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In 1914, the physics discipline had reached a very similar stage of development in Australia and Japan. A generation later the paths of development had considerably diverged. A systematic comparison of the evolution of physics in the two countries during these years identifies factors—political, economic and cultural—that led to this divergence, but it also uncovers a number of underlying parallels.  相似文献   

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Die Entwicklung des Schalenmodells, deren Skizzierung an dieser Stelle abgebrochen wird, unterteilt sich deutlich in mehrere zeitlich voneinander getrennte Phasen. Ausgangspunkt der Entstehung des Schalenmodells ist die Betrachtung der bekannten Isotope, die erst mit der Entdeckung des Neutrons die schon vorhandene Idee des Kernschalenaufbaus quantitativ erfaßbar macht, und zwar durch noch ungenau bekannte ausgezeichnete Zahlen (1932–1934). Wie oft in der Geschichte der Naturwissenschaften wird eine solche erste Phase durch verschiedene spekulative Annahmen begleitet, die sich auf wenige Anhaltspunkte stützen müssen. Bereits 1933 setzt eine andere Entwicklung ein, die neben der Darstellung empirischer Ergebnisse durch den Versuch gekennzeichnet ist, eine theoretische Begründung des Schalenmodells mit verschiedenen Kernpotentialen zu lieform. Es gelingt jedoch nicht, alle aufgetretenen Fragen befriedigend zu klären.

Deutlich getrennt von der Entwicklung der ersten Jahre beginnt erst 1948 eine weitere Entstehungsphase des Schalenmodells. Im Unterschied zur den Jahren 1932–35 liegt 1948 eine Fülle empirischen Materials vor, dessen Erklärung erneut zur Betrachtung eines Schalenmodells anregt. Damit gelingt es, die meisten der offenen Fragen im wesentlichen mit Hilfe der Kernpotentiale und einer starken Spin-Bahn-Wechselwirkung zu beantworten.  相似文献   

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Summary The cytoplasm of the restrictive form of the amycelial mutant ofNeurospora crassa, growing on sucrosemedium, contains paracrystalline, microfilamentous inclusions and mitochondria with internal membranous whorls lacking in acetate-grown cultures.The support of the Fonds national suisse de la recherche scientifique is gratefully acknowledged.  相似文献   

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This paper reconstructs the history of the introduction and use of iterative algorithms in conservation biology in the 1980s and early 1990s in order to prioritize areas for protection as nature reserves. The importance of these algorithms was that they led to greater economy in spatial extent (“efficiency”) in the selection of areas to represent biological features adequately (that is, to a specified level) compared to older methods of scoring and ranking areas using criteria such as biotic “richness” (the number of features of interest). The development of these algorithms was critical to producing a research program for conservation biology that was distinct from ecology and eventually led to what came to be called systematic conservation planning. Very similar algorithmic approaches were introduced independently in the 1980–1990 period in Australia, South Africa, and (arguably) the United Kingdom. The key rules in these algorithms were the use of rarity and what came to be called complementarity (the number of new or under-represented features in an area relative to those that had already been selected). Because these algorithms were heuristic, they were not guaranteed to produce optimal (most “efficient”) solutions. However, complementarity came to be seen as a principle rather than a rule in an algorithm and its use was also advocated for the former reason. Optimal solutions could be produced by reformulating the reserve selection problem in a mathematical programming formalism and using exact algorithms developed in that context. A dispute over the relevance of full optimality arose and was never resolved. Moreover, exact algorithms could not easily incorporate criteria determining the spatial configuration of networks of selected areas, in contrast to heuristic algorithms. Meanwhile metaheuristic algorithms emerged in the 1990s and came to be seen as a credible more effective alternative to the heuristic algorithms. Ultimately what was important about these developments was that the reserve selection problem came to be viewed a complex optimal decision problem under uncertainty, resource, and other constraints. It was a type of problem that had no antecedent in traditional ecology.  相似文献   

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Neuroblastoma (NB) is a tumor of the sympathoadrenal system arising in children under 15 years of age. In Germany, NB accounts for 7% of childhood cancer cases, but 11% of cancer deaths. It originates from highly migratory progenitor cells that leave the dorsal neural tube and contribute neurons and glial cells to sympathetic ganglia, and chromaffin and supportive cells to the adrenal medulla and paraganglia. Clinically, histologically and molecularly, NBs present as extremely heterogeneous, ranging from very good to very poor prognosis. The etiology of NB still remains unclear and needs to be elucidated, however, aberrant auto- and paracrine embryonic cell communications seem to be likely candidates to initiate or facilitate the emergence, progression and regression of NB. The wingless-type MMTV integration site (WNT) family of proteins represents an evolutionary highly conserved signaling system that orchestrates embryogenesis. At least 19 ligands in the human, numerous receptors and co-receptors are known, which control not only proliferation, but also cell polarity, migration and differentiation. Here we seek to interconnect aspects of WNT signaling with sympathoadrenal and paraganglionic development to define new WNT signaling cues in the etiology and progression of NB.  相似文献   

