185 research outputs found
Fragmentation and Limits to Dynamical Scaling in Viscous Coarsening: An Interrupted in situ X-Ray Tomographic Study
X-Ray microtomography was used to follow the coarsening of the structure of a
ternary silicate glass experiencing phase separation in the liquid state. The
volumes, surfaces, mean and Gaussian curvatures of the domains of minority
phase were measured after reconstruction of the 3D images and segmentation. A
linear growth law of the characteristic length scale was
observed. A detailed morphological study was performed. While dynamical scaling
holds for most of the geometrical observables under study, a progressive
departure from scaling invariance of the distributions of local curvatures was
evidenced. The latter results from a gradual fragmentation of the structure in
the less viscous phase that also leads to a power-law size distribution of
isolated domains
ISO observations of four active galaxies
We present ISO PHOT-S spectra of four galaxies known or suspected to host a
central AGN, selected from the initial Iras/Rosat sample of Boller et al.
(1992). Two of them had no obvious Seyfert features in their previous optical
spectra: IRAS 14201+2956, and IRAS 21582+1018. The latter was bright enough to
also allow SWS observations around selected neon lines, to establish its
excitation. While both PHOT-S spectra are characteristic of starburst-dominated
galaxies, the neon line ratios in IRAS 21582+1018 indicate the presence of a
hard excitation source. New, high-resolution, optical spectra show only a weak,
broad component around Halpha, classifying now these two objects as Sey 1.9
galaxies. The two other galaxies observed are the NLS1 galaxies Mrk 359 and Mrk
1388. Their ISO spectra however do not reveal the typical, strong PAH features
found in the starburst galaxies and are more like those of standard Seyferts.
These results show therefore that, although IR observations were expected to be
able to always reveal the presence of an active nucleus by piercing through the
central obscuration, the result may be ambiguous: the broad band IR energy
distribution can still be dominated by starburts located in a circumnuclear
region, and the AGN appear only in specific observations (high-excitation lines
in the IR, or optical spectra with better quality than classification spectra).
The obscuration needs however to be patchy rather than complete, to explain the
detection of the high-excitation lines or broad Balmer wings. Only high-energy
observations can then establish the strength of the central
AGN and the amount of extinction with certainty.Comment: 8 pages, 8 figures, accepted in Astronomy & Astrophysic
Ultra-Efficient On-Chip Supercontinuum Generation from Sign-Alternating-Dispersion Waveguides
Fully integrated supercontinuum sources on-chip are critical to enabling
applications such as portable and mechanically-stable medical imaging devices,
chemical sensing and LiDAR. However, the low-efficiency of current
supercontinuum generation schemes prevent full on-chip integration. In this
letter, we present a scheme where the input energy requirements for integrated
supercontinuum generation is drastically lowered by orders of magnitude, for
bandwidth generation of the order of 500 to 1000 nm. Through sign-alternating
the dispersion in a CMOS compatible silicon nitride waveguide, we achieve an
efficiency enhancement by factors reaching 3800. We show that the pulse energy
requirement for large bandwidth supercontinuum generation at high spectral
energy (e.g., 1/e level) is lowered from nanojoules to 6 picojoules. The
lowered pulse energy requirements enables that chip-integrated laser sources,
such as mode-locked heterogeneously or hybrid integrated diode lasers, can be
used as a pump source, enabling fully integrated on-chip high-bandwidth
supercontinuum sources
ErtrĂ€ge und NĂ€hrstoffgehalte von alten, biologisch und konventionell gezĂŒchteten Winterweizensorten in verschiedenen landwirtschaftlichen Systemen
Due to limited nutrient conditions in organic farming winter wheat cultivars can often
not perform to the full extent of their genetic potential. This study aims to assess
nutrient acquisition potential and yields of old, organically and conventionally bred
winter wheat cultivars. Ten cultivars were tested within the DOK long-term experiment
in two organic systems at low and moderate intensity, a conventional stockless system
and an unfertilized control. Yields and nutrient contents of grain and straw were
significantly affected by cultivars and systems. Cultivar x system interactions were not
detected. Yields were increasing with nutrient level and year of release of cultivars.
Under organic conditions all cultivars performed equally well with respect to yield.
