7,614 research outputs found
OVERLEVELSE AF INDIKATORORGANISMER OG SMITSTOFFER I KOMPOSTTOILETTER OG VED SIMULERET CENTRALISERET EFTERKOMPOSTERING AF AFFØRING FRA MENNESKER
Som resultat af projekterne kan drages følgende hovedkonklusioner om kompostering af fæces fra mennesker: Fæces fra de undersøgte typer af kompostbeholdere bør ikke anvendes til jordbrugsformål uden viderebehandling, da dette skønnes at være behæftet med hygiejne- og sundhedsrisici. Det skyldes, at der ikke blev dokumenteret egentlige termofile temperaturstigninger i fæcesmaterialet i komposttoiletenhederne i Hjortshøj, Dyssekilde og Sverige, og at fækale indikatorbakteriers antal varierede voldsomt, og der ingen entydig tendens var til forekomst af lavere kimtal ved lange opbevaringstider af de opsamlede fækalier
Screening of organically based fungicides for apple scab (Venturia inaequalis) control and a histopathological study of the mode of action of a resistance inducer.
A range of possible substitutes for copper-based fungicides for control of apple scab (Venturia inaequalis) in organic growing were tested in laboratory and growth chamber experiments in the Danish project StopScab (2002-2004). Eighteen crude plant extracts, 19 commercial plant-based products and 6 miscellaneous compounds were tested for their ability to reduce scab symptoms on apple seedlings. Most of the compounds were also tested for their effect on conidium germination on glass slides. Fourteen of the crude plant extracts, 13 of the commercial plant products and 5 of the miscellaneous compounds showed promising control efficacies when used either preventively or curatively in the plant assay. A histopathological study was carried out on the mode of action of the resistance inducer, acibenzolar-S-methyl (ASM), which reduced scab severity and sporulation on apple seedlings in several plant assays when applied as preventive treatment. The effect of the inducer on key pre- and post-penetration events of V. inaequalis was studied and compared to these events in water-treated control leaves. The histopathological study showed that the inducer had its strongest effect on post-penetration events indicated by delayed infection and reduced stroma development. In addition, a small but significant inhibition of conidial germination and a stimulation of germ tube length were observed. This investigation provides new histopathological evidence for the mode of action of ASM against V. inaequalis and serves as a model for evaluation of the mechanisms by which the organically based fungicides reduce infection of V. inaequalis
The Faber-Jackson relation for early-type galaxies: Dependence on the magnitude range
We take a sample of early-type galaxies from the Sloan Digital Sky Survey
(SDSS-DR7, 90 000 galaxies) spanning a range of approximately 7 in
both and filters and analyse the behaviour of the Faber-Jackson
relation parameters as functions of the magnitude range. We calculate the
parameters in two ways: i) We consider the faintest (brightest) galaxies in
each sample and we progressively increase the width of the magnitude interval
by inclusion of the brighter (fainter) galaxies
(increasing-magnitude-intervals), and ii) we consider narrow-magnitude
intervals of the same width ( ) over the whole magnitude
range available (narrow-magnitude-intervals). Our main results are that: i) in
both increasing and narrow-magnitude-intervals the Faber-Jackson relation
parameters change systematically, ii) non-parametric tests show that the
fluctuations in the values of the slope of the Faber-Jackson relation are not
products of chance variations. We conclude that the values of the Faber-Jackson
relation parameters depend on the width of the magnitude range and the
luminosity of galaxies within the magnitude range. This dependence is caused,
to a great extent by the selection effects and because the geometrical shape of
the distribution of galaxies on the plane depends on
luminosity. We therefore emphasize that if the luminosity of galaxies or the
width of the magnitude range or both are not taken into consideration when
comparing the structural relations of galaxy samples for different wavelengths,
environments, redshifts and luminosities, any differences found may be
misinterpreted.Comment: 15 pages, 5 figures. A&A. Accepte
On the origin of H_2CO abundance enhancements in low-mass protostars