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Résumé On a étudié les effets du lithium, de la -phényléthylamine et de la tyrosine sur le développement embryonnaire deXenopus laevis. La tyrosine n'a pas d'effet, mais le lithium ou la -phényléthylamine ont végétalisé les embryons s'ils ont été exposés avant le stade blastula.  相似文献   

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Summary In this paper I discuss the development of mathematical analysis during the second and third decades of the nineteenth century; and in particular I assert that the well-known correspondence of new ideas to be found in the writings of Bolzano and Cauchy is not a coincidence, but that Cauchy had read one particular paper of Bolzano and drew on its results without acknowledgement. The reasons for this conjecture involve not only the texts in question but also the state of development of mathematical analysis itself, Cauchy both as personality and as mathematician, and the rivalries which were prevalent in Paris at that time.  相似文献   

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This paper explores the history of a unique assemblage of researchers in the geodetic and allied sciences organised at Ohio State University (OSU) in 1947 at the beginning of the Cold War. From about 1950 to 1970, the OSU geodetic sciences group was the most significant group of geodetic researchers in the world. Funded almost entirely by military and intelligence agencies, they pioneered the technologies, organised the research initiatives, ordered the data sets, and trained the generation of geodesists who eventually created the Cold War Figure of the Earth to both prosecute and prevent global nuclear war. They devised elaborate mechanisms to pursue in secrecy and isolation research that had hitherto been performed collaboratively and globally. They invented methods to maintain professional associations and protocols, both to distribute—and disguise—the fruits of their geodetic research. In accomplishing this, their work also undermined the basic hypothesis of isostasy that had been foundational to geodesy for the previous century.Fundamental progress in the geosciences and military and intelligence directives were inextricably linked during the Cold War, although the extent of their convergence has been masked by the security protocols organised to disguise it. With the declassification of key programmes underway, it is now both possible and necessary to substantially revise the history of Cold War-era geosciences and their associated technologies.  相似文献   

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This paper investigates the functioning of the ‘Copernican paradox’ (stating that the Sun stands still and the Earth revolves around the Sun) in the late sixteenth- and early seventeenth-century England, with particular attention to Edward Gresham's (1565–1613) little-known and hitherto understudied astronomical treatise – Astrostereon, or A Discourse of the Falling of the Planet (1603). The text, which is fully appreciative of the heliocentric system, is analysed within a broader context of the ongoing struggles with the Copernican theory at the turn of the seventeenth century. The article finds that apart from having a purely rhetorical function, the ‘Copernican paradox’ featured in the epistemological debates on how early modern scientific knowledge should be constructed and popularised. The introduction of new scientific claims to sceptical audiences had to be done both through mathematical demonstrations and by referring to the familiar concepts and tools drawn from the inventory of humanist education. As this article shows, Gresham's rhetorical techniques used for the rejection of paradoxicality of heliocentrism are similar to some of the practices which Thomas Digges and William Gilbert employed in order to defend their own findings and assertions.  相似文献   

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Emmy Noether’s many articles around the time that Felix Klein and David Hilbert were arranging her invitation to Göttingen include a short but brilliant note on invariants of finite groups highlighting her creativity and perspicacity in algebra. Contrary to the idea that Noether abandoned Paul Gordan’s style of mathematics for Hilbert’s, this note shows her combining them in a way she continued throughout her mature abstract algebra.  相似文献   

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A superfamily of proteins often conserves a common structural scaffold but develops diverse biochemical and biological functions during evolution. The understanding of evolutionary mechanisms responsible for this diversity is of fundamental importance not only in structural genomics but also in nature-guided drug design. A superfamily of peptides with a conserved CSalphabeta structural motif provides a considerably intriguing example to approach such an issue. The peptides from this superfamily have wide origins, ranging from plants to animals, and exhibit diverse biological activities, varying from a sweet-tasting protein to antibacterial defensins and animal toxins targeting ion channels. This review describes the phylogenetic distribution and structural classifi cation of this unique scaffold and provides new insights into its functional diversity from the perspective of sequence, structure and evolution.  相似文献   

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