西藏结则茶卡湖岸沉积物中铀系年龄及意义

通过对藏北高原西北部结则茶卡湖泊及其沿岸地质地貌调查,发现其为一个富含硼、锂、钾、锶的封闭型盐湖,沿岸海拔4 850 m拔湖325 m有一条明显的高位湖岸线,该湖岸线到湖面之间有六级湖积阶地发育,六级以上阶地保存零星。沿湖岸不同高度上的湖积物U系年龄分别为(14.2±1.2)ka BP(T2)、(38.0±3.5)ka BP(T4)和(41.6±3.2)ka BP(T5)。湖面下降的幅度是藏北高原迄今所知最大。根据湖面平均下降速度推算高位湖岸线和高位湖积层的形成年龄在(120~90)ka BP,与东部的纳木错和西部的甜水海基本一致,说明藏北高原在晚更新世初期有一个明显的泛湖期。大约100 ka BP结则茶卡湖面开始下降,晚更新世以来湖泊演化是在封闭体系干旱环境下进行的,盐湖形成于14 ka BP左右,藏北高原在晚更新世以来气候变化可能为自西向东逐渐变为干寒。     

Spectroscopic study of the peculiar galaxy UGC 5119

We present the results of our study of the stellar kinematics in the elliptical galaxy UGC 5119, which has previously been suspected to be a polar-ring galaxy. We have detected a rapidly rotating disk in the central region (r ≤ 3.2 kpc) of the galaxy’s main body and found a radial velocity gradient along its minor axis (in the putative ring). We conclude that UGC 5119 is a medium-luminosity elliptical galaxy with a rapidly rotating disk component and a stellar (probably polar) ring. We have calculated the Lick indices of the Hβ, Mggb, Fe 5270, and Fe 5335 absorption lines and compared them with evolutionary synthesis models. Differences in the [Mg/Fe] ratios, metallicities, and ages of the stars have been found: the young stellar population with a solar [Mg/Fe] ratio and a high metallicity dominates in the circumnuclear region (r ≤ 1 kpc), while the old one with a low metal abundance dominates in the ring.     

基于MSA特征的遥感图像多目标关联算法

遥感图像中多目标关联存在以下两个问题:一是低时间分辨率观测使得目标状态信息无法准确估计,基于Kalman滤波的多目标关联算法不再适用;二是基于图像特征的目标关联算法又无法处理大场景观测中多个目标关联引起的模糊性.针对上述问题,提出一种基于多尺度自卷积特征匹配和关联代价矩阵最优化的多目标关联算法.实验表明该算法对遥感图像中多目标关联问题具有一定的适用性.     

基于多时相多极化差值图的稻田识别研究

提出了一种基于多时相多极化差值图的稻田识别方法,该方法在简化稻田识别算法的同时,仍具有较好的稻田识别精度.以江西省高安地区的早稻识别为例,利用两景ENVISA ASAR交叉极化模式数据(VV/HH)计算了同时相多极化差值图和同极化多时相差值图.由于稻田含有水层和水稻的垂直株型等属性特征,稻田在两时相上VV极化和HH极化后向散射差异都很大,且与其他地物具有明显差别,因此利用同时相多极化差值图可以很好地分辨出稻田来;从时间变化看,HH极化雷达波对水稻生长和稻田的变化比对其他地物的变化更敏感,使稻田分布信息在HH极化多时相差值图中反应突出.而VV极化对地物的时相变化不够敏感.因此,建立最优差值图组合,分别采用阈值分类方法和监督分类方法对差值图组合进行分类提取稻田.通过比较分类结果,认为基于统计分析的监督分类方法更好,其稻田识别的精度达到84.92%.文章最后对提出的稻田识别方法及分类结果进行了分析.     

闽东南沿海老红砂沉积地层与形成时代

采用岩石地层学、磁性地层学和地球化学等方法,结合TL、ESR和¹⁴C等测年,对广泛分布于闽东南沿海的老红砂沉积地层及其形成时代进行了划分。结果表明,该区老红砂沉积地层可综合划分为5个地层段,其中老红砂层可分出3个地层段,分属60~40 ka B.P.、30~25 ka B.P.和20~10 ka B.P.所形成;两个古土层,反映大约在40~30 ka B.P.和25~20 ka B.P.老红砂的发育有过两次较长时间的沉积间断或减弱。     

Assessment of Nitrate—Nitrogen Distribution in Kansas Groundwater, 1990–1998

Nitrate-nitrogen (nitrate-N) in groundwater is a potential problem in many parts of Kansas.From 1990 to 1998, 747 water samples were collected from domestic, irrigation, monitoring,and public water supply wells primarily from the western two-thirds of the state, and analyzedfor nitrate-N by the Kansas Geological Survey. Nitrate-N concentrations of the 747 samplesanalyzed range from 29% with less than or equal to 3 mg/L, 51% between 3 and 10 mg/L,and 20% greater than or equal to 10 mg/L. Factors that show a statistically significantrelationship with the occurrence of nitrate-N in Kansas groundwater in this assessment includegeographic area of the state, depth of well, and age of well. Nitrate-N levels of wells screenedin the High Plains aquifer in south-central Kansas showed a statistically higher concentrationthan samples collected from the High Plains aquifer in the western portion of the state.Comparison of nitrate-N with depth of well indicated that shallower wells throughout the stategenerally have higher nitrate-N values than deeper wells. Irrigation wells older than 1975showed statistically higher nitrate-N concentration than wells installed during and since 1975,possibly related to changes in well-construction practices and regulations that occurred in 1975.     

