检索结果-南通市图书馆

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

在线全文

学校读者我要写书评

暂无评论

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

Nonlinear free vibration of piezoelectric cylindrical nanoshells

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2019年第5期40卷 601-620页

作者： Yanqing wANG Yunfei LIU j.w.ZU Department of Mechanics Northeastern University Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines Northeastern University Schaefer School of Engineering and Science Stevens Institute of Technology

The nonlinear vibration characteristics of the piezoelectric circular cylindrical nanoshells resting on an elastic foundation are analyzed. The small scale effect and thermo-electro-mechanical loading are taken into account. Based on the nonlocal elasticity theory and Donnell's nonlinear shell theory, the nonlinear governing equations and the corresponding boundary conditions are derived by employing Hamilton's principle. Then,the Galerkin method is used to transform the governing equations into a set of ordinary differential equations, and subsequently, the multiple-scale method is used to obtain an approximate analytical solution. Finally, an extensive parametric study is conducted to examine the effects of the nonlocal parameter, the external electric potential, the temperature rise, and the winkler-Pasternak foundation parameters on the nonlinear vibration characteristics of circular cylindrical piezoelectric nanoshells.

关键词： piezoelectric cylindrical nanoshell nonlinear vibration Donnell's nonlinear shell theory nonlocal elasticity theory multiple-scale method size effect

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

在线全文

学校读者我要写书评

暂无评论

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

Repeated hydrogen peroxide dosing briefly reduces cyanobacterial blooms and microcystin while increasing fecal bacteria indicators in a eutrophic pond

在线全文

学校读者我要写书评

暂无评论

journal of Environmental Sciences 2023年第2期124卷 522-543页

作者： Mark w.Lusty Christopher j.Gobler School of Marine and Atmospheric Sciences Stony Brook UniversitySouthamptonNY 11968USA

This study explored the effects of H_(2)O_(2)on Cyanobacteria and non-target microbes using fluorometry,microscopy,flow cytometry,and high throughput DNA sequencing of the 16S rRNA gene during a series of mesocosm and whole-ecosystem experiments in a eutrophic pond in NY,*** addition of H_(2)O_(2)(8 mg/L)significantly reduced Cyanobacteria concentrations during a majority of experiments(66%;6 of 9)and significantly increased eukaryotic green and unicellular brown algae in 78%and 45%of experiments,*** heterotrophic bacteria declined significantly following H_(2)O_(2)addition in all experiments,bacteria indicative of potential fecal contamination(Escherichia coli,Enterococcus,fecal coliform bacteria)consistently and significantly increased in response to H_(2)O_(2),evidencing a form of‘pollution swapping’.H_(2)O_(2)more effectively reduced Cyanobacteria in enclosed mesocosms compared to whole-ecosystem *** whole-pond H_(2)O_(2)applications over a twoyear period temporarily reduced cyanobacterial levels but never reduced concentrations below bloom thresholds and populations always rebounded in two weeks or *** bacterial phyla of Cyanobacteria,Actinobacteria,and Planctomycetes were the most negatively impacted by H_(2)O_(2).Microcystis was always reduced by H_(2)O_(2),as was the toxin microcystin,but Microcystis remained dominant even after repeated H_(2)O_(2)*** H_(2)O_(2)favored the growth of eukaryotic algae over potentially harmful Cyanobacteria,the inability of H_(2)O_(2)to end cyanobacterial blooms in this eutrophic waterbody suggests it is a non-ideal mitigation approach in high biomass ecosystems and should be used judiciously due to potential negative impacts on non-target organisms and promotion of bacteria indicative of fecal contamination.

关键词： Indicator bacteria Toxic cyanobacteria Microcystin Microcystis Hydrogen peroxide Bacteria Enterococcus E.coli Pollution swapping

Difference in the Hot Compressive Behavior and Processing Maps between the As-cast and Homogenized Al-Zn-Mg-Cu(7075) Alloys

在线全文

学校读者我要写书评

暂无评论

journal of Materials Science & Technology 2016年第7期32卷 660-670页

作者： S.Y. Park w.j. Kim Department of Materials Science and Engineering Hongik University 72-1 Sangsu-dong Mapo-gu Seoul 121-791 Republic of Korea Advanced Fusion Process R&D Group Korea Institute of Industrial Technology 994-32 Dongchun-dong Yeonsu-gu Incheon 406-130 Republic of Korea

The deformation mechanisms and processing maps of the as-cast Al-Zn-Mg-Cu （？0？5） aluminum （AI） alloy were studied and compared with those of the homogenized 7075 Al alloy in the temperature range of 573-723 K and in the strain rate range of 10 3-10 s-1 to explore a possibility for directly using the as- cast 7075 Al alloy as a billet for hot working. The as-cast and homogenized 7075 A1 alloys had similar grain sizes and showed similar high-temperature deformation behaviors. The as-cast 7075 Al alloy, however, exhibited higher power efficiencies and smaller unstable flow regions compared to the homogenized 7075 AI alloy because of the presence of secondary phases （MgZn2） segregated at the dendritic interfaces in the as-cast microstructure, which were formed during non-equilibrium solidification. These segregated phases provided nucleation sites for dynamic recovery or continuous dynamic recrystallization, and as a result a fine and more homogeneous （sub）grain structure could be obtained from the as-cast micro- structure compared to the homogenized microstructure. The current work suggested the possibility and advantage of using as-cast microstructures for hot working of aluminum alloys with high content of solutes.

