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The Science of Nature - 相似文献
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We use hydra as a model system to understand how growth and differentiation and, as a consequence of this, pattern formation are controlled at the molecular level. We have found that four substances control head and foot formation in hydra: an activator and an inhibitor of head formation and an activator and an inhibitor of foot formation. The two activators are peptides with molecular weights around 1000 daltons, the inhibitors are smaller in molecular weight (<500), have an overall positive charge and do not contain peptide bonds. In normal animals all four substances are present and most likely produced by nerve cells. We hope to understand how these substances act and interact to create the spatial and temporal pattern of growth and differentiation typical for hydra. 相似文献
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Christopher R. Ellis Jerry Champlin Heinz G. Stefan 《Journal of the American Water Resources Association》1997,33(6):1363-1374
ABSTRACT: Evidence is presented that snowmelt runoff from an urban watershed can produce density current intrusions (underflows) in a lake. Several episodes of density current intrusions are documented. Water temperatures and salinities measured near the bottom of a 10 m deep Minneapolis lake during the late winter warming periods in 1989, 1990, 1991, and 1995 show significant rapid changes which are correlated with observed higher air temperatures and snowmelt runoff. The snowmelt runoff entering this particular lake (Ryan Lake) has increased electrical conductivity, salinity, and density. The source of the salinity is the salt spread on urban streets in the winter. Heating of littoral waters in spring may also contribute to the occurrence of the sinking flows, but is clearly not the only cause. 相似文献
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Heinz Rüdel Winfried Schröder Karl Theo von der Trenck Gerhard Andreas Wiesmüller 《Environmental science and pollution research international》2009,16(5):486-498
Background Due to the requirements of the EU Water Framework Directive and other legal regulations (e.g., national laws like the German
Federal Soil Protection Act), but also due to the implementation of the new EU chemicals management system REACH, environmental
monitoring will gain increasing importance for the surveillance of environmental quality as well as for the assessment of
chemicals. Against this background, the Work Group on ‘Environmental Monitoring’ of the Division of ‘Environmental Chemistry
and Ecotoxicology’ within the German Chemical Society has compiled a position paper on substance-related environmental monitoring.
Scope Core elements of this position paper are the definitions of important terms like monitoring, exposure monitoring, effect monitoring,
and integrated monitoring. Moreover, temporal and spatial aspects (monitoring of spatial distributions, trend monitoring,
and retrospective monitoring) and their applications are discussed. The main focus of this position paper is the coverage
of aspects which have to be observed for the preparation and implementation of a monitoring program. Essential is the clear
specification of the targets of the monitoring which determine the development of the monitoring concept and its realization,
e.g., if environmental media (compartments) or organisms are most appropriate as samples for the aim of the study. Of course,
also the properties of the target substances are important (e.g., lipophilicity/bioaccumulation as pre-requisite for an exposure
monitoring with organisms). Finally, the monitoring phases of sample planning, sampling, storage and transport of samples,
selection of analytical methods, quality assurance measures as well as reporting are discussed.
Perspectives An important issue for the future is to link the quantification of chemicals in environmental compartments (exposure and pollution
monitoring) more closely to the study of biological effects (effect monitoring) than has been the case up to now. Furthermore,
by inclusion of a spatial differentiation, a comprehensive evaluation of the state of an ecosystem can be obtained and the
relevance of the results improved. Practical examples of monitoring studies which illustrate various aspects covered in this
position paper will be presented in a series of publications by members of the Work Group in the following issues of this
journal.
相似文献
Gerhard Andreas WiesmüllerEmail: |