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1.
Colin PALMER 《地球学报》2010,31(Z1):53-53
The wing of a pterosaur is unique in many ways, not least in its basic morphology, comprising a single supporting structure along the anterior edge of a flexible membrane lifting surface. No other flying vertebrate has adopted this morphology and there are no direct analogues in mechanical aerodynamics, the closest being sailboat mainsails. 相似文献
2.
Pterosaurs exhibit a large size range with the smallest approximately the size of a sparrow and the largest about the size of a small airplane. Based on studies of extant flying vertebrates and principles of allometry (Norberg & Rayner, 1987; Rayner, 1988), a reasonable assumption is that pterosaurs of different sizes used their wings differently during flight. 相似文献
3.
During the last two decades more than twenty phylogenetic analyses of pterosaur relationships have been published. These range from small scale studies restricted to a few species from one clade, to comprehensive analyses that include the majority of known taxa. Most of these contributions can be traced back to data sets published either by Kellner (2003) or Unwin (2003), who, in turn, incorporated data from earlier analyses by Howse and Bennett. 相似文献
4.
The anatomical term tuba vertebralis was introduced by Martill et al. (1998) to describe a bony tube which enclosed the spinal cord in the type cervical vertebra of the giant azhdarchid pterosaur Arambourgiania philadelphiae, from the Late Cretaceous of Jordan. 相似文献
5.
David PETERS 《地球学报》2010,31(Z1):55-56
Currently there is no ready reference source of pterosaur pedes available to match ichnotaxa to potential trackmakers. While presently recognized pterosaur ichnites all indicate a plantigrade pes and a quadrupedal mode of locomotion, those configurations were not basal or universal. 相似文献
6.
Ross A. ELGIN 《地球学报》2010,31(Z1):18-19
The Pterosaur Flight Dynamics Research Group was established just over three years ago as part of a Karlsruhe based initiative to investigate the aerodynamics of pterodactyloid pterosaurs. 相似文献
7.
Azhdarchid pterosaurs include the largest known flying animals, with the largest species reaching a potential mass of over 250 kg. Prior work suggests that several features of azhdarchid anatomy could be associated with a soaring-dominated lifestyle, including large size, burst-flapping adapted pectoral girdle and proximal forelimb, moderate to high wing aspect ratio, and exceptional pneumaticity. 相似文献
8.
Cearadactylus atrox is one of the first pterosaurs unearthed from the Araripe Basin (Northeast Brazil) (Leonardi and Borgomanero 1983, 1985) (Fig.1). The fossil was preserved in a calcareous concretion typical of the Romualdo Formation and comprised an almost complete skull with lower jaw, but lacked the occipital region. 相似文献
9.
The anurognathids are a rare group of ‘rhamphorhynchoid’ pterosaurs although increasing numbers of specimens are being described (e.g. Bennett, 2007, Gao et al., 2009). 相似文献
10.
INTRODUCTION Manganese deposits are the most important mineral resources of Chin-hsien. To these manganese fields the author paid a visit of some days in April, 1929. The present paper is a summary of the manganese deposits of 相似文献
11.
Reginald E. Newell 《Quaternary Research》1974,4(2):117-127
It is proposed that the two preferred modes of temperature and circulation of the atmosphere which occurred over the past 100,000 yr correspond to two modes of partitioning of the poleward energy flux between the atmosphere and ocean. At present the ocean carries an appreciable fraction of the transport, for example about three-eighths at 30°N. In the cold mode it is suggested that the ocean carries less, and the atmosphere more, than at present. During the formation of the ice, at 50,000 BP, for example, the overall flux is expected to be slightly lower than at present and during melting, at 16,000 BP, slightly higher. The transition between the modes is seen as a natural imbalance in the atmosphere-ocean energy budget with a gradual warming of the ocean during an Ice Age eventually cluminating in its termination. At the present the imbalance is thought to correspond to a natural cooling of the ocean, which will lead to the next Ice Age.The magnitude of temperature changes in the polar regions differ between the hemispheres in the same way as present seasonal changes, being larger in the northern than in the southern hemisphere.Overall the atmospheric energy cycle was more intense during the Ice Ages than now.Observational tests are proposed by which predictions from the present arguments may be compared with deductions about the environment of the past.Data used for the present state of the atmospheric general circulation are the latest global data available and contain no known major uncertainties. However, data for the oceanic circulation and energy budget are less well known for the present and almost unknown for the past. Hence the proposed imbalances must be treated as part of a speculative hypothesis, but one which eventually may be subject to observational test as no solar variability is invoked. 相似文献
12.
