Characterizing and Generating Bivariate Empirical Rank Distributions Satisfying Certain Positive Dependence Concepts

Abstract

This article introduces an approach for characterizing the classes of empirical distributions that satisfy certain positive dependence notions. Mathematically, this can be expressed as studying certain subsets of the class S_N of permutations of 1, …, N, where each subset corresponds to some positive dependence notions. Explicit techniques for it-eratively characterizing subsets of S_N that satisfy certain positive dependence concepts are obtained and various counting formulas are given. Based on these techniques, graph-theoretic methods are used to introduce new and more efficient algorithms for constructively generating and enumerating the elements of various of these subsets of S_N. For example, the class of positively quadrant dependent permutations in S_N is characterized in this fashion.     

基于机器视觉的点餐自动提示器设计

针对在外就餐中的盲目消费,不健康饮食等问题,提出基于机器视觉的点餐自动提示器系统;从组成系统的关键软硬件技术入手,基于光源设计、镜头及图像采集卡的选择、图像处理控制系统的设计集成,分析了系统的工作原理,设计了系统的原理结构,并在此基础上进行了原型设计;最后通过对原型系统实践应用得到的数据分析,表明该设计有助于实现科学点餐,文明就餐的预期目标,在成本得到进一步控制的前提下具有一定的应用前景。     

Synthesis and Liquid Crystalline Behavior of Random Copolymer of Poly(ethylene oxide) Macromonomer and Liquid Crystalline Monomer by the Photon Transmission Technique

Random copolymers of poly(ethylene oxide) macromonomer with p‐vinylbenzyl end‐functional group (PEOVB) and liquid crystalline monomer, namely 6‐(4‐cyanobiphenyl‐4′‐oxy)hexyl acrylate (COA), were prepared by conventional free radical polymerization. A living anionic polymerization technique was employed for the synthesis of PEO macromonomers bearing p‐vinylbenzyl moiety at one end. The photon transmission method was also applied to study the phase transitions of COA monomer and its random copolymer with PEO. It was found that, for both samples, the nematic‐smectic A transition is continuous, but the critical fluctuation regions do not allow to obtain 3D XY values. Instead, we have obtained the values close to mean field regime. Scaling of thermal hystersis for random copolymer sample near the nematic‐isotropic transition was studied as well. Thermal hysteresis loops were produced under linearly varying temperature. It was shown that the areas of the hysteresis loops scale with the temperature scanning rate with an exponent being equal to 0.614 which is in good agreement with the field‐theoretical value.     

Flow-induced ordering of particles and flow velocity profile transition in a tube flow of graphene oxide dispersions

We measured the S- and P-order parameters of flow-induced ordered graphene oxide (GO) particles and the flow velocity profiles for a flowing aqueous GO dispersion in a tube, by using an optical method. The order parameters clearly exhibit increasing concentric biaxial ordering as the flow velocity increases, with the exception of a disordered centre. Newtonian to non-Newtonian transition in the flow velocity profile is found, changing from a parabolic shape to a fuller shape at very low Reynolds numbers less than 10. This is attributed to the shear thinning effect (i.e., an ordering-induced reduction in viscosity). In the Newtonian flow, a uniaxial ordering was dominant; whereas a biaxial ordering sharply increased in the non-Newtonian flow, indicating that both the ordering of GO particles and the interparticle interactions influence the flow profile transition.     

Microstructures and soft magnetic properties of Fe80P20-xSix (x = 4.5–6.5) amorphous ribbons

Fe-based amorphous ribbons with excellent soft magnetic properties and mechanical properties were prepared in the Fe–Si–P ternary system. Enhanced soft magnetic properties could be achieved through annealing treatment of the ribbons for 1 h at 325 °C, which is far below the glass transition temperatures (462–474 °C). Icosahedral medium-range ordering with a size range of around 2 nm occurred throughout the amorphous matrix during the low-temperature annealing treatment. The annealed ribbons exhibited improved magnetic saturation of over 185 emu/g while maintaining good mechanical flexibility. During icosahedral ordering, the distance between the Fe atoms and the coordination number within the amorphous ribbon can be optimised for achieving high magnetic saturation. However, nanocrystallisation of the SiP and Fe₂P transition phases embedded within the amorphous matrix occurred after the annealing treatment for 1 h at 385 °C, which caused deterioration of the soft magnetic properties and mechanical flexibility of the ribbons. Therefore, the combination of high magnetic saturation and mechanical flexibility of the amorphous ribbons could be optimised through low-temperature annealing treatment without any nanocrystallisation.     

