197 research outputs found
Data-driven model of the solar corona above an active region
We aim to reproduce the structure of the corona above a solar active region
as seen in the extreme ultraviolet (EUV) using a three-dimensional
magnetohydrodynamic (3D MHD) model. The 3D MHD data-driven model solves the
induction equation and the mass, momentum, and energy balance. To drive the
system, we feed the observed evolution of the magnetic field in the photosphere
of the active region AR 12139 into the bottom boundary. This creates a hot
corona above the cool photosphere in a self-consistent way. We synthesize the
coronal EUV emission from the densities and temperatures in the model and
compare this to the actual coronal observations. We are able to reproduce the
overall appearance and key features of the corona in this active region on a
qualitative level. The model shows long loops, fan loops, compact loops, and
diffuse emission forming at the same locations and at similar times as in the
observation. Furthermore, the low-intensity contrast of the model loops in EUV
matches the observations. In our model the energy input into the corona is
similar as in the scenarios of fieldline-braiding or flux-tube tectonics, that
is, energy is transported to the corona through the driving of the vertical
magnetic field by horizontal photospheric motions. The success of our model
shows the central role that this process plays for the structure, dynamics, and
heating of the corona.Comment: 5 pages, 3 Figures, published in A&A letter
Current systems of coronal loops in 3D MHD simulations
We study the magnetic field and current structure associated with a coronal
loop. Through this we investigate to what extent the assumptions of a
force-free magnetic field break down and where they might be justified. We
analyse a 3D MHD model of the solar corona in an emerging active region with
the focus on the structure of the forming coronal loops. The lower boundary of
this simulation is taken from a model of an emerging active region. As a
consequence of the emerging magnetic flux and the horizontal motions at the
surface a coronal loop forms self-consistently. We investigate the current
density along magnetic field inside (and outside) this loop and study the
magnetic and plasma properties in and around it. We find that the total current
along the loop changes its sign from being antiparallel to parallel to the
magnetic field. This is caused by the inclination of the loop together with the
footpoint motion. Around the loop the currents form a complex non-force-free
helical structure. This is directly related to a bipolar current structure at
the loop footpoints at the base of the corona and a local reduction of the
background magnetic field (i.e. outside the loop) caused by the plasma flow
into and along the loop. The locally reduced magnetic pressure in the loop
allows the loop to sustain a higher density, which is crucial for the emission
in extreme UV. The acting of the flow on the magnetic field hosting the loop
turns out to be also responsible for the observed squashing of the loop. The
complex magnetic field and current system surrounding it can be modeled only in
3D MHD models where the magnetic field has to balance the plasma pressure. A 1D
coronal loop model or a force-free extrapolation can not capture the current
system and the complex interaction of the plasma and the magnetic field in the
coronal loop, despite the fact that the loop is under low- conditions.Comment: 10 pages, 11 figures, published in A&
Stellar X-rays and magnetic activity in 3D MHD coronal models
Observations suggest a power-law relation between the coronal emission in
X-rays, , and the total (unsigned) magnetic flux at the stellar
surface, . The physics basis for this relation is poorly understood. We
use three-dimensional (3D) magnetohydrodynamics (MHD) numerical models of the
coronae above active regions, that is, strong concentrations of magnetic field,
to investigate the versus relation and illustrate this
relation with an analytical model based on simple well-established scaling
relations. In the 3D MHD model horizontal (convective) motions near the surface
induce currents in the coronal magnetic field that are dissipated and heat the
plasma. This self-consistently creates a corona with a temperature of 1 MK. We
run a series of models that differ in terms of the (unsigned) magnetic flux at
the surface by changing the (peak) magnetic field strength while keeping all
other parameters fixed. In the 3D MHD models we find that the energy input into
the corona, characterized by either the Poynting flux or the total volumetric
heating, scales roughly quadratically with the unsigned surface flux .