High angular resolution H_2CO 218 GHz line observations have been carried out toward the low-mass protostars IRAS 16293-2422 and L1448-C using the Owens Valley Millimeter Array at ~2" resolution. Simultaneous 1.37 mm continuum data reveal extended emission which is compared with that predicted by model envelopes constrained from single-dish data. For L1448-C the model density structure works well down to the 400 AU scale to which the interferometer is sensitive. For IRAS 16293-2422 , a known proto-binary object, the interferometer observations indicate that the binary has cleared much of the material in the inner part of the envelope, out to the binary separation of ~800 AU. For both sources there is excess unresolved compact emission centered on the sources, most likely due to accretion disks ≾200 AU in size with masses of ≳0.02 M_☉ (L1448-C) and ≳0.1 M_☉ (IRAS 16293-2422). The H_2CO data for both sources are dominated by emission from gas close to the positions of the continuum peaks. The morphology and velocity structure of the H_2CO array data have been used to investigate whether the abundance enhancements inferred from single-dish modelling are due to thermal evaporation of ices or due to liberation of the ice mantles by shocks in the inner envelope. For IRAS 16293-2422 the H_2CO interferometer observations indicate the presence of rotation roughly perpendicular to the large scale CO outflow. The H_2CO distribution differs from that of C^(18)O, with C^(18)O emission peaking near MM1 and H_2CO stronger near MM2. For L1448-C, the region of enhanced H_2CO emission extends over a much larger scale >1" than the radius of 50-100 K (0."6-0".15) where thermal evaporation can occur. The red-blue asymmetry of the emission is consistent with the outflow; however the velocities are significantly lower. The H_2CO 3_(22)-2_(21)/3_(03)-2_(02) flux ratio derived from the interferometer data is significantly higher than that found from single-dish observations for both objects, suggesting that the compact emission arises from warmer gas. Detailed radiative transfer modeling shows, however, that the ratio is affected by abundance gradients and optical depth in the 3_(03)-2_(02) line. It is concluded that a constant H_2CO abundance throughout the envelope cannot fit the interferometer data of the two H_2CO lines simultaneously on the longest and shortest baselines. A scenario in which the H_2CO abundance drops in the cold dense part of the envelope where CO is frozen out but is undepleted in the outermost region provides good fits to the single-dish and interferometer data on short baselines for both sources. Emission on the longer baselines is best reproduced if the H_2CO abundance is increased by about an order of magnitude from ~ 10^(-10) to ~ 10^(-9) in the inner parts of the envelope due to thermal evaporation when the temperature exceeds ~50 K. The presence of additional H_2CO abundance jumps in the innermost hot core region or in the disk cannot be firmly established, however, with the present sensitivity and resolution. Other scenarios, including weak outflow-envelope interactions and photon heating of the envelope, are discussed and predictions for future generation interferometers are presented, illustrating their potential in distinguishing these competing scenarios
Classifying the embedded young stellar population in Perseus and Taurus & the LOMASS database
Context. The classification of young stellar objects (YSOs) is typically done
using the infrared spectral slope or bolometric temperature, but either can
result in contamination of samples. More accurate methods to determine the
evolutionary stage of YSOs will improve the reliability of statistics for the
embedded YSO population and provide more robust stage lifetimes. Aims. We aim
to separate the truly embedded YSOs from more evolved sources. Methods. Maps of
HCO+ J=4-3 and C18O J=3-2 were observed with HARP on the James Clerk Maxwell
Telescope (JCMT) for a sample of 56 candidate YSOs in Perseus and Taurus in
order to characterize emission from high (column) density gas. These are
supplemented with archival dust continuum maps observed with SCUBA on the JCMT
and Herschel PACS to compare the morphology of the gas and dust in the
protostellar envelopes. The spatial concentration of HCO+ J=4-3 and 850 micron
dust emission are used to classify the embedded nature of YSOs. Results.
