The steric effect of aromatic pendant groups and electrical bistability in π-stacked polymers for memory devices

In order to investigate the steric effect of aromatic pendant groups and the electrical bistability in nonconjugated polymers potentially for memory device applications, two π-stacked polymers with different steric structures are synthesized and characterized. They exhibit two conductivity states and can be switched from an initial low-conductivity (OFF) state to a high-conductivity (ON) state. Additionally, they demonstrate nonvolatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 10(4), and flash memory behavior with an ON/OFF current ratio of approximately 10(5). Both steady-state and time-resolved fluorescence spectroscopies are used to examine the conformational change of the polymers responding to an applied external electrical voltage. The results provide useful information on different steric effects of pendant groups in polymer chains, resulting in various electrical behaviors. The possibility in realizing an "erasable" behavior through breaking π-stacked structures of pendant groups by a reversal of the electric field was also discussed on the basis of temperature-dependent fluorescence spectroscopy investigation. These results may thus offer a guideline for the design of practical polymer memory devices via tuning steric structure of π-stacked polymers.     

Effects of oxygen partial pressure on resistive switching characteristics of ZnO thin films by DC reactive magnetron sputtering

Cu/ZnO/n⁺-Si structures were prepared by magnetron sputtering of a layer of ZnO thin film onto heavily doped silicon substrate, followed by thermal evaporation of a thin layer of metallic Cu. The resistive switching characteristics of Cu/ZnO/n⁺-Si structures were investigated as a function of oxygen partial pressure during ZnO deposition. Reproducible resistive switching characteristics were observed in ZnO thin films deposited at 20%, 33% and 50% oxygen partial pressure ratios while ZnO thin film deposited at 10% oxygen partial pressure ratio did not show resistive switching behavior. The conduction mechanisms in high and low resistance states are dominated by space-charge-limited conduction and ohmic behavior respectively, which suggests that resistive switching behaviors in such structures are related to filament formation and rupture. It is also found that the reset current decreases as oxygen partial pressure increases, due to the variation of oxygen vacancy concentration in the ZnO thin films.     

带非线性扩散项的脉冲时滞抛物方程的振动性与渐近性

研究一类带非线性扩散项的脉冲时滞抛物方程在Dirichlet边值条件下的振动性问题,借助脉冲时滞微分不等式,建立了该类方程一切解u(x,t)振动或者limt→+∞∫Ωu(x,t)dx=0的若干新的充分性判据.     

Influence of alkyl length on properties of piezofluorochromic aggregation induced emission compounds derived from 9,10-bis[(N-alkylphenothiazin-3-yl)vinyl]anthracene

Three 9,10-bis[(N-alkylphenothiazin-3-yl)vinyl]anthracene derivatives with different propyl, hexyl, and dodecyl side chains (AnPh₃, AnPh₆, and AnPh₁₂) were synthesized and confirmed by standard spectroscopic methods. All of the compounds exhibited obvious aggregation induced emission (AIE) and piezofluorochromic (PFC) properties. The PFC behaviors were investigated and showed that proportional alkyl-length dependent relationship existed not only in the ground states of the compounds, but also in the melted states compared with the fumed states of the compounds. The PFC mechanism was explored and ascribed to the crystalline–amorphous phase transformation. More importantly, these derivatives showed reversible significant PFC properties and reproducibility in various states including fumed, ground, annealed, and melted states, making them promising stimuli-responsive and smart luminescent materials for pressure-sensors, information-recording, and light-emitting device applications.     

Oscillation Results for BVPs of Even Order Nonlinear Neutral Partial Differential Equations

A class of boundary value problems (BVPs) of even order neutral partial functional differential equations with continuous distribution delay and nonlinear diffusion term are studied. By applying the integral average and Riccati’s method, the high-dimensional oscillatory problems are changed into the one-dimensional ones, and some new sufficient conditions are obtained for oscillation of all solutions of such boundary value problems under first boundary condition. The results generalize and improve some results of the latest literature.     

Clifford分析中多个未知函数向量的非线性边值问题

设fi（x），1≤i≤p为取值在实2n－1维代数An（R）上的函数．我们称F（x）＝（f1，f2，...，fp）为函数向量，而fi，1≤i≤p为向量F的分量，本文借助于向量值分析的思想，利用积分方程方法、Shauder不动点原理和压缩映射原理研究多个未知函数的函数向量F带位移又带共轭值的四元素非线性过值问题解的存在性和相应线性边值问题解的存在唯一性．     

New thermally stable aggregation-induced emission enhancement compounds for non-doped red organic light-emitting diodes

New thermally stable aggregation-induced emission enhancement compounds were synthesized. A non-doped red device showed a maximum brightness of 13,535 cd m(-2), a maximum current efficiency of 6.81 cd A(-1), a maximum power efficiency of 4.96 lm W(-1) and a low turn-on voltage of 4.3 V.     

Combustion characteristics in a supersonic combustor with hydrogen injection upstream of cavity flameholder

Combustion characteristics in a supersonic combustor with hydrogen injection upstream of a cavity flameholder were investigated both experimentally and numerically. The combustion was observed to be stabilized in the cavity mode around the shear layer via a dynamic balance and then spread into the main stream in the region around the jet centerplane where the flow was decelerated and turned to the main stream, supplying a favorable condition for the combustion to spread. The combustion spreading from the cavity shear layer to the main stream seemed to be dominated not only by the traditional diffusion process but also by the convection process associated with the extended recirculation flows resulting from the heat release and the interaction between the jet and the cavity shear layer. Therefore, the cavity-stabilized combustion appeared to be a strongly coupled process of flow and heat release around the cavity flameholder.