Modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies     

James Q.Feng  C.F.Gallo 《中国天文和天体物理学报》2011,(12)

We present an efficient,robust computational method for modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies.With appropriate mathematical treatments,the apparent numerical difficulties associated with singularities in computing elliptic integrals are completely removed.Using a boundary element discretization procedure,the governing equations are transformed into a linear algebra matrix equation that can be solved by straightforward Gauss elimination in one step without further ...  相似文献   

Cultural impacts to tribes from climate change influences on forests     

Garrit Voggesser  Kathy Lynn  John Daigle  Frank K. Lake  Darren Ranco 《Climatic change》2013,120(3):615-626

Climate change related impacts, such as increased frequency and intensity of wildfires, higher temperatures, extreme changes to ecosystem processes, forest conversion and habitat degradation are threatening tribal access to valued resources. Climate change is and will affect the quantity and quality of resources tribes depend upon to perpetuate their cultures and livelihoods. Climate impacts on forests are expected to directly affect culturally important fungi, plant and animal species, in turn affecting tribal sovereignty, culture, and economy. This article examines the climate impacts on forests and the resulting effects on tribal cultures and resources. To understand potential adaptive strategies to climate change, the article also explores traditional ecological knowledge and historical tribal adaptive approaches in resource management, and contemporary examples of research and tribal practices related to forestry, invasive species, traditional use of fire and tribal-federal coordination on resource management projects. The article concludes by summarizing tribal adaptive strategies to climate change and considerations for strengthening the federal-tribal relationship to address climate change impacts to forests and tribal valued resources.  相似文献   

A dynamic theory of hydrocarbon migration   总被引：1，自引：0，他引：1  

Fareed I. Siddiqui  Larry W. Lake 《Mathematical Geology》1992,24(3):305-327

This paper presents a new analysis of secondary migration of hydrocarbon that does not require capillary forces for trapping, but instead uses the method of characteristics and wave theory. The waves change speed and either reflect or refract (or partially reflect and partially refract) as they contact with layers of different flow capacities. Reflection of a certain wave from a boundary starts hydrocarbon accumulation below that boundary. The method is easy to use and conforms readily to graphical solution. For the sake of simplicity there is only two-phase flow. The application of this method gives new insights into the physics of migration and entrapment of oil. The method gives realistic times for oil accumulation and points to oil generation rate as the most sensitive variable. Oil and water densities, viscosities, and permeability are also important. We find that at the very small generation rates usually assumed the time required to develop a given column thickness is insensitive to the distance from the source rock. In general, the method also predicts a non-uniform saturation in the oil column caused by an interaction between buoyancy and viscous forces. Being based on the dynamic interactions of viscous and buoyancy forces, our theory is considerably at odds with hydrostatic approaches. We assume no capillary pressure, one-dimensional flow, and no regional groundwater flow, conditions which are not realized in actual migration. The theory should be viewed therefore as an end member of a more general theory; nevertheless, the largely graphical solutions give fundamental insights that are difficult to obtain by other techniques.  相似文献   

A strategy for frequency spectra of quaternary climate records     

Andre Berger  JL Melice  L Hinnov 《Climate Dynamics》1991,5(4):227-240

The paleoclimatic variability at frequencies ranging from 10^–4 cycle per year (cpy) to 10^–5 cpy is investigated using a set of four deep-sea cores from the Atlantic, Pacific and Indian Oceans. Dominant features are the presence of orbital frequencies corresponding to mean periods of 117.7, 43.6, 24.9 and 19.3 kyr. These are statistically significant according to such advanced spectral tools as Blackman-Tukey, maximum entropy and the highly efficient Thomson technique. However, the main purpose of this paper is methodological, describing the statistical analyses of time series with modern methods in order to stress their relative power, advantages and disadvantages. The more advanced statistical methods confirm the coincidence of the dominant periods in the deep sea cores and those in the astronomical elements, including combination tones. Three frequency bands of high paleoclimatic variability centred at 15.4, 13 and 10.8 kyr are indeed also detected. These two last periods are very close to those predicted by the climatic non-linear model of Ghil and Le Treut and found by Pestiaux et al. and Yiou et al.  相似文献   

