7,073 research outputs found
Strawberry breeding for disease resistance in Dresden
Verticillium resistance is one of the most important breeding goals in strawberry resistance
breeding at Dresden-Pillnitz. Resistance evaluation of cultivars, advanced selections and
seedlings is realized under natural conditions at a provocation field and by artificial
inoculation in the greenhouse. Introgression of Fragaria chiloensis L. (Miller) into Fragaria
×ananassa Duch. resulted in highly tolerant breeding selections. After back-crossing with
cultivars of F. ×ananassa first genotypes were selected which can be evaluated in
experimental cultivar trials at different locations in Germany
Phase separation and competition of superconductivity and magnetism in the two-dimensional Hubbard model: From strong to weak coupling
Cooperation and competition between the antiferromagnetic, d-wave
superconducting and Mott-insulating states are explored for the two-dimensional
Hubbard model including nearest and next-nearest-neighbor hoppings at zero
temperature. Using the variational cluster approach with clusters of different
shapes and sizes up to 10 sites, it is found that the doping-driven transition
from a phase with microscopic coexistence of antiferromagnetism and
superconductivity to a purely superconducting phase is discontinuous for strong
interaction and accompanied by phase separation. At half-filling the system is
in an antiferromagnetic Mott-insulating state with vanishing charge
compressibility. Upon decreasing the interaction strength U below a certain
critical value of roughly U=4 (in units of the nearest-neighbor hopping),
however, the filling-dependent magnetic transition changes its character and
becomes continuous. Phase separation or, more carefully, the tendency towards
the formation of inhomogeneous states disappears. This critical value is in
contrast to previous studies, where a much larger value was obtained. Moreover,
we find that the system at half-filling undergoes the Mott transition from an
insulator to a state with a finite charge compressibility at essentially the
same value. The weakly correlated state at half-filling exhibits
superconductivity microscopically admixed to the antiferromagnetic order. This
scenario suggests a close relation between phase separation and the
Mott-insulator physics.Comment: 7 pages, 8 figures, revised version to be published in Phys. Rev.
Correlated band structure of electron-doped cuprate materials
We present a numerical study of the doping dependence of the spectral
function of the n-type cuprates. Using a variational cluster-perturbation
theory approach based upon the self-energy-functional theory, the spectral
function of the electron-doped two-dimensional Hubbard model is calculated. The
model includes the next-nearest neighbor electronic hopping amplitude and
a fixed on-site interaction at half filling and doping levels ranging
from to . Our results support the fact that a comprehensive
description of the single-particle spectrum of electron-doped cuprates requires
a proper treatment of strong electronic correlations. In contrast to previous
weak-coupling approaches, we obtain a consistent description of the ARPES
experiments without the need to introduce a doping-dependent on-site
interaction .Comment: 7 pages 4 eps figure
The strong Novikov conjecture for low degree cohomology
We show that for each discrete group G, the rational assembly map
K_*(BG) \otimes Q \to K_*(C*_{max} G) \otimes \Q is injective on classes dual
to the subring generated by cohomology classes of degree at most 2 (identifying
rational K-homology and homology via the Chern character). Our result implies
homotopy invariance of higher signatures associated to these cohomology
classes. This consequence was first established by Connes-Gromov-Moscovici and
Mathai.
Our approach is based on the construction of flat twisting bundles out of
sequences of almost flat bundles as first described in our previous work. In
contrast to the argument of Mathai, our approach is independent of (and indeed
gives a new proof of) the result of Hilsum-Skandalis on the homotopy invariance
of the index of the signature operator twisted with bundles of small curvature.Comment: 11 page
Accessing topological superconductivity via a combined STM and renormalization group analysis
The search for topological superconductors has recently become a key issue in
condensed matter physics, because of their possible relevance to provide a
platform for Majorana bound states, non-Abelian statistics, and fault-tolerant
quantum computing. We propose a new scheme which links as directly as possible
the experimental search to a material-based microscopic theory for topological
superconductivity. For this, the analysis of scanning tunneling microscopy,
which typically uses a phenomenological ansatz for the superconductor gap
functions, is elevated to a theory, where a multi-orbital functional
renormalization group analysis allows for an unbiased microscopic determination
of the material-dependent pairing potentials. The combined approach is
highlighted for paradigmatic hexagonal systems, such as doped graphene and
water-intercalated sodium cobaltates, where lattice symmetry and electronic
correlations yield a propensity for a chiral singlet topological superconductor
state. We demonstrate that our microscopic material-oriented procedure is
necessary to uniquely resolve a topological superconductor state.Comment: phenomenological STM predictions and temperature dependence of
conductance as well as references added (28 pages, 8 figures
Breeding of resistant strawberry cultivars for organic fruit production – Diallel crossing strategies and resistance tests for Botrytis cinerea and Xanthomonas fragariae
Organic strawberry production suffers from high yield losses caused by numerous fungal and bacterial diseases. Two of the most important diseases are the grey mould disease caused by Botrytis cinerea Pers. (teleomorph Botryotinia fuckeliana), and the bacterial angular leaf spot disease caused by Xanthomonas fragariae (Kennedy & King). Beside cultivation methods and organic plant protection measures, the development of resistant cultivars seems to be the most promising strategy in order to improve the productivity in organic strawberry cultivation. Therefore, we established resistance tests to determine resistant and susceptible strawberry cultivars and breeding selections. In a first run, 40 different cultivars and selections were tested for their susceptibility towards B. cinerea by artificial inoculation of fruits and leaves and evaluation of the disease symptoms. Plants of 40 cultivars were tested for susceptibility to X. fragariae by artificial inoculation in the greenhouse. In a diallel crossing approach, 12 commonly cultivated strawberry cultivars have been crossed reciprocally and propagated in a field trial. Important characteristics of the progeny such as ripening time, yield, morphological traits and occurrence of diseases have been evaluated for a period of two consecutive years and lead to the determination of general (GCA) and specific (SCA) combining abilities. Together with the results of the resistance tests we identified a set of genotypes that show resistant characteristics towards B. cinerea and might be suitable for use in organic cultivation systems. Furthermore, they can be used for targeted breeding experiments in the future
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