639 research outputs found
Searching new targets for the control of Black Rot: following the role of host factors modulating the infection process of Phyllosticta ampelicida
Black Rot is a grapevine disease caused by the ascomycete Phyllosticta ampelicida. Neglected so far, this is developing into a pertinent problem in organic viticulture as resistant varieties are still lacking. Here, we follow cellular details of the infection process in the susceptible vinifera variety MĂŒller-Thurgau and screen the ancestral European wild grapevine (V. vinifera sylvestris) for resistance to Black Rot.
Using a standardized infection assay, we follow fungal development using LTSEM and quantify key stages on different hosts using fluorescence microscopy.
There is considerable variation in susceptibility, which is associated with more rapid leaf maturation. Hyphal growth on different carbon sources shows a preference for pectins over starch, cellulose or xylans. In the resistant sylvestris genotypes Ketsch 16 and Ketsch 18 we find that neither spore attachment nor appressorium formation, but hyphal elongation is significantly inhibited as compared to MĂŒller-Thurgau. Moreover, defence-related oxidative burst and accumulation of phenolic compounds is stimulated in the resistant genotypes.
We arrive at a model, where more rapid maturation of the cell wall in these sylvestris genotypes sequesters pectins as major food source and thus block hyphal elongation. This paves the way for introgression of genetic factors responsible for cell wall maturation into V. vinifera to develop Black Rot-resistant varieties of grapevine
Attosecond sampling of arbitrary optical waveforms
Advances in the generation of ultrashort laser pulses, and the emergence of new research areas such as attosecond science, nanoplasmonics, coherent control, and multidimensional spectroscopy, have led to the need for a new class of ultrafast metrology that can measure the electric field of complex optical waveforms spanning the ultraviolet to the infrared. Important examples of such waveforms are those produced by spectral control of ultrabroad bandwidth pulses, or by Fourier synthesis. These are typically tailored for specific purposes, such as to increase the photon energy and flux of high-harmonic radiation, or to control dynamical processes by steering electron dynamics on subcycle time scales. These applications demand a knowledge of the full temporal evolution of the field. Conventional pulse measurement techniques that provide estimates of the relative temporal or spectral phase are unsuited to measure such waveforms. Here we experimentally demonstrate a new, all-optical method for directly measuring the electric field of arbitrary ultrafast optical waveforms. Our method is based on high-harmonic generation (HHG) driven by a field that is the collinear superposition of the waveform to be measured with a stronger probe laser pulse. As the delay between the pulses is varied, we show that the field of the unknown waveform is mapped to energy shifts in the high-harmonic spectrum, allowing a direct, accurate, and rapid retrieval of the electric field with subcycle temporal resolution at the location of the HHG
Environmental Health Indicators: A review of initiatives worldwide
Purpose
â The extent to which research into the design and development of environmental health indicators (EHIs) has translated into operational programmes is unclear. The purpose of this paper is to identify EHI initiatives worldwide, distil the EHIs and draw lessons from the experience.
Design/methodology/approach
â A systematic internet-based review was undertaken. Programmes were selected for inclusion if they: first, had the ability to monitor both the physical environment and associated health outcomes; and second, the parent agency had the ability to influence policies related to the environment and health.
Findings
â The small number of eligible programmes indicates EHI initiatives are not yet well established, especially in developing countries. The use of indicators was also limited by uncertainties in the exposure-response relationships that they implied, and the consequent inability to translate the indicators into a common measure of health impact. In addition, there is no information on the extent to which the indicators have been applied in decision making, nor on the policy implications of using indicators.
Practical implications
â More effort is needed to encourage the development and use of more balanced and informative sets of indicators, and to evaluate their use and outcomes in terms of health benefits.