河北阳原东目连第四纪叠层石古环境分析   总被引：7，自引：3，他引：7  

闵隆瑞  迟振卿  朱关祥  姚培毅  牛平山 《地质学报》2002,76(4):446-453

组成阳原县东目连湖积台地的第四纪“泥河湾层”地层中,发育多层藻迹层和一层“菜花形”、“锥体状”大叠层石(个体高20 cm),大叠层石层延伸1 km,构成古藻坪微地貌。经OSL和古地磁测试,大叠层石年龄推测为220 ka左右。镜下叠层石片子中见蓝藻门的纤细席藻种Phormidium tenue(Menegh)Genegh和湖泊鞘丝藻种Lyngbya Limnetica Lemmermann等。不同形态叠层石反映不同发育阶段,藻迹发育于高水位边缘部位,大叠层石发育于高水位与低水位之间边缘部位。亮层和暗层交替出现的纹层构造是组成叠层石的基本结构构造,它们是由蓝藻丝体生长代谢活动所致。据同位素、磁化率、粒度、地球化学元素、X衍射、孢粉和生物化石等分析,认为气候暖干、盐度高及大量苔藓虫、介形虫、龙介科蠕虫等生物存在的环境有利于大叠层石形成。叠层石可能属半咸水湖、滨湖浅水环境,但据首次在第四纪泥河湾层中发现的苔藓虫和龙介科蠕虫管分析,其成因是否与海水有过联系尚待进一步研究。  相似文献   

The Evolution of the Quaternary Salt Lakes in the Qaidam Basin     

Wei Xinjun  Jiang Jixue Qinghai Research Institute of Salt Lake Exploration  Exploitation  Golmu  Q inghai 《《地质学报》英文版》1994,68(1):71-82

The paper discusses the distribution of Quaternary sediments, occurrence of saline minerals and phases of neotectonic movements and their manifestations in the Qaidam basin. The formation of four successive lacustrine terraces in Tertiary anticlinal zones in the western part of the basin was related to the neotectonic movements that took place 100 Ka ago, and the distribution of such terraces discloses, in a way. the evolutionary history of the Quaternary salt lakes. According to the distribution of the terraces coupled with the distribution of Quaternary sediments and features of salt deposition, four periods of Quaternary salt lake evolution in the basin may be distinguished, which correspond to four stages of salt deposition respectively.  相似文献   

A deterministic, coherent, and dual-polarized laboratory study of microwave backscattering from water waves, Part I: Short gravity waves without wind     

Kwoh  D. Lake  B. 《Oceanic Engineering, IEEE Journal of》1984,9(5):291-308

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Spectral shifts near compact objects     

Kayll Lake  Eric Myra 《Astrophysics and Space Science》1981,79(2):515-519

We show that radiation emitted from material freely falling toward a black hole or neutron star cannot be blue-shifted as recently claimed by Cohen and Struble. The relativistic corrections to the classical apparent limb angle are given explicitly for spherical sources in collapse.  相似文献   

On poetry,pragmatism and the urban possibility of creative democracy   总被引：1，自引：1，他引：0  

Robert W. Lake 《Urban geography》2017,38(4):479-494

Democracy everywhere is under siege, overwhelmed by oligarchy, apathy, bureaucracy, and spectacle, at best an ideal that has never been achieved. Yet against the dystopian vision of post-democracy and the post-political is what John Dewey, more than a half-century ago, called “creative democracy,” a moral practice of radical equality in the pragmatic, collective project of hammering out answers to the question of how we should live. This article explores Dewey’s concept of creative democracy as a moral idea, a personal ethic, a collective commitment, and a precondition for political practice. Establishing the conditions for creative democracy requires a significant reconsideration of the education of democratically competent citizens and of the democratic practice of research and knowledge production. Creative democracy is a poetic project, an imaginative opening, an ethical possibility, a shared responsibility, and a practice of hope that opens a path to achieving a better kind of life to be lived.  相似文献   

A commentary on “how to interpret expert judgment assessments of twenty-first century sea-level rise” by Hylke de Vries and Roderik SW van de Wal     

JL Bamber  WP Aspinall  RM Cooke 《Climatic change》2016,137(3-4):321-328

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