Search

Copyright of Der Ophthalmologe is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The gas sensing behaviour of granular tungsten oxide films under the influence of a polarizing electrical field is investigated. The Ohmic resistance of the film in the direction of applied voltage is altered in a reversible way due to ionic transport processes in the film. Several processes with a wide range of time constants from ∼100 ms to 100 s occur. A model is proposed to describe the movement of bulk donors and related changes of the surface charge. Within the model sensor instabilities are described which can be prevented by a pulse technique for readout. As an benefit a single sensor element used in different polarization states can discern several gases. [ABSTRACT FROM AUTHOR]

Copyright of Materials & Structures is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We analyse theoretically the generation of second and higher harmonics for sodium clusters deposited on an insulating surface. To this end, we use the time-dependent local-density approximation solved on a three-dimensional grid. We explore the impact of the various laser parameters (intensity, frequency, polarisation) on the efficiency of second harmonic generation. The success sensitively depends on a proper tuning of these parameters. We find optimum conditions for which the laser frequency is half the resonance frequency of the system, if the polarisation is directed orthogonal to the surface of the substrate, and if the intensity is large but safely below the critical value for destruction of the electron cloud. [ABSTRACT FROM AUTHOR]

Laser excitation of metal clusters depends on various parameters such as frequency, intensity, and pulse time. We give here an overview of relevant time scales and forces for the example of Na clusters. Variation of laser intensity is studied in connection with second harmonic generation. We see a rather sudden transition from a perturbative regime at low intensities to a field-dominated regime for larger intensities. We use the non-linearized time-dependent local density approximation (TDLDA), together with a local pseudopotential for the interaction of the valence electrons with the ions. Explicit ionic motion is taken into account in one test case where we demonstrate the importance of ionic effects for the detailed time evolution at times larger than 100 fs. [ABSTRACT FROM AUTHOR]

We investigate spin modes in the ground state and the polarized first isomer of the Na12 cluster describing the valence electrons in time-dependent local-spin-density approximation (TDLSDA) and the detailed ionic background using local pseudopotentials. The spin modes show a collective redshift compared to the unperturbed particle-hole excitations. They are strongly fragmented and the average energy of the modes along the principal axes are related to the underlying geometry (triaxial or axially symmetric). For the polarized isomer, we find significant cross talk between the spin modes and the dipole plasmon, which hints at a possible spectroscopic identification. [ABSTRACT FROM AUTHOR]

We present results on ground state properties for Na clusters with N=2−20 electrons using a jellium model with fully triaxial shapes and employing the spin degree-of-freedom for the electrons. The proper treatment of spin turns out to be crucial for the description of ionization potentials in this range of cluster sizes. Spontaneous spin polarization is observed in some triaxially soft, even clusters. [ABSTRACT FROM AUTHOR]

We discuss and compare dipole resonance modes in nuclei and metal clusters. In both systems, we observe well-developed collectivity with harmonic oscillations which persist high up into the regime of multiple resonances. Deformations tend to induce spectral fragmentation. In clusters, these effects are hardly strong enough to destroy all collectivity, except for the extreme of a fissioning cluster. Nuclear surface modes, on the other hand, are found to interfere strongly with the giant resonances being able to dissolve them completely. [ABSTRACT FROM AUTHOR]

The positive inotropic effect of the alpha-adrenoceptor agonist phenylephrine is accompanied by an increase in the presumed second messengers inositol 1,4,5-trisphosphate (1,4,5-IP) and inositol 1,3,4,5-tetrakisphosphate (1,3,4,5-IP). Both 1,4,5-IP and 1,3,4,5-IP sensitize myocardial contractile proteins in chemically skinned fibers. In addition to the Ca releasing effect of 1,4,5-IP from the sarcoplasmic reticulum the Ca-sensitizing effect of the inositol phosphates may play a role in alpha-adrenergic positive inotropism. In isolated heart muscle preparations from patients with endstage heart failure (due to dilated cardiomyopathy) beta-adrenergic as well as alpha-adrenergic effects are reduced compared to preparations from healthy hearts. The reduced beta-adrenergic effects can in part be explained by an increased content of signal transducing G-proteins. It is tempting to investigate whether other G proteins are also altered in severe congestive heart failure. [ABSTRACT FROM AUTHOR]

We discuss and compare the dipole resonance modes in nuclei and metal clusters under varying conditions: different excitation mechanisms in the case of nuclei, changed back-ground structure in the case of clusters. The resonances are generally nicely harmonic modes, even those with a large amplitude. Only extreme shapes, as they occur in fusion and fission, can perturb this harmonicity. [ABSTRACT FROM AUTHOR]

Structure and electron dynamics of sodium clusters are investigated within the local-density approximation for the electrons. We compare results from detailed ionic structure with those from a structure averaged jellium model and find that the dominance of the electron cloud overlays most of the differences in the background. Ionic structure is indispensable, however, to compute the surface energy of clusters and to provide an unprejudiced picture of cluster fission. For all cases, we compute the resonance spectra associated with electron dynamics. In particular, the very strong deformations during fission deliver unusual resonance modes with a broad spectral fragmentation. [ABSTRACT FROM AUTHOR]

Methane in air can be detected by the conductivity increase of Ga2O3 films. Films (200 μm) of β-Ga2O3 were prepared by depositing a suspension of β-Ga2O3 powder (Johnson Matthey; 32102; 99,99%) on alumina substrates. The films were exposed to 20 kPa O2 for 15 min at 934 K. In thermal desorption spectroscopy (TDS, β = 4,6 K/s, UHV conditions) only O2 occured at temperatures above 934 K. On reduction in 100 Pa H2 for 5 min at 800 K, only a suboxide, Ga2O (above 880 K), indicating a destabilisation of the lattice [1], a broad hydrogen peak (440–930 K) and the formation of water (700–900 K) were observed. No Ga2O3 and O2 were found in desorption. At temperatures between 260 K and 934 K the film was exposed to methane (100 Pa, 5 min). For exposure temperatures between 630 K and 934 K, CO, CO2, H2, and small amounts of CH4 and the suboxide Ga2O appeared in desorption. A reaction scheme for the decomposition of methane is proposed. It includes the adsorption of CH4, the dissociation of CH4, the desorption of H2O and the formation of oxygen vacancies. These vacancies and the adsorbed hydrogen both acting as donors may explain the conductance increase on exposure to methane observed by other authors. [ABSTRACT FROM AUTHOR]