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Sample records for brniem ar dzirdes

  1. Ar-Ar_Redux: rigorous error propagation of 40Ar/39Ar data, including covariances

    NASA Astrophysics Data System (ADS)

    Vermeesch, P.

    2015-12-01

    Rigorous data reduction and error propagation algorithms are needed to realise Earthtime's objective to improve the interlaboratory accuracy of 40Ar/39Ar dating to better than 1% and thereby facilitate the comparison and combination of the K-Ar and U-Pb chronometers. Ar-Ar_Redux is a new data reduction protocol and software program for 40Ar/39Ar geochronology which takes into account two previously underappreciated aspects of the method: 1. 40Ar/39Ar measurements are compositional dataIn its simplest form, the 40Ar/39Ar age equation can be written as: t = log(1+J [40Ar/39Ar-298.5636Ar/39Ar])/λ = log(1 + JR)/λ Where λ is the 40K decay constant and J is the irradiation parameter. The age t does not depend on the absolute abundances of the three argon isotopes but only on their relative ratios. Thus, the 36Ar, 39Ar and 40Ar abundances can be normalised to unity and plotted on a ternary diagram or 'simplex'. Argon isotopic data are therefore subject to the peculiar mathematics of 'compositional data', sensu Aitchison (1986, The Statistical Analysis of Compositional Data, Chapman & Hall). 2. Correlated errors are pervasive throughout the 40Ar/39Ar methodCurrent data reduction protocols for 40Ar/39Ar geochronology propagate the age uncertainty as follows: σ2(t) = [J2 σ2(R) + R2 σ2(J)] / [λ2 (1 + R J)], which implies zero covariance between R and J. In reality, however, significant error correlations are found in every step of the 40Ar/39Ar data acquisition and processing, in both single and multi collector instruments, during blank, interference and decay corrections, age calculation etc. Ar-Ar_Redux revisits every aspect of the 40Ar/39Ar method by casting the raw mass spectrometer data into a contingency table of logratios, which automatically keeps track of all covariances in a compositional context. Application of the method to real data reveals strong correlations (r2 of up to 0.9) between age measurements within a single irradiation batch. Propertly taking

  2. Ar-Ar ages and trapped Ar components in Martian shergottites RBT 04262 and LAR 06319

    NASA Astrophysics Data System (ADS)

    Park, Jisun; Bogard, Donald D.; Nyquist, Laurence E.; Garrison, Daniel H.; Mikouchi, Takashi

    2013-11-01

    We made 39Ar-40Ar (Ar-Ar) analyses of whole rock (WR) and mineral samples of two Martian shergottites, RBT 04262 (RBT) and LAR 06319 (LAR), in order to determine their Ar-Ar ages and the 40Ar/36Ar ratios of the trapped Martian Ar they contain. All samples released trapped (excess) 40Ar and 36Ar and suggested Ar-Ar ages older than their formation ages. Because trapped Ar components having different 40Ar/36Ar were released at different extraction temperatures, we utilized only a portion of the data to derive preferred Ar-Ar ages. We obtain Ar-Ar ages of 171 ± 8 Ma for RBT plagioclase and 163 ± 13 Ma for LAR whole rock. We identify two trapped Ar components. At low temperatures, particularly for plagioclase, Trapped-A with 40Ar/36Ar 285 ± 3 was released, and we believe this is most likely absorbed terrestrial air. At high extraction temperatures, particularly for pyroxene, Trapped-B with 40Ar/36Ar 1813 ± 127 was released. The poikilitic/non-poikilitic texture of RBT and the presence of large pyroxene oikocrysts allowed a clear definition of Trapped-B. This Ar component is Martian, and its isotopic similarity to the Martian atmospheric composition suggests that it may represent Martian atmospheric Ar incorporated into the shergottite melt via crustal rocks. Trapped-B partitioned into pyroxene at a constant molar ratio of K/36ArTr = 33.2 ± 9.5 × 106 for RBT 04262, and 80 ± 21 × 106 for LAR 06319. Trapped-A mixed in different proportions with Trapped-B could give apparently intermediate trapped 40Ar/36Ar compositions commonly observed in shergottites.

  3. Identification of excess 40Ar by the 40Ar 39Ar, age spectrum technique

    USGS Publications Warehouse

    Lanphere, M.A.; Brent, Dalrymple G.

    1976-01-01

    40Ar 39Ar incremental heating experiments on igneous plagioclase, biotite, and pyroxene that contain known amounts of excess 40Ar indicate that saddle-shaped age spectra are diagnostic of excess 40Ar in igneous minerals as well as in igneous rocks. The minima in the age spectra approach but do not reach the crystallization age. Neither the age spectrum diagram nor the 40Ar 36Ar versus 39Ar 36Ar isochron diagram reliably reveal the crystallization age in such samples. ?? 1976.

  4. Superdeformation of Ar hypernuclei

    NASA Astrophysics Data System (ADS)

    Isaka, Masahiro; Kimura, Masaaki; Hiyama, Emiko; Sagawa, Hiroyuki

    2015-10-01

    We investigate the differences in the Λ separation energies (S_Λ ) of the ground and superdeformed (SD) states in {}^{37}_Λ Ar, ^{39}_Λ Ar, and ^{41}_Λ Ar within the framework of antisymmetrized molecular dynamics (AMD). In this study, we find that the calculated S_Λ values in the SD states are much smaller than those in the ground states, unlike the result using the relativistic mean-field (RMF) calculation [B.-N. Lu et al., Phys. Rev. C, 89, 044307 (2014)]. One of the reasons for this difference between the present work and the RMF calculation is the difference in the density profile of the SD states in the core nuclei. We also find that the property of the Λ N odd-parity interaction affects the S_Λ trend between the ground and SD states.

  5. ARS Biodiesel Research Initiatives

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biodiesel activities within ARS are concerned with the production, quality, and properties of this alternative fuel from agriculturally derived fats and oils. Currently, in the absence of tax incentives, biodiesel production when using refined fats and oils and conventional alkali transesterificati...

  6. ARS Culture Collection

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The internationally recognized Agricultural Research Service (ARS) Culture Collection will be described to include the microorganisms maintained by the collection, preservation methods and worldwide distribution of cultures. The impact of the germplasm will be described to include discovery of the f...

  7. STEREO Observing AR903

    NASA Technical Reports Server (NTRS)

    2006-01-01

    A close up of loops in a magnetic active region. These loops, observed by STEREO's SECCHI/EUVI telescope, are at a million degrees K. This powerful active region, AR903, observed here on Dec. 4, 2006, produced a series of intense flares, particle storms, and coronal mass ejections over the next few days.

  8. Ar-Ar ages and thermal histories of enstatite meteorites

    NASA Astrophysics Data System (ADS)

    Bogard, Donald D.; Dixon, Eleanor T.; Garrison, Daniel H.

    2010-05-01

    Compared with ordinary chondrites, there is a relative paucity of chronological and other data to define the early thermal histories of enstatite parent bodies. In this study, we report 39Ar-40Ar dating results for five EL chondrites: Khairpur, Pillistfer, Hvittis, Blithfield, and Forrest; five EH chondrites: Parsa, Saint Marks, Indarch, Bethune, and Reckling Peak 80259; three igneous-textured enstatite meteorites that represent impact melts on enstatite chondrite parent bodies: Zaklodzie, Queen Alexandra Range 97348, and Queen Alexandra Range 97289; and three aubrites, Norton County, Bishopville, and Cumberland Falls Several Ar-Ar age spectra show unusual 39Ar recoil effects, possibly the result of some of the K residing in unusual sulfide minerals, such as djerfisherite and rodderite, and other age spectra show 40Ar diffusion loss. Few additional Ar-Ar ages for enstatite meteorites are available in the literature. When all available Ar-Ar data on enstatite meteorites are considered, preferred ages of nine chondrites and one aubrite show a range of 4.50-4.54Ga, whereas five other meteorites show only lower age limits over 4.35-4.46Ga. Ar-Ar ages of several enstatite chondrites are as old or older as the oldest Ar-Ar ages of ordinary chondrites, which suggests that enstatite chondrites may have derived from somewhat smaller parent bodies, or were metamorphosed to lower temperatures compared to other chondrite types. Many enstatite meteorites are brecciated and/or shocked, and some of the younger Ar-Ar ages may record these impact events. Although impact heating of ordinary chondrites within the last 1Ga is relatively common for ordinary chondrites, only Bethune gives any significant evidence for such a young event.

  9. 40Ar/36Ar analyses of historic lava flows

    USGS Publications Warehouse

    Dalrymple, G.B.

    1969-01-01

    The ratio 40Ar/36Ar was measured for 26 subaerial historic lava flows. Approximately one-third of the samples had 40Ar/36Ar ratios either higher or lower than the atmospheric value of 295.5 at the 95% confidence level. Excess radiogenic 40Ar in five flows ranged from about 1 ?? 10-13 to 1.5 ?? 10-12 mol/g. Possible excess 36Ar in three flows was on the order of 10-16 to 10-15 mol/g. Upper 95% confidence limits for excess 40Ar in samples with normal 40Ar/36Ar ratios are generally less than 3 ?? 10-13 mol/g. The origin of the excess 36Ar is unknown but it may be due either to the incorporation of primitive argon that has been stored in the mantle in very low potassium environments or to enrichment in 36Ar as atmospheric argon diffuses into the rocks after they cool. ?? 1969.

  10. Ar-39-Ar-40 ages of four ureilites

    NASA Technical Reports Server (NTRS)

    Bogard, D. D.; Garrison, D. H.

    1994-01-01

    Ureilites Novo Urei, Havero, and Kenna show strong evidence of one or more Ar-40 degassing events in the time period of 3.3-4.1 Ga ago. These ages may be compared to current interpretations of ureilite chronology. These include the suggestion of metasomatic activity on the parent body 3.7 Ga ago that reset some Sm-Nd ages and the suggestion that ureilites have experienced terrestrial contamination of several trace elements (including Pb and LREE), which makes suspect ages younger than approximately 4.5 Ga. Because the K-Ar chronometer can be sensitive to metamorphic events, we made Ar-39-Ar-40 determinations on bulk samples (0.12-0.14 g each) of four ureilites. The Ar-39-Ar-40 age spectra and K/Ca ratios as a function of cumulative Ar release from stepwise temperature extractions for the four ureilites analyzed are shown. Because Ar-39-Ar-40 ages shown by low and high temperature extractions may be suspect, we examined the intermediate temperature extractions. Although interpretation of these spectra is obviously uncertain, we believe that the most recent times of Ar degassing can be roughly inferred. These times are approximately 3.3 Ga for Havero, 3.3-3.7 Ga for Novo Urei, and approximately 4.1 Ga for Kenna, for which Ar degassing may not have been complete. The indication of Ar-39-Ar-40 degassing ages of 3.3-4.1 Ga for three ureilites that also contain an enhanced LREE component and (excepting Havero) produce a 3.74 Ga Sm-Nd age, suggests that both chronometers may have responded to the same parent body event. On the other hand, it is also possible that the Ar data reflect one or more separate events that did not strongly affect the Sm-Nd system, a situation that commonly occurs in eucrites. Thus the existence of reset Ar ages does not require similarly reset Sm-Nd ages.

  11. AR-39-AR-40 "Age" of Basaltic Shergottite NWA-3171

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Park, Jisun

    2007-01-01

    North-West-Africa 3171 is a 506 g, relatively fresh appearing, basaltic shergottite with similarities to Zagami and Shergotty, but not obviously paired with any of the other known African basaltic shergottites. Its exposure age has the range of 2.5-3.1 Myr , similar to those of Zagami and Shergotty. We made AR-39-AR-40 analyses of a "plagioclase" (now shock-converted to maskelynite) separate and of a glass hand-picked from a vein connected to shock melt pockets.. Plagioclase was separated using its low magnetic susceptibility and then heavy liquid with density of <2.85 g/cm(exp 3). The AR-39-AR-40 age spectrum of NWA-317 1 plag displays a rise in age over 20-100% of the 39Ar release, from 0.24 Gyr to 0.27 Gy.

  12. A metrological approach to measuring 40Ar* concentrations in K-Ar and 40Ar/39Ar mineral standards

    NASA Astrophysics Data System (ADS)

    Morgan, Leah E.; Postma, Onno; Kuiper, Klaudia F.; Mark, Darren F.; van der Plas, Wim; Davidson, Stuart; Perkin, Michael; Villa, Igor M.; Wijbrans, Jan R.

    2011-10-01

    In geochronology, isotopic ages are determined from the ratio of parent and daughter nuclide concentrations in minerals. For dating of geological material using the K-Ar system, the simultaneous determination of 40Ar and 40K concentrations on the same aliquot is not possible. Therefore, a widely used variant, the 40Ar/39Ar technique, involves the production of 39Ar from 39K by neutron bombardment and the reliance on indirect natural calibrators of the neutron flux, referred to as "mineral standards." Many mineral standards still in use rely on decades-old determinations of 40Ar concentrations; resulting uncertainties, both systematic and analytical, impede the determination of higher accuracy ages using the K-Ar decay system. We discuss the theoretical approach and technical design of a gas delivery system which emits metrologically traceable amounts of 40Ar and will allow for the sensitivity calibration of noble gas mass spectrometers. The design of this system is based on a rigorous assessment of the uncertainty budget and detailed tests of a prototype system. A number of obstacles and proposed resolutions are discussed along with the selection of components and their integration into a pipette system.

  13. Comparison of conventional K-Ar and 40Ar/39Ar dating of young mafic volcanic rocks

    USGS Publications Warehouse

    Lanphere, M.A.

    2000-01-01

    K-Ar and 40Ar/39Ar ages have been measured on nine mafic volcanic rocks younger than 1 myr from the Snake River Plain (Idaho), Mount Adams (Washington), and Crater Lake (Oregon). The K-Ar ages were calculated from Ar measurements made by isotope dilution and K2O measurements by flame photometry. The 40Ar/39Ar ages are incremental-heating experiments using a low-blank resistance-heated furnace. The results indicate that high-quality ages can be measured on young, mafic volcanic rocks using either the K-Ar or the 40Ar/39Ar technique. The precision of an 40Ar/39Ar plateau age generally is better than the precision of a K-Ar age because the plateau age is calculated by pooling the ages of several gas increments. The precision of a plateau age generally is better than the precision of an isotope correlation (isochron) age for the same sample. For one sample the intercept of the isochron yielded an 40Ar/36Ar value significantly different from the atmospheric value of 295.5. Recalculation of increment ages using the isochron intercept for the composition of nonradiogenic Ar in the sample resulted in much better agreement of ages for this sample. The results of this study also indicate that, given suitable material and modern equipment, precise K-Ar and 40Ar/39Ar ages can be measured on volcanic rocks as young as the latest Pleistocene, and perhaps even the Holocene.

  14. Neutron-hole states in 45Ar from 1H(46Ar, d) 45Ar reactions

    NASA Astrophysics Data System (ADS)

    Lu, F.; Lee, Jenny; Tsang, M. B.; Bazin, D.; Coupland, D.; Henzl, V.; Henzlova, D.; Kilburn, M.; Lynch, W. G.; Rogers, A. M.; Sanetullaev, A.; Sun, Z. Y.; Youngs, M.; Charity, R. J.; Sobotka, L. G.; Famiano, M.; Hudan, S.; Horoi, M.; Ye, Y. L.

    2013-07-01

    To improve the effective interactions in the pf shell, it is important to measure the single-particle and single-hole states near the N = 28 shell gap. In this paper, the neutron spectroscopic factors of hole states from the unstable neutron-rich 45Ar (Z = 18,N = 27) nucleus have been studied using the 1H(46Ar,d) 45Ar transfer reaction in inverse kinematics. Comparison of our results with the particle states of 45Ar produced in 2H(44Ar, p) 45Ar reaction shows that the two reactions populate states with different angular momenta. Using the angular distributions, we are able to confirm the spin assignments of four low-lying states of 45Ar. These are the ground state (f7/2), the first-excited state (p3/2), and the s1/2 and d3/2 states. While large basis shell-model predictions describe spectroscopic properties of the ground and p3/2 states very well, they fail to describe the s1/2 and d3/2 hole states.

  15. Pulsed discharge production Ar* metastables

    NASA Astrophysics Data System (ADS)

    Han, Jiande; Heaven, Michael C.; Emmons, Daniel; Perram, Glen P.; Weeks, David E.; Bailey, William F.

    2016-03-01

    The production of relatively high densities of Ar* metastables (>1012 cm-3) in Ar/He mixtures, at total pressures close to 1 atm, is essential for the efficient operation of an optically pumped Ar* laser. We have used emission spectroscopy and diode laser absorption spectroscopy measurements to observe the production and decay of Ar* in a parallel plate pulsed discharge. With discharge pulses of 1 μs duration we find that metastable production is dominated by processes occurring within the first 100 ns of the gas break-down. Application of multiple, closely spaced discharge pulses yields insights concerning conditions that favor metastable production. This information has been combined with time-resolved measurements of voltage and current. The experimental results and preliminary modeling of the discharge kinetics are presented.

  16. Ar-39-Ar-40 Ages of Two Nakhlites, MIL03346 and Y000593: A Detailed Analysis

    NASA Technical Reports Server (NTRS)

    Park, Jisun; Garrison, Daniel; Bogard, Donald

    2007-01-01

    Radiometric dating of martian nakhlites by several techniques have given similar ages of approx.1.2-1.4 Ga [e.g. 1, 2]. Unlike the case with shergottites, where the presence of martian atmosphere and inherited radiogenic Ar-40 produce apparent Ar-39-Ar-40 ages older than other radiometric ages, Ar-Ar ages of nakhlites are similar to ages derived by other techniques. However, even in some nakhlites the presence of trapped martian Ar produces some uncertainty in the Ar-Ar age. We present here an analysis of such Ar-Ar ages from the MIL03346 and Y000593 nakhlites.

  17. Ar-Ar Age of Shergottite Dhofar 378: Formation or Early Shock Event?

    NASA Technical Reports Server (NTRS)

    Park, J.; Bogard, Don D.

    2006-01-01

    The Ar-39-Ar40 data for 16 stepwise temperature extractions of mixed mesostasis plus plagioclase show the following major characteristics. Changes in the K/Ca ratio and in the differential rate of Ar-39 release with extraction temperature suggest three distinct, but overlapping Ar diffusion domains: <13%, 13-45%, and >45% cumulative Ar-39 release:. The youngest Ar-Ar age, approx.162-165 Myr is observed at approx.28-40% Ar-39 release, which we attribute primarily to the mesostasis. Extractions releasing >45% Ar-39, probably from plagioclase, suggest older Ar-Ar ages and indicate release of trapped martian Ar-40. An isochron plot for 8 extractions, releasing 3-45% of the Ar-39 and corrected for 36Arcos using directly measured 36Arcos, gives an Ar-Ar age of 143+/-4 Myr (where the +/- ignores the uncertainty in applying a correction for Ar-36cos). Applying a correction assuming only one-half of the measured Ar-36cos gives an age of 159+/-2 Myr. Correcting for cos-Ar-36 using the minimum measured Ar-36/Ar-37 ratio gives a minimum possible age of 138+/-5 Myr. All of these ages are within combined uncertainties of the Sm-Nd age of 157+/-24 Myr [4]. The trapped Ar-40/Ar-36 ratio obtained from the isochron is largely defined by the highest [K] data.

  18. NeAr Dating: New Dimensions for Ar-Ar Dating Using Nucleogenic Neon Isotopes

    NASA Astrophysics Data System (ADS)

    Hall, C. M.

    2007-12-01

    The neutron reactions that produce 37Ar from Ca, 38Ar from Cl and 39Ar from K form the very heart of the 40Ar/39Ar dating system. Not only can ages be derived, but much can be deduced from the effective mineral separation performed by step-heating analysis. However, the normal suite of elements detected using Ar isotopes cannot determine the presence of some minerals. Specifically, the absence of Na means that it is not possible in principle to uniquely determine the compositions of degassing feldpsars and the inability to measure Mg limits the discrimination of some mafic phases. Mineral and glass samples of known composition have been irradiated to determine the important nucleogenic Ne isotopes produced from F, Na and Mg. Mg produces two isotopes from the reactions 24Mg(n,α)21Ne and 25Mg(n,α)22Ne, with a production ratio for (22Ne/21Ne)Mg of about 0.25. For Na, the important reactions are 23Na(n,α)20F(β-)20Ne with a production ratio for (20Ne/22Ne)Na of about 5.3. The thermal neutron reaction for F is 19F(n,γ)20F(β-)20Ne with (20Ne)F/(39Ar)K equal to about 1.1. Because there are only 3 isotopes and 4 end member isotopic compositions, it is not possible to uniquely deconvolve the above nucleogenic sources along with atmospheric Ne. Fortunately, most unirradiated minerals analyzed have had extremely low levels of atmospheric Ne. A maximal correction for atmospheric Ne can be done assuming an atmospheric 20Ne/36Ar ratio. Measuring Ne isotopes along with Ar isotopes is challenging, requiring extra time and cryo-separation of the two species. In addition, there are unresolved issues dealing with the relative rates of Ne and Ar diffusion and Ne recoil effects. However, there is promise for the method for all whole-rock samples, amphiboles, feldspars and any mineral with expected complex exsolution textures. Examples of a variety of Ne-enhanced argon age spectra will be shown.

  19. REGISTRATION OF BIRDSFOOT TREFOIL GERMPLASM ARS-2622

    Technology Transfer Automated Retrieval System (TEKTRAN)

    ARS-2622 broadleafed birdsfoot trefoil (Lotus corniculatus L.) germplasm was released by the USDA-ARS in cooperation with the Missouri Agricultural Experiment Station in August 2002. The merit of ARS-2622 is that it is a rhizome producing population with a broad genetic base. ARS-2622 was developed ...

  20. ARS Grape Quality Research Update

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In ARS much of the research on grape quality is overseen by National Program 306, entitled Quality Preservation, Characterization and Enhancement and New Processes, New Uses and Value-Added Foods. The mission of the Processed Foods Research Unit at the Western Regional Research Center in Albany, CA...

  1. USDA-ARS Quartlerly News

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This quarterly article is an update of research going on at The USDA-ARS Thad Cochran Southern Horticultural Laboratory in Poplarville, MS to be published in the Louisiana Nursery and Landscape Associations (LANLA) quarterly newsletter. This is one of three publications that I am sending out to the ...

  2. Oldest human footprints dated by Ar/Ar

    NASA Astrophysics Data System (ADS)

    Scaillet, Stéphane; Vita-Scaillet, Grazia; Guillou, Hervé

    2008-11-01

    Fossilized human trackways are extremely rare in the geologic record. These bear indirect but invaluable testimony of human/hominid locomotion in open air settings and can provide critical information on biomechanical changes relating to bipedalism evolution throughout the primitive human lineage. Among these, the "Devil's footsteps" represent one of the best preserved human footprints suite recovered so far in a Pleistocene volcanic ash of the Roccamonfina volcano (southern Italy). Until recently, the age of these footprints remained speculative and indirectly correlated with a loosely dated caldera-forming eruption that produced the Brown Leucitic Tuff. Despite extensive hydrothermal alteration of the pyroclastic deposit and variable contamination with excess 40Ar, detailed and selective 40Ar/ 39Ar laser probe analysis of single leucite crystals recovered from the ash deposit shows that the pyroclastic layer and the footprints are 345 ± 6 kyr old (1 σ), confirming for the first time that these are the oldest human trackways ever dated, and that they were presumably left by the modern human predecessor, Homo heidelbergensis, close to Climatic Termination IV.

  3. Resolvable miscalibration of the 40Ar/39Ar geochronometer

    NASA Astrophysics Data System (ADS)

    Mundil, R.; Renne, P. R.; Min, K. K.; Ludwig, K. R.

    2006-12-01

    U/Pb and 40Ar/39Ar isotopic dating techniques are the most widely applied geochronometers, both capable of 0.1% internal precision. A robust intercalibration between the two isotopic systems is fundamental for reconstructing short term processes and events in geologic time. However, whereas the U decay constants are known precisely (to ca 0.1%), the currently used 40K decay constant (5.543×10^{-10}/yr, (1)) is associated with an unstated uncertainty that is about an order of magnitude larger than the former, making high-resolution comparisons of ages from the two isotopic systems impossible. We present an indirect calibration by comparing radio-isotopic ages derived from both isotopic systems of rapidly cooled volcanic rocks in order to minimize effects from protracted cooling history. Eleven data pairs of 206Pb/238U and conventional 40Ar/39Ar ages exhibit a bias between the two isotopic systems ranging from >-1.5% for young rocks to ca -0.5% for rocks as old as 2 Ga (possibly even smaller for rocks >2 Ga), with the 40Ar/39Ar ages being consistently younger. All Mesozoic and Paleozoic samples display a bias of about -1%. Most of this bias is probably the result of miscalibration of the electron capture decay constant of 404→ 40Ar (λ40Kec) by ca -1%, in combination with a miscalibration of smaller magnitude and opposite sense of the β- decay constant (λ40Kβ-) of 40K→ 40Ca. Bias greater than 1% for younger Cenozoic samples probably reflects pre-eruptive zircon saturation (magma residence time) whose effects become proportionately negligible beyond ca. 200 Ma. Whereas the currently used decay constant for 40K (see above) is based on an arguably arbitrary selection from counting experiments associated with large and sometimes incomprehensible uncertainties (mostly from experiments conducted in the 1940s to 1960s) two recent recalibrations of λ40Ktotal using liquid scintillation counting techniques suggest precise and mutually consistent values of 5.553 ± 0

  4. CEAP ARS watershed assessment study - overview

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The symposium “Conservation Effects Assessment Project: Accomplishments from USDA-ARS Benchmark Watersheds” will illustrate the opportunities for ARS research accomplishments to support conservation policy. Specifically, their long-term databases provide scientific bases for regional assessment outc...

  5. arXiv.org and Physics Education

    ERIC Educational Resources Information Center

    Ramlo, Susan

    2007-01-01

    The website arXiv.org (pronounced "archive") is a free online resource for full-text articles in the fields of physics, mathematics, computer science, nonlinear science, and quantitative biology that has existed for about 15 years. Available directly at http://www.arXiv.org, this e-print archive is searchable. As of Jan. 3, 2007, arXiv had open…

  6. 40Ar-39Ar Analyses of Antarctic Dust Particles

    NASA Astrophysics Data System (ADS)

    Knott, S. F.; Turner, G.; Maurette, M.

    1993-07-01

    Eleven particles from the 100-400-micrometer-sized fraction of a sample of dust (vial G1-35) retrieved from Antarctica early in 1991 [1] have been analyzed using high-sensitivity noble gas mass spectrometry and, where possible, SEM/EDX techniques. The bulk sample was possibly heavily contaminated with terrestrial material but an attempt was made to preselect angular unmelted grains of extraterrestrial origin. Particles were examined optically and then split, where possible, into three parts to provide samples for 40Ar-39Ar, SEM, and He isotope analysis. Samples for 40Ar-39Ar studies were irradiated in the University of Michigan reactor, where they received a fast neutron fluence of approximately 10^18 cm^-2 (J = 0.0097, beta = 3.16). SEM analyses indicated that three particles (SK64, SK69, and SK72) have chondritic compositions, while a fourth (SK71) was thought to be extraterrestrial on the basis of its morphology. Two particles (SK65 and SK73) appeared to be terrestrial based on their location on an Mg-Fe-Si plot [2]. No SEM analyses are available for five of the samples (SK63, SK66, SK67, SK70, and SK71), and their origins are unknown. Gas was extracted from the samples for the argon analyses using a pulsed Nd laser. Step-heating was performed on each particle by defocusing the laser beam to reduce the heating effect. The laser delivered about 200 mJ per pulse; the initial heating was done with the beam covering approximately 150 micrometers. A broad overview of the data from nine particles analyzed in a seven-day sequence is shown in Fig. 1. Gas release, in units of 10^-12 ccSTP, is plotted as a function of run number with sample analyses interspersed with system blanks. Only two terrestrial particles, with well-defined ages of 200 Ma and 1000 Ma, released large amounts of gas and are omitted from the plot. The remaining particles analyzed so far released very little 40Ar and contrast sharply with the much larger amounts observed by Saxton et al. [3] in a suite

  7. ARS-NLT-SALT AND ARS-NLT-SALT/B SALINE TOLERANT NARROW LEAF TREFOIL GERMPLASM

    Technology Transfer Automated Retrieval System (TEKTRAN)

    ARS-NLT-SALT and ARS-NLT-SALT/B are narrow leaf trefoil germplasm that are tolerant of saline germination conditions that were developed from the broad based narrow leaf trefoil germplasm ARS-1207 using two cycles of saline condition selection during seed germination. ARS-NLT-SALT was developed usin...

  8. Age measurements of potassium-bearing sulfide minerals by the 40Ar/39Ar technique

    USGS Publications Warehouse

    Czamanske, G.K.; Lanphere, M.A.; Erd, Richard C.; Blake, M.C., Jr.

    1978-01-01

    K-Ar ages have been determined for sulfide minerals for the first time. The occurrence of adequate amounts of potassium-bearing sulfides with ideal compositions K3Fe10S14 (???10 wt.% K) and KFe2S3 (???16 wt.% K) in samples from a mafic alkalic diatreme at Coyote Peak, California, prompted an attempt to date these materials. K3Fe10S14, a massive mineral with conchoidal fracture, gives an age of 29.4 ?? 0.5 m.y. (40Ar/39Ar), indistinguishable from the 28.3 ?? 0.4 m.y. (40Ar/39Ar) and 30.2 ?? 1.0 m.y.8 (conventional K-Ar) ages obtained for associated phlogopite (8.7 wt.% K). KFe2S3, a bladed, fibrous sulfide, gives a younger age, 26.5 ?? 0.5 m.y. (40Ar/39Ar), presumably owing to Ar loss. ?? 1978.

  9. 40Ar/39Ar Interlaboratory Calibration into the Holocene.

    NASA Astrophysics Data System (ADS)

    Heizler, M. T.; Jicha, B.; Koppers, A. A. P.; Miggins, D. P.

    2015-12-01

    Advances in 40Ar/39Ar analytical precision for very young rocks requires collaborative efforts amongst argon geochronology labs to demonstrate age reproducibility commensurate with high precision. NM Tech (NMT), the University of Wisconsin (UW) and Oregon State University (OSU) have each dated Quaternary flux monitor standard AC-2 sanidine (~1.185 Ma), a blind sanidine described as being 50-100 ka (BS) and sanidine from the Qixiangshan (QIX) flow (~10 ka), Changbaishan volcano, China. The samples were irradiated in a single package with FC-2 sanidine (28.201 Ma) as the flux monitor and the irradiated material was distributed amongst the labs. Heizler was present during analysis at both OSU and UW and Jicha attended OSU during analysis. Physical presence was key towards gaining understanding of individual protocols and prompted valuable discussions. Analyses were carried out on single crystals using total fusion and/or step heating approaches. Age agreement was achieved within 2s uncertainty that ranged between (0.03-0.3%, 0.13-0.37% and 1.8-2.6%) for AC-2, BS and QIX, respectively. Each lab found AC-2 to vary somewhat beyond a normal distribution and to yield an age relative to FC-2 of ~1.185 Ma that is ~1.3% (~5-10 sigma) lower than some published estimates. A key cause of the variation between this study and previous results may be variable gas pressure equilibration times between extraction line and mass spectrometer coupled with variable choices to estimate time zero by other laboratories. The majority of our efforts concentrated on the QIX sanidine where prior data obtained by our labs revealed a factor of two spread in age (~11 and 23 ka) based on experiments carried out by total fusion and bulk incremental heating. By conducting single crystal age spectrum analysis we were able to mitigate effects of melt inclusion hosted excess argon and xenocrystic contamination towards obtaining analytical agreement with apparent ages near 10 ka. However, philosophical

  10. 39Ar-40Ar Dating of Thermal Events on Meteorite Parent Bodies

    NASA Astrophysics Data System (ADS)

    Bogard, D. D.; Garrison, D. H.

    1999-03-01

    A summary of 39Ar-40Ar ages reveals the impact and thermal history of several meteorite parent bodies, i.e., eucrites, chondrites, mesosiderites, acapulcoites/lodranites, winonaites, enstatites, and IAB and IIE irons.

  11. The Chelyabinsk Meteorite: Variable Shock Effects Recorded by the 40Ar-39Ar System

    NASA Astrophysics Data System (ADS)

    Korochantseva, E. V.; Buikin, A. I.; Hopp, J.; Lorenz, C. A.; Trieloff, M.

    2015-07-01

    Shocked lithologies of the Chelyabinsk LL chondrite have higher apparent 40Ar-39Ar ages than the very young light lithology. We interpret previous impact events made shocked lithologies more retentive and resistant against thermal reset.

  12. First-principles calibration of 40Ar/39Ar mineral standards and complete extraction of 40Ar* from sanidine

    NASA Astrophysics Data System (ADS)

    Morgan, L. E.; Kuiper, K.; Mark, D.; Postma, O.; Villa, I. M.; Wijbrans, J. R.

    2010-12-01

    40Ar/39Ar geochronology relies on comparing argon isotopic data for unknowns to those for knowns. Mineral standards used as neutron fluence monitors must be dated by the K-Ar method (or at least referenced to a mineral of known K-Ar age). The commonly used age of 28.02 ± 0.28 Ma for the Fish Canyon sanidine (FCs) (Renne et al., 1998) is based upon measurements of radiogenic 40Ar in GA1550 biotite (McDougall and Roksandic, 1974), but underlying full data were not published (these measurements were never intended for use as an international standard), so uncertainties are difficult to assess. Recent developments by Kuiper et al. (2008) and Renne et al. (2010) are limited by their reliance on the accuracy of other systems. Modern technology should allow for more precise and accurate calibration of primary K-Ar and 40Ar/39Ar standards. From the ideal gas law, the number of moles of 40Ar in a system can be calculated from measurements of pressure, volume, and temperature. Thus we have designed and are proceeding to build a pipette system to introduce well-determined amounts of 40Ar into noble gas extraction lines and mass spectrometers. This system relies on components with calibrations traceable to SI unit prototypes, including a diaphragm pressure gauge (MKS Instruments), thermocouples, and a “slug” of an accurately determined volume to be inserted into the reservoir for volume determinations of the reservoir and pipette. The system will be renewable, with a lifetime of ca. 1 month for gas in the reservoir, and portable, to permit interlaboratory calibrations. The quantitative extraction of 40Ar* from the mineral standard is of highest importance; for sanidine standards this is complicated by high melt viscosity during heating. Experiments adding basaltic “zero age glass” (ZAG) to decrease melt viscosity are underway. This has previously been explored by McDowell (1983) with a resistance furnace, but has not been quantitatively addressed with laser heating

  13. Ion kinetics in Ar/H2 cold plasmas: the relevance of ArH+

    PubMed Central

    Jiménez-Redondo, Miguel; Cueto, Maite; Doménech, José Luis; Tanarro, Isabel; Herrero, Víctor J.

    2015-01-01

    The recent discovery of ArH+ in the interstellar medium has awakened the interest in the chemistry of this ion. In this work, the ion-molecule kinetics of cold plasmas of Ar/H2 is investigated in glow discharges spanning the whole range of [H2]/([H2]+[Ar]) proportions for two pressures, 1.5 and 8 Pa. Ion concentrations are determined by mass spectrometry, and electron temperatures and densities, with Langmuir probes. A kinetic model is used for the interpretation of the results. The selection of experimental conditions evinces relevant changes with plasma pressure in the ion distributions dependence with the H2 fraction, particularly for the major ions: Ar+, ArH+ and H3+. At 1.5 Pa, ArH+ prevails for a wide interval of H2 fractions: 0.3<[H2]/([H2]+[Ar])<0.7. Nevertheless, a pronounced displacement of the ArH+ maximum towards the lowest H2 fractions is observed at 8 Pa, in detriment of Ar+, which becomes restricted to very small [H2]/([H2]+[Ar]) ratios, whereas H3+ becomes dominant for all [H2]/([H2]+[Ar]) > 0.1. The analysis of the data with the kinetic model allows the identification of the sources and sinks of the major ions over the whole range of experimental conditions sampled. Two key factors turn out to be responsible for the different ion distributions observed: the electron temperature, which determines the rate of Ar+ formation and thus of ArH+, and the equilibrium ArH+ + H2 ⇄ H3+ + Ar, which can be strongly dependent of the degree of vibrational excitation of H3+. The results are discussed and compared with previously published data on other Ar/H2 plasmas. PMID:26702354

  14. Re-Evaluation of Ar-39 - Ar-40 Ages for Apollo Lunar Rocks 15415 and 60015

    NASA Technical Reports Server (NTRS)

    Park, J.; Nyquist, L. E.; Bogard, D. D.; Garrison, D. H.; Shih, C.-Y.

    2010-01-01

    We re-analyzed 39Ar-40Ar ages of Apollo lunar highland samples 15415 and 60015, two ferroan anorthosites analyzed previously in the 1970 s, with a more detailed approach and with revised decay constants. From these samples we carefully prepared 100-200 mesh mineral separates for analysis at the Noble Gas Laboratory at NASA-Johnson Space Center. The Ar-39-Ar-40 age spectra for 15415 yielded an age of 3851 +/- 38 Ma with 33-99% of Ar39 release, roughly in agreement with previously reported Ar-Ar ages. For 60015, we obtained an age of 3584 +/- 152 Ma in 23-98% of Ar39 release, also in agreement with previously reported Ar-Ar ages of approximately 3.5 Ga. Highland anorthosites like these are believed by many to be the original crust of the moon, formed by plagioclase floatation atop a magma ocean, however the Ar-Ar ages of 15415 and 60015 are considerably younger than lunar crust formation. By contrast, recently recovered lunar anorthosites such as Dhofar 489, Dhofar 908, and Yamato 86032 yield older Ar-Ar ages, up to 4.35 Ga, much closer to time of formation of the lunar crust. It follows that the Ar-Ar ages of the Apollo samples must have been reset by secondary heating, and that this heating affected highland anorthosites at both the Apollo 15 and Apollo 16 landing sites but did not affect lunar highland meteorites. One obvious consideration is that while the Apollo samples were collected from the near side of the moon, these lunar meteorites are thought to have originated from the lunar far side

  15. 40Ar/39Ar age spectra of some undisturbed terrestrial samples

    USGS Publications Warehouse

    Brent, Dalrymple G.; Lanphere, M.A.

    1974-01-01

    40Ar/39Ar age spectra and 40Ar/36Ar vs 39Ar/36Ar isochrons were determined by incremental heating for 11 terrestrial rocks and minerals whose geology indicates that they represent essentially undisturbed systems. The samples include muscovite, biotite, hornblende, sanidine, plagioclase, dacite, diabase and basalt and range in age from 40 to 1700 m.y. For each sample, the 40Ar/39Ar ratios, corrected for atmospheric and neutron-generated argon isotopes, are the same for most of the gas fractions released and the age spectra, which show pronounced plateaus, thus are consistent with models previously proposed for undisturbed samples. Plateau ages and isochron ages calculated using plateau age fractions are concordant and appear to be meaningful estimates of the crystallization and cooling ages of these samples. Seemingly anomalous age spectrum points can be attributed entirely to small amounts of previously unrecognized argon loss and to gas fractions that contain too small (less than 2 per cent) a proportion of the 39Ar released to be geologically significant. The use of a quantitative abscissa for age spectrum diagrams is recommended so that the size of each gas fraction is readily apparent. Increments containing less than about 4-5 per cent of the total 39Ar released should be interpreted cautiously. Both the age spectrum and isochron methods of data reduction for incremental heating experiments are worthwhile, as each gives slightly different but complementary information about the sample from the same basic data. Use of a least-squares fit that allows for correlated errors is recommended for 40Ar/36Ar vs 39Ar/36Ar isochrons. The results indicate that the 40Ar/39Ar incremental heating technique can be used to distinguish disturbed from undisturbed rock and mineral systems and will be a valuable geochronological tool in geologically complex terranes. ?? 1994.

  16. Ar-Ar Age of NWA-1460 and Evidence For Young Formation Ages of the Shergottites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Park, Jisun

    2006-01-01

    Agreement of Ar-Ar, Sm-Nd, and Rb-Sr ages for NWA1460, and the inconsistency between a low shock-heating temperature for Zagami and the proposition that a 4.0 Gyr-old Zagami lost most of its Ar-40 are inconsistent with ancient formation ages for these shergottites, but are consistent with relatively young igneous formation ages.

  17. 244-AR Vault Interim Stabilization Project Plan

    SciTech Connect

    LANEY, T.

    2000-03-24

    The 244-AR Vault Facility, constructed between 1966 and 1968, was designed to provide lag storage and treatment for the Plutonium-Uranium Extraction Facility (PUREX) tank farm sludges. Tank farm personnel transferred the waste from the 244-AR Vault Facility to B Plant for recovery of cesium and strontium. B Plant personnel then transferred the treatment residuals back to the tank farms for storage of the sludge and liquids. The last process operations, which transferred waste supporting the cesium/strontium recovery mission, occurred in April 1978. After the final transfer in 1978, the 244-AR facility underwent a cleanout. However, 2,271 L (600 gal) of sludge were left in Tank 004AR from an earlier transfer from Tank 241-AX-104. When the cleanout was completed, the facility was placed in a standby status. The sludge had been transferred to Tank 004AR to support Pacific Northwest National Laboratory [PNNL] vitrification work. Documentation of waste transfers suggests that a portion of the sludge may have been moved from Tank 004AR to Tank 002AR in preparation for transfer back to the AX Tank Farm; however, quantities of the sludge that were moved to Tank 002AR from that transfer must be estimated.

  18. USDA/ARS Organic Production Research

    Technology Transfer Automated Retrieval System (TEKTRAN)

    For much of its history, USDA/ARS had little to do with research on organic agriculture, however research in organic systems has made considerable gains at the agency over the past decade. In the 1980's and 1990's, as the organic food industry was taking off, ARS researchers who wanted to serve orga...

  19. The effect of SEM imaging on the Ar/Ar system in feldspars

    NASA Astrophysics Data System (ADS)

    Flude, S.; Sherlock, S.; Lee, M.; Kelley, S. P.

    2010-12-01

    Complex microtextures form in K-feldspar crystals as they cool and are affected by deuteric alteration. This complex structure is the cause of variable closure temperatures for Ar-Ar, a phenomenon which has been utilized in multi domain diffusion (MDD) modelling to recover thermal histories [1]. However, there has been substantial controversy regarding the precise interaction between feldspar microtextures and Ar-diffusion [2,3]. A number of studies have addressed this issue using coupled SEM imaging and Ar/Ar UV laser ablation microprobe (UV-LAMP) analysis on the same sample, to enable direct comparison of microtextures with Ar/Ar age data [4]. Here we have tested the idea that SEM work may affect Ar/Ar ages, leading to inaccurate results in subsequent Ar/Ar analyses. Three splits of alkali feldspar from the Dartmoor Granite in SW England were selected for Ar/Ar UV-LAMP analysis. Split 1 (“control”) was prepared as a polished thick section for Ar/Ar analysis. Split 2 (“SEM”) was prepared as a polished thick section, was chemically-mechanically polished with colloidal silica and underwent SEM imaging (uncoated) and focussed ion beam (FIB) milling (gold coated); electron beam damage in the SEM was maximised by leaving the sample at high magnification for eight minutes. Split 3 (“Etch”) is a cleavage fragment that was etched with HF vapour and underwent low to moderate magnification SEM imaging. The control split gave a range of laser-spot ages consistent with the expected cooling age of the granite and high yields of radiogenic 40Ar* (>90%). The area of the “SEM” split that experienced significant electron beam damage gave younger than expected ages and 40Ar* yields as low as 57%. These are interpreted as a combination of implantation of atmospheric Ar and local redistribution of K within the sample. The area of “SEM” that underwent FIB milling gave ages and 40Ar* yields comparable to the control split, suggesting that the Au-coat minimises FIB

  20. Revised error propagation of 40Ar/39Ar data, including covariances

    NASA Astrophysics Data System (ADS)

    Vermeesch, Pieter

    2015-12-01

    The main advantage of the 40Ar/39Ar method over conventional K-Ar dating is that it does not depend on any absolute abundance or concentration measurements, but only uses the relative ratios between five isotopes of the same element -argon- which can be measured with great precision on a noble gas mass spectrometer. The relative abundances of the argon isotopes are subject to a constant sum constraint, which imposes a covariant structure on the data: the relative amount of any of the five isotopes can always be obtained from that of the other four. Thus, the 40Ar/39Ar method is a classic example of a 'compositional data problem'. In addition to the constant sum constraint, covariances are introduced by a host of other processes, including data acquisition, blank correction, detector calibration, mass fractionation, decay correction, interference correction, atmospheric argon correction, interpolation of the irradiation parameter, and age calculation. The myriad of correlated errors arising during the data reduction are best handled by casting the 40Ar/39Ar data reduction protocol in a matrix form. The completely revised workflow presented in this paper is implemented in a new software platform, Ar-Ar_Redux, which takes raw mass spectrometer data as input and generates accurate 40Ar/39Ar ages and their (co-)variances as output. Ar-Ar_Redux accounts for all sources of analytical uncertainty, including those associated with decay constants and the air ratio. Knowing the covariance matrix of the ages removes the need to consider 'internal' and 'external' uncertainties separately when calculating (weighted) mean ages. Ar-Ar_Redux is built on the same principles as its sibling program in the U-Pb community (U-Pb_Redux), thus improving the intercomparability of the two methods with tangible benefits to the accuracy of the geologic time scale. The program can be downloaded free of charge from

  1. The B AB AR detector

    NASA Astrophysics Data System (ADS)

    Aubert, B.; Bazan, A.; Boucham, A.; Boutigny, D.; De Bonis, I.; Favier, J.; Gaillard, J.-M.; Jeremie, A.; Karyotakis, Y.; Le Flour, T.; Lees, J. P.; Lieunard, S.; Petitpas, P.; Robbe, P.; Tisserand, V.; Zachariadou, K.; Palano, A.; Chen, G. P.; Chen, J. C.; Qi, N. D.; Rong, G.; Wang, P.; Zhu, Y. S.; Eigen, G.; Reinertsen, P. L.; Stugu, B.; Abbott, B.; Abrams, G. S.; Amerman, L.; Borgland, A. W.; Breon, A. B.; Brown, D. N.; Button-Shafer, J.; Clark, A. R.; Dardin, S.; Day, C.; Dow, S. F.; Fan, Q.; Gaponenko, I.; Gill, M. S.; Goozen, F. R.; Gowdy, S. J.; Gritsan, A.; Groysman, Y.; Hernikl, C.; Jacobsen, R. G.; Jared, R. C.; Kadel, R. W.; Kadyk, J.; Karcher, A.; Kerth, L. T.; Kipnis, I.; Kluth, S.; Kral, J. F.; Lafever, R.; LeClerc, C.; Levi, M. E.; Lewis, S. A.; Lionberger, C.; Liu, T.; Long, M.; Luo, L.; Lynch, G.; Luft, P.; Mandelli, E.; Marino, M.; Marks, K.; Matuk, C.; Meyer, A. B.; Minor, R.; Mokhtarani, A.; Momayezi, M.; Nyman, M.; Oddone, P. J.; Ohnemus, J.; Oshatz, D.; Patton, S.; Pedrali-Noy, M.; Perazzo, A.; Peters, C.; Pope, W.; Pripstein, M.; Quarrie, D. R.; Rasson, J. E.; Roe, N. A.; Romosan, A.; Ronan, M. T.; Shelkov, V. G.; Stone, R.; Strother, P. D.; Telnov, A. V.; von der Lippe, H.; Weber, T. F.; Wenzel, W. A.; Zizka, G.; Bright-Thomas, P. G.; Hawkes, C. M.; Kirk, A.; Knowles, D. J.; O'Neale, S. W.; Watson, A. T.; Watson, N. K.; Deppermann, T.; Koch, H.; Krug, J.; Kunze, M.; Lewandowski, B.; Peters, K.; Schmuecker, H.; Steinke, M.; Andress, J. C.; Barlow, N. R.; Bhimji, W.; Chevalier, N.; Clark, P. J.; Cottingham, W. N.; De Groot, N.; Dyce, N.; Foster, B.; Mass, A.; McFall, J. D.; Wallom, D.; Wilson, F. F.; Abe, K.; Hearty, C.; McKenna, J. A.; Thiessen, D.; Camanzi, B.; Harrison, T. J.; McKemey, A. K.; Tinslay, J.; Antohin, E. I.; Blinov, V. E.; Bukin, A. D.; Bukin, D. A.; Buzykaev, A. R.; Dubrovin, M. S.; Golubev, V. B.; Ivanchenko, V. N.; Kolachev, G. M.; Korol, A. A.; Kravchenko, E. A.; Mikhailov, S. F.; Onuchin, A. P.; Salnikov, A. A.; Serednyakov, S. I.; Skovpen, Yu. I.; Telnov, V. I.; Yushkov, A. N.; Booth, J.; Lankford, A. J.; Mandelkern, M.; Pier, S.; Stoker, D. P.; Zioulas, G.; Ahsan, A.; Arisaka, K.; Buchanan, C.; Chun, S.; Faccini, R.; MacFarlane, D. B.; Prell, S. A.; Rahatlou, Sh.; Raven, G.; Sharma, V.; Burke, S.; Callahan, D.; Campagnari, C.; Dahmes, B.; Hale, D.; Hart, P. A.; Kuznetsova, N.; Kyre, S.; Levy, S. L.; Long, O.; Lu, A.; May, J.; Richman, J. D.; Verkerke, W.; Witherell, M.; Yellin, S.; Beringer, J.; DeWitt, J.; Dorfan, D. E.; Eisner, A. M.; Frey, A.; Grillo, A. A.; Grothe, M.; Heusch, C. A.; Johnson, R. P.; Kroeger, W.; Lockman, W. S.; Pulliam, T.; Rowe, W.; Sadrozinski, H.; Schalk, T.; Schmitz, R. E.; Schumm, B. A.; Seiden, A.; Spencer, E. N.; Turri, M.; Walkowiak, W.; Wilder, M.; Williams, D. C.; Chen, E.; Dubois-Felsmann, G. P.; Dvoretskii, A.; Hanson, J. E.; Hitlin, D. G.; Kolomensky, Yu. G.; Metzler, S.; Oyang, J.; Porter, F. C.; Ryd, A.; Samuel, A.; Weaver, M.; Yang, S.; Zhu, R. Y.; Devmal, S.; Geld, T. L.; Jayatilleke, S.; Jayatilleke, S. M.; Mancinelli, G.; Meadows, B. T.; Sokoloff, M. D.; Bloom, P.; Broomer, B.; Erdos, E.; Fahey, S.; Ford, W. T.; Gaede, F.; van Hoek, W. C.; Johnson, D. R.; Michael, A. K.; Nauenberg, U.; Olivas, A.; Park, H.; Rankin, P.; Roy, J.; Sen, S.; Smith, J. G.; Wagner, D. L.; Blouw, J.; Harton, J. L.; Krishnamurthy, M.; Soffer, A.; Toki, W. H.; Warner, D. W.; Wilson, R. J.; Zhang, J.; Brandt, T.; Brose, J.; Dahlinger, G.; Dickopp, M.; Dubitzky, R. S.; Eckstein, P.; Futterschneider, H.; Kocian, M. L.; Krause, R.; Müller-Pfefferkorn, R.; Schubert, K. R.; Schwierz, R.; Spaan, B.; Wilden, L.; Behr, L.; Bernard, D.; Bonneaud, G. R.; Brochard, F.; Cohen-Tanugi, J.; Ferrag, S.; Fouque, G.; Gastaldi, F.; Matricon, P.; Mora de Freitas, P.; Renard, C.; Roussot, E.; T'Jampens, S.; Thiebaux, C.; Vasileiadis, G.; Verderi, M.; Anjomshoaa, A.; Bernet, R.; Di Lodovico, F.; Muheim, F.; Playfer, S.; Swain, J. E.; Falbo, M.; Bozzi, C.; Dittongo, S.; Folegani, M.; Piemontese, L.; Ramusino, A. C.; Treadwell, E.; Anulli, F.; Baldini-Ferroli, R.; Calcaterra, A.; de Sangro, R.; Falciai, D.; Finocchiaro, G.; Patteri, P.; Peruzzi, I. M.; Piccolo, M.; Xie, Y.; Zallo, A.; Bagnasco, S.; Buzzo, A.; Contri, R.; Crosetti, G.; Fabbricatore, P.; Farinon, S.; Lo Vetere, M.; Macri, M.; Minutoli, S.; Monge, M. R.; Musenich, R.; Pallavicini, M.; Parodi, R.; Passaggio, S.; Pastore, F. C.; Patrignani, C.; Pia, M. G.; Priano, C.; Robutti, E.; Santroni, A.; Bartoldus, R.; Dignan, T.; Hamilton, R.; Mallik, U.; Cochran, J.; Crawley, H. B.; Fischer, P. A.; Lamsa, J.; McKay, R.; Meyer, W. T.; Rosenberg, E. I.; Albert, J. N.; Beigbeder, C.; Benkebil, M.; Breton, D.; Cizeron, R.; Du, S.; Grosdidier, G.; Hast, C.; Höcker, A.; Lacker, H. M.; LePeltier, V.; Lutz, A. M.

    2002-02-01

    B AB AR, the detector for the SLAC PEP-II asymmetric e +e - B Factory operating at the ϒ(4 S) resonance, was designed to allow comprehensive studies of CP-violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagnetic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by d E/d x measurements in the tracking detectors and by a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems, VME- and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented.

  2. 40Ar/39Ar and K-Ar data bearing on the metamorphic and tectonic history of western New England.

    USGS Publications Warehouse

    Sutter, J.F.; Ratcliffe, N.M.; Mukasa, S.B.

    1985-01-01

    40Ar/39Ar ages of coexisting biotite and hornblende from Proterozoic Y gneisses of the Berkshire and Green Mt massifs, as well as 40Ar/39Ar and K/Ar mineral and whole-rock ages from Palaeozoic metamorphic rocks, suggest that the thermal peaks for the dominant metamorphic recrystallization in western New England occurred 465 + or - 5 m.y. (Taconian). 40Ar/39Ar age data from a poorly-defined terrain along the eastern strip of the area suggests that the area has been retrograded during a metamorphism that peaked at least 376 + or - 5 m.y. (Acadian). Available age and petrological data from western New England indicate the presence of at least three separate metamorphic-structure domains of Taconic age: 1) a small area of relict high-P and low-T metamorphism, 2) a broad area of normal Barrovian metamorphism from chlorite to garnet grade characterized by a gentle metamorphic gradient and, 3) a rather narrow belt of steep-gradient, Barrovian series metamorphic rocks. Areas of maximum metamorphic intensity within the last domain coincide with areas of maximum crustal thickening in the later stage of Taconic orogeny. -L.di H

  3. 40Ar/39Ar Ages of Carbonaceous Xenoliths in 2 HED Meteorites

    NASA Technical Reports Server (NTRS)

    Turrin, B.; Lindsay, F. N.; Park, J.; Herzog, G. F.; Delaney, J. S.; Swisher, C. C., III; Johnson, J.; Zolensky, M.

    2016-01-01

    The generally young K/Ar and 40Ar/39Ar ages of CM chondrites made us wonder whether carbonaceous xenoliths (CMX) entombed in Howardite–Eucrite–Diogenite (HED) meteorites might retain more radiogenic 40Ar than do ‘free-range’ CM-chondrites. To find out, we selected two HED breccias with carbonaceous inclusions in order to compare the 40Ar/39Ar release patterns and ages of the inclusions with those of nearby HED material. Carbonaceous inclusions (CMXs) in two HED meteorites lost a greater fraction of radiogenic 40Ar than did surrounding host material, but a smaller fraction of it than did free-range CM-chondrites such as Murchison or more heavily altered ones. Importantly, however, the siting of the CMXs in HED matrix did not prevent the 40Ar loss of about 40 percent of the radiogenic 40Ar, even from phases that degas at high laboratory temperatures. We infer that carbonaceous asteroids with perihelia of 1 astronomical unit probably experience losses of at least this size. The usefulness of 40Ar/39Ar dating for samples returned from C-type asteroids may hinge, therefore, on identifying and analyzing separately small quantities of the most retentive phases of carbonaceous chondrites.

  4. 40Ar/39Ar ages of lunar impact glasses: Relationships among Ar diffusivity, chemical composition, shape, and size

    NASA Astrophysics Data System (ADS)

    Zellner, N. E. B.; Delano, J. W.

    2015-07-01

    Lunar impact glasses, which are quenched melts produced during cratering events on the Moon, have the potential to provide not only compositional information about both the local and regional geology of the Moon but also information about the impact flux over time. We present in this paper the results of 73 new 40Ar/39Ar analyses of well-characterized, inclusion-free lunar impact glasses and demonstrate that size, shape, chemical composition, fraction of radiogenic 40Ar retained, and cosmic ray exposure (CRE) ages are important for 40Ar/39Ar investigations of these samples. Specifically, analyses of lunar impact glasses from the Apollo 14, 16, and 17 landing sites indicate that retention of radiogenic 40Ar is a strong function of post-formation thermal history in the lunar regolith, size, and chemical composition. This is because the Ar diffusion coefficient (at a constant temperature) is estimated to decrease by ∼3-4 orders of magnitude with an increasing fraction of non-bridging oxygens, X(NBO), over the compositional range of most lunar impact glasses with compositions from feldspathic to basaltic. Based on these relationships, lunar impact glasses with compositions and sizes sufficient to have retained ∼90% of their radiogenic Ar during 750 Ma of cosmic ray exposure at time-integrated temperatures of up to 290 K have been identified and are likely to have yielded reliable 40Ar/39Ar ages of formation. Additionally, ∼50% of the identified impact glass spheres have formation ages of ⩽500 Ma, while ∼75% of the identified lunar impact glass shards and spheres have ages of formation ⩽2000 Ma. Higher thermal stresses in lunar impact glasses quenched from hyperliquidus temperatures are considered the likely cause of poor survival of impact glass spheres, as well as the decreasing frequency of lunar impact glasses in general with increasing age. The observed age-frequency distribution of lunar impact glasses may reflect two processes: (i) diminished

  5. Ar-40/Ar-39 laser-probe dating of diamond inclusions from the Premier kimberlite

    NASA Technical Reports Server (NTRS)

    Phillips, D.; Onstott, T. C.; Harris, J. W.

    1989-01-01

    The results of Ar-40/Ar-39 laser-probe analyses of individual eclogitic clinopyroxene inclusions from Premier diamonds are reported which yield a mean age of 1198 + or - 14 Myr. This age agrees well with Sm-Nd and Ar-40/Ar-39 analyses on similar Premier inclusions and is indistinguishable from the inferred time of emplacement of the host kimberlite, which implies that diamond formation was essentially synchronous with kimberlite generation. The extrapolated nonradiogenic Ar-40/Ar-36 ratio of 334 + or - 102 is similar to the present-day atmospheric composition. This value is inconsistent with Sr and Nd isotopic signatures from Premier eclogite inclusions, which suggest a depleted mantle source. Preentrapment equilibration of the inclusions with an Ar-36-rich fluid is the most probable explanation for the low nonradiogenic composition.

  6. arXiv.org and Physics Education

    NASA Astrophysics Data System (ADS)

    Ramlo, Susan

    2007-09-01

    The website arXiv.org (pronounced archive) is a free online resource for full-text articles in the fields of physics, mathematics, computer science, nonlinear science, and quantitative biology that has existed for about 15 years. Available directly at http://www.arXiv.org, this e-print archive is searchable. As of Jan. 3, 2007, arXiv had open access to 401,226 e-prints in the topic areas. Those who sign up for an ID and password can also sign up for daily submission abstract emails for specific subject classes of arXiv, including physics education, physics and society, and history of physics. Founded and developed by Paul Ginsparg when he was at Los Alamos National Laboratory, arXiv's original name was the LANL preprint archive or xxx.lanl.gov. The location and name changed after Ginsparg moved to the physics department at Cornell University. Today, arXiv is hosted and operated by Cornell University library. Mirror sites for arXiv exist worldwide.2

  7. The 40Ar/39Ar dating technique applied to planetary sciences

    NASA Astrophysics Data System (ADS)

    Jourdan, F.

    2012-12-01

    The 40Ar/39Ar technique is a powerful geochronological method that can help to unravel the evolution of the solar system. The 40Ar/39Ar system can not only record the timing of volcanic and metamorphic processes on asteroids and planets, it finds domain of predilection in dating impact events throughout the solar system. However, the 40Ar/39Ar method is a robust analytical technique if, and only if, the events to be dated are well understood and data are not over interpreted. Yet, too many 'ages' reported in the literature are still based on over-interpretation of perturbed age spectra which tends to blur the big picture. This presentation is centred on the most recent applications of the 40Ar/39Ar technique applied to planetary material and through several examples, will attempt to demonstrate the benefit of focusing on statistically robust data. For example, 40Ar/39Ar dating of volcanic events on the Moon suggests that volcanism was mostly concentrated between ca. 3.8 and 3.1 Ga but statistical filtering of the data allow identifying a few well-defined eruptive events. The study of lunar volcanism would also benefit from dating of volcanic spherules. Rigorous filtering of the 40Ar/39Ar age database of lunar melt breccias yielded concordant and ages with high precision for two major basins (i.e. Imbrium & Serenitatis) of the Moon. 40Ar/39Ar dating of lunar impact spherules recovered from four different sites and with high- and low-K compositions shows an increase of ages younger than 400 Ma suggesting a recent increase in the impact flux. The impact history of the LL parent body (bodies?) has yet to be well constrained but may mimic the LHB observed on the Moon, which would indicate that the LL parent body was quite large. 40Ar/39Ar dating (in progress) of grains from the asteroid Itokawa recovered by the japanese Hayabusa mission have the potential to constrain the formation history and exposure age of Itokawa and will allow us to compare the results with the

  8. Instrumentation development for planetary in situ 40Ar/39Ar geochronology

    NASA Astrophysics Data System (ADS)

    Davidheiser-Kroll, B.; Morgan, L. E.; Munk, M.; Warner, N. H.; Gupta, S.; Slaybaugh, R.; Harkness, P.; Mark, D. F.

    2015-12-01

    The chronology of the Solar System, particularly the timing of formation of extraterrestrial bodies and their features, is a major outstanding problem in planetary science. Although various chronological methods for in situ geochronology have been proposed (e.g. Rb-Sr, K-Ar), and even applied (K-Ar, Farley et al., 2014), the reliability, accuracy, and applicability of the 40Ar/39Ar method makes it by far the most desirable chronometer for dating extraterrestrial bodies. The method however relies on the neutron irradiation of samples, and thus a neutron source. We will discuss the challenges and feasibility of deploying a passive neutron source to planetary surfaces for the in situ application of the 40Ar/39Ar chronometer. Requirements in generating and shielding neutrons, as well as analyzing samples are discussed, along with an exploration of limitations such as mass, power, and cost. Two potential solutions for the in situ extraterrestrial deployment of the 40Ar/39Ar method will be presented. Although this represents a challenging task, developing the technology to apply the 40Ar/39Ar method on planetary surfaces would represent a major advance towards constraining the timescale of solar system formation and evolution.

  9. Ar-40/Ar-39 Studies of Martian Meteorite RBT 04262 and Terrestrial Standards

    NASA Technical Reports Server (NTRS)

    Park, J.; Herzog, G. F.; Turrin, B.; Lindsay, F. N.; Delaney, J. S.; Swisher, C. C., III; Nagao, K.; Nyquist, L. E.

    2014-01-01

    Park et al. recently presented an Ar-40/Ar-39 dating study of maskelynite separated from the Martian meteorite RBT 04262. Here we report an additional study of Ar-40/Ar-39 patterns for smaller samples, each consisting of only a few maskelynite grains. Considered as a material for Ar-40/Ar-39 dating, the shock-produced glass maskelynite has both an important strength (relatively high K concentration compared to other mineral phases) and some potentially problematic weaknesses. At Rutgers, we have been analyzing small grains consisting of a single phase to explore local effects that might be averaged and remain hidden in larger samples. Thus, to assess the homogeneity of the RBT maskelynite and for comparison with the results of, we analyzed six approx. 30 microgram samples of the same maskelynite separate they studied. Furthermore, because most Ar-40/Ar-39 are calculated relative to the age of a standard, we present new Ar-40/Ar-39 age data for six standards. Among the most widely used standards are sanidine from Fish Canyon (FCs) and various hornblendes (hb3gr, MMhb-1, NL- 25), which are taken as primary standards because their ages have been determined by independent, direct measurements of K and A-40.

  10. Improvements Needed in the 40Ar/39Ar Study of Geomagnetic Excursion Chronology

    NASA Astrophysics Data System (ADS)

    Champion, D. E.; Turrin, B. D.

    2015-12-01

    Our knowledge of the existence and frequency of brief geomagnetic polarity. excursions only increases with time. Precise and accurate 40Ar/39Ar ages will be required to document this, because 25 or more excursions may have occurred within the Brunhes Epoch (780ky) separated in time by as little as 10ky. Excursions are and will dominantly be discovered in mafic, low K2O rocks. Improvements in the analytical protocol to 40Ar/39Ar date low K2O, "young", and thus low 40Arrad rocks are required. While conventional K/Ar dating "worked", the assumption of perfect atmospheric equilibration is flawed. In particular, using a measured isochron intercept (±2s) to embrace an atmospheric intercept assumption turns a 40Ar/39Ar diffusive extraction into a series of "K/Ar-lite" experiments. The near ubiquitous excess 40Ar exhibited in final steps of "matrix" or "groundmass" fractions from whole-rock experiments (no glass, crystals) suggests equilibration with the atmosphere is not achieved. Removing magnetic sample splits (glass?) thought subject to poor argon retention, and crystals subject to 40Ar inheritance are routinely done without documenting different isochrons. Short 15 to 20 minute irradiation times effectively eliminate recoil and dramatically minimize isotopic corrections, and the assumption of equivalence in Ar isotope recoil behavior. Assuming no pressure dependency and constancy of mass discrimination value ignores knowledge from other gas mass spectroscopy (O, H, He, Ne). Dynamic mass spectroscopy in stable isotopic analysis allows routine per mil and 0.1 per mil ratios to be measured. Maintaining more than daily bracketing air pipette measurements at differing pressures, and controlling the range of pressures from each diffusive step will approximate this dynamic precision. Experiments will be discussed that exhibit aspects of 40Ar/39Ar dating protocols with which precision and accuracy can be improved.

  11. Estimate of the 42Ar content in the Earth's atmosphere

    NASA Astrophysics Data System (ADS)

    Barabash, A. S.; Kornoukhov, V. N.; Jants, V. E.

    1997-02-01

    42Ar is a potential source of background in large volume argon-based detectors. The production of the 42Ar isotope both by cosmic rays and by neutrons produced by testing of nuclear weapons is discussed. We demonstrate that main channel of the 42Ar production is from atmospheric testing of nuclear bombs from 1945 to 1962 and the 42Ar content must be less than 1.3 × 10 -23 parts of 42Ar per part of natAr.

  12. LASER MICROPROBE **4**0Ar/**3**9Ar DATING OF MINERAL GRAINS IN SITU.

    USGS Publications Warehouse

    Sutter, J.F.; Hartung, J.B.

    1984-01-01

    A laser-microprobe attached to a mass spectrometer for **4**0Ar/**3**9Ar age determination of single mineral grains in geological materials has been made operational at the US Geological Survey, Reston, VA. This microanalytical technique involves focusing a pulsed laser beam onto a sample contained in an ultra-high vacuum chamber attached to a rare-gas mass spectrometer. Argon in the neutron-irradiated sample is released by heating with the laser pulse and its isotopic composition is measured to yield an **4**0Ar/**3**9Ar age. Laser probe **4**0Ar/**3**9Ar ages of single mineral grains measured in situ can aid greatly in understanding the chronology of many geological situations where datable minerals are present but are not physically separable in quantities needed for conventional age dating.

  13. Ar-39-Ar-40 Ages of Euerites and the Thermal History of Asteroid 4-Vesta

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.

    2002-01-01

    Eucrite meteorites are igneous rocks that derive from a large asteroid, probably 4 Vesta. Prior studies have shown that after eucrites formed, most were subsequently metamorphosed to temperatures up to equal to or greater than 800 C, and much later many were brecciated and heated by large impacts into the parent body surface. The uncommon basaltic, unbrecciated eucrites also formed near the surface but presumably escaped later brecciation, whereas the cumulate eucrites formed at depth where metamorphism may have persisted for a considerable period. To further understand the complex HED parent body thermal history, we determined new Ar-39-Ar-40 ages for nine eucrites classified as basaltic but unbrecciated, six eucrites classified as cumulate, and several basaltic-brecciated eucrites. Relatively precise Ar-Ar ages of two cumulate eucrites (Moama and EET87520) and four unbrecciated eucrites give a tight cluster at 4.48 +/1 0.01 Gyr. Ar-Ar ages of six additional unbrecciated eucrites are consistent with this age, within their larger age uncertainties. In contrast, available literature data on Pb-Pb isochron ages of four cumulate eucrites and one unbrecciated eucrite vary over 4.4-4.515 Gyr, and Sm-147 - Nd-143 isochron ages of four cumulate and three unbrecciated eucrites vary over 4.41-4.55 Gyr. Similar Ar-Ar ages for cumulate and unbrecciated eucrites imply that cumulate eucrites do not have a younger formation age than basaltic eucrites, as previously proposed. Rather, we suggest that these cumulate and unbrecciated eucrites resided at depth where parent body temperatures were sufficiently high to cause the K-Ar and some other chronometers to remain open diffusion systems. From the strong clustering of Ar-Ar ages at approximately 4.48 Gyr, we propose that these meteorites were excavated from depth in a single large impact event approximately 4.48 Gyr ago, which quickly cooled the samples and started the K-Ar chronometer. A large (approximately 460 km) crater

  14. The ArsD As(III) metallochaperone

    PubMed Central

    Ajees, A. Abdul; Yang, Jianbo

    2013-01-01

    Arsenic, a toxic metalloid widely existing in the environment, causes a variety of health problems. The ars operon encoded by Escherichia coli plasmid R773 has arsD and arsA genes, where ArsA is an ATPase that is the catalytic subunit of the ArsAB As(III) extrusion pump, and ArsD is an arsenic chaperone for ArsA. ArsD transfers As(III) to ArsA and increases the affinity of ArsA for As(III), allowing resistance to environmental concentrations of arsenic. Cys12, Cys13 and Cys18 in ArsD form a three sulfur-coordinated As(III) binding site that is essential for metallochaperone activity. ATP hydrolysis by ArsA is required for transfer of As(III) from ArsD to ArsA, suggesting that transfer occurs with a conformation of ArsA that transiently forms during the catalytic cycle. The 1.4 Å x-ray crystal structure of ArsD shows a core of four β-strands flanked by four α-helices in a thioredoxin fold. Docking of ArsD with ArsA was modeled in silico. Independently ArsD mutants exhibiting either weaker or stronger interaction with ArsA were selected. The locations of the mutations mapped on the surface of ArsD are consistent with the docking model. The results suggest that the interface with ArsA involves one surface of α1 helix and metalloid binding site of ArsD. PMID:21188475

  15. Rapid kimberlite ascent and the significance of Ar-Ar ages in xenolith phlogopites

    PubMed

    Kelley; Wartho

    2000-07-28

    Kimberlite eruptions bring exotic rock fragments and minerals, including diamonds, from deep within the mantle up to the surface. Such fragments are rapidly absorbed into the kimberlite magma so their appearance at the surface implies rapid transport from depth. High spatial resolution Ar-Ar age data on phlogopite grains in xenoliths from Malaita in the Solomon Islands, southwest Pacific, and Elovy Island in the Kola Peninsula, Russia, indicate transport times of hours to days depending upon the magma temperature. In addition, the data show that the phlogopite grains preserve Ar-Ar ages recorded at high temperature in the mantle, 700 degrees C above the conventional closure temperature. PMID:10915621

  16. Ar-39-Ar-40 Evidence for Early Impact Events on the LL Parent Body

    NASA Technical Reports Server (NTRS)

    Dixon, E. T.; Bogard, D. D.; Garrison, D. H.; Rubin, A. E.

    2006-01-01

    We determined Ar-39-Ar-40 ages of eight LL chondrites, and one igneous inclusion from an LL chondrite, with the object of understanding the thermal history of the LL-chondrite parent body. The meteorites in this study have a range of petrographic types from LL3.3 to LL6, and shock stages from S1 to S4. These meteorites reveal a range of K-Ar ages from 23.66 to 24.50 Ga, and peak ages from 23.74 to 24.55 Ga. Significantly, three of the eight chondrites (LL4, 5, 6) have K-Ar ages of -4.27 Ga. One of these (MIL99301) preserves an Ar-39-Ar-40 age of 4.23 +/- 0.03 Ga from low-temperature extractions, and an older age of 4.52 +/- 0.08 Ga from the highest temperature extractions. In addition, an igneous-textured impact melt DOM85505,22 has a peak Ar-39-Ar-40 age of >= 4.27 Ga. We interpret these results as evidence for impact events that occurred at about 4.27 Ga on the LL parent body that produced local impact melts, reset the Ar-39-Ar-40 ages of some meteorites, and exhumed (or interred) others, resulting in a range of cooling ages. The somewhat younger peak age of 3.74 Ga from GR095658 (LL3.3) suggests an additional impact event close to timing of impact-reset ages of some other ordinary chondrites between 3.6-3.8 Ga. The results from MIL99301 suggest that some apparently unshocked (Sl) chondrites may have substantially reset Ar-39-Ar-40 ages. A previous petrographic investigation of MIL99301 suggested that reheating to temperatures less than or equal to type 4 petrographic conditions (600C) caused fractures in olivine to anneal, resulting in a low apparent shock stage of S1 (unshocked). The Ar-39-Ar-40 age spectrum of MIL99301 is consistent with this interpretation. Older ages from high-T extractions may date an earlier impact event at 4.52 +/- 0.08 Ga, whereas younger ages from lower-T extractions date a later impact event at 4.23 Ar-39-Ar-40 0.03 Ga that may have caused annealing of feldspar and olivine

  17. 40Ar/39Ar technique of KAr dating: a comparison with the conventional technique

    USGS Publications Warehouse

    Brent, Dalrymple G.; Lanphere, M.A.

    1971-01-01

    K-Ar ages have been determined by the 40Ar/39Ar total fusion technique on 19 terrestrial samples whose conventional K-Ar ages range from 3.4 my to nearly 1700 my. Sample materials included biotite, muscovite, sanidine, adularia, plagioclase, hornblende, actinolite, alunite, dacite, and basalt. For 18 samples there are no significant differences at the 95% confidence level between the KAr ages obtained by these two techniques; for one sample the difference is 4.3% and is statistically significant. For the neutron doses used in these experiments (???4 ?? 1018 nvt) it appears that corrections for interfering Ca- and K-derived Ar isotopes can be made without significant loss of precision for samples with K/Ca > 1 as young as about 5 ?? 105 yr, and for samples with K/Ca < 1 as young as about 107 yr. For younger samples the combination of large atmospheric Ar corrections and large corrections for Ca- and K-derived Ar may make the precision of the 40Ar/39Ar technique less than that of the conventional technique unless the irradiation parameters are adjusted to minimize these corrections. ?? 1971.

  18. Saddle-shaped 40Ar /39Ar age spectra from young, microstructurally complex potassium feldspars

    NASA Astrophysics Data System (ADS)

    Zeitler, Peter K.; Fitz Gerald, John D.

    1986-06-01

    A suite of young potassium feldspars show markedly saddle-shaped 40Ar /39Ar age spectra as a result of incorporating 10 -10 to 10 -9 mol/g of excess 40Ar. The minima of these age spectra record reasonable cooling ages, based on the known thermal history and geology of the samples. Acid etching of one sample indicates that excess 40Ar is concentrated near grain margins. The release of a substantial portion of this excess Ar at high temperatures in the laboratory requires that this component be situated in a more retentive site than radiogenic 40Ar. Anion vacancies have been proposed to act in this role in plagioclase, and we speculate that this is so in K-feldspar as well. Such a mechanism would explain the observation that relative to radiogenic 40Ar, excess 40Ar is incorporated at low temperatures in nature but is released at high temperatures in the laboratory. Oxygen diffusion provides an appropriate analogy for this phenomenon, being relatively fast under natural, hydrothermal conditions, but extremely slow in anhydrous environments such as an Ar-extraction system. TEM observations made on two of the samples confirm that their effective grain sizes for diffusion are likely to be on the order of ten microns, due to the presence of such microstructures as incoherent exsolution lamellae, dislocations, and stepped twins. TEM observations also reveal the presence in one sample of orthoclase enclaves in a microcline host.

  19. 40Ar/39Ar age of Cretaceous-Tertiary boundary tektites from Haiti

    USGS Publications Warehouse

    Izett, G.A.; Dalrymple, G.B.; Snee, L.W.

    1991-01-01

    40Ar/39Ar dating of tektites discovered recently in Cretaceous-Tertiary (K-T) boundary marine sedimentary rocks on Haiti indicates that the K-T boundary and impact event are coeval at 64.5 ?? 0.1 million years ago. Sanidine from a bentonite that lies directly above the K-T boundary in continental, coal-bearing, sedimentary rocks of Montana was also dated and has a 40Ar/39Ar age of 64.6 ?? 0.2 million years ago, which is indistinguishable statistically from the age of the tektites.

  20. 40Ar/39Ar ages of the AD 79 eruption of Vesuvius, Italy

    USGS Publications Warehouse

    Lanphere, M.; Champion, D.; Melluso, L.; Morra, V.; Perrotta, A.; Scarpati, C.; Tedesco, D.; Calvert, A.

    2007-01-01

    The Italian volcano, Vesuvius, erupted explosively in AD 79. Sanidine from pumice collected at Casti Amanti in Pompeii and Villa Poppea in Oplontis yielded a weighted-mean 40Ar/39Ar age of 1925??66 years in 2004 (1?? uncertainty) from incremental-heating experiments of eight aliquants of sanidine. This is the calendar age of the eruption. Our results together with the work of Renne et al. (1997) and Renne and Min (1998) demonstrate the validity of the 40Ar/39Ar method to reconstruct the recent eruptive history of young, active volcanoes. ?? Springer-Verlag 2006.

  1. 40Ar/39Ar ages in deformed potassium feldspar: evidence of microstructural control on Ar isotope systematics

    NASA Astrophysics Data System (ADS)

    Reddy, Steven M.; Potts, Graham J.; Kelley, Simon P.

    2001-05-01

    Detailed field and microstructural studies have been combined with high spatial resolution ultraviolet laser 40Ar/39Ar dating of naturally deformed K-feldspar to investigate the direct relationship between deformation-related microstructure and Ar isotope systematics. The sample studied is a ~1,000 Ma Torridonian arkose from Skye, Scotland, that contains detrital feldspars previously metamorphosed at amphibolite-facies conditions ~1,700 Ma. The sample was subsequently deformed ~430 Ma ago during Caledonian orogenesis. The form and distribution of deformation-induced microstructures within three different feldspar clasts has been mapped using atomic number contrast and orientation contrast imaging, at a range of scales, to identify intragrain variations in composition and lattice orientation. These variations have been related to thin section and regional structural data to provide a well-constrained deformation history for the feldspar clasts. One hundred and forty-three in-situ 40Ar/39Ar analyses measured using ultraviolet laser ablation record a range of apparent ages (317-1030 Ma). The K-feldspar showing the least strain records the greatest range of apparent ages from 420-1,030 Ma, with the oldest apparent ages being found close to the centre of the feldspar away from fractures and the detrital grain boundary. The most deformed K-feldspar yields the youngest apparent ages (317-453 Ma) but there is no spatial relationship between apparent age and the detrital grain boundary. Within this feldspar, the oldest apparent ages are recorded from orientation domain boundaries and fracture surfaces where an excess or trapped 40Ar component resides. Orientation contrast images at a similar scale to the Ar analyses illustrate a significant deformation-related microstructural difference between the feldspars and we conclude that deformation plays a significant role in controlling Ar systematics of feldspars at both the inter- and intragrain scales even at relatively low

  2. 40Ar/39Ar systematics and argon diffusion in amber: implications for ancient earth atmospheres

    USGS Publications Warehouse

    Landis, G.P.; Snee, L.W.

    1991-01-01

    Argon isotope data indicate retained argon in bulk amber (matrix gas) is radiogenic [40Ar/39Ar ???32o] than the much more abundant surface absorbed argon [40Ar/39Ar ???295.5]. Neutron-induced 39Ar is retained in amber during heating experiments to 150?? -250??C, with no evidence of recoiled 39Ar found after irradiation. A maximum permissible volume diffusion coefficient of argon in amber (at ambient temperature) D???1.5 x 10-17 cm2S-1 is calculated from 39Ar retention. 40Ar/39Ar age calculations indicate Dominican Republic amber is ??? 45 Ma and North Dakota amber is ??? 89 Ma, both at least reasonable ages for the amber based upon stratigraphic and paleontological constraints and upon the small amount of radiogenic 40Ar. To date, over 300 gas analyses of ambers and resins of Cretaceous to Recent age that are geographically distributed among fifteen noted world locations identify mixtures of gases in different sites within amber (Berner and Landis, 1988). The presence of multiple mixing trends between compositionally distinct end-members gases within the same sample and evidence for retained radiogenic argon within the amber argue persuasivley against rapid exchange by diffusion of amber-contained gases with moder air. Only gas in primary bubbles entrapped between successive flows of tree resin has been interpreted as original "ancient air", which is an O2-rich end-member gas with air-like N2/Ar ratios. Gas analyses of these primary bubbles indicate atmospheric O2 levels in the Late Cretaceous of ??? 35%, and that atmospheric O2 dropped by early Tertiary time to near a present atmospheric level of 21% O2. A very low argon diffusion coefficient in amber persuasively argues for a gas in primary bubbles trapped in amber being ancient air (possibly modified only by O2 reaction with amber). ?? 1991.

  3. Comparative 40Ar/39Ar and K-Ar dating of illite-type clay minerals: A tentative explanation for age identities and differences

    NASA Astrophysics Data System (ADS)

    Clauer, Norbert; Zwingmann, Horst; Liewig, Nicole; Wendling, Raymond

    2012-10-01

    The 40K/40Ar (K-Ar) and 40Ar/39Ar dating methods are applied here to the same, very small, micrometric illite-type particles that crystallized under low-temperature (< 175 °C) hydrothermal conditions in deeply buried Rotliegend (Permian) gas-bearing sandstones of NW Germany. Four samples with a total of fifteen size fractions from < 2 to 20-40 μm yield K-Ar ages that range from 166.0 ± 3.4 to 214.0 ± 5.9 Ma. The same size fractions dated by the 40Ar/39Ar method give total-gas ages ranging from 173.3 ± 2.0 to 228.8 ± 1.6 Ma. Nearly all 40Ar/39Ar total-gas ages are slightly older, which cannot be explained by the recoil effect only, the impact of which being amplified by the inhomogeneous shape of the clay minerals and their crystallographic characteristics, with varied crystallinity indices, and a particle width about 10 times large than thickness. The 40Ar/39Ar data outline some advantages, such as the plateaus obtained by incremental step heating of the various size fractions, even if not translatable straight as ages of the illite populations; they allow identification of two generations of authigenic illite that formed at about 200 and 175 Ma, and one detrital generation. However, 40Ar/39Ar dating of clay minerals remains challenging as technical factors, such as the non-standardized encapsulation, may have potential unexpected effects. Both dating methods have their limitations: (1) K-Ar dating requires relatively large samples (ca. 10-20 mg) incurring potential sample homogeneity problems, with two aliquots required for K and Ar analysis for an age determination, also inducing a higher analytical uncertainty; (2) an identified drawback of 40Ar/39Ar dating is Ar recoil and therefore potential loss that occurs during neutronic creation of 39Ar from 39K, mostly in the finer mineral particles. If all the recoiled 39Ar is redistributed into adjacent grains/minerals, the final 40Ar/39Ar age of the analyzed size fraction remains theoretically identical, but it

  4. Hazard evaluation for 244-AR vault facility

    SciTech Connect

    BRAUN, D.J.

