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Nanosized complex fluorides based on Eu^(3+) doped sr_2LnF_7(Ln=La, Gd)

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Journal of Rare Earths 2014年第3期32卷 242-247页

作者： M.Runowski s.Balabhadra s.Lis Department of Rare Earths Faculty of Chemistry Adam Mickiewicz University

A simple co-precipitation approach taking place between Ln3＋, sr2＋ cations and F anions, led to the formation of nanocrystalline Eu3＋ doped sr2LnF7 （Ln-La and Gd） complex fluorides. The reaction was carried out in the presence of polyeth- ylene glycol, PEG 6000 as a surfactant/surface modifier, providing small size and homogeneity of the products. The synthesized compounds were composed of small nanoparticles with an average size of 15 nm. All obtained Eu3＋ doped compounds exhibited an intensive red luminescence. In the case of gadolinium based compounds, the energy transfer phenomena could be observed from Gd3＋ ions to Eu3＋ ions. In order to study the structure and morphology of the synthesized fluorides, powder X-ray diffraction （XRD） and transmission electron microscopy （TEM） measurements were performed. Also FT-IR spectra of the products were re- corded, revealing the presence of PEG molecules on the nanoparticles suN＇ace. A spectrofluorometry technique was applied to examine optical properties of the synthesized nanoparticles. Excitation and emission spectra as well as luminescence decay curves were measured and analysed. The performed analysis revealed a red luminescence, typical for the Eu3＋ ion situated in the inorganic, highly symmetric matrix. Concentration quenching phenomena and lifetimes shortening, together with an increasing of the Eu3＋ doping level, were observed and discussed. Judd-Ofelt analysis was also performed for all doped samples, in order to support the registered spectroscopic data and examine in details structural and optoelectronic properties of the synthesized nanomaterials.

关键词： luminescence Eu3+ doping complex strontium lanthanide fluorides nanoparticles sr2LnF7 sr0.69La0.31F2.31 rare earths

Condition assessment of structures under unknown support excitation

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Earthquake Engineering and Engineering Vibration 2009年第1期8卷 103-114页

作者： Zhang Kun s. s. Law Duan Zhongdong school of Civil Engineering Harbin Institute of Technology Harbin 150090 China Civil and structural Engineering Department Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong China

A new method is proposed to assess the condition of structures under unknown support excitation by simultaneously detecting local damage and identifying the support excitation from several structural dynamic responses. The support excitation acting on a structure is modeled by orthogonal polynomial approximations, and the sensitivities of structural dynamic response with respect to its physical parameters and orthogonal coefficients are derived. The identification equation is based on Taylor＇s first order approximation, and is solved with the damped least-squares method in an iterative procedure. A fifteen-story shear building model and a five-story three-dimensional steel frame structure are studied to validate the proposed method. Numerical simulations with noisy measured accelerations show that the proposed method can accurately detect local damage and identify unknown support excitation from only several responses of the structure. This method provides a new approach for detecting structural damage and updating models with unknown input and incomplete measured output information.

关键词： condition assessment damage detection support excitation identification dynamic response sensitivity

Hidden periodicity in stripe 82 with saraswati supercluster—a fractal analysis

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Communications in Theoretical Physics 2021年第1期73卷 71-77页

作者： Vimal Raj M s swapna s sankararaman Department of Optoelectronics University of KeralaTrivandrumKerala695581-India

The manuscript attempts to explore the periodicity in the distribution of galaxies in the recently reported saraswati supercluster and the stripe 82 region containing it as an *** report of 120 Mpc periodicity in the Abell galaxy clusters by power spectrum analysis is the motivation behind the *** power spectral analysis across the central part of the stripe 82 region shows a periodic variation of 3.09°or 71 Mpc in fractal dimension whereas an average angular periodicity of 3.45°or 94 Mpc is observed across the stripe 82 *** refers to the periodicity of complexity or cluster density of galaxy *** texture of the distribution pattern understood through lacunarity analysis indicates a near symmetric *** dimensions like box-counting dimension,information dimension and correlation dimension are also found through multifractal *** the information dimension tells about the distribution density of galactic points,the correlation dimension details the distribution of galaxies in the neighbourhood.

