64 research outputs found
Superflare G and K Stars and the Lithium abundance
We analyzed here the connection of superflares and the lithium abundance in G
and K stars based on Li abundance determinations conducted with the echelle
spectra of a full set of 280 stars obtained with the ELODIE spectrograph. For
high-active stars we show a definite correlation between and the
chromosphere activity. We show that sets of stars with high Li abundance and
having superflares possess common properties. It relates, firstly, to stars
with activity saturation. We consider the X-ray data for G, K, and M stars
separately, and show that transition from a saturation mode to solar-type
activity takes place at values of rotation periods 1.1, 3.3, and 7.2 days for
G2, K4 and M3 spectral types, respectively. We discuss bimodal distribution of
a number of G and K main-sequence stars versus an axial rotation and location
of superflare stars with respect to other Kepler stars. We conclude that
superflare G and K stars are mainly fast rotating young objects, but some of
them belong to stars with solar-type activity. At the same time, we found a
group of G stars with high Li content , but being
slower rotators with rotation periods > 10 days, which are characterized by low
chromospheric activity. This agrees with a large spread in Li abundances in
superflare stars. A mechanism leading to this effect is discussed.Comment: 6 pages, 8 figures. The 19th Cambridge Workshop on Cool Stars,
Stellar Systems, and the Su
Plasmonic detection and visualization of directed adsorption of charged single nanoparticles to patterned surfaces
Some aspects of comparing the operational properties of synchronous machines with a conventional and two mutually shifted excitation windings
A comparative analysis of the operational properties of traditional and two-valve synchronous machines with a rotor, having a reciprocating axis, excited from independent regulated DC sources, is generalized. On the basis of research, it has been shown that the use of a control quadrature excitation winding significantly improves the performance of synchronous machines at low costs for its manufacture. The authors have shown a significant improvement in the performance of machines with different operating modes based on the results of theoretical and experimental studies carried out on synchronous machines with a rotating axis of magnetic saturation, attached to various designs of quadrature excitation winding. It has been recognized that neglecting magnetic saturation in performance calculations for synchronous machines leads to significant estimation errors properties of the studied machine. In addition, the advantages of synchronous machines with sine-cosine field winding are shown. With an insignificant complication of the manufacturing technology, it opens the way to solving the problem of creating energy-saving turbine generators, which have a property that is very important for the practice of operation, i.e. an almost unchanged (sinusoidal) shape of the resulting magnetic field in the air gap of the machine within the allowable range of load variation under steady-state symmetric modes
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