SO_2-rock interaction on Io: Reaction under highly oxidizing conditions

Laboratory simulations have been carried out to test the possibility that interactions of SO_2 and silicates can produce Na-S compounds which can account for the observed surface enrichment of Na relative to Si on Io. A wide variety of silicate compositions were heated under oxidizing conditions with a SO_2/O_2 = 1 gas phase at a mid-level crustal temperature for Io (1123K). All experiments produced sulfate deposits on the silicate surfaces. The nature of the sulfate changed systematically with the silicate Ca/Na ratio, with mixtures of CaSO_4 and Na-rich sulfate formed by basaltic compositions having higher Ca/Na but only alkali-rich sulfates formed for more granitic (low Ca/Na) compositions. For crystalline albite and an albite-orthoclase eutectic glass composition, K and Al-rich sulfates were formed. Assuming that burial of SO_2 to the temperatures of our experiments is plausible on Io and that somewhat less oxidizing conditions do not qualitatively change the results, SO_2-rock interactions producing Na-rich sulfates could account for the Io surface enrichment in Na. Observations on minor elements, such as K or Ca, in the atomic cloud or in magnetospheric ion spectra could be used to identify sulfates as Io surface phases and, conceivably, even define Ionian crustal magma types. Many analyses show significant S excesses which are best interpreted as due to the presence of bisulfate (HSO_4.) components, and NaHSO_4 deserves consideration as an Io surface mineral. The possibility of elemental S on Io can be regarded as a totally separate issue from the problem of the surface Na enrichment

Barley Growing

Iowa has never grown a large acreage of barley in proportion to that of oats in spite of the somewhat higher acre value of the barley crop either for feed or for market. The acreage of oats has steadily increased thruout the last 25 years, while that of barley-originally small-has gradually decreased. But as the low acre value of oats has become relatively lower, with the replacement during the past 12 years by motor power of more than one-third of all the horses in cities and on farms, farmers in increasing numbers are becoming interested in crops which may advantageously replace a part of the present large oat acreage. Apparently barley is the most promising one available for this purpose

Streetlights, augmented intelligence, and information discovery

ISSN:2504 - 185

The effect of levonorgestrel intrauterine device placement on serum CA‐125 levels in healthy premenopausal women

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135190/1/ijgo179.pd

Phase diagram analysis and crystal growth of solid solutions Ca_{1-x}Sr_xF_2

The binary phase diagram CaF$_2$--SrF$_2$ was investigated by differential thermal analysis (DTA). Both substances exhibit unlimited mutual solubility with an azeotropic point showing a minimum melting temperature of T_\mathrm{min}=1373^{\circ}$C for the composition Ca$_{0.582}$Sr$_{0.418}$F$_2$. Close to this composition, homogeneous single crystals up to 30 mm diameter without remarkable segregation could be grown by the Czochralski method.Comment: accepted for publication in J. Crystal Growt

