114,281 research outputs found
Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. III. X-ray emission from wind-embedded shocks
X-rays/EUV radiation emitted from wind-embedded shocks in hot, massive stars
can affect the ionization balance in their outer atmospheres, and can be the
mechanism responsible for the production of highly ionized species. To allow
for these processes in the context of spectral analysis, we have implemented
such emission into our unified, NLTE model atmosphere/spectrum synthesis code
FASTWIND.
The shock structure and corresponding emission is calculated as a function of
user-supplied parameters. We account for a temperature and density
stratification inside the post-shock cooling zones, calculated for radiative
and adiabatic cooling in the inner and outer wind, respectively. The
high-energy absorption of the cool wind is considered by adding important
K-shell opacities, and corresponding Auger ionization rates have been included
into the NLTE network.
We tested and verified our implementation carefully against corresponding
results from various alternative model atmosphere codes, and studied the
effects from shock emission for important ions from He, C, N, O, Si, and P.
Surprisingly, dielectronic recombination turned out to play an essential role
for the ionization balance of OIV/OV around Teff = 45,000 K. Finally, we
investigated the behavior of the mass absorption coefficient, kappa_nu(r),
important in the context of X-ray line formation in massive star winds.
In almost all considered cases, direct ionization is of major influence, and
Auger ionization significantly affects only NVI and OVI. The approximation of a
radially constant kappa_nu is justified for r > 1.2 Rstar and lambda < 18 A,
and also for many models at longer wavelengths. To estimate the actual value of
this quantity, however, the HeII opacities need to be calculated from detailed
NLTE modeling, at least for wavelengths longer than 18 to 20 A, and information
on the individual CNO abundances has to be present.Comment: accepted by A&
Electroluminescent light sources via soft lithography
Purpose: Microcontact printing is a process used to print high resolution protein arrays for biosensors. We investigate using these techniques to print electrically conductive fine line structures for electroluminescent (E/L) light sources.
Approach: The viability of using microcontact printing as a process for electronics fabrication is investigated. Polydimethylsiloxane (PDMS) stamps inked with alkanethiol compounds form Self Assembled Monolayers (SAM) on substrate surfaces, acting as the resist to subsequent etching processes. The printed lines are characterized with regard to their performance as high electric field generators in electroluminescent displays.
Findings: It has been demonstrated that microcontact printing is a cheap, repeatable process for fabricating electronic devices. The results demonstrate the viability of the process to fabricate electric field generator structures for E/L light sources with reduced driving voltages.
Value: It has been demonstrated that microcontact printing can produce electrically conductive fine-line structures with high resolution, confirming its viability in printed electronics manufacture
Bio-inspired Tensegrity Soft Modular Robots
In this paper, we introduce a design principle to develop novel soft modular
robots based on tensegrity structures and inspired by the cytoskeleton of
living cells. We describe a novel strategy to realize tensegrity structures
using planar manufacturing techniques, such as 3D printing. We use this
strategy to develop icosahedron tensegrity structures with programmable
variable stiffness that can deform in a three-dimensional space. We also
describe a tendon-driven contraction mechanism to actively control the
deformation of the tensegrity mod-ules. Finally, we validate the approach in a
modular locomotory worm as a proof of concept.Comment: 12 pages, 7 figures, submitted to Living Machine conference 201
Multiscale and multimodel simulation of Bloch point dynamics
We present simulation results on the structure and dynamics of micromagnetic
point singularities with atomistic resolution. This is achieved by embedding an
atomistic computational region into a standard micromagnetic algorithm. Several
length scales are bridged by means of an adaptive mesh refinement and a
seamless coupling between the continuum theory and a Heisenberg formulation for
the atomistic region. The code operates on graphical processing units and is
able to detect and track the position of strongly inhomogeneous magnetic
regions. This enables us to reliably simulate the dynamics of Bloch points,
which means that a fundamental class of micromagnetic switching processes can
be analyzed with unprecedented accuracy. We test the code by comparing it with
established results and present its functionality with the example of a
simulated field-driven Bloch point motion in a soft-magnetic cylinder
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