Originality/value
â The time is right for a substantial review paper on EHIs as they are now being used by a number of organisations and to the knowledge this is the first review of operational EHI programmes worldwide
Optimisation of Quantum Trajectories Driven by Strong-field Waveforms
Quasi-free field-driven electron trajectories are a key element of
strong-field dynamics. Upon recollision with the parent ion, the energy
transferred from the field to the electron may be released as attosecond
duration XUV emission in the process of high harmonic generation (HHG). The
conventional sinusoidal driver fields set limitations on the maximum value of
this energy transfer, and it has been predicted that this limit can be
significantly exceeded by an appropriately ramped-up cycleshape. Here, we
present an experimental realization of such cycle-shaped waveforms and
demonstrate control of the HHG process on the single-atom quantum level via
attosecond steering of the electron trajectories. With our optimized optical
cycles, we boost the field-ionization launching the electron trajectories,
increase the subsequent field-to-electron energy transfer, and reduce the
trajectory duration. We demonstrate, in realistic experimental conditions, two
orders of magnitude enhancement of the generated XUV flux together with an
increased spectral cutoff. This application, which is only one example of what
can be achieved with cycle-shaped high-field light-waves, has farreaching
implications for attosecond spectroscopy and molecular self-probing
Thymic Dendritic Cell Subsets Display Distinct Efficiencies and Mechanisms of Intercellular MHC Transfer
Thymic dendritic cells (DC) delete self-Ag-specific thymocytes, and drive development of FoxP3-expressing immunoregulatory T cells. Unlike medullary thymic epithelial cells (mTEC), which express and present peripheral self-Ag, DC must acquire self-Ag to mediate thymic negative selection. One such mechanism entails the transfer of surface MHC-self peptide complexes from mTEC to thymic DC. Despite the importance of thymic DC âcross-dressingâ in negative selection, the factors that regulate the process, and the capacity of different thymic DC subsets to acquire MHC and stimulate thymocytes are poorly understood. Here intercellular MHC transfer by thymic DC subsets was studied using a MHC-mismatch-based in vitro system. Thymic conventional DC (cDC) subsets SIRPα+ and CD8α+ readily acquired MHC class I and II from TEC but plasmacytoid DC (pDC) were less efficient. Intercellular MHC transfer was donor cell-specific; thymic DC readily acquired MHC from TEC plus thymic or splenic DC, whereas thymic or splenic B cells were poor donors. Furthermore DC origin influenced cross-dressing; thymic versus splenic DC exhibited an increased capacity to capture TEC-derived MHC, which correlated with direct expression of EpCAM by DC. Despite similar capacities to acquire MHC-peptide complexes, thymic CD8α+ cDC elicited increased T cell stimulation relative to SIRPα+ cDC. DC cross-dressing was cell-contact dependent and unaffected by lipid raft disruption of donor TEC. Furthermore, blocking PI3K signaling reduced MHC acquisition by thymic CD8α+ cDC and pDC but not SIRPα+ cDC. These findings demonstrate that multiple parameters influence the efficiency of and distinct mechanisms drive intercellular MHC transfer by thymic DC subsets
Powdery mildew responsive genes of resistant grapevine cultivar 'Regent'
The ascomycete Erysiphe necator causes powdery mildew disease of grapevine, a disastrous infection which is commonly defeated with multiple fungicide applications in viticulture. Breeding for natural resistance of quality grapes (Vitis vinifera) is thus a major aim of current efforts. The cultivar 'Regent' is resistant to powdery mildew due to an introgression from an American Vitis sp. resistance donor. To identify key regulatory elements in defense responses of 'Regent' we performed transcript analyses after challenging with E. necator inoculation in comparison with a susceptible grapevine. A set of genes selected from preliminary microarray hybridization results were investigated by RT-qPCR. The data indicate an important role of transcription factors MYB15, WRKY75, WRKY33, WRKY7, ethylene responsive transcription factors ERF2 and ERF5 as well as a CZF1/ZFAR transcripton factor in regulating the early defense when the fungus starts the interaction with its host by the formation of haustoria
Plasmon signatures in high harmonic generation
High harmonic generation in polarizable multi-electron systems is
investigated in the framework of multi-configuration time-dependent
Hartree-Fock. The harmonic spectra exhibit two cut offs. The first cut off is
in agreement with the well established, single active electron cut off law. The
second cut off presents a signature of multi-electron dynamics. The strong
laser field excites non-linear plasmon oscillations. Electrons that are ionized
from one of the multi-plasmon states and recombine to the ground state gain
additional energy, thereby creating the second plateau.Comment: Major revision, 12 pages, 5 figures, submitted to J. Phys. B (2005),
accepte
Carrier-envelope phase stability of hollow-fibers used for high-energy, few-cycle pulse generation
We investigated the carrier-envelope phase (CEP) stability of a hollow-fiber
setup used for high-energy, few-cycle pulse generation. Saturation of the
output pulse energy is observed at 0.6 mJ for a 260 um inner-diameter, 1 m long
fiber, statically filled with neon, with the pressure adjusted to achieve an
output spectrum capable of supporting sub-4fs pulses. The maximum output pulse
energy can be increased to 0.8mJ by using either differential pumping, or
circularly polarized input pulses. We observe the onset of an
ionization-induced CEP instability, which does not increase beyond an input
pulse energy of 1.25 mJ due to losses in the fiber caused by ionization. There
is no significant difference in the CEP stability with differential pumping
compared to static-fill, demonstrating that gas flow in differentially pumped
fibers does not degrade the CEP stabilization.Comment: 4 pages, 4 figure
Attosecond streaking of photoelectron emission from disordered solids
Attosecond streaking of photoelectrons emitted by extreme ultraviolet light
has begun to reveal how electrons behave during their transport within simple
crystalline solids. Many sample types within nanoplasmonics, thin-film physics,
and semiconductor physics, however, do not have a simple single crystal
structure. The electron dynamics which underpin the optical response of
plasmonic nanostructures and wide-bandgap semiconductors happen on an
attosecond timescale. Measuring these dynamics using attosecond streaking will
enable such systems to be specially tailored for applications in areas such as
ultrafast opto-electronics. We show that streaking can be extended to this very
general type of sample by presenting streaking measurements on an amorphous
film of the wide-bandgap semiconductor tungsten trioxide, and on
polycrystalline gold, a material that forms the basis of many nanoplasmonic
devices. Our measurements reveal the near-field temporal structure at the
sample surface, and photoelectron wavepacket temporal broadening consistent
with a spread of electron transport times to the surface
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