Влияние газовой фазы на величину тока в ячейке бесконтактного восстановления

Для исследования процесса восстановления окиси железа углеродом использована методика, основанная на измерении тока, возникающего между нагретыми телами. С этой целью сконструирована кварцевая ячейка, позволяющая жестко устанавливать образцы графита и окиси железа на определенном расстоянии друг от друга. Изучено влияние отдельных реакций на каждом электроде на суммарный ток. Для этого проведена серия опытов в нейтральной, окисленной и восстановительной атмосферах. Установлено, что окисление графита в среде воздуха сопровождается возрастанием тока положительной полярности. В среде водорода значения тока невелики. В нейтральной среде гелия ток имеет положительную полярность, а величина его не зависит от присутствия того или иного реагента. Необходима дальнейшая работа по повышению величины полезного сигнала в ре­гистрируемом токе

One particle interchain hopping in coupled Hubbard chains

Interchain hopping in systems of coupled chains of correlated electrons is investigated by exact diagonalizations and Quantum-Monte-Carlo methods. For two weakly coupled Hubbard chains at commensurate densities (e.g. n=1/3) the splitting at the Fermi level between bonding and antibonding bands is strongly reduced (but not suppressed) by repulsive interactions extending to a few lattice spacings. The magnitude of this reduction is directly connected to the exponent $\alpha$ of the 1D Luttinger liquid. However, we show that the incoherent part of the single particle spectral function is much less affected by the interchain coupling. This suggests that incoherent interchain hopping could occur for intermediate $\alpha$ values.Comment: 4 pages, LaTeX 3.0, 7 PostScript figures in uuencoded for

A pulsed, mono-energetic and angular-selective UV photo-electron source for the commissioning of the KATRIN experiment

The KATRIN experiment aims to determine the neutrino mass scale with a sensitivity of 200 meV/c^2 (90% C.L.) by a precision measurement of the shape of the tritium $\beta$-spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. To determine the transmission properties of the KATRIN main spectrometer, a mono-energetic and angular-selective electron source has been developed. In preparation for the second commissioning phase of the main spectrometer, a measurement phase was carried out at the KATRIN monitor spectrometer where the device was operated in a MAC-E filter setup for testing. The results of these measurements are compared with simulations using the particle-tracking software "Kassiopeia", which was developed in the KATRIN collaboration over recent years.Comment: 19 pages, 16 figures, submitted to European Physical Journal

The spectral weight of the Hubbard model through cluster perturbation theory

We calculate the spectral weight of the one- and two-dimensional Hubbard models, by performing exact diagonalizations of finite clusters and treating inter-cluster hopping with perturbation theory. Even with relatively modest clusters (e.g. 12 sites), the spectra thus obtained give an accurate description of the exact results. Thus, spin-charge separation (i.e. an extended spectral weight bounded by singularities) is clearly recognized in the one-dimensional Hubbard model, and so is extended spectral weight in the two-dimensional Hubbard model.Comment: 4 pages, 5 figure

Interrelation of Superconducting and Antiferromagnetic Gaps in High-Tc Compounds: a Test Case for a Microscopic Theory

Recent angle resolved photoemission (ARPES) data, which found evidence for a d-wave-like modulation of the antiferromagnetic gap, suggest an intimate interrelation between the antiferromagnetic insulator and the superconductor with its d-wave gap. This poses a new challenge to microscopic descriptions, which should account for this correlation between, at first sight, very different states of matter. Here, we propose a microscopic mechanism which provides a definite correlation between these two different gap structures: it is shown that a projected SO(5) theory, which aims at unifying antiferromagnetism and d-wave superconductivity via a common symmetry principle while explicitly taking the Mott-Hubbard gap into account, correctly describes the observed gap characteristics. Specifically, it accounts for both the dispersion and the order of magnitude difference between the antiferromagnetic gap modulation and the superconducting gap.Comment: 8 pages, 5 figure

Mice with genetically altered glucocorticoid receptor expression show altered sensitivity for stress-induced depressive reactions

