The Braunschweig meteorite − a recent L6 chondrite fall in Germany

On April 23rd 2013 at 2:07 a.m., a 1.3 kg meteorite fell in the Braunschweig suburb Melverode (52° 13′ 32.19″ N. 10° 31′ 11.60″ E). Its estimated velocity was 250 km/h and it formed an impact pit in the concrete fall site with a diameter of 7 cm and a depth of 3 cm. Radial dust striae are present around the impact pit. As a result of the impact, the meteorite disintegrated into several hundred fragments with masses up to 214 g. The meteorite is a typical L6 chondrite, moderately shocked (S4) – but with a remarkably high porosity (up to 20 vol%). The meteorite was ejected from its parent body as an object with a radius of about 10–15 cm (15–50 kg). The U,Th-He gas retention age of ∼550 Ma overlaps with the main impact event on the L-chondrite parent body ∼470 Ma ago that is recorded by many shocked L chondrites. The preferred cosmic-ray exposure age derived from production of radionuclides and noble gas isotopes is (6.0 ± 1.3) Ma.     

一种基于组合重构算法的对流层层析技术

在经典的对流层层析模型基础上提出一种新的层析模型。首先采用非迭代重构算法估算出层析网格顶点处的水汽密度值,然后根据网格顶点处的湿度信息内插出网格中心点处的水汽密度值,并将其作为初始值,通过迭代重构算法对其进行再次修正。组合重构算法能够为迭代重构算法提供高质量、高可靠性的初始值。试算结果表明,组合重构算法相比单一重构算法具有更高的精度。     

复杂地震波场的自适应流预测插值方法

地震数据本质上是非平稳的,如何解决复杂非平稳地震波场的数据缺失问题是地震勘探数据处理的重要环节之一。预测滤波器在地震数据处理和分析中具有重要的作用,该技术可以有效地解决地震数据缺失问题,但传统的平稳预测滤波方法无法很好地适应地震数据的非平稳特征;因此,开发高效的复杂地震波场自适应预测插值方法具有重要的工业价值。本文将预测滤波器加入"流处理"的概念,滤波器系数随着地震数据的变化同时更新,此计算过程仅需矢量点积运算,能够提高计算效率并降低内存空间;并以此为基础开发基于流预测滤波的地震数据插值方法。利用多次波的动力学信息,通过互相关技术构建虚拟一次波,有效地解决了缺失数据位置滤波系数估计不准的问题,为插值过程提供了更为合理的滤波器估计,更好地解决了非平稳地震数据的重建问题。对Sigsbee 2B模型和实际数据的测试结果表明,该方法可以合理地针对复杂地震信息完成缺失数据的重建。     

Huygens probe entry trajectory and attitude estimated simultaneously with Titan atmospheric structure by Kalman filtering

Space probes entering planetary atmospheres are used for in situ study of their physical structures. During the entry phase aerodynamic forces exerted on the probe depend on atmospheric density. As a consequence accelerations measured by on-board sensors can be used to derive probe trajectory as well as atmospheric density, pressure and temperature profiles. In this work acceleration data acquired by the Huygens Atmospheric Structure Instrument (HASI) have been used to reconstruct the probe trajectory and the Titan's atmospheric structure from down to of altitude. An accurate six degree of freedom model of Huygens during the entry phase has been developed and a new reconstruction technique based on Kalman filtering is presented. This technique estimates simultaneously the probe trajectory, the attitude profile consistent with measured data and the atmospheric density, pressure and temperature.     

基于结构光的不规则工业钣金件三维曲面重建

钣金件表面缺乏适合于影像匹配的纹理,设计了用投影器投射结构光到钣金件表面,对由CCD相机摄取的此影像进行结构光纹理特征提取的线与投影器本身投出的虚拟影像进行线匹配,通过空间前方交会解算出钣金件表面的空间点。实验证明,此方法为实现工业零件的自动化三维重建探索出一条可行的途径。     

基于近景摄影测量的规则几何部件的建模研究

基于近景摄影测量的方法重建具有规则的几何模型的部件需要参数化的表达方法,利用已知模型确定的几何性质,在影像上提取特征并量测确定模型的空间位置和自由度,在精度要求较高的情况下,需要结合影像进行高精度的匹配量测。通过对线框模型的三角化获取适合纹理映射的表面模型,从而尽可能的构建出真实感的部件。     

