基于双谱滤波的综合脉冲星时算法研究

毫秒脉冲星的自转频率非常稳定,提供了一种独立的基于遥远自然天体并能持续数百万乃至数十亿年的时间基准,具有稳定性强、运行时间长、服务范围广等特点.为了减弱毫秒脉冲星计时观测中各种高斯噪声对脉冲星时的影响,研究了一种基于双谱滤波的综合脉冲星时构建算法,处理分析了国际脉冲星计时阵(International Pul-sar Timing Array,IPTA)最新发布的4颗毫秒脉冲星(PSR J0437-4715、J0613-0200、J1713+0747和J1909-3744)的观测数据,分析了不同时间尺度综合脉冲星时的稳定性,并与构成国际原子时(International Atomic Time,TAI)的4家授时单位原子钟稳定性进行了比较.结果表明:双谱滤波算法能够较好地抑制观测噪声,提高综合脉冲星时的稳定性.相比于经典加权算法,综合脉冲星时1 yr、10 yr稳定度从7.77×10^-14、8.56×10^-16分别提高到1.50×10^-14、3.50×10^-16,单脉冲星时稳定性的提升也类似.同时发现,综合脉冲星时稳定性在5 yr及以上时间尺度上优于原子钟稳定性,可用于改善当前原子时的长期稳定性.     

基于GPU的地形可视化加速算法研究

地形可视化是利用数字高程模型DEM,采用计算机图形学和图像处理技术进行三维地形模拟显示。该技术在深部矿产预测、矿产资源评价、虚拟现实、娱乐游戏、飞行模拟等诸多领域有着广泛的应用。随着数据量的增大,三维地形可视化的实时、流畅视觉效果受到当前的计算机硬件技术水平限制。针对这一问题,本文运用ROAM算法进行地形建模,利用GPU高速并行运算性能加速地形可视化建模速度,加速模型显示效果。实验对比表明:当计算量比较小时,加速效果不显著;随着计算量的增大,计算效果越来越明显;当计算量达到一定值时,加速效果达到一个稳定的加速趋势。研究结果为地形可视化及矿产资源评价等类似工作提供了原创性可视化技术支撑。     

帕米尔高原Rushan-Pshart古特提斯洋或中特提斯洋争论的岩石地球化学证据

帕米尔高原上广泛分布的加里东期火山岩,印支期火山岩与燕山期火山岩被认为是块体依次向北俯冲拼贴到欧亚板块上的产物。特别是燕山期火山岩被认为是Rushan-Pshart中特提斯洋闭合的产物。但近年来地层古生物、火山岩证据不断表明Rushan-Pshart洋闭合时间在晚三叠一早侏罗世,由此限定Rushan-Pshart古特提斯洋性质,而帕米尔高原上广泛分布的燕山期火山岩是更南部的Shyok中特提斯洋闭合的产物。目前,中国境内Rushan-Pshart缝合带属性的研究工作展开较晚,研究程度较低。我们对塔什库尔干明铁盖沟一线燕山期火山岩带展开的工作发现零星分布的印支期花岗岩。印支期花岗岩错石U・Pb年龄显示岩体侵位时间在201 Ma左右。全岩主量元素特征表明岩石为I型高钾钙碱性闪长花岗岩;稀土元素在球粒陨石标准化图解中呈轻稀土元素相对富集,重稀土元素相对亏损的右倾海鸥型。明铁盖岩体的微量元素显示大离子亲石元素明显富集,而高场强元素明显亏损。稀土微量元素特征倾向花岗岩属性为岛弧型花岗岩,Sr-Nd-Hf同位素比值特征显示岩体形成于下地壳部分熔融环境。岩体的地化特征表明岩体形成的构造环境为板块汇聚的洋壳俯冲阶段,结合区域地质特征,我们将花岗岩体归为Rushan-Pshart古特提斯洋壳俯冲消减的产物。Rushan-Pshart缝合带传统上认为是中特提斯带,近年的研究进展认为其为古特提斯缝合带,本文的工作支持这种观点。Rushan-Pshart古特提斯缝合带的确立对帕米尔高原与青藏高原主体的块体对比提供了可信的对比方案,并对青藏高原新生代陆内变形方式的争论提供了可靠的证据。     

