A life detection problem in a High Arctic microbial community

Fluorescent labeling of bacterial cell walls, DNA, and metabolic processes demonstrates high (potentially single molecule) sensitivity, is non-invasive, and in some cases can differentiate strains and species. Robust microscopes such as the custom instruments presented here can provide good image quality in the field and are potentially suitable for flight. However, ambiguous or false-positive results with bacterial stains can occur and can create difficulties in interpretation even on Earth. We present a “real” life detection problem in a sample of biofilms taken from the Canadian High Arctic. The samples consisted of numerous small sulfur-oxidizing bacteria and larger structures resembling fungi or diatoms. The identity of these latter structures remained ambiguous until electron microscopy and X-ray spectroscopy were performed, indicating that they were unusual sulfur minerals probably precipitated by the bacterial communities. While such mineral structures may possibly serve as biosignatures after the cells have disappeared, it is important that they not be mistaken for cells themselves. It is also possible that unusual mineral structures will be performed under extraterrestrial conditions, so great care is needed to differentiate cell structures from minerals.     

绿色巴夫藻硒多糖的提取、分离与纯化

于１９９５年３－７月采用本实验室培养的绿色巴夫藻,经沸水提取及去除蛋白,小分子物等杂质后,通过ＳｅｐｈａｄｅｘＧ－５０柱层进行分离,纯化实验。结果表明,分离纯化得到的两种多糖－４Ｐ１和４Ｐ２,通过醋酸纤维素薄膜电脉及ＳｅｐｈａｄｅｘＧ－１００凝胶过滤检验纯度后,证实其均为单一含硒多糖,且都带负电。两种硒多糖含硒量都较低,分别为７７ｍｇ／ｇ和２２０ｍｇ／ｇ。     

Impacts of recurring ice jams on channel geometry and geomorphology in a small high-boreal watershed

River ice jams are generally perceived as significant erosive events and are well known to impact both channel morphology and geometry. However, the extent of these impacts and the frequency of events required to maintain erosion-induced morphologies remain unexplored in most cold region watersheds. In this study, we investigated downstream variations in channel width, cross-sectional area, depth, and geomorphological characteristics in a small high-boreal basin. We coupled these observations to dendrochronological data on ice jam frequency. Our results show that channels affected by ice erosion appear enlarged and present an important retreat of the upper bank. Such enlarged channels present a typical two-level, ice-scoured morphology when ice jams recur more often than once every 5 years. By contrast, channels appear unaffected when ice jams are less frequent. These results suggest that ice jams maintain ice-scoured and enlarged morphologies once a minimal frequency-of-occurrence threshold is exceeded. We therefore conclude that ice jam frequencies should be taken into account in order to better define the role of ice as a geomorphological agent in cold environments.     

Petrology, geochronology and tectonic implications of Mesozoic high Ba–Sr granites in the Haemi area, Hongseong Belt, South Korea

Collision between the North and South China continental blocks began in the Korean peninsula during the Permian (290–260 Ma). The Haemi area in the Hongseong collision belt (proposed as the eastern extension in South Korea of the Dabie–Sulu collision zone of China) within the Gyeonggi Massif comprises post-collisional high Ba–Sr granite with intermediate enclaves that intruded into the Precambrian rocks. The intermediate enclaves have a shoshonitic affinity whereas the granite is a high-K calc-alkaline variety. The chondrite-normalized rare earth element (REE) pattern with relative enrichment of LREE over HREE and absence of a significant negative Eu anomaly typifies both enclaves and granite. Geochemical similarities of enclaves and granite are attributed to the involvement of enriched mantle sources in their genesis. However, dominant crustal components were involved in the formation of high Ba–Sr granites. A granite crystallization age of 233 ± 2 Ma was obtained from SHRIMP U–Pb zircon dating. This age is slightly younger than the Triassic collision event in the Hongseong Belt. Geochemical data, U–Pb zircon age, and regional tectonics indicate that the Haemi high Ba–Sr granite formed in a post-collisional tectonic environment. A Mesozoic post-collisional lithospheric delamination model can account for the genesis of high Ba–Sr granite in the Haemi area.     

