New insight into the ultra-long lifetime of excitons in organic-inorganic perovskite： Reverse intersystem crossing

Recently, an effective exciton diffusion length L exceeding 100μm has been reported for organic- inorganic halide perovskites owing to both the high mobility and ultra-long lifetime of the excitons; however, the origin of ultra-long L is still unclear in nature. In some photoelectric materials, reverse intersystem crossing （RISC） from the triplet to the singlet state can enhance the quantum yield of pho- toluminescence greatly. In this study, our theoretical investigation indicated that the energy difference △E_st between the singlet state and the triplet state of CH_3NH_3Pbl_3 was less than 0.1 eV, which represents one crucial prerequisite for the occurrence of RISC. Meanwhile, the experimental results showed that the photoluminescence lifetime increased with the increasing temperature, a typical feature of RISC. Based on this study, we put forward the hypothesis that the ultra-long lifetime of excitons in organic-inorganic halide perovskite might be caused by the RISC process. This may provide a new insight into the important photophysical properties of such novel photovoltaic materials.

Room-temperature continuous-wave operation of GaN-based blue-violet laser diodes with a lifetime longer than 1000h

GaN-based continuous-wave operated blue-violet laser diodes(LDs) with long lifetime are demonstrated, which are grown on a c-plane GaN substrate by metal organic chemical vapor deposition with a 10 × 600 μm^2 ridge waveguide structure.The electrical and optical characteristics of a blue-violet LD are investigated under direct-current injection at room temperature(25 °C). The stimulated emission wavelength and peak optical power of the LD are around 413 nm and over 600 mW, respectively.In addition, the threshold current density and voltage are as small as 1.46 kA/cm^2 and 4.1 V, respectively. Moreover, the lifetime is longer than 1000 hours under room-temperature continuous-wave operation.

Long Lifetime Ultracold Plasma Produced by a Nanosecond Laser in a Supersonic Nitric Oxide Molecular Beam Environment

Ultracold plasma provides a possible route to approach the strongly-coupled regime under laboratory conditions. Normally, the lifetime of ultracold plasma is very limited due to plasma heating and expansion mechanisms. We present a new method to generate long lifetime ultracold plasmas consisting mainly of cations and anions. This plasma demonstrates a capability of traversing a DC barrier of up to 5 （or -3） V. The lifetime of this plasma is expected to be more than 250us. Finally, molecular dynamics （MD） simulation is used to explain how anions slow the expansion rate and prolong the lifetime of this plasma.

Atmospheric lifetimes and traveling distances of airborne carcinogenic polycyclic aromatic hydrocarbons

Atmospheric lifetimes and traveling distances of 15 PAHs(Ac:acenaphthylene,Ace:acenaphthene,Ph:phenanthrene,MePh3:3-methyl-phenanthrene,MePh9:9-methyl-phenanthrene,MePh1:1-methyl-phenanthrene,MePh2:2-methyl-phenanthrene,Ret:retene,B[a]A:benzo[a]anthracene,Chry:chrysene,B[b,j,k]F:benzo[b,j,k]fluoranthene,B[e]P:benzo[e]pyrene,B[a]P:benzo[a]pyrene,Ind:indeno[1,2,3-cd]pyrene,B[g,h,i]P:benzo[g,h,i]perylene)at Whitbourne,UK,were estimated by using the rate constants for reaction with OH,O3,and the first order rate constants of eight species of high molecular weight PAHs(i.e.B[a]A,Chry,B[b]F,B[k]F,B[a]P,Ind,B[g,h,i]P and Ret)as a function of humidity,solar intensity and temperature by using Multiple Regression Analysis.The predicted atmospheric lifetime of Ac,Ace,Ph,MePh3,MePh9,MePh2 and MePh1 ranged between 11.42 h-79.12 h in cold period and 1/31 h-14.33 h in warm period respectively.The binary ratios of atmospheric lifetime of B[k]F/B[g,h,i]P,B[k]F/B[g,h,i]P,B[g,h,i]P/Ind and B[k]F/Ind displayed non-significant differences between cold and warm period,indicating that high molecular weight PAHs are difficult to be decomposed by UV light and thus may be conveyed to the rural regions via long range atmospheric transportation(LRAT).The decreased level of the atmospheric lifetime of low molecular weight PAHs in summer can be attributed to an increased level of OH radical content and solar radiation.

