ALBERT

Description: [1]  We have developed a new method (LRISMA: Least Residual Iterative Spectral Mixture Analysis) to semi-quantitatively determine major rock forming minerals (feldspar, pyroxene, olivine, high-silica phases and quartz) with multispectral thermal infrared data. Sub-libraries of minerals are generated from a master library of minerals based on prior knowledge to produce a suite of realistic mineral end-member combinations to fit the target spectra. Mineral abundances that correspond to the least root-mean-square (RMS) errors (best fit) generally agree best with previous petrographic studies of laboratory measured rock samples and thermal infrared hyperspectral analysis of materials on the surface of Mars, given the greatly reduced spectral range and resolution of Thermal Emission Imaging System (THEMIS). The accuracy and reproducibility of LRISMA is ~4-16% and ~5-20% respectively, while the accuracy of petrographic and previous hyperspectral studies is ~5-15% [ e . g. Feely and Christensen , 1999]. LRISMA can be applied to semi-quantitatively refine the bulk surface mineralogy of small-scale (~1 km 2 ) geologic features with high quality THEMIS spectral data (high surface temperature: 〉260 K, low atmospheric opacity: total ice 〈 0.04 and total dust 〈 0.15) with the ultimate goal of better understanding regional geologic processes.

Description: When using a special forming technology called “Die-Less Hydroforming” to create objects, due to the lack of a conventional forming tool (like a die or a punch) and depending on a particular cutting of the blank geometry, it is possible to generate some special clamping effects when inflating the seal-welded blanks. In our contribution, we present results of a study of these clamping effects in extracts, which have been investigated by means of practical inflating tests as well as numerical forming simulations using LS-DYNA with “Die-Less-Hydroforming”-samples having a special geometry that looks like a “Pac-Man”. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Author(s): M. Strebel, T.-O. Müller, B. Ruff, F. Stienkemeier, and M. Mudrich Elastic scattering cross sections are measured for lithium atoms colliding with rare-gas atoms and SF 6 molecules at tunable relative velocities down to ∼50 m/s. Our scattering apparatus combines a velocity-tunable molecular beam with a magneto-optic trap which provides an ultracold cloud of lithium ... [Phys. Rev. A 86, 062711] Published Fri Dec 21, 2012

Description: We used a suite of techniques, including those emulating compositional data sets obtained from Mars orbit and obtainable at the Mars surface, to examine aqueous alteration of basaltic rocks from Iceland as a mineralogic and geochemical analog for Noachian environments on Mars. A sample suite was collected for laboratory measurement of (1) whole-rock visible/near-infrared (VNIR) reflectance and thermal infrared (TIR) emission spectra; (2) VNIR and TIR reflectance spectra of particle-size separates derived from the bulk rock and from materials extracted from fractures/vesicles; (3) X-ray diffraction (XRD) patterns for determination of quantitative modal mineralogy; (4) major element chemistry using flux fusion of whole-rock powders; and (5) electron microprobe analyses of minerals in thin sections. Conclusions about aqueous alteration can be influenced by technique. For these basalts, whole-rock chemical data showed scant evidence for chemical fractionation, but TIR, VNIR, and XRD measurements identified distinctive assemblages of hydrous silicate minerals, differing by sample. XRD provided the most complete and accurate quantitative determination of sample mineralogy. However, VNIR spectroscopy was the technique most useful for determining composition of low-abundance smectite clays, and TIR spectroscopy was the most useful for recognizing hydrated silicates in thin surface coatings. High spatial resolution mineralogical and chemical data sets were useful for understanding the texture and distribution of alteration products and variations in fluid chemistry. No single approach provides a complete assessment of the environment of alteration, demonstrating the importance of employing multiple, synergistic mineralogical and geochemical techniques and instruments in exploration of rock strata from aqueous paleoenvironments on Mars.

Description: Author(s): Lucile Savary, Kate A. Ross, Bruce D. Gaulin, Jacob P. C. Ruff, and Leon Balents Here we establish the systematic existence of a U (1) degeneracy of all symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice, at the mean-field level. By extracting the Hamiltonian of Er 2 Ti 2 O 7 from inelastic neutron scattering measurements, we then show that the U (1)-degener... [Phys. Rev. Lett. 109, 167201] Published Mon Oct 15, 2012

Description: Author(s): J. P. C. Ruff, J.-H. Chu, H.-H. Kuo, R. K. Das, H. Nojiri, I. R. Fisher, and Z. Islam In addition to unconventional high- T c superconductivity, the iron arsenides exhibit strong magnetoelastic coupling and a notable electronic anisotropy within the a - b plane. We relate these properties by studying underdoped Ba(Fe 1 - x Co x ) 2 As 2 by x-ray diffraction in pulsed magnetic fields up to 27.5 T.... [Phys. Rev. Lett. 109, 027004] Published Wed Jul 11, 2012

