A semi-algebraic approach for asymptotic stability analysis

This paper deals with the problem of computing Lyapunov functions for asymptotic stability analysis of autonomous polynomial systems of differential equations. We propose a new semi-algebraic approach by making advantage of the local property of the Lyapunov function as well as its derivative. This is done by first constructing a semi-algebraic system and then solving this semi-algebraic system in an adaptive way. Experiment results show that our semi-algebraic approach is more efficient in practice, especially for low-order systems.     

Triterpenoid saponins from the fruits of Akebiae quinata

Three new triterpenoid saponins together with eight known compounds have been isolated from the fruits of Akebiae quinata. On the basis of the spectroscopic and physiochemical evidence, the new compounds were elucidated as 3-O-beta-D-xylopyranosyl-(1-->2)-alpha-L-arabinopyranosyl gypsogenin, 3-O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl gypsogenin and 3-O-beta-D-xylopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-28-O-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl gypsogenin.     

Concise asymmetric total synthesis of obolactone

The first efficient asymmetric synthesis of obolactone 1 has been accomplished in 11 steps and with a 15% overall yield in which