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Shihao Cao,Rongshan Yang,Luhui Shi,Jiali Li,Xueyi Liu 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.2
In the areas which have rich rain and poor drainage, there may be obvious water damage existed in the interlamination of ballastless track. The damage is mainly caused by repeated hydraulic fracturing. Aimed at this problem, the calculation model of water pressure under the train load was established on the basis of fluid-structure interaction theory, and the influence of crack geometry and train operation condition on water pressure were analyzed. The results show that, when the train is close to and far away from the location of the crack, the water pressure changes periodically under the train load, and the pressure peak occurs at the crack front. Simultaneously, the positive and negative pressure may both exist in the crack. The crack geometry affects the distribution of water pressure significantly, the value of water pressure is inversely proportional to the vertical opening of crack, and proportional to the cubic polynomial of horizontal crack depth. The water pressure increases firstly with the increase of longitudinal crack length, then decreases gradually and tends to be stable finally. The train operation condition is also an important factor affecting the distribution of water pressure, the value of water pressure is linear with the axle load, and proportional to the square of train speed. These research results will provide a hydraulic boundary condition for further study of water damage mechanism.
Effects of ion irradiation on microstructure and properties of zirconium alloysdA review
Chunguang Yan,Rongshan Wang,Yanli Wang,Xitao Wang,Guanghai Bai 한국원자력학회 2015 Nuclear Engineering and Technology Vol.47 No.3
Zirconium alloys are widely used in nuclear reactors as structural materials. During the operation, they are exposed to fast neutrons. Ion irradiation is used to simulate the damage introduced by neutron irradiation. In this article, we briefly review the neutron irradiation damage of zirconium alloys, then summarize the effect of ion irradiation on microstructural evolution, mechanical and corrosion properties, and their relationships. The microstructure components consist of dislocation loops, second phase precipitates, and gas bubbles. The microstructure parameters are also included such as domain size and microstrain determined by X-ray diffraction and the S-parameter determined by positron annihilation. Understanding the relationships of microstructure and properties is necessary for developing new advanced materials with higher irradiation tolerance.
Why is the number of superplumes so limited?
Xiong Xiong,Uk Han,Rongshan Fu,Jiwen Teng 한국지질과학협의회 2002 Geosciences Journal Vol.6 No.2
Numerical simulation shows that the hot plumescan be formed by the self-accelerated process if local thermal per-turbation is present. Since the local thermal perturbation mayexist extensively near the CMB and the transition zone around670 km, the number of the hot plumes should be great. The coldplume seems to be originated by the subduction slabs. Because thesubduction belts distribute extensively on the Earths surface, thenumber of the cold plume should be also great. However, theobserved number of the superplumes is much less than the sup-posed ones. A simple 2D model of whole mantle convection isdesigned to investigate the interaction between plumes and ther-mal anomalies. The hot thermal anomalies (HTA) are imposed atCMB and a depth of about 670 km discontinuity, corresponding totwo plausible locations of the hot plumes origination. And, the coldthermal anomalies (CTA) are imposed near the surface and670 km discontinuity, corresponding to the subducted slabs andpossible accumulation of slabs at 670 km discontinuity. Thenumerical results show that the fixed HTA does not originate anew plume. It draws the hot plume to move towards itself and sta-bilizes the plume at its own position. The imposed free HTA movestowards the hot plume, and finally merge with the plume. The sit-uation for the CTA is similar to that for the hot one. From thenumerical results, we can reach the following conclusions. It isvery dificult for the HTA/CTA to originate a new hot/cold plumein a convective flow field. The boundary instability is suppressedby the developed plumes. Instead of originating new hot/coldplumes, the HTA/CTA interact with the plumes to form hugesuperplumes. This might be one reason for the question, why thenumber of the superplumes is so limited.
Optical and structural investigation of stacked Ge quantum dots
Ning Deng,Peiyi Chen,Rongshan Wei,Zhijian Li 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
Stacked Ge quantum dots were grown on Si(100) by ultra-high vacuum chemical vapor deposition( UHV/CVD). The morphology and the size distributions of stacked Ge dots were investigated by AFM and TEM. The in uences of the number of layers and thickness of Si spacer layers on upper Ge dots were investigated. Results show that the total density of upper Ge dots decreases with increasing of the number of layers. To obtain vertical correlated Ge dots, the thickness of Si spacer layers should be smaller than 48nm. Obvious blueshift (87meV) observed from PL spectrum under 10K demonstrates strong quantum connement in Ge dots. FWHM of Ge dots NP peak is about 46meV that indicates the narrow size distribution of stacked Ge dots grown by UHV/CVD. Finally, a photodetector using stacked Ge quantum dots as active region was demonstrated as well.
Application of the French Codes to the Pressurized Thermal Shocks Assessment
Mingya Chen,Guian Qian,Jinhua Shi,Rongshan Wang,Weiwei Yu,Feng Lu,Guodong Zhang,Fei Xue,Zhilin Chen 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.6
The integrity of a reactor pressure vessel (RPV) related to pressurized thermal shocks (PTSs)has been extensively studied. This paper introduces an integrity assessment of an RPVsubjected to a PTS transient based on the French codes. In the USA, the “screening criterion”for maximum allowable embrittlement of RPV material is developed based on theprobabilistic fracture mechanics. However, in the French RCC-M and RSE-M codes, whichare developed based on the deterministic fracture mechanics, there is no “screening criterion”. In this paper, the methodology in the RCC-M and RSE-M codes, which are used forPTS analysis, are firstly discussed. The bases of the French codes are compared with ASMEand FAVOR codes. A case study is also presented. The results show that the method in theRCC-M code that accounts for the influence of cladding on the stress intensity factor (SIF)may be nonconservative. The SIF almost doubles if the weld residual stress is considered. The approaches included in the codes differ in many aspects, which may result in significantdifferences in the assessment results. Therefore, homogenization of the codes inthe long time operation of nuclear power plants is needed.