A cytotoxic dimeric furanoheliangolide from Piptocoma rufescens

A new sesquiterpene lactone, rufescenolide C (1), the first furanoheliangolide dimer, was isolated from the leaves of Piptocoma rufescens, collected in the Dominican Republic. Its structure was determined by interpretation of its spectroscopic data, with the absolute configuration being established by analysis of the CD spectrum. A plausible biogenesis of this dimer is proposed. This compound showed potent cytotoxicity with an IC₅₀ value of 150 nM, when tested against HT-29 human colon cancer cells.     

台风过境下大型单桩式海上风机结构动力特性研究

风机大型化是我国海上风电技术发展的重要方向. 东南沿海是我国海上风电发展的重要基地, 这一区域频繁发生的台风对海上风机的影响不可忽略. 台风风场与常规大风风场有不同的湍流特性, 同时台风期间较高的风速会引起巨大的台风浪. 本文考虑台风经过期间独特的风场及波浪场, 开展风浪联合作用对大型单桩海上风机影响的研究. 基于DTU 10 MW大型单桩风机, 运用一体化分析软件SIMA建立风浪联合作用下大型单桩风机的耦合数值模型, 研究台风经过不同阶段大型风力机的动力响应特性. 计算结果显示, 叶片变桨能有效降低台风经过时风机叶片所受风载荷, 变桨状态下单桩风机所受风载荷主要来源于塔筒. 在台风经过的不同阶段, 大型单桩海上风机结构表现出不同的动力特性. 台风全过程塔筒运动均受波浪激发一阶频率控制, 塔基上方结构动力载荷以惯性载荷为主, FOVS至FEWS阶段及BOVS阶段至BEWS阶段塔筒运动一阶频率处响应能量增长较小, 响应能量向低频及波频转移. 塔基下方泥面线处剪力响应受波频控制, 弯矩响应受一阶频率控制.      

Nonlinear vibration isolation via an innovative active bionic variable stiffness adapter (ABVSA)

Nonlinear Dynamics - During the process of spacecraft launch, the extreme vibration environment is the major influence factor that induces the failure of the mission. Inspired by the smooth motions...     

Experimental evaluation of mixed-mode fracture in adhesive bonds

Previous tests have shown that the mode II and mode III fracture energies of adhesive bonds coincide, with the nominal value dictated by post-yield shear deformation in the interlayer. This suggests that the complete mixed-mode fracture behavior may be dellineated by determining the interaction curve in either theG _I -G _II orG _I -G _III plane. A DCB-type specimen capable of delivering the entire opening versus shearing toughness spectrum in a single test was used. A brittle and a ductile epoxy resin were evaluated, with the adhesive thickness varying from a few micrometers up to 0.6 mm. Excluding very thin bonds, the mixed-mode fracture curve was approximately bilinear; when the applied energy release rate in shear,G _s , was relatively small, the total fracture energy equaledG _IC but otherwise, the fracture curve decreased essentially linearly with increasingG _S . In the case of the ductile adhesive, the transition in trends occurred whenG _S was approximately 55 percent of the shearing fracture energy. When the bond thickness was decreased to a few micrometers, the mixed-mode curve displayed a concave shape, with mode interaction occurring promptly. SEM analysis and analytical considerations suggest that this change in mixed-mode behavior was due to the development of a triaxial state of stress in the interlayer. Based on previous fracture studies of the individual fracture modes in adhesive bonds and laminated composites, the present results should be also applicable to mixed-mode interlaminar fracture of laminated composites.Herzl Chai, formerly associated with Polymers Division, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899     

离散变量优化设计的方向差商法

本文根据离散变量的特点，提出了方向差商的概念，并且针对一类目标函数、约束函数具有单调性的优化设计问题，发展了一种在可行集外由目标函数最小的点出发，沿目标函数增加最小、约束函数降低最多的方向逐步搜索，逐步靠近可行集边界的方向差商法。并将此方法应用于离散变量结构优化设计中。     

A novel imaging tool for hepatic portal system using phase contrast technique with hydrogen peroxide‐generated O2 gas

The objective of this study was to investigate the potential of hydrogen peroxide‐generated oxygen gas‐based phase contrast imaging (PCI) for visualizing mouse hepatic portal veins. The O₂ gas was made from the reaction between H₂O₂ and catalase. The gas production was imaged by PCI in real time. The H₂O₂ was injected into the enteric cavity of the lower sigmoid colon to produce O₂ in the submucosal venous plexus. The generated O₂ gas could be finally drained into hepatic portal veins. Absorption contrast imaging (ACI) and PCI of O₂‐filled portal veins were performed and compared. PCI offers high resolution and real‐time visualization of the O₂ gas production. Compared with O₂‐based ACI, O₂‐based PCI significantly enhanced the revealing of the portal vein in vivo. It is concluded that O₂‐based PCI is a novel and promising imaging modality for future studies of portal venous disorders in mice models.     

