13,006 research outputs found
Estimating the magnetic field strength from magnetograms
A properly calibrated longitudinal magnetograph is an instrument that
measures circular polarization and gives an estimation of the magnetic flux
density in each observed resolution element. This usually constitutes a lower
bound of the field strength in the resolution element, given that it can be
made arbitrarily large as long as it occupies a proportionally smaller area of
the resolution element and/or becomes more transversal to the observer and
still produce the same magnetic signal. Yet, we know that arbitrarily stronger
fields are less likely --hG fields are more probable than kG fields, with
fields above several kG virtually absent-- and we may even have partial
information about its angular distribution. Based on a set of sensible
considerations, we derive simple formulae based on a Bayesian analysis to give
an improved estimation of the magnetic field strength for magnetographs.Comment: 8 pages, 7 figures, accepted for publication in A&
Near-IR internetwork spectro-polarimetry at different heliocentric angles
The analysis of near infrared spectropolarimetric data at the internetwork at
different regions on the solar surface could offer constraints to reject
current modeling of these quiet areas.
We present spectro-polarimetric observations of very quiet regions for
different values of the heliocentric angle for the Fe I lines at 1.56 micron,
from disc centre to positions close to the limb. The spatial resolution of the
data is 0.7-1". We analyze direct observable properties of the Stokes profiles
as the amplitude of circular and linear polarization as well as the total
degree of polarization. Also the area and amplitude asymmetries are studied.
We do not find any significant variation of the properties of the
polarimetric signals with the heliocentric angle. This means that the magnetism
of the solar internetwork remains the same regardless of the position on the
solar disc. This observational fact discards the possibility of modeling the
internetwork as a Network-like scenario. The magnetic elements of internetwork
areas seem to be isotropically distributed when observed at our spatial
resolution.Comment: Sorry, this is the version with the correct bibliography. Some
figures had to be compressed. Accepted for publication in A&
A near-IR line of Mn I as a diagnostic tool of the average magnetic energy in the solar photosphere
We report on spectropolarimetric observations of a near-IR line of Mn I
located at 15262.702 A whose intensity and polarization profiles are very
sensitive to the presence of hyperfine structure. A theoretical investigation
of the magnetic sensitivity of this line to the magnetic field uncovers several
interesting properties. The most important one is that the presence of strong
Paschen-Back perturbations due to the hyperfine structure produces an intensity
line profile whose shape changes according to the absolute value of the
magnetic field strength. A line ratio technique is developed from the intrinsic
variations of the line profile. This line ratio technique is applied to
spectropolarimetric observations of the quiet solar photosphere in order to
explore the probability distribution function of the magnetic field strength.
Particular attention is given to the quietest area of the observed field of
view, which was encircled by an enhanced network region. A detailed theoretical
investigation shows that the inferred distribution yields information on the
average magnetic field strength and the spatial scale at which the magnetic
field is organized. A first estimation gives ~250 G for the mean field strength
and a tentative value of ~0.45" for the spatial scale at which the observed
magnetic field is horizontally organized.Comment: 42 pages, 17 figures, accepted for publication in the Astrophysical
Journal. Figures 1 and 9 are in JPG forma
Temperature dependent charge transport mechanisms in carbon sphere/polymer composites
Carbon spheres (CS) with diameters in the range were prepared
via hydrolysis of a sucrose solution at and later annealed in
at The spheres were highly conducting but difficult to process into
thin films or pressed pellets. In our previous work, composite samples of CS
and the insulating polymer polyethylene oxide (PEO) were prepared and their
charge transport was analyzed in the temperature range
Here, we analyze charge transport in CS coated with a thin polyaniline (PANi)
film doped with hydrochloric acid (HCl), in the same temperature range. The
goal is to study charge transport in the CS using a conducting polymer (PANi)
as a binder and compare with that occurring at CS/PEO. A conductivity maxima
was observed in the CS/PEO composite but was absent in CS/PANi. Our data
analysis shows that variable range hopping of electrons between polymeric
chains in PANi-filled gaps between CS takes on a predominant part in transport
through CS/PANi composites, whereas in CS/PEO composites, electrons travel
through gaps between CS solely by means of direct tunneling. This difference in
transport mechanisms results in different temperature dependences of the
conductivity.Comment: 7 pages, 6 figure
Assessment of the structures contribution (crystalline and mesophases) and mechanical properties of polycaprolactone/pluronic blends
Films of biodegradable blends of polycaprolactone (PCL) and Pluronics F68 and F127 were manufactured by an
industrial thermo-mechanical process to be applied as potential delivery systems. The effects of Pluronics on the
structure (mesophase organization), and thermal and mechanical properties of polycaprolactone were investigated
using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD),
polarized optical microscopy (POM) and tensile mechanical tests. The addition of Pluronics affected the crystallization
process by changing the relative amounts of crystalline, amorphous, and meso- (condis + plastic)
phases. The melting transition and XRD profiles were deconvoluted to assess the individual contribution of the
different crystal morphologies. Furthermore, it was found that the mechanical properties of the blends depended
on the ratio and type of Pluronic. Thus, Pluronic F127 showed a larger mesophase content than its F68 counterpart
with PCL and blends with enhanced ductilityFunding for open access charge was provided by Universidad de Huelva / CBUA. The authors gratefully acknowledge the financial support
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