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Precambrian supercontinents,glaciations,atmospheric oxygenation,metazoan evolution and an impact that may have changed the second half of Earth history

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Geoscience Frontiers 2013年第3期4卷 247-261页

作者： Grant M.young Department of Earth Sciences Western University1151 Richmond Street NLondonOntarioCanada N6A 5B7

In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturba- tions, when extensive glaciations occurred, together with alternating warm periods which were accom- panied by atmospheric oxygenation. The younger of these two episodes of climatic oscillation preceded the Cambrian ＂explosion＂ of metazoan life forms, but similar extreme climatic conditions existed between about 2.4 and 2.2 Ga. Over long time periods, changing solar luminosity and mantle temperatures have played important roles in regulating Earth＇s climate but both periods of climatic upheaval are associated with supercontinents. Enhanced weathering on the orogenically and thermally buoyed supercontinents would have stripped CO2 from the atmosphere, initiating a cooling trend that resulted in continental glaciation. Ice cover prevented weathering so that CO2 built up once more, causing collapse of the ice sheets and ushering in a warm climatic episode. This negative feedback loop provides a plausible explanation for multiple glaciations of the Early and Late Proterozoic, and their intimate association with sedimentary rocks formed in warm climates. Between each glacial cycle nutrients were flushed into world oceans, stimulating photosynthetic activity and causing oxygenation of the atmosphere. Accommodation for many ancient glacial deposits was provided by rifting but escape from the climatic cycle was predicated on break- up of the supercontinent, when flooded continental margins had a moderating influence on weathering. The geochemistry of Neoproterozoic cap carbonates carries a strong hydrothermal signal, suggesting that they precipitated from deep sea waters, overturned and spilled onto continental shelves at the termination of glaciations. Paleoproterozoic （Huronian） carbonates of the Espanola Formation were probably formed as a result of ponding and evaporation in a hydrothermally influenced, restricted rift setting. Why did metazoan evolution not take off a

关键词： Proterozoic supercontinents Glaciations Impacts Oxygenation Metazoa

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Did prolonged two-stage fragmentation of the supercontinent Kenorland lead to arrested orogenesis on the southern margin of the Superior province?

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Geoscience Frontiers 2015年第3期6卷 419-435页

作者： Grant M.young Department of Earth Sciences University of Western Ontario

Recent geochronological investigations reinforce the early suggestion that the upper part of the Paleoproterozoic Huronian Supergroup of Ontario, Canada is present in the Animikie Basin on the south shore of Lake Superior. These rocks, beginning with the glaciogenic Gowganda Formation, are interpreted as passive margin deposits. The absence of the lower Huronian （rift succession） from the Animikie Basin may be explained by attributing the oldest Paleoroterozoic rocks in the Animikie Basin （Chocolay Group） to deposition on the upper plate of a north-dipping detachment fault, which lacks sediments of the rift phase. Following thermal uplift that led to opening of the Huronian Ocean on the south side of what is now the Superior province, renewed uplift （plume activity） caused large-scale gravitational folding of the Huronian Supergroup accompanied by intrusion of the Nipissing diabase suite and Senneterre dikes at about 2.2 Ga. Termination of passive margin sedimentation is normally followed by ocean closure but in the Huronian and Animikie basins there was a long hiatus - the Great Stratigraphic Gap - which lasted for about 350 Ma. This hiatus is attributed to a second prolonged thermal uplift of part of Kenorland that culminated in complete dismemberment of the supercontinent shortly before 2.0 Ga by opening of the Circum-Superior Ocean. These events caused regional uplift （the Great Stratigraphic Gap） and delayed completion of the Huronian Wilson Cycle until a regional compressional tectonic episode, including the Penokean orogeny, belatedly flooded the southern margin of the Superior province with foreland basin deposits, established the limits of the Superior structural province and played an important role in constructing Laurentia.

关键词： Paleoproterozoic Glaciation Plate tectonics Mantle plumes Supercontinents

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Environmental upheavals of the Ediacaran period and the Cambrian “explosion” of animal life

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Geoscience Frontiers 2015年第4期6卷 523-535页

作者： Grant M.young Department of Earth Sciences University of Western Ontario

The second half of the Ediacaran period began with a large impact - the Acraman impact in South Australia, which was accompanied by a negative δ^13Ccarb anomaly and an extinction-radiation event involving acritarchs. A few million years later （-570 Ma？） there was a second, deeper and longer-lived world-wide δ^13Ccarb anomaly （the Shuram anomaly） which coincides with extinction of the acanthomorphic acritarchs. Wide distribution of the Shuram event is exemplified by stratigraphic sections from South Australia, Oman, southern California and South China. The widespread anomaly has been tentatively attributed to a marine impact. During recovery from the Shuram event the enigmatic Ediacaran biota achieved its zenith, only to be extirpated and replaced by a polyphyletic assemblage of shelly animals in what is known as the Cambrian ＂explosion＂. This extinction-radiation cycle was preceded by glaciation, another δ^13Ccarb excursion and the highest ^87Sr/^86Sr values known from marine carbonates. These high Sr ratios have been linked to weathering of extensive tracts of continental crust that were elevated during amalgamation of the supercontinent Gondwana. Introduction of essential nutrients to the oceans would have promoted biological production of oxygen and provided P and Ca for the important skeletonization that characterizes the Cambrian ＂explosion＂ and caused a quantum leap in the preservation potential of animal remains. Turbulent events of the last 50 million years of Precambrian time include three glaciations, two large impacts and a massive orogenic episode. These dramatic environmental upheavals are held responsible for three consecutive extinction-radiation cycles that culminated in the appearance of a diverse array of shelly fossils. Various lines of evidence suggest that the metazoans have deep roots so that they too may have been subjected to the environmental pressures of the late Ediacaran period clearly illustrated by acritarchs and the Ediacaran biota but

