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| 1 | Study onpreparation of mesoporous silica aerogels with low densityand high properties via ambient pressure drying显示文摘 | Geng Gangqiang Bi Weitao Zhang Yu | 2011 | Peo-ples R China2011，，： | 1 |
| 2 | Three distinct optical-switching states in phase-change materials containing impurities:From physical origin to material design显示文摘Ge2 Sb2 Te5 is the most widely utilized chalcogenide phase-change material for non-volatile photonic applications,which undergoes amorphous-cubic and cubic-hexagonal phase transition under external excitations.However,the cubic-hexagonal optical contrast is negligible,only the amorphous-cubic phase transition of Ge_(2)Sb_(2)Te_(5) is available.This limits the optical switching states of traditional active displays and absorbers to two.We find that increasing structural disorder difference of cubic-hexagonal can increase optical contrast close to the level of amorphous-cubic.Therefore,an amorphous-cubichexagonal phase transition with high optical contrast is realized.Using this phase transition,we have developed display and absorber with three distinct switching states,improving the switching performance by 50%.Through the combination of first-principle calculations and experiments,we reveal that the key to increasing structural disorder difference of amorphous,cubic and hexagonal phases is to introduce small interstitial impurities(like N)in Ge2 Sb2 Te5,rather than large substitutional impurities(like Ag)previously thought.This is explained by the formation energy and lattice distortion.Based on the impurity atomic radius,interstitial site radius and formation energy,C and B are also potential suitable impurities.In addition,introducing interstitial impurities into phase-change materials with van der Waals gaps in stable phase such as GeSb_(4) Te_(7),GeSb_(2) Te_(4),Ge_(3)Sb_(2) Te_(6),Sb_(2)Te_(3) will produce high optical contrast amorphous-metastable-stable phase transition.This research not only reveals the important role of interstitial impurities in increasing the optical contrast between metastable-stable phases,but also proposes varieties of candidate matrices and impurities.This provides new phase-change materials and design methods for non-volatile optical devices with multi-switching states. | Chaobin Bi Kaicheng Xu Chaoquan Hu Ling Zhang Zhongbo Yang Shuaipeng Tao Weitao Zheng | 2021 | Journal of Materials Science & Technology2021，，16： | 1 |
| 3 | β-distribution for Reynolds stress and turbulent heat flux in relaxation turbulent boundary layer of compression ramp显示文摘A challenge in the study of turbulent boundary layers(TBLs) is to understand the non-equilibrium relaxation process after separation and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model. | YanChao Hu WeiTao Bi ShiYao Li ZhenSu She | 2017 | Science China(Physics,Mechanics & Astronomy)2017，60，12： | 0 |
| 4 | Accurately predicting hypersonic transitional flow on cone via a symmetry approach显示文摘A new algebraic transition model is proposed based on a Structural Ensemble Dynamics(SED)theory of wall turbulence,for accurately predicting the hypersonic flow heat transfer on cone.The model defines the eddy viscosity in terms of a two-dimensional multi-regime distribution of a Stress Length(SL)function,and hence is named as SED-SL.This paper presents clear evidence of precise predictions of transition onset location and peak heat flux of a wide range of hypersonic Transitional Boundary Layers(TrBL)around straight cone at zero incidence,to an unprecedented accuracy as validated by over 70 measurements for varying five crucial influential factors(Mach number,temperature ratio,cone half angle,nose Reynolds number and noise level).The results demonstrate the universality of the postulated multi-regime similarity structure,in characterizing not only the spatial non-uniform distribution of the eddy viscosity in hypersonic TrBL on cone,but also the dependence of the transition onset location on the five influential factors.The latter yields a novel correlation formula for transition center Reynolds number which takes similar functional form as the SL function within the symmetry approach.It is concluded that the SED-SL model simulates TrBL around cone with uniformly high accuracy,and then points out to an optimistic alternative way to construct hypersonic transition model. | Weitao BI Kexin ZHENG Zhou WEI Zhensu SHE | 2023 | Chinese Journal of Aeronautics2023，36，7： | 0 |
| 5 | Multi-layer analytic solution for k-ωmodel equations via a symmetry approach显示文摘Despite being one of the oldest and most widely-used turbulence models in engineering computational fluid dynamics(CFD),the k-ωmodel has not been fully understood theoretically because of its high nonlinearity and complex model parameter setting.Here,a multi-layer analytic expression is postulated for two lengths(stress and kinetic energy lengths),yielding an analytic solution for the k-ωmodel equations in pipe flow.Approximate local balance equations are analyzed to determine the key parameters in the solution,which are shown to be rather close to the empirically-measured values from the numerical solution of the Wilcox k-ωmodel,and hence the analytic construction is fully validated.The results provide clear evidence that the k-ωmodel sets in it a multilayer structure,which is similar to but different,in some insignificant details,from the Navier-Stokes(N-S)turbulence.This finding explains why the k-ωmodel is so popular,especially in computing the near-wall flow.Finally,the analysis is extended to a newlyrefined k-ωmodel called the structural ensemble dynamics(SED)k-ωmodel,showing that the SED k-ωmodel has improved the multi-layer structure in the outer flow but preserved the setting of the k-ωmodel in the inner region. | Fan TANG Weitao BI Zhensu SHE | 2023 | Applied Mathematics and Mechanics(English Edition)2023，44，2： | 0 |
| 6 | New design for highly durable infrared-reflective coatings显示文摘The fundamental challenge in designing durable infrared-reflective coatings is achieving the ideal combination of both high reflectivity and durability.Satisfying these competing demands is traditionally achieved by deposition of durable layers on highly reflective metals.We overturn the traditional logic of‘first reflectivity and then durability’and propose an alternative of‘first durability and then reflectivity’:First,a transition-metal compound is selected as a durable base;then its reflectivity is improved by incorporating silver/gold to form an alloy or by overcoating a multilayer stack.Two validation experiments prove that the new strategy works extremely well:the coatings thus obtained have infrared reflectivities close to that of aluminum,and their hardness and acid and salt corrosion resistances are 27–50,400–1500 and 7500–25000 times that of aluminum.The traditional mirror coating(e.g.,Al/SiO2 films)is more suitable for moderate environments,while our mirror coating that was obtained by the new strategy(e.g.,an Ag-doped hafnium nitride film)is more suitable for harsh environments,such as ones with dust,windblown sand,moisture,acid rain or salt fog.This work opens up new opportunities for highly durable infrared-reflective coatings and rejuvenates the study of transition metal compounds in a completely new area of optics. | Chaoquan Hu Jian Liu Jianbo Wang Zhiqing Gu Chao Li Qian Li Yuankai Li Sam Zhang Chaobin Bi Xiaofeng Fan Weitao Zheng | 2017 | Light(Science & Applications)2017，6，1： | 0 |
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