A three-layer structure model for the effect of a soft middle layer on Love waves propagating in layered piezoelectric systems

A three-layer structure model is proposed for investigating the effect of a soft elastic middle layer on the propagation behavior of Love waves in piezoelectric layered systems, with "soft" implying that the bulk-shear-wave velocity of the middle layer is smaller than that of the upper sensitive layer. Dispersion equations are obtained for unelectroded and traction-free upper surfaces which, in the limit, can be reduced to those for classical Love waves. Systematic parametric studies are subsequently carried out to quantify the effects of the soft middle layer upon Love wave propagation, including its thickness, mass density, dielectric constant and elastic coefficient. It is demonstrated that whilst the thickness and elastic coefficient of the middle layer affect significantly Love wave propagation, its mass density and dielectric constant have negligible influence. On condition that both the thickness and elastic coefficient of the middle layer are vanishingly small so that it degenerates into an imperfectly bonded interface, the three-layer model is also employed to investigate the influence of imperfect interfaces on Love waves propagating in piezoelectric layer/elastic substrate systems. Upon comparing with the predictions obtained by employing the traditional shear-lag model, the present three-layer structure model is found to be more accurate as it avoids the unrealistic displacement discontinuity across imperfectly bonded interfaces assumed by the shearlag model, especially for long waves when the piezoelectric layer is relatively thin.     

SHEAR-HORIZONTAL WAVES IN A ROTATED Y-CUT QUARTZ PLATE WITH AN ISOTROPIC ELASTIC LAYER OF FINITE THICKNESS

We study shear-horizontal (SH) waves in a rotated Y-cut quartz plate carrying an isotropic elastic layer of finite thickness.The three-dimensional theories of anisotropic elasticity and isotropic elast...     

ITER第一壁实验件的铍-铜连接界面分析

在ITER第一壁实验件的研究中,采用热等静压扩散连接技术对Be与CuCrZr合金进行连接实验,对完成扩散连接的部分连接件采用退火处理。对所有连接件进行超声波无损探伤后,检测到未退火的连接件Be/Cu连接界面存在缺陷。为分析扩散界面缺陷产生原因,从连接件的无缺陷区取样并进行界面微观分析。通过观察微观形貌和分析界面扩散层合金元素的变化,发现退火处理过的Be-Cu扩散界面的Cu-Ti扩散层和未扩散的Ti层厚度增加,中间层中Be与Cu元素形成脆性相的几率降低,整个扩散层厚度变大,扩散范围加大。实验表明退火工艺能改变Be/Cu热等静压扩散层连接结构组成,扩大扩散连接范围。     

An explicit analytical expression for bed-load layer thickness based on maximum entropy principle

The present study aims to derive an analytical model on bed-load layer thickness in an open channel turbulent flow carrying sediments. Determination of the thickness of the bed-load layer is of utmost importance in the study of bed-load transport as it is required to determine the bed-load transport rate, as well as in the study of suspended load transport as it acts as reference level for the particles in suspension. Apart from the several deterministic approaches available in the literature, the work adopts probabilistic approach based on entropy theory to determine the bed-load layer thickness. The concept of entropy theory developed by Shannon is used and the method of Lagrange multipliers is employed for the maximization of entropy function to find the least biased probability distribution. To calculate the Lagrange multipliers, present in the probabilistic model of dimensionless bed-load layer thickness, two different methodologies are presented. The model of bed-load layer thickness is a function of dimensionless shear stress and also depends on three other parameters which are found to be functions of specific gravity of sediment particle and dimensionless particle diameter from a non-linear regression analysis. The proposed model is validated with wide sets of experimental data available in literature and a good agreement is achieved. Apart from comparison with data, the model is also compared with existing deterministic model and computation of relative percentage error proves the better efficiency of the present model.     