This is expected from heating through field-line braiding. Our central result
is the nonlinear scaling of the X-ray emission as . This scaling is slightly steeper than found in recent
observations that give power-law indices of up to only 2 or 3. Assuming that on
a real star, not only the peak magnetic field strength in the active regions
changes but also their number (or surface filling factor), our results are
consistent with observations. Our model provides indications of what causes the
steep increase in X-ray luminosity by four orders of magnitude from solar-type
activity to fast rotating active stars.Comment: Updated version after review: 15 pages, 12 figures, Accepted for
publication in Astronomy and Astrophysic
Distinct microRNA profiles in the perilymph and serum of patients with Menière\u27s disease
Hypothesis: Menière's disease microRNA (miRNA) profiles are unique and are reflected in the perilymph and serum of patients. Background: Development of effective biomarkers for Menière's disease are needed. miRNAs are small RNA sequences that downregulate mRNA translation and play a significant role in a variety of disease states, ultimately making them a promising biomarker. miRNAs can be readily isolated from human inner ear perilymph and serum, and may exhibit disease-specific profiles. Methods: Perilymph sampling was performed in 10 patients undergoing surgery; 5 patients with Meniere's disease and 5 patients with otosclerosis serving as controls. miRNAs were isolated from the serum of 5 patients with bilateral Menière's disease and compared to 5 healthy age-matched controls. For evaluation of miRNAs an Agilent miRNA gene chip was used. Analysis of miRNA expression was carried out using Qlucore and Ingenuitey Pathway Analysis software. Promising miRNAs biomarkers were validated using qPCR. Results: In the perilymph of patients with Menière's disease, we identified 16 differentially expressed miRNAs that are predicted to regulate over 220 different cochlear genes. Six miRNAs are postulated to regulate aquaporin expression and twelve miRNAs are postulated to regulate a variety of inflammatory and autoimmune pathways. When comparing perilymph with serum samples, miRNA-1299 and−1270 were differentially expressed in both the perilymph and serum of Ménière's patients compared to controls. Further analysis using qPCR confirmed miRNA-1299 is downregulated over 3-fold in Meniere's disease serum samples compared to controls. Conclusions: Patients with Ménière's disease exhibit distinct miRNA expression profiles within both the perilymph and serum. The altered perilymph miRNAs identified can be linked to postulated Ménière's disease pathways and may serve as biomarkers. miRNA-1299 was validated to be downregulated in both the serum and perilymph of Menière's patients
Coatings of different carbon nanotubes on platinum electrodes for neuronal devices: Preparation, cytocompatibility and interaction with spiral ganglion cells
Cochlear and deep brain implants are prominent examples for neuronal prostheses with clinical relevance. Current research focuses on the improvement of the long-term functionality and the size reduction of neural interface electrodes. A promising approach is the application of carbon nanotubes (CNTs), either as pure electrodes but especially as coating material for electrodes. The interaction of CNTs with neuronal cells has shown promising results in various studies, but these appear to depend on the specific type of neurons as well as on the kind of nanotubes. To evaluate a potential application of carbon nanotube coatings for cochlear electrodes, it is necessary to investigate the cytocompatibility of carbon nanotube coatings on platinum for the specific type of neuron in the inner ear, namely spiral ganglion neurons. In this study we have combined the chemical processing of as-delivered CNTs, the fabrication of coatings on platinum, and the characterization of the electrical properties of the coatings as well as a general cytocompatibility testing and the first cell culture investigations of CNTs with spiral ganglion neurons. By applying a modification process to three different as-received CNTs via a reflux treatment with nitric acid, long-term stable aqueous CNT dispersions free of dispersing agents were obtained. These were used to coat platinum substrates by an automated spray-coating process. These coatings enhance the electrical properties of platinum electrodes, decreasing the impedance values and raising the capacitances. Cell culture investigations of the different CNT coatings on platinum with NIH3T3 fibroblasts attest an overall good cytocompatibility of these coatings. For spiral ganglion neurons, this can also be observed but a desired positive effect of the CNTs on the neurons is absent. Furthermore, we found that the well-established DAPI staining assay does not function on the coatings prepared from single-wall nanotubes. © 2016 Burblies et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.DFG/EXC 1077/1 “Hearing4all
Development of Neuronal Guidance Fibers for Stimulating Electrodes: Basic Construction and Delivery of a Growth Factor
State-of-the-art treatment for sensorineural hearing loss is based on electrical stimulation of residual spiral ganglion neurons (SGNs) with cochlear implants (CIs). Due to the anatomical gap between the electrode contacts of the CI and the residual afferent fibers of the SGNs, spatial spreading of the stimulation signal hampers focused neuronal stimulation. Also, the efficiency of a CI is limited because SGNs degenerate over time due to loss of trophic support. A promising option to close the anatomical gap is to install fibers as artificial nerve guidance structures on the surface of the implant and install on these fibers drug delivery systems releasing neuroprotective agents. Here, we describe the first steps in this direction. In the present study, suture yarns made of biodegradable polymers (polyglycolide/poly-ε-caprolactone) serve as the basic fiber material. In addition to the unmodified fiber, also fibers modified with amine groups were employed. Cell culture investigations with NIH 3T3 fibroblasts attested good cytocompatibility to both types of fibers. The fibers were then coated with the extracellular matrix component heparan sulfate (HS) as a biomimetic of the extracellular matrix. HS is known to bind, stabilize, modulate, and sustainably release growth factors. Here, we loaded the HS-carrying fibers with the brain-derived neurotrophic factor (BDNF) which is known to act neuroprotectively. Release of this neurotrophic factor from the fibers was followed over a period of 110 days. Cell culture investigations with spiral ganglion cells, using the supernatants from the release studies, showed that the BDNF delivered from the fibers drastically increased the survival rate of SGNs in vitro. Thus, biodegradable polymer fibers with attached HS and loaded with BDNF are suitable for the protection and support of SGNs. Moreover, they present a promising base material for the further development towards a future neuronal guiding scaffold. Copyright © 2022 Wille, Harre, Oehmichen, Lindemann, Menzel, Ehlert, Lenarz, Warnecke and Behrens
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