453 research outputs found
Superconductor Dynamics
Superconductors used in magnet technology could carry extreme currents
because of their ability to keep the magnetic flux motionless. The dynamics of
the magnetic flux interaction with superconductors is controlled by this
property. The cases of electrical transport in a round wire and the
magnetization of wires of various shapes (circular, elliptical, plate) in an
external magnetic field are analysed. Resistance to the magnetic field
penetration means that the field produced by the superconducting magnet is no
longer proportional to the supplied current. It also leads to a dissipation of
electromagnetic energy. In conductors with unequal transverse dimensions, such
as flat cables, the orientation with respect to the magnetic field plays an
essential role. A reduction of magnetization currents can be achieved by
splitting the core of a superconducting wire into fine filaments; however, new
kinds of electrical currents that couple the filaments consequently appear.
Basic formulas allowing qualitative analyses of various flux dynamic cases are
presented.Comment: 19 pages, contribution to the CAS-CERN Accelerator School:
Superconductivity for Accelerators, Erice, Italy, 24 April - 4 May 2013,
edited by R. Baile
Evidence of quiet Sun chromospheric activity related to an emerging small-scale magnetic loop
Aims: We investigate the temporal evolution of magnetic flux emergence in the
quiet Sun atmosphere close to disk center. Methods: We combine high-resolution
SoHO/MDI magnetograms with TRACE observations taken in the 1216 {\AA} channel
in order to analyze the temporal evolution of an emerging small-scale magnetic
loop and its traces in the chromosphere. Results: At first place, we find
signatures of flux emergence very close to the edge of a supergranular network
boundary located at disk center. The new emerging flux appears first in the MDI
magnetograms in form of an asymmetric bipolar element, i.e. the patch with
negative polarity is roughly two-times weaker than the corresponding patch with
opposite polarity. The average values of magnetic flux and magnetic flux
densities reach 1.6 x 10^18 Mx, -8.5 x 10^17 Mx, and 55 Mx cm^-2, -30 Mx cm^-2,
respectively. The spatial distance between the opposite polarity patches of the
emerged feature increases from about 2.5" to 5.0" during the lifetime of the
loop which was not longer than 36 min. A more precise lifetime-estimate of the
feature was not possible because of a gap in the temporal sequence of the MDI
magnetograms. The chromospheric response to the emerged magnetic dipole occurs
~ 9 minutes later with respect to the photospheric magnetograms. It consists of
a quasi-periodic sequence of time-localized brightenings visible in the 1216
{\AA} TRACE channel apparent for ~ 14 minutes and being co-spatial with the
axis connecting the two patches of opposite magnetic polarity. Conclusions: We
identify the observed event as a small-scale magnetic loop emerging at
photospheric layers and subsequently rising up to the chromosphere. We discuss
the possibility that the fluctuations detected in the chromospheric emission
probably reflect magnetic field oscillations which propagate to the
chromosphere in form of waves.Comment: 6 pages, 4 figures, 1 table, Astronomy and Astrophysics, in pres
Hysteretic ac losses in a superconductor strip between flat magnetic shields
Hysteretic ac losses in a thin, current-carrying superconductor strip located
between two flat magnetic shields of infinite permeability are calculated using
Bean's model of the critical state. For the shields oriented parallel to the
plane of the strip, penetration of the self-induced magnetic field is enhanced,
and the current dependence of the ac loss resembles that in an isolated
superconductor slab, whereas for the shields oriented perpendicular to the
plane of the strip, penetration of the self-induced magnetic field is impaired,
and the current dependence of the ac loss is similar to that in a
superconductor strip flanked by two parallel superconducting shields. Thus,
hysteretic ac losses can strongly augment or, respectively, wane when the
shields approach the strip.Comment: 9 pages, 5 figures, submitted to PR
Model mass spectrometric study of competitive interactions of antimicrobial bisquaternary ammonium drugs and aspirin with membrane phospholipids
The aim of the study is to reveal molecular mechanisms of possible activity modulation of antimicrobial bis-quaternary ammonium compounds (BQAC) and aspirin (ASP) through noncovalent competitive complexation under their combined introduction into the model systems with membrane phospholipids. Methods. Binary and triple systems containing either decamethoxinum or ethonium, or thionium and aspirin, as well as dipalmitoyl-phosphatidylcholine (DPPC) have been investigated by electrospray ionization mass spectrometry. Results. Basing on the analysis of associates recorded in the mass spectra, the types of nonocovalent complexes formed in the systems studied were determined and the supposed role of the complexation in the BQAC and ASP activity modulation was discussed. The formation of associates of BQAC dications with ASP anion is