液体薄层中的超声空化*

液体薄层中的超声空化,因其边界及所处空间的特殊性,而呈现出非常独特的空化结构和演化行为,在超声清洗、超声钎焊、表面处理、近场声悬浮、超声化学等领域都有所应用。该文梳理了近几年该课题组在液体薄层中的超声空化研究中的一些成果,力图揭示液体薄层内空泡、空化云、空化场的运动和分布规律,及其产生、发展和演化过程,以期对液体薄层中的超声空化行为有一个相对清晰和完整的认识。     

Morphology and elemental behaviour in the alteration layer of borosilicate glass in simulated groundwater

To understand the behaviour of nuclear waste glass in groundwater, borosilicate glasses were placed in simulated groundwater for more than 200 days. The composition of the simulated groundwater was similar to that of the groundwater in Beishan (a potential nuclear waste site). The pH value of groundwater was adjusted to 7.5, and the ratio of the surface area of glass to the volume of the solution (SA/V) was set to 10?m^?1. Solutions and bulk glasses were characterised to obtain the elemental behaviour and surface morphology of the glass/solution interface, which was named the alteration layer. The mean thicknesses of the alteration layer were 5.16?±?0.11?µm and 11.67?±?0.28?µm at 70°C and 90°C, respectively. A thicker alteration layer was attributed to the lower surface activation energy of the glass and a high ion exchange between K⁺ and Na⁺ in the interface between the glass surface and the solution. For the elemental behaviour, mobile species B and Na were depleted, while K and Ca from the solution were enriched in the alteration layer due to ion exchange. Network species Si decreased in the layer, leading to the corrosion of the backbone of the glass; however, species Al increased, which implied that some [SiO₄] units were partially replaced by [AlO₄] units. In this work, glass in groundwater suffered much more intense corrosion than that in de-ionised water.     

Quasi-radial wall jets as a new concept in boundary layer flow control

This work aims to introduce a novel concept of wall jets wherein the flow is radially injected into a medium through a sector of a cylinder, called quasi-radial (QR) wall jets. The results revealed that fluid dynamics of the QR wall jet flow differs from that of conventional wall jets. Indeed, lateral and normal propagations of a conventional three-dimensional wall jet are via shear stresses. While, lateral propagation of a QR wall jet is due to mean lateral component of the velocity field. Moreover, discharged Arrays of conventional three-dimensional wall jets in quiescent air lead to formation of a combined wall jet at large distant from the nozzles, while QR wall jet immediately spread in lateral direction, meet each other and merge together very quickly in a short distance downstream of the jet nozzles. Furthermore, in discharging the conventional jets into an external flow, there is no strong interaction between them as they are moving parallel. While, in QR wall jets the lateral components of the velocity field strongly interact with boundary layer of the external flow and create strong helical vortices acting as vortex generators.     

Improved efficiency of small-molecular (S-M) tandem organic solar cells (TOSCs) by employing low work function alloy nanoparticle intermediate layer

We improved the power conversion efficiency (PCE) of the small molecular (S-M) tandem organic solar cells (TOSCs) by employing different low work function alloy nanoparticle intermediate layers. The enhancement of the PCE was mainly attributed to the gap states formed at the interface between the buffer layer and alloy nanoparticle intermediate layer. The gap states result in the disappearance of the electron injection barrier. Compared with the planar heterojunction (PHJ) TOSCs with single Ag nanoparticle intermediate layer, the PCE of the PHJ TOSC with the Mg-Ag alloy nanoparticle intermediate layer exhibits an enhancement of 7.5%. Moreover, the Mg-Ag alloy nanoparticle intermediate layer was also employed in the bulk-heterojunction (BHJ) TOSCs. Compared with the PHJ TOSCs, the PCE of the BHJ TOSCs with Mg-Ag alloy nanoparticle intermediate layer is doubled and achieves a value of 5.54%.     

有机/无机复合双层电子传输层的量子点发光二极管

采用有机/无机复合双层电子传输层（ETL）研制绿色QLEDs,其中有机ETL采用OLED中常见的ETL材料,无机ETL采用ZnO纳米颗粒,并通过调控有机ETL厚度改变电子注入,使电子/空穴达到平衡。制备的器件结构为:ITO/PEDOT:PSS/TFB/QDs/ZnO NPs/TPBI:Liq/Al,其中有机电子传输层TPBI:Liq采用真空蒸镀沉积。与仅采用ZnO电子传输层的器件相比,可以使器件性能得到大幅提升:器件的最大电流效率从11.53 cd/A提升到22.77 cd/A,同时器件的启亮电压、电致发光光谱无明显变化。判断有机ETL的主要作用是抑制了过量电子的注入和传输,在发光亮度变化不大的情况下,降低了器件的无效复合（例如俄歇复合）电流,从而使电流效率明显提升。