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41.
42.
Résumé L'action de la gastrine de porc a été étudiée chez des rats mâles munis de fistules gastriques. La gastrine était injectée par voie s.c. à des doses de 1–2 ml: 1 ml équivalant à l'activité de 10 g de muqueuse de porc. Le volume de suc gastrique, le volume de suc gastrique par 100 g, l'acidité totale et le débit d'acide accusèrent une pointe dans la première h, alors que la concentration en acide atteignit son maximum vers la troisième h. Le débit de la pepsine diminua entre la troisième et la cinquième h et augmenta légèrement entre la cinquième et la sixième h.
This research was supported in part by grants from the National Science Foundation (No. GB 6105) and from the AMA ERF, to J. H. T. — Dr.Robitscher of Ayerst Laboratories kindly supplied the ICI-50123. 相似文献
This research was supported in part by grants from the National Science Foundation (No. GB 6105) and from the AMA ERF, to J. H. T. — Dr.Robitscher of Ayerst Laboratories kindly supplied the ICI-50123. 相似文献
43.
R Sanchis-Ojeda DC Fabrycky JN Winn T Barclay BD Clarke EB Ford JJ Fortney JC Geary MJ Holman AW Howard JM Jenkins D Koch JJ Lissauer GW Marcy F Mullally D Ragozzine SE Seader M Still SE Thompson 《Nature》2012,487(7408):449-453
The Sun's equator and the planets' orbital planes are nearly aligned, which is presumably a consequence of their formation from a single spinning gaseous disk. For exoplanetary systems this well-aligned configuration is not guaranteed: dynamical interactions may tilt planetary orbits, or stars may be misaligned with the protoplanetary disk through chaotic accretion , magnetic interactions or torques from neighbouring stars. Indeed, isolated 'hot Jupiters' are often misaligned and even orbiting retrograde. Here we report an analysis of transits of planets over starspots on the Sun-like star Kepler-30 (ref. 8), and show that the orbits of its three planets are aligned with the stellar equator. Furthermore, the orbits are aligned with one another to within a few degrees. This configuration is similar to that of our Solar System, and contrasts with the isolated hot Jupiters. The orderly alignment seen in the Kepler-30 system suggests that high obliquities are confined to systems that experienced disruptive dynamical interactions. Should this be corroborated by observations of other coplanar multi-planet systems, then star-disk misalignments would be ruled out as the explanation for the high obliquities of hot Jupiters, and dynamical interactions would be implicated as the origin of hot Jupiters. 相似文献
44.
The spectral purity of an oscillator is central to many applications, such as detecting gravity waves, defining the second, ground-state cooling and quantum manipulation of nanomechanical objects, and quantum computation. Recent proposals suggest that laser oscillators which use very narrow optical transitions in atoms can be orders of magnitude more spectrally pure than present lasers. Lasers of this high spectral purity are predicted to operate deep in the 'bad-cavity', or superradiant, regime, where the bare atomic linewidth is much less than the cavity linewidth. Here we demonstrate a Raman superradiant laser source in which spontaneous synchronization of more than one million rubidium-87 atomic dipoles is continuously sustained by less than 0.2 photons on average inside the optical cavity. By operating at low intracavity photon number, we demonstrate isolation of the collective atomic dipole from the environment by a factor of more than ten thousand, as characterized by cavity frequency pulling measurements. The emitted light has a frequency linewidth, measured relative to the Raman dressing laser, that is less than that of single-particle decoherence linewidths and more than ten thousand times less than the quantum linewidth limit typically applied to 'good-cavity' optical lasers, for which the cavity linewidth is much less than the atomic linewidth. These results demonstrate several key predictions for future superradiant lasers, which could be used to improve the stability of passive atomic clocks and which may lead to new searches for physics beyond the standard model. 相似文献
45.
46.
Method for measuring the leaf surface area of complex shoots 总被引:1,自引:0,他引:1
47.
