4,391 research outputs found
Segmented superconducting magnet for a broadband traveling wave maser Patent
Segmented superconducting magnet producing staggered magnetic field and suitable for broadband traveling wave maser
Observations of Subarcsecond Bright Dots in the Transition Region above Sunspots with the Interface Region Imaging Spectrograph
Observations with the Interface Region Imaging Spectrograph (IRIS) have
revealed numerous sub-arcsecond bright dots in the transition region above
sunspots. These bright dots are seen in the 1400\AA{} and 1330\AA{} slit-jaw
images. They are clearly present in all sunspots we investigated, mostly in the
penumbrae, but also occasionally in some umbrae and light bridges. The bright
dots in the penumbrae typically appear slightly elongated, with the two
dimensions being 300--600 km and 250--450 km, respectively. The long sides of
these dots are often nearly parallel to the bright filamentary structures in
the penumbrae but sometimes clearly deviate from the radial direction. Their
lifetimes are mostly less than one minute, although some dots last for a few
minutes or even longer. Their intensities are often a few times stronger than
the intensities of the surrounding environment in the slit-jaw images. About
half of the bright dots show apparent movement with speeds of
10--40~km~s in the radial direction. Spectra of a few bright dots
were obtained and the Si~{\sc{iv}}~1402.77\AA{} line profiles in these dots are
significantly broadened. The line intensity can be enhanced by one to two
orders of magnitude. Some relatively bright and long-lasting dots are also
observed in several passbands of the Atmospheric Imaging Assembly onboard the
Solar Dynamics Observatory, and they appear to be located at the bases of
loop-like structures. Many of these bright dots are likely associated with
small-scale energy release events at the transition region footpoints of
magnetic loops.Comment: 5 figures, will appear in ApJ
Nonlinear Force-Free Field Modeling of the Solar Magnetic Carpet and Comparison with SDO/HMI and Sunrise/IMaX Observations
In the quiet solar photosphere, the mixed polarity fields form a magnetic
carpet, which continuously evolves due to dynamical interaction between the
convective motions and magnetic field. This interplay is a viable source to
heat the solar atmosphere. In this work, we used the line-of-sight (LOS)
magnetograms obtained from the Helioseismic and Magnetic Imager (HMI) on the
\textit{Solar Dynamics Observatory} (\textit{SDO}), and the Imaging
Magnetograph eXperiment (IMaX) instrument on the \textit{Sunrise} balloon-borne
observatory, as time dependent lower boundary conditions, to study the
evolution of the coronal magnetic field. We use a magneto-frictional relaxation
method, including hyperdiffusion, to produce time series of three-dimensional
(3D) nonlinear force-free fields from a sequence of photospheric LOS
magnetograms. Vertical flows are added up to a height of 0.7 Mm in the modeling
to simulate the non-force-freeness at the photosphere-chromosphere layers.
Among the derived quantities, we study the spatial and temporal variations of
the energy dissipation rate, and energy flux. Our results show that the energy
deposited in the solar atmosphere is concentrated within 2 Mm of the
photosphere and there is not sufficient energy flux at the base of the corona
to cover radiative and conductive losses. Possible reasons and implications are
discussed. Better observational constraints of the magnetic field in the
chromosphere are crucial to understand the role of the magnetic carpet in
coronal heating.Comment: Accepted for publication in The Astrophysical Journal (13 pages, 10
figures
Dynamics of the solar magnetic bright points derived from their horizontal motions
The sub-arcsec bright points (BP) associated with the small scale magnetic
fields in the lower solar atmosphere are advected by the evolution of the
photospheric granules. We measure various quantities related to the horizontal
motions of the BPs observed in two wavelengths, including the velocity
auto-correlation function. A 1 hr time sequence of wideband H
observations conducted at the \textit{Swedish 1-m Solar Telescope}
(\textit{SST}), and a 4 hr \textit{Hinode} \textit{G}-band time sequence
observed with the Solar Optical telescope are used in this work. We follow 97
\textit{SST} and 212 \textit{Hinode} BPs with 3800 and 1950 individual velocity
measurements respectively. For its high cadence of 5 s as compared to 30 s for
\textit{Hinode} data, we emphasize more on the results from \textit{SST} data.
The BP positional uncertainty achieved by \textit{SST} is as low as 3 km. The
position errors contribute 0.75 km s to the variance of the observed
velocities. The \textit{raw} and \textit{corrected} velocity measurements in
both directions, i.e., , have Gaussian distributions with standard
deviations of and km s respectively. The BP
motions have correlation times of about s. We construct the power
spectrum of the horizontal motions as a function of frequency, a quantity that
is useful and relevant to the studies of generation of Alfv\'en waves.
Photospheric turbulent diffusion at time scales less than 200 s is found to
satisfy a power law with an index of 1.59.Comment: Accepted for publication in The Astrophysical Journal. 24 pages, 9
figures, and 1 movie (not included
Testing the Integrity of Liquid Containing Hermetically Sealed Containers by the Use of Radioactive Markers
A method for detecting leaky ampules filled with a liquid such as a parenteral solution. The ampules to be tested are immersed in a solution containing a short-lived radionuclide, and a pressure differential is imposed between the solution containing the radionuclide and the parenteral solution or other liquid contained in the ampules. The ampules are then removed from solution, decontaminated to remove any solution adhering to the outer surface and pores thereof, dried, and finally examined for electromagnetic radiation, preferably gamma radiation, emanating from the interior of the ampules which would indicate a leaky condition thereof
Effect of Concave Wall Geometry on Heat Transfer in Hypersonic Boundary Layers
Heat transfer measurements are made to investigate the effects of concave surface curvature on a high-stagnation enthalpy boundary layer in a Mach 5.1 flow. Experiments are
carried out using two curved models with 16 and 25 degree turning angles, and baseline
planar models (at plate and linear ramp) for comparative study. Streamwise and spanwise
cross-sections are obtained. Significant destabilization of the boundary layer is observed
over the adverse pressure gradient geometries. For the curved surfaces, the heat flux distribution appears to exhibit a quadratic dependence with streamwise distance, in contrast
with the linear dependence observed on the linear ramp
Propagating EUV disturbances in the solar corona : two-wavelength observations
Quasi-periodic EUV disturbances simultaneously observed in 171 Ã… and 195 Ã… TRACE bandpasses propagating outwardly in a fan-like magnetic structure of a coronal active region are analysed. Time series of disturbances observed in the different bandpasses have a relatively high correlation coefficient (up to about 0.7). The correlation has a tendency to decrease with distance along the structure: this is consistent with an interpretation of the disturbances in terms of parallel-propagating slow magnetoacoustic waves. The wavelet analysis does not show a significant difference between waves observed in different bandpasses. Periodic patterns of two distinct periods: 2-3 min and 5-8 min are detected in both bandpasses, existing simultaneously and at the same distance along the loop, suggesting the nonlinear generation of the second harmonics
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