3,550 research outputs found
Q-complements on log surfaces
In this paper the log surfaces without \QQ-complement are classified. In
particular, they are non-rational always. This result takes off the restriction
in the theory of complements and allows one to apply it in the most wide class
of log surfaces.Comment: Latex2e, 3 page
Comment on The Evidence for a Pentaquark and Kinematic Reflections
The Regge exchange model used by Dzierba et al. is shown to be questionable,
since the pion pole term is not allowed. Hence the Regge amplitudes in their
calculation are exaggerated. The amount of kinematic reflection in the mass
spectrum of the (nK+) system, which is one decay channel of a possible
pentaquark, is not well justified in the fitting procedure used by Dzierba et
al., as shown by comparison with the (K+K-) invariant mass spectrum, which is
one decay channel of the a_2 and f_2 tensor mesons. While kinematic reflections
are still a concern in some papers that have presented evidence for the
pentaquark, better quantitative calculations are needed to demonstrate the
significance of this effect.Comment: Comment submitted to Phys. Rev. D (no figures
Kink-antikink interactions in the double sine-Gordon equation and the problem of resonance frequencies
We studied the kink-antikink collision process for the "double sine-Gordon"
(DSG) equation in 1+1 dimensions at different values of the potential parameter
. For small values of we discuss the problem of resonance frequencies.
We give qualitative explanation of the frequency shift in comparison with the
frequency of the discrete level in the potential well of isolated kink. We show
that in this region of the parameter the effective long-range interaction
between kink and antikink takes place.Comment: 9 pages, LaTeX, 4 figures (eps
The variation of the magnetic field of the Ap star HD~50169 over its 29 year rotation period
Context. The Ap stars that rotate extremely slowly, with periods of decades
to centuries, represent one of the keys to the understanding of the processes
leading to the differentiation of stellar rotation.
Aims. We characterise the variations of the magnetic field of the Ap star HD
50169 and derive constraints about its structure.
Methods. We combine published measurements of the mean longitudinal field
of HD 50169 with new determinations of this field moment from circular
spectropolarimetry obtained at the 6-m telescope BTA of the Special
Astrophysical Observatory of the Russian Academy of Sciences. For the mean
magnetic field modulus , literature data are complemented by the analysis of
ESO spectra, both newly acquired and from the archive. Radial velocities are
also obtained from these spectra.
Results. We present the first determination of the rotation period of HD
50169, Prot = (29.04+/-0.82) y. HD 50169 is currently the longest-period Ap
star for which magnetic field measurements have been obtained over more than a
full cycle. The variation curves of both and have a significant degree
of anharmonicity, and there is a definite phase shift between their respective
extrema. We confirm that HD 50169 is a wide spectroscopic binary, refine its
orbital elements, and suggest that the secondary is probably a dwarf star of
spectral type M.
Conclusions. The shapes and mutual phase shifts of the derived magnetic
variation curves unquestionably indicate that the magnetic field of HD 50169 is
not symmetric about an axis passing through its centre. Overall, HD 50169
appears similar to the bulk of the long-period Ap stars.Comment: 10 pages, 3 figures, accepted for publication in A&
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