3,519 research outputs found
Friends with benefits, or a reluctant threesome? : arbuscular mycorrhizal partnerships and their effects on crop pathogens
High yield losses of crops due to plant pathogens represent a serious problem in agriculture. More effective and sustainable control measures, such as biological control, are essential. Most terrestrial plants, including important crop plants, benefit from a mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi through enhanced nutrition and improved immune responses. Although this latter phenomenon, known as Mycorrhiza Induced Resistance (MIR), is well-reported and molecular responses to AM symbiosis have been observed, how AM fungi prime disease resistance is still poorly understood. Several factors and mechanisms have been suggested to impact the outcome of MIR, but how this phenomenon occurs and how different factors impact MIR is not known. Evidence suggests that AM fungal species differ in their abilities to defend plants and that plant species, and even varieties, can have differing colonisation levels leading to changing outcomes of MIR. However, the underlying molecular mechanisms on a biochemical level leading to alterations of MIR are not well understood and require examination of patterns related to MIR effects and involved molecular factors in these interactions to exploit the biocontrol potential of AM fungi. To achieve this, my doctoral thesis investigates some of these fundamental MIR knowledge gaps by combining interdisciplinary research including phenotyping observations as well as molecular approaches (transcriptomics and metabolomics). The results of my PhD research provide increased and novel insights into comprehensive phenotypic, transcriptional and biochemical patterns and mechanisms related to mediation of MIR. Investigation of basic plant gene expression patterns revealed the involvement of beneficial and pathogenic microbes in non-defence-related biological processes and shows that MIR is involved in a large number of processes within the transcriptomic profile. This thesis provided further evidence of the importance of AM fungal identity on the outcome of MIR and showed that the differences in metabolic profiles reflect these observations. My thesis also highlights the importance of studying MIR in natural contexts, where plants interact with diverse fungal communities, by showing the non-additive effects of AM fungal communities compared to single species observations. I also show that plant varieties with different potentials for AM fungal colonisation demonstrate opposing MIR metabolomic responses. Moreover, the potential involvement of down-regulated metabolic pathways to protect plants against pathogen addition has been demonstrated. These studies highlight the need for further investigations of the biochemical networks leading to the strength of MIR
Stochastic Gene Expression in a Lentiviral Positive Feedback Loop: HIV-1 Tat Fluctuations Drive Phenotypic Diversity
Stochastic gene expression has been implicated in a variety of cellular
processes, including cell differentiation and disease. In this issue of Cell,
Weinberger et al. (2005) take an integrated computational-experimental approach
to study the Tat transactivation feedback loop in HIV-1 and show that
fluctuations in a key regulator, Tat, can result in a phenotypic bifurcation.
This phenomenon is observed in an isogenic population where individual cells
display two distinct expression states corresponding to latent and productive
infection by HIV-1. These findings demonstrate the importance of stochastic
gene expression in molecular "decision-making."Comment: Supplemental data available as q-bio.MN/060800
A Dusty Disk Around GD 362, a White Dwarf With a Uniquely High Photospheric Metal Abundance
Eighteen years after an infrared excess was discovered associated with the
white dwarf G29-38, we report ground-based measurements (JHKL'N') with
mJy-level sensitivity of GD 362 that show it to be a second single white dwarf
with an infrared excess. As a first approximation, the excess around GD 362,
which amounts to about 3% of the total stellar luminosity, can be explained by
emission from a passive, flat, opaque dust disk that lies within the Roche
radius of the white dwarf. The dust may have been produced by the tidal
disruption of a large parent body such as an asteroid. Accretion from this
circumstellar disk could account for the remarkably high abundance of metals in
the star's photosphere.Comment: 12 pages, 2 figures. ApJ Letters, in pres
Tunable spin transport in CrAs: role of correlation effects
Correlation effects on the electronic structure of half-metallic CrAs in
zinc-blende structure are studied for different substrate lattice constants.