Approximately 30% of Class 0+I sources in Perseus and Taurus are not Stage I,
but are likely to be more evolved Stage II pre-main sequence (PMS) stars with
disks. An additional 16% are confused sources with an uncertain evolutionary
stage. Conclusions. Separating classifications by cloud reveals that a high
percentage of the Class 0+I sources in the Perseus star forming region are
truly embedded Stage I sources (71%), while the Taurus cloud hosts a majority
of evolved PMS stars with disks (68%). The concentration factor method is
useful to correct misidentified embedded YSOs, yielding higher accuracy for YSO
population statistics and Stage timescales. Current estimates (0.54 Myr) may
overpredict the Stage I lifetime on the order of 30%, resulting in timescales
of 0.38 Myr for the embedded phase.Comment: 33 pages, 21 figures, 6 tables, Accepted to be published in A&
A deeply embedded young protoplanetary disk around L1489 IRS observed by the submillimeter array
Circumstellar disks are expected to form early in the process that leads to
the formation of a young star, during the collapse of the dense molecular cloud
core. It is currently not well understood at what stage of the collapse the
disk is formed or how it subsequently evolves. We aim to identify whether an
embedded Keplerian protoplanetary disk resides in the L1489 IRS system. Given
the amount of envelope material still present, such a disk would respresent a
very young example of a protoplanetary disk. Using the Submillimeter Array
(SMA) we have observed the HCO 3--2 line with a resolution of about
1. At this resolution a protoplanetary disk with a radius of a few hundred
AUs should be detectable, if present. Radiative transfer tools are used to
model the emission from both continuum and line data. We find that these data
are consistent with theoretical models of a collapsing envelope and Keplerian
circumstellar disk. Models reproducing both the SED and the interferometric
continuum observations reveal that the disk is inclined by 40 which is
significantly different to the surrounding envelope (74). This
misalignment of the angular momentum axes may be caused by a gradient within
the angular momentum in the parental cloud or if L1489 IRS is a binary system
rather than just a single star. In the latter case, future observations looking
for variability at sub-arcsecond scales may be able to constrain these
dynamical variations directly. However, if stars form from turbulent cores, the
accreting material will not have a constant angular momentum axis (although the
average is well defined and conserved) in which case it is more likely to have
a misalignment of the angular momentum axes of the disk and the envelope.Comment: 11 pages, 13 figures, accepted by A&
On C*-algebras generated by pairs of q-commuting isometries
We consider the C*-algebras O_2^q and A_2^q generated, respectively, by
isometries s_1, s_2 satisfying the relation s_1^* s_2 = q s_2 s_1^* with |q| <
1 (the deformed Cuntz relation), and by isometries s_1, s_2 satisfying the
relation s_2 s_1 = q s_1 s_2 with |q| = 1. We show that O_2^q is isomorphic to
the Cuntz-Toeplitz C*-algebra O_2^0 for any |q| < 1. We further prove that
A_2^{q_1} is isomorphic to A_2^{q_2} if and only if either q_1 = q_2 or q_1 =
complex conjugate of q_2. In the second part of our paper, we discuss the
complexity of the representation theory of A_2^q. We show that A_2^q is *-wild
for any q in the circle |q| = 1, and hence that A_2^q is not nuclear for any q
in the circle.Comment: 18 pages, LaTeX2e "article" document class; submitted. V2 clarifies
the relationships between the various deformation systems treate
Absolute dimensions of solar-type eclipsing binaries. EF Aquarii: a G0 test for stellar evolution models
Recent studies have shown that stellar chromospheric activity, and its effect
on convective energy transport in the envelope, is most likely the cause of
significant radius and temperature discrepancies between theoretical evolution
models and observations. We aim to determine absolute dimensions and abundances
for the solar-type detached eclipsing binary EF Aqr, and to perform a detailed
comparison with results from recent stellar evolutionary models. uvby-beta
standard photometry was obtained with the Stromgren Automatic Telescope. The
broadening function formalism was applied on spectra observed with HERMES at
the Mercator telescope in La Palma, to obtain radial velocity curves. Masses
and radii with a precision of 0.6% and 1.0% respectively have been established
for both components of EF Aqr. The active 0.956 M_sol secondary shows star
spots and strong Ca II H and K emission lines. The 1.224 M_sol primary shows
signs of activity as well, but at a lower level. An [Fe/H] abundance of
0.00+-0.10 is derived with similar abundances for Si, Ca, Sc, Ti, V, Cr, Co,
and Ni. Solar calibrated evolutionary models such as Yonsei-Yale,
Victoria-Regina and BaSTI isochrones and evolutionary tracks are unable to
reproduce EF Aqr, especially for the secondary, which is 9% larger and 400 K
cooler than predicted. Models adopting significantly lower mixing length
parameters l/H_p remove these discrepancies, as seen in other solar type
binaries. For the observed metallicity, Granada models with a mixing length of
l/H_p=1.30 (primary) and 1.05 (secondary) reproduce both components at a common
age of 1.5+-0.6 Gyr. Observations of EF Aqr suggests that magnetic activity,
and its effect on envelope convection, is likely to be the cause of
discrepancies in both radius and temperature, which can be removed by adjusting
the mixing length parameter of the models downwards.Comment: 11 pages, 8 figures, accepted for publication by A&
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