Demonstration of joule-level chirped pulse amplification based on tiled Ti:sapphire amplifier

A novel tiled Ti:sapphire(Ti:S)amplifier was experimentally demonstrated with>1 J amplified chirped pulse output.Two Ti:S crystals having dimensions of 14 mm×14 mm×25 mm were tiled as the gain medium in a four-pass amplifier.Maximum output energy of 1.18 J was obtained with 2.75 J pump energy.The energy conversion efficiency of the tiled Ti:S amplifier was comparable with a single Ti:S amplifier.The laser pulse having the maximum peak power of 28 TW was obtained after the compressor.Moreover,the influence of the beam gap on the far field was discussed.This novel tiled Ti:S amplifier technique can provide a potential way for 100 PW or EW lasers in the future.     

基于错位格雷码的动态三维形貌测量方法

格雷码辅助相移技术可以实现具有较强鲁棒性与抗噪能力的三维（3D）形貌测量。为解决由待测物体不均匀的表面反射率、噪声和物体运动等因素造成的级次边沿误码问题，提出了一种基于错位格雷码的动态3D形貌测量方法。将传统格雷码图案在投影前预先移动半个条纹周期得到错位格雷码图案，再采用传统格雷码解码方法对二值化后的错位格雷码图案解码，可得到与截断相位完全错开的解码结果。对该解码结果进行修正后即可利用得到的正确的相位级次辅助截断相位成功展开。同时，为了提高测量精度，引入了一个虚拟相位平面以进一步拓展投影条纹周期数。实验结果表明，所提方法在使用N帧格雷码图案的情况下，可以编码周期数为2^N+1的投影条纹进行3D测量，其无需任何附加图案即可避免级次边沿误码问题，并有效提升了测量精度。复杂动态场景的3D重建结果证明，所提方法能够以2381 frame/s的速率实现高精度、高效率和高速的3D形貌测量。     

Tuning Emission Wavelength of Polymorphous Crystal via Controllable Alkyl Chain Stacking and Its Vapor- and Thermo-Responsive Fluorescence

Tuning fluorescence colour of solid-state materials has become a topic of increasing interest for both fundamental mechanism study and practical applications such as sensors, optical recording and security printing. In this work, a fluorescent colour tuneable molecule BA-C16 is rationally designed and facilely synthesized by attaching flexible long alkyl chains to 2-hydroxybenzophenone azine ( BA ), which shows both aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics. Compared to BA , the simple introduction of long alkyl chains in BA-C16 leads to an emission wavelength redshift from 542 to 558 nm. This strategy of extending emission wavelength is rarely reported, and is ascribed to the enlarged through-space π-conjugation between interplanar molecules in the aggregate of BA-C16 . Three crystals of BA-C16 are obtained with green, yellowish green and yellow emission. According to characterization by X-ray crystallography, X-ray powder diffraction and differential scanning calorimetry, alkyl chains play an important role in inducing different stacking modes of the three crystals, which further leads to polymorph-dependent fluorescence colour. BA-C16 exhibits tuneable solid-state fluorescence upon vapor fumigation, or annealing based on a transition between a “near-monomer” crystalline state and a “dimer” crystalline state. BA-C16 is further applied for rewritable fluorescence printing tuned by vapor- and thermal-treatment.     

基于毛竹叶片理化参数的刚竹毒蛾危害检测研究

虫害检测算法研究是开展虫害快速、准确监测，制定精准森防检疫措施的重要基础。以毛竹叶片为研究尺度，基于刚竹毒蛾危害下的寄主外部形态与内部生理现象总结，选择并实测叶损量LL、相对叶绿素含量RCC、相对含水量RWC、原始光谱的733.66~898.56 nm值(ρ_{733.66~898.56})、一阶微分光谱的562.95~585.25 nm值(ρ′_{562.95~585.25})与706.18~725.41 nm值(ρ′_{706.18~725.41})等理化参数，随机划分实验组(63组)和验证组(37组)并设计5次重复实验；分别运用Fisher判别分析、BP神经网络、随机森林等三种方法建立刚竹毒蛾危害等级的检测模型，从检测精度、Kappa系数及R2等指标对模型的检测效果予以分析和比较。结果显示，Fisher判别分析、BP神经网络、随机森林的检测精度分别为69.19%，65.41%，83.78%，Kappa系数分别为0.576 9，0.532 4和0.778 8，R2分别为0.722 2，0.582 6和0.870 9，总体而言，三种方法均具备刚竹毒蛾危害的检测能力，随机森林的检测效果最优，Fisher判别分析次之，再次为BP神经网络；从分等级来看，随机森林的检测精度亦优于Fisher判别分析与BP神经网络，但3种方法对中度危害等级的检测精度均有所不足。该成果可为刚竹毒蛾危害及其他病虫害检测算法的选择提供参考，并为进一步建立冠层、遥感影像像元等尺度的虫害检测模型奠定基础。     

Crystal structures of silicon-rich lithium silicides at high pressure

Silicon (Si) is one of the most essential elements, as it is indispensable for modern electronic technology. The standard Si structure at ambient conditions is the cubic diamond structure, and it has an indirect band gap, which prevents it from being considered as a next-generation platform for semiconductor technologies. Therefore, the search for new allotropes of silicon has attracted great attention. Herein, first principles swarm-intelligence structure searches coupled with density-functional theory were performed to explore the stable high-pressure phases of silicon-rich lithium containing compounds, LiSi_x ($x=4\text{–}8$). The LiSi₄ stoichiometry was predicted to be stable, and it was found to assume one of the following space groups, P4/mnc, Cmmm, and C2/m within the pressure range of 0 to 50 GPa. By removing the Li atoms from these compounds, three silicon allotropes were obtained that were metastable at ambient pressures. Our work illustrates how novel silicon allotropes can be predicted using the CALYPSO method.     

