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Superplastic behavior of an ultrafine-grained Mg-13Zn-1.55Y alloy with a high volume fraction of icosahedral phases prepared by high-ratio differential speed rolling

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journal of Materials Science & technology 2017年第9期33卷 919-925页

作者： t.Y.Kwak W.j.Kim Rare Metal R&BD Group Korea Institute of Industrial Technology Department of Materials Science and Engineering Hongik University

An ultrafine-grained（UFG） Mg-13Zn-1.55 Y alloy（ZW132） with a high volume fraction（7.4%） of icosahedral phase（I-phase, Mg;Zn;Y） particles was prepared by applying high-ratio differential speed rolling（HRDSR） on the cast microstructure following homogenization. the alloy exhibited excellent superplasticity at low temperatures(tensile elongations of 455% and 1021% 473 K-10;s;and 523 K-10;s;,respectively). Compared with UFG Mg-9.25Zn-1.66 Y alloy（ZW92） with a lower volume fraction of I-phase particles（4.1%）, which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond523 K, leading to a loss of superplasticity. the high-temperature deformation behavior of the HRDSRprocessed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 K.

关键词： Magnesium alloy Superplastic deformation Ultrafine grain Icosahedral quasicrystal Grain growth

Critical review of superplastic magnesium alloys with emphasis on tensile elongation behavior and deformation mechanisms

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journal of Magnesium and Alloys 2022年第5期10卷 1133-1153页

作者： H.t.jeong W.j.Kim Department of Materials Science and Engineering Hongik UniversitySangsu-dong 72-1 Mapo-guSeoul 121-791South Korea

the tensile elongation behavior and deformation mechanisms of superplastic Mg alloys and Mg composites were examined by extensively reviewing the literature published from the time of the first report on the superplasticity of Mg alloys to the present *** on the superplasticity of Mg alloys have been conducted mainly on Mg-Al-Zn(AZ)series alloys,Mg-Zn-Zr(ZK),Mg-Li and Mg-RE(rare earth)alloys,and in recent years,Mg-RE alloys have attracted the greatest *** effect of grain size and the type and amount of secondary phase particles on the superplasticity of Mg alloys was systematically examined and *** alloys processed by severe plastic deformation(SPD)and powder-metallurgy methods have smaller grain sizes and exhibit superior superplasticity compared to conventionally processed(by extrusion and rolling)Mg *** the AZ alloys,as the volume fraction of the Mg17Al12phase increases,smaller grains are obtained,and the low-temperature superplasticity(LtS)and high-strain-rate superplasticity(HSRS)characteristics become *** ZK60 alloy with finely dispersed Mg Zn2particles exhibits excellent LtS,while the Mg-RE alloys with a high fraction of thermally stable particles exhibit excellent ***-Li alloys can exhibit LtS even at room temperature due to the presence of a high-volume fraction of the body centered cubic(BCC)phase where atomic diffusivity is *** boundary diffusion-and lattice diffusion-controlled grain boundary sliding are found to operate as the dominant deformation mechanisms below~473 K and above~673 K,respectively,at small grain *** mechanism maps were constructed based on the analysis of the deformation behavior of superplastic Mg alloys,and from the maps,the critical conditions for achieving LtS,HSRS and simultaneous achievement of LtS and HRSR were calculated and proposed,and their importance was discussed.

关键词： Magnesium alloys Superplastic Grain size Secondary phase Grain boundary sliding

Effect of refinement of grains and icosahedral phase on hot compressive deformation and processing maps of Mg-Zn-Y magnesium alloys with different volume fractions of icosahedral phase

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journal of Materials Science & technology 2019年第1期35卷 181-191页

作者： t.Y.Kwak W.j.Kim Department of Materials Science and Engineering Hongik University

the effect of the volume fraction of I-phase on the hot compressive behavior and processing maps of the extruded Mg-Zn-Y alloys was examined, and the obtained results were compared with those of the cast alloys in a previous work. the average grain sizes, fractions of dynamically recrystallized(DRXed) grains,and sizes of DRXed grains of the extruded alloys after compressive deformation were significantly smaller,higher and smaller, respectively, than those of the cast alloys after compressive deformation under the same experimental conditions. this was because the microstructures of the extruded alloys, having much more grain boundaries and more refined I-phase particles than the cast alloys, provided a larger number of nucleation sites for dynamic recrystallization than those of the cast alloys. the constitutive equations for high-temperature deformation of the extruded and cast alloys could be derived using the same activation energy for plastic flow, which was close to the activation energy for lattice diffusion in *** with the cast alloys, the onset of the power law breakdown(PLB) occurred at larger ZenerHolloman(Z) parameter values in the extruded alloys. this was because the extruded alloys had finer initial grain sizes and higher fractions of finer DRXed grains compared to the cast alloys, such that the onset of PLB caused by creation of excessive concentrations of deformation-induced vacancies was delayed to a higher strain rate and a lower temperature. the flow-stress difference between the extruded alloys and the cast alloys could be attributed to the difference in the fraction of DRXed grains. According to the processing maps, the extruded alloys exhibited higher power dissipation efficiency and flow stability than the cast alloys. this agreed with the microstructural observations.