南极格罗夫山陨石的研究与展望

本文综述了我国第 1 5次 ( 1 998/ 1 999)、1 6次 ( 1 999/ 2 0 0 0 )南极科学考察队在东南极格罗夫山冰区回收的 32块陨石的岩石矿物学特征及其分类。这些陨石包括 :2 3块平衡型普通球粒陨石、6块非平衡型普通球粒陨石、1块二辉橄榄岩质火星陨石、1块钙长辉长无球粒陨石、1块未分群的铁陨石。文中还对南极格罗山冰区的陨石富集机制、GRV 980 0 4 (H5 )球粒陨石异常低的宇宙射线暴露年龄、火星陨石的溅射年龄等进行了初步的讨论 ,并对今后格罗夫山陨石的研究提出一些初步想法。     

On the age calibration of the geomagnetic polarity timescale

Knowledge of the age of undated events is not null if a time-order relationship can be found among these events. The knowledge of such a time-ordered sequence can be formalized by using non-informative (uniform) prior probability densities for the ages of undated events and Bayes' theorem to introduce the time-order relationship condition. We show that the conditional probability densities of the ages of events of unknown age are given by various forms of Euler's beta distribution. These distributions yield an estimate of the probability for an undated event to occur in a given age interval.
  We use this method to propose appropriate probabilistic representations of our actual knowledge of the dating of the magnetic polarity reversals during the Cenozoic. These representations take into account the uncertainties arising from irregularities in accretion process and from the quality of a few calibration points. Both types of uncertainties generate large ambiguities in the age of magnetic reversals, which should be taken into consideration when the geomagnetic polarity timescale is used for dating purposes. We propose to use the entropy function to quantify these ambiguities.     

Quantifying the variability and allocation patterns of aboveground carbon stocks across plantation forest types,structural attributes and age in sub-tropical coastal region of KwaZulu Natal,South Africa using remote sensing

Quantifying the variability and allocation patterns of aboveground carbon stocks across plantation forests is central in deriving accurate and reliable knowledge and understanding of the extent to which these species contribute to the global carbon cycle and towards minimizing climate change effects. The principal objective of this study was to quantify the variability and allocation patterns of aboveground carbon stocks across Pinus and Eucalyptus plantation forests, tree-structural attributes (i.e. stems, barks, branches and leaves) and age groups, using models developed based on remotely sensed data. The results of this study demonstrate that aboveground carbon stocks significantly (α = 0.05) vary across different plantation forest species types, structural attributes and age. Pinus taeda and Eucalyptus grandis species contained aboveground carbon stocks above 110 t C ha⁻¹, and Eucalyptus dunii had 20 t C ha⁻¹. Across plantation forest tree structural attributes, stems contained the highest aboveground carbon stocks, when compared to barks, branches and leaves. Aboveground carbon stock estimates also varied significantly (α = 0.05) with stand age. Mature plantation forest species (i.e. between 7 and 20 years) contained the highest aboveground carbon stock estimates of approximately 120 t C ha⁻¹, when compared to younger species (i.e. between 3 and 6 years), which had approximately 20 t C ha⁻¹. The map of aboveground carbon stocks showed distinct spatial patterns across the entire study area. The findings of this study are important for understanding the contribution of different plantation forest species, structural attributes and age in the global carbon cycle and possible climate change moderation measures. Also, this study demonstrates that data on vital tree structural attributes, previously difficult to obtain, can now be easily derived from cheap and readily-available satellite data for inventorying carbon stocks variability.     

Preliminary palaeomagnetic results of an Archaean dolerite dyke of west Greenland: geomagnetic field intensity at 2.8 Ga

The geomagnetic field intensity during Archaean times is evaluated from a palaeomagnetic and chronological study of a dolerite dyke intruded into the 3000 Ma Nuuk Gneisses at Nuuk (64.2°N, 51.7°W), west Greenland. Plagioclase from the dolerite dyke yields a mean K-Ar age of 2752 Ma. Palaeomagnetic directions after thermal demagnetization of the dyke and the gneiss reveal a positive baked-contact test, indicating that the high-temperature-component magnetization of the dyke is primary. Thellier experiments on 12 dyke specimens yield a palaeointensity value of 13.5±4.4 μT. The virtual dipole moment at ca. 2.8 Ga is 1.9±0.6 × 10²² Am², which is about one-quarter of the present value. The present study and other available data imply that the Earth's magnetic field at 2.7 ∼ 2.8 Ga was characterized by a weak dipole moment and that a fairly strong geomagnetic field similar to the present intensity followed the weak field after ca. 2.6 Ga.