以最新钻取的SE2孔沉积物为重点研究对象,对晚第四纪以来钱塘江下切河谷充填物的沉积特征和沉积相进行了精细研究,重建了研究区地层结构和层序地层格架,总结了强潮型钱塘江河口湾和下切河谷的沉积模式。钱塘江下切河谷充填物自下而上依次发育河床、河漫滩、古河口湾、近岸浅海和现代河口湾5种沉积相类型,表现为一个较完整的Ⅰ型层序,其内部层序界面、初始海泛面、最大海泛面、海侵和海退潮流侵蚀面、体系域内海侵面发育。钱塘江下切河谷充填物自海向陆可划分为海向段、近海段、近陆段和陆向段4段,各段沉积序列和海陆相互作用程度不同。在钱塘江下切河谷充填物中海陆过渡部位首次明确划分出了古河口湾相,并对其沉积特征和分布模式进行了初步探讨;其形成时间在9000 a BP左右,具有与现代河口湾不同的沉积特征,表现为中部为潮道砂体沉积,向陆渐变为受潮流影响的河流沉积,两侧被潮坪或盐沼沉积包围,沉积物在平面上自陆向海呈现粗-细-粗的分布模式。现代河口湾平面上自陆向海依次发育受潮流影响的河流沉积、粉砂质砂坎、潮道-潮流砂脊复合体和湾口泥质沉积区,沉积物呈现粗-细-粗-细的分布模式,与大多数河口湾常见的粗-细-粗的分布格局明显不同。 相似文献
13.
在土地利用现状变更调查中,双点图解交会法较好地解决了由于变更图斑形状的变化,线状地物与土地现状图部分失真,无法采用简易补测法进行补测变更图斑的问题。该方法灵活方便,实用性强,补测精度较高,对在土地利用现状变更调查中外业补测图斑有一定的利用价值。 相似文献
14.
Boris Jeremi&#x; Gerik Scheuermann Jan Frey Zhaohui Yang Bernd Hamann Kenneth I. Joy Hans Hagen 《国际地质力学数值与分析法杂志》2002,26(10):925-944
We present a novel technique for visualizing tensors in three dimensional (3D) space. Of particular interest is the visualization of stress tensors resulting from 3D numerical simulations in computational geomechanics. To this end we present three different approaches to visualizing tensors in 3D space, namely hedgehogs, hyperstreamlines and hyperstreamsurfaces. We also present a number of examples related to stress distributions in 3D solids subjected to single and load couples. In addition, we present stress visualizations resulting from single‐pile and pile‐group computations. The main objective of this work is to investigate various techniques for visualizing general Cartesian tensors of rank 2 and it's application to geomechanics problems. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
15.
Thomas J. Crowley 《Quaternary Research》1984,21(1):105-110
Models of atmospheric circulation in the North Atlantic sector during glacial inception can be expanded to a hemispheric scale with the aid of diagnostic studies of the present climate. The present “Greenland Above” (GA) atmospheric circulation type may be a candidate for the atmospheric circulation type required during glacial inception. The pattern is an amplification, with only minor phase shifts, of the present average winter circulation pattern in the extratropical Northern Hemisphere. Southerly flow in the northwest Atlantic is associated with warm ocean temperatures, low sea ice in the Davis Strait, and increased precipitation over northeast Canada. Evidence from modeling of the present climate indicates that the GA pattern could be maintained by increased snow cover over eastern North America. Enhanced snow cover, due to decreased Northern Hemisphere summer insolation, could cause a similar response on an ice-age time scale. 相似文献
16.