Time‐resolved investigation of Cu(In,Ga)Se2 growth and Ga gradient formation during fast selenisation of metallic precursors

Ga segregation at the backside of Cu(In,Ga)Se₂ solar cell absorbers is a commonly observed phenomenon for a large variety of sequential fabrication processes. Here, we investigate the correlation between Se incorporation, phase formation and Ga segregation during fast selenisation of Cu–In–Ga precursor films in elemental selenium vapour. Se incorporation and phase formation are analysed by real‐time synchrotron‐based X‐ray diffraction and fluorescence analysis. Correlations between phase formation and depth distributions are gained by interrupting the process at several points and by subsequent ex situ cross‐sectional electron microscopy and Raman spectroscopy. The presented results reveal that the main share of Se incorporation takes place within a few seconds during formation of In–Se at the top part of the film, accompanied by outdiffusion of In out of a ternary Cu–In–Ga phase. Surprisingly, CuInSe₂ starts to form at the surface on top of the In–Se layer, leading to an intermediate double graded Cu depth distribution. The remaining Ga‐rich metal phase at the back is finally selenised by indiffusion of Se. On the basis of a proposed growth model, we discuss possible strategies and limitations for the avoidance of Ga segregation during fast selenisation of metallic precursors. Solar cells made from samples selenised with a total annealing time of 6.5 min reached conversion efficiencies of up to 14.2 % (total area, without anti‐reflective coating). The evolution of the Cu(In,Ga)Se₂ diffraction signals reveals that the minimum process time for high‐quality Cu(In,Ga)Se₂ absorbers is limited by cation ordering rather than Se incorporation. Copyright © 2014 John Wiley & Sons, Ltd.     

Phase behavior of amphiphiles at liquid crystals/water interface: A coarse-grained molecular dynamics study

We present a coarse-grained molecular dynamics simulation study of phase behavior of amphiphilic monolayers at the liquid crystal （LC）/water interface. The results revealed that LCs at interface can influence the lateral ordering of amphiphiles. Particularly, the amphiphile tails along with perpendicularly penetrated LCs between tails undergo a two-dimension phase transition from liquid-expanded into a liquid-condensed phase as their area density at interface reaches 0.93. While, the liquid-condensed phase of the monolayer never appears at oil/water interface with isotropic shape oil particles. These findings reveal the penetration of anisotropic LC can promote ordered lateral organization of amphiphiles. Moreover, we find the phase transition point is shifted to lower surface coverage of amphiphiles when the LCs have larger affinity to the amphiphile tails.     

熵驱大分子胶体粒子的柱状受限结晶

熵是物理化学的基本状态参量,在统计力学和热力学中处于核心位置.按照玻尔兹曼的微观解释,熵可以由孤立系统微观状态的数目(W)给出,即S=kBlnW,这里kB为玻尔兹曼常数[1,2].根据此公式,微观状态数越多,系统越混乱,熵越大,所以熵常被视作体系无序程度的度量.但熵增仅对应体系微观状态数的增加,与可观测的结构有序程度无关[3~5].在一些典型的软物质体系中,结构越有序熵反而越大,如胶体硬球在随机密堆积点的有序结晶[6]及描述各向异性棒状分子从各向同性相到向列相转变的Onsager原理[7].     

Ordered Solid‐State Microstructures of Conjugated Polymers Arising from Solution‐State Aggregation

Controlling the solution‐state aggregation of conjugated polymers for producing specific microstructures remains challenging. Herein, a practical approach is developed to finely tune the solid‐state microstructures through temperature‐controlled solution‐state aggregation and polymer crystallization. High temperature generates significant conformation fluctuation of conjugated backbones in solution, which facilitates the polymer crystallization from solvated aggregates to orderly packed structures. The polymer films deposited at high temperatures exhibit less structural disorders and higher electron mobilities (up to two orders of magnitude) in field‐effect transistors, compared to those deposited at low temperatures. This work provides an effective strategy to tune the solution‐state aggregation to reveal the relationship between solution‐state aggregation and solid‐state microstructures of conjugated polymers.