4,342 research outputs found
Improved immunological detection of S pongospora subterranea
The genus Spongospora has two members which are important pathogens of vegetables, S. subterranea f.sp. subterranea (Sss) and S. subterranea f.sp. nasturtii (Ssn). The close taxonomic relationship of these formae speciales is based on similar cystosori morphology. The potato disease powdery scab, caused by Sss, is difficult to control. The key control measure is avoidance, aimed at planting clean seed in clean soil. For the development of routine tests for the presence of the pathogen on tubers and in soil, a monoclonal antibody (MAb) was developed using Sss cystosori as immunogen. It detected less than one Sss cystosorus and recognised Sss material from many parts of the world. No cross-reactions with other Plasmodiophoromycetes including Plasmodiophora brassicae, Polymyxa betae, Polymyxa graminis and different Streptomyces species causing common and netted scab of potatoes were observed. A novel tuber sample test method was developed using a kitchen peeling machine. This detected two tubers with one powdery scab lesion each in a sample including eighteen uninfected tubers. When soil samples spiked with cystosori were tested with the MAb, different Sss infestation levels could be discriminated. Ssn cystosori gave absorbance values in ELISA as high as Sss cystosori, whereas fresh crook roots of watercress containing Ssnzoosporangia and plasmodia or mud from an Ssninfected watercress bed gave low absorbance values or no reaction. The potential of these findings for the development of a disease control management are discusse
NT1-Tau Is Increased in CSF and Plasma of CJD Patients, and Correlates with Disease Progression
This study investigates the diagnostic and prognostic potential of different forms of tau in biofluids from patients with Creutzfeldt-Jakob disease (CJD). Extracellular tau, which is molecularly heterogeneous, was measured using ultra-sensitive custom-made Simoa assays for N-terminal (NT1), mid-region, and full-length tau. We assessed cross-sectional CSF and plasma from healthy controls, patients with Alzheimer’s disease (AD) and CJD patients. Then, we evaluated the correlation of the best-performing tau assay (NT1-tau) with clinical severity and functional decline (using the MRC Prion Disease Rating Scale) in a longitudinal CJD cohort (n = 145). In a cross-sectional study, tau measured in CSF with the NT1 and mid-region Simoa assays, separated CJD (n = 15) from AD (n = 18) and controls (n = 21) with a diagnostic accuracy (AUCs: 0.98–1.00) comparable to or better than neurofilament light chain (NfL; AUCs: 0.96–0.99). In plasma, NT1-measured tau was elevated in CJD (n = 5) versus AD (n = 15) and controls (n = 15). Moreover, in CJD plasma (n = 145) NT1-tau levels correlated with stage and rate of disease progression, and the effect on clinical progression was modified by the PRNP codon 129. Our findings suggest that plasma NT1-tau shows promise as a minimally invasive diagnostic and prognostic biomarker of CJD, and should be further investigated for its potential to monitor disease progression and response to therapies
The biogeographical history of the interaction between mycoheterotrophic Thismia (Thismiaceae) plants and mycorrhizal Rhizophagus (Glomeraceae) fungi
Aim Achlorophyllous mycoheterotrophic plants and mycorrhizal fungi often have highly specific interactions that potentially limit the plants’ distribution and diversification potential. However, specificity in biotic interactions may differ considerably over a species’ distribution range and therefore interactions need to be studied over their entire range to assess their evolution in space and time. The present study investigates the biogeographical history of the interaction between five closely related mycoheterotrophic Thismia species and arbuscular mycorrhizal fungi over the distribution range of the plant species. Location Temperate south-east Australia and New Zealand. Methods Phylogenetic relationships of Thismia (nrITS and mtcob) and their arbuscular mycorrhizal fungi (partial nrSSU) were reconstructed based on data from 65 plant specimens. The diversification times in Thismia were estimated with a Bayesian relaxed clock approach using a Dioscoreales framework (nrSSU, mtatp1, mtmatR, mtnad1 b-c). Ancestral geographical ranges were reconstructed using a maximum likelihood approach. The same approach was used to reconstruct ancestral mycorrhizal associations. Results Our analysis shows that Thismia plants have highly specific, phylogenetically conserved and evolutionarily persistent interactions with Rhizophagus fungi. Nevertheless, Thismia was able to diversify and radiate recently due to the wide geographical distribution of the host fungi. In addition, we find that although the mycorrhizal interactions of this clade of mycoheterotrophs are strictly bound to a fungal lineage, host switches remain possible. Main conclusions In this clade of closely related mycoheterotrophs, dependency on highly specific fungal interactions is the result of phylogenetic niche conservatism, acting over at least 12 million years. Nevertheless, plants that are dependent on highly specific fungal interactions have ample opportunities to disperse and radiate over the geographical range of their hosts. Our study highlights the need to link the ecology and evolution of species interactions over broad geographical and evolutionary scales for understanding mycorrhizal interactions
