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hot cracking in AZ31 and AZ61 Magnesium Alloy

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Journal of Materials Science & Technology 2011年第7期27卷 633-640页

作者： c.J. huang c.M. cheng c.P. chou F.h. chen Department of Mechanical Engineering National Chiao Tung University Hsinchu 300 Taiwan China Department of Industrial Education National Taiwan Normal University Taipei 106 Taiwan China

This paper examined the impact of the number of thermal cycles and augmented strain on hot cracking in AZ31 and AZ61 magnesium alloy. Statistical analyses were performed. Following observation using a scanning electron microscope （SEM）, an energy dispersive spectrometer （EDS） was used for component analysis. Results showed that Al content in magnesium alloy has an effect on hot cracking susceptibility. In addition, the nonequilibrium solidification process produced segregation in Al content, causing higher liquid Mg-alloy rich Al content at grain boundaries, and resulting into liquefied grain boundaries of partially melted zone （PMZ）. In summary, under multiple thermal cycles AZ61 produced serious liquation cracking. AZ61 has higher （6 wt%） Al content and produced much liquefied Mg17Al12 at grain boundaries under multiple thermal cycles. The liquefied Mg17Al12 were pulled apart and hot cracks formed at weld metal hAZ due to the augmented strain. Since AZ31 had half the Al content of AZ61, its hot-cracking susceptibility was lower than AZ61. In addition, AZ61 showed longer total crack length （TcL） in one thermal cycle compared to that in three thermal cycles. This phenomenon was possibly due to high-temperature gasification of Al during the welding process, which resulted in lower overall Al content. consequently, shorter hot cracks exhibited in three thermal cycles. It was found the Al content of AZ31 and AZ61 can be used to assess the hot-cracking susceptibility.

关键词： Varestraint test Thermal cycles hot-cracking susceptibility Gas tungsten arc welding (GTAW) AZ31 AZ61

Improved thermoelectric property of cation-substituted caMnO_3

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chinese Physics B 2015年第9期24卷 542-547页

作者： Pradeep Kumar Subhash c.Kashyap Vijay Kumar Sharma h.c.Gupta Department of Physics Shyam Lal CollegeUniversity of Delhi Department of Physics Indian Institute of Technology Delhi

Single-phase pristine and cation-substituted calcium manganite（ca1-xBixMn1-yVyO3-δ） polycrystalline samples were synthesized by the solid state reaction technique. Their thermoelectric properties were measured by a set up that was designed and assembled in the laboratory. The ca1-x BixMn1-yVyO3-δsample with x = y = 0.04 has shown a power factor（S^2σ） of 176 μW/m/K^2 at 423 K, which is nearly two orders of magnitude higher than that of the pristine sample（2.1 μW/m/K2）. The power factor of the substituted oxide remains almost temperature independent as the Seebeck coefficient increases monotonically with temperature, along with the simultaneous decrease in electrical resistivity which is attributed to enhanced electron density due to co-doping of bismuth and vanadium and grain boundary scattering. These cation-substituted calcium manganites can be used as a potential candidate for an n-type leg in a thermoelectric generator（module）.

关键词： thermoelectric materials solid state reaction Seebeck coefficient power factor

Torsional characteristics of Single Walled carbon Nanotube with Water Interactions by Using Molecular Dynamics Simulation

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Nano-Micro Letters 2014年第3期6卷 268-279页

作者： V.Vijayaraghavan c.h.Wong School of Mechanical and Aerospace Engineering Nanyang Technological University

The torsional characteristics of single walled carbon nanotube(SWcNT) with water interactions are studied in this work using molecular dynamics simulation method. The torsional properties of carbon nanotubes(cNTs) in a hydrodynamic environment such as water are critical for its key role in determining the lifetime and stability of cNT based nano-fluidic devices. The effect of chirality, defects and the density of water encapsulation is studied by subjecting the SWcNT to torsion. The findings show that the torsional strength of SWcNT decreases due to interaction of water molecules and presence of defects in the SWcNT. Additionally,for the case of water molecules encapsulated inside SWcNT, the torsional response depends on the density of packing of water molecules. Our findings and conclusions obtained from this paper is expected to further compliment the potential applications of cNTs as promising candidates for applications in nano-biological and nano-fluidic devices.