    1999-08-25

    This document presents the results of a hazard identification and evaluation performed on the 244-AR Vault Facility to close a USQ (USQ No.TF-98-0785, Potential Inadequacy in Authorization Basis (PIAB): To Evaluate Miscellaneous Facilities Listed In HNF-2503 And Not Addressed In The TWRS Authorization Basis) that was generated as part of an evaluation of inactive TWRS facilities. A hazard evaluation for the Hanford Site 244-AR Vault Facility was performed. The process and results of the hazard evaluation are provided in this document. A previous hazard evaluation was performed for the 244-AR Vault Facility in 1996 in support of the Basis for Interim Operation (BIO) (HNF-SD-WM-BIO-001, 1998, Revision 1) of the Tank Waste Remediation System (TWRS). The results of that evaluation are provided in the BIO. Upon review of those results it was determined that hazardous conditions that could lead to the release of radiological and toxicological material from the 244-AR vaults due to flooding was not addressed in the original hazards evaluation. This supplemental hazard evaluation addresses this oversight of the original hazard evaluation. The results of the hazard evaluation were compared to the current TWRS BIO to identify any hazardous conditions where Authorization Basis (AB) controls may not be sufficient or may not exist. This document is not part of the AB and is not a vehicle for requesting changes to the AB. It is only intended to provide information about hazardous conditions associated with the condition and configuration of the 244-AR vault facility. The AB Control Decision process could be used to determine the applicability and adequacy of existing AB controls as well as any new controls that may be needed for the identified hazardous conditions associated with 244-AR vault flooding. This hazard evaluation does not constitute an accident analysis.

  5. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2005-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39- Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50-4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4557.9+/-0.1 Myr and 4557-4560 Myr, respectively, relative to an age of 4562.3 Myr for Shallowater. Considering all reported Ar-Ar degassing ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older Ar ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later 40Ar diffusion loss. The older Ar-Ar ages for IABs are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the Ar-Ar ages and IAB cooling rates deduced from Ni concentration profiles in IAB metal (Herpfer et al., 1994) are consistent if the time of the post-assembly metamorphism was as late as approx.4.53 Gyr ago. However, I-Xe ages reported for some IABs define much older ages of approx.4558-4566 Myr, which cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages. An explanation for the difference in radiometric ages of IABs may reside in combinations of the following: a) I-Xe ages have very

  6. Penning ionization : In benzene · Ar and fluorobenzene · Ar van der waals molecules and in collisions of benzene with metastable Ar atoms

    NASA Astrophysics Data System (ADS)

    Rühl, E.; Bisling, P.; Brutschy, B.; Beckmann, K.; Leisen, O.; Morgner, H.

    1986-08-01

    The photoion efficiency curves of the van der Waals complexes benzene ·Ar (Bz·Ar) and fluorobenzene·Ar (Fb·Ar) exhibit sharp resonances, which correspond to excitation to the Ar 2P 3/24s and 2P 1/24s resonance states. The peaks are redshifted relative to their asymptotic values (Bz·Ar, Δ E = -70 ± 10 meV; Fb·Ar, Δ E = -40 ± 10 meV). These findings are supported by electron spectroscopy studies of the Penning ionization of benzene by state-selected metastable Ar ( 3p 2, 3p 0) atoms. Strong evidence is presented that Penning ionization is the process observed in both cases.

  7. 40Ar/39Ar and K/Ar dating of low grade metamorphism: examples on metabasites from Central Chile

    NASA Astrophysics Data System (ADS)

    Aguirre, L.; Feraud, G.; Fuentes, F.; Delbar, M.; Morata, D.

    2003-04-01

    Dating low to very low-grade burial metamorphic assemblages is often difficult because of (1) few mineral phases compositionally suitable to apply the 40Ar/39Ar and K-Ar methods, and (2) small amount in which these phases are commonly found. K-feldspar adularia, sericitic mica, and celadonite are the best known K-bearing secondary minerals. We present some successful attempts to analyse two distinct secondary phases from a same volcanic formation that allow to test the validity of the measured ages. These ages have been also compared with the crystallisation age of the volcanic rocks in which the secondary phases were lately developed. Adularia and sericite were selected from basic lava flows from a 3 to 13 km thick Cretaceous sequence from the Coastal Range of central Chile, at two different locations: the Bustamante Hill (west from Santiago), and the Cordón de Chacana, c. 80 km further north. Adularia came from a low-variance assemblage with pumpellyite, chlorite and low-albite contained in amygdules whereas sericite was present in milky-white strongly sericitized plagioclase crystals. While small clusters of rare fresh plagioclase grains from lava flows from Bustamante and Chacana displayed concordant plateau ages 119.4 ± 2.4 (2 sigma) and 118.7 ± 0.6 Ma, respectively, the adularia from the same formations gave sensibly younger ages around 94 Ma (high temperature steps), and 96.8 ± 0.2 Ma (plateau age) in Bustamante and Chacana, respectively. Sericite ages were measured in situ into single crystals of strongly transformed plagioclases. The relative proportion of sericite and plagioclase corresponding to each degasing step was monitored by measuring the Ca/K ratio (deduced from 37ArCa/39Ar_K). While intermediate ages were measured on some sericite of both sites (corresponding to a variable but permanent contribution of plagioclase on each step), a plateau age of 97.0 ± 1.6 Ma (concordant with adularia) could be obtained on a strongly sericitized plagioclase

  8. Ar-Ar Impact Heating Ages of Eucrites and Timing of the LHB

    NASA Technical Reports Server (NTRS)

    Bogard, Donald; Garrison, Daniel

    2009-01-01

    Eucrites and howardites, more than most meteorite types, show extensive impact resetting of their Ar-39-Ar-40 (K-Ar) ages approximately equal to 3.4-4.1 Ga ago, and many specimens show some disturbance of other radiometry chronometers as well. Bogard (1995) argued that this age resetting occurred on Vesta and was produced by the same general population of objects that produced many of the lunar impact basins. The exact nature of the lunar late heavy bombardment (LHB or 'cataclysm') remains controversial, but the timing is similar to the reset ages of eucrites. Neither the beginning nor ending time of the lunar LHB is well constrained. Comparison of Ar-Ar ages of brecciated eucrites with data for the lunar LHB can resolve both the origin of these impactors and the time period over which they were delivered to the inner solar system. This abstract reports some new Ar-Ar age data for eucrites, obtained since the authors' 1995 and 2003 papers.

  9. Ar-40/Ar-39 Ages of Maskelynite Grains from ALHA 77005

    NASA Technical Reports Server (NTRS)

    Turrin, B.; Park, J.; Herzog, G. F.; Lindsay, F. N.; Delaney, J. S.; Nyquist, L. E.; Swisher, C., III

    2013-01-01

    We present Ar-40/Ar-39 measurements for twelve small (20-60 micro-g) maskelynite samples from the heavily shocked martian meteorite ALHA 77005. The reported modal composition for ALHA 77005 is 50-60% olivine (Fa28), 30-40% pyroxene (Wo5Fs23En72), approx.8% maskelynite (An53), and approx.2% opaques by volume [1]). The meteorite is usually classified as a lherzolite. Previous Studies - Ar-40/Ar-39 results from previous work display disturbed release spectra [2,3]. In study [2], Ar-40/Ar-39 measurements on a 52-mg whole-rock sample produced an extremely disturbed release spec-trum, with all calculated apparent ages > 1 Ga, (Fig. 1). In a subsequent study [3], a light and a dark phase were analyzed. A 2.3-mg sample of the light, relatively low-K phase produced a disturbed release spectrum. For the first 20% of the Ar-39(sub K), most of the apparent ages exceeded >1 Ga; the remaining 80% yielded ages between 0.3-0.5 Ga. The integrated age for this phase is 0.9 Ga.

  10. Application of deuteron-deuteron (D-D) fusion neutrons to 40Ar/39Ar geochronology.

    PubMed

    Renne, Paul R; Knight, Kim B; Nomade, Sébastien; Leung, Ka-Ngo; Lou, Tak-Pui

    2005-01-01

    Neutron irradiation of samples for 40Ar/39Ar dating in a 235U fission reactor requires error-producing corrections for the argon isotopes created from Ca, K, and, to a lesser extent, Cl. The fission spectrum includes neutrons with energies above 2-3 MeV, which are not optimal for the 39K(n,p)39Ar reaction. These higher-energy neutrons are responsible for the largest recoil displacements, which may introduce age artifacts in the case of fine-grained samples. Both interference corrections and recoil displacements would be significantly reduced by irradiation with 2.45 MeV neutrons, which are produced by the deuteron-deuteron (D-D) fusion reaction 2H(d,n)3He. A new generation of D-D reactors should yield sufficiently high neutron fluxes (>10(12) n cm(-2)s(-1)) to be useful for 40Ar/39Ar dating. Modeling indicates that irradiation with D-D neutrons would result in scientific benefits of improved accuracy and broader applicability to fine-grained materials. In addition, radiological safety would be improved, while both maintenance and operational costs would be reduced. Thus, development of high-flux D-D fusion reactors is a worthy goal for 40Ar/39Ar geochronology. PMID:15498681

  11. Study of Ar and Ar-CO2 microwave surfaguide discharges by optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Silva, Tiago; Britun, Nikolay; Godfroid, Thomas; van der Mullen, Joost; Snyders, Rony

    2016-05-01

    A surfaguide microwave discharge operating at 2.45 GHz in Ar and Ar-CO2 mixtures is studied using diagnostics methods based on optical emission spectroscopy. The population densities of Ar metastable and resonant states of the lowest group of excited levels ( 1 s x ) are investigated for several experimental conditions using the self-absorption technique. It is found that the densities of these levels, ranging from 1017 to 1016 m-3 for the pure Ar case, are dependent on the discharge pressure and applied power. The electron temperature and electron density are calculated via the balances of creation/loss mechanisms of radiative and metastable levels. In the range of the studied experimental conditions (50-300 W of applied power and 0.5-6 Torr of gas pressure), the results have shown that lower values of electron temperature correspond to higher values of power and pressure in the discharge. Adding CO2 to the argon plasma results in a considerable decrease (about 3 orders of magnitude) of the Ar metastable atom density. The feasibility of using the ratio of two Ar emission line intensities to measure the electron temperature in CO2 discharges with small Ar admixtures is studied.

  12. Potassium Isotopic Compositions of NIST Potassium Standards and 40Ar/39Ar Mineral Standards

    NASA Technical Reports Server (NTRS)

    Morgan, Leah; Tappa, Mike; Ellam, Rob; Mark, Darren; Higgins, John; Simon, Justin I.

    2013-01-01

    Knowledge of the isotopic ratios of standards, spikes, and reference materials is fundamental to the accuracy of many geochronological methods. For example, the 238U/235U ratio relevant to U-Pb geochronology was recently re-determined [1] and shown to differ significantly from the previously accepted value employed during age determinations. These underlying values are fundamental to accurate age calculations in many isotopic systems, and uncertainty in these values can represent a significant (and often unrecognized) portion of the uncertainty budget for determined ages. The potassium isotopic composition of mineral standards, or neutron flux monitors, is a critical, but often overlooked component in the calculation of K-Ar and 40Ar/39Ar ages. It is currently assumed that all terrestrial materials have abundances indistinguishable from that of NIST SRM 985 [2]; this is apparently a reasonable assumption at the 0.25per mille level (1s) [3]. The 40Ar/39Ar method further relies on the assumption that standards and samples (including primary and secondary standards) have indistinguishable 40K/39K values. We will present data establishing the potassium isotopic compositions of NIST isotopic K SRM 985, elemental K SRM 999b, and 40Ar/39Ar biotite mineral standard GA1550 (sample MD-2). Stable isotopic compositions (41K/39K) were measured by the peak shoulder method with high resolution MC-ICP-MS (Thermo Scientific NEPTUNE Plus), using the accepted value of NIST isotopic SRM 985 [2] for fractionation [4] corrections [5]. 40K abundances were measured by TIMS (Thermo Scientific TRITON), using 41K/39K values from ICP-MS measurements (or, for SRM 985, values from [2]) for internal fractionation corrections. Collectively these data represent an important step towards a metrologically traceable calibration of 40K concentrations in primary 40Ar/39Ar mineral standards and improve uncertainties by ca. an order of magnitude in the potassium isotopic compositions of standards.

  13. Overview of the ARS Culture Collection

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Agricultural Research Service (ARS) Culture Collection in Peoria, IL, maintains more than 95,000 strains of agriculturally and industrially important bacteria and fungi. Most of these isolates are maintained in an open collection that distributes 6,000 – 8,000 strains annually in response to req...

  14. Experiences from the ARS croplands CEAP program

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The multi-agency Conservation Effects Assessment Project (CEAP) within USDA produced a number of lessons that should be applicable to the use of landscape approaches to place bioenergy crops. Results from the ARS Croplands Watersheds CEAP, the NRCS CEAP, and the NIFA CEAP Watershed Assessment Studie...

  15. RECENTLY RELEASED USDA/ARS GRAPE VARIETIES

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The production practices for the latest table grape varieties released by ARS, SJVASC, Parlier, California are summarized along with their performance. Sweet Scarlet provides growers with a mid-season, red seedless grape with a light Muscat flavor. It has exceptional eating quality because of its ...

  16. Lignocellulosic Biofuels: Bioenergy Research at ARS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The growth and long-term viability of bioenergy production in the Nation are impeded by a number of technical and commercial barriers. Agricultural Research Service (ARS) addresses technical barriers and does so by leveraging its strengths and unique capabilities to (1) pursue technical barriers th...

  17. USDA-ARS BRAMBLE RESEARCH AT BELTSVILLE

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The USDA-ARS bramble cultivar development program at Beltsville, Maryland has a long history. Perhaps the greatest success from this program has been the development of several thornless blackberry cultivars including Chester, which currently is the most commonly grown blackberry cultivar in the Ea...

  18. The USDA/ARS Raisin Breeding Program

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The USDA/ARS breeding program is developing: 1) natural dry-on-the-vine raisin grape cultivars; 2) powdery mildew resistant raisin grape cultivars; 3) Pierce’s Disease resistant raisin grape cultivars; and 4) raisin grape cultivars with increased anthocyanins for health benefits. A natural dry-on-t...

  19. The ChArMEx database

    NASA Astrophysics Data System (ADS)

    Ferré, Hélène; Belmahfoud, Nizar; Boichard, Jean-Luc; Brissebrat, Guillaume; Cloché, Sophie; Descloitres, Jacques; Fleury, Laurence; Focsa, Loredana; Henriot, Nicolas; Mière, Arnaud; Ramage, Karim; Vermeulen, Anne; Boulanger, Damien

    2015-04-01

    The Chemistry-Aerosol Mediterranean Experiment (ChArMEx, http://charmex.lsce.ipsl.fr/) aims at a scientific assessment of the present and future state of the atmospheric environment in the Mediterranean Basin, and of its impacts on the regional climate, air quality, and marine biogeochemistry. The project includes long term monitoring of environmental parameters , intensive field campaigns, use of satellite data and modelling studies. Therefore ChARMEx scientists produce and need to access a wide diversity of data. In this context, the objective of the database task is to organize data management, distribution system and services, such as facilitating the exchange of information and stimulating the collaboration between researchers within the ChArMEx community, and beyond. The database relies on a strong collaboration between ICARE, IPSL and OMP data centers and has been set up in the framework of the Mediterranean Integrated Studies at Regional And Locals Scales (MISTRALS) program data portal. ChArMEx data, either produced or used by the project, are documented and accessible through the database website: http://mistrals.sedoo.fr/ChArMEx. The website offers the usual but user-friendly functionalities: data catalog, user registration procedure, search tool to select and access data... The metadata (data description) are standardized, and comply with international standards (ISO 19115-19139; INSPIRE European Directive; Global Change Master Directory Thesaurus). A Digital Object Identifier (DOI) assignement procedure allows to automatically register the datasets, in order to make them easier to access, cite, reuse and verify. At present, the ChArMEx database contains about 120 datasets, including more than 80 in situ datasets (2012, 2013 and 2014 summer campaigns, background monitoring station of Ersa...), 25 model output sets (dust model intercomparison, MEDCORDEX scenarios...), a high resolution emission inventory over the Mediterranean... Many in situ datasets

  20. Neutron spectroscopic factors of Ar34 and Ar46 from (p,d) transfer reactions

    NASA Astrophysics Data System (ADS)

    Lee, Jenny; Tsang, M. B.; Bazin, D.; Coupland, D.; Henzl, V.; Henzlova, D.; Kilburn, M.; Lynch, W. G.; Rogers, A. M.; Sanetullaev, A.; Sun, Z. Y.; Youngs, M.; Charity, R. J.; Sobotka, L. G.; Famiano, M.; Hudan, S.; Shapira, D.; O'Malley, P.; Peters, W. A.; Chae, K. Y.; Schmitt, K.

    2011-01-01

    Single-neutron-transfer measurements using (p,d) reactions have been performed at 33 MeV per nucleon with proton-rich Ar34 and neutron-rich Ar46 beams in inverse kinematics. The extracted spectroscopic factors are compared to the large-basis shell-model calculations. Relatively weak quenching of the spectroscopic factors is observed between Ar34 and Ar46. The experimental results suggest that neutron correlations have a weak dependence on the asymmetry of the nucleus over this isotopic region. The present results are consistent with the systematics established from extensive studies of spectroscopic factors and dispersive optical-model analyses of Ca40-49 isotopes. They are, however, inconsistent with the trends obtained in knockout-reaction measurements.

  1. Age and origin of carlsbad cavern and related caves from 40Ar/39Ar of alunite

    PubMed

    Polyak; McIntosh; Guven; Provencio

    1998-03-20

    40Ar/39Ar dating of fine-grained alunite that formed during cave genesis provides ages of formation for the Big Room level of Carlsbad Cavern [4.0 to 3.9 million years ago (Ma)], the upper level of Lechuguilla Cave (6.0 to 5.7 Ma), and three other hypogene caves (11.3 to 6.0 Ma) in the Guadalupe Mountains of New Mexico. Alunite ages increase and are strongly correlative with cave elevations, which indicates an 1100-meter decline in the water table, apparently related to tectonic uplift and tilting, from 11.3 Ma to the present. 40Ar/39Ar dating studies of the hypogene caves have the potential to help resolve late Cenozoic climatic, speleologic, and tectonic questions. PMID:9506939

  2. Planar defects as Ar traps in trioctahedral micas: A mechanism for increased Ar retentivity in phlogopite

    NASA Astrophysics Data System (ADS)

    Camacho, A.; Lee, J. K. W.; Fitz Gerald, J. D.; Zhao, J.; Abdu, Y. A.; Jenkins, D. M.; Hawthorne, F. C.; Kyser, T. K.; Creaser, R. A.; Armstrong, R.; Heaman, L. W.

    2012-08-01

    The effects of planar defects and composition on Ar mobility in trioctahedral micas have been investigated in samples from a small marble outcrop (∼500 m2) in the Frontenac Terrane, Grenville Province, Ontario. These micas crystallized during amphibolite-facies metamorphism at ∼1170 Ma and experienced a thermal pulse ∼100 Ma later at shallow crustal levels associated with the emplacement of plutons. 87Rb/86Sr ages of the phlogopites range from ∼950 to ∼1050 Ma, consistent with resetting during the later thermal event. The same phlogopites however, give 40Ar/39Ar ages between ∼950 and 1160 Ma, spanning the age range of the two thermal events. This result is intriguing because these micas have undergone the same thermal history and were not deformed after peak metamorphic conditions. In order to understand this phenomenon, the chemical, crystallographical, and microstructural nature of four mica samples has been characterized in detail using a wide range of analytical techniques. The scanning electron microscope (SEM), electron microprobe (EMP), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data show that the micas are chemically homogeneous (with the exception of Ba) and similar in composition. The Fourier transform infrared spectroscopy and Mossbauer results show that the M sites for three of the micas are dominated by divalent cations and the Fe3+/(Fe2++Fe3+) ratio for all four phlogopites ranges from 0.10 to 0.25. The stable-isotopic data for calcite indicate that this outcrop was not affected by hydrothermal fluids after peak metamorphism. No correlation between chemical composition and 87Rb/86Sr and 40Ar/39Ar age or between crystal size and 40Ar/39Ar age is observed. The only major difference among all of the micas was revealed through transmitted electron microscope (TEM), which shows that the older 1M micas contain significantly more layer stacking defects, associated with crystallization, than the younger micas. We

  3. Ar-39/Ar-40 and Space Exposure Ages of the Unique Portales Valley H-Chondrite

    NASA Technical Reports Server (NTRS)

    Garrison, D. H.; Bogard, D. D.

    2001-01-01

    The space exposure age of the unique Portales Valley H-chondrite is approx. 40-45 Myr. The 39 Ar-40 Ar ages of two samples are 4.477 +/- 0.016 and 4.46 +/- 0.02 Ga and show no evidence of more recent disturbance, in contrast to previous radiometric determinations Additional information is contained in the original extended abstract..

  4. Early Pleistocene 40Ar/39Ar ages for Bapang Formation hominins, Central Jawa, Indonesia

    PubMed Central

    Larick, Roy; Ciochon, Russell L.; Zaim, Yahdi; Sudijono; Suminto; Rizal, Yan; Aziz, Fachroel; Reagan, Mark; Heizler, Matthew

    2001-01-01

    The Sangiran dome is the primary stratigraphic window for the Plio-Pleistocene deposits of the Solo basin of Central Jawa. The dome has yielded nearly 80 Homo erectus fossils, around 50 of which have known findspots. With a hornblende 40Ar/39Ar plateau age of 1.66 ± 0.04 mega-annum (Ma) reportedly associated with two fossils [Swisher, C.C., III, Curtis, G. H., Jacob, T., Getty, A. G., Suprijo, A. & Widiasmoro (1994) Science 263, 1118–1121), the dome offers evidence that early Homo dispersed to East Asia during the earliest Pleistocene. Unfortunately, the hornblende pumice was sampled at Jokotingkir Hill, a central locality with complex lithostratigraphic deformation and dubious specimen provenance. To address the antiquity of Sangiran H. erectus more systematically, we investigate the sedimentary framework and hornblende 40Ar/39Ar age for volcanic deposits in the southeast quadrant of the dome. In this sector, Bapang (Kabuh) sediments have their largest exposure, least deformation, and most complete tephrostratigraphy. At five locations, we identify a sequence of sedimentary cycles in which H. erectus fossils are associated with epiclastic pumice. From sampled pumice, eight hornblende separates produced 40Ar/39Ar plateau ages ranging from 1.51 ± 0.08 Ma at the Bapang/Sangiran Formation contact, to 1.02 ± 0.06 Ma, at a point above the hominin-bearing sequence. The chronological sequence of 40Ar/39Ar ages follows stratigraphic order across the southeast quadrant. An intermediate level yielding four nearly complete crania has an age of about 1.25 Ma. PMID:11309488

  5. Ar-Ar Dating of Martian Meteorite, Dhofar 378: An Early Shock Event?

    NASA Technical Reports Server (NTRS)

    Park, J.; Bogard, D. D.

    2006-01-01

    Martian meteorite, Dhofar 378 (Dho378) is a basaltic shergottite from Oman, weighing 15 g, and possessing a black fusion crust. Chemical similarities between Dho378 and the Los Angeles 001 shergottite suggests that they might have derived from the same Mars locale. The plagioclase in other shergottites has been converted to maskelenite by shock, but Dho378 apparently experienced even more intense shock heating, estimated at 55-75 GPa. Dho378 feldspar (approximately 43 modal %) melted, partially flowed and vesiculated, and then partially recrystallized. Areas of feldspathic glass are appreciably enriched in K, whereas individual plagioclases show a range in the Or/An ratio of approximately 0.18-0.017. Radiometric dating of martian shergottites indicate variable formation times of 160-475 Myr, whereas cosmic ray exposure (CRE) ages of shergottites indicate most were ejected from Mars within the past few Myr. Most determined Ar-39-Ar-40 ages of shergottites appear older than other radiometric ages because of the presence of large amounts of martian atmosphere or interior Ar-40. Among all types of meteorites and returned lunar rocks, the impact event that initiated the CRE age very rarely reset the Ar-Ar age. This is because a minimum time and temperature is required to facilitate Ar diffusion loss. It is generally assumed that the shock-texture characteristics in martian meteorites were produced by the impact events that ejected the rocks from Mars, although the time of these shock events (as opposed to CRE ages) are not directly dated. Here we report Ar-39-Ar-40 dating of Dho378 plagioclase. We suggest that the determined age dates the intense shock heating event this meteorite experienced, but that it was not the impact that initiated the CRE age.

  6. Ar-40-Ar-39 microanalysis of single 74220 glass balls and 72435 breccia clasts

    NASA Technical Reports Server (NTRS)

    Huneke, J. C.

    1978-01-01

    Ar-40-Ar-39 age measurements on single orange glass balls from the Apollo 17 soil 74220 and individual clasts from the Apollo 17 highland breccia 72435 are reported. The measurements required the use of newly established microanalytical techniques to obtain high quality analyses on about 0.5 mg particles with only a few hundred ppm K. An age of 3.60 plus or minus 0.04 b.y. is determined for the orange glass. No corrections for a trapped Ar-40 component were required. The glass forming event occurred at the very end of or after the extrusion of the mare basalts at the Apollo 17 site. An extremely well defined age plateau at 3.86 plus or minus 0.04 b.y. was determined for a 72435 plagioclase clast with attached matrix. A second large plagioclase crystal yielded significantly older ages over the last 60% of Ar release at high temperatures and is a relict clast incompletely degassed at the time of breccia formation. 72435 also contains plagioclase clasts with primitive Sr and a 4.55 AE old dunite clast. The Ar results provide additional evidence for the association of chemically unequilibrated, relict clasts with both primitive Sr and older K/Ar ages.

  7. Laser {sup 40}Ar/{sup 39}Ar microprobe analyses of fine-grained illite

    SciTech Connect

    Onstott, T.C.; Mueller, C.; Vrolijk, P.J.; Pevear, D.R.

    1997-09-01

    Fine-grained (<0.02 {mu}m) to coarse-grained (2.0-0.2 {mu}m) illite separates and finely powdered muscovite standards were analyzed with a microencapsulation technique and an {sup 40}Ar/{sup 39}Ar laser microprobe. The integrated ages of the illite agreed within error with conventional K/Ar analyses, even though the sample sizes, 1-100 micrograms, were at least a 10,000-fold less. Incremental laser heating of an artificial mixture of illite and muscovite of two different ages yielded a stair step profile, where the youngest and oldest incremental ages approximately coincided with their K/Ar ages. The thermally activated argon release rate from illite was distinct from that of the muscovite and may result from differences in grain thickness, lower K concentration, and the presence of cis vs. trans-sited vacancies. Incremental heating, therefore, may prove capable of delineating detrital from authigenic components in illite extracted from shale and sandstone. Microencapsulation and laser {sup 40}Ar/{sup 39}Ar analyses, when combined with sophisticated techniques for separating clays, will permit dating of samples where clay is a minor constituent, such as sandstones and meteorites, and will enhance identification of endmember ages in naturally occurring clay. 45 refs., 9 figs., 2 tabs.

  8. The ChArMEx database

    NASA Astrophysics Data System (ADS)

    Ferré, Hélène; Descloitres, Jacques; Fleury, Laurence; Boichard, Jean-Luc; Brissebrat, Guillaume; Focsa, Loredana; Henriot, Nicolas; Mastrorillo, Laurence; Mière, Arnaud; Vermeulen, Anne

    2013-04-01

    The Chemistry-Aerosol Mediterranean Experiment (ChArMEx, http://charmex.lsce.ipsl.fr/) aims at a scientific assessment of the present and future state of the atmospheric environment in the Mediterranean Basin, and of its impacts on the regional climate, air quality, and marine biogeochemistry. The project includes long term monitoring of environmental parameters, intensive field campaigns, use of satellite data and modelling studies. Therefore ChARMEx scientists produce and need to access a wide diversity of data. In this context, the objective of the database task is to organize data management, distribution system and services such as facilitating the exchange of information and stimulating the collaboration between researchers within the ChArMEx community, and beyond. The database relies on a strong collaboration between OMP and ICARE data centres and falls within the scope of the Mediterranean Integrated Studies at Regional And Locals Scales (MISTRALS) program data portal. All the data produced by or of interest for the ChArMEx community will be documented in the data catalogue and accessible through the database website: http://mistrals.sedoo.fr/ChArMEx. The database website offers different tools: - A registration procedure which enables any scientist to accept the data policy and apply for a user database account. - Forms to document observations or products that will be provided to the database in compliance with metadata international standards (ISO 19115-19139; INSPIRE; Global Change Master Directory Thesaurus). - A search tool to browse the catalogue using thematic, geographic and/or temporal criteria. - Sorted lists of the datasets by thematic keywords, by measured parameters, by instruments or by platform type. - A shopping-cart web interface to order in situ data files. At present datasets from the background monitoring station of Ersa, Cape Corsica and from the 2012 ChArMEx pre-campaign are available. - A user-friendly access to satellite products

  9. Application of the 40Ar/39Ar technique to date the Minoan Tuff, Santorini

    NASA Astrophysics Data System (ADS)

    Wijbrans, J. R.; Kuiper, K.; Morgan, L. E.; Klaver, M.; Vroon, P. Z.

    2012-12-01

    The age of the catastrophic eruption of the volcano of Santorini during the Bronze Age is well established from 14C dating at 3344.9 ± 7.5 a1 (uncertainties quoted as 1-σ). Application of the 40Ar/39Ar technique to products from this eruption is used here to (1) investigate the limits of the technique using conventional single collector mass spectrometry on a MAP215-50 instrument, (2) analyse sources of uncertainty to identify major contributing factors for the uncertainty of young 40Ar/39Ar ages, and (3) provide 40Ar/39Ar ages for a sample that has been previously dated via 14C and dendrochronology to further investigate issues with the accuracy of 40Ar/39Ar dating in the late Quaternary. We have separated the plagioclase fraction from the lower Minoan Tuff that immediately overlies the Cape Riva (rp6) tuff in a bay on the west coast of Thira, NW of the town of Oia. Using the calibration of 40Ar/36Ar of Lee et al.2, the decay constant recommended by Min at al.3, and the FCs age of Kuiper et al.4, we calculate an inverse isochron age of 3.7 ± 1.6 ka and a trapped 40Ar/36Ar intercept of 299.8 ± 1.2, slightly higher than the ratio for atmospheric argon of 298.56 ± 0.31, when all steps with ages > 50 ka are included in the regression. Enrichment in radiogenic 40Ar in the steps used for the isochron is extremely low, given the low concentration of K2O in plagioclase and the extremely young age. The stepwise heating approach proved useful because in all 5 replicate experiments unexpectedly high ages showed up at higher step temperatures, suggesting that in each separate some older contaminant was present. The plateaus of each of the replicate experiments had quite reproducible ages, however, and a pooled age was calculated for 23 out of 48 individual steps. The pooled age for the plateau was 17.6 ± 4.1 ka, which is high due to the slight component of excess 40Ar in the non-radiogenic component, as revealed from regression analysis. refs: 1SW Manning et al. (2006

  10. A natural laboratory for 40Ar/39Ar geochronology: ICDP cores from Lake Van, Turkey

    NASA Astrophysics Data System (ADS)

    Engelhardt, Jonathan; Sudo, Masafumi; Oberhänsli, Roland

    2015-04-01

    Pore water samples from ICDP Paleovan cores indicate a limited pore water exchange within Quaternary lake sediments. The core's volcaniclastic sections bear unaltered K-rich ternary feldspar and fresh to altered glass shards of predominantly rhyolitic composition. Whereas applying the 40Ar/39Ar method on feldspars resulted in ages timing a late-stage crystallization, glass shards had the potential to date the eruption. Volcanic glass is prone to modifications such as hydrous alteration (palagonitization) and devitrification (Cerling et al., 1985). These modifications affect the glass' chemistry and challenge the application of the 40Ar/39Ar method. Gaining precise radiometric ages from two phases has the potential to strengthen a climate-stratigraphic age-model (Stockhecke et al., 2014), and to significantly increase the temporal resolution on the deposition of the lake sediments. Vice versa the core's previous age model has the ability to question the reliability of 40Ar/39Ar eruption ages derived from ternary feldspars and glass shards. Multi- and single-grain total fusion on alkali feldspars from six volcaniclastic deposits resulted in Pleistocene ages that are in good agreement with the predicted age model. Feldspar phenocrysts from three ashes in the core's youngest section yielded consistent isochron ages that are significantly older than the model's prediction. Several distinct stratigraphic and paleomagnetic time markers of similar stratigraphic positions contradict to the older radiometric dates (Stockhecke et al., 2014). Partial resorption features of inherited feldspar domains and the involvement of excess 40Ar indicate incomplete degassing of older domains. To evaluate the magmatic history of the different domains EMPA mappings of trace elements that could be interpreted as Ar diffusion couples are currently conducted. Geochronology on Paleovan cores offers unique opportunities to monitor the effect of alteration on the Ar-systematics of volcanic glass

  11. Ar-Ar Age Distributions of Glacially Derived Hornblende Grains in the Eastern Weddell Sea

    NASA Astrophysics Data System (ADS)

    Dahlhauser, E. M.; Pierce, E. L.; Hemming, S. R.; Williams, T.; Steponaitis, E. A.; Brachfeld, S. A.

    2010-12-01

    How the East Antarctic Ice Sheet has responded to past changes in climate is an important question in paleo- and future-climate research. Subglacial water is increasingly recognized as a major weakness that allows the destabilization of glaciers, and thus an important avenue of provenance research around Antarctica is to characterize the composition of glaciogenic detritus on the perimeter of Antarctica downstream from large subglacial lakes. For this study we use the Ar-Ar method to date detrital hornblendes from thirteen marine sediment cores from the Eastern Weddell Sea and off the coast of Dronning Maud Land. This area could be an important iceberg source in some climate conditions due to its proximity to the Recovery Subglacial Basin (Bell et al., 2007, Nature), a potential weak spot in the ice sheet. Research conducted by Roy et al., (2007, Chemical Geology) and Williams et al., (2010, EPSL) demonstrates that Ar-Ar of glacially derived detrital hornblende grains from marine sediments can be used: 1) to characterize Antarctica’s subglacial geology and 2) as a sedimentary provenance tool to study Antarctic Ice Sheet dynamics. The purpose of this project is to learn more about the subglacial geology around the Eastern Weddell Sea by characterizing the composition of ice rafted detritus (IRD). The relatively high closure temperature of Ar-Ar in hornblende (~500°C) allows this system to record the last major tectonothermal event to effect a body of Antarctic rock such as orogenic metamorphism or, often, initial crystallization from magma. The detrial hornblende ages are consistent with limited on-land ages showing dominant populations of 400-600 Ma, 900-1100 Ma, and 2800-3200 Ma. These ages correspond to the Pan-African, Grenville, and Humboldt orogenies respectively. Comparison of the Ar-Ar ages and the core sites’ proximities to the ice streams and ice divides allows us to determine the likely source areas. The ~500 Ma population to corresponds to the

  12. Calibration of a Carboniferous U-Pb and Ar-Ar Standard

    NASA Astrophysics Data System (ADS)

    Shea, E. K.; Machlus, M.; Hemming, S. R.; Bowring, S. A.

    2015-12-01

    An important goal of the EARTHTIME initiative is to produce an accurate and precise sequence of geologic events, allowing the evaluation of the rates of geologic processes. Toward this end, the Ar-Ar and U-Pb communities require a set of standards that permit inter-laboratory and inter-technique comparisons. Natural zircon and sanidine samples that are extensively analyzed by multiple labs play a critical role for these comparisons, but are currently limited in number (Plesovice, R33, Temora 2 zircons; Fish Canyon, Alder Creek, Taylor Creek sanidine). Calibration between the sanidine Ar-Ar and zircon U-Pb is sparse and complexity in one or both of the systems is a general problem. Further, there is currently no Paleozoic sanidine monitor standard for Ar-Ar geochronology. The sanidine- and zircon-bearing Carboniferous Fire Clay tonstein provides potential natural Paleozoic standards for these two systems. The Fire Clay tonstein is a voluminous Carboniferous ash bed from the Appalachian basin. Exposures of the tonstein span over 300 km, making it a valuable marker bed for Appalachian geology. Here we report the results of 64 single-grain zircon U-Pb TIMS analyses and 223 single-grain sanidine Ar/Ar analyses. Although previous efforts have been plagued by xenocrystic zircons, by careful selection of only elongate crystals we were able to entirely avoid discordant analyses older than 316 Ma. Unfiltered analyses of zircons analyzed from a population of acicular crystals give a range of dates between ~315 and ~314 Ma with 2 sigma uncertainties of ~0.2 Ma. A weighted mean of these dates has an MSWD of ~4.0, suggesting geological complexity in the magma chamber or post-eruption lead loss. Sanidine ages have a range of less than 1 %, and only a single population can be distinguished with precision at the 1 Ma level for individual crystals. The ability to select crystals of both zircon and sanidine that give a narrow range of ages suggests that the Fire Clay tonstein holds

  13. 40Ar* loss in experimentally deformed muscovite and biotite with implications for 40Ar/39Ar geochronology of naturally deformed rocks

    USGS Publications Warehouse

    Cosca, M.; Stunitz, H.; Bourgeix, A.-L.; Lee, J.P.

    2011-01-01

    The effects of deformation on radiogenic argon (40Ar*) retentivity in mica are described from high pressure experiments performed on rock samples of peraluminous granite containing euhedral muscovite and biotite. Cylindrical cores, ???15mm in length and 6.25mm in diameter, were drilled from granite collected from the South Armorican Massif in northwestern France, loaded into gold capsules, and weld-sealed in the presence of excess water. The samples were deformed at a pressure of 10kb and a temperature of 600??C over a period 29 of hours within a solid medium assembly in a Griggs-type triaxial hydraulic deformation apparatus. Overall shortening in the experiments was approximately 10%. Transmitted light and secondary and backscattered electron imaging of the deformed granite samples reveals evidence of induced defects and for significant physical grain size reduction by kinking, cracking, and grain segmentation of the micas.Infrared (IR) laser (CO2) heating of individual 1.5-2.5mm diameter grains of muscovite and biotite separated from the undeformed granite yield well-defined 40Ar/39Ar plateau ages of 311??2Ma (2??). Identical experiments on single grains separated from the experimentally deformed granite yield results indicating 40Ar* loss of 0-35% in muscovite and 2-3% 40Ar* loss in biotite. Intragrain in situ ultraviolet (UV) laser ablation 40Ar/39Ar ages (??4-10%, 1??) of deformed muscovites range from 309??13 to 264??7Ma, consistent with 0-16% 40Ar* loss relative to the undeformed muscovite. The in situ UV laser ablation 40Ar/39Ar ages of deformed biotite vary from 301 to 217Ma, consistent with up to 32% 40Ar* loss. No spatial correlation is observed between in situ 40Ar/39Ar age and position within individual grains. Using available argon diffusion data for muscovite the observed 40Ar* loss in the experimentally treated muscovite can be utilized to predict average 40Ar* diffusion dimensions. Maximum 40Ar/39Ar ages obtained by UV laser ablation overlap those

  14. 40Ar ∗ loss in experimentally deformed muscovite and biotite with implications for 40Ar/ 39Ar geochronology of naturally deformed rocks

    NASA Astrophysics Data System (ADS)

    Cosca, Michael; Stunitz, Holger; Bourgeix, Anne-Lise; Lee, John P.

    2011-12-01

    The effects of deformation on radiogenic argon ( 40Ar ∗) retentivity in mica are described from high pressure experiments performed on rock samples of peraluminous granite containing euhedral muscovite and biotite. Cylindrical cores, ˜15 mm in length and 6.25 mm in diameter, were drilled from granite collected from the South Armorican Massif in northwestern France, loaded into gold capsules, and weld-sealed in the presence of excess water. The samples were deformed at a pressure of 10 kb and a temperature of 600 °C over a period 29 of hours within a solid medium assembly in a Griggs-type triaxial hydraulic deformation apparatus. Overall shortening in the experiments was approximately 10%. Transmitted light and secondary and backscattered electron imaging of the deformed granite samples reveals evidence of induced defects and for significant physical grain size reduction by kinking, cracking, and grain segmentation of the micas. Infrared (IR) laser (CO 2) heating of individual 1.5-2.5 mm diameter grains of muscovite and biotite separated from the undeformed granite yield well-defined 40Ar/ 39Ar plateau ages of 311 ± 2 Ma (2σ). Identical experiments on single grains separated from the experimentally deformed granite yield results indicating 40Ar ∗ loss of 0-35% in muscovite and 2-3% 40Ar ∗ loss in biotite. Intragrain in situ ultraviolet (UV) laser ablation 40Ar/ 39Ar ages (±4-10%, 1σ) of deformed muscovites range from 309 ± 13 to 264 ± 7 Ma, consistent with 0-16% 40Ar ∗ loss relative to the undeformed muscovite. The in situ UV laser ablation 40Ar/ 39Ar ages of deformed biotite vary from 301 to 217 Ma, consistent with up to 32% 40Ar ∗ loss. No spatial correlation is observed between in situ40Ar/ 39Ar age and position within individual grains. Using available argon diffusion data for muscovite the observed 40Ar ∗ loss in the experimentally treated muscovite can be utilized to predict average 40Ar ∗ diffusion dimensions. Maximum 40Ar/ 39Ar ages

  15. Alpha gas state in 36Ar

    NASA Astrophysics Data System (ADS)

    Akimune, Hidetoshi; Gibelin, Julien; Harakeh, Muhsin; Itoh, Masatoshi; Kawabata, Takahiro; Tamii, Atsushi; Fujiwara, Mamoru; Miki, Kenjiro; Iwamoto, Chiro; Otsu, Hideaki; Oha, Shinsuke; Tanihata, Isao; Muramoto, Tomoyuki; Kadono, Chika; Kalantar, Nasser; Ando, Shun; Leblond, Sylvian; Ayyad, Yassid; Furuno, Tatsuya; Tsynyra, Miho; Baba, Tasuo; Adachi, Satoshi; Freer, Martin

    2014-09-01

    The α cluster structures in light nuclei with N = Z are expected to appear abov the threshold energy of breakup into α particles. After the proposal of an α cluster wave function with α particle condensate type, such condensate states are both theoretically and experimentally discussed extensively. Theoretically, the existence of dilute α cluster state in nuclei with mass region of A > 16, experimentally, is not confirmed for N- α cluster states in nuclei heavier than A = 16. Recently, we measured α inelastic scattering of 36Ar followed by α decay in an inverse kinematics setup. A 50 MeV/u 36Ar beam from RCNP ring cyclotron was used to bombard a 4He gas target. α particles were detected in the magnetic spectrometer LAS which was set at 0 degrees. The α cluster structures in light nuclei with N = Z are expected to appear abov the threshold energy of breakup into α particles. After the proposal of an α cluster wave function with α particle condensate type, such condensate states are both theoretically and experimentally discussed extensively. Theoretically, the existence of dilute α cluster state in nuclei with mass region of A > 16, experimentally, is not confirmed for N- α cluster states in nuclei heavier than A = 16. Recently, we measured α inelastic scattering of 36Ar followed by α decay in an inverse kinematics setup. A 50 MeV/u 36Ar beam from RCNP ring cyclotron was used to bombard a 4He gas target. α particles were detected in the magnetic spectrometer LAS which was set at 0 degrees. Taro Hirao Grant-in-Aid for Scientific Research.

  16. Comparison of Ca and Ar Diffusion in Phlogopite: Implications for K-Ca and K-Ar Geochronology

    NASA Astrophysics Data System (ADS)

    Cruz, M. F.; Szilas, K.; Grove, M. J.

    2015-12-01

    Coupled geochronology based upon branched decay of 40K-40Ar and 40K-40Ca decay is rarely exploited because 40Ca is the major common isotope of calcium and 40Ca and 40K are difficult to resolve isotopically without resorting to isotope dilution wet chemistry. Recently developed ion microprobe methods based upon measurement of doubly ionized species partially overcome the latter problem and have been applied to high K/Ca micas. The ability to interpret K-Ar and K-Ca results is limited due to uncertainty in the relative diffusion properties of Ca and Ar. To address this problem, we are performing Ar and Ca diffusion experiments and fluid-crystal Ar partitioning experiments with anhydrous F-phlogopite that is stable to 1390°C. As an additional check, we are comparing K-Ca and K-Ar ages from natural mantle phlogopites from a variety of settings to assess the relative retentivity of Ar and Ca. South African xenoliths tend to yield 40Ar/39Ar ages that are much older than K-Ca ages from the same phologopites. Possible excess 40Ar and high common Ca render the comparisons inconclusive, but this suggests that Ca diffuses more readily than Ar in phlogopite. Our most definitive K-Ca phlogopite results (i.e., least affected by common Ca) come from the Archean Seqi dunite of SW Greenland. The K-Ca ages of Seqi phlogopites is 927 ± 26 Ma (2s). Incremental heating 40Ar/39Ar results from the same sample yields a much older result with a terminal age of 3.5 Ga. However, the first 5-10% of 39Ar release are consistent with transient heating at ca. 900 Ma. Considered together, the K-Ca and 40Ar/39Ar results from the Seqi dunite locality strongly suggest that Ca diffusion is more rapid than Ar diffusion in phlogopite.

  17. CCAR1 promotes chromatin loading of androgen receptor (AR) transcription complex by stabilizing the association between AR and GATA2

    PubMed Central

    Seo, Woo-Young; Jeong, Byong Chang; Yu, Eun Ji; Kim, Hwa Jin; Kim, Seok-Hyung; Lim, Joung Eun; Kwon, Ghee Young; Lee, Hyun Moo; Kim, Jeong Hoon

    2013-01-01

    Androgen receptor (AR), a ligand-dependent transcription factor, plays a critical role in prostate cancer onset and progression, and its transcriptional function is mediated largely by distinct nuclear receptor co-regulators. Here, we show that cell cycle and apoptosis regulator 1 (CCAR1) functions as an AR co-activator. CCAR1 interacted with and enhanced the transcriptional activity of AR. Depletion of CCAR1 caused reduction in androgen-dependent expression of a subset of AR target genes. We further showed that CCAR1 is required for recruitment of AR, MED1 and RNA polymerase II to the enhancers of AR target genes and for androgen-induced long-range prostate specific antigen enhancer–promoter interaction. The molecular mechanism underlying CCAR1 function in AR-mediated transcription involves CCAR1-mediated enhanced recruitment of GATA2, a pioneer factor for AR, to AR-binding sites. CCAR1 stabilized the interaction between AR and GATA2 by interacting directly with both proteins, thereby facilitating AR and GATA2 occupancy on the enhancers. Furthermore, CCAR1 depletion inhibited the growth, migration, invasion of prostate cancer cells and reduced the tumorigenicity of prostate cancer cells in vivo. Our results firmly established CCAR1 as an AR co-activator that plays a key role in AR transcription complex assembly and has an important physiological role in androgen signaling and prostate tumorigenesis. PMID:23887938

  18. 40Ar retention in the terrestrial planets.

    PubMed

    Watson, E Bruce; Thomas, Jay B; Cherniak, Daniele J

    2007-09-20

    The solid Earth is widely believed to have lost its original gases through a combination of early catastrophic release and regulated output over geologic time. In principle, the abundance of 40Ar in the atmosphere represents the time-integrated loss of gases from the interior, thought to occur through partial melting in the mantle followed by melt ascent to the surface and gas exsolution. Here we present data that reveal two major difficulties with this simple magmatic degassing scenario--argon seems to be compatible in the major phases of the terrestrial planets, and argon diffusion in these phases is slow at upper-mantle conditions. These results challenge the common belief that the upper mantle is nearly degassed of 40Ar, and they call into question the suitability of 40Ar as a monitor of planetary degassing. An alternative to magmatism is needed to release argon to the atmosphere, with one possibility being hydration of oceanic lithosphere consisting of relatively argon-rich olivine and orthopyroxene. PMID:17882213

  19. Call for Development of New Mineral Standards for 40Ar/39Ar Dating

    NASA Astrophysics Data System (ADS)

    Deino, A. L.; Turrin, B. D.; Renne, P. R.; Hemming, S. R.

    2015-12-01

    Age determination via the 40Ar/39Ar dating method relies on the intercomparison of measured 40Ar*/39ArK ratios of geological unknowns with those of co-irradiated mineral standards. Good analytical procedure dictates that these ratios (and the evolution of the Ar ion beams underpinning them) be as similar as practical for the greatest accuracy. Unfortunately, throughout several intervals of the geological time scale this 'best practice' cannot be achieved with existing widely used standards. Only two internationally utilized sanidine standards are available for the middle to late Cenozoic: the Alder Creek Rhyolite sanidine (ACs), at ~1.2 Ma (Turrin et al., 1994; Nomade et al., 2005), and the Fish Canyon Tuff sanidine (FCs) at ~28.2 Ma (e.g., Kuiper et al., 2008; Renne et al, 2011). The situation is even worse throughout much of the rest of the Phanerozoic, as the next oldest standard in common use is the Hb3gr hornblende standard with an age of ~1.1 Ga (Turner, 1971; Jourdan et al., 2006). We propose, as a community effort, the development a set of standards covering the entire target range of high-precision 40Ar/39Ar dating, i.e. the Phanerozoic. Their ages would be stepped in a regular fashion with no more than approximately a factor of 3 between standards, such that in the worse case the 40Ar*/39Ar ratios of standards and unknown need differ by no more than a factor of two. While somewhat arbitrary, an approximately 3 X age progression allows the entire time scale to be covered by a manageable number of standards. Anchoring the progression in the widely used ACs, FCs, and Hb3gr (in bold, below) yields the following set of suggested standard ages: 0.4, 1.2, 3.3, 9.4, 28.2, 95, 320, and 1100 Ma. A suitable standard should be highly reproducible in age at the grain-to-grain and sub-grain levels, and highly radiogenic. The mineral should be abundant and easily separated from the host rock. These criteria may be most easily achieved by focusing on sanidine phenocrysts

  20. Potassium isotopic compositions of NIST potassium standards and 40Ar/39Ar mineral standards

    NASA Astrophysics Data System (ADS)

    Morgan, L. E.; Tappa, M.; Ellam, R. M.; Mark, D. F.; Lloyd, N. S.; Higgins, J. A.; Simon, J. I.

    2013-12-01

    Knowledge of the isotopic ratios of standards, spikes, and reference materials is fundamental to the accuracy of many geochronological methods. For example, the 238U/235U ratio relevant to U-Pb geochronology was recently re-determined [1] and shown to differ significantly from the previously accepted value employed during age determinations. These underlying values are fundamental to accurate age calculations in many isotopic systems, and uncertainty in these values can represent a significant (and often unrecognized) portion of the uncertainty budget for determined ages. The potassium isotopic composition of mineral standards, or neutron flux monitors, is a critical, but often overlooked component in the calculation of K-Ar and 40Ar/39Ar ages. It is currently assumed that all terrestrial materials have abundances indistinguishable from that of NIST SRM 985 [2]; this is apparently a reasonable assumption at the 0.25‰ level (1σ) [3]. The 40Ar/39Ar method further relies on the assumption that standards and samples (including primary and secondary standards) have indistinguishable 40K/39K values. We will present data establishing the potassium isotopic compositions of NIST isotopic K SRM 985, elemental K SRM 999b, and 40Ar/39Ar biotite mineral standard GA1550 (sample MD-2). Stable isotopic compositions (41K/39K) were measured by the peak shoulder method with high resolution MC-ICP-MS (Thermo Scientific NEPTUNE Plus), using the accepted value of NIST isotopic SRM 985 [2] for fractionation [4] corrections [5]. 40K abundances were measured by TIMS (Thermo Scientific TRITON), using 41K/39K values from ICP-MS measurements (or, for SRM 985, values from [2]) for internal fractionation corrections. Collectively these data represent an important step towards a metrologically traceable calibration of 40K concentrations in primary 40Ar/39Ar mineral standards and improve uncertainties by ca. an order of magnitude in the potassium isotopic compositions of standards. [1] Hiess

  1. First 40Ar/39Ar dating of intense Late Palaeogene lateritic weathering in Peninsular India

    NASA Astrophysics Data System (ADS)

    Bonnet, Nicolas J.; Beauvais, Anicet; Arnaud, Nicolas; Chardon, Dominique; Jayananda, Mudlappa

    2014-01-01

    Lateritic surface processes have shaped large platform and cratons of the tropical belt. Constraining the timing of such processes is crucial to decipher their role in cratonic morphogenesis and their response to long-term climatic change and lithospheric deformation. Weathering histories have been documented for South America, Africa and Australia, but precise time constraints of the lateritic weathering processes in South India are still lacking. We present 40Ar/39Ar ages of supergene cryptomelane (K-Mn oxide) formed in the Sandur Mn ore deposits exposed on the highest lateritic paleolandsurface that once covered the Mysore plateau and the adjacent Deccan Traps. Significant 40Ar/39Ar ages are estimated between ∼36 and ∼26 Ma from well-defined plateaus in step heating 39Ar release spectra and from best-fitted inverse isochrones. These ages constitute firm time constraints that document intense late Eocene-Oligocene lateritic weathering over Peninsular India under the influence of warm and wet climate comparable to that prevailing in tropical humid forests. These results imply that Southern India was weathered between ∼36 and 26 Ma and may have been dissected mostly in the Neogene.

  2. A test of the 40Ar/39Ar age spectrum technique on some terrestrial materials

    USGS Publications Warehouse

    Lanphere, M.A.; Brent, Dalrymple G.

    1971-01-01

    40Ar/39Ar age spectra were determined for 10 terrestrial rock and mineral samples whose geologic history is known from independent evidence. The spectra for six mineral and whole rock samples, including biotite, feldspar, hornblende, muscovite, and granodiorite, that have experienced post-crystallization heating did not reveal the age of crystallization in any obvious way. Minima in the spectra, however, give reasonable maximum ages for reheating and high-temperature maxima can be interpreted as minimum crystallization ages. High-temperature ages of microcline and albite that have not been reheated are approximately 10% younger than the known crystallization age. Apparently there are no domains in these feldspars that have retained radiogenic 40Ar quantitatively. Spectra from two diabase samples that contain significant quantities of excess argon might mistakenly be interpreted as spectra from reheated samples and do not give the age of emplacement. The 40Ar/39Ar age spectrum technique may be a potentially valuable tool for the study of geologic areas with complex histories, but the interpretation of age spectra from terrestrial samples seems to be more difficult than suggested by some previous studies. ?? 1971.

  3. Measuring 36Ar without H35Cl interference

    NASA Astrophysics Data System (ADS)

    Saxton, John

    2015-04-01

    Noble gas measurements are usually made in static mode, when the mass spectrometer sensitivity is inversely proportional to volume: this makes the building of very large instruments to obtain high mass resolution impracticable. A particularly challenging interference has hitherto been H35Cl, which differs in mass from 36Ar by 1 part in 3937. We have developed a method which makes improved use of the available MRP to remove interferences, and used it to obtain HCl-free 36Ar measurements on a multicollector instrument with MRP of only ~6000 (MRP= mass resolving power = m/dm 5-95% on side of peak). By arranging that the target mass position on a minor isotope (e.g. 36Ar), from which the interference must be removed, coincides with the ~50% point on the side of a major isotope (e.g. 40Ar), it is possible both to set the mass accurately and to verify the mass position and stability during measurements. The peak top of 40Ar is measured in a separate mass step. Two small corrections are necessary. One compensates for the residual HCl tail at the 36Ar position. The other arises because the peak is not totally flat in the region of interest: 40Ar and 36Ar+HCl are measured on the peak top, whilst 36Ar is measured at the extreme edge, with slightly lower efficiency. The required correction parameters can be obtained from a series of air calibrations with different target/interference ratios. With samples containing 4x10-15to 3x10-14moles of 40Ar, 36Ar/40Ar was measured, without HCl interference, to a 1σ precision of 0.5%, only slightly worse than counting statistics. This is potentially useful for 40Ar/39Ar dating, where 36Ar is used to correct for trapped air, and may be particularly significant for smaller or younger samples.

  4. KAr and {40Ar }/{39}Ar study of metamorphic rocks associated with the Oman ophiolite: Tectonic implications

    NASA Astrophysics Data System (ADS)

    Montigny, R.; Le Mer, O.; Thuizat, R.; Whitechurch, H.

    1988-09-01

    K-Ar analyses on extracted minerals are reported for a variety of metamorphic rocks associated with the Sumail ophiolite. Amphibolites lying at the sole of the ophiolite yield ages of 95-100 Ma, which are viewed as reflecting times of crystallization. High-pressure metamorphics of the Saih Hatat reveal complex results: white micas range in age from 80 to 131 Ma whereas blue amphiboles indicate ages that are systematically lower than those of coexisting white micas. Investigation of a few white micas by the {40Ar }/{39Ar } step heating method yields rather intricate age spectra, featuring low apparent ages in the first and the last stages of gas release and high apparent ages in between. Two explanations can be equally envisaged for these convex-upward age spectra. The first is the mixing of two generations of micas, corresponding to two main metamorphisms. The first one ( M1) is a low- to medium-temperature, high-pressure event which conceivably occurred between 130 and 114 m.y. ago. The second ( M2) overprints M1 and has produced rocks typical of the greenschist facies. It took place 80 m.y. ago and also affected the sole of the ophiolites. The second is the presence of excess argon in mica mixtures with complex degassing properties. Thus, the two metamorphic phases identified by microscopic inspection are not significantly different in age. They occurred in the 70-80 Ma interval. Moreover, K-Ar dates on amphibole from gabbroic dikes intersecting the peridotites suggest that they are genetically linked to the mafic part of the ophiolites. Assuming that metamorphism is a tracer of tectonic events, we view the infraophiolitic amphibolites as the result of an intraoceanic thrusting which took place near a spreading center. Nevertheless, the uncertainty as to the age of the blueschist metamorphism precludes the possibility of indicating a timetable, based on metamorphic ages, for the motion shift of Africa relative to Eurasia during the Late Cretaceous. A tentative

  5. Paleotemperatures at the lunar surfaces from open system behavior of cosmogenic 38Ar and radiogenic 40Ar

    DOE PAGESBeta

    Shuster, David L.; Cassata, William S.

    2015-02-10

    The simultaneous diffusion of both cosmogenic 38Ar and radiogenic 40Ar from solid phases is controlled by the thermal conditions of rocks while residing near planetary surfaces. Combined observations of 38Ar/37Ar and 40Ar/39Ar ratios during stepwise degassing analyses of neutron-irradiated Apollo samples can distinguish between diffusive loss of Ar due to solar heating of the rocks and that associated with elevated temperatures during or following impact events; the data provide quantitative constraints on the durations and temperatures of each process. From sequentially degassed 38Ar/37Ar ratios can be calculated a spectrum of apparent 38Ar exposure ages versus the cumulative release fraction ofmore » 37Ar, which is particularly sensitive to conditions at the lunar surface typically over ~106–108 year timescales. Due to variable proportions of K- and Ca-bearing glass, plagioclase and pyroxene, with variability in the grain sizes of these phases, each sample will have distinct sensitivity to, and therefore different resolving power on, past near-surface thermal conditions. Furthermore, we present the underlying assumptions, and the analytical and numerical methods used to quantify the Ar diffusion kinetics in multi-phase whole-rock analyses that provide these constraints.« less

  6. Direct dating of weathering phenomena by [sup 40]Ar/[sup 39]Ar and K-Ar analysis of supergene K-Mn oxides

    SciTech Connect

    Vasconcelos, P.M.; Brimhall, G.H. ); Renne, P.R.; Becker, T.A. )

    1994-03-01

    Potassium-bearing manganese oxides, cryptomelane, K[sub 1-2](Mn[sup 3+]Mn[sup 4+])[sub 8] O[sub 16] [center dot] xH[sub 2]O, and hollandite, (K,Ba)[sub 1-2](Mn[sup 3+],Mn[sup 4+])[sub 8] O[sub 16] [center dot] xH[sub 2]O, are often authigenically precipitated in weathering profiles. Dating of these phases allows timing of the progression of oxidation fronts during weathering and pedogenic processes. Potential problems in manganese oxide dating, such as Ar and/or K losses, excess argon, [sup 39]Ar loss by recoil during neutron irradiation, etc. are addressed. The K-Ar and [sup 40]Ar/[sup 39]Ar analytical results indicate that Ar and/or K losses, excess [sup 40]Ar, and [sup 39]Ar recoil seem not to pose problems in manganese oxide dating. This investigation suggests that the fine scale, laser-probe [sup 40]Ar/[sup 39]Ar technique is most appropriate for dating of weathering phenomena because this technique permits identification of contaminating phases and the presence of multiple generations of weathering minerals in the inherently complex mineral assemblage characteristic of weathering profiles. K-Ar and [sup 40]Ar/[sup 39]Ar dating of supergene K-bearing manganese oxides formed during lateritization of Archean and Proterozoic bedrocks in the Carajas Region, Amazonia, Brazil, indicates that weathering started before 72 [+-] 6 Ma. Petrographic, electron microscope, and electron microprobe investigation reveal multiple generations of manganese oxide precipitation. Age clusters at 65-69, 51-56, 40-43, 33-35, 20, 24, 12-17 Ma, and zero-age (0.2 [+-] 0.2 Ma) suggest episodic precipitation of K-Mn oxides resulting form changing weathering conditions in the Amazon throughout the Cenozoic. K-Ar and [sup 40]Ar/[sup 39]Ar dating of supergene cryptomelane from weathering profiles in eastern Minas Gerais, southeastern Brazil, suggests continuous weathering from 10 to 5.6 Ma ago, possibly reflecting local climatic conditions due to the proximity with the Atlantic Ocean.

  7. Potential energy surface and bound states of the NH3-Ar and ND3-Ar complexes.

    PubMed

    Loreau, J; Liévin, J; Scribano, Y; van der Avoird, A

    2014-12-14

    A new, four-dimensional potential energy surface for the interaction of NH3 and ND3 with Ar is computed using the coupled-cluster method with single, double, and perturbative triple excitations and large basis sets. The umbrella motion of the ammonia molecule is explicitly taken into account. The bound states of both NH3-Ar and ND3-Ar are calculated on this potential for total angular momentum values from J = 0 to 10, with the inclusion of Coriolis interactions. The energies and splittings of the rovibrational levels are in excellent agreement with the extensive high-resolution spectroscopic data accumulated over the years in the infrared and microwave regions for both complexes, which demonstrates the quality of the potential energy surface. PMID:25494745

  8. Ar-Ar and Rb-Sr Ages of the Tissint Olivine-phyric Martian Shergottite

    NASA Technical Reports Server (NTRS)

    Park, J.; Herzog, G. F.; Nyquist, L. E.; Shih, C.-Y.; Turin, B.; Lindsay, F. N.; Delaney, J. S.; Swisher, C. C., III; Agee, C.

    2013-01-01

    The fifth martian meteorite fall, Tissint, is an olivine-phyric shergottite that contains olivine macrocrysts (approximately 1.5 mm) [1]. [2] reported the Sm-Nd age of Tissint as 596 plus or minus 23 Ma along with Rb-Sr data that defined no isochron. [3] reported Lu-Hf and Sm-Nd ages of 583 plus or minus 86 Ma and 616 plus or minus 67 Ma, respectively. The cosmic-ray exposure ages of Tissint are 1.10 plus or minus 0.15 Ma based on 10Be [4], and 1.0-1.1 Ma, based on 3He, 21Ne, and 38Ar [5,6].We report Ar-Ar ages and Rb-Sr data.

  9. Laser /39/Ar-/40/Ar dating of two clasts from consortium breccia 73215

    NASA Technical Reports Server (NTRS)

    Eichhorn, G.; Schaeffer, O. A.; James, O. B.; Mueller, H. W.

    1978-01-01

    A laser Ar-39-Ar-40 study of the components of an ANT-suite anorthositic gabbro and a black aphanite from a consortium breccia is reported. A wide range of K-Ar ages is found for the plagioclase in the anorthositic gabbro; at the centers of the largest grains is material showing the greatest age (older than 4.11 billion years) while the youngest material (3.81-3.88 billion years) is found near the grain margins. Partial outgassing of the clasts upon incorporation into the breccia could account for the age patterns. The black aphanite clast appears to be cogenetic with the aphanite that forms the breccia matrix. The time of crystallization of a lunar granite has also been measured by the laser technique.

  10. Oldest reliable Ar-40/Ar-39 ages for terrestrial rocks Barberton Mountain komatiites

    NASA Astrophysics Data System (ADS)

    Lopez Martinez, M.; York, D.; Hall, C. M.; Hanes, J. A.

    1984-01-01

    The first Ar-40/Ar-39 ages for komatiites and komatiitic basalts from the Barberton Mountain Greenstone Belt on the Transvaal-Swaziland border in southern Africa are reported. Both rock types display remarkable argon retentivity. While some variation is found among the samples, the best argon age estimate for the time of metamorphism is in the 3450-3490 Myr range. This age is only slightly less than that found in komatiites from the same area by Sm-Nd dating. The results show that the principal pervasive greenschist metamorphism in the area must have occurred within 100 Myr of the eruption of the komatiite. These results represent by far the oldest reliable ages obtained for terrestrial rocks using the K-Ar system.

  11. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2004-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Nay Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39-Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50- 4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4561.9 +/-0.1 Myr and 4560-4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later Ar-40 diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the post-assembly metamorphism may have been as late as approx.4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx.4560 to approx.4576 My. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and suggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni concentration

  12. Ar-Ar and I-XE Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2006-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39- Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50- 4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx. 4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx. 3.23-4.56 Gyr. New I-129-Xe-129 ges for Caddo County and EET8333 are 4561.9 plus or minus 0.1 Myr and 4560-4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx. 4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later 40Ar diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the postassembly metamorphism may have been as late as approx. 4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx. 4560 to approx. 4576 Myr. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and suggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni

  13. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2004-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39-Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50-4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4561.9+/-0.1 Myr and 4560- 4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later Ar-40 diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the post-assembly metamorphism may have been as late as approx.4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx.4560 to approx.4576 Myr. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and s,uggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni concentration

  14. MEIS1 functions as a potential AR negative regulator

    SciTech Connect

    Cui, Liang; Yang, Yutao; Hang, Xingyi; Cui, Jiajun; Gao, Jiangping

    2014-10-15

    The androgen receptor (AR) plays critical roles in human prostate carcinoma progression and transformation. However, the activation of AR is regulated by co-regulators. MEIS1 protein, the homeodomain transcription factor, exhibited a decreased level in poor-prognosis prostate tumors. In this study, we investigated a potential interaction between MEIS1 and AR. We found that overexpression of MEIS1 inhibited the AR transcriptional activity and reduced the expression of AR target gene. A potential protein–protein interaction between AR and MEIS1 was identified by the immunoprecipitation and GST pull-down assays. Furthermore, MEIS1 modulated AR cytoplasm/nucleus translocation and the recruitment to androgen response element in prostate specific antigen (PSA) gene promoter sequences. In addition, MEIS1 promoted the recruitment of NCoR and SMRT in the presence of R1881. Finally, MEIS1 inhibited the proliferation and anchor-independent growth of LNCaP cells. Taken together, our data suggests that MEIS1 functions as a novel AR co-repressor. - Highlights: • A potential interaction was identified between MEIS1 and AR signaling. • Overexpression of MEIS1 reduced the expression of AR target gene. • MEIS1 modulated AR cytoplasm/nucleus translocation. • MEIS1 inhibited the proliferation and anchor-independent growth of LNCaP cells.

  15. K/Ar dating of lunar soils. II

    NASA Technical Reports Server (NTRS)

    Alexander, E. C., Jr.; Bates, A.; Coscio, M. R., Jr.; Dragon, J. C.; Murthy, V. R.; Pepin, R. O.; Venkatesan, T. R.

    1976-01-01

    An attempt is made to identify those K/Ar techniques which extract the most reliable chronological information from lunar soils and to define the situations in which the best data are obtainable. Results are presented for determinations of the exposure and K/Ar ages of five lunar soil samples, which were performed by applying correlation techniques for a two-component argon structure to stepwise-heated and neutron-irradiated aliquots of grain-sized separates. It is found that ages deduced from Ar-40/surface-correlated Ar-36 vs K-40/surface-correlated Ar-36 and analogous plots of data from grain-sized separates appear to be the best available K/Ar ages of submature to mature lunar soils, that ages deduced from Ar-40 vs Ar-36 and analogous plots which assume a uniform K content can be significantly in error, and that stepwise-heating (Ar-40)-(Ar-39) experiments yield useful information only for simple immature soils where the K-Ar systematics are dominated by a single component.

  16. [sup 40]Ar/[sup 39]Ar thermochronology in the northern Bitterroot mylonite zone, Mt

    SciTech Connect

    House, M.A.; Hodges, K.V. . Dept. of Earth, Atmospheric, and Planetary Sciences)

    1993-04-01

    The extensional Bitterroot mylonite zone defines the eastern and southern border of the Bitterroot metamorphic core complex and is generally interpreted to be the major structure which accommodated unroofing of the metamorphic core. The most commonly cited evidence for the age of mylonitization are [sup 40]Ar/[sup 39]Ar ages for hornblend, muscovite, biotite, and potassium feldspar from the southern Bitterroot mylonite zone that indicate rapid cooling of the core rocks between 45.5 and 43.5 Ma. More recently, an [sup 40]Ar/[sup 39]Ar K-feldspar age of 46.4 [+-] 0.8 Ma for an undeformed rhyolite dike that cuts across the mylonitic fabric places a minimum age constraint on the southern part of the shear zone. The authors have obtained new [sup 40]Ar/[sup 39]Ar data for metapelitic rocks and amphibolites from the northeast border of the Bitterroot metamorphic core complex near an area where mylonitized granitoid rocks yielding 48--52 Ma U-Pb zircon crystallization ages constrain the maximum age of mylonitization. Isochran ages of 47.9 [+-] 0.9 and 49 [+-] 1 Ma for hornblende separated from deformed amphibolite pods in the northeast border zone are within analytical uncertainty of the younger mylonitized granitoid crystallization ages and indicate rapid post-crystallization cooling through temperatures of [approximately]780--800 K. They attribute this cooling to denudation related to shear zone development. Muscovite and biotite isochron ages from metapelitic rocks within the shear zone are significantly younger, between 42 and 44 Ms., and generally agree with mica ages obtained by Garmezy and Sutter for the southern part of the shear zone. However, all mica ages from the Bitterroot shear zone are younger than the minimum age of the shear zone deduced from the age of cross-cutting rhyolite dikes.

  17. The ChArMEx database

    NASA Astrophysics Data System (ADS)

    Ferré, Helene; Belmahfoud, Nizar; Boichard, Jean-Luc; Brissebrat, Guillaume; Descloitres, Jacques; Fleury, Laurence; Focsa, Loredana; Henriot, Nicolas; Mastrorillo, Laurence; Mière, Arnaud; Vermeulen, Anne

    2014-05-01

    The Chemistry-Aerosol Mediterranean Experiment (ChArMEx, http://charmex.lsce.ipsl.fr/) aims at a scientific assessment of the present and future state of the atmospheric environment in the Mediterranean Basin, and of its impacts on the regional climate, air quality, and marine biogeochemistry. The project includes long term monitoring of environmental parameters, intensive field campaigns, use of satellite data and modelling studies. Therefore ChARMEx scientists produce and need to access a wide diversity of data. In this context, the objective of the database task is to organize data management, distribution system and services, such as facilitating the exchange of information and stimulating the collaboration between researchers within the ChArMEx community, and beyond. The database relies on a strong collaboration between OMP and ICARE data centres and has been set up in the framework of the Mediterranean Integrated Studies at Regional And Locals Scales (MISTRALS) program data portal. All the data produced by or of interest for the ChArMEx community will be documented in the data catalogue and accessible through the database website: http://mistrals.sedoo.fr/ChArMEx. At present, the ChArMEx database contains about 75 datasets, including 50 in situ datasets (2012 and 2013 campaigns, Ersa background monitoring station), 25 model outputs (dust model intercomparison, MEDCORDEX scenarios), and a high resolution emission inventory over the Mediterranean. Many in situ datasets have been inserted in a relational database, in order to enable more accurate data selection and download of different datasets in a shared format. The database website offers different tools: - A registration procedure which enables any scientist to accept the data policy and apply for a user database account. - A data catalogue that complies with metadata international standards (ISO 19115-19139; INSPIRE European Directive; Global Change Master Directory Thesaurus). - Metadata forms to document

  18. 40Ar/39Ar and cosmic ray exposure ages of plagioclase-rich lithic fragments from Apollo 17 regolith, 78461

    NASA Astrophysics Data System (ADS)

    Das, J. P.; Baldwin, S. L.; Delano, J. W.

    2016-01-01

    Argon isotopic data is used to assess the potential of low-mass samples collected by sample return missions on planetary objects (e.g., Moon, Mars, asteroids), to reveal planetary surface processes. We report the first 40Ar/39Ar ages and 38Ar cosmic ray exposure (CRE) ages, determined for eleven submillimeter-sized (ranging from 0.06 to 1.2 mg) plagioclase-rich lithic fragments from Apollo 17 regolith sample 78461 collected at the base of the Sculptured Hills. Total fusion analysis was used to outgas argon from the lithic fragments. Three different approaches were used to determine 40Ar/39Ar ages and illustrate the sensitivity of age determination to the choice of trapped (40Ar/36Ar)t. 40Ar/39Ar ages range from ~4.0 to 4.4 Ga with one exception (Plag#10). Surface CRE ages, based on 38Ar, range from ~1 to 24 Ma. The relatively young CRE ages suggest recent re-working of the upper few centimeters of the regolith. The CRE ages may result from the effect of downslope movement of materials to the base of the Sculptured Hills from higher elevations. The apparent 40Ar/39Ar age for Plag#10 is >5 Ga and yielded the oldest CRE age (i.e., ~24 Ma). We interpret this data to indicate the presence of parentless 40Ar in Plag#10, originating in the lunar atmosphere and implanted in lunar regolith by solar wind. Based on a chemical mixing model, plagioclase compositions, and 40Ar/39Ar ages, we conclude that lithic fragments originated from Mg-suite of highland rocks, and none were derived from the mare region.

  19. 40Ar/39Ar thermochronology of isotopically zoned micas: Insights from the southwestern USA proterozoic orogen

    NASA Astrophysics Data System (ADS)

    Hodges, K. V.; Bowring, S. A.

    1995-08-01

    We have used three different 40Ar/39Ar laser microprobe methods to explore the distribution of radiogenic 40Ar in 1.0-1.5-mm biotite crystals from the ca. 1680 Ma Horse Mountain monzogranite of central Arizona. Incremental heating of two single crystals with a defocused laser beam produced flat age spectra with near-plateau ages of ˜1190 Ma, showing no indication of intracrystalline 40Ar inhomogeneity. In contrast, total fusion of twenty-five biotite fragments (˜ 100 pm) yielded apparent ages ranging from 1006.7 to 1212.0 Ma. Detailed age mapping in the {001} plane of two crystals, with the laser focused to a minimum spot size, confirms that the age dispersion in the fragment data reflects the existence of 200 m.y. age gradients in single crystals. The two mapped crystals display very different age distribution patterns that suggest radiogenic 40Ar loss through two mechanisms: volume diffusion on a scale comparable to that of the grain radius, and more rapid diffusion along discrete zones of high crystal defect density. Simple inverse modeling of the overall age dispersion in the two mapped crystals and the fragment population is consistent with the development of the observed age gradients by slow cooling at an average rate of ˜0.5 K/m.y. The Horse Mountain results, as well as previously published studies, indicate that conventional, incremental heating of hydrous phases can homogenize intracrystalline gradients in 40Ar, thereby masking important details of the thermal history of analyzed samples. In contrast, detailed isotopic mapping studies offer a wealth of information, and will become more powerful with continued improvement in the spatial resolution of 40Ar/39Ar laser microprobes. Total-fusion studies of crystal fragment populations can be readily automated, making them less labor-intensive than mapping studies. Our preliminary experiment on a limited Horse Mountain fragment population suggests that this procedure has great potential as a reconnaissance

  20. The barents sea magmatic province: Geological-geophysical evidence and new 40Ar/39Ar dates

    NASA Astrophysics Data System (ADS)

    Shipilov, E. V.; Karyakin, Yu. V.

    2011-07-01

    Resulting from study of the geological structure of the Franz Josef Land and Svalbard archipelagoes, this work presents new 17 40Ar/39Ar age datings for basalts taken during coastal expeditions in 2006-2010. Radiological age determination for intrusive units (sills) located in the western part of Nordensciold Land (Spitzbergen Island) has been made for the first time. In relation to use of the interpretation results of marine geological-geophysical data, the distribution peculiarities and time ranges for Jurassic-Cretaceous basic magmatism within the studied regions of the Barents Sea continental margin and within the Arctic as a whole are discussed.

  1. Ar-Ar Dating of Martian Chassignites, NWA2737 and Chassigny, and Nakhlite MIL03346

    NASA Technical Reports Server (NTRS)

    Bogard, D. D.; Garrison, D. H.

    2006-01-01

    Until recently only three nakhlites and one chassignite had been identified among martian meteorites. These four exhibit very similar radiometric ages and cosmic ray exposure (CRE) ages, indicating that they may have derived from a common location on Mars and were ejected into space by a single impact. This situation is quite different from that of martian shergottites, which exhibit a range of radiometric ages and CRE ages (1). Recently, several new nakhlites and a new martian dunite (NWA2737) have been recognized. Here we report our results of Ar-39-Ar-40 dating for the MIL03346 nakhlite and the NWA2737 "chassignite", along with new results on Chassigny.

  2. SUMER-IRIS Observations of AR11875

    NASA Astrophysics Data System (ADS)

    Schmit, Donald; Innes, Davina

    2014-05-01

    We present results of the first joint observing campaign of IRIS and SOHO/SUMER. While the IRIS datasets provide information on the chromosphere and transition region, SUMER provides complementary diagnostics on the corona. On 2013-10-24, we observed an active region, AR11875, and the surrounding plage for approximately 4 hours using rapid-cadence observing programs. These datasets include spectra from a small C -class flare which occurs in conjunction with an Ellerman-bomb type event. Our analysis focusses on how the high spatial resolution and slit jaw imaging capabilities of IRIS shed light on the unresolved structure of transient events in the SUMER catalog.

  3. Theoretical photoabsorption spectra of Ar n+ clusters

    NASA Astrophysics Data System (ADS)

    Doltsinis, Nikos L.; Knowles, Peter J.

    2000-08-01

    The photoabsorption spectra of selected Ar n+ clusters ( n=7, 8, 17, 19, 23) have been investigated theoretically using an extended Diatomics-in-Molecules approach including induced dipole - induced dipole and spin-orbit coupling interaction effects. Our calculations at 0 K confirm the experimentally observed spectral red-shift of the visible photoabsorption peak in the region 15< n<20 [Levinger et al., J. Chem. Phys. 89 (1988) 5654]. Furthermore, we have been able to reproduce the additional red-shift measured for 7⩽ n⩽9 [Haberland et al., Phys. Rev. Lett. 67 (1991) 3290] by carrying out finite temperature Monte Carlo simulations.

  4. Lu Hf and Ar Ar chronometry supports extreme rate of subduction zone metamorphism deduced from geospeedometry

    NASA Astrophysics Data System (ADS)

    Philippot, Pascal; Blichert-Toft, Janne; Perchuk, Alexei; Costa, Sylvie; Gerasimov, Vladimir

    2001-12-01

    Recent diffusion modeling of eclogitic garnets from the Great Caucasus, Russia, and Yukon, Canada, have shown that the preservation of garnet growth zoning in rocks that have equilibrated at high temperature (680-700 °C) is possible only if rates of pressure and temperature change on the burial and/or exhumation paths are in the order of several cm/year and several hundreds of °C/Ma. In order to confirm this observation, we performed Lu-Hf and Sm-Nd dating of garnet and Ar-Ar dating of mica on the same samples that were used for geospeedometry measurements in an earlier study. In both localities, garnet grew during prograde metamorphism at 690±40 °C and >1.5 GPa (Yukon) and 680±40 °C and >1.6 GPa (Great Caucasus). In contrast, phengite formed soon after the main eclogitic foliation at 520±50 °C (Yukon) and 600±40 °C (Great Caucasus). Garnet of the Yukon samples yielded Lu-Hf ages of 252±7, 255±7, 257±6 and 264±6 Ma that fall within error of phengite Ar-Ar integrated ages of 261±2 (laser spot date) and 256±3 Ma (age of mineral separates). No Sm-Nd ages were measured on the Yukon samples. For Great Caucasus samples, all Sm-Nd ages with the exception of one garnet-whole rock pair yielding a Sm-Nd age of 311±22 Ma are poorly constrained. In contrast, the Lu-Hf garnet chronometer yields ages of 322±14, 316±5 and 296±11 Ma that again fall within error of the phengite Ar-Ar mean age of 303±5 Ma. Because the geospeedometry approach provides information on cooling rates, information on the closure temperature of a given isotopic system can be extracted from the analytical solution of Dodson [Contrib. Mineral. Petrol. 40 (1973) 259] using appropriate sets of experimentally determined diffusion data. The results of these calculations indicate that uncertainties of more than 200 °C are to be expected for the Sm-Nd and Lu-Hf closure temperatures for both the Great Caucasus (750±150 °C) and Yukon samples (710±120 °C). In all cases, calculated closure

  5. Genetic mapping of the interface between the ArsD metallochaperone and the ArsA ATPase

    PubMed Central

    Yang, Jianbo; Ajees, Abdul; Salam, Abdul; Rosen, Barry P.

    2011-01-01

    Summary The ArsD metallochaperone delivers trivalent metalloids, As(III) or Sb(III), to the ArsA ATPase, the catalytic subunit of the ArsAB As(III) efflux pump. Transfer of As(III) increases the affinity of ArsA for As(III), allowing resistance to environmental arsenic concentrations. As(III) transfer is channeled from chaperone to ATPase, implying that ArsD and ArsA form an interface at their metal binding sites. A genetic approach was used to test this hypothesis. Thirteen ArsD mutants exhibiting either weaker or stronger interaction with ArsA were selected by either repressed transactivator yeast two-hybrid or reverse yeast two-hybrid assays. Additionally, Lys-37 and Lys-62 were identified as being involved in ArsD function by site-directed mutagenesis and chemical modification. Substitution at either position with arginine was tolerated, suggesting participation of a positive charge. By yeast two-hybrid analysis K37A and K62A mutants lost interaction with ArsA. All fifteen mutations were mapped on the surface of the ArsD structure, and their locations are consistent with a structural model generated by in silico docking. Four are close to metalloid binding site residues Cys-12, Cys-13 and Cys18, and seven are on the surface of helix 1. These results suggest that the interface involves one surface of helix 1 and the metalloid binding site. PMID:21299644

  6. The role of mitochondrial fusion and StAR phosphorylation in the regulation of StAR activity and steroidogenesis.

    PubMed

    Castillo, Ana F; Orlando, Ulises; Helfenberger, Katia E; Poderoso, Cecilia; Podesta, Ernesto J

    2015-06-15

    The steroidogenic acute regulatory (StAR) protein regulates the rate-limiting step in steroidogenesis, i.e. the delivery of cholesterol from the outer (OMM) to the inner (IMM) mitochondrial membrane. StAR is a 37-kDa protein with an N-terminal mitochondrial targeting sequence that is cleaved off during mitochondrial import to yield 30-kDa intramitochondrial StAR. StAR acts exclusively on the OMM and its activity is proportional to how long it remains on the OMM. However, the precise fashion and the molecular mechanism in which StAR remains on the OMM have not been elucidated yet. In this work we will discuss the role of mitochondrial fusion and StAR phosphorylation by the extracellular signal-regulated kinases 1/2 (ERK1/2) as part of the mechanism that regulates StAR retention on the OMM and activity. PMID:25540920

  7. Chandra's First Decade Observing AR Lac

    NASA Astrophysics Data System (ADS)

    Ratzlaff, Peter; Drake, Jeremy J.; Durham, R. Nicholas; Kashyap, Vinay; Posson-Brown, Jennifer; Wargelin, Bradford J.