Effect of Altitude, Right Ascension of Ascending Node and Inclination on Lifetime of Circular Lunar Orbits

The lifetime of a lunar satellite orbit is constrained by the non-spherical nature of the Moon’s gravity field. The orbital lifetime of lunar orbits depends significantly on the initial conditions of the orbit. Right ascension of ascending node (Ω) is one of the important orbital parameter affecting the orbital lifetime. In the present work we have analyzed the effect of Ω on the variation of lifetime with altitude for circular lunar orbits. It is found that at a particular initial altitude, a small increase in the altitude results in substantial increase in the orbital lifetime due to effect of the long periodic terms of Earth’s gravity on eccentricity and this transition altitude is different for different Ω. Further, it is observed that the variation of transition altitude with Ω follows a definite, but different trend for orbits with different inclinations. The transition altitude for polar orbits is found to be higher without the effect of Sun and Earth gravity. Variation of transition altitude with orbital inclination is also analyzed. Lifetimes of high altitude circular lunar orbits are analyzed and it is observed that at high altitudes lifetime decreases with altitude.

Linker aggregation engineering of TADF materials to tune carrierbalance for highly efficient organic LEDs with long operationallifetime

Thermally activated delayedfluorescence(TADF)molecules are regarded as promis-ing materials for realizing high-performance organic light-emitting diodes(OLEDs).The connecting groups between donor(D)and acceptor(A)units in D–A type TADF molecules could affect the charge transfer and luminescence performance of TADF materials in aggregated states.In this work,we design and synthesize four TADF molecules using planar and twisted linkers to connect the aza-azulene donor(D)and triazine acceptor(A).Compared with planar linkers,the twisted ones(Az-NP-T and Az-NN-T)can enhance A–A aggregation interaction between adjacent molecules to balance hole and electron density.As a result,highly efficient and stable deep-red top-emission OLEDs with a high electroluminescence efficiency of 57.3%and an impressive long operational lifetime(LT_(95)∼30,000 h,initial luminance of 1000 cd m^(-2))are obtained.This study provides a new strategy for designing more effi-cient and stable electroluminescent devices through linker aggregation engineering in donor–acceptor molecules.

One-step rapid synthesis,crystal structure and 3.3 microseconds long excited-state lifetime of Pd1Ag28 nanocluster

Doping foreign atom(s)in metal nanoclusters is an effective strategy to engineer the properties and functionalities of metal nanoclusters.However,until now,to dope Pd atom into Ag nanoclusters remains a huge challenge.Here we develop a one-step rapid method to synthesize the Pd-doped Ag nanocluster with high yield.The prepared Pd1Ag28 nanocluster was characterized by mass spectroscopy,X-ray photoelectron spectroscopy,X-ray crystallography,fluorescence spectroscopy,ultraviolet-visible absorption spectroscopy and transient absorption spectroscopy.The nanocluster exhibits a perfect face-centered cubic(FCC)kernel structure with a tetrahedron-like shell.Of note,Pd1Ag28 nanocluster had an unexpectedly long excited-state lifetime of 3.3 microseconds,which is the longest excited-state lifetime for Ag-based nanoclusters S0 far.Meanwhile,the excellent near-infrared luminescence indicated the nanocluster has the potential in fluorescent bio-imaging.Besides,it was revealed that Pd1Ag28 nanocluster could be transformed into Au1Ag28 nanocluster via ion exchange reaction of AuPPhzCl with Pd1Ag28 nanocluster.This work provides an efficient synthetic protocol of alloy nanoclusters and wil contribute to study the effect of foreign atom on the properties of metal nanoclusters.

