153 research outputs found
Horizontal supergranule-scale motions inferred from TRACE ultraviolet observations of the chromosphere
We study horizontal supergranule-scale motions revealed by TRACE observation
of the chromospheric emission, and investigate the coupling between the
chromosphere and the underlying photosphere. A highly efficient
feature-tracking technique called balltracking has been applied for the first
time to the image sequences obtained by TRACE (Transition Region and Coronal
Explorer) in the passband of white light and the three ultraviolet passbands
centered at 1700 {\AA}, 1600 {\AA}, and 1550 {\AA}. The resulting velocity
fields have been spatially smoothed and temporally averaged in order to reveal
horizontal supergranule-scale motions that may exist at the emission heights of
these passbands. We find indeed a high correlation between the horizontal
velocities derived in the white-light and ultraviolet passbands. The horizontal
velocities derived from the chromospheric and photospheric emission are
comparable in magnitude. The horizontal motions derived in the UV passbands
might indicate the existence of a supergranule-scale magnetoconvection in the
chromosphere, which may shed new light on the study of mass and energy supply
to the corona and solar wind at the height of the chromosphere. However, it is
also possible that the apparent motions reflect the chromospheric brightness
evolution as produced by acoustic shocks which might be modulated by the
photospheric granular motions in their excitation process, or advected partly
by the supergranule-scale flow towards the network while propagating upward
from the photosphere. To reach a firm conclusion, it is necessary to
investigate the role of granular motions in the excitation of shocks through
numerical modeling, and future high-cadence chromospheric magnetograms must be
scrutinized.Comment: 5 figures, accepted by Astronomy & Astrophysic
Evidence for the photospheric excitation of incompressible chromospheric waves
Observing the excitation mechanisms of incompressible transverse waves is vital for determining how energy propagates through the lower solar atmosphere. We aim to show the connection between convectively driven photospheric flows and incompressible chromospheric waves. The observations presented here show the propagation of incompressible motion through the quiet lower solar atmosphere, from the photosphere to the chromosphere. We determine photospheric flow vectors to search for signatures of vortex motion and compare results to photospheric flows present in convective simulations. Further, we search for the chromospheric response to vortex motions. Evidence is presented that suggests incompressible waves can be excited by the vortex motions of a strong magnetic flux concentration in the photosphere. A chromospheric counterpart to the photospheric vortex motion is also observed, presenting itself as a quasi-periodic torsional motion. Fine-scale, fibril structures that emanate from the chromospheric counterpart support transverse waves that are driven by the observed torsional motion. A new technique for obtaining details of transverse waves from time-distance diagrams is presented and the properties of transverse waves (e.g., amplitudes and periods) excited by the chromospheric torsional motion are measured
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
Glecaprevir-Pibrentasvir for 8 or 12 Weeks in HCV Genotype 1 or 3 Infection
The trials (NCT02604017, NCT02640157) were funded by AbbVie Inc
Plastisol Foaming Process. Decomposition of the Foaming Agent, Polymer Behavior in the Corresponding Temperature Range and Resulting Foam Properties
The decomposition of azodicarbonamide, used as foaming agent in PVC - plasticizer (1/1) plastisols was studied by DSC. Nineteen different plasticizers, all belonging to the ester family, two being polymeric (polyadipates), were compared. The temperature of maximum decomposition rate (in anisothermal regime at 5 K min-1 scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J g -1. Some trends of variation of these parameters appear significant and are discussed in terms of solvent (matrix) and viscosity effects on the decomposition reactions. The shear modulus at 1 Hz frequency was determined at the temperature of maximum rate of foaming agent decomposition, and differs significantly from a sample to another. The foam density was determined at ambient temperature and the volume fraction of bubbles was used as criterion to judge the efficiency of the foaming process. The results reveal the existence of an optimal shear modulus of the order of 2 kPa that corresponds roughly to plasticizer molar masses of the order of 450 ± 50 g mol-1. Heavier plasticizers, especially polymeric ones are too difficult to deform. Lighter plasticizers such as diethyl phthalate (DEP) deform too easily and presumably facilitate bubble collapse
New perspectives for preventing hepatitis C virus liver graft infection
publisher: Elsevier articletitle: New perspectives for preventing hepatitis C virus liver graft infection journaltitle: The Lancet Infectious Diseases articlelink: http://dx.doi.org/10.1016/S1473-3099(16)00120-1 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved
Fully covered self-expandable metal stents (SEMS), partially covered SEMS and self-expandable plastic stents for the treatment of benign esophageal ruptures and anastomotic leaks
Mean-field transport theory for the two-flavour NJL model
By making decomposition of the Wigner function simultaneously in both the
spinor and the isospin spaces we derive a set of kinetic equations for the
quark distribution functions and the spin densities. A detailed analysis of the
consequences imposed by the chiral invariance on the form of the transport
equations is presented.Comment: Revtex, 25 pages, no figure
- …