Description: Density functional theory computations have been performed on the oxidations of sulfides and sulfoxides with hypochlorite ion (OCl − ), hypochlorous acid, and alkyl hypochlorites to study the mechanism of the reactions. The OCl − anion transforms sulfides to sulfoxides and sulfoxides to sulfones in oxygen transfers. The oxygen atom of QOCl hypochlorites (Q = H, Me, t -Bu) attacks at the sulfur atom of the substrates, and oxysulfonium cation intermediates are formed; the departure of the leaving Cl − is catalyzed by soft Lewis acids. The structures of the early transition states are determined by highest occupied molecular orbital–lowest unoccupied molecular orbital interactions. The sulfur compounds are the electron acceptors in the reaction with OCl − , but they are the electron donors in the reactions with QOCl. The attack of Cl − at the oxygen atom of oxysulfonium cation intermediates leads to the sulfide and QOCl precursors and can result in racemization, oxygen exchange, and reduction of oxysulfonium salts in reversible reactions. The attack of Cl − at the sulfur atom of oxysulfonium salts produces λ 4 -sulfane intermediates. Oxysulfonium cations can be transformed into sulfoxide products with the attack of Cl − or water at the α-carbon atom of the O-alkyl group. The attack of water at the sulfur atom of oxysulfonium cation leads to hydrolysis or oxygen exchange reactions. Racemization and oxygen exchange of sulfoxides proceeds in similar reactions, through the formation of hydroxysulfonium cation intermediates in acidic media in the presence of Cl − . Chlorosulfonium cations are of very high energy; their intermediacy can be ruled out in the reactions of sulfides with hypochlorites. Copyright © 2012 John Wiley & Sons, Ltd. The density functional theory calculations supported that the oxygen atom of hypochlorites attacks at the sulfur atom of sulfides and sulfoxides, resulting in the formation of oxysulfonium cation intermediates. The reactions of alkoxysulfonium cations and protonated sulfoxides with Cl − or water can lead to racemization, oxygen exchange, reduction, and hydrolysis. The intermediacy of chlorosulfonium cations of very high energy can be ruled out.

Description: Prior work has shown that probability distributions of column water vapor and several passive tropospheric chemical tracers exhibit longer-than-Gaussian (approximately exponential) tails. The tracer-advection prototypes explaining the formation of these long-tailed distributions motivate exploration of observed surface temperature distributions for non-Gaussian tails. Stations with long records in various climate regimes in National Climatic Data Center Global Surface Summary of Day observations are used to examine tail characteristics for daily average, maximum and minimum surface temperature probability distributions. Each is examined for departures from a Gaussian fit to the core (here approximated as the portion of the distribution exceeding 30% of the maximum). While the core conforms to Gaussian for most distributions, roughly half the cases exhibit non-Gaussian tails in both winter and summer seasons. Most of these are asymmetric, with a long, roughly exponential, tail on only one side. The shape of the tail has substantial implications for potential changes in extreme event occurrences under global warming. Here the change in the probability of exceeding a given threshold temperature is quantified in the simplest case of a shift in the present-day observed distribution. Surface temperature distributions with long tails have a much smaller change in threshold exceedances (smaller increases for high-side and smaller decreases for low-side exceedances relative to exceedances in current climate) under a given warming than do near-Gaussian distributions. This implies that models used to estimate changes in extreme event occurrences due to global warming should be verified regionally for accuracy of simulations of probability distribution tails.

Description: Ecology, Volume 0, Issue 0, Ahead of Print.

Description: The presence of outcrops and soil (regolith) rich in opaline silica (∼65–92 wt % SiO2) in association with volcanic materials adjacent to the “Home Plate” feature in Gusev crater is evidence for hydrothermal conditions. The Spirit rover has supplied a diverse set of observations that are used here to better understand the formation of silica and the activity, abundance, and fate of water in the first hydrothermal system to be explored in situ on Mars. We apply spectral, chemical, morphological, textural, and stratigraphic observations to assess whether the silica was produced by acid sulfate leaching of precursor rocks, by precipitation from silica-rich solutions, or by some combination. The apparent lack of S enrichment and the relatively low oxidation state of the Home Plate silica-rich materials appear inconsistent with the originally proposed Hawaiian analog for fumarolic acid sulfate leaching. The stratiform distribution of the silica-rich outcrops and their porous and brecciated microtextures are consistent with sinter produced by silica precipitation. There is no evidence for crystalline quartz phases among the silica occurrences, an indication of the lack of diagenetic maturation following the production of the amorphous opaline phase.