157,732 research outputs found
Speed of Meridional Flows and Magnetic Flux Transport on the Sun
We use the magnetic butterfly diagram to determine the speed of the magnetic
flux transport on the solar surface towards the poles. The manifestation of the
flux transport is clearly visible as elongated structures extended from the
sunspot belt to the polar regions. The slopes of these structures are measured
and interpreted as meridional magnetic flux transport speed. Comparison with
the time-distance helioseismology measurements of the mean speed of the
meridional flows at the depth of 3.5--12 Mm shows a generally good agreement,
but the speeds of the flux transport and the meridional flow are significantly
different in areas occupied by the magnetic field. The local circulation flows
around active regions, especially the strong equatorward flows on the
equatorial side of active regions affect the mean velocity profile derived by
helioseismology, but do not influence the magnetic flux transport. The results
show that the mean longitudinally averaged meridional flow measurements by
helioseismology may not be used directly in solar dynamo models for describing
the magnetic flux transport, and that it is necessary to take into account the
longitudinal structure of these flows.Comment: 4 pages, 3 figures, accepted in ApJ Letter
Effect of oxygen stoichiometry on T(sub c) of Bi-based superconductors
The role of oxygen stoichiometry on T(sub c) is relatively well established on La2CuO(4+x) and the YBa2Cu3O(7-x) (123) superconductors, as compared to the Bi-based superconductors. Results are presented of investigations on the effects of oxygen stoichiometry on the transition temperature T(sub c) of Bi2Sr2CaCu2O(8+x) (2212 phase), and Pb-doped Bi2Sr2Ca2Cu3O(10+X) (2223 phase). It is shown that the effects of oxygen stoichiometry on T(sub c) of these two phases are very different. These results may be helpful in understanding the mechanism of superconductivity in the Bi-based superconductors
Dependence of transition temperature on hole concentration per CuO2 sheet in the Bi-based superconductors
The recently observed variations of the transition temperature (T sub c) with oxygen content in the Bi based (2212) and (2223) superconductors are analyzed in terms of p+, the hole concentration per CuO2 sheet. This analysis shows that in this system, T sub c increases with p+ initially, reaching maxima at p+ = 0.2 approx. 0.3, followed by monotonic decrease of T sub c with p+. The forms of these variations are similar to those observed in the La(2-x)Sr(x)CuO4 and YBa2Cu3Oy systems, suggesting that p+ may be an important variable governing superconductivity in the cuprate superconductors
Killing Spinors for the Bosonic String
We obtain the effective action for the bosonic string with arbitrary
Yang-Mills fields, up to the \alpha' order, in general dimensions. The form of
the action is determined by the requirement that the action admit well-defined
Killing spinor equations, whose projected integrability conditions give rise to
the full set of equations of motion. The success of the construction suggests
that the hidden "pseudo-supersymmetry" associated with the Killing spinor
equations may be a property of the bosonic string itself.Comment: 9 page
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