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Influence of nickel addition on the microstructure and mechanical properties of Al2o3–5vol%Zro2 ceramic composites prepared via precipitation method

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International Journal of Minerals,Metallurgy and Materials 2019年第7期26卷 908-914页

作者： Betül Kafkasl?o?lu Y?ld?z Hüseyin Y?lmaz Yahya Kemal Tür Department of Materials Science and Engineering Gebze Technical University

The aim of this work was to investigate the microstructure and mechanical properties of 1vol%-Ni-added yttria-stabilized zirconia (YSZ) toughened alumina composites. First, Ni powders were heterogeneously precipitated in an alumina–zirconia powder mixture suspended in water;the prepared specimens were then pressureless sintered at 1550°C/2 h in a 90vol%Ar/10vol% H2 atmosphere. The structure of phases and microstructure of the composites were characterized by X-ray diffraction and scanning electron microscopy, respectively. Mechanical characterization of the specimens was carried out through Vickers hardness, Vickers indentation toughness, and three-point flexural bending tests. The fine Ni particles were homogeneously dispersed throughout the alumina matrix because of the employed processing method. Furthermore, hardness and toughness values were found to increase by 8% and 50%, respectively, with Ni addition, whereas the relative densities and flexural strength values were found to remain unchanged.

关键词： alumina zirconia ceramic matrix microstructure hardness strength toughness

Effective simulation of flexible lateral boundaries in two-and three-dimensional DEM simulations

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Particuology 2008年第6期6卷 483-500页

作者： Geraldine Cheung Catherine o'Sullivan Department of Civil and Environmental Engineering Imperial College London

Discrete element method （DEM） models to simulate laboratory element tests play an important role in advancing our understanding of the mechanics of granular material response, including bonded or cemented, particulate materials. Comparisons of the macro-scale response observed in a real physical test and a ＂virtual＂ DEM-simulated test can calibrate or validate DEM models. The detailed, particle scale information provided in the DEM simulation can then be used to develop our understanding of the material behaviour. It is important to accurately model the physical test boundary conditions in these DEM simulations. This paper specifically considers triaxial tests as these tests are commonly used in soil mechanics. In a triaxial test, the test specimen of granular material is enclosed within a flexible latex membrane that allows the material to deform freely during testing, while maintaining a specified stress condition. Triaxial tests can only be realistically simulated in 3D DEM codes, however analogue, 2D, biaxial DEM simulations are also often considered as it is easier to visualize particle interactions in two dimensions. This paper describes algorithms to simulate the lateral boundary conditions imposed by the latex membrane used in physical triaxial tests in both 2D and 3D DEM simulations. The importance of carefully considering the lateral boundary conditions in DEM simulations is illustrated by considering a 2D biaxial test on a specimen of frictional unbonded disks and a 3D triaxial test on a bonded （cemented） specimen of spheres. The comparisons indicate that the lateral boundary conditions have a more significant influence on the local, particle-scale response in comparison with the overall macro-scale observations.

关键词： Triaxial testing Discrete element simulations Boundary conditions

The contribution of botanic gardens to ex situ conservation through seed banking

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Plant Diversity 2017年第6期39卷 373-378页

作者： Katherine o'Donnell Suzanne Sharrock Botanic Gardens Conservation International Descanso House

Target 8 of the Global Strategy for Plant Conservation calls for 'at least 75 per cent of threatened plant species in ex situ collections, preferably in the country of origin, and at least 20 per cent available for recovery and restoration programmes by 2020'.Botanic gardens make a significant contribution to ex situ conservation of wild species with more than a third of plant species represented in botanic gardens collections. These collections are a combination of living collection and seed banked material. Seed banking can provide an efficient form of conservation for wild plant genetic *** from Botanic Gardens Conservation International's(BGCI) databases(GardenSearch,PlantSearch, ThreatSearch and GlobalTreeSearch) has been analysed as well as survey data to report on global, regional and national seed banking *** from BGCI's databases indicates that there are at least 350 seed banking botanic gardens in 74 countries. In total 56,987 taxa have been banked including more than 9000 taxa that are threatened with extinction. 6881 tree species are stored in ex situ seed bank collections. More than half(3562) of these tree species are single country endemics and represent species from more than 166 *** study suggests that institutions are increasingly conserving plant species via seed *** the majority of species in collections that have a conservation assessment are not threatened with extinction. This disjunction between species that are threatened and those conserved in seed banks needs to be addressed. Data from BGCI's databases can be used to enable prioritisation of threatened plant species for collection and conservation in seed banks. Further recommendations for botanic gardens involved in seed conservation are presented.