甘肃柳园地区早二叠世正长花岗斑岩脉锆石U-Pb年代学、岩石地球化学特征——对北山造山带晚古生代构造背景的指示

甘肃北山地区位于中亚造山带中段，是诠释中亚造山带构造演化的关键区域之一，长期以来受到地质学界的广泛关注。柳园地区位于甘肃北山南带，区内脉岩发育，这些岩脉的研究可以为阐释北山造山带晚古生代构造背景提供更多证据。基于此，本文选取位于甘肃柳园地区的正长花岗斑岩脉开展了系统的锆石U-Pb-Hf同位素和全岩主量、微量元素分析。LA-ICP-MS锆石U-Pb分析显示，岩脉侵位于早二叠世（（288.5±1.4）Ma）。全岩地球化学分析显示，正长花岗斑岩脉的SiO₂和全碱质量分数较高，Fe、Mg、Ca、Al和P质量分数较低，Rb、Th、U和Pb相对富集，Ba、Nb、La、Ce、Sr和Ti等元素相对亏损，Eu负异常显著，具有较高的Rb/Sr值和较低的K/Rb值及锆石饱和温度（730~844℃，集中于740℃左右），显示该岩脉为高钾钙碱性高分异I型花岗岩，并具有俯冲带岩浆活动的地球化学特征。正长花岗斑岩脉具有较低的Zr/Hf值（18.42~28.01，平均值为22.37）和Th/U值（3.82~7.99，平均值为5.34），与平均地壳组分接近，锆石ε_Hf（t）值为2.94~9.66，平均值为5.72，T_DM2值为955~611 Ma，指示源区主体为新元古代地壳的部分熔融，并存在幔源物质加入。根据构造判别图解并结合前人关于二叠纪区域构造变形、盆地沉积物源、岩浆演化等方面的研究结果，笔者认为该正长花岗斑岩脉形成于俯冲作用过程中的局部伸展环境，并认为北山地区增生造山事件至少持续到早二叠世。     

Soil Organic Carbon Contents and Stocks in Coastal Salt Marshes with Spartina alterniflora Following an Invasion Chronosequence in the Yellow River Delta,China

Plant invasion alters the fundamental structure and function of native ecosystems by affecting the biogeochemical pools and fluxes of materials and energy. Native(Suaeda salsa) and invasive(Spartina alterniflora) salt marshes were selected to study the effects of Spartina alterniflora invasion on soil organic carbon(SOC) contents and stocks in the Yellow River Delta. Results showed that the SOC contents(g/kg) and stocks(kg/m~2) were significantly increased(P 0.05) after Spartina alterniflora invasion of seven years, especially for the surface soil layer(0–20 cm). The SOC contents exhibited an even distribution along the soil profiles in native salt marshes, while the SOC contents were gradually decreased with depth after Spartina alterniflora invasion of seven years. The natural ln response ratios(Ln RR) were applied to identify the effects of short-term Spartina alterniflora invasion on the SOC stocks. We also found that Spartina alterniflora invasion might cause soil organic carbon losses in a short-term phase(2–4 years in this study) due to the negative Ln RR values, especially for 20–60 cm depth. And the SOCD in surface layer(0–20 cm) do not increase linearly with the invasive age. Spearman correlation analysis revealed that silt + clay content was exponentially related with SOC in surface layer(Adjusted R~2 = 0.43, P 0.001), suggesting that soil texture could play a key role in SOC sequestration of coastal salt marshes.     

Degradation induces changes in the soil C:N:P stoichiometry of alpine steppe on the Tibetan Plateau

