159 research outputs found
Post-melting encapsulation of glass microwires for multipath light waveguiding within phosphate glasses
Glass waveguides remain the fundamental component of advanced photonic
circuits and with a significant role in other applications such as quantum
information processing, light generation, imaging, data storage, and sensing
platforms. Up to date, the fabrication of glass waveguides relies mainly on
demanding chemical processes or on the employment of expensive ultrafast laser
equipment. In this work, we demonstrate the feasibility of a simple,
low-temperature, post-melting encapsulation procedure for the development of
advanced glass waveguides. Namely, silver iodide phosphate glass microwires
(MWs) are drawn from typical splat-quenched samples. Following this, the MWs
are incorporated in a controlled manner within previously prepared transparent
silver phosphate glass rectangular prisms. The composition of the employed
glasses is chosen so that the host phosphate glass has a lower refractive index
than the embedded MWs. In such case, the waveguide mechanism relies on the
propagation of light inside the encapsulated higher refractive index MWs.
Moreover, the presence of silver nanoparticles within the MWs enhances the
light transmission due to scattering effects. Waveguide devices with either one
or two incorporated MWs were fabricated. Remarkably, in the latter case, the
transmission of light of different colors and in multipath direction is
possible, rendering the developed waveguides outstanding candidates for various
photonic circuits, optoelectronic, and smart sign glass applications
Neutron-induced background in the CONUS experiment
CONUS is a novel experiment aiming at detecting elastic neutrino nucleus
scattering in the fully coherent regime using high-purity Germanium (Ge)
detectors and a reactor as antineutrino () source. The detector setup
is installed at the commercial nuclear power plant in Brokdorf, Germany, at a
very small distance to the reactor core in order to guarantee a high flux of
more than 10/(scm). For the experiment, a good
understanding of neutron-induced background events is required, as the neutron
recoil signals can mimic the predicted neutrino interactions. Especially
neutron-induced events correlated with the thermal power generation are
troublesome for CONUS. On-site measurements revealed the presence of a thermal
power correlated, highly thermalized neutron field with a fluence rate of
(74530)cmd. These neutrons that are produced by nuclear
fission inside the reactor core, are reduced by a factor of 10 on
their way to the CONUS shield. With a high-purity Ge detector without shield
the -ray background was examined including highly thermal power
correlated N decay products as well as -lines from neutron
capture. Using the measured neutron spectrum as input, it was shown, with the
help of Monte Carlo simulations, that the thermal power correlated field is
successfully mitigated by the installed CONUS shield. The reactor-induced
background contribution in the region of interest is exceeded by the expected
signal by at least one order of magnitude assuming a realistic ionization
quenching factor of 0.2.Comment: 28 pages, 28 figure
X-ray Evidence of the Common Envelope Phase of V471 Tauri
Chandra Low Energy Transmission Grating Spectrograph observations of the
pre-cataclysmic binary V471 Tau have been used to estimate the C/N abundance
ratio of the K dwarf component for the first time. While the white dwarf
component dominates the spectrum longward of 50 AA, at shorter wavelengths the
observed X-ray emission is entirely due to coronal emission from the K dwarf.
