1,202 research outputs found
Sortenversuche 2002 im ökologischen Landbau in Deutschland: Sommerweizen - Bundesweite Auswertung der Ergebnisse der Arbeitsgruppe Ökologischer Versuchsansteller
Deutschlandweite Auswertung der Sortenversuche Sommerweizen
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Sortenversuche 2002 im ökologischen Landbau in Deutschland: Hafer - Bundesweite Auswertung der Ergebnisse der Arbeitsgruppe Ökologischer Versuchsansteller
Die vorliegende deutschlandweite Auswertung der Sortenversuche "Hafer" beruht auf den Versuchen der in der Arbeitsgruppe Ökologischer Versuchsansteller des Verbands der Landwirtschaftskammern e.V. (VLK) vertretenen Einrichtungen (Landwirtschaftskammern und Versuchsanstalten der Bundesländer).
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On the stability of polaronic superlattices in strongly coupled electron-phonon systems
We investigate the interplay of electron-phonon (EP) coupling and strong
electronic correlations in the frame of the two-dimensional (2D) Holstein t-J
model (HtJM), focusing on polaronic ordering phenomena for the quarter-filled
band case. The use of direct Lanczos diagonalization on finite lattices allows
us to include the effects of quantum phonon fluctuations in the calculation of
spin/charge structure factors and hole-phonon correlation functions. In the
adiabatic strong coupling regime we found evidence for ``self-localization'' of
polaronic carriers in a charge-modulated structure, a type of
superlattice solidification reminiscent of those observed in the nickel
perovskites .Comment: 2 pages, Latex. Submitted to Physica C, Proc. Int. Conf. on M2HTSC
Post-training load-related changes of auditory working memory: An EEG study
Working memory (WM) refers to the temporary retention and manipulation of information, and its capacity is highly susceptible to training. Yet, the neural mechanisms that allow for increased performance under demanding conditions are not fully understood. We expected that post-training efficiency in WM performance modulates neural processing during high load tasks. We tested this hypothesis, using electroencephalography (EEG) (N = 39), by comparing source space spectral power of healthy adults performing low and high load auditory WM tasks. Prior to the assessment, participants either underwent a modality-specific auditory WM training, or a modality-irrelevant tactile WM training, or were not trained (active control). After a modality-specific training participants showed higher behavioral performance, compared to the control. EEG data analysis revealed general effects of WM load, across all training groups, in the theta-, alpha-, and beta-frequency bands. With increased load theta-band power increased over frontal, and decreased over parietal areas. Centro-parietal alpha-band power and central beta-band power decreased with load. Interestingly, in the high load condition a tendency toward reduced beta-band power in the right medial temporal lobe was observed in the modality-specific WM training group compared to the modality-irrelevant and active control groups. Our finding that WM processing during the high load condition changed after modality-specific WM training, showing reduced beta-band activity in voice-selective regions, possibly indicates a more efficient maintenance of task-relevant stimuli. The general load effects suggest that WM performance at high load demands involves complementary mechanisms, combining a strengthening of task-relevant and a suppression of task-irrelevant processing
Time and frequency resolved spontaneous emission from supramolecular pheophorbide-a complexes: A mixed quantum classical computation
A mixed quantum classical methodology is utilized to compute the time and frequency resolved emission spectrum of a chromophore complex dissolved in ethanol. The single complex is formed by a butanediamine dendrimer to which pheophorbide-a molecules are covalently linked. The electronic excitations are described in a Frenkel-exciton model treated quantum mechanically and all nuclear coordinates are described classically by carrying out room-temperature MD simulations. Starting with the full quantum formula for the emission spectrum, it is translated to the mixed quantum classical case and used to compute time resolved spectra up to 2 ns. To account for radiative decay the chromophore complex excited-state dynamics have to be described in a density matrix theory. While the full emission spectrum only reflects excited-state decay the introduction of partial spectra allows to uncover details of excitation energy redistribution among the chromophores
Low Temperature Magnetic Properties of the Double Exchange Model
We study the {\it ferromagnetic} (FM) Kondo lattice model in the strong
coupling limit (double exchange (DE) model). The DE mechanism proposed by Zener
to explain ferromagnetism has unexpected properties when there is more than one
itinerant electron. We find that, in general, the many-body ground state of the
DE model is {\it not} globally FM ordered (except for special filled-shell
cases). Also, the low energy excitations of this model are distinct from spin
wave excitations in usual Heisenberg ferromagnets, which will result in unusual
dynamic magnetic properties.Comment: 5 pages, RevTeX, 5 Postscript figures include
Finite temperature strong-coupling expansions for the Kondo lattice model
Strong-coupling expansions, to order , are derived for the Kondo
lattice model of strongly correlated electrons, in 1-, 2- and 3- dimensions at
arbitrary temperature. Results are presented for the specific heat, and spin
and charge susceptibilities.Comment: revtex
The role of SGLT1 and GLUT2 in intestinal glucose transport and sensing.