关键词： Hot compression Magnesium alloy Processing map Grain refinement Dynamic recrystallization

Fano-type resonances induced by a boson mode in Andreev conductance

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Chinese Physics B 2015年第1期24卷 449-456页

作者： j.Barański t.Domański Institute of Physics M. Curie-Skodowska University20-031 Lublin Poland

We study spectroscopic signatures of a monochromatic boson mode interacting with a t-shape double quantum dot coupled between the metallic and superconducting leads. Focusing on a weak interdot coupling, we find that the proximity effect together with the bosonic mode are responsible for the series of Fano-type resonances appearing simultaneously at negative and positive energies. We investigate these interferometric features and discuss their influence on the subgap Andreev conductance taking into account the correlation effects driven by the Coulomb repulsion.

关键词： Fano interference Andreev scattering polaronic features

the hot compressive deformation behavior of cast Mg-Gd-Y-Zn-Zr alloys with and without LPSO phase in their initial microstructures

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journal of Magnesium and Alloys 2022年第10期10卷 2901-2917页

作者： H.t.jeong W.j.Kim Departmentof Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

Samples of Mg-8.2Gd-3.8Y-1.1Zn-0.4Zr alloy with and without an intragranular lamellae-shaped long period stacking ordered(LPSO)phase were prepared through heat treatment and a series of hot compression tests on these materials were conducted to examine and evaluate the influence of LPSO on the hot compressive deformation behavior and deformation mechanisms at a given alloy *** values of activation energy for plastic flow(Qc)of the solution treated(without LPSO phase)and annealed alloys(with intragranular LPSO phase)were larger than that for pure Mg,indicating that the presence of a high amount of rare earth(RE)elements and LPSO in the Mg matrix significantly increases *** Qcvalue of the annealed alloy was larger than that of the solution treated alloy at all the strain levels(223.3 vs.195.5 k j/mol in average)and the largest difference in Qcbetween the two alloys was recorded at the smallest strain of 0.1 where precipitation of LPSO during deformation was limited in the solution treated *** observations imply that the formation of LPSO phase out of the RE-rich solid solution matrix during deformation increases Qc,but the increment is not so *** of the hot compressive data of the alloys with LPSO phase and the alloys with RE-rich solid solution matrix in literatures indicates the similarity of the effect of the LPSO and RE-rich solid solution matrix phases on Qcand high-temperature strength.

关键词： Magnesium alloys LPSO Deformation mechanism Dynamic recrystallization Activation energy for plastic flow Processing maps

the effects of gonadal hormones on learning and memory in male mammals： A review

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Current Zoology 2011年第4期57卷 543-558页

作者： Stuart t. LEONARD Peter j. WINSAUER Department of Pharmacology and Experimental therapeutics Louisiana State University Health Sciences Center 1901 Perdido Street New Orleans LA 70112-1393

the primary role of the gonadal steroid hormones in mammals is to regulate reproduction and related behaviors; however, both androgens and estrogens are also integrally involved in mediating higher brain function and processes including cognition, neural development, and neural plasticity. In particular, a number of studies show that estradiol modulates dendritic spine growth and synapse density （synaptic plasticity） in the hippocampus of females, and that increased estradiol levels are generally associated with improvements on a variety of learning and memory tasks. While the majority of research has focused on the beneficial effects of estradiol in females, much less attention has been given to testosterone and its effects on learning and memory in males. Similar to estradiol titers in females, testosterone titers in males decline with age, albeit more gradually, and this decline has been correlated with impairment of certain cognitive tasks. Moreover, studies involving both humans and animals indicate that testosterone and its metabolites can augment responding on certain behavioral tasks, depending on the subject＇s current hormonal state, the response required, and the stimuli involved （e.g., those involving spatial or nonspatial stimuli）. While the exact mechanisms by which testosterone exerts its effects on learning and memory are not fully understood, recent findings suggest that testosterone modulates learning and memory in males through an interaction with the cholinergic system. the overall objective of this review is to discuss studies investigating the role of the gonadal hormones in mediating learning and memory processes in male mammals [Current Zoology 57 （4）： 543-558, 2011].

