1,252 research outputs found
Dielectric constant of glasses: first observation of a two-dimensional behavior
The 1kHz real part of the dielectric constant of a structural glass
was measured at low temperature down to 14 mK. Reducing the sample
thickness to 10 nm suppresses the usual minimum of for measuring
fields MV/m. This contradicts the Two Level System (TLS) model but is
well accounted for by including TLS-TLS interactions where excitations
delocalize between TLS's through a -induced mechanism recently designed: for
small 's this interaction is reduced, which explains the two-dimensional
behavior of . Hence, interactions play a key role in standard thick
samples.Comment: latex finesse3.tex, 5 files, 4 figures, 4 pages [SPEC-S02/050],
submitted to Phys. Rev. Let
Developement of real time diagnostics and feedback algorithms for JET in view of the next step
Real time control of many plasma parameters will be an essential aspect in
the development of reliable high performance operation of Next Step Tokamaks.
The main prerequisites for any feedback scheme are the precise real-time
determination of the quantities to be controlled, requiring top quality and
highly reliable diagnostics, and the availability of robust control algorithms.
A new set of real time diagnostics was recently implemented on JET to prove the
feasibility of determining, with high accuracy and time resolution, the most
important plasma quantities. With regard to feedback algorithms, new
model–based controllers were developed to allow a more robust control of
several plasma parameters. Both diagnostics and algorithms were successfully
used in several experiments, ranging from H-mode plasmas to configuration with
ITBs. Since elaboration of computationally heavy measurements is often
required, significant attention was devoted to non-algorithmic methods like
Digital or Cellular Neural/Nonlinear Networks. The real time hardware and
software adopted architectures are also described with particular attention to
their relevance to ITER.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
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Engineering transkingdom signalling in plants to control gene expression in rhizosphere bacteria
Abstract: The root microbiota is critical for agricultural yield, with growth-promoting bacteria able to solubilise phosphate, produce plant growth hormones, antagonise pathogens and fix N2. Plants control the microorganisms in their immediate environment and this is at least in part through direct selection, the immune system, and interactions with other microorganisms. Considering the importance of the root microbiota for crop yields it is attractive to artificially regulate this environment to optimise agricultural productivity. Towards this aim we express a synthetic pathway for the production of the rhizopine scyllo-inosamine in plants. We demonstrate the production of this bacterial derived signal in both Medicago truncatula and barley and show its perception by rhizosphere bacteria, containing bioluminescent and fluorescent biosensors. This study lays the groundwork for synthetic signalling networks between plants and bacteria, allowing the targeted regulation of bacterial gene expression in the rhizosphere for delivery of useful functions to plants
Non-linear temperature oscillations in the plasma centre on Tore Supra and their interplay with MHD
Regular oscillations of the central electron temperature have been observed
by means of ECE and SXR diagnostics during non-inductively driven discharges on
Tore Supra. These oscillations are sustained by LHCD, do not have a helical
structure and, therefore, cannot be ascribed as MHD phenomena. The most
probable explanation of this oscillating regime (O-regime) is the assumption
that the plasma current density (and, thus, the q-profile) and the electron
temperature evolve as a non-linearly coupled predator-pray system. The
integrated modelling code CRONOS has been used to demonstrate that the coupled
heat transport and resistive diffusion equations admit solutions for the
electron temperature and the current density which have a cyclic behaviour.
Recent experimental results in which the O-regime co-exists with MHD modes will
be presented. Because both phenomena are linked to details of the q-profile,
some interplay between MHD and oscillations may occur. The localisation of
magnetic islands allows to obtain an accurate picture of the q-profile in the
plasma core. In some case, MHD-driven reconnection helps in maintaining a
weakly inverted q-profile that is found to be, in the CRONOS simulations, a
necessary condition to trigger the oscillations.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
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