101 research outputs found
Oscillation of solar radio emission at coronal acoustic cut-off frequency
Recent SECCHI COR2 observations on board STEREO-A spacecraft have detected
density structures at a distance of 2.5--15~R propagating with periodicity of
about 90~minutes. The observations show that the density structures probably
formed in the lower corona. We used the large Ukrainian radio telescope URAN-2
to observe type IV radio bursts in the frequency range of 8--32~MHz during the
time interval of 08:15--11:00~UT on August 1, 2011. Radio emission in this
frequency range originated at the distance of 1.5--2.5 R according to the
Baumbach-Allen density model of the solar corona. Morlet wavelet analysis
showed the periodicity of 80~min in radio emission intensity at all
frequencies, which demonstrates that there are quasi-periodic variations of
coronal density at all heights. The observed periodicity corresponds to the
acoustic cut-off frequency of stratified corona at a temperature of 1~MK. We
suggest that continuous perturbations of the coronal base in the form of
jets/explosive events generate acoustic pulses, which propagate upwards and
leave the wake behind oscillating at the coronal cut-off frequency. This wake
may transform into recurrent shocks due to the density decrease with height,
which leads to the observed periodicity in the radio emission. The recurrent
shocks may trigger quasi-periodic magnetic reconnection in helmet streamers,
where the opposite field lines merge and consequently may generate periodic
density structures observed in the solar wind.Comment: 10 pages, 6 figures, accepted in A&
The influence of contaminated hydraulic fluid on the relative volume flow rate and the wear of rubbing parts of the aviation plunger pump
Still, there is the problem of the plunger pumps failures due to pollution of the working fluid with mechanical impurities in civil aviation. The article deals with experimental research the change of relative volume flow rate of plunger pump model NP-72M which depends on the working fluid purity. In particular, the negative effect of increasing the particle size of impurities (electrocorundum about 3 μm, 10 μm, 20 μm) and increasing particles concentration (about 25–150 mg/L) with the constant particle size on pump operation has presented. This has manifested in increased wear of rubbing parts and reduced the relative volume flow rate. A visual inspection of the pump parts has carried out, and the most damaged areas have identified
Radio seismology of the outer solar corona
Observed oscillations of coronal loops in EUV lines have been successfully
used to estimate plasma parameters in the inner corona (< 0.2 R_0, where R_0 is
the solar radius). However, coronal seismology in EUV lines fails for higher
altitudes because of rapid decrease in line intensity. We aim to use radio
observations to estimate the plasma parameters of the outer solar corona (> 0.2
R_0). We use the large Ukrainian radio telescope URAN-2 to observe type IV
radio burst at the frequency range of 8-32 MHz during the time interval of
09:50-12:30 UT in April 14, 2011. The burst was connected to C2.3 flare, which
occurred in AR 11190 during 09:38-09:49 UT. The dynamic spectrum of radio
emission shows clear quasi-periodic variations in the emission intensity at
almost all frequencies. Wavelet analysis at four different frequencies (29 MHz,
25 MHz, 22 MHz and 14 MHz) shows the quasi-periodic variation of emission
intensity with periods of 34 min and 23 min. The periodic variations can be
explained by the first and second harmonics of vertical kink oscillation of
transequatorial coronal loops, which were excited by the same flare. The apex
of transequatorial loops may reach up to 1.2 R_0 altitude. We derive and solve
the dispersion relation of trapped MHD oscillations in a longitudinally
inhomogeneous magnetic slab. The analysis shows that a thin (with width to
length ratio of 0.1), dense (with the ratio of internal and external densities
of > 20) magnetic slab with weak longitudinal inhomogeneity may trap the
observed oscillations. Seismologically estimated Alfv\'en speed inside the loop
at the height of 1 R_0 is 1000 km/s. Then the magnetic field strength at this
height is estimated as 0.9 G. Extrapolation of magnetic field strength to the
inner corona gives 10 G at the height of 0.1 R_0.Comment: 12 pages, 10 figures, Accepted in A&
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