In this paper we report on an alternative technique for the preparation of ytterbium (Yb)-doped silica fibers and their characteristics compared to the conventional modified chemical vapor deposition ...(MCVD) process in combination with solution doping and powder sinter technology (REPUSIL). In the case of the technique applied here, the active core diameter in the preform can be significantly increased via the deposition of Yb and the most important codopant, aluminum (Al), in the gas phase through the high-temperature evaporation of the Yb chelate compound and Al chloride in the MCVD process. The prepared preform shows a homogenous distribution of the refractive index and dopant concentration. The background loss of the drawn fiber was measured to be 25 dB km−1 at 1200 nm. Efficient lasing up to 200 W, showing a slope efficiency of about 80%, was demonstrated, which is comparable to fibers made via MCVD/solution doping and the REPUSIL technique.
We discuss the role and importance of dynamics in the brain and biological neural networks and argue that dynamics is one of the main missing elements in conventional Boolean logic and circuits. We ...summarize a simple dynamics based computing method, and categorize different techniques that we have introduced to realize logic, functionality, and programmability. We discuss the role and importance of coupled dynamics in networks of biological excitable cells, and then review our simple coupled dynamics based method for computing. In this paper, for the first time, we show how dynamics can be used and programmed to implement computation in any given base, including but not limited to base two.
Zusammenfassung
Neben Kosten rücken vermehrt die ökologischen Auswirkungen von Produktionsprozessen in den Fokus von Unternehmen und ihrer Stakeholder. Neuartige Formen der integrierten Analyse ...unterstützen dabei, Kosten und, ökologische Einflüsse parallel bewerten und die wichtigsten Stellhebel zur, Verbesserung identifizieren zu können. Dieser Beitrag beschreibt einen solchen, Ansatz auf Basis der Ökobilanzierung und der Lebenszykluskostenrechnung. Gegenüber dem Life Cycle Assessment (LCA) steht bei dem vorgestellten Ansatz, durch die Kombination von LCA und Costing (LCC) eine integrierte Bewertung von, Kosten und ökologischen Auswirkungen im Vordergrund.
A novel route to synthesize large area ZnO/Zn(OH)2 origami thin films at air/liquid interface is reported. ZnO materials derived from this route show the largest blue‐shifted band‐to‐band emission at ...3.85 eV (3.37 eV in bulk ZnO) so far, resulting from the quantum confinement in the ultrathin ZnO/Zn(OH)2 nanosheets. Interband defect levels (IDLs) related broadband photoluminescence is observed from UV to red region by excitation wavelength dependent photoluminescence measurements. The ZnO origami structures show photocatalytic methylene blue degradation (MB‐degradation) activity even under sub‐bandgap visible light illumination from 405 nm to green region at 505 nm, measured by low power monochromatic light emitting diode light sources. From the consistent light absorption, luminescence, and MB‐degradation activity, it can be concluded that the broadband visible light MB‐degradation activity is attributed to photogenerated carriers via IDLs. The 2D ZnO‐nanosheets in the origami structure better solve the dilemma of the IDLs in bulk materials, i.e., they are beneficial for light absorption in visible range but detrimental for enhanced recombination loss of carriers, and they can be quickly extracted to the surface without substantial recombination. This finding makes the ZnO origami a promising candidate for efficient photocatalyst that harvesting the sunlight and for indoor applications.
ZnO origami structure consisting of quasi 2D nanosheets is grown at the interface of air/liquid. The ZnO origami shows large blue‐shift of the band‐to‐band emission to 3.85 eV, and very broadband visible light driven photocatalytic degradation of methylene blue reaching to the green region at 505 nm, correlating to the carrier generation via interband defect levels.
The photosensitivity of various cerium-doped fibers has been experimentally investigated for both excimer- and femtosecond-laser illumination. The results of single-pulse, few-pulse and multi-pulse ...inscription of fiber-Bragg-gratings with both laser systems and the thermal aging of those gratings demonstrated the restrictions of the conventional color center model for cerium-doped fibers. To explain the short-term stability of single-pulse gratings against long-term stability of multi-pulse gratings, an extension into a two-step-model was deduced.
