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排序方式: 共有180条查询结果,搜索用时 15 毫秒
31.
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Falcke H Apel WD Badea AF Bähren L Bekk K Bercuci A Bertaina M Biermann PL Blümer J Bozdog H Brancus IM Buitink S Brüggemann M Buchholz P Butcher H Chiavassa A Daumiller K de Bruyn AG de Vos CM Di Pierro F Doll P Engel R Gemmeke H Ghia PL Glasstetter R Grupen C Haungs A Heck D Hörandel JR Horneffer A Huege T Kampert KH Kant GW Klein U Kolotaev Y Koopman Y Krömer O Kuijpers J Lafebre S Maier G Mathes HJ Mayer HJ Milke J Mitrica B Morello C Navarra G Nehls S Nigl A Obenland R Oehlschläger J 《Nature》2005,435(7040):313-316
The nature of ultrahigh-energy cosmic rays (UHECRs) at energies >10(20) eV remains a mystery. They are likely to be of extragalactic origin, but should be absorbed within approximately 50 Mpc through interactions with the cosmic microwave background. As there are no sufficiently powerful accelerators within this distance from the Galaxy, explanations for UHECRs range from unusual astrophysical sources to exotic string physics. Also unclear is whether UHECRs consist of protons, heavy nuclei, neutrinos or gamma-rays. To resolve these questions, larger detectors with higher duty cycles and which combine multiple detection techniques are needed. Radio emission from UHECRs, on the other hand, is unaffected by attenuation, has a high duty cycle, gives calorimetric measurements and provides high directional accuracy. Here we report the detection of radio flashes from cosmic-ray air showers using low-cost digital radio receivers. We show that the radiation can be understood in terms of the geosynchrotron effect. Our results show that it should be possible to determine the nature and composition of UHECRs with combined radio and particle detectors, and to detect the ultrahigh-energy neutrinos expected from flavour mixing. 相似文献
33.
M. Wintzerith N. Klein L. Mandel P. Mandel 《Cellular and molecular life sciences : CMLS》1959,15(4):140-142
Summary Animals having an ascites hepatoma show an increase in the incorporation of P32 into ribonucleic acid and desoxyribonucleic acid of the pancreas, whereas no change is seen in the kidneys. The variations noted in the pancreas may be compared with those observed previously in the liver and the adrenals. It can therefore be presumed that a substance which stimulates biosynthesis or disrupts the normal metabolic balance is produced by the ascites cells.
Travail effectué avec l'aide matérielle de l'Institut National d'Hygiène. 相似文献
Travail effectué avec l'aide matérielle de l'Institut National d'Hygiène. 相似文献
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Bahar R Hartmann CH Rodriguez KA Denny AD Busuttil RA Dollé ME Calder RB Chisholm GB Pollock BH Klein CA Vijg J 《Nature》2006,441(7096):1011-1014
38.
Mice with t factors belonging to the same complementation group carry similar, if not identical, H--2 haplotypes although these factors were derived from widely separated geographical areas. This association between t and H--2 complexes suggests more than a casual relationship between the two complexes, at least at the population level. 相似文献
39.
Influence of a knot on the strength of a polymer strand. 总被引:3,自引:0,他引:3
Many experiments have been done to determine the relative strengths of different knots, and these show that the break in a knotted rope almost invariably occurs at the point just outside the 'entrance' to the knot. The influence of knots on the properties of polymers has become of great interest, in part because of their effect on mechanical properties. Knot theory applied to the topology of macromolecules indicates that the simple trefoil or 'overhand' knot is likely to be present in any long polymer strand. Fragments of DNA have been observed to contain such knots in experiments and computer simulations. Here we use ab initio computational methods to investigate the effect of a trefoil knot on the breaking strength of a polymer strand. We find that the knot weakens the strand significantly, and that, like a knotted rope, it breaks under tension at the entrance to the knot. 相似文献
40.
A new early cretaceous dinosaur track assemblage and the first definite non-avian theropod swim trackway from China 总被引:1,自引:0,他引:1
XING LiDa LOCKLEY Martin G ZHANG JianPing MILNER Andrew R C KLEIN Hendrik LI DaQing PERSONS IV W Scott EBI JieFang 《科学通报(英文版)》2013,58(19):2370-2378
The trackway of a swimming theropod (ichnogenus Characichnos) is reported from the Lower Cretaceous Feitianshan Formation of Sichuan, China. These swim tracks help confirm that non-avian theropods were capable of forging moderately deep bodies of water. The trackway occurs on the same surface as a typical walking trackway of a sauropod (ichnogenus Brontopodus). Both occurrences are the first reported from the Cretaceous of Sichuan, and the swim tracks are the first well-preserved example of a Characichnos trackway from China. Additionally, a theropod walking trackway and several ornithopod walking trackways (similar to the ichnogenus Caririchnium) occur in the same horizon. The ornithopod trackways show a parallel orientation, suggesting gregarious behavior of the trackmakers, which may have been iguanodontiforms and/or hadrosauriforms. The co-occurrence of theropod swim tracks and theropod walking tracks suggests a fluctuation of water depth within a distinct time span. 相似文献