关键词： Seed banking GSPC ex situ conservation Conservation assessments Botanic gardens

Glaciation-induced features or sediment gravity flows——An analytic review

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Journal of Palaeogeography 2023年第4期12卷 487-545页

作者： Mats o.Molen Umea FoU AB Vallmov 61S-90352 Ume aSweden

For more than 150 years, geologic characteristics claimed to be evidence for pre-Pleistocene glaciations have been debated. Advancements in recent decades, in understanding features generated by mainly glacial and mass flow processes, are here reviewed. Detailed studies of data offered in support of prePleistocene glaciations have led to revisions that involve environments of mass movements. Similarities and differences between Quaternary glaciogenic and mass movement features are examined, to provide a more systematic methodology for analysing the origins of more ancient deposits. Analyses and evaluation of data are from a) Quaternary glaciogenic sediments, b) formations which have been assigned to pre-Pleistocene glaciations, and c) formations with comparable features associated with mass movements(and occasionally tectonics). Multiple proxies are assembled to develop correct interpretations of ancient strata. The aim is not per se to reinterpret specific formations and past climate changes, but to enable data to be evaluated using a broader and more inclusive conceptual *** occurring pre-Pleistocene features interpreted to be glaciogenic, have often been shown to have few or no Quaternary glaciogenic equivalents. These same features commonly form by sediment gravity flows or other non-glacial processes, which may have led to misinterpretations of ancient deposits. These features include, for example, environmental affinity of fossils, grading, bedding, fabrics, size and appearance of erratics, polished and striated clasts and surfaces(“pavements”), dropstones, and surface *** decades of progress in research relating to glacial and sediment gravity flow processes have resulted in proposals by geologists, based on more detailed field data, more often of an origin by mass movements and tectonism than *** most coherent data of this review, i.e., appearances of features produced by glaciation, sediment gravity flows and a fe

关键词： Diamictite Tillite Sediment gravity flow(SGF) Striation Groove Dropstone Paleoclimate Fossil vegetation Glaciogenic proxies Surface microtexture Late Paleozoic ice age

Study on creep-fatigue damage evaluation for advanced 9%–12% chromium steels under stress controlled cycling

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Acta Metallurgica Sinica(English Letters) 2011年第2期24卷 148-154页

作者： Peng ZHA o Fuzhen XUAN Key Laboratory of Safety Science of Pressurized System Ministry of Education School of Mechanical andPower Engineering East China University of Science and Technology Shanghai 200237 China

Creep-fatigue interaction is one of the main damage mechanisms in high temperature plants and their components. Assessment of creep-fatigue properties is of practical importance for design and operation of high temperature components. However, the standard evaluation techniques, i.e. time fraction rule and ductility exhaustion one have limitations in accounting for the effects of control mode on the cyclic deformations. It was found that conventional linear cumulative damage rule failed in accurately evaluating the creep-fatigue life under stress controlled condition. The calculated creep damages by time fraction rule were excessively high, which led to overly conservative prediction of failure lives. In the present study, it was suggested that such over estimation of creep damage was mainly caused by anelastic strain upon stress loading. For precise assessment under conditions of stress control, a modified creep damage model accounting for the effect of anelastic creep was proposed. The assessments of creep fatigue data under stress controlled condition were performed with the new approach developed in this paper for a rotor material and a boiler material used in ultra supercritical power plants. It was shown that a more moderate amount of creep damage was obtained by the new model, which gave better predictions of failure life.

