Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping

We present an exact diagonalization study of the dynamical spin and density correlation function of the 2D t-J model for hole doping < 25%. Both correlation functions show a remarkably regular, but completely different scaling behaviour with both hole concentration and parameter values: the density correlation function is consistent with that of bosons corresponding to the doped holes and condensed into the lowest state of the noninteracting band of width 8t, the spin correlation function is consistent with Fermions in a band of width J. We show that the spin bag picture gives a natural explanation for this unusual behaviour.Comment: Revtex-file, 4 PRB pages + 5 figures attached as uu-encoded ps-files Hardcopies of figures (or the entire manuscript) can also be obtained by e-mailing to: [email protected]

Marker für die Zulassung von Maispopulationssorten

The genetic resource of adapted German maize landraces is threatened to get lost. Unsolved admission standards at the Federal Office for Plant Varieties are a main obstacle for breeders to use such material. Until now each application for admission has been rejected due to missing homogeneity. Therefore, population specific marker alleles should be developed and deposited at the Federal Office for Plant Varieties as further selection criteria. A first step is the development of markers for phenotypic apparent traits. We developed three markers for red and white cob glume color and used them for selection of two maize populations. The next step would be the development of non-genic markers. Although these markers have no phenotypic effects they also do not influence yield or other physiological important traits

Entwicklung von Populationen bei Mais (Zea mays L.) Selektionseffizienz und Leistungsfähigkeit

Maize is one of the most important crops around the world. Global players in seed production offer more than hundreds of different varieties. All of them are hybrids whereas open pollinated varieties (OPVs) are rare or extinct. In Germany (and many other European countries) no new OPVs are registered; efforts to do so failed in the past. The main advantage of OPVs is their phenotypic and genetic heterogeneity and thus their ability to adapt to different environmental conditions. This could be of utmost interest facing the complex challenge of climate change. Populations based on new breeding material were developed and tested in comparison to actual hybrids and landraces. While the new populations achieved about 80 % of the hybrid yield, landraces failed with only 65 %. The efficiency of selection methods needs to be improved

Watch the target! Effects in the affective misattribution procedure become weaker (but not eliminated) when participants are motivated to provide accurate responses to the target

Previous research showed that priming effects in the affective misattribution procedure (AMP) are unaffected by direct warnings to avoid an influence of the primes. The present research examined whether a priming influence is diminished by task procedures that encourage accurate judgments of the targets. Participants were motivated to categorize the affective meaning of nonsense targets accurately by being made to believe that a true word was presented in each trial and by providing feedback on (allegedly) incorrect responses. This condition produced robust priming effects. Priming was however reduced and less reliable relative to more typical AMP conditions in which participants guessed the meaning of openly presented nonsense targets. Affective judgments of nonsense targets were not affected by advance knowledge of the response mapping during the priming phase, which argues against a response-priming explanation of AMP effects. These findings show that affective primes influence evaluative judgments even in conditions in which the motivation to provide accurate responses is high and a priming of motor responses is not possible. Priming effects were however weaker with high accuracy motivation, suggesting that a focus on accurate judgments is an effective strategy to control for an unwanted priming influence in the AMP

Landau mapping and Fermi liquid parameters of the 2D t-J model

We study the momentum distribution function n(k) in the 2D t-J model on small clusters by exact diagonalization. We show that n(k) can be decomposed systematically into two components with Bosonic and Fermionic doping dependence. The Bosonic component originates from the incoherent motion of holes and has no significance for the low energy physics. For the Fermionic component we exlicitely perform the one-to-one Landau mapping between the low lying eigenstates of the t-J model clusters and those of an equivalent system of spin-1/2 quasiparticles. This mapping allows to extract the quasiparticle dispersion, statistics, and Landau parameters. The results show conclusively that the 2D t-J model for small doping is a Fermi liquid with a `small' Fermi surface and a moderately strong attractive interaction between the quasiparticles.Comment: Revtex file, 5 pages with 5 embedded eps-files, hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to: [email protected]

Inverse photoemission in strongly correlated electron systems

Based on exact results for small clusters of 2D t-J model we demonstrate the existence of several distinct `channels' in its inverse photoemission (IPES) spectrum. Hole-like quasiparticles can either be annihilated completely, or leave behind a variable number of spin excitations, which formed the `dressing cloud' of the annihilated hole. In the physical parameter regime the latter processes carry the bulk of IPES weight and although the Fermi surface takes the form of hole pockets, the distribution of spectal weight including these `magnon-bands' in the IPES spectrum is reminiscent of free electrons. The emerging scenario for Fermiology and spectral weight distribution is shown to be consistent with photoemission, inverse photemission and de Haas--van Alphen experiments on cuprate superconductors.Comment: Revtex file, 4 PRB pages + three figures appended as uu-encoded postscript. Hardcopies of figures (or the entire manuscript) can also be obtained by e-mail request to: [email protected]

A Logic Programming Approach to Predict Effective Compiler Settings for Embedded Software

AbstractThis paper introduces a new logic-based method for optimising the selection of compiler flags on embedded architectures. In particular, we use Inductive Logic Programming (ILP) to learn logical rules that relate effective compiler flags to specific program features. Unlike earlier work, we aim to infer human-readable rules and we seek to develop a relational first-order approach which automatically discovers relevant features rather than relying on a vector of predetermined attributes. To this end we generated a data set by measuring execution times of 60 benchmarks on an embedded system development board and we developed an ILP prototype which outperforms the current state-of-the-art learning approach in 34 of the 60 benchmarks. Finally, we combined the strengths of the current state of the art and our ILP method in a hybrid approach which reduced execution times by an average of 8% and up to 50% in some cases.</jats:p

Operant evaluative conditioning

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Excitation spectrum of the homogeneous spin liquid

We discuss the excitation spectrum of a disordered, isotropic and translationally invariant spin state in the 2D Heisenberg antiferromagnet. The starting point is the nearest-neighbor RVB state which plays the role of the vacuum of the theory, in a similar sense as the Neel state is the vacuum for antiferromagnetic spin wave theory. We discuss the elementary excitations of this state and show that these are not Fermionic spin-1/2 `spinons' but spin-1 excited dimers which must be modeled by bond Bosons. We derive an effective Hamiltonian describing the excited dimers which is formally analogous to spin wave theory. Condensation of the bond-Bosons at zero temperature into the state with momentum (pi,pi) is shown to be equivalent to antiferromagnetic ordering. The latter is a key ingredient for a microscopic interpretation of Zhang's SO(5) theory of cuprate superconductivityComment: RevTex-file, 16 PRB pages with 13 embedded eps figures. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to: [email protected]