Beitrag zum Problem der heterosynaptischen Facilitation in Aplysia californica

1. Heterosynaptic facilitation (H.S.F.) of single neurons in the central nervous system of Aplysia can be repeated virtually indefinitely, provided sufficient time is allowed for recovery between the trials.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47439/1/424_2004_Article_BF00362956.pd

High temperature optical absorption investigation into the electronic transitions in sol–gel derived C12A7 thin films

Optical absorption into 6 mm thick sol–gel derived films, annealed at 1300 °C of 12CaO·7Al2O3 calcium aluminate binary compound on MgO〈100〉 single crystal substrates was studied at temperatures ranging from room temperature to 300 °C. Experimental data were analysed in both Tauc and Urbach regions. The optical band gap decreased from 4.088 eV at 25 °C to 4.051 eV at 300 °C, while Urbach energy increased from 0.191 eV at 25 °C to 0.257 eV at 300 °C. The relationship between the optical band gap and the Urbach energy at different temperatures showed an almost linear relationship from which the theoretical values of 4.156 and 0.065 eV were evaluated for the band gap energy and Urbach energy of a 12CaO·7Al2O3 crystal with zero structural disorder at 0 K

High-Pressure Amorphous Nitrogen

The phase diagram and stability limits of diatomic solid nitrogen have been explored in a wide pressure--temperature range by several optical spectroscopic techniques. A newly characterized narrow-gap semiconducting phase $\eta$ has been found to exist in a range of 80--270 GPa and 10--510 K. The vibrational and optical properties of the $\eta$ phase produced under these conditions indicate that it is largely amorphous and back transforms to a new molecular phase. The band gap of the $\eta$ phase is found to decrease with pressure indicating possible metallization by band overlap above 280 GPa.Comment: 5 pages, 4 figure

Multiphase photo-capillary reactors coated with TiO2 films: preparation, characterization and photocatalytic performance

Quartz capillaries were assessed as multiphase photocatalytic reactors. The tested reaction was the salicylic acid (2-dihidroxibenzoic acid) oxidation. The catalyst (TiO2) was either in slurry or immobilized by sol-gel method onto the capillary wall. All experiments were conducted under oxygen flow and Taylor flow hydrodynamic regime. TiO2 Films were characterized by Raman spectroscopy, diffuse reflectance UV-Vis spectroscopy and scanning electronic microscopy. The effect of two synthesis variables was established. These variables were volumetric ratio of precursors solutions (i-PrO:2-propanol:nitric acid) and number of capillary coating cycles. These variables were found to importantly affect film homogeneity and oxidation rate. The highest initial reaction rate (106.32x10-6 mol dm-3s-1) was obtained when using the TiO2 as film prepared with a precursors volumetric ratio of 1:15:1 and with two coating cycles. For comparison purposes, the same oxidation process was conducted in a stirred reactor and it was found that the reaction rate value is diminished by almost four times in comparison with that obtained under Taylor flow in the capillary reactor. Selectivity was found to be dependant on the type of catalyst addition, slurry or immobilized. Catalytic films employed in this non-common reaction system were 2 reused three times losing less than 10% of their photocatalytic activity. The photonic efficiency was found to be two orders of magnitude higher in the coated capillary reactor than in the slurry stirred reactor.L. Hurtado acknowledges CONACYT-Mexico the scholarship No. 56499. Project PRODEP for advanced oxidation processes is also acknowledged for financial support

Optical characterisation of silicon nanocrystals embedded in SiO2/Si3N4 hybrid matrix for third generation photovoltaics

Silicon nanocrystals with an average size of approximately 4 nm dispersed in SiO2/Si3N4 hybrid matrix have been synthesised by magnetron sputtering followed by a high-temperature anneal. To gain understanding of the photon absorption and emission mechanisms of this material, several samples are characterised optically via spectroscopy and photoluminescence measurements. The values of optical band gap are extracted from interference-minimised absorption and luminescence spectra. Measurement results suggest that these nanocrystals exhibit transitions of both direct and indirect types. Possible mechanisms of absorption and emission as well as an estimation of exciton binding energy are also discussed

Optical properties of MgH2 measured in situ in a novel gas cell for ellipsometry/spectrophotometry

The dielectric properties of alpha-MgH2 are investigated in the photon energy range between 1 and 6.5 eV. For this purpose, a novel sample configuration and experimental setup are developed that allow both optical transmission and ellipsometric measurements of a transparent thin film in equilibrium with hydrogen. We show that alpha-MgH2 is a transparent, colour neutral insulator with a band gap of 5.6 +/- 0.1 eV. It has an intrinsic transparency of about 80% over the whole visible spectrum. The dielectric function found in this work confirms very recent band structure calculations using the GW approximation by Alford and Chou [J.A. Alford and M.Y. Chou (unpublished)]. As Pd is used as a cap layer we report also the optical properties of PdHx thin films.Comment: REVTeX4, 15 pages, 12 figures, 5 table