关键词： Creep-fatigue Creep damage 9%–12%Cr steels Stress control Time fraction rule

Chemoselective synthesis of δ-lactones via benzyl radical cyclization utilizing K_2S_2o_8-CuCl_2

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Chinese Chemical Letters 2008年第12期19卷 1431-1434页

作者： N.o.Mahmoodi K.Tabatabaeian M.Kosari S.Zarrabi Department of Chemistry Faculty of ScienceUniversity of GuilanRashtP.O.Box 1914Iran

Direct chemoselective oxidation of δ-lactones via highly stable benzyl radical cyclization is reported. The one-pot conversion of premade substituted 5-aryl pentanoic acid and 8-benzyl-1-naphthoic acid in the presence of K2S2os--CuCl2 results to the δ-lactones in moderate to good yields. The advantages of this methodology is using water as a solvent and utilizing available starting materials.

关键词： δ-Lactones Benzyl radical Chemoselective oxidation K2S2o8-CuCl2

Thermal shock and fatigue behavior of pressureless sintered Al_(2)o_(3)-Sio_(2)-Zro_(2) composites

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Journal of Advanced Ceramics 2015年第3期4卷 190-198页

作者： G.MEBRAHIToM ASMELASH o.MAMAT F.AHMAD A.K.PRASADA RAo Faculty of Manufacturing Engineering Universiti Malaysia PahangPekanPahangMalaysia Universiti Teknologi PETRoNAS Bandar Seri Iskandar31750 TronohPerakMalaysia

The thermal shock and fatigue behavior of pressureless sintered Al_(2)o_(3)-Sio_(2)-Zro_(2)(ASZ)composites was *** influence of the thermal shock and fatigue on the strengthening response of ASZ has been investigated by measuring the strength retention and microstructural *** magnitude of the flexural strength and fracture of the ASZ has been compared with that of the monolithic Al_(2)o_(3)(A)and Al_(2)o_(3)-Sio_(2)-Zro_(2)(AZ)composites under the same experimental *** indicated that the ASZ composites possess the highest resistance against thermal shock and fatigue,in comparison with A and *** improvements were attributed to the enhancement in the fracture toughness of ASZ and the presence of multi-phase reinforcement.

关键词： ceramics flexural strength fracture toughness pressureless sintering thermal fatigue thermal shock

Lessons from zebrafish on reprogramming the epigenetic ：ode after fertilisation

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Asian Journal of Andrology 2013年第5期15卷 582-583页

作者： Chris o'Neill Centre for Developmental and Regenerative Medicine Kolling Institute for Medical Research Sydney MedicalSchool University of Sydney NSW 2065 Australia

Methylation of cytosine bases encodes epigenetic information that governs lineage-specific patterns of gene expression. Remodelling the methylated genome accompanies major transitions during embryo development, including fertilisation, blastulation and gastrulation. The first whole genome epigenetic maps of this modification across these embryonic transitions in a metazoan has been reported in the zebrafish,

关键词： Lessons zebrafish fertilisation

Space-time description of transverse photons: near-field aspects

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Science China(Physics,Mechanics & Astronomy) 2012年第8期55卷 1389-1393页

作者： KELLER o. Institute of Physics and Nanotechnology Aalborg University

A mean position state based on the gauge invariant transverse vector potential is used to convert single-photon states in Hilbert space to photon wave packets in direct space. The resulting photon wave-mechanical description leads to scalar products which relate to covariant integration on the light cone. A new correlation matrix displays the spatial localization problem for single photons in an explicit manner in space-time. The correlation matrix essentially is the projection of the time-ordered Feynman photon propagator onto the transverse photon subspace. The present photon wave-mechanical formalism is generalized to two-photon dynamics. In the diamagnetic limit the transverse photon becomes massive in its interaction with matter, and the correlation matrix for massivephoton interaction, which can be used in studies of evanescent-photon mediated couplings, is analyzed. on the basis of the present formalism the existence of a dynamical near-field Aharonov-Bohm effect is predicted.

关键词： one-photon wave mechanics near-field optics correlation matrix transverse photon mass