Intestinal glucose absorption is mediated by SGLT1 whereas GLUT2 is considered to provide basolateral exit. Recently, it was proposed that GLUT2 can be recruited into the apical membrane after a high luminal glucose bolus allowing bulk absorption of glucose by facilitated diffusion. Moreover, SGLT1 and GLUT2 are suggested to play an important role in intestinal glucose sensing and incretin secretion. In mice that lack either SGLT1 or GLUT2 we re-assessed the role of these transporters in intestinal glucose uptake after radiotracer glucose gavage and performed Western blot analysis for transporter abundance in apical membrane fractions in a comparative approach. Moreover, we examined the contribution of these transporters to glucose-induced changes in plasma GIP, GLP-1 and insulin levels. In mice lacking SGLT1, tissue retention of tracer glucose was drastically reduced throughout the entire small intestine whereas GLUT2-deficient animals exhibited higher tracer contents in tissue samples than wild type animals. Deletion of SGLT1 resulted also in reduced blood glucose elevations and abolished GIP and GLP-1 secretion in response to glucose. In mice lacking GLUT2, glucose-induced insulin but not incretin secretion was impaired. Western blot analysis revealed unchanged protein levels of SGLT1 after glucose gavage. GLUT2 detected in apical membrane fractions mainly resulted from contamination with basolateral membranes but did not change in density after glucose administration. SGLT1 is unequivocally the prime intestinal glucose transporter even at high luminal glucose concentrations. Moreover, SGLT1 mediates glucose-induced incretin secretion. Our studies do not provide evidence for GLUT2 playing any role in either apical glucose influx or incretin secretion
Polarons and bipolarons in strongly interacting electron-phonon systems
The Holstein Hubbard and Holstein t--J models are studied for a wide range of
phonon frequencies, electron--electron and electron--phonon interaction
strengths on finite lattices with up to ten sites by means of direct Lanczos
diagonalization. Previously the necessary truncation of the phononic Hilbert
space caused serious limitations to either very small systems (four or even two
sites) or to weak electron--phonon coupling, in particular in the adiabatic
regime. Using parallel computers we were able to investigate the transition
from `large' to `small' polarons in detail. By resolving the low--lying
eigenstates of the Hamiltonian and by calculating the spectral function we can
identify a polaron band in the strong--coupling case, whose dispersion deviates
from the free--particle dispersion at low and intermediate phonon frequencies.
For two electrons (holes) we establish the existence of bipolaronic states and
discuss the formation of a bipolaron band. For the 2D Holstein t--J model we
demonstrate that the formation of hole--polarons is favoured by strong Coulomb
correlations. Analyzing the hole--hole correlation functions we find that hole
binding is enhanced as a dynamical effect of the electron--phonon interaction.Comment: 23 pages (Revtex) with 13 figures (ps, uuencoded
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