Depending on the substrate the spectral weight of the non-quasiparticle states
might be tuned from a well developed value in the case of InAs substrate to an
almost negligible contribution for the GaAs one. A piezoelectric material that
would allow the change in the substrate lattice parameters opens the
possibility for practical investigations of the switchable (tunable)
non-quasiparticle states. Since the latter are important for the tunneling
magnetoresistance and related phenomena it creates new opportunities in
spintronics.Comment: 12 pages, 3 figures, 2 tables. accepted PRB 71, 1 (2005
Splitting along a submanifold pair
The paper introduces a group of obstructions for splitting a homotopy
equivalence along a pair of submanifolds. We develop exact sequences relating
the -groups with various surgery obstruction groups for manifold triple
and structure sets arising from triples of manifolds. The natural map from the
surgery obstruction group of the ambient manifold to the -group provides
an invariant when elements of the Wall group are not realized by normal maps of
closed manifolds. Some -groups are computed precisely.Comment: K-theory, to appea
HST-STIS Spatially Resolved Spectroscopy and Coronagraphic Imaging of the TW Hydrae Circumstellar Disk
We present the first spatially resolved spectrum of scattered light from the
TW Hydrae protoplanetary disk. This nearly face-on disk is optically thick,
surrounding a classical T Tauri star in the nearby 10 Myr old TW Hya
association. The spectrum was taken with the HST-STIS CCD, providing resolution
R ~ 360 over the wavelength range 5250 - 10300 A. Spatially resolved
spectroscopy of circumstellar disks is difficult due to the high contrast ratio
between the bright star and faint disk. Our novel observations provide optical
spectra of scattered light from the disk between 40 AU and 155 AU from the
star. The scattered light has the same color as the star (gray scattering) at
all radii, except the innermost region. This likely indicates that the
scattering dust grains are larger than about 1 micron all the way out to large
radii. From the spectroscopic data, we also obtained radial profiles of the
integrated disk brightness at two position angles, over almost the same region
as previously observed in HST-WFPC2 and NICMOS coronagraphic images (35 AU to
173 AU from the star). The profiles have the same shape as the earlier ones,
but show a small azimuthal asymmetry in the disk not previously noted. Our STIS
broad-band coronagraphic images of TW Hya confirm the reality of this
asymmetry, and show that the disk surface brightness interior to 140 AU has a
sinusoidal dependence on azimuthal angle. The maximum brightness occurs at a
position angle of 233.6 +/- 5.7 degrees East of North. This might be caused by
the combination of forward-scattering and an increase in inclination in the
inner region of the disk, suggesting that the TW Hya disk has a warp like that
seen in the Beta Pictoris debris disk.Comment: 18 pages, 9 figures (some in color). First version submitted to ApJ
2004-08-29, posted to astro-ph 2004-10-10. Revised version accepted for
publication in ApJ 2004-12-07, posted to astro-ph 2004-12-0
Heterogeneous Face Recognition with CNNs
International audienceHeterogeneous face recognition aims to recognize faces across different sensor modalities. Typically, gallery images are normal visible spectrum images, and probe images are infrared images or sketches. Recently significant improvements in visible spectrum face recognition have been obtained by CNNs learned from very large training datasets. In this paper, we are interested in the question to what extent the features from a CNN pre-trained on visible spectrum face images can be used to perform heterogeneous face recognition. We explore different metric learning strategies to reduce the discrepancies between the different modalities. Experimental results show that we can use CNNs trained on visible spectrum images to obtain results that are on par or improve over the state-of-the-art for heterogeneous recognition with near-infrared images and sketches
Fully relativistic calculation of magnetic properties of Fe, Co and Ni adclusters on Ag(100)
We present first principles calculations of the magnetic moments and magnetic
anisotropy energies of small Fe, Co and Ni clusters on top of a Ag(100) surface
as well as the exchange-coupling energy between two single adatoms of Fe or Co
on Ag(100). The calculations are performed fully relativistically using the
embedding technique within the Korringa-Kohn-Rostoker method. The magnetic
anisotropy and the exchange-coupling energies are calculated by means of the
force theorem. In the case of adatoms and dimers of iron and cobalt we obtain
enhanced spin moments and, especially, unusually large orbital moments, while
for nickel our calculations predict a complete absence of magnetism. For larger
clusters, the magnitudes of the local moments of the atoms in the center of the
cluster are very close to those calculated for the corresponding monolayers.
Similar to the orbital moments, the contributions of the individual atoms to
the magnetic anisotropy energy strongly depend on the position, hence, on the
local environment of a particular atom within a given cluster. We find strong
ferromagnetic coupling between two neighboring Fe or Co atoms and a rapid,
oscillatory decay of the exchange-coupling energy with increasing distance
between these two adatoms.Comment: 8 pages, ReVTeX + 4 figures (Encapsulated Postscript), submitted to
PR
Age-related alterations in default mode network: Impact on working memory performance
The default mode network (DMN) is a set of functionally connected brain regions which shows deactivation (task-induced deactivation, TID) during a cognitive task. Evidence shows an age-related decline in task-load-related modulation of the activity within the DMN during cognitive tasks. However, the effect of age on the functional coupling within the DMN and their relation to cognitive performance has hitherto been unexplored. Using functional magnetic resonance imaging, we investigated functional connectivity within the DMN in older and younger subjects during a working memory task with increasing task load. Older adults showed decreased connectivity and ability to suppress low frequency oscillations of the DMN. Additionally, the strength of the functional coupling of posterior cingulate (pCC) with medial prefrontal cortex (PFC) correlated positively with performance and was lower in older adults. pCC was also negatively coupled with task-related regions, namely the dorsolateral PFC and cingulate regions. Our results show that in addition to changes in canonical task-related brain regions, normal aging is also associated with alterations in the activity and connectivity of brain regions within the DMN. These changes may be a reflection of a deficit in cognitive control associated with advancing age that results in deficient resource allocation to the task at hand
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