Results 1 - 10 of 11330
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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] In analogy to f(R) theory, recently a new modified gravity theory, namely the so-called f(T) theory, has been proposed to drive the current accelerated expansion without invoking dark energy. In the present work, by extending Bisabr's idea, we try to constrain f(T) theories with the varying fine structure 'constant', α≡e2/hc. We find that the constraints on f(T) theories from the observational Δα/α data are very severe. In fact, they make f(T) theories almost indistinguishable from ΛCDM model.
[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.