Altered glucocorticoid receptor (GR) signaling is a postulated mechanism for the pathogenesis of major depression. To mimic the human situation of altered GR function claimed for depression, we generated mouse strains that underexpress or overexpress GR, but maintain the regulatory genetic context controlling the GR gene. To achieve this goal, we used the following: (1) GR-heterozygous mutant mice (GR+/-) with a 50% GR gene dose reduction, and (2) mice overexpressing GR by a yeast artificial chromosome resulting in a twofold gene dose elevation. GR+/- mice exhibit normal baseline behaviors but demonstrate increased helplessness after stress exposure, a behavioral correlate of depression in mice. Similar to depressed patients, GR+/- mice have a disinhibited hypothalamic-pituitary-adrenal (HPA) system and a pathological dexamethasone/corticotropin-releasing hormone test. Thus, they represent a murine depression model with good face and construct validity. Overexpression of GR in mice evokes reduced helplessness after stress exposure, and an enhanced HPA system feedback regulation. Therefore, they may represent a model for a stress-resistant strain. These mouse models can now be used to study biological changes underlying the pathogenesis of depressive disorders. As a first potential molecular correlate for such changes, we identified a downregulation of BDNF protein content in the hippocampus of GR+/- mice, which is in agreement with the so-called neurotrophin hypothesis of depression

Critical Properties in Dynamical Charge Correlation Function for the One-Dimensional Mott Insulator

Critical properties in the dynamical charge correlation function for the one-dimensional Mott insulator are studied. By properly taking into account {\it the final-state interaction} between the charge and spin degrees of freedom, we find that the edge singularity in the charge correlation function is governed by massless spinon excitations, although it is naively expected that spinons do not directly contribute to the charge excitation over the Hubbard gap. We obtain the momentum-dependent anomalous critical exponent by applying the finite-size scaling analysis to the Bethe ansatz solution of the half-filled Hubbard model.Comment: 7 pages, REVTe

Potentielle Wirkung von Unkräutern auf die P-Mobilisierung unter Mais

Die Rhizosphäre ist ein Hot Spot pflanzlicher und mikrobieller Aktivität zur Nährstoffmobilisierung und die Effizienz der Nutzung von Phosphor (P) unterscheidet sich pflanzen- artenspezifisch. Während die P-Mobilisierung in der Rhizosphäre verschiedener Kulturpflanzen intensiv untersucht wurde, ist die Bedeutung der Unkräuter auf die P-Verfügbarkeit für die vergesellschafteten Kulturpflanzen in Balance von Nährstoffkonkurrenz und Mobilisierungsleistung wenig bekannt. In der vorliegenden Untersuchung wird geprüft, ob eine zeitweise Toleranz von Unkräutern im Bestand die P-Verfügbarkeit für die Nutzpflanze Mais (Zea mays) durch die Mobilisierungsaktivität der Unkrautarten verbessern kann. Zu diesem Zweck wurden in zwei Versuchsjahren (2015 und 2016) Gefäßversuche unter Halbfreilandbedingungen mit einem P-defizienten Boden etabliert. Mais als mykorrhizierte Testpflanze wurde alleine und in Kombination mit sechs verschiedenen sowohl mykorrhizierten als auch nicht mykorrhizierten Unkrautarten kultiviert (Chenopodium album, Echinochloa crus-galli, Tripleurospermum perforatum, Polygonum convolvulus, Solanum nigrum, Viola arvensis). Um einen möglichen unkrautartspezifischen Einfluss auf die P-Mobilisierung unter Mais zu erfassen, wurden Boden- (u.a. Phosphatasen-Aktivitäten, mikrobieller Biomasse-P, pflanzenverfügbarer P) und Pflanzenparameter (Ertrag, Nährstoffgehalte und Mykorrhizierungsgrad der Feinwurzeln) untersucht. Die Ergebnisse belegen signifikante pflanzenkombinationsspezifische Unterschiede in der P-Mobilisierung und P-Aufnahme