Phonon renormalization from local and transitive electron-lattice couplings in strongly correlated systems

Within the time-dependent Gutzwiller approximation (TDGA) applied to Holstein- and SSH-Hubbard models we study the influence of electron correlations on the phonon self-energy. For the local Holstein coupling we find that the phonon frequency renormalization gets weakened upon increasing the onsite interaction $U$ for all momenta. In contrast, correlations can enhance the phonon frequency shift for small wave-vectors in the SSH-Hubbard model. Moreover the TDGA applied to the latter model provides a mechanism which leads to phonon frequency corrections at intermediate momenta due to the coupling with double occupancy fluctuations. Both models display a shift of the nesting-induced to a $q=0$ instability when the onsite interaction becomes sufficiently strong and thus establishing phase separation as a generic phenomenon of strongly correlated electron-phonon coupled systems.Comment: 14 pages, 11 figure

Experimentelle Untersuchung an einem offenen Absorptionssystem zur Entfeuchtung in Kreuzstromfahrweise

Die Herstellung und Aufrechterhaltung von behaglichen Raumluftkonditionen ist im heutigen Wissenszeitalter für die Dienstleistungsunternehmen ein wichtiger Produktivitätsfaktor geworden. Um diese Raumluftkonditionen energie-wirtschaftlich optimal zu erreichen, ist es notwendig, die Luftbehandlungs-funktionen so eigenständig wie möglich zu betrachten. Die Trennung der thermodynamischen Prozesse Entfeuchten und Kühlen ist energiewirtschaftlich relevant, da die Bereitstellung der Kälte und damit der Energieaufwand einer herkömmlichen raumlufttechnischen Anlage massgeblich durch die geforderte Entfeuchtungsleistung bestimmt wird. Eine energetisch rationellere Entfeuchtung ist durch den Einsatz von hygroskopischen Salzen möglich, so dass zu diesem Zweck auf die klassische Kälteerzeugung verzichtet werden könnte. Das Ziel dieser Arbeit ist die Integration einer für die Klimatechnik ausreichenden sorptiven Entfeuchtung in eine raumlufttechnische Anlage. Hierfür wird zunächst in der Voruntersuchung die Grundlage der möglichen messtechnischen Regelbarkeit und die konstruktive Umsetzung einer mit wässrigen Salzlösung arbeitenden Entfeuchtungsanlage erarbeitet. In der Hauptuntersuchung werden zwei Entfeuchter mit unterschiedlichen Oberflächen ausgestattet. Die möglichen Entfeuchtungsleistungen werden in Abhängigkeit der Überströmgeschwindigkeit, der Anfangskonzentration der Salzlösung und der Massenstromverhältnisse gemessen. Durch umfangreiche Temperatur- und Konzentrationsmessungen der wässrigen Salzlösung wird die Leistungsfähigkeit und Praxistauglichkeit für die Entfeuchtung getestet. Die entstehenden Entfeuchtungsbreiten und Druckverluste dieses offenen Absorptionssystemes werden mit anderen entfeuchtenden Komponenten verglichen. Mithilfe der Messergebnisse werden die Stoffübergangs- und Wärmedurchgangskoeffizienten berechnet, sowie die Aufteilung der sensiblen zur umgewandelten latenten Wärme dargestellt. Abschließend werden anhand der gefundenen Ergebnisse konstruktive Optimierungen aufgezeigt

Beyond Technology - Children's Voices and Digital Realities at School

Research project funded by Nordplus Junio

Time-Dependent Gutzwiller Theory for Multiband Hubbard Models

Based on the variational Gutzwiller theory, we present a method for the computation of response functions for multiband Hubbard models with general local Coulomb interactions. The improvement over the conventional random-phase approximation is exemplified for an infinite-dimensional two-band Hubbard model where the incorporation of the local multiplet-structure leads to a much larger sensitivity of ferromagnetism on the Hund coupling. Our method can be implemented into LDA+Gutzwiller schemes and will therefore be an important tool for the computation of response functions for strongly correlated materials.Comment: 4 pages, 3 figure