基于压缩感知的一维海面与二维舰船复合后向电磁散射快速算法研究

矩量法作为数值方法中积分方程方法的代表, 具有计算精度高、所用格林函数自动满足辐射条件、无须额外设置边界条件等优点. 但是在舰船目标与海面复合后向电磁散射仿真中, 传统矩量法需针对每个入射角反复求解矩阵方程组, 导致其在处理后向散射问题时计算量大, 耗时长, 仿真效率低下. 为解决上述问题, 本文提出了一种基于压缩感知技术的矩量法的改进算法. 该算法在求解复合后向散射问题时, 首先利用观测矩阵与传统矩量法中的电压矩阵相乘, 得到一组新的低维度的电压矩阵; 其次通过求解新电压矩阵下的矩阵方程组, 获得电流矩阵的观测值; 最后利用恢复算法(本文采用正交匹配追踪算法)重构出所需的原始入射源照射下的电流系数. 通过与传统矩量法的计算结果对比, 表明本文所提算法能够在保证计算精度的前提下, 明显减少计算时间, 提高计算效率.     

基于阿秒抖动光纤锁模激光器的时钟同步

光纤锁模激光器结构简单, 运转稳定, 且输出的超短脉冲序列具有极高的时钟稳定性, 在抽运探测、脉冲相干合成等要求高精度时钟同步的前沿领域有着广阔的应用前景. 本文通过激光器腔内的电光调制器进行反馈控制, 实现了两台光纤锁模激光器之间的紧密时钟信号同步; 并且通过平衡光学互相关方法, 对残余的时钟误差信号进行了测量, 分辨率达到了13 as. 通过优化激光器的腔内动力学过程及反馈环路的参数, 在[1 Hz, 10 MHz]的积分区间内得到了109 as的残余时钟误差, 对应单台激光器的平均时间抖动为77 as.     

Gold and Carbene Relay Catalytic Enantioselective Cycloisomerization/Cyclization Reactions of Ynamides and Enals

The combined use of gold as transition metal catalyst and N‐heterocyclic carbene (NHC) as organic catalyst in the same solution for relay catalytic reactions was disclosed. The ynamide substrate was activated by gold catalyst to form unsaturated ketimine intermediate that subsequently reacted with the enals (via azolium enolate intermediate generated with NHC) effectively to form bicyclic lactam products with excellent diastereo‐ and enantio‐selectivities. The gold and NHC coordination and dissociation can be dynamic and tunable events, and thus allow the co‐existence of both active metal and carbene organic catalysts in appreciable concentrations, for the dual catalytic reaction to proceed.     

Unraveling the Impact of Gold(I)–Thiolate Motifs on the Aggregation‐Induced Emission of Gold Nanoclusters

Aggregation‐induced emission (AIE) provides an efficient strategy to synthesize highly luminescent metal nanoclusters (NCs), however, rational control of emission energy and intensity of metal NCs is still challenging. This communication reveals the impact of surface Au^I‐thiolate motifs on the AIE properties of Au NCs, by employing a series of water‐soluble glutathione (GSH)‐coordinated Au complexes and NCs as a model ([Au₁₀SR₁₀], [Au₁₅SR₁₃], [Au₁₈SR₁₄], and [Au₂₅SR₁₈]^?, SR=thiolate ligand). Spectroscopic investigations show that the emission wavelength of Au NCs is adjustable from visible to the near‐infrared II (NIR‐II) region by controlling the length of the Au^I‐SR motifs on the NC surface. Decreasing the length of Au^I‐SR motifs also changes the origin of cluster luminescence from AIE‐type phosphorescence to Au⁰‐core‐dictated fluorescence. This effect becomes more prominent when the degree of aggregation of Au NCs increases in solution.