30,848 research outputs found
Stochastic analysis of ocean wave states with and without rogue waves
This work presents an analysis of ocean wave data including rogue waves. A
stochastic approach based on the theory of Markov processes is applied. With
this analysis we achieve a characterization of the scale dependent complexity
of ocean waves by means of a Fokker-Planck equation, providing stochastic
information of multi-scale processes. In particular we show evidence of Markov
properties for increment processes, which means that a three point closure for
the complexity of the wave structures seems to be valid. Furthermore we
estimate the parameters of the Fokker-Planck equation by parameter-free data
analysis. The resulting Fokker-Planck equations are verified by numerical
reconstruction. This work presents a new approach where the coherent structure
of rogue waves seems to be integrated into the fundamental statistics of
complex wave states.Comment: 18 pages, 13 figure
Designable buried waveguides in sapphire by proton implantation
Buried and stacked planar as well as buried single and parallel channel waveguides are fabricated in sapphire by proton implantation. Good control of the implantation parameters provides excellent confinement of the guided light in each structure. Low propagation losses are obtained in fundamental-mode, buried channel waveguides without postimplantation annealing. Choice of the implantation parameters allows one to design mode shapes with different ellipticity and/or mode asymmetry in each orthogonal direction, thus demonstrating the versatility of the fabrication method. Horizontal and vertical parallelization is demonstrated for the design of one- or two-dimensional waveguide arrays in hard crystalline materials
Carbon line formation and spectroscopy in O-type stars
The determination of chemical abundances constitutes a fundamental
requirement for obtaining a complete picture of a star. Particularly in massive
stars, CNO abundances are of prime interest, due to the nuclear CNO-cycle and
various mixing processes which bring these elements to the surface.
We aim at enabling a reliable carbon spectroscopy for our unified NLTE
atmosphere code FASTWIND.
We develop a new carbon model atom including CII/III/IV/V, and discuss
problems related to carbon spectroscopy in O-type stars. We describe different
tests to examine the reliability of our implementation, and investigate which
mechanisms influence the carbon ionization balance. By comparing with
high-resolution spectra from six O-type stars, we check in how far
observational constraints can be reproduced by our new carbon line synthesis.
Carbon lines are even more sensitive to a variation of temperature, gravity,
and mass-loss rate, than hydrogen/helium lines. We are able to reproduce most
of the observed lines from our stellar sample, and to estimate those specific
carbon abundances which bring the lines from different ions into agreement. For
hot dwarfs and supergiants earlier than O7, X-rays from wind-embedded shocks
can impact the synthesized line strengths, particularly for CIV, potentially
affecting the abundance determination.
We have demonstrated our capability to derive realistic carbon abundances by
means of FASTWIND, using our recently developed model atom. We found that
complex effects can have a strong influence on the carbon ionization balance in
hot stars. For a further understanding, the UV range needs to be explored as
well. By means of detailed nitrogen and oxygen model atoms available to use, we
will be able to perform a complete CNO abundance analysis for larger samples of
massive stars, and to provide constraints on corresponding evolutionary models
and aspects.Comment: 22 pages, 16 figures, 6 table
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&
Sapphire planar waveguides fabricated by H+ ion beam implantation
1.1-MeV proton-implanted sapphire waveguides are investigated for the first time. Optical measurements show that the planar waveguides support low-order transverse-mode propagation with good guiding properties without the need to anneal the samples
Proton implanted sapphire planar and channel waveguides
We report low-order transverse-mode planar waveguides in sapphire fabricated for the first time by proton implantation. The waveguides show good guiding properties without post-implantation annealing. Channel waveguiding was achieved by polyimide strip-loading
Shock-wave therapy of gastric outlet syndrome caused by a gallstone
A patient with gastric outlet syndrome (Bouveret's syndrome) caused by a large gallstone impacted in the duodenal bulb was successfully treated by extracorporeal shock-wave lithotripsy. Thus, open abdominal surgery could be avoided. For disintegration of the stone, three consecutive lithotripsy procedures were necessary. Thereafter, stone fragments could be extracted endoscopically. Extracorporeal shock-wave lithotripsy could become a non-surgical alternative in patients with obstruction of the duodenum caused by a gallstone
Flow direction measurement criteria and techniques planned for the 40- by 80-/80- x 120-foot wind tunnel integrated systems tests
A study was performed in order to develop the criteria for the selection of flow direction indicators for use in the Integrated Systems Tests (ISTs) of the 40 by 80/80 by 120 Foot Wind Tunnel System. The problems, requirements, and limitations of flow direction measurement in the wind tunnel were investigated. The locations and types of flow direction measurements planned in the facility were discussed. A review of current methods of flow direction measurement was made and the most suitable technique for each location was chosen. A flow direction vane for each location was chosen. A flow direction vane that employs a Hall Effect Transducer was then developed and evaluated for application during the ISTs
Non-LTE models for synthetic spectra of type Ia supernovae. III. An accelerated lambda iteration procedure for the mutual interaction of strong spectral lines in SN Ia models with and without energy deposition
Context. Spectroscopic analyses to interpret the spectra of the brightest
supernovae from the UV to the near-IR provide a powerful tool with great
astrophysical potential for the determination of the physical state of the
ejecta, their chemical composition, and the SNe distances even at significant
redshifts.
Methods. We report on improvements of computing synthetic spectra for SNIa
with respect to i) an improved and sophisticated treatment of thousands of
strong lines that interact intricately with the "pseudo-continuum" formed
entirely by Doppler- shifted spectral lines, ii) an improved and expanded
atomic database, and iii) the inclusion of energy deposition within the ejecta.
Results. We show that an accelerated lambda iteration procedure we have
developed for the mutual interaction of strong spectral lines appearing in the
atmospheres of SNeIa solves the longstanding problem of transferring the
radiative energy from the UV into the optical regime. In detail we discuss
applications of the diagnostic technique by example of a standard SNIa, where
the comparison of calculated and observed spectra revealed that in the early
phases the consideration of the energy deposition within the spectrum-forming
regions of the ejecta does not qualitatively alter the shape of the spectra.
Conclusions. The results of our investigation lead to an improved
understanding of how the shape of the spectrum changes radically as function of
depth in the ejecta, and show how different emergent spectra are formed as a
result of the particular physical properties of SNe Ia ejecta and the resulting
peculiarities in the radiative transfer. This provides an important insight
into the process of extracting information from observed SNIa spectra, since
these spectra are a complex product of numerous unobservable SNIa spectral
features which are thus analyzed in parallel to the observable spectral
features.Comment: 27 pages, 19 figures. Submitted to A&A, revised versio
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