4,237 research outputs found
Phenalenone-type phytoalexins mediate resistance of banana plants (Musa spp.) to the burrowing nematode Radopholus similis
The global yield of bananas, one of the most important food crops is severely hampered by parasites, such as nematodes, which cause yield losses up to 75%. Plant nematode interactions of two banana cultivars differing in susceptibility to Radopholus similis were investigated by combining the conventional and spatially resolved analytical techniques 1H NMR spectroscopy, matrix-free UV-laser desorption/ionization mass spectrometric imaging, and Raman microspectroscopy. This innovative combination of analytical techniques was applied to isolate, identify, and locate the banana-specific type of phytoalexins, phenylphenalenones, in the R. similis-caused lesions of the plants. The striking antinematode activity of the phenylphenalenone anigorufone, its ingestion by the nematode, and its subsequent localization in lipid droplets within the nematode is reported. The importance of varying local concentrations of these specialized metabolites in infected plant tissues, their involvement in the plant's defense system, and derived strategies for improving banana resistance are highlighted
Comment on `Experimental and Theoretical Constraints of Bipolaronic Superconductivity in High Materials: An Impossibility'
We show that objections raised by Chakraverty (Phys. Rev. Lett. 81,
433 (1998)) to the bipolaron model of superconducting cuprates are the result
of an incorrect approximation for the bipolaron energy spectrum and misuse of
the bipolaron theory. The consideration, which takes into account the multiband
energy structure of bipolarons and the unscreened electron-phonon interaction
clearly indicates that cuprates are in the Bose-Einstein condensation regime
with mobile charged bosons.Comment: 1 page, no figure
Boson-fermion model beyond mean-field approximation
A model of hybridized bosons and fermions is studied beyond the mean field
approximation. The divergent boson self-energy at zero temperature makes the
Cooper pairing of fermions impossible.The frequency and momentum dependence of
the self- energy and the condensation temperature of initially
localized bosons are calculated analytically. The value of the boson
condensation temperature is below which rules out the
boson-fermion model with the initially localized bosons as a phenomenological
explanation of high-temperature superconductivity. The intra-cell
density-density fermion-boson interaction dominates in the fermion self-energy.
The model represents a normal metal with strongly damped bosonic excitations.
The latter play the role of normal impurities.Comment: 16 pages, Latex, 5 figures available upon reques
An infinitesimally nonrigid polyhedron with nonstationary volume in the Lobachevsky 3-space
We give an example of an infinitesimally nonrigid polyhedron in the
Lobachevsky 3-space and construct an infinitesimal flex of that polyhedron such
that the volume of the polyhedron isn't stationary under the flex.Comment: 10 pages, 2 Postscript figure
Hall effect and resistivity in underdoped cuprates
The behaviour of the Hall ratio as a function of temperature is
one of the most intriguing normal state properties of cuprate superconductors.
One feature of all the data is a maximum of in the normal state that
broadens and shifts to temperatures well above with decreasing doping. We
show that a model of preformed pairs-bipolarons provides a selfconsistent
quantitative description of together with in-plane resistivity and
uniform magnetic susceptibility for a wide range of doping.Comment: 4 pages, 2 figures, the model and fits were refine
S-duality in Twistor Space
In type IIB string compactifications on a Calabi-Yau threefold, the
hypermultiplet moduli space must carry an isometric action of the modular
group SL(2,Z), inherited from the S-duality symmetry of type IIB string theory
in ten dimensions. We investigate how this modular symmetry is realized at the
level of the twistor space of , and construct a general class of
SL(2,Z)-invariant quaternion-Kahler metrics with two commuting isometries,
parametrized by a suitably covariant family of holomorphic transition
functions. This family should include corrected by D3-D1-D(-1)-instantons
(with fivebrane corrections ignored) and, after taking a suitable rigid limit,
the Coulomb branch of five-dimensional N=2 gauge theories compactified on a
torus, including monopole string instantons. These results allow us to
considerably simplify the derivation of the mirror map between type IIA and IIB
fields in the sector where only D1-D(-1)-instantons are retained.Comment: 29 pages, 1 figur
Semi-classical theory of magnetic quantum oscillations in a two-dimensional multiband canonical Fermi liquid
The semi-classical Lifshitz-Kosevich (LK) description of quantum oscillations
is extended to a multiband two-dimensional Fermi liquid with a constant number
of electrons. The amplitudes of novel oscillations with combination
frequencies, recently predicted and observed experimentally, are analytically
derived and compared with the single-band amplitudes. The combination
amplitudes decay with temperature exponentially faster than the standard
harmonics, and this provides a valuable tool for their experimental
identification.Comment: 3 pages, REVTeX 3.0, one eps-figure included in the tex
Key pairing interaction in layered doped ionic insulators
A controversial issue on whether the electron-phonon interaction (EPI) is
crucial for high-temperature superconductivity or it is weak and inessential
has remained one of the most challenging problems of contemporary condensed
matter physics. We employ a continuum RPA approximation for the dielectric
response function allowing for a selfconsistent semi-analytical evaluation of
the EPI strength, electron-electron attractions, and the carrier mass
renormalisation in layered high-temperature superconductors. We show that the
Fr\"{o}hlich EPI with high-frequency optical phonons in doped ionic lattices is
the key pairing interaction, which is beyond the BCS-Migdal-Eliashberg
approximation in underdoped superconductors, and it remains a significant
player in overdoped compounds.Comment: 4 pages, 4 figure
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