    2009-09-01

    X-ray observations of the eclipsing RS CVn-type binary AR Lacertae have been obtained every year from 1999 to 2008 with the Chandra High Resolution Camera imaging and spectroscopic detectors (HRC-I, HRC-S) as part of their gain and point spread function calibration. These represent the best quality data yet obtained on the long term variability of the X-ray emission of an RS CVn star, and are rendered especially valuable for the multi-epoch coverage of the AR Lac eclipses. The data are characterised by stochastic variability by factors of ˜2 on timescales of one to several ks, and by minor flaring events in which count rates are observed to be elevated by slightly larger factors. During primary eclipse, the X-ray count rate is generally observed at approximately 60% of its value outside of eclipse and during periods of relative quiescence. Little evidence for secondary eclipses is present in the data, reminiscent of earlier X-ray and EUV observations. The X-ray count rate modulation through the eclipses allow us to place an upper limit on the extent of a spherically symmetric coronae of about two stellar radii, the exact limit depending on the details of the coronal models and partition of emission between the component stars. We compare the observed Chandra count rates to earlier EUVE, EINSTEIN, EXOSAT and ROSAT observations and comment on the apparent lack of cyclic coronal activity on RS CVn-type binaries.

  8. 40Ar/39Ar age of material returned from asteroid 25143 Itokawa

    NASA Astrophysics Data System (ADS)

    Park, Jisun; Turrin, Brent D.; Herzog, Gregory F.; Lindsay, Fara N.; Delaney, Jeremy S.; Swisher, Carl C.; Uesugi, Masayuki; Karouji, Yuzuru; Yada, Toru; Abe, Masanao; Okada, Tatsuaki; Ishibashi, Yukihiro

    2015-11-01

    The Hayabusa mission to asteroid 25143, Itokawa, brought back 2000 small particles, which most closely resemble material found in LL4-6 chondrites. We report an 40Ar/39Ar age of 1.3 ± 0.3 Ga for a sample of Itokawa consisting of three grains with a total mass of ~2 μg. This age is lower than the >4.0 Ga ages measured for 75% of LL chondrites but close to one for Y-790964 and its pairs. The flat 40Ar/39Ar release spectrum of the sample suggests complete degassing 1.3 Ga ago. Recent solar heating in Itokawa's current orbit does not appear likely to have reset that age. Solar or impact heating 1.3 Ga ago could have done so. If impact heating was responsible, then the 1.3 Ga age sets an upper bound on the time at which the Itokawa rubble pile was assembled and suggests that rubble pile creation was an ongoing process in the inner solar system for at least the first 3 billion years of solar system history.

  9. Ar40-Ar39 systematics in rocks and separated minerals from Apollo 14.

    NASA Technical Reports Server (NTRS)

    Turner, G.; Huneke, J. C.; Podosek, F. A.; Wasserburg, G. J.

    1972-01-01

    The Ar40-Ar39 dating technique has been applied to separated minerals (plagioclase, pyroxene, quintessence and an 'ilmenite' concentrate), and whole rock samples of Apollo 14 rocks 14310 and 14073. Plagioclase shows the best gas retention characteristics, with no evidence of anomalous behavior and only a small amount of gas loss in the initial release. Ages determined from the plagioclase of 14310 and 14073 are (3.87 plus or minus 0.05) and (3.88 plus or minus 0.05) AE respectively. Low apparent ages at low release temperatures, which are frequently observed in whole rock Ar40-Ar39 experiments on lunar basalts, are shown to be principally due to gas loss in the high-K interstitial glass (quintessence) phase, confirming earlier suggestions. The decrease in apparent ages in the high-temperature release previously observed in several total rock samples of Apollo 14 basalts has been identified with the pyroxene. Plagioclase is also found to be the most suitable mineral for the determination of cosmic ray exposure ages, and exposure ages of 280 and 113 m.y. are found for 14310 and 14073, respectively, indicating that these rocks, which are very similar in many respects, have different exposure histories.

  10. New high-precision 40Ar/39Ar ages on Oligocene volcanic rocks of northwestern Kenya

    NASA Astrophysics Data System (ADS)

    Brown, Francis H.; Jicha, Brian R.

    2016-02-01

    New, high-precision 40Ar/39Ar ages from volcanic rocks in northwestern Kenya are provided for some areas of exposure in this remote area. We report seven 40Ar/39Ar ages generated from single crystal total fusion experiments on alkali feldspar separated from volcanic rocks in the Mogila, Songot, and Lokwanamur Ranges and the Gatome valley. A rhyolite from the lower part of the sequence in the Mogila Range yielded ages of 32.31 ± 0.06 Ma and 32.33 ± 0.07 Ma, and a rhyolite near the top of that sequence yielded 31.67 ± 0.04 Ma. A single sample from the Songot Range yielded an age of 32.49 ± 0.07 Ma, slightly older than the rocks collected from Mogila. In both ranges the early Oligocene rhyolites are underlain by basalts, as is also the case in the Labur Range. Ages of 25.95 ± 0.03 Ma, 25.91 ± 0.04 Ma, and 27.15 ± 0.03 Ma were measured on alkali feldspar from rhyolites from the Lokwanamur Range, and the nearby Gatome valley. All of these rocks are part of an episode of widespread volcanism in northwestern Kenya in the mid-to late Oligocene that is not currently known from the Ethiopian Rift Valley.

  11. The 40Ar/39Ar and K/Ar dating of lavas from the Hilo 1-km core hole, Hawaii Scientific Drilling Project

    USGS Publications Warehouse

    Sharp, W.D.; Turrin, B.D.; Renne, P.R.; Lanphere, M.A.

    1996-01-01

    Mauna Kea lava flows cored in the HilIo hole range in age from <200 ka to about 400 ka based on 40Ar/39Ar incremental heating and K-Ar analyses of 16 groundmass samples and one coexisting plagioclase. The lavas, all subaerially deposited, include a lower section consisting only of tholeiitic basalts and an upper section of interbedded alkalic, transitional tholeiitic, and tholeiitic basalts. The lower section has yielded predominantly complex, discordant 40Ar/39Ar age spectra that result from mobility of 40Ar and perhaps K, the presence of excess 40Ar, and redistribution of 39Ar by recoil. Comparison of K-Ar ages with 40Ar/39Ar integrated ages indicates that some of these samples have also lost 39Ar. Nevertheless, two plateau ages of 391 ?? 40 and 400 ?? 26 ka from deep in the hole, combined with data from the upper section, show that the tholeiitic section accumulated at an average rate of about 7 to 8 m/kyr and has an mean recurrence interval of 0.5 kyr/flow unit. Samples from the upper section yield relatively precise 40Ar/39Ar plateau and isotope correlation ages of 326 ?? 23, 241 ?? 5, 232 ?? 4, and 199 ?? 9 ka for depths of -415.7 m to -299.2 m. Within their uncertainty, these ages define a linear relationship with depth, with an average accumulation rate of 0.9 m/kyr and an average recurrence interval of 4.8 kyr/flow unit. The top of the Mauna Kea sequence at -280 m must be older than the plateau age of 132 ?? 32 ka, obtained for the basal Mauna Loa flow in the corehole. The upward decrease in lava accumulation rate is a consequence of the decreasing magma supply available to Mauna Kea as it rode the Pacific plate away from its magma source, the Hawaiian mantle plume. The age-depth relation in the core hole may be used to test and refine models that relate the growth of Mauna Kea to the thermal and compositional structure of the mantle plume.

  12. 40Ar/39Ar dating of tourmaline as a tool for high-temperature metamorphism thermochronology

    NASA Astrophysics Data System (ADS)

    Jourdan, Fred; Thern, Eric

    2014-05-01

    Tourmaline is an ubiquitous mineral, with properties making it ideal for studying metamorphic processes as well as a useful tool for a wide range of applications (e.g, magmatism, metasomatism, ore deposits [1]), mostly because it is not sensitive to chemical or mechanical alteration and is stable over a wide range of pressure-temperature conditions (up to 6 GPa and 850° C [2]). Typical metamorphic tourmaline types include dravite and shorl which, along with elbaite, belong to the alkali group [1]. The alkali group is notable because tourmalines from this group tend to incorporate trace amounts of K2O and therefore, can be dated using the 40Ar/39Ar technique. In order to understand the maximum temperature below which the K/Ar chronometer stays closed to argon loss by thermally activated diffusion, we carried out temperature controlled furnace diffusion experiments on well-behaved 40Ar/39Ar plateau-forming Archean tourmaline of 2935 ± 9 Ma [3]. Each experiment yielded an Arrhenius profile (Do vs. 1/temperature) that shows that the 39Ar data form two linear arrays with two distinct slopes. The first array only includes a few % of the total gas, has a shallow slope and shows very fast diffusivity at low temperature. We interpret these data as indicating very fast release of argon by cracks and defects. The second array of data points includes most of the gas of each experiment and forms a much steeper slope. These data yielded Ea (activation energy) values ranging from 120 to 157 Kcal/mol and D0 (pre-exponential diffusion factor) values ranging from 1.9x106 to 2.5x109 cm2/s for crystals with an average radius of 100 ± 25 μm. Three additional experiments using a laser (resulting in poor temperature control) suggest similar values although the latter experiments are considered semi-quantitative. The furnace experiments suggest that tourmaline has a weighted mean closure temperature of 804 ± 90 ° C (1σ) for a cooling rate of 10° C/Ma. Monte Carlo simulations using

  13. The bombardment history of the Moon as recorded by 40Ar-39Ar chronology

    NASA Astrophysics Data System (ADS)

    Fernandes, V. A.; Fritz, J.; Weiss, B. P.; Garrick-Bethell, I.; Shuster, D. L.

    2013-02-01

    New petrography and 40Ar-39Ar ages have been obtained for 1-3 mm sized rock fragments from Apollo 16 Station 13 soil 63503 (North Ray crater ejecta) and chips from three rocks collected by Apollo 16 and Apollo 17 missions. Selection of these samples was aimed at the old 40Ar-39Ar ages to understand the early history of the lunar magnetic field and impact flux. Fifteen samples were studied including crustal material, polymict feldspathic fragmental breccias, and impact melts. The impact ages obtained range between approximately 3.3 and 4.3 billion years (Ga). Polymict fragmental breccia 63503,1 exhibits the lowest signs of recrystallization observed and a probable old relic age of 4.547 ± 0.027. The plateau age of 4.293 ± 0.044 Ga obtained for impact melt rock 63503,13 represents the oldest known age for such a lithology. Possibly, this age represents the minimum age for the South Pole-Aitken (SPA) Basin. In agreement with literature data, these results show that impact ages >3.9 Ga are found in lunar rocks, especially within soil 63503. Impact exhumation of deep-seated warm crustal material onto the lunar surface is considered to explain the common 4.2 Ga ages obtained for weakly shocked samples from soil 63503 and Apollo 17. This would directly imply that one or more basin-forming events occurred at that time. Some rock fragments showing none to limited petrologic features indicate thermal annealing. These rocks may have lost Ar while resident within the hot-ejecta of a large basin. Concurrent with previous studies, these results lead us to advocate for a complex impact flux in the inner solar system during the initial approximately 1.3 Ga.

  14. Androgen Receptor-Mediated Growth Suppression of HPr-1AR and PC3-Lenti-AR Prostate Epithelial Cells

    PubMed Central

    Bolton, Eric C.

    2015-01-01

    The androgen receptor (AR) mediates the developmental, physiologic, and pathologic effects of androgens including 5α-dihydrotestosterone (DHT). However, the mechanisms whereby AR regulates growth suppression and differentiation of luminal epithelial cells in the prostate gland and proliferation of malignant versions of these cells are not well understood, though they are central to prostate development, homeostasis, and neoplasia. Here, we identify androgen-responsive genes that restrain cell cycle progression and proliferation of human prostate epithelial cell lines (HPr-1AR and PC3-Lenti-AR), and we investigate the mechanisms through which AR regulates their expression. DHT inhibited proliferation of HPr-1AR and PC3-Lenti-AR, and cell cycle analysis revealed a prolonged G1 interval. In the cell cycle, the G1/S-phase transition is initiated by the activity of cyclin D and cyclin-dependent kinase (CDK) complexes, which relieve growth suppression. In HPr-1AR, cyclin D1/2 and CDK4/6 mRNAs were androgen-repressed, whereas CDK inhibitor, CDKN1A, mRNA was androgen-induced. The regulation of these transcripts was AR-dependent, and involved multiple mechanisms. Similar AR-mediated down-regulation of CDK4/6 mRNAs and up-regulation of CDKN1A mRNA occurred in PC3-Lenti-AR. Further, CDK4/6 overexpression suppressed DHT-inhibited cell cycle progression and proliferation of HPr-1AR and PC3-Lenti-AR, whereas CDKN1A overexpression induced cell cycle arrest. We therefore propose that AR-mediated growth suppression of HPr-1AR involves cyclin D1 mRNA decay, transcriptional repression of cyclin D2 and CDK4/6, and transcriptional activation of CDKN1A, which serve to decrease CDK4/6 activity. AR-mediated inhibition of PC3-Lenti-AR proliferation occurs through a similar mechanism, albeit without down-regulation of cyclin D. Our findings provide insight into AR-mediated regulation of prostate epithelial cell proliferation. PMID:26372468

  15. One-electron pseudopotential investigation of the RbAr and FrAr van der Waals systems

    NASA Astrophysics Data System (ADS)

    Dhiflaoui, J.; Berriche, H.

    2012-12-01

    The potential energy curves of the ground state and many excited states of RbAr and FrAr van der Waals systems have been determined using a one-electron pseudopotential approach. The pseudopotential technique is used to replace the effect of the Rb+ and Fr+ cores and the electron-Ar interaction. In addition a core-core interaction is included. This has permitted to reduce the number of active electrons of the RbAr and FrAr systems to only one electron, the valence electron. This has led to use very large basis sets for Rb, Fr and Ar atoms. In this context, the potential energy curves of the ground and many excited states are performed at the SCF level. The core-core interactions for Rb+Ar and Fr+Ar are included using the CCSD(T) accurate potentials of Hickling et al. [H. Hickling, L. Viehland, D. Shepherd, P. Soldan, E. Lee and T. Wright, Phys. Chem. Chem. Phys. 6 (2004) 4233]. In addition, the spectroscopic constants of these states are derived and compared with the available theoretical works. Such comparison for RbAr has shown a very good agreement for the ground and the first excited states. However, the FrAr system was not studied previously and its spectroscopic constants are presented here for the first time.

  16. Geochemistry and Ar/Ar dating of upper pleistocene volcanic rocks from Kerguelen islands (Indian Ocean)

    NASA Astrophysics Data System (ADS)

    Ethien, R.; Feraud, G.; Gerbe, M. C.; Cottin, J. Y.; O'Reilly, S. Y.; Giret, A.

    2003-04-01

    The Kerguelen islands archipelago (6500 Km^2) is the third largest oceanic island in the world, after Island and Hawaï. It is located upon the Kerguelen plateau, which is the second Large Igneous Province (LIP) after Ontong-Java. This oceanic plateau consist of an accumulation of flood basalts, related to the long-lived ˜119 Ma Kerguelen plume. The flood basalts (˜29-24 Ma; Nicolaysen et al., 2000) represent 85% of the rocks of Kerguelen. The Rallier-du-Baty (R.d.B.) peninsula, which forms the southwestern part of the Kerguelen archipelago, is mostly made of alkaline rocks constituting two well-defined ring-complexes. The northern ring-complex consists of a succession of seven discrete syenitic ring-dykes, one later caldera volcano and a more recent volcanic complex. The volcanism is bimodal with trachy-basalts and trachy-andesites, with true scarce basalts constituting the mafic lavas and trachytes and rhyolites constituting the felsic lavas. The felsic magmas were erupted as abundant pyroclastic deposits and lava flows. The mineralogy of those volcanic rocks is typical of an alcaline series, with the presence of K-feldspars (sanidines) in the most differentiated volcanic rocks. The evolution from trachyte to rhyolite seems to be controlled by crystal fractionation, with some trace element distribution and Sr isotopic ratios largely disturbed by open-system processes such as assimilation of hydrothermally altered crust and interaction with seawater. The studies of the oxygen isotopes confirm this hypothesis. Indeed, the high values of δ18O for the rhyolites (δ18O= 10.3 and 12.4) could be interpreted by an alteration by fluids at low temperatures. The Nd isotopic ratio are typical of mantellic values, with no significant variations. Whereas some units of the northern R.d.B. plutonic complex yield a narrow range of K/Ar ages on bulk rocks, from 6.2 ± 0.2 Ma to 4.9 ± 0.2 Ma (Dosso and al., 1979), the formation of a discrete caldera centered on the "Table de l

  17. Plasma AR and abiraterone-resistant prostate cancer.

    PubMed

    Romanel, Alessandro; Gasi Tandefelt, Delila; Conteduca, Vincenza; Jayaram, Anuradha; Casiraghi, Nicola; Wetterskog, Daniel; Salvi, Samanta; Amadori, Dino; Zafeiriou, Zafeiris; Rescigno, Pasquale; Bianchini, Diletta; Gurioli, Giorgia; Casadio, Valentina; Carreira, Suzanne; Goodall, Jane; Wingate, Anna; Ferraldeschi, Roberta; Tunariu, Nina; Flohr, Penny; De Giorgi, Ugo; de Bono, Johann S; Demichelis, Francesca; Attard, Gerhardt

    2015-11-01

    Androgen receptor (AR) gene aberrations are rare in prostate cancer before primary hormone treatment but emerge with castration resistance. To determine AR gene status using a minimally invasive assay that could have broad clinical utility, we developed a targeted next-generation sequencing approach amenable to plasma DNA, covering all AR coding bases and genomic regions that are highly informative in prostate cancer. We sequenced 274 plasma samples from 97 castration-resistant prostate cancer patients treated with abiraterone at two institutions. We controlled for normal DNA in patients' circulation and detected a sufficiently high tumor DNA fraction to quantify AR copy number state in 217 samples (80 patients). Detection of AR copy number gain and point mutations in plasma were inversely correlated, supported further by the enrichment of nonsynonymous versus synonymous mutations in AR copy number normal as opposed to AR gain samples. Whereas AR copy number was unchanged from before treatment to progression and no mutant AR alleles showed signal for acquired gain, we observed emergence of T878A or L702H AR amino acid changes in 13% of tumors at progression on abiraterone. Patients with AR gain or T878A or L702H before abiraterone (45%) were 4.9 and 7.8 times less likely to have a ≥50 or ≥90% decline in prostate-specific antigen (PSA), respectively, and had a significantly worse overall [hazard ratio (HR), 7.33; 95% confidence interval (CI), 3.51 to 15.34; P = 1.3 × 10(-9)) and progression-free (HR, 3.73; 95% CI, 2.17 to 6.41; P = 5.6 × 10(-7)) survival. Evaluation of plasma AR by next-generation sequencing could identify cancers with primary resistance to abiraterone. PMID:26537258

  18. Stark beats of Ar Rydberg states

    NASA Astrophysics Data System (ADS)

    Morioka, Y.; Aoto, T.; Yoshii, H.

    2001-11-01

    Vacuum ultraviolet fluorescence decay spectra of Ar atom resonance lines excited by pulsed vacuum ultraviolet light in a synchrotron single bunch operation were obtained under a static electric field. When an atom under the static electric field was excited simultaneously to both the magnetic sublevels M=0 and \\|M\\|=1 by polarized light and the observation area was asymmetric, Stark beats were observed in the fluorescent decay spectra. All observed beat frequencies varied proportionally to the square of the external electric field. The results for 8d and 9d doublet lines were compared with those obtained by the usual second order perturbation theory, assuming mixing ratios between three jl coupling scheme d-type states. The beat frequencies were also measured for other resonance lines.

  19. Unmixing 40Ar/39Ar Muscovite Ages Using Powder X-ray Diffraction

    NASA Astrophysics Data System (ADS)

    McAleer, R. J.; Kunk, M. J.; Valley, P. M.; Walsh, G. J.; Bish, D. L.; Wintsch, R. P.

    2014-12-01

    Whole rock powder X-ray diffraction (XRD) experiments from eight samples collected across a retrograde ductile shear zone in the Devonian Littleton Formation near Claremont, NH, exhibit broad and asymmetric to bimodal muscovite 00l reflections. These composite 00l reflections exhibit a systematic change in shape with increasing retrograde strain. Microtextural relationships, electron microprobe quantitative analyses, and element mapping indicate that the change in peak shape reflects progressive dissolution of metastable Na-rich muscovite and the precipitation of stable Na-poor muscovite. 40Ar/39Ar step heating experiments on muscovite concentrates from these samples show a decrease in total gas age from 274 to 258 Ma as the highest strain zone is approached, and steps within individual spectra range in age by ~20 m.y. The correlation between age and 00l peak shape suggests that the argon isotopic system also tracks the dissolution-precipitation process. Furthermore, the variation in age during step heating indicates that these populations exhibit different in-vacuo degassing behavior. Comparison of whole rock and muscovite concentrate XRD patterns from the same samples shows that the mineral separation process can fractionate these muscovite populations. With this knowledge, four muscovite concentrates were prepared from a single hand sample, analyzed by XRD, and dated. Combining modal estimates from XRD experiments with total gas ages, the four splits narrowly define a mixing line that resolves end-member ages of 250 and 300 Ma for the neocrystallized and earlier high grade populations of muscovite, respectively. These ages are consistent with age data from all other samples. The results show that, in some settings, powder XRD provides a powerful and time effective method to both identify the existence of and establish the proportions of multiple compositional populations of muscovite prior to 40Ar/39Ar analysis. This approach will be especially useful in

  20. Statistical estimation of mineral age by K-Ar method

    SciTech Connect

    Vistelius, A.B.; Drubetzkoy, E.R.; Faas, A.V. )

    1989-11-01

    Statistical estimation of age of {sup 40}Ar/{sup 40}K ratios may be considered a result of convolution of uniform and normal distributions with different weights for different minerals. Data from Gul'shad Massif (Nearbalkhash, Kazakhstan, USSR) indicate that {sup 40}Ar/{sup 40}K ratios reflecting the intensity of geochemical processes can be resolved using convolutions. Loss of {sup 40}Ar in biotites is shown whereas hornblende retained the original content of {sup 40}Ar throughout the geological history of the massif. Results demonstrate that different estimation methods must be used for different minerals and different rocks when radiometric ages are employed for dating.

  1. Age and Duration of Weathering by 40K-40Ar and 40Ar/39Ar Analysis of Potassium-Manganese Oxides.

    PubMed

    Vasconcelos, P M; Becker, T A; Renne, P R; Brimhall, G H

    1992-10-16

    Supergene cryptomelane [K(1-2)(Mn(3+)Mn(4+))(8)O(16). chiH(2)O] samples from deeply weathered pegmatites in southeastern Brazil subjected to (40)K-(40)Ar and (40)Ar/(39)Ar analysis yielded (40)K-(40)Ar dates ranging from 10.1 +/- 0.5 to 5.6 +/- 0.2 Ma (million years ago). Laser-probe (40)Ar/(39)Ar step-heating of the two most disparate samples yielded plateau dates of 9.94 +/- 0.05 and 5.59 +/- 0.10 Ma, corresponding, within 2 sigma, to the (40)K-(40)Ar dates. The results imply that deep weathering profiles along the eastern Brazilian margin do not reflect present climatic conditions but are the result of a long-term process that was already advanced by the late Miocene. Weathering ages predate pulses of continental sedimentation along the eastern Brazilian margin and suggest that there was a time lag between weathering and erosion processes and sedimentation processes. PMID:17833140

  2. 40Ar/39Ar ages from the rhyolite of Alder Creek, California: age of the Cobb Mountain normal-polarity subchron revisited

    USGS Publications Warehouse

    Turrin, B.D.; Donnelly-Nolan, J. M.; Hearn, B.C., Jr.

    1994-01-01

    New 40Ar/39Ar age determinations on sanidine from the rhyolite of Alder Creek, California, indicate a 1.186 ?? 0.006 Ma age for the Cobb Mountain Normal-Polarity Subchron. The hew age is statistically older (?? = 0.05) than the previously reported K-Ar age (1.12 ?? 0.02 Ma) and agrees with the age suggested by the astronomical polarity time scale. Incomplete extraction of radiogenic 40Ar (40Ar*) from the sanidine is the most likely reason for the disparity between the 40Ar/39Ar and K-Ar ages. Because the Cobb Mountain subchron is a worldwide, short-duration event, and because no widely used interlaboratory 40Ar/39Ar standard younger than 27 Ma exists, it is proposed that sanidine from the rhyolite of Alder Creek be considered for use as a new Quaternary 40Ar/39Ar mineral standard. -Authors

  3. Ar-39 - Ar-40 Evidence for an Approximately 4.26 Ga Impact Heating Event on the LL Parent Body

    NASA Technical Reports Server (NTRS)

    Dixon, E. T.; Bogard, D. D.; Rubin, A. E.

    2003-01-01

    Miller Range 99301 is a type 6, unbrecciated LL chondrite. MIL 99301 is of interest because some compositional and petrographic features suggest it experienced rather high shock grades, whereas other features suggest it is relatively unshocked. Inconsistent shock indicators could be explained if MIL 99301 was shocked but then partly annealed by heat produced by impacts on the parent body. The hypothesis that MIL 99301 experienced high temperature metamorphism (type 6) followed by a later shock event that heated, but did not melt, the constituent feldspar can be evaluated using (39)Ar-(40)Ar chronology. This is because (39)Ar-(40)Ar ages of shocked ordinary chondrites are generally <4.2 Ga, whereas (39)Ar-(40)Ar ages of unshocked meteorites are generally older, and between 4.52 - 4.38 Ga.

  4. Differential unroofing within the central metasedimentary Belt of the Grenville Orogen: constraints from 40Ar/39Ar thermochronology

    USGS Publications Warehouse

    Cosca, M.A.; Essene, E.J.; Kunk, M.J.; Sutter, J.F.

    1992-01-01

    An 40Ar/39Ar thermochronological investigation of upper greenschist to granulite facies gneiss, amphibolite and marble was conducted in the Central Metasedimentary Belt (CMB), Ontario, to constrain its cooling history. Incremental 40Ar/39Ar release spectra indicate that substantial differential unroofing occurred in the CMB between ??? 1000 and ??? 600 Ma. A consistent pattern of significantly older hornblende and phlogopite 40Ar/3Ar cooling ages on the southeast sides of major northeast striking shear zones is interpreted to reflect late displacement due to extensional deformation. Variations in hornblende 40Ar/39Ar age plateaus exceeding 200 Ma occur over distances less than 50 km with major age discontinuities occurring across the Robertson Lake shear zone and the Sharbot Lake mylonite zone which separate the Sharbot Lake terrane from the Elzevir and Frontenac terranes. Extensional displacements of up to 14 km are inferred between the Frontenac and Elzevir terranes of the CMB. No evidence for significant post argon-closure vertical displacement is indicated in the vicinity of the Perth Road mylonite within the Frontenac terrane. Variations of nearly 100 Ma in phlogopite 40Ar/39Ar plateau ages occur in undeformed marble on either side of the Bancroft Shear Zone. Phlogopites from sheared and mylonitized marble within the shear zone yield 40Ar/39Ar diffusional loss profiles, but have older geologically meaningless ages thought to reflect incorporation of excess argon. By ??? 900 Ma, southeast directed extension was occurring throughout the CMB, possibly initiated along previous zones of compressional shearing. An easterly migration of active zones of extension is inferred, possibly related to an earlier, overall easterly migration of active zones of regional thrusting and easterly migration of an ancient subduction zone. The duration of extensional shearing is not well constrained, but must have ceased before ??? 600 Ma as required by the deposition of overlying

  5. In-situ Ar isotope, 40Ar/39Ar analysis and mineral chemistry of nosean in the phonolite from Olbrück volcano, East Eifel volcanic field, Germany: Implication for the source of excess 40Ar

    NASA Astrophysics Data System (ADS)

    Sudo, Masafumi; Altenberger, Uwe; Günter, Christina

    2014-05-01

    Since the report by Lippolt et al. (1990), hauyne and nosean phenocrysts in certain phonolites from the northwest in the Quaternary East Eifel volcanic field in Germany were known to contain significant amounts of excess 40Ar, thus, show apparent older ages than the other minerals. However, its petrographic meaning have not been well known. Meanwhile, Sumino et al. (2008) has identified the source of the excess 40Ar in the plagioclase phenocrysts from the historic Unzen dacite lava as the melt inclusions in the zones parallely developed to the plagioclase rim by in-situ laser Ar isotope analysis. In order to obtain eruption ages of very young volcanoes as like Quaternary Eifel volcanic field by the K-Ar system, it is quite essential to know about the location of excess 40Ar in volcanic rocks. We have collected phonolites from the Olbrück volcano in East Eifel and investigated its petrography and mineral chemistry and also performed in-situ Ar isotope analyses of unirradiated rock section sample and also in-situ 40Ar/39Ar analysis of neutron irradiated section sample with the UV pulse laser (wavelength 266 nm) and 40Ar/39Ar analytical system of the University of Potsdam. Petrographically, nosean contained fine melt and/or gas inclusions of less than 5 micrometer, which mostly distribute linearly and are relatively enriched in chlorine than the areas without inclusions. Solid inclusions of similar sizes contain CaO and fluorine. In nosean, typically around 5 wt% of sulfur is contained. The 40Ar/39Ar dating was also performed to leucite, sanidine and groundmass in the same section for comparison of those ages with that of nosean. In each analysis, 200 micrometer of beam size was used for making a pit with depth of up to 300 micrometer by laser ablation. As our 40Ar/39Ar analyses were conducted one and half year after the neutron irradiation, thus, short lived 37Ar derived from Ca had decayed very much, we measured Ca and K contents in nosean by SEM-EDS then applied

  6. Acoustic resonance spectroscopy (ARS): ARS300 operations manual, software version 2.01

    SciTech Connect

    1996-07-25

    Acoustic Resonance Spectroscopy (ARS) is a nondestructive evaluation technology developed at the Los Alamos National Laboratory. The ARS technique is a fast, safe, and nonintrusive technique that is particularly useful when a large number of objects need to be tested. Any physical object, whether solid, hollow, or fluid filled, has many modes of vibration. These modes of vibration, commonly referred to as the natural resonant modes or resonant frequencies, are determined by the object`s shape, size, and physical properties, such as elastic moduli, speed of sound, and density. If the object is mechanically excited at frequencies corresponding to its characteristic natural vibrational modes, a resonance effect can be observed when small excitation energies produce large amplitude vibrations in the object. At other excitation frequencies, i.e., vibrational response of the object is minimal.

  7. 40Ar/39Ar age of the Lathrop Wells volcanic center, Yucca Mountain, Nevada

    USGS Publications Warehouse

    Turrin, B.D.; Champion, D.; Fleck, R.J.

    1991-01-01

    Paleomagnetic and 40Ar/39Ar analyses from the Lathrop Wells volcanic center, Nevada, indicate that two eruptive events have occurred there. The ages (136 ?? 8 and 141 ?? 9 thousand years ago) for these two events are analytically indistinguishable. The small angular difference (4.7??) between the paleomagnetic directions from these two events suggests they differ in age by only about 100 years. These ages are consistent with the chronology of the surficial geological units in the Yucca Mountain area. These results contradict earlier interpretations of the cinder-cone geomorphology and soil-profile data that suggest that at least five temporally discrete eruptive events occurred at Lathrop Wells approximately 20,000 years ago.

  8. 40Ar/39Ar Age of the Lathrop Wells Volcanic Center, Yucca Mountain, Nevada.

    PubMed

    Turrin, B D; Champion, D; Fleck, R J

    1991-08-01

    Paleomagnetic and (40)Ar/(39)Ar analyses from the Lathrop Wells volcanic center, Nevada, indicate that two eruptive events have occurred there. The ages (136 +/- 8 and 141 +/- 9 thousand years ago) for these two events are analytically indistinguishable. The small angular difference (4.7 degrees ) between the paleomagnetic directions from these two events suggests they differ in age by only about 100 years. These ages are consistent with the chronology of the surficial geological units in the Yucca Mountain area. These results contradict earlier interpretations of the cinder-cone geomorphology and soil-profile data that suggest that at least five temporally discrete eruptive events occurred at Lathrop Wells approximately 20,000 years ago. PMID:17772371

  9. Ar-39 - Ar-40 Dating of Two Angrites and Two Brachnites

    NASA Technical Reports Server (NTRS)

    Garrison, Daniel; Bogard, Donald

    2003-01-01

    Angrites are a rare group (approx.7 known) of igneous meteorites with basalt-like composition, which probably derive from a relatively small parent body that differs from those of other igneous meteorites. Angrites show evidence for extinct Mn-53, Sm-146, and Pu-244, and precise U-Pb, and Pb-Pb ages of 4.558 Gyr for two angrites define the time of early parent body differentiation. The S-147 - Nd-143 ages of two angrites range between 4.53+/-0.04 and 4.56+/-0.04 Gyr, but no Ar-39 - Ar-40 or Rb-Sr ages have been reported. Most angrites show no evidence for either shock brecciation or metamorphism.

  10. 40Ar/39Ar geochronology and paleomagnetism of Independence volcano, Absaroka volcanic supergroup, Beartooth mountains, Montana

    USGS Publications Warehouse

    Harlan, S.S.; Snee, L.W.; Geissman, J.W.

    1996-01-01

    Independence volcano is a major volcanic complex in the lower part of the Absaroka Volcanic Supergroup (AVS) of Montana and Wyoming. Recently reported Rb-Sr mineral dates from the complex give apparent ages of 91 and 84 Ma, whereas field relationships and the physical and compositional similarity of the rocks with other dated parts of the AVS indicate an Early to Middle Eocene age for eruption and deposition. To resolve the conflict between age assignments based on stratigraphic correlations and Rb-Sr dates, we report new paleomagnetic data and 40Ar/39Ar dates for Independence volcano. Paleomagnetic data for the stock and an and andesite plug that cuts the stock are well grouped, of reverse polarity, and yield a virtual geomagnetic pole that is essentially identical to Late Cretaceous and Tertiary reference poles. The reverse polarity indicates that the magnetization of these rocks is probably younger than the Cretaceous normal superchron, or less than about 83.5 Ma. Hornblende from a volcanic breccia near the base of the volcanic pile gives a 40Ar/39Ar age of 51.57 Ma, whereas biotites from a dacite sill and a granodiorite stock that forms the core of the volcano give dates that range from 49.96 to 48.50 Ma. These dates record the age of eruption and intrusion of these rocks and clearly show that the age of Independence volcano is Early to Middle Eocene, consistent with stratigraphic relations. We suggest that the Rb-Sr mineral dates from the Independence stock and related intrusions are unreliable.

  11. Refining lunar impact chronology through high spatial resolution (40)Ar/(39)Ar dating of impact melts.

    PubMed

    Mercer, Cameron M; Young, Kelsey E; Weirich, John R; Hodges, Kip V; Jolliff, Bradley L; Wartho, Jo-Anne; van Soest, Matthijs C

    2015-02-01

    Quantitative constraints on the ages of melt-forming impact events on the Moon are based primarily on isotope geochronology of returned samples. However, interpreting the results of such studies can often be difficult because the provenance region of any sample returned from the lunar surface may have experienced multiple impact events over the course of billions of years of bombardment. We illustrate this problem with new laser microprobe (40)Ar/(39)Ar data for two Apollo 17 impact melt breccias. Whereas one sample yields a straightforward result, indicating a single melt-forming event at ca. 3.83 Ga, data from the other sample document multiple impact melt-forming events between ca. 3.81 Ga and at least as young as ca. 3.27 Ga. Notably, published zircon U/Pb data indicate the existence of even older melt products in the same sample. The revelation of multiple impact events through (40)Ar/(39)Ar geochronology is likely not to have been possible using standard incremental heating methods alone, demonstrating the complementarity of the laser microprobe technique. Evidence for 3.83 Ga to 3.81 Ga melt components in these samples reinforces emerging interpretations that Apollo 17 impact breccia samples include a significant component of ejecta from the Imbrium basin impact. Collectively, our results underscore the need to quantitatively resolve the ages of different melt generations from multiple samples to improve our current understanding of the lunar impact record, and to establish the absolute ages of important impact structures encountered during future exploration missions in the inner Solar System. PMID:26601128

  12. The Berkeley Instrumental Neutron Generator (BINGE) for 40Ar/39Ar geochronology

    NASA Astrophysics Data System (ADS)

    Renne, P. R.; Becker, T. A.; Bernstein, L.; Firestone, R. B.; Kirsch, L.; Leung, K. N.; Rogers, A.; Van Bibber, K.; Waltz, C.

    2014-12-01

    The Berkeley Instrumental Neutron Generator (BINGE) facility is the product of a consortium involving the Berkeley Geochronology Center (BGC), the U.C. Berkeley Nuclear Engineering Dept. (UCB/NE), and Lawrence Berkeley (LBNL) and Lawrence Livermore (LLNL) National Labs. BINGE was initially designed (and funded by NSF) for 40Ar/39Ar geochronology. BINGE uses a plasma-based deuteron ion source and a self-loading Ti-surfaced target to induce deuteron-deuterium (DD) fusion via the reaction 2H(d,n)3He, producing 2.45 MeV neutrons. The limited neutron energy spectrum is aimed at reducing recoil effects, interfering nuclear reactions, and unwanted radioactive byproducts, all of which are undesirable consequences of conventional irradiation with 235U fission spectrum neutrons. Minimization of interfering reactions such as 40Ca(n,na)36Ar greatly reduces penalties for over-irradiation, enabling improved signal/background measurement of e.g. 39Ar. BINGE will also be used for a variety of nuclear physics and engineering experiments that require a high flux of monoenergetic neutrons. Neutron energies lower than 2.45 MeV can be obtained via irradiation ports within and external to polyethylene shielding. Initial commissioning produced a neutron flux of 108 n/sec/cm2 at 1 mA source current and 100 kV anode voltage, as expected. When scaled up to the 1 A source current as planned, this indicates that BINGE will achieve the design objective neutron flux of 1011 n/sec/cm2. Further progress towards this goal will be reported. Supported by NSF (grant #EAR-0960138), BGC, UCB/NE, University of California Office of the President, and DOE through LLNL under contract #DE-AC52-07NA27344 and LBNL under contract #DE-AC02-05CH11231.

  13. Ar-40/Ar-39 Age of Hornblende-bearing R Chondrite LAP 04840

    NASA Technical Reports Server (NTRS)

    Righter, K.; Cosca, M.

    2014-01-01

    Chondrites have a complex chronology due to several variables affecting and operating on chondritic parent bodies such as radiogenic heating, pressure and temperature variation with depth, aqueous alteration, and shock or impact heating [1]. Unbrecciated chondrites can record ages from 4.56 to 4.4 Ga that represent cooling in small parent bodies. Some brecciated chondrites exhibit younger ages (<<4 to 4.4 Ga) that may reflect the age of brecciation, disturbance, or shock and impact events (<< 4 Ga). A unique R chondrite was recently found in the LaPaz Icefield of Antarctica - LAP 04840 [2]. This chondrite contains approx.15% hornblende and trace amounts of biotite, making it the first of its kind. Studies have revealed an equigranular texture, mineral equilibria yielding equilibration near 650-700 C and 250-500 bars, hornblende that is dominantly OH-bearing (very little Cl or F), and high D/H ratios [8,9,10]. To help gain a better understanding of the origin of this unique sample, we have measured the Ar-40/Ar-39 age. Age of 4.290 +/- 0.030 Ga is younger than one would expect for a sample that has cooled within a small body [4], and one might instead attribute the age to a younger shock event, On the other hand, there is no evidence for extensive shock in this meteorite (shock stage S2; [3]), so this sample may have been reannealed after the shock event. This age is similar to Ar-Ar ages determined for some other R chondrites

  14. Union of /sup 40/Ar//sup 38/Ar with paleomagnetism

    SciTech Connect

    York, D.

    1985-01-01

    To interpret the paleomagnetic record written in Precambrian igneous and metamorphic rocks, it is essential to know the post-crystallization thermal histories of these bodies. The best method (i.e., if only one decay scheme is used) to determine the latter is to apply the /sup 40/Ar//sup 38/Ar step-heating technique to the minerals derived from the rocks containing the magnetic record. Thus the argon blocking temperatures of amphiboles, micas and feldspars span the range of magnetic blocking temperatures usually found. Illustrations will be given of how such a combined thermochronometric-paleomagnetic approach has been used to begin the unravelling of some of the Precambrian plate motions of North America, South America and Africa. Two illustrations will also be given of how this combined isotopic-magnetic approach has revealed the hitherto unsuspected existence of mild thermal events in certain regions of the Grenville and Superior Provinces. Finally, it will be shown that old ages and/or very low potassium contents (/approx/80 p.p.m.) are not insuperable barriers to the successful determination of thermal histories with the /sup 40/Ar//sup 38/Ar age spectrum approach. Examples of this will be taken from Barberton Mountain komatiites (3.5 b.y.), a Superior Province ultra-mafic intrusive (2.7 b.y.) and Sudbury silicates (1.85 b.y.). The results presented in this paper represent the work of numerous people, based at the University of Toronto, Queen's University, Kingston (Ontario), and Princeton University (N.J.).

  15. CHEMILUMINESCENT CHEMI-IONIZATION: Ar* + Ca AND THE CaAr+ EMISSION SPECTRUM

    SciTech Connect

    Hartman, Dennis C.; Winn, John S.

    1980-09-01

    A flowing afterglow chemiluminescence apparatus has been used to analyze visible fluorescence in the Ar* ({sup 3}P{sub 2}{sup o}) + Ca ({sup 1}S{sub 0}) reaction. The rate constants for production of Ca{sup +} ({sup 2}P{sub 3/2}{sup o}) and Ca{sup +} ({sup 2}P{sub 1/2}{sup o}) were measured to be 1.6 x 10{sup -10} cm{sup 3}-molecule{sup -1} sec{sup -1} and 3.2 x 10{sup -11} cm{sup 3} molecule{sup -1} sec{sup -1}, respectively. These results demonstrate a transfer of the total electronic angular momentum polarization in Ar* tothe excited ion levels. The molecular band spectrum of the associative ionization product CaAr{sup +} (A{sup 2}{Pi}) was observed. Molecular fluorescence constituted 14% of the total fluorescence from all ion products. This spectrum was analyzed with a model (exp-Z4) potential, yielding, for the ground state, {Chi}{sup 2}{Sigma}{sup +}, R{sub e} = 2.8 {angstrom}, {omega}''{sub e} = 87 cm{sup -1}, and D''{sub e} = 1000 cm{sup -1}, and, for the A{sup 2}{Pi} state, R{sub e} = 2.6 {angstrom}, {omega}'{sub e} = 200 cm{sup -1}, and D'{sub e} = 4900 cm{sup -1}. The nascent internal state distribution in CaAr{sup +} is found to consist of a fairly narrow range of high vibrational levels. The analysis of spectra from chemiluminescent reaction is a well established technique for elucidating the product state distributions of elementary processes. In this paper, they use the analysis of the chemiluminescent chemi-ionization reactions between metastable argon atoms and calcium atoms to expose the dynamics of associative ionization (AI) and to measure the branching ratios for chemi-ionization into more than one product channel.

  16. 40Ar/39Ar thermochronology of mesoproterozoic metamorphism in the Colorado Front Range

    USGS Publications Warehouse

    Shaw, C.A.; Snee, L.W.; Selverstone, J.; Reed, J.C., Jr.

    1999-01-01

    A low-pressure metamorphic episode in the Colorado Front Range has been identified by the presence of staurolite, andalusite, cordierite, and garnet porphyroblasts overprinting earlier assemblages. The overprinting assemblages and reaction textures are most consistent with porphyroblast growth on a prograde metamorphic path with peak temperatures exceeding ~525??C. Twenty-eight 40Ar/39Ar dates on hornblende, muscovite, biotite, and microcline were used to infer the age and thermal conditions of metamorphism. Muscovite and biotite 40Ar/39Ar ages fall mainly in the interval 1400-1340 Ma, consistent with cooling through the closure temperature interval of micas (~400??-300??C) after about 1400 Ma. In contrast, hornblende apparent ages (T(c)~500??-550??C) between 1600 and 1390 Ma reflect variable retention of radiogenic argon. Forward modeling of argon diffusion shows that the distribution of hornblende and mica ages is consistent with the partial resetting of argon systematics ca. 1400 Ma by a thermal pulse reaching maximum temperatures around 550??C and decaying within <20 m.yr. These temperatures match the conditions inferred from the overprinting assemblage; thus, muscovite and biotite ages are interpreted to date the cooling phase of this metamorphic event. This late metamorphism is broadly coeval with the intrusion of ca. 1400-Ma granitic plutons in the study area and throughout the southwestern United States. However, thermal effects are observed far from pluton margins, suggesting pervasive, regional crustal heating rather than restricted contact metamorphism. Our results suggest that ca. 1400-Ma metamorphism and plutonism are manifestations of a regional thermal episode that both partially melted the lower crust and pervasively metamorphosed middle crustal rocks.

  17. Refining lunar impact chronology through high spatial resolution 40Ar/39Ar dating of impact melts

    PubMed Central

    Mercer, Cameron M.; Young, Kelsey E.; Weirich, John R.; Hodges, Kip V.; Jolliff, Bradley L.; Wartho, Jo-Anne; van Soest, Matthijs C.

    2015-01-01

    Quantitative constraints on the ages of melt-forming impact events on the Moon are based primarily on isotope geochronology of returned samples. However, interpreting the results of such studies can often be difficult because the provenance region of any sample returned from the lunar surface may have experienced multiple impact events over the course of billions of years of bombardment. We illustrate this problem with new laser microprobe 40Ar/39Ar data for two Apollo 17 impact melt breccias. Whereas one sample yields a straightforward result, indicating a single melt-forming event at ca. 3.83 Ga, data from the other sample document multiple impact melt–forming events between ca. 3.81 Ga and at least as young as ca. 3.27 Ga. Notably, published zircon U/Pb data indicate the existence of even older melt products in the same sample. The revelation of multiple impact events through 40Ar/39Ar geochronology is likely not to have been possible using standard incremental heating methods alone, demonstrating the complementarity of the laser microprobe technique. Evidence for 3.83 Ga to 3.81 Ga melt components in these samples reinforces emerging interpretations that Apollo 17 impact breccia samples include a significant component of ejecta from the Imbrium basin impact. Collectively, our results underscore the need to quantitatively resolve the ages of different melt generations from multiple samples to improve our current understanding of the lunar impact record, and to establish the absolute ages of important impact structures encountered during future exploration missions in the inner Solar System. PMID:26601128

  18. Results of 40Ar/39Ar dating of phlogopites from kelyphitic rims around garnet grains (Udachnaya-Vostochnaya kimberlite pipe)

    NASA Astrophysics Data System (ADS)

    Yudin, D. S.; Tomilenko, A. A.; Alifirova, T. A.; Travin, A. V.; Murzintsev, N. G.; Pokhilenko, N. P.

    2016-07-01

    40Ar/39Ar dating of phlogopite from kelyphitic rims around garnet grains from the Udachnaya-Vostochnaya kimberlite pipe in the Sakha (Yakutia) Republic (Russia) revealed that when this mineral has contact with a kimberlite melt its age corresponds (within error limits) to that of the formation of the kimberlite pipe, thus indicating that the method may be used for dating kimberlites and related rocks. In mantle xenoliths, kelyphitic phlogopites rimming garnet grains partially lose radiogenic Ar, which results in a complex age spectrum. Rejuvenation of the K/Ar system in them is determined by the thermal impact of the kimberlite melt on captured rocks.

  19. High-resolution 40Ar 39Ar chronology of Oligocene volcanic rocks, San Juan Mountains, Colorado

    USGS Publications Warehouse

    Lanphere, M.A.

    1988-01-01

    The central San Juan caldera complex consists of seven calderas from which eight major ash-flow tuffs were erupted during a period of intense volcanic activity that lasted for approximately 2 m.y. about 26-28 Ma. The analytical precision of conventional K-Ar dating in this time interval is not sufficient to unambiguously resolve this complex history. However, 40Ar 39Ar incremental-heating experiments provide data for a high-resolution chronology that is consistent with stratigraphie relations. Weighted-mean age-spectrum plateau ages of biotite and sanidine are the most precise with standard deviations ranging from 0.08 to 0.21 m.y. The pooled estimate of standard deviation for the plateau ages of 12 minerals is about 0.5 percent or about 125,000 to 135,000 years. Age measurements on coexisting minerals from one tuff and on two samples of each of two other tuffs indicate that a precision in the age of a tuff of better than 100,000 years can be achieved at 27 Ma. New data indicate that the San Luis caldera is the youngest caldera in the central complex, not the Creede caldera as previously thought. ?? 1988.

  20. Age of Popigai impact event using the Ar-40 - Ar-39 method

    NASA Astrophysics Data System (ADS)

    Bottomley, R. J.; Grieve, R. A. F.

    1993-03-01

    The Popigai impact structure of central Siberia is the largest known impact crater in the Commonwealth of Independent States with an original diameter of some 100 km. The age of the crater is constrained by the existing stratigraphy to a period between 5-65 Ma. Attempts to date the impact event using conventional K-Ar on whole rock samples and fission track dating on glasses yield a spread of ages between 30 and 45 Ma. Argon step-heating analyses of several whole-rock samples performed with the Argon Laserprobe at the University of Toronto indicated an age of impact of about 36 Ma. However, a more recently reported Ar-40 - Ar-49 result on glass separated from a suevite sample gave a 65 Ma age and raised the possibility that Popigai was involved with the K/T boundary event. We have pursued further analyses at the University of Toronto on a broader spectrum of Popigai samples. These results confirm an age of about 36 Ma for the formation of this crater, and indicate that Popigai was not associated with the K/T boundary event.

  1. Age of Popigai impact event using the Ar-40 - Ar-39 method

    NASA Technical Reports Server (NTRS)

    Bottomley, R. J.; Grieve, R. A. F.

    1993-01-01

    The Popigai impact structure of central Siberia is the largest known impact crater in the Commonwealth of Independent States with an original diameter of some 1OO km. The age of the crater is constrained by the existing stratigraphy to a period between 5-65 Ma. Attempts to date the impact event using conventional K-Ar on whole rock samples and fission track dating on glasses yield a spread of ages between 30 and 45 Ma. Argon step-heating analyses of several whole-rock samples performed with the Argon Laserprobe at the University of Toronto indicated an age of impact of about 36 Ma. However, a more recently reported Ar-40 - Ar-49 result on glass separated from a suevite sample gave a 65 Ma age and raised the possibility that Popigai was involved with the K/T boundary event. We have pursued further analyses at the University of Toronto on a broader spectrum of Popigai samples. These results confirm an age of about 36 Ma for the formation of this crater, and indicate that Popigai was not associated with the K/T boundary event.

  2. 40Ar/39Ar Ages for the Sentinel-Arlington Volcanic Field, Southwestern Arizona

    NASA Astrophysics Data System (ADS)

    Cave, S. R.; Greeley, R.; Champion, D. E.; Turrin, B. D.

    2007-12-01

    .16-51.48. Geochronology using 40Ar/39Ar method revealed an age of 1.94 +/- 0.85 Ma for Painted Rock Low Shield (New Mexico Geochronology Research Laboratory), 1.64 +/- 0.14 Ma for Theba Low Shield (Rutgers University) and 1.24 +/- 0.040 Ma for Wild Horse Low Shield (Rutgers University). Some ages were precise enough to correspond to the Matuyama reversed polarity epoch, with SAVF initiation possibly within the Olduvai normal polarity event. These dates represent an overall improvement in precision and accuracy over previous dates (values corresponding to 6.20 Ma to 1.28 Ma) collected in the late 1970s and early 1980s using K-Ar technique. The 40Ar/39Ar ages correspond to expected magnetic polarities and stratigraphic sequences.

  3. 40Ar/39Ar constraints on the activity of the Temsamane extensional detachment (eastern Rif, Morocco)

    NASA Astrophysics Data System (ADS)

    Jabaloy Sánchez, A.; Booth-Rea, G.; Azdimousa, A.; Asebriy, L.; Vázquez-Vílchez, M.; Martínez-Martínez, J. M.; Gabites, J.

    2012-04-01

    The subducted North Maghrebian passive margin was exhumed by an upper crustal brittle-ductile extensional detachment and brittle low-angle normal faults in a continental subduction transform setting. The Temsamane detachment in the eastern Rif is defined by a ductile shear zone approximately 100 m thick with a low-angle ramp geometry that cuts down into the Temsamane fold-nappe stack. The shear zone shows southwestward kinematics and separates epizone metapelites of the Temsamane units below from the epizone to diagenetic rocks of the Tanger-Ketama-Aknoul units above. To the east, the detachment becomes brittle, branching into a listric-fan that cuts through 10-6 Ma sediments and volcanoclastics in the Tres Forcas cape. New 40Ar/39Ar radiometric ages on amphiboles and micas from the footwall of the Temsamane detachment indicate that the metamorphic peak was reached in the footwall (Temsamane units) at ca. 21 Ma, producing the amphibolite epidote facies in the Ras Afrou Unit. The cooling of the footwall rocks below the 325 °C occurred between the 16 and 13 Ma, while apatite fission track ages indicate that the cooling below the 120 °C occurred at ca. 11 Ma. The 40Ar/39Ar radiometric ages on amphiboles and micas of the metamorphic klippes over the Temsamene units (Ait-Amrâne massif) indicates that the Jurassic marbles of the Tanger-Ketama Unit reached their metamorphic peak at ca. 80 Ma, in agreement with previously published K/Ar ages in micas. The rocks of the Tanger-Ketama Unit cooled below the 120 °C between 17.0 ± 2.4 Ma and 13.9 ± 1.8 Ma. We interpret the increase of cooling rates of the footwall rocks between 15-13 Ma and 11 Ma as due to the activity of the Temsamane detachment fault. Thus, both the North Maghrebian and the South Iberian subducted passive margins were exhumed in the Betic and Rif branches of the Gibraltar arc by SW-directed brittle-ductile detachments during the Late Miocene in an oblique collisional setting.

  4. Experimental introduction of excess Ar40 into a granitic melt

    USGS Publications Warehouse

    Fyfe, W.S.; Lanphere, M.A.; Dalrymple, G.B.

    1969-01-01

    Samples of a Precambrian granite were melted in sealed capsules to produce a radiogenic Ar40 atmosphere over the melt. The amount of Ar40 incorporated in the quenched charge was then determined. Under these experimental conditions the amount of argon dissolved in the quenched melt was appreciable and could be an important source of error in potassiumargon dating. ?? 1969 Springer-Verlag.

  5. 75 FR 12162 - Class E Airspace; Manila, AR

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-15

    ... read as follows: Authority: 49 U.S.C. 106(g); 40103, 40113, 40120; E.O. 10854, 24 FR 9565, 3 CFR, 1959... Federal Aviation Administration 14 CFR Part 71 Class E Airspace; Manila, AR AGENCY: Federal Aviation... Class E airspace at Manila, AR. Decommissioning of the Manila non-directional beacon (NDB) at...

  6. 75 FR 12165 - Class E Airspace; Batesville, AR

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-15

    ... read as follows: Authority: 49 U.S.C. 106(g); 40103, 40113, 40120; E.O. 10854, 24 FR 9565, 3 CFR, 1959... TRANSPORTATION Federal Aviation Administration 14 CFR Part 71 Class E Airspace; Batesville, AR AGENCY: Federal... proposes to amend Class E airspace at Batesville, AR. Decommissioning of the Independence County...

  7. USDA-ARS RESEARCH ON BIOLOGICAL CONTROL OF ARTHROPODS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    During 1999-2001, ARS scientists published over 100 papers on biocontrol of 30 insect pests. These papers address issues crucial to the three strategies of biological control: conservation, augmentation, and introduction. ARS scientists have been very active in determining the effects of pesticides...

  8. Dating the longevity of ductile shear zones: Insight from 40Ar/39Ar in situ analyses

    NASA Astrophysics Data System (ADS)

    Schneider, Susanne; Hammerschmidt, Konrad; Rosenberg, Claudio L.

    2013-05-01

    We attempt to improve temporal constraints on the longevity and the termination of ductile shear zones by performing texturally-controlled in situ 40Ar/39Ar analyses of pre-kinematic muscovite, biotite and K-feldspars, of syn-kinematic phengite and K-feldspar, and of post-kinematic phengite within the same samples of sinistral shear zones from the western Tauern Window (Eastern Alps). Additionally two samples were dated by the Rb/Sr method (microsampling). Relative sequences of mineral formation based on microstructural, cross-cutting relationships were confirmed by in situ 40Ar/39Ar analyses, showing that syn-kinematic minerals are, in general, younger than pre-kinematic minerals and older or of equal age than the post-kinematic minerals of the same sample. From the rim to the core of the western Tauern Window syn-kinematic phengite and K-feldspar reveal a set of formation ages varying between 33 and 15 Ma for the northernmost and peripheral shear zone (Ahorn Shear Zone), between 24 and 12 Ma for the intermediate shear zone network (Tuxer Shear Zones), and between 20 and 7 Ma for the southernmost and central shear zone (Greiner Shear Zone). The age variation of syn-kinematic phengite and K-feldspar analyses is larger than the analytical error of each age obtained. In addition, isochron calculations of the syn-kinematic minerals reveal atmospheric-like 40Ar/36Ar intercepts. Therefore, the obtained age values of the syn-kinematic minerals are interpreted as formation ages which date increments of a long lasting deformation period. The time range of deformation of each shear zone system is bracketed by the oldest and youngest formation ages of syn-kinematic phengite and K-feldspar. Post-kinematic phengite laths show the youngest formation ages and overlap with the youngest syn-kinematic formation ages. This relationship indicates that post-kinematic growth occurred immediately after syn-kinematic mineral formation at the end of ductile sinistral shear. Hence, the

  9. Ar-40/Ar-39 age constraints for the Jaramillo Normal Subchron and the Matuyama-Brunhes geomagnetic boundary

    NASA Astrophysics Data System (ADS)

    Izett, Glen A.; Obradovich, John D.

    1994-02-01

    Our mid-Pleistocene Ar-40/Ar-39 age recalibration of the geomagnetic polarity timescale is nearly in accord with the oxygen isotope, climate record calibration of the astronomical timescale proposed by Johnson (1982) and Shackleton et al. (1990). Ar-40/Ar-39 ages of a normally magnetized rhyolite dome in the Valles caldera, northern Mexico, yielded a weighted-mean age of 1.004 +/- 0.019 Ma. A K-Ar age of 0.909 +/- 0.019 Ma for this rock by Doell and Dalrymple (1966) was the linchpin for the recognition and calibration of the Jaramillo Normal Subchron (JNS). Other Ar-40/Ar-39 ages from the Valles caldera and Ar-40/Ar-39 ages of Ivory Coast tektites indicate that the JNS began at about 1.11 Ma and ended before 0.92 Ma, probably near 0.97 Ma. The Matuyama-Brunhes boundary occurred between 0.79 Ma and 0.76 Ma on the basis of Ar-40/Ar-39 sanidine ages from (1) three reversely magnetized rhyolite domes of the Valles caldera (0.793 +/- 0.018 Ma, 0.794 +/- 0.007 Ma, and 0.812 +/- 0.023 Ma) and pumice (0.789 +/- 0.006 Ma) from the reversely magnetized Oldest Toba Tuff of Sumatra and (2) pumice (0.764 +/- 0.005 Ma and 0.757 +/- 0.009 Ma) from the lower and upper units of the normally magnetized Bishop Tuff. The age of the boundary may be close to 0.77 Ma as deduced from rates of sedimentation in ancient Lake Bonneville, Utah.

  10. On the doubly ionized states of Ar{sub 2} and their intra- and interatomic decay to Ar{sub 2}{sup 3+}

    SciTech Connect

    Stoychev, Spas D.; Kuleff, Alexander I.; Tarantelli, Francesco; Cederbaum, Lorenz S.

    2008-01-07

    Potential energy curves of the Auger state Ar{sup +}(2p{sup -1})-Ar, the different one- and two-site dicationic states Ar{sub 2}{sup ++} (with energies in the range of 32-77 eV), and the lowest two-site tricationic states Ar{sup ++}-Ar{sup +} (with energies in the range of 64-76 eV) computed using elaborated ab initio methods are reported. The accessible relaxation channels of the electronic states of Ar{sup ++}-Ar populated by Auger decay are studied. In particular, we study in detail the interatomic Coulombic decay following the population of one-site satellite states of Ar{sup ++}(3s{sup -1}3p{sup -1})-Ar recently observed experimentally. Other relaxation pathways of Ar{sup ++}-Ar, including radiative charge transfer, nuclear dynamics through curve crossing, and intra-atomic decay processes are also investigated.

  11. Androgen Receptor (AR) Physiological Roles in Male and Female Reproductive Systems: Lessons Learned from AR-Knockout Mice Lacking AR in Selective Cells1

    PubMed Central

    Chang, Chawnshang; Lee, Soo Ok; Wang, Ruey-Sheng; Yeh, Shuyuan; Chang, Ta-Min

    2013-01-01

    ABSTRACT Androgens/androgen receptor (AR) signaling is involved primarily in the development of male-specific phenotypes during embryogenesis, spermatogenesis, sexual behavior, and fertility during adult life. However, this signaling has also been shown to play an important role in development of female reproductive organs and their functions, such as ovarian folliculogenesis, embryonic implantation, and uterine and breast development. The establishment of the testicular feminization (Tfm) mouse model exploiting the X-linked Tfm mutation in mice has been a good in vivo tool for studying the human complete androgen insensitivity syndrome, but this mouse may not be the perfect in vivo model. Mouse models with various cell-specific AR knockout (ARKO) might allow us to study AR roles in individual types of cells in these male and female reproductive systems, although discrepancies are found in results between labs, probably due to using various Cre mice and/or knocking out AR in different AR domains. Nevertheless, no doubt exists that the continuous development of these ARKO mouse models and careful studies will provide information useful for understanding AR roles in reproductive systems of humans and may help us to develop more effective and more specific therapeutic approaches for reproductive system-related diseases. PMID:23782840

  12. Effect of surface derived hydrocarbon impurities on Ar plasma properties

    SciTech Connect

    Fox-Lyon, Nick; Oehrlein, Gottlieb S.; Godyak, Valery

    2014-05-15

    The authors report on Langmuir probe measurements that show that hydrocarbon surfaces in contact with Ar plasma cause changes of electron energy distribution functions due to the flux of hydrogen and carbon atoms released by the surfaces. The authors compare the impact on plasma properties of hydrocarbon species gasified from an etching hydrocarbon surface with injection of gaseous hydrocarbons into Ar plasma. They find that both kinds of hydrocarbon injections decrease electron density and slightly increase electron temperatures of low pressure Ar plasma. For low percentages of impurities (∼1% impurity in Ar plasma explored here), surface-derived hydrocarbon species and gas phase injected hydrocarbon molecules cause similar changes of plasma properties for the same number of hydrocarbon molecules injected into Ar with a decrease in electron density of ∼4%.

  13. Touch interface for markless AR based on Kinect

    NASA Astrophysics Data System (ADS)

    Hsieh, Ching-Tang; Kuo, Tai-Ku; Wang, Hui-Chun; Wu, Yeh-Kuang; Chang, Liung-Chun

    2014-01-01

    We develop an augmented reality (AR) environment with hidden-marker via touch interface using Kinect device, and then also set up a touch painting game with the AR environment. This environment is similar to that of the touch screen interface which allows user to paint picture on a tabletop with his fingers, and it is designed with depth image information from Kinect device setting up above a tabletop. We incorporate support vector machine (SVM) to classify painted pictures which correspond to the inner data and call out its AR into the tabletop in color images information from Kinect device. Because users can utilize this similar touch interface to control AR, we achieve a marker-less AR and interactive environment.

  14. Search for cosmogenic Ar-42 in meteorites

    NASA Astrophysics Data System (ADS)

    Cini Castagnoli, G.; Cane, D.; Taricco, C.; Bhandari, N.

    2003-04-01

    We have evidence for decreasing galactic cosmic ray (GCR) flux in the past 3 centuries by a factor about two [1]. The measurements of the activity of cosmogenic 44Ti (T1/2 = 59.2 y) produced by GCR in stony meteorites that fell during the last two centuries are in good agreement with the calculated values and validate the decreasing trend of GCR flux. The measurements were obtained by an hyperpure (372 cm3) Ge-NaI(Tl) spectrometer operating in the Monte dei Cappuccini laboratory in Torino[2]. To further improve upon statistical precision of 44Ti data and also to be able to measure the 42Ar (T1/2 = 33 y) which is produced in even smaller amounts by GCR in meteorites, we have set up in the same laboratory a larger (581 cm3) hyperpure Ge detector operating in coincidence with a 100 kg NaI(Tl) crystal assembly. This should enable us to confirm the above results about GCR variations. We wish to acknowledge our deep gratitude to professor Bonino, deceased on September 29, 2002, to whom the assemblage of the new equipment is due. [1] G. Bonino, G. Cini Castagnoli, D. Cane, C. Taricco and N. Bhandari,Proc. XXVII Intern. Cosmic Ray Conf. (Hamburg, 2001) 3769-3772. [2] Bonino G., Cini Castagnoli G., Cane D., Taricco C., Bhandari N, textit {34th COSPAR Sci. Ass. Houston 2002 (Adv. Space Res.)}, in press

  15. A compilation of K-Ar-ages for southern California

    USGS Publications Warehouse

    Miller, Fred K.; Morton, Douglas M.; Morton, Janet L.; Miller, David M.

    2014-01-01

    The purpose of this report is to make available a large body of conventional K-Ar ages for granitic, volcanic, and metamorphic rocks collected in southern California. Although one interpretive map is included, the report consists primarily of a systematic listing, without discussion or interpretation, of published and unpublished ages that may be of value in future regional and other geologic studies. From 1973 to 1979, 468 rock samples from southern California were collected for conventional K-Ar dating under a regional geologic mapping project of Southern California (predecessor of the Southern California Areal Mapping Project). Most samples were collected and dated between 1974 and 1977. For 61 samples (13 percent of those collected), either they were discarded for varying reasons, or the original collection data were lost. For the remaining samples, 518 conventional K-Ar ages are reported here; coexisting mineral pairs were dated from many samples. Of these K-Ar ages, 225 are previously unpublished, and identified as such in table 1. All K-Ar ages are by conventional K-Ar analysis; no 40Ar/39Ar dating was done. Subsequent to the rock samples collected in the 1970s and reported here, 33 samples were collected and 38 conventional K-Ar ages determined under projects directed at (1) characterization of the Mesozoic and Cenozoic igneous rocks in and on both sides of the Transverse Ranges and (2) clarifying the Mesozoic and Cenozoic tectonics of the eastern Mojave Desert. Although previously published (Beckerman et al., 1982), another eight samples and 11 conventional K-Ar ages are included here, because they augment those completed under the previous two projects.

  16. Paleomagnetic and 40Ar/39Ar geochronologic data from late Proterozoic mafic dikes and sills, Montana and Wyoming

    USGS Publications Warehouse

    Harlan, Stephen S.; Geissman, John William; Snee, Lawrence W.

    1997-01-01

    Paleomagnetic and 40Ar/39Ar results from mafic dikes and sills in northwestern Wyoming and western Montana yield similar virtual geomagnetic poles and isotopic dates. In combination with paleomagnetic and geochronologic data from elsewhere in the western Cordillera, these data provide evidence for a regional mafic magnetic event at 780 to 770 Ma that affected a large area of western North America.

  17. Differential distribution of cAMP receptors cAR2 and cAR3 during Dictyostelium development.

    PubMed

    Yu, Y; Saxe, C L

    1996-01-10

    Signal transduction via a family of cAMP receptor subtypes (cARs) is critical for proper development in the cellular slime mold Dictyostelium. Genes encoding four related subtypes have been cloned and their expression, based on RNA accumulation, has been previously reported. Here we report the differential spatial and temporal distribution of cAR2 and cAR3 proteins, based on indirect double immunofluorescence. Cells were transformed with a carB::lacZ construct, and an antibody against beta-galactosidase was used to visualize cAR2 expression. Simultaneously, a cAR3-specific antibody was used to identify cAR3-expressing cells. Results indicate that by the time of tip formation (12-14 hr) both receptors are expressed and distribute in a virtually nonoverlapping pattern, with cAR2 being expressed on anterior, prestalk cells and cAR3 present in the rest of the organism. Differential distribution of these two receptor subtypes may result in distinct cAMP signaling mechanisms in the two major regions of the organism. PMID:8575636

  18. On Full Disclosure and Transparent Data Flow from 40Ar/39Ar Geochronology Measurements to Data Reduction to Online Repositories

    NASA Astrophysics Data System (ADS)

    Koppers, A. A. P.

    2015-12-01

    Arguably 40Ar/39Ar geochronology is one of the most versatile techniques available to Earth scientists today for the dating of rocks and minerals and determining the rates of geological processes on Earth and in our solar system. Over the last four decades large quantities of high (and lower) quality 40Ar/39Ar data have been produced using many different generations of mass spectrometry instrumentation. This wealth of data is only as useful as its description and availability of metadata allows. Many online data sets or compilations available in the science literature only carry the resulting product, an age and a related uncertainty in millions of years, for example. These data points are far from desirable as these don't allow recalculation against modern-day age standards, decay constants and other parameters essential in 40Ar/39Ar geochronology. Over time these data will become less useful to the research community and eventually these will be put by the wayside. In this presentation I will emphasize the need for full disclosure of all data and metadata involved in 40Ar/39Ar geochronology. I will give examples of how a complex data flow can be kept transparent from sample preparation to measurement to data reduction and eventually the uploading into online data repositories. Without the full disclosure of our data and a transparent data flow, it is evident that we cannot live up to one of the governing doctrines in the sciences, namely reproducibility of our scientific experiments and findings.

  19. ``Smoking From The Same Pipe": Developement of an 40Ar/39Ar Datting Intercalibration PIpette System (Invited)

    NASA Astrophysics Data System (ADS)

    Turrin, B. D.; Swisher, C. C.; Deino, A.; Hemming, S. R.; Hodges, K.; Renne, P. R.

    2010-12-01

    The precision and accuracy of Ar isotope ratio measurements is one of the main limiting factors in the uncertainties of an 40Ar/39Ar age. Currently, it is relatively common to measure Ar isotopic ratios to a precision of 1-2‰ or better on an intralaboratory basis. This level of analytical precision equates to a comparable level of precision (1-3‰) in the calculated age, depending on the extent of atmospheric Ar contamination, importance of nucleogenic interference corrections, and other factors. However, it has become clear that improving the precision of mass spectrometry is not the only bottleneck towards improving the accuracy and precision of 40Ar/39Ar dating in general. Rather, the most urgent issue is interlaboratory reproducibility. This became obvious in a recent EARTHTIME initiative undertaken to intercalibrate two commonly used 40Ar/39Ar standards [the Fish Canyon sanidine (FCs) and the Alder Creek sanidine (ACs)]. This effort revealed variations amongst laboratories (at the 1-2% level), an order of magnitude greater than the internal analytical precisions. To address these issues, we have proposed (to NSF) to construct two identical pipette systems loaded to identical starting pressures and with identical isotopic compositions. One pipette system will travel between participating 40Ar/39Ar labs and the second system will not travel and serve as the “Master” system to test for any fractionation or undocumented depletion of the traveling pipette system. In order to ensure delivery of uniform amounts of homogenous gas, the pipette system will be computer-controlled with preprogrammed routines and lockouts to prevent compromising the reservoirs. The pipette systems will deliver three gas samples with different isotopic ratios at two different pressures/concentrations. One pipette bulb will be of atmospheric isotopic composition, and the other two pipette bulbs will have 40Ar*/39ArK ratios corresponding to co-irradiated ACs and FCs fixed by their

  20. Evaluation of the IPCC Models (AR4 and AR5) in the Precipitation Simulation in the Northeast of Brazil

    NASA Astrophysics Data System (ADS)

    Alves, José; Vasconcelos Junior, Francisco; Chaves, Rosane; Silva, Emerson; Servain, Jacques; Costa, Alexandre; Sombra, Sérgio; Barbosa, Augusto; Dos Santos, Antonio

    2016-04-01

    With the simulations of the models used in the latest reports from the Intergovernmental Panel on Climate Change (IPCC), comparative studies are necessary between observations and the so-called historical run (C20) and future projections of the AR4 (A2) and AR5 (RCP8.5) experiments, in order to assess whether the AR5 models had a better performance in the representation of physical processes. This article compares the sensitivity of IPCC models (AR4 and AR5) in representing the anuall average and seasonal rainfall variation (summer and autumn) in three regions of the Northeast of Brazil between 1979 and 2000, using the CMAP - CPC (Merged Analysis of Precipitation) data as reference. The projections made by these models for the period 2040-2070 were also analyzed.

  1. Toward a high-resolution 40Ar/39Ar geochronology of the Tatun Volcano Group, Taiwan

    NASA Astrophysics Data System (ADS)

    Mesko, G. T.; Song, S.; Chang, S.; Hemming, S. R.; Turrin, B. D.

    2010-12-01

    The Tatun Volcano Group [TVG] consists of five volcanic subgroups of which ~30 edifices have been identified, all in close proximity to the densely populated Taipei Basin to its south (Song et al., 2000, Journal of the Geological Society of China, in Chinese). Evidence of eruptions is in the form of mostly lava flows, with pyroclastic flows, and ash deposition (Tsai et al., 2010, TAO), consistent with vulcanian and plinian eruptions that are only minimally preserved because of the region’s high weathering rate (Belousov et al., 2010, Journal of Volcanology and Geothermal Research). The TVG is made up of calc-alkaline andesite, with few interspersed basaltic lava flows that bear geochemical signatures consistent with subduction volcanism, yet due to tectonic location Teng (1996, Geology) describes it as Ryukyu back-arc basin volcanism, and still others attribute volcanism here to post-collisional collapse of the Taiwan orogen (Wang et al., 1999, Tectonophysics and 2004, Journal of Petrology). Various TVG samples were previously K-Ar dated by Juang and Chen (1989, Bulletin of Central Geological Survey, in Chinese), Tsao (1994, Bulletin of Central Geological Survey, in Chinese), and 40Ar/39Ar whole rock analyses by Lee (1996, masters thesis, National Taiwan University) to suggest volcanism from 2.8-2.5Ma and then from 1.5-.22Ma after which volcanic events ceased. In contrast, radiocarbon dates obtained from charcoal in related sediment by Chen et al. (2010, TAO) and Belousov et al. (2010, Journal of Volcanology Geothermal Research) suggest volcanic activity was present at 20ka and 6ka respectively. The andesite samples are microcrystalline; therefore hand picked aliquots of groundmass from the hand magnetic fraction were subjected to several iterations of sonic rinse in glycine-based soap, then 4N HNO3, then quartz-distilled water in a preparation modified from Nicolaysen et al. (2000, EPSL). Samples were co-irradiated at the USGS facility in Denver using Alder

  2. Ar-Ar investigations on Quarternary volcanic sequences of Monte Vulture (Southern Italy)

    NASA Astrophysics Data System (ADS)

    Buettner, A.; Principe, C.; Villa, I. M.

    2003-04-01

    Volcanic sanidines and phlogopites from feldspathoid- or sanidine-bearing volcanic sequences of Monte Vulture (Southern Italy) were analysed using Ar-Ar stepwise heating. In all samples phlogopite and sanidine are internally inhomogeneous as observed in a plot of Cl/K ratio vs step-age. At least two phases that are degassed during different temperature steps can be distinguished, resulting in internal discordance. Hence, all samples are affected by impurities and have to be treated as heterochemical mixtures. These effects are strongest in phlogopite. The high uncertainty of the calculated ages mirrors the statistically significant age discordance. The calculation of average ages was focused on isochemical steps. Isochron calculations necessarily give less precise ages because of the excessive scatter of datapoints. Moreover, most coarse grained phlogopites could contain excess 40Ar (as suggested by non-atmospheric intercepts in isochron plots) which could be of mantle origin. The analysed phlogopites from carbonatitic and melilite-foiditolite rocks of the upper stratigraphical sequence of Monte Vulture are Mg-rich, which indicates a mantle provenance (Stoppa and Woolley, 1997). All calculated phlogopite ages have, therefore, to be considered with caution. One sample, PG5, contains both sanidine and matrix phlogopite. This offers the possibility to directly compare the analytical results and further decipher possible inconsistencies. Ages were calculated as the average of isochemical steps, and errors are indicated at the 95% confidence level. Sanidine gives a weighted average age of 752±13 ka in agreement with the phlogopite age of 801±88 ka. In comparison to these average step ages, an isochron over five sanidine-steps yields an age of 737±35 ka (MSWD=1.5) and an atmospheric intercept of 295±49. The eruptive time-span covered by the analysed samples is 75±20 ka, confirming that the eruption history of Monte Vulture has been organised in clusters of activity

  3. 40Ar/39Ar constraints on the temporal evolution of Graciosa Island, Azores (Portugal)

    NASA Astrophysics Data System (ADS)

    Larrea, Patricia; Wijbrans, Jan R.; Galé, Carlos; Ubide, Teresa; Lago, Marceliano; França, Zilda; Widom, Elisabeth

    2014-02-01

    Lava flows spanning the eruptive record of Graciosa Island (Azores archipelago) and a gabbro xenolith were dated by 40Ar/39Ar in order to constrain the Pleistocene and Holocene volcanic evolution of the island. The results range from 1.05 Ma to 3.9 ka, whereas prior published K-Ar and 14C ages range from 620 to 2 ka. The formation of the Serra das Fontes shield volcano started at minimum 1.05 Ma, and the magmatic system was active for ca. 600 ky, as suggested by the formation of the gabbro xenolith by magmatic differentiation. Evolved magmas making up the Serra das Fontes-Serra Branca composite volcano were generated at ca. 450 ka. After a period of ca. 110 ky of volcanic inactivity and erosion of volcanic edifices, volcanism was reactivated with the formation of the Vitória Unit NW platform. Later, the development of the Vulcão Central Unit started with the formation of monogenetic cones located to the south of the Serra das Fontes-Serra Branca-Vitória Unit. This volcanism became progressively more evolved and was concentrated in a main eruptive center, forming the Vulcão Central stratovolcano with an age older than 50 ka. The caldera related to this stratovolcano is older than 47 ka and was followed by effusion of basaltic magmas into the caldera, resulting in the formation of a lava lake, which ultimately spilled over the caldera rim at ca. 11 ka. The most recent eruptions on Graciosa formed two small pyroclastic cones within the caldera and the Pico do Timão cone within the Vitória Unit at ca 3.9 ka.

  4. Unique Thermal Histories from Whole-Rock 40Ar/39Ar Step-heating Data

    NASA Astrophysics Data System (ADS)

    Boehnke, P.; Harrison, M.; Heizler, M. T.; Lovera, O. M.; Warren, P. H.

    2014-12-01

    Step-heating 40Ar/39Ar analysis can reveal spatial distributions of 40Ar* at the micron scale imparted by post- crystallization heating events through complex, multi-diffusion domain models. These efforts have largely focused on single-phase, terrestrial samples with only scant attention paid to multi-phase or extra-terrestrial materials. Generalizing these models to incorporate the multiple activation energies (E) expected from bulk rock samples introduces significant interpretational ambiguity. This is because the thermal crossovers explicit in multi-E cases make the age spectrum a function of the lab heating schedule in thermally disturbed samples. A further difficulty is that unique interpretation of the associated Arrhenius plot is no longer possible and a range of E's can be fitted with equal goodness of fit. In order to address these challenges, we developed a new computational approach that simultaneously inverts the Arrhenius spectra and release pattern using a variant of the Adaptive Particle Swarm Optimization (APSO) algorithm for a square-pulse heating event. Our version uses a Levy Flight to break the swarm out of a local minima rather than randomly modifying a single dimension as in the original APSO. Further we explored issues of Pareto efficiency arising from fitting two fitness functions (i.e., the fit to the age spectra and to the Arrhenius plot) and found an adequate resolution to the classic inability to have a single best fit. By utilizing multiple-E samples, we are able to obtain unique thermal history solutions. Application of these methods to high resolution age spectra of the Jilin chondrite and Apollo 16 samples (North Ray Crater) and found fits of sufficiently high fidelity to constrain the absolute temperature of the thermal episode to better than ±10%.

  5. A new approach to cosmogenic corrections in 40Ar/39Ar chronometry: Implications for the ages of Martian meteorites

    NASA Astrophysics Data System (ADS)

    Cassata, W. S.; Borg, L. E.

    2016-08-01

    Anomalously old 40Ar/39Ar ages are commonly obtained from Shergottites and are generally attributed to uncertainties regarding the isotopic composition of the trapped component and/or the presence of excess 40Ar. Old ages can also be obtained if inaccurate corrections for cosmogenic 36Ar are applied. Current methods for making the cosmogenic correction require simplifying assumptions regarding the spatial homogeneity of target elements for cosmogenic production and the distribution of cosmogenic nuclides relative to trapped and reactor-derived Ar isotopes. To mitigate uncertainties arising from these assumptions, a new cosmogenic correction approach utilizing the exposure age determined on an un-irradiated aliquot and step-wise production rate estimates that account for spatial variations in Ca and K is described. Data obtained from NWA 4468 and an unofficial pairing of NWA 2975, which yield anomalously old ages when corrected for cosmogenic 36Ar using conventional techniques, are used to illustrate the efficacy of this new approach. For these samples, anomalous age determinations are rectified solely by the improved cosmogenic correction technique described herein. Ages of 188 ± 17 and 184 ± 17 Ma are obtained for NWA 4468 and NWA 2975, respectively, both of which are indistinguishable from ages obtained by other radioisotopic systems. For other Shergottites that have multiple trapped components, have experienced diffusive loss of Ar, or contain excess Ar, more accurate cosmogenic corrections may aid in the interpretation of anomalous ages. The trapped 40Ar/36Ar ratios inferred from inverse isochron diagrams obtained from NWA 4468 and NWA 2975 are significantly lower than the Martian atmospheric value, and may represent upper mantle or crustal components.

  6. Ar Ar dating of authigenic K-feldspar: Quantitative modelling of radiogenic argon-loss through subgrain boundary networks

    NASA Astrophysics Data System (ADS)

    Mark, D. F.; Kelley, S. P.; Lee, M. R.; Parnell, J.; Sherlock, S. C.; Brown, D. J.

