基于MODIS植被指数的浑善达克沙地植被物候变化

基于近20a MODIS的2种植被指数数据，利用Logistic曲线曲率极值法和动态阈值法，对浑善达克沙地植被物候进行了提取，分析其时空变化，并利用研究结果数据，分析植被物候对高程和气象因子的响应.结果表明，2000~2019年间研究区的植被物候呈微弱波动趋势，浑善达克沙地植被返青期（SOS）主要集中在110~140d，枯黄期（EOS）主要集中在250~280d，整体呈微弱推迟趋向（0.28d/a），生长季长度（LOS）主要集中在120~170d，整体呈微弱延长趋向（0.23d/a）.在空间分布上，占研究区51.51%的区域植被SOS呈提前趋势；占研究区67.02%的区域植被EOS呈提前趋势，并且占研究区32.98%的区域植被EOS呈推迟趋势.占研究区62.71%的区域植被LOS呈延长趋势.在海拔900~1500m区间，随着海拔升高，SOS显著推迟，EOS不显著提前，LOS显著缩短.前一年11、12月和当年1、2、4月降水量对SOS有提前作用.6、7、8、9月份气温和降水都对EOS推迟有明显的作用.总的来说，浑善达克沙地植被物候与气候因子的相应规律比较复杂，表现出季节性的差别及地形的差异性.     

Element mobility and partitioning along a soil acidity gradient in central Ontario forests, Canada

The potential environmental risk posed by metals in forest soils is typically evaluated by modeling metal mobility using soil-solution partitioning coefficients (K(d)), although such information is generally restricted to a few well-studied metals. Soil-solution partitioning coefficients were determined for 17 mineral elements (Al, As, Be, Ba, Ca, Cr, Cu, Fe, Ga, K, Li, Mg, Rb, Sr, Tl, U and V) in A-horizon (0-5 cm) soil at 46 forested sites that border the Precambrian Shield in central Ontario, where soil pH(aq) varied from 3.9 to 8.1. Sites were dominated by mature sugar maple (Acer saccharum Marsh.), white birch (Betula papyrifera Marsh.), balsam fir (Abies balsamea (L.) Mill.) or white pine (Pinus strobus L.). Log K(d) values for all elements could be predicted by empirical linear regression with soil pH (r (2) = 0.17-0.77) independent of forest type, although this relationship was greatly affected by positive relationships between acid-extractable metal concentration and pH(aq) for 13 of the 17 elements. Elements that exhibited strong or moderate (r (2)> 0.29; p < 0.001) relationships with soil pH(aq) in soil water extracts include Al, Ba, Fe, Ga, K, Li, Rb, Tl, V (negative) and Ca (positive). Elemental partitioning in mineral soil was independent of forest type; tree species differed in their response to chemical differences in mineral soil. For example, Rb, Ba, and Sr concentrations in foliage of sugar maple and white birch significantly increased with increasing soil acidity, whereas Rb, Ba, and Sr concentrations in balsam fir and white pine foliage exhibited no response to soil pH(aq). While K(d) values can provide useful information on the potential mobility and bioavailability of mineral elements in forest soils, care must be used when interpreting the relative contribution of solid and aqueous phases to this relationship and the differing responses of vegetation in elemental cycling in forests must also be considered.     

Base Cation Losses from a Coniferous Catchment in Central Ontario,Canada

Long-term monitoring of a predominantlyconiferous catchment (PC-1) in central Ontario has enabledmass budgets of base cations to be estimated between 1983and 1998. During this period, sulphur deposition decreasedby approximately 30%, although this region still receivesacid deposition that exceeds the critical load with respectto acidity for forest soils. Between 1983 and 1998 therewas a net loss of 76.3 kg ha^-1 Ca and 13.7 kg ha^-1Mg from PC-1, and a net retention of K of 55.7 kg ha^-1. A net loss of Ca and Mg occurred every year during the studyperiod (except 1986/87 for Mg), although annual losses of Caand Mg have been generally lower in recent years. On anannual basis, net losses of Ca and Mg were extremelyvariable and were strongly related to export of SO₄,which in turn appeared to be strongly influenced by climatefactors. Measured losses of Ca and Mg over the 16-yearperiod represented 37% and 59% of their respectiveexchangeable pools measured in the upland soils in 1983.These values probably overestimate base cation losses fromthe upland however, because losses from organic soils in thecatchment were proportionately greater during yearsfollowing El Niño events. There was no change in basal areabetween 1983 and 1998, although there was a shift towardless nutrient-demanding species (white pine, hemlock). Pools of Ca and Mg in tree biomass are approximately doubletheir exchangeable pools in podzols, and so losses from soilmay be offset by changes in forest structure (size,composition) in the short-term (decades). If net losses ofCa and Mg continue due to harvesting and/or acid depositionand estimates of weathering and exchangeable pools arecorrect, then the long-term sustainability of the uplandforest at PC-1 must be in doubt.     

R/S法的土石坝施工期沉降规律及预警标准研究

为提高施工期土石坝沉降安全性,研究其具有复杂非线性特征的施工期沉降规律和相应的预警标准。基于国内某在建高土石坝的沉降数据,采用R/S法分析坝体不同高程测点、同高程测点和同测点不同时期沉降数据的Hurst指数及分形维数,提出评价坝体施工期沉降安全性的预警标准。结果表明:各测点的Hurst指数最小值为0.763,坝内各处沉降仍处于快速增长阶段;坝体下部比上部、中部比下游堆石区沉降能更快趋于稳定,且坝体下部的沉降速率已经渐趋平缓。     

民营企业安全文化模型及其实证分析

针对民营企业特点,基于交互安全文化模型,建立民营企业安全文化模型并辨识 关键元素,以赛轮金宇股份有限公司为例进行实证分析。在广泛参考国内外相关研究的 基础上,设计调查问卷,运用粗糙集ROSETTA软件对测量结果进行属性简约,最终确定 15个安全文化元素;借助MATLAB,采用熵权法确定各元素权重,然后进行可拓综合评价 。评价结果表明该企业的“高层管理者重视”一项得分为4.82,水平较高,整体文化等 级属于“良”,级别特征变量j*=3.138 1。“创造安全舒适的工作环境”、“建立合理 的奖惩制度”、“定期进行应急演练”3个方面得分偏低,是安全文化建设需要重点加 强的方面。