关键词： galaxy distribution fractal analysis multifractals lacunarity saraswati supercluster stripe 82

strip Casting of High Performance structural Alloys

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Journal of Rare Earths 2004年第z2期22卷 78-84页

作者： s s Park J G Lee Nack J Kim Center for Advanced Aerospace Materials Pohang University of Science and TechnologyPohang 790-784Korea Center for Advanced Aerospace MaterialsPohang University of Science and TechnologyPohang 790-784Korea Center for Advanced Aerospace MaterialsPohang University of Science and TechnologyPohang 790-784Korea

There exists a great need for the development of high performance alloys due to increasing demands for energy conservation and environmental protection. Application of strip casting shows a strong potential for the improvement of properties of existing alloys and also for the development of novel alloy systems with superior properties. The present paper reviews our Center's activities in the development of high performance alloys by strip casting. Examples include (1) Al alloys, (2) wrought Mg alloys, and (3) bulk metallic glass (BMG) alloys.

关键词： strip casting 6061 Al alloy AZ Mg alloy bulk metallic glass (BMG) alloy dispersion hardening

Enhancing fatigue performance of AZ31 magnesium alloy components fabricated by cold metal transfer-based wire arc directed energy deposition through LPB

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Journal of Magnesium and Alloys 2024年第4期12卷 1638-1662页

作者： shambhu Kumar Manjhi srikanth Bontha A.s.s.Balan Department of Mechanical Engineering National Institute of Technology KarnatakaSurathkalSrinivasanagarMangaloreKarnataka 575025India

Cold Metal Transfer-Based Wire Arc Directed Energy Deposition(CMT-WA-DED)presents a promising avenue for the rapid fabrication of components crucial to automotive,shipbuilding,and aerospace ***,the susceptibility to fatigue of CMT-WA-DED-produced AZ31 Mg alloy components has impeded their widespread adoption for critical load-bearing *** this study,a comprehensive investigation into the fatigue behaviour of WA-DED-fabricated AZ31 Mg alloy has been carried out and compared to commercially available wrought AZ31 *** findings indicate that the as-deposited parts exhibit a lower fatigue life than wrought Mg alloy,primarily due to poor surface finish,tensile residual stress,porosity,and coarse grain microstructure inherent in the WA-DED *** Plasticity Burnishing(LPB)treatment is applied to mitigate these issues,which induce significant plastic deformation on the *** treatment resulted in a remarkable improvement of fatigue life by 42%,accompanied by a reduction in surface roughness,grain refinement and enhancement of compressive residual stress ***,during cyclic deformation,WA-DED specimens exhibited higher plasticity and dislocation density compared to both wrought and WA-DED+LPB specimens.A higher fraction of Low Angle Grain Boundaries(LAGBs)in WA-DED specimens contributed to multiple crack initiation sites and convoluted crack paths,ultimately leading to premature *** contrast,wrought and WA-DED+LPB specimens displayed a higher percentage of High Angle Grain Boundaries(HAGBs),which hindered dislocation movement and resulted in fewer crack initiation sites and less complex crack paths,thereby extending fatigue *** findings underscore the effectiveness of LPB as a post-processing technique to enhance the fatigue performance of WA-DED-fabricated AZ31 Mg alloy *** study highlights the importance of LPB surface treatment on AZ31 Mg components produced by CMT-WA-DED to remove surface d

关键词： Wire arc additive manufacturing AZ31 Mg alloy Low plasticity burnishing Low cycle fatigue test strain amplitude

Influence of spark Plasma sintering Temperature on the Densification, Microstructure and Mechanical Properties of Al-4.5 wt.%Cu Alloy

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Acta Metallurgica sinica(English Letters) 2013年第6期26卷 761-771页

作者： s.Devaraj s.sankaran R.Kumar Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras (IIT Madras)

The effect of sintering temperature on the densification mechanisms, microstructural evolution and mechanical properties of spark plasma sintered （sPs） compacts of a gas atomized Al-4.5 wt.%Cu alloy was investigated. The powder particles whose size varied between 10 to 500μm was subjected to sPs at 400, 450 and 500℃ at a pressure of 30 MPa. The compact sintered at 500℃ exhibited fully dense microstructure which was characterized by a uniform distribution of the secondary phase, free of dendrites and micro-porosity. Microscopy and the sPs data reveal that the events such as particle rearrangement, localized deformation and bulk deformation appear to be the sequence of sintering mechanisms depending on the size range of powder particles used for consolidation. The compact sintered at 500℃ exhibited the highest hardness and compression strength since the microstructure was characterized by fine distribution of precipitates, large fraction of submicron grains and complete metallurgical bonding.

