欧洲高速铁路的发展历史与经济效应

本文回顾了欧洲高速铁路的发展历史,包括国家层面上的高铁网络如何发展和解决各种问题;在此基础上,介绍了高速铁路概念的变化,其目标在于为航空和短距离通勤提供补充性的服务;最后,介绍了高铁网络扩张过程中所面临的经济和评估问题,以及与欧盟的综合交通网络规划的关系。     

Towards a true 4‐dimensional data assimilation algorithm: application of a cycling representer algorithm to a simple transport problem

3‐dimensional variational algorithms are widely used for atmospheric data assimilation at the present time, particularly on the synoptic and global scales. However, mesoscale and convective scale phenomena are considerably more chaotic and intermittent and it is clear that true 4‐dimensional data assimilation algorithms will be required to properly analyze these phenomena. In its most general form, the data assimilation problem can be posed as the minimization of a 4‐dimensional cost function with the forecast model as a weak constraint. This is a much more difficult problem than the widely discussed 4DVAR algorithm where the model is a strong constraint. Bennett and collaborators have considered a method of solution to the weak constraint problem, based on representer theory. However, their method is not suitable for the numerical weather prediction problem, because it does not cycle in time. In this paper, the representer method is modified to permit cycling in time, in a manner which is entirely internally consistent. The method was applied to a simple 1‐dimensional constituent transport problem where the signal was sampled (perfectly and imperfectly) with various sparse observation network configurations. The cycling representer algorithm discussed here successfully extracted the signal from the noisy, sparse observations     

Palynological investigations of Permian rocks from Nordaustlandet, Svalbard

Palynological investigations of nine sections covering the upper part of the Nordenskioldbreen Formation, Gipshuken Formation, and the lower part of the Kapp Starostin Formation in the Wahlenbergfjorden area, Nordaustlandet. yielded palynomorphs in three sections. Three assemblages are recognized. A tentative correlation with the Sverdrup Basin suggests a Sakmarian to Artinskian age for the uppermost Nordenskioldbreen and lower Gipshuken Formations. Thermal maturity is low. The palynoflora is dominated by striate pollen suggesting an arid climate throughout the deposition of the Nordenskioldbreen and Gipshuken Formations.