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Nanocrystalline Silicon Thin Films Fabricated at 80℃ by Using Electron Cyclotron Resonance Chemical Vapor Deposition

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Plasma Science and Technology 2010年第5期12卷 608-613页

作者： I.y.y.BU A.J.FLEwITT w.I.MILINE Department of Microelectronics Engineering National Kaohsiung Marine University Electrical Engineering Division Engineering Department Cambridge University

Deposition of nanocrystalline silicon （nc-Si） on glass at very low temperatures by electron cyclotron resonance （ECR） plasma enhanced chemical vapour deposition （PECVD） was investigated. It was shown that nc-Si could be deposited from hydrogen diluted silane gas at a substrate temperature of 80℃ with a crystalline fraction up to 80% and a lateral grain size of around 50 nm. This was achieved by growing the nc-Si in a low pressure regime which ensured that mono-silyl species were the dominant deposition precursor. Furthermore, a high flux of energetic hydrogen ions was required to induce crystallisation of the silicon material through a chemical annealing process.

关键词： low temperature nanocrystalline silicon ECR

Microstructure and mechanical optimization of probeless friction stir spot welded joint of an Al-Li alloy

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Journal of Materials Science & Technology 2018年第10期34卷 1739-1746页

作者： Q. Chu w.y. Li X.w. yang J.J. Shen A. Vairis w.y. Feng w.B. wang State Key Laboratory of Solidification Processing Shaanxi Key Laboratory of Friction Welding Technologies Northwestern Polytechnical University Xi'an710072 China Helmholtz-Zentrum Geesthacht Institute of Materials Research Materials Mechanics Geesthacht 21502 Germany Mechanical Engineering Department TEl of Crete Heraklion Crete 71004 Greece China PSw Center Beijing 100024 China

In this work, a third generation AI-Li alloy has been successfully spot welded with probeless friction stir spot welding （P-FSSw）, which is a variant of conventional friction stir welding. The Box-Behnken exper-imental design in response surface methodology （RSM） was applied to optimize the P-FSSw parameters to attain maximum tensile/shear strength of the spot joints. Results show that an optimal failure load of 7.83 kN was obtained under a dwell time of 7.2 s, rotation speed of 950 rpm and plunge rate of 30 mm/rain. Sufficient dwell time is essential for heat conduction, material flow and expansion of the stir zone to form a sound joint. Two fracture modes were observed, which were significantly affected by hook defect. In addition to mechanical testing, electron backscattering diffraction （EBSD） and differential scanning calorimetry （DSC） were used for microstructure evolution and property analysis. The precipitation of GP zone and AI3Li as well as the ultrafine grains were responsible for the high microhardness in the stir zone.

关键词： Probeless friction stir spot welding Precipitation Mechanical property Fracture mechanism

A wavelength Monitoring System Using Tunable MEMS Filter Calibrated by F-P Laser

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光学学报 2003年第S1期23卷 615-616页

作者： H. y. Tam P. K. A. wai w. H. chung Photonics Research Center Department of Electrical Engineering The Hong Kong Polytechnic University Hong Kong SAR ChinaPhotonics Research Center Department of Electronic and Information Engineering The Hong Kong Polytechnic University Hong Kong SAR ChinaPhotonics Research Center Department of Electrical Engineering The Hong Kong Polytechnic University Hong Kong SAR China

we report a wavelength and power monitoring system based on a scanning MEMS filter as wavelength discriminator and a near threshold-biased Fabry-Perot diode laser as wavelength reference. This system is capable of mon... 详细信息

关键词： DwDM FP LD MEMS A wavelength Monitoring System Using Tunable MEMS Filter Calibrated by F-P Laser by

The effect of downstream resistance on flow diverter treatment of a cerebral aneurysm at a bifurcation: A joint computational-experimental study

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Journal of Hydrodynamics 2018年第5期30卷 803-814页

作者： ANDerson C.O.Tsang Billy y.S.yiu Abraham y.S.Tang w.C.chung Gilberto K.K.Leung AlexANDer K.K.Poon Alfred C.H.yu Simon S.M.Lai K.w.Chow Department of Surgery Li Ka Shing Faculty of Medicine University of Hong Kong Department of Electrical and Computer Engineering University of Waterloo Department of Mechanical Engineering University of Hong Kong Department of Electrical and Electronic Engineering University of Hong Kong

