Atmospheric variations and meteorite production on Mars

Through a combination of aerobraking (drag deceleration) and ablation, meteoroids which enter planetary atmospheres may be slowed sufficiently to soft-land as meteorites. Results of an earlier study suggest that the current 6 mbar atmosphere of Mars is sufficient to aerobrake significant numbers of small (<10 kg) asteroidal-type meteoroids into survivable, low-velocity (<500 m s⁻¹) impacts with the planet's surface. Since rates of meteorite production depend upon the density of Mars's atmosphere, they must also change as the martian climate changes. However, to date, martian meteorite production has received relatively little attention in the literature Here we expand upon our previous work to study martian meteorite production rates and how they depend upon variations of the martian atmosphere, and to estimate the ranges of mass, velocity and entry-angle that produce meteorites. We find that even the current atmosphere of Mars is sufficient to soft-land significant fractions of incident stony and iron objects, and that these fractions increase dramatically for denser martian atmospheres. Therefore, like impact cratering, meteorite populations may preserve evidence of past martian climates.     

Late Glacial fluvial response of the Niers‐Rhine (western Germany) to climate and vegetation change

The Niers valley was part of the Rhine system that came into existence during the maximum Saalian glaciation and was abandoned at the end of the Weichselian. The aim of the study was to explain the Late Pleniglacial and Late Glacial fluvial dynamics and to explore the external forcing factors: climate change, tectonics and sea level. The sedimentary units have been investigated by large‐scale coring transects and detailed cross‐sections over abandoned channels. The temporal fluvial development has been reconstructed by means of geomorphological relationships, pollen analysis and ¹⁴C dating. The Niers‐Rhine experienced a channel pattern change from braided, via a transformational phase, to meandering in the early Late Glacial. This change in fluvial style is explained by climate amelioration at the Late Pleniglacial to Late Glacial transition (at ca. 12.5 k ¹⁴C yr BP) and climate‐related hydrological, lithological and vegetation changes. A delayed fluvial response of ca. 400 ¹⁴C yr (transitional phase) was established. The channel transformations are not related to tectonic effects and sea‐level changes. Successive river systems have similar gradients of ca. 35–40 cm km^?1. A meandering river system dominated the Allerød and Younger Dryas periods. The threshold towards braiding was not crossed during the Younger Dryas, but increased aeolian activity has been observed on the Younger Dryas point bars. The final abandonment of the Niers‐Rhine was dated shortly after the Younger Dryas to Holocene transition. Traces of Laacher See pumice have been found in the Niers valley, indicating that the Niers‐Rhine was still in use during the Younger Dryas. Copyright © 2005 John Wiley & Sons, Ltd.     

抓住时机,大力推行系统总体设计和软件开发的工程化

气象部门研制的业务系统应用软件,取得了明显的社会效益及一定的经济效益。但由于注意标准化系统化不够,难以推广移植。而九十年代因更多信息交换的需要,不仅要注意软件开发的工程化,还应注意系统总体设计。在八五课题实施研究的时机,应大力推行系统总体设计和软件开发的工程化。     

Supereruptions as a Threat to Civilizations on Earth-like Planets

The largest explosive volcanic eruptions (supereruptions) produce >1000 km³ of ejected material and ≥1000 Mt (10¹⁵ g) of submicron atmospheric aerosols and dust. These eruptions may be capable of creating global climatic disturbances sufficient to cause severe problems for world agriculture and modern civilization. Supereruptions are estimated to occur on average about every 50,000 years, which is about twice the frequency of impacts by comets and asteroids ≥1 km diameter predicted to cause similar climatic effects. Prediction, prevention, and mitigation of global volcanic climatic disasters may be potentially more difficult than planetary protection from the threat of large impacts, so that explosive volcanism might limit the longevity of technological civilizations.     