Two-dimensional,high-resolution modeling of urban dam-break flooding: A case study of Baldwin Hills,California

Modeling of dam-break flooding in an urban residential area in southern California is presented. Modeling is performed using BreZo, an unstructured grid, Godunov-type, finite volume model that solves the shallow-water equations. The model uses terrain data from a 1.5 m Light Detection and Ranging (LiDAR) Digital Terrain Model (DTM) and contour data depicting the reservoir and breach geometry. A spatially distributed Manning coefficient based on a landcover classification derived from digital orthophotos and vector data (e.g., parcel outlines) is also used, and the interception of flow by storm drains is modeled with sink terms in the 2D continuity equation. The model is validated with flood extent and stream flow measurements, and a sensitivity analysis is completed to identify the necessary level of data and model complexity for accuracy purposes. Results show street depressions in the land surface should be resolved by the computational mesh for flood extent and stream flow accuracy. A ca. 5 m resolution mesh that spans streets by approximately 3 cells achieves a good balance between accuracy and computational effort. Results also show that heterogeneous resistance is important for stream flow accuracy, and the interception of overland flow by storm sewers is important for flood extent accuracy. The sensitivity of predictions to several additional factors such as the reservoir level, breach geometry and DTM source (LiDAR, National Elevation Data, Shuttle Radar Topography Mission Data) is also reported.     

Inter- and intraspecific variations of the chemical properties of high-Arctic mosses along water-regime gradients

We examined and compared the contents of organic chemical components (lignin-like compounds, total carbohydrates and extractives), carbon and nutrients (nitrogen, phosphorus, potassium, calcium, magnesium) among the mosses Calliergon giganteum, Hylocomium splendens, Racomitrium lanuginosum, and among three populations of H. splendens collected from habitats in contrasting water regimes in the Canadian high-arctic tundra. C:N:P ratios were analyzed among and within moss species. Mosses from hydric habitats had lower total carbohydrate and higher nutrients contents than did mosses from drier habitats; however, we found no intraspecific variations in nitrogen and calcium contents in the different populations of H. splendens along water-regime gradients. The contents in lignin-like compounds, extractives and carbon showed no clear trends along water-regime gradients. Mosses from hydric habitats had lower C:N, C:P and N:P ratios than mosses from drier habitats, although we found no intraspecific variations in C:N ratios in H. splendens along water-regime gradients. These results suggest that chemical properties of mosses, especially nutrient contents, are strongly correlated with water availability in high-Arctic tundra.     

波动方程的高阶广义屏叠前深度偏移

不同于常规广义屏传播算子的推导中使用散射理论,本文利用单平方根算子的渐近展开,推导出了单程波方程广义屏传播算子的高阶表达式.高阶广义屏传播算子不仅可提高常规广义屏传播算子的计算精度,而且还能改善广义屏传播算子对速度强横向变化介质的适应性.把高阶广义屏传播算子应用于波动方程叠前深度偏移,可得到比常规广义屏传播算子更好的效果.高阶广义屏传播算子的阶数越高,计算精度越高,但计算量也越多.以SEG EAGE二维盐丘模型数据的波动方程叠前深度偏移为例,二阶广义屏传播算子相对于常规（一阶）广义屏传播算子增加了30%的计算量.高阶广义屏传播算子是常规广义屏传播算子理论的发展和完善.     