Grain nitrogen content was increasing in line with nitrogen input, but dropping along
year of release of cultivar
Toward integrated synchronously pumped optical parametric oscillators in silicon nitride
We present a tunable, hybrid waveguide-fiber optical parametric oscillator
(OPO) synchronously pumped by an ultra-fast fiber laser exploiting four-wave
mixing (FWM) generated in silicon nitride waveguides. Parametric oscillation
results in a 35 dB enhancement of the idler spectral power density in
comparison to spontaneous FWM, with the ability of wide wavelength tuning over
86 nm in the O-band. Measurements of the oscillation threshold and the
efficiency of the feedback loop reveal how an integration of the OPO on a
single silicon nitride chip can be accomplished at standard repetition rates of
pump lasers in the order of 100 MHz
NASAs Land, Atmosphere near Real-Time Capability for EOS (LANCE): Delivering Data and Imagery to Meet the Needs of near Real-Time Applications
No abstract availabl
Impact of long-term conventional and organic farming on the diversity of arbuscular mycorrhizal fungi
Previous work has shown considerably enhanced soil fertility in agroecosystems managed by organic farming as compared to conventional farming. Arbuscular mycorrhizal fungi (AMF) play a crucial role in nutrient acquisition and soil fertility. The objective of this study was to investigate the diversity of AMF in the context of a long-term study in which replicated field plots, at a single site in Central Europe, had been cultivated for 22years according to two "organicâ and two "conventionalâ farming systems. In the 23rd year, the field plots, carrying an 18-month-old grass-clover stand, were examined in two ways with respect to AMF diversity. Firstly, AMF spores were isolated and morphologically identified from soil samples. The study revealed that the AMF spore abundance and species diversity was significantly higher in the organic than in the conventional systems. Furthermore, the AMF community differed in the conventional and organic systems: Glomus species were similarly abundant in all systems but spores of Acaulospora and Scutellospora species were more abundant in the organic systems. Secondly, the soils were used to establish AMF-trap cultures using a consortium of Plantago lanceolata, Trifolium pratense and Lolium perenne as host plants. The AMF spore community developing in the trap cultures differed: after 12months, two species of the Acaulosporaceae (A. paulinae and A. longula) were consistently found to account for a large part of the spore community in the trap cultures from the organic systems but were found rarely in the ones from the conventional systems. The findings show that some AMF species present in natural ecosystems are maintained under organic farming but severely depressed under conventional farming, indicating a potentially severe loss of ecosystem function under conventional farmin
Correlations among Multi-Wavelength Luminosities of Star-Forming Galaxies
It has been known for two decades that a tight correlation exists between
far-infrared (FIR) and radio (1.4 and 4.8 GHz) global fluxes/luminosities from
galaxies, which may be explained in terms of massive star formation activities
in these galaxies. For this very reason, a correlation might also exist between
X-ray and FIR/radio global luminosities of galaxies. We analyze data from {\it
ROSAT} All-Sky Survey and {\it IRAS} to show that such correlation does indeed
exist between FIR (42.5m) and soft X-ray (0.12.4keV) luminosities
in active star-forming galaxies (ASFGs).In order to establish a physical
connection between the L_{\rmX}-L_{\rm FIR} correlation and global star
formation rate (SFR) in galaxies, we empirically derive both and relations. Futhermore, we propose a relation
between soft X-ray luminosity and SFR in star-forming galaxies. To further
understand the relation, we construct an empirical
model in which both FIR and X-ray emissions consist of two components with one
being closely associated with star formation and the other not.Comment: 9 pages, 6 figures, accepted by MNRA
Imaging Carbon Monoxide Emission in the Starburst Galaxy NGC 6000
We present measurements of carbon monoxide emission in the central region of
the nearby starburst NGC 6000 taken with the Submillimeter Array. The J=2-1
transition of 12CO, 13CO, and C18O were imaged at a resolution of ~3''x2''
(450x300 pc). We accurately determine the dynamical center of NGC 6000 at
R.A(J2000.0)=15h49m49.5s and dec(J2000.0)=-29d23'13'' which agrees with the
peak of molecular emission position. The observed CO dynamics could be
explained in the context of the presence of a bar potential affecting the
molecular material, likely responsible for the strong nuclear concentration
where more than 85% of the gas is located. We detect a kinematically detached
component of dense molecular gas at relatively high velocity which might be
fueling the star formation. A total nuclear dynamical mass of 7x10^9 Msun is
derived and a total mass of gas of 4.6x10^8 Msun, yielding a Mgas/Mdyn~6%,
similar to other previously studied barred galaxies with central starbursts. We
determined the mass of molecular gas with the optically thin isotopologue C18O
and we estimate a CO-to-H2 conversion factor X(CO)=0.4x10^20 cm-2/(K km s-1) in
agreement with that determined in other starburst galaxies.Comment: 31 pages, 7 figures. Accepted for publication in Astronomical
Journal
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