The automated classification of astronomical light curves using Kohonen self-organizing maps     

David R. Brett  Richard G. West  Peter J. Wheatley 《Monthly notices of the Royal Astronomical Society》2004,353(2):369-376

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Mass Fractions of S,Cu, Se,Mo, Ag,Cd, In,Te, Ba,Sm, W,Tl and Bi in Geological Reference Materials and Selected Carbonaceous Chondrites Determined by Isotope Dilution ICP‐MS          下载免费PDF全文

Zaicong Wang  Harry Becker  Frank Wombacher 《Geostandards and Geoanalytical Research》2015,39(2):185-208

Mass fractions of S, Cu, Se, Mo, Ag, Cd, In, Te, Ba, Sm, W and Tl were determined by isotope dilution sector field ICP‐MS in the same sample aliquot of reference materials using HF‐HNO₃ digestion in PFA beakers in pressure bombs and glassy carbon vessels in a high‐pressure asher (HPA‐S) for comparison. Additionally, Bi was determined by internal standardisation relative to Tl. Because isobaric and oxide interferences pose problems for many of these elements, efficient chromatographic separation methods in combination with an Aridus desolvator were employed to minimise interference effects. Repeated digestion and measurement of geological reference materials (BHVO‐1, BHVO‐2, SCo‐1, MAG‐1, MRG‐1 and UB‐N) gave results with < 5% relative intermediate precision (1s) for most elements, except Bi. Replicates of NIST SRM 612 glass digested on a hot plate were analysed by the same methods, and the results agree with reference values mostly within 2% relative deviation. Data for the carbonaceous chondrites Allende, Murchison, Orgueil and Ivuna are also reported. Digestion in a HPA‐S was as efficient as in pressure bombs, but some elements displayed higher blank levels following HPA‐S treatment. Pressure bomb digestion yielded precise data for volatile S, Se and Te, but may result in high blanks for W.  相似文献   

Benchmark Test of Differential Emission Measure Codes and Multi-thermal Energies in Solar Active Regions     

Markus J. Aschwanden  Paul Boerner  Amir Caspi  James M. McTiernan  Daniel Ryan  Harry Warren 《Solar physics》2015,290(10):2733-2763

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Petrology and trace element geochemistry of Tissint,the newest shergottite fall          下载免费PDF全文

J. Brian Balta  Matthew E. Sanborn  Arya Udry  Meenakshi Wadhwa  Harry Y. McSween 《Meteoritics & planetary science》2015,50(1):63-85

The fall and recovery of the Tissint meteorite in 2011 created a rare opportunity to examine a Martian sample with a known, short residence time on Earth. Tissint is an olivine‐phyric shergottite that accumulated olivine antecrysts within a single magmatic system. Coarse olivine grains with nearly homogeneous cores of Mg# >80 suggest slow re‐equilibration. Many macroscopic features of this sample resemble those of LAR 06319, including the olivine crystal size distribution and the presence of evolved oxide and olivine compositions. Unlike LAR 06319, however, no magmatic hydrous phases were found in the analyzed samples of Tissint. Minor and trace element compositions indicate that the meteorite is the product of closed‐system crystallization from a parent melt derived from a depleted source, with no obvious addition of a LREE‐rich (crustal?) component prior to or during crystallization. The whole‐rock REE pattern is similar to that of intermediate olivine‐phyric shergottite EETA 79001 lithology A, and could also be approximated by a more olivine‐rich version of depleted basaltic shergottite QUE 94201. Magmatic oxygen fugacities are at the low end of the shergottite range, with log fO₂ of QFM‐3.5 to ‐4.0 estimated based on early‐crystallized minerals and QFM‐2.4 estimated based on the Eu in pyroxene oxybarometer. These values are similarly comparable to other depleted shergottites, including SaU 005 and QUE 94201. Tissint occupies a previously unsampled niche in shergottite chemistry: containing olivines with Mg# >80, resembling the enriched olivine‐phyric shergottite LAR 06319 in its crystallization path, and comparable to intermediate olivine‐phyric shergottite EETA 79001A, depleted olivine‐phyric shergottite DaG 476, and depleted basaltic shergottite QUE 94201 in its trace element abundances and oxygen fugacity. The apparent absence of evidence for terrestrial alteration in Tissint (particularly in trace element abundances in the whole‐rock and individual minerals) confirms that exposure to the arid desert environment results in only minimal weathering of samples, provided the exposure times are brief.  相似文献   

