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Granular titanite from the Roter Kamm crater in Namibia:Product of regional metamorphism,not meteorite impact

Geoscience Frontiers 2022年第3期13卷 156-163页

作者： Aaron j.Cavosie Christopher j.Spencer Noreen evans Kai Rankenburg Robert j.Thomas Paul H.Macey Space Science and Technology Centre and The Institute for Geoscience Research School of Earth and Planetary ScienceCurtin UniversityPerthWA 6102Australia Dept.of Geological Sciences and Geological Engineering Queen’s UniversityOntarioCanada john de Laeter Centre Curtin UniversityPerthWA 6102Australia Council for Geoscience BellvilleWestern CapeSouth Africa

Accessory minerals with so-called granular texture have risen in importance as geochronological tools for U-Pb dating of meteorite impact events. Grain-scale recrystallization, typically triggered by a combination of high-strain deformation and post-impact heating, can create a polycrystalline microstructure consisting of neoblasts that expel radiogenic Pb, which are thus ideal for isotopic dating. While granular domains in zircon and monazite from shocked rocks have been demonstrated to preserve impact ages,few U-Pb dating studies have been conducted on granular microstructures in titanite(CaTiSiO;). Here we report the occurrence of granular-textured titanite from ~2020 Ma granite basement rock exposed in the rim of the 4–5 Ma Roter Kamm impact structure in Namibia. Orientation mapping reveals two microstructurally distinct titanite populations: one consisting of strained/deformed grains, and the other consisting of grains that comprise aggregates of strain-free neoblasts. In situ U-Pb geochronology on 37 grains shows that most grains from both titanite populations yield indistinguishable U-Pb dates of ca.1025 Ma, consistent with the observed microstructures forming during the Mesoproterozoic Namaqua Orogeny. Only four grains preserved older age domains, recording ca. 1875 Ma Paleoproterozoic metamorphism. Two significant observations emerge:(1) none of the analyzed titanite grains yield the 2020 Ma igneous crystallization age previously established from zircon in the same sample, and(2) no age-resetting was detected that could be attributed to the 4 to 5 Ma Roter Kamm impact *** the similarity of the neoblastic microstructure to minerals from other sites with an established impact provenance, the granular texture and near-complete Pb-loss in titanite from Roter Kamm granite instead records a Paleo-to Mesoproterozoic polymetamorphic history, rather than Miocene age shockrelated processes. These results highlight the critical importance of grain-scale cont

关键词： Namibia Roter Kamm Titanite EBSD Geochronology

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Strategies towards robust interpretations of in situ zircon Lu-Hf isotope analyses

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Geoscience Frontiers 2020年第3期11卷 843-853页

作者： C.j.Spencer C.L.Kirkland N.M.W.Roberts N.j.evans j.Liebmann School of Earth and Planetary Sciences The Institute for Geoscience Research(TIGeR)Curtin UniversityPerthAustralia Department of Geological Sciences and Geological Engineering Queen’s UniversityKingstonCanada Centre for Exploration Targeting-Curtin Node The Institute for Geoscience ResearchSchool of Earth and Planetary SciencesCurtin UniversityPerthAustrali Geochronology and Tracers Facility British Geological SurveyNottinghamUK john de Laeter Centre GeoHistory Facility School of Earth and Planetary SciencesCurtin UniversityPerthAustralia

The combination of U-Pb and Lu-Hf compositions measured in zircon crystals is a remarkably powerful isotopic couplet that provides measures on both the timing of mineral growth and the radiogenic enrichment of the source from which the zircon *** U-Pb age documents the timing of zircon crystallization/recrystallization and Hf isotopes inform on the degree to which the host melt was derived from a radiogenic reservoir(*** mantle) versus an unradiogenic reservoir(*** continental crust),or some mixture of these *** ease of generating large quantities of zircon U-Pb and Lu-Hf data has been in large part facilitated by instrument ***,the dramatic increase in time constrained zircon Lu-Hf analyses in the Earth science community has brought to the fore the importance of careful data collection and reduction workflows,onto which robust geological interpretations may be *** this work,we discuss the fundamentals of Lu-Hf isotopes in zircon,which then allows us to provide a robust,accessible,methodology for the assessment of data ***,we discuss some novel techniques for:data visualization—that facilitates better transparency of data interpretation;integration of geographic information—that may reveal spatial trends where temporal trends were only apparent before;and some novel statistical evaluation tools—that may provide more rigorous interand intra-sample comparisons.