Relict grains in CAls, revisited

Although the Type B CAI are clearly igneous rocks, they were probably not completely molten (1, 2), thus the possibility exists that preexisting materials can be recognized and characterized. Relict phases were proposed to explain high U and Th concentrations in both melilite and fassaite which would require unreasonably high partition coefficients (D} if due to crystal-liquid partitioning (3). More detailed study showed very rare perovskite grains and enigmatic Ti hot spots in melilite (4). Kuehner et al. (5) subsequently reported very high lithophile trace element contents, including actinides, for fassaite inclusions in melilite which they proposed as relict phases, but Simon et al. (6) show that the fassaite inclusions can be better explained as being the last drops of liquid crystallization. In any case, the original observations and interpretations of (3) still point to an actinide-rich relict host phase. To be able to say what levels of Ti, U, and Th in melilite can be explained by igneous partitioning, we have measured D(mel) for these elements in a synthetic CAI composition under controlled fD_2 conditions, extended down to nebular conditions by carrying out experiments in graphite crucibles in pure CO. Actinide partition coefficients are quite low: D(Th} = 0.008 and D(U) = 0.0007 (possibly a record low in measured D values). The D for trivalent U should be around 0.1-0.3 depending on Ak content as the ionic radius of U^(+3) is similar to La. Thus, for solar nebula fD_2's and CAI compositions less than 1 % of the U is trivalent. The measured D prove that igneous partitioning fails to explain the average U contents of type B CAI melilites, the difference being a factor of 600. D(Ti) is 0.018 at Ak23 and increases with Ak content. D(Ti) is relatively similar in air and at solar nebula fD_2s, surprising given the documented importance of trivalent Ti. In any case, the measured D(Ti) show that melilite Ti levels around 200-300 ppm in early crystallizing melilite can be explained by igneous partitioning, but higher levels would be indicative of resorbed Ti-rich relict phases (e.g., perovskite). To make a closer comparison ofU and Ti in CAI melilites, the fission track images of (3) have been quantitatively mapped at 20 microns resolution for two mm-sized rim and one mantle melilite. High resolution quantitative U distribution data on adjacent fassaites were also obtained. One rim grain shows several U-rich fassaites like those of(5), but the other melilites do not. There are broad U-rich regions in all grains which will be characterized in more detail. The mantle grain is especially rich in detail, but some of this may be correlated with secondary alteration. There is rough correlation ofU content and Ti in the rim grains, but the scale of the Ti analyses, based on electron probe points, is much smaller than that for U. If relict phases, e.g., perovskite, dominate the actinide distributions, they might also affect other lithophile trace elements, e.g., REE. References: (1) Wark D. (1983) thesis. (2) Stolper E. and Paque J. (1986) Geochim., Cosmochim. SO, 2159. (3) Murrell M. and Burnett D. (1987) Geochim. Cosmochim. SI, 985. (4) Johnson M., Burnett D. and Woolum D. (1988) Meteoritics 23, 276. (5) Kuehner S., Davis A. and Grossman L. (1989) Geophys. Res. Lett. 16, 775. (6) Simon S., Davis A. and Grossman L. (1990) LPSC 21, 1161

Relict Refractory Element Rich Phases in Type B CAI

Of the possible processes involved in Type B CAI history, igneous processes are the most tractable for study. Temperature and time scales inferred are commensurate with feasible laboratory simulations. We have previously reported melilite (mel) crystal liquid partition coefficients, Di, for Sm, Yb, Sr (Eu^(++) analog), and Y (Ho analog). Our data for akermanite (Ak) 30 mel compositions is in good agreement with literature data where direct/extrapolated comparisons are possible. Even allowing for significant variations in Di with progressive crystallization, comparisons of predictions for the initial (0-30%) fractional crystallization of mel with our Sr, Y contents obtained for mel cores in Allende Type B CAI, with comparable Ak contents, indicate that the natural data substantially exceed (factors of 1.5-2.5 x) those predicted. Similar results are obtained for Y, Zr in fassaite (fass) based on estimates of the Di from literature data. In this case, excesses of these trace elements are up to factors of about x 5. Thus, while the trace elements observed in natural CAI (Sr in mel and Y, Zr in fass) are in qualitative agreement with igneous partitioning, the trace element abundances are higher than quantitative predictions

The Knudsen temperature jump and the Navier-Stokes hydrodynamics of granular gases driven by thermal walls

Thermal wall is a convenient idealization of a rapidly vibrating plate used for vibrofluidization of granular materials. The objective of this work is to incorporate the Knudsen temperature jump at thermal wall in the Navier-Stokes hydrodynamic modeling of dilute granular gases of monodisperse particles that collide nearly elastically. The Knudsen temperature jump manifests itself as an additional term, proportional to the temperature gradient, in the boundary condition for the temperature. Up to a numerical pre-factor of order unity, this term is known from kinetic theory of elastic gases. We determine the previously unknown numerical pre-factor by measuring, in a series of molecular dynamics (MD) simulations, steady-state temperature profiles of a gas of elastically colliding hard disks, confined between two thermal walls kept at different temperatures, and comparing the results with the predictions of a hydrodynamic calculation employing the modified boundary condition. The modified boundary condition is then applied, without any adjustable parameters, to a hydrodynamic calculation of the temperature profile of a gas of inelastic hard disks driven by a thermal wall. We find the hydrodynamic prediction to be in very good agreement with MD simulations of the same system. The results of this work pave the way to a more accurate hydrodynamic modeling of driven granular gases.Comment: 7 pages, 3 figure