Non-Arrhenius ionic conductivities in glasses due to a distribution of activation energies

Previously observed non-Arrhenius behavior in fast ion conducting glasses [\textit{Phys.\ Rev.\ Lett.}\ \textbf{76}, 70 (1996)] occurs at temperatures near the glass transition temperature, $T_{g}$, and is attributed to changes in the ion mobility due to ion trapping mechanisms that diminish the conductivity and result in a decreasing conductivity with increasing temperature. It is intuitive that disorder in glass will also result in a distribution of the activation energies (DAE) for ion conduction, which should increase the conductivity with increasing temperature, yet this has not been identified in the literature. In this paper, a series of high precision ionic conductivity measurements are reported for $0.5{Na}_{2}{S}+0.5[x{GeS}_{2}+(1-x){PS}_{5/2}]$ glasses with compositions ranging from $0 \leq x \leq 1$. The impact of the cation site disorder on the activation energy is identified and explained using a DAE model. The absence of the non-Arrhenius behavior in other glasses is explained and it is predicted which glasses are expected to accentuate the DAE effect on the ionic conductivity.Comment: 2 figure

Mineralogy and petrography of the anomalous carbonaceous chondrites Yamato-86720, Yamato-82162, and Belgica-7904

As a part of the consortium study on antarctic meteorites with affinities to CI-chondrites we studied the samples of Yamato (Y)-86720,Y-82162,and Belgica (B)-7904. These carbonaceous chondrites are unique samples and do not perfectly fit in the traditional classification schemes. Therefore, they have to be considered as very important samples to carry distinct information about processes in the early solar system. Y-82162 is a very fine-grained carbonaceous chondrite. Based on the occurrence of abundant clasts (up to several mm in size) we suggest that this sample is a chondritic breccia. The dominating phases are phyllosilicates; abundant sulfide grains are scattered throughout the entire sample. However, the abundances of sulfides vary from clast to clast. Y-86720 contains about 13 vol% of light objects embedded in a fine-grained, phyllosilicate-rich groundmass. Some of these objects appear to be relict chondrules; however, they essentially consist of phyllosilicates. Most light, round to irregularly-shaped components exhibit well-preserved accretionary dust mantles ("dark rims") similar to those found in CM-chondrites. Y-86720 is mineralogically more closely related to the CI-chondrites than to any other chondrite group; texturally, however, it appears to be an intermediate chondrite between CI and CM as also suggested by bulk chemical criteria (G. W. KALLEMEYN; Papers Presented to the 13th symposium on Antarctic Meteorites, June 7-9,1988,Tokyo, NIPR, 132,1988). B-7904 contains 18 vol% of objects larger than about 70μm in size. 42 vol% of these components are chondrules or chondrule fragments. The most abundant constituents are, however, olivine-bearing, fragment-like objects (45.9 vol%) unknown from other chondrites. The olivines within these components are embedded in a fine-grained brownish-grey matrix. Other constituents include fine-grained CAIs, olivine aggregates, and mineral fragments. B-7904 is a new kind of carbonaceous chondrite and we do not like to classify this meteorite as a CM-type chondrite because of the following reasons : a) A great number of chondrules in B-7904 is much larger (0.5-3mm) than measured for the mean size of chondrules in CM-chondrites (0.3mm). b) Many components (olivine-bearing, fragment-like objects, Cr, Al-rich fine-grained particles) are unknown from CM-chondrites. c) The oxygen isotope composition and the low H_2O-contents are untypical for CM-chondrites

Geometry and Kinematics in the Central Broad-Line Region of a Seyfert 1 Galaxy

We recorded spectra of the highly variable Seyfert 1 galaxy Mrk110 in a variability campaign with the 9.2m Hobby-Eberly Telescope at McDonald Observatory in order to study the detailed line profile variations of the broad emission lines. Here we show that only an AGN model predicting the formation of the broad Hb line emission in the wind of an accretion disk matches the observed 2-D variability pattern. Furthermore, we derive an improved mass of the central supermassive black hole of M = 1.0(+1.0,-0.5)E7 M_sun from the Hb velocity-delay map.Comment: 4 pages, 10 figures. A&A Letters, in pres