Dose‐dependent exposure profile and metabolic characterization of notoginsenoside R1 in rat plasma by ultra‐fast liquid chromatography–electrospray ionization–tandem mass spectrometry

Notoginsenoside R₁ (NGR₁), a diagnostic protopanaxatriol‐type (ppt‐type) saponin in Panax notoginseng, possesses potent biological activities including antithrombotic, anti‐inflammatory, neuron protection and improvement of microcirculation, yet its pharmacokinetics and metabolic characterization as an individual compound remain unclear. The aim of this study was to investigate the exposure profile of NGR₁ in rats after oral and intravenous administration and to explore the metabolic characterization of NGR₁. A simple and sensitive ultra‐fast liquid chromatographic–tandem mass spectrometric method was developed and validated for the quantitative determination of NGR₁ and its major metabolites, and for characterization of its metabolic profile in rat plasma. The blood samples were precipitated with methanol, quantified in a negative multiple reaction monitoring mode and analyzed within 6.0 min. Validation parameters (linearity, precision and accuracy, recovery and matrix effect, stability) were within acceptable ranges. After oral administration, NGR₁ exhibited dose‐independent exposure behaviors with t_1/2 over 8.0 h and oral bioavailability of 0.25–0.29%. A total of seven metabolites were characterized, including two pairs of epimers, 20(R)‐notoginsenoside R₂/20(S)‐notoginsenoside R₂ and 20(R)‐ginsenoside Rh₁/20(S)‐ginsenoside Rh₁, with the 20(R) form of saponins identified for the first time in rat plasma. Five deglycometabolites were quantitatively determined, among which 20(S)‐notoginsenoside R₂, ginsenoside Rg₁, ginsenoside F₁ and protopanaxatriol displayed relatively high exploration, which may partly explain the pharmacodynamic diversity of ginsenosides after oral dose.     

Fabrication of Microporous Metal–Organic Frameworks in Uninterrupted Mesoporous Tunnels: Hierarchical Structure for Efficient Trypsin Immobilization and Stabilization

Hierarchically porous metal–organic frameworks (HP-MOFs) are promising in various applications. Most reported HP-MOFs are prepared based on the generation of mesopores in microporous frameworks, and the formed mesopores are connected by microporous channels, limiting the accessibility of mesopores for bulky molecules. A hierarchical structure is formed by constructing microporous MOFs in uninterrupted mesoporous tunnels. Using the confined space in as-prepared mesoporous silica, highly dispersed metal precursors for MOFs are coated on the internal surface of mesoporous tunnels. Ligand vapor-induced crystallization is employed to enable quantitative formation of MOFs in situ, in which sublimated ligands diffuse into mesoporous tunnels and react with metal precursors. The obtained hierarchically porous composites exhibit record-high adsorption capacity for the bulky molecule trypsin. The thermal and storage stability of trypsin is improved upon immobilization on the composites.     

Nonlinear vibration effects on the fatigue life of fluid-conveying pipes composed of axially functionally graded materials

Nonlinear Dynamics - Fatigue is inevitable in pipes conveying fluid due to unwanted vibration. Internal resonance occurs in such pipes due to pre-pressure. For the first time, the effects of...     

气体压强对纳秒激光诱导空气等离子体特性的影响

环境气体的压强对激光诱导等离子体特性有重要影响.基于发射光谱法开展了气体压强对纳秒激光诱导空气等离子体特性影响的研究,探讨了气体压强对空气等离子体发射光谱强度、电子温度和电子密度的影响.实验结果表明,在10-100 kPa空气压强条件下,空气等离子体发射光谱中的线状光谱和连续光谱依赖于气体压强变化,且原子谱线和离子谱线强度随气体压强的变化有明显差别.随着空气压强增大,激光击穿作用区域的空气密度增加,造成激光诱导击穿空气几率升高,从而等离子体辐射光谱强度增大.空气等离子体膨胀区域空气的约束作用,增加了等离子体内粒子间的碰撞几率以及能量交换几率,并且使离子-电子-原子的三体复合几率增加,因此造成原子谱线OⅠ777.2 nm与NⅠ821.6 nm谱线强度随着气体压强增大而增大,在80 kPa时谱线强度最高,随后谱线强度缓慢降低.而离子谱线N Ⅱ 500.5 nm谱线强度在40 kPa时达到最大值,气体压强大于40 kPa后,谱线强度随压强增加而逐渐降低.空气等离子体电子密度均随压强升高而增大,在80 kPa后增长速度变缓.等离子体电子温度在30 kPa时达到最大值,气体压强大于30 kPa后,等离子体电子温度逐渐降低.研究结果可为不同海拔高度的激光诱导空气等离子体特性的研究提供重要实验基础,为今后激光大气传输、大气组成分析提供重要的技术支持.     

The Applications of Order Reduction Methods in Nonlinear Dynamic Systems

Two different order reduction methods of the deterministic and stochastic systems are discussed in this paper. First, the transient proper orthogonal decomposition (T-POD) method is introduced based on the high-dimensional nonlinear dynamic system. The optimal order reduction conditions of the T-POD method are provided by analyzing the rotor-bearing system with pedestal looseness fault at both ends. The efficiency of the T-POD method is verified via comparing with the results of the original system. Second, the polynomial dimensional decomposition (PDD) method is applied to the 2 DOFs spring system considering the uncertain stiffness to study the amplitude-frequency response. The numerical results obtained by the PDD method agree well with the Monte Carlo simulation (MCS) method. The results of the PDD method can approximate to MCS better with the increasing of the polynomial order. Meanwhile, the Uniform-Legendre polynomials can eliminate perturbation of the PDD method to a certain extent via comparing it with the Gaussian-Hermite polynomials.