水蒸气蒸馏法与超临界CO2萃取法结合气相色谱-质谱分析胡椒木精油成分

以水蒸气蒸馏(SD)法和超临界CO_2萃取(SC-CO_2)法分别提取胡椒木叶片精油,经气相色谱-质谱(GC-MS)分析其组分差异,并通过DPPH·自由基清除能力和还原力测定对提取液品质进行判断。结果表明:SD法和SC-CO_2法获得的主要成分为脂类和烯烃类物质,且组分数量同为34种,但两种方法获得的化学成分有所不同。SD法中相对含量较高的为苯乙烯(43. 15%)、顺式肉桂酸甲酯(30. 33%)、α-石竹烯(1. 81%)、α-月桂烯(8. 41%)等;而SC-CO_2法获得相对含量较高的物质为顺式肉桂酸甲酯(73. 91%)、柠檬烯(11. 13%)、α-石竹烯(4. 12%)等。抗氧化试验表明,SC-CO_2法提取精油清除DPPH·自由基能力在8 mg/mL达到2,6-二叔丁基-4-甲基苯酚(BHT)抑制率的97. 27%,IC_(50)为3. 173 3,还原力在20 mg/mL达到Vc的34. 86%; SD法在20 mg/mL的抑制率仅为BHT的14. 27%,还原力在20 mg/mL时仅为Vc的5. 98%。两种提取方法的分析结果显示,不同提取工艺的选择对获得胡椒木精油中活性成分存在明显差异,差异主要为酚类、萜类等还原性和抗氧化性较强的物质,且SC-CO_2法获得的胡椒木精油中含有较多的驱虫抗菌活性物质,提取效果优于SD法。     

铁高压熔化线的测量——熔化机理的影响

 铁的高压熔化线是高压物理和地球物理研究领域的一个重要课题。就目前的研究成果来看,存在一个公认的问题：静高压实验测得的熔化温度系统地低于来自动态加载实验的熔化数据——在核-幔边界压力下（330 GPa）,动压数据比静压数据高了近一倍（3 000 K）。从熔化相变的物理理论出发,对目前铁高压熔化线实验研究中的实验手段进行评述,并应用有关熔化相变理论的研究成果,对这一重要而未澄清的事实进行初步的探讨。结果表明：在目前铁高压熔化线的实验研究中,计及预熔化和冲击过热在静压和动压实验中对铁熔化温度的影响,可以得到相对自洽的实验结果。这一结果表明,地球核-幔边界压力下铁的熔化温度为3 850 K,外推可以得到铁在内核-外核边界压力下的熔化温度为6 000 K,核心压力下的熔化温度为6 300 K。这一结果还表明,地球液态外核的温度在3 500～5 100 K之间,与Anderson（1998）等推荐的数据一致。     

Ir–V nanoparticles supported on microstructure controlled carbon nanofibers as electrocatalyst for oxygen reduction reaction

Ir–V nanoparticles supported on microstructure controlled carbon nanofibers (CNFs) or on carbon black, Vulcan XC-72 (XC-72), have been synthesized via chemical reduction, and the oxygen reduction reaction (ORR) properties of catalysts are investigated in this paper. The physico-chemical properties are characterized by high resolution transmission electron microscope (HRTEM), N₂ physisorption and electrochemical analysis. HRTEM results show that the metal nanoparticles are separated on carbon support with well-controlled particle size, dispersity, and composition uniformity. Moreover, the metal nanoparticles on CNFs have a smaller size than those on XC-72. Cyclic voltammetric analysis reveals that Ir–V/CNFs exhibits a higher ORR activity than Ir–V/XC-72, and this may be associated with the smaller metal nanoparticles and the stronger metal-support interaction of Ir–V/CNFs. Linear sweep voltammetric analysis at different rotation rates proves that ORR on the Ir–V/CNFs electrode is a 4e^? process.     