One major effect that can deteriorate the geometric accuracy of a calibrated machine tool is the elastic deformation of its structure due to heat transferred into it. Different solutions to this ...problem have been presented in the past—e.g. temperature-controlled structural parts and environments—but they are complex and expensive. In an on-going Collaborative Research Centre funded by the German Research Foundation scientists are working on model-based compensation and correction strategies. In this paper, a different approach is discussed using point diffraction interferometry to directly measure the three-dimensional distance between tool centre point and workpiece coordinate system. Commercially available three-dimensional measurement systems are introduced representing the state of the art before explaining the basics of point diffraction interferometry. Different parameters are investigated using simulation tools and the achievable accuracy of the approach is evaluated. Additionally, some suggestions are made concerning hardware requirements of a planned demonstrator.
Recent years have seen tremendous progress in experimental techniques to
create uniaxial strain. Motivated by these advances we investigate the effect
of uniaxial strain on LaMnO$_3$ employing ...ab-initio dynamical mean-field
theory, and put it in contrast to biaxial strain that occurs in epitaxial
systems. Projecting on the low-energy subspace of Mn $3d$ states, and solving
multi-impurity problems, our approach emphasizes on local dynamic correlations
at Mn sites. At ambient pressures, LaMnO$_3$ crystallizes in an orthorhombic
unit cell, with in-plane lattice constants $a<b$, and shows an A-type
antiferromagnetic ground state. If we apply uniaxial compressive strain such
that the in-plane lattice becomes square with lattice constant $a$, we find a
ferromagnetic insulating state. This is in sharp contrast to DFT results using
various functionals like PBE, PBE+$U$, and hybrid functionals like HSE, which
all predict a half-metallic ferromagnetic behaviour. Interestingly, applying
uniaxial tensile strain, such that the in-plane lattice becomes square with the
longer lattice constant $b$, an antiferromagnetic insulating state is observed.
We trace back these results to the reduction in Jahn-Teller distortion in the
case of compressive strain, favoring a ferromagnetic state. This reduction is
absent in the tensile case, and the antiferromagnetic state therefore survives.
Our study shows that it is the flavour of the strain (compressive or tensile)
which is decisive for the magnitude of Jahn-Teller distortions and, hence, the
magnetic state.
Recent years have seen tremendous progress in experimental techniques to create uniaxial strain. Motivated by these advances we investigate the effect of uniaxial strain on LaMnO\(_3\) employing ...ab-initio dynamical mean-field theory, and put it in contrast to biaxial strain that occurs in epitaxial systems. Projecting on the low-energy subspace of Mn \(3d\) states, and solving multi-impurity problems, our approach emphasizes on local dynamic correlations at Mn sites. At ambient pressures, LaMnO\(_3\) crystallizes in an orthorhombic unit cell, with in-plane lattice constants \(a<b\), and shows an A-type antiferromagnetic ground state. If we apply uniaxial compressive strain such that the in-plane lattice becomes square with lattice constant \(a\), we find a ferromagnetic insulating state. This is in sharp contrast to DFT results using various functionals like PBE, PBE+\(U\), and hybrid functionals like HSE, which all predict a half-metallic ferromagnetic behaviour. Interestingly, applying uniaxial tensile strain, such that the in-plane lattice becomes square with the longer lattice constant \(b\), an antiferromagnetic insulating state is observed. We trace back these results to the reduction in Jahn-Teller distortion in the case of compressive strain, favoring a ferromagnetic state. This reduction is absent in the tensile case, and the antiferromagnetic state therefore survives. Our study shows that it is the flavour of the strain (compressive or tensile) which is decisive for the magnitude of Jahn-Teller distortions and, hence, the magnetic state.
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