探究了含有多个椭球夹杂的双材料和半无限大空间的稳态传热解.双材料的界面由包含连续性条件的双材料空间格林函数考虑,通过调整参数,该函数可退化为半无限大空间或者无限大空间格林函数.利用Eshelby等效夹杂法(equivalent inclusion method,EIM),将椭球夹杂等效为基底材料和夹杂内连续分布的本征温度梯度场.基于含多项式密度的椭球积分,椭球夹杂的扰动作用由本征温度梯度场和双材料格林函数域积分精确描述.本征场由夹杂形心展开的泰勒级数,并通过各个夹杂形心建立的多项式等效热流方程求解,求解精度由有限元法(finite element method,FEM)验证,实现了无网格求解双材料和半无限大空间中多个椭球夹杂的稳态传热问题.
Multi-principal element solid solutions are prone to develop local chemical inhomogeneities,i.e.,chemi-cal order/clustering and/or compositional undulation.However,these structural details from short-range(first couple of nearest-neighbor atomic shells)to nanometer length scale are very challenging to re-solve in both experimental characterization and computer simulations.For instance,Monte Carlo model-ing based on density-functional-theory calculations is severely limited by the sample size and the sim-ulation steps practical in the simulations.Adopting the cluster expansion approach,here we systemati-cally reveal the local chemical inhomogeneity,including chemical order and compositional fluctuation,in three representative equiatomic TiZrNb-based body-centered cubic refractory high-entropy alloys(HEAs):TiZrNb,TiZrHfNb and TiZrHfNbTa.Ti-Zr pairs are found to exhibit the highest degree of chemical pref-erence among all atomic pairs.Such chemical short-range order(CSRO)induces an accompanying com-positional undulation,both extending to characteristic dimensions of the order of one nanometer.The chemical inhomogeneity trend uncovered for this series of TiZrNb-based HEAs is expected to impact their mechanical properties;e.g.,incorporating the CSRO effects in a current model significantly improves its agreement with experimental measured yield strength.
Kaihui XunBozhao ZhangQi WangZhen ZhangJun DingEn Ma
The closed-form solutions of the dynamic problem of heterogeneous piezoelectric materials are formulated by introducing polarizations into a reference medium and using the generalized reciprocity theorem.These solutions can be reduced to the ones of an elastodynamic problem.Based on the effective medium method,these closedform solutions can be used to establish the self-consistent equations about the frequencydependent effective parameters,which can be numerically solved by iteration.Theoretical predictions are compared with the experimental results,and good agreement can be found.Furthermore,the analyses on the effects of microstructure and wavelength on the effective properties,resonance frequencies,and attenuation are also presented,which may provide some guidance for the microstructure design and analysis of piezoelectric composites.
In theory,nanobubbles can stably exist with a lifetime of microseconds at most,but numerous experimental observations demonstrate that nanobubbles in bulk solution can be stable from hours to weeks.Although various conjectures on the stability mechanism of bulk nanobubbles,such as the contaminant mechanism,skin mechanism,surface zeta potential mechanism,are proposed,there has not yet been a unified conclusion.Since bulk nanobubbles show great potential in a wide spectrum of applications and are relevant to a number of unsolved questions on cavitation and nucleation,the debate over their stability mechanisms has been active.In the past,extensive studies have been carried out to understand the mechanism of nanobubble stability,and important insights have already been provided.This paper will provide a brief overview of our current understanding of the unexpected stability of bulk nanobubbles.
We report on the temperature-dependent Schottky barrier in organic solar cells based on PTB7:PC71BM.The ideality factor is found to increase with temperature decreasing,which is explained by a model in which the solar cell is taken as Schottky barrier diode.Accordingly,the dark current in the device originates from the thermally emitted electrons across the Schottky barrier.The fittings obtained with the thermal emission theory are systematically studied at different temperatures.It is concluded that the blend/Ca/Al interface presents great inhomogeneity,which can be described by 2 sets of Gaussian distributions with large zero bias standard deviations.With the decrease of temperature,electrons favor going across the Schottky barrier patches with lower barrier height and as a consequence the ideally factor significantly increases at low temperature.
Brahim Ait AliReda MoubahAbdelkader BoulezharHassan Lassri