Harmonic <Emphasis Type="Italic">p</Emphasis>-forms on Hadamard manifolds with finite total curvature

In the present note, the geometric structures and topological properties of harmonic p-forms on a complete noncompact submanifold \(M^{n}(n\ge 4)\) immersed in Hadamard manifold \(N^{n+m}\) are discussed, where \(M^{n}\) and \(N^{n+m}\) are assumed to have flat normal bundle and pure curvature tensor, respectively. Firstly, under the assumption that \(M^{n}\) satisfies the \((\mathcal {P}_\rho )\) property (i.e., the weighted Poincaré inequality holds on \(M^{n}\)) and the \((p,n-p)\)-curvature of \(N^{n+m}\) is not less than a given negative constant, using Moser iteration, the space of all \(L^{2}\) harmonic p-forms on \(M^{n}\) is proven to have finite dimensions if \(M^{n}\) has finite total curvature. Furthermore, if the total curvature is small enough or \(M^{n}\) has at most Euclidean volume growth, two vanishing theorems are, respectively, established for harmonic p-forms. Note that the two vanishing theorems extend several previous results obtained by H. Z. Lin.     

Indecomposable Coverings with Concave Polygons

We show that for any concave polygon that has no parallel sides and for any k, there is a k-fold covering of some point set by the translates of this polygon that cannot be decomposed into two coverings. Moreover, we give a complete classification of open polygons with this property. We also construct for any polytope (having dimension at least three) and for any k, a k-fold covering of the space by its translates that cannot be decomposed into two coverings.     

吸气式激光推进中激光能量沉积过程的数值模拟

 结合辐射输运方程,在流体力学方程组的能量方程中加入包括空气吸收的激光能量以及高温气体向周围辐射损失的能量源项,转化为辐射流体力学方程组,建立了用于模拟吸气式激光推进中能量沉积过程的物理力学模型和计算方法。该辐射流体力学计算程序可以很好地模拟激光能量沉积过程中空气对激光能量的吸收、等离子体对激光的屏蔽作用以及激光维持的爆轰波的传播规律,计算得到激光能量的沉积效率约为57%,激光维持的爆轰波的传播速度与同等条件下的理论和实验结果吻合得较好。     

HF/DF激光传输的大气衰减特性

 大气中的水汽对DF激光主要强线的吸收相对较小，而HF激光的大多数谱线受水汽和CO₂分子等的吸收较大。利用较新的HITRAN96数据库和我国不同地区的气象资料，采用逐线积分法计算了HF/DF 激光的大气衰减情况。所选的谱线中，在合肥地区（年平均）， HF的水汽吸收系数最大值可达到10km^-1的数量级，二氧化碳吸收系数最大可达10^-4~10^-3km^-1量级，P2(8)线吸收最弱；DF激光水汽吸收系数最大值可达到10^-1km^-1,比HF低2个量级，且随高度衰减很快，10km处就到10^-5~10^-4km^-1量级，P2(8)线吸收最弱。在我国，由南向北，由夏季到冬季，水汽浓度减少，大气对HF/DF激光的吸收率也相应地递减。     

虚阴极振荡器中束流质量影响的粒子模拟

 采用二维半全电磁PIC程序对轴向提取反馈式虚阴极振荡器中束流质量影响进行了模拟研究。结果表明：上凸前沿可使虚阴极振荡器达到饱和振荡的时间缩短，束脉冲前沿对微波饱和功率基本无影响；束流脉宽应大于16ns；当能散度为5%时，束波转换效率从单能束时的3.8%降至1.5%；束流质量（除能散度外）对微波频率基本上没有影响。     

微波法制备石墨烯及石墨烯基材料的研究进展

石墨烯(Gr)由于其独特的单原子层二维结构及优异的性能,在材料、电子、化学、能源、生物医药等众多领域具有广阔的应用前景,引起了众多学者的研究兴趣。如何高产量获得高质量的Gr对其未来的开发和应用至关重要。微波法是制备Gr的重要方法之一,具有绿色、高效、简便快捷等特点。本文综述了近几年微波法制备Gr、掺杂Gr和Gr基纳米复合材料的研究进展以及后者在锂离子电池负极材料方面的应用,并对其发展方向进行了展望。