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排序方式: 共有126条查询结果,搜索用时 31 毫秒
111.
Amoretti M Amsler C Bonomi G Bouchta A Bowe P Carraro C Cesar CL Charlton M Collier MJ Doser M Filippini V Fine KS Fontana A Fujiwara MC Funakoshi R Genova P Hangst JS Hayano RS Holzscheiter MH Jørgensen LV Lagomarsino V Landua R Lindelöf D Lodi Rizzini E Macrì M Madsen N Manuzio G Marchesotti M Montagna P Pruys H Regenfus C Riedler P Rochet J Rotondi A Rouleau G Testera G Variola A Watson TL van der Werf DP;ATHENA Collaboration 《Nature》2002,419(6906):456-459
A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem-experimental investigations involving comparisons of particles with antiparticles are numerous. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN) and at Fermilab, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector. 相似文献
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DNA-directed DNA polymerase activity in oncogenic RNA viruses 总被引:34,自引:0,他引:34
S Spiegelman A Burny M R Das J Keydar J Schlom M Travnicek K Watson 《Nature》1970,227(5262):1029-1031
114.
Oaks JL Gilbert M Virani MZ Watson RT Meteyer CU Rideout BA Shivaprasad HL Ahmed S Chaudhry MJ Arshad M Mahmood S Ali A Khan AA 《Nature》2004,427(6975):630-633
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An important component of the New England Electric System Companies' (the 'System') total electricity sales is attributable to commercial customers. Commercial growth has recently been strong; moreover the System's peak demand is highly sensitive to commercial load. In a typical month this class represents 33 per cent of total System sales. Accurate short-run forecasts of total kWh sales are important for rate making, budgeting, fuel cause proceedings, and corporate planning. In this study we use a variety of econometric and time-series techniques to produce short-run forecasts of commercial sales for two geographical areas served by two separate retail companies;. 相似文献
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Hjorth J Sollerman J Møller P Fynbo JP Woosley SE Kouveliotou C Tanvir NR Greiner J Andersen MI Castro-Tirado AJ Castro Cerón JM Fruchter AS Gorosabel J Jakobsson P Kaper L Klose S Masetti N Pedersen H Pedersen K Pian E Palazzi E Rhoads JE Rol E van den Heuvel EP Vreeswijk PM Watson D Wijers RA 《Nature》2003,423(6942):847-850
Over the past five years evidence has mounted that long-duration (>2 s) gamma-ray bursts (GRBs)-the most luminous of all astronomical explosions-signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model. 相似文献
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S. Arnott A. W. Davie J. M. Robertson G. A. Sim D. G. Watson 《Cellular and molecular life sciences : CMLS》1960,16(2):49-51
Zusammenfassung Die Struktur desepi-Limonol-jodoacetates (C26H31O8) COCH2I, wurde durch dreidimensionale Röntgenanalyse bestimmt. Es gelang, die Lage sämtlicher Atome in zwei kristallographisch unabhängigen, jedoch chemisch identischen Molekeln zu ermitteln. Dieses Resultat stellt eine vollständige Bestimmung der Konstitution und der Stereochemie des Limonins dar. 相似文献