Due to the Tibetan Plateau's unique high altitude and low temperature climate conditions,the region's alpine steppe ecosystem is highly fragile and is suffering from severe degradation under the stress of increasing population,overgrazing,and climate change.The soil stoichiometry,a crucial part of ecological stoichiometry,provides a fundamental approach for understanding ecosystem processes by examining the relative proportions and balance of the three elements.Understanding the impact of degradation on the soil stoichiometry is vital for conservation and management in the alpine steppe on the Tibetan Plateau.This study aims to examine the response of soil stoichiometry to degradation and explore the underlying biotic and abiotic mechanisms in the alpine steppe.We conducted a field survey in a sequent degraded alpine steppe with seven levels inNorthern Tibet.The plant species,aboveground biomass,and physical and chemical soil properties such as the moisture content,temperature,pH,compactness,total carbon(C),total nitrogen(N),and total phosphorus(P)were measured and recorded.The results showed that the contents of soil C/N,C/P,and N/P consistently decreased along intensifying degradation gradients.Using regression analysis and a structural equation model(SEM),we found that the C/N,C/P,and N/P ratios were positively affected by the soil compactness,soil moisture content and species richness of graminoids but negatively affected by soil pH and the proportion of aboveground biomass of forbs.The soil temperature had a negative effect on the C/N ratio but showed positive effect on the C/P and N/P ratios.The current study shows that degradation-induced changes in abiotic and biotic conditions such as soil warming and drying,which accelerated the soil organic carbon mineralization,as well as the increase in the proportion of forbs,whichwere difficult to decompose and input less organic carbon into soil,resulted in the decreases in soil C/N,C/P,and N/P contents to a great extent.Our results provide a sound basis for sustainable conservation and management of the alpine steppe.     

sPL震相在巴东M4.3地震序列震源深度测定中的应用

根据近震深度震相sPL的基本特征，对2017-06-16巴东M4.3地震序列震源深度进行分析，运用频率-波数（F-K）方法模拟不同深度下的理论地震图，并与实际波形拟合对比，得出震源深度分布。结果显示，该地震序列的震源深度集中在3~4 km范围内，误差约为1 km，表明在三峡地区利用sPL震相可以获得较为可靠的震源深度。     

Petrogenesis of Early Cretaceous hornblende gabbro in Khanka Massif: evidence from geochronology and geochemistry

The authors report zircon U-Pb geochronological,whole-rock geochemical and zircon Lu-Hf isotope data for the hornblende gabbro within the Khanka Massif,with the aim of constraining its formation time and petrogenesis. The zircon U-Pb dating shows that ~(206)Pb/~(238)Pb ages of zircons from the hornblende gabbro range from 120 to 129 Ma,yielding a weighted mean age of 123 ± 2 Ma,i. e.,the Early Cretaceous. The hornblende gabbro has SiO_2 of 44. 77%--46. 58% and belongs to the tholeiitic series on FeO~t/MgO-SiO_2 diagram. It displays a right-inclined REE pattern with( La/Yb)_N ratios of 3. 44 to 4. 42. The trace element spidergram shows that they are enriched in large ion lithophile elements( LILE) such as Rb,Th,U,K and Pb,and depleted in high field strength elements( HFSE) such as Nb,Ta,Ti and P,indicating an affinity to arc igneous rocks.The ε_(Hf)( t) values of zircons vary from -2. 6 to + 3. 9 and Hf model ages( T_(DM1)) range from 622 to 883 Ma.These geochemical characteristics indicate that primary magma of the hornblende gabbro could be derived from partial melting of young mantle material accreted during the Neoproterozoic. Combined with the Early Cretaceous igneous rock assemblages in NE Asia. It is concluded that the hornblende gabbro formed in an active continental margin related to the westward subduction of the Paleo-Pacific Plate beneath the Khanka Massif.     

Hydrological management strategies for the control of algal blooms in regulated lowland rivers

Reservoirs of lowland floodplain rivers with eutrophic backgrounds cause variations in the hydrological and hydraulic conditions of estuaries and low-dam reservoir areas, which can promote planktonic algae to proliferate and algal bloom outbreaks. Understanding the ecological effects of variations in hydrological and hydraulic processes in lowland rivers is important for algal bloom control. In this study, the middle and lower reaches of the Han River, China, a typical regulated lowland river with a eutrophic background, are selected. Based on the effect of hydrological and hydraulic variability on algal blooms, a hydrological management strategy for river algal bloom control is proposed. The results showed that (a) differences in river morphology and background nutrient levels cause significant differences in the critical threshold flow velocities for algal bloom outbreaks between natural river and low-dam reservoir sections; there is no uniform threshold flow velocity for algal bloom control. (b) There are significant differences in the river hydrological/hydraulic conditions between years with and without algal blooms. The average river flow, water level and velocity in years with algal blooms are significantly lower than those in years without algal blooms. (c) For different river sections where algal blooms occur and to meet the threshold flow velocities, the joint operation of cascade reservoirs and diversion projects is an effective method to prevent and control algal blooms in regulated lowland rivers. This study is expected to deepen our understanding of the ecological significance of special hydrological processes and guide algal bloom management in regulated lowland rivers.