    2008-06-01

    We have analysed two distinct generations of authigenic K-feldspar in Fucoid Bed sandstones from An-t-Sron and Skiag Bridge, NW Highlands, Scotland, which have experienced post-growth heating to levels in excess of the predicted Ar-closure temperature. Authigenic K-feldspars show microtextural similarities to patch perthites; that is subgrains separated by dislocation-rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon. The two generations of authigenic K-feldspar in the Fucoid Bed sandstones can be distinguished by different microtextural zones, bulk mineral compositions, fluid-inclusion populations, and inferred temperatures and chemistries of parent fluids. Ar-Ar age data obtained using high-resolution ultraviolet laser ablation, show that the first cementing generation is Ordovician and the second cementing generation is Silurian. Modelling of Ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono-thermal thrust model assuming transient heating of the Fucoid Beds is inconsistent with observed data. Removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed Ar-Ar ages for both generations of cement. Alternatively, Ar-diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the Fucoid Bed palaeothermal maxima and determined Ar-Ar age ages for the two generations of K-feldspar cement. Based on this alternate explanation, we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic K-feldspars, explaining the apparent robustness of authigenic K-feldspar with respect to Ar-retention.

  7. Ar-40/Ar-39 age determinations for the Rotoiti eruption, New Zealand

    NASA Astrophysics Data System (ADS)

    Flude, S.; Storey, M.

    2013-12-01

    The contemporaneous Rotoiti and Earthquake Flat ignimbrites, erupted from the Taupo Volcanic zone, New Zealand, form a distinctive tephrostratigraphic horizon in the Southern Pacific. Radioisotopic dating results for these eruptions remain controversial, with published ages ranging from 35.1 × 2.8 ka [1] to 71 × 6 ka [2], with 61.0 × 1.5 ka [3] often being cited as the most widely accepted age. These eruptions are difficult to date as their age is near the limit for various radiometric dating techniques, which are complicated by a large proportion of inherited material (xenocrysts) and a lack of phases suitable for dating. Glass-bearing plutonic blocks erupted with the Rotoiti and Earthquake Flat ignimbrites have previously been interpreted as deriving from a slowly cooled and incompletely solidified magma body that was sampled by the eruptions. They contain large vugs lined with euhedral quartz, sanidine and biotite crystals, indicating that these crystals grew in a gas or aqueous fluid rich environment and are interpreted to have formed shortly before or during eruption. Here we will present Ar-40/Ar-39 ages for sanidines and biotites extracted from vugs in lithic blocks erupted as part of the Earthquake Flat ignimbrite. We show that, even for vug-lining material, inherited ages remain a problem and are the likely source of the wide variation in published radiometric ages. Nevertheless, many of the Ar-40/Ar-39 ages are much younger than the 61 ka age [3] and are more consistent with the recent stratigraphic, C-14 and U-238/Th-230+(U-Th)/He ages that have been suggested (e.g. [4,5]). 1. Whitehead, N. & Ditchburn, R. New Zealand Journal of Geology and Geophysics 37, 381-383 (1994). 2. Ota, Y., Omura, A. & Iwata, H. New Zealand Journal of Geology and Geophysics 32, 327-331 (1989). 3. Wilson, C. J. N. et al. Quaternary Science Reviews 26, 1861-1870 (2007). 4. Molloy, C., Shane, P. & Augustinus, P. Geological Society of America Bulletin 121, 1666-1677 (2009). 5

  8. High-precision 40Ar/39Ar age for the Jehol Biota

    NASA Astrophysics Data System (ADS)

    Chang, S.; Zhang, H.; Renne, P. R.; Fang, Y.

    2008-12-01

    Abundant fossils of the terrestrial Jehol Biota, including plants, insects, dinosaurs, birds, mammals and freshwater invertebrates, were discovered from the Yixian Formation and the overlying Jiufotang Formation in Inner Mongolia, Hebei Province and Liaoning Province, northeastern China. Because of the exceptional preservation of fossils, the Jehol Biota is one of the most important Mesozoic fossil outcrops and referred to as a "Mesozoic Pompeii". The Jehol Biota has provided a rare opportunity to address questions about the origin of birds, the evolution of feathers and flight, the early diversification of angiosperms and the timing of the radiation of placental mammals. The Tuchengzi Formation, which lies unconformably just below the Yixian Formation and consists mainly of variegated sandstones, is less fossiliferous than the two overlying formations. However, dinosaur tracks, silicified wood and compressed plants are found in this formation. A systematic 40Ar/39Ar dating of the Yixian and the Jiufotang formations was undertaken to provide a framework for understanding the timing and duration of the Jehol Biota and evolutionary events represented within it. Furthermore, determining the absolute age of the Tuchengzi Formation provides information to interpret abundant dinosaur tracks within and provide better age constrains for the beginning of the Jehol Biota. Here we present robust high-precision 40Ar/39Ar data for six tuff samples and two basalt samples collected from the Tuchengzi, the Yixian and the Jiufotang formations near the classic outcrops in western Liaoning, NE China. We obtain an age of 139.5 ± 1.0 Ma for the uppermost Tuchengzi Formation, an age of 129.7 ± 0.5 Ma for a basaltic lava from the bottom of the Yixian Formation and an age of 122.1 ± 0.3 Ma for a tuff from the base of the overlying Jiufotang Formation. Our data indicate that the Yixian Formation was deposited during the Early Cretaceous, the Barremian to early Aptian, within a time span

  9. New 40Ar/39Ar Ages From Southwest Bolivia Refine the Timing of APVC Volcanism

    NASA Astrophysics Data System (ADS)

    Salisbury, M.; de Silva, S. L.; Jicha, B.; Singer, B.; Jiménez, N.; Ort, M.

    2008-12-01

    The Altiplano-Puna Volcanic Complex (APVC) of the Central Andes has produced prodigious silicic volcanism (at least 11,000 km3 of magma) over the last 10 Ma including some of the largest known ignimbrites on Earth. Despite excellent exposure, little previous work had been conducted on the timing and distribution of ignimbrite volcanism in the Lípez region of southwestern Bolivia, the heart of the APVC. To address this deficiency we have performed ~612 single crystal laser-fusion 40Ar/39Ar analyses from 39 pumice and bulk matrix samples collected from the main ignimbrite units within the Lípez region. Geochemistry of pumice and mineral samples, and paleomagnetic data are also being used to correlate individual ignimbrite units. Our new 40Ar/39Ar results establish new or refined eruption ages (with 2σ error) from the Vilama caldera at 8.41±0.02 Ma, Pastos Grandes caldera at 5.45±0.02 and 2.94±0.01 Ma, and Guacha caldera at 5.65±0.01, and 3.57±0.02 Ma. New ages were also determined for eruptions from the Panizos ignimbrite shield (6.86±0.03 Ma), Juvina ignimbrite shield (5.23±0.01 Ma), and the Laguna Colorado ignimbrite shield (2.21±0.05 and 1.95±0.03 Ma). The oldest ignimbrite we have found in the area is 10.33±0.64 Ma, a local unit beneath the Vilama ignimbrite. The youngest units have been identified west of the Guacha caldera with eruption ages of 1.70±0.6 Ma and 0.70±0.01 Ma. These results demonstrate that ignimbrite-producing eruptions in the Lípez region span the age of APVC volcanism previously established, with the largest eruptions occurring from long-lived, cyclic supervolcano caldera systems like Guacha and Pastos Grandes. The aggregate data from the APVC support the hypothesis that the APVC developed predominantly during distinct pulses of massive ignimbrite eruptions at ~8, 6, and 4 Ma and attest to episodic behavior of the magmatic system. Ignimbrites of <1 Ma, the cyclical nature of activity, and the continued geothermal presence and

  10. Implications of new 40Ar/39Ar data for the Cretaceous-Paleogene boundary

    NASA Astrophysics Data System (ADS)

    Renne, P. R.; Deino, A.; Hilgen, F.; Kuiper, K.; Mark, D. F.; Mitchell, W. S.; Morgan, L. E.; Smit, J.

    2012-12-01

    The cause of the mass extinctions across the Cretaceous-Paleogene boundary (KPB) is still controversial. Previous geochronological data [1-3] appear to preclude the Chicxulub impact as a causal mechanism as they indicate that the KPB predated the impact by 181 ± 71 ka (1σ here and throughout). New 40Ar/39Ar data, determined blind in the BGC and SUERC labs, for the terrestrial KPB (IrZ-coal bentonite) from the Hell Creek area of northeastern Montana yield an age of 66.044 ± 0.011/0.045 Ma (without/with systematic uncertainties, calibrated per [4]). New 40Ar/39Ar data for Haitian tektites, combined with previous work [2,3], yield an age of 66.038 ± 0.025/0.049 Ma thereby establishing synchrony between the terrestrial KPB and the Chicxulub bolide impact to within 33 ka. The absolute boundary age of 66.044 Ma ± 0.045 [4] or 65.837 ± 0.061 Ma [5] allows clear discrimination between Earth's 405 ka orbital eccentricity cycles and both calibrations favor the orbital tuning chronology of [5] for the KPB at Zumaia, Spain. The former calibration is corroborated by U/Pb data [6]. In contrast, a recent orbital chronology proposed for the Zumaia section [7] infers an age of 65.2 Ma for the KPB, suggesting that the tuning missed two 405 ka eccentricity cycles. New data for tuffs above the KPB indicate a dramatic reduction in the post-KPB timescale of faunal recovery during the Puercan1 NALMA substage, and for the restoration of pre-KPB atmospheric δ13C values, to several tens of ka at most. Our new data clearly implicate a significant role for the Chicxulub impact in the KPB extinctions, but this cannot explain the significant pre-KPB climate instability or precursory faunal turnover [8]. The Chicxulub impact likely delivered the final blow to stressed ecosystems rather than being the sole cause of the KPB extinctions. The role of roughly synchronous phenomena such as eruption of the multiphased Deccan Traps [9] remains to be tested via high-precision geochronology. Refs

  11. 40Ar/(39)Ar dating of the Kapthurin Formation, Baringo, Kenya.

    PubMed

    Deino, Alan L; McBrearty, Sally

    2002-01-01

    The(40)Ar/(39)Ar radiometric dating technique has been applied to tuffs and lavas of the Kapthurin Formation in the Tugen Hills, Kenya Rift Valley. Two variants of the(40)Ar/(39)Ar technique, single-crystal total fusion (SCTF) and laser incremental heating (LIH) have been employed to date five marker horizons within the formation: near the base, the Kasurein Basalt at 0.61+/-0.04 Ma; the Pumice Tuff at 0.543+/-0.004 Ma; the Upper Kasurein Basalt at 0.552+/-0.015 Ma; the Grey Tuff at 0.509+/-0.009 Ma; and within the upper part of the formation, the Bedded Tuff at 0.284+/-0.012 Ma. The new, precise radiometric age determination for the Pumice Tuff also provides an age for the widespread Lake Baringo Trachyte, since the Pumice Tuff is the early pyroclastic phase of this voluminous trachyte eruption. These results establish the age of fossil hominids KNM-BK 63-67 and KNM-BK 8518 at approximately 0.510-0.512 Ma, a significant finding given that few Middle Pleistocene hominids are radiometrically dated. The Kapthurin hominids are thus the near contemporaries of those from Bodo, Ethiopia and Tanzania. A flake and core industry from lacustrine sediments in the lower part of the formation is constrained by new dates of 0.55-0.52 Ma, a period during which the Acheulian industry, characterized by handaxes, is known throughout East Africa. Points, typical of the Middle Stone Age (MSA), are found in Kapthurin Formation sediments now shown to date to between 0.509+/-0.009 Ma and 0.284+/-0.012 Ma. This date exceeds previous estimates for the age of the MSA elsewhere in East Africa by 49 ka, and establishes the age of Acheulian to MSA transition for the region. Evidence of the use of the Levallois technique for the manufacture of both small flakes and biface preforms, the systematic production of blades, and the use and processing of red ochre also occurs in this interval. The presence of blades and red ochre at this depth is important as blades signify a high degree of technical

  12. Molecular modeling of the effects of 40Ar recoil in illite particles on their K-Ar isotope dating

    NASA Astrophysics Data System (ADS)

    Szczerba, Marek; Derkowski, Arkadiusz; Kalinichev, Andrey G.; Środoń, Jan

    2015-06-01

    The radioactive decay of 40K to 40Ar is the basis of isotope age determination of micaceous clay minerals formed during diagenesis. The difference in K-Ar ages between fine and coarse grained illite particles has been interpreted using detrital-authigenic components system, its crystallization history or post-crystallization diffusion. Yet another mechanism should also be considered: natural 40Ar recoil. Whether this recoil mechanism can result in a significant enough loss of 40Ar to provide observable decrease of K-Ar age of the finest illite crystallites at diagenetic temperatures - is the primary objective of this study which is based on molecular dynamics (MD) computer simulations. All the simulations were performed for the same kinetic energy (initial velocity) of the 40Ar atom, but for varying recoil angles that cover the entire range of their possible values. The results show that 40Ar recoil can lead to various deformations of the illite structure, often accompanied by the displacement of OH groups or breaking of the Si-O bonds. Depending on the recoil angle, there are four possible final positions of the 40Ar atom with respect to the 2:1 layer at the end of the simulation: it can remain in the interlayer space or end up in the closest tetrahedral, octahedral or the opposite tetrahedral sheet. No simulation angles were found for which the 40Ar atom after recoil passes completely through the 2:1 layer. The energy barrier for 40Ar passing through the hexagonal cavity from the tetrahedral sheet into the interlayer was calculated to be 17 kcal/mol. This reaction is strongly exothermic, therefore there is almost no possibility for 40Ar to remain in the tetrahedral sheet of the 2:1 layer over geological time periods. It will either leave the crystal, if close enough to the edge, or return to the interlayer space. On the other hand, if 40Ar ends up in the octahedral sheet after recoil, a substantially higher energy barrier of 55 kcal/mol prevents it from leaving

  13. Cell biological approaches to investigate polyglutamine-expanded AR metabolism.

    PubMed

    Cooper, Lori J; Merry, Diane E

    2013-01-01

    Spinal and bulbar muscular atrophy (SBMA) is a late-onset neurodegenerative disease caused by a polyglutamine expansion in the androgen receptor (AR). In vivo and in vitro studies have suggested that some steps of normal AR function and metabolism, such as hormone binding and nuclear translocation of the AR, are necessary for toxicity and aggregation of the mutant protein. Mutation of discreet functional domains of the AR and sites of posttranslational modification enable the detailed analysis of the role of AR function and metabolism in toxicity and aggregation of polyglutamine-expanded AR. This analysis could potentially lead to the development of targeted therapy for the treatment of SBMA. We have developed a stably transfected, tetracycline-inducible, cell model that replicates many of the hallmarks of disease, including ligand-dependent aggregation and toxicity, and provides a relatively quick system for the reliable expression and analysis of the mutated polyglutamine-expanded AR. Multiple cell lines, each expressing the androgen receptor with a distinct functional mutation, can be created and the dose of tetracycline modulated to produce equal protein expression across lines in order to evaluate the structural and functional requirements of AR toxicity and aggregation. Results from these studies can then be validated in a disease-relevant cell type, spinal motor neurons, using viral delivery of the gene of interest into dissociated spinal cord cultures. Utilization of these cell models provides a relatively rapid, cost-effective experimental pathway to analyze the role of distinct steps in AR metabolism in disease pathogenesis using in vitro systems. PMID:23719921

  14. A generic interface element for COMET-AR

    NASA Technical Reports Server (NTRS)

    Mccleary, Susan L.; Aminpour, Mohammad A.

    1995-01-01

    The implementation of an interface element capability within the COMET-AR software system is described. The report is intended for use by both users of currently implemented interface elements and developers of new interface element formulations. Guidance on the use of COMET-AR is given. A glossary is provided as an Appendix to this report for readers unfamiliar with the jargon of COMET-AR. A summary of the currently implemented interface element formulation is presented in Section 7.3 of this report.

  15. The Mono Lake Excursion Recorded in Phonolitic Lavas From Tenerife (Canary Islands): Paleomagnetic Analyses and Coupled K/Ar and Ar/Ar Dating.

    NASA Astrophysics Data System (ADS)

    Kissel, C.; Guillou, H.; Laj, C. E.; Carracedo, J. C.; Nomade, S.; Perez-Torrado, F.; Wandres, C.

    2011-12-01

    Studies of geomagnetic excursions is important for the knowledge of the geodynamo, and also because they may be used as precise time markers in various geological records (sediments, lavas and ice via their impact on the production of cosmogenic isotopes). In volcanic rocks, the identification of excursions is very challenging given the sporadic nature of the volcanic eruptions. However, it is a critical step because it allows absolute paleointensity determinations to be obtained, coupled with absolute dating methods. We present here a coupled paleomagnetic/dating investigation conducted on three different lava flows from the island of Tenerife (Canary Islands; Spain) erupted during the Mono Lake excursion (MLE). Paleomagnetic analyses consist in zero field demagnetizations (AF and/or thermal) and of Thellier and Thellier experiments using the PICRIT-03 set of criteria to select reliable intensity determinations. For dating, the unspiked K-Ar and the 40Ar/39Ar methods were coupled at LSCE for two of the flows and the third flow, with lower content in radiogenic 40Ar (40Ar*) was dated only using the unspiked K-Ar method. One of the flows is characterized by a direction largely deviated from the one expected from an axial geocentric dipole (GAD) field. Its paleointensity value is very low (7.8 μT). The two other sites are characterized by inclinations slightly shallower than the GAD value and by low intensity values (about 12 and 21 μT; present value: 38μT). The three K/Ar ages combined with two 40Ar/39Ar ages range from 32.0 to 33.2 ka and they are not statistically distinguishable from one another. It therefore appears that these lavas have recorded the MLE (the only excursion in this time interval) confirming its brief duration (shorter than the minimum age uncertainties available). The mean age is younger but, within the uncertainties and depending on the age of the standard we use, consistent with the age of the 10Be peak and of the marine intensity low when

  16. Mass Spectrometric and Langmuir Probe Measurements in Inductively Coupled Plasmas in Ar, CHF3/Ar and CHF3/Ar/O2 Mixtures

    NASA Technical Reports Server (NTRS)

    Kim, J. S.; Rao, M. V. V. S.; Cappelli, M. A.; Sharma, S. P.; Meyyappan, M.; Arnold, Jim (Technical Monitor)

    2000-01-01

    Absolute fluxes and energy distributions of ions in inductively coupled plasmas of Ar, CHF3/Ar, and CHF3/Ar/O2 have been measured. These plasmas were generated in a Gaseous Electronics Conference (GEC) cell modified for inductive coupling at pressures 10-50 mTorr and 100-300 W of 13.56 MHz radio frequency (RF) power in various feedgas mixtures. In pure Ar plasmas, the Ar(+) flux increases linearly with pressure as well as RF-power. Total ion flux in CHF3 mixtures decreases with increase in pressure and also CHF3 concentration. Relative ion fluxes observed in the present studies are analyzed with the help of available cross sections for electron impact ionization and charge-exchange ion-molecule reactions. Measurements of plasma potential, electron and ion number densities, electron energy distribution function, and mean electron energy have also been made in the center of the plasma with a RF compensated Langmuir probe. Plasma potential values are compared with the mean ion energies determined from the measured ion energy distributions and are consistent. Electron temperature, plasma potential, and mean ion energy vary inversely with pressure, but increase with CHF3 content in the mixture.

  17. 40Ar/ 39Ar dating of the emplacement of the Muslim Bagh ophiolite, Pakistan

    NASA Astrophysics Data System (ADS)

    Mahmood, Khalid; Boudier, Françoise; Gnos, Edwin; Monié, Patrick; Nicolas, Adolphe

    1995-11-01

    The obduction-related basal part of the Muslim Bagh ophiolite (Baluchistan, Pakistan) and the underlying metamorphic sequence were studied structurally which demonstrated a WSW-ENE-trending thrusting sequence for the initial obduction. 40Ar/ 39Ar measurements on amphiboles and plagioclase from the subophiolitic metamorphic rocks, and on plastically deformed and recrystallized dolerite samples from the base of the sheeted dyke complex give apparent ages between 70.7 ± 5.0 and 65.1 ± 4.1 Ma interpreted as cooling ages dating approximately the formation of the plastic deformation and obduction. The results indicate that the Muslim Bagh ophiolite represents a segment of ocean floor from the small and slow-spreading ocean branch of the Neo-Tethys located between the Indo-Pakistani and the Afro-Arabian plates. The WSW-ENE-oriented obduction of the Muslim Bagh ophiolite onto the Indo-Pakistani continental margin occurred with the convergence of the Neo-Tethys branch during the Late Cretaceous and before the Tertiary collision of the Indo-Pakistani plate with the Eurasian plate.

  18. (40)Ar/(39)Ar Age of Hornblende-Bearing R Chondrite LAP 04840

    NASA Technical Reports Server (NTRS)

    Righter, K.; Cosca, M.

    2015-01-01

    Chondrites have a complex chronology due to several variables affecting and operating on chondritic parent bodies such as radiogenic heating, pressure and temperature variation with depth, aqueous alteration, and shock or impact heating. Unbrecciated chondrites can record ages from 4.56 to 4.4 Ga that represent cooling in small parent bodies. Some brecciated chondrites exhibit younger ages (much less than 4 to 4.4 Ga) that may reflect the age of brecciation, disturbance, or shock and impact events (much less than 4 Ga). A unique R chondrite was recently found in the LaPaz Icefield of Antarctica - LAP 04840. This chondrite contains approximately 15% hornblende and trace amounts of biotite, making it the first of its kind. Studies have revealed an equigranular texture, mineral equilibria yielding equilibration near 650-700 C and 250-500 bars, hornblende that is dominantly OH-bearing (very little Cl or F), and high D/H ratios. To help gain a better understanding of the origin of this unique sample, we have measured the (40)Ar/(39)Ar age (LAP 04840 split 39).

  19. Soft X-Ray Emission Lines of Argon, ArIX -- ArXVI

    NASA Astrophysics Data System (ADS)

    Lepson, J. K.; Beiersdorfer, P.; Chen, H.; Behar, E.; Kahn, S. M.

    2002-04-01

    The soft x-ray region of 20 - 50 Å is nearly unknown territory to astrophysicists. This spectral band remains virtually unstudied, even in solar observations, and laboratory measurements are similarly lacking. Spectra obtained from Chandra and XMM-Newton X-Ray Observatories show a wealth of lines in this region, albeit weak in most cases. Most of these lines remain unidentified as observations have now outpaced the available databases. In support of these missions we have undertaken laboratory measurements of astrophysically relevant ions in the extreme ultraviolet and soft x-ray regions using the Livermore electron beam ion trap EBIT-II. We present here results of argon, covering ArIX - ArXVI between 20 - 50 Åand compare our spectra with calculations from the Hebrew University - Lawrence Livermore Atomic Code HULLAC. EBIT-II data agree broadly with HULLAC calculations, with accuracy of ± 0.3 Å for most major lines. Given the density of lines in Chandra and XMM-Newton spectra, this accuracy is often insufficient for line identification in the absence of careful laboratory mesaurements. Work performed under auspices of DOE by UC LLNL and funded by NASA SARA.

  20. 40Ar/39Ar dating of Pleistocene tuffs: an accurate age for the Matuyama-Brunhes geomagnetic reversal (MBGR)

    NASA Astrophysics Data System (ADS)

    Mark, D. F.; Renne, P. R.; Morgan, L. E.; Deino, A.; Smith, V. C.; Ellis, B. S.; Pearce, N. J.

    2012-12-01

    Recent recalibrations of the 40Ar/39Ar system [1,2] reveal inconsistencies with some previous ages inferred for the MBGR. An Ar/Ar age [3] for the Bishop Tuff (BT) (which post-dates the MBGR by at least 15.3 ± 2.2 ka [3]) recalculated [2] yields an age of 778.0 ± 3.8 ka (1σ, full systematic uncertainty). The age is c. 10 ka older than the BT zircon ID-TIMS U-Pb age [4] and places the MBGR at c. 793 ka, c. 13 and 20 ka older than astronomical ages for the MBGR of 780 ka [5] and 773 ka [6], respectively. To determine an accurate age for the MBGR, we have made a series of 40Ar/39Ar age determinations for Pleistocene tuffs from both Indonesia and North America that have direct relationships to the MBGR. Blind analyses were conducted at SUERC and BGC. We observed excellent inter-laboratory agreement and no systematic offset in data. Ar/Ar ages are reported relative to [2] (1σ, full systematic uncertainty). Drill cores from ODP Site 758 show the precise location of the MBGR. Below the MBGR are two distal tephra horizons that we have identified as products of two temporally distinct Old Toba Tuff (OTT) eruptions (layer d OTT1 and layer D OTT2). Continuous sedimentation between OTT1 (802.8 ± 0.7 ka, n = 100, MSWD 1.2) and OTT2 (796.2 ± 0.8 ka, n = 62, MSWD 1.3) allows for calculation of an accurate sedimentation rate and for extrapolation of an age from OTT2 to the MBGR. Data define an age for the MBGR of 795.2 ± 0.9 ka. Using tephra above the MBGR boundary, the Middle Toba Tuff (layer C) and Young Toba Tuff (layer A), extrapolation down core supports a MBGR age of c. 795 ka. Recent age data for BT sanidine reported relative to FCs at 28.172 Ma (767.4 ± 1.1 Ma) [7] oddly yielded an Ar/Ar age that was indistinguishable from the BT zircon U-Pb age [4], which is consistent with previous 40Ar/39Ar age measurements made relative to FCs at 28.02 Ma [3]. Thus we made a series of 40Ar/39Ar measurements on the exact same sample as used by Rivera et al. [7] and observed

  1. Geology and 40Ar/39Ar Geochronology of Akutan Volcano, Eastern Aleutian Islands

    NASA Astrophysics Data System (ADS)

    Coombs, M. L.; Jicha, B. R.

    2013-12-01

    40Ar/39Ar dating and new whole-rock geochemical analyses are used to establish an eruptive chronology for Akutan volcano, Akutan Island, in the eastern Aleutian island arc. Akutan Island (166° W, 54.1° N) is the site of long-lived volcanism and the entire island comprises volcanic rocks as old as 3.3 Ma (Richter et al., 1998, USGS Open-File 98-135). Our current focus is on the 225 km2 western half of the island, which is home to the Holocene active cone, Holocene to latest Pleistocene satellite vents, and underlying middle Pleistocene volcanic basement rocks. Eruptive products span the tholeiitic-calc-alkaline boundary, are medium-K, and range from basalt to dacite. Furnace incremental heating experiments on groundmass separates of 38 samples resulted in 29 40Ar/39Ar ages. The remainder did not yield radiogenic 40Ar contents and are likely Holocene in age. The oldest ages (1251×10 and 1385×12 ka) are from a wedge of flat-lying dissected lavas north of the Holocene cone; these likely represent the upper part of the volcanic basement that underlies the entire island. Above a major unconformity lie basaltic andesite to dacite lavas that range from 765× 4 to 522×8 ka. The eroded remnants of the source volcano for these flows appears to crop out as a series of variably hydrothermally altered breccias and domes 5 km east-northeast of the current summit. A 625 m-tall eroded basaltic center, Lava Peak, sits 6 km northwest of the summit; its deeply incised western flank exposes lava flows and a plug. Two flows are dated at 598×16 and 602×15 ka. A high ridge 1.5 km south of the summit is made of oxidized, mostly andesitic lavas 284-249 ka old; these are presumably the remnants of an eruptive center located near the current cone. Flat Top Peak, 3.5 km southwest of the summit, produced almost exclusively basalts and six dated lavas range from 155×8 to 98×18 ka. Lavas from Flat Top (1065 m asl) are deeply eroded suggesting extensive ice cover during marine isotope

  2. Experimental study of NO2 reduction in N2/Ar and O2/Ar mixtures by pulsed corona discharge.

    PubMed

    Zhu, Xinbo; Zheng, Chenghang; Gao, Xiang; Shen, Xu; Wang, Zhihua; Luo, Zhongyang; Cen, Kefa

    2014-11-01

    Non-thermal plasma technology has been regarded as a promising alternative technology for NOx removal. The understanding of NO2 reduction characteristics is extremely important since NO2 reduction could lower the total NO oxidation rate in the plasma atmosphere. In this study, NO2 reduction was experimentally investigated using a non-thermal plasma reactor driven by a pulsed power supply for different simulated gas compositions and operating parameters. The NO2 reduction was promoted by increasing the specific energy density (SED), and the highest conversion rates were 33.7%, 42.1% and 25.7% for Ar, N2/Ar and O2/Ar, respectively. For a given SED, the NO2 conversion rate had the order N2/Ar>Ar>O2/Ar. The highest energy yield of 3.31g/kWh was obtained in N2/Ar plasma and decreased with increasing SED; the same trends were also found in the other two gas compositions. The conversion rate decreased with increasing initial NO2 concentration. Furthermore, the presence of N2 or O2 led to different reaction pathways for NO2 conversion due to the formation of different dominating reactive radicals. PMID:25458679

  3. 40Ar/39Ar and U-Th-Pb dating of separated clasts from the Abee E4 chondrite

    USGS Publications Warehouse

    Bogard, D.D.; Unruh, D.M.; Tatsumoto, M.

    1983-01-01

    Determinations of 40Ar/39Ar and U-Th-Pb are reported for three clasts from the Abee (E4) enstatite chondrite, which has been the object of extensive consortium investigations. The clasts give 40Ar/39Ar plateau ages and/or maximum ages of 4.5 Gy, whereas two of the clasts give average ages of 4.4 Gy. Within the range of 4.4-4.5 Gy these data do not resolve any possible age differences among the three clasts. 206Pb measured in these clasts is only ???1.5-2.5% radiogenic, which leads to relatively large uncertainties in the Pb isochron age and in the 207Pb/206Pb model ages. The Pb data indicate that the initial 207Pb/206Pb was no more than 0.08??0.07% higher than this ratio in Can??on Diablo troilite. The U-Th-Pb data are consistent with the interpretation that initial formation of these clasts occurred 4.58 Gy ago and that the clasts have since remained closed systems, but are contaminated with terrestrial Pb. The 40Ar/39Ar ages could be gas retention ages after clast formation or impact degassing ages. The thermal history of Abee deduced from Ar data appears consistent with that deduced from magnetic data, and suggests that various Abee components experienced separate histories until brecciation no later than 4.4 Gy ago, and experienced no appreciable subsequent heating. ?? 1983.

  4. Inductively Coupled Plasma Etching of III-V Antimonides in BCl(3)/Ar and Cl(2)/Ar

    SciTech Connect

    Leavitt, R.P.; Lester, L.F.; Shul, R.J.; Willison, C.G.; Zhang, L.

    1998-11-04

    Inductively coupled plasma (ICP) etching characteristics of GaSb and AIGaAsSb have been investigated in BC13/Ar and Clz/Ar plasmas. The etch rates and selectivity between GaSb and AIGaAsSb are reported as functions of plasma chemistry, ICP power, RF self-bias, and chamber pressure. It is found that physical sputtering resorption of the etch products plays a dominant role in BC13/Ar ICP etching, while in Clz/Ar plasma, the chemical reaction dominates the etching. GaSb etch rates exceeding 2 ~rnhnin are achieved in Clz/Ar plasmas with smooth surfaces and anisotropic profiles. In BC13/Ar plasmas, etch rates of 5100 Mmin and 4200 Mmin are obtained for GaSb and AIGaAsSb, respectively. The surfaces of both GaSb and AIGaAsSb etched in BC13/Ar plasmas remain smooth and stoichiometric over the entire range of plasma conditions investigated. This result is attributed to effective removal of etch products by physical sputtering. For a wide range of plasma conditions, the selectivity between GaSb and AIGaAsSb is close to unity, which is desirable for fabricating etched mirrors and gratings for Sb-based mid-IR laser diodes.

  5. Comparison Between 40Ar/39Ar and U/Pb Geochronometers at ca. 2.1 Ga

    NASA Astrophysics Data System (ADS)

    Renne, P. R.; Renne, P. R.; Min, K.; Schmitz, M. D.; Bowring, S. A.; de Wit, M. J.; Morelli, C.

    2001-12-01

    Recent sudies have revealed 1-2% age bias between conventional calibrations of the 40Ar/39Ar and U/Pb geochronologic methods applied to quickly cooled volcanic rocks whose isotopic systems should be uncomplicated by differential retention of radiogenic daughter isotopes. The U-Pb system serves as an ideal basis for comparison because of its rigorous internal reliability criteria and precisely-determined decay constants via alpha counting. Studies capable of providing useful comparison have been limited to samples younger than 1.1 Ga, which offers useful constraints primarily on 40Ar/40K of 40Ar/39Ar standards and the electron capture decay constant of 40K. The magnitude of observed bias for these samples is within the range of realistically propagated errors in those quantities. The beta decay constant of 40K is comparably poorly constrained, leading to ambiguities about early solar system cooling rates among other issues, and is more difficult to test directly due to a paucity of appropriate (e.g., minimally altered with demonstrably simple thermal history) rocks for comparison. A strikingly fresh hornblende-biotite dacite from the Eglab region of the Requibat massif, West Africa, offers an exceptional opportunity for head-to-head comparison of the two geochronometers at nearly twice the age limit currently available. Zircons from this unit are concordant to nearly concordant.and indicate an age of ca 2076 Ma. 40Ar/39Ar analysis of individual hornblende grains, step-heated with a CO2 laser, reveal some complexities but generally yield plateau ages of 2050-2060 Ma based on IUGS 1977 decay constants and 28.02 Ma for the Fish Canyon sanidine. Thus the bias between 40Ar/39Ar and U/Pb systems in this case is of order 1%, suggesting that relative error in the conventional beta decay constant is somewhat less than that of the electron capture constant for 40K.

  6. The Thermo Scientific HELIX-SFT noble gas mass spectrometer: (preliminary) performance for 40Ar/39Ar geochronology

    NASA Astrophysics Data System (ADS)

    Barfod, D. N.; Mark, D. F.; Morgan, L. E.; Tomkinson, T.; Stuart, F.; Imlach, J.; Hamilton, D.

    2011-12-01

    The Thermo Scientific HELIX-platform Split Flight Tube (HELIX-SFT) noble gas mass spectrometer is specifically designed for simultaneous collection of helium isotopes. The high mass spur houses a switchable 1011 - 1012 Ω resistor Faraday cup and the low mass spur a digital pulse-counting secondary electron multiplier (SEM). We have acquired the HELIX-SFT with the specific intention to measure argon isotopes for 40Ar/39Ar geochronology. This contribution will discuss preliminary performance (resolution, reproducibility, precision etc.) with respect to measuring argon isotope ratios for 40Ar/39Ar dating of geological materials. We anticipate the greatest impact for 40Ar/39Ar dating will be increased accuracy and precision, especially as we approach the techniques younger limit. Working with Thermo Scientific we have subtly modified the source, alpha and collector slits of the HELIX-SFT mass spectrometer to improve its resolution for resolving isobaric interferences at masses 36 to 40. The enhanced performance will allow for accurate and precise measurement of argon isotopes. Preliminary investigations show that we can obtain a valley resolution of >700 and >1300 (compared to standard HELIX-SFT specifications of >400 and >700) for the high and low mass spurs, respectively. The improvement allows for full resolution of hydrocarbons (C3+) at masses 37 - 40 and almost full resolution at mass 36. The HELIX-SFT will collect data in dual collection mode with 40Ar+ ion beams measured using the switchable 1011 - 1012 Ω resistor Faraday cup and 39Ar through 36Ar measured using the SEM. The HELIX-SFT requires Faraday-SEM inter-calibration but negates the necessity to inter-calibrate multiple electron multipliers. We will further present preliminary data from the dating of mineral standards: Alder Creek sanidine, Fish Canyon sanidine and Mount Dromedary biotite (GA1550).

  7. Argon diffusion in Apollo 16 impact glass spherules: Implications for 40Ar/39Ar dating of lunar impact events

    NASA Astrophysics Data System (ADS)

    Gombosi, David J.; Baldwin, Suzanne L.; Watson, E. Bruce; Swindle, Timothy D.; Delano, John W.; Roberge, Wayne G.

    2015-01-01

    The 40Ar/39Ar technique applied to impact glass has been used to date both terrestrial and lunar impact events. The ability to utilize the 40Ar/39Ar technique rests on the assumption that impact glasses are closed to the loss of daughter product, 40Ar∗, after formation. Diffusion experiments were performed on three Apollo 16 lunar impact glasses and yielded activation energies for 39Ar of ∼17 to 20 kcal mol-1 and log10(D0/a2) values of -5.2 to -6.0 s-1. The resulting diffusion coefficients are interpreted as minimum values and the Apollo 16 glass is probably some of the least retentive of lunar glasses, as the degree of non-bridging oxygen is at one end of the range in lunar glasses. At temperatures below the glass transition temperature (i.e., ∼660 °C), the data can be explained by volume diffusion from a single diffusion domain. Modeling shows that Apollo 16 composition glass could lose significant quantities of radiogenic argon (40Ar∗) (∼90-100% over 20-40 Myr assuming a diffusion domain size (a) of 75 μm) due to diurnal temperature variations on the lunar surface, although 40Ar∗ loss is highly sensitive to exposure duration and effective diffusion domain size. Modeling shows that loss from transient thermal events (e.g., heating to ∼200 °C for 102 yr duration) can also cause partial resetting of apparent 40Ar/39Ar ages. In small (a = 75 μm) glasses a maximum of 50-60% of 40Ar∗ is lost over 4 Ga when buried to depths corresponding to temperatures of -15 °C. Results indicate that caution should be exercised in interpreting lunar impact glass 40Ar/39Ar ages, as the assumption of closed system behavior may have been violated, particularly in glasses with low fractions of non-bridging oxygen.

  8. Differential regulation of metabolic pathways by androgen receptor (AR) and its constitutively active splice variant, AR-V7, in prostate cancer cells

    PubMed Central

    Shafi, Ayesha A.; Putluri, Vasanta; Arnold, James M.; Tsouko, Efrosini; Maity, Suman; Roberts, Justin M.; Coarfa, Cristian; Frigo, Daniel E.; Putluri, Nagireddy; Sreekumar, Arun; Weigel, Nancy L.

    2015-01-01

    Metastatic prostate cancer (PCa) is primarily an androgen-dependent disease, which is treated with androgen deprivation therapy (ADT). Tumors usually develop resistance (castration-resistant PCa [CRPC]), but remain androgen receptor (AR) dependent. Numerous mechanisms for AR-dependent resistance have been identified including expression of constitutively active AR splice variants lacking the hormone-binding domain. Recent clinical studies show that expression of the best-characterized AR variant, AR-V7, correlates with resistance to ADT and poor outcome. Whether AR-V7 is simply a constitutively active substitute for AR or has novel gene targets that cause unique downstream changes is unresolved. Several studies have shown that AR activation alters cell metabolism. Using LNCaP cells with inducible expression of AR-V7 as a model system, we found that AR-V7 stimulated growth, migration, and glycolysis measured by ECAR (extracellular acidification rate) similar to AR. However, further analyses using metabolomics and metabolic flux assays revealed several differences. Whereas AR increased citrate levels, AR-V7 reduced citrate mirroring metabolic shifts observed in CRPC patients. Flux analyses indicate that the low citrate is a result of enhanced utilization rather than a failure to synthesize citrate. Moreover, flux assays suggested that compared to AR, AR-V7 exhibits increased dependence on glutaminolysis and reductive carboxylation to produce some of the TCA (tricarboxylic acid cycle) metabolites. These findings suggest that these unique actions represent potential therapeutic targets. PMID:26378018

  9. Hydrothermal fluids, argon isotopes and mineralization ages of the Fankou Pb-Zn deposit in south China: Insights from sphalerite 40Ar/39Ar progressive crushing

    NASA Astrophysics Data System (ADS)

    Jiang, Ying-De; Qiu, Hua-Ning; Xu, Yi-Gang

    2012-05-01

    Hydrothermal fluid geochemistry and mineralization timing are two important factors in the genesis of a hydrothermal deposit. 40Ar/39Ar analyses of fluid inclusions not only provide time constraints for the mineralization but also help to clarify the K-Ca-Cl-Ar characteristics for the ore-forming fluids. In this study, six sphalerite samples collected from the Fankou lead-zinc sulfide deposit are investigated by 40Ar/39Ar in vacuo crushing. Gases liberated from the early and late crushing steps exhibit distinct Ar isotopic compositions and 40Ar/39Ar apparent ages. Argon released in the early steps has much higher 40Ar and 38ArCl and lower 37ArCa contents than those in the late steps. The significant excess Ar (40ArE) extracted in the early crushing steps shows a strong correlation with 38ArCl with very high 40ArE/38ArCl ratios. In contrast, those of the late steps mainly consist of atmospheric Ar and K-correlated radiogenic Ar with a constant 40ArR/39ArK ratio and the atmospheric initial 40Ar/36Ar ratio. As a result, all samples yield similar declining age spectra: the fore segments with anomalously old apparent ages decline quickly in the early crushing steps and the rear ones are flat with concordant apparent ages in the late crushing steps. The data points of the early steps define linear correlations in plots of 40ArNA/39ArK vs. 38ArCl/39ArK and 38ArCl/40ArNA vs. 39ArK/40ArNA (NA for non-atmospheric) and most yield ages of 240-230 Ma. On the other hand, the data of the late steps always construct well-defined isochrons in the plots of 36ArA/40ArNA vs. 39ArK/40ArNA with consistent ages of ˜300 Ma. We interpret that gases released in the early steps were from the secondary fluid inclusions (SFIs) due to their distribution characteristics along cracks leading to be easily extracted, and those released in the later steps represented the contribution of the primary fluid inclusions (PFIs). The initial 40Ar/36Ar ratios of SFIs, much higher than the modern

  10. Structure of the N=27 isotones derived from the {sup 44}Ar(d,p){sup 45}Ar reaction

    SciTech Connect

    Gaudefroy, L.; Beaumel, D.; Blumenfeld, Y.; Fortier, S.; Franchoo, S.; Hammache, F.; Roussel, P.; Stanoiu, M.; Tryggestad, E.; Dombradi, Z.; Sohler, D.; Grevy, S.; St Laurent, M. G.; Roussel-Chomaz, P.; Kratz, K. L.; Lukyanov, S. M.; Penionzhkevich, Yu.-E.

    2008-09-15

    The {sup 44}Ar(d,p){sup 45}Ar neutron transfer reaction was performed at 10A MeV. Measured excitation energies, deduced angular momenta, and spectroscopic factors of the states populated in {sup 45}Ar are reported. A satisfactory description of these properties is achieved in the shell model framework using a new sdpf interaction. The model analysis is extended to more exotic even-Z nuclei down to {sub 14}{sup 41}Si{sub 27} to study how collectivity impacts the low-lying structure of N=27 neutron-rich nuclei.

  11. Single-crystal 40Ar/39Ar incremental heating reveals bimodal sanidine ages in the Bishop Tuff

    NASA Astrophysics Data System (ADS)

    Andersen, N. L.; Jicha, B. R.; Singer, B. S.

    2015-12-01

    The 650 km3 Bishop Tuff (BT) is among the most studied volcanic deposits because it is an extensive marker bed deposited just after the Matuyama-Brunhes boundary. Reconstructions of the vast BT magma reservoir from which high-silica rhyolite erupted have long influenced thinking about how large silicic magma systems are assembled, crystallized, and mixed. Yet, the longevity of the high silica rhyolitic melt and exact timing of the eruption remain controversial due to recent conflicting 40Ar/39Ar sanidine vs. SIMS and ID-TIMS U-Pb zircon dates. We have undertaken 21 40Ar/39Ar incremental heating ages on 2 mm BT sanidine crystals from pumice in 3 widely separated outcrops of early-erupted fall and flow units. Plateau ages yield a bimodal distribution: a younger group has a mean of 766 ka and an older group gives a range between 772 and 782 ka. The younger population is concordant with the youngest ID-TIMS and SIMS U-Pb zircon ages recently published, as well as the astronomical age of BT in marine sediment. Of 21 crystals, 17 yield older, non-plateau, steps likely affected by excess Ar that would bias traditional 40Ar/39Ar total crystal fusion ages. The small spread in older sanidine ages, together with 25+ kyr of pre-eruptive zircon growth, suggest that the older sanidines are not partially outgassed xenocrysts. A bimodal 40Ar/39Ar age distribution implies that some fraction of rhyolitic melt cooled below the Ar closure temperature at least 10 ky prior to eruption. We propose that rapid "thawing" of a crystalline mush layer released older crystals into rhyolitic melt from which sanidine also nucleated and grew immediately prior to the eruption. High precision 40Ar/39Ar dating can thus provide essential information on thermo-physical processes at the millenial time scale that are critical to interpreting U-Pb zircon age distributions that are complicated by large uncertainties associated with zircon-melt U-Th systematics.

  12. Collisional-radiative modelling of an Ar helicon plasma discharge

    NASA Astrophysics Data System (ADS)

    Loch, Stuart

    2005-10-01

    We report on recent modelling results of emission observed from a helicon plasma, comparing theoretical and observed line intensities and line ratios of Ar, Ar^+ and Ar^2+. Our Helicon plasma is from the ASTRAL device at Auburn University, with spectral measurements from 275 nm through to 1015 nm. We concentrate on the Ar^+ ion stage, and present the results of a collisional-radiative model using various qualities of atomic data. In particular, we compare the modelling results using Plane-Wave Born, Distorted-Wave and R-matrix electron impact excitation data with those observed from the plasma. As part of the modelling work, we investigate the potential use of various lines as plasma diagnostic tools.

  13. Ar2 photoelectron spectroscopy mediated by autoionizing states.

    PubMed

    Briant, Marc; Poisson, Lionel; Hochlaf, Majdi; de Pujo, Patrick; Gaveau, Marc-André; Soep, Benoît

    2012-11-01

    This experimental work focuses on the complex autoionization dynamics of Ar(2) clusters below the first ionization energy of the argon atom. Ar(2) is submitted to vacuum ultraviolet radiation, and the photoelectron spectra are collected in coincidence with the cluster ions. The ionization dynamics is revealed by the dependence on the photon energy. We applied a new experimental method which we developed to analyze the photoelectron signal. Thus, we were able (i) to get the complete vibrational progression of Ar(2)(+) that was never observed up to now, especially identifying the 0-0 transition overcoming the usual Franck-Condon limitations during single photoionization, and (ii) to obtain the projections of the vibrational wave functions of the autoionizing states over the Ar(2)(+) functions. This method provides a powerful tool to test the potential energy curves computed by high level theoretical calculations on Rydberg states. PMID:23215381

  14. Electron capture and fragmentation in Ar11+ + CO collisions

    NASA Astrophysics Data System (ADS)

    Ben-Itzhak, I.; Wells, E.; Stöckli, M. P.; Tawara, H.; Carnes, K. D.

    1997-01-01

    Collisions between 32.2, 130.5 and 570.5 keV Ar11+ ions and CO molecules have been studied using the Macdonald Laboratory CRYEBIS. Coincidence time of flight was used to detect all recoil ions originating from each molecule and a position sensitive detector was used to determine final projectile charge states. Single-and double-electron capture cross-sections are much larger than those for ionization at these collision energies. The dominant recoil channel associated with the Ar10+ final charge state is the CO+ molecular ion. The main ion-pair channel is the C+ + O+ dissociation of CO2+ while the relative yields of higher charge states of the transient COq+ fall off rapidly. The dissociated ions corresponding to charge states up to CO4+ were detected in coincidence with Ar10+ (and Ar9+), indicating that multielectron capture followed by autoionization occurs.

  15. 76 FR 29284 - Arkansas Disaster Number AR-00049

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-20

    ... From the Federal Register Online via the Government Publishing Office SMALL BUSINESS ADMINISTRATION Arkansas Disaster Number AR-00049 AGENCY: U.S. Small Business Administration. ACTION: Amendment 1... original declaration remains unchanged. ] (Catalog of Federal Domestic Assistance Numbers 59002 and...

  16. Nitrogen Dissociation in N_2-Ar Microwave Plasmas

    NASA Astrophysics Data System (ADS)

    Henriques, J.; Tatarova, E.; Ferreira, C. M.

    2002-10-01

    Microwave N_2-Ar discharges driven by a traveling surface wave (SW) attract attention due to their advantageous properties for plasma processing technologies, in particular for nitriding surfaces. Nitrogen atoms are the most important precursors in gas discharge nitriding and the study of their production and loss mechanisms is of fundamental importance. The kinetics of dissociation of N2 in N_2-Ar microwave plasmas was investigated as a function of the spatial position, mixture composition and pressure. A theoretical model(J. Henriques, E. Tatarova, V. Guerra and C.M. Ferreira, J. Appl. Phys. 91 5622 (2002).) was developed for the following situation: an azimuthally symmetric SW (TM_00, ω/2π=2.45 GHz) propagates and sustains an N_2-Ar plasma column in a dielectric tube (a=0.75 cm, \\varepsilon_d=3.78) surrounded by a metal screen (R=2.5 cm). The model account in a self-consistent way for the electron and heavy particle kinetics, gas thermal balance and wave electrodynamics. It is demonstrated that charge transfer Ar^+ + N2 arrow N_2^+ + Ar followed by dissociative recombination e + N_2^+ arrow N(^4S) + N(^4S) increases the dissociation degree of nitrogen at high Ar fractional percentage in the mixture. The predictions are validated by optical emission spectroscopy(J. Henriques, E. Tatarova, F.M. Dias and C.M. Ferreira, J. Appl. Phys. 91 5632 (2002).).

  17. Effect and mechanism of AR-6 in experimental rheumatoid arthritis.

    PubMed

    Sun, Shi-xue; Li, Yun-man; Fang, Wei-rong; Cheng, Peng; Liu, Lifang; Li, Fengwen

    2010-06-01

    The root of Clematis chinensis Osbeck has been used widely in rheumatoid arthritis in Chinese traditional medicine and AR-6 is a triterpene saponin isolated from it. In this present study, we investigated in vivo effects of oral AR-6 in chronic rat adjuvant-induced arthritis (AA) and in vitro effect in macrophage and synoviocytes cells. Arthritic scores and serum inflammatory mediators were evaluated 19 days after AA induction by endermic injection of Freund's complete adjuvant in Sprague-Dawley(S-D) rats. Oral administration of AR-6 to arthritic rats resulted in a clear decrease of clinical signs compared to untreated controls. The synoviocyte and macrophage response ex vivo were then analyzed. Anti-arthritic effects of AR-6 correlated with significant decrease of NO and TNF-alpha produced by peritoneal macrophages, ex vivo and in vitro. AR-6 also significant decreased the proliferation of synoviocyte. These data indicate that AR-6 is a potential anti-inflammatory therapeutic and preventive agent. PMID:19842015

  18. Improving the Precision of the Half Life of 34Ar

    NASA Astrophysics Data System (ADS)

    Iacob, V. E.; Hardy, J. C.; Bencomo, M.; Chen, L.; Horvat, V.; Nica, N.; Park, H. I.

    2016-03-01

    Currently, precise ft-values measured for superallowed 0+ -->0+ β transitions provide the most accurate value for Vud, the up-down quark mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. This enables the most demanding test of CKM unitarity, one of the pillars of the Standard Model. Further improvements in precision are possible if the ft values for pairs of mirror 0+ -->0+ transitions can be measured with 0.1% precision or better. The decays of 34Ar and 34Cl are members of such a mirror pair, but so far the former is not known with sufficient precision. Since our 2006 publication of the half-life of 34Ar, we have improved significantly our acquisition and analysis techniques, adding refinements that have led to increased accuracy. The 34Cl half-life is about twice that of 34Ar. This obscures the 34Ar contribution to the decay in measurements such as ours, which detected the decay positrons and was thus unable to differentiate between the parent and daughter decays. We report here two experiments aiming to improve the half-life of 34Ar: The first detected positrons as in but with improved controls; the second measured γ rays in coincidence with positrons, thus achieving a clear separation of 34Ar decay from 34Cl.

  19. 40Ar/39Ar Dating of the Brunhes-Matuyama Geomagnetic Field Reversal.

    PubMed

    Baksi, A K; Hsu, V; McWilliams, M O; Farrar, E

    1992-04-17

    Magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale (GPTS) to date events in the range 0 to 5 million years ago. A critical tie point on the GPTS is the potassium-argon age of the most recent (Brunhes-Matuyama) geomagnetic field reversal. Astronomical values for the forcing frequencies observed in the oxygen isotope record in Ocean Drilling Project site 677 suggest that the age of this last reversal is 780 ka (thousand years ago), whereas the potassium-argon-based estimate is 730 ka. Results from 4039; Ar incremental heating studies on a series of lavas from Maui that straddle the Brunhes-Matuyama reversal give an age of 783 + 11 ka, in agreement with the astronomically derived value. The astronomically based technique appears to be a viable tool for dating young sedimentary sequences. PMID:17743111

  20. A reconnaissance 40Ar/39Ar geochronologic study of ore-bearing and related rocks, Siberian Russia

    USGS Publications Warehouse

    Dalrymple, G.B.; Czamanske, G.K.; Fedorenko, V.A.; Simonov, O.N.; Lanphere, M.A.; Likhachev, A.P.

    1995-01-01

    40Ar/39Ar age spectra of biotite from a mineralized vein in the ore-bearing, Noril'sk I intrusion and from picritic-like gabbrodolerite from the weakly mineralized, Lower Talnakh intrusion show that these bodies were emplaced at 249 ?? 2 Ma, which is not significantly different from the age of the Permian-Triassic boundary. The ore-bearing intrusions postdate the lower third of the flood-basalt sequence in the Noril'sk area and, on the basis of geochemistry, can best be correlated with lavas slightly younger than those which they cut. Thus, flood basalt was erupted at the time of the Permian-Triassic mass extinction event, although its role in this event is, as yet, ill defined. Additional new 40Ar/39Ar age data for a group of intrusive and extrusive rocks on the western margin of the Siberian craton are discussed. -from Authors

  1. Combined U-Th/He and 40Ar/39Ar geochronology of post-shield lavas from the Mauna Kea and Kohala volcanoes, Hawaii

    SciTech Connect

    Aciego, S.M.; Jourdan, F.; DePaolo, D.J.; Kennedy, B.M.; Renne, P.R.; Sims, K.W.W.

    2009-10-01

    Late Quaternary, post-shield lavas from the Mauna Kea and Kohala volcanoes on the Big Island of Hawaii have been dated using the {sup 40}Ar/{sup 39}Ar and U-Th/He methods. The objective of the study is to compare the recently demonstrated U-Th/He age method, which uses basaltic olivine phenocrysts, with {sup 40}Ar/{sup 39}Ar ages measured on groundmass from the same samples. As a corollary, the age data also increase the precision of the chronology of volcanism on the Big Island. For the U-Th/He ages, U, Th and He concentrations and isotopes were measured to account for U-series disequilibrium and initial He. Single analyses U-Th/He ages for Hamakua lavas from Mauna Kea are 87 {+-} 40 ka to 119 {+-} 23 ka (2{sigma} uncertainties), which are in general equal to or younger than {sup 40}Ar/{sup 39}Ar ages. Basalt from the Polulu sequence on Kohala gives a U-Th/He age of 354 {+-} 54 ka and a {sup 40}Ar/{sup 39}Ar age of 450 {+-} 40 ka. All of the U-Th/He ages, and all but one spurious {sup 40}Ar/{sup 39}Ar ages conform to the previously proposed stratigraphy and published {sup 14}C and K-Ar ages. The ages also compare favorably to U-Th whole rock-olivine ages calculated from {sup 238}U - {sup 230}Th disequilibria. The U-Th/He and {sup 40}Ar/{sup 39}Ar results agree best where there is a relatively large amount of radiogenic {sup 40}Ar (>10%), and where the {sup 40}Ar/{sup 36}Ar intercept calculated from the Ar isochron diagram is close to the atmospheric value. In two cases, it is not clear why U-Th/He and {sup 40}Ar/{sup 39}Ar ages do not agree within uncertainty. U-Th/He and {sup 40}Ar/{sup 39}Ar results diverge the most on a low-K transitional tholeiitic basalt with abundant olivine. For the most alkalic basalts with negligible olivine phenocrysts, U-Th/He ages were unattainable while {sup 40}Ar/{sup 39}Ar results provide good precision even on ages as low as 19 {+-} 4 ka. Hence, the strengths and weaknesses of the U-Th/He and {sup 40}Ar/{sup 39}Ar methods are

  2. Evolution of the northern Sierra Nevada metamorphic belt: Petrological, structural, and Ar/Ar constraints

    SciTech Connect

    Hacker, B.R.

    1993-05-01

    The Sierra Nevada metamorphic belt constitutes an important record of the growth of continental crust from essentially oceanic materials. In the northern Sierra, the central part of the belt is made up of volcanoplutonic arcs and sediment-dominated units inferred to be accretionary wedges or closed ocean basins. The latter are broken formation and melange composed of radiolarian chert, lava, and volcanogenic and continental turbidites. Sedimentary detritus in the largest of these units can be plausibly linked to sources farther east in the Sierra, suggesting that deposition occurred near the eastern Sierran arc. Isoclinal folds, steeply dipping foliations, and steeply plunging down-dip lineations are characteristics structures. The westernmost unit is only feebly recrystallized, and deformation was accomplished principally by stress solution and local redeposition in veins. More easterly, inboard units are compositionally similar, but they recrystallized at pumpellyite-actinolite-and blueschist-facies conditions and deformed via solution-transfer and dislocation creep. Phengite silica contents, the degree of quartz veining, and the locations of pseudo-isograds support an eastward increase in metamorphic pressure and temperature. Metamorphic conditions during the growth of pumpellyite and actinolite ranged from {approximately}150-350 {degrees}C and 200-400 MPa, compatible with recrystallization and deformation in subduction zones or the deeper levels of magmatic arcs. Ar/Ar ages of volcanisclastic rocks and crosscutting plutons constrain the age of deformation and metamorphism in the western part of the region to 174-165 Ma. Deformation and recrystallization in more easterly units may have been coeval or begun as early as Triassic time. 58 refs., 14 figs., 4 tabs.

  3. Volcanic history and 40Ar/39Ar and 14C geochronology of Terceira Island, Azores, Portugal

    USGS Publications Warehouse

    Calvert, A.T.; Moore, R.B.; McGeehin, J.P.; Rodrigues da Silva, A.M.

    2006-01-01

    Seven new 40Ar/39Ar and 23 new radiocarbon ages of eruptive units, in support of new geologic mapping, improve the known chronology of Middle to Late Pleistocene and Holocene volcanic activity on the island of Terceira, Azores and define an east-to-west progression in stratovolcano growth. The argon ages indicate that Cinco Picos Volcano, the oldest on Terceira, completed its main subaerial cone building activity by about 370-380??ka. Collapse of the upper part of the stratovolcanic edifice to form a 7 ?? 9??km caldera occurred some time after 370??ka. Postcaldera eruptions of basalt from cinder cones on and near the caldera floor and trachytic pyroclastic flow and pumice fall deposits from younger volcanoes west of Cinco Picos have refilled much of the caldera. The southern portion of Guilherme Moniz Volcano, in the central part of the island, began erupting prior to 270??ka and produced trachyte domes, flows, and minor pyroclastic deposits until at least 111??ka. The northern part of Guilherme Moniz Caldera is less well exposed than the southern part, but reflects a similar age range. The northwest portion of the caldera was formed sometime after 44??ka. Several well-studied ignimbrites that blanket much of the island likely erupted from Guilherme Moniz Volcano. The Pico Alto Volcanic Center, a tightly spaced cluster of trachyte domes and short flows, is a younger part of Guilherme Moniz Volcano. Stratigraphic studies and our new radiocarbon ages suggest that most of the Pico Alto eruptions occurred during the period from about 9000 to 1000??years BP. Santa Barbara Volcano is the youngest stratovolcano on Terceira, began erupting prior to 29??ka, and has been active historically. ?? 2006.

  4. Chronostratigraphy of Monte Vulture volcano (southern Italy): secondary mineral microtextures and 39Ar-40Ar systematics

    NASA Astrophysics Data System (ADS)

    Villa, Igor M.; Buettner, Annett

    2009-12-01

    The eruptive history of Monte Vulture has been the subject of several geochronological investigations during the past decades, which reliably dated only a small number of eruptions. Understanding the causes of sub-optimum data yield in the past requires an interdisciplinary approach. We re-analyzed samples from previous works and present new data on samples from the main volcano-stratigraphic units of Monte Vulture, so as to provide an improved, consistent chronostratigraphic database. Imaging of minerals by cathodoluminescence and backscattered electrons reveals that heterochemical, high-temperature deuteric reaction textures are ubiquitous. Such observations are common in metamorphic rocks but had not frequently been reported from volcanic rocks. In view of the mineralogical complexity, we base our chronological interpretation on isochemical steps, defined as steps for which the Cl/K and/or the Ca/K ratios are constant. Isochemical steps carry the isotopic signature of chemically homogeneous mineral phases and therefore allow a well-constrained age interpretation. Comparison of old and new 39Ar-40Ar data proves the reproducibility of age spectra and their shapes. This quantifies the analytical reliability of the irradiation and mass-spectrometric analyses. Anomalous age spectra are a reproducible property of some specific samples and correlate with mineralogical anomalies. The present data allow us to fine-tune the age of the volcanostratigraphic units of Monte Vulture during the known interval of main volcanic activity from ca. 740 to 610 ka. After a very long stasis, the volcanic activity in the Monte Vulture area resumed with diatremic eruptions, one of which (Lago Piccolo di Monticchio, the site of a palynological-paleoclimatological drilling) was dated at ca. 140 ka.

  5. Ar-Ar Analysis of Chelyabinsk: Evidence for a Recent Impact

    NASA Technical Reports Server (NTRS)

    Beard, S. P.; Kring, D. A.; Isachsen, C. E.; Lapen, T. J.; Zolensky, M. E.; Swindle, T. D.

    2014-01-01

    The Chelyabinsk meteorite is an LL5 ordinary chondrite that fell as a spectacular fireball on February 15th, 2013, over the Ural region in Russia. The meteoroid exploded at an altitude of 25-30 km, producing shockwaves that broke windowpanes in Chelyabinsk and surrounding areas, injuring some 1500 people. Analyses of the samples show that the meteorite underwent moderate shock metamorphism (stage S4; 25-35 GPa) [1]. Most of the samples have a fusion crust ranging from 0.1-1mm thick, and roughly a third of the samples were composed of a dark fine-grained impact melt with chondrule fragments which were targeted for chronometry. A Pb-Pb age obtained by [2] of a shock-darkened and potentially melted sample of Chelyabinsk is reported as 4538.3 +/- 2.1 Ma, while a U-Pb study [3] gave an upper concordia intercept of 4454 +/- 67 Ma and a lower intercept of 585 +/- 390. Galimov et al. 2013 [1] suggest the Sm-Nd system records a recent impact event [290 Ma] that may represent separation from the parent body, while the Rb-Sr isotopic system is disturbed and does not give any definitive isochron. In order to better understand its history, we have performed 40Ar-39Ar analysis on multiple splits of two Chelyabinsk samples; clast- rich MB020f,2 and melt-rich MB020f,5. The term "clast-rich" lithology is meant to indicate a mechanical mixture of highly shock-darkened and less shocked components, both with some shock melt veining.

  6. Stanniferrous granites of Vietnam: Rb-Sr and Ar-Ar isotope age, composition, sources, and geodynamic formation conditions

    NASA Astrophysics Data System (ADS)

    Anh, Phan Luu; Vladimirov, A. G.; Kruk, N. N.; Polyakov, G. V.; Ponomarchuk, V. A.; Hoa, Tran Trong; Phuong, Ngo Thi; Kuibida, M. L.; Annikova, I. Yu.; Pavlova, G. G.; Kiseleva, V. Yu.

    2010-06-01

    Stanniferrous granite-leucogranite massifs in Vietnam to which the bedrock and placer commercial deposits of cassiterite are associated (Timtuc etc.) are of late Cretaceous age (˜85 Ma by Rb-Sr and Ar-Ar isotope dating). These massifs are presented by stocks and fracture intrusions (to 100 km2 in area) of simple homodromic structure: biotite granites ⇒ two-mica and muscovite leucogranites ⇒ topaz-containing aplites ⇒ rare-metal pegmatites.

  7. A Late Mesoproterozoic 40Ar/39Ar age for a melt breccia from the Keurusselkä impact structure, Finland

    NASA Astrophysics Data System (ADS)

    Schmieder, Martin; Jourdan, Fred; Moilanen, Jarmo; Buchner, Elmar; Öhman, Teemu

    2016-02-01

    Field investigations in the eroded central uplift of the ≤30 km Keurusselkä impact structure, Finland, revealed a thin, dark melt vein that intersects the autochthonous shatter cone-bearing target rocks near the homestead of Kirkkoranta, close to the center of the impact structure. The petrographic analysis of quartz in this melt breccia and the wall rock granite indicate weak shock metamorphic overprint not exceeding ~8-10 GPa. The mode of occurrence and composition of the melt breccia suggest its formation as some kind of pseudotachylitic breccia. 40Ar/39Ar dating of dark and clast-poor whole-rock chips yielded five concordant Late Mesoproterozoic miniplateau ages and one plateau age of 1151 ± 10 Ma [± 11 Ma] (2σ; MSWD = 0.11; P = 0.98), considered here as the statistically most robust age for the rock. The new 40Ar/39Ar age is incompatible with ~1.88 Ga Svecofennian tectonism and magmatism in south-central Finland and probably reflects the Keurusselkä impact, followed by impact-induced hydrothermal chloritization of the crater basement. In keeping with the crosscutting relationships in the outcrop and the possible influence of postimpact alteration, the Late Mesoproterozoic 40Ar/39Ar age of ~1150 Ma should be treated as a minimum age for the impact. The new 40Ar/39Ar results are consistent with paleomagnetic results that suggested a similar age for Keurusselkä, which is shown to be one of the oldest impact structures currently known in Europe and worldwide.

  8. Functional Promiscuity of Homologues of the Bacterial ArsA ATPases

    PubMed Central

    Castillo, Rostislav; Saier, Milton H.

    2010-01-01

    The ArsA ATPase of E. coli plays an essential role in arsenic detoxification. Published evidence implicates ArsA in the energization of As(III) efflux via the formation of an oxyanion-translocating complex with ArsB. In addition, eukaryotic ArsA homologues have several recognized functions unrelated to arsenic resistance. By aligning ArsA homologues, constructing phylogenetic trees, examining ArsA encoding operons, and estimating the probable coevolution of these homologues with putative transporters and auxiliary proteins unrelated to ArsB, we provide evidence for new functions for ArsA homologues. They may play roles in carbon starvation, gas vesicle biogenesis, and arsenic resistance. The results lead to the proposal that ArsA homologues energize four distinct and nonhomologous transporters, ArsB, ArsP, CstA, and Acr3. PMID:20981284

  9. Ar-40/Ar-39 Ages for Maskelynites and K-Rich Melt from Olivine-Rich Lithology in (Kanagawa) Zagami

    NASA Technical Reports Server (NTRS)

    Park, J.; Herzog, G. F.; Nyquist, L. E.; Lindsay, F.; Turrin, B.; Swisher, C. C., III; Delaney, J. S.; Shih, C.-Y.; Niihara, T.; Misawa, K.

    2013-01-01

    We report Ar/Ar release patterns for small maskelynite grains and samples of a K-rich phase separated from the basaltic shergottite Zagami. The purpose of the work is to investigate the well-known discrepancy between published Ar/Ar ages of Zagami, >200 Ma, and its age of approx. 170 Ma as determined by other methods [1-6]. Niihara et al. [7] divide less abundant darker material present in Zagami into an olivine-rich lithology (ORL), from which most of our samples came, and a pyroxene-rich one (Dark Mottled-Lithology: DML) [8, 9]. ORL consists of vermicular fayalitic olivine, coarse-grained pyroxene, maskelynite, and a glassy phase exceptionally rich in K (up to 8.5 wt%), Al, and Si, but poor in Fe and Mg. The elemental composition suggests a late-stage melt, i.e., residual material that solidified late in a fractional crystallization sequence. Below we refer to it as "K-rich melt." The K-rich melt contains laths of captured olivine, Ca-rich pyroxene, plagioclase, and opaques. It seemed to offer an especially promising target for Ar-40/Ar-39 dating.

  10. 40Ar/ 39Ar dating and preliminary paleointensity determination on a single lava flow from Chifeng, Inner Mongolia

    NASA Astrophysics Data System (ADS)

    Shi, Ruiping; Hill, Mimi J.; Zhu, Rixiang; He, Huaiyu; Shaw, John

    2005-09-01

    A precise 40Ar/ 39Ar age and paleointensity data for the Cretaceous lava flow from Chifeng, southern Inner Mongolia, northeastern China are presented in this study. Detailed rock magnetic investigations including the variation of magnetization with temperature, low temperature susceptibility and hysteresis loops show that pseudo single domain (PSD) grain size high-Ti titanomagnetite is the main magnetic mineral in the studied lava flow. Both the microwave and double heating Thellier techniques were used to determine the paleointensity, yielding mean flow paleointensities of 15.6 ± 3.2 μT and 23.9 ± 8.0 μT, respectively. However, the paleointensity results using the microwave technique are of higher quality (mean q = 12 for microwave compared to q = 2 for Thellier) and yield higher internal consistency for the flow mean (21% standard deviation about the mean for microwave compared to 34% for Thellier). The microwave paleointensity result, 15.6 ± 3.2 μT is therefore deemed the more reliable estimate for the paleointensity of the Niutoushan lava flow. 40Ar/ 39Ar age determination on the lava flow is 106.42 ± 0.48 Ma (2 σ, relative to GA-1550 biotite: 98.79 ± 0.96 Ma). Combining our 40Ar/ 39Ar dating and paleointensity results with other published paleointensity data suggests that the intensity of the Earth's magnetic field during the middle Cretaceous normal superchron (CNS) was weak, but variable throughout the whole CNS.

  11. Acoustic Resonance Spectroscopy (ARS) Munition Classification System enhancements. Final report

    SciTech Connect

    Vela, O.A.; Huggard, J.C.

    1997-09-18

    Acoustic Resonance Spectroscopy (ARS) is a non-destructive evaluation technology developed at the Los Alamos National Laboratory (LANL). This technology has resulted in three generations of instrumentation, funded by the Defense Special Weapons Agency (DSWA), specifically designed for field identification of chemical weapon (CW) munitions. Each generation of ARS instrumentation was developed with a specific user in mind. The ARS1OO was built for use by the U.N. Inspection Teams going into Iraq immediately after the Persian Gulf War. The ARS200 was built for use in the US-Russia Bilateral Chemical Weapons Treaty (the primary users for this system are the US Onsite Inspection Agency (OSIA) and their Russian counterparts). The ARS300 was built with the requirements of the Organization for the Prohibition of Chemical Weapons (OPCW) in mind. Each successive system is an improved version of the previous system based on learning the weaknesses of each and, coincidentally, on the fact that more time was available to do a requirements analysis and the necessary engineering development. The ARS300 is at a level of development that warrants transferring the technology to a commercial vendor. Since LANL will supply the computer software to the selected vendor, it is possible for LANL to continue to improve the decision algorithms, add features where necessary, and adjust the user interface before the final transfer occurs. This paper describes the current system, ARS system enhancements, and software enhancements. Appendices contain the Operations Manual (software Version 3.01), and two earlier reports on enhancements.

  12. Calibration of a Pleistocene Geomagnetic Instability Time Scale (GITS) using 40Ar/39Ar-dated lavas

    NASA Astrophysics Data System (ADS)

    Singer, B. S.; Hoffman, K. A.

    2005-12-01

    Advances in measuring paleomagnetic intensity recorded by marine sediments, and 40Ar/39Ar dating of paleomagnetic directional recordings in lava flows, offer a means of calibrating a global magnetostratigraphy for the last 2 m.y. This involves moving beyond the classic geomagnetic polarity time scale (GPTS) and resolving not only the undisputed polarity reversals, but also the many short-lived geomagnetic "events" or cryptochrons thought to signal brief periods of geodynamo instability. Many short events are distinguished as intensity minima in global sediment records (SINT-800; GLOPIS-75) that are dated by astrochronology. Thus, when the degree of stability of the geodynamo is considered, rather than lengths of polarity intervals, an alternative approach to the GPTS is appropriate. We are developing a Geomagnetic Instability Time Scale (GITS) via 40Ar/39Ar dating of transitionally-magnetized lava flows younger than 2 Ma. As an example, the Laschamp event--expressed as a sharp intensity minimum in the GLOPIS-75 sediment stack--was dated by matching O-isotope variations in North Atlantic sediments to those recorded in annually counted layers of the GISP2 ice core. Matching 14C ages from the sediments to specific varves in the ice core shows the paleointensity minimum to span 1500 yr between 41 and 39 ka. 40Ar/39Ar and unspiked K-Ar dating of two basaltic lava flows that record the event at Laschamps, France yield an age of 40.4±1.1 ka (± 2 sigma, analytical uncertainty). Thus, despite systematic uncertainty in the 40K decay constant, both the accuracy and precision of the K-Ar clock can be remarkably good, i.e., better than 2% for the Pleistocene. Intercomparison of several 40Ar/39Ar-dated geomagnetic events, including the Matuyama-Brunhes polarity reversal (776 ± 2 ka), Big Lost event (579 ± 6 ka) and Pringle Falls/Albuquerque event (211 ± 11 ka) implies either that: 1) the astrochronology-based age models used for the SINT-800 paleointensity stack are

  13. 40Ar/39Ar dating of the Honghuaqiao Formation in SE China

    NASA Astrophysics Data System (ADS)

    Chang, S.; Zhang, H.; Hemming, S. R.; Mesko, G. T.; Fang, Y.

    2010-12-01

    The Jehol Biota, defined as the characteristic Eosestheria-Ephemeropsis-Lycoptera assemblage (Grabau, 1923, Bulletin of the Geological Survey of China), is widely distributed in eastern and central Asia (Li et al., 1982, Acta Geologica Sinica; Chen, 1988, Acta Palaeontologica Sinica). Abundant and varied fossils of the terrestrial Jehol Biota, including plants, insects, dinosaurs, birds, mammals, and freshwater invertebrates, have been discovered from the Dabeigou, the Yixian and the Jiufotang Formations (or their correlative strata) in northeast China from the Liaoning and Hebei Provinces and Inner Mongolia (Chen and Jin, 1999, Acta Palaeontologica Sinica). In addition, strata that may be correlative with the classic Jehol fossil-bearing formations have been identified extensively in central and eastern China, the Korean Peninsula, Mongolia, and Siberia. In the past three decades mollusk, conchostracan, ostracod, insect, fish, and plant fossils from localities in southeastern China, interpreted as related to the Jehol biota of the northeast, have been found (Mateer and Chen, 1986, Cretaceous Research; Li, 2003, Chinese Science Bulletin; Chen, Li and Batten, 2007, Geological Journal). However, a detailed correlation between the classic Jehol outcrops and the more recently found localities to the South and West has yet to emerge. Volcanic rocks from the Honghuaqiao fossil-bearing Formation in Tuzhou City of eastern Anhui Province, southeastern China provide an excellent opportunity to rectify this situation. Preliminary results of a pilot study suggest that the Honghuaqiao Formation is equivalent to the Longwanshan Formation of Anhui Province, southeastern China and the Yixian Formation, northeastern China (Chang et al., 2009, AGU abstract). Initial 40Ar/39Ar results indicate that conchostracans from the upper Honghuaqiao Formation are approximately 130 Ma. Our ongoing work aims to establish a high-resolution chronostratigraphy for Tuzhou City in Anhui Province

  14. 40Ar/39Ar dating of the eruptive history of Mount Erebus, Antarctica: volcano evolution

    NASA Astrophysics Data System (ADS)

    Esser, Richard P.; Kyle, Philip R.; McIntosh, William C.

    2004-12-01

    Mt. Erebus, a 3,794-meter-high active polygenetic stratovolcano, is composed of voluminous anorthoclase-phyric tephriphonolite and phonolite lavas overlying unknown volumes of poorly exposed, less differentiated lavas. The older basanite to phonotephrite lavas crop out on Fang Ridge, an eroded remnant of a proto-Erebus volcano and at other isolated locations on the flanks of the Mt. Erebus edifice. Anorthoclase feldspars in the phonolitic lavas are large (~10 cm), abundant (~30 40%) and contain numerous melt inclusions. Although excess argon is known to exist within the melt inclusions, rigorous sample preparation was used to remove the majority of the contaminant. Twenty-five sample sites were dated by the 40Ar/39Ar method (using 20 anorthoclase, 5 plagioclase and 9 groundmass concentrates) to examine the eruptive history of the volcano. Cape Barne, the oldest site, is 1,311±16 ka and represents the first of three stages of eruptive activity on the Mt. Erebus edifice. It shows a transition from sub-aqueous to sub-aerial volcanism that may mark the initiation of proto-Erebus eruptive activity. It is inferred that a further ~300 ky of basanitic/phonotephritic volcanism built a low, broad platform shield volcano. Cessation of the shield-building phase is marked by eruptions at Fang Ridge at ~1,000 ka. The termination of proto-Erebus eruptive activity is marked by the stratigraphically highest flow at Fang Ridge (758±20 ka). Younger lavas (~550 250 ka) on a modern-Erebus edifice are characterized by phonotephrites, tephriphonolites and trachytes. Plagioclase-phyric phonotephrite from coastal and flank flows yield ages between 531±38 and 368±18 ka. The initiation of anorthoclase tephriphonolite occurred in the southwest sector of the volcano at and around Turks Head (243±10 ka). A short pulse of effusive activity marked by crustal contamination occurred ~160 ka as indicated by at least two trachytic flows (157±6 and 166±10 ka). Most

  15. Factor Structure of CIWA-Ar in Alcohol Withdrawal.

    PubMed

    Bakhla, Ajay Kumar; Khess, Christoday R J; Verma, Vijay; Hembram, Mahesh; Praharaj, Samir Kumar; Soren, Subhas

    2014-01-01

    Objective. To identify the underlying factor structure of alcohol withdrawal syndrome, as measured with CIWA-Ar. Methods. Exploratory factor analysis was conducted on the items of CIWA-Ar. On 201 alcohol-dependent male patients seeking treatment for alcohol withdrawal at 36 hours of abstinence. Results. A three-factor solution was obtained that accounted for 68.74% of total variance. First factor had loading from four items (34.34% variance), second factor also had four items (24.25% variance), and the third had two items (10.04% variance). Conclusions. Factor analysis reveals the existence of multidimensionality of alcohol withdrawal as measured with CIWA-Ar and we found three factors that can be named as delirious, autonomic and nonspecific factors. PMID:24826372

  16. Factor Structure of CIWA-Ar in Alcohol Withdrawal

    PubMed Central

    Bakhla, Ajay Kumar; Khess, Christoday R. J.; Verma, Vijay; Hembram, Mahesh; Praharaj, Samir Kumar; Soren, Subhas

    2014-01-01

    Objective. To identify the underlying factor structure of alcohol withdrawal syndrome, as measured with CIWA-Ar. Methods. Exploratory factor analysis was conducted on the items of CIWA-Ar. On 201 alcohol-dependent male patients seeking treatment for alcohol withdrawal at 36 hours of abstinence. Results. A three-factor solution was obtained that accounted for 68.74% of total variance. First factor had loading from four items (34.34% variance), second factor also had four items (24.25% variance), and the third had two items (10.04% variance). Conclusions. Factor analysis reveals the existence of multidimensionality of alcohol withdrawal as measured with CIWA-Ar and we found three factors that can be named as delirious, autonomic and nonspecific factors. PMID:24826372

  17. Modelling Ar II spectral emission from the ASTRAL helicon plasma

    NASA Astrophysics Data System (ADS)

    Munoz Burgos, Jorge; Boivin, Robert; Loch, Stuart; Kamar, Ola; Ballance, Connor; Pindzola, Mitch

    2008-11-01

    We describe our spectral modeling of ArII emission from the ASTRAL helicon plasma at Auburn University. Collisional-radiative theory is used to model the emitted spectrum, with account being taken for the density and temperature variation along the line of sight. This study has two main aims. Firstly to test the atomic data used in the model and secondly to identify spectral line ratios in the 200 nm - 1000 nm range that could be used as temperature diagnostics. Using the temperature at which Ar II emission starts to be seen we have been able to test recent ionization and recombination data. Using selected spectral lines we were then able to test the importance of the continuum-coupling effects included in the most recent Ar+ electron impact excitation data. Selected spectral line ratios have been identified that show a strong temperature variation and have potential as a temperature diagnostic.

  18. The rotational spectrum of CF3Clsbnd Ar

    NASA Astrophysics Data System (ADS)

    Evangelisti, Luca; Gou, Qian; Feng, Gang; Caminati, Walther

    2016-06-01

    The microwave spectrum of the van der Waals complex CF3Clsbnd Ar has been investigated by pulsed jet Fourier transform microwave spectroscopy. The observed spectra of the 35Cl and 37Cl isotopologues are typical of asymmetric tops, with rotational constants A, B, C = 3373.118(4), 988.2529(4), 879.5788(3) and 3286.66(4), 985.50(3), 871.359(8) MHz, respectively. The Ar atom is almost "L-shaped" with respect to the Clsbnd C bond, at a r0 distance of 3.824(2) Å from the center of mass (CM) of CF3Cl and with the angle Clsbnd CMsbnd Ar = 81(2)°. The dissociation energy has been estimated to be 2.3 kJ mol-1.

  19. Fission-fragment nuclear lasing of Ar/He/-Xe

    NASA Technical Reports Server (NTRS)

    De Young, R. J.; Shiu, Y. J.; Williams, M. D.

    1980-01-01

    Nuclear-pumped lasing of Ar-Xe and He-Xe has been demonstrated using (U-235)F6 fission-fragment excitation. Fission fragments were created by absorption of thermal neutrons in a combination of gaseous (U-235)F6 and laser-tube wall coatings formed from UF6 chemical reaction products. At a pressure of 600 torr Ar-(3%)Xe, lasing occurred at 2.65 microns in Xe. Up to 3 torr of gaseous (U-235)F6 was added to 600 torr Ar-Xe before serious laser quenching occurred. With 3 torr of (U-235)F6 added, 38% of the energy deposition came from gaseous UF6 and the remainder from the uranium wall coating. The neutron flux at lasing threshold was found to be 4 x 10 to the 15th n/sq cm sec.

  20. Ab initio transport coefficients of Ar+ ions in Ar for cold plasma jet modeling

    NASA Astrophysics Data System (ADS)

    Chicheportiche, A.; Lepetit, B.; Gadéa, F. X.; Benhenni, M.; Yousfi, M.; Kalus, R.

    2014-06-01

    Collision cross sections and transport coefficients are calculated for Ar+ ions, in the ground state 2P3/2 and in the metastable state 2P1/2, colliding with their parent gas. Differential and integral collision cross sections are obtained using a numerical integration of the nuclear Schrödinger equation for several published interaction potentials. The Cohen-Schneider semi-empirical model is used for the inclusion of the spin-orbit interaction. The corresponding differential collision cross sections are then used in an optimized Monte Carlo code to calculate the ion transport coefficients for each initial ion state over a wide range of reduced electric field. Ion swarm data results are then compared with available experimental data for different proportions of ions in each state. This allows us to identify the most reliable interaction potential which reproduces ion transport coefficients falling within the experimental error bars. Such ion transport data will be used in electrohydrodynamic and chemical kinetic models of the low temperature plasma jet to quantify and to tune the active species production for a better use in biomedical applications.