地壳形变分形研究中的几个问题

本文针对地壳形变分形研究中实际存在的几个问题,包括1)分形研究是否避开了模式方法;2)地壳形变分形问题的性质和类属;3)地壳形变分形测算实施;4)形变参数时间序列Liapunov指数计算,开展了讨论,旨在促进地壳形变分形研究的进—步开展。     

2005年度天文学科科学基金项目申请和资助情况分析

介绍了2005年度天文学科科学基金申请、资助的基本情况,并对其结果进行了分析。     

A terrestrial record of Last Interglacial climate preserved by voluminous debris avalanche inundation in Taranaki,New Zealand

At Airedale Reef, western North Island, New Zealand, a ca. 4 m thick volcanogenic debris avalanche deposit has facilitated the preservation of an enveloping sequence of peats with interbedded andesitic tephras spanning marine isotope (MIS) 5. The sequence closely overlies a wave‐cut terrace correlated to MIS 5e and, in turn, is overlain by andic beds with tephra interbeds including the Rotoehu and Kawakawa tephras deposited during early MIS 3 and mid‐MIS 2, respectively. Pollen analysis of the organic sequence shows a coherent pattern of fluctuating climate for the Last Interglacial–Last Glacial transition that corresponds with marine isotope stratigraphy and supports the contention that orbital variations were a primary factor in late Quaternary southern mid‐latitude climate change. A five‐stage subdivision of MIS 5 is clearly recognised, with marine isotope substage (MISS) 5b drier than MISS 5d, and the cooling transition from 5a to MIS 4 also may have been comparatively dry and characterised by natural fire, perhaps associated with volcanism. Several other examples of volcanic impact on vegetation and the landscape are evident. The Airedale Reef sequence exhibits strong similarities with fragmentary MIS 5 pollen records preserved elsewhere in New Zealand and enables the proxy record of southern mid‐latitude climatic variability during the Last Interglacial–Glacial cycle to be extended. Copyright © 2004 John Wiley & Sons, Ltd.     

自适应双层网格的空间索引研究

空间数据索引是GIS系统中的关键技术,针对目前主流的网格空间索引方法进行了充分的研究比较,指出了网格索引方法对空间要素进行索引是高效的,但对于非规则地图它是不适应的.在此基础上设计了一种新的空间索引的方法,即自适应双层网格索引.详细地介绍了这种模型的实现过程,并且用实验充分论证了这个模型的效率,认为利用自适应双层网格索引检索空间数据时,处理、查询效率和占用空间等各方面具有较大优势.     

移动轨迹聚类方法研究综述

轨迹数据是人类移动行为的表征,能够映射出人的出行模式和社会属性等信息。怎样有效挖掘轨迹数据蕴藏的人类活动规律一直是研究的热点。通过轨迹聚类发现行为相似的类簇,从而探究群体的移动模式是轨迹挖掘和深度应用常见的方法之一。本文首先根据轨迹数据的特点,将轨迹数据模型分为轨迹点模型和轨迹段模型,并据此定义相应的相似性度量：空间相似性度量和时空相似性度量;然后,对两类模型的聚类方法进行了综述,并总结不同聚类算法的优缺点,以期为不同应用选取聚类算法提供科学依据;最后对移动轨迹数据聚类方法研究的发展趋势进行了讨论。     

岩浆-热液成矿系统中铁同位素地球化学研究现状

铁元素是岩浆-热液成矿系统中参与成矿的重要金属元素之一,岩浆-热液矿床中富铁矿物(黄铁矿、磁铁矿、黄铜矿、磁黄铁矿、斑铜矿、毒砂、菱铁矿)的δ⁵⁶Fe值变化较大(-2.07‰～+1.58‰),指示铁同位素在岩浆演化、流体出溶和热液演化过程中均存在明显的分馏,因此,在约束岩浆-热液成矿系统中成矿金属的迁移-富集-沉淀过程和示踪成矿物质来源方面具有巨大的应用潜力。通过整理和分析前人研究资料,文章总结了岩浆-热液成矿系统岩浆演化、流体出溶和热液演化过程中铁同位素地球化学行为的研究现状。岩浆演化过程中铁同位素会发生显著分馏,如部分熔融过程中,熔体相比残余固相富集重铁同位素;矿物分离结晶会引起残余熔体铁同位素组成的变化,主要受含Fe²⁺或Fe³⁺矿物结晶的影响,如磁铁矿分离结晶会导致残余熔体铁同位素组成变轻,总体反映岩浆氧化还原状态对铁同位素分馏的主要控制作用,因此,含矿岩体铁同位素组成及其变化可用于确定岩浆的氧化还原状态。流体出溶是含矿岩浆演化成为岩浆热液矿床的关键过程,出溶流体相对于母岩富集轻铁同位素,但实验研究表明出溶流体铁...