Continental European Eemian and early Würmian climate evolution: comparing signals using different quantitative reconstruction approaches based on pollen     

Stefan Klotz  Joel Guiot  Volker Mosbrugger   《Global and Planetary Change》2003,36(4):277-294

Analyses of Eemian climate dynamics based on different reconstruction methods were conducted for several pollen sequences in the northern alpine foreland. The modern analogue and mutual climate sphere techniques used, which are briefly presented, complement one another with respect to comparable results. The reconstructions reveal the occurrence of at least two similar thermal periods, representing temperate oceanic conditions warmer and with a higher humidity than today. Intense changes of climate processes become obvious with a shift of winter temperatures of about 15 °C from the late Rissian to the first thermal optimum of the Eemian. The transition shows a pattern of summer temperatures and precipitation increasing more rapidly than winter temperatures. With the first optimum during the Pinus–Quercetum mixtum–Corylus phase (PQC) at an early stage of the Eemian and a second optimum period at a later stage, which is characterised by widespread Carpinus, climate gradients across the study area were less intense than today. Average winter temperatures vary between −1.9 and 0.4 °C (present-day −3.6 to 1.4 °C), summer temperatures between 17.8 and 19.6 °C (present-day 14 to 18.9 °C). The timberline expanded about 350 m when compared to the present-day limit represented by Pinus mugo. Whereas the maximum of temperature parameters is related to the first optimum, precipitation above 1100 mm is higher during the second warm period concomitant to somewhat reduced temperatures. Intermediate, smaller climate oscillations and a cooling becomes obvious, which admittedly represent moderate deterioration but not extreme chills. During the boreal semicontinental Eemian Pinus–Picea–Abies phase, another less distinct fluctuation occurs, initiating the oscillating shift from temperate to cold conditions.  相似文献   

图象重建中的基本定理及其数值计算     

王卫东  包尚联 《CT理论与应用研究》2001,10(3):6-9

本文系统地给出了基于投影的图像重建的6个基本定理及其数值计算方法，研究了变焦束投影的扫描方式主要用于单光子断层扫描（SPECT）中以提高信噪比和分辨力。  相似文献   

Testing the Landscape Reconstruction Algorithm for spatially explicit reconstruction of vegetation in northern Michigan and Wisconsin     

Shinya Sugita  Tim Parshall 《Quaternary Research》2010,74(2):289-300

The Landscape Reconstruction Algorithm (LRA) overcomes some of the fundamental problems in pollen analysis for quantitative reconstruction of vegetation. LRA first uses the REVEALS model to estimate regional vegetation using pollen data from large sites and then the LOVE model to estimate vegetation composition within the relevant source area of pollen (RSAP) at small sites by subtracting the background pollen estimated from the regional vegetation composition. This study tests LRA using training data from forest hollows in northern Michigan (35 sites) and northwestern Wisconsin (43 sites). In northern Michigan, surface pollen from 152-ha and 332-ha lakes is used for REVEALS. Because of the lack of pollen data from large lakes in northwestern Wisconsin, we use pollen from 21 hollows randomly selected from the 43 sites for REVEALS. RSAP indirectly estimated by LRA is comparable to the expected value in each region. A regression analysis and permutation test validate that the LRA-based vegetation reconstruction is significantly more accurate than pollen percentages alone in both regions. Even though the site selection in northwestern Wisconsin is not ideal, the results are robust. The LRA is a significant step forward in quantitative reconstruction of vegetation.  相似文献   

西门子多排螺旋CT新技术   总被引：4，自引：0，他引：4  

徐晓东  邵军明  孔军 《CT理论与应用研究》2006,15(2):22-27

多排螺旋CT的推出使得CT临床应用能力大大提高,CT扫描仪进入了一个快速发展的时期。本文通过介绍双向飞焦点Z-Sharp技术、自由螺旋SureView等技术,比较各种螺旋重建算法,以及剂量调节方案CAREDose4D等新的西门子CT技术,呈现西门子在CT革新中所作的努力,Sensation64排CT在市场上大受欢迎证明了这些技术的优越性。  相似文献   