  1. Ar-Ar chronology of the Martian meteorite ALH84001: evidence for the timing of the early bombardment of Mars.

    PubMed

    Turner, G; Knott, S F; Ash, R D; Gilmour, J D

    1997-09-01

    ALH84001, a cataclastic cumulate orthopyroxenite meteorite from Mars, has been dated by Ar-Ar stepped heating and laser probe methods. Both methods give ages close to 3,900 Ma. The age calculated is dependent on assumptions made about 39Ar recoil effects and on whether significant quantities of 40Ar from the Martian atmosphere are trapped in the meteorite. If, as suggested by xenon and nitrogen isotope studies, Martian atmospheric argon is present, then it must reside predominantly in the K-rich phase maskelynite. Independently determined 129Xe abundances in the maskelynite can be used to place limits on the concentration of the atmospheric 40Ar. These indicate a reduction of around 80 Ma to ages calculated on the assumption that no Martian atmosphere is present. After this correction, the nominal ages obtained are: 3940 +/- 50, 3870 +/- 80, and 3970 +/- 100 Ma. by stepped heating, and 3900 +/- 90 Ma by laser probe (1 sigma statistical errors), giving a weighted mean value of 3,920 Ma. Ambiguities in the interpretation of 39Ar recoil effects and in the contribution of Martian atmospheric 40Ar lead to uncertainties in the Ar-Ar age which are difficult to quantify, but we suggest that the true value lies somewhere between 4,050 and 3,800 Ma. This age probably dates a period of annealing of the meteorite subsequent to the shock event which gave it its cataclastic texture. The experiments provide the first evidence of an event occurring on Mars coincident with the time of the late heavy bombardment of the Moon and may reflect a similar period of bombardment in the Southern Highlands of Mars. Whether the age determined bears any relationship to the time of carbonate deposition in ALH84001 is not known. Such a link depends on whether the temperature associated with the metasomatic activity was sufficient to cause argon loss from the maskelynite and/or whether the metasomatism and metamorphism were linked in time through a common heat source. PMID:11541217

  2. 40Ar/39Ar laser probe evidence concerning the age and associated hazards of the Lake Nyos Maar, Cameroon

    USGS Publications Warehouse

    Dalrymple, G.B.; Lockwood, J.P.

    1990-01-01

    The waters of Lake Nyos are impounded by a fragile natural dam composed of pyroclastic rocks ejected during the formation of the lake crater (maar). Lateral erosion of this dam has reduced its width from over 500 m to only 45 m. Published whole-rock K-Ar ages of about 100 ka on juvenile basalt from the dam suggests that erosion has been slow and that the dam poses no imminent threat. New apparent 40Ar/39Ar ages of 1.4 to 232 Ma on xenocrystic K-feldspar contained in the basalt show that the xenocrysts, whose source is the 528-Ma crystalline basement, are carriers of inherited radiogenic 40Ar and would cause the whole-rock K-Ar ages to be too old. The best estimate for the age of the maar is provided by a 14C age of 400 ?? 100 yr BP on charcoal from the base of the dam. This young age indicates that the dam is eroding at a relatively rapid rate; its failure, perhaps within a few decades, would result in a major flood and imperil thousands of people living downstream in Cameroon and eastern Nigeria. ?? 1990 Kluwer Academic Publishers.

  3. Etching characteristics and mechanisms of Mo thin films in Cl2/Ar and CF4/Ar inductively coupled plasmas

    NASA Astrophysics Data System (ADS)

    Lim, Nomin; Efremov, Alexander; Yeom, Geun Young; Choi, Bok-Gil; Kwon, Kwang-Ho

    2014-11-01

    The etching characteristics and mechanism of Mo thin films in Cl2/Ar and CF4/Ar inductively coupled plasmas under the same operating conditions (pressure, 6 mTorr; input power, 700 W; bias power, 200 W) were investigated. For both gas mixtures, an increase in the Ar fraction or gas pressure at a fixed gas mixing ratio was found to cause a non-monotonic change in the Mo etching rates. The X-ray photoelectron spectroscopy (XPS) diagnostics indicated contamination of the etched surfaces by reaction products. The Cl2/Ar and CF4/Ar plasma parameters were also investigated using a combination of a zero-dimensional plasma model and plasma diagnostics using Langmuir probes. An analysis of the etching kinetics with the model-predicted fluxes of the plasma active species suggests that: 1) the Mo etching process occurs in the transitional regime of the ion-assisted chemical reaction, and 2) the non-monotonic Mo etching rate is probably associated with opposing changes in the fluxes of the reactive neutral species and ion energy.

  4. Uncertainty Quantification of Ar-37 Transport in Fractured Rock

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Carrigan, C. R.; Chen, M.; Wagoner, J. L.

    2011-12-01

    Underground nuclear explosions produce radioactive noble gas isotopes, such as Ar-37 that may migrate through fractured rock and soil from the detonation site to the ground surface. For the on site inspection monitoring protocol of the Comprehensive Nuclear Test Ban Treaty, the detection of Ar-37 above its background level is therefore an indicator of a nuclear test. However, Ar-37 is also produced in the subsurface due to cosmic-neutron activation of calcium by the 40Ca(n,α)37Ar reaction. The cosmic-neutron induced production rate of Ar-37 in the subsurface depends on many uncertain parameters, including the calcium content, the depth below ground surface, the geological structure, and other rock/soil properties. It is therefore important to distinguish the cosmic-neutron induced and test relevant Ar-37 transport in fractured rock and soil. The physical model is conceptualized as a deep dual permeability bedrock layer consisting of overlapping fracture and porous matrix continua overlain by a shallow layer of interconnected clay and sand alluvium. In this study supporting a subsurface gas tracer migration experiment at the National Center for Nuclear Security, we use numerical simulation of non-isothermal multi-phase and multi-component transport to investigate gas-component production, release, and transport in this combined fractured rock and clay-sand alluvium system. In addition to the spatial and temporal domain, we extend the modeling to a high-dimensional space including parameters characterized by a range of uncertainties using the PSUADE code, developed at Lawrence Livermore National Laboratory. Using PSUADE, we consider the dependence of the detectability on these uncertain parameters with the goal of understanding how to optimize the detection of an underground nuclear test. (LLNL-ABS-491792). This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  5. Earth-atmosphere evolution based on new determination of Devonian atmosphere Ar isotopic composition

    NASA Astrophysics Data System (ADS)

    Stuart, Finlay M.; Mark, Darren F.; Gandanger, Pierre; McConville, Paul

    2016-07-01

    The isotopic composition of the noble gases, in particular Ar, in samples of ancient atmosphere trapped in rocks and minerals provides the strongest constraints on the timing and rate of Earth atmosphere formation by degassing of the Earth's interior. We have re-measured the isotopic composition of argon in the Rhynie chert from northeast Scotland using a high precision mass spectrometer in an effort to provide constraints on the composition of Devonian atmosphere. Irradiated chert samples yield 40Ar/36Ar ratios that are often below the modern atmosphere value. The data define a 40Ar/36Ar value of 289.5 ± 0.4 at K/36Ar = 0. Similarly low 40Ar/36Ar are measured in un-irradiated chert samples. The simplest explanation for the low 40Ar/36Ar is the preservation of Devonian atmosphere-derived Ar in the chert, with the intercept value in 40Ar-39Ar-36Ar space representing an upper limit. In this case the Earth's atmosphere has accumulated only 3% (5.1 ± 0.4 ×1016 mol) of the total 40Ar inventory since the Devonian. The average accumulation rate of 1.27 ± 0.09 ×108 mol40Ar/yr overlaps the rate over the last 800 kyr. This implies that there has been no resolvable temporal change in the outgassing rate of the Earth since the mid-Palaeozoic despite the likely episodicity of Ar degassing from the continental crust. Incorporating the new Devonian atmosphere 40Ar/36Ar into the Earth degassing model of Pujol et al. (2013) provides the most precise constraints on atmosphere formation so far. The atmosphere formed in the first ∼100 Ma after initial accretion during a catastrophic degassing episode. A significant volume of 40Ar did not start to accumulate in the atmosphere until after 4 Ga which implies that stable K-rich continental crust did not develop until this time.

  6. Paleotemperatures at the lunar surfaces from open system behavior of cosmogenic 38Ar and radiogenic 40Ar

    SciTech Connect

    Shuster, David L.; Cassata, William S.

    2015-02-10

    The simultaneous diffusion of both cosmogenic 38Ar and radiogenic 40Ar from solid phases is controlled by the thermal conditions of rocks while residing near planetary surfaces. Combined observations of 38Ar/37Ar and 40Ar/39Ar ratios during stepwise degassing analyses of neutron-irradiated Apollo samples can distinguish between diffusive loss of Ar due to solar heating of the rocks and that associated with elevated temperatures during or following impact events; the data provide quantitative constraints on the durations and temperatures of each process. From sequentially degassed 38Ar/37Ar ratios can be calculated a spectrum of apparent 38Ar exposure ages versus the cumulative release fraction of 37Ar, which is particularly sensitive to conditions at the lunar surface typically over ~106–108 year timescales. Due to variable proportions of K- and Ca-bearing glass, plagioclase and pyroxene, with variability in the grain sizes of these phases, each sample will have distinct sensitivity to, and therefore different resolving power on, past near-surface thermal conditions. Furthermore, we present the underlying assumptions, and the analytical and numerical methods used to quantify the Ar diffusion kinetics in multi-phase whole-rock analyses that provide these constraints.

  7. Interatomic scattering in energy dependent photoelectron spectra of Ar clusters

    SciTech Connect

    Patanen, M.; Benkoula, S.; Nicolas, C.; Goel, A.; Antonsson, E.; Neville, J. J.; Miron, C.

    2015-09-28

    Soft X-ray photoelectron spectra of Ar 2p levels of atomic argon and argon clusters are recorded over an extended range of photon energies. The Ar 2p intensity ratios between atomic argon and clusters’ surface and bulk components reveal oscillations similar to photoelectron extended X-ray absorption fine structure signal (PEXAFS). We demonstrate here that this technique allows us to analyze separately the PEXAFS signals from surface and bulk sites of free-standing, neutral clusters, revealing a bond contraction at the surface.

  8. SEARCH FOR FLOW IN THE REACTION Ar + Pb

    SciTech Connect

    Renfordt, R.E.

    1983-08-01

    Interactions between Ar projectiles and lead are studied in terms of global observables. The Streamer Chamber at the Berkeley BEVALAC was used to record all charged particles produced in collisions between 0.8 GeV/{mu} Ar projectiles with a Pb{sub 3}O{sub 4} target. A hardware trigger selected central collisions with PB nuclei corresponding to a trigger cross section of 1 barn. In a geometrical picture this is equivalent to an impact parameter range of 0--5 fm.

  9. Ubiquitous Argonium, ArH^+, in the Diffuse Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Schilke, P.; Müller, Holger S. P.; Comito, C.; Sanchez-Monge, A.; Neufeld, D. A.; Indriolo, Nick; Bergin, Edwin; Lis, D. C.; Gerin, Maryvonne; Black, J. H.; Wolfire, M. G.; Pearson, John; Menten, Karl; Winkel, B.

    2014-06-01

    ArH^+ is isoelectronic with HCl. The J = 1 - 0 and 2 - 1 transitions of 36ArH^+ near 617.5 and 1234.6 GHz, respectively, have been identified very recently as emission lines in spectra obtained with Herschel toward the Crab Nebula supernova remnant. On Earth, 40Ar is by far the most abundant isotope, being almost exclusively formed by the radioactive decay of 40K. However, 36Ar is the dominant isotope in the Universe. In the course of unbiased line surveys of the massive and very luminous Galactic Center star-forming regions Sagittarius B2(M) and (N) with the high-resolution instrument HIFI on board of Herschel, we detected the J = 1 - 0 transition of 36ArH^+ as a moderately strong absorption line initially associated with an unidentified carrier. In both cases, the absorption feature is unique in its appearance at all velocity components associated with diffuse foreground molecular clouds, together with its conspicuous absence at velocities related to the denser sources themselves. Model calculations are able to reproduce the derived ArH^+ column densities and suggest that argonium resides in the largely atomic, diffuse interstellar medium with a molecular fraction of no more than ˜10-4. The 38ArH^+ isotopolog was also detected. Subsequent observations toward the continuum sources W51, W49, W31C, and G34.3+0.1 resulted in unequivocal detections of 36ArH^+ absorption. Hence, argonium is a good probe of the transition zone between atomic and molecular gas, in particular in combination with OH^+ and H_2O^+, whose abundances peak at a molecular fraction of ˜0.1. Moreover, argonium is a good indicator of an enhanced cosmic ray ionization rate. Therefore, it may be prominent toward, e.g., active galactic nuclei (AGNs) in addition to supernova remnants. M. J. Barlow et al., Science 342 (2013) 1343. H. S. P. Müller et al., Proceedings of the IAU Symposium 297, 2013, "The Diffuse Interstellar Bands", Eds. J. Cami & N. Cox.

  10. Interatomic scattering in energy dependent photoelectron spectra of Ar clusters

    NASA Astrophysics Data System (ADS)

    Patanen, M.; Benkoula, S.; Nicolas, C.; Goel, A.; Antonsson, E.; Neville, J. J.; Miron, C.

    2015-09-01

    Soft X-ray photoelectron spectra of Ar 2p levels of atomic argon and argon clusters are recorded over an extended range of photon energies. The Ar 2p intensity ratios between atomic argon and clusters' surface and bulk components reveal oscillations similar to photoelectron extended X-ray absorption fine structure signal (PEXAFS). We demonstrate here that this technique allows us to analyze separately the PEXAFS signals from surface and bulk sites of free-standing, neutral clusters, revealing a bond contraction at the surface.

  11. Silver nano particle formation on Ar plasma - treated cinnamyl alcohol

    NASA Astrophysics Data System (ADS)

    Dahle, S.; Marschewski, M.; Wegewitz, L.; Viöl, W.; Maus-Friedrichs, W.

    2012-02-01

    Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy are employed to study the adsorption of silver on cinnamyl alcohol films prepared on Au(111) substrates by thermal evaporation. Additionally, the impact of an Ar atmosphere dielectric barrier discharge plasma applied to the cinnamyl alcohol film preliminary to the Ag adsorption is investigated. In both cases silver nano particles with an average diameter of 9 nm are formed. These particles do not interact chemically with the underlying cinnamyl alcohol film. We do not find any influence of the preliminary Ar plasma-treatment on the adsorption behavior at all.

  12. Elongated shape isomers in the Ar36 nucleus

    NASA Astrophysics Data System (ADS)

    Cseh, József; Darai, Judit; Sciani, Wagner; Otani, Yul; Lépine-Szily, Alinka; Benjamim, Elisangela A.; Chamon, Luiz Carlos; Filho, Rubens Lichtenthäler

    2009-09-01

    A recent analysis of the C12+Mg24 scattering [W. Sciani , Phys. Rev. C 80, 034319 (2009)] suggests the existence of a hyperdeformed band in the Ar36 nucleus, completely in line with the predictions of α [W. D. M. Rae and A. C. Merchant, Phys. Lett. B279, 207 (1992)] and binary cluster calculations [J. Cseh , Phys. Rev. C 70, 034311 (2004)]. Here we review the structural understanding of the superdeformed and the hyperdeformed states of Ar36 and present new results on the shape isomers as well. Special attention is paid to the clusterization of these states, which indicates the appropriate reaction channels for their formation.

  13. Large volume multiple path nuclear lasing of /He-3/-Ar

    NASA Technical Reports Server (NTRS)

    De Young, R. J.; Hohl, F.

    1980-01-01

    Output power of 550 W has been achieved from a nuclear-pumped multiple path laser system containing (He-3)-Ar by using the (He-3)(n, p)3(H) nuclear reaction for power deposition. Lasing was achieved in Ar at 1790 nm. The complex beam profile was resolved by an InAs array detector. Laser output was directly proportional to thermal neutron flux, and also increased proportionally with increasing (He-3) pressure up to 292.6 kPa. The variation of the laser output power with the number of passes through the excited medium was found to peak at 5-7 passes.

  14. Transcriptional and posttranscriptional regulation of Bacillus sp. CDB3 arsenic-resistance operon ars1

    PubMed Central

    Yu, Xuefei; Zheng, Wei; Bhat, Somanath; Aquilina, J. Andrew

    2015-01-01

    Bacillus sp. CDB3 possesses a novel eight-gene ars cluster (ars1, arsRYCDATorf7orf8) with some unusual features in regard to expression regulation. This study demonstrated that the cluster is a single operon but can also produce a short three-gene arsRYC transcript. A hairpin structure formed by internal inverted repeats between arsC and arsD was shown to diminish the expression of the full operon, thereby probably acting as a transcription attenuator. A degradation product of the arsRYC transcript was also identified. Electrophoretic mobility shift analysis demonstrated that ArsR interacts with the ars1 promoter forming a protein-DNA complex that could be impaired by arsenite. However, no interaction was detected between ArsD and the ars1 promoter, suggesting that the CDB3 ArsD protein may not play a regulatory role. Compared to other ars gene clusters, regulation of the Bacillus sp. CDB3 ars1 operon is more complex. It represents another example of specific mRNA degradation in the transporter gene region and possibly the first case of attenuator-mediated regulation of ars operons. PMID:26355338

  15. Transcriptional and posttranscriptional regulation of Bacillus sp. CDB3 arsenic-resistance operon ars1.

    PubMed

    Yu, Xuefei; Zheng, Wei; Bhat, Somanath; Aquilina, J Andrew; Zhang, Ren

    2015-01-01

    Bacillus sp. CDB3 possesses a novel eight-gene ars cluster (ars1, arsRYCDATorf7orf8) with some unusual features in regard to expression regulation. This study demonstrated that the cluster is a single operon but can also produce a short three-gene arsRYC transcript. A hairpin structure formed by internal inverted repeats between arsC and arsD was shown to diminish the expression of the full operon, thereby probably acting as a transcription attenuator. A degradation product of the arsRYC transcript was also identified. Electrophoretic mobility shift analysis demonstrated that ArsR interacts with the ars1 promoter forming a protein-DNA complex that could be impaired by arsenite. However, no interaction was detected between ArsD and the ars1 promoter, suggesting that the CDB3 ArsD protein may not play a regulatory role. Compared to other ars gene clusters, regulation of the Bacillus sp. CDB3 ars1 operon is more complex. It represents another example of specific mRNA degradation in the transporter gene region and possibly the first case of attenuator-mediated regulation of ars operons. PMID:26355338

  16. Characterization of the ars Gene Cluster from Extremely Arsenic-Resistant Microbacterium sp. Strain A33▿ †

    PubMed Central

    Achour-Rokbani, Asma; Cordi, Audrey; Poupin, Pascal; Bauda, Pascale; Billard, Patrick

    2010-01-01

    The arsenic resistance gene cluster of Microbacterium sp. A33 contains a novel pair of genes (arsTX) encoding a thioredoxin system that are cotranscribed with an unusual arsRC2 fusion gene, ACR3, and arsC1 in an operon divergent from arsC3. The whole ars gene cluster is required to complement an Escherichia coli ars mutant. ArsRC2 negatively regulates the expression of the pentacistronic operon. ArsC1 and ArsC3 are related to thioredoxin-dependent arsenate reductases; however, ArsC3 lacks the two distal catalytic cysteine residues of this class of enzymes. PMID:19966021

  17. Formation of ArF from LPdAr(F): catalytic conversion of aryl triflates to aryl fluorides.

    PubMed

    Watson, Donald A; Su, Mingjuan; Teverovskiy, Georgiy; Zhang, Yong; García-Fortanet, Jorge; Kinzel, Tom; Buchwald, Stephen L

    2009-09-25

    Despite increasing pharmaceutical importance, fluorinated aromatic organic molecules remain difficult to synthesize. Present methods require either harsh reaction conditions or highly specialized reagents, making the preparation of complex fluoroarenes challenging. Thus, the development of general methods for their preparation that overcome the limitations of those techniques currently in use is of great interest. We have prepared [LPd(II)Ar(F)] complexes, where L is a biaryl monophosphine ligand and Ar is an aryl group, and identified conditions under which reductive elimination occurs to form an Ar-F bond. On the basis of these results, we have developed a catalytic process that converts aryl bromides and aryl triflates into the corresponding fluorinated arenes by using simple fluoride salts. We expect this method to allow the introduction of fluorine atoms into advanced, highly functionalized intermediates. PMID:19679769

  18. Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records

    PubMed Central

    Storey, Michael; Roberts, Richard G.; Saidin, Mokhtar

    2012-01-01

    The Toba supereruption in Sumatra, ∼74 thousand years (ka) ago, was the largest terrestrial volcanic event of the Quaternary. Ash and sulfate aerosols were deposited in both hemispheres, forming a time-marker horizon that can be used to synchronize late Quaternary records globally. A precise numerical age for this event has proved elusive, with dating uncertainties larger than the millennial-scale climate cycles that characterized this period. We report an astronomically calibrated 40Ar/39Ar age of 73.88 ± 0.32 ka (1σ, full external errors) for sanidine crystals extracted from Toba deposits in the Lenggong Valley, Malaysia, 350 km from the eruption source and 6 km from an archaeological site with stone artifacts buried by ash. If these artifacts were made by Homo sapiens, as has been suggested, then our age indicates that modern humans had reached Southeast Asia by ∼74 ka ago. Our 40Ar/39Ar age is an order-of-magnitude more precise than previous estimates, resolving the timing of the eruption to the middle of the cold interval between Dansgaard–Oeschger events 20 and 19, when a peak in sulfate concentration occurred as registered by Greenland ice cores. This peak is followed by a ∼10 °C drop in the Greenland surface temperature over ∼150 y, revealing the possible climatic impact of the eruption. Our 40Ar/39Ar age also provides a high-precision calibration point for other ice, marine, and terrestrial archives containing Toba sulfates and ash, facilitating their global synchronization at unprecedented resolution for a critical period in Earth and human history beyond the range of 14C dating. PMID:23112159

  19. Late Cretaceous remagnetization of Proterozoic mafic dikes, southern Highland Mountains, southwestern Montana: A paleomagnetic and 40Ar/39Ar study

    USGS Publications Warehouse

    Harlan, S.S.; Geissman, J.W.; Snee, L.W.; Reynolds, R.L.

    1996-01-01

    Paleomagnetic results from Early Proterozoic metabasite sills and Middle Proterozoic diabase dikes from the southern Highland Mountains of southwestern Montana give well-defined, dual-polarity magnetizations that are statistically identical to those from a small Late Cretaceous pluton that cuts the dikes. The concordance of paleomagnetic directions from rocks of three widely separated ages indicates that the Proterozoic rocks were remagnetized, probably during Late Cretaceous time. Paleomagnetic, rock magnetic, and petrographic observations from the metabasite and diabase samples indicate that remanence is carried primarily by low-Ti magnetite. Combining virtual geomagnetic poles from metabasite sills, diabase dikes, and the Late Cretaceous pluton, we obtain a paleomagnetic pole at 85.5??N, 310.7??E (K = 19.9, A95 = 9.1??, N = 14 sites) that is similar to a reference pole from the 74 Ma Adel Mountain Volcanics of western Montana. Biotite and hornblende 40Ar/39Ar isotopic dates from host basement geneiss and a hornblende from a remagnetized metabasite sill yield ages of ca. 1800 Ma; these dates probably record cooling of the southern Highland Mountains following high-grade metamorphism at 1.9-1.8 Ga. The gneiss and metabasite age spectra show virtually no evidence of disturbance, indicating that the basement rocks were never heated to temperatures sufficient to cause even partial resetting of their argon systems. Thus, the overprint magnetization of the Highland Mountains rocks is not a thermoremanent magnetization acquired during conductive cooling of nearby Late Cretaceous plutons. Remagnetization of the metabasite sills and diabase dikes was probably caused by localized thermochemical and thermoviscous effects during circulation of Late Cretaceous hydrothermal fluids related to epithermal mineralization. The absence of significant disturbance to the 40Ar/39Ar age spectrum from the remagnetized metabasite hornblende indicates that some secondary magnetizations may

  20. Thermal History of the Felsite Unit, Geysers Geothermal Field, From Thermal Modeling of 40Ar/39Ar Incremental Heating Data

    SciTech Connect

    T. M. Harrison; G. B. Dalrymple; J. B. Hulen; M. A. Lanphere; M. Grove; O. M. Lovera

    1999-08-19

    An Ar-40/Ar-39 and U-Pb study was performed of the Geysers plutonic complex of the Geysers Geothermal Field in California. Sixty-nine ion microprobe spot analyses of zircons from four granite samples from the plutonic complex that underlies the Geysers geothermal field yielded Pb-207/Pb-206 vs. U-238/Pb-206 concordia ages ranging from 1.13 {+-} 0.04 Ma to 1.25 {+-} 0.04 Ma. The U-Pb ages coincide closely with Ar-40/Ar-39 age spectrum plateau and ''terminal'' ages from coexisting K-feldspars and with the eruption ages of overlying volcanic rocks. The data indicate that the granite crystallized at 1.18 Ma and had cooled below 350 C by {approximately}0.9-1.0 Ma. Interpretation of the feldspar Ar-40/Ar-39 age data using multi-diffusion domain theory indicates that post-emplacement rapid cooling was succeeded either by slower cooling from 350-300 C between 1.0 and 0.4 Ma or transitory reheating to 300-350 C at about 0.4-0.6 Ma. Heat flow calculations constrained with K-feldspar thermal histories and the pre sent elevated regional heal flow anomaly demonstrate that appreciable heat input from sources external to the known Geysers plutonic complex is required to maintain the geothermal system. This requirement is satisfied by either a large, underlying, convecting magma chamber (now solidified) emplaced at 1.2 Ma or episodic intrusion of smaller bodies from 1.2-0.6 Ma.

  1. Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records

    NASA Astrophysics Data System (ADS)

    Storey, Michael; Roberts, Richard G.; Saidin, Mokhtar

    2012-11-01

    The Toba supereruption in Sumatra, ∼74 thousand years (ka) ago, was the largest terrestrial volcanic event of the Quaternary. Ash and sulfate aerosols were deposited in both hemispheres, forming a time-marker horizon that can be used to synchronize late Quaternary records globally. A precise numerical age for this event has proved elusive, with dating uncertainties larger than the millennial-scale climate cycles that characterized this period. We report an astronomically calibrated 40Ar/39Ar age of 73.88 ± 0.32 ka (1σ, full external errors) for sanidine crystals extracted from Toba deposits in the Lenggong Valley, Malaysia, 350 km from the eruption source and 6 km from an archaeological site with stone artifacts buried by ash. If these artifacts were made by Homo sapiens, as has been suggested, then our age indicates that modern humans had reached Southeast Asia by ∼74 ka ago. Our 40Ar/39Ar age is an order-of-magnitude more precise than previous estimates, resolving the timing of the eruption to the middle of the cold interval between Dansgaard-Oeschger events 20 and 19, when a peak in sulfate concentration occurred as registered by Greenland ice cores. This peak is followed by a ∼10 °C drop in the Greenland surface temperature over ∼150 y, revealing the possible climatic impact of the eruption. Our 40Ar/39Ar age also provides a high-precision calibration point for other ice, marine, and terrestrial archives containing Toba sulfates and ash, facilitating their global synchronization at unprecedented resolution for a critical period in Earth and human history beyond the range of 14C dating.

  2. AR-40 AR-39 Age of an Impact-Melt Lithology in DHOFAR 961

    NASA Technical Reports Server (NTRS)

    Frasl, B.; Cohen, B. A.; Li, Z.-H.; Jolliff, B.; Korotev, R.; Zeigler, R.

    2016-01-01

    , although they note that further age dating of all the stones is required to test this hypothesis. We received a split of Dhofar 961 from R. Zeigler consisting of a large clast of IM Lithology B, with some light-colored, friable matrix clinging to the external margins of the impact-melt clast. This lithology was not present in the samples investigated by Joy et al. and thus does not have corresponding U-Pb ages on it. We created multiple subsplits of both the IM and matrix lithologies, each weighing several tens of micrograms. We conducted Ar-40 Ar-39 dating of this candidate SPA material by high-resolution step heating and comparing it with the regolith that surrounds it.

  3. New 40Ar/39Ar Chronostratigraphy for Olduvai Gorge, Tanzania, and Orbital Forcing of Lacustrine Sedimentation

    NASA Astrophysics Data System (ADS)

    Deino, A.

    2011-12-01

    The Pleistocene sedimentary and volcanic deposits of Olduvai Gorge, north-central Tanzania, have been a focus of geological, paleontological, paleoanthropological and archaeological investigation since Louis Leakey initiated fossil and artifact excavations there in 1931. Although more than half a century of effort has been applied to radiometric dating of the volcaniclastic strata within this sequence, vexing questions persist regarding details of the chronostratigraphy. Renewed dating efforts have enabled revision of the chronostratigraphy of Bed I, providing a more accurate evaluation of the absolute ages of volcanic events, and the rates of geological processes. The new 40Ar/39Ar geochronology, based primarily on phenocrystic K-feldspar from interbedded marker tuffs, resolves some of the anomalies apparent in earlier Olduvai basin Bed I chronostratigraphies. A new age of 1.88 ± 0.05 for Tuff IA near the base of Bed I, while relatively imprecise, agrees with a projected age 1.91 Ma based on magnetostratigraphy and sedimentation rates toward the base of Bed I. The key marker tuff IB in the upper part of Bed I has a well-determined age of 1.848 ± 0.003 Ma. Comparative dating of early and late erupted phases of this unit yields identical ages, resolving the conundrum of an apparent hiatus of ~80 ka between the crystal-rich fallout base and the body of the Tuff IB ignimbrite in the eastern exposures proposed by Walter et al. (1991, 1992). New ages for tuffs above Tuff IB to the top of Bed I (i.e., Tuff IE 'vitric,' Tuff IE, Ng'eju tuff, and Tuff IF), fall in stratigraphic order and are consistent with the paleomagnetic age constraint of 1.778 Ma imposed by the top of the Olduvai Subchron in overlying Bed II. The new high-precision chronostratigraphy provides age control for a series of wet/dry paleoclimate indicators previously documented in upper Bed I (Hay, 1976; Hay and Kyser, 2001; Sikes and Ashley, 2007). The most prominent event is a major lake expansion

  4. Emerald dating through Ar-40/Ar-39 step-heating and laser spot analysis of syngenetic phlogopite

    NASA Astrophysics Data System (ADS)

    Cheilletz, A.; Feraud, G.; Giuliani, G.; Ruffet, G.

    1993-12-01

    Emerald, occurring in K-metasomatic rocks developed at the contact of the Carnaiba leucogranite with serpentinite (Bahia State, Brazil), has been dated using an original Ar-40/Ar-39 procedure. It combines step heating and spot fusion experiments on two types of phlogopite crystals: (1) bulk samples and individual grains extracted from the enclosing K-metasomatic host rocks; and (2) syngenetic solid inclusions precipitated along growing zones of the emerald host crystals. The second procedure uses in situ laser probe experiments on rock sections. In spite of the huge amounts of excess Ar-40 detected in adjacent emerald, we could measure reliable ages of 1951 +/- 8 Ma and 1934 +/- 8 Ma for the Trecho Velho and Braulia occurrences, respectively. Spot fusion data had higher discrepancy than the step heating data, but minute crystals of phlogopite included in emeralds bearing excess argon do not reveal excess argon. A muscovite belonging to the same granite hydrothermal complex gave a plateau age of 1976 +/- 8 Ma, which may correspond to a higher closure temperature of the K-Ar system during the cooling of the whole pluton and associated hydrothermal halo. These accurate measurements lead to the following conclusions: (1) direct emerald dating is possible; (2) in spite of a polyphase history during the Transamazonian orogenesis (2 Ga), combined step heating and spot fusion experiments give a better precision for granite-related emerald mineralization than the scattered ages obtained by Rb-Sr and K-Ar methods; (3) the late-Transamazonian tectonothermal retrograde event which probably caused the dispersion of previous Rb-Sr and K-Ar data is not revealed by our procedure; (4) the emerald mineralization and K-metamorphism appear to be linked with the thermal history of the leucogranite; (5) in addition to its use in polyphase crustal domains, accurate Ar-40/Ar-39 dating is of major interest in the field of metallogenic models, even, for instance, for mineralizations

  5. Revised age for the Gosses Bluff impact structure, Northern Territory, Australia, based on Ar-40Ar-39 dating

    NASA Astrophysics Data System (ADS)

    Milton, Daniel J.; Sutter, John F.

    1987-09-01

    Ar-40Ar-39 dating of a pumiceous suevite clast from the melt breccia at Gosses Bluff consisting largely of extremely fine-grained sanidine yields a discordant age spectrum, probably reflecting some diffusional loss of argon. High-temperature increments that together yield a near-plateau age of 142.5 Ma are apparently not affected by argon loss and offer the best estimate of the date of the Gosses Bluff event. The event may fall in the latest Jurassic Period, but more likely falls in the earliest Cretaceous, probably in one of the reverse-polarity magnetochrons M16, M17, or M18.

  6. 40Ar/39Ar chronology and paleomagnetism of Quaternary basaltic lavas from the Perşani Mountains (East Carpathians)

    NASA Astrophysics Data System (ADS)

    Panaiotu, C. G.; Jicha, B. R.; Singer, B. S.; Ţugui, A.; Seghedi, I.; Panaiotu, A. G.; Necula, C.

    2013-08-01

    Quaternary volcanism in the Perşani Mountains forms an Na-alkali basaltic province inside the bend area of the Carpathians in the southeastern part of Europe. Previous K-Ar ages and paleomagnetic data reveal several transitional virtual geomagnetic poles, which were tentatively associated with the Cobb Mountain subchron and a Brunhes chron excursion. We report a new paleomagnetic and rock-magnetic study coupled with 40Ar/39Ar geochronology to better constrain the age of geomagnetic reversals or excursions that might be recorded and the timing of volcanism. Of the paleomagnetic directions obtained from sampled lava flows 4 are reversed polarity, 19 are normal polarity and 16 have transitional polarity. 40Ar/39Ar plateau ages determined from incremental heating experiments on groundmass indicate that two of the reversely magnetized lavas erupted at 1142 ± 41 and 800 ± 25 ka, four of the normally magnetized lavas erupted at 1060 ± 10, 1062 ± 24, 684 ± 21, and 683 ± 28 ka, and two transitionally magnetized lavas formed at 1221 ± 11 and 799 ± 21 ka. Both the new 40Ar/39Ar ages and the paleomagnetic data suggest at least five episodes of volcanic activity with the most active periods during the Jaramillo and Brunhes chrons. This results shows that the last phases of alkalic and calc-alkaline magmatism in the South-East Carpathians were contemporaneous. The age of the older transitionally magnetized lava flow is within error of recent unspiked K-Ar and astrochronologic ages for the reversal that defines the onset of the Cobb Mountain normal polarity subchron. The age of the younger transitional lava is similar to that of an excursion that preceded the Matuyama-Brunhes polarity reversal and which has come to be known as the Matuyama-Brunhes precursor. Omitting the excursion data, the dispersion of the virtual geomagnetic poles (around 19°) is larger than the expected value around 45°N from the global compilation, but closer to the value obtained only from the

  7. Shock tube study of the reaction H plus O2 plus Ar yields HO2 plus Ar

    NASA Technical Reports Server (NTRS)

    Jachimowski, C. J.; Houghton, W. M.

    1972-01-01

    Rate coefficient data for the recombination reaction H + 02 + Ar yields H02 + Ar have been determined from studies of lean hydrogen-oxygen mixtures behind incident shock waves over the temperature range of 948 to 1125 K. Hydroxyl radical concentration profiles were measured by ultraviolet absorption spectroscopy, and rate data were obtained through analysis of induction time and exponential growth parameter data. Analysis of the data yielded a rate coefficient which was generally lower than most of the more recent values obtained from shock tube studies. The effect of boundary layer formation on the conditions behind the shock was also examined and found to be negligible.

  8. USDA-ARS and EMBRAPA Scientists Build Bridges With Strawberries

    Technology Transfer Automated Retrieval System (TEKTRAN)

    At the '3rd Simposio Nacional do Morango'and '2nd Encontro de Pequenas Frutas e Frutas Nativas do Mercosul' at Pelotas, Rio Grande Do Sul, Brazil, held 7 - 10 November 2006, I was invited to describe strawberry breeding in the United States and also my own USDA-ARS strawberry breeding program at Bel...

  9. Postharvest treatment research at USDA-ARS: stored product fumigation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The overall goal of this USDA-ARS research is to ensure the protection and quality of stored product foodstuffs. The results of this research directly enhance production, distribution, and safety of foodstuffs, promote and retain access of United States-grown crops to domestic and foreign markets, a...

  10. Big data computing: Building a vision for ARS information management

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Improvements are needed within the ARS to increase scientific capacity and keep pace with new developments in computer technologies that support data acquisition and analysis. Enhancements in computing power and IT infrastructure are needed to provide scientists better access to high performance com...

  11. Spectroscopy Study of Ar + CO2 Plasmas in ASTRAL.

    NASA Astrophysics Data System (ADS)

    Munoz, Jorge; Boivin, Robert; Kamar, Ola; Loch, Stuart; Ballance, Connor

    2006-10-01

    A spectroscopy study of the ASTRAL (Auburn Steady sTate Research fAciLity) helicon plasma source running Ar + CO2 gas mix is presented. ASTRAL produces Ar plasmas: ne = 10^10 to 10^13 cm-3, Te = 2 to 10 eV and Ti = 0.03 to 0.5 eV. A series of 7 large coils produce an axial magnetic field up to 1.3 kGauss. A fractional helix antenna is used to introduce rf power up to 2 kWatt. A spectrometer which features a 0.33 m Criss-Cross monochromator and a CCD camera is used for this study. Very different plasmas are produced following the relative importance of CO2 in the gas mixture. At low CO2 concentration, the plasmas are similar to those obtained with pure Ar with weak CO2, CO2^+, CO and CO^+ bands. The usual blue plasma core associated with intense Ar II transitions is observed with however a significant white glow coming from the outer plasma regions. At higher CO2 concentration, the plasma becomes essentially molecular and can be described as an intense white plasma column. Molecular dissociative processes associated with the production of strong C and O atomic lines are observed under specific plasma conditions. The atomic spectral lines are compared with ADAS modeling results. This study indicates the possible advantages of using a helicon source to control the CO2 plasma chemistry for industrial applications.

  12. The USDA/ARS Table Grape Breeding Program

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The USDA/ARS table grape breeding program is developing: 1) a series of seedless table grape cultivars with naturally large berries, early to late maturity, and red, white or black fruit; 2) powdery mildew resistant table grape cultivars; and 3) Pierce’s Disease resistant table grape cultivars. Fif...

  13. 75 FR 12161 - Establishment of Class E Airspace; Marianna, AR

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-15

    ... continues to read as follows: Authority: 49 U.S.C. 106(g); 40103, 40113, 40120; E.O. 10854, 24 FR 9565, 3... Regulatory Policies and Procedures (44 FR 11034; February 26, 1979); and (3) does not warrant preparation of... Federal Aviation Administration 14 CFR Part 71 Establishment of Class E Airspace; Marianna, AR...

  14. 76 FR 38717 - Arkansas Disaster Number AR-00048

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-01

    ... From the Federal Register Online via the Government Publishing Office U.S. SMALL BUSINESS ADMINISTRATION Arkansas Disaster Number AR-00048 AGENCY: U.S. Small Business Administration. ACTION: Amendment 8... loan applications to: U.S. Small Business Administration, Processing and Disbursement Center,...

  15. 76 FR 35937 - Arkansas Disaster Number AR-00048

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-06-20

    ... From the Federal Register Online via the Government Publishing Office U.S. SMALL BUSINESS ADMINISTRATION Arkansas Disaster Number AR-00048 AGENCY: U.S. Small Business Administration. ACTION: Amendment 6... loan applications to: U.S. Small Business Administration, Processing and Disbursement Center,...

  16. USDA-ARS METEOROLOGICAL MONITORING IN NORTHEASTERN OREGON

    Technology Transfer Automated Retrieval System (TEKTRAN)

    In order to collect accurate and reliable meteorological data for research purposes, a well-designed monitoring plan must be implemented. The Agricultural Research Service Columbia Plateau Conservation Research Center (ARS-CPCRC) meteorological monitoring network was designed and developed in order...

  17. Coulomb excitation of 44Ca and 46Ar

    NASA Astrophysics Data System (ADS)

    Calinescu, S.; Cáceres, L.; Grévy, S.; Sorlin, O.; Dombrádi, Z.; Stanoiu, M.; Astabatyan, R.; Borcea, C.; Borcea, R.; Bowry, M.; Catford, W.; Clément, E.; Franchoo, S.; Garcia, R.; Gillibert, R.; Guerin, I. H.; Kuti, I.; Lukyanov, S.; Lepailleur, A.; Maslov, V.; Morfouace, P.; Mrazek, J.; Negoita, F.; Niikura, M.; Perrot, L.; Podolyák, Z.; Petrone, C.; Penionzhkevich, Y.; Roger, T.; Rotaru, F.; Sohler, D.; Stefan, I.; Thomas, J. C.; Vajta, Z.; Wilson, E.

    2016-04-01

    The reduced transition probabilities B (E 2 ;0g.s . +→21+) of the 46Ar and 44Ca nuclei were studied using the Coulomb excitation technique at intermediate energy at the LISE/GANIL facility. The in-flight γ rays, emitted after the Coulomb excitation of their first 2+ states, were detected in an array of 64 BaF2 crystals. The present B(E 2 ↑ ) value for 44Ca, 475(36) e2fm4 , agrees well with the value of 495(35) e2fm4 obtained by averaging results of previous experiments. Consistent B (E 2 ;0g.s . +→21+) values of 225(29) e2fm4 and 234(19) e2fm4 have been obtained for 46Ar from an absolute and a relative measurement, normalized to the 44Ca value. Both results agree with the ones obtained with the same experimental technique at the NSCL facility but are a factor of 2 smaller than the shell model predictions. The drop in B (E 2 ;0g.s . +→21+) in the Ar chain at N =28 , confirmed in this experiment, shows that 46Ar is sensitive to the N =28 shell closure.

  18. Interacting with Visual Poems through AR-Based Digital Artwork

    ERIC Educational Resources Information Center

    Lin, Hao-Chiang Koong; Hsieh, Min-Chai; Liu, Eric Zhi-Feng; Chuang, Tsung-Yen

    2012-01-01

    In this study, an AR-based digital artwork called "Mind Log" was designed and evaluated. The augmented reality technique was employed to create digital artwork that would present interactive poems. A digital poem was generated via the interplay between a video film and a text-based poem. This artwork was created following a rigorous design flow,…

  19. Pulsed electric field (PEF)research at USDA, ARS, ERRC

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This article summarizes the effects of pulsed electric fields on the microbiological safety and quality aspects of various liquid food matrices, obtained at USDA, ARS, Eastern Regional Research Center under CRIS Project No. 1935-41420-013-00D, Processing Intervention Technologies for Enhancing the S...

  20. 75 FR 12163 - Class E Airspace; Mountain View, AR

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-15

    ...; (2) is not a ``significant rule'' under DOT Regulatory Policies and Procedures (44 FR 11034; February...: Authority: 49 U.S.C. 106(g); 40103, 40113, 40120; E.O. 10854, 24 FR 9565, 3 CFR, 1959-1963 Comp., p. 389... Federal Aviation Administration 14 CFR Part 71 Class E Airspace; Mountain View, AR AGENCY:...

  1. Electron impact ionization of Ar/sup 8 +/

    SciTech Connect

    Defrance, P.; Rachafi, S.; Jureta, J.; Meyer, F.; Chantrenne, S.

    1986-01-01

    Absolute electron impact ionization cross-sections have been measured for the Neon-like Ar/sup 8 +/ in the energy range from below the threshold for the metastable state to 2500 eV. No contribution of metastable states is observed. The results are well reproduced by the Distorted Wave Born Approximation. 12 refs., 1 fig.

  2. Data management and database structure at the ARS Culture Collection

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The organization and management of collection data for the 96,000 strains held in the ARS Culture Collection has been an ongoing process. Originally, the records for the four separate collections were maintained by individual curators in notebooks and/or card files and subsequently on the National C...

  3. The beta decay asymmetry parameter of /sup 35/Ar

    SciTech Connect

    Garnett, J.D.

    1987-11-01

    The beta decay asymmetry parameter for /sup 35/Ar = /sup 35/Cl + e/sup +/ + nu/sub e/ has been remeasured in order to resolve a long standing puzzle. Previous asymmetry measurements, when combined with the comparative half-life, yield a value for the vector coupling constant, G/sub v/, that is in serious disagreement with the accepted value. We produced polarized /sup 35/Ar by a (p,n) reaction on /sup 35/Cl using the polarized proton beam provided by Lawrence Berkeley Laboratory's 88-Inch Cyclotron. The polarization of the /sup 35/Ar was determined by measuring the asymmetry of the positrons produced in /sup 35/Ar decay to the first excited state in /sup 35/Cl (branching ratio = 1.3%) in coincidence with a 1219.4 keV gamma ray. Our result, A/sub 0/ = 0.49 +- 0.10, combined with the comparative half-life yields a value for G/sub v/ in agreement with the accepted value.

  4. The ARS Culture Collection and Developments in Biotechnology

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The ARS Culture Collection (NRRL) has played a prominent role in the development of biotechnology since its founding in 1940 when the Northern Regional Research Laboratory opened. Early discoveries included selection of production strains for penicillin, dextran blood extender, xanthan gum and the v...

  5. Artificial neutrino source based on the {sup 37}Ar isotope

    SciTech Connect

    Barsanov, V. I.; Dzhanelidze, A. A.; Zlokazov, S. B.; Kotelnikov, N. A.; Markov, S. Yu.; Selin, V. V.; Shakirov, Z. N.; Abdurashitov, D. N.; Veretenkin, E. P.; Gavrin, V. N.; Gorbachev, V. V.; Ibragimova, T. V.; Kalikhov, A. V.; Mirmov, I. N. Shikhin, A. A.; Yants, V. E.; Khomyakov, Yu. S.; Cleveland, B. T.

    2007-02-15

    In April 2004, a neutrino source was produced by irradiating a 330-kg piece of pressed calcium oxide at the fast-neutron reactor BN-600 (Zarechny, Russia) for six months. The {sup 37}Ar isotope was obtained via the (n, {alpha}) reaction on {sup 40}Ca, and {sup 37}Ar was extracted from an aqueous solution of nitric acid in which the solid target was dissolved. After that, {sup 37}Ar was purified and sealed into a capsule. This source was used to measure the neutrino-capture rate in metalic gallium for neutrinos from {sup 37}Ar decay, which have an energy close to that of the main line of solar {sup 7}Be neutrinos (863 keV). The target of the SAGE Gallium-Germanium Neutrino Telescope was irradiated by using this source at the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences). The source activity was measured by several methods during its production, in the course of irradiation, and after its completion. The weighted mean of the activity for six measurements was 409 {+-} 2 kCi at the beginning of irradiation of the gallium target (04:00 Moscow time, 30.04.2004). The scatter in the activity values obtained by different methods does not exceed 5%.

  6. Quantum vibrational dynamics of the Ar2ICl cluster

    NASA Astrophysics Data System (ADS)

    Valdés, Álvaro; Prosmiti, Rita

    2016-03-01

    Quantum mechanical multiconfiguration time-dependent Hartree (MCTDH) calculations are presented for the Ar2ICl cluster. The Hamiltonian operator is expressed in satellite coordinates, with its potential term being represented as a sum of the three-body ArICl ab initio parameterized interactions plus the Ar-Ar ones. The potential surface shows different type of low-lying minima (global and local), that influence the vibrational dynamics of the system. The vibrational ground state properties and specific vibrationally excited states are obtained from improved relaxation MCTDH calculations employing a large number of basis set functions, especially for the angular part, to achieve convergence. By analyzing the spatial density distributions of the vibrational states we are able to characterize the corresponding states to different isomers, such as tetrahedral, linear, bending type ones. The binding energy of each isomer is also computed, and they contribute to evaluate their relative stability, as well as the importance of the underlying multiple minima of the potential surface.

  7. Studying Teacher Behavior with the OScAR Technique.

    ERIC Educational Resources Information Center

    Medley, Donald M.

    Educational Testing Service is involved in a measurement approach to research in teaching with a goal of developing procedures for obtaining objective quantitive descriptions of teacher behavior, in terms of a minimum number of dimensions, on the basis of direct observation. The Observation Schedule and Record (OScAR), a card which contains a list…

  8. 78 FR 41838 - Establishment of Class E Airspace; Colt, AR

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-12

    ... Federal Aviation Administration 14 CFR Part 71 Establishment of Class E Airspace; Colt, AR AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Final rule. SUMMARY: This action establishes Class E airspace... Federal Register a notice of proposed rulemaking (NPRM) to establish Class E airspace for the Colt,...

  9. Near-contact Binaries IZ Monocerotis and AR Draconis

    NASA Astrophysics Data System (ADS)

    Yang, Yuan-Gui; Dai, Hai-Feng; Zhou, Zheng; Li, Qun

    2016-05-01

    We present multi-color photometric observations for two neglected near-contact binaries, IZ Mon (P=0\\_\\_AMP\\_\\_fd;77980) and AR Dra (P=0\\_\\_AMP\\_\\_fd;67584). By the aid of the updated W-D analysis code, the photometric solutions were deduced from the multi-color light curves (LCs). IZ Mon is a semi-detached binary with a mass ratio of q=0.388(+/- 0.002), while AR Dra is a detached star with a mass ratio of q=0.652(+/- 0.002). The asymmetric LCs of IZ Mon were modeled by a hot spot on the secondary’s surface, which may be attributed to mass transfer from the primary. Based on all collected eclipse times for two systems, we constructed their timing residual curves. The orbital period for IZ Mon may be continuously decreasing at a rate of {dP}/{dt}=-2.06(+/- 0.04) {days} {{yr}}-1, which may result from mass and angular momentum loss from the central system. For AR Dra, there exists a cyclic variation with a period of {P}3=104.9(+/- 2.9) {yr} due to light-time orbit effect via the presence of the third body, whose mass is more than 0.28(+/- 0.02) {M}ȯ . Finally, two near-contact binaries, IZ Mon and AR Dra, will evolve into contact binaries.

  10. ARS NP212 Climate change, soils and emissions program update

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Agricultural Research Service National Program 212 (Climate Change, Soils, and Emissions) has a significant component focused on air quality studies. Presented here for the Agricultural Air Quality Task Force is an update on the status of ARS programs with focus on air quality. National Program ...

  11. Expansion of the USDA ARS Aerial Application spray atomization models

    Technology Transfer Automated Retrieval System (TEKTRAN)

    An effort is underway to update the USDA ARS aerial spray nozzle models using new droplet sizing instrumen-tation and measurement techniques. As part of this effort, the applicable maximum airspeed is being increased from 72 to 80 m/s to provide guidance to applicators when using new high speed air...

  12. Experimental ion mobility measurements in Ar-CO2 mixtures

    NASA Astrophysics Data System (ADS)

    Encarnação, P. M. C. C.; Cortez, A. F. V.; Pinto, M. G. A.; Neves, P. N. B.; Trindade, A. M. F.; Escada, J.; Santos, F. P.; Borges, F. I. G. M.; Barata, J. A. S.; Conde, C. A. N.

    2015-01-01

    In this paper we present the experimental results for the mobility of ions in argon-carbon dioxide gaseous mixtures (Ar-CO2) for pressures ranging from 6 to 10 Torr and for reduced electric fields in the 10 Td to 25 Td range, at room temperature.The time-of-arrival spectra of the several mixture ratios studied revealed that the relative abundance of the ions and their mobilities depend on the mixture ratio. For Ar concentrations below 80% only one peak was observed in the spectra which was attributed to CO2+, while for Ar concentrations above 80% a second peak appears at the left side of the main peak, which may be due to impurities, probably H2O+. In this work, the time-of-arrival spectra from which reduced mobilities were obtained for Ar concentrations of 20% (K0 = 1.141±0.004 cm2V-1s-1), 50% (K0 = 1.385±0.009 cm2V-1s-1), 85% (K0 = 1.690±0.022 cm2V-1s-1) and 95% (K0 = 1.954±0.043 cm2V-1s-1) are displayed as well as other reduced mobilities values obtained similarly. The ion mobility study was performed at reduced electric field values typically used in gaseous detectors.

  13. USDA-ARS support of the USDA small watershed program

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The USDA-ARS Hydraulic Engineering Research Unit (HERU) has had a rich history supporting the USDA Small Watershed Program. The Small Watershed Program was established by the passage of legislation that allowed the USDA-Natural Resources Conservation Service to provide financial and technical suppo...

  14. 36Cl-36Ar Exposure Ages of Chondritic Metals

    NASA Astrophysics Data System (ADS)

    Graf, Th.; Caffee, M. W.; Finkel, R. C.; Marti, K.; Nishiizumi, K.; Ponganis, K. V.

    1995-09-01

    Metal separates were prepared to determine ^36Cl-^36Ar exposure ages for six H4 p.m. falls (with reported bulk exposure ages of 4 to 10Ma), for ten H5 a.m. falls (T(sub)e = 4-10 Ma) and for the Acapulco meteorite (T(^36Cl-^36Ar)= 5.7 Ma). This dating method uses production rate ratios P(^36Cl)/P(^36Ar) and is independent of the shielding-sensitive absolute production rates. It is also known that for protons the production rate ratio is rather insensitive to changes in the energy spectrum; the dependence of this ratio for secondary neutrons is at present less understood. First results were already reported [1]. The cosmic-ray-produced ^3He/^38Ar ratios show a bimodal distribution with two clusters at about 15 and about 9 (Fig. 1). About half of the ^3He is produced via ^3H which is known to diffuse in metal at relatively low temperatures. Therefore, Fig. 1 provides evidence for a quasi-continuous loss of ^3H from such metals. If this loss mechanism is due to solar heating, perihelia <1 AU are indicated for these meteorites. Losses are prominent for H5 a.m. falls, but not for H4 p.m. falls. The orbital implications are consistent with those already known from the time-of-fall parameter (p.m. falls / total falls) which was used in the selection of the H4,H5 sample sets [2]. The exposure age histograms of both H groups show the well known clusters at about 7 Ma. The width of the exposure age peaks differ, however, and the collisional break-up event can be further constrained. Except for Nassirah, all members of the H4 p.m. group fall into the range 7.0 +/- 0.3 Ma. Bulk rock ages (8.2-9.3 Ma) [3] as well as the ^36Cl-^36Ar age (8.3 Ma) of Nassirah are higher and may indicate that this meteorite does not belong to the collisional event. We observe a small but systematic difference in calculated exposure ages by the ^36Cl-^36Ar method, when compared with ages obtained by conventional noble gas production rates. This shift (about 10%) does not appear to be dependent on

  15. Production of 37Ar in The University of Texas TRIGA reactor facility

    SciTech Connect

    Egnatuk, Christine M.; Lowrey, Justin; Biegalski, S.; Bowyer, Ted W.; Haas, Derek A.; Orrell, John L.; Woods, Vincent T.; Keillor, Martin E.

    2011-06-19

    The detection of {sup 37}Ar is important for on-site inspections for the Comprehensive Nuclear-Test-Ban Treaty monitoring. In an underground nuclear explosion this radionuclide is produced by {sup 40}Ca(n,{alpha}){sup 37}Ar reaction in surrounding soil and rock. With a half-life of 35 days, {sup 37}Ar provides a signal useful for confirming the location of an underground nuclear event. An ultra-low-background proportional counter developed by Pacific Northwest National Laboratory is used to detect {sup 37}Ar, which decays via electron capture. The irradiation of Ar gas at natural enrichment in the 3L facility within the Mark II TRIGA reactor facility at The University of Texas at Austin provides a source of {sup 37}Ar for the calibration of the detector. The {sup 41}Ar activity is measured by the gamma activity using an HPGe detector after the sample is removed from the core. Using the {sup 41}Ar/{sup 37}Ar production ratio and the {sup 41}Ar activity, the amount of {sup 37}Ar created is calculated. The {sup 41}Ar decays quickly (half-life of 109.34 minutes) leaving a radioactive sample of high purity {sup 37}Ar and only trace levels of {sup 39}Ar.

  16. Xe and Ar nanobubbles in Al studied by photoemission spectroscopy

    SciTech Connect

    Dhaka, R. S.; Biswas, C.; Shukla, A. K.; Barman, S. R.; Chakrabarti, Aparna

    2008-03-01

    We have studied xenon and argon bubbles formed in the subsurface region of Al(111) by x-ray photoelectron spectroscopy. As a consequence of the nanometer size of the bubbles, the photohole formed by Xe 3d or Ar 2p photoemission is screened by the Al conduction electrons, which substantially lowers the binding energy (BE) as compared to the gas phase. As the bubble size increases, the Al conduction electron screening decreases and the BE increases. On the basis of density functional theory, we show that the change in the bubble pressure with size is not responsible for the BE shift of inner shell core levels, such as Xe 3d or Ar 2p. On the other hand, an increase in BE with bubble size for outer shell core levels, such as Ar 3p, could be due to a decrease in both pressure and Al conduction electron screening. The core level line shape also changes with bubble size. For example, the spectra are broadened due to the distribution of the bubble radius around its mean value, and an asymmetry for small bubbles is observed that decreases for larger bubbles. An annealing of Xe and Ar bubbles after an implantation up to 640 K shows that the BE increases with annealing temperature. Since it is well known that bubble size increases with annealing temperature, this further supports our contention of BE shift with bubble size. A defect induced partial disorder of the Al(111) surface by Xe and Ar bombardment is observed by low energy electron diffraction, but this does not affect the Al 2p BE and line shape.

  17. Precision angle-resolved autoionization resonances in Ar and Ne

    SciTech Connect

    Berrah, N.; Langer, B.; Gorczyca, T.W.

    1997-04-01

    Theoretical work has shown that the electron angular distribution and the shape of the autoionization resonances are crucial to the understanding of certain types of electron-electron correlation. Autoionization resonances in Ne (Ar) result from the decay of the excited discrete state Ne{sup *} 2s2p{sup 6} np (Ar{sup *} 3s3p{sup 6} np) into the continuum state Ne{sup +} 2s{sup 2}2p{sup 5} + e{sup {minus}} (ks,kd) (Ar{sup +} 3s{sup 2}3p{sup 5} + e{sup {minus}} (ks,kd)). Since the continuum can also be reached by direct photoionization, both paths add coherently, giving rise to interferences that produce the characteristic Beutler-Fano line shape. In this work, the authors report on quantitative angle-resolved electron spectrometry studies of (a) the Ne 2s{sup 2}2p{sup 6} {r_arrow} 2s2p{sup 6} np (n=3-5) autoionizing resonances and the 2s{sup 2}2p{sup 6} {r_arrow} 2p{sup 4}3s3p doubly excited resonance, (b) the Ar 3s{sup 2}3p{sup 6} {r_arrow} 3s3p{sup 6} np (n=4-9) autoionization resonances and extended R-matrix calculations of the angular-distribution parameters for both Ne and Ar measurements. Their results are compared with previous theoretical work by Taylor.

  18. Evaluation of sintering effects on SiC incorporated UO2 kernels under Ar and Ar-4%H2 environments

    SciTech Connect

    Silva, Chinthaka M; Lindemer, Terrence; Hunt, Rodney Dale; Collins, Jack Lee; Terrani, Kurt A; Snead, Lance Lewis

    2013-01-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO2 kernels used for TRISO particle fuels to lower oxygen potential and prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that internal gelation process can be used to incorporate SiC in urania fuel kernels. Sintering in either Ar or Ar-4%H2 at 1500 C lowered the SiC content in the UO2 kernels to some extent. Formation of UC was observed as the major chemical phase in the process, while other minor phases such as U3Si2C2, USi2, U3Si2, and UC2 were also identified. UC formation was presumed to be occurred by two reactions. The first was the SiC reaction with its protective SiO2 oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO2 to form UC. The second process was direct UO2 reaction with SiC grains to form SiO, CO, and UC, especially in Ar-4%H2. A slightly higher density and UC content was observed in the sample sintered in Ar-4%H2, but the use of both atmospheres produced kernels with ~95% of theoretical density. It is suggested that incorporating CO in the sintering gas would prevent UC formation and preserve the initial SiC content.

  19. 40Ar/39Ar dated climatic and hydrological variability between MIS20 and MIS18 at Sulmona Basin (central Italy)

    NASA Astrophysics Data System (ADS)

    Zanchetta, Giovanni; Giaccio, Biagio; Eleonora, Reagattieri; Nomade, Sebastien; Renne, Paul R.; Sprain, Courtney J.; Drysdale, Russell N.; Tzedakis, Polychronis C.; Messina, Paolo; Scardia, Giancarlo; Sposato, Andrea

    2015-04-01

    Understanding spatial-temporal variability, magnitude and different expressions of Quaternary millennial-scale palaeoclimatic changes is one of the frontier challenges of modern palaeoclimatology. Addressing this issue requires the acquisition of regionally representative, and ideally independently-dated, records of climatic variability. Multiproxy record (stable isotopes, XRF, MS, %CaCO3) from lacustrine succession of Sulmona basin (central Italy), highlights climatic and hydrological variability at orbital to millennial scales between MIS20 and MIS18. The record highlights the presence of interesting millennial scale variability within MIS19, considered to be the best orbital analogue of the current interglacial. The presence of several tephra layers precisely dated by 40Ar/39Ar technique, allow placement of the record within a robust time frame. Assembling a high-resolution paleoclimatic record for MIS19 anchored to a high-precision 40Ar/39Ar chronology, it is possible to show that the MIS 19c interglacial started shortly before the boreal summer insolation and obliquity maximum/precession minimum at 790-788 ka, and ended 11.6 ± 2.3 kyr later, when orbital parameters assumed a configuration similar to the present one.

  20. Ar-Ar Ages of Nakhlites Y000593, NWA998, and Nakhla and CRE Ages of NWA998

    NASA Technical Reports Server (NTRS)

    Garrison, D. H.; Bogard, D. D.

    2005-01-01

    The seven known Martian nakhlites are Nakhla, Lafayette, Governador Valadares, and four recent finds from hot and cold deserts: MIL03346 from the Transantarctic Mountains, a paired group from the Yamato Mountains (Y000593, Y000749, and Y000802, and two from Morocco (NWA998 and NWA817. Radiometric ages (Sm-Nd, Rb-Sr, U-Pb, and Ar-Ar) for the first three nakhlites, along with Chassigny, fall in the range of 1.19-1.37 Gyr and may suggest a common formation age. These meteorites also show very similar cosmic-ray (space) exposure ages, suggesting a single ejection event from Mars. The ages for nakhlites are different from those of Martian shergottites, whose radiometric ages vary by nearly a factor of three (approx. 165-475 Myr) and whose space exposure ages vary over a factor of approx. 20. Shergottite ages suggest that multiple locations on the Martian surface have been sampled, whereas nakhlite data imply sampling of only one Mars surface location. Because older Martian surfaces are expected to be more abundant, it seems surprising that all nakhlites would represent only one Martian impact event. To address this issue, we are measuring the (39)Ar-(40)Ar ages of Y-000593, NWA-998, Nakhla, and MIL-03346, and the space (CRE) exposure age of NWA998. Additional information is included in the original extended abstract.

  1. Pressure broadening and shift rates for Ar (s-p) transitions observed in an Ar-He discharge

    NASA Astrophysics Data System (ADS)

    Eshel, Ben; Rice, Christopher A.; Perram, Glen P.

    2016-08-01

    The pressure broadening and shift rates have been measured for the 801.699 nm (s5 →p8), 800.836 nm (s4 →p6) and 795.036 nm (s3 →p4) transitions in argon perturbed by 10-200 Torr of helium and argon at a temperature of 440 ± 20 K using a radio-frequency, capacitively coupled discharge. For a 10% Ar in He plasma the pressure broadening and shift rates were measured as 14.18 ± 0.65 and 1.81 ± 0.30 MHz / Torr, 17.85 ± 0.78 and 0.72 ± 0.32 MHz / Torr, and 16.59 ± 1.22 and 2.94 ± 0.48 MHz / Torr for the 801.699 nm, 800.836 nm and 795.036 nm transitions, respectively. The influence of the slightly varying gas temperature on the broadening and shift rates is less than 1%. Stark broadening and shifting by electrons in the discharge are not measurable due to low electron densities and temperatures. Phase-changing collisional cross-sections in the literature decrease with temperature, in good agreement with the Lindholm-Foley T-0.2 trend based on the Lennard-Jones potential. Further investigation of the Ar*-Ar and Ar*-He interaction potentials is necessary to understand the behavior of the cross sections.

  2. 40Ar 39Ar Ages and tectonic setting of ophiolite from the Neyriz area, southeast Zagros Range, Iran

    USGS Publications Warehouse

    Lanphere, M.A.; Pamic, J.

    1983-01-01

    An ophiolite, considered to be an allochthonous fragment of Tethyan oceanic crust and mantle, crops out near Neyriz in the Zagros Range, Iran. 40Ar 39Ar ages ranging from 76.8 ?? 23.8 Ma to 105 ?? 23.3 Ma were measured on hornblende from five samples of plagiogranite and diabase from the ophiolite. The most precise ages are 85.9 ?? 3.8 Ma for a diabase and 83.6 ?? 8.4 Ma for a plagiogranite. The weighted mean age of hornblende from the five samples is 87.5 ?? 7.2 Ma which indicates that the igneous part of the Neyriz ophiolite formed during the early part of the Late Cretaceous. Pargasite from amphibolite below peridotite of the Neyriz ophiolite has a 40Ar 39Ar age of 94.9 ?? 7.6 Ma. The pargasite age agrees within analytical uncertainty with the ages measured on diabase and plagiogranite. Comparable ages have been measured on igneous rocks from the Samail ophiolite of Oman and on amphibolite below peridotite of the Samail ophiolite. ?? 1983.

  3. Geology and 40Ar/39Ar geochronology of the medium- to high-K Tanaga volcanic cluster, western Aleutians

    USGS Publications Warehouse

    Jicha, Brian R.; Coombs, Michelle L.; Calvert, Andrew T.; Singer, Brad S.

    2012-01-01

    We used geologic mapping and geochemical data augmented by 40Ar/39Ar dating to establish an eruptive chronology for the Tanaga volcanic cluster in the western Aleutian arc. The Tanaga volcanic cluster is unique in comparison to other central and western Aleutian volcanoes in that it consists of three closely spaced, active, volumetrically significant edifices (Sajaka, Tanaga, and Takawangha), the eruptive products of which have unusually high K2O contents. Thirty-five new 40Ar/39Ar ages obtained in two different laboratories constrain the duration of Pleistocene–Holocene subaerial volcanism to younger than 295 ka. The eruptive activity has been mostly continuous for the last 150 k.y., unlike most other well-characterized arc volcanoes, which tend to grow in discrete pulses. More than half of the analyzed Tanaga volcanic cluster lavas are basalts that have erupted throughout the lifetime of the cluster, although a considerable amount of basaltic andesite and basaltic trachyandesite has also been produced since 200 ka. Major- and trace-element variations suggest that magmas from Sajaka and Tanaga volcanoes are likely to have crystallized pyroxene and/or amphibole at greater depths than the older Takawangha magmas, which experienced a larger percentage of plagioclase-dominated fractionation at shallower depths. Magma output from Takawangha has declined over the last 86 k.y. At ca. 19 ka, the focus of magma flux shifted to the west beneath Tanaga and Sajaka volcanoes, where hotter, more mafic magma erupted.

  4. Langmuir Probe Measurements of Inductively Coupled CHF3/Ar and Ar/CHF3/O2 Plasmas

    NASA Technical Reports Server (NTRS)

    Sharma, S. P.; Rao, M. V. V. S.; Meyyappan, M.

    2000-01-01

    Plasma parameters, such as, electron number density (ne), electron temperature (Te), y electron energy distribution function (EEDF), mean electron energy (Ee), ion number density (ni), and plasma potential (Vp), have been measured by using Langmuir probe in low-pressure (10-50 mTorr) inductively coupled CHF3/Ar and CHF3/Ar/O2 plasmas generated in the GEC cell. The measurements were made at the center of the plasma, keeping the lower electrode grounded, for various CHF3/Ar and Ar/CHF3/O2 mixtures operating at 10-50 mTorr pressures and two input RF power levels, 200 and 300 W. EEDF data show a strong Druyvesteyn distribution with relatively lower number of low energy electrons as compared to a Maxwell distribution and a large electron population with energies higher than the plasma potential. The results further show that at low CHF3 concentrations (less than 50%) the electron number density remains nearly constant with increase in pressure. At higher CHF3 concentrations, however, it decreases with increase in pressure. Plasma potential and electron temperature increase with decrease in pressure and with increase in CHF3 concentration. An analysis of the above observations and mechanisms will be presented.

  5. 40Ar/ 39Ar ages for the alkaline volcanism and the basement of Gorringe Bank, North Atlantic ocean

    NASA Astrophysics Data System (ADS)

    Féraud, Gilbert; Gastaud, Janine; Auzende, Jean-Marie; Olivet, Jean-Louis; Cornen, Guy

    1982-01-01

    Gorringe Bank is situated on the Europe-Africa plate boundary at the eastern end of the Azores-Gibraltar fracture zone. It has two summits, Gettysburg Bank to the Southwest and Ormonde Bank to the northeast. We applied the 40Ar/ 39Ar stepwise heating method to date six samples of the alkaline volcanic rocks, two gabbros from the Ormonde Bank and a dolerite from the Gettysburg Bank. The results that the alkaline volcanism lasted probably for less than 6 Ma(66-60 Ma). Although the nature of this volcanism precludes any subduction feature during its setting, the alkaline volcanism of Ormonde is probably linked to Upper Cretaceous/Eocene compressive tectonic events. The basement rocks of Gorringe Bank reveal distrubed 40Ar/ 39Ar age spectra. One plagioclase and one biotite from a gabbro give evidence for a thermic event whose age is tentatively estimated at about 75 Ma, and related to a variation in the direction of the relative movement between Europe and Africa. The more probable age given by a plagioclase of another gabbro and by a dolerite (110 Ma) corresponds to tilting northeastward of the Gorringe massif.

  6. Combined oxygen, hydrogen, /sup 40/Ar//sup 39/Ar isotopic evaluation of molybdenite mineralization, east Pioneer Mountains, Montana

    SciTech Connect

    Chesley, J.T.; Snee, L.W.; O'Neil, J.R.

    1985-01-01

    The Pear Lake molybdenite (moly) prospect is in the Eastern Pioneer Wilderness Area, 30 km south of the Cannivan Gulch moly deposit. It lies on a NW-SE trend with other prospects that are contemporaneous. Mineralized veins outcrop sporadically over a 4 square mile area, with a major concentration in the center of the study area. Previous studies have suggested potential moly-mineralization at depth. /sup 40/Ar//sup 39/Ar age-spectra on hornblend (hb) from the granodiorite host rock indicate emplacement at 75.0 +/- 1 Ma, with biotite closure at 69.0 +/- .3 Ma, in the vicinity of Pear Lake. Hydrothermal muscovites from the moly-bearing veins have ages of 68.0 +/- .5 Ma. partial resetting of biotite cooling dates in the vicinity of mineralization are observed, but biotites on the outer portion of the mineralizing system are undisturbed. These relations suggest that mineralization occurred after the host pluton had cooled to below 280/sup 0/C. Quartz-magnetite isotopic temperatures are 380 to 420/sup 0/C for moly-veins. These data suggest that magmatic hydrothermal fluids operated in the upper portion of this molysystem. These isotopic data, combined with geologic mapping, suggest that the Pear Lake moly prospect resulted from a weak, short-lived magmatic hydrothermal event at depth, and is unlikely to contain economic levels of molybdenum. The combined /sup 40/Ar//sup 39/Ar-stable isotope approach should prove useful in evaluating other hydrothermal systems.

  7. 40Ar/39Ar impact ages and time-temperature argon diffusion history of the Bunburra Rockhole anomalous basaltic achondrite

    NASA Astrophysics Data System (ADS)

    Jourdan, Fred; Benedix, Gretchen; Eroglu, Ela.; Bland, Phil. A.; Bouvier, Audrey.

    2014-09-01

    The Bunburra Rockhole meteorite is a brecciated anomalous basaltic achondrite containing coarse-, medium- and fine-grained lithologies. Petrographic observations constrain the limited shock pressure to between ca. 10 GPa and 20 GPa. In this study, we carried out nine 40Ar/39Ar step-heating experiments on distinct single-grain fragments extracted from the coarse and fine lithologies. We obtained six plateau ages and three mini-plateau ages. These ages fall into two internally concordant populations with mean ages of 3640 ± 21 Ma (n = 7; P = 0.53) and 3544 ± 26 Ma (n = 2; P = 0.54), respectively. Based on these results, additional 40Ar/39Ar data of fusion crust fragments, argon diffusion modelling, and petrographic observations, we conclude that the principal components of the Bunburra Rockhole basaltic achondrite are from a melt rock formed at ∼3.64 Ga by a medium to large impact event. The data imply that this impact generated high enough energy to completely melt the basaltic target rock and reset the Ar systematics, but only partially reset the Pb-Pb age. We also conclude that a complete 40Ar∗ resetting of pyroxene and plagioclase at this time could not have been achieved at solid-state conditions. Comparison with a terrestrial analog (Lonar crater) shows that the time-temperature conditions required to melt basaltic target rocks upon impact are relatively easy to achieve. Ar data also suggest that a second medium-size impact event occurred on a neighbouring part of the same target rock at ∼3.54 Ga. Concordant low-temperature step ages of the nine aliquots suggest that, at ∼3.42 Ga, a third smaller impact excavated parts of the ∼3.64 Ga and ∼3.54 Ga melt rocks and brought the fragments together. The lack of significant impact activity after 3.5 Ga, as recorded by the Bunburra Rockhole suggests that (1) either the meteorite was ejected in a small secondary parent body where it resided untouched by large impacts, or (2) it was covered by a porous heat

  8. Mineralogy and Ar-39 - Ar-40 of an old pristine basalt: Thermal history of the HED parent body

    NASA Astrophysics Data System (ADS)

    Takeda, H.; Mori, H.; Bogard, D. D.

    1994-03-01

    Previous investigations of mineral chemistry and Rb-Sr and Sm-Nd ages indicated that clast,84 from eucrite Yamato 75011 had preserved the pristine nature of its initial crystallization during an early stage of the HED parent body. Microscale mineralogy and Ar-39-Ar-40 ages of this clast, however, revealed local disturbance of microtextures and partially reset ages. This evidence suggests that, in addition to initial crystallization and rapid cooling, the Y75011,84 clast experienced shock deformation, reheating of short duration at higher temperature, and brecciation. These characteristics suggest two or more impact events. Fe-rich olivine filling fractures in pyroxene may have been introduced during the accompanying shock fracturing. The inferred Ar-39-Ar-40 degassing ages for Y75011 matrix and clast, 84 are 3.94 +/- 0.04 Ga and 3.98 +/- 0.03 Ga, respectively. The suggested degassing age for a clast from Y790020, believed to be paired with Y75011, is approximately 4.03 Ga, but could be younger. We consider it likely that all three samples experienced a common degassing event 3.95 +/- 0.05 Ga ago, but we cannot rule out two or more events spaced over a approximately 0.1 Ga interval. Higher temperature extractions of the two clast samples show significantly older apparent ages up to approximately 4.5 Ga and suggest that the time/temperature regime of this event was not sufficient to degas Ar totally. Most likely, the K-Ar ages were reset by thermal metamorphism associated with one or more impact events associated with shock fracturing, formation of Fe-rich olivine veins, and/or meteorite brecciation. The pyroxene annealing that commonly occurs in many eucrites is likely to be a much earlier process than the impact-produced textural changes and reset K-Ar ages observed in these meteorites. The existence of mineralogical and chronological evidence for metamorphism in an otherwise pristine eucrite suggests that the HED parent body experienced an extensive degree of

  9. Mineralogy and Ar-39 - Ar-40 of an old pristine basalt: Thermal history of the HED parent body

    NASA Technical Reports Server (NTRS)

    Takeda, Hiroshi; Mori, Hiroshi; Bogard, Donald D.

    1994-01-01

    Previous investigations of mineral chemistry and Rb-Sr and Sm-Nd ages indicated that clast,84 from eucrite Yamato 75011 had preserved the pristine nature of its initial crystallization during an early stage of the HED parent body. Microscale mineralogy and Ar-39-Ar-40 ages of this clast, however, revealed local disturbance of microtextures and partially reset ages. This evidence suggests that, in addition to initial crystallization and rapid cooling, the Y75011,84 clast experienced shock deformation, reheating of short duration at higher temperature, and brecciation. These characteristics suggest two or more impact events. Fe-rich olivine filling fractures in pyroxene may have been introduced during the accompanying shock fracturing. The inferred Ar-39-Ar-40 degassing ages for Y75011 matrix and clast, 84 are 3.94 +/- 0.04 Ga and 3.98 +/- 0.03 Ga, respectively. The suggested degassing age for a clast from Y790020, believed to be paired with Y75011, is approximately 4.03 Ga, but could be younger. We consider it likely that all three samples experienced a common degassing event 3.95 +/- 0.05 Ga ago, but we cannot rule out two or more events spaced over a approximately 0.1 Ga interval. Higher temperature extractions of the two clast samples show significantly older apparent ages up to approximately 4.5 Ga and suggest that the time/temperature regime of this event was not sufficient to degas Ar totally. Most likely, the K-Ar ages were reset by thermal metamorphism associated with one or more impact events associated with shock fracturing, formation of Fe-rich olivine veins, and/or meteorite brecciation. The pyroxene annealing that commonly occurs in many eucrites is likely to be a much earlier process than the impact-produced textural changes and reset K-Ar ages observed in these meteorites. The existence of mineralogical and chronological evidence for metamorphism in an otherwise pristine eucrite suggests that the HED parent body experienced an extensive degree of

  10. Mineralogy, 40Ar/ 39Ar dating and apatite fission track dating of rocks along the Castle Mountain fault, Alaska

    NASA Astrophysics Data System (ADS)

    Parry, W. T.; Bunds, M. P.; Bruhn, R. L.; Hall, C. M.; Murphy, J. M.

    2001-07-01

    The Castle Mountain fault is a 200-km-long, right-lateral fault that forms the northern boundary of the Cook Inlet basin and Matanuska Valley, Alaska. Fault gouge and fault rock at six localities contain the clay minerals illite, smectite, chlorite, and interstratified illite/smectite. At one locality, gouge contains deformed illite/smectite with very little wall rock chlorite contamination. Fine (<0.03 μm), medium (0.03-0.2 μm), and coarse (0.2-2.0 μm) illite/smectite from this site were dated using 40Ar/ 39Ar micro-encapsulation and laser microprobe methods. Total gas ages for the three size fractions are 28.21±0.12, 32.42±0.11 and 36.24±0.08 Ma for fine to coarse sizes respectively. Argon retention ages obtained from 40Ar and 39Ar retained in the three size fractions of illite at room temperature during neutron irradiation are 37.36±0.15, 42.11±0.14 and 47.20±0.10 respectively. Apatite fission track ages were measured in arkose at a locality on the fault 60 km west of the gouge locality. Three samples of arkose were dated: one within 10 m of the fault core, one 170 m from the fault, and one 335 m from the fault. The sample nearest to the fault yielded an age of 29.3±2.8 Ma, but it only had four track lengths at 10-13 μm. Two apatite grains from the intermediate sample yielded a pooled age of 34.3±6.1 Ma. The distant sample (25 grains counted, 101 track lengths) yielded an age of 32.0±2.9 Ma. This sample has a broad distribution of track lengths and a broad distribution of individual grain ages ranging from 14.8±5.1 to 67.8±8.8 Ma. Monte Carlo modeling of the apatite age and track length data is consistent with hydrothermal mineralization at 37-39 Ma followed by rapid uplift and cooling after 10 Ma. The 40Ar/ 39Ar total gas ages (K-Ar) are minimum ages, and the argon retention ages are maximum ages. The thermal model derived from the fission track data, and the argon retention age for the finest illite fraction of ˜37 Ma date a hydrothermal

  11. Crater Retention Ages from (4) Vesta Matching Independent Ar-Ar Ages of HED Meteorites

    NASA Astrophysics Data System (ADS)

    Schmedemann, Nico; Kneissl, Thomas; Ivanov, Boris A.; Michael, Gregory G.; Neukum, Gerhard; Nathues, Andreas; Sierks, Holger; Wagner, Roland; Krohn, Katrin; Le Corre, Lucille; Reddy, Vishnu; Ruesch, Ottaviano; Hiesinger, Harald; Jaumann, Ralf; Raymond, Carol A.; Russell, Christopher T.

    2013-04-01

    .054/-0.087) Ga and 3.63 (+0.058/-0.096) Ga. We also find seismic (miniscule ejecta blanket from Rheasilvia) resurfacing events in the time frame of ~3.56 to ~3.59 Ga at several areas in the northern hemisphere, indicative for a major seismic activity probably connected to the Rheasilvia formation. An antipodal activity is also suggested by hydrocode modeling [9]. By summation of age probability curves of measurements we link to the Rheasilvia formation, we find 3.58 (+0.07/-0.12) Ga. Using a similar attempt we find 3.75 (+0.05/-0.21) Ga for the Veneneia formation. Both crater retention ages correspond within the error bars with prominent peaks of independent Ar-Ar ages of Vesta related HED meteorites [10]. Acknowledgement: This work has been supported by the German Space Agency (DLR) on behalf of the Federal Ministry of Economics and Technology, grants 50OW1101(NS,TK), 50QM1001 (GM) and 50OW1102 (OR,HH). References: [1] Russell et al. (2007): Advances in Space Research 40(2): pp193-201, 2007. [2] Neukum and Ivanov: In: Gehrels T (ed) "Hazards due to comets and asteroids". University of Arizona Press, Tucson, 359-416, 1994. [3] O'Brien and Greenberg (2005): Icarus 178(1): 179-212. [4] Nesvorny et al. (2009): Icarus 200(2): 698-701. [5] Ivanov (2001): Chronology and Evolution of Mars 96, 87-104, 2001. [6] Schmedemann et al. (2012): 43.LPSC, The Woodlands, #1659. [7] Morbidelli et al. (2003): Icarus 162, 328-336. [8] Marchi et al. (2012): Science 336, 690. [9] Bowling et al. (2012): 75th Annual Meeting of the Meteoritical Society, 2012, Cairns, Australia. Meteoritics and Planetary Science Supplement, id.5256. [10] Bogard, D. D. (2011): Chemie der Erde - Geochemistry, vol. 71, issue 3: 207-226.

  12. AR-39Ar-40 dating of basalts and rock breccias from Apollo 17 and the malvern achondrite

    NASA Technical Reports Server (NTRS)

    Kirsten, T.; Horn, P.

    1977-01-01

    The principles and the potential of the Ar-39/Ar-40 dating technique are illustrated by means of results obtained for 12 Apollo 17 rocks. Emphasis is given to methodical problems and the geological interpretation of lunar rock ages. Often it is ambigious to associate a given lunar breccia with a certain formation, or a formation with a basin. In addition, large-scale events on the Moon have not necessarily reset radiometric clocks completely. One rock fragment has a well-defined plateau age of 4.28 b.y., but the ages of two Apollo 17 breccias define an upper limit for the formation age of the Serenitatis basin at 4.05 b.y. Ages derived from five mare basalts indicate cessation of mare volcanism at Taurus-Littrow approximately 3.78 b.y. ago. Ca/Ar-37 exposure ages show that Camelot Crater was formed by an impact approximately 95 m.y. ago. After a short summary of the lunar timetable as it stands at the end of the Apollo program, we report about Ar-39/Ar-40 and rare gas studies on the Malvern meteorite. This achondrite resembles lunar highland breccias in texture as well as in rare-gas patterns. It was strongly annealed at some time between 3.4 and 3.8 b.y. ago. The results indicate that very similar processes have occurred on the Moon and on achondritic parent bodies at comparable times, leading to impact breccias with strikingly similar features, including the retention of rare-gas isotopes from various sources.

