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1.
Summary The effect of potassium ions on the formation of adenosine 3,5-monophosphate (cAMP) in the rat cerebral cortex in vivo was studied under conditions where development of spreading depression had been blocked by pretreatment of the cerebral cortex by topically applied magnesium ions. A linear relationship between potassium concentrations applied to the cortical surface and levels of cAMP has been found. Moreover, potentiation of the K+-effect by magnesium ions has been observed.  相似文献   

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Recently developed structural models of the global crude oil market imply that the surge in the real price of oil between mid 2003 and mid 2008 was driven by repeated positive shocks to the demand for all industrial commodities, reflecting unexpectedly high growth mainly in emerging Asia. We evaluate this proposition using an alternative data source and a different econometric methodology. Rather than inferring demand shocks from an econometric model, we utilize a direct measure of global demand shocks based on revisions of professional real gross domestic product (GDP) growth forecasts. We show that forecast surprises during 2003–2008 were associated primarily with unexpected growth in emerging economies (in conjunction with much smaller positive GDP‐weighted forecast surprises in the major industrialized economies), that markets were repeatedly surprised by the strength of this growth, that these surprises were associated with a hump‐shaped response of the real price of oil that reaches its peak after 12–16 months, and that news about global growth predict much of the surge in the real price of oil from mid 2003 until mid 2008 and much of its subsequent decline. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

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The goal of this paper, both historical and philosophical, is to launch a new case into the scientific realism debate: geocentric astronomy. Scientific realism about unobservables claims that the non-observational content of our successful/justified empirical theories is true, or approximately true. The argument that is currently considered the best in favor of scientific realism is the No Miracles Argument: the predictive success of a theory that makes (novel) observational predictions while making use of non-observational content would be inexplicable unless such non-observational content approximately corresponds to the world “out there”. Laudan's pessimistic meta-induction challenged this argument, and realists reacted by moving to a “selective” version of realism: the approximately true part of the theory is not its full non-observational content but only the part of it that is responsible for the novel, successful observational predictions. Selective scientific realism has been tested against some of the theories in Laudan's list, but the first member of this list, geocentric astronomy, has been traditionally ignored. Our goal here is to defend that Ptolemy's Geocentrism deserves attention and poses a prima facie strong case against selective realism, since it made several successful, novel predictions based on theoretical hypotheses that do not seem to be retained, not even approximately, by posterior theories. Here, though, we confine our work just to the detailed reconstruction of what we take to be the main novel, successful Ptolemaic predictions, leaving the full analysis and assessment of their significance for the realist thesis to future works.  相似文献   

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This paper addresses the question of how scientists determine which type of hypothesis is most suitable for tackling a particular problem by examining the historical case of the anomalous β spectrum in early nuclear physics (1927–1934), a puzzle that occasioned the most diverse hypotheses amongst physicists at the time. It is shown that such determinations are most often implicitly informed by scientists' individual perspectives on the structural relations between the various elements of the theory and the problem at hand. In addition to this main result, it is suggested that Wolfgang Pauli's neutrino idea may well have been an adaptation of Ernst Rutherford's original and older neutron idea, which would provide evidence that the adaptation of older ideas is a more common practice than is often thought.  相似文献   

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Periodicity in predatory activity was observed in overwintered females ofTyphlodromus pyri Scheuten (Acari: Phytoseiidae). Chronobiometrical analysis revealed that an approximately circabiseptan (about-14-day) rhythm is statistically significant, with a striking depression around the full moon.  相似文献   

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This paper presents a survey of the literature on the problem of contingency in science. The survey is structured around three challenges faced by current attempts at understanding the conflict between “contingentist” and “inevitabilist” interpretations of scientific knowledge and practice. First, the challenge of definition: it proves hard to define the positions that are at stake in a way that is both conceptually rigorous and does justice to the plethora of views on the issue. Second, the challenge of distinction: some features of the debate suggest that the contingency issue may not be sufficiently distinct from other philosophical debates to constitute a genuine, independent philosophical problem. And third, the challenge of decidability: it remains unclear whether and how the conflict could be settled on the basis of empirical evidence from the actual history of science. The paper argues that in order to make progress in the present debate, we need to distinguish more systematically between different expressions that claims about contingency and inevitability in science can take. To this end, it introduces a taxonomy of different contingency and inevitability claims. The taxonomy has the structure of an ordered quadruple. Each contingency and each inevitability claim contains an answer to the following four questions: (how) are alternatives to current science possible, what types of alternatives are we talking about, how should the alternatives be assessed, and how different are they from actual science?  相似文献   

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Zusammenfassung Gibt man L(+)-Lysin--15N oder in allen Stellungen mit14C markiertes L(+)-Lysin zu keimfreien Kulturen von abgeschnittenen Wurzeln vonNicotiana tabacum, so erzeugen die Wurzeln Nikotin, welches kleine Mengen15N oder14C enthält. Ferner enthält das Nikotin mehr15N oder14C im Pyrrolidinring als im Pyridinring. Lysin liegt daher nicht auf dem direkten biogenetischen Weg zum Nikotin.