关键词： carbon nanotube Water interaction Torsion Water encapsulation Nano-fluid Molecular dynamics

Pocket formula for mass attenuation coefficient, effective atomic number, and electron density of human tissues

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Nuclear Science and Techniques 2019年第3期30卷 1-8页

作者： h.c.Manjunatha L.Seenappa Department of Physics Government College for Women

We have proposed a pocket formula for mass attenuation coefficient(μ/ρ), mass energy absorption coefficient(μ_(en)/ρ), and effective atomic number(Z_(eff)) in different tissues of human organs. We have also assigned a new chemical formula for all studied tissues based on their composition. We have introduced a new parameter called effective composition index(c_(eff)). Based on this, we have introduced a new method to compute the effective atomic number. The evaluated photon interaction parameters are graphically represented. The evaluated average, maximum,minimum, and standard deviations of effective atomic number are tabulated. The proposed formula produces a mass attenuation coefficient, mass energy absorption coefficient, and effective atomic number from their

关键词： Effective atomic number Mass attenuation coefficient Tissues

consolidation and dynamics of 3D unsaturated porous seabed under rigid caisson breakwater loaded by hydrostatic pressure and wave

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Science china(Technological Sciences) 2012年第8期55卷 2362-2376页

作者： YE Jianhong JENG DongSheng chAN A h c Division of civil Engineering University of DundeeDundee DD14HNUK Department of civil Engineering University of BirminghamBirminghamB152TTUK

In this study,based on the dynamic Biot＇s theory ＂u-p＂ approximation,a 3D finite element method（FEM） numerical soil model is developed,in which the Generalized Newmark-β method is adopted to determine the time *** developed 3D FEM soil model is a part of the coupled model PORO-WSSI 3D for 3D wave-seabed-marine structures interaction problem,and is validated by the analytical solution proposed by Wang（2000） for a laterally infinite seabed loaded by a uniform *** adopting the developed 3D soil model,the consolidation of seabed under a caisson breakwater and hydrostatic pressure is *** numerical results show that the caisson breakwater built on seabed has very significant effect on the stresses/displacements fields in the seabed foundation after the transient deformation and primary consolidation are *** parametric study indicates that the Young＇s modulus E of seabed is the most important parameter to affect the settlement of breakwater,and the displacement fields in seabed *** the consolidation status as the initial condition,the interaction between ocean wave,caisson breakwater and seabed foundation is briefly *** 3D ocean wave is determined by solving the Navier-Stokes equations with finite volume method（FVM）.The numerical results indicate that there is intensive interaction between oceean wave, caisson breakwater and seabed foundation; and the breakwater indeed can effectively block the wave energy propagating to the coastline.

关键词： consolidation wave-seabed-breakwater interaction unsaturated seabed breakwater Biot's theory Navier-Stokes equation

high-cycle Fatigue Life Extension of Glass Fiber/Polymer composites with carbon Nanotubes

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Journal of Wuhan University of Technology(Materials Science) 2009年第2期24卷 167-173页

作者： christopher S Grimmer c K h Dharan Berkeley composites Laboratory University of California 5135 Etcheverry Hall Berkeley CA94720-1740 USA

The present work shows that the addition of small volume fractions of multi-walled carbon nanotubes （cNTs） to the matrix results in a significant increase in the high-cycle fatigue life. It is proposed that carbon nanotubes tend to inhibit the formation of large cracks by nucleating nano-scale damage zones. In addition, the contribution to energy absorption from the fracture of nanotubes bridging across nano-scale cracks and from nanotube pull-out from the matrix are mechanisms that can improve the fatigue life. An energy-based model was proposed to estimate the additional strain energy absorbed in fatigue. The distributed nanotubes in the matrix appear to both distribute damage as well as inhibit damage propagation resulting in an overall improvement in the fatigue strength of glass fiber composites.

