1,721,123 research outputs found
Mapping Holocene pollen data and vegetation of China
No full textHolocene pollen maps of China north of the Yangtze River are presented for six time slices at 2000 year intervals and for ten taxa or taxon combinations on the basis of a data set of pollen diagrams of 142 sites. In spite of the problems with the differentiated data quality, a general correspondence of modern pollen maps with actual vegetation distribution justifies the feasibility of using the pollen maps to illustrate the past temporal and spatial patterns of vegetation change and to tentatively reconstruct palaeo-biomes for the specific time slices. The pollen maps reveal large changes in Holocene vegetation. In the southeastern half of the study area, arboreal taxa generally expanded in the early Holocene times, reaching their maximum at 6 or 4 ka BP, and then shrank during the late Holocene. An exception was found for eastern and northern Northeast China where the maximum development of arboreal taxa occurred during the last 4000 or 2000 years. The evident drop in AP percentages, and therefore the decline of forests, occurred after 6 ka BP in the most southeastern regions, especially in the middle and lower reaches of the Yellow River, and may have been caused by the expansion of farming since the Yangshao Culture period. The reconstructed biomes enable the visual expression of palaeo-vegetation change. A relatively open forest with Pinus as its dominant component developed in the southeastern Loess Plateau and western North China Plain from 8 to 6 ka BP, but it came to an end at about 4 ka BP. On the other hand, cold temperate conifer forest, and temperate mixed conifer and deciduous forest in Northeast China did not yet exist between 10 and 6 ka BP. They appeared at 4 ka BP and then continued to develop through time. Warm temperate deciduous forest experienced a remarkable reduction during the last 6000 years. Alpine valley Picea/Abies forest in the eastern Qinghai-Tibet Plateau developed in the early and mid Holocene, but started to decline at 4 ka BP, and has almost disappeared today. (C) 2002 Elsevier Science Ltd. All rights reserved
Southeast trade wind variations during the last 135 kyr: evidence from pollen spectra in eastern South Atlantic sediments
No full textInflux of aeolian pollen trapped in marine sediments off Namibia provides a wind variation record for the last 135 kyr. The influx of major pollen components is derived from the southwest African desert/semi-desert zone and shows six periods during which enhanced southeast trade winds contributed to strong upwelling and reduced sea surface temperatures. The most prominent of these occurred during 17-23 cal. kyr, 42-56 kyr and before 130 kyr B.P. Correspondence between the pollen influx record and the Vostok deuterium isotope record suggests that pronounced glacial Antarctic cooling was accompanied by intensification of the southeast trades throughout the Late Quaternary. However, during 42-23 kyr B.P. the combination of strong Antarctic glaciation with a decrease of wind zonality induced by low latitude precessional insolation changes caused strong alongshore winds and Ekman pumping that resulted in strong upwelling and reduced sea surface temperatures without pollen influx enhancement. (C) 2001 Elsevier Science B.V. All rights reserved
Correlation between vegetation in southwestern Africa and oceanic upwelling in the past 21,000 years
No full textDinoflagellate cyst and pollen records from marine sediments off the southwestern African coast reveal three major aridification periods since the last glaciation and an environmental correlation between land and sea. Abundant pollen of desert, semi-desert, and temperate plants 21,000-17,500 cal yr B.P. show arid and cold conditions in southwestern Africa that correspond to low sea surface temperatures and enhanced upwelling shown by dinoflagellate cysts. Occurrence of Restionaceae in the pollen record suggests northward movement of the winter-rain regime that influenced the study area during the last glacial maximum. Decline of Asteroideae, Restionaceae, and Ericaceae in the pollen record shows that temperate vegetation migrated out of the study area about 17,500 cal yr B.P., probably because of warming during the last deglaciation. The warming in southwestern Africa was associated with weakened upwelling and increased sea surface temperatures, 2000-2800 years earlier than in the Northern Hemisphere. Aridification 14,300-12,600 cal Jr B.P. is characterized by a prominent increase of desert and semi-desert pollen without the return of temperate vegetation. This aridification corresponds to enhanced upwelling off Namibia and cooler temperatures in Antarctica, and it might have been influenced by oceanic thermohaline circulation. Aridification 11,000-8900 cal yr B.P, is out of phase with the northern African climate. Reduction of the water vapor supply in southwestern Africa at that time may be related to northward excursions of the Intertropical Convergence Zone. (C) 2000 University of Washington
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Raf plus TGF beta-dependent EMT is initiated by endocytosis and lysosomal degradation of E-cadherin
No full textOncogenic Ras interferes with adhesive functions of epithelial cells, but requires tumor growth factor Β (TGFΒ) signaling to cause epithelial-mesenchymal transition (EMT) and tumor progression in model systems. To investigate the mechanisms by which Ras and TGFΒ pathways cooperate in EMT induction, we introduced a tamoxifen-inducible version of Raf-1 (RafER) into fully polarized, mammary epithelial cells (EpH4). EMT characterized by loss of E-cadherin expression and upregulation of invasiveness-promoting genes was induced by TGFΒ plus 4-hydroxytamoxifen (4HT) activation of RafER. Downregulation of E-cadherin by RafER plus TGFΒ was detectable in total cell lysates after 48 h and much earlier in detergent-insoluble fractions of E-cadherin. Both pathways cooperated to strongly enhance endocytosis of E-cadherin, mainly via the clathrin-dependent route. Pulse-chase experiments showed decreased E-cadherin protein stability in cells stimulated with TGFΒ and 4HT and increased E-cadherin half-life in the presence of monensin. Monensin and chloroquine prevented E-cadherin degradation to different extent, but only monensin effectively blocked the loss of E-cadherin from the junctional complexes. Both lysosome inhibitors caused accumulation of E-cadherin vesicles, some of which were positive for Cathepsin D and lysosome-associated membrane protein 1 (LAMP-1). In addition, TGFΒ and mitogen-activated protein kinase hyperactivation synergistically induced E-cadherin ubiquitination, suggesting that the cooperation of Raf and TGFΒ favors lysosomal degradation of E-cadherin instead of its recycling. Our data indicate that early stages of EMT involve cooperative, post-translational downregulation of E-cadherin, whereas loss of E-cadherin via transcriptional repression is a late event in EMT. © 2006 Nature Publishing Group All rights reserved
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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