Comparing alpine watershed attributes from LiDAR,Photogrammetric, and Contour‐based Digital Elevation Models     

Chris Hopkinson  Masaki Hayashi  Derek Peddle 《水文研究》2009,23(3):451-463

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The legacy of Allan Hills 84001     

Derek Sears  Ed Scott  Paul Warren 《Meteoritics & planetary science》1998,33(4):545-546

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Diagenesis of plant biopolymers: Decay and macromolecular preservation of Metasequoia     

Neal S. Gupta  Hong Yang  Qin Leng  Derek E.G. Briggs  George D. Cody  Roger E. Summons 《Organic Geochemistry》2009,40(7):802-809

Analysis of modern Metasequoia leaves revealed the presence of the structural polyester cutin, guaiacyl lignin units and polysaccharides. Analysis of environmentally decayed Metasequoia leaves revealed that guaiacyl lignin units and cellulose were degraded more than vinyl phenol (the last being the primary pyrolysis product of cutin and plant cuticles) suggesting that cutin is more stable than lignin and cellulose during degradation, contrary to some previous studies. This observation is supported by electron microscopy showing changes in the cellular structure and cuticle of modern, decayed and fossil Metasequoia leaves. Metasequoia fossils from the Eocene of Republic (Washington State) showed a significant aliphatic component, but biopolymeric lignin and polysaccharides were not detected. Fossils from the Eocene of Axel Heiberg revealed the presence of lignin and an aliphatic polymer up to C₂₉ with cellulose, and fossils from the Miocene Clarkia deposit (Idaho) revealed lignin and an aliphatic polymer up to C₂₇ without any polysaccharides. Modern Metasequoia needles heated experimentally in confined conditions generated a macromolecular composition with an aliphatic polymer up to C₃₂ and additional phenolic compounds similar to those present in the fossils. Experimental heating of cutin is known to generate an aliphatic polymer with carbon chain length units <C₂₀. Thus, the n-alkyl component with chain length units >C₂₀ in the heated Metasequoia needles is a product of incorporation of longer chain plant waxes, indicated by the odd/even predominance of the >C₂₇ n-alkanes. The resistant nature of cutin compared to lignin and polysaccharides explains the presence of an n-alkyl component (<C₂₀) in fossil leaves even when polysaccharides are absent and lignin has decayed; cutin and its diagenetically altered products contribute significantly to the presence of aliphatic components in terrestrially derived sedimentary organic matter.  相似文献   

Aeolian fetch distance and secondary airflow effects: the influence of micro‐scale variables on meso‐scale foredune development     

Kevin Lynch  Derek W. T. Jackson  J. Andrew G. Cooper 《地球表面变化过程与地形》2008,33(7):991-1005

Unsuccessful attempts to use process‐scale models to predict long‐term aeolian sediment transport patterns have long been a feature of aeolian research. It has been proposed that one approach to overcome these problems is to identify micro‐scale variables that are important at longer timescales. This paper assesses the contribution of two system variables (secondary airflow patterns and fetch distance) to medium‐term (months to years) dune development. The micro‐scale importance of these variables had been established during previous work at the site (Magilligan Strand, Northern Ireland). Three methods were employed. First, sand drift potentials were calculated using 2 years of regional wind data and a sediment transport model. Second, wind data and large trench traps (2 m length × 1 m width × 1·5 m depth) were used to assess the actual sediment transport patterns over a 2‐month period. Third, a remote‐sensing technique for the identification of fetch distance, a saltation impact sensor (Safire) and wind data were utilized to gauge, qualitatively, sediment transport patterns over a 1‐month period. Secondary airflow effects were found to play a major role in the sediment flux patterns at these timescales, with measured and predicted rates matching closely during the trench trap study. The results suggest that fetch distance is an unimportant variable at this site. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Long-Term Variations in Seasonal Weather Conditions Important to Corn Production in Illinois     

