Niederfrequente akustische Messungen an Quarzglas

In dieser Arbeit wurden Messungen der inneren Reibung und der relativen Schallgeschwindigkeitsänderung an Quarzglas im Bereich von 5mK bis 40K für vier verschiedene Frequenzen zwischen 334 und 5030Hz durchgeführt. Für die Experimente wurde ein mechanischer Oszillator, das sogenannte Double Paddle, verwendet, der sich durch seine im Vergleich zur früher verwendeten Vibrating-Reed-Methode deutlich geringere Untergrunddämpfung sowie das vielfältige Modenspektrum auszeichnet. Bei Temperaturen unterhalb von 30mK wurde ein Anstieg der inneren Reibung beobachtet, der proportional zu $T^{eta}$ verläuft, wobei $eta$ monoton mit der Meßfrequenz von 0,85 bis 1,74 zunimmt und damit deutlich abweicht vom $T^{3}$-Verhalten des Tunnelmodells, welches die Tieftemperatureigenschaften von Gläsern phänomenologisch beschreibt. Die mutmaßliche Ursache dieser Diskrepanzen liegt in der vom Tunnelmodell nicht berücksichtigten gegenseitigen Wechselwirkung der Tunnelsysteme, die besonders bei tiefen Temperaturen wichtig wird. Für den Dämpfungswert im Plateaubereich wurde eine schwache Abhängigkeit von der Meßfrequenz beobachtet. Aus der Frequenzabhängigkeit der Lage des Dämpfungsmaximums bei ca. 30K konnte eine Dominanz von thermisch aktivierten Prozessen gegenüber inkohärentem Tunneln in diesem Temperaturbereich gefolgert werden

Heart failure therapy in diabetic patients-comparison with the recent ESC/EASD guideline

<p>Abstract</p> <p>Background</p> <p>To assess heart failure therapies in diabetic patients with preserved as compared to impaired systolic ventricular function.</p> <p>Methods</p> <p>3304 patients with heart failure from 9 different studies were included (mean age 63 ± 14 years); out of these, 711 subjects had preserved left ventricular ejection fraction (≥ 50%) and 994 patients in the whole cohort suffered from diabetes.</p> <p>Results</p> <p>The majority (>90%) of heart failure patients with reduced ejection fraction (SHF) and diabetes were treated with an ACE inhibitor (ACEi) or angiotensin receptor blocker (ARB) or with beta-blockers. By contrast, patients with diabetes and preserved ejection fraction (HFNEF) were less likely to receive these substance classes (p < 0.001) and had a worse blood pressure control (p < 0.001). In comparison to patients without diabetes, the probability to receive these therapies was increased in diabetic HFNEF patients (p < 0.001), but not in diabetic SHF patients. Aldosterone receptor blockers were given more often to diabetic patients with reduced ejection fraction (p < 0.001), and the presence and severity of diabetes decreased the probability to receive this substance class, irrespective of renal function.</p> <p>Conclusions</p> <p>Diabetic patients with HFNEF received less heart failure medication and showed a poorer control of blood pressure as compared to diabetic patients with SHF. SHF patients with diabetes were less likely to receive aldosterone receptor blocker therapy, irrespective of renal function.</p

Materials for Magnetic Recording Applications

In the first part of this work, the influence of hydrogen on the structural and magnetic properties of Fe/V(001) superlattices was studied. The local structure of the vanadium-hydride layers was determined by extended x-ray absorption fine structure (EXAFS) measurements. The magnetic ordering in a weakly coupled Fe/V(001) superlattice was investigated using the magneto-optical Kerr effect (MOKE). The interlayer exchange coupling is weakened upon alloying with hydrogen and a phase with short-range magnetic order was observed. The second part is concerned with first-principles calculations of magnetic materials, with a focus on magnetic recording applications. The uniaxial magnetic anisotropy energy (MAE) of Fe, Co, and Ni was calculated for tetragonal and trigonal structures. Based on an analysis of the electronic states of tetragonal Fe and Co at the center of the Brillouin zone, tetragonal Fe-Co alloys were proposed as a material that combines a large uniaxial MAE with a large saturation magnetization. This was confirmed by experimental studies on (Fe,Co)/Pt superlattices. The large uniaxial MAE of L10 FePt is caused by the large spin-orbit interaction on the Pt sites in connection with a strong hybridization between Fe and Pt. Furthermore, it was shown that the uniaxial MAE can be increased by alloying the Fe sublattice with Mn. The combination of the high-moment rare-earth (RE) metals with the high-TC 3d transition metals in RE/Cr/Fe multilayers (RE = Gd, Tb, Dy) gives rise to a strong ferromagnetic effective exchange interaction between the Fe layers and the RE layer. The MAE of hcp Gd was found to have two principal contributions, namely the dipole interaction of the large localized 4f spins and the band electron magnetic anisotropy due to the spin-orbit interaction. The peculiar temperature dependence of the easy axis of magnetization was reproduced on a qualitative level

G_q-Mediated Arrhythmogenic Signaling Promotes Atrial Fibrillation

Background: Atrial fibrillation (AF) is promoted by various stimuli like angiotensin II, endothelin-1, epinephrine/norepinephrine, vagal activation, or mechanical stress, all of which activate receptors coupled to G-proteins of the Gαq/Gα11-family (Gq). Besides pro-fibrotic and pro-inflammatory effects, Gq-mediated signaling induces inositol trisphosphate receptor (IP3R)-mediated intracellular Ca2+ mobilization related to delayed after-depolarisations and AF. However, direct evidence of arrhythmogenic Gq-mediated signaling is absent. Methods and results: To define the role of Gq in AF, transgenic mice with tamoxifen-inducible, cardiomyocyte-specific Gαq/Gα11-deficiency (Gq-KO) were created and exposed to intracardiac electrophysiological studies. Baseline electrophysiological properties, including heart rate, sinus node recovery time, and atrial as well as AV nodal effective refractory periods, were comparable in Gq-KO and control mice. However, inducibility and mean duration of AF episodes were significantly reduced in Gq-KO mice—both before and after vagal stimulation. To explore underlying mechanisms, left atrial cardiomyocytes were isolated from Gq-KO and control mice and electrically stimulated to study Ca2+-mobilization during excitation–contraction coupling using confocal microscopy. Spontaneous arrhythmogenic Ca2+ waves and sarcoplasmic reticulum content-corrected Ca2+ sparks were less frequent in Gq-KO mice. Interestingly, nuclear but not cytosolic Ca2+ transient amplitudes were significantly decreased in Gq-KO mice. Conclusion: Gq-signaling promotes arrhythmogenic atrial Ca2+-release and AF in mice. Targeting this pathway, ideally using Gq-selective, biased receptor ligands, may be a promising approach for the treatment and prevention of AF. Importantly, the atrial-specific expression of the Gq-effector IP3R confers atrial selectivity mitigating the risk of life-threatening ventricular pro-arrhythmic effects

Perpendicular magnetocrystalline anisotropy in tetragonally distorted Fe-Co alloys

We report on the experimental realization of tetragonal Fe-Co alloys as a constituent of Fe(0.36)Co(0.64)/Pt superlattices with huge perpendicular magnetocrystalline anisotropy energy, reaching 210 mu eV/atom, and a saturation magnetization of 2.5 mu(B)/atom at 40 K, in qualitative agreement with theoretical predictions. At room temperature the corresponding values 150 mu eV/atom and 2.2 mu(B)/atom are achieved. This suggests that Fe-Co alloys with carefully chosen combinations of composition and distortion are good candidates for high-density perpendicular storage materials