Subtypes of medulloblastoma have distinct developmental origins 总被引:2,自引:0,他引:2
Gibson P Tong Y Robinson G Thompson MC Currle DS Eden C Kranenburg TA Hogg T Poppleton H Martin J Finkelstein D Pounds S Weiss A Patay Z Scoggins M Ogg R Pei Y Yang ZJ Brun S Lee Y Zindy F Lindsey JC Taketo MM Boop FA Sanford RA Gajjar A Clifford SC Roussel MF McKinnon PJ Gutmann DH Ellison DW Wechsler-Reya R Gilbertson RJ 《Nature》2010,468(7327):1095-1099
Medulloblastoma encompasses a collection of clinically and molecularly diverse tumour subtypes that together comprise the most common malignant childhood brain tumour. These tumours are thought to arise within the cerebellum, with approximately 25% originating from granule neuron precursor cells (GNPCs) after aberrant activation of the Sonic Hedgehog pathway (hereafter, SHH subtype). The pathological processes that drive heterogeneity among the other medulloblastoma subtypes are not known, hindering the development of much needed new therapies. Here we provide evidence that a discrete subtype of medulloblastoma that contains activating mutations in the WNT pathway effector CTNNB1 (hereafter, WNT subtype) arises outside the cerebellum from cells of the dorsal brainstem. We found that genes marking human WNT-subtype medulloblastomas are more frequently expressed in the lower rhombic lip (LRL) and embryonic dorsal brainstem than in the upper rhombic lip (URL) and developing cerebellum. Magnetic resonance imaging (MRI) and intra-operative reports showed that human WNT-subtype tumours infiltrate the dorsal brainstem, whereas SHH-subtype tumours are located within the cerebellar hemispheres. Activating mutations in Ctnnb1 had little impact on progenitor cell populations in the cerebellum, but caused the abnormal accumulation of cells on the embryonic dorsal brainstem which included aberrantly proliferating Zic1(+) precursor cells. These lesions persisted in all mutant adult mice; moreover, in 15% of cases in which Tp53 was concurrently deleted, they progressed to form medulloblastomas that recapitulated the anatomy and gene expression profiles of human WNT-subtype medulloblastoma. We provide the first evidence, to our knowledge, that subtypes of medulloblastoma have distinct cellular origins. Our data provide an explanation for the marked molecular and clinical differences between SHH- and WNT-subtype medulloblastomas and have profound implications for future research and treatment of this important childhood cancer. 相似文献
48.
The nature of the solar activity during the Maunder Minimum revealed by the Guliya ice core record 总被引:2,自引:0,他引:2
Fig. . Annually variations of NO-concentration in the Guliya ice core in the period of through AD. 《科学通报(英文版)》2000,45(23):2118-2125
Whether the solar activity was very low, and especially whether the solar cycle existed, during the Maunder Minimum (1645–1715
AD), have been disputed for a long time. In this paper we use the Guliya NO3
− data, which can reflect the solar activity, to analyze the characteristics of the solar activity during the Maunder Minimum.
The results show that the solar activity was indeed low, and solar cycle displayed normal as present, i.e. about 11a, in that
period. Moreover, it was found that the solar activity contains a 36-year periodic component probably, which might be related
to the variations in the length of the sunspot cycle. This finding is of importance for the study of the relationship between
the sun variability and the Earth climate change. 相似文献
49.
Management decisions affecting the rare plant Arizona willow ( Salix arizonica ) will be aided by understanding genetic similarities among populations of this species. Random Amplified Polymorphic DNA (RAPD) analysis was conducted on 20 populations of S. arizonica , 12 populations of 5 congeners, and 2 samples of outgroup, Populus tremuloides . A phenogram based on DNA markers shows clear separation of populations of S. arizonica from those of co-occurring willow species, but similarity is low (~ 37%) between Utah and Arizona populations of S. arizonica . Evaluation of the relationship of habitat characteristics and geographic distance to genetic similarity reveals that environment and genetic similarity are poorly correlated. Considering Arizona versus Utah populations, we found a significant negative relationship between geographic distance and genetic similarity ( r = 0.936), but no significant relationship between interpopulation distance and genetic similarity within Arizona or Utah. The wide geographic disjunction of S. arizonica populations in Utah and Arizona appears to have existed for a long period during which genetic drift, random mutations, and selection for somewhat different habitats have pushed the 2 regional complexes along separate evolutionary trajectories. Preservation of genetic variation within S. arizonica will require protection of multiple populations in Arizona and Utah. 相似文献
50.
Franklin's Gulls first arrived in southeast Oregon in 1943, but the first nest was not located until 1948. From 1949 to 1964 gull numbers showed annual fluctuations. An increase began in 1965 and continued through 1980. By 1980 an estimated 2500 Franklin's Gulls were nesting on Malheur National Wildlife Refuge, Harney County, Oregon. The species arrives in April and nesting begins by 1 June. Average nest and egg measurements were similar to those from other areas within the species range. 相似文献