Research performed under the auspices of the United States Atomic Energy Commission.  相似文献   

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For more than three decades, there has been significant debate about the relation between Feyerabend and Popper. The discussion has been nurtured and complicated by the rift that opened up between the two and by the later Feyerabend's controversial portrayal of his earlier self. The first part of the paper provides an overview of the accounts of the relation that have been proposed over the years, disentangles the problems they deal with, and analyses the evidence supporting their conclusions as well as the methodological approaches used to process that evidence. Rather than advancing a further speculative account of the relation based on Feyerabend's philosophical work or autobiographical recollections, the second part of the paper strives to clarify the problems at issue by making use of a wider range of evidence. It outlines a historical reconstruction of the social context within which Feyerabend's intellectual trajectory developed, putting a special emphasis on the interplay between the perceived intellectual identity of Feyerabend, Feyerabend's own intellectual self-concept, and the peculiar features of the evolving Popperian research group.  相似文献   

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Over many years, Aharonov and co-authors have proposed a new interpretation of quantum mechanics: the two-time interpretation. This interpretation assigns two wavefunctions to a system, one of which propagates forwards in time and the other backwards. In this paper, I argue that this interpretation does not solve the measurement problem. In addition, I argue that it is neither necessary nor sufficient to attribute causal power to the backwards-evolving wavefunction Φ| and thus its existence should be denied, contra the two-time interpretation. Finally, I follow Vaidman in giving an epistemological reading of Φ|.  相似文献   

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The prevalence of liver diseases is increasing globally. Orthotopic liver transplantation is widely used to treat liver disease upon organ failure. The complexity of this procedure and finite numbers of healthy organ donors have prompted research into alternative therapeutic options to treat liver disease. This includes the transplantation of liver cells to promote regeneration. While successful, the routine supply of good quality human liver cells is limited. Therefore, renewable and scalable sources of these cells are sought. Liver progenitor and pluripotent stem cells offer potential cell sources that could be used clinically. This review discusses recent approaches in liver cell transplantation and requirements to improve the process, with the ultimate goal being efficient organ regeneration. We also discuss the potential off-target effects of cell-based therapies, and the advantages and drawbacks of current pre-clinical animal models used to study organ senescence, repopulation and regeneration.  相似文献   

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Here, we briefly review the notion of observational indistinguishability within the context of classical general relativity. We settle a conjecture given by Malament [(1977). Observationally indistinguishable space-times. In J. Earman, C. Glymour, & J. Statchel (Eds.), Foundations of space–time theories. Minnesota studies in the philosophy of science (Vol. VIII, pp. 61–80). Minneapolis: University of Minnesota Press] concerning the subject and then strengthen the result considerably. The upshot is this: There seems to be a robust sense in which the global structure of every cosmological model is underdetermined.  相似文献   

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Zusammenfassung Die angebliche Aufhebung der entzündungshemmenden Wirkung des Cortisons durch Thyreo-Parathyreoidektomie wurde experimentell nachgeprüft. Für die objektive Messung des Entzündungsgrades wurden drei Methoden benutzt: Die sogenannte «granuloma pouch» nach Krotonöl und die sogenannte «topical irritation arthritis» nach Formalin und Dextran.In allen drei Testen war es unmöglich, die entzündungshemmende Wirkung des Cortisons durch Thyreo-Parathyreoidektomie zu verhindern.  相似文献   

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The observation that in some cases tumors undergo spontaneous regression concomitantly with autoimmune manifestations has been interpreted as an indication of the involvement of the immune system in tumor rejection. This raised the conceptual possibility that the immune system could be used against the tumor. However, since tumor cells are poorly immunogenic by themselves, early attempts to develop immune-based approaches for cancer therapy saw the use of tumor cells transduced with genes coding for cytokines or costimulatory molecules to enhance in vivo immunity. The identification of cytotoxic T lymphocyte (CTL)-defined tumor associated antigens has allowed the development of new strategies for cancer immunotherapy. Novel adjuvants have been identified, and different modes of antigen delivery were devised which aim at inducing efficient CTL responses in patients. This review will discuss some of what is currently considered as relevant aspects of antitumor immunization.Received 19 July 2002; received after revision 11 December 2002; accepted 13 December 2002  相似文献   

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