关键词： glass fiber composites carbon nanotubes fatigue strain energy

System Dynamic Modelling of Patient Flow and Transferral Problem in a Mixed Public-Private healthcare System:A case Study of hong Kong SAR

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Journal of Systems Science and Systems Engineering 2020年第5期29卷 590-608页

作者： c.K.M.LEE W.c.TAI Kam K.h.NG Department of Industrial and Systems Engineering The Hon g Kong Polytechnic UniversityHung HornHong Kong SARChina School of Mechanical and Aerospace Engineering Nanyang Technological University50 Nanyang AvenueSingapore 639798Singapore

The current healthcare system in hong Kong is experiencing pressure due to constrained resources,with dramatic increases in inpatient services queue lengths,dissatisfaction with the working environment,unacceptable workforce arrangements and high turnover rate of hospital *** maintain the robustness of the healthcare system and a sustainable inpatients flow,the Food and health Bureau launched a public-private partnership programme to utilise the resources of the public and private *** research investigates the potential for extension of the programme and further enhancing the sustainability of the long-term inpatient services under a mixed public-private healthcare policy via system dynamic *** findings show that an increase of human resources in public hospitals does not substantially improve inpatient flow rate ***,the results from the system dynamic approach provide insights into the expansion of the service areas of the programme and suggest increasing the number of referrals to private hospitals.

关键词： System dynamic models scenario analysis inpatient transferral mixed public-private healthcare system

The use of the node-based smoothed finite element method to estimate static and seismic bearing capacities of shallow strip footings

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第1期14卷 180-196页

作者： h.c.Nguyen T.Vo-Minh Department of civil and environmental engineering imperial college londonuk Department of civil engineering and industrial design university of liverpoolliverpooluk Faculty of civil engineering ho chi minh city university of technology(hutech)ho chi minh cityviet nam

The node-based smoothed finite element method(NS-FEM)is shortly presented for calculations of the static and seismic bearing capacities of shallow strip footings.A series of computations has been performed to assess variations in seismic bearing capacity factors with both horizontal and vertical seismic *** results obtained agree very well with those using the slip-line method,revealing that the magnitude of the seismic bearing capacity is highly dependent upon the combinations of various directions of both components of the seismic *** upward vertical seismic acceleration reduces the seismic bearing capacity compared to the downward vertical seismic acceleration in *** addition,particular emphasis is placed on a separate estimation of the effects of soil and superstructure inertia on each seismic bearing capacity *** the effect of inertia forces arising in the soil on the seismic bearing capacity is non-trivial,and the superstructure inertia is the major contributor to reductions in the seismic bearing *** tables and charts are given for practical application to the seismic design of the foundations.

关键词： Limit analysis Node-based smoothed finite element method(NS-FEM) Second-order cone programming(SOcP) Seismic bearing capacity Strip footing

Recent progress of interconnecting layer for tandem organic solar cells

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Science china chemistry 2017年第4期60卷 460-471页

作者： Shunmian Lu Dan Ouyang Wallace c.h. choy Department of Electrical and Electronic Engineering The University of Hong Kong Pok Fu Lam Road Hong Kong China

This paper has reviewed:(1) the two unique advantages of tandem organic solar cells(OScs) compared to single OScs;(2) the challengings as well as strategies to develop qualified interconnecting layer(IcL) for tandem *** specifically,firstly,the two key advantages unique to tandem OScs as compared to single OScs,namely minimizing sub-bandgap transmission and thermalization loss as well as realizing optical thick and electrical thin structures,have been ***,the IcL,as one of the most challenging issue in tandem OScs that needs to fulfill the optical,electrical and mechanical requirements simultaneously to realize a qualified IcL has been *** one of the most challenging requirement among the three,the electrical requirement and its corresponding three different solving strategies have been discussed in detail,revealing a bright future for developing a general strategy to realizing qualified IcL composed of different hole transporting layer(hTL) and electron transporting layer(ETL).

关键词： tandem organic solar cell interconnecting layer