considered as one of the possible ways of deactivation of ionic forms of the medications. The formation of stable complexes of BQAC with DPPC and ASP with DPPC in binary systems as well as the complexes distribution in triple-components systems BQAC:ASP:DPPC point to the existence of competition between drugs of these two types for the binding to DPPC. Conclusions. The results obtained point to the competitive complexation in the model molecular systems containing the BQAC, aspirin and membrane phospholipids. The observed phenomenon testifies to the possibility of modulating the activity of bisquaternary antimicrobial agents and aspirin under their combined usage, due to the competition between the drugs for binding to the target membrane phospholipid molecules and also due to the formation of stable noncovalent complexes between BQAC and ASP
Spectral Characteristics of the He I D3 Line in a Quiescent Prominence Observed by THEMIS
We analyze the observations of a quiescent prominence acquired by the
Telescope Heliographique pour l'Etude du Magnetisme et des Instabilites
Solaires (THEMIS) in the He I 5876 A (He I D3) multiplet aiming to measure the
spectral characteristics of the He I D3 profiles and to find for them an
adequate fitting model. The component characteristics of the He I D3 Stokes I
profiles are measured by the fitting system approximating them with a double
Gaussian. This model yields an He I D3 component peak intensity ratio of
, which differs from the value of 8 expected in the optically thin
limit. Most of the measured Doppler velocities lie in the interval km/s,
with a standard deviation of km/s around the peak value of 0.4 km/s.
The wide distribution of the full-width at half maximum has two maxima at 0.25
A and 0.30 A for the He I D3 blue component and two maxima at 0.22 A and 0.31 A
for the red component. The width ratio of the components is . We
show that the double-Gaussian model systematically underestimates the blue wing
intensities. To solve this problem, we invoke a two-temperature multi-Gaussian
model, consisting of two double-Gaussians, which provides a better
representation of He I D3 that is free of the wing intensity deficit. This
model suggests temperatures of 11.5 kK and 91 kK, respectively, for the cool
and the hot component of the target prominence. The cool and hot components of
a typical He I D3 profile have component peak intensity ratios of 6.6 and 8,
implying a prominence geometrical width of 17 Mm and an optical thickness of
0.3 for the cool component, while the optical thickness of the hot component is
negligible. These prominence parameters seem to be realistic, suggesting the
physical adequacy of the multi-Gaussian model with important implications for
interpreting He I D3 spectropolarimetry by current inversion codes.Comment: 25 pages,1 movie, 10 figures, 2 tables, 2 equations. The final
publication is available at Springer via
http://dx.doi.org/10.1007/s11207-017-1118-z The supplementary movie is
available for viewing and download at
https://www.dropbox.com/s/7tskvnc593tlbyv/Prominence_HeID3_GONG_AIA.mpg?dl=
Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare
We analyzed high-cadence sit-and-stare observations acquired with the
Hinode/EIS spectrometer and HXR measurements acquired with RHESSI during an
M-class flare. During the flare impulsive phase, we observe no significant
flows in the cooler Fe XIII line but strong upflows, up to 80-150 km/s, in the
hotter Fe XVI line. The largest Doppler shifts observed in the Fe XVI line were
co-temporal with the sharp intensity peak. The electron density obtained from a
Fe XIII line pair ratio exhibited fast increase (within two minutes) from the
pre-flare level of 5.01x10^(9) cm^(-3) to 3.16x10^(10) cm^(-3) during the flare
peak. The nonthermal energy flux density deposited from the coronal
acceleration site to the lower atmospheric layers during the flare peak was
found to be 1.34x10^(10) erg/s/cm^(2) for a low-energy cut-off that was
estimated to be 16 keV. During the decline flare phase, we found a secondary
intensity and density peak of lower amplitude that was preceded by upflows of
15 km/s that were detected in both lines. The flare was also accompanied by a
filament eruption that was partly captured by the EIS observations. We derived
Doppler velocities of 250-300 km/s for the upflowing filament material.The
spectroscopic results for the flare peak are consistent with the scenario of
explosive chromospheric evaporation, although a comparatively low value of the
nonthermal energy flux density was determined for this phase of the flare. This
outcome is discussed in the context of recent hydrodynamic simulations. It
provides observational evidence that the response of the atmospheric plasma
strongly depends on the properties of the electron beams responsible for the
heating, in particular the steepness of the energy distribution.Comment: 13 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Properties of the inner penumbral boundary and temporal evolution of a decaying sunspot
It was empirically determined that the umbra-penumbra boundaries of stable
sunspots are characterized by a constant value of the vertical magnetic field.