关键词： Ediacaran Sburam Impacts Orogeny Cambrian explosion

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Selective reduction of NO by photo-SCR with ammonia in an annular fixed-film photoreactor

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Frontiers of Environmental Science & Engineering 2012年第2期6卷 149-155页

作者： YiangChen CHOU young KU Department of Chemical Engineering Taiwan University of Science and Technology Taipei 10607 China

Gaseous NO was photocatalytically reduced at room temperature by photo-assisted selective catalytic reduction （photo-SCR） with ammonia over TiO2 in this study. NO reduction efficiency and N2 selectivity were determined from gases composition at the outlet stream of photoreactor. Effect of operating conditions, e.g. light intensity and inlet concentrations of ammonia and oxygen, on the NO reduction efficiency and N2 selectivity were discussed to determine the feasible operating condition for photocatalytic reduction of NO. Experimental results showed that selective catalytic reduction of NO with ammonia over TiO2 in the presence of oxygen was a spontaneous reaction in dark. The photoirradiation on the TiO2 surface caused remarkable photocatalytic reduction of NO to form N2, NO2, and N20 under 254 nm UV illuminations, while almost 90% of N2 selectivity was achieved in this study. The ammonia and oxygen molecules played the roles of reductant and oxidant for NO reduction and active sites regeneration, respectively. The reduction of NO was found to be increased with the increase of inlet ammonia and oxygen concentrations until specific concentrations because of the limited active sites on the surface of TiO2. The kinetic model proposed in this study can be used to reasonably describe the reaction mechanism of photo-SCR.

关键词： photo-SCR photocatalysis NO reduction,Eley-Rideal model

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THE VACUUM IN NONISENTROPIC GAS DYNAMICS

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Acta Mathematica Scientia 2012年第1期32卷 339-351页

作者： Geng Chen Robin young Department of Mathematics Pennsylvania State University University Park PA 16802 USA Department of Mathematics University of Massachusetts Amherst MA 01003 USA

We investigate the vacuum in nonisentropic gas dynamics in one space vari- able, with the most general equation of states allowed by thermodynamics. We recall physical constraints on the equations of state and give explicit and easily checkable conditions under which vacuums occur in the solution of the Riemann problem. We then present a class of models for which the Riemann problem admits unique global solutions without vacuums.

关键词： nonisentropic gas dynamics conservation laws vacuum large data Riemann problem

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Evaluation of early-age strains and stresses in roller-compacted concrete pavement

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Journal of Traffic and Transportation Engineering(English Edition) 2022年第1期9卷 93-105页

作者： Tetsya Sok young Kyu Kim Jun young Park Seung Woo Lee Public Infrastructure Department Ministry of Public Works and TransportPhnom Penh 12100Cambodia Institute for Disaster Prevention Gangneung-Wonju National UniversityGangneung-si 25457South Korea Korea Expressway Research Institute Korea Expressway CorporationHwaseong-si 18489South Korea Civil Engineering Department Gangneung-Wonju National UniversityGangneung-si 25457South Korea

In the structural design of a roller-compacted concrete pavement(RCCP), it is crucial to estimate strain and stress developments in the RCCP slab realistically. Since the RCCP mix uses less cement and lower amount of water, shrinkage strain and concrete temperature during the hardening stage are expected to be reduced as compared to those of conventional concrete mixture, resulting in a reduction of the concrete early-age deformation and stress developments in the RCCP slab. In this paper, early-age concrete strain and stress developments in RCCP slab subjected to environmental loads were evaluated. A full-scale test section of RCCP under real climatic conditions was monitored. The early-age total strains,stress-independent strains, shrinkage strains, and coefficient of thermal expansion(CTE) of the RCCP were measured and analyzed. Using the results of measured strains, in-situ CTE and shrinkage strain, and temperature, the early-age concrete stress development is computed by incorporating a viscoelastic property of the early-age concrete. The results revealed that the shrinkage strain of the RCCP is quite low as compared to that of conventional concrete. The early-age stress developments in the RCCP slab are strongly governed by the thermal-induced stresses. Shrinkage-induced stresses were quite small and might be negligible in a preliminary estimation of early-age stress developments in the RCCP slab.