关键词： Zircon Geochronology Isotope geochemistry Lu-Hf isotopes Geostatistics Data visualization

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Flow of Steel in Mold Region During Continuous Casting

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journal of Iron and Steel Research International 2007年第2期14卷 30-35,41页

作者： ZHANG Xing-guo ZHANG Wen-xiao jIN jun-ze j. W. evans Research Center of Foundry Engineering Dalian University of Technology Dalian 116023 Liaoning China Department of Material Science and Engineering University of California at Berkeley Berkeley CA94720 USA

The particle image velocimetry （PIV） technique was used to study the fluid flow phenomena that occurred during continuous casting, using a water model with dimensions of 1 840mm× 280 mm. Two types of solidified shells, i. e. , the smooth type and the coarse type, were used to characterize the dendrite in order to simulate different liquid-solid interfacial conditions. The influence of the nozzle angle and the immersion depth of nozzle, as well as the casting speed on the flow behavior was investigated quantitatively. The results were as follows：（1） There are two large recirculations above and below the fluid jet in the mold, respectively, under the smooth interface condition. However, in the case of the dendrite solidified shell, it was found that the flow velocity of the fluid decreased and more smaller vortices appeared in the upper region of the mold. （2） The angle and the immersion depth of nozzle are two important factors affecting the flow pattern, and they are also capable of bringing about the change in the flow direction. （3） The higher the casting speed, the higher are the jet stream and the impacting point on the narrow face. However, the high casting speed causes serious fluctuation of the meniscus, and correspondingly leads to various defects.

关键词： particle image velocimetry continuous casting steel fluid flow

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A call for international research on COVID-19-induced brain dysfunctions

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National Science Review 2021年第12期8卷 13-14页

作者： Pedro A.Valdes-Sosa Alan C.evans Mitchell j.Valdes-Sosa Mu-ming Poo Global Brain Consortium University of Electronic Sciences and Technology of China (UESTC) Cuban Neuroscience Center (CNEURO) Cuban Academy of Sciences Global Brain Consortium Royal Society of CanadaMc Gill Center for Integrative Neuroscience Mc Gill University Center for Excellence in Brain Science and Intelligence Technology Institute of NeuroscienceChinese Academy of Sciences

The COVID-19 pandemic, still raging worldwide, imposes staggering human and economic costs. These will only increase as many convalescent patients suffer consequences for many *** the virus can target multiple organ s...

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Relativistic domain-wall dynamics in van der Waals antiferromagnet MnPS_(3)

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npj Computational Materials 2022年第1期8卷 27-35页

作者： Ignacio M.Alliati Richard F.L.evans Kostya S.Novoselov Elton j.G.Santos School of Mathematics and Physics Queen’s University BelfastBelfastBT71NNUK Department of Physics The University of YorkYorkYO105DDUK Institute for Functional Intelligent Materials National University of SingaporeSingapore117544Singapore Institute for Condensed Matter Physics and Complex Systems School of Physics and AstronomyThe University of EdinburghEdinburghEH93FDUK Higgs Centre for Theoretical Physics The University of EdinburghEdinburghEH93FDUK

The discovery of two-dimensional(2D)magnetic van der Waals(vdW)materials has flourished an endeavor for fundamental problems as well as potential applications in computing,sensing and storage *** particular interest are antiferromagnets,which due to their intrinsic exchange coupling show several advantages in relation to ferromagnets such as robustness against external magnetic *** we show that,despite of this cornerstone,the magnetic domains of recently discovered 2D vdW MnPS_(3)antiferromagnet can be controlled via magnetic fields and electric *** achieve ultrafast domain-wall dynamics with velocities up to~3000 m s^(−1)within a relativistic *** contraction and emission of spin-waves in the terahertz gap are observed with dependence on the edge termination of the *** results indicate that the implementation of 2D antiferromagnets in real applications can be further controlled through edge engineering which sets functional characteristics for ultrathin device platforms with relativistic features.