  13. Geology and preliminary [sup 40]Ar/[sup 39]Ar geochronology of the Sliderock Mountain volcano, south-central Montana

    SciTech Connect

    Du Bray, E.A.; Harlan, S.S. )

    1993-04-01

    The Sliderock Mountain Volcano is a deeply eroded, Upper Cretaceous basaltic andesite stratovolcano complex located along the northeastern margin of the Laramide Beartooth uplift of south-central Montana. Historically, these rocks have been included in the Livingston Group and correlated with Upper Cretaceous, dominantly epiclastic sedimentary rocks of the Livingston Group in the Crazy Mountains Basin. Recent geologic mapping has identified several map units including: basaltic andesite of Derby Ridge (lava flows, and minor interbedded pyroclastic flows including welded tuff, block and ash flows, and lahars); volcaniclastic sedimentary rocks; lahar deposits; dioritic plutons and sills (including the diorite of Sliderock Mountain); basaltic andesite lavas; and basaltic trachyandesite dikes. Stratigraphic relations indicate that initial volcanic activity was dominated by eruption of the basaltic andesite of Derby Ridge. Cross-cutting relations indicate that dioritic plutons and sills are younger than the basaltic andesite of Derby Ridge and the lahars but age relations with the second set of basaltic andesite lavas are indeterminate. The volcanic and dike rocks of the stratovolcano are cpx-plag rocks, characterized by limited compositional variation, whereas intrusive rocks are hbl-plag rocks whose compositions are principally that of diorite, but range to granite. [sup 40]Ar/[sup 39]Ar isotopic analysis of hornblende from the Lodgepole intrusion, a hypabyssal intrusion that may constitute part of the volcano's solidified magma chamber, gives an age of 76.2 [+-] 0.3 Ma (1[sigma]), significantly younger than a previously reported K-Ar biotite age of 82 Ma. [sup 40]Ar/[sup 39]Ar analyses of sericite from weakly mineralized Au-bearing quartz veins hosted by the diorite of Sliderock Mountain give slightly younger isochron ages of 73--74 Ma indicating that gold mineralization is probably associated with the late stages of cooling of the Sliderock Mountain magma system.

  14. 40Ar/39Ar geochronology, paleomagnetism, and evolution of the Boring volcanic field, Oregon and Washington, USA

    USGS Publications Warehouse

    Fleck, Robert J.; Hagstrum, Jonathan T.; Calvert, Andrew T.; Evarts, Russell C.; Conrey, Richard M.

    2014-01-01

    The 40Ar/39Ar investigations of a large suite of fine-grained basaltic rocks of the Boring volcanic field (BVF), Oregon and Washington (USA), yielded two primary results. (1) Using age control from paleomagnetic polarity, stratigraphy, and available plateau ages, 40Ar/39Ar recoil model ages are defined that provide reliable age results in the absence of an age plateau, even in cases of significant Ar redistribution. (2) Grouping of eruptive ages either by period of activity or by composition defines a broadly northward progression of BVF volcanism during latest Pliocene and Pleistocene time that reflects rates consistent with regional plate movements. Based on the frequency distribution of measured ages, periods of greatest volcanic activity within the BVF occurred 2.7–2.2 Ma, 1.7–0.5 Ma, and 350–50 ka. Grouped by eruptive episode, geographic distributions of samples define a series of northeast-southwest–trending strips whose centers migrate from south-southeast to north-northwest at an average rate of 9.3 ± 1.6 mm/yr. Volcanic activity in the western part of the BVF migrated more rapidly than that to the east, causing trends of eruptive episodes to progress in an irregular, clockwise sense. The K2O and CaO values of dated samples exhibit well-defined temporal trends, decreasing and increasing, respectively, with age of eruption. Divided into two groups by K2O, the centers of these two distributions define a northward migration rate similar to that determined from eruptive age groups. This age and compositional migration rate of Boring volcanism is similar to the clockwise rotation rate of the Oregon Coast Range with respect to North America, and might reflect localized extension on the trailing edge of that rotating crustal block.

  15. sup 40 Ar- sup 39 Ar and K-Ar dating of K-rich rocks from the Roccamonfina volcano, Roman Comagmatic Region, Italy

    SciTech Connect

    Di Brozolo, F.R.; Di Girolamo, P.; Turi, B.; Oddone, M. )

    1988-06-01

    Roccamonfina is the northernmost Volcano of the Campanian area of the K-rich Roman comagmatic Region of Italy. It erupted a huge amount of pyroclastics and lavas belonging to both the Leucite-Basanite and Leucitite Series (LBLS) and the Shoshonite Series (SS), spread over an area of about 300 km{sup 2}. The above series correspond to the High-K Series (HKS) and Low-K Series (LKS) of Appleton (1971), respectively. {sup 40}Ar-{sup 39}Ar and K-Ar dating of samples from both series gave ages ranging from 0.656 to 0.096 Ma for the SS and from 1.03( ) to 0.053 Ma for the LBLS. These results indicate that the products of the two series were outpoured together at least between 0.7 and 0.1 Ma age, i.e. during both the so-called pre-caldera phase and the post-caldera phase of activity. The latest products of the volcanism at Roccamonfina were erupted just before the deposition of the Grey Campanian Ignimbrite, which erupted from vents located about 50 km to the south in the Phlegrean Fields near Naples and has an age of about 33,000 years. Taking into account all the available all the available radiometric data the authors conclude that Roccamonfina was active between 1.5 and 0.05 Ma ago, in excellent agreement with the stratigraphic evidence. In this same time span is concentrated the activity of all the centers of the Roman Region north of Naples.

  16. The Mono Lake excursion recorded in phonolitic lavas from Tenerife (Canary Islands): Paleomagnetic analyses and coupled K/Ar and Ar/Ar dating

    NASA Astrophysics Data System (ADS)

    Kissel, C.; Guillou, H.; Laj, C.; Carracedo, J. C.; Nomade, S.; Perez-Torrado, F.; Wandres, C.

    2011-08-01

    We present a coupled paleomagnetic/dating investigation conducted on three different lava flows from the island of Tenerife (Canary Islands; Spain) erupted during the Mono Lake excursion (MLE). Paleomagnetic analyses consist in zero field demagnetizations (AF and/or thermal) and of Thellier and Thellier experiments using the PICRIT-03 set of criteria to select reliable intensity determinations. One of the flows is characterized by a direction largely deviated from the one expected from an axial geocentric dipole (GAD) field. Its paleointensity value is very low (7.8 μT). The two other sites are characterized by inclinations slightly shallower than the GAD value and by low intensity values (about 12 and 21 μT; present value: 38 μT). The three K/Ar ages combined with two 40Ar/ 39Ar ages range from 32.0 to 33.2 ka and they are not statistically distinguishable from one another. It therefore appears that these lavas have recorded the MLE (the only excursion in this time interval) confirming its brief duration (shorter than the minimum age uncertainties available). The mean age is younger but, within the uncertainties, consistent with the age of the 10Be peak and of the marine intensity low when reported in the most recent ice age model. These new results are the first ones with radiometric dating produced from the northern hemisphere. Combined with existing cosmogenic, marine and volcanic paleomagnetic data, these results are discussed in terms of dating, and geometry of the earth magnetic field during the excursion.

  17. Ar Atmosphere: Implications for Structure and Composition of Mercury's Crust

    NASA Technical Reports Server (NTRS)

    Killen, R. M.; Morgan, T. H.

    2001-01-01

    We examine the possibilities of sustaining an argon atmosphere by diffusion from the upper 10 km of crust, and alternatively by effusion from a molten or previously molten area at great depth . Ar-40 in the atmospheres of the planets is a measure of potassium abundance in the interiors since Ar-40 is a product of radiogenic decay of K-40 by electron capture with the subsequent emission of a 1.46 eV gamma-ray. Although the Ar-40 in the earth's atmosphere is expected to have accumulated since the late bombardment, Ar-40 in surface-bounded exospheres is eroded quickly by photoionization and electron impact ionization. Thus, the argon content in the exospheres of the Moon, Mercury and probably Europa is representative of current effusion rather than accumulation over the lifetime of the body. Argon content will be a function of K content, temperature, grain size distribution, connected pore volume and possible seismic activity. Although Mercury and the Moon differ in many details, we can train the solutions to diffusion equations to predict the average lunar atmosphere. Then these parameters can be varied for Hermean conditions. Assuming a lunar crustal potassium abundance of 300 ppm, the observed argon atmosphere requires equilibrium between the argon production in the upper 9 Km of the moon (1.135 x 10(exp -3) cm(exp -3) s(exp -1)) and its loss. Hodges et al. conclude that this loss rate and the observed time variability requires argon release through seismic activity, tapping a deep argon source. An important observation is that the extreme surface of the Moon is enhanced in argon rather than depleted, as one would expect from outgassing of radiogenic argon. Manka and Michel concluded that ion implantation explains the surface enhancement of Ar-40. About half of the argon ions produced in the lunar atmosphere would return to the surface, where they would become embedded in the rocks. Similarly, at Mercury we expect the surface rocks to be enhanced in Ar-40 wherever

  18. Mechanistic Support for Combined MET and AR Blockade in Castration-Resistant Prostate Cancer12

    PubMed Central

    Qiao, Yuanyuan; Feng, Felix Y.; Wang, Yugang; Cao, Xuhong; Han, Sumin; Wilder-Romans, Kari; Navone, Nora M.; Logothetis, Christopher; Taichman, Russell S.; Keller, Evan T.; Palapattu, Ganesh S.; Alva, Ajjai S.; Smith, David C.; Tomlins, Scott A.; Chinnaiyan, Arul M.; Morgan, Todd M.

    2016-01-01

    A recent phase III trial of the MET kinase inhibitor cabozantinib in men with castration-resistant prostate cancer (CRPC) failed to meet its primary survival end point; however, most men with CRPC have intact androgen receptor (AR) signaling. As previous work supports negative regulation of MET by AR signaling, we hypothesized that intact AR signaling may have limited the efficacy of cabozantinib in some of these patients. To assess the role of AR signaling on MET inhibition, we first performed an in silico analysis of human CRPC tissue samples stratified by AR signaling status (+ or −), which identified MET expression as markedly increased in AR− samples. In vitro, AR signaling inhibition in AR+ CRPC models increased MET expression and resulted in susceptibility to ligand (HGF) activation. Likewise, MET inhibition was only effective in blocking cancer phenotypes in cells with MET overexpression. Using multiple AR+ CRPC in vitro and in vivo models, we showed that combined cabozantinib and enzalutamide (AR antagonist) treatment was more efficacious than either inhibitor alone. These data provide a compelling rationale to combine AR and MET inhibition in CRPC and may explain the negative results of the phase III cabozantinib study in CRPC. Similarly, the expression of MET in AR− disease, whether due to AR inhibition or loss of AR signaling, suggests potential utility for MET inhibition in select patients with AR therapy resistance and in AR− prostate cancer. PMID:26806347

  19. The 1.4 Å crystal structure of the ArsD arsenic metallochaperone provides insights into its interaction with the ArsA ATPase†

    PubMed Central

    Ye, Jun; Ajees, A. Abdul; Yang, Jianbo; Rosen, Barry P.

    2010-01-01

    Arsenic is a carcinogen that tops the Superfund list of hazardous chemicals. Bacterial resistance to arsenic is facilitated by ArsD, which delivers As(III) to the ArsA ATPase, the catalytic subunit of the ArsAB pump. Here we report the structure of the arsenic metallochaperone ArsD at 1.4 Å, and a model for its binding of metalloid. There are two ArsD molecules in the asymmetric unit. The overall structure of the ArsD monomer has a thioredoxin fold, with a core of four β-strands flanked by four α-helices. Based on data from structural homologues, ArsD was modeled with and without bound As(III). ArsD binds one arsenic per monomer coordinated with the three sulfur atoms of Cys12, Cys13 and Cys18. Using this structural model, an algorithm was used to dock ArsD and ArsA. The resulting docking model provides testable predictions of the contact points of the two proteins and forms the basis for future experiments. PMID:20507177

  20. The 1.4 Å Crystal Structure of the ArsD Arsenic Metallochaperone Provides Insights into Its Interaction with the ArsA ATPase

    SciTech Connect

    Ye, Jun; Ajees, A. Abdul; Yang, Jianbo; Rosen, Barry P.

    2010-12-07

    Arsenic is a carcinogen that tops the Superfund list of hazardous chemicals. Bacterial resistance to arsenic is facilitated by ArsD, which delivers As(III) to the ArsA ATPase, the catalytic subunit of the ArsAB pump. Here we report the structure of the arsenic metallochaperone ArsD at 1.4 {angstrom} and a model for its binding of metalloid. There are two ArsD molecules in the asymmetric unit. The overall structure of the ArsD monomer has a thioredoxin fold, with a core of four {beta}-strands flanked by four {alpha}-helices. Based on data from structural homologues, ArsD was modeled with and without bound As(III). ArsD binds one arsenic per monomer coordinated with the three sulfur atoms of Cys12, Cys13, and Cys18. Using this structural model, an algorithm was used to dock ArsD and ArsA. The resulting docking model provides testable predictions of the contact points of the two proteins and forms the basis for future experiments.

  1. Dielectric behavior of Ar{sup +} implanted CR-39 polymer

    SciTech Connect

    Shekhawat, Nidhi; Sharma, Annu; Aggarwal, Sanjeev; Deshpande, S. K.; Nair, K. G. M.

    2012-06-05

    The frequency dependent dielectric response of Ar{sup +} implanted CR-39 specimens has been studied. Samples were implanted with 130 keV Ar{sup +} ions to various doses ranging from 5x10{sup 14} to 1x10{sup 16} cm{sup -2}. The frequency response of dielectric constant (e) and dielectric loss has been studied both in the pristine and argon ion implanted samples of CR-39 polymer in the frequency range 10{sup 4} to 10{sup 8} Hz. Structural changes produced in CR-39 specimens due to implantation have been studied using Attenuated total reflectance (ATR) Fourier transform infrared spectroscopic technique. Results of dielectric analysis indicate the lowering in dielectric constant ({epsilon}') and similar behavior of dielectric loss with increase in ion fluence. An attempt has been made to correlate these changes produced in the dielectric properties of implanted specimens with the structural changes produced due to implantation.

  2. Spectral analysis of walking improvement utilizing AR modeling.

    PubMed

    Tsuruoka, Masako; Tsuruoka, Yuriko

    2008-01-01

    This study analyzes the walking improvement based on 1/f fluctuations and impulse responses utilizing Auto-Regressive (AR) modeling. Once subjects were aware of the correct posture, the fluctuation of subject's both sides of the hip while walking was improved more rhythmic. The analysis of impulse response utilizing AR modeling provided clear results for the evaluation of improvement to walking stability. After the subjects understood their own walking condition, based on 1/f fluctuation, and had received suitable rehabilitation and shoes, their walking stability improved satisfactorily. This study provides a useful method of medical evaluation in rehabilitation and physical fitness, and a means for subjects to maintain a state of well being. PMID:19163860

  3. ArF photoresist system using alicyclic polymer

    NASA Astrophysics Data System (ADS)

    Park, Joo Hyeon; Kim, Seong-Ju; Park, Sun-Yi; Lee, Hosull; Jung, Jae Chang; Bok, Cheol-Kyu; Baik, Ki-Ho

    1997-07-01

    We have developed a chemically amplified photoresist for use in ArF lithography based on alicyclic polymer. 3- Bicyclo(2,2,1)hept-2-yl-3-(2-methyl allyoxy)-propionic acid tert-butyl ester (BHPE) was prepared as a new kind of protected acid-labile monomer. Terpolymer, poly(BHPE-NBO-MAL), was prepared with BHPE, 5-norbornen-2-ol (NBO), and maleic anhydride (MAL) monomers by radical polymerization. Photoresist of poly(BHPE-NBO-MAL) displayed good adhesion, dry-etch resistance, and development. As a result, we obtained 0.16 micrometer line-and-space positive patterns with 2.38 wt% TMAH aqueous solution using an ArF exposure system.

  4. Attosecond pulses generated by the lighthouse effect in Ar gas

    NASA Astrophysics Data System (ADS)

    Tosa, Valer; Lee, Ji Su; Kim, Hyung Taek; Nam, Chang Hee

    2015-05-01

    We numerically investigate harmonic generation in Ar gas under high ionization conditions and demonstrate that a lighthouse effect is present. We examine the structure of the driving field during propagation in temporal, spectral, and spatial domains, and conclude that the complete depletion of neutral Ar on axis gives rise to additional wavelets at off-axis regions. We show that these wavelets propagate with increasing divergence as the radial distances from the axis increase, generating the rotation of the wave front, thus fulfilling a necessary condition for the lighthouse effect. We obtain attosecond bursts of light emitted with different divergences in successive optical half-cycles so that in the far field these bursts arrive at different distances from the beam axis.

  5. Elongated shape isomers in the {sup 36}Ar nucleus

    SciTech Connect

    Cseh, Jozsef; Darai, Judit; Sciani, Wagner; Otani, Yul; Lepine-Szily, Alinka; Benjamim, Elisangela A.; Chamon, Luiz Carlos; Filho, Rubens Lichtenthaeler

    2009-09-15

    A recent analysis of the {sup 12}C+{sup 24}Mg scattering [W. Sciani et al., Phys. Rev. C 80, 034319 (2009)] suggests the existence of a hyperdeformed band in the {sup 36}Ar nucleus, completely in line with the predictions of {alpha}[W. D. M. Rae and A. C. Merchant, Phys. Lett. B279, 207 (1992)] and binary cluster calculations [J. Cseh et al., Phys. Rev. C 70, 034311 (2004)]. Here we review the structural understanding of the superdeformed and the hyperdeformed states of {sup 36}Ar and present new results on the shape isomers as well. Special attention is paid to the clusterization of these states, which indicates the appropriate reaction channels for their formation.

  6. Infrared spectrum and predissociation dynamics of H2O+ -Ar.

    PubMed

    Dopfer, O; Engel, V

    2004-12-22

    The infrared (IR) spectrum and vibrational predissociation of the proton-bound H(2)O(+)-Ar ionic complex are investigated within an ab initio and quantum dynamical study. For this purpose, a two-dimensional potential energy surface (2D PES) is determined as a function of the HO-H and OH-Ar coordinates. This PES is then employed in a wave-packet calculation to determine spectral properties of the system and to calculate the IR absorption spectrum. The vibrational energy levels and relative IR intensities agree well with the experimental spectrum reported earlier. On the other hand, the predissociation lifetimes in the nanosecond regime derived from the 2D PES are in disagreement with the experimental observations, indicating the importance of the neglected degrees of freedom for a correct description of the dynamics of the complex. PMID:15606253

  7. Precision Fast Ion Beam Laser Spectroscopy of Ar{sup +}

    SciTech Connect

    Lioubimov, V.; Kolomenskii, A. A.; Schuessler, H. A.; Wada, M.; Nakamura, T.; Schury, P.; Ogawa, M.; Takamine, A.; Yamazaki, Y.; Iimura, H.; Okada, K.

    2009-03-17

    Absolute measurements of spectral lines of Ar{sup +} ions using collinear and anticollinear geometries were performed. To provide a precise reference for the laser wavelength, iodine saturation spectroscopy was applied. The precision of this reference is effected by observing the beat node between the spectroscopy laser and the corresponding mode of a femtosecond laser frequency comb. Laser-induced fluorescence allowed to perform precision frequency measurements of an Ar{sup +} transition in collinear and anticollinear geometries simultaneously; then an exact relativistic formula for the absolute transition frequency V{sub 0} = {radical}(V{sub c}V{sub a}) was used. In this geometry the influence of ion source instabilities due to pressure and anode voltage fluctuations was minimized. The result is v{sub 0} = 485,573,619.7(3) MHz, which corresponds to {delta}v/v = 6*10{sup -10}. This represents an improvement of two orders of magnitude over the previous NIST published value.

  8. Precision Fast Ion Beam Laser Spectroscopy of Ar+

    NASA Astrophysics Data System (ADS)

    Lioubimov, V.; Wada, M.; Ogawa, M.; Takamine, A.; Nakamura, T.; Schury, P.; Iimura, H.; Okada, K.; Kolomenskii, A. A.; Schuessler, H. A.; Yamazaki, Y.

    2009-03-01

    Absolute measurements of spectral lines of Ar+ ions using collinear and anticollinear geometries were performed. To provide a precise reference for the laser wavelength, iodine saturation spectroscopy was applied. The precision of this reference is effected by observing the beat node between the spectroscopy laser and the corresponding mode of a femtosecond laser frequency comb. Laser-induced fluorescence allowed to perform precision frequency measurements of an Ar+ transition in collinear and anticollinear geometries simultaneously; then an exact relativistic formula for the absolute transition frequency V0= √VcVa was used. In this geometry the influence of ion source instabilities due to pressure and anode voltage fluctuations was minimized. The result is v0 = 485,573,619.7(3) MHz, which corresponds to Δv/v = 6*10-10. This represents an improvement of two orders of magnitude over the previous NIST published value.

  9. Testing of a prototype of calibration facility for noble gas monitoring using 41Ar.

    PubMed

    Saibathulham, Holnisar; Wurdiyanto, Gatot; Marsum, Pujadi

    2012-09-01

    A prototype of a calibration facility for noble gas monitoring using (41)Ar in the PTKMR-BATAN has been tested. The facility was designed in such a way that the standard source of gas can be reused. The radioactive (41)Ar source was obtained by thermal neutron reaction of (40)Ar(n, γ)(41)Ar using a thermal neutron flux of 4.8×10(13) neutrons per cm(2) per second in two minutes on the multipurpose G.A. Siwabessy Reactor (Batan, Serpong, Indonesia). Gamma spectrometry was used to measure the radioactivity and purity of (41)Ar. The spectrum of the (41)Ar observed yields an energy of 1294 keV because of the highest intensity (99.2%). The activity of (41)Ar was 2821 kBq and 4% of the expanded uncertainty. The time required for (41)Ar to reach homogeneity was 7 min, and the effectiveness of resuse was 53%. PMID:22516716

  10. Constraining the alteration history of a Late Cretaceous Patagonian volcaniclastic bentonite-ash-mudstone sequence using K-Ar and 40Ar/39Ar isotopes

    NASA Astrophysics Data System (ADS)

    Warr, L. N.; Hofmann, H.; van der Pluijm, B. A.

    2016-03-01

    Smectite is typically considered unsuitable for radiometric dating, as argon (40Ar) produced from decay of exchangeable potassium (40K) located in the interlayer sites can be lost during fluid-rock interaction and/or during wet sample preparation in the laboratory. However, age analysis of Late Cretaceous Argentinian bentonites and associated volcaniclastic rocks from Lago Pellegrini, Northern Patagonia, indicates that, in the case of these very low-permeability rocks, the radioactive 40Ar was retained and thus can provide information on smectite age and the timing of rock alteration. This study presents isotopic results that indicate the ash-to-bentonite conversion and alteration of the overlying tuffaceous mudstones in Northern Patagonia was complete ~13-17 my after middle Campanian sedimentation when the system isotopically closed. The general absence of illite in these smectite-rich lithologies reflects the low activity of K and the low temperature (<60 °C) of the formation waters that altered the parent ash.

  11. Communication: overtone (2NH) spectroscopy of NH3-Ar.

    PubMed

    Didriche, K; Földes, T; Vanfleteren, T; Herman, M

    2013-05-14

    The Π (1(1)) ← Σ (0(0)) 2NH (ν1+ν3) band of the NH3-Ar van der Waals complex formed in a supersonic jet expansion, with origin at 6628 cm(-1) was recorded at high-resolution using cavity ring down spectroscopy. The analysis leads to upper state rotational constants and J-dependent predissociation lifetimes estimated from linewidth analysis, with a mean value about 0.6 ns. PMID:23676017

  12. Steering magnet power supply control system for the TRISTAN AR

    SciTech Connect

    Kubo, T.; Endo, K.; Fukuma, H.; Kabe, A.; Ozaki, T.

    1985-10-01

    The closed orbit distortion of TRISTAN Accumulation Ring (AR) is corrected by the steering magnets (correction dipole magnets). These magnets are excited by the bipolar power supplies with the rated power of about 1 KVA. The power supplies are controlled remotely through the serial camac dataway. The camac modules which include the microprocessor are developed for this system and these modules send out the reference current patterns to the individual power supply.

  13. (53110) 1999 AR7: A New NEA Binary Discovery

    NASA Astrophysics Data System (ADS)

    Warner, Brian D.

    2016-04-01

    Analysis of CCD photometric observations of the near- Earth asteroid (53110) 1999 AR7 made in 2015 December show it to be a binary system with a primary period of 2.7375 ± 0.0005 h and orbital period of 31.31 ± 0.02 h. The depth of the secondary mutual event indicates a minimum effective diameter ratio (Ds/Dp) of 0.41 ± 0.02.

  14. 40Ar/39Ar thermochronologic constraints on the tectonothermal evolution of the Northern East Humboldt range metamorphic core complex, Nevada

    USGS Publications Warehouse

    McGrew, A.J.; Snee, L.W.

    1994-01-01

    The northern East Humboldt Range (NEHR) of northeastern Nevada exposes a suite of complexly deformed migmatitic, upper amphibolite-facies rocks in the footwall of the Ruby Mountains-East Humboldt Range (RM-EHR) detachment fault. New 40Ar/39Ar data on hornblende, muscovite, biotite, and potassium feldspar help constrain the kinematic and thermal evolution of this terrain during Tertiary extensional exhumation. Hornblende samples from relatively high structural levels yield discordant age spectra that suggest initial cooling during early Tertiary time (63-49 Ma). When coupled with petrological constraints indicating a strongly decompressional P-T-t path above 550??C, the hornblende data suggest that exhumation of the RM-EHR may have initiated in early Tertiary time, approximately coincident with the initial phases of unroofing in the Wood Hills immediately to the east and with the end of thrusting in the late Mesozoic to early Tertiary Sevier orogenic belt of eastern Nevada and western Utah. This temporal coincidence suggests that gravitational collapse of tectonically thickened crust in the internal zone of the Sevier belt could have driven the initial phases of unroofing. Thermal history during the final stage of exhumation of the NEHR is constrained by discordant hornblende cooling ages of 36-29 Ma from deep structural levels and biotite, muscovite, and potassium feldspar cooling ages of 27-21 Ma from a range of structural levels. Comparison of muscovite, biotite, and potassium feldspar cooling ages with previously published fission-track cooling ages implies very rapid cooling rates at temperatures below the closure temperature for muscovite (270??-350??C), but time gaps of > 7 m.y. between hornblende and mica cooling ages suggest that cooling at higher temperatures was more gradual. In addition, comparison of 40Ar 39Ar mica cooling ages with previously published fission-track apatite cooling ages suggests pronounced thermal gradients between the NEHR and

  15. Direct dating of folding events by 40Ar/39Ar analysis of synkinematic muscovite from flexural-slip planes

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Zwingmann, Horst; Zhou, Liyun; Lo, Ching-hua; Viola, Giulio; Hao, Jinhua

    2016-02-01

    Timing of folding is usually dated indirectly, with limited isotopic dating studies reported in the literature. The present study investigated the timing of intracontinental, multi-stage folding in Upper Proterozoic sandstone, limestone, and marble near Beijing, North China, and adjacent regions. Detailed field investigations with microstructural, backscattered electron (BSE) images and electron microprobe analyses indicate that authigenic muscovite and sericite crystallized parallel to stretching lineations/striations or along thin flexural-slip surfaces, both developed during the complex deformation history of the study area, involving repeated compressional, extensional and strike-slip episodes. Muscovite/sericite separates from interlayer-slip surfaces along the limbs and from dilatant sites in the hinges of folded sandstones yield muscovite 40Ar/39Ar plateau ages of ∼158-159 Ma, whereas those from folded marble and limestone samples yield ages of 156 ± 1 Ma. Muscovite from thin flexural-slip planes on fold limbs and hinges yields ages within analytical error of ∼155-165 Ma. Further muscovite samples collected from extensionally folded limestone and strike-slip drag folds yield younger ages of 128-125 Ma with well-defined plateaus. To assess the potential influence of the detrital mica component of the host rock on the age data, two additional muscovite samples were investigated, one from a folded upper Proterozoic-Cambrian sandstone outside the Western Hills of Beijing and one from a folded sandstone sampled 20 cm from folding-related slip planes. Muscovite separates from these samples yield significantly older ages of 575 ± 2 Ma and 587 ± 2 Ma, suggesting that the timing of folding can be directly determined using the 40Ar/39Ar method. This approach enables the identification and dating of distinct deformation events that occur during multi-stage regional folding. 40Ar/39Ar dating can be used to constrain the timing of muscovite and sericite growth at

  16. 40Ar/ 39Ar thermochronologic constraints on the tectonothermal evolution of the Northern East Humboldt range metamorphic core complex, Nevada

    NASA Astrophysics Data System (ADS)

    McGrew, Allen J.; Snee, Lawrence W.

    1994-11-01

    The northern East Humboldt Range (NEHR) of northeastern Nevada exposes a suite of complexly deformed migmatitic, upper amphibolite-facies rocks in the footwall of the Ruby Mountains-East Humboldt Range (RM-EHR) detachment fault. New 40Ar/ 39Ar data on hornblende, muscovite, biotite, and potassium feldspar help constrain the kinematic and thermal evolution of this terrain during Tertiary extensional exhumation. Hornblende samples from relatively high structural levels yield discordant age spectra that suggest initial cooling during early Tertiary time (63-49 Ma). When coupled with petrological constraints indicating a strongly decompressional P-T-t path above 550°C, the hornblende data suggest that exhumation of the RM-EHR may have initiated in early Tertiary time, approximately coincident with the initial phases of unroofing in the Wood Hills immediately to the east and with the end of thrusting in the late Mesozoic to early Tertiary Sevier orogenic belt of eastern Nevada and western Utah. This temporal coincidence suggests that gravitational collapse of tectonically thickened crust in the internal zone of the Sevier belt could have driven the initial phases of unroofing. Thermal history during the final stage of exhumation of the NEHR is constrained by discordant hornblende cooling ages of 36-29 Ma from deep structural levels and biotite, muscovite, and potassium feldspar cooling ages of 27-21 Ma from a range of structural levels. Comparison of muscovite, biotite, and potassium feldspar cooling ages with previously published fission-track cooling ages implies very rapid cooling rates at temperatures below the closure temperature for muscovite (270°-350°C), but time gaps of > 7 m.y. between hornblende and mica cooling ages suggest that cooling at higher temperatures was more gradual. In addition, comparison of {40Ar }/{39Ar } mica cooling ages with previously published fission-track apatite cooling ages suggests pronounced thermal gradients between the NEHR and

  17. High Precision 40Ar/39Ar Geochronology of Servilleta Basalts of the Rio Grande Gorge, New Mexico

    NASA Astrophysics Data System (ADS)

    Cosca, M. A.; Thompson, R. A.; Turner, K. J.

    2014-12-01

    New geologic mapping and high-precision 40Ar/39Ar geochronology within the Taos Plateau in northern New Mexico indicate a period of vigorous volcanic activity between ~5.5 and ~1 Ma. Over 50 visible volcanic centers formed during this time together with an unresolved number of vents, fissures, and volcanic centers buried by intercalated volcanic rock and sedimentary basin fill. Defining the volcanic stratigraphy is essential for models of regional groundwater flow and for understanding the geologic evolution of the Pliocene to Recent Rio Grande rift. A spectacular stratigraphic section of volcanic rock related to Rio Grande rifting is visible from the High Bridge, just a few miles outside of Taos, NM, where a 240 m canyon is incised through the basal, middle, and upper Servilleta basalt flow packages (Dungan et al., 1984). Fresh basalt from a vertical transect of the canyon near the High Bridge were analyzed by 40Ar/39Ar methods on ~3 mm3 rock fragments using an ARGUS VI mass spectrometer and the resulting 40Ar/39Ar ages define a precise emplacement chronology of the entire stratigraphic section. The basal flow package records ages of 4.78 ± 0.03 Ma (relative to FCT sanidine = 28.204 Ma; all errors 2 sigma) at river level, 4.77 ± 0.03 Ma at mid flow, and 4.50 ± 0.04 Ma at the top of the flow. The middle flow package records ages of 4.11 ± 0.03 Ma at the base of the flow, 4.08 ± 0.04 Ma mid flow, and 4.02 ± 0.06 Ma at the top of the flow. The upper basalt package records ages of 3.69 ± 0.06 Ma at the base of the flow and 3.59 ± 0.08 Ma at the top of the flow. These data support rapid effusion of voluminous lava flows on time scales of 100-200 ka. Two reddish paleosols separating the Servilleta packages each developed during a 400 ka period of volcanic quiescence. First order calculations using exposed lava thicknesses in the gorge and areal exposures suggest each flow package represents emplacement of ~200 km3 of basalt. Because no exposed vent of

  18. Diamond provenance studies from 40Ar/ 39Ar dating of clinopyroxene inclusions: An example from the west coast of Namibia

    NASA Astrophysics Data System (ADS)

    Phillips, D.; Harris, J. W.

    2009-11-01

    The west coast of Namibia is host to substantive detrital diamond deposits located in onshore and offshore beach gravels, desert deflation deposits and lower Orange river terraces. The origin of the Namibian diamonds is controversial, with some studies favouring derivation from distal Cretaceous/Jurassic kimberlites on the Kaapvaal craton, and others arguing that most diamonds originated from proximal Dwyka glacial deposits (~ 300 Ma), which incorporated diamonds from older (≥ 500 Ma), pre-Karoo kimberlites. Previous studies have demonstrated that clinopyroxene inclusions extracted from their host diamonds give 40Ar/ 39Ar ages approaching the time of source kimberlite eruption. This behaviour is attributed to diffusion of argon to lattice defect sites and the diamond/inclusion interface region during mantle residence, with subsequent loss of the latter component on cleaving of the diamond to release the inclusion(s). In this study, we measured 40Ar/ 39Ar ages of extracted clinopyroxene inclusions from Namibian detrital diamonds, in order to determine potential kimberlite sources, craton erosion histories and palaeo-drainage evolution in southern Africa. 40Ar/ 39Ar step-heating data were obtained for eclogitic and peridotitic clinopyroxene inclusions from 50 Namibian diamonds. Low temperature steps produced older apparent ages than high temperature (fusion) steps, consistent with partial retention of pre-eruption argon in defect sites. With one exception, fusion steps yielded younger ages, ranging from 62 ± 30 Ma to 1441 ± 700 Ma. The majority (80%) of inclusions have fusion ages < 300 Ma, indicating that most Namibian detrital diamonds originated from post-Dwyka (< 300 Ma) kimberlites. Six inclusion aliquots (13%) produced ages unique to Cretaceous Group I kimberlites, confirming erosion of diamonds from these sources. The proportion of diamonds sourced from Group II kimberlites is uncertain, although forward modelling suggests roughly equal quantities from

  19. U/Pb and Ar/Ar Dating of Latest Permian Magnetic Polarity Reversals in the Ochoan of western Texas

    NASA Astrophysics Data System (ADS)

    Chang, S.; Mundil, R.; Renne, P. R.

    2006-12-01

    Correlating global marine and non-marine Permo-Triassic boundary sections, a key to establishing the paleoenvironmental context and causal mechanism(s) of the mass extinction, has been difficult because of the absence of key biota suitable for correlation across environments. The magnetostratigraphic time scale is potentially a powerful tool for establishing the high resolution chronostratigraphy of the global Permo-Triassic boundary sections. The main pulse of the biotic crisis recorded in marine sediments coincides with a reverse to normal transition and is dated to ca 252.5 Ma by U/Pb single-zircon techniques (Mundil et al., 2004). Although magnetostratrigraphic data have been published for terrestrial sections, there is a notorious lack of high-resolution geochronology and thus the possibility to correlate these in detail with marine records. The red bed Dewey Lake Formation (DLF) in western Texas and New Mexico, believed to be the youngest Permian formation in southwestern North America, contains volcanic tuffs which enable age calibration of magnetic reversals. In western Texas, a detailed magnetostratigraphy which spans three reserved- polarity intervals in a section of the DLF at Caprock Canyons State Park has been reported (Steiner, 2001). Silicic tuffs interbedded in the DLF provide unprecedented opportunities for high-precision age calibration of the latest Permian reversal time scale, based on U/Pb dating of zircon and 40Ar/39Ar dating of sanidine and biotite. Our previous 40Ar/39Ar dating of tuffs in sections at Caprock Canyons (2 tuffs; Chang et al., 2005) and Palo Duro (1 tuff; Renne et al., 2001) yield indistinguishable ages at 250 Ma, coincident with the 40Ar/39Ar for the P-T boundary in China (Renne et al., 1995). A tuff at Palo Duro, distinct mineralogically from those at Caprock Canyons, yields a zircon 206Pb/238U age of 253.0 ± 0.7 Ma (uncertainties given at the 2σ level). Preliminary U/Pb dating from the upper Caprock Canyons tuff yields an

  20. Extending the ARS Experimental Watersheds to Address Regional Issues

    NASA Astrophysics Data System (ADS)

    Marks, D.; Goodrich, D. C.; Winstral, A.; Bosch, D. D.; Pool, D.

    2001-12-01

    The USDA-Agricultural Research Service's (ARS) Watershed Research Program maintains and operates a diverse, geog raphically distributed, nested, multi-scale, national ex perimental watershed network. This network, much of which has been operational for more than 40 years (several more than 60 years), constitutes one the best networks of its kind in the world. The watershed network and its instrumentation was primarily established to assess the hydrologic impacts of watershed conservation and management practices. It has evolved, through development of long-term hydrologic data, as a network of high quality outdoor laboratories for addressing emerging science issues facing hydrologists and resource managers. While the value of the experimental watershed for investigating precipitation, climatic, and hydrologic processes is unquestioned, extending the results from these investigations to other sites and larger areas is more difficult. ARS experimental watersheds are a few hundred km2 or smaller making it challenging to address regional scale issues. To address this the ARS watershed program is, with a suite of partners from universities and other federal agencies, enlarging its research focus to extend beyond the boundaries of the experimental watershed. In this poster we present several examples of this effort, with suggestions on how, using the experimental watershed and its core, a larger scale hydrologic observatory could be developed and maintained.

  1. Xrt And Shinx Joint Flare Study: Ar 11024

    NASA Astrophysics Data System (ADS)

    Engell, Alexander; Sylwester, J.; Siarkowski, M.

    2010-05-01

    From 12:00 UT on July 3 through July 7, 2009 SphinX (Solar Photometer IN X-rays) observes 130 flares with active region (AR) 11024 being the only AR on disk. XRT (X-Ray Telescope) is able to observe 64 of these flare events. The combination of both instruments results in a flare study revealing (1) a relationship between flux emergence and flare rate, (2) that the presence of active region loops typically results in different flare morphologies (single and multiple loop flares) then when there is a lack of an active region loop environment where more cusp and point-like flares are observed, (3) cusp and point-like flares often originate from the same location, and (4) a distribution of flare temperatures corresponding to the different flare morphologies. The differences between the observed flare morphologies may occur as the result of the heated plasma through the flaring process being confined by the proximity of loop structures as for the single and multiple loop flares, while for cusp and point-like flares they occur in an early-phase environment that lack loop presence. The continuing flux emergence of AR 11024 likely provides different magnetic interactions and may be the source responsible for all of the flares.

  2. Photomask cleaning process improvement to minimize ArF haze

    NASA Astrophysics Data System (ADS)

    Graham, Michael; McDonald, Andrew

    2008-04-01

    Growth of "haze" defects on photomasks exposed in ArF lithography is recognized as a serious problem. Haze defects that have grown to detectable sizes can be analysed in situ by techniques such as EDX or Raman, but to analyze at the photomask manufacturing stage requires extraction of residues by solution in DI water. The effect of extraction conditions, including surface area and material, water volume, time, and temperature, has been studied. A standard method to compare residual ion levels is proposed. Various methods for reducing residual ion levels from the photomask cleaning process have been published. These include SPM reduction, oxygen plasma, SC1 dilution, Megasonic agitation, hot rinse, UV exposure, thermal bake, ozone water, ozone gas, and hydrogenated water. Critical parameters for the cleaning process, besides residual ion levels and contamination removal efficiency, include CD shift, AR/chrome damage, scatter bar damage, and on phase shift masks, the change in phase and transmission. An optimized process combining conventional and novel techniques is described. Data is presented to show the importance of controlling all resist strip and clean processes, not just the final clean. It has achieved sulphate levels of 0.2ng/cm2 (well below the critical level for haze growth), as well as improved results for the other critical parameters. This process has been demonstrated to allow ArF exposure of large numbers of wafers without the appearance of haze defects.

  3. Hyperthermal Ar atom scattering from a C(0001) surface.

    PubMed

    Gibson, K D; Sibener, S J; Upadhyaya, Hari P; Brunsvold, Amy L; Zhang, Jianming; Minton, Timothy K; Troya, Diego

    2008-06-14

    Experiments and simulations on the scattering of hyperthermal Ar from a C(0001) surface have been conducted. Measurements of the energy and angular distributions of the scattered Ar flux were made over a range of incident angles, incident energies (2.8-14.1 eV), and surface temperatures (150-700 K). In all cases, the scattering is concentrated in a narrow superspecular peak, with significant energy exchange with the surface. The simulations closely reproduce the experimental observations. Unlike recent experiments on hyperthermal Xe scattering from graphite [Watanabe et al., Eur. Phys. J. D 38, 103 (2006)], the angular dependence of the energy loss is not approximated by the hard cubes model. The simulations are used to investigate why parallel momentum conservation describes Xe scattering, but not Ar scattering, from the surface of graphite. These studies extend our knowledge of gas-surface collisional energy transfer in the hyperthermal regime, and also demonstrate the importance of performing realistic numerical simulations for modeling such encounters. PMID:18554044

  4. ArF pellicle degradation mechanism for resolving CD variation

    NASA Astrophysics Data System (ADS)

    Choi, Hyungseok; Ahn, Yohan; Ryu, Jua; Lee, Yangkoo; An, Bumhyun; Lee, Seokryeol

    2007-03-01

    With the introduction of ArF laser, a binary mask is preferred because a PSM mask is still weak to the crystal defect called as photomask haze although extensive studies trying to resolve the haze impact to a photomask have been performed by various researchers in company and school. However, a new problem was happened after a binary mask introduction that CD variation in an exposure shot is appeared and is gradually increased. And finally, CD variation considerably causes defects in wafer level. It was proven that CD variation is closely related to the change of the reticle transmittance by a lot of researches. In this study, the mechanism of ArF pellicle degradation is focused on because the pellicle degradation affects a reticle transmittance in direct. The components outgassed from a pellicle by the high photon energy of ArF laser, for example carbon or fluorine, are absorbed on the surface of the reticle, so that the transmittance of the reticle is decreased. The phenomena of the pellicle degradation have been studied by the various viewpoints, theoretical background, experiment and results tested in mass production line in this study. Therefore, this study has the important meaning by providing the substantial clues to resolve CD variation problem in a near future.

  5. Fragmentation dynamics of Ar2^+ dimers in intense laser fields

    NASA Astrophysics Data System (ADS)

    Magrakvelidze, M.; Wu, J.; Dörner, R.; Thumm, U.

    2012-06-01

    We studied the fragmentation dynamics of the Ar2 dimers in 790 nm pump and 1400 nm probe pulses with intensities of 10^14 W/cm^2 by analyzing kinetic energy release (KER) spectra as a function of the pump probe delay. The KER spectra are measured by detecting Ar-ion fragments in a COLTRIMS [1] setup and are compared with model calculations based on the numerical propagations of the time-dependent Schr"odinger equation [2]. The measured spectra are best reproduced by two-state calculations that include the adiabatic electronic states I(1/2)u and II(1/2)g of Ar2^+, dipole coupled in the pump- and probe-laser electric fields. [4pt] [1] J. Wu, A. Vredenborg, B. Ulrich, L. Ph. H. Schmidt, M. Meckel, S. Voss, H. Sann, H. Kim, T. Jahnke, and R. D"orner, PRA 83, 061403(R) (2011) [0pt] [2] M. Magrakvelidze, F. He, Th. Niederhausen, I. V. Litvinyuk, and U. Thumm, PRA 79, 033410 (2009).

  6. K-Ar dating of young volcanic rocks

    SciTech Connect

    Damon, P.E.; Shafiqullah, M.

    1991-01-31

    Potassium-Argon (K-Ar) age dates were determined for forty-two young geologic samples by the Laboratory of Isotope Geochemistry, Department of Geosciences, in the period February 1, 1986 to June 30, 1989. Under the terms of Department of Energy Grant No. FG07-86ID12622, The University of Arizona was to provide state-of-the-art K-Ar age dating services, including sample preparation, analytical procedures, and computations, for forty-two young geologic samples submitted by DOE geothermal researchers. We billed only for forty samples. Age dates were determined for geologic samples from five regions with geothermal potential: the Cascade Mountains (Oregon); the Cascade Mountains (Washington); Ascension Island, South Atlantic Ocean; Cerro Prieto, Mexico; and Las Azufres, Mexico. The ages determined varied from 5.92 m.a. to 0.62 m.a. The integration of K-Ar dates with geologic data and the interpretation in terms of geologic and geothermal significance has been reported separately by the various DOE geothermal researchers. Table 1 presents a detailed listing of all samples dated, general sample location, researcher, researcher's organization, rock type, age, and probable error (1 standard deviation). Additional details regarding the geologic samples may be obtained from the respective geothermal researcher. 1 tab.

  7. 1. OVERALL VIEW TO NORTH, SHOWING BOMBER REVETMENT AR8 IN ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. OVERALL VIEW TO NORTH, SHOWING BOMBER REVETMENT AR-8 IN RELATION TO THE HANGARS OF MAIN BASE IN THE FAR DISTANCE, AND THE AIRPLANE FIREFIGHTING TRAINING MODEL (STRUCTURE NO. 273) AT FAR RIGHT. PURSUIT PLANE REVETMENT AR-9 IS DIRECTLY BEHIND AR-8, THROUGH HIDDEN FROM THIS ANGLE. (Panoramic view number 1 of 2 for AR-8). - Edwards Air Force Base, South Base, Rammed Earth Aircraft Dispersal Revetments, Western Shore of Rogers Dry Lake, Boron, Kern County, CA

  8. Ar-40/Ar-39 age spectra of Apollo 15 impact melt rocks by laser step-heating and their bearing on the history of lunar basin formation

    NASA Astrophysics Data System (ADS)

    Dalrymple, G. B.; Ryder, G.

    1993-07-01

    Results are reported on 26 high-resolution (16-51 steps) Ar-40/Ar-39 age spectra obtained on 12 Apollo-15 melt rocks of different composition using a continuous laser system on submg fragments of recrystallized melt and single-crystal plagioclase clasts from impact melt rocks collected at the Apennine Front where the Imbrium and Serenitatis basins intersect. A table is presented with the summary of the Ar-40/Ar-39 spectrum data, which represent 891 individual temperature step analyses. Also presented are 20 of the 26 age spectra along with their respective K/Ca plots. Melt rock fragments and plagioclase clasts from seven of the 12 samples analyzed yielded reproducible, intermediate-T Ar-40/Ar-39 age spectrum plateaus, which were interpreted as crystallization ages that represent the times of impact of bolides onto the lunar surface.

  9. An Approximately 4.35 Ga Ar-Ar Age for GRA 8 and the Complex Chronology of its Parent Body

    NASA Technical Reports Server (NTRS)

    Park, J.; Nyquist, Laurence E.; Bogard, D. D.; Garrison, D. H.; Shih, C.-Y.; Reese, Y. D.

    2010-01-01

    GRA06128 and GRA06129 (hereafter GRA 8 and GRA 9) are partial melts of a parent body of approximately chondritic composition. We reported a conventional Sm-147-Nd-143 isochron age of 4.559+/-0.096 Ga and a 146 Sm-142Nd model age of 4.549+/-0.036 for combined data for the two rocks. Plagioclase plus whole rock and leachate (approx.phosphate) samples gave a secondary Sm-147-Nd-143 age of 3.4+/-0.4 Ga. An Ar-39-Ar-40 age of 4.460+/-0.028 Ga was interpreted as dating metamorphism in GRA 9. We report Ar-39-Ar-40 ages in the range approx.4344-4366 Ma for GRA 8, establishing similar but different Ar-39-Ar-40 ages for the two rocks, consistent with their different Sr-isotopic systematics, and discuss these ages in the context of the complex sequence of events that affected these samples.

  10. The Manson Impact Structure: 40Ar/39Ar age and its distal impact ejecta in the pierre shale in southeastern South Dakota

    USGS Publications Warehouse

    Izett, G.A.; Cobban, W.A.; Obradovich, J.D.; Kunk, M.J.

    1993-01-01

    The 40Ar/39Ar ages of a sanidine clast from a melt-matrix breccia of the Manson, Iowa, impact structure (MIS) indicate that the MIS formed 73.8 ?? 0.3 million years ago (Ma) and is not coincident with the Cretaceous-Tertiary boundary (64.43 ?? 0.05 Ma). The MIS sanidine is 9 million years older than 40Ar/39Ar age spectra of MIS shock-metamorphosed microcline and melt-matrix breccia interpreted earlier to be 64 to 65 Ma. Grains of shock-metamorphosed quartz, feldspar, and zircon were found in the Crow Creek Member (upper Campanian) at a biostratigraphic level constrained by radiometric ages in the Pierre Shale of South Dakota that are consistent with the 40Ar/39Ar age of 73.8 ?? 0.3 Ma for MIS reported herein.

  11. The Manson Impact Structure: 40Ar/39Ar Age and Its Distal Impact Ejecta in the Pierre Shale in Southeastern South Dakota

    NASA Astrophysics Data System (ADS)

    Izett, G. A.; Cobban, W. A.; Obradovich, J. D.; Kunk, M. J.

    1993-10-01

    The 40Ar/39Ar ages of a sanidine clast from a melt-matrix breccia of the Manson, lowa, impact structure (MIS) indicate that the MIS formed 73.8 ± 0.3 million years ago (Ma) and is not coincident with the Cretaceous-Tertiary boundary (64.43 ± 0.05 Ma). The MIS sanidine is 9 million years older than 40Ar/39Ar age spectra of MIS shock-metamorphosed microcline and melt-matrix breccia interpreted earlier to be 64 to 65 Ma. Grains of shock-metamorphosed quartz, feldspar, and zircon were found in the Crow Creek Member (upper Campanian) at a biostratigraphic level constrained by radiometric ages in the Pierre Shale of South Dakota that are consistent with the 40Ar/39Ar age of 73.8 ± 0.3 Ma for MIS reported herein.

  12. ArsR arsenic-resistance regulatory protein from Cupriavidus metallidurans CH34.

    PubMed

    Zhang, Yian-Biao; Monchy, Sébastien; Greenberg, Bill; Mergeay, Max; Gang, Oleg; Taghavi, Safiyh; van der Lelie, Daniel

    2009-08-01

    The Cupriavidus metallidurans CH34 arsR gene, which is part of the arsRIC(2)BC(1)HP operon, and its putative arsenic-resistance regulatory protein were identified and characterized. The arsenic-induced transcriptome of C. metallidurans CH34 showed that the genes most upregulated in the presence of arsenate were all located within the ars operon, with none of the other numerous heavy metal resistance systems present in CH34 being induced. A transcriptional fusion between the luxCDABE operon and the arsR promoter/operator (P/O) region was used to confirm the in vivo induction of the ars operon by arsenite and arsenate. The arsR gene was cloned into expression vectors allowing for the overexpression of the ArsR protein as either his-tagged or untagged protein. The ability of the purified ArsR proteins to bind to the ars P/O region was analyzed in vitro by gel mobility shift assays. ArsR showed an affinity almost exclusively to its own ars P/O region. Dissociation of ArsR and its P/O region was metal dependent, and based on decreasing degrees of dissociation three groups of heavy metals could be distinguished: As(III), Bi(III), Co(II), Cu(II), Ni(II); Cd(II); Pb(II) and Zn(II), while no dissociation was observed in the presence of As(V). PMID:19238575

  13. ArsR arsenic-resistance regulatory protein from Cupriavidus metallidurans CH34

    SciTech Connect

    Zhang, Y.; van der Lelie, D.; Monchy, S.; Greenberg, B.; Gang, O.; Taghavi, S.

    2009-08-01

    The Cupriavidus metallidurans CH34 arsR gene, which is part of the arsRIC{sub 2}BC{sub 1}HP operon, and its putative arsenic-resistance regulatory protein were identified and characterized. The arsenic-induced transcriptome of C. metallidurans CH34 showed that the genes most upregulated in the presence of arsenate were all located within the ars operon, with none of the other numerous heavy metal resistance systems present in CH34 being induced. A transcriptional fusion between the luxCDABE operon and the arsR promoter/operator (P/O) region was used to confirm the in vivo induction of the ars operon by arsenite and arsenate. The arsR gene was cloned into expression vectors allowing for the overexpression of the ArsR protein as either his-tagged or untagged protein. The ability of the purified ArsR proteins to bind to the ars P/O region was analyzed in vitro by gel mobility shift assays. ArsR showed an affinity almost exclusively to its own ars P/O region. Dissociation of ArsR and its P/O region was metal dependent, and based on decreasing degrees of dissociation three groups of heavy metals could be distinguished: As(III), Bi(III), Co(II), Cu(II), Ni(II); Cd(II); Pb(II) and Zn(II), while no dissociation was observed in the presence of As(V).

  14. 2. LOOKING NORTHEAST TOWARD ROGERS DRY LAKE. REVETMENTS AR7 (NEAR ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. LOOKING NORTHEAST TOWARD ROGERS DRY LAKE. REVETMENTS AR-7 (NEAR DISTANCE) AND AR-2 (FAR DISTANCE) ARE VISIBLE TO THE RIGHT OF THE FIREFIGHTING TRAINING MODEL AT LEFT. (Panoramic view number 2 OF 2 for AR-8). - Edwards Air Force Base, South Base, Rammed Earth Aircraft Dispersal Revetments, Western Shore of Rogers Dry Lake, Boron, Kern County, CA

  15. 3. THE LONG SOUTHWEST WALL OF AR8 AT CENTER, ALSO ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. THE LONG SOUTHWEST WALL OF AR-8 AT CENTER, ALSO SHOWING THE SOUTH WALL WITH THE ATTACHED LOW WALLED CREW SHELTER. AR-9 IS VISIBLE AT THE LEFT, AND AR-2 IS VISIBLE AT THE FAR RIGHT. - Edwards Air Force Base, South Base, Rammed Earth Aircraft Dispersal Revetments, Western Shore of Rogers Dry Lake, Boron, Kern County, CA

  16. 40Ar/39Ar age and chemistry of manganese mineralization in the Moab and Lisbon fault systems, southeastern Utah

    NASA Astrophysics Data System (ADS)

    Chan, Marjorie A.; Parry, William T.; Petersen, Erich U.; Hall, Chris M.

    2001-04-01

    Diagenetic iron and manganese mineralization is associated with the Moab and Lisbon faults and is an important indicator of fluid flow in Jurassic Navajo Sandstone of southeastern Utah. Reducing brines originating from the Pennsylvanian Paradox Formation (with or without hydrocarbons) mobilized disseminated iron and manganese in the Jurassic sandstones and mixed with shallow, oxygenated groundwater to precipitate both iron and manganese mineralization. Mineralization consists of colliform and concretionary hematite, pyrolusite, and cryptomelane-hollandite that contains 1.33 2.12 wt% K. The 40Ar/39Ar dating of vacuum-encapsulated cryptomelane yields age estimates of 25 20 Ma, indicating mineralization coincident with either a Colorado Plateau uplift episode or La Sal Mountains volcanism.

  17. Resolving the early chronology of Mono Craters volcanism with combined 238U-230Th and 40Ar/39Ar dating

    NASA Astrophysics Data System (ADS)

    Vazquez, J. A.; Calvert, A. T.; Marcaida, M.; Mangan, M.; Lidzbarski, M. I.; Stelten, M. E.

    2013-12-01

    California's largest locus of Pleistocene-Holocene rhyolitic volcanism is the Mono Lake-Long Valley region of eastern California. The Mono Craters chain marks the northern portion of this locus, and is composed of at least 28 individual domes of high-silica rhyolite. The record of Holocene volcanism at Mono Craters is relatively well constrained by tephrostratigraphy and radiocarbon dating. However, the timing and frequency of late Pleistocene dome emplacement is poorly resolved, with most of the chronology based on hydration-rind dating of obsidian. A well-exposed archive of late Pleistocene volcanism from Mono Craters is recorded by tephra beds (ashes numbered 1-19, youngest to oldest) of the informal Wilson Creek formation that accumulated in ancestral Mono Lake. To resolve a precise chronology for late Pleistocene volcanism at Mono Craters and tune the time-series of explosive volcanism preserved by Wilson Creek tephras, we performed ion microprobe 238U-230Th dating of allanite and zircon together with laser-fusion 40Ar/39Ar dating of sanidine from rhyolite domes that yield the oldest hydration rind ages and have relatively subdued morphology. Sanidine from multiple domes, including both hornblende-biotite and fayalite-bearing rhyolite types, yield 40Ar/39Ar ages up to ca. 25 ka. Ion microprobe analyses of unpolished rims on indium-mounted allanite and zircon crystals yield U-Th isochron ages that are indistinguishable from their associated sanidine 40Ar/39Ar ages. However, the interiors of sectioned allanite crystals yield model U-Th ages that may be up to 30 kyr older than their rims. Rims on allanite and zircon from ashes 7-19 in the lower portion of the Wilson Creek stratigraphy yield isochron ages of ca. 27-62 ka [1], which are supported by ages from magnetostratigraphy [2]. Ash 3 contains titanomagnetites that are compositionally distinct from other Wilson Creek tephras, but match those in the hornblende-biotite rhyolite of dome 11. Rims on allanite and

  18. Interactions of relativistic {sup 36}Ar and {sup 40}Ar nuclei in hydrogen: Isotopic production cross sections

    SciTech Connect

    Knott, C.N.; Waddington, C.J.; Albergo, S.; Caccia, Z.; Costa, S.; Insolia, A.; Potenza, R.; Russo, G.V.; Tuve, C.; Chen, C.; Guzik, T.G.; Testard, O.; Wefel, J.P.; Crawford, H.J.; Cronqvist, M.; Engelage, J.; Greiner, L.; Lindstrom, P.J.; Tull, C.E.; Mitchell, J.W.; Webber, W.R.

    1997-07-01

    The interactions of {sup 36}Ar projectile nuclei with energies of 361, 546, and 765 MeV/nucleon and {sup 40}Ar nuclei with 352 MeV/nucleon, have been studied in a liquid-hydrogen target as part of a program to study interactions of relevance to the problem of cosmic-ray propagation in the interstellar medium. We have measured the cross sections for the production of isotopic fragments of the projectile nuclei in these interactions. The variations of these cross sections with mass, charge, and energy, are examined for insights into any systematic features of this type of fragmentation reaction that might aid predictions of other, unmeasured cross sections. These cross sections are also compared with the values derived from the most commonly used prediction techniques. It is suggested that these techniques could be improved by taking account of the systematic features identified here. {copyright} {ital 1997} {ital The American Physical Society}

  19. 40Ar/39Ar Dating of Zn-Pb-Ag Mineralization in the Northern Brooks Range, Alaska

    USGS Publications Warehouse

    Werdon, Melanie B.; Layer, Paul W.; Newberry, Rainer J.

    2004-01-01

    The 40Ar/39Ar laser step-heating method potentially can be used to provide absolute ages for a number of formerly undatable, low-temperature ore deposits. This study demonstrates the use of this method by determining absolute ages for Zn-Pb-Ag sediment-hosted massive sulfide deposits and vein-breccia occurrences found throughout a 300-km-long, east-west-trending belt in the northern Brooks Range, Alaska. Massive sulfide deposits are hosted by Mississippian to Pennsylvanian(?) black carbonaceous shale, siliceous mudstone, and lesser chert and carbonate turbidites of the Kuna Formation (e.g., Red Dog, Anarraaq, Lik (Su), and Drenchwater). The vein-breccia occurrences (e.g., Husky, Story Creek, West Kivliktort Mountain, Vidlee, and Kady) are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine clastic rocks (the Endicott Group) that stratigraphically underlie the Kuna Formation. The vein-breccias are mineralogically similar to, but not spatially associated with, known massive sulfide deposits. The region's largest shale-hosted massive sulfide deposit is Red Dog; it has reserves of 148 Mt grading 16.6 percent zinc, 4.5 percent lead, and 77 g of silver per tonne. Hydrothermally produced white mica in a whole-rock sample from a sulfide-bearing igneous sill within the Red Dog deposit yielded a plateau age of 314.5 Ma. The plateau age of this whole-rock sample records the time at which temperatures cooled below the argon closure temperature of the white mica and is interpreted to represent the minimum age limit for massive sulfide-related hydrothermal activity in the Red Dog deposit. Sulfide-bearing quartz veins at Drenchwater crosscut a hypabyssal intrusion with a maximum biotite age of 337.0 Ma. Despite relatively low sulfide deposition temperatures in the vein-breccia occurrences (162°-251°C), detrital white mica in sandstone immediately adjacent to large vein-breccia zones was partially to

  20. sup 40 Ar- sup 39 Ar dating of the Beja gabbro: Timing of the accretion of southern Portugal

    SciTech Connect

    Ruffet, G. )

    1990-11-01

    The {sup 40}Ar-{sup 39}Ar dating of the amphibole from the Beja gabbro (Southern Portugal) yields a plateau age at 336.4 {plus minus} 0.8 Ma (2{sigma} level). The corresponding calculated isotopic closure temperature is around 800C. The comparison of this temperature with the magnetic blocking temperature ({approximately}570C) allows an estimation of a probable thermoremanent acquisition age for the characteristic magnetization component of the Beja gabbro between 335Ma and 315Ma, assuming cooling rates between 10C/Ma and 100C/Ma. These results, combined wtih paleomagnetic results from the Beja gabbro and Late Paleozoic rocks from Southern Portugal (Perroud et al., 1985), suggest that the southermost part of Spain and Portugal was separated from Northern Iberia in Early Carboniferous times and was accreted to Europe during the Late Carboniferous.

  1. Constraints on the Jurassic time scale by /sup 40/Ar//sup 39/Ar dating of North Caucasian volcanic rocks

    SciTech Connect

    Hess, J.C.; Lippolt, H.J.; Borsuk, A.M.

    1987-07-01

    /sup 40/Ar//sup 39/Ar age measurements on biotites and high-temperature plagioclases of Jurassic basaltic to rhyolitic subvolcanic rocks from the Northern Great Caucasus (USSR) yielded plateau and total argon ages between 190 and 180 Ma. The dated rocks are intrusive sills, dikes and laccoliths in sediments of the middle to upper Pliensbachian and of the lower Toarcian (Lower Jurassic). Pebbles of the volcanic rocks exist in the basal conglomerates of the Aalenian (base of the Middle Jurassic). Thus, their stratigraphic age is restricted to the Lower Jurassic stages of middle to upper Pliensbachian and Toarcian. Because of the scarcity of tie-points in the Lower Jurassic, the isotopic ages of these volcanic rocks, in spite of their rather large stratigraphic range, may serve as new calibration points for the improvement of the Jurassic time-scale.

  2. Ar-40/Ar-39 age of the Shergotty achondrite and implications for its post-shock thermal history

    NASA Technical Reports Server (NTRS)

    Bogard, D. D.; Nyquist, L. E.; Husain, L.

    1979-01-01

    Ar-40/Ar-39 measurements are used to determine the age of the Shergotty achondrite and the chronology of the shock event responsible for the complete conversion of its plagioclase to maskelynite is discussed. Apparent ages are found to vary between 240 and 640 million years for the whole rock sample, with a plateau age of 254 million years for a maskelynite separate. The Rb-Sr age of 165 million years determined by Nyquist at al (1978) suggests that the maskelynite as well as the whole rock was incompletely degassed. Argon diffusion characteristics indicate a post-shock cooling time greater than 1000 years and a burial depth greater than 300 m for a thermal model of a cooling ejecta blanket of variable thickness. It is concluded that the shock event which degassed the argon and reset the Rb-Sr systematics occurred between 165 and 250 million years ago when the parent body experienced a collision in the asteroid belt.

  3. An ab initio potential energy surface and dynamics of the Ar+H2+ → ArH + + H reaction

    NASA Astrophysics Data System (ADS)

    Liu, Xinguo; Liu, Huirong; Zhang, Qinggang

    2011-04-01

    An ab initio potential energy surface (PES) for the ground state (1 2A') of the chemical reaction Ar+H2+ → ArH + + H has been constructed from a set of accurate ab initio data, which we have computed using the coupled-cluster theory including all single and double excitations plus perturbative corrections for the triples UCCSD(T) with a large orbital basis set of aug-cc-pV5Z. The new PES has a root-mean-square (rms) error of 0.5341 kcal/mol. The total integral reaction cross-sections have been calculated at three collision energies by means of the quasi-classical trajectory (QCT) calculation based on the new PES and compared with previous TSH results.

  4. Production of metastable Ar[sup +] ions by electron-impact ionization of Ar measured by translational-energy spectroscopy

    SciTech Connect

    Kamber, E.Y. ); Enos, C.S.; Brenton, A.G. )

    1993-07-01

    The translational-energy-spectroscopy technique has been used to measure the apparent ionization-excitation functions for the metastable states 3 [sup 4]D, 3[ital d] [sup 4]F, 3[ital d] [sup 2]F, and 3[ital d][prime] [sup 2][ital F] of an Ar[sup +] ion beam extracted from an electron-impact ion source. The initial states were identified from the measured energy loss in the translational-energy spectra for single-electron stripping from ground-state and metastable Ar[sup +] ions in collisions with O[sub 2]. This technique provides an alternative method of selectivity in the study of electron-impact ionization and excitation processes.

  5. [sup 40]Ar/[sup 39]Ar evidence for delayed post-Acadian cooling in the southernmost Connecticut Valley Synclinorium

    SciTech Connect

    Moecher, D.P. . Dept. of Geological Science); Cosca, M.A. )

    1992-01-01

    Available Ar-40/Ar-39 data for the Connecticut Valley Synclinorium (CVS) of the New England segment of the Appalachian Orogen indicate rapid post-Acadian cooling. However, new data indicate this pattern does not extend the entire length of the CVS. Ar-40/Ar-39 ages obtained from hornblende and muscovite in The Straits Schist indicate delayed cooling and a more complex post-Acadian thermal history. Data for the Seymour area are consistent with the studies above for the vicinity of the Waterbury Dome. The data farther south indicate one or more of the following: (1) slow (2--3C/Ma) post-Acadian cooling and uplift through the Permian; (2) post-Acadian cooling through Hbl closure in the Mississippian with a subsequent Alleghanian metamorphism that did not exceed 500 C; or (3) post-Acadian cooling with subsequent metamorphism that approached 500 C or involved ductile recrystallization, partly resetting hornblende and totally resetting muscovite south of Derby. Petrologic evidence supporting (2) or (3) consists of widespread but not pervasive greenschist facies retrogression of Hbl + Pl + Sph assemblages in amphibolites to Act + Ep, and Grt + Ky + St assemblages in metapelites to Chl + Bt + Qz. The present data cannot resolve between (2) or (3). However, both are consistent with results of a study in the Bridgeport Synform that yield (1) a U-Pb monazite age of 296 [+-] 2 Ma from the Ansonia Leucogranite, implying the occurrence of an Alleghanian thermal event that promoted monazite growth; and, (2) a U-Pb cooling age of 360 Ma from sphene in the Pumpkin Ground Granodiorite, indicating that Alleghanian events did not exceed ca. 550 C.

  6. Episodic Holocene eruption of the Salton Buttes rhyolites, California, from paleomagnetic, U-Th, and Ar/Ar dating

    USGS Publications Warehouse

    Wright, Heather M.; Vazquez, Jorge A.; Champion, Duane E.; Calvert, Andrew T.; Mangan, Margaret T.; Stelten, Mark E.; Cooper, Kari M.; Herzig, Charles; Schriener Jr., Alexander

    2015-01-01

    In the Salton Trough, CA, five rhyolite domes form the Salton Buttes: Mullet Island, Obsidian Butte, Rock Hill, North and South Red Hill, from oldest to youngest. Results presented here include 40Ar/39Ar anorthoclase ages, 238U-230Th zircon crystallization ages, and comparison of remanent paleomagnetic directions with the secular variation curve, which indicate that all domes are Holocene. 238U-230Th zircon crystallization ages are more precise than but within uncertainty of 40Ar/39Ar anorthoclase ages, suggesting that zircon crystallization proceeded until shortly before eruption in all cases except one. Remanent paleomagnetic directions require three eruption periods: (1) Mullet Island, (2) Obsidian Butte, and (3) Rock Hill, North Red Hill, and South Red Hill. Borehole cuttings logs document up to two shallow tephra layers. North and South Red Hills likely erupted within 100 years of each other, with a combined 238U-230Th zircon isochron age of: 2.83 ± 0.60 ka (2 sigma); paleomagnetic evidence suggests this age predates eruption by hundreds of years (1800 cal BP). Rock Hill erupted closely in time to these eruptions. The Obsidian Butte 238U-230Th isochron age (2.86 ± 0.96 ka) is nearly identical to the combined Red Hill age, but its Virtual Geomagnetic Pole position suggests a slightly older age. The age of aphyric Mullet Island dome is the least well constrained: zircon crystals are resorbed and the paleomagnetic direction is most distinct; possible Mullet Island ages include ca. 2300, 5900, 6900, and 7700 cal BP. Our results constrain the duration of Salton Buttes volcanism to between ca. 5900 and 500 years.

  7. Episodic Holocene eruption of the Salton Buttes rhyolites, California, from paleomagnetic, U-Th, and Ar/Ar dating

    NASA Astrophysics Data System (ADS)

    Wright, Heather M.; Vazquez, Jorge A.; Champion, Duane E.; Calvert, Andrew T.; Mangan, Margaret T.; Stelten, Mark; Cooper, Kari M.; Herzig, Charles; Schriener, Alexander

    2015-04-01

    In the Salton Trough, CA, five rhyolite domes form the Salton Buttes: Mullet Island, Obsidian Butte, Rock Hill, North and South Red Hill, from oldest to youngest. Results presented here include 40Ar/39Ar anorthoclase ages, 238U-230Th zircon crystallization ages, and comparison of remanent paleomagnetic directions with the secular variation curve, which indicate that all domes are Holocene. 238U-230Th zircon crystallization ages are more precise than but within uncertainty of 40Ar/39Ar anorthoclase ages, suggesting that zircon crystallization proceeded until shortly before eruption in all cases except one. Remanent paleomagnetic directions require three eruption periods: (1) Mullet Island, (2) Obsidian Butte, and (3) Rock Hill, North Red Hill, and South Red Hill. Borehole cuttings logs document up to two shallow tephra layers. North and South Red Hills likely erupted within 100 years of each other, with a combined 238U-230Th zircon isochron age of: 2.83 ± 0.60 ka (2 sigma); paleomagnetic evidence suggests this age predates eruption by hundreds of years (1800 cal BP). Rock Hill erupted closely in time to these eruptions. The Obsidian Butte 238U-230Th isochron age (2.86 ± 0.96 ka) is nearly identical to the combined Red Hill age, but its Virtual Geomagnetic Pole position suggests a slightly older age. The age of aphyric Mullet Island dome is the least well constrained: zircon crystals are resorbed and the paleomagnetic direction is most distinct; possible Mullet Island ages include ca. 2300, 5900, 6900, and 7700 cal BP. Our results constrain the duration of Salton Buttes volcanism to between ca. 5900 and 500 years.

  8. 40Ar/39Ar Age Constraints on Caldera Formation of the Emmons Lake Volcanic Center, Alaska Peninsula, Alaska

    NASA Astrophysics Data System (ADS)

    Drake, J.; Layer, P. W.; Mangan, M. T.; Miller, T. P.; Waythomas, C. F.

    2001-12-01

    The Emmons Lake Volcanic Center located on the Alaska Peninsula is a large shield/stratovolcano complex composed of basaltic to andesitic lava flows and dacite to rhyolite pyroclastic flows, domes and ashfall. Two caldera forming eruptions in Pleistocene time each produced more than 50 cubic kilometers of silicic ejecta and created a nested depression measuring 20 km long and 10 km wide. We conducted 40Ar/39Ar whole rock dating of units associated with the first caldera forming event, which because of broad geochemical similarities, has been suggested as a possible source of the Old Crow Tephra, dated throughout interior Alaska and the Yukon at about 140 ka. Samples dated ranged in composition from ~62 to 69 wt % SiO2 and contained 2 - 3 wt % K2O. For each sample, 15 specimens, consisting of small ( ~1 mm) whole rock chips, were fused with an argon ion laser. From these analyses, weighted mean and isochron ages were calculated. For all samples, the initial 40Ar/36Ar ratio was indistinguishable from that of the present-day atmosphere (295.5), indicating that these samples do not contain significant quantities of excess argon. The age of a welded tuff interpreted to be from the opening plinian phase of the eruption is 233 +/- 6 ka, and is identical to the age of a post-collapse rheomorphic tuff (234 +/- 5 ka). A lithic fragment from a syn-collapse lag breccia has an age of 419 +/- 9 ka, which we interpret as representing incorporation of older material. Younger tuffs and domes were dated at 99 +/- 7 ka and 16 +/- 10 ka and imply that the complex was active throughout the late Quaternary. Based on these new age data, and subtle but significant trace element differences in glass and Fe-Ti oxide composition, we conclude that the first major caldera building event occurred at approximately 230 ka, and is probably not responsible for the deposition of the Old Crow tephra.

  9. NWA 7034 Martian breccia: Ar/Ar ages of ca. 1.2 to 1.4 Ga

    NASA Astrophysics Data System (ADS)

    Cohen, B. E.; Mark, D. F.; Cassata, W.; Lee, M. R.; Smith, C. L.

    2015-12-01

    NWA 7034 and its paired stones are some of the oldest and most diverse of the Martian meteorites. They are complex polymict breccias of impact, igneous, and sedimentary clasts set in a dark grey matrix [1; 2]. The rock also contains angular mineral fragments, including K-feldspar, plagioclase feldspar, and pyroxene [1; 2]. Mineral fragments are often > 1 mm wide, and clasts can be > 1 cm. This diverse breccia assemblage indicates formation via repeated impact events, supported by Rb-Sr, Sm-Nd and U-Pb ages ranging from 1.3 to 4.4 Ga [1, 2, and references therein]. In this study we investigate the distribution of ages yielded by Ar/Ar, with nine aliquots analyzed to date, and additional analyses planned. In order to analyze only single phases, chips of matrix/clasts were restricted to visibly monomict fragments < 1 mm diameter, while mineral separates were analyzed as single crystals. Cosmogenic Ar corrections are from [3]. Analyses were undertaken at SUERC and Lawrence Livermore National Laboratory, and the results pooled. The bulk of aliquots (n = 8) yielded ages of ca. 1.2-1.4 Ga indicating a major thermal event occurred at around the same time as crystallization of the Nakhlite group of meteorites. Select step ages are considerably older (> 2 Ga), supporting results of other chronometers that much older material is present in this sample. These results also demonstrate that some older fragments retained Ar during breccia formation. [1] Wittmann A. et al. (2015) Meteoritics & Planet. Sci., 50, 326-352. [2] Santos A. R. et al. (2015) GCA, 157, 56-85. [3] Cassata W. S., and Borg L. E. (2015) 46th LPSC, Abstract #2742.

  10. Paleozoic accretionary orogenesis in the eastern Beishan orogen: constraints from zircon U-Pb and 40Ar/39Ar geochronology

    NASA Astrophysics Data System (ADS)

    Ao, Songjian; Xiao, Wenjiao; Windley, Brian; Mao, Qigui

    2016-04-01

    The continental growth mechanism of the Altaids in Central Asia is still in controversy between models of continuous subduction-accretion versus punctuated accretion by closure of multiple oceanic basins. The Beishan orogenic belt, located in the southern Altaids, is a natural laboratory to address this controversy. Key questions that are heavily debated are: the closure time and subduction polarity of former oceans, the emplacement time of ophiolites, and the styles of accretion and collision. This paper reports new structural data, zircon ages and Ar-Ar dates from the eastern Beishan Orogen that provide information on the accretion process and tectonic affiliation of various terranes. Our geochronological and structural results show that the younging direction of accretion was northwards and the subduction zone dipped southwards under the northern margin of the Shuangyingshan micro-continent. This long-lived and continuous accretion process formed the Hanshan accretionary prism. Our field investigations show that the emplacement of the Xiaohuangshan ophiolite was controlled by oceanic crust subduction beneath the forearc accretionary prism of the Shuangyingshan-Mazongshan composite arc to the south. Moreover, we address the age and terrane affiliation of lithologies in the eastern Beishan orogen through detrital zircon geochronology of meta-sedimentary rocks. We provide new information on the ages, subduction polarities, and affiliation of constituent structural units, as well as a new model of tectonic evolution of the eastern Beishan orogen. The accretionary processes and crustal growth of Central Asia were the result of multiple sequences of accretion and collision of manifold terranes. Reference: Ao, S.J., Xiao, W., Windley, B.F., Mao, Q., Han, C., Zhang, J.e., Yang, L., Geng, J., Paleozoic accretionary orogenesis in the eastern Beishan orogen: Constraints from zircon U-Pb and 40Ar/39Ar geochronology. Gondwana Research, doi: http://dx.doi.org/10.1016/j

  11. Geochemical and 40Ar/39Ar constraints on the evolution of volcanism in the Woodlark Rift, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Catalano, Joseph P.

    The tectonic mechanisms producing Pliocene to active volcanism in eastern Papua New Guinea (PNG) have been debated for decades. In order to assess mechanisms that produce volcanism in the Woodlark Rift, we evaluate the evolution of volcanism in eastern PNG using 40Ar/39Ar thermochronology and whole rock geochemistry. Active volcanism in southeastern Papua New Guinea occurs on the Papuan Peninsula (Mt. Lamington, Mt. Victory and Waiwa), in the Woodlark Rift (Dobu Island, SE Goodenough Island, and Western Fergusson Island), and in the Woodlark Basin. In the Woodlark Basin, seafloor spreading is active and decompression melting of the upper mantle is producing basaltic magmatism. However, the cause of Pliocene and younger volcanism in the Woodlark Rift is controversial. Two hypotheses for the tectonic setting have been proposed to explain Pliocene and younger volcanism in the Woodlark Rift: (1) southward subduction of Solomon Sea lithosphere beneath eastern PNG at the Trobriand Tough and (2) decompression melting of mantle, previously modified by subduction, as the lithosphere undergoes extension associated with the opening of the Woodlark Basin. A comparison of 40Ar/39Ar ages with high field strength element (HFSE) concentrations in primary magmas indicates that HFSE concentrations correlate with age in the Woodlark rift. These data support the hypothesis that Pliocene to active volcanism in the Woodlark Rise and D'Entrecasteaux Islands results from decompression melting of a relict mantle wedge. The subduction zone geochemical signatures (negative HFSE anomalies) in Woodlark Rift lavas younger than 4 m.y. are a relict from older subduction beneath eastern Papua, likely in the middle Miocene. As the lithosphere is extended ahead of the tip of the westward propagating seafloor spreading center in the Woodlark Basin, the composition of volcanism is inherited from prior arc magmatism (via flux melting) and through time evolves toward magmatism associated with a rifting

  12. Mineralogy and Ar-Ar Age of the Tarahumara IIE Iron, with Reference to the Origin of Alkali-Rich Materials

    NASA Technical Reports Server (NTRS)

    Takeda, Hiroshi; Bogard, Donald D.; Otsuki, Mayumi; Ishii, Teruaki

    2003-01-01

    Silicate inclusions in nine known IIE irons show diversity in mineralogy, and Colomera, Kodaikanal, Elga and Miles contain alkali-rich silicate inclusions. Bogard et al. showed evidence of a complex parent body evolution for IIE irons based on Ar-39-Ar-40 ages. Colomera contained a sanidine-rich surface inclusion and the K-enrichment trends in the Na-rich inclusions are different from those of other IIEs. To elucidate the origin of K-rich materials, we studied the mineralogy and Ar-Ar age of silicate inclusions from the Tarahumara IIE iron meteorite.

  13. Evaluation of gene expression changes of serotonin receptors, 5-HT3AR and 5-HT2AR as main stress factors in breast cancer patients.

    PubMed

    Hejazi, Seyed Hesam; Ahangari, Ghasem; Pornour, Majid; Deezagi, Abdolkhaleagh; Aminzadeh, Saeed; Ahmadkhaniha, Hamid Reza; Akbari, Mohamad Esmail

    2014-01-01

    Breast cancer is a serious and potentially lethal multi-factor disease among 40-50 aged women in both developed and developing countries. Also, various studies have pointed to roles of neurotransmitters like serotonin in development of cancers, through action on various types of receptors. This study was conducted to evaluate serotonin receptor (5HT2AR and 5HT3AR) genes expression in peripheral blood mononuclear cells (PBMCs) of breast cancer patients in comparison with the healthy people and in the MCF7 cell line. Peripheral blood samples were obtained from 30 patients and 30 healthy individuals. Total RNA was extracted from PBMCs and MCF-7 cells. and 5HT2AR and 5HT3AR were detected by RT-PCR techniques. Finally, serotonin receptor gene expression variation in breast cancer patients and MCF-7 cells were determined by real time-PCR. This latter indicated significant promotion in expression of 5HT3AR and 5HT2AR in PBMCs in breast cancer patients but expression of 5HT2AR in the MCF-7 cell line was significantly decreased. In conclusion, after performing complimentary tests, determine of gene expression changes in serotonin receptors (5HT2AR and 5HT3AR) may be useful as a new approach in treatment of breast cancer based on use of antagonists. PMID:24969868

  14. Experimental Constraints on He, Ne, Ar Behavior at Mantle Conditions

    NASA Astrophysics Data System (ADS)

    Jackson, C.; Kelley, S. P.; Parman, S. W.; Cooper, R. F.

    2010-12-01

    We have experimentally constrained He, Ne and Ar mineral-melt partitioning for olivine, enstatite and spinel under mantle P-T conditions. The experiments were run in a piston cylinder apparatus. Run products were analyzed by UV laser ablation microprobe (UVLAMP). Our data (Ol, Opx, Sp), along with literature data (Cpx), suggest He, Ne and Ar are incompatible during mantle melting. Gem quality crystals of En100, Sp and Fo90 were polished using colloidal silica and loaded along with a MgO rich, synthetic MORB powder into a graphite inner and Pt outer capsule. Within the inner capsule, crystals were faced against graphite, an identical crystal or polished glassy carbon. Equal pressures (40-60 total bars) of He, Ne and Ar were loaded into the outer capsule before it was welded closed. The run conditions were 1450C and 1-2 GPa for 10 hrs (Brown University). Depth profiles of the mineral faces were obtained using a 193 nm excimer laser (Open University). The large crystal area and short wavelength laser allows for measurements with high depth resolution and concentration precision: a 400 um aperture with 150 nm ablation depth can provide a detection limit (3 sigma > blank) of ~500 ppb He, ~1 ppm Ne and ~500 ppb Ar. Three mineral ablation pits were imaged using a white light interferometer at Tufts University and indicate an ablation rate of ~25 nm/pulse. Glass ablation rates are estimated using previous measurements. The melts were generally understaturated with respect to He, Ne and Ar (1-10, 3-200 and 4-1000 PPM, respectively). Concentrations in the minerals were mostly below detection limits. Where detectable, near surface gas concentrations visually correlate with the amount of adhering graphite. This could be due to trapped/adsorbed gas in the graphite or to surface deformation produced by the graphite. The surface with the least adhering graphite and smoothest surface (faced against glassy carbon) shows no observable near surface enrichment of He, Ne or Ar. Given

  15. Atmospheric pressure plasma jet utilizing Ar and Ar/H2O mixtures and its applications to bacteria inactivation

    NASA Astrophysics Data System (ADS)

    Cheng, Cheng; Shen, Jie; Xiao, De-Zhi; Xie, Hong-Bing; Lan, Yan; Fang, Shi-Dong; Meng, Yue-Dong; Chu, Paul K.

