Two New Nimbolinin‐Type Limonoids from the Fruits of Melia toosendan

Two new nimbolinin‐type limonoids, 12‐ethoxynimbolinins E and F ( 1 and 2 , resp.), together with seven known analogues, 1α‐benzoyloxy‐3α‐acetoxyl‐7α‐hydroxy‐12β‐ethoxynimbolinin ( 3 ), nimbolinin B ( 4 ), meliatoosenin L ( 5 ), 14,15‐deoxy‐11‐oxohavanensin 3,12‐diacetate ( 6 ), 12α‐hydroxymeliatoosenin ( 7 ), toosendansin A ( 8 ), and toosendansin C ( 9 ), were isolated from the fruits of Melia toosendan. The structures of these compounds were elucidated by spectroscopic analysis. All the compounds were evaluated for their cytotoxicity against five tumor cell lines.     

Two New Triterpenoid Glycosides from the Roots of Rosa cymosa Tratt.

Two new triterpenoid glycosides, 3α,19α,23α‐trihydroxy‐2‐oxo‐12‐ursen‐28‐O‐β‐d ‐glucopyranoside ( 1 ) and 3α,19α,23α‐trihydroxy‐2‐oxoolean‐12‐en‐28‐O‐β‐d ‐glucopyranoside ( 2 ) as well as three known compounds, 2α,3α,19α‐trihydroxyolean‐12‐en‐28‐O‐β‐d ‐glucopyranoside ( 3 ), 2α,3α,19α,23‐tetrahydroxy‐12‐ursen‐28‐O‐β‐d ‐glucopyranoside ( 4 ), and 2α,3β,19α,23‐tetrahydroxyurs‐12‐en‐28‐oic acid ( 5 ) were isolated from 75% EtOH extract of Rosa cymosa. Their structures were elucidated by extensive spectroscopic methods. All the isolated compounds displayed moderate inhibitory activity against LPS‐induced NO production in macrophages.     

Green Synthesis of Spiro[indoline‐3,4′‐pyrazolo[3,4‐b][1,6]naphthyridine]‐2,5′(1′H)‐diones Catalyzed by TsOH in Ionic Liquids

A three‐component reaction of isatin, 3‐methyl‐1‐phenyl‐1H‐pyrazol‐5‐amine, and piperidine‐2,4‐dione was treated in ionic liquids catalyzed by TsOH and provided an efficient and green method for the synthesis of spiro[indoline‐3,4′‐pyrazolo[3, 4‐b][1,6]naphthyridine]‐2,5′(1′H)‐dione derivatives in high yields.     

两个基于4-(1H-1,2,4-三氮唑)苯甲酸的4d-4f异核配位聚合物的合成、结构及荧光性质

以4-(1H-1,2,4-三氮唑)苯甲酸(Htbc)为配体,采用水热法合成了两种新型4d-4f配位聚合物{[EuAg(tbc)₃(H₂O)]ClO₄·H₂O}_n(1)和{[Eu₂Ag₃(tbc)₆(NO₃)₂(H₂O)₂](ClO₄)₂·2H₂O}_n(2)。运用X射线单晶衍射法对该配位聚合物进行了结构测定,并对其进行了元素分析、红外光谱、PXRD及荧光光谱表征。单晶结构表明,配位聚合物1为正交晶系,空间群P2₁2₁2₁,由一维三股螺旋链(其中2股右手螺旋和1股左手螺旋)通过Ag将其连成二维平面。配位聚合物2属于三斜晶系,空间群为P1,由内消旋一维两股螺旋链通过Ag将其连成二维平面。配位聚合物1和2的二维链结构均通过非共价键作用形成三维超分子, 同时也表征了配位聚合物1和2的荧光性质。     

对无功功率物理意义的讨论

有功功率和无功功率是电工理论中非常重要的基本概念,有功功率物理意义明确,是瞬时功率在一个周期内的平均值,而无功功率概念模糊,正弦稳态电路中,一端口网络无功功率的值为端口电压有效值与电流有效值及电压与电流相位差的正弦函数三者的乘积,即Q=UIsinφ,有的教材将无功功率解释为网络内部与外部电源能量交换的最大规模,本文通过纯电阻、纯电感和纯电容电路,以及对RL与C并联电路的分析,证实对无功功率的这种解释是有歧义的.     

Analysis and experiment of a vibration isolator using a novel magnetic spring with negative stiffness

The vibration isolator using a novel magnetic spring with negative stiffness (MS-NS) is proposed in this paper. The proposed isolator which combines a positive stiffness spring with the MS-NS in parallel possesses the characteristic of high-static–low-dynamic stiffness. The MS-NS is composed of three cuboidal magnets configured in repulsive interaction. An analytical expression of the stiffness of the MS-NS is derived by using the magnetic charge model, and the approximation to the exact analytical expression is sought. Then, the nonlinearity of the stiffness is analyzed, and it is shown that the MS-NS is approximately linear for small oscillations. In order to validate the correctness and effectiveness of the MS-NS, the vibration transmissibility of the proposed isolator with and without the MS-NS is measured. The experimental results demonstrate that combining a vibration isolator with the MS-NS in parallel can lower the natural frequency of the isolator; and the analytical calculations and experimental results show a good consistency.     

Detection H2S mixed with natural gas using hollow-core photonic bandgap fiber

An optical fiber gas sensor using hollow-core photonic bandgap fiber as a gas cell is proposed to detect H₂S mixed with natural gas. This sensor is advantageous for eliminating instability of light source, impact of thermal zero drift, and zero shift of photoelectric device. The gas sensing probe of configuration is using two shorter pieces of hollow-core photonic bandgap fiber (HC-PBF) with the same overall length instead of one long piece of HC-PBF to improve the system response. The experimental dates indicate that a minimum detectivity of 10 ppm for the system configuration was estimated.     

A novel acoustic emission beamforming method with two uniform linear arrays on plate-like structures

A novel acoustic emission (AE) source localization approach based on beamforming with two uniform linear arrays is proposed, which can localize acoustic sources without accurate velocity, and is particularly suited for plate-like structures. Two uniform line arrays are distributed in the x-axis direction and y-axis direction. The accurate x and y coordinates of AE source are determined by the two arrays respectively. To verify the location accuracy and effectiveness of the proposed approach, the simulation of AE wave propagation in a steel plate based on the finite element method and the pencil-lead-broken experiment are conducted, and the AE signals obtained from the simulations and experiments are analyzed using the proposed method. Moreover, to study the ability of the proposed method more comprehensive, a plate of carbon fiber reinforced plastics is taken for the pencil-lead-broken test, and the AE source localization is also realized. The results indicate that the two uniform linear arrays can localize different sources accurately in two directions even though the localizing velocity is deviated from the real velocity, which demonstrates the effectiveness of the proposed method in AE source localization for plate-like structures.     

Methodological Study on AMS Measurement of U Isotope Ratios in Nanogram U Samples

The determination of uranium isotopic composition in trace samples is important in different fields. A new measurement method that uses an accelerator mass spectrometry （AMS） technique has been developed for the analysis of uranium isotopic ratios in ultra-trace uranium samples at the China Institute of Atomic Energy. As result, about 5-nanogram level uranium samples analyzed with AMS is achieved.     

Small amplitude ion-acoustic double layers with cold electron beam and q-nonextensive electrons

Small amplitude ion-acoustic double layers in an unmagnetized and collisionless plasma consisting of cold positive ions, q-nonextensive electrons, and a cold electron beam are investigated. Small amplitude double layer solution is obtained by expanding the Sagdeev potential truncated method. The effects of entropic index q, speed and density of cold electron beam on double layer structures are discussed.