Intracranial aneurysm can lead to hemorrhagic stroke upon rupture. Deployment of flow diverters can restrict the blood flow into aneurysm and mitigate the rupture risk. Computational fluid dynamics（CFD） and ultrasonography with pulse-wave and color Doppler ultrasound measurements were employed jointly to investigate the complex flow pattern in cerebral aneurysms, both before and after the deployment of flow diverters. Patient-specific configurations of both bifurcation and side-wall aneurysms were selected. The effect of downstream flow resistance was investigated by adjusting the volume flow rate and pressure at the outlet vessels computationally and experimentally. Velocity profiles in the aneurysm measured from ultrasonography showed good agreement with those from computer simulations. The discrepancy in velocity between the computational and experimental sets of data is less than 10%. The downstream resistance can alter the volume flux into a bifurcation aneurysm with a flow diverter deployed by 236%, while the corresponding value of a side-wall aneurysm is negligible. The vorticity of the aneurysmal flow was reduced by more than 80% in both cases after stenting. This study demonstrated that careful investigation of downstream flow resistance of a bifurcation aneurysm is essential to provide an accurate assessment of the aneurysmal flow dynamics after flow diverter deployment.

关键词： Intracranial aneurysms computational fluid dynamics (CFD) doppler ultrasound

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

Performance of LIDAR- and radar-based turbulence intensity measurement in comparison with anemometer-based turbulence intensity estimation based on aircraft data for a typical case of terrain-induced turbulence in association with a typhoon

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2013年第7期14卷 469-481页

作者： P.w.CHAN y.F.LEE Hong Kong Observatory

The Hong Kong Observatory (HKO) provides low-level turbulence alerting service for the Hong Kong International Airport (HKIA) through the windshear and turbulence warning system (wTwS). In the wTwS, turbulence intensities along the flight paths of the airport are estimated based upon correlation equations established between the surface anemometer data and the turbulence data from research aircraft before the opening of the airport. The research aircraft data are not available on day-to-day basis. The remote sensing meteorological instruments, such as the Doppler light detection and ranging (LIDAR) and radar, may be used to provide direct measurements of turbulence intensities over the runway corridors. The performances of LIDAR- and radar-based turbulence intensity data are studied in this paper based on actual turbulence intensity measurements made on 423 commercial jets for a typical case of terrain-induced turbulence in association with a typhoon. It turns out that, with the tuning of the relative operating characteristic (ROC) curve between hit rate and false alarm rate, the LIDAR-based turbulence intensity measurement performs better than the anemometer-based estimation of wTwS for turbulence intensity at moderate level or above. On the other hand, the radar-based measurement does not perform as well when compared with wTwS. By combining LIDAR- and radar-based measurements, the performance is slightly better than wTwS, mainly as a result of contribution from LIDAR-based measurement. As a result, the LIDAR-based turbulence intensity measurement could be used to replace anemometer-based estimate for non-rainy weather conditions. Further enhancements of radar-based turbulence intensity measurement in rain would be necessary.

关键词： Fault tolerant High availability quadruple vital computer (HAQVC) Reliability availability maintainability and safety (RAMS)

AN IN-SITU STUDy ON DISLOCATION BEHAVIOR OF CRACK-TIP IN Ti_3Al-Nb ALLOy

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中国有色金属学会会刊：英文版 1997年第3期7卷 31-37页

作者： wu, y Zhen, L yang, DZ Liang, w HARBIN INST TECHNOL SCH MAT SCI & ENGN HARBIN 150001 PEOPLES R CHINA TAIyUAN UNIV TECHNOL DETECTING CTR TAIYUAN 030024 PEOPLES R CHINA

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关键词： Ti 3Al Nb alloy tensile deformation crack propagation dislocation

Programmed cell death in developing human fetal CNS

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Chinese Science Bulletin 2000年第22期45卷 2082-2084页

作者： Chan w.y. Department of Anatomy Faculty of MedicineThe Chinese University of Hong KongShatinN.T.Hong KongChina

The spatial and temporal distributions of programmed cell death (PCD) in developing central nervous system (CNS) of human fetuses ranging from 12 to 39 weeks of gestation were investigated using techniques of flow cytometry and terminal transferase-mediated nick end labeling (TUNEL). The results showed that PCD did occur in every representative brain region of all fetuses examined in different stages. It was found that there were two peaks of PCD appearing at the 12th and 39th weeks respectively, which suggested that the first peak of apoptosis may be involved in the selective elimination of neurons overproduced during the early development and the second may play an important role in establishing the correct neuronal circuitry.

关键词： programmed cell death (PCD) fetus central nervous system development.

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