Stanley A. Changnon  Derek Winstanley 《Climatic change》2000,47(4):353-372

An analysis of long-term records ofcorn yields and seasonal weather conditions inIllinois found major temporal shifts and importantspatial variations in the types of seasonal weatherconditions, expressed as the normality of temperatureand rainfall conditions, that create positive andnegative impacts on yields. Nineteen different typesof corn-weather seasons (May–August) occurred during1901–1997, and 9 of these seasons accounted for mostof the high corn yields (top 20 of the 97) and 8seasonal types produced most low yields (lowest 20values). Assessment of the years with either high orlow yields revealed (1) some corn-weather seasonaltypes were uniformly distributed throughout thecentury; (2) others were unevenly time distributed,some occurring only in early decades and others onlyin the last few decades; and (3) certain weather typesvaried regionally. The yield responses to certainseasonal types varied over time, being good early andnot so later, or vice versa. The findings indicatethat time changes in farming practices, cornvarieties, and agricultural technology have alteredhow certain types of growing season weather affectcorn yields. Regional differences in yield outcomesfrom a given set of weather conditions reflect varyingsoil and climate differences across Illinois. Thespatial and temporal differences reveal the importanceof using weather-impact results to define seasonalweather extremes. The kinds of seasons creating highyields predominated during 1901–1910 and 1961–1997,and most seasons creating low yields were concentratedbetween 1911 and 1960. Comparison of the 1901–1997temporal distributions of yield extremes (high andlow) with the temporal distributions of cyclonepassages and the incidence of ENSO conditions thataffect growing season weather conditions revealed agenerally good relationship. The shifting temporalresponses to various kinds of seasonal weatherconditions during the 20th century reveal some ofthe difficulties facing efforts to project realisticand detailed impacts in agriculture from alteredfuture seasonal weather conditions.  相似文献   

Cross-border movement and the dynamics of transition processes in Southeastern Europe     

Derek Hall 《GeoJournal》2000,50(2-3):249-253

This paper attempts to provide an evaluation of cross-border movement - short-term, long-term and permanent - in southeastern Europe, identifying the functions of such movement in relation to ongoing restructuring processes. It also suggests a range of theoretical frameworks appropriate for further research in this area. While refugee flight and permanent displacement have resulted from some of the more pernicious and explicit processes of reinvigorated nationalism in the region, patterns of petty and larger scale trading, labour and education migration, leisure mobility and tourism, better reflect the differential impact of local, regional and global push and pull factors and the new configurations of national boundaries and neighbourly relations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The non‐trivial problem of meteorite pairing     

Paul h. Benoit  Derek w. g. Sears  J. m. c. Akridge  P. a. Bland  F. j. Berry  C. t. Pillinger 《Meteoritics & planetary science》2000,35(2):393-417

Abstract— Pairing is the procedure of identifying fragments of a single meteorite fall (that were separated during atmospheric passage or during terrestrial history) by establishing the similarity of two or more meteorite fragments. We argue that pairing is governed by two principles, that only a single mismatch of properties is required to refute a proposed pairing, and that virtually all pairings bear some degree of uncertainty. Using data distributions for modern falls, we take a probability approach to estimate degrees of certainty associated with proposed pairings, emphasizing the importance of unusual features. For new pairing criteria or new analytical additions to old criteria, the degree of variation within individual meteorites must be delineated and the degree of variation within meteorite classes must be quantified. Criteria for pairing can be divided into (1) parent body history indicators, (2) meteoroid space history indicators, and (3) terrestrial history indicators. Included in these categories are 11 specific criteria, including petrographic textures, mineralogy and mineral composition, terrestrial age estimates, cosmic‐ray exposure ages, and natural thermoluminescence (TL) levels. Not all criteria are applicable to all meteorite types. About 2275 pairings suggested in the literature have been subjected to this analysis. Many literature pairings, especially those involving common meteorite types, bear large uncertainties due to lack of data.  相似文献   

Reflections on the place of Larkin     

Derek Spooner 《Area》2000,32(2):209-216

Summary The close association of the poet Larkin with the city of Hull has induced references to Larkinland, though commercial exploitation of this concept is very limited. This paper examines Larkin's sense of place and explores his relationship with Hull and its environs. In drawing on his own personal landscapes, Larkin intermittently involves the reader in the pleasure of recognition. For the inhabitant of Hull, some poems have added value. 'Here' paints an evocative picture of Hull in the 1950s, but also links to the interpretation of Larkin as the poet of provincial England. However, Larkinland, either as Hull or as provincial mid-century England, has a slender basis.  相似文献   

New Memorial Landscapes in the American South: An Introduction     

Derek H. Alderman 《The Professional geographer》2000,52(4):658-660

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A Street Fit for a King: Naming Places and Commemoration in the American South     

Derek H. Alderman 《The Professional geographer》2000,52(4):672-684

The naming of streets after Martin Luther King, Jr. (MLK) is an importantarena for African Americans as they rewrite the landscape of southern identity and commemoration. While less ornate and ostentatious than museums and monuments, MLK streets are powerful and highly contested cultural geographies because of their potential to connect disparate communities and incorporate a vision of the past into the spatial practices of everyday life. They reveal the importance of location, particularly intra‐urban location, to public memorialization. Naming streets for King is a significant part of the nonmetropolitan South as well as larger cities and dependent upon the relative size of a city's African‐American population. When estimating the intra‐urban character of MLK streets within several southern states, findings suggest that they are located in census areas that are generally poorer and with more African Americans than citywide averages. Analysis reveals a geographic unevenness in the frequency of businesses having an address identified with King. When compared with the stereotypical American thoroughfare of “Main” Street, the address composition of MLK streets appears to be more residential in nature, although there is significant state by state variation.  相似文献