高功率气体开关长寿命设计和初步实验

针对初期设计的尼龙外壳同轴三电极开关完成了寿命实验,三只开关样品的寿命分别为20.4万次、43.3万次和15.1万次。根据寿命实验结果同时对开关结构和外壳材料进行了改进,初步实验结果表明,改进后的5只气体开关样品除陶瓷外壳开关提前损坏以外,其余3只有机玻璃外壳开关均已完成30万次寿命实验,并且其自击穿电压各自保持了较好的稳定性,标准偏差未明显变大。补充开展的触发实验结果表明,3只有机玻璃外壳开关触发性能基本稳定。根据自击穿电压的变化情况以及30万次寿命实验后开关的触发延时和抖动等参数,预期改进设计开关的寿命将会超过原初设计开关。

长寿期小型棒控压水堆控制棒方案研究

小型棒控压水堆舍弃了可溶硼,并高度依赖控制棒与可燃毒物棒控制堆芯的反应性。为研究控制棒对堆芯关键性能的影响,本文以核动力破冰船用KLT-40模型为对象,以轴向功率偏移、堆芯寿期、燃料利用率与径向功率峰因子为指标,开展长寿期小型棒控压水堆控制棒布置与动作策略设计分析。首先,基于OpenMC程序开发带棒燃耗程序;其次,比较堆芯带控制棒与无控制棒运行时的堆芯寿期等指标;最后,分析不同动作策略对轴向功率偏移等指标的影响。结果表明:控制棒将堆芯寿期从590 EFPDs(等效满功率天,Effective full power days)延长至650~698 EFPDs;低价值棒组优先动作策略使轴向功率偏移程度由−0.69与+0.80分别下降至−0.29与+0.52。因此,要准确计算长寿期压水堆寿期必须采用带控制棒燃耗计算策略,并且通过合理的动作策略能够有效减小控制棒带来的轴向功率偏移。

光与时间魔法的奇妙碰撞——追寻长余辉寿命的足迹

发光寿命是光化学的重要概念,也是体现发光材料性质的一项重要参数。尽管发光材料在人类生产生活、军事及航空航天领域有广泛的应用,但是普通大众对于“发光寿命有长有短”这一科学概念并没有清晰的认识。本项目以生活中的光为切入点,以发光寿命在人眼可识别范围内(>100 ms)的长余辉材料作为展示媒介。通过探究三聚氰胺与苯二甲酸在水介质中的自组装,设计并合成了一类寿命长、亮度高的有机长余辉材料,因其合成方法简单、原料便宜易得、实验现象明显且重现性高,非常适合作为科普主题;同时在日常生活中探寻发光现象,创新设计趣味动画、“光绘涂鸦”等新型科普模式,寓教于乐、寓教于做,点燃人们探究化学世界的热情;借助Bilibili、抖音等网络平台广泛宣传,拓宽化学知识的普及范围。针对具有不同年龄和知识结构对象群体的特点和需求,科普内容设立了多个独立互动模块,“量体裁衣”,力求获得“覆盖面广、接受度高”的效果,让发光寿命真正贴近生活、走向大众。

Long lifetime of nanobubbles due to high inner density

As predicted by classical macroscopic theory, the lifetime for nanoscale gas bub-bles is extremely short. However, stable gas nanobubbles have been experimen-tally observed in recent years. In this report, we theoretically show that, if the inner density of gas bubbles is sufficiently high, the lifetime of nanobubbles can increase by at least 4 orders of magnitude, and even approaches the timescale for experi-mental observations.

