became much higher. Before general slope failure, electrical conductivity (EC) and sulfate ion (SO₄ ²⁻) concentration of the seepage water increased significantly. The time when EC of the seepage water started to increase rapidly was much earlier than that when displacement of the slope started to increase significantly. Therefore, from the hazard mitigation view, there will be a longer time for response if EC of the seepage water was monitored.     

Geochemical distribution and removal of As,Fe, Mn and Al in a surface water system affected by acid mine drainage at a coalfield in Southwestern China

The chemical characteristics, formation and natural attenuation of pollutants in the coal acid mine drainage (AMD) at Xingren coalfield, Southwest China, are discussed in this paper based on the results of a geochemical investigation as well as geological and hydrogeological background information. The chemical composition of the AMD is controlled by the dissolution of sulfide minerals in the coal seam, the initial composition of the groundwater and the water–rock interaction. The AMD is characterized by high sulfate concentrations, high levels of dissolved metals (Fe, Al, Mn, etc.) and low pH values. Ca²⁺ and SO₄ ²⁻ are the dominant cation and anion in the AMD, respectively, while Ca²⁺ and HCO₃ ⁻ are present at significant levels in background water and surface water after the drainage leaves the mine site. The pH and alkalinity increase asymptotically with the distance along the flow path, while concentrations of sulfate, ferrous iron, aluminum and manganese are typically controlled by the deposition of secondary minerals. Low concentrations of As and other pollutants in the surface waters of the Xingren coalfield could be due to relatively low quantities being released from coal seams, to adsorption and coprecipitation on secondary minerals in stream sediments, and to dilution by unpolluted surface recharge. Although As is not the most serious water quality problem in the Xingren region at present, it is still a potential environmental problem. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

堰塞坝坝体材料渗流特性研究现状及展望

目前,国内外对地震堰塞坝体稳定性的研究较多,但多数为个例研究。在影响坝体稳定性的众因素中,堰塞坝体的材料组成及其渗透特性对坝体破坏模式有重要的决定作用。本文在前人研究的基础上,从渗流的基本规律、数值模拟、室内试验3个方面总结了针对堰塞坝坝体材料渗流的机理和研究方法。重点分析总结了堰塞坝坝体材料渗透性的研究进展,指出几何条件和水力条件共同决定土体发生渗透变形和渗透稳定性。最后分析了目前针对坝体材料渗透研究存在的问题,提出未来可能的研究方向。     

基于拟静力法的弹簧刚度计算方法讨论

本文讨论了拟静力法在动力状态下的地基基础协同分析中的应用,通过分析假定动力状态下岩土体的剪切模量和剪切应变的关系,将地震力转化为等效的惯性力系。对于不同类型的岩土体,剪切模量G和剪切应变Y的对应关系是有区别的,且地震过程是不可预知的,过程无法模拟。研究表明,采用线性方法简化地震力衰减过程,仍可以得到较准确的计算结果。本文还采用FLAC-3D软件对上述关系进行了模拟,通过工程实例计算验证其可行性,提供了一套在动力状态下计算弹簧刚度参数的方法。