关键词： Road engineering Roller-compacted concrete pavement Concrete strain Concrete stress Shrinkage strain Environmental loads

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Evaluation the Properties of Titanium Matrix Composites by Melting Route Synthesis

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Journal of Materials Science & Technology 2008年第1期24卷 105-109页

作者： Bong-Jae Choi Si-young Sung Myoung-Gyun Kim young-Jig Kim Department of Advanced Materials Engineering Sungkyunkwan University SuwonKorea Department of Advanced Materials Engineering Sungkyunkwan University SuwonKorea Materials & Processing Engineering CenterR&D DivisionKorea Automotive Technology InstituteChonanChungnamKorea Research Institute of Industrial Science and Technology Pohang Korea

The main purpose of this study is an in-situ synthesis of （TiB＋TiC） hybrid titanium matrix composites （TMCs） by vacuum induction melting method and to verify its mechanical *** melting route was adopted to synthesize the commercial pure titanium （cp Ti） and granular boron carbide （B-4C）.The reinforcements,the fraction of 10 ***,were formed by adding 1.88 wt pct B-4C to cp *** in-situ synthesis of TMCs,electron probe micro-analysis elemental mapping was carried out to confirm the distribution and shape of *** cone-on-disk type sliding wear test was also done for the identification of *** is concluded that （TiB＋TiC） hybrid TMCs can be in-situ synthesized and has better wear properties than H13.

关键词： Titanium matrix composites H13 In-situ Wear

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Joining Technology of Dissimilar Materials for Automotive Components(Ⅱ)

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Journal of Rare Earths 2004年第z2期22卷 35-37页

作者： Meung Ho Rhee Jong Ho Song Woo young Chung young Myoung Kim Korea Automotive Technology Institute 74 Yongjung-RiPungse-MyunChonanChungnam330-912KOREA Korea Automotive Technology Institute74 Yongjung-RiPungse-MyunChonanChungnam330-912KOREA Korea Automotive Technology Institute74 Yongjung-RiPungse-MyunChonanChungnam330-912KOREA Korea Automotive Technology Institute74 Yongjung-RiPungse-MyunChonanChungnam330-912KOREA

Joining techniques of dissimilar materials for lightweight multi-material automotive body structure were discussed. The joining of 1 .4 mm thickness steel and 2 mm thickness of Al were performed by the new method that is hybrid laser welding system. After aluminum and steel were welded by laser hybrid welding process, the micro-structure investment and the micro-hardness test were carried out. Hybrid laser welding promises a bright future in joining technology of dissimilar materials for automotive components.

关键词： multi-material automotive body dissimilar materials hybrid laser welding

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Advancements in hemostatic strategies for managing upper gastrointestinal bleeding: A comprehensive review

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World Journal of Gastroenterology 2024年第15期30卷 2087-2090页

作者： Ah young Lee Joo young Cho Division of Gastroenterology Department of Internal MedicineCha Gangnam Medical CenterCha University College of MedicineSeoul 06135Korea

Upper gastrointestinal(GI)hemorrhage presents a substantial clinical *** management typically involves resuscitation and endoscopy within 24 h,although the benefit of very early endoscopy(<12 h)for high-risk patients is *** goals include stopping acute bleeding,preventing rebleeding,and using a multimodal approach encompassing endoscopic,pharmacological,angiographic,and surgical *** agents such as vasopressin,prostaglandins,and proton pump inhibitors are effective,but the increase in antithrombotic use has increased GI bleeding *** hemostasis,particularly for nonvariceal bleeding,employs techniques such as electrocoagu-lation and heater probes,with concerns over tissue injury from monopolar *** methods such as Hemospray and Endoclot show promise in creating mechanical tamponades but have ***,the first-line therapy includes thermal probes and hemoclips,with over-the-scope clips emerging for larger ulcer *** gold probe,combining bipolar electrocoagulation and injection,offers targeted coagulation but has faced device-related *** advancements involve combining techniques and improving endoscopic imaging,with studies exploring combined approaches showing *** research is crucial for developing standardized and effective hemorrhage management strategies.

关键词： Upper gastrointestinal bleeding Hemostasis Endoscopy Probe Spray Clip

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Mg Alloy Foam Fabrication via Melt Foaming Method

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Journal of Materials Science & Technology 2008年第3期24卷 302-304页

作者： Changhwan SEO Bo-young HUR i-Cube Center ERISchool of Nano & Advanced Materials EngineeringGyeongsang National University

For the first time AZ91 （MgAl9Zn1） and AM60 （MgAl6） Mg alloy foams with homogeneous pore structures were prepared successfully via melt foaming method using CaCO3 as blowing agent. It is revealed that the blowing gas to foam the melt is not CO2 but CO, which comes from liquid-solid reaction between Mg melt. The reaction temperature is more than 100℃ lower than CaCO3 decomposition, which makes Mg alloy melts foam into cellular structure much more easily in the temperature range from 690℃ to 750℃.

关键词： Mg alloy foam CaCO3 Blowing gas

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