新疆艾丁湖与柴窝堡湖记录、玛纳斯湖记录、巴里坤湖记录、伊犁黄土-古土壤记录、罗布泊沉积记录和塔里木盆地南缘克里雅河流阶地钙质结核层记录,青海察尔汗盐湖以及内蒙古古居延海沉积记录、白碱湖和吉兰泰盐湖、巴丹吉林沙漠钙质胶结层等记录均显示40～30kaB.P.时期整个西北地区气候温暖湿润.其中,内蒙古西部温度较现代高2.～3℃,西北大部分地区降水量成倍增加,气候显著湿润化.其成因可能是由于当时中、低纬度岁差周期高辐射所造成的海洋表面温度升高,蒸发加强,西风环流和夏季风为西北提供的水汽大幅度增多的缘故. 相似文献
17.
通过对苏北盆地海安凹陷T40反射层现今构造应力场、次级凹陷边界二级断裂和次级凹陷内三、四级断裂力学性质及其构造活动样式等分析研究认为:海安凹陷现今最大主应力方向为NE 70°左右;现今最大主应力为50 MPa左右,现今最小主应力为30 MPa左右。海安凹陷内次级凹陷边界二级断裂现今主要表现为张性或张扭性活动特征,张扭性活动方式既有顺扭也有反扭,并且同一断裂不同部位活动性质存在差异;海安凹陷内次级凹陷三、四级断裂现今也主要表现为张性或张扭性活动特征,张扭性活动方式既有顺扭也有反扭,个别表现为压性和压扭性活动,并且同一断裂不同部位活动性质存在差异。 相似文献
18.
Regional administrations present themselves in many different ways on the internet. A content analysis of regional websites in the Netherlands and Northwest Germany revealed this diversity. Geographical factors can partly explain these differences. Mapping the five principal aspects of the geographical representations of regional administrations revealed some spatial clusters. These regional representations are also linked to the geographical characteristics of regions. Competitive mid-sized regions focus more on economic items. Different types of peripheries vary much more in how they present themselves on the internet. The way regions present themselves is linked to the polarising influence of regional competition, but there is still considerable freedom for regions to present a distinct region image. 相似文献
19.
The island of Newfoundland, Canada, is situated close to the former margins of the Laurentide ice sheet. The post-glacial sea-level history is complex, dominated by the effects of an ice-marginal crustal forebulge produced by isostatic deformation of the lithosphere. Marine fossils found above present sea-level can be 14 C dated, and examination of the temporal and geographical distribution of these 14 C dates in combination with geomorphological indicators of past sea-levels indicates regional trends of relative sea-level change. For most of the island (apart from the Northern Peninsula) no samples have been recovered that date younger than 8000 BP. suggesting that sea-level lay below the present one in these areas for the last 8000 years. The same areas commonly show geomorphological evidence for stands of sea-level both above and below present sea-level. This evidence is interpreted as showing that over most of Newfoundland, following deglaciation, sea-level fell to below present levels, and subsequently rose to the modern level. Exceptions to this pattern are the north of the Northern Peninsula, which shows a history of continuous emergence, or a more complex pattern of sea-levels falling below present, subsequently rising above present, and currently falling; and the northeast Avalon Peninsula, which may have had sea-levels below present throughout post glacial times. This pattern of relative sea-level change is interpreted as being mostly due to isostatic recovery, with the main factor being northerly migration of the forebulge. Mapping the time at which sea-level fell below the present level allows estimation of the rate of northerly migration and collapse of the forebulge at between 4.5 and 11 km/100 years; this is considerably faster than previous estimates. 相似文献
20.
M. Baumann R. Astudillo Y. Qiu E. Y. M. Ang M. B. van Gijzen R.-É. Plessix 《Computational Geosciences》2018,22(1):43-61
In this work, we present a new numerical framework for the efficient solution of the time-harmonic elastic wave equation at multiple frequencies. We show that multiple frequencies (and multiple right-hand sides) can be incorporated when the discretized problem is written as a matrix equation. This matrix equation can be solved efficiently using the preconditioned IDR(s) method. We present an efficient and robust way to apply a single preconditioner using MSSS matrix computations. For 3D problems, we present a memory-efficient implementation that exploits the solution of a sequence of 2D problems. Realistic examples in two and three spatial dimensions demonstrate the performance of the new algorithm. 相似文献