A tale of two population crises in recent Chinese history     

Harry F. Lee  David D. Zhang 《Climatic change》2013,116(2):285-308

The fall of the Ming dynasty in the first half of the 17th century and the Taiping Rebellion from 1851–1864 were two of the most chaotic periods in Chinese history, and each was accompanied by large-scale population collapses. The ‘Kang-Qian Golden Age’ (also known as ‘High Qing’), during which population size expanded rapidly, falls in between the two. Scholars remain divided in their opinions concerning the above alternation of population growth and decline as to whether variations in population size or climate change should be identified as the root cause. In either case, the synergistic impact of population growth and climate change upon population growth dynamics is overlooked. In the present study, we utilized high-resolution empirical data, qualitative survey, statistical comparison and time-series analysis to investigate how the two factors worked synergistically to drive population cycles in 1600–1899. To facilitate our research, we posited a set of simplified pathways for population growth in historical agrarian China. Our results confirm that the interrelation between population growth, climate change and population crises in recent Chinese history basically followed our posited pathways. The recurrences of population crises were largely determined by the combination of population growth and climate change. Our results challenge classic Malthusian/post-Malthusian interpretations and historians’ views of historical Chinese population cycles.  相似文献   

Extent of chondrule melting: Evaluation of experimental textures,nominal grain size,and convolution index     

Jeffrey W. Nettles  Gary E. Lofgren  William D. Carlson  Harry Y. McSween 《Meteoritics & planetary science》2006,41(7):1059-1071

Abstract— Dynamic crystallization experiments on the ordinary chondrite Queen Alexandra Range (QUE) 97008 document textural features that occur in partially melted chondrules with changes in the degree of partial melting and cooling rate. We carried out a matrix of experiments, at peak temperatures of 1250, 1350, 1370, and 1450 °C, and cooling rates of 1000, 100, and 10 °C/h, and quenched. All experimentally produced textures closely resemble textures of porphyritic chondrules. Because peak temperatures were well below the liquidi for typical chondrule compositions, the textural similarities support an incomplete melting origin for most porphyritic chondrules. Our experiments can be used to determine the extent of melting of natural chondrules by comparing textural relationships among the experimental results with those of natural chondrules. We used our experiments along with X‐ray computerized tomography scans of a Semarkona chondrule to evaluate two other methods that have been used previously to quantify the degree of melting: nominal grain size and convolution index. Proper applications of these methods can result in valid assessments of a chondrule's degree of melting, but only if accompanied by careful interpretation, as chondrule textures are controlled by more than just the extent of melting. Such measurements of single aspects of chondrule textures might be coupled with qualitative analysis of other textural aspects to accurately determine degree of melting.  相似文献   