关键词： relativistic dynamics antiferromagnet

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Isogeometric Collocation:A Mixed Displacement-Pressure Method for Nearly Incompressible Elasticity Dedicated to Professor Karl Stark Pister for his 95th birthday

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Computer Modeling in Engineering & Sciences 2021年第12期129卷 1125-1150页

作者： S.Morganti F.Fahrendorf L.De Lorenzis j.A.evans T.j.R.Hughes A.Reali Department of Electrical Computer and Biomedical EngineeringUniversita degli Studi di PaviaPavia27100Italy Institute of Applied Mechanics Technische Universitat BraunschweigBraunschweig38106Germany Department of Mechanical and Process Engineering Zurich8092Switzerland Department of Aerospace Engineering Sciences University of Colorado BoulderColorado80309USA Institute for Computational Engineering and Sciences The University of Texas at AustinTexas78712USA Department of Civil Engineering and Architecture Universita degli Studi di PaviaPavia27100Italy

We investigate primal and mixed u−p isogeometric collocation methods for application to nearly-incompressible isotropic *** primal method employs Navier’s equations in terms of the displacement unknowns,and the mixed method employs both displacement and pressure *** benchmarks for what might be considered acceptable accuracy,we employ constant-pressure Abaqus finite elements that are widely used in engineering *** a basis of comparisons,we present results for compressible *** the methods were completely satisfactory for the compressible ***,results for low-degree primal methods exhibited displacement locking and in general deteriorated in the nearly-incompressible *** results for the mixed methods behaved very well for two of the problems we studied,achieving levels of accuracy very similar to those for the compressible *** third problem,which we consider a“torture test”presented a more complex story for the mixed methods in the nearly-incompressible case.

关键词： Isogeometric analysis isogeometric collocation nearly-incompressible elasticity

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Improving modeling of low-altitude particulate matter emission and dispersion:A cotton gin case study

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journal of Environmental Sciences 2023年第11期133卷 8-22页

作者： Zijiang Yang Michael N.evans Michael D.Buser Cathleen j.Hapeman Alba Torrents Derek P.Whitelock Department of Civil and Environmental Engineering University of Maryland College Park1173 Glenn L.Martin HallCollege ParkMaryland 20742United States Department of Geology University of Maryland College Park1212B Chemistry BuildingCollege ParkMaryland 20742United States Earth System Science Interdisciplinary Center 1120 Geology BuildingUniversity of MarylandCollege ParkMaryland 20742United States United States Department of Agriculture Agricultural Research ServiceOffice of National Programs5601 Sunnyside Ave(GWCC 4–2282)BeltsvilleMaryland 20705United States United States Department of Agriculture Agricultural Research ServiceHenry A.Wallace Beltsville Agricultural Research Center10300 Baltimore AvenueBeltsvilleMaryland 20705United States United States Department of Agriculture Agricultural Research ServiceSouthwestern Cotton Ginning Research LaboratoryPO Box 578Mesilla ParkNew Mexico 88047United States

Monitoring and modeling of airborne particulate matter(PM)from low-altitude sources is becoming an important regulatory target as the adverse health consequences of PM become better ***,application of models not specifically designed for simulation of PM from low-altitude emissions may bias *** address this problem,we describe the modification and validation of an air dispersion model for the simulation of lowaltitude PM dispersion from a typical cotton ginning *** found that the regulatory recommended model(AERMOD)overestimated pollutant concentrations by factors of 64.7,6.97 and 7.44 on average for PM 2.5,PM 10,and TSP,*** concentrations were negatively correlated with height(pjustment and application of pre-existing models for risk assessment and development of remediation *** same approach may also be applied to improve simulations of other air pollutants and environmental conditions of concern.