利用树轮资料重建通天河流域 518年径流量

利用长江源区曲麻莱、治多的树木年轮宽度资料,通过分析树木生长与流量变化的关系,重建了长江源区通天河流域直门达水文站1485年以来年径流量的变化,并进行了变化特征分析。结果表明:在重建的518年中,直门达水文站年径流量最显著的丰水期发生在19世纪前半叶,最显著的枯水期发生在17世纪的后半叶。特丰水年有96年,偏丰水年有117年,特枯水年有86年,偏枯水年有81年,正常水年有138年。重建序列存在43年、37年、32年、5年和2年左右的显著周期。     

桂林地区水南洞14～25万年石笋的碳氧同位素记录和古气候重建

通过对桂林水南洞石笋进行高精度的热电离质谱(TIMS－U)测年和碳氧同位素分析,建立了桂林地区245.20 ka BP至147.90 ka BP间的古气候变化时间序列,确定了石笋记录的时段B与时段C分界的年龄为242.5±6.4 ka BP(相当于深海岩芯氧同位素标准曲线时段7与时段8分界的年龄)、时段A与时段B分界的年龄为 192.6±3.9 ka BP(相当于深海岩芯氧同位素标准曲线时段6与时段7分界的年龄)。桂林地区245.20～147.90 ka BP石笋记录的冷暖事件所反映出的古气候变化,大致可分为3个气候变化阶段:(1) 245.2～242.6 ka BP, 相当于深海岩芯氧同位素标准曲线阶段8的末期;(2) 242.5～192.6 ka BP,相当于深海岩芯氧同位素标准曲线时段7;(3)192.6～147.9 ka BP间的倒数第2次冰期, 相当于深海岩芯氧同位素标准曲线时段6的早中期。石笋的TIMS－U测年和碳氧同位素记录揭示,桂林地区245.2～147.9 ka BP的古气候演变历史与深海岩芯时段8末期、时段7和时段6的氧同位素,深海岩芯中记录的孢子花粉组合、CaCO3含量、海平面的升降变化以及与中国北方黄土、古土壤中记录的孢子花粉组合、成壤程度、全铁富集程度、磁化率变化、原生碎屑CaCO3含量和淋溶强度等所揭示的古气候和古季风变化具有极好的对应关系,表明桂林地区中更新世晚期以来的古气候演变既有全球性特征,又有着强烈的区域性特征。     

基于双曲Radon变换的混采地震数据重建

采用多级中值滤波分离混采数据,可以很好地保持单炮的有效信息;对分离后的单炮数据,采用双曲Radon变换进行地震数据道重建,可以在Radon域获得极高的分辨率从而准确地重建地震数据。单炮道重建时,通过稀疏约束控制Radon变换来提高地震数据的重建精度。双曲Radon变换计算耗时较长,在算子求解时,本文采用快速迭代收缩阈值算法(FISTA),明显加快收敛速度,提高计算效率。模拟数据和实际数据表明,采用多级中值滤波和双曲Radon变换的方法重建混采地震数据可以获得较高的重建精度。     

10,000 years of climate control over carbon accumulation in an Iberian bog(southwestern Europe)

The northwest region of the Iberian Peninsula is home to a unique ecosystem of bogs,which are particularly sensitive to projected climate cha nge.In this context,the rate of carbon(C)accumulation in Chao de Veiga Mol.an intact raised bog,was analysed.Changes in the accumulation rate over the past10 millennia were determined in a peat core of 847 cm in depth,with a high mean rate of peat growth(11 yr cm^-1,0.09 cm yr^-1).An age-depth model was generated from 22 14C dates and fallout radionuclides.Chronological,stratigraphical and physico-chemical data confirmed the existence of a single cycle of peat formation throughout the Holocene and the formation of ombrotrophic peat 9500 years ago.The total mean C content was 50.2%,and over 10 millennia 583 kg C m^-2 accumulated at a mean rate of 35.3 g C m^-2 yr^-1,with a long-term(apparent)rate of carbon accumulation in the catotelm of59.9 g C m^-2 yr^-1.These values are much higher than reported for other Iberian peatlands and are amongst the highest documented for peatlands in the northern hemisphere.The dynamics of C accumulation and other measured parameters reveals important variations throughout the Holocene.They could be associated with the main climatic events described in the northern hemisphere and are highly consistent with models established for northern latitudes.The Chao de Veiga Mol raised bog is unique and of great potential value for carrying out high resolution palaeoenvironmental studies,especially in relation to regional and Iocal modulations in southern Europe.