    2014-07-01

    An atmospheric pressure plasma jet generated with Ar with H2O vapor is characterized and applied to inactivation of Bacillus subtilis spores. The emission spectra obtained from Ar/H2O plasma shows a higher intensity of OH radicals compared to pure argon at a specified H2O concentration. The gas temperature is estimated by comparing the simulated spectra of the OH band with experimental spectra. The excitation electron temperature is determined from the Boltzmann's plots and Stark broadening of the hydrogen Balmer Hβ line is applied to measure the electron density. The gas temperature, excitation electron temperature, and electron density of the plasma jet decrease with the increase of water vapor concentration at a fixed input voltage. The bacteria inactivation rate increases with the increase of OH generation reaching a maximum reduction at 2.6% (v/v) water vapor. Our results also show that the OH radicals generated by the Ar/H2O plasma jet only makes a limited contribution to spore inactivation and the shape change of the spores before and after plasma irradiation is discussed.

  16. Pneumatically sprayed Cu2ZnSnS4 films under Ar and Ar-H2 atmosphere

    NASA Astrophysics Data System (ADS)

    Espindola Rodriguez, M.; Sylla, D.; Sanchez, Y.; López-Marino, S.; Fontané, X.; López-García, J.; Placidi, M.; Pérez-Rodríguez, A.; Vigil-Galán, O.; Saucedo, E.

    2014-06-01

    Cu2ZnSnS4 (CZTS) thin films have been deposited by pneumatic spray pyrolysis onto soda-lime glass and Mo-coated glass substrates by using a special reactor designed for working under controlled atmospheres. The films were grown using both Ar and Ar-H2 as the carrier gas and atmosphere, aiming to eliminate the oxygen-containing atmosphere from the classical spray pyrolysis configuration that uses air as the carrier gas. Thin films with different compositions were prepared and thermally annealed to investigate its compositional and physical properties and its performance as absorber layers in solar cells. To know the impact of the thermal annealing, two different annealing temperatures were used: 550 and 580 °C, both for 30 min. The last temperature showed a great improvement in the crystallinity and allowed a better incorporation of Sn into the films. The optical band gap of the annealed films was found to be around 1.45 eV. Cu-S and ZnO were found as contaminant phases in the as-grown Ar-sprayed samples, but were effectively transformed after annealing. ZnS was detected in both the as-grown and annealed films as the main secondary phase. Solar cells free of scarce elements were fabricated showing an improved conversion efficiency of 1.4%, evidencing the higher potential of this approach for the synthesis of device-grade films.

  17. 40Ar/39Ar dating of microgram feldspar grains from the paired feldspathic achondrites GRA 06128 and 06129

    NASA Astrophysics Data System (ADS)

    Lindsay, Fara N.; Herzog, Gregory F.; Park, Jisun; Delaney, Jeremy S.; Turrin, Brent D.; Swisher, Carl C.

    2014-03-01

    40Ar/39Ar ages of single feldspar grains from the paired meteorites Graves Nunatak 06128 (GRA8; 8 grains) and 06129 (GRA9; 26 grains) are presented. Plateau ages (⩾70% of the 39Ar released) ranged from 4000 to 4600 Ma with an average 1-σ uncertainty of ±90 Ma. The most precise ages obtained were 4267 ± 17 Ma for a grain from GRA8 and 4437 ± 19 Ma and 4321 ± 18 Ma for two grains from GRA9. Isotope correlation diagrams yield less precise ages ranging from 3800 to 5200 Ma with an average 1-σ uncertainty of 250 Ma; they indicate a negligible trapped component. Plateau ages, integrated total fusion ages, and isochron ages are internally concordant at the 95% confidence level. The distribution of the plateau ages for GRA9 is bimodal with peaks at 4400 and 4300 Ma. In contrast, the plateau age distribution for GRA8 peaks at about 4260 Ma with broad wings extending toward younger and older ages. To explain the distributions of grain ages we prefer a scenario that includes a major post-formation event about 4400 Ma ago and a later melt intrusion event that heated GRA8 more than some parts of GRA9.

  18. sup 40 Ar/ sup 39 Ar ages of six Apollo 15 impact melt rocks by laser step heating

    SciTech Connect

    Dalrymple, G.B. ); Ryder, G. )

    1991-06-01

    The authors have obtained 15 high resolution (21-51 step) {sup 40}Ar/{sup 39}Ar age spectra on six Apollo 15 impact melt rocks of different compositions using a continuous laser system on submilligram subsamples and on single crystal plagioclase clasts. Four of the six samples gave reproducible age spectra with well-defined intermediate temperature plateaus over 48% or more of the {sup 39}AR released; the plateaus are interpreted as crystallization ages. Samples 15304,7,69, 15294,6,21, and 15314,26,156 gave virtually identical plateau ages whose weighted mean is 3,870 {plus minus} 6 Ma. These three melt rocks differ in composition and likely formed in three separate impact events. Sample 15356,9 gave replicate plateau ages that average 3,836 {plus minus} 12 Ma and date a fourth and younger impact event. The age spectra for samples 15308,9 and 15414,3,36 increase with increasing increment temperature and may have been formed in or affected by impacts at about 2,700 Ma and 3,870 Ma, respectively. So far there continues to be no convincing evidence in the lunar record for impact melts older than about 3.9 Ga.

  19. State-selected ion-molecule reactions: N 2+(X, v″), N 2+(A, v') + Ar → N 2 + Ar +

    NASA Astrophysics Data System (ADS)

    Govers, Thomas R.; Guyon, Paul Marie; Baer, Thomas; Cole, Keith; Fröhlich, Horst; Lavollée, Michel

    1984-07-01

    The total, absolute cross sections for charge transfer between N 2+(X, A, v) and Ar have been measured at 8, 14 and 20 eV center of mass translational energy. The internal energy of the N 2+ ions was selected by threshold photoelectron-photoion coincidence using pulsed synchrotron radiation from the ACO storage ring. The vibrational levels investigated were v″ = 0-4 for the X state, and v' = 0-6 for the A state. The data for the A state were corrected for the fraction of ions which fluoresced to the X state prior to reaction with Ar. The N 2+(X, v″ = 0) state was found to be much less reactive (by a factor ≥ 10) than the other X-state levels, at all three translational energies. The levels N 2+(A, v' ⩾ 3) were found to react with cross-sections which depend strongly on the relative translational energy. The data are interpreted in terms of the interaction between vibronic curves as discussed by Bauer, Fisher and Gilmore. This model accounts well for the low reactivity of the N 2+(X, 0) level. It is proposed that the variation in the cross section of the N 2+(A, v' ⩾ 3) + Ar reactions is a result of competition with a radiationless transition which converts N 2+(A, v') ions into N 2+(X, v″) ions.

  20. WA1ms: A ∼2.61 Ga muscovite standard for 40Ar/39Ar dating

    NASA Astrophysics Data System (ADS)

    Jourdan, Fred; Frew, Adam; Joly, Aurore; Mayers, Celia; Evans, Noreen J.

    2014-09-01

    The 40Ar/39Ar dating technique requires the use of neutron fluence monitors (standards) to allow calculation of the age of a sample. Precise calibration of these standards is crucial to obtaining accurate ages and decreasing the uncertainties associated with 40Ar/39Ar dates. Few fully intercalibrated 40Ar/39Ar standards with a sufficient total fusion grain-to-grain reproducibility are currently in use in the argon community. For Precambrian samples, only Hb3gr hornblende (∼1.08 Ga) yields sufficient grain-to-grain reproducibility and has an appropriate age for acceptable argon isotopic ratio measurements. Here, we present chemical and intercalibration results for a new ∼2.61 Ga standard. WA1ms is a muscovite extracted from an Archaean shear zone in the Lake Johnston greenstone belt, Western Australia. In situ trace element analysis by ELA-ICPMS revealed consistent K contents, subtle zonation and intra-grain and grain-to-grain heterogeneities in Rb, Sr, Ti, and Fe but a lack of mineral inclusions.WA1ms has been investigated over 3 irradiations ranging from 25 to 40 h, in two reactors, with several disc positions and three grains sizes and has been calibrated against FCs and GA1550, and Hb3gr. Overall, we carried out 48 total fusion and 4 step-heating experiments of WA1ms crystals. Flat age spectra and average F-value (40Ar∗/39ArK) relative standard deviations ranging from of 0.43% to 0.60% (P = 0.15-0.83) for 47/48 analyses demonstrate the reproducibility of WA1ms and its suitability as a reliable 40Ar/39Ar standard. We calculated R[WA1ms/FCs] = 205.59 ± 0.25, R[WA1ms/GA1550] = 57.25 ± 0.06 and R[WA1ms/Hb3gr] = 3.9713 ± 0.014 (all with P > 0.14) allowing direct comparison between WA1ms and any standards in used in the community, provided that they have been calibrated against any of the three standards used in the calibration and regardless of the age adopted for each of these standards. The recently revised decay constant values and standard ages proposed

  1. Rheasilvia provenance of the Kapoeta howardite inferred from ∼ 1 Ga40Ar/39Ar feldspar ages

    NASA Astrophysics Data System (ADS)

    Lindsay, Fara N.; Delaney, Jeremy S.; Herzog, Gregory F.; Turrin, Brent D.; Park, Jisun; Swisher, Carl C.

    2015-03-01

    We report 40Ar/39Ar ages for several lithological components of the brecciated howardite Kapoeta and compare the ages with results for asteroid 4 Vesta as observed by the Dawn mission. Our Kapoeta sample has an unusual, millimeter wide glass vein that intruded into a complex breccia. The plateau ages of three lithic clasts of basaltic composition that were remote from the glass vein range from 4.2 to 4.5 Ga. Such ages are typical of eucritic material; the oldest reflects early magmatic crystallization (∼ 4.5 Ga), the younger (4.2-4.5 Ga) reflect magmatism associated with protracted cooling. Samples of the glass vein itself, which include relict grains, give apparent ages between 3.1 and 3.9 Ga as do chips from the matrix. We consider both glass and bulk matrix ages as mixing ages; not marking the time of a single event, but dating regolith activity (< 3.1- 4.1 Ga). Eight feldspar grains close to the glass vein give markedly younger plateau ages averaging 1.4 Ga. The Ar release spectra for glass vein and breccia subsamples indicate a disturbance in the last 1.4 Ga. Taken together, these younger ages suggest a recent, major thermal event in the history of howardites that has been under-reported - perhaps the impact that formed the Rheasilvia basin on Vesta.

  2. CD metrology for avoiding shrinkage of ArF resist patterns in 100 nm ArF lithography

    NASA Astrophysics Data System (ADS)

    You, Tae-Jun; Bok, Cheol-Kyu; Shin, Ki-Soo

    2002-07-01

    ML 4689-80 CD Metrology for Avoiding Shrinkage of ArF Resist Patterns in 100nm ArF Lithography Tae-Jun You, Cheolkyu Bok, Ki-Soo Shin Hynix Semiconductor, San 136-1 Amiri, Bubal-eub, Ichon-si, Kyongki-do 467-701, Korea We have observed CD(Critical Dimension) shrinkage of acrylate type ArF resist patterns during SEM measurement. CD change was 30% shrinkage for line pattern and 10% expansion for contact hole patterns after 30 times measurement. CD shrinkage was proportion to line pattern size but no relation with LER(Line Edge Roughness). We confirm that CD shrinkage different from resist to resist and SEM measurement condition. CD shrinkage was bigger for acrylate type resist than COMA(Cyclo Olefin Maleic Anhydride) type resist and smaller at lower electron voltage and current conditions. In order to get the improvement of CD shrinkage, we performed electron-beam curing before SEM measurement. Above (see paper for formula) electron-beam dose condition, CD shrinkage improved from 10% to 3%. However, this method caused OPC(Optical Proximity Correction) issue as CD also changed after electron-beam curing. Therefore, we tried to develop a new measurement method instead of applying additional process technique. In this paper, we will describe our CD measurement method, Off-Site measurement technique, for 100nm DRAM lithography. The Off-Site CD measurement repeatability (formula available in paper) was controlled below (see paper).

  3. Constraints on the development of Proterozoic basins in central India from 40Ar/39Ar analysis of authigenic glauconitic minerals

    USGS Publications Warehouse

    Conrad, J.E.; Hein, J.R.; Chaudhuri, A.K.; Patranabis-Deb, S.; Mukhopadhyay, J.; Deb, G.K.; Beukes, N.J.

    2011-01-01

    Ages of some key stratigraphic sequences in central Indian Proterozoic basins are based predominantly on lithostratigraphic relationships that have been constrained by only a few radioisotopic dates. To help improve age constraints, single grains of glauconitic minerals taken from sandstone and limestone in two Proterozoic sequences in the Pranhita-Godavari Valley and the Chattisgarh basin were analyzed by the 40Ar/39Ar incremental heating method. Analysis of the age spectra distinguishes between ages that are interpreted to reflect the time of glauconite formation, and anomalous ages that result from inherited argon or postcrystallization heating. The analyses indicate an age of 1686 ± 6 Ma for the Pandikunta Limestone and 1566 ± 6 Ma for the Ramgundam Sandstone, two units in the western belt of Proterozoic sequences in Pranhita-Godavari Valley. Glauconite from the Chanda Limestone, in the upper part of this sequence, contains inherited 40Ar but is interpreted to reflect an age of ca. 1200 Ma. Glauconite from the Somanpalli Group in the eastern belt of the Pranhita-Godavari Valley gives an age of 1620 ± 6 Ma. In the Chattisgarh basin, glauconite from two units gives disturbed ages that suggest a period of regional heating in the Chattisgarh basin at ca. 960–1000 Ma. These new ages indicate that these sequences are 200–400 m.y. older than previously recognized, which has important implications for geochemical studies of Mesoproterozoic ocean redox conditions in addition to providing important constraints on regional tectonics and lithostratigraphy.

  4. Scaling laws for the atomic Xe laser in Ne/Ar/Xe and He/Ar/Xe gas mixtures

    SciTech Connect

    Vogel, M.S.; Jong, W.; Kushner, S.

    1992-12-01

    The atomic Xe laser oscillates on 6 transitions (1.73 {mu}m - 3.7 {mu}m) between the 5d and 6p manifolds. Ar/Xe gas mixtures usually produce the highest laser efficiencies at 1.73 {mu}m, however gas heating from energy loading can reduce or terminate laser output due to an increase in the electron density. One is therefore motivated to increase the gas pressure by adding a lighter rare gas (He or Ne). The scaling of the atomic Xe laser using Ne/Ar/Xe and He/Ar/Xe gas mixtures have been investigated using a computer model. Addition of Ne significantly alters the kinetic pathways leading to increased pumping of the 6p manifold by dissociative recombination of Xe{sub 2}{sup +} thereby decreasing laser power. Increasing the heat capacity of the mixture by adding Ne can regain some of this loss at high energy loading. He addition is less disruptive with respect to the ion chemistry, but preferential quenching of the lower laser levels causes osciallation to be dominantly at 2.03 {mu}m.

  5. Evaluation of sintering effects on SiC-incorporated UO2 kernels under Ar and Ar-4%H2 environments

    NASA Astrophysics Data System (ADS)

    Silva, Chinthaka M.; Lindemer, Terrence B.; Hunt, Rodney D.; Collins, Jack L.; Terrani, Kurt A.; Snead, Lance L.

    2013-11-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO2 kernels used for tristructural isotropic (TRISO) particle fuels and to prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that an internal gelation process can be used to incorporate SiC in UO2 fuel kernels. Even though the presence of UC in either argon (Ar) or Ar-4%H2 sintered samples suggested a lowering of the SiC up to 3.5-1.4 mol%, respectively, the presence of other silicon-related chemical phases indicates the preservation of silicon in the kernels during sintering process. UC formation was presumed to occur by two reactions. The first was by the reaction of SiC with its protective SiO2 oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO2 to form UC. The second process was direct UO2 reaction with SiC grains to form SiO, CO, and UC. A slightly higher density and UC content were observed in the sample sintered in Ar-4%H2, but both atmospheres produced kernels with ˜95% of theoretical density. It is suggested that incorporating CO in the sintering gas could prevent UC formation and preserve the initial SiC content.

  6. 40Ar* loss in experimentally deformed muscovite and biotite with implications for 40Ar/39Ar geochronology of naturally deformed rocks

    USGS Publications Warehouse

    Cosca, Michael; Stunitz, Holger; Bourgiex, Anne-Lise; Lee, John P.

    2011-01-01

    The effects of deformation on radiogenic argon (40Ar*) retentivity in mica are described from high pressure experiments performed on rock samples of peraluminous granite containing euhedral muscovite and biotite. Cylindrical cores, ~15 mm in length and 6.25 mm in diameter, were drilled from granite collected from the South Armorican Massif in northwestern France, loaded into gold capsules, and weld-sealed in the presence of excess water. The samples were deformed at a pressure of 10 kb and a temperature of 600 degrees C over a period 29 of hours within a solid medium assembly in a Griggs-type triaxial hydraulic deformation apparatus. Overall shortening in the experiments was approximately 10%. Transmitted light and secondary and backscattered electron imaging of the deformed granite samples reveals evidence of induced defects and for significant physical grain size reduction by kinking, cracking, and grain segmentation of the micas.

  7. Comparison of Ne and Ar seeded radiative divertor plasmas in JT-60U

    NASA Astrophysics Data System (ADS)

    Nakano, T.

    2015-08-01

    In H-mode plasmas with Ne, Ar and a mixture of Ne and Ar injection, the divertor radiation power fractions amongst these impurities in addition to an intrinsic impurity, C, are investigated. In plasmas with the inner divertor plasma attached, carbon is the biggest radiator, whichever impurity, Ne, Ar or a mixture of Ar and Ne is injected. In contrast, in plasmas with the inner divertor plasma detached, Ne is the biggest radiator due to a significantly high recombination radiation from Ne VIII. Ar is always a minor contributor in plasmas with the inner divertor both attached and detached.

  8. Duration of Louisville hotspot volcanism at IODP 330 sites Canopus, Burton, and Rigil via 40Ar/39Ar geochronology

    NASA Astrophysics Data System (ADS)

    Cohen, B. E.; Vasconcelos, P. M.; Koppers, A. A.; Thiede, D. S.

    2013-12-01

    The Louisville seamount trail is a chain of intraplate volcanoes constructed over the past ~80 million years, as the Pacific plate moved 4300 km over a long-lived mantle melting anomaly. During IODP Expedition 330, over 800 m of alkaline mafic volcanic lavas, as well as interbedded and overlying sediments, were recovered from five of these seamounts in the older (~80-50 Ma) part of the chain. In this study we have undertaken geochronology of the volcanic units to provide time constraints for the magmatic evolution of the volcanoes. Sixteen of these drilled lava flows have been successfully dated using MAP-215-50 spectrometers, with six samples analyzed at Oregon State University (Koppers et al. 2012) and 12 flows analyzed at The University of Queensland. To check for consistency, two lava flows were dated at both laboratories; both samples yielded results within 2σ error. To minimize the effects of seawater alteration, only samples with well-crystallized groundmass were picked, and material cleaned via HNO3 and HCl acid pretreatment. Plateaus comprise 61 to 87% of the 39Ar released, and 40Ar/36Ar vs. 39Ar/36Ar correlation diagrams reveal all samples contained trapped argon within error of modern-day atmosphere. All ages determined are consistent with stratigraphic constraints, and we interpret the results to be reliable estimates of eruption ages. Units from Burton Guyot (site U1376A) yield ages from 70.8 × 0.5 to 64.1 × 0.5 Ma (2σ, using the atmospheric argon ratio and decay constants from Steiger & Jäger (1978) and a Fish Canyon sanidine age of 28.02 (Renne et al. 1998)). This long (~7 Ma) duration is consistent with petrologic evidence for substantial post-shield volcanic activity at this site. Meanwhile, at Canopus (site U1372A) and Rigil (sites U1373A and U1374A), lavas from the base, middle, and top of the respective volcanic piles yielded ages within analytical error. At the two deepest sites (U1372A and 1374A) 187 and 505 m of volcanic rocks were

  9. Coherence of the Dabie Shan UHPM terrane investigated by Lu-Hf and 40Ar/39Ar dating of eclogites

    NASA Astrophysics Data System (ADS)

    Brouwer, F. M.; Groen, M.; Nebel, O.; Wijbrans, J. R.; Qiu, H.

    2009-12-01

    The Central China Orogenic Belt is the largest known ultrahigh-pressure metamorphic (UHPM) belt. Currently exposed UHP metamorphic rocks reflect subduction of massive swathes of continental crust to depths exceeding 100 km. Subsequent uplift exposed the voluminous sequence more or less intact. Deciphering responsible exhumation processes requires well constrained P-T-time paths. Most workers accept Triassic (~240 and 220-200 Ma) peak UHP metamorphism on the basis of zircon U-Pb ages in Central and Eastern Dabie Shan, while Western Dabie Shan, Qinling, North Qaidam and Altyn Tagh exhibit Ordovician (420-500 Ma) UHPM. However, contrasting reports of Carboniferous and Ordovian UHPM in Eastern Dabie Shan (Jian et al. 2001; Qiu & Wijbrans, 2006, 2008), and Ordovician, Carboniferous and Triassic (U)HPM in Western Dabie Shan (Wu et al. 2009) question this simple East-West gradient. Here, we investigate PTt-paths for localities throughout Dabie Shan to determine how far west the Triassic UHP event is documented, and how far east the Carboniferous and Ordovician events can be traced. Based on this distribution we aim to establish whether the Dabie Shan terrane is an amalgam of blocks that underwent UHPM at different times rather than a single coherent terrane. Eclogite samples are investigated for thermobarometry, Lu-Hf Grt-Cpx geochronology, and 40Ar/39Ar thermochronology. For fresh eclogites Thermocalc was used to establish equilibration conditions of the UHPM assemblage, Grt and Cpx of which were subsequently used for Lu-Hf isotope analysis. In addition, retrogressed eclogites, two fresh eclogites and two orthogneisses were analysed for 40Ar/39Ar isotope distributions in Phg, Bt, Amp and Kfs. Four fresh eclogites, all collected at reported UHP-localities confirm established PT-estimates for peak-metamorphism above the Coe-in reaction at 450-680 °C, with higher T for eastern Dabie. In one sample this is confirmed by the presence of a Coe inclusion in Cpx. Lu-Hf Grt

  10. An 40Ar/39Ar age for Geomagnetic Instability Recorded at the Albuquerque Volcanoes and Pringle Falls, Oregon

    NASA Astrophysics Data System (ADS)

    Singer, B. S.; Jicha, B. R.; Kirby, B. T.; Zhang, X.; Geissman, J. W.; Herrero-Bervera, E.

    2005-12-01

    The timing and frequency of short-lived geomagnetic events, including excursions and aborted reversal attempts, provide important observational constraints on models of geodynamo behavior as well as calibration points for stratigraphic and paleoclimatic age models derived from marine sediments. The number of potential geomagnetic events during the Quaternary period has proliferated as more detailed paleodirectional and paleointensity data have emerged from sediments worldwide. Yet, determining ages for these events remains a challenge because astronomical dating of sediment cores is subject to assumptions and non-systematic errors that are difficult to quantify and vary from core to core. 40Ar/39Ar geochronology applied to lava flows or ash falls that record geomagnetic excursions can yield radioisotopic ages sufficiently precise to verify individual events, test correlations among seemingly disparate events, and quantify periods between events. Seventeen furnace incremental heating experiments on 100-200 mg groundmass samples from six sites in the transitionally magnetized basalt of the Albuquerque Volcanoes yield an isochron of 211 ± 22 ka* that is within error of previous K-Ar (155 ± 94 ka) and U-Th isochron (156 ± 58 ka) age determinations, but is 3 to 4 times more precise. At Pringle Falls, Oregon, Ash D was deposited during the onset of an excursion recorded by a lacustrine sediment sequence. Sixteen laser incremental heating experiments on 20-40 mg samples of plagioclase crystals from Ash D gave 64 concordant plateau age points that define an 40Ar/39Ar isochron of 211 ± 13 ka which is an order of magnitude more precise than the isochron (198 ± 118 ka) associated with the published plateau age from a single plagioclase age spectrum (221 ± 20 ka). Although the Virtual Geomagnetic Pole (VGP) recorded by the Albuquerque Volcanoes lies near, bot not on, the VGP path of the Pringle Falls excursion, these two sites are 15 arc degrees apart and need not record

  11. Repression of Runx2 by Androgen Receptor (AR) in Osteoblasts and Prostate Cancer Cells: AR Binds Runx2 and Abrogates Its Recruitment to DNA

    PubMed Central

    Baniwal, Sanjeev K.; Khalid, Omar; Sir, Donna; Buchanan, Grant; Coetzee, Gerhard A.; Frenkel, Baruch

    2009-01-01

    Runx2 and androgen receptor (AR) are master transcription factors with pivotal roles in bone metabolism and prostate cancer (PCa). We dissected AR-mediated repression of Runx2 in dihydrotestosterone (DHT)-treated osteoblastic and PCa cells using reporter assays and endogenous Runx2 target genes. Repression required DHT, but not AR’s transactivation function, and was associated with nuclear colocalization of the two proteins. Runx2 and AR coimmunoprecipitated and interacted directly in glutathione-S-transferase pull-down assays. Interaction was ionic in nature. Intact AR DNA-binding domain (DBD) was necessary and sufficient for both interaction with Runx2 and its repression. Runx2 sequences required for interaction were the C-terminal 132 amino acid residues together with the Runt DBD. Runx2 DNA binding was abrogated by endogenous AR in chromatin immunoprecipitation assays and by recombinant AR-DBD in gel shift assays. Furthermore, AR caused increased nuclear mobility of Runx2 as indicated by faster fluorescence recovery after photobleaching. Thus, AR binds Runx2 and abrogates its binding to DNA and possibly to other nuclear components. Clinical relevance of our results was suggested by an inverse correlation between expression of AR-responsive prostate-specific antigen and osteocalcin genes in PCa biopsies. Given the tumor suppressor properties of Runx2, its repression by AR may constitute a mechanism of hormone carcinogenesis. Attenuation of Runx2 by AR in osteoblasts may play a role in skeletal metabolism: the bone-sparing effect of androgens is attributable, in part, to keeping Runx2 activity in check and preventing high-turnover bone disease such as seen after castration and in transgenic mice overexpressing Runx2 in osteoblasts. PMID:19389811

  12. Dual mode of energy coupling by the oxyanion-translocating ArsB protein.

    PubMed Central

    Dey, S; Rosen, B P

    1995-01-01

    The arsA and arsB genes of the ars operon of R-factor R773 confer arsenite resistance in Escherichia coli by coding for an anion-translocating ATPase. Arsenite resistance and the in vivo energetics of arsenite transport were compared in cells expressing the arsA and arsB genes and those expressing just the arsB gene. Cells expressing the arsB gene exhibited intermediate arsenite resistance compared with cells expressing both the arsA and arsB genes. Both types of cells exhibited energy-dependent arsenite exclusion. Exclusion of 73AsO2- from cells expressing only the arsB gene was coupled to electrochemical energy, while in cells expressing both genes, transport was coupled to chemical energy, most likely ATP. These results suggest that the Ars anion transport system can be either an obligatory ATP-coupled primary pump or a secondary carrier coupled to the proton motive force, depending on the subunit composition of the transport complex. PMID:7814328

  13. Partners in crime: deregulation of AR activity and androgen synthesis in prostate cancer

    PubMed Central

    Knudsen, Karen E.; Penning, Trevor

    2010-01-01

    Prostate cancer remains a leading cause of cancer death, as there are no durable means to treat advanced disease. Treatment of non-organ confined prostate cancer hinges on its androgen dependence. First line therapeutic strategies suppress androgen receptor (AR) activity, via androgen ablation and direct AR antagonists. While initially effective, incurable, "castration-resistant" tumors arise due to resurgent AR activity. Alterations of AR and/or associated regulatory networks are known to restore receptor activity and support resultant therapy-resistant tumor progression. However, recent evidence also reveals an unexpected contribution of AR ligand, wherein alterations in pathways controlling androgen synthesis support castrate-resistant AR activity. Herein, mechanisms underlying the lethal pairing of AR deregulation and aberrant androgen synthesis in prostate cancer progression will be discussed. PMID:20138542

  14. Theoretical study of the interaction of Fe, Fe/sup +/, and FeCO with Ar

    SciTech Connect

    Braga, M.; Almeida, A.L.; Taft, C.A.; Hammond, B.L.; Lester W.A. Jr.

    1988-10-15

    Ab initio Hartree--Fock calculations were performed on FeAr and FeAr/sup +/ in order to determine the interaction of both neutral and singly-ionized Fe atoms trapped in Ar, and on ArFeCO and FeCOAr in order to ascertain the effect of an Ar matrix on the FeCO molecule. Quadrupole splittings and isomer shifts are computed using ab initio orbital populations and charge densities scaled by a relativistic factor. Good agreement between calculated and experimental hyperfine parameters is found in each case. The interaction energy for Fe/sup +/--Ar has been computed by ab initio Hartree--Fock and effective-core potential (ECP) methods. Both approaches yield a minimum between Fe/sup +/ and Ar at approximately 7.6 bohr.

  15. Protein kinase D1 (PKD1) influences androgen receptor (AR) function in prostate cancer cells

    SciTech Connect

    Mak, Paul; Jaggi, Meena; Chauhan, Subhash C.; Balaji, K.C.

    2008-09-05

    Protein kinase D1 (PKD1), founding member of PKD protein family, is down-regulated in advanced prostate cancer (PCa). We demonstrate that PKD1 and androgen receptor (AR) are present as a protein complex in PCa cells. PKD1 is associated with a transcriptional complex which contains AR and promoter sequence of the Prostate Specific Antigen (PSA) gene. Ectopic expression of wild type PKD1 and the kinase dead mutant PKD1 (K628W) attenuated the ligand-dependent transcriptional activation of AR in prostate cancer cells and yeast cells indicating that PKD1 can affect AR transcription activity, whereas knocking down PKD1 enhanced the ligand-dependent transcriptional activation of AR. Co-expression of kinase dead mutant with AR significantly inhibited androgen-mediated cell proliferation in both LNCaP and DU145 PC cells. Our data demonstrate for the first time that PKD1 can influence AR function in PCa cells.

  16. Rotational Spectrum of Ar...PROPARGYL Alcohol Complex

    NASA Astrophysics Data System (ADS)

    Mani, Devendra; Shahi, Abhishek; Arunan, E.

    2012-06-01

    Pure rotational spectrum for Ar...Propargyl alcohol complex has been observed and fitted. Fitted rotational constants for the complex are : A=4346.17307(90) MHz, B=1617.15317(19)MHz and C= 1245.42065(15) MHz. These rotational constants are very close to the ab-initio rotational constants for the geometry, in which propargyl alcohol exists in gauche conformation and Ar interacts with both, the hydroxyl group and the acetylenic group of propargyl alcohol. Rotational spectrum of deuterated isotopologue (-OD) of the complex further confirms the existence of the above mentioned geometry. In previous studies tunneling frequency corresponding to -OH tunneling motion in propargyl alocohol monomer was determined to be 652.4 GHz and for -OD tunneling motion in mono-deuterated species, it was 213.5 GHz. In Ar...Propargyl alcohol complex also, a-type and c-dipole transitions show tunneling splitting. In the parent complex, for a-type transitions, tunneling splitting was 10 KHz and for c-type transitions (c-dipole of the complex is in the same direction as in propargyl alcohol monomer, and it is antisymmetric with respect to OH tunneling motion in both monomer and the complex), it was 2.59 MHz. In deuterated complex (OD) splitting was not resolvable for a-type transitions while for c-type it reduces to 900 KHz. Search for C-13 isotopologues is in progress. Moreover, propargyl alcohol offers several possibilities for H-bonding and we are planning to study its complexes with water in near future. Results will be presented in the talk. E. Hirota,J. Mol. Spectrosc. 26 (1968) 335-350. J.C. Pearson, B.J. Drouin, J. Mol. Spectrosc. 234 (2005) 149-156.

  17. Experimental Constraints on He, Ne, and Ar Solubility in Serpentinite

    NASA Astrophysics Data System (ADS)

    Krantz, J. A.; Parman, S. W.; Kelley, S. P.; Smye, A.; Jackson, C.; Cooper, R. F.

    2015-12-01

    Experiments have been performed to constrain the solubility of He, Ne, and Ar in natural samples of antigorite from three locations. Geochemical analyses of exhumed subduction zone material [1] and well gases [2] indicate that noble gases are recycled from the surface of the earth into the mantle. The mechanism by which uncharged atoms can be bound to a mineral and subsequently recycled remains unclear, but recent experimental work suggests that ring structures in silicate minerals are ideal sites for noble gases [3]. Serpentine contains such ring structures and is abundant in subducting slabs, providing significant potential for control of the recycling of noble gases. Experiments were performed in a cold seal pressure vessel at 350°C using a mix of equal parts He, Ne, and Ar as the pressure media (Brown University, USA). Pressures varied from 0.15 to 1.13 kbar total pressure and durations varied from 20 to 188 hours. Samples were analyzed by UV laser ablation, noble gas mass spectrometry (Open University, UK). He and Ne reached equilibrium during the experiments and both exhibit Henrian behavior. Data from the cleanest sample reduces the error by approximately an order of magnitude over previous work [3] and confirms that He is significantly more soluble (HCHe=6.05x10-10 mol/g/bar) than Ne (HCNe=5.12x10-12 mol/g/bar) in antigorite. Preliminary data from the cleanest sample suggests that Ar is more soluble than both He and Ne (HCAr=1.94x10-10 mol/g/bar). This provides a mechanism for fractionation of noble gases during recycling. 1. Kendrick, M.A., Scambelluri, M., Honda, M., Phillips, D., Nature Geoscience, 4, 807-812, 2011 2. Holland, G., and Ballentine, C.J., Nature, 441, 186-191, 2006 3. Jackson, C.R.M., Parman, S.W., Kelley, S.P., Cooper, R.F., GCA, 159, 1-15, 2015

  18. Estudio del sistema simbiótico AR Pavonis

    NASA Astrophysics Data System (ADS)

    Quiroga, C.; Brandi, E.; Ferrer, O.; García, L.; Barbá, R.

    Se presenta un estudio espectroscópico y polarimétrico de la binaria eclipsante AR Pavonis a partir de observaciones obtenidas con el telescopio de 2.15 m. del CASLEO (San Juan). El estudio de la naturaleza del sistema se realizó a través del análisis de algunos espectros reunidos entre los años 1990 y 1995 y de datos polarimétricos correspondientes al intervalo 1995 y 1997. El análisis espectroscópico indica que AR Pav está compuesta por una gigante roja M3.7 y una componente caliente compacta, con una temperatura mayor a 90000 K y una luminosidad del orden de 500Lsolar. A lo largo del período orbital, las variaciones observadas en flujo y en velocidades radiales, reflejan que las emisiones permitidas se forman en una región que rodea la componente caliente. El estudio de la polarización lineal de AR Pav indica que además de una componente interestelar, existe una componente intrínseca del sistema que varía temporalmente y con la longitud de onda de la luz polarizada. El distinto comportamiento del grado de polarización y del ángulo de posición observado en fases diferentes, sugiere que distintos mecanismos pueden estar actuando, dependiendo de la región de scattering observado a lo largo de la línea de la visual.

  19. Oscillator strengths for Ar VII, Ca IX and Fe XV

    NASA Technical Reports Server (NTRS)

    Tayal, S. S.

    1986-01-01

    The excitation energies and oscillator strengths are calculated for electric-dipole-allowed and intercombination transitions between 3s2 1S, 3s3p(1,3)P0, 3p2 3P, 1D, 1S and 3s3d(1,3)D states in Ar VII, Ca IX, and Fe XV ions of the magnesium sequence. These states are represented by the fairly large configuration-interaction expansions. The calculations have been carried out in both LS and intermediate coupling schemes. The relativistic corrections have been included through the Breit-Pauli Hamiltonian. The results are compared with previous theoretical calculations and with measurements.

  20. Dusty Plasma in He-Ar Glow Discharge

    SciTech Connect

    Maiorov, S. A.; Ramazanov, T. S.; Dzhumagulova, K. N.; Dosbolayev, M. K.; Jumabekov, A. N.

    2008-09-07

    The paper reports on the first experiments with plasma-dust formations in dc gas discharge plasma for He-Ar mixture. It is shown that under the conventional conditions of the experiments with dusty structures in plasma, the choice of light and heavy gases for the mixture suppresses electron heating in electric field and results in a supersonic jet with high Mach numbers. Distribution functions for drifting ions in the gas mixture are calculated for various mixture concentrations, electric field strengths and gas pressures.

  1. Modeling of advanced ECLSS/ARS with ASPEN

    NASA Technical Reports Server (NTRS)

    Kolodney, M.; Lange, K. E.; Edeen, M. A.

    1991-01-01

    System-level ASPEN models were developed for the CO2 partial reduction subsystem and a bioregenerative life support subsystem (BRLSS). The individual component and subsystem models were integrated into three different system-level atmospheric revitalization subsystem (ARS) models: baseline physico-chemical, BRLSS, and partial reduction of Martian CO2. The Aspen models were based on FORTRAN interfaces necessary for integration with another program, G189A, to perform quasi-transient modeling. Detailed reactor models were prepared for the two CO2 reduction reactors (Bosch and Advanced Carbon Formation), and the low-temperature trace contaminant oxidation reactor.

  2. Adsorption of Ar on individual carbon nanotubes, graphene, and graphite

    NASA Astrophysics Data System (ADS)

    Dzyubenko, Boris; Kahn, Joshua; Vilches, Oscar; Cobden, David

    2015-03-01

    We compare and contrast results of adsorption measurements of Ar on single-walled carbon nanotubes, graphene, and graphite. Adsorption isotherms on individual suspended nanotubes were obtained using both the mechanical resonance frequency shift (sensitive to mass adsorption) and the electrical conductance. Isotherms on graphene mounted on hexagonal boron nitride were obtained using only the conductance. New volumetric adsorption isotherms on bulk exfoliated graphite were also obtained, paying special attention to the very low coverage region (less than 2% of a monolayer). This allowed us to compare the degree of heterogeneity on the three substrate types, the binding energies, and the van der Waals 2D parameters. Research supported by NSF DMR 1206208.

  3. A global potential energy surface for ArH2

    NASA Technical Reports Server (NTRS)

    Schwenke, David W.; Walch, Stephen P.; Taylor, Peter R.

    1992-01-01

    We describe a simple analytic representation of the ArH2 potential energy surface which well reproduces the results of extensive ab initio electronic structure calculations. The analytic representation smoothly interpolates between the dissociated H2 and strong bonding limits. In the fitting process, emphasis is made on accurately reproducing regions of the potential expected to be important for high temperature (ca. 3000 K) collision processes. Overall, the anisotropy and H2 bond length dependence of the analytic representation well reproduce the input data.

  4. The readout system for the ArTeMis camera

    NASA Astrophysics Data System (ADS)

    Doumayrou, E.; Lortholary, M.; Dumaye, L.; Hamon, G.

    2014-07-01

    During ArTeMiS observations at the APEX telescope (Chajnantor, Chile), 5760 bolometric pixels from 20 arrays at 300mK, corresponding to 3 submillimeter focal planes at 450μm, 350μm and 200μm, have to be read out simultaneously at 40Hz. The read out system, made of electronics and software, is the full chain from the cryostat to the telescope. The readout electronics consists of cryogenic buffers at 4K (NABU), based on CMOS technology, and of warm electronic acquisition systems called BOLERO. The bolometric signal given by each pixel has to be amplified, sampled, converted, time stamped and formatted in data packets by the BOLERO electronics. The time stamping is obtained by the decoding of an IRIG-B signal given by APEX and is key to ensure the synchronization of the data with the telescope. Specifically developed for ArTeMiS, BOLERO is an assembly of analogue and digital FPGA boards connected directly on the top of the cryostat. Two detectors arrays (18*16 pixels), one NABU and one BOLERO interconnected by ribbon cables constitute the unit of the electronic architecture of ArTeMiS. In total, the 20 detectors for the tree focal planes are read by 10 BOLEROs. The software is working on a Linux operating system, it runs on 2 back-end computers (called BEAR) which are small and robust PCs with solid state disks. They gather the 10 BOLEROs data fluxes, and reconstruct the focal planes images. When the telescope scans the sky, the acquisitions are triggered thanks to a specific network protocol. This interface with APEX enables to synchronize the acquisition with the observations on sky: the time stamped data packets are sent during the scans to the APEX software that builds the observation FITS files. A graphical user interface enables the setting of the camera and the real time display of the focal plane images, which is essential in laboratory and commissioning phases. The software is a set of C++, Labview and Python, the qualities of which are respectively used

  5. Noble Gases in the Monahans Chondrite and Halite: Ar-39 - Ar-40 Age, Space Exposure Age, Trapped Solar Gases, and Neutron Fluence

    NASA Technical Reports Server (NTRS)

    Garrison, Daniel H.; Bogard, Donald D.

    2000-01-01

    For the Monahans chondrite and halite, we determined Ar-39 - Ar-40 ages of silicate = 4.53 Ga, halite > 4.3 Ga; a space exposure age of approx. 5 Ma; a regolith pre-irradiation; solar gas concentrations in the dark phase; and a regolith thermal neutron fluence.

  6. Joint determination of 40K decay constants and 40Ar∗/ 40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/ 39Ar geochronology

    NASA Astrophysics Data System (ADS)

    Renne, Paul R.; Mundil, Roland; Balco, Greg; Min, Kyoungwon; Ludwig, Kenneth R.

    2010-09-01

    40Ar/ 39Ar and K-Ar geochronology have long suffered from large systematic errors arising from imprecise K and Ar isotopic data for standards and imprecisely determined decay constants for the branched decay of 40K by electron capture and β - emission. This study presents a statistical optimization approach allowing constraints from 40K activity data, K-Ar isotopic data, and pairs of 238U- 206Pb and 40Ar/ 39Ar data for rigorously selected rocks to be used as inputs for estimating the partial decay constants ( λ ɛ and λ β) of 40K and the 40Ar∗/ 40K ratio ( κFCs) of the widely used Fish Canyon sanidine (FCs) standard. This yields values of κFCs = (1.6418 ± 0.0045) × 10 -3, λ ɛ = (0.5755 ± 0.0016) × 10 -10 a -1 and λ β = (4.9737 ± 0.0093) × 10 -10 a -1. These results improve uncertainties in the decay constants by a factor of >4 relative to values derived from activity data alone. Uncertainties in these variables determined by our approach are moderately to highly correlated (cov( κFCs, λ ɛ) = 7.1889 × 10 -19, cov( κFCs, λ β) = -7.1390 × 10 -19, cov( λ ɛ, λ β) = -3.4497 × 10 -26) and one must take account of the covariances in error propagation by either linear or Monte Carlo methods. 40Ar/ 39Ar age errors estimated from these results are significantly reduced relative to previous calibrations. Also, age errors are smaller for a comparable level of isotopic measurement precision than those produced by the 238U/ 206Pb system, because the 40Ar/ 39Ar system is now jointly calibrated by both the 40K and 238U decay constants, and because λ ɛ( 40K) < λ( 238U). Based on this new calibration, the age of the widely used Fish Canyon sanidine standard is 28.305 ± 0.036 Ma. The increased accuracy of 40Ar/ 39Ar ages is now adequate to provide meaningful validation of high-precision U/Pb or astronomical tuning ages in cases where closed system behavior of K and Ar can be established.

  7. A 13 ± 3 ka age determination of a tholeiite, Pinacate volcanic field, Mexico, and improved methods for 40Ar/ 39Ar dating of young basaltic rocks

    NASA Astrophysics Data System (ADS)

    Turrin, Brent D.; Gutmann, James T.; Swisher, Carl C., III

    2008-11-01

    Among the youngest lava flows of the Pinacate volcanic field, Sonora, Mexico, is a large outpouring of tholeiite, the Ives flow. This tube-fed pahoehoe flow contrasts sharply with other Pinacate lavas in its great volume, alkali-poor composition and morphologic features, which include novel small structures named "spatter tubes." Despite its K-poor character, young age, and the presence of excess 40Ar, we determined a 40Ar/ 39Ar age on samples of this flow at 13 ± 3 ka. Such an age determination is made possible via careful monitoring of the mass discrimination of the mass spectrometer and by stacking results from multiple incremental-heating experiments into a single, composite isochron. This age is among the youngest ever to be determined with such precision by the 40Ar/ 39Ar method on a K-poor tholeiite.

  8. Spectroscopic identification of the Ar⋯I2 intermolecular levels bound throughout the Ar + I2(B,ν‧) potential

    NASA Astrophysics Data System (ADS)

    Makarem, Camille; Loomis, Richard A.

    2016-05-01

    Action spectra were recorded to identify the Ar⋯I2 intermolecular vibrational levels bound within the Ar + I2(B,ν‧ = 20-23) excited-state potentials. Features associated with transitions of the linear and T-shaped Ar⋯I2(X,ν″ = 0) ground-state conformers are identified. Due to the overlap of levels bound within different Ar + I2(B,ν‧) potentials there is a high density of spectral features. Comparisons of the spectral shifts of the features from different I2 B-X, ν‧-0 bands are used to identify those levels bound within each of the Ar + I2(B,ν‧) potentials. At least 17 bound intermolecular vibrational levels that span nearly the entire potential are identified.

  9. Comparison of the surface characteristics of polypropylene films treated by Ar and mixed gas (Ar/O2) atmospheric pressure plasma.

    PubMed

    Kwon, Oh-June; Myung, Sung-Woon; Lee, Chang-Soo; Choi, Ho-Suk

    2006-03-15

    In an attempt to modify the hydrophobic surface properties of polypropylene (PP) films, this study examined the optimum process parameters of atmospheric pressure plasma (APP) using Ar gas. Under optimized conditions, the effects of a mixed gas (Ar/O2) plasma treatment on the surface-free energy of a PP film were investigated as a function of the O2 content. The polar contribution of the surface-free energy of the PP film increased with increasing O2 content in the gas mixture. However, slightly more oxygen-containing polar functional groups such as CO, CO, and COO were introduced on the PP film surface by the Ar gas only rather than by the Ar/O2 gas mixture. In addition, AFM analysis showed that the Ar plasma treatment of the PP film produced the smoothest surface as a result of the relatively homogeneous etching process. PMID:16310799

  10. Preservation of Sub-Microscopic Scale Structural Relics in Biotite: Implications for 40AR/39AR Geochronology

    NASA Astrophysics Data System (ADS)

    Beltrando, M.; Di Vincenzo, G.; Ferraris, C.

    2012-12-01

    Relic crystals of magmatic biotite that undewent eclogite facies metamorphism were investigated by laser step-heating and laser in-situ 40Ar/39Ar techniques, in conjunction with SEM, EMP and TEM analyses, to elucidate the influence of recrystallization on K-Ar systematics. Samples were collected from meta-granitoids of the Gran Paradiso Massif (Western Alps), emplaced at upper crustal depths (P~0.25-0.35 GPa) in the Permian and metamorphosed at P>2.0 GPa and T~500-600°C in the Middle-Late Eocene. Two different samples, which underwent different degrees of Alpine re-equilibration, were examined. Sample JT1007 still preserves the original cm-sized magmatic quartz, k-feldspar and brown biotite (Bt 1), rarely rimmed by small green biotite crystals (Bt 2) related to Alpine metamorphism. Sample JT1008, instead, is characterized by a larger degree of Alpine re-equilibration, with static re-crystallization of the original magmatic quartz into aggregates of fine-grained polygonal crystals and common green biotite rims around brown Bt 1. Compositional profiling across Bt 1 in sample JT1007 reveals a progressive decrease in Ti content towards the crystal rims, which overlap with the composition of Bt 2. Compositional profiling across Bt 1 in sample JT1008, instead, reveals a homogeneous Ti content across the grain. This compositional pattern is mirrored by TEM investigation at the sub-micron scale, revealing a systematic zoning in Bt 1 from sample JT1007, with high-temperature magmatic politypes, surrounded by 1M politypes, still preserved in crystal cores. Crystal rims, instead, are characterized by 1M politypes only. Biotites from JT1008, instead, are homogeneous, solely consisting of 1M politypes. Infrared laser step-heating experiments on mineral separates from the two samples gave contrasting results: JT1008 yielded a flat spectrum, for more than 90% of the released 39ArK, with an error-weighted mean age of 36.5±0.3 Ma; JT1007 yielded a slightly saddle-shaped profile

  11. 40Ar/39Ar dates from alkaline intrusions of the northern Crazy Mountains, south-central Montana

    NASA Astrophysics Data System (ADS)

    Harlan, S. S.

    2005-05-01

    The Crazy Mountains basin of south-central Montana is a complex foreland basin that formed during the interaction of thin-skinned, decollement-style folds of the Montana thrust belt and the basement-involved folds and thrust faults of the Rocky Mountain foreland province. Near the depositional center of the basin, synorogenic strata of the Paleocene Fort Union Formation have been intruded and locally thermally metamorphosed by strongly alkaline to subalkaline Tertiary intrusive rocks. The subalkaline rocks are found mostly in the southern Crazy Mountains and form stocks (Big Timber stock, Loco Mountain stock), radiating dikes and sills. With the exception of the Ibex Mountain sill (?), the alkaline rocks are restricted to the northern Crazy Mountains. New 40Ar/39Ar dates are reported from the strongly alkaline rocks, including the Comb Creek stock and dike swarm, the Ibex Mountain sill(?), and sills from the Robinson anticline intrusive complex. The alkaline rocks of the Robinson anticline intrusive complex are exposed in the easternmost folds of the Cordilleran fold and thrust belt, but despite their arcuate and apparently folded map geometry they have been shown to post-date folding. Hornblende from a trachyte sill in the Robinson anticline intrusive complex yielded a relatively simple age spectrum with a weighted mean of 50.61 ± 0.14 Ma (2σ), which probably records the age of sill emplacement. Nepheline syenite and mafic nepheline syenites of the Comb Creek stock and a dike from its radial dike swarm, two sills from the Robinson antlicline intrusive complex, and the Ibex Mountains sill(?) gave biotite plateau dates ranging from 50.03 to 50.22 Ma, with 2σ errors of ± 0.11 to 0.19 Ma. Because these dates are from fairly small, hypabyssal intrusions, they must have cooled quickly and thus these dates closely approximate the emplacement age of the intrusions. These data indicate that the strongly alkaline intrusions were emplaced during a fairly restricted

  12. The sup 40 Ar/ sup 39 Ar geochronology of the Pelona schist and related rocks, southern California

    SciTech Connect

    Jacobson, C.E. )

    1990-01-10

    Seventeen {sup 40}Ar/{sup 39}Ar ages for hornblende, celadonitic muscovite, and biotite from the Pelona, Orocopia, Rand, and Portal Ridge (POR) schists range from 39 to 85 Ma. Two muscovites and one hornblende from the Rand Schist have ages of 72 to 74 Ma, indistinguishable from the K-Ar age of 74 Ma for hornblende from a posttectonic granodiorite that intrudes the schist, but younger than the 70 Ma U-Pb age of the intrusion. Four muscovite and two hornblende ages for schist and mylonite from the East Fork area of the San Gabriel Mountains range from 55 to 61 Ma. Concordance of schist and upper plate ages confirms structural and metamorphic evidence that the Vincent thrust in the San Gabriel Mountains has not undergone significant postmetamorphic disruption. Ages from the Orocopia Mountains are 75 Ma for hornblende from nonmylonitic upper plate, 52 Ma for muscovite from structurally high Orocopia Schist that is mylonitic, and 41 Ma for muscovite from nonmylonitic Orocopia Schist. These are consistent with field evidence that the Orocopia thrust is a postmetamorphic normal fault. Muscovite and hornblende from the Gavilan Hills have ages of 48 to 50 Ma, younger than ages from the San Gabriel Mountains but similar to schist ages from the Orocopia Mountains. The geochronologic and structural complexities of the Vincent, Chocolate Mountains, Orocopia, and Rand thrusts imply that previously cited northeastward vergence may not relate to prograde metamorphism (subduction) of the POR schists. The data indicate substantial uplift of the POR schists prior to middle Tertiary detachment faulting, which confirms other geochronologic evidence of uplift in southern California and southern Arizona during the Late Cretaceous-early Tertiary.

  13. Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: 40Ar/39Ar data from metamorphic and plutonic rocks

    USGS Publications Warehouse

    Dusel-Bacon, C.; Lanphere, M.A.; Sharp, W.D.; Layer, P.W.; Hansen, V.L.

    2002-01-01

    We present new 40Ar/39Ar ages for hornblende, muscovite, and biotite from metamorphic and plutonic rocks from the Yukon-Tanana Upland, Alaska. Integration of our data with published 40Ar/39Ar, kinematic, and metamorphic pressure (P) and temperature (T) data confirms and refines the complex interaction of metamorphism and tectonism proposed for the region. The oldest metamorphic episode(s) postdates Middle Permian magmatism and predates the intrusion of Late Triassic (215-212 Ma) granitoids into the Fortymile River assemblage (Taylor Mountain assemblage of previous papers). In the eastern Eagle quadrangle, rapid and widespread Early Jurassic cooling is indicated by ???188-186 Ma 40Ar/39Ar plateau ages for hornblende from plutons that intrude the Fortymile River assemblage, and for metamorphic minerals from the Fortymile River assemblage and the structurally underlying Nasina assemblage. We interpret these Early Jurassic ages to represent cooling resulting from northwest-directed contraction that emplaced the Fortymile River assemblage onto the Nasina assemblage to the north as well as the Lake George assemblage to the south. This cooling was the final stage of a continuum of subduction-related contraction that produced crustal thickening, intermediate- to high-P metamorphism within both the Fortymile River assemblage and the structurally underlying Lake George assemblage, and Late Triassic and Early Jurassic plutonism in the Fortymile River and Nasina assemblages. Although a few metamorphic samples from the Lake George assemblage yield Jurassic 40Ar/39Ar cooling ages, most yield Early Cretaceous 40Ar/39Ar ages: hornblende ???135-115 Ma, and muscovite and biotite ???110-108 Ma. We interpret the Early Cretaceous metamorphic cooling, in most areas, to have resulted from regional extension and exhumation of the lower plate, previously tectonically thickened during Early Jurassic and older convergence.

  14. First ^4^0Ar/^3^9Ar geochronology of lateritic manganiferous pisolites: Implications for the Palaeogene history of a West African landscape [rapid communication

    NASA Astrophysics Data System (ADS)

    Colin, F.; Beauvais, A.; Ruffet, G.; Hénocque, O.

    2005-09-01

    A pisolitic superficial formation deriving from the geochemical degradation of a previous massive manganiferous crust has been investigated in West Africa using 40Ar/ 39Ar laser probe analysis on different generations of cryptomelane from Fe-Mn pisolites and their embedding lateritic matrices. Prior to the 40Ar- 39Ar geochronological analysis, a detailed petrographical study has allowed the identification of successive assemblages from Mn-pisolites to (Fe,Mn)-pisolites embedded in Mn-rich and Fe-rich matrices, respectively. The age spectra obtained for pisolites, including cores, cortices and matrices enables the definition of three age clusters around 56-59, 44-47, and 24-27 Ma. The first two age clusters with the petrographical and geochemical results obtained on the different assemblages indicate that the development of the pisolitic crust first induced Mn-leaching and Fe-Al accumulations due to warmer and wetter climatic conditions in the age interval 56-47 Ma that characterizes the Tertiary greenhouse effect period propitious to bauxite formation in West Africa. The absence of 40Ar/ 39Ar ages between 44 and 27 Ma only means that geochemical conditions for cryptomelane crystallisation were not fulfilled, but could still be favourable to Fe- and/or Al-oxy-hydroxides formation, before drier climatic conditions became rather effective at the Oligocene period to sustain mechanical erosion rather than chemical weathering processes. The age cluster 24-27 Ma indicates however a reactivation of the manganiferous lateritic weathering late Oligocene. The 40Ar/ 39Ar dating results are discussed in terms of climatic condition changes during the Palaeogene that were favourable to the genesis of either Al- and Fe- or Mn-oxy-hydroxides in the course of development and evolution of the pisolitic formation. The 40Ar/ 39Ar dating also provides a new highlight to large-scale geomorphological patterns of West Africa.

  15. Transport of electrons in Ar/H2 mixtures

    NASA Astrophysics Data System (ADS)

    Nikitović, Ž.; Stojanović, V.; Petrović, Z. Lj.

    2012-08-01

    In this work we present transport coefficients for electrons in Ar/H2 mixtures for the conditions used in plasma-assisted technologies for semiconductor production, i.e., in moderate and very high E/N. We used a two-term numerical solution of the Boltzmann equation at the lowest E/N (E is the electric field; N is the gas density) and correspondingly at the lowest mean energies. We also use the Monte Carlo simulation technique at moderate and high E/N. We show that a good agreement with experimental data exists for low and moderate E/N and that based on the tests for pure H2 and Ar we can model properly the swarm properties at high E/N. For the conditions of very high electric fields runaway peaks develop in the electron energy distribution function and appreciable contribution of backscattered high-energy electrons produces additional emission of Hα emission close to the anode (made of stainless steel). Results are obtained for abundances of H2 from 1% to 30%, which are necessary in kinetic models for this mixture in a number of applications.

  16. Ar + CO2 and He + CO2 Plasmas in ASTRAL

    NASA Astrophysics Data System (ADS)

    Boivin, R. F.; Gardner, A.; Munoz, J.; Kamar, O.; Loch, S.

    2007-11-01

    Spectroscopy study of the ASTRAL helicon plasma source running Ar + CO2 and He + CO2 gas mixes is presented. ASTRAL produces plasmas with the following parameters: ne = 10^10 - 10^13 cm-3, Te = 2 - 10 eV and Ti = 0.03 - 0.5 eV, B-field <= 1.3 kGauss, rf power <= 2 kWatt. A 0.33 m scanning monochromator is used for this study. Using Ar + CO2 gas mixes, very different plasmas are observed as the concentration of CO2 is changed. At low CO2 concentration, the bluish plasma is essentially atomic and argon transitions dominate the spectra. Weak C I and O I lines are present in the 750 - 1000 nm range. At higher CO2 concentration, the plasma becomes essentially molecular and is characterized by intense, white plasma columns. Here, spectra are filled with molecular bands (CO2, CO2^+, CO and CO^+). Limited molecular dissociative excitation processes associated with the production of C I and O I emission are also observed. On the other hand, He + CO2 plasmas are different. Here, rf matches are only possible at low CO2 concentration. Under these conditions, the spectra are characterized by strong C I and O I transitions with little or no molecular bands. Strong dissociative processes observed in these plasmas can be link to the high Te associated with He plasmas. An analysis of the spectra with possible scientific and industrial applications will be presented.

  17. archAR: an archaeological augmented reality experience

    NASA Astrophysics Data System (ADS)

    Wiley, Bridgette; Schulze, Jürgen P.

    2015-03-01

    We present an application for Android phones or tablets called "archAR" that uses augmented reality as an alternative, portable way of viewing archaeological information from UCSD's Levantine Archaeology Laboratory. archAR provides a unique experience of flying through an archaeological dig site in the Levantine area and exploring the artifacts uncovered there. Using a Google Nexus tablet and Qualcomm's Vuforia API, we use an image target as a map and overlay a three-dimensional model of the dig site onto it, augmenting reality such that we are able to interact with the plotted artifacts. The user can physically move the Android device around the image target and see the dig site model from any perspective. The user can also move the device closer to the model in order to "zoom" into the view of a particular section of the model and its associated artifacts. This is especially useful, as the dig site model and the collection of artifacts are very detailed. The artifacts are plotted as points, colored by type. The user can touch the virtual points to trigger a popup information window that contains details of the artifact, such as photographs, material descriptions, and more.

  18. Mode transition in CF4 + Ar inductively coupled plasma

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Gao, Fei; Zhao, Shu-Xia; Li, Xue-Chun; Wang, You-Nian

    2013-12-01

    The E to H mode transitions are studied by a hairpin probe and optical emission spectroscopy in inductively coupled CF4 + Ar plasmas. Electron density, optical emission intensity of Ar, and the voltage and current are measured during the E to H mode transitions. It is found that the electron density and plasma emission intensity increase continuously at low pressure during the E to H mode transition, while they jump up discontinuously at high pressure. Meanwhile, the transition threshold power and △P (the power interval between E and H mode) increase by increasing the pressure. When the ratio of CF4 increases, the E to H mode transition happens at higher applied power, and meanwhile, the △P also significantly increases. Besides, the effects of CF4 gas ratio on the plasma properties and the circuit electrical properties in both pure E and H modes were also investigated. The electron density and plasma emission intensity both decrease upon increasing the ratio of CF4 at the two modes, due to the stronger electrons loss scheme. The applied voltages at E and H modes both increase as increasing the CF4 gas ratio, however the applied current at two modes behave just oppositely with the gas ratio.

  19. An industrial approach to design compelling VR and AR experience

    NASA Astrophysics Data System (ADS)

    Richir, Simon; Fuchs, Philippe; Lourdeaux, Domitile; Buche, Cédric; Querrec, Ronan

    2013-03-01

    The convergence of technologies currently observed in the field of VR, AR, robotics and consumer electronic reinforces the trend of new applications appearing every day. But when transferring knowledge acquired from research to businesses, research laboratories are often at a loss because of a lack of knowledge of the design and integration processes in creating an industrial scale product. In fact, the innovation approaches that take a good idea from the laboratory to a successful industrial product are often little known to researchers. The objective of this paper is to present the results of the work of several research teams that have finalized a working method for researchers and manufacturers that allow them to design virtual or augmented reality systems and enable their users to enjoy "a compelling VR experience". That approach, called "the I2I method", present 11 phases from "Establishing technological and competitive intelligence and industrial property" to "Improvements" through the "Definition of the Behavioral Interface, Virtual Environment and Behavioral Software Assistance". As a result of the experience gained by various research teams, this design approach benefits from contributions from current VR and AR research. Our objective is to validate and continuously move such multidisciplinary design team methods forward.

  20. Arsenic Binding and Transfer by the ArsD As(III) Metallochaperone†

    PubMed Central

    Yang, Jianbo; Rawat, Swati; Stemmler, Timothy L.; Rosen, Barry P.

    2010-01-01

    ArsD is a metallochaperone that delivers trivalent metalloids [As(III) or Sb(III)] to the ArsA ATPase, the catalytic subunit of the ArsAB pump encoded by the arsRDABC operon of Escherichia coli plasmid R773. Interaction with ArsD increases the affinity of ArsA for As(III), conferring resistance to environmental concentrations of arsenic. Previous genetic analysis suggested that ArsD residues Cys12, Cys13, and Cys18 are involved in the transfer of As(III) to ArsA. Here X-ray absorption spectroscopy was used to show that As(III) is coordinated with three sulfur atoms, consistent with the three cysteine residues forming the As(III) binding site. Two single-tryptophan derivatives of ArsD exhibited quenching of intrinsic protein fluorescence upon binding of As(III) or Sb(III), which allowed estimation of the rates of binding and affinities for metalloids. Substitution of Cys12, Cys13, or Cys18 decreased the affinity for As(III) more than 10-fold. Reduced glutathione greatly increased the rate of binding of As(III) to ArsD but did not affect binding of As(III) to ArsA. This suggests that in vivo cytosolic As(III) might be initially bound to GSH and transferred to ArsD and then to ArsAB, which pumps the metalloid out of the cell. The As(III) chelator dimercaptosuccinic acid did not block the transfer from ArsD to ArsA, consistent with channeling of the metalloid from one protein to the other, as opposed to release and rebinding of the metalloid. Finally, transfer of As(III) from ArsD to ArsA occurred in the presence of MgATP at 23 °C but not at 4 °C. Neither MgADP nor MgATP-γ-S could replace MgATP. These results suggest that transfer occurs with a conformation of ArsA that transiently forms during the catalytic cycle. PMID:20361763

  1. Arsenic binding and transfer by the ArsD As(III) metallochaperone.

    PubMed

    Yang, Jianbo; Rawat, Swati; Stemmler, Timothy L; Rosen, Barry P

    2010-05-01

    ArsD is a metallochaperone that delivers trivalent metalloids [As(III) or Sb(III)] to the ArsA ATPase, the catalytic subunit of the ArsAB pump encoded by the arsRDABC operon of Escherichia coli plasmid R773. Interaction with ArsD increases the affinity of ArsA for As(III), conferring resistance to environmental concentrations of arsenic. Previous genetic analysis suggested that ArsD residues Cys12, Cys13, and Cys18 are involved in the transfer of As(III) to ArsA. Here X-ray absorption spectroscopy was used to show that As(III) is coordinated with three sulfur atoms, consistent with the three cysteine residues forming the As(III) binding site. Two single-tryptophan derivatives of ArsD exhibited quenching of intrinsic protein fluorescence upon binding of As(III) or Sb(III), which allowed estimation of the rates of binding and affinities for metalloids. Substitution of Cys12, Cys13, or Cys18 decreased the affinity for As(III) more than 10-fold. Reduced glutathione greatly increased the rate of binding of As(III) to ArsD but did not affect binding of As(III) to ArsA. This suggests that in vivo cytosolic As(III) might be initially bound to GSH and transferred to ArsD and then to ArsAB, which pumps the metalloid out of the cell. The As(III) chelator dimercaptosuccinic acid did not block the transfer from ArsD to ArsA, consistent with channeling of the metalloid from one protein to the other, as opposed to release and rebinding of the metalloid. Finally, transfer of As(III) from ArsD to ArsA occurred in the presence of MgATP at 23 degrees C but not at 4 degrees C. Neither MgADP nor MgATP-gamma-S could replace MgATP. These results suggest that transfer occurs with a conformation of ArsA that transiently forms during the catalytic cycle. PMID:20361763

  2. Evolution of the Southwest Indian continental divergent margin: Constraints from 40Ar-39Ar dating of lateritic paleolandsurfaces

    NASA Astrophysics Data System (ADS)

    Bonnet, Nicolas; Beauvais, Anicet; Chardon, Dominique; Arnaud, Nicolas

    2015-04-01

    The western continental passive margin of Peninsular India is marked by the Western Ghats escarpment, which separates a coastal lowland from an East-dipping highland plateau and is carved both into the 63-Ma old Deccan traps and their Archean basement. Previous studies suggested establishment of the escarpment by differential erosion across an elevated rift shoulder, and thermochronologic models predicted escarpment formation from higher denudation in the coastal lowland than on the plateau until ~ 50 Ma. We provided complementary time constraints on the evolution of the passive margin by 40Ar-39Ar dating of supergene K-Mn oxides (cryptomelane) sampled in lateritic formations exposed on paleosurfaces, which are preserved as relicts on both sides of the escarpment. Three main lateritic paleosurfaces were identified in the highland at altitude ranges of 1200-1000 m (S1), 1000-900 m (S2) and 850-600 m (S3), and a lower paleosurface in the lowland at 150-50 m (S4). All the 40Ar-39Ar ages obtained on either side of the escarpment document major weathering periods for each paleosurface: 53 to 45 Ma (S1-S4) synchronously with the bauxitic weathering, 40 to 32 Ma (S2), 30 to 23 Ma (S3), and 24 to 19 Ma (S4). These ages indicate that most of the incision and dissection of plateau landsurfaces S1, S2, and S3 must therefore have taken place after 45, 32 and 23 Ma respectively, while the coastal lowland surface S4 was incised after 19 Ma. Preservation of laterites as old as 47 Ma in the coastal lowland implies that the escarpment already existed in the Mid-Eocene while intense bauxitic weathering was taking place on both sides of the escarpment. The ages obtained in the lowland are also indicative of limited erosion (~ 4 m Ma-1) at the foot of the escarpment since 45 Ma, and particularly low incipient incision of the lowland (~ 5 m Ma-1) since 19 Ma. Ages obtained on the highland plateau indicate further Neogene denudation inland but at less than 15 m Ma-1 since 45 Ma, and

  3. A new Application of Ar-40/Ar-39 Dating: A Provenance Study of Middle Stone Age Obsidian Tools from Ethiopia

    NASA Astrophysics Data System (ADS)

    Nomade, S.; Vogel, N.; Renne, P. R.; Negash, A.

    2004-12-01

    The identification and geographic origin of potential sources for obsidian tools manufactured by MSA (Middle Stone Age) hominid groups is important to reconstruct source utilization and trade routes. Obsidian sourcing is done by geochemical investigation of obsidian artifacts and potential source materials and the identification of possible matches between them [e.g., 1]. Due to uncertainties arising, e.g., from intrasource inhomogeneities [2] additional methods are desirable. As a part of a pilot study, we dated by Ar-40/Ar-39 stepwise heating numerous debitage pieces of obsidian artifacts from an MSA excavation site and several potential source rock samples from a nearby obsidian outcrop in the Gademotta-Kulkuletti area near Ziway lake, Ethiopia. The ages were used, along with chemical data, to trace possible source rocks used to manufacture the artifacts. Most of the debitage samples show ages around 1.29 Ma and exhibit flat, well behaved spectra. Less well behaved spectra are obtained for two debitage samples with ages of about 1.26 Ma, and two with ages of about 0.62 Ma. We point out that despite this significant spread in the ages found, all debitage samples as well as the potential source rocks show homogeneous major and trace elemental compositions generally indicating a positive match in archeological sourcing. The ages of two potential source rocks are about 1.26 and 0.87 Ma. Thus, while there is a match with the two debitage pieces dated at 1.26 Ma, the exact outcrop of the major source for the 1.29 Ma old artifacts has not been identified yet. A second set of samples with further possible source materials for the Kulkuletti artifacts as well as another potential debitage-source material pair from a second excavation site in the Ziway lake area, Porc Epic, are currently being dated and will be presented at the conference. Already this first set of data shows not only the general applicability of Ar-40/Ar-39 dating to archeological obsidian sourcing, but

  4. The tectonic evolution of Cenozoic extensional basins, northeast Brazil: Geochronological constraints from continental basalt 40Ar/39Ar ages

    NASA Astrophysics Data System (ADS)

    de Souza, Zorano Sérgio; Vasconcelos, Paulo Marcos; Knesel, Kurt Michael; da Silveira Dias, Luiz Gustavo; Roesner, Eduardo Henrique; Cordeiro de Farias, Paulo Roberto; de Morais Neto, João Marinho

    2013-12-01

    The Boa Vista and Cubati Basins, Paraíba, Brazil, are NW-SE extension-related intracratonic basins that resulted from tectonic stresses after the opening of the South Atlantic. These basins contain lacustrine fossiliferous sediments, bentonite beds, and basalt flows that preserve Cenozoic continental records. 40Ar/39Ar ages for six whole-rocks from two distinct basaltic flows underlying the sediments in the Boa Vista basin are 27.3 ± 0.8 and 25.4 ± 1.3 Ma, while three grains from a basaltic flow overlying the sediments yield 22.0 ± 0.2 Ma. The sediments at the nearby Cubati Basin are overlain by a basalt flow with ages of ˜25.4 Ma. Three whole-rocks from an NE-SW-trending trachytic dyke cross cutting the sediments at the Boa Vista Basin yield 40Ar/39Ar ages of ˜12.45 ± 0.06, 12.59 ± 0.07, and 12.58 ± 0.07 Ma. Three whole-rocks from a nearby volcanic plug (Chupador) yield an age of 23.4 ± 0.1 Ma. The geochronological results combined with stratigraphic correlations between the two basins allow bracketing the age of the main sedimentary and bentonic units within the Boa Vista and Cubati Basins between 25.5 ± 1.3 and 24.9 ± 0.1 Ma. The ages, combined with field observations reveal that the formation of the Boa Vista and Cubati basins is associated with mantle-derived magmas channelled through reactivated Precambrian shear zones. Our geochronological results suggest that a temporal link with the Fernando de Noronha and Saint Helena hot spots can be excluded as possible sources of the Boa Vista and Cubati magmas. Rather, the extensional tectonics in the 30-20 Ma interval, long after Gondwana break-up, may be associated with the re-activation of continental-scale shear zones that channelled small batches of mantle-derived magmas.

  5. Dating mylonitic deformation by the Ar-40-Ar-39 method: An example from the Norumbega fault zone, Maine

    NASA Astrophysics Data System (ADS)

    West, David P., Jr.; Lux, Daniel R.

    1993-12-01

    Strongly mylonitic rocks associated with the regionally extensive Norumbega fault zone in south-central Maine provide an excellent opportunity for testing the effects of mylonitization on argon isotopic systems in muscovite. Ar-40/Ar-39 muscovite age spectra from samples outside the zone of mylonitization are relatively undisturbed and have well defined Early Carboniferous plateau ages. In contrast to these nonmylonitized samples, all age spectra for muscovite from the mylonites are highly discordant. They are characterized by young ages at low extraction temperatures, which systematically increase to ages that equal the plateau ages for muscovite collected outside the mylonite zone. Detailed petrographic observations suggest that these systematic discordances reflect a mixing of argon components from older, relict, muscovite porphyroclasts and fine-grained white mica aggregates that recrystallized during mylonitic deformation. Total gas ages of five different grain size fractions separated from the same mylonite sample become progressively younger with decreasing grain size; indicating a larger component of the recrystallized grains in the finer grain size fractions. Although the three finest grain size fractions give different total gas ages and do not overlap in age for most of their release spectra, their initial increments do coincide, at approximately 290 Ma. This indicates a minimal older age contribution from the relict porphyroclasts in the initial increments and suggests the 290 Ma age provides a good estimate for the time of mineral growth associated with mylonitic deformation. These data, combined with kinematic analysis, reveal that the segment of the Norumbega fault zone studied, the Sandhill Corner fault, is a Late Carboniferous-Early Permian dextral strike-slip fault. A lack of significant offset in regional Early Carboniferous mineral age patterns across the fault suggests that displacement was probably less than 30 km. This study demonstrates that

  6. Ethnic variation in allele distribution of the androgen receptor (AR) (CAG)n repeat.

    PubMed

    Ackerman, Christine M; Lowe, Lynn P; Lee, Hoon; Hayes, M Geoffrey; Dyer, Alan R; Metzger, Boyd E; Lowe, William L; Urbanek, Margrit

    2012-01-01

    The androgen receptor (AR) is important in reproductive organ development, as well as tissue homeostasis of the pancreas, liver, and skeletal muscle in adulthood. The trinucleotide (CAG)(n) repeat polymorphism in exon 1 of the AR gene is thought to regulate AR activity, with longer alleles conferring reduced receptor activity. Therefore, the evaluation of the allelic distribution of the AR (CAG)(n) repeat in various ethnic groups is crucial in understanding the interindividual variability in AR activity. We evaluated ethnic variation of this AR polymorphism by genotyping individuals from the multiethnic Hyperglycemia and Adverse Pregnancy Outcome study cohort. We genotyped 4421 Caucasian mothers and 3365 offspring of European ancestry; 1494 Thai mothers and 1742 offspring; 1119 Afro-Caribbean mothers and 1142 offspring; and 780 Hispanic mothers and 770 offspring of Mexican ancestry from Bellflower, California. The distributions of (CAG)(n) alleles among all 4 ethnic groups are significantly different (P < .0001). Pairwise tests confirmed significant differences between each pair of ethnicities tested (P < 10(-28)). The relative AR (CAG)(n) repeat length in the different groups was as follows: Afro-Caribbean (shortest repeat lengths and greatest predicted AR activity) < Caucasian < Hispanic < Thai (longest repeat length and lowest predicted AR activity). Significant interethnic differences in the allele frequencies of the AR exon 1 (CAG)(n) polymorphism exist. Our results suggest that there may be potential ethnic differences in androgenic pathway activity and androgen sensitivity. PMID:21597087

  7. Molecular identification of arsenic-resistant estuarine bacteria and characterization of their ars genotype.

    PubMed

    Sri Lakshmi Sunita, M; Prashant, S; Bramha Chari, P V; Nageswara Rao, S; Balaravi, Padma; Kavi Kishor, P B

    2012-01-01

    In the present study, 44 arsenic-resistant bacteria were isolated through serial dilutions on agar plate with concentrations ≥0.05 mM of sodium arsenite and ≥10 mM of sodium arsenate from Mandovi and Zuari--estuarine water systems. The ars genotype characterization in 36 bacterial isolates (resistant to 100 mM of sodium arsenate) revealed that only 17 isolates harboured the arsA (ATPase), B (arsenite permease) and C (arsenate reductase) genes on the plasmid DNA. The arsA, B and C genes were individually detected using PCR in 16, 9 and 13 bacterial isolates respectively. Molecular identification of the 17 isolates bearing the ars genotype was carried using 16S rDNA sequencing. A 1300 bp full length arsB gene encoding arsenite efflux pump and a 409 bp fragment of arsC gene coding for arsenate reductase were isolated from the genera Halomonas and Acinetobacter. Phylogenetic analysis of arsB and arsC genes indicated their close genetic relationship with plasmid borne ars genes of E. coli and arsenate reductase of plant origin. The putative arsenate reductase gene isolated from Acinetobacter species complemented arsenate resistance in E. coli WC3110 and JM109 validating its function. This study dealing with isolation of native arsenic-resistant bacteria and characterization of their ars genes might be useful to develop efficient arsenic detoxification strategies for arsenic contaminated aquifers. PMID:21879358

  8. The importance of non-nuclear AR signaling in prostate cancer progression and therapeutic resistance.

    PubMed

    Zarif, Jelani C; Miranti, Cindy K

    2016-05-01

    The androgen receptor (AR) remains the major oncogenic driver of prostate cancer, as evidenced by the efficacy of androgen deprivation therapy (ADT) in naïve patients, and the continued effectiveness of second generation ADTs in castration resistant disease. However, current ADTs are limited to interfering with AR ligand binding, either through suppression of androgen production or the use of competitive antagonists. Recent studies demonstrate 1) the expression of constitutively active AR splice variants that no longer depend on androgen, and 2) the ability of AR to signal in the cytoplasm independently of its transcriptional activity (non-genomic); thus highlighting the need to consider other ways to target AR. Herein, we review canonical AR signaling, but focus on AR non-genomic signaling, some of its downstream targets and how these effectors contribute to prostate cancer cell behavior. The goals of this review are to 1) re-highlight the continued importance of AR in prostate cancer as the primary driver, 2) discuss the limitations in continuing to use ligand binding as the sole targeting mechanism, 3) discuss the implications of AR non-genomic signaling in cancer progression and therapeutic resistance, and 4) address the need to consider non-genomic AR signaling mechanisms and pathways as a viable targeting strategy in combination with current therapies. PMID:26829214

  9. ID4 promotes AR expression and blocks tumorigenicity of PC3 prostate cancer cells.

    PubMed

    Komaragiri, Shravan Kumar; Bostanthirige, Dhanushka H; Morton, Derrick J; Patel, Divya; Joshi, Jugal; Upadhyay, Sunil; Chaudhary, Jaideep

    2016-09-01

    Deregulation of tumor suppressor genes is associated with tumorigenesis and the development of cancer. In prostate cancer, ID4 is epigenetically silenced and acts as a tumor suppressor. In normal prostate epithelial cells, ID4 collaborates with androgen receptor (AR) and p53 to exert its tumor suppressor activity. Previous studies have shown that ID4 promotes tumor suppressive function of AR whereas loss of ID4 results in tumor promoter activity of AR. Previous study from our lab showed that ectopic ID4 expression in DU145 attenuates proliferation and promotes AR expression suggesting that ID4 dependent AR activity is tumor suppressive. In this study, we examined the effect of ectopic expression of ID4 on highly malignant prostate cancer cell, PC3. Here we show that stable overexpression of ID4 in PC3 cells leads to increased apoptosis and decreased cell proliferation and migration. In addition, in vivo studies showed a decrease in tumor size and volume of ID4 overexpressing PC3 cells, in nude mice. At the molecular level, these changes were associated with increased androgen receptor (AR), p21, and AR dependent FKBP51 expression. At the mechanistic level, ID4 may regulate the expression or function of AR through specific but yet unknown AR co-regulators that may determine the final outcome of AR function. PMID:27462022

  10. AR3 messenger ribonucleic acid expression and its functional implication in human primary testicular failure.

    PubMed

    Tian, F; Wu, Y-S; Zhao, J; Li, W

    2014-10-01

    AR3, a major one of androgen receptor (AR) splice variants, has been shown to play a pivotal role in concert with AR signalling in prostate cancer. The present study was undertaken to characterise the expression pattern of AR3 in normal and impaired spermatogenesis. Expression of AR3 mRNA showed significantly lower level in testicular tissues with impaired spermatogenesis when compared to normal tissues. This aberrant expression profile of AR3 in human pathological testes was further confirmed by immunoblotting analysis. Moreover, in situ hybridisation studies revealed that the transcripts of the gene were dominantly localised in the pachytene spermatocytes and round spermatids, suggesting a potential involvement of this transcriptional regulator in the auto-/paracrine regulation of meiotic and post-meiotic differentiation. This hypothesis was strengthened by the observation that AR3 mRNA expression was positively correlated to average seminiferous tubule score and was negatively correlated to serum FSH level. To the best of our knowledge, such a distinct expression profile of AR3 has not been reported previously in human testis. Overall, our data are suggestive of a novel site of action of AR3 during human spermatogenesis and should shed light on the complicated circuit composed of AR and its splice variants. PMID:24124902

  11. Acetalated Dextran Encapsulated AR-12 as a Host-directed Therapy to Control Salmonella Infection

    PubMed Central

    Hoang, Ky V.; Borteh, Hassan M.; Rajaram, Murugesan V. S.; Peine, Kevin J.; Curry, Heather; Collier, Michael A.; Homsy, Michael L.; Bachelder, Eric M.; Gunn, John S.; Schlesinger, Larry S.; Ainslie, Kristy M.

    2014-01-01

    AR-12 has been evaluated in clinical trials as an anti-cancer agent but also has demonstrated host-directed, broad-spectrum clearance of bacteria. We have previously shown that AR-12 has activity in vitro against Salmonella enterica serovar Typhimurium and Francisella species by inducing autophagy and other host immune pathways. AR-12 treatment of S. Typhimurium-infected mice resulted in a 10-fold reduction in bacterial load in the liver and spleen and an increased survival time. However, AR-12 treatment did not protect mice from death, likely due poor formulation. In the current study, AR-12 was encapsulated in a microparticulate carrier formulated from the novel degradable biopolymer acetalated dextran (Ace-DEX) and subsequently evaluated for its activity in human monocyte-derived macrophages (hMDMs). Our results show that hMDMs efficiently internalized Ace-DEX microparticles (MPs), and that encapsulation significantly reduced host cell cytotoxicity compared to unencapsulated AR-12. Efficient macrophage internalization of AR-12 loaded MPs (AR-12/MPs) was further demonstrated by autophagosome formation that was comparable to free AR-12 and resulted in enhanced clearance of intracellular Salmonella. Taken together, these studies provide support that Ace-DEX encapsulated AR-12 may be a promising new therapeutic agent to control intracellular bacterial pathogens of macrophages by targeting delivery and reducing drug toxicity. PMID:25447826

  12. Evaluation of surface damage on organic materials irradiated with Ar cluster ion beam

    SciTech Connect

    Yamamoto, Y.; Ichiki, K.; Ninomiya, S.; Matsuo, J.; Seki, T.; Aoki, T.