关键词： Air quality Particulate matter Air dispersion modelling Cotton gin

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Case study of a driven pile foundation in diatomaceous soil.I:Site characterization and engineering properties

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journal of Rock Mechanics and Geotechnical Engineering 2021年第2期13卷 431-445页

作者： jiayao Wang Ehsan Yazdani T.Matthew evans School of Civil and Construction Engineering Oregon State UniversityCorvallisOR97331USA

Diatomaceous soils are comprised of the silica frustules of diatom microalgae that are present in marine and lacustrine environments throughout the *** to their unique origin,diatomaceous soils are typically characterized by high intraparticle porosity,complex particle shapes,and uniform mineralogy,causing them to exhibit atypical physical and engineering behaviors.A substantial deposit of diatomaceous silt was observed during site exploration for construction of the Buck Creek Bridge on OR140 near Klamath Falls,OR,USA.A comprehensive laboratory and in situ testing program indicated that the diatomaceous soil possessed“non-textbook”engineering ***,tested samples had high liquid limits(≈100%-140%)with natural water contents at or near the liquid ***,the soil is expected to be normally consolidated,yet high apparent overconsolidation ratios(OCR)(≈15-40)were observed both in oedometric consolidation tests and through cone penetration test(CPT)*** penetration test(SPT)results show a corrected standard penetration resistance consistent with a medium-dense sand(i.e.(N1)_(60)≈25).CPT results include corrected tip resistances(qt)of approximately 7-10 MPa and excess pore pressures(u_(2))of up to 4 *** CPT dissipation tests,pore water pressures(PWPs)returned to hydrostatic pressure in less than 1 *** this work,we synthesize these seemingly disparate material properties in an attempt to infer appropriate engineering properties for the diatomaceous deposit at the Buck Creek Bridge and attempt to provide insight into the underlying reasons for the observed behavior.

关键词： Diatomaceous soil Problematic soil Site characterization Laboratory testing

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Case study of a driven pile foundation in diatomaceous ***:Pile installation,dynamic analysis,and pore pressure generation

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journal of Rock Mechanics and Geotechnical Engineering 2021年第2期13卷 446-456页

作者： Ehsan Yazdani jiayao Wang T.Matthew evans School of Civil and Construction Engineering Oregon State UniversityCorvallisOR97331USA

This paper presents the results from a case study highlighting the difficulties of pile driving in diatomaceous *** the companion(first)paper to this article,results of an extensive laboratory and in situ testing program were presented while the results from pile driving and further analysis of field observations were presented *** high pile rebound(HPR)was observed during driving of a closed-end pipe pile,with refusal occurring at a depth of less than 5 *** open-ended piles were thus *** and case pile wave analysis program(CAPWAP)data were collected during driving of both closed-and open-end *** data indicated that negative pore water pressures(PWPs)were generated while the closed-ended pile exhibited high *** from in situ tests indicated change in material stiffness and strong dilative tendencies near the depth of refusal.A hypothesis for observed behavior was proposed that considers the soil beneath the pile as a medium with an effectively infinite bulk modulus.

关键词： Diatomaceous soil Problematic soil Site characterization Laboratory testing

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Ultrasound-assisted microfeeding of fine powders

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Particuology 2008年第1期6卷 2-8页

作者： Xuesong Lu Shoufeng Yang julian R.G. evans Department of Materials Queen Mary University of London Mile End Road London E1 4NS UK

Ultrasonic microfeeding of powders is a new and promising method for use in solid freeforming and pharmaceutical dosing. In this work, computer-controlled microfeeding systems using ultrasonic vibration of a capillary were built. A wide range of controlled, stable rates of flow and switching control were achieved in the acoustic vibration system and uniform powder doses were obtained in the ultrasonic system. Experimental results show that nozzle diameter, transmission fluid depth, waveform, voltage amplitude, frequency and oscillation duration all influence the dose mass. Among these factors, nozzle diameter, voltage amplitude and oscillation duration can be best used to control the dose mass. An artificial neural network （ANN） technique was applied to predict the dose mass. Based on these research results, four types of microfeeding were proposed.

关键词： Microfeeding Ultrasound Fine powders

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