关键词： Al-based alloysProcessing mapHot compressionAs-cast microstructureSegregationRecrystallization

Speeding up transmissions of unknown quantum information along Ising-type quantum channels

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2017年第1期26卷 125-130页

作者： w j Guo L F wei Quantum Optoelectronics Laboratory Southwest Jiaotong University Chengdu 610031 China State Key Laboratory of Optoelectronic Materials and Technologies School of Physics Sun Yat-Sen University Guangzhou 510275 China

Quantum teleportation with entanglement channels and a series of two-qubit SwAP gates between the nearestneighbor qubits are usually utilized to achieve the transfers of unknown quantum state from the sender to the distant receiver. In this paper, by simplifying the usual SwAP gates we propose an approach to speed up the transmissions of unknown quantum information, specifically including the single-qubit unknown state and two-qubit unknown entangled ones,by a series of entangling and disentangling operations between the remote qubits with distant interactions. The generic proposal is demonstrated specifically with experimentally-existing Ising-type quantum channels without transverse interaction; liquid NMR-molecules driven by global radio frequency electromagnetic pulses and capacitively-coupled josephson circuits driven by local microwave pulses. The proposal should be particularly useful to set up the connections between the distant qubits in a chip of quantum computing.

关键词： unknown quantum information transfers Ising-type quantum chains NMR molecules superconducting circuits

Effects of Processing Parameters on Microstructure and Properties of Ultra High Strength Linepipe Steel

在线全文

学校读者我要写书评

暂无评论

journal of Materials Science & Technology 2012年第10期28卷 889-894页

作者： Xiaodan wu Hakcheol lee Young Min Kim Nack j.Kim University of Pittsburgh Pittsburghl PA 15213USA Pohang University of Science and Technology Pohang 790-784Korea

To examine the effect of processing parameters on microstructural evolution and to obtain the excellent combination of strength and toughness, simulation of thermo-mechanical processing was conducted using the Gleeble machine. Trial production was then conducted under the conditions obtained by Gleeble tests. Based on the results of microstructure analysis and mechanical property evaluation, the relationship between microstructural features and mechanical properties was elucidated. The result shows that the volume fraction of constituted phases can be controlled through adjusting the cooling rate and finish cooling temperature in order to get different strength levels. As cooling rate increases, the volume fraction of upper bainite increases, which leads to the increase of strength. The upper shelf energy （USE） increases with increasing volume fraction of acicular ferrite in bainite base because of the small effective acicular ferrite grain size. Ductile-brittle transition temperature （DBTT） decreases with increasing acicular ferrite volume fraction. High reduction in the rough stage has great influence on grain refinement.

关键词： Linepipe steel Microstructure Gleeble test TMCP (thermomechanicalcontrol process)

FURTHER EXTENSIONS OF SOME TRUNCATED HECKE TYPE IDENTITIES

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Scientia 2022年第1期42卷 73-90页

作者： Helen w.j.ZHANG School of Mathematics Hunan UniversityChangsha 410082China

The main purpose of this paper is to generalize the study of the Hecke-Rogers type series,which are the extensions of truncated theorems obtained by Andrews,Merca,wang and *** proofs rely heavily on the theory of Bail... 详细信息

关键词： theta functions truncated series Bailey pair Bailey transform

One-step multi-compositional oxidation of YSi alloy:Experiments and ab initio computation

在线全文

学校读者我要写书评

暂无评论

journal of Materials Science & Technology 2023年第27期158卷 253-262页

作者： w.j.wang j.C.Luo L.Chen G.j.Yang State Key Laboratory for Mechanical Behavior of Materials School of Materials Science and EngineeringXi’an Jiaotong UniversityXi’an 710049China Xi’an jiaotong University Suzhou Institute Suzhou 215123China

YSi alloy is a promising candidate as oxidation resistant coatings for both the bond coat of environmental barrier coatings(EBCs)and anti-ablation coatings at a high temperature of∼1300℃.In this study,a one-step multi-compositional oxidation by rapid heating oxidation mode is proposed to reduce the oxidation rate by 3.6 times compared to conventional slow heating oxidation *** show that preferentially formed Y_(2)O_(3) oxide initiates a multi-step oxidation,produces a cracking and porous oxides,and thereby resulting in a fast oxidation with *** one-step multi-compositional oxidation with a compact and dense Y_(2)Si_(2)O_(7)scale contributes to the much better oxidation resistance for rapid heating oxidation mode of YSi *** stable formation of Y_(2)Si_(2)O_(7)scale is comprehensively understood by the energy barrier,charge density and electronic level based on density functional *** study demonstrates a promising application of YSi alloy by rapid heating oxidation mode.

关键词： YSi alloy One-step oxidation Multi-compositional scale Y_(2)Si_(2)O_(7) Energy barrier