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61.
Küppers M Bertini I Fornasier S Gutierrez PJ Hviid SF Jorda L Keller HU Knollenberg J Koschny D Kramm R Lara LM Sierks H Thomas N Barbieri C Lamy P Rickman H Rodrigo R;OSIRIS team 《Nature》2005,437(7061):987-990
Comets spend most of their life in a low-temperature environment far from the Sun. They are therefore relatively unprocessed and maintain information about the formation conditions of the planetary system, but the structure and composition of their nuclei are poorly understood. Although in situ and remote measurements have derived the global properties of some cometary nuclei, little is known about their interiors. The Deep Impact mission shot a projectile into comet 9P/Tempel 1 in order to investigate its interior. Here we report the water vapour content (1.5 10(32) water molecules or 4.5 10(6) kg) and the cross-section of the dust (330 km2 assuming an albedo of 0.1) created by the impact. The corresponding dust/ice mass ratio is probably larger than one, suggesting that comets are 'icy dirtballs' rather than 'dirty snowballs' as commonly believed. High dust velocities (between 110 m s(-1) and 300 m s(-1)) imply acceleration in the comet's coma, probably by water molecules sublimated by solar radiation. We did not find evidence of enhanced activity of 9P/Tempel 1 in the days after the impact, suggesting that in general impacts of meteoroids are not the cause of cometary outbursts. 相似文献
62.
R. Keller 《Cellular and molecular life sciences : CMLS》1958,14(5):181-182
Summary Investigations in the cofactor-fibrinogen system have shown that serotonin and tryptamine, although only in relatively high doses, reduce the antithrombin time prolonged by the action of heparin. Histamine has no such effect on the action of heparin, nor have tyramine and isoamylamine.
Für wertvolle Ratschläge im Verlaufe der Untersuchungen sind wir den Herren Dr.R. Marbet, Dr.André Studer und PD Dr.A. Winterstein, Wissenschaftliche Laboratorien der F. Hoffmann-La Roche & Co. AG. in Basel zu Dank verpflichtet. 相似文献
Für wertvolle Ratschläge im Verlaufe der Untersuchungen sind wir den Herren Dr.R. Marbet, Dr.André Studer und PD Dr.A. Winterstein, Wissenschaftliche Laboratorien der F. Hoffmann-La Roche & Co. AG. in Basel zu Dank verpflichtet. 相似文献
63.
Summary Freshly dissolved heparin substance, in contrast to heparin which is commercially available, causes no decontraction of the isolated atropinized guinea-pig ileum contracted in response to histamine. Phenol and Cresol, in the amounts in which they are normally present in commercially available heparin preparations, have the same effect as commercial heparin. 相似文献
64.
Evelyn Fox Keller 《自然科学史研究》2005,24(Z1):23-30
1 Biology for the 21st Century
In a recent article in the New York Times (3/23/05), reporting on yet another upset to received views of the ways in which cells make use of their DNA, a prominent geneticist is quoted as remarking, "biologists have gotten used to the unexpected." Indeed, they have, as indeed, they have had to. Over the last few years, our understanding of molecular and developmental genetics has mutated dramatically in response to ever more complex analyses of ever more abundant and more complex data. 相似文献
65.
Chromatin assembly during S phase: contributions from histone deposition, DNA replication and the cell division cycle 总被引:7,自引:0,他引:7
During S phase of the eukaryotic cell division cycle, newly replicated DNA is rapidly assembled into chromatin. Newly synthesised
histones form complexes with chromatin assembly factors, mediating their deposition onto nascent DNA and their assembly into
nucleosomes. Chromatin assembly factor 1, CAF-1, is a specialised assembly factor that targets these histones to replicating
DNA by association with the replication fork associated protein, proliferating cell nuclear antigen, PCNA. Nucleosomes are
further organised into ordered arrays along the DNA by the activity of ATP-dependent chromatin assembly and spacing factors
such as ATP-utilising chromatin assembly and remodelling factor ACF. An additional level of controlling chromatin assembly
pathways has become apparent by the observation of functional requirements for cyclin-dependent protein kinases, casein kinase
II and protein phosphatases. In this review, we will discuss replication-associated histone deposition and nucleosome assembly
pathways, and we will focus in particular on how nucleosome assembly is linked to DNA replication and how it may be regulated
by the cell cycle control machinery. 相似文献
66.
The Earth has cooled over the past 4.5 billion years (Gyr) as a result of surface heat loss and declining radiogenic heat production. Igneous geochemistry has been used to understand how changing heat flux influenced Archaean geodynamics, but records of systematic geochemical evolution are complicated by heterogeneity of the rock record and uncertainties regarding selection and preservation bias. Here we apply statistical sampling techniques to a geochemical database of about 70,000 samples from the continental igneous rock record to produce a comprehensive record of secular geochemical evolution throughout Earth history. Consistent with secular mantle cooling, compatible and incompatible elements in basalts record gradually decreasing mantle melt fraction through time. Superimposed on this gradual evolution is a pervasive geochemical discontinuity occurring about 2.5?Gyr ago, involving substantial decreases in mantle melt fraction in basalts, and in indicators of deep crustal melting and fractionation, such as Na/K, Eu/Eu* (europium anomaly) and La/Yb ratios in felsic rocks. Along with an increase in preserved crustal thickness across the Archaean/Proterozoic boundary, these data are consistent with a model in which high-degree Archaean mantle melting produced a thick, mafic lower crust and consequent deep crustal delamination and melting--leading to abundant tonalite-trondhjemite-granodiorite magmatism and a thin preserved Archaean crust. The coincidence of the observed changes in geochemistry and crustal thickness with stepwise atmospheric oxidation at the end of the Archaean eon provides a significant temporal link between deep Earth geochemical processes and the rise of atmospheric oxygen on the Earth. 相似文献
67.
H. W. Cho L. Prilipko H. Y. Meltzer C. Keller 《Cellular and molecular life sciences : CMLS》1977,33(2):166-167
Summary Creatine phosphokinase activity was found in human lymphocytes. Only MM type of the enzyme was detected in lymphocytes and polymorphonuclear leukocytes.Supported by U.S.P.H.S. MH 16 127. H.Y.M. is recipient of RCSA MH 47 808. 相似文献
68.
H. U. Keller J. H. Wissler M. W. Hess H. Cottier 《Cellular and molecular life sciences : CMLS》1977,33(4):534-536
Summary The effect of chemotactic peptides which lack chemokinetic activity has been investigated. The neutrophil response is proportional to the logarithm of the stimulus intensity, or alternatively a power function with an exponent of 0.3. Equal responses are obtained for equal ratios between the peptide concentration in the lower compartment and the threshold concentration. The significance of Weber-Fechner's law in leucocyte chemotaxis is discussed.We thank Miss B. Zanolari, Mrs M. Marti, Mrs Hauck and Mr Dietz for excellent technical assistance. This work was supported by the Swiss National Foundation for Scientific Research. 相似文献
69.
70.
On the ultrastructure of mammalian tendon 总被引:1,自引:0,他引:1