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[en] By using first-principles calculations, we calculate the vibronic fine structure in photoelectron spectra of C20- clusters. Based on our results, we assign one of the recently observed spectra [H. Prinzbach et al. Nature (London) 407, 60 (2000)] to the fullerene structure and, therefore, confirm the experimental claim that the smallest fullerene is really synthesized
[en] In the chiral limit, the amplitude of the decay π0 → γγ is determined by the anomaly induced on the neutral iso-triplet axial current by the EM field. The amplitude is thus given in terms of the only available quantities in that limit, namely, the fine structure and the pion-decay constants.
[en] High precision measurements of the fine structure intervals in the 1s2p3PJ state of helium have the potential to provide an atomic physics measurement of the fine structure constant α. The interpretation of measurements at this level of accuracy (±10 kHz or better), requires an extension of the known relativistic and QED corrections to include terms of order α7. Starting from a fully covariant relativistic formalism, the authors have now completed an evaluation of all terms up to order α7 ln α. Equivalent nonrelativistic operators are derived whose expectation values can be calculated to high precision and added to previous results. The predicted transition frequencies are ν01=29 616 914.4 kHz and ν12 = 2 291 182.2 kHz. The additional uncertainty due to terms of O(α7) not yet included is estimated to be ±20 kHz. Work on these terms is in progress. A comparison with recent high precision measurements will be made
[en] One scenario proposed to explain the million degree solar corona is a finely stranded corona where each strand is heated by a rapid pulse. However, such fine structure has neither been resolved through direct imaging observations nor conclusively shown through indirect observations of extended superhot plasma. Recently, it has been shown that the observed difference in the appearance of cool and warm coronal loops (∼1 MK and ∼2-3 MK, respectively)-warm loops appearing 'fuzzier' than cool loops-can be explained by models of loops composed of subarcsecond strands, which are impulsively heated up to ∼10 MK. That work predicts that images of hot coronal loops (∼> 6 MK) should again show fine structure. Here we show that the predicted effect is indeed widely observed in an active region with the Solar Dynamics Observatory, thus supporting a scenario where impulsive heating of fine loop strands plays an important role in powering the active corona.
[en] The splitting of the magnetic sublevels of the 3--63D/sub 2,3/ states of He I has been studied by time-resolved quantum-beat spectroscopy. For the 33D/sub 2,3/ levels the experimental results and the results of a statistical analysis agree well with theoretical predictions. When the axis of the polarizer is in a certain orientation with respect to the velocity of the exciting electrons, the beats due to the interference of the magnetic sublevels with Vertical Barm/sub J/1-m/sub J/2Vertical Bar = 2 and Vertical Barm/sub J/1-m/sub J/2Vertical Bar = 0 can be observed separately. This circumstance significantly simplifies the quantum-beat signal, so that it becomes possible to distinguish the region of the first four crossings of magnetic sublevels with Vertical Barm/sub J/ = 2-m/sub J/ = 3Vertical Bar = 2 for 43D (20--24 Oe) and for 53D (approx.9 Oe). The fine-structure frequencies are found to be Δ(33D3-33D2) = (73.4 +- 1.1), Δ(43D3-43D2) = (35.89 +- 0.14), Δ(53D3-53D2) = (19.32 +- 0.15), and Δ(63D3-63D2) = (12.38 +- 0.20) MHz
[en] We describe the results of a search for time variability of the fine structure constant α using absorption systems in the spectra of distant quasars. Three large optical data sets and two 21 cm and mm absorption systems provide four independent samples, spanning ∼23% to 87% of the age of the universe. Each sample yields a smaller α in the past and the optical sample shows a 4σ deviation: Δα/α=-0.72±0.18 x 10-5 over the redshift range 0.5< z<3.5 . We find no systematic effects which can explain our results. The only potentially significant systematic effects push Δα/α towards positive values; i.e., our results would become more significant were we to correct for them
[en] The fine-structure intervals of the lowest two triplet D states of 4He have been obtained by a new method: Ground-state atoms are excited by a discharge to the triplet metastable state, which then undergoes a two-step optical excitation to the triplet D states, where level-crossing measurements are made. The experimental results for 3D1-3D3 (MHz) are 1400.67 plus-or-minus 0.29 and 591.25 plus-or-minus 0.14 for the 3 3D and 4 3D states, respectively; for 3D2-3D3 (MHz) they are 75.97 plus-or-minus 0.23 and 36.15 plus-or-minus 0.24 for 3 3D and 4 3D. These values are much more precise than the previously available data, obtained by optical, particle-bombardment level crossing, or beam-foil quantum-beat spectroscopy, and are consistent with the previous data except for one case, where a previous measurement of 3 3D2-3 3D3 by electron bombardment level-crossing spectroscopy is believed to be in error. These new experimental values for the fine structures of the triplet D state of 4He clearly indicate the inadequateness of existing theoretical calculations of these fine structures