3,185 research outputs found
MHD wave propagation from the sub-photosphere to the corona in an arcade-shaped magnetic field with a null point
The aim of this work is to study the energy transport by means of MHD waves
propagating in quiet Sun magnetic topology from layers below the surface to the
corona. Upward propagating waves find obstacles, such as the equipartition
layer with plasma b=1 and the transition region, and get converted, reflected
and refracted. Understanding the mechanisms by which MHD waves can reach the
corona can give us information about the solar atmosphere and the magnetic
structures. We carry out two-dimensional numerical simulations of wave
propagation in a magnetic field structure that consists of two vertical flux
tubes separated by an arcade shaped magnetic field. This configuration contains
a null point in the corona, that significantly modifies the behaviour of the
waves. We describe in detail the wave propagation through the atmosphere under
different driving conditions. We also present the spatial distribution of the
mean acoustic and magnetic energy fluxes and the spatial distribution of the
dominant frequencies in the whole domain. We conclude that the energy reaches
the corona preferably along vertical magnetic fields, inside the flux tubes,
and it has an acoustic nature. Most of the magnetic energy keeps concentrated
below the transition region due to the refraction of the magnetic waves and the
continuous conversion of acoustic-like waves into fast magnetic waves in the
equipartition layer located in the photosphere. However, part of the magnetic
energy reaches the low corona when propagating in the region where the arcades
are located, but waves are sent back downwards to the lower atmosphere at the
null point surroundings. This phenomenon, together with the reflection and
refraction of waves in the TR and the lower turning point, act as a re-feeding
of the atmosphere. In the frequency distribution, we find that high frequency
waves can reach the corona outside the vertical flux tubes.Comment: 13 pages, 13 figure
Stray field and superconducting surface spin valve effect in LaCaMnO/YBaCuO bilayers
Electronic transport and magnetization measurements were performed on
LaCaMnO/YBaCuO (LCMO/YBCO) bilayers
below the superconducting transition temperature in order to study the
interaction between magnetism and superconductivity. This study shows that a
substantial number of weakly pinned vortices are induced in the YBCO layer by
the large out-of-plane stray field in the domain walls. Their motion gives rise
to large dissipation peaks at the coercive field. The angular dependent
magnetoresistance (MR) data reveal the interaction between the stripe domain
structure present in the LCMO layer and the vortices and anti-vortices induced
in the YBCO layer by the out-of-plane stray field. In addition, this study
shows that a superconducting surface spin valve effect is present in these
bilayers as a result of the relative orientation between the magnetization at
the LCMO/YBCO interface and the magnetization in the interior of the LCMO layer
that can be tuned by the rotation of a small . This latter finding will
facilitate the development of superconductive magnetoresistive memory devices.
These low-magnetic field MR data, furthermore, suggest that triplet
superconductivity is induced in the LCMO layer, which is consistent with recent
reports of triplet superconductivity in LCMO/YBCO/LCMO trilayers and LCMO/YBCO
bilayers.Comment: 14 pages, 3 figure
High frequency waves in the corona due to null points
This work aims to understand the behavior of non-linear waves in the vicinity
of a coronal null point. In previous works we have showed that high frequency
waves are generated in such magnetic configuration. This paper studies those
waves in detail in order to provide a plausible explanation of their
generation. We demonstrate that slow magneto-acoustic shock waves generated in
the chromosphere propagate through the null point and produce a train of
secondary shocks that escape along the field lines. A particular combination of
the shock wave speeds generates waves at a frequency of 80 mHz. We speculate
that this frequency may be sensitive to the atmospheric parameters in the
corona and therefore can be used to probe the structure of this solar layer
Simulated interaction of MHD shock waves with a complex network-like region
We provide estimates of the wave energy reaching the solar chromosphere and
corona in a network-like magnetic field topology, including a coronal null
point. The waves are excited by an instantaneous strong subphotospheric source
and propagate through the subphotosphere, photosphere, chromosphere, transition
region, and corona with the plasma beta and other atmospheric parameters
varying by several orders of magnitude. We compare two regimes of the wave
propagation: a linear and nonlinear regime. While the amount of energy reaching
the corona is similar in both regimes, this energy is transmitted at different
frequencies. In both cases the dominant periods of waves at each height
strongly depend on the local magnetic field topology, but this distribution is
only in accordance with observations in the nonlinear case.Comment: 4 page
How value-glamour investors use financial information: UK evidence of investor's confirmation bias
The paper investigates investor’s behaviour in the context of value–glamour investing and fundamental analysis, and provides a direct test of the confirmation bias by bringing together the evidence from several strands of literature into a well-defined framework of investor behaviour. The empirical evidence presented is in line with a model of
investor’s asymmetric reaction to good and bad news due to confirmation bias. Pessimistic value investors typically under-react to good financial information, but they process bad information rationally or over-confidently. On the contrary, glamour investors are often too optimistic to timely update prices following bad financial information, but they are likely to fairly price or even over-react when receiving good information
Predicting Caries by Measuring Its Activity Using Quantitative Light-Induced Fluorescence in vivo: A 2-Year Caries Increment Analysis
The aim of this study was to analyse the predictive power of several clinical baseline parameters and the de-/remineralisation properties of in vivo etched sites measured with quantitative light-induced fluorescence (QLF) for subsequent 2-year caries increment. At baseline, in 44 children (8.23 ± 1.5 years) two areas (diameter 2 mm) of the buccal surface of a primary posterior tooth were etched with 36% phosphoric acid gel for 1 and 4 min, respectively. The etched sites were analysed immediately after etching (ΔQ1) and 24 h (ΔQ2) later by QLF. Additionally, caries status (deft/DMFT and initial caries), approximal plaque, bleeding on probing, and the patient’s current use of fluorides were recorded. In the 2-year follow-up, 29 children were re-assessed. After clinical examination, the caries increment was calculated (ΔDMFT) and correlated with the baseline clinical variables and the QLF readings. Results showed a significant positive correlation between ΔQ1 min and the ΔDMFT (r = 0.44, p = 0.02). The ΔDMFT was significantly correlated with the baseline deft (r = 0.56, p = 0.002), cavitated active caries lesions (r = 0.52, p = 0.003), and filled teeth (r = 0.53, p = 0.003). In a regression analysis the use of fluoridated salt (SC = –0.10) and fluoride gel (SC = –0.14) were negatively associated with ΔDMFT. In conclusion, these findings suggest that the demineralisation properties of the etched sites and the outcome of the 24-hour measurements with QLF are significantly associated with caries increment. Previous caries experience strongly correlated with caries increment in this group of children
Lepton Number Violating Radiative Decay in Models with R-parity Violation
Models with explicit R-parity violation can induce new rare radiative decay
modes of the boson into single supersymmetric particles which also violate
lepton number. We examine the rate and signature for one such decay,
, and find that such a mode will be very difficult
to observe, due its small branching fraction, even if the lepton number
violating coupling in the superpotential is comparable in strength to
electromagnetism. This parallels a similar result obtained earlier by Hewett in
the case of radiative decays.Comment: 10 pages, 2 figures(available on request), LaTex, ANL-HEP-PR-92-8
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