    2011-01-07

    The sputtering yields of organic materials under large cluster ion bombardment are much higher than those under conventional monomer ion bombardment. The sputtering rate of arginine remains constant with fluence for an Ar cluster ion beam, but decreases with fluence for Ar monomer. Additionally, because Ar cluster etching induces little damage, Ar cluster ion can be used to achieve molecular depth profiling of organic materials. In this study, we evaluated the damage to poly methyl methacrylate (PMMA) and arginine samples irradiated with Ar atomic and Ar cluster ion beams. Arginine samples were analyzed by secondary ion mass spectrometry (SIMS) and PMMA samples were analyzed by X-ray photoelectron spectroscopy (XPS). The chemical structure of organic materials remained unchanged after Ar cluster irradiation, but was seriously damaged. These results indicated that bombardment with Ar cluster ions induced less surface damage than bombardment with Ar atomic ion. The damage layer thickness with 5 keV Ar cluster ion bombardment was less than 1 nm.

  13. Preclinical evaluation of the AR inhibitor enzalutamide in triple-negative breast cancer cells.

    PubMed

    Caiazza, Francesco; Murray, Alyson; Madden, Stephen F; Synnott, Naoise C; Ryan, Elizabeth J; O'Donovan, Norma; Crown, John; Duffy, Michael J

    2016-04-01

    The androgen receptor (AR) is present in approximately 80% of invasive breast cancer patients and in up to 30% of patients with triple-negative breast cancer (TNBC). Therefore, our aim was to investigate the targeting of AR as a possible hormonal approach to the treatment of TNBC. Analysis of 2091 patients revealed an association between AR expression and poor overall survival, selectively in patients with the basal subtype of breast cancer, the vast majority of which are TNBC. IC50 values for the second-generation anti-androgen enzalutamide across 11 breast cancer cell lines varied from 4 µM to >50 µM. The activity of enzalutamide was similar in TN and non-TN cell lines but was dependent on the presence of AR. Enzalutamide reduced clonogenic potential and cell growth in a 3D matrix in AR-positive cells. In addition, enzalutamide also inhibited cell migration and invasion in an AR-dependent manner. Enzalutamide appeared to mediate these processes through down-regulation of the transcription factors AP-1 and SP-1. The first-generation anti-androgen flutamide similarly blocked cell growth, migration and invasion. AR-positive TNBC cells clustered separately from AR-negative cells based on an androgen-related gene expression signature, independently of TNBC subtype. We conclude that targeting of the AR with drugs such as enzalutamide may provide an alternative treatment strategy for patients with AR-positive TNBC. PMID:26932782

  14. Spatial control of the βAR system in heart failure: the transverse tubule and beyond

    PubMed Central

    Gorelik, Julia; Wright, Peter T.; Lyon, Alexander R.; Harding, Sian E.

    2013-01-01

    The beta1-adrenoceptors (β1AR) and beta-2 (β2AR) adrenoceptors represent the predominant pathway for sympathetic control of myocardial function. Diverse mechanisms have evolved to translate signalling via these two molecules into differential effects on physiology. In this review, we discuss how the functions of the βAR are organized from the level of secondary messengers to the whole heart to achieve this. Using novel microscopy and bio-imaging methods researchers have uncovered subtle organization of the control of cyclic adenosine monophosphate (cAMP), the predominant positively inotropic pathway for the βAR. The β2AR in particular is demonstrated to give rise to highly compartmentalized, spatially confined cAMP signals. Organization of β2AR within the T-tubule and caveolae of cardiomyocytes concentrates this receptor with molecules which buffer and shape its cAMP signal to give fine control. This situation is undermined in various forms of heart failure. Human and animal models of heart failure demonstrate disruption of cellular micro-architecture which contributes to the change in response to cardiac βARs. Loss of cellular structure has proved key to the observed loss of confined β2AR signalling. Some pharmacological and genetic treatments have been successful in returning failing cells to a more structured phenotype. Within these cells it has been possible to observe the partial restoration of normal β2AR signalling. At the level of the organ, the expression of the two βAR subtypes varies between regions with the β2AR forming a greater proportion of the βAR population at the apex. This distribution may contribute to regional wall motion abnormalities in Takotsubo cardiomyopathy, a syndrome of high sympathetic activity, where the phosphorylated β2AR can signal via Gi protein to produce negatively inotropic effects. PMID:23345264

  15. (40)Ar/(39)Ar dating of Bed I, Olduvai Gorge, Tanzania, and the chronology of early Pleistocene climate change.

    PubMed

    Deino, Alan L

    2012-08-01

    (40)Ar/(39)Ar dating of tuffs and lavas of the late Pleistocene volcanic and sedimentary sequence of Olduvai Gorge, north-central Tanzania, provides the basis for a revision of Bed I chronostratigraphy. Bed I extends from immediately above the Naabi Ignimbrite at 2.038 ± 0.005 Ma to Tuff IF at 1.803 ± 0.002 Ma. Tuff IB, a prominent widespread marker tuff in the basin and a key to understanding hominin evolutionary chronologies and paleoclimate histories, has an age of 1.848 ± 0.003 Ma. The largest lake expansion event in the closed Olduvai lake basin during Bed I times encompassed the episode of eruption and emplacement of this tuff. This lake event is nearly coincident with the maximum precessional insolation peak of the entire Bed I/Lower Bed II interval, calculated from an astronomical model of the boreal summer orbital insolation time-series. The succeeding precessional peak also apparently coincides with the next youngest expansion of paleo-Lake Olduvai. The extreme wet/dry climate shifts seen in the upper part of Bed I occur during an Earth-orbital eccentricity maximum, similar to episodic lake expansions documented elsewhere in the East African Rift during the Neogene. PMID:22809744

  16. Single-crystal sup 40 Ar/ sup 39 Ar dating of the Eocene-Oligocene transition in North America

    SciTech Connect

    Swisher, C.C. III ); Prothero, D.R. )

    1990-08-17

    Explanations for the causes of climatic changes and associated faunal and floral extinctions at the close of the Eocene Epoch have long been controversial because of, in part, uncertainties in correlation and dating of global events. New single-crystal laser fusion (SCLF) {sup 40}Ar/{sup 39}Ar dates on tephra from key magnetostratigraphic and fossil-bearing sections necessitate significant revision in North American late Paleogene chronology. The Chadronian-Orellan North American Land Mammal Age boundary, as a result, is shifted from 32.4 to 34.0 Ma (million years ago), the Orellan-Whitneyan boundary is shifted from 30.8 to 32.0 Ma, and the Whitneyan-Arikareean boundary is now approximately 29.0 Ma. The new dates shift the correlation of Chron C12R from the Chadronian to within the Orellan-Whitneyan interval, the Chadronian becomes late Eocene in age, and the North American Oligocene is restricted to the Orellan, Whitneyan, and early Arikareean. The Eocene-Oligocene boundary, and its associated climate change and extinction events, as a result, correlates with the Chadronian-Orellan boundary, not the Duchesnean-Chadronian boundary. 30 refs., 1 fig., 1 tab.

  17. Carbon isotope stratigraphy, magnetostratigraphy, and 40Ar/39Ar age of the Cretaceous South Atlantic coast, Namibe Basin, Angola

    NASA Astrophysics Data System (ADS)

    Strganac, Christopher; Salminen, Johanna; Jacobs, Louis L.; Polcyn, Michael J.; Ferguson, Kurt M.; Mateus, Octávio; Schulp, Anne S.; Morais, Maria Luísa; Tavares, Tatiana da Silva; Gonçalves, António Olímpio

    2014-11-01

    We present the δ13C and paleomagnetic stratigraphy for marine strata at the coast of southern Angola, anchored by an intercalated basalt with a whole rock 40Ar/39Ar radiometric age of 84.6 ± 1.5 Ma, being consistent with both invertebrate and vertebrate biostratigraphy. This is the first African stable carbon isotope record correlated to significant events in the global carbon record spanning the Late Cenomanian to Early Maastrichtian. A positive ∼3‰ excursion seen in bivalve shells below the basalt indicates the Cenomanian-Turonian Boundary Event at 93.9 Ma, during Oceanic Anoxic Event 2. Additional excursions above the basalt are correlated to patterns globally, including a negative ∼3‰ excursion near the top of the section interpreted as part of the Campanian-Maastrichtian Boundary Events. The age of the basalt ties the studied Bentiaba section to a pulse of Late Cretaceous magmatic activity around the South Atlantic and significant tectonic activity, including rotation, of the African continent.

  18. Structural and Temporal Requirements for Geomagnetic Field Reversal Deduced From 40Ar/39Ar Dated Lava Flows

    NASA Astrophysics Data System (ADS)

    Singer, B. S.; Hoffman, K. A.; Coe, R. S.; Brown, L. L.; Jicha, B. R.; Pringle, M. S.; Chauvin, A.

    2004-12-01

    40Ar/39Ar dating of lavas on Tahiti, long thought to record the primary part of the Matuyama-Bruhnes (M-B) reversa1, gives an age of 795+/- 7 ka, indistinguishable from that of transitional lavas in Chile and La Palma, but older than the accepted age for the reversal. Only the transitional lavas on Maui and one from La Palma (dated at 776 +/- 2 ka), agree with the astronomical age for the M-B reversal. Virtual geomagnetic poles (VGPs) associated with the Tahitian and Chilean lavas cluster near Australia, as do VGPs recorded on Tahiti during the Big Lost and Punaruu events, two apparently unsuccessful reversals. These findings, suggestive of a recurring, mantle-held flux pattern at the outer core surface during reversal attempts, are also theoretically equivalent to the situation that would arise today if the axial dipole were to continue to weaken and vanish. Hence, we propose that the 795 ka lavas record the onset of a dynamo process--one which only on occasion would result in polarity change. This initial instability, associated with the first of two decreases in field intensity, began 18 kyrs prior to the actual polarity switch. These data may provide the first observational support to the claim that complete reversals require a significant interval of time for magnetic flux to escape from the solid inner core and sufficiently weaken its stabilizing effect.

  19. 40Ar-39Ar Age Constraints on Volcanism and Tectonism in the Terror Rift of the Ross Sea, Antarctica

    USGS Publications Warehouse

    2007-01-01

    Volcanic sills and dikes inferred from seismic reflection profiles and geophysical studies of the Ross Sea are thought to be related to the rift basins in the region, and their emplacement to be coeval with extension. However, lack of precise geochronology in the Terror Rift of the Ross Sea region has left these inferred relationships poorly constrained and has hindered neotectonic studies, because of the large temporal gaps between seismic reflectors of known ages. New 40Ar/39Ar geochronology presented here for submarine volcanic rocks provides better age constraints for neotectonic interpretations within the Terror Rift. Several samples from seamounts yielded young ages between 156 ± 21 and 122 ± 26 Ka. These ages support interpretations that extension within the Terror Rift was active at least through the Pleistocene. Three evenly spaced samples from the lowermost 100 m of Franklin Island range in age from 3.28 ± 0.04 to 3.73 ± 0.05 Ma. These age determinations demonstrate that construction of a small volcanic edifice such as Franklin Island took at least several hundred thousand years, and therefore that much larger ones in the Erebus Volcanic Province are likely to have taken considerably longer than previously inferred. This warrants caution in applying a limited number of age determinations to define the absolute ages of events in the Ross Sea region

  20. Geochemical composition, petrography and 40Ar/39Ar age of the Heldburg phonolite: implications on magma mixing and mingling

    NASA Astrophysics Data System (ADS)

    Abratis, Michael; Viereck, Lothar; Pfänder, Jörg A.; Hentschel, Roland

    2015-11-01

    Differentiated magmatic rocks such as trachyte and phonolite are volumetrically subordinate to mafic volcanic rocks within the Cenozoic Central European Volcanic Province (exceptions are the East Eifel and the Rhön volcanic fields). Within the volcanic field of the "Heldburg dike swarm" (Heldburger Gangschar), the phonolite of the Burgberg near Heldburg represents the only known occurrence of differentiated magmatic rocks. However, the Heldburg phonolite is famous foremost for containing mantle xenoliths (spinel lherzolite). Former studies proposing a cogenetic relationship between the phonolite and the peridotites concluded that the phonolite magma must have evolved under upper mantle conditions. Herewith, we present petrographic and geochemical evidence for magma mixing and mingling in the Heldburg phonolite melt due to the intrusion of mantle-derived basanitic magma, which is exposed today as dikes at the foot of the Heldburg Burgberg. During this process, the mantle xenoliths were introduced into the phonolite melt as they all contain rims of basanitic magma. Extensive mingling features (e.g., schlieren layers, load casts, flame structures, mafic enclaves) are developed, indicating that the basanite and the zoned phonolitic body were melts at the time of mixing. These petrographic and geochemical indications of two coeval melts of different composition are substantiated by 40Ar/39Ar dating, revealing identical ages of ca. 15 Ma.

  1. A Carnian 40Ar/39Ar age for the Paasselkä impact structure (SE Finland)—An update

    NASA Astrophysics Data System (ADS)

    Schwarz, Winfried H.; Schmieder, Martin; Buchner, Elmar; Trieloff, Mario; Moilanen, Jarmo; Öhman, Teemu

    2015-01-01

    A recrystallized band of pale feldspathic impact melt in a gneissic impact breccia from the approximately 10 km Paasselkä impact structure in southeast Finland was dated via 40Ar/39Ar step-heating. The newly obtained plateau age of 228.7 ± 1.8 (2.2) Ma (2σ) (MSWD = 0.32; p = 0.93) is equal to the previously published pseudoplateau age of 228.7 ± 3.0 (3.4) (2σ) for the impact event. According to the current international chronostratigraphic chart and using the most recent published suggestions for the K decay constants, a Carnian (Late Triassic) age for the Paasselkä impact structure of 231.0 ± 1.8 (2.2) Ma (2σ) is calculated and considered the most precise and accurate age for this impact structure. The new plateau age for Paasselkä confirms the previous dating result but is, based on its internal statistics, much more compelling.

  2. Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

    USGS Publications Warehouse

    Schlup, M.; Steck, A.; Carter, A.; Cosca, M.; Epard, J.-L.; Hunziker, J.

    2011-01-01

    New fission track and Ar/Ar geochronological data provide time constraints on the exhumation history of the Himalayan nappes in the Mandi (Beas valley) - Tso Morari transect of the NW Indian Himalaya. Results from this and previous studies suggest that the SW-directed North Himalayan nappes were emplaced by detachment from the underthrusted upper Indian crust by 55. Ma and metamorphosed by ca. 48-40. Ma. The nappe stack was subsequently exhumed to shallow upper crustal depths (<10. km) by 40-30. Ma in the Tso Morari dome (northern section of the transect) and by 30-20. Ma close to frontal thrusts in the Baralacha La region. From the Oligocene to the present, exhumation continued slowly.Metamorphism started in the High Himalayan nappe prior to the Late Oligocene. High temperatures and anatexis of the subducting upper Indian crust engendered the buoyancy-driven ductile detachment and extrusion of the High Himalayan nappe in the zone of continental collision. Late extrusion of the High Himalayan nappe started about 26. Ma ago, accompanied by ductile extensional shearing in the Zanskar shear zone in its roof between 22 and 19. Ma concomitant with thrusting along the basal Main Central Thrust to the south. The northern part of the nappe was then rapidly exhumed to shallow depth (<10. km) between 20 and 6. Ma, while its southern front reached this depth at 10-5. Ma. ?? 2010 Elsevier Ltd.

  3. 40Ar/39Ar geochronology and geochemical reconnaissance of the Eocene Lowland Creek volcanic field, west-central Montana

    USGS Publications Warehouse

    Dudas, F.O.; Ispolatov, V.O.; Harlan, S.S.; Snee, L.W.

    2010-01-01

    We report geochronological and geochemical data for the calc-alkalic Lowland Creek volcanic field (LCVF) in westcentral Montana. 40Ar/ 39Ar age determinations show that the LCVF was active from 52.9 to 48.6 Ma, with tuff-forming eruptions at 52.9 ?? 0.14 and 51.8 ?? 0.14 Ma. These dates span the age range of vigorous Eocene igneous activity in the Kamloops-Absaroka-Challis belt. The LCVF evolved upward from basal rhyolites (SiO 2>71 wt%) to dacites and andesites (SiO 2 > 62 wt%). Compositional change parallels a transition from early explosive volcanism to late effusive activity. Four geochemical components can be detected in the rocks. A component with 206Pb/204Pb < 16.5 and epsilon;Nd near-15 is predominant in anhydrous, two-pyroxene dacites; hydrous rhyolites, rhyodacites, and dacites with epsilon;Nd below-10 are dominated by a second component; hydrous rocks with 206Pb/ 204Pb > 18.3 and epsilon;Nd>-9 contain a third component; and an andesite with low Nd content and epsilon;Nd near-9 probably contains a fourth component. The first three components probably derive from the lower and middle crust, whereas the fourth is probably from the lithospheric mantle. ?? 2010 by The University of Chicago.

  4. 40Ar/ 39Ar mineral ages from basement rocks in the Eastern Kunlun Mountains, NW China, and their tectonic implications

    NASA Astrophysics Data System (ADS)

    Liu, Yongjiang; Genser, Johann; Neubauer, Franz; Jin, Wei; Ge, Xiaohong; Handler, Robert; Takasu, Akira

    2005-04-01

    40Ar/ 39Ar dating and estimates of regional metamorphic P- T conditions were carried out on the basement rocks of the Eastern Kunlun Mountains, Western China. Samples from the Jinshuikou, Xiaomiao, Kuhai, Wanbaogou, and Nachitai groups revealed distinct metamorphic events and four age groups. The age group in the range from 363 to 439 Ma is interpreted to represent cooling after Middle Silurian-Late Devonian granulite(?) and amphibolite facies metamorphism, which is dominated by low-middle pressure/high temperature conditions. This tectono-thermal event is related to the closure of an oceanic basin or marginal sea. An age group of 212-242 Ma represents cooling after Triassic metamorphic overprint, which is probably associated with magmatic intrusions. This thermal event, together with the Permo-Triassic ophiolite zone along the South Kunlun Fault, relates to the closure of a major ocean (between India and Eurasia) and the eventual N-ward accretion of the Qiangtang block in Permo-Triassic times. The significance of the age group of 104-172 Ma may be related to the ductile deformation along the Xidatan fault due to the northward-directed accretion of the Lhasa block. Biotites from Nachitai record a partial isotopic resetting at ca. 32 Ma that is interpreted to represent a late-stage exhumation caused by further crustal shortening.

  5. Single-Crystal 40Ar/39Ar Dating of the Eocene-Oligocene Transition in North America.

    PubMed

    Swisher, C C; Prothero, D R

    1990-08-17

    Explanations for the causes of climatic changes and associated faunal and floral extinctions at the close of the Eocene Epoch have long been controversial because of, in part, uncertainties in correlation and dating of global events. New single-crystal laser fusion (SCLF) (40)Ar/(39)Ar dates on tephra from key magnetostratigraphic and fossilbearing sections necessitate significant revision in North American late Paleogene chronology. The Chadronian-Orellan North American Land Mammal "Age" boundary, as a result, is shifted from 32.4 to 34.0 Ma (million years ago), the Orellan-Whitneyan boundary is shifted from 30.8 to 32.0 Ma, and the Whitneyan-Arikareean boundary is now approximately 29.0 Ma. The new dates shift the correlation of Chron C12R from the Chadronian to within the Orellan-Whitneyan interval, the Chadronian becomes late Eocene in age, and the North American Oligocene is restricted to the Orellan, Whitneyan, and early Arikareean. The Eocene-Oligocene boundary, and its associated climate change and extinction events, as a result, correlates with the Chadronian-Orellan boundary, not the Duchesnean-Chadronian boundary. PMID:17756788

  6. Single-Crystal 40Ar/39Ar Dating of the Eocene-Oligocene Transition in North America

    NASA Astrophysics Data System (ADS)

    Swisher, Carl C., III; Prothero, D. R.

    1990-08-01

    Explanations for the causes of climatic changes and associated faunal and floral extinctions at the close of the Eocene Epoch have long been controversial because of, in part, uncertainties in correlation and dating of global events. New single-crystal laser fusion (SCLF) 40Ar/39Ar dates on tephra from key magnetostratigraphic and fossil-bearing sections necessitate significant revision in North American late Paleogene chronology. The Chadronian-Orellan North American Land Mammal "Age" boundary, as a result, is shifted from 32.4 to 34.0 Ma (million years ago), the Orellan-Whitneyan boundary is shifted from 30.8 to 32.0 Ma, and the Whitneyan-Arikareean boundary is now approximately 29.0 Ma. The new dates shift the correlation of Chron C12R from the Chadronian to within the Orellan-Whitneyan interval, the Chadronian becomes late Eocene in age, and the North American Oligocene is restricted to the Orellan, Whitneyan, and early Arikareean. The Eocene-Oligocene boundary, and its associated climate change and extinction events, as a result, correlates with the Chadronian-Orellan boundary, not the Duchesnean-Chadronian boundary.

  7. Characterization of two paralogous StAR genes in a teleost, Nile tilapia (Oreochromis niloticus).

    PubMed

    Yu, Xiangguo; Wu, Limin; Xie, Lang; Yang, Shijie; Charkraborty, Tapas; Shi, Hongjuan; Wang, Deshou; Zhou, Linyan

    2014-07-01

    Steroidogenic acute regulatory protein (StAR) transports cholesterol, the substrate for steroid synthesis, to the inner membranes of mitochondria. It is well known that estrogen is essential for female sex determination/differentiation in fish. However, no reports showed that the conventional StAR, which was supposed to be essential for estrogen production, was expressed in female gonads during the critical timing of sex determination/differentiation. In this study, two different StAR isoforms, named as StAR1 and StAR2, were characterized from the gonads of Nile tilapia (Oreochromis niloticus). Phylogenetic and synteny analysis revealed that two StAR genes existed in teleosts, Xenopus and chicken indicating that the duplication event occurred before the divergence of teleosts and tetrapods. Real-time PCR revealed that StAR1 was dominantly expressed in the testis, head kidney and kidney; while StAR2 was expressed exclusively in the gonads. In situ hybridization and immunohistochemistry demonstrated that StAR1 was expressed in the interrenal cells of the head kidney and Leydig cells of the testis; while StAR2 was expressed in the Leydig cells of the testis and the interstitial cells of the ovary. Ontogenic analysis demonstrated that StAR2 was expressed abundantly from 5 days after hatching (dah) in the somatic cells in XX gonads, whereas in XY gonads, both StARs could be detected from 30 dah until adulthood. Intraperitoneal injection of human chorionic gonadotropin experiments showed that expression of StAR1 and 2 was significantly elevated at 8h and persisted until 24h after injection in the testis. Taken together, our data suggested that StAR1 is likely to be required for cortisol production in the head kidney, and StAR2 is probably involved in estrogen production during early sex differentiation in XX gonads. In contrast, both StARs might be required for androgen production in testes. For the first time, our data demonstrated that two fish StARs might be involved

  8. Detailed 40Ar/39Ar chronology of the Tancítaro Volcanic Field, Michoacán, Mexico

    NASA Astrophysics Data System (ADS)

    Ownby, S.; Delgado-Granados, H.; Lange, R.; Hall, C. M.

    2005-12-01

    The Tancítaro volcanic field (TVF) is characterized by over 300 cinder cones and fissure fed lava flows, in addition to the ~10 shield volcanoes and 1 large andesite stratovolcano, ~60 km3 Volcán Tancítaro. The TVF is part of the larger Michoacán Guanajuato volcanic field (MGVF) in the Trans Mexican Volcanic Belt, related to subduction of the Cocos plate. We report new 40Ar/39Ar age constraints on the most recent activity from Volcán Tancítaro. Previously, there was only one K-Ar date 530±60 ka for this volcano; Ban et al. (1992). It has been the site of at least two debris avalanche deposits (Capra et al., 2002; Garduno-Monroy, 1999; Ownby et al., 2004), and continues to threaten the cities of Uruapan and Apatzingán in the state of Michoacán, which have a combined population of >300,000. The most recent activity produced a thin blanket of ash (~1-5 m thick along the flanks of the volcano); this ash is tightly bracketed by dates on two nearby shield volcanoes, one underneath (268±14 ka) and the other on top (267±12 ka) of this ash layer. It appears to have triggered a large debris avalanche deposit off the steep slopes of V. Tancítaro (the distinctive ash is mixed in with this avalanche deposit), which itself is bracketed by two cinder cones, one underneath (425±45 ka) and the other on top (179±77 ka). The timing of this ash eruption is close to that for four different andesite lavas from near the summit of V. Tancítaro, which yielded ages of 251±25 ka, 241±25 ka, 228±16 ka, 223±23 ka, respectively. Other dates from the main edifice of V. Tancítaro reveal two earlier episode of activity at ~450 and ~700 ka. We also report an additional set of ~50 40Ar/39Ar ages on various cinder cones, shields, and fissure-fed flows that are peripheral to V. Tancítaro. The samples range in age from ~980 ka to the present, with no obvious breaks in time. They range continuously from 51-62 wt% SiO2, with no breaks in composition. It appears that neither dacite

  9. High Precision 40Ar/39Ar Geochronology of Servilleta basalt flows in the Rio Grande Gorge, New Mexico

    NASA Astrophysics Data System (ADS)

    Cosca, M. A.; Lee, J. P.; Thompson, R. A.; Turner, K. J.

    2013-12-01

    New geologic mapping and high-precision 40Ar/39Ar geochronology within the Taos Plateau in northern New Mexico indicate a period of vigorous volcanic activity between ~5.5 and ~1 Ma. Over 50 volcanic centers formed during this time together with an unresolved number of vents, fissures, and volcanic centers buried by intercalated volcanic rock and sedimentary basin fill. Defining the volcanic stratigraphy is essential for models of regional groundwater flow and for understanding the geologic evolution of the Pliocene to Recent Rio Grande rift. A spectacular stratigraphic section of volcanic rock related to Rio Grande rifting is visible from the High Bridge on NM State Hwy 64 , approximately 24 km northwest of Taos, NM, where a 240 m canyon is incised through the basal, middle, and upper Servilleta basalt flow packages (Dungan et al., 1984). Fresh basalt from a vertical transect of the canyon near the High Bridge was collected and sized into ~3 mm3 fragments and irradiated with fast neutrons at the USGS TRIGA reactor. The irradiated rock fragments were incrementally heated with a CO2 laser and Ar isotopes were measured using both MAP 215-50 and ARGUS-VI mass spectrometers. Only the argon isotope measurements using the ARGUS-VI had sufficient precision to make accurate corrections for argon isotopic sources and the resulting 40Ar/39Ar ages define a precise emplacement chronology of the entire stratigraphic section. The basal flow package records ages of 4.76 × 0.03 Ma (FCT sanidine = 28.201 Ma; all errors 2 sigma) at river level, 4.75 × 0.04 Ma at mid flow package, and 4.47 × 0.04 at the top of the flow package. The middle flow package records ages of 4.10 × 0.03 Ma at the base of the flow package, 4.14 × 0.10 Ma mid flow package, and 3.98 × 0.08 at the top of the flow package. The upper basalt package records ages of 3.69 × 0.07 Ma at the base of the flow package and 3.59 × 0.10 Ma at the top. The upper and middle flow packages were erupted rapidly, whereas

  10. Metasomatism in the Chain of Ponds K-feldspars: Reassessing Discrete Domain 39Ar-40Ar Modelling

    NASA Astrophysics Data System (ADS)

    Villa, I. M.; Chafe, A. N.; Hanchar, J. M.; Wirth, R.

    2012-12-01

    The post-crystallization petrology of K-feldspar (Kfs) is mostly controlled by fluids. Accordingly, [1] documented that successive mineral generations in Kfs grains of the Aar metagranite can be concordantly identified by both cathodoluminescence (CL) and back-scattered electron (BSE) imaging, elemental, and multi-isotope techniques. Imaging microstructures is a particularly powerful tool appreciated by many U-Pb geochronologists, and its use in 39Ar-40Ar dating is beginning to show beneficial progress [2]. However, a dissenting reviewer of [1] argued that the Aar sample was not typical of "orthodox" Kfs and the results could not be generalized to all Kfs [3]. On a different front, [4] demonstrated that the mathematical modeling that assumed Fickian diffusion in discrete domains, defined once and for all by [5], lacked internal consistency on several counts. As Chain of Ponds Pluton (CPP) Kfs sample MH-10 played a foundational role in the development of the mathematical model by [5], we decided to obtain direct evidence whether the numerous internal inconsistencies of the model are due to the previously undescribed petrological history of MH-10. We collected sample JH-02-01 on the same CPP outcrop as MH-10 [6]. All age spectra of different sieve fractions of the Kfs separate, both handpicked and unpicked, show a staircase shape. The Arrhenius diagram of apparent diffusivity agrees with the original MH-10 [5] and shows the same apparent r/r0 behavior. However, Arrhenius trajectories for all size fractions are parallel to each other and self-similar, as predicted by [4], instead of being joined at low temperature ("small domains") and diverging only at high T ("largest domain"), as would be implicit in the model by [5]. The CL and BSE images demonstrate several successive Kfs generations of diverse luminescence and chemical and isotopic properties. Microchemical analyses document patchy Ba enrichment, a tell-tale fingerprint of deuteric fluid interaction and

  11. Study of electron impact excitation of argon in the extreme ultraviolet - Emission cross section of resonance lines of Ar I, Ar II

    NASA Technical Reports Server (NTRS)

    Ajello, Joseph M.; James, Geoffrey K.; Franklin, Brian; Howell, Simon

    1990-01-01

    In a crossed-beam experiment under optically thin conditions the EUV spectrum of argon produced by electron impact excitation is studied. The cross sections of the resonance lines of Ar I and II are measured. The resonance lines of Ar I at 104.8 nm and 106.7 nm, and of Ar II at 91.96 nm and 93.21 nm are the most prominent features of the EUV spectrum between 40 and 110 nm. The relative-flow technique is used to measure the absolute cross sections of these lines at 200 eV. The measurements are compared with previous estimates. The measured emission cross section values at 200 eV for the Ar I lines at 104.8 nm and 106.7 nm, when compared to the electron energy loss estimates of the direct excitation cross sections, establish that cascading is larger for the Ar I resonance lines than previous emission experiments have indicated. In addition, all the emission cross sections for the Ar I and II Rydberg series in the EUV are measured at 0.5 nm resolution. The FUV spectrum is also surveyed and found to consist of Ar II multiplets from simultaneous ionization-excitation.

  12. Starving the addiction: new opportunities for durable suppression of AR signaling in prostate cancer

    PubMed Central

    Knudsen, Karen E.; Scher, Howard I.

    2009-01-01

    Clinical data and models of human disease indicate that androgen receptor (AR) activity is essential for prostate cancer development, growth and progression. The dependence of prostatic adenocarcinoma on AR signaling at all stages of disease has thereby been exploited in the treatment of disseminated tumors, for which ablation of AR function is the goal of first line therapy. Although these strategies are initially effective, recurrent tumors arise with restored AR activity, and no durable treatment has yet been identified to combat this stage of disease. New insights into AR regulation and the mechanisms underlying resurgent AR activity have provided fertile ground for the development of novel strategies to more effectively inhibit receptor activity and prolong the transition to therapeutic failure. PMID:19638458

  13. Li^+ attachment mass spectrometric investigation of high-mass neutral species in the downstream region of Ar/CF4, Ar/CF4/O2 and Ar/CF4/H2 plasmas

    NASA Astrophysics Data System (ADS)

    Furuya, Kenji; Okumura, Hiroshi; Tamai, Yuji; Ide, Akihiro; Harata, Akira

    2008-10-01

    Recently gaseous high-mass species have received significant attentions as important contributors to the nucleation of films and particulates in fluorocarbon plasmas. We have unambiguously identified the gaseous high-mass neutral species in the downstream region of the Ar/CF4 plasma [1], using the Li^+ attachment ionization technique that is a fragment-free ionization method. In this report, we show the results of mass analysis of high-mass neutral species in the Ar/CF4/O2 and Ar/CF4/H2 plasmas as well as Ar/CF4. In the Ar/CF4 plasma, we observed CnF2n+2 (n = 2-7) and CnF2n (n = 4-8) as neutral species. Adding O2 to the Ar/CF4 plasma resulted in the intensity decrease of CnF2n+2 and CnF2n, especially of those with relatively small n values. CnF2nO (n = 1-7) were newly observed in the Ar/CF4/O2 plasma. In contrast, adding H2 to the Ar/CF4 plasma resulted in the production of various new compounds, such as CnF2n-2 (n=3-8), CnF2n-4 (n=3-9), CnF2n+1H (n=1-7), CnF2n-1H (n=2-8), CnF2n-3H (n=4-9) and CnF2n-5H (n=5-9). These species are produced through the abstraction of F from various CnFm species by the H radical and the addition of H to them. [1] K. Furuya, S. Yukita, H. Okumura, A. Harata, Chem. Lett. 34, 224 (2005).

  14. The sup 40 Ar/ sup 39 Ar thermochronology of the eastern Mojave Desert, California, and adjacent western Arizona with implications for the evolution of metamorphic core complexes

    SciTech Connect

    Foster, D.A.; Harrison, T.M. ); Miller, C.F. ); Howard, K.A. )

    1990-11-10

    The application of {sup 40}Ar/{sup 39}Ar thermochronology provides information about the timing and nature of thrusting, plutonism, metamorphism, denudation, and detachment faulting. The {sup 40}Ar/{sup 39}Ar ages of 175 to 125 Ma from the Clipper, Piute, Turtle, Mohave, Bill Williams, and Hualapai Mountains are interpreted to be the result of a middle Mesozoic thermal event(s) caused by crustal thickening. The {sup 40}Ar/{sup 39}Ar data from the Clipper and Piute Mountains suggest that this thermal event was followed by a period of cooling at rates of 1-5C/m.y. Orogenesis culminated during the Late Cretaceous when rocks exposed in the Old Woman-Piute, Chemehuevi, and Sacramento Mountains attained temperatures >500C which reset the K-Ar systems of minerals from Proterozoic rocks. High-grade metamorphism in the Old Woman Mountains area was caused by the intrusion of the Old Woman-Piute batholith at 73 {plus minus} 1 Ma. Cooling rates following batholith emplacement in the Old Woman Mountains were {approximately}100C/m.y. between 73 and 70 Ma and 5-10C/m.y. from 70 to {approximately}30 Ma. By 30 Ma, rocks exposed in the Old Woman-Piute, Marble, Ship, Clipper, and Turtle Mountains were below {approximately}100C. The {sup 49}Ar/{sup 39}Ar ages from the Sacramento Mountains suggest that mylonization caused by the onset of regional extension occurred at 23 {plus minus} 1 Ma. When extension started in the Chemehuevi Mountains, rocks exposed in the southwestern and northeastern portions of footwall to the Chemehuevi detachment fault were at {approximately}180C and {approximately}350C, respectively. Unroofing of the footwalls to detachment faults in the Sacramento and Chemehuevi Mountains resulted in average cooling rates of 10-50C/m.y. between 22 and 15 Ma.

  15. The Contribution of ArsB to Arsenic Resistance in Campylobacter jejuni

    PubMed Central

    Shen, Zhangqi; Han, Jing; Wang, Yang; Sahin, Orhan; Zhang, Qijing

    2013-01-01

    Arsenic, a toxic metalloid, exists in the natural environment and its organic form is approved for use as a feed additive for animal production. As a major foodborne pathogen of animal origin, Campylobacter is exposed to arsenic selection pressure in the food animal production environments. Previous studies showed that Campylobacter isolates from poultry were highly resistant to arsenic compounds and a 4-gene operon (containing arsP, arsR, arsC, and acr3) was associated with arsenic resistance in Campylobacter. However, this 4-gene operon is only present in some Campylobacter isolates and other arsenic resistance mechanisms in C. jejuni have not been characterized. In this study, we determined the role of several putative arsenic resistance genes including arsB, arsC2, and arsR3 in arsenic resistance in C. jejuni and found that arsB, but not the other two genes, contributes to the resistance to arsenite and arsenate. Inactivation of arsB in C. jejuni resulted in 8- and 4-fold reduction in the MICs of arsenite and arsenate, respectively, and complementation of the arsB mutant restored the MIC of arsenite. Additionally, overexpression of arsB in C. jejuni 11168 resulted in a 16-fold increase in the MIC of arsenite. PCR analysis of C. jejuni isolates from different animals hosts indicated that arsB and acr3 (the 4-gene operon) are widely distributed in various C. jejuni strains, suggesting that Campylobacter requires at least one of the two genes for adaptation to arsenic-containing environments. These results identify ArsB as an alternative mechanism for arsenic resistance in C. jejuni and provide new insights into the adaptive mechanisms of Campylobacter in animal food production environments. PMID:23554953

  16. EXPERIMENTAL AND THEORETICAL STUDIES OF THE CN-AR VAN DER WAALS COMPLEX

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The CN-Ar van der Waals complex has been observed using B2E+-X2E+ and A2II-X2E+ electronic transitions. The spectra yielded a dissociation energy of D0"=109+2 cm1 and a zero point rational constant of B0"=0.067+0.005 cm-1 for CN(x)-Ar. The dissociation energy for Cn(A)-Ar was found to be D0"=132+2...

  17. Tracking the timing of subduction and exhumation using 40Ar/39Ar phengite ages in blueschist- and eclogite-facies rocks (Sivrihisar, Turkey)

    NASA Astrophysics Data System (ADS)

    Fornash, Katherine F.; Cosca, Michael A.; Whitney, Donna L.

    2016-07-01

    Geochronologic studies of high-pressure/low-temperature rocks can be used to determine the timing and rates of burial and exhumation in subduction zones by dating different stages of the pressure-temperature history. In this study, we present new in situ UV laser ablation 40Ar/39Ar phengite ages from a suite of lawsonite blueschist- and eclogite-facies rocks representing different protoliths (metabasalt, metasediment), different structural levels (within and outside of a high-strain zone), and different textural positions (eclogite pod core vs. margin) to understand the timing of these events in an exhumed Neo-Tethyan subduction zone (Sivrihisar Massif, Tavşanlı Zone, Turkey). Weighted mean in situ 40Ar/39Ar ages of phengite from the cores of lawsonite eclogite pods (90-93 Ma) are distinctly older than phengite from retrogressed, epidote eclogite (82 ± 2 Ma). These ages are interpreted as the age of peak and retrograde metamorphism, respectively. Eclogite records the narrowest range of ages (10-14 m.y.) of any rock type analyzed. Transitional eclogite- and blueschist-facies assemblages and glaucophane-rimmed lawsonite + garnet + phengite veins from eclogite pod margins record a much wider age range of 40Ar/39Ar ages (~20 m.y.) with weighted mean ages of ~91 Ma. Blueschists and quartzites record more variable 40Ar/39Ar ages that may in part be related to structural position: samples within a high-strain zone at the tectonic contact of the HP rocks with a meta-ultramafic unit have in situ UV laser ablation 40Ar/39Ar ages of 84.0 ± 1.3-103.7 ± 3.1 Ma, whereas samples outside this zone range to older ages (84.6 ± 2.4-116.7 ± 2.7 Ma) and record a greater age range (22-38 m.y.). The phengite ages can be correlated with the preservation of HP mineral assemblages and fabrics as well as the effects of deformation. Collectively, these results show that high-spatial resolution UV laser ablation 40Ar/39Ar phengite data, when considered in a petrologic and structural

  18. Planktic foraminifer census data from Northwind Ridge cores PI-88-AP P3, PI-88-AR P7 and PI-88-AR P9, Arctic Ocean

    USGS Publications Warehouse

    Foley, Kevin M.; Poore, Richard Z.

    1993-01-01

    The U.S. Geological Survey recovered 9 piston cores from the Northwind Ridge in the Canada Basin of the Arctic Ocean from a cruise of the USCGC Polar Star during 1988. Preliminary analysis of the cores suggests sediments deposited on Northwind Ridge preserve a detailed record of glacial and interglacial cycles for the last few hundred-thousand to one million years. This report includes quantitative data on foraminifers and selected sediment size-fraction data in 98 samples from Northwind Ridge core PI-88AR P3, 51 samples from core PI-88-AR P7 and 117 samples from core PI-88-AR P9.

  19. The Detrital White Mica 40Ar/39Ar Record of the Katawaz Remnant Ocean Basin, Pakistan, and Tectonic Implications for the Himalayan Source Region

    NASA Astrophysics Data System (ADS)

    Zhuang, G.; Najman, Y.; Wijbrans, J. R.; Millar, I.; Carter, A.

    2014-12-01

    The Paleogene-Neogene sedimentary rocks in the Katawaz remnant ocean basin, Pakistan were thought to be a product of a fan-deltaic system, analogous to the modern Indus River and delta. A preliminary detrital zircon U-Pb study (Carter et al 2010) supported materials derived from the nascent western Himalaya and associated magmatic arc but that study was based on too few samples to fully characterize the whole series. Moreover, the chronology in the Katawaz basin was previously not well constrained, which impedes accurate comparison to other Himalaya foreland records. Here, we present a densely sampled study of detrital white mica 40Ar/39Ar. This study aims to: (1) constrain sedimentary ages of major lithostratigraphic units, (2) understand the exhumation history of the source region, and (3) reconstruct the paleodrainage system in NW Himalayan foreland. New 40Ar/39Ar data, together with a complementary study of detrital zircon U-Pb, constrain the sand-rich, fluvial-dominated Shaigalu Member to span from <34-36 Ma (basal sample) to <22 Ma (uppermost sample). The basal Shaigalu Member demonstrates similarity of ages of detrital zircon U-Pb and detrital white mica 40Ar/39Ar; both are characterized by a dominant peak of ca. 37 Ma. The dominant 37 Ma peak of detrital white mica 40Ar/39Ar ages has also been identified in the late Eocene Balakot Formation (Najman et al. 2001), the oldest terrestrial unit in the Himalayan peripheral foreland basin, and which is Himalayan-derived. We interpret the similarity in youngest age peak (37 Ma) between U-Pb and 40Ar/39Ar as a signal of rapid exhumation related to a rising western Himalaya. Our new 40Ar/39Ar data also reveal that sediment sources changed through time, as demonstrated by the disappearance of the 37 Ma population up-section and re-occurrence at the top. This could be related to either migration of the drainage system and/or changes in sediment sources. Finally, our study indicates that the latest Eocene rapid

  20. The Ars alchemie: the first Latin text on practical alchemy.

    PubMed

    Vinciguerra, Antony

    2009-03-01

    The Ars alchemie is a collection of alchemical recipes associated with the names of the Arabic-Latin translator Michael Scot and the major general of the Friars Minor, Elias Cortona, of the first half of the thirteenth century. This articles investigates the various forms in which this text appears in the four manuscripts that contain it. It shows the dependence of one of its prologues on the work of an earlier translator, Hugo of Santalla, and the overlap of its contents with other alchemical treatises: Liber luminis luminum, Liber Dedali, Liber de aluminibus et salibus and Liber Hermetis de blchkmkb. Its mention of the alum of Aleppo corresponds with references to trade in this material in the thirteenth century. Its main characteristics are its compilatory nature and its emphasis on practical applications. PMID:19831260

  1. Lifetimes of superdeformed rotational states in {sup 36}Ar.

    SciTech Connect

    Svensson, C. E.; Macchiavelli, A. O.; Juodagalvis, A.; Poves, A.; Ragnarsson, I.; Aberg, S.; Appelbe, D. E.; Austin, R. A. E.; Ball, G. C.; Carpenter, M. P.; Caurier, E.; Clark, R. M.; Cromaz, M.; Deleplanque, M. A.; Diamond, R. M.; Fallon, P.; Janssens, R. V. F.; Lane, G. J.; Lee, I. Y.; Nowacki, F.; Sarantites, D. G.; Stephens, F. S.; Vetter, K.; Ward, D.; Physics; LBNL; Lund Inst. of Tech.; Univ. Autonoma de Madrid; McMaster Univ.; TRIUMF; Univ. Louis Pasteur; Washington Univ.

    2001-06-01

    Lifetimes have been measured in a superdeformed rotational band recently identified in the N=Z nucleus {sup 36}Ar. A large low-spin quadrupole deformation ({beta}{sub 2}=0.46{+-}0.03) is confirmed and a decrease in the collectivity is observed as the high-spin band termination at I{sup {pi}}=16{sup +} is approached. Detailed comparisons of the experimental B(E2) values with the results of cranked Nilsson-Strutinsky and large-scale (s{sub 1/2}d{sub 3/2})-pf spherical shell model calculations indicate the need for a more refined treatment of transition matrix elements close to termination in the former, and the inclusion of the complete sd-pf model space in the latter description of this highly-collective rotational band.

  2. Dual- and triple-band AR coatings for IR systems

    NASA Astrophysics Data System (ADS)

    Cohen, Daniel; Stolov, Yevgeni; Azran, Amnon; Gilo, Mordechai

    2013-06-01

    Dual-band infrared camera systems allow viewing and comparison of the 3-5µ and 8-12µ spectrum regions, improve visibility at sunrise/sunset and help distinguish between targets and decoys. They also enhance the ability to defeat many IR countermeasures such as smoke, camouflage and flares. As dual band 3rd generation FLIR systems progress, we introduce coatings for these systems. This paper describes advanced dual band coatings for the 3-5µ and 8-12µ spectrum regions, with reference to single band coatings. Theoretical and measured designs are shown for ZnSe, ZnS, Ge and IG-6 substrates. Triple band AR coatings with additional transmittance at 1.06µ are also demonstrated.

  3. Nuclear-pumped He/3/-Ar laser modeling

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Deyoung, R. J.; Harries, W. L.

    1979-01-01

    A first-order model of He(3)-Ar 1.79-micron laser is developed, compared to experimental results, and used to explain the qualitative features of this system. Results indicate that direct excitation of the argon upper level is at best very inefficient for population inversion. For argon concentrations which give the most efficient laser operation, the He-3(n,p)He-3(n,p)He-3 energy is used to produce atomic He ions that quickly convert into He molecular ions. These molecular ions subsequently form argon atomic ions through charge transfer. The dominant pumping mechanism is collisional-radiative recombination of the argon atomic ion and subsequent radiative cascading into the upper laser level.

  4. Doppler imaging of AR Lacertae at three epochs

    NASA Technical Reports Server (NTRS)

    Walter, Frederick M.; Neff, James E.; Linsky, Jeffrey L.; Rodono, Marcello

    1988-01-01

    Observations from IUE were used to study the structure of the lower chromosphere of AR Lacertae in the light of Mg II k. Sequences of LWR/P-HI images distributed around the binary period at three epochs were obtained. Discrete plage-like regions of enhanced Mg II surface flux in this system are identified. There are temporal variations in the Mg II flux on timescales of hours as well as substantial changes in chromospheric morphology on timescales of years. Even with the limited S/N attainable with the IUE, one can map the gross structures of active stellar atmospheres. With such information, one can begin to study the true 3-D structure of the atmospheres of late-type stars.

  5. Modification of surface properties of polyethylene by Ar plasma discharge

    NASA Astrophysics Data System (ADS)

    Švorčík, V.; Kotál, V.; Slepička, P.; Bláhová, O.; Špírková, M.; Sajdl, P.; Hnatowicz, V.

    2006-03-01

    Polyethylene (PE) surface was modified by Ar plasma discharge. The changes of surface morphology and surface wettability (characterized by contact angle) were followed using AFM microscopy and standard goniometry, respectively. The changes of chemical structure of PE polymeric chain were characterized by FTIR and XPS techniques. A nanoindenter was used to study mechanical properties (microhardness, elasticity module and microscratch test) of modified PE. After exposition to the plasma discharge a fast decline of the contact angle is observed. The decline depends on the discharge power and the time elapsed from the plasma exposition. FTIR and XPS measurements indicate an oxidation of degraded polymeric chains and creation of hydroxyl, carbonyl, ether, ester and carboxyl groups. Surface morphology of modified PE depends on the plasma discharge power and exposure time. Maximum microhardness and elastic module, observed on PE specimens exposed to plasma discharge for 240 s, may be connected with PE crosslinking initiated by plasma discharge.

  6. Calculation of pressure-broadened linewidths for CO in Ar

    NASA Technical Reports Server (NTRS)

    Green, S.

    1985-01-01

    Calculations of the pressure-broadening cross sections of CO in Ar have been made within the infinite-order sudden (IOS) and coupled states (CS) quantum scattering approximations. Two intermolecular potentials were used, a pairwise additive atom-atom potential which has been employed previously in semiclassical (modified Anderson theory) studies of this system and one calculated ab initio within an electron gas formalism. Predictions from the two potentials generally agree within about 25 percent and bracket experimental values (except for some recent high temperature data obtained in shock tube experiments). The CS approximation appears to be quite accurate although computationally expensive. The much cheaper IOS approximation is accurate for the J = 0-1 line but does not properly predict the dependence on line number. The quantum results are also compared with earlier semiclassical values.

  7. Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians

    NASA Astrophysics Data System (ADS)

    Kellett, Dawn A.; Warren, Clare; Larson, Kyle P.; Zwingmann, Horst; van Staal, Cees R.; Rogers, Neil

    2016-06-01

    White mica 40Ar/39Ar analyses may provide useful constraints on the timing of tectonic processes, but complex geological and thermal histories can perturb Ar systematics in a variety of ways. Ductile shear zones represent excellent case studies for exploring the link(s) between dynamic re-/neo-crystallization of white mica and coeval enhanced fluid flow, and their effect on 40Ar/39Ar dates. White mica 40Ar/39Ar dates were collected from compositionally similar granites that record different episodes of deformation with proximity to the Dover Fault, a terrane-bounding strike-slip shear zone in the Appalachian orogen, Newfoundland, Canada. 40Ar/39Ar data were collected in situ by laser ablation and by step heating single crystals. Results were compared to each other and against complementary U-Pb zircon and monazite, and K-Ar fault gouge analysis. Although step-heat 40Ar/39Ar is a widely applied method in orogenic settings, this dataset shows that relatively flat step-heat 40Ar/39Ar spectra are in contradiction with wide spreads in in-situ40Ar/39Ar dates from the same samples, and that plateau dates in some cases yielded mixed dates of equivocal geological significance. This result indicates that the step-wise release of Ar from white mica likely homogenizes and obscures spatially-controlled Ar isotope reservoirs in white mica from sheared rocks. In contrast, in situ laser ablation 40Ar/39Ar analysis preserves the spatial resolution of 40Ar reservoirs that have been variably reset by deformation and fluid interaction. This study therefore suggests that laser ablation is the best method for dating the timing of deformation recorded by white mica. Final interpretation of results should be guided by microstructural analysis, estimation of deformation temperature, chemical characterization of white mica, and complementary chronometers. Overall the dataset shows that granitic protoliths were emplaced between 430 and 422 Ma (U-Pb zircon). High strain deformation along the

  8. Stereodynamics in NO(X) + Ar inelastic collisions

    NASA Astrophysics Data System (ADS)

    Brouard, M.; Chadwick, H.; Gordon, S. D. S.; Hornung, B.; Nichols, B.; Aoiz, F. J.; Stolte, S.

    2016-06-01

    The effect of orientation of the NO(X) bond axis prior to rotationally inelastic collisions with Ar has been investigated experimentally and theoretically. A modification to conventional velocity-map imaging ion optics is described, which allows the orientation of hexapole state-selected NO(X) using a static electric field, followed by velocity map imaging of the resonantly ionized scattered products. Bond orientation resolved differential cross sections are measured experimentally for a series of spin-orbit conserving transitions and compared with quantum mechanical calculations. The agreement between experimental results and those from quantum mechanical calculations is generally good. Parity pairs, which have previously been observed in collisions of unpolarized NO with various rare gases, are not observed due to the coherent superposition of the two j = 1/2, Ω = 1/2 Λ-doublet levels in the orienting field. The normalized difference differential cross sections are found to depend predominantly on the final rotational state, and are not very sensitive to the final Λ-doublet level. The differential steric effect has also been investigated theoretically, by means of quantum mechanical and classical calculations. Classically, the differential steric effect can be understood by considering the steric requirement for different types of trajectories that contribute to different regions of the differential cross section. However, classical effects cannot account quantitatively for the differential steric asymmetry observed in NO(X) + Ar collisions, which reflects quantum interference from scattering at either end of the molecule. This quantum interference effect is dominated by the repulsive region of the potential.

  9. Stereodynamics in NO(X) + Ar inelastic collisions.

    PubMed

    Brouard, M; Chadwick, H; Gordon, S D S; Hornung, B; Nichols, B; Aoiz, F J; Stolte, S

    2016-06-14

    The effect of orientation of the NO(X) bond axis prior to rotationally inelastic collisions with Ar has been investigated experimentally and theoretically. A modification to conventional velocity-map imaging ion optics is described, which allows the orientation of hexapole state-selected NO(X) using a static electric field, followed by velocity map imaging of the resonantly ionized scattered products. Bond orientation resolved differential cross sections are measured experimentally for a series of spin-orbit conserving transitions and compared with quantum mechanical calculations. The agreement between experimental results and those from quantum mechanical calculations is generally good. Parity pairs, which have previously been observed in collisions of unpolarized NO with various rare gases, are not observed due to the coherent superposition of the two j = 1/2, Ω = 1/2 Λ-doublet levels in the orienting field. The normalized difference differential cross sections are found to depend predominantly on the final rotational state, and are not very sensitive to the final Λ-doublet level. The differential steric effect has also been investigated theoretically, by means of quantum mechanical and classical calculations. Classically, the differential steric effect can be understood by considering the steric requirement for different types of trajectories that contribute to different regions of the differential cross section. However, classical effects cannot account quantitatively for the differential steric asymmetry observed in NO(X) + Ar collisions, which reflects quantum interference from scattering at either end of the molecule. This quantum interference effect is dominated by the repulsive region of the potential. PMID:27306001

  10. National Research Networks Facilitate Mutually Beneficial Research at ARS Locations

    NASA Astrophysics Data System (ADS)

    Seyfried, M. S.; Holbrook, W. S.; Fellows, A.; Kormos, P.; Lohse, K. A.; Marks, D. G.; Flerchinger, G. N.

    2015-12-01

    A major benefit of participation in research networks such as the Long Term Agroecosystem Research (LTAR) network is that multidisciplinary research on a broad range of topics is facilitated. The interaction between the Agricultural Research Service long-term experimental watersheds and LTAR exemplifies this. At the Reynolds Creek Experimental Watershed (RCEW), this is further enhanced by participation in the Critical Zone Observatory (CZO) network. The RCEW has a long history (55 years) of experimentation, modeling and monitoring emphasizing hydrologic processes, which are inevitably related to biogeochemical processes, but rarely linked directly in RCEW research. New research with the Reynolds Creek CZO (RC CZO) emphasizes biogeochemistry. The background research and infrastructure at the RCEW provides an ideal platform for that research. At the same time, RC CZO products are enabling ARS to extend its research activities. We highlight three examples: (i) forcing data sets used to facilitate physical modeling of hydrologic and biogeochemical processes, (ii) linkage of hydrology and geophyscis to extend our understanding of subsurface processes, and (iii) climate/elevation linkages to ecosystem productivity, which are closely related in water limited environments such as the RCEW. The addition of the RCEW to the LTAR is further extended ARS capabilities. For example, the RCEW is now monitoring net carbon balance and productivity at sites along an elevation/climatic gradient. The addition of LTAR research enhances that work by extending the climate gradient and introducing management and land surface change effects. We anticipate that these interactions will grow and that cross-site experiments will be initiated as the results begin to accumulate.

  11. Resetting of Neoarchaean hornblendes from the Murmansk Terrane (Kola Peninsula, Russia) revealed by a combined 40Ar/39Ar and Rb-Sr analysis

    NASA Astrophysics Data System (ADS)

    de Jong, K.; Timmerman, M. J.; Cliff, R. A.; Wijbrans, J. R.; Daly, J. S.; Balagansky, V. V.

    2003-04-01

    We present isotope data from amphiboles from the 2.6--2.8 Ga Murmansk Terrane in the northern foreland of the 1.9 Ga Lapland-Kola Orogen of northern Fennoscandia. Most amphiboles are zoned with tschermakitic cores that progressively change to actinolite in 5--10 μm wide areas in rims, defect zones or adjacent to biotite. Biotite chiefly occurs along cleavages, fractures and grain boundaries of amphibole, showing that its hydration and fluid ingress are confined to lattice imperfections. Furnace step heating of hornblende separate MT-11 gave spectra with increasing apparent ages and Ca/K ratios (a proxy for 37ArCa/39Ar_K). Hornblende is intergrown with biotite that also occurs in the matrix. Yet, laser step heating of single hornblende grain MT-11 yielded flat spectra with Neoarchaean apparent ages and constant Ca/K ratios. This suggests that the hornblende grain that was drilled from a thin section and which was not affected by biotite growth retained its Neoarchaean age. In contrast, the hornblende separate with intergrown biotite from this sample has a partially reset Neoarchaean isotope system. Hornblende MT-27 has Neoarchaean apparent ages and lacks low Ca/K ratios in both single grain and mineral separate spectra; it is not affected by biotite growth and this mineral is also absent from the matrix. Age spectra of other hornblende separates have increasing apparent ages to 2.56--2.65 Ga during final 39Ar release; their Ca/K ratio spectra similarly increase. Low Ca/K ratios for gas release below 950^oC imply degassing of included biotite. Apparent ages of the first heating increments may be as young as 1.8 Ga, comparable to the K-Ar and 40Ar/39Ar ages of the youngest biotites. Hornblende-plagioclase pairs from aliquots used for 40Ar/39Ar furnace step heating yielded sharply discordant Rb-Sr ages. MT-11 yielded an 1881 ± 23 Ma Rb-Sr age that compares well with the K-Ar and 40Ar/39Ar ages of biotite in the sample. In contrast, hornblende of sample MT-27 has a

  12. Neutron-Proton Asymmetry Dependence of Spectroscopic Factors in Ar Isotopes

    NASA Astrophysics Data System (ADS)

    Lee, Jenny; Tsang, M. B.; Bazin, D.; Coupland, D.; Henzl, V.; Henzlova, D.; Kilburn, M.; Lynch, W. G.; Rogers, A. M.; Sanetullaev, A.; Signoracci, A.; Sun, Z. Y.; Youngs, M.; Chae, K. Y.; Charity, R. J.; Cheung, H. K.; Famiano, M.; Hudan, S.; O'Malley, P.; Peters, W. A.; Schmitt, K.; Shapira, D.; Sobotka, L. G.

    2010-03-01

    Spectroscopic factors have been extracted for proton-rich Ar34 and neutron-rich Ar46 using the (p, d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton-rich nucleus Ar34 compared to that of Ar46. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements.

  13. Ar II Emission Processes and Emission Rate Coefficients in ASTRAL Helicon Plasmas

    NASA Astrophysics Data System (ADS)

    Boivin, R. F.; Gardner, A.; Kamar, O.; Kesterson, A.; Loch, S.; Munoz, J.; Ballance, C.

    2008-11-01

    Emission processes for Ar II line emission are described for low temperature plasmas (Te < 10 eV). It is found that Ar II emission results primarily from Ar ion ground state excitation rather than from any Ar neutral state. This suggests that Ar II emission results from stepping processes which includes ionization and then excitation of the neutral Ar atom filling the vacuum chamber. The Ar II emission rate coefficients are measured in the ASTRAL helicon plasma source using a 0.33 m monochromator and a CCD camera. ASTRAL produces Ar plasmas with the following parameters: ne = 1E11 -- 1E13 cm-3 and Te = 2 - 10 eV, B-field <= 1.3 kGauss, rf power <= 2 kWatt. RF compensated Langmuir probes are used to measure Te and ne. In this experiment, Ar II transitions are monitored as a function of Te while ne is kept constant. Experimental emission rates are obtained as a function of Te and compared to theoretical predictions. Theoretical predictions make use of the ADAS suite of codes as well as recent R-matrix electron-impact excitation calculations that includes pseudo-states contributions. Our collisional-radiative formalism assumes that the excited levels are in quasi-static equilibrium with the ground and metastable populations.

  14. Atmospheric Ar and Ne returned from mantle depths to the Earth's surface by forearc recycling.

    PubMed

    Baldwin, Suzanne L; Das, J P

    2015-11-17

    In subduction zones, sediments, hydrothermally altered lithosphere, fluids, and atmospheric gases are transported into the mantle, where ultrahigh-pressure (UHP) metamorphism takes place. However, the extent to which atmospheric noble gases are trapped in minerals crystallized during UHP metamorphism is unknown. We measured Ar and Ne trapped in phengite and omphacite from the youngest known UHP terrane on Earth to determine the composition of Ar and Ne returned from mantle depths to the surface by forearc recycling. An (40)Ar/(39)Ar age [7.93 ± 0.10 My (1σ)] for phengite is interpreted as the timing of crystallization at mantle depths and indicates that (40)Ar/(39)Ar phengite ages reliably record the timing of UHP metamorphism. Both phengite and omphacite yielded atmospheric (38)Ar/(36)Ar and (20)Ne/(22)Ne. Our study provides the first documentation, to our knowledge, of entrapment of atmospheric Ar and Ne in phengite and omphacite. Results indicate that a subduction barrier for atmospheric-derived noble gases does not exist at mantle depths associated with UHP metamorphism. We show that the crystallization age together with the isotopic composition of nonradiogenic noble gases trapped in minerals formed during subsolidus crystallization at mantle depths can be used to unambiguously assess forearc recycling of atmospheric noble gases. The flux of atmospheric noble gas entering the deep Earth through subduction and returning to the surface cannot be fully realized until the abundances of atmospheric noble gases trapped in exhumed UHP rocks are known. PMID:26542683

  15. Alteration of natural (37)Ar activity concentration in the subsurface by gas transport and water infiltration.

    PubMed

    Guillon, Sophie; Sun, Yunwei; Purtschert, Roland; Raghoo, Lauren; Pili, Eric; Carrigan, Charles R

    2016-05-01

    High (37)Ar activity concentration in soil gas is proposed as a key evidence for the detection of underground nuclear explosion by the Comprehensive Nuclear Test-Ban Treaty. However, such a detection is challenged by the natural background of (37)Ar in the subsurface, mainly due to Ca activation by cosmic rays. A better understanding and improved capability to predict (37)Ar activity concentration in the subsurface and its spatial and temporal variability is thus required. A numerical model integrating (37)Ar production and transport in the subsurface is developed, including variable soil water content and water infiltration at the surface. A parameterized equation for (37)Ar production in the first 15 m below the surface is studied, taking into account the major production reactions and the moderation effect of soil water content. Using sensitivity analysis and uncertainty quantification, a realistic and comprehensive probability distribution of natural (37)Ar activity concentrations in soil gas is proposed, including the effects of water infiltration. Site location and soil composition are identified as the parameters allowing for a most effective reduction of the possible range of (37)Ar activity concentrations. The influence of soil water content on (37)Ar production is shown to be negligible to first order, while (37)Ar activity concentration in soil gas and its temporal variability appear to be strongly influenced by transient water infiltration events. These results will be used as a basis for practical CTBTO concepts of operation during an OSI. PMID:26939033

  16. Neutron-Proton Asymmetry Dependence of Spectroscopic Factors in Ar Isotopes

    SciTech Connect

    Lee, Jenny; Tsang, Betty; Shapira, Dan

    2010-01-01

    Spectroscopic factors have been extracted for proton-rich 34Ar and neutron-rich 46Ar using the (p, d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton-rich nucleus 34Ar compared to that of 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements.

  17. Auger decay of Ar 2p satellite states studied with a multielectron coincidence method

    NASA Astrophysics Data System (ADS)

    Nakano, M.; Hikosaka, Y.; Lablanquie, P.; Penent, F.; Huttula, S.-M.; Suzuki, I. H.; Soejima, K.; Kouchi, N.; Ito, K.

    2012-04-01

    The Auger decay channels of the Ar 2p satellite states have been investigated using a multielectron coincidence technique, using a magnetic bottle time-of-flight electron spectrometer. For the Ar+(2p-13p-1np) satellite states the 2p hole is filled first, while for the Ar+(2p-13s-14s) satellite states the 3s hole is filled first with leading to Ar2+(2p-13p-1) states, which subsequently undergo an Auger decay leading to the filling of the 2p hole.

  18. A study of the trace 39Ar content in argon from deep underground sources

    NASA Astrophysics Data System (ADS)

    Xu, J.; Calaprice, F.; Galbiati, C.; Goretti, A.; Guray, G.; Hohman, T.; Holtz, D.; Ianni, An.; Laubenstein, M.; Loer, B.; Love, C.; Martoff, C. J.; Montanari, D.; Mukhopadhyay, S.; Nelson, A.; Rountree, S. D.; Vogelaar, R. B.; Wright, A.

    2015-06-01

    The discovery of argon from deep underground sources with significantly less 39Ar than atmospheric argon was an important step in the development of direct dark matter detection experiments using argon as the active target. We report on the design and operation of a low-background single-phase liquid argon detector that was built to study the 39Ar content of this underground argon. Underground argon from the Kinder Morgan CO2 plant in Cortez, Colorado was determined to have less than 0.65% of the 39Ar activity in atmospheric argon, or 6.6 mBq/kg specific 39Ar activity.

  19. Defining the Tristan-Gough Hotspot: High-Resolution 40Ar/39Ar Dating of Volcanism at Tristan da Cunha

    NASA Astrophysics Data System (ADS)

    Schnur, S.; Koppers, A. A. P.

    2015-12-01

    Explaining the spatial distribution of intra-plate volcanism is an important geologic problem. The Walvis Ridge is a uniquely-shaped hotspot trail in the South Atlantic that is not fully explained by the prevailing mantle plume paradigm. About halfway through its 130 Myr history, Walvis shows a morphological shift from a continuous ridge to a diffuse region of guyots arranged in two volcanic tracks. Recent volcanism at both Tristan da Cunha and Gough Island suggests these tracks are produced by two hotspots sourced from a single plume. However, the islands are located more than 400 km apart, which does not conform to our understanding of plumes as narrow, semi-stationary upwellings. It remains unclear which of the two islands better represents the current plume position. New ages from previously unstudied seamounts show that Tristan is younger than surrounding volcanism, whereas Gough appears to fit the local age progression (Schnur et al. 2014). Modern radiometric ages suggest the main island of Tristan may have been active for up to 1.3 ± 0.2 Myr (O'Connor and le Roex 1992). However, the seemingly older Inaccessible, Nightingale and Middle islands have yet to be reliably dated and could be up to 18 ± 4 Ma based on K-Ar ages (Miller in Baker et al. 1964). In order to confidently delineate the duration of volcanism at Tristan, we present the results of 29 new 40Ar/39Ar step-heating experiments on biotite, hornblende, plagioclase and groundmass separates from rocks collected on Inaccessible, Nightingale and Middle islands. Our results show that volcanism on all three islands is young, in most cases < 600 ka. Previous ages from Nightingale and Middle islands are therefore too old and should be ignored in interpretations of plume dynamics. These results also show that magma was being supplied simultaneously to both Tristan and Gough over recent geologic time. Two possible explanations for this are that (1) there is a broad plume underlying the area, with focus

  20. The tectonic significance of pre-Scandian 40Ar/39Ar phengite cooling ages in the Caledonides of western Norway

    USGS Publications Warehouse

    Andersen, T.B.; Berry, H.N., IV; Lux, D.R.; Andresen, A.

    1998-01-01

    Pre-Silurian continental-margin deposits in western Norway, non-conformably overlying allochthonous continental orthogneisses retain Ordovician 40Ar/39Ar cooling ages for phengites, implying either rapid cooling immediately after a Late Ordovician orogenic event, or less likely, a slow cooling following an Early Ordovician or older orogeny. The Dalsfjord Suite-H??yvik Group basement-cover pair are probably a lateral equivalent to Late Proterozoic sandstones ('sparagmites') covering the Jotun Nappe gneisses of the Middle Allochthon in central-south Norway. The H??yvik Group underwent polyphase deformation, greenschist-facies metamorphism (Tmax <450??C) and exhumation prior to deposition of the unconformably overlying Wenlockian continental-margin deposits of the Herland Group. The H??yvik Group was only weakly metamorphosed during obduction of the Solund-Stavfjord Ophiolite and the Scandian continental collision between Baltica and Laurentia. Phengitic white micas from the H??yvik Group yield cooling ages of 446.1 ?? 3.0, 449.1 ?? 2.2 and 447.5 ?? 4.0 Ma, respectively, identical within experimental error. One sample gives a plateau over 72% of the gas analysed, whereas the other samples were slightly disturbed after initial cooling, as indicated by systematically lower apparent ages at low experimental extraction temperatures. Minor 40Ar loss probably occurred during subsequent Scandian deformation and late to post-orogenic extension. The H??yvik Group rocks were unroofed before the Wenlock time (423-428 Ma) and cooled through the temperature for argon retention in phengite at c. 447 ?? 4 Ma, indicating a maximum cooling rate between 14 and 22??C/Ma-1 through Ashgill and Llandovery times before being subjected to low-grade metamorphism during the Scandian orogeny. Rapid pre-Scandian cooling, combined with peak metamorphic conditions of 450??C or less, may indicate that the Dalsfjord-H??yvik basement-cover pair were affected by an orogenic event during the Late

  1. Friedel-Craft acylation of ar-himachalene: synthesis of acyl-ar-himachalene and a new acyl-hydroperoxide.

    PubMed

    Hossini, Issam; Harrad, Mohamed Anoir; Ait Ali, Mustapha; El Firdoussi, Larbi; Karim, Abdallah; Valerga, Pedro; Puerta, M Carmen

    2011-01-01

    Friedel-Craft acylation at 100 °C of 2,5,9,9-tetramethyl-6,7,8,9-tetrahydro-5H-benzocycloheptene [ar-himachalene], a sesquiterpenic hydrocarbon obtained by catalytic dehydrogenation of α-, β- and γ-himachalenes, produces a mixture of two compounds: (3,5,5,9-tetramethyl-6,7,8,9-tetrahydro-5H-benzocyclohepten-2-yl)-ethanone (2, in 69% yield), with a conserved reactant backbone, and 3, with a different skeleton, in 21% yield. The crystal structure of 3 reveals it to be 1-(8-ethyl-8-hydroperoxy-3,5,5-trimethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-ethanone. In this compound O-H…O bonds form dimers. These hydrogen-bonds, in conjunction with weaker C-H…O interactions, form a more extended supramolecular arrangement in the crystal. PMID:21760570

  2. /sup 40/Ar//sup 39/Ar age of detrital muscovite within Lower Ordovician sandstone in the coastal plain basement of Florida: implications for west African terrane linkages

    SciTech Connect

    Dallmeyer, R.D.

    1987-11-01

    Detrital muscovite was concentrated from a core of Lower Ordovician sandstone recovered from 1282 m in the Sun Oil Company, H.T. Parker No.1 well, Marion County, Florida. The concentrate records a /sup 40/Ar//sup 39/Ar plateau age of 504.1 +/- 2.1 Ma. The Paleozoic sedimentary section penetrated in this well is part of an extensive subsurface Lower Ordovician-Middle Devonian sedimentary succession characterized by Gondwanan paleontological affinities. The succession has been correlated with sequences of similar age in the Bove Basin of west Africa which unconformably overlie metamorphic units of the Bassaride and Rokelide orogens in Senegal and Guinea. Muscovite within these metamorphic rocks records ca. 500-510 Ma postmetamorphic /sup 40/Ar//sup 39/Ar cooling ages and was likely a proximal source for the lower Paleozoic clastic detritus represented in the pre-Mesozoic sedimentary sequences beneath the southeastern US coastal plain.

  3. High resolution spectroscopy of the Ar-D2O and Ar-HDO molecular complexes in the near-infrared range.

    PubMed

    Didriche, K; Földes, T

    2013-03-14

    Three rovibrational bands of Ar-D2O and two rovibrational bands of Ar-HDO were observed in the 1.5 μm range by continuous wave cavity ringdown spectroscopy. Their analyses led to the determination of rotational constants for the upper states and vibrational shifts indicating that the potential energy surface is only slightly affected by the vibrational excitation. Some Coriolis couplings were identified. The observed lines were fitted to retrieve a 3.5 ns lifetime of the upper state, showing that even with a triple or double excitation quanta in the water subunit, the Ar-D2O and Ar-HDO complexes are long-lived species. PMID:23514489

  4. Measurements of the 40Ar(n, γ)41Ar radiative-capture cross section between 0.4 and 14.8 MeV

    NASA Astrophysics Data System (ADS)

    Bhike, Megha; Fallin, B.; Tornow, W.

    2014-09-01

    The 40Ar(n, γ)41Ar neutron capture cross section has been measured between 0.4 and 14.8 MeV neutron energy using the activation technique. The data are important for estimating backgrounds in argon-based neutrino and dark-matter detectors and in the neutrino-less double-beta decay search GERDA, which uses liquid argon as cooling and shielding medium. For the first time the 40Ar(n, γ)41Ar cross section has been measured for neutron energies above 1 MeV. Our results are compared to the evaluation ENDF/B-VII.1 and the calculated prediction TENDL-2013. The latter agrees very well with the present results.

  5. Optical emission diagnostics with electric probe measurements of inductively coupled Ar/O{sub 2}/Ar-O{sub 2} plasmas

    SciTech Connect

    Chung, T. H.; Kang, Hae Ra; Bae, Min Keun

    2012-11-15

    Physical properties of low-pressure inductively coupled argon, oxygen, and Ar-O{sub 2} mixture plasmas are investigated using optical emission spectroscopy (OES) combined with an rf-compensated Langmuir probe measurement. In each gas discharge, the electron density and the electron temperature were obtained by using the probe. The electron temperature was also obtained by OES models and compared with that measured by the probe. The electron temperature was observed to decrease with increasing power and pressure and also observed to decrease with increasing Ar content. Argon metastable densities were calculated based on an optical transition model. In Ar-O{sub 2} discharges, the dissociation fraction of O{sub 2} molecules was estimated using optical emission actinometry. The dissociation fraction was observed to increase with increasing power and Ar content.

  6. RECOMBINANT ANDROGEN RECEPTOR (AR) BINDING ACROSS VERTEBRATE SPECIES: COMPARISON OF BINDING OF ENVIRONMENTAL COMPOUNDS TO HUMAN, RAINBOW TROUT AND FATHEAD MINNOW AR.

    EPA Science Inventory

    In vitro screening assays designed to identify androgen mimics or antagonists typically use mammalian (rat, human) androgen receptors (AR). Although the amino acid sequences of receptors from nonmammalian vertebrates are not identical to the mammalian receptors, it is uncertain ...

  7. High resolution sup 40 Ar/ sup 39 Ar chronostratigraphy of the Late Cretaceous El Gallo Formation, Baja California del Norte, Mexico

    SciTech Connect

    Fulford, M.M.; Busby-Spera, C. ); Renne, P.R.

    1991-03-01

    Laser probe {sup 40}Ar/{sup 39}Ar analyses of individual sanidine grains from four tuffs in the alluvial Late Cretaceous (Campanian) El Gallo Formation yield statistically distinct mean dates ranging from 74.87 {plus minus} 0.05 Ma to 73.59 {plus minus} 0.09 Ma. The exceptional precision of these dates permits calculation of statistically significant sediment accumulation rates that are much higher than passive sediment loading would cause, implying rapid tectonically induced subsidence. The dates bracket tightly the age of important dinosaur and mammalian faunas previously reported from the El Gallo Formation. The dates support an age less than 73 Ma for the Campanian/Maastrichtian stage boundary, younger than indicated by several currently used time scales. Further application of the single grain {sup 40}Ar/{sup 39}Ar technique may be expected to greatly benefit stratigraphic studies of Mesozoic sedimentary basins and contribute to calibration of biostratigraphic and magnetostratigraphic time scales.

  8. Thermochronology of economic mineral deposits: dating the stages of mineralization at Panasqueira, Portugal, by high-precision 40Ar/ 39Ar age spectrum techniques on muscovite

    USGS Publications Warehouse

    Snee, L.W.; Sutter, J.F.; Kelly, W.C.

    1988-01-01

    This study is an example of a new and powerful application of 40Ar/39Ar age spectrum dating of muscovite. It is now possible to establish time constraints necessary for solving some of the long-standing problems in economic geology. Beyond this, the unique geologic situation of Panasqueira has allowed us to quantify the thermal characteristics of muscovite. Published fluid inclusion data have been used to estimate a muscovite argon closure temperature of ~325??C during rapid cooling or short reheating and a temperature of ~270??C during slow cooling or extended reheating. Argon-loss patterns displayed by all dated muscovites resulted from reheating after original closure; the mechanism for this argon loss appears to have been argon transport by volume diffusion. Thus, 40Ar/39Ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age, duration, and number of episodes of mineralization. -from Authors

  9. A volcanological and geochemical investigation of Boa Vista, Cape Verde Islands; 40Ar/ 39Ar geochronology and field constraints

    NASA Astrophysics Data System (ADS)

    Dyhr, Charlotte T.; Holm, Paul M.

    2010-01-01

    Boa Vista, the easternmost island in the Cape Verde archipelago, consists of volcanic products, minor intrusions and a thin partial sedimentary cover. The first 15 age results from 40Ar/ 39Ar incremental heating analysis of groundmass separates from volcanic and plutonic rocks from Boa Vista are presented. The combination of age results and field observations demonstrates that the volcanic activity that formed the island occurred in three main stages: (1) > 16 Ma, (2) 15-12.5 Ma and (3) 9.5-4.5 Ma. The first stage, restricted to the north eastern part of the island, is dominated by ankaramitic lavas. The second stage, consisting of evolved lavas of phonolitic-trachytic compositions and nepheline syenites, makes up large central parts of the island. The large volume of evolved rocks and the extended eruption period of several Ma make stage 2 in Boa Vista unique to Cape Verde. Mainly basanites and nephelinites were erupted during the third stage, initially dominated by eruption of subaerial mafic lavas around 9 Ma. Pillow lavas are erupted around 7 Ma whereupon dominantly subaerial mafic lavas were erupted. Stage 3 saw volcanism in many centres distributed mainly along the present coastline and with activity partly overlapping in time. The volcanic evolution of Boa Vista constrains the initiation of volcanic activity in the Cape Verde archipelago to the eastern islands. Major and trace element geochemistry of 160 volcanic and plutonic rocks representing the entire exposed chronological sequence on Boa Vista is presented, revealing an extremely well developed Daly Gap. Only a little was modified from the mafic magmas that rose in small batches from the mantle. Compositional variation distinguishes each volcanic complex and was to a large extent present in the mantle melts. The highly evolved stage 2 phonolites and trachytes are related through the fractional crystallization of three compositionally distinct magmas. Two of these may have been derived by crystal

  10. 40Ar/39Ar dating of the eruptive history of Mount Erebus, Antarctica: Summit flows, tephra, and caldera collapse

    USGS Publications Warehouse

    Harpel, C.J.; Kyle, P.R.; Esser, R.P.; McIntosh, W.C.; Caldwell, D.A.

    2004-01-01

    Eruptive activity has occurred in the summit region of Mount Erebus over the last 95 ky, and has included numerous lava flows and small explosive eruptions, at least one plinian eruption, and at least one and probably two caldera-forming events. Furnace and laser step-heating 40Ar/39Ar ages have been determined for 16 summit lava flows and three englacial tephra layers erupted from Mount Erebus. The summit region is composed of at least one or possibly two superimposed calderas that have been filled by post-caldera lava flows ranging in age from 17 ?? 8 to 1 ?? 5 ka. Dated pre-caldera summit flows display two age populations at 95 ?? 9 to 76 ?? 4 ka and 27 ?? 3 to 21 ??4 ka of samples with tephriphonolite and phonolite compositions, respectively. A caldera-collapse event occurred between 25 and 11 ka. An older caldera-collapse event is likely to have occurred between 80 and 24 ka. Two englacial tephra layers from the flanks of Mount Erebus have been dated at 71 ?? 5 and 15 ?? 4 ka. These layers stratigraphically bracket 14 undated tephra layers, and predate 19 undated tephra layers, indicating that small-scale explosive activity has occurred throughout the late Pleistocene and Holocene eruptive history of Mount Erebus. A distal, englacial plinian-fall tephra sample has an age of 39 ?? 6 ka and may have been associated with the older of the two caldera-collapse events. A shift in magma composition from tephriphonolite to phonolite occurred at around 36 ka. ?? Springer-Verlag 2004.

  11. 40Ar/39Ar dating of the eruptive history of Mount Erebus, Antarctica: summit flows, tephra, and caldera collapse

    NASA Astrophysics Data System (ADS)

    Harpel, Christopher J.; Kyle, Philip R.; Esser, Richard P.; McIntosh, William C.; Caldwell, David A.

    2004-12-01

    Eruptive activity has occurred in the summit region of Mount Erebus over the last 95 ky, and has included numerous lava flows and small explosive eruptions, at least one plinian eruption, and at least one and probably two caldera-forming events. Furnace and laser step-heating 40Ar/39Ar ages have been determined for 16 summit lava flows and three englacial tephra layers erupted from Mount Erebus. The summit region is composed of at least one or possibly two superimposed calderas that have been filled by post-caldera lava flows ranging in age from 17 ± 8 to 1 ± 5 ka. Dated pre-caldera summit flows display two age populations at 95 ± 9 to 76 ± 4 ka and 27 ± 3 to 21 ± 4 ka of samples with tephriphonolite and phonolite compositions, respectively. A caldera-collapse event occurred between 25 and 11 ka. An older caldera-collapse event is likely to have occurred between 80 and 24 ka. Two englacial tephra layers from the flanks of Mount Erebus have been dated at 71 ± 5 and 15 ± 4 ka. These layers stratigraphically bracket 14 undated tephra layers, and predate 19 undated tephra layers, indicating that small-scale explosive activity has occurred throughout the late Pleistocene and Holocene eruptive history of Mount Erebus. A distal, englacial plinian-fall tephra sample has an age of 39 ± 6 ka and may have been associated with the older of the two caldera-collapse events. A shift in magma composition from tephriphonolite to phonolite occurred at around 36 ka.

  12. New palynology-based astronomical and revised 40Ar/39Ar ages for the Eocene maar lake of Messel (Germany)

    NASA Astrophysics Data System (ADS)

    Lenz, Olaf K.; Wilde, Volker; Mertz, Dieter F.; Riegel, Walter

    2015-04-01

    The annually laminated oil shale from the Eocene maar lake at Messel (Federal State of Hessen, Germany) provides unique paleoenvironmental data for a time interval of ~640 ka during the Paleogene greenhouse phase. As a consequence of orbitally controlled changes in the vegetation in the vicinity of the lake, the lacustrine laminites can now be astronomically tuned. Dating is based on the short eccentricity amplitude modulations of the regional pollen rain and their correlation to the astronomical La2010a/La2010d solutions in combination with a revised 40Ar/39Ar age of a basalt fragment from a lapilli tuff section below the first lacustrine sediments. Depending on different newly suggested ages for the Fish Canyon sanidine used as monitor for neutron irradiation, the age for the eruption at Messel is between 48.27 ± 0.22