基于VMD-LSTM-SVR的IGBT寿命特征时间序列预测

绝缘栅双极型晶体管(IGBT)失效是变频器等电力电子设备故障的主要原因,精确预测其寿命是解决该问题的方法之一,这对寿命预测模型的准确性和可靠性提出了更高要求。关断瞬态尖峰电压(Vce,peak)可以反映IGBT的老化状态,首先通过变分模态分解(VMD)技术将Vce,peak构成的时间序列分解为趋势序列和波动序列,再利用长短期记忆(LSTM)网络的时间序列特征提取优势和支持向量机回归(SVR)的非线性求解能力,建立VMD-LSTM-SVR组合模型,提升模型的预测性能。模型预测对比实验结果表明,VMD-LSTM-SVR模型提升了IGBT寿命特征时间序列预测能力,与其他模型相比,该模型的预测精度指标均方根误差下降至0.0411 V,决定系数提升至0.75111。

A simple strategy to simultaneously improve the lifetime and activity of classical iridium complex for photocatalytic water-splitting

Herein,we design and synthesize a series of oligomers[Ir(ppy)2(dabpy)-ODPA]n(D1-n)by copolymerization of[Ir(ppy)2(dabpy)][PF6](D2)with 4,4′-Oxydiphthalic anhydride(ODPA),to resolve the problem of simultaneous improvement of sta-bility and activity of classical iridium complex for photocatalytic water-splitting.Fourier-transform infrared spectroscopy,X-ray photoelectron spectroscopy,solid-state nuclear magnetic resonance,and gel permeation chromatography results indicate that the degree of polymerization(n)of D1-n could be tuned by the syn-thesis method.The best photocatalytic performance is reached by D1-n with n at of 2 and/or 3(D1-2/3),which exhibits a photocatalytic lifetime up to 676 h and a photocatalytic hydrogen evolution of 162055.1 Compared with classicalμmol⋅g-1.iridium complex D2,the photocatalytic lifetime of D1-2/3 is about 38 times longer and the photocatalytic activity is 1.3 times higher.Further increase of n leads to a decrease in both photocatalytic lifetime and activity.According to the spectro-scopic characterizations,photoelectrochemical experiments,and density functional theory calculation,the significantly enhanced photocatalytic performance of D1-2/3 originates from the oligomeric structure.The oligomer chain of D1-2/3 with suit-able length acts as a large steric hindrance to reduce the undesired photoinduced decomposition and prolong its lifetime.The possible coupling of adjacent Ir com-plexes in D1-2/3 lowers the energy gap and increases the utilization of visible light,which overcomes the adverse effect of large steric hindrance andfinally improve the activity.This workfirst provides a simple strategy for constructing oligomeric Ir photosensitizers to simultaneously achieve long lifetime and high activity,it will lay the foundation for the design of highly efficient photosensitizers in the future.

长寿命同轴三电极气体火花开关设计和实验

设计了一种新型的同轴三电极结构,仿真计算结果表明开关在充电及触发时电场最大值区域均匀性良好。引入循环吹气系统能够控制放电产物的流向,减小对开关绝缘结构内壁的污染,可在提高气体绝缘恢复能力的同时延长开关绝缘外壳寿命。在重频实验条件下(±40kV/20kA/0.1 Hz)进行了寿命考核实验,目前单个开关寿命考核实验已大于17.2万发次,开关工作稳定,自击穿电压特性和触发延时抖动特性良好。

高可靠DC-DC混合电源长寿命评价技术研究

随着科学技术的发展、设计和制造水平的大幅度提高,高可靠长寿命DC-DC混合电源产品在军事及航空航天领域应用越来越广泛,如何预测其寿命是值得深入研究的重要问题。采用加速退化试验方法,对一款高可靠DC-DC混合电源进行可靠性评价与寿命预测。此研究成果对解决高可靠性电源产品的可靠性保证和寿命预测问题具有很好的工程意义。