An Efficient and Precise Method for Calculating the Dense Ephemeris of High Eccentricity Orbit

Detection and cataloguing of space targets are an important issue for spacecraft safety. The large number of space targets makes the workload of orbit calculation very heavy. Being fast in calculation, the analytical method however cannot handle the processing of high-precision observational data. The numerical method on the contrary is good at the orbit determination for such targets. The cataloguing of space targets generally involves the production and calculation of dense ephemeris, for which an effective technique procedure that can calculate the orbit of High Eccentricity with both high accuracy and high efficiency has not yet formed, making the cataloguing difficult. In this paper, we propose a fast processing method that is suitable for the precise calculation of dense ephemeris for orbits with High Eccentricity, and optimize the parameters through numerical experiments. The superiority of the method is verified by examples.     

中硫型浅成低温热液金多金属矿床基本特征、研究进展与展望

继20世纪80年代以来低硫型和高硫型浅成低温金矿床概念提出及成矿模型建立之后,相继发现一些浅成低温热液矿床不具上述两类矿床端元的成矿特点,相反兼具过渡性质;很多学者将其作为单一矿床类型,定义为中硫型浅成低温热液矿床。作为一个新的矿床类型,中硫型矿床是否有单独划分的必要?该类矿床具有什么样的地质特征?长期以来这些问题令人困惑。本文从大量文献中,在全球范围内甄别出24个比较明确的中硫型浅成低温热液金(多金属)矿床,基于其基本特征和研究进展的系统梳理与分析,从中硫型矿床的时空展布、地质特征、矿物组合、金属源区特征、中硫型与高硫型金(铜)矿和低硫型金矿的主要区别,以及目前国际研究进展及难点等方面进行总结阐述。中硫型金多金属矿床具有如下六大特征:(1)发育富碳酸盐-贱金属硫化物成矿体系,碳酸盐矿物可见于各成矿阶段热液脉系中,尤其在热液晚阶段以碳酸盐矿物为主;贱金属硫化物主要为Cu、Pb、Zn、Fe等的硫化物;(2)发育中硫化态矿物组合,如贱金属硫化物黄铜矿、闪锌矿、方铅矿、黄铁矿、黝铜矿等;可少量发育明矾石和冰长石;(3)含矿脉系中富硫化物(总量大于5%),且在斑岩铜矿系统中较富黄铜矿;(4)普遍发育浅色贫铁闪锌矿(有待进一步证实);(5)普遍赋存在挤压岛弧背景下斑岩Cu-Au-Mo矿的外围;(6)空间上可与高硫型和低硫型金多金属矿床共存。普遍发育斑岩型Cu-Au-(Mo)矿床和浅成低温热液型矿床的世界著名三大成矿域(滨太平洋成矿域、古亚洲洋成矿域和特提斯-喜马拉雅成矿域),同样具有形成中硫型矿床的有利成矿条件。未来关于中硫型矿床的研究亟需解决以下几个关键问题:(1)目前尚未有文献对"富碳酸盐-贱金属(Cu、Pb、Zn、Fe等)"进行详细报道,这种成矿体系是如何形成的?流体中CO_2、H_2S及贱金属元素对Au的运移和沉淀有何影响?此问题是认识中硫型金多金属矿床成矿机制的关键所在。(2)中硫化态矿物的矿物(黄铁矿、闪锌矿、方铅矿、黝铜矿、砷黝铜矿、黄铜矿等)的沉淀环境?与高硫化态、低硫化态矿物有何区别?(3)从成矿系统、成矿过程和矿物形成的复杂性来考虑,显然以闪锌矿中Fe S的含量多少作为区别IS型、HS型、LS型矿床的特征地化标志过于简单,且与已有关于闪锌矿的矿物学研究成果相矛盾,因此仍需进一步工作。(4)早期形成的作为赋矿围岩的火山岩地层或者次火山岩体是否提供了成矿物质?是否充当了浅成低温热液矿物沉淀的地球化学屏障?其具体过程是怎样的?以上问题的解决可辅助揭示IS型矿床的成因机制和形成过程,并为同类型矿床的勘查工作提供支持。     

高密度电法探测地下空洞

简要介绍了高密度电法的基本原理及其特点,结合探查地下空洞实例,说明高密度电法寻找地下空洞的利弊。