We analyzed the evolution of the photospheric magnetic field properties of a
decaying sunspot belonging to NOAA 11277 between August 28 - September 3, 2011.
The observations were acquired with the spectropolarimeter on-board of the
Hinode satellite. We aim to proof the validity of the constant vertical
magnetic-field boundary between the umbra and penumbra in decaying sunspots. A
spectral-line inversion technique was used to infer the magnetic field vector
from the full-Stokes profiles. In total, eight maps were inverted and the
variation of the magnetic properties in time were quantified using linear or
quadratic fits. We found a linear decay of the umbral vertical magnetic field,
magnetic flux, and area. The penumbra showed a linear increase of the vertical
magnetic field and a sharp decay of the magnetic flux. In addition, the
penumbral area quadratically decayed. The vertical component of the magnetic
field is weaker on the umbra-penumbra boundary of the studied decaying sunspot
compared to stable sunspots. Its value seem to be steadily decreasing during
the decay phase. Moreover, at any time of the shown sunspot decay, the inner
penumbra boundary does not match with a constant value of the vertical magnetic
field, contrary to what was seen in stable sunspots. During the decaying phase
of the studied sunspot, the umbra does not have a sufficiently strong vertical
component of the magnetic field and is thus unstable and prone to be
disintegrated by convection or magnetic diffusion. No constant value of the
vertical magnetic field was found for the inner penumbral boundary.Comment: Accepted for publication in Astronomy & Astrophysics, 6 pages, 7
figure
Magnetic loop emergence within a granule
We investigate the temporal evolution of magnetic flux emerging within a
granule in the quiet-Sun internetwork at disk center. We combined IR
spectropolarimetry performed in two Fe I lines at 1565 nm with
speckle-reconstructed G-band imaging. We determined the magnetic field
parameters by a LTE inversion of the full Stokes vector using the SIR code, and
followed their evolution in time. To interpret the observations, we created a
geometrical model of a rising loop in 3D. The relevant parameters of the loop
were matched to the observations where possible. We then synthesized spectra
from the 3D model for a comparison to the observations. We found signatures of
magnetic flux emergence within a growing granule. In the early phases, a
horizontal magnetic field with a distinct linear polarization signal dominated
the emerging flux. Later on, two patches of opposite circular polarization
signal appeared symmetrically on either side of the linear polarization patch,
indicating a small loop-like structure. The mean magnetic flux density of this
loop was roughly 450 G, with a total magnetic flux of around 3x10^17 Mx. During
the ~12 min episode of loop occurrence, the spatial extent of the loop
increased from about 1 to 2 arcsec. The middle part of the appearing feature
was blueshifted during its occurrence, supporting the scenario of an emerging
loop. The temporal evolution of the observed spectra is reproduced to first
order by the spectra derived from the geometrical model. The observed event can
be explained as a case of flux emergence in the shape of a small-scale loop.Comment: 10 pages, 13 figures; accepted for Astronomy and Astrophysics; ps and
eps figures in full resolution are available at
http://www.astro.sk/~koza/figures/aa2009_loop
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