First-principles equation of state and phase stability for the Ni-Al system under high pressures

The equation of state (EOS) of alloys at high pressures is generalized with the cluster expansion method. It is shown that this provides a more accurate description. The low temperature EOSs of Ni-Al alloys on FCC and BCC lattices are obtained with density functional calculations, and the results are in good agreement with experiments. The merits of the generalized EOS model are confirmed by comparison with the mixing model. In addition, the FCC phase diagram of the Ni-Al system is calculated by cluster variation method (CVM) with both spin-polarized and non-spin-polarized effective cluster interactions (ECI). The influence of magnetic energy on the phase stability is analyzed. A long-standing discrepancy between ab initio formation enthalpies and experimental data is addressed by defining a better reference state. This aids both evaluation of an ab initio phase diagram and understanding the thermodynamic behaviors of alloys and compounds. For the first time the high-pressure behavior of order-disorder transition is investigated by ab initio calculations. It is found that order-disorder temperatures follow the Simon melting equation. This may be instructive for experimental and theoretical research on the effect of an order-disorder transition on shock Hugoniots.Comment: 27 pages, 12 figure

Progressive induction of left ventricular pressure overload in a large animal model elicits myocardial remodeling and a unique matrix signature

ObjectivePatients with severe left ventricular pressure overload secondary to aortic stenosis can present with signs and symptoms of heart failure despite normal left ventricular ejection fraction. This process occurs, at least in part, as a result of left ventricular pressure overload–induced extracellular matrix remodeling that promulgates increased left ventricular stiffness and impaired diastolic function. However, the determinants that drive extracellular matrix remodeling in this form of left ventricular pressure overload remain to be fully defined.MethodsLeft ventricular pressure overload was induced in mature pigs (n = 15) by progressive ascending aortic cuff inflation (once per week for 4 weeks), whereby left ventricular mass, left ventricular ejection fraction, and regional myocardial stiffness (rKm) were compared with referent controls (n = 12). Determinants of extracellular matrix remodeling were assessed by measuring levels of mRNA expression for fibrillar collagens, matrix metalloproteinases, and tissue inhibitors of matrix metalloproteinase 1 and 4.ResultsWith left ventricular pressure overload, left ventricular mass and rKm increased by 2- and 3-fold, respectively, compared with control, with no change in left ventricular ejection fraction. Left ventricular myocardial collagen increased approximately 2-fold, which was accompanied by reduced solubility (ie, increased cross-linking) with left ventricular pressure overload, but mRNA expression for fibrillar collagen and matrix metalloproteinases remained relatively unchanged. In contrast, a robust increase in mRNA expression for tissue inhibitors of matrix metalloproteinase-1 and 4 occurred with left ventricular pressure overload.ConclusionsIn a progressive model of left ventricular pressure overload, which recapitulates the phenotype of aortic stenosis, increased extracellular matrix accumulation and subsequently increased myocardial stiffness were not due to increased fibrillar collagen expression but rather to determinants of post-translational control that included increased collagen stability (thereby resistant to matrix metalloproteinase degradation) and increased endogenous matrix metalloproteinase inhibition. Targeting these extracellular matrix post-translational events with left ventricular pressure overload may hold both diagnostic and therapeutic relevance

Isotope effect and bond-stretching phonon anomaly in high-Tc cuprates

We analyse a model where the anomalies of the bond-stretching LO phonon mode are caused by the coupling to electron dynamic response in the form of a damped oscillator and explore the possibility to reconstruct the spectrum of the latter from the phonon measurements. Preliminary estimates point to its location in the mid infrared region and we show how the required additional information can be extracted from the oxygen isotope effect on the phonon spectrum. The model predicts a significant measurable deviation from the "standard value" of the isotope effect even if the phonon frequency is far below the electron spectrum, provided the latter is strongly incoherent. In this regime, which corresponds to the "mid infrared scenario", the phonon linewidth becomes a sensitive and informative probe of the isotope effect.Comment: 10 pages, 2 figures, added reference