12,778 research outputs found
Opposite polarity field with convective downflow and its relation to magnetic spines in a sunspot penumbra
We discuss NICOLE inversions of Fe I 630.15 nm and 630.25 nm Stokes spectra
from a sunspot penumbra recorded with the CRISP imaging spectropolarimeter on
the Swedish 1-m Solar Telescope at a spatial resolution close to 0.15". We
report on narrow radially extended lanes of opposite polarity field, located at
the boundaries between areas of relatively horizontal magnetic field (the
intra-spines) and much more vertical field (the spines). These lanes harbor
convective downflows of about 1 km/s. The locations of these downflows close to
the spines agree with predictions from the convective gap model (the "gappy
penumbra") proposed six years ago, and more recent 3D MHD simulations. We also
confirm the existence of strong convective flows throughout the entire
penumbra, showing the expected correlation between temperature and vertical
velocity, and having vertical RMS velocities of about 1.2 km/s.Comment: Accepted for publication in A&A (06-March-2013). Minor corrections
made in this version
Hydrodynamics of thermally-driven chiral propulsion and separation
Considerable effort has been directed towards the characterization of chiral
mesoscale structures, as shown in chiral protein assemblies and carbon
nanotubes. Here, we establish a thermally-driven hydrodynamic description for
the actuation and separation of mesoscale chiral structures in a fluid medium.
Cross flow of a Newtonian liquid with a thermal gradient gives rise to chiral
structure propulsion and separation according to their handedness. In turn, the
chiral suspension alters the liquid flow which thus acquires a transverse
(chiral) velocity component. Since observation of the predicted effects
requires a low degree of sophistication, our work provides an efficient and
inexpensive approach to test and calibrate chiral particle propulsion and
separation strategies
Genetic relationships within and among Iberian fescues (Festuca L.) based on PCR-amplified markers
The genus Festuca comprises approximately 450 species and is widely distributed around the world. The Iberian Penninsula, with more than 100 taxa colonizing very diverse habitats, is one of its main centers of diversification. This study was conducted to assess molecular genetic variation and genetic relatedness among 91 populations of 31 taxa of Iberian fescues, based on several molecular markers (random amplified polymorphic DNA, amplified fragment length polymorphisms, and trnL sequences). The analyses showed the paraphyletic origin of the broad-leaved (subgenus Festuca, sections Scariosae and Subbulbosae, and subgenus Schedonorus) and the fine-leaved fescues (subgenus Festuca, sections Aulaxyper, Eskia, and Festuca). Schedonorus showed a weak relationship with Lolium rigidum and appeared to be the most recent of the broad-leaved clade. Section Eskia was the most ancient and Festuca the most recent of the fine-leaved clade. Festuca and Aulaxyper were the most related sections, in concordance with their taxonomic affinities. All taxa grouped into their sections, except F. ampla and F. capillifolia (section Festuca), which appeared to be more closely related to Aulaxyper and to a new independent section, respectively. Most populations clustered at the species level, but some subspecies and varieties mixed their populations. This study demonstrated the value in combining different molecular markers to uncover hidden genetic relationships between populations of Festuca
Polyelectrolytes in the presence of multivalent ions: gelation versus segregation
We analyze solutions of strongly charged chains bridged by linkers such as
multivalent ions. The gelation induced by the strong short range electrostatic
attractions is dramatically suppressed by the long range electrostatic
correlations due to the charge along the uncrosslinked monomers and ions. A
modified Debye-Huckel approach of crosslinked clusters of charged chains is
used to determined the mean field gelation transition self-consistently. Highly
dilute polyelectrolyte solutions tend to segregate macroscopically. Semidilute
solutions can form gels if the Bjerrum length and the distance between
neighboring charged monomers along the chain are both greater than the ion
size
Spectropolarimetric Inversions of the Ca ii 8542 Ă… Line in an M-class Solar Flare
We study the M1.9 class solar flare SOL2015-09-27T10:40 UT using
high-resolution full-Stokes imaging spectropolarimetry of the Ca ii 8542 {\AA}
line obtained with the CRISP imaging spectropolarimeter at the Swedish 1-m
Solar Telescope. Spectropolarimetric inversions using the non-LTE code NICOLE
are used to construct semi-empirical models of the flaring atmosphere to
investigate the structure and evolution of the flare temperature and magnetic
field. A comparison of the temperature stratification in flaring and
non-flaring areas reveals strong heating of the flare ribbon during the flare
peak. The polarization signals of the ribbon in the chromosphere during the
flare maximum become stronger when compared to its surroundings and to pre- and
post- flare profiles. Furthermore, a comparison of the response functions to
perturbations in the line-of-sight magnetic field and temperature in flaring
and non-flaring atmospheres shows that during the flare the Ca ii 8542 {\AA}
line is more sensitive to the lower atmosphere where the magnetic field is
expected to be stronger. The chromospheric magnetic field was also determined
with the weak-field approximation which led to results similar to those
obtained with the NICOLE inversions.Comment: 11 pages, 9 figures, accepted in Ap
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