关键词： spark plasma sintering sintering mechanisms Precipitation Compression strength

Dispersion and attenuation of torsional wave in a viscoelastic layer bonded between a layer and a half-space of dry sandy media

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Applied Mathematics and Mechanics(English Edition) 2017年第9期38卷 1313-1328页

作者： P.ALAM s.KUNDU s.GUPTA Department of Applied Mathematics Indian Institute of Technology(Indian School of Mines)Dhanbad 826004JhrkhandIndia

Propagation of a torsional wave in a doubly-layered half-space structure of an initially stressed heterogeneous viscoelastic layer sandwiched between a layer and a half-space of heterogeneous dry sandy media is studied. A closed form complex expression for the velocity profile is obtained under effective boundary conditions. The real part of the complex expression provides a dispersion equation, and the imaginary part yields a damping equation. The derived dispersion and damped equations are in well agreement with the classical Love wave condition. In addition, to study the effect of the dissipation factor, the attenuation coefficient, the sandy parameters, the initial stress, the hetero- geneity parameters, and the thickness ratio parameter, some noteworthy contemplations are made by numerical calculations and graphical visuals. The results of this paper may present a deeper insight into the behaviour of propagation phenomena in heterogeneous viscoelastic and heterogeneous dry sandy materials that can provide a theoretical guide for the design and optimization in the field of earthquake engineering. The study also reveals that the presence of a damping part due to viscoelasticity affects the torsional wave propagation significantly.

关键词： attenuation dissipation viscoelastic sandy heterogeneous initial stress,phase damping

Inverse methodology as applied to reconstruct local textile features from measured pressure field

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Journal of Materials science & Technology 2021年第12期71卷 241-247页

作者： s.Bancora C.Binetruy s.Advani Comas-Cardona Ecole Centrale de Nantes Research Institute in Civil Engineering and Mechanics(GeM)UMR CNRS 618344321 Nantes Cedex 3France Department of Mechanical Engineering University of DelawareNewarkDelaware 19716USA

One can compute the final deformation of a known geometry under specific boundary conditions using the constitutive laws of mechanics that describe their stress strain *** such cases the initial geometry is known,and all operators mapping the deformation are defined on the reference ***,there are situations in which the final configuration of a deformation might be known but not the *** inverse formulation allows one to determine the initial geometry of a domain,given its final deformation state,the material behavior law and a set of boundary *** the present work we propose a method to reconstruct the mesoscale geometry of a textile based on its mechanical response during *** do so,stress boundary conditions are acquired by means of a pressuresensitive *** adopting an appropriate material law,the thickness and width information of the yarns are deduced from the pressure field experienced by the compacted *** 3 D scanning techniques such as-CT,the proposed method can be applied on any domain size,allowing long-range variability to be *** the best of the authors’knowledge,there are no previous works that use a pressure-sensitive film on a large domain to capture the input data for a shape *** example application serves as a demonstration of a methodology which could be applied to other classes of materials.

关键词： Textiles Pressure sensors Inverse method Digital twin Geometry reconstruction Hyperelasticity

Dynamic responses of two buildings connected by viscoelastic dampers under bidirectional earthquake excitations

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Earthquake Engineering and Engineering Vibration 2014年第1期13卷 137-150页

作者： Z.D. Yang Eddie s.s. Lam Department of Civil and Environmental Engineering The Hong Kong Polytechnic University

In this study,dynamic responses of two buildings connected by viscoelastic dampers under bidirectional excitations are extensively *** two buildings are a 10-story building and a 16-story building,with the shorter building on the *** dampers are installed at all fl oors of the shorter *** of motion are formulated using a fractional derivative model to represent the viscoelastic *** cases are considered with mass eccentricities at 0,10% and-10% with respect to the dimensions of the *** responses of the buildings are numerically predicted at different damper *** simulation results indicated that the maximum horizontal responses of the buildings without eccentricities are signifi cantly ***,torsional effects are adversely *** asymmetric buildings,the effectiveness of the connecting dampers is affected by building *** a result,mass eccentricities must be taken into account in damper *** compared with vibrations induced by unidirectional excitations,bidirectional excitations can increase the responses of coupled asymmetric *** addition,installing dampers only at the top fl oor of the shorter building may cause a sudden change in lateral stiffness of the taller ***,the story shear envelopes of the taller building are changed.

关键词： bidirectional excitations connecting dampers adjacent buildings fractional derivative