Interpretation of the complex dune morphology on Mars: dune activity,modelling and a terrestrial analogue     

S. Silvestro  L. K. Fenton  T. I. Michaels  A. Valdez  G. G. Ori 《地球表面变化过程与地形》2012,37(13):1424-1436

In this work we analyze a dark erg on Mars that could be considered a mega‐dune (draa) where secondary dunes of different morphology are superposed over a main crescent‐shaped bedform (primary dune). The presence of a complex, multi‐directional wind regime is indicated as one of the main causes for the accumulation of a tall draa, presenting an analogy to the Great Sand Dunes in Colorado. In both cases, main regional winds from the SW blow in opposition to winds from the NE which are enhanced by the topography. Such a complex wind regime leads to the development of star and reversing dunes and is accurately predicted by atmospheric models on a regional and local scale. Signs of activity in the form of grainflow scars are also noted over the slip faces of many dunes, suggesting that easterly winds are actively shaping the study draa in the present‐day climatic setting. The presence of this draa on Mars suggests a complex interaction between regional and local topographically controlled flows and a consistent availability of sand. The future study of an analogue terrestrial site such as the Great Sand Dunes could be fundamental for understanding the evolution of similar Martian dune fields. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The abundance and diversity of larval and juvenile fish in a tropical estuary     

A. Tito de Morais  L. Tito de Morais 《Estuaries and Coasts》1994,17(1):216-225

The larval and juvenile fish of the Cayenne river estuary (French Guiana, South America) were sampled at two stations from June 1989 until October 1990. A total of 52,989 individuals from 59 species, some still incompletely identified, were collected. Three families, Engraulidae, Gobiidae and Sciaenidae, accounted for over 97% of the total number of juveniles. The analysis of data over this period showed low diversity, and a difference in diversity between the two sampling locations (H′ = 1.24 and 1.68). The results conform to some theoretical models of abundance that suggest a relative equilibrium of juvenile assemblages. In contrast, the seasonal variations in diversity and abundance and the results of a correspondence analysis showed significant differences in species distribution and in their relative abundance at the two sampling locations at certain periods, mainly in the rainy season. Our study indicates that, in spite of an apparent stability, the year to year variation in salinity and freshwater inputs could affect juvenile recruitment of some species and induces modifications in the composition of larval and juvenile estuarine fish assemblages.  相似文献   

Recent advances in the chemistry and properties of atmospheric nucleants: a review     

Alberto C. Montefinale  Tito Montefinale  Henry M. Papée 《Pure and Applied Geophysics》1971,91(1):171-210

Summary A survey is carried out of recent progress in the investigation of weather-active atmospheric nucleants. Emphasis is placed on the work date during the last decade, and some resulting implications are discussed.  相似文献   

Broadening participation,creating community,and learning that it never goes as planned     

James  Autumn C.  Alyasiri  Elaf  Howe  Matthew  James  Ryan D.  Jin  Yiwei  Lwanga  Kyagaba  McClain  Bailey  Moore  Andrea  Shao  Yaxiong  Valdez  Felipe 《GeoJournal》2021,87(2):281-292

This paper presents the experience of a service-learning course which used community geography to study a proposed research and community center in DeKalb, IL. The center was proposed as a jointly-developed project by the Northern Illinois University and local governmental entities. The original goal of the course was to explore the viability of the proposed project and solicit feedback from the community through traditional engaged planning and public participation. As students began interacting with university and residential communities, it became clear that both communities had input for the center, and found similarities in their experiences and perceptions. While noted divisions in interest groups are known in DeKalb, both communities found themselves surprisingly interested in meaningful discussion to better understand each other through their shared experiences. In response, our theoretical approach shifted to community geography. Students, university employees, and local residents introduced and analyzed questions together as researchers and participants, and developed recommendations to address shared concern. Students then prepared a report advocating for those concerns to submit to university and community leaders. Following the evolution of this project, this paper presents lessons learned and areas for application of community geography as a pedagogical technique, as an important component of geography curriculum, and as a research framework for town-gown relationship inquiry.

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