The rocks of Mars,from far and near     

Harry Y. McSween 《Meteoritics & planetary science》2002,37(1):7-25

Abstract— The age, structure, composition, and petrogenesis of the martian lithosphere have been constrained by spacecraft imagery and remote sensing. How well do martian meteorites conform to expectations derived from this geologic context? Both data sets indicate a thick, extensive igneous crust formed very early in the planet's history. The composition of the ancient crust is predominantly basaltic, possibly andesitic in part, with sediments derived from volcanic rocks. Later plume eruptions produced igneous centers like Tharsis, the composition of which cannot be determined because of spectral obscuration by dust. Martian meteorites (except Allan Hills 84001) are inferred to have come from volcanic flows in Tharsis or Elysium, and thus are not petrologically representative of most of the martian surface. Remote‐sensing measurements cannot verify the fractional crystallization and assimilation that have been documented in meteorites, but subsurface magmatic processes are consistent with orbital imagery indicating thick crust and large, complex magma chambers beneath Tharsis volcanoes. Meteorite ejection ages are difficult to reconcile with plausible impact histories for Mars, and oversampling of young terrains suggests either that only coherent igneous rocks can survive the ejection process or that older surfaces cannot transmit the required shock waves. The mean density and moment of inertia calculated from spacecraft data are roughly consistent with the proportions and compositions of mantle and core estimated from martian meteorites. Thermal models predicting the absence of crustal recycling, and the chronology of the planetary magnetic field agree with conclusions from radiogenic isotopes and paleomagnetism in martian meteorites. However, lack of vigorous mantle convection, as inferred from meteorite geochemistry, seems inconsistent with their derivation from the Tharsis or Elysium plumes. Geological and meteoritic data provide conflicting information on the planet's volatile inventory and degassing history, but are apparently being reconciled in favor of a periodically wet Mars. Spacecraft measurements suggesting that rocks have been chemically weathered and have interacted with recycled saline groundwater are confirmed by weathering products and stable isotope fractionations in martian meteorites.  相似文献   

Spatially resolved methane band photometry of Saturn: I. Absolute reflectivity and center-to-limb variations in the 6190-, 7250-, and 8900-Å bands     

Robert A. West  Martin G. Tomasko  Bradford A. Smith  Mahendra P. Wijesinghe  Lyn R. Doose  Harold J. Reitsema  Stephen M. Larson 《Icarus》1982,51(1):51-64

We present spatially resolved measurements of Saturn's absolute reflectivity in methane bands at 6190, 7250, and 8900 Å and in nearby continuum regions. Images were obtained through narrow-band interference filters with a 500 × 500-pixel charge-coupled device. Band/continuum ratios were measured to high accuracy by referencing to the ring brightness in each image. Several data processing techniques enhanced the quality of the observations. These are the use of the ring symmetry to find center position and orientation, accurate subtraction of ring light, and constrained image deconvolution. Uncertainty in the continuum absolute reflectivity is ±10%. Uncertainties in band/continuum ratios are from one to several percent. The Equatorial Zone was much brighter than any other latitude in the strong 8900 band image. Northern mid-latitudes were brighter than southern mid-latitudes. The latter observation indicates fewer high-altitude aerosols in the south, a possible result of atmospheric dynamics or seasonal sublimation of NH₃ crystals. The data are tabulated and presented in a form suitable for quantitative scattering model analyses.  相似文献   

Leonard Medal Citation for Klaus Keil     

Harry Y. McSween 《Meteoritics & planetary science》1988,23(3):316-316

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A critical evaluation of oxidation versus reduction during metamorphism of L and LL group chondrites,and implications for asteroid spectroscopy     

Heather K. Gastineau‐Lyons  Harry Y. McSween  Michael J. Gaffey 《Meteoritics & planetary science》2002,37(1):75-89

Abstract— Modal mineralogies of individual, equilibrated (petrologic type 4–6 L and LL chondrites have been measured using an electron microprobe mapping technique, and the chemical compositions of coexisting silicate minerals have been analyzed. Progressive changes in the relative abundances and in the molar Fe/Mn and Fe/Mg ratios of olivine, low‐Ca pyroxene, and diopside occur with increasing metamorphic grade. Variations in olivine/low‐Ca pyroxene ratios (Ol/Px) and in metal abundances and compositions with petrologic type support the hypothesis that oxidation of metallic iron accompanied thermal metamorphism in ordinary chondrites. Modal Ol/Px ratios are systematically lower than normative Ol/Px ratios for the same meteorites, suggesting that the commonly used C.I.P.W. norm calculation procedure may not adequately estimate silicate mineral abundances in reduced chondrites. Ol/Px ratios calculated from visible and near‐infrared (VISNIR) reflectance spectra of the same meteorites are not in agreement with other Ol/Px determinations, possibly because of spectral complexities arising from other minerals in chondrites. Characteristic features in VISNIR spectra are sensitive to the proportions and compositions of olivine and pyroxenes, the minerals most affected by oxidative metamorphism. This work may allow spectral calibration for the determination of mineralogy and petrologic type, and thus may be useful for spectroscopic studies of asteroids.  相似文献