May-June precipitation reconstruction of southwestern Anatolia, Turkey during the last 900 years from tree rings   总被引：1，自引：0，他引：1  

Ramzi Touchan  Ünal Akkemik  Nesat Erkan 《Quaternary Research》2007,68(2):196-202

A May-June precipitation reconstruction (AD 1097-2000) has been developed for southwestern Anatolia in Turkey, the longest reported to date in this region. The reconstruction was derived from a regional Juniperus excelsa chronology that was built from material sampled at four sites in the Antalya and Mersin Districts. The regional tree-ring chronology accounts for 51% of the variance of instrumentally observed May-June precipitation. The years AD 1518 to 1587 are the most humid period in the reconstruction, coinciding with a major shift in European climate. The driest 70-year period in the reconstruction is AD 1195 to 1264. The period AD 1591-1660 represents the third driest and was characterized by instability climatically, politically, and socially in Anatolia.  相似文献   

由投影重建图像的对称网格迭代算法   总被引：1，自引：0，他引：1  

邱钧  王亮 《CT理论与应用研究》2007,16(2):20-30

本文对于工业CT检测中常用的代数迭代重建算法提出了改进,利用投影射线之间存在的几何对称结构,提出了图像重建的对称网格迭代算法(简写为SM-IRT).该算法简化了投影系数矩阵的计算,调整了迭代算法逐线校正的迭代顺序.对模拟数据和工业CT实测数据进行了重建图像的数值实验,结果表明:与常规算法比较,本文提出的新算法重建速度快,成像精度高.  相似文献   

全球超级古陆重建研究的新进展   总被引：1，自引：0，他引：1  

谭富文  潘桂棠 《四川地质学报》2000,20(1):6-11

介绍了新元古代－早古生代超级大陆的重建研究,表明中元古代以来,地球上先后经历了罗迪尼亚－冈瓦纳－潘基亚等几次超级大陆的拼合与裂解过程,罗迪尼亚古陆的拼合源于中元古代晚期（１３００～１０００Ｍａ）发生的全球性格林威尔造山事件。东冈瓦纳（澳大利亚、东南极和部分非河）作为一个整体最早与劳伦古陆分离,导致了太平洋的张开。进一步的裂解产生了组成西冈与纳的各克拉通块体。在泛非造山和期间（７２０～５００Ｍａ）西  相似文献   

青海都兰过去2000年来的气候重建及其变迁   总被引：35，自引：4，他引：35  

康兴成  张其花  Paul Sheppard 《地球科学进展》2000,15(2):215-221

根据青海都兰地区树木年轮样本建立了目前我国最长的年轮年表序列。通过年表与气候要素间相关函数、响应函数及响应面分析,选择了可被重建的气候因子,建立了重建方程,恢复了青海都兰地区历史时期的平均温度;并分析讨论了近2 000年来该地区的气候变化。阐述了这个地区的冷暖交替及周期循环。对一些重大气候事件,如中世纪暖期、小冰期和近一个世纪以来的升温等,逐个事件进行了剖析。并与全球温度变化进行了对照。都兰温度曲线为青藏高原东部地区提供了一个较好的气候变化信息表。  相似文献   

恢复生态学及其发展   总被引：54，自引：1，他引：54  

赵晓英  孙成权 《地球科学进展》1998,13(5):474-480

简述了国内外恢复生态学的发展概况，分析了我国在生态系统退化的原因、生态学过程以及退化生态系统恢复重建的方法和生态学机理等方面的研究进展。针对我国在恢复生态学研究和退化生态系统恢复实践中存在的问题，提出了加强我国恢复生态学研究的建议。  相似文献   

张掖市震灾预防和灾后重建工作     

张掖市地震局 《地震工程学报》2005,27(4):392-393

0前言在省委、省政府的正确领导下,在省地震局具体指导和大力支持下,张掖市政府和地震局认真贯彻“预防为主,防御与救助相结合”的防震减灾工作方针,始终把防震减灾工作当作事关人民生命财产安全、经济发展和社会稳定的大事来抓,切实加强对全市防震减灾工作的领导,狠抓震害预防  相似文献