0000000000115539
AUTHOR
Christian Schäfer
showing 9 related works from this author
Nitric Oxide Opposes Myogenic Pressure Responses Predominantly in Large Arterioles In Vivo
1998
Abstract —A myogenic vasoconstriction may amplify the effects of circulating vasoconstrictors. In cremaster arterioles, the contribution of a myogenic component to the constriction on intravenous infusion of norepinephrine (NE) or angiotensin II (Ang II) was studied. Second, the role of endothelium-derived nitric oxide (NO) in the control of these myogenic constrictions and its site of action in the resistance vascular bed was investigated. In 30 anesthetized (pentobarbital) hamsters, the cremaster was prepared for intravital microscopy, and a pneumatic vessel occluder was placed around the aorta to vary blood pressure in the hindquarter of the animal. Intravenous infusion of NE (0.5 nmol/…
Simulating Terahertz Field-Induced Ferroelectricity in Quantum Paraelectric SrTiO3
2021
Recent experiments have demonstrated that light can induce a transition from the quantum paraelectric to the ferroelectric phase of SrTiO3. Here, we investigate this terahertz field-induced ferroelectric phase transition by solving the time-dependent lattice Schrödinger equation based on first-principles calculations. We find that ferroelectricity originates from a light-induced mixing between ground and first excited lattice states in the quantum paraelectric phase. In agreement with the experimental findings, our study shows that the nonoscillatory second harmonic generation signal can be evidence of ferroelectricity in SrTiO3. We reveal the microscopic details of this exotic phase transi…
Elevation of plasma viscosity induces sustained NO-mediated dilation in the hamster cremaster microcirculation in vivo
1997
We studied whether a flow-independent increase of luminal wall shear stress (WSS) could dilate hamster arterioles in vivo and which endothelial mediators are potentially involved. To this end the plasma viscosity was elevated by exchanging blood for dextran-erythrocyte solution thereby augmenting WSS. Diameters of small and large arterioles as well as red blood cell velocities were measured before and after exchange of blood for solutions of identical haematocrit containing either high- (HMWD) or low-molecular weight dextran (LMWD). The potential role of endothelial autacoids was investigated by local application of the NO-synthase inhibitor NG-nitro-L-arginine (L-NNA), the inhibitor of cyc…
The Ferroelectric Photo-Groundstate of SrTiO$_3$: Cavity Materials Engineering
2021
Significance Controlling collective phenomena in quantum materials is a promising route toward engineering material properties on demand. Strong THz lasers have been successful at inducing ferroelectricity in S r T i O 3 . Here we demonstrate, from atomistic calculations, that cavity quantum vacuum fluctuations induce a change in the collective phase of S r T i O 3 in the strong light–matter coupling regime. Under these conditions, the ferroelectric phase is stabilized as the ground state, instead of the quantum paraelectric one. We conceptualize this light–matter hybrid state as a material photo ground state: Fundamental properties such as crystal structure, phonon frequencies, and the col…
Octopus, a computational framework for exploring light-driven phenomena and quantum dynamics in extended and finite systems
2020
Over the last few years, extraordinary advances in experimental and theoretical tools have allowed us to monitor and control matter at short time and atomic scales with a high degree of precision. An appealing and challenging route toward engineering materials with tailored properties is to find ways to design or selectively manipulate materials, especially at the quantum level. To this end, having a state-of-the-art ab initio computer simulation tool that enables a reliable and accurate simulation of light-induced changes in the physical and chemical properties of complex systems is of utmost importance. The first principles real-space-based Octopus project was born with that idea in mind,…
The quantum paraelectric phase of SrTiO$_3$ from first principles
2021
We demonstrate how the quantum paraelectric ground state of SrTiO$_3$ can be accessed via a microscopic $ab~initio$ approach based on density functional theory. At low temperature the quantum fluctuations are strong enough to stabilize the paraelectric phase even though a classical description would predict a ferroelectric phase. We find that accounting for quantum fluctuations of the lattice and for the strong coupling between the ferroelectric soft mode and lattice elongation is necessary to achieve quantitative agreement with experimental frequency of the ferroelectric soft mode. The temperature dependent properties in SrTiO$_3$ are also well captured by the present microscopic framework.
Wahrscheinlichkeitsrechnung und induktive Statistik
2009
Die Untersuchung allgemeiner Gesetzmasigkeiten kann nur in wenigen seltenen Fallen mit allen hierf¨ur relevanten statistischen Einheiten erfolgen. Grunde dafur sind bspw. die hohen Erhebungskosten, ein groser Zeitaufwand oder die Zerstorung der relevanten Merkmalstrager bei der Beobachtung. Daher versucht man in Fallen, in denen eine Totalerhebung unmoglich bzw. nicht sinnvoll erscheint, auf Basis einer Stichprobe Ruckschlusse auf Gesetzmasigkeiten der Grundgesamtheit zu ziehen. Dieses Verfahren, vom Speziellen auf das Allgemeine zu schliesen, bezeichnet man als Induktion.
Programmbeispiele in R
2009
R ist ein Programmpaket, welches fur ein breites Anwendungsspektrum statistischer Fragestellungen bestens geeignet ist. Es basiert auf einer objektorientierten Programmiersprache und ist frei verfugbar, was es im Vergleich zu anderen statistischen Programmpaketen gerade fur den Einsatz im Bereich der Lehre und den studentischen und privaten Einsatz interessant macht. Der Anwender kann auf eine grose Bibliothek von Funktionen zur statischen Analyse und graphischen Darstellung von Daten zuruckgreifen. Diese Bibliothek steht allen Anwendern auf der offiziellen Homepage des R-Projektes www.r-project.org zur freien Verfugung und wird laufend durch Beitrage von R-Anwendern weiterentwickelt.
Engineering quantum materials with chiral optical cavities.
2021
Nature materials 20, 438 – 442 (2020). doi:10.1038/s41563-020-00801-7