关键词： testosterone Learning and memory Cholinergic system Mammals Cognition Androgens

Chromium from Hydrolyzed Leather Affects Soybean Growth and Nodulation

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Pedosphere 2019年第1期29卷 95-101页

作者： jovana BAVARESCO jess R.FINK Moacir t.MORAES antonio R.SNCHEZ-RODRGUEZ Ibanor ANGHINONI Department of Soils Federal University of Rio Grande do Sul Laboratory of Soil Federal Institute of Paraná Department of Agronomy University of C'ordoba

Hydrolyzed leather, obtained from industrial leather waste, is an organic nitrogenous fertilizer with a high chromium(Cr) *** crops can be adversely affected by the presence of residual Cr in soil after application of hydrolyzed leather fertilizer. the aim of this work was to assess the effect of hydrolyzed leather on Cr absorption, root development, and symbiotic nodulation of soybean plants grown on three different soils including two Lixisols and a Gleysol. these soils were previously fertilized with hydrolyzed leather at three different rates(0.0, 0.1, and 0.8 kg m^(-2)). Soybean shoot height, root development, nodulation, and mineral nutrient concentrations in plant tissues were determined after 45 d of crop growth. the application of hydrolyzed leather significantly increased Cr content in soil and Cr uptake by plants. Surprisingly, Cr was stored mainly in the aerial part of the plants. the presence of Cr had an adverse impact on shoot dry matter(41% reduction) and number of nodules(49% reduction) per plant grown on the soil with the lowest cation exchange capacity. However, no other significant effect was observed in nodule weight, diameter, or any other measured parameters.

关键词： Cr absorption Cr accumulation plant growth root development symbiotic nodulation

Bright,high-repetition-rate water window soft X-ray source enabled by nonlinear pulse self-compression in an antiresonant hollow-core fibre

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Light(Science & Applications) 2021年第3期10卷 313-319页

作者： M.Gebhardt t.Heuermann R.Klas C.Liu A.Kirsche M.Lenski Z.Wang C.Gaida j.E.antonio-Lopez A.Schülzgen R.Amezcua-Correa j.Rothhardt j.Limpert Institute of Applied Physics Abbe Center of PhotonicsFriedrich-Schiller-Universitat JenaAlbert-Einstein-Str.1507745 JenaGermany Helmholtz-Institute jena Frobelstieg 307743 JenaGermany CREOL College of Optics and PhotonicsUniversity of Central FloridaOrlandoFL 32816USA Fraunhofer Institute for Applied Optics and Precision Engineering Albert-Einstein-Str.707745 JenaGermany Active Fiber Systems GmbH Ernst-Ruska-Ring 1707745 JenaGermany

Bright,coherent soft X-ray radiation is essential to a variety of applications in fundamental research and life *** date,a high photon flux in this spectral region can only be delivered by synchrotrons,free-electron lasers or high-order harmonic generation sources,which are driven by kHz-class repetition rate lasers with very high peak ***,we establish a novel route toward powerful and easy-to-use SXR sources by presenting a compact experimentin which nonlinear pulse self-compression to the few-cycle regime is combined with phase-matched high-orderharmonic generation in a single,helium-illed antiresonant hollow-core *** enables the first 100 kHz-classrepetition rate,table-top soft X-ray source that delivers an application-relevant flux of 2.8×10^6 photon s^-1 eV^-1 around 300 *** fibre integration of temporal pulse self-compression(leading to the formation of the necessarystrong-field waveforms)and pressure-controlled phase matching will allow compact,high-repetition-rate lasertechnology,including commercially available systems,to drive simple and cost-effective,coherent high-flux softX-ray sources.

关键词： pulse repetition fibre

Seismic analysis of long tunnels:A review of simplified and unified methods

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Underground Space 2017年第2期2卷 73-87页

作者： Haitao Yu Yong Yuan antonio Bobet Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education Tongji UniversityShanghai 200092China State Key Laboratory for GeoMechanics and Deep Underground Engineering China University of Mining and TechnologyBeijing 100083China State Key Laboratory of Disaster Reduction in Civil Engineering Tongji UniversityShanghai 200092China High-End Foreign Expert at tongji University Shanghai 200092China Lyles School of Civil Engineering Purdue UniversityWest LafayetteIN 47907USA

Seismic analysis of long tunnels is important for safety evaluation of the tunnel structure during *** models of long tunnels are commonly adopted in seismic design by practitioners,in which the tunnel is usually assumed as a beam supported by the *** models can be conveniently used to obtain the overall response of the tunnel structure subjected to seismic ***,simplified methods are limited due to the assumptions that need to be made to reach the solution,*** tunnels are assembled with segments and bolts to form a lining ring and such structural details may not be included in the simplified *** most cases,the design will require a numerical method that does not have the shortcomings of the analytical solutions,as it can consider the structural details,non-linear behavior,***,long tunnels have significant length and pass through different *** of these would require large-scale seismic analysis of long tunnels with three-dimensional models,which is difficult due to the lack of available computing *** paper introduces two types of methods for seismic analysis of long tunnels,namely simplified and unified *** models,including the mass-spring-beam model,and the beam-spring model and its analytical solution are presented as examples of the simplified *** unified method is based on a multiscale framework for long tunnels,with coarse and refined finite element meshes,or with the discrete element method and the finite difference method to compute the overall seismic response of the tunnel while including detailed dynamic response at positions of potential damage or of interest.A bridging scale term is introduced in the framework so that compatibility of dynamic behavior between the macro-and meso-scale subdomains is *** are presented to demonstrate the applicability of the simplified and the unified methods.

关键词： Earthquake engineering tunnel structure Seismic analysis Simplified method Multiscale method