平面空穴流的数值模拟

本文利用各向异性K-ε模型对工程上常见的平面空穴流进行数值模拟,得到了合理的速度场、压力场和其它湍流特征量的分市。不仅如此,还预报了在主流和回流交汇处的多个旋涡结构.精细地模拟了这种复杂的湍流场。

伴有空穴流、液柱分离瞬态过程的实验研究

本文着重介绍了研究伴有空穴流、液柱分离瞬态过程的实验装置和部分实验结果.这套实验装置由主循环回路、水质和含气量处理系统.液体抗拉强度测定系统及测试和控制系统组成.它不仅能得出压力波动过程和空化发展过程,而且能灵活改变和控制主要的初始因素.实验结果包括机理研究和主要的初始因素影响的研究,应用空化理论和气液两相流理论对实验结果进行了分析,得出了一些认识该瞬态过程的实质,防止其危害的有益的结论.

高水头船闸平面阀门底缘空穴流的试验研究

本文主要介绍了船闸平面阀门底缘空穴流的一些初步研究成果,包括五种阀门底缘型式及三种阀门后廊道顶坡扩大比的临界空穴数资料,比较了阀门后廊道连接型式及阀门门槽对临界空穴数的影响。此外,本文还分析讨论了平面阀门临界空穴数变化的一些特性,以及它与反弧形阀门临界空穴数变化特性的一些区别和原因.最后,推荐了较优的阀门底缘型式,可供设计船闸平面阀门时参考。

Numerical Study of Optimization of Layer Thickness in Bilayer Organic Light-Emitting Diodes

A numerical model for bilayer organic light-emitting diodes (OLEDs) is developed under the basis of trapped charge limited conduction.The dependences of the current density on the layer thickness,trap properties and carrier mobility of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure anode/HTL/EML/cathode are numerically investigated.It is found that,for given values of the total thickness of organic layers,reduced depth of trap,total density of trap,and carrier mobility of HTL as well as EML,there exists an optimal thickness ratio of HTL to EML,by which a maximal quantum efficiency can be achieved.Through optimization of the thickness ratio,an enhancement of current density and quantum efficiency of as much as two orders of magnitude can be obtained.The dependences of the optimal thickness ratio to the characteristic trap energy,total density of trap and carrier mobility are numerically analyzed.

The Collapse Intensity of Cavities and the Concentration of Free Hydroxyl Radical Released in Cavitation Flow

Enhancing the chemical reaction processes by means of the energy released in the collapse of micro bubbles or cavities in the cavitation flow is a new research area. In the previous work, a new approach of measuring concentration of free hydroxyl radicals induced in cavitation flow by using methylene blue as the indicator was developed and used to study concentration of free radical induced in Venturi cavitation flow under various experimental conditions. In the present research, the radial evolution of a cavity bubble and the corresponding collapse pressure in sonic cavitation field are obtained by solving three different bubble dynamics equations： Rayleigh equation, Rayleigh-Plesset equation and Gilmore equation. By comparing with the experimental data on the radial evolution of a cavity bubble in the literature, it is found that the predicted results by the Gilmore equation, which takes account of the compressibility of fluid in addition to the viscosity and interfacial tension, agree with the experimental ones better than those by other two equations. Moreover, the theoretically predicted collapse pressures are consistent with the concentration of the free hydroxyl radical induced in the experimental venture. Thus, the concentration of the liberated free hydroxyl radical not only influences the reaction rate but also is used as an available parameter for measuring collapse intensity of cavities.

The Theory of Field-Effect Transistors:XI. The Bipolar Electrochemical Currents(1-2-MOS-Gates on Thin-Thick Pure-Impure Base)

The field-effect transistor is inherently bipolar, having simultaneously electron and hole surface and volume channels and currents. The channels and currents are controlled by one or more externally applied transverse electric fields. It has been known as the unipolar field-effect transistor for 55-years since Shockley＇s 1952 invention,because the electron-current theory inevitably neglected the hole current from over-specified internal and boundary conditions, such as the electrical neutrality and the constant hole-electrochemical-potential, resulting in erroneous solutions of the internal and terminal electrical characteristics from the electron channel current alone, which are in gross error when the neglected hole current becomes comparable to the electron current, both in subthreshold and strong inversion. This report presents the general theory, that includes both electron and hole channels and currents. The rectangular （ x, y, z） parallelepiped transistors,uniform in the width direction （z-axis）,with one or two MOS gates on thin and thick,and pure and impure base, are used to illustrate the two-dimensional effects and the correct internal and boundary conditions for the electric and the electron and hole electrochemical potentials. Complete analytical equations of the DC current-voltage characteristics of four common MOS transistor structures are derived without over-specification： the 1-gate on semi-infinite-thick impure-base （the traditional bulk transistor）, the 1-gate on thin impure-silicon layer over oxide-insulated silicon bulk （SOI） ,the 1-gate on thin impure-silicon layer deposited on insulating glass （SOI TFT）, and the 2-gates on thin pure-base （FinFETs）.

Graphdiyne oxide-accelerated charge carrier transfer and separation at the interface for efficient binary organic solar cells

Interfacial engineering for the regulation of the charge carrier dynamics in solar cells is a critical factor in the fabrication of high-efficiency devices.Based on the successful preparation of highly dispersible graphdiyne oxide(GDYO)with a large number of functional groups,we fabricated organic solar cells employing GDYO-modified poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate)(PEDOT:PSS)as hole transport materials.Results show that theπ±πinteraction between GDYO and PEDOT:PSS is beneficial to the formation of an optimized charge carrier transfer channel and improves the conductivity and charge carrier mobility in the hole transport layer.Moreover,the improved interfacial contact contributes to the suppression of charge carrier recombination and the elevation of charge carrier extraction between the hole transport layer and the active layer.More importantly,the occurrence of charge carrier separation benefits from the optimized morphology of the active layer,which efficiently improves the performance,as proven by the results of transient absorption measurements.Therefore,with the holistic management approach to the multiobjective optimization of the charge carrier dynamics,a photoelectric conversion efficiency of 17.5%(with the certified value of 17.2%)is obtained for binary organic solar cells.All of these results indicate the potential application of the functionalized graphdiyne in the field of organic optoelectronic devices.

Carbon nanotubes assisting interchain charge transport in semiconducting polymer thin films towards much improved charge carrier mobility

Conjugated polymers attracted much attention in the past few decades due to their wide applications in various optoelectronic devices and circuits. The charge transport process in conjugated polymers mainly occurs in the intrachain and interchain parts, where the interchain charge transport is generally slower than intrachain transport and may slow down the whole charge transport properties. Aiming at this issue, herein we employ semiconducting single-walled carbon nanotubes(s-SWNTs) as efficient charge-transporting jointing channels between conjugated polymer chains for improving the charge transport performance. Taking the typical conjugated polymer, ploy-N-alkyl-diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene(PDPP-TT) as an example, polymer thin film transistors(PTFTs) based on the optimized blended films of PDPP-TT/s-SWNTs exhibit an obviously increasing device performance compared with the devices based on pure PDPP-TT films, with the hole and electron mobility increased from 2.32 to 12.32 cm^2 V^-1 s^-1 and from 2.02 to 5.77 cm^2 V^-1 s^-1, respectively. This result suggests the importance of forming continuous conducting channels in conjugated polymer thin films, which can also be extended to other polymeric electronic and optoelectronic devices to promote their potential applications in large-area, low-cost and high performance polymeric electronic devices and circuits.

A-D-A small molecule donors based on pyrene and diketopyrrolopyrrole for organic solar cells

Three new electron donating small molecules （SMs）, Pyr（EH-DPP）2, Pyr（HD-DPP）2 and PyrA（EH-DPP）2, are designed and synthesized through coupling electron rich pyrene core with electron deficient diketopyrrolopyrrole （DPP） terminals, of which the derived organic solar cells （OSCs） exhibit interesting structure-performance correlation. It shows that the tune of their solubilizing side chains and n-bridge for the acceptor-donor-acceptor （A-D-A） SMs can significantly alter the resultant short-circuit current density and power conversion efficiency （PCE） in OSCs. The Pyr（EH-DPP）2 with short side chains displays broader absorption and higher hole mobility than the Pyr（HD-DPP）2 with long side chains. Although showing planar structure, the acetylene bridge-incorporated PyrA（EH-DPP）2 adapts an undesired edge-on packing and strong aggregation in film, leading to non-ideal morphology and poor miscibility with fullerene acceptors. As a result, the PCE of the solar cell based on Pyr（EH-DPP）2 is several times higher than those based on Pyr（HD-DPP）： and PyrA（EH-DPP）2, indicating the A-D-A combination of polyaromatics with DPP would be the promising skeleton for developing photovoltaic semiconductors.