The H-like resonance lines of C and N yield an estimate of their logarithmic
abundance ratio relative to the Sun of [C/N]=-0.38+/-0.15 - half of the
currently accepted solar value. We interpret this result as the first clear
observational evidence for the presumed common envelope phase of this system,
during which the surface of the K dwarf was contaminated by CN-cycle processed
material dredged up into the red giant envelope. We use the measured C/N ratio
to deduce that 0.015-0.04 Msun was accreted by the K dwarf while engulfed, and
show that this is consistent with a recent tentative detection of 13C in the K
dwarf photosphere, and with the measured Li abundance in the scenario where the
red giant companion was Li-rich during the common envelope phase.Comment: 6 pages, 2 figures, ApJL accepte
Calpain I remains intact and intracellular during platelet activation. Immunochemical measurements with monoclonal and polyclonal antibodies
Fundamental Parameters of He-Weak and He-Strong Stars
We carried out low resolution spectroscopic observations in the wavelength
range 3400-4700 A of 20 He-weak and 8 He-strong stars to determine their
fundamental parameters by means of the Divan-Chalonge-Barbier (BCD)
spectrophotometric system. For a few He-weak stars we also estimate the
effective temperatures and the angular diameters by integrating absolute fluxes
observed over a wide spectral range. Non-LTE model calculations are carried out
to study the influence of the He/H abundance ratio on the emergent radiation of
He-strong stars and on their Teff determination. We find that the effective
temperatures, surface gravities and bolometric absolute magnitudes of He-weak
stars estimated with the BCD system and the integrated flux method are in good
agreement between each other, and they also agree with previous determinations
based on several different methods. The mean discrepancy between the visual
absolute magnitudes derived using the Hipparcos parallaxes and the BCD values
is on average 0.3 mag for He-weak stars, while it is 0.5 mag for He-strong
stars. For He-strong stars, we note that the BCD calibration, based on stars in
the solar environment, leads to overestimated values of Teff. By means of model
atmosphere calculations with enhanced He/H abundance ratios we show that larger
He/H ratios produce smaller BD which naturally explains the Teff
overestimation. We take advantage of these calculations to introduce a method
to estimate the He/H abundance ratio in He-strong stars. The BD of HD 37479
suggests that the Teff of this star remains fairly constant as the star
spectrum undergoes changes in the intensity of H and He absorption lines. Data
for the He-strong star HD 66765 are reported for the first time.Comment: Accepted for publication in A&
The Carina-Near Moving Group
We identify a group of ~20 co-moving, mostly southern hemisphere, ~200 Myr
old stars near Earth. Of the stars likely to be members of this Carina-Near
Moving Group, in either its nucleus (~30 pc from Earth) or surrounding stream,
all but 3 are plausible members of a multiple star system. The nucleus is
(coincidentally) located quite close to the nucleus of the AB Doradus moving
group notwithstanding that the two groups have substantially different ages and
Galactic space motions, UVW.Comment: 9 pages, 1 table, 2 figures. Accepted in ApJ
Coronal X-Ray Emission from the Stellar Companions to Transiently Accreting Black Holes
Observations of soft X-ray transients (SXTs) in quiescence have found that
the binaries harboring black holes are fainter than those that contain a
neutron star. Narayan and collaborators postulated that the faint X-ray
emission from black hole binaries was powered by an advection dominated
accretion flow (ADAF). We explore an alternative explanation for the quiescent
X-ray emission from the black hole systems: coronal emission from the rapidly
rotating optical companion. This is commonly observed and well studied in other
tidally locked binaries, such as the RS CVns. We show that two of the three
X-ray detected black hole binaries (A0620-00 and GRO J1655-40) exhibit X-ray
fluxes entirely consistent with coronal emission. The X-ray spectra of these
objects should be best fit with thermal Raymond-Smith models rich in lines when
coronal emission predominates. One black hole system (V404 Cyg) is too X-ray
bright to be explained as coronal emission. The quiescent X-ray emission from
the neutron star binaries is far too bright for coronal emission. It might be
that all SXT's have variable accretion rates in quiescence and that the basal
quiescent X-ray flux is set by either coronal emission from the companion or --
when present -- by thermal emission from the neutron star. We also show that
the lithium abundances in the black hole systems are comparable to those in the
RS CVns, reducing the need for production mechanisms that involve the compact
object.Comment: ApJ, accepted (v541; Oct 1, 2000); Changes to figures and tables,
minor modifications to text. Uses emulateapj.sty. 14 pages, 3 figure
The rapidly pulsating sdO star, SDSS J160043.6+074802.9
A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system
containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields
Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely
type of K3V for the secondary star. We compare our results with atmospheric
parameters derived by Fontaine et al. (2008) and in the context of existing
evolution models for sdO stars. New and more extensive photometry is also
presented which recovers most, but not all, frequencies found in an earlier
paper. It therefore seems probable that some pulsation modes have variable
amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO
models show those having log g > 5.3 to be more likely to be unstable and
capable of driving pulsation in the observed frequency range.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 2009
September
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