强激光能源系统用气体开关的研究

针对强激光能源系统对开关元件的要求,在比较高库仑量大电流气体开关的3种主要类型:三电极场畸变开关、两电极同轴结构开关、旋弧开关后提出并研制了强激光能源系统开关定型上应优先考虑的两电极同轴结构开关。对开关电极材料的选取进行了理论和实验上的探讨,为了减少电极的烧蚀,需选择比热、密度、相变潜热大、熔点高的电极材料。理论分析和15 kV、200 kA下的开关样机实验结果表明,高密度石墨较为适合做大电流气体火花开关电极,电极材料的显微结构对开关电极的烧蚀和寿命影响较大。

光伏型长波HgCdTe红外探测器的数值模拟研究

报道了光伏型长波Hg1-xCdxTe(x=0.224)n-on-p红外探测器数值模拟研究的结果.采用二维模型,在背照射方式下,以p区厚度、两电极间距离、结区杂质浓度分布、少子寿命为参量,模拟计算了R0A积、零偏光电流与这些参量之间的变化关系.计算表明,随p区厚度增加,R0A积下降;R0A积随电极之间距离增大而增加,但量子效率随距离增大而降低,电极之间最佳距离大约为100μm;R0A积和光电流对结区杂质浓度分布形状不敏感;随少子(电子)寿命降低,R0A积和光电流下降.二维模型弥补了一维模型难以计算横向电流、电场的缺点.

长寿命高选择性液膜碘离子电极的研究

合成了ＰＶＣ－双硫腙－Ｈｇ（Ⅱ）载体．以该载体物质制备了高选择性碘离子电极，其选择性次序为：Ｉ－ＣｌＯ－４＞ＳＣＮ－＞ＮＯ－２Ｓａｌ－～Ｂｒ－＞ＮＯ－３＞Ｃｌ－．电极对碘离子的线性响应范围为１×１０－３～５×１０－７ｍｏｌ／Ｌ，检测下限为２×１０－７ｍｏｌ／Ｌ，斜率为（５９±１）ｍＶ／ｄｅｃａｄｅ（１６℃）．并研究了电极的响应机理，表明系碘离子与载体中金属汞原子直接作用．将该电极应用于食盐中碘的测定。

植物绝缘油及其应用研究关键问题分析与展望

植物绝缘油作为一种高燃点、可降解的环保液体电介质,被普遍认为是矿物绝缘油的良好替代品。目前,植物绝缘油已在配电变压器中得到良好应用,并逐步开始应用在大型电力变压器中。介绍了植物绝缘油及其应用研究的历史与现状,分析了植物绝缘油在制备方法、电气与理化特性以及植物油纸绝缘寿命模型和植物绝缘油变压器故障诊断方法等方面取得的进展。通过对关键问题的分析,说明了植物绝缘油相比矿物绝缘油具有的一些新的优点。植物油纸绝缘可有效延缓绝缘纸的老化速率,通过良好的变压器设计和运行维护,植物绝缘油可提高变压器的过负荷能力,植物绝缘油变压器将比矿物绝缘油变压器具有更低的全寿命周期成本。最后,提出了植物绝缘油及其应用在未来研究中,应重点关注植物绝缘油化学及纳米改性、油中长间隙放电、植物绝缘油变压器运行维护和纳米植物绝缘油等方面的关键问题。

基于加速磨损试验的止推轴承磨损寿命预测

为进行耐磨性良好的止推轴承寿命验证,结合退化模型进行了基于加速磨损试验的止推轴承寿命预测研究,建立了止推轴承加速磨损寿命方程.在失效机理分析基础上,以加载力为加速应力开展了7200 h的止推轴承加速磨损试验,得到反映耐磨性能下降的体积磨损量变化数据,预测得到置信度90%时,止推轴承在使用条件下运行10 a的可靠度为0.94.该项研究表明,对磨损进程极为缓慢的高可靠性、长寿命止推轴承,利用加速磨损试验数据预测其寿命,能节约试验时间和费用.