High-mass star formation at high luminosities: W31 at >10^6 L_sun
Context: High-mass star formation has been a very active field over the last
decade, however, most studies targeted regions of luminosities between 10^4 and
10^5 L_sun. Methods: We selected the W31 star-forming complex with a total
luminosity of ~6x10^6 L_sun for a multi-wavelength spectral line and continuum
study covering wavelengths from the near- and mid-infrared via (sub)mm
wavelength observations to radio data in the cm regime. Results: While the
overall structure of the multi-wavelength continuum data resembles each other
well, there are several intriguing differences. The 24mum emission stemming
largely from small dust grains follows tightly the spatial structure of the cm
emission tracing the ionized free-free emission. Hence warm dust resides in
regions that are spatially associated with the ionized hot gas (~10^4 K) of the
HII regions. Furthermore, we find several evolutionary stages within the same
complexes, ranging from infrared-observable clusters, via deeply embedded
regions associated with active star formation traced by 24\,m and cm
emission, to at least one high-mass gas clump devoid of any such signature. The
13CO(2-1) and C18O(2-1) spectral line observations reveal a large kinematic
breadth in the entire region with a total velocity range of approximately 90
km/s. While the average virial mass ratio for W31 is close to unity, the line
width analysis indicates large-scale evolutionary differences between the
southern and northern sub-regions (G10.2-0.3 and G10.3-0.1) of the whole W31
complex. The clump mass function - tracing cluster scales and not scales of
individual stars - derived from the 875mum continuum data has a slope of
1.5+-0.3, consistent with previous cloud mass functions.Comment: 13 pages, 11 figures, accepted for Astronomy and Astrophysics,
high-resolution version of paper at
http://www.mpia.de/homes/beuther/papers.htm
Observation of isotonic symmetry for enhanced quadrupole collectivity in neutron-rich 62,64,66Fe isotopes at N=40
The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied
using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb
excitation reactions. The deduced E2 strengths illustrate the enhanced
collectivity of the neutron-rich Fe isotopes up to N=40. The results are
interpreted by the generalized concept of valence proton symmetry which
describes the evolution of nuclear structure around N=40 as governed by the
number of valence protons with respect to Z~30. The deformation suggested by
the experimental data is reproduced by state-of-the-art shell calculations with
a new effective interaction developed for the fpgd valence space.Comment: 4 pages, 2 figure
The hot core-ultracompact HII connection in G10.47+0.03
We present infrared imaging and spectroscopic data of the complex massive
star-forming region G10.47+0.03. The detection of seven mid-infrared (MIR)
sources in our field combined with a sensitive Ks/ISAAC image allows to
establish a very accurate astrometry, at the level of 0.3". Two MIR sources are
found to be coincident with two ultracompact HII regions (UCHIIs) within our
astrometric accuracy. Another MIR source lies very close to three other UCHII
regions and to the hot molecular core (HMC) in G10.47+0.03. Spectroscopy of two
of the most interesting MIR sources allows to identify the location and
spectral type of the ionizing sources. We discuss in detail the relationship
between the HMC, the UCHII regions and the nearby MIR source. The nature of the
other MIR sources is also investigated.Comment: 12 pages, 5 figures, Accepted by Astronomy and Astrophysic
Adaptive Lévy processes and area-restricted search in human foraging
A considerable amount of research has claimed that animals’ foraging behaviors display movement lengths with power-law distributed tails, characteristic of Lévy flights and Lévy walks. Though these claims have recently come into question, the proposal that many animals forage using Lévy processes nonetheless remains. A Lévy process does not consider when or where resources are encountered, and samples movement lengths independently of past experience. However, Lévy processes too have come into question based on the observation that in patchy resource environments resource-sensitive foraging strategies, like area-restricted search, perform better than Lévy flights yet can still generate heavy-tailed distributions of movement lengths. To investigate these questions further, we tracked humans as they searched for hidden resources in an open-field virtual environment, with either patchy or dispersed resource distributions. Supporting previous research, for both conditions logarithmic binning methods were consistent with Lévy flights and rank-frequency methods–comparing alternative distributions using maximum likelihood methods–showed the strongest support for bounded power-law distributions (truncated Lévy flights). However, goodness-of-fit tests found that even bounded power-law distributions only accurately characterized movement behavior for 4 (out of 32) participants. Moreover, paths in the patchy environment (but not the dispersed environment) showed a transition to intensive search following resource encounters, characteristic of area-restricted search. Transferring paths between environments revealed that paths generated in the patchy environment were adapted to that environment. Our results suggest that though power-law distributions do not accurately reflect human search, Lévy processes may still describe movement in dispersed environments, but not in patchy environments–where search was area-restricted. Furthermore, our results indicate that search strategies cannot be inferred without knowing how organisms respond to resources–as both patched and dispersed conditions led to similar Lévy-like movement distributions
Tracing the evolutionary stage of Bok globules: CCS and NH3
We pursue the investigation of a previously proposed correlation between
chemical properties and physical evolutionary stage of isolated low-mass
star-forming regions. In the past, the NH3/CCS abundance ratio was suggested to
be a potentially useful indicator for the evolutionary stage of cloud cores. We
aim to study its applicability for isolated Bok globules. A sample of 42 Bok
globules with and without signs of current star formation was searched for
CCS(2-1) emission, the observations were complemented with NH3 measurements
available in the literature and own observations. The abundance ratio of both
molecules is discussed with respect to the evolutionary stage of the objects
and in the context of chemical models. The NH3/CCS ratio could be assessed for
18 Bok globules and is found to be moderately high and roughly similar across
all evolutionary stages from starless and prestellar cores towards internally
heated cores harbouring protostars of Class 0, Class I or later. Bok globules
with extremely high CCS abundance analogous to carbon-chain producing regions
in dark cloud cores are not found. The observed range of NH3/CCS hints towards
a relatively evolved chemical state of all observed Bok globules.Comment: 12 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
On the Identification of High Mass Star Forming Regions using IRAS: Contamination by Low-Mass Protostars
We present the results of a survey of a small sample (14) of low-mass
protostars (L_IR < 10^3 Lsun) for 6.7 GHz methanol maser emission performed
using the ATNF Parkes radio telescope. No new masers were discovered. We find
that the lower luminosity limit for maser emission is near 10^3 Lsun, by
comparison of the sources in our sample with previously detected methanol maser
sources. We examine the IRAS properties of our sample and compare them with
sources previously observed for methanol maser emission, almost all of which
satisfy the Wood & Churchwell criterion for selecting candidate UCHII regions.
We find that about half of our sample satisfy this criterion, and in addition
almost all of this subgroup have integrated fluxes between 25 and 60 microns
that are similar to sources with detectable methanol maser emission. By
identifying a number of low-mass protostars in this work and from the
literature that satisfy the Wood & Churchwell criterion for candidate UCHII
regions, we show conclusively for the first time that the fainter flux end of
their sample is contaminated by lower-mass non-ionizing sources, confirming the
suggestion by van der Walt and Ramesh & Sridharan.Comment: 8 pages with 2 figures. Accepted by Ap
An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277
All massive galaxies likely have supermassive black holes at their centers,
and the masses of the black holes are known to correlate with properties of the
host galaxy bulge component. Several explanations have been proposed for the
existence of these locally-established empirical relationships; they include
the non-causal, statistical process of galaxy-galaxy merging, direct feedback
between the black hole and its host galaxy, or galaxy-galaxy merging and the
subsequent violent relaxation and dissipation. The empirical scaling relations
are thus important for distinguishing between various theoretical models of
galaxy evolution, and they further form the basis for all black hole mass
measurements at large distances. In particular, observations have shown that
the mass of the black hole is typically 0.1% of the stellar bulge mass of the
galaxy. The small galaxy NGC4486B currently has the largest published fraction
of its mass in a black hole at 11%. Here we report observations of the stellar
kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x
10^11 Msun. From the data, we determine that the mass of the central black hole
is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have
properties similar to NGC 1277 and therefore may also contain over-sized black
holes. It is not yet known if these galaxies represent a tail of a
distribution, or if disk-dominated galaxies fail to follow the normal black
hole mass scaling relations.Comment: 7 pages. 6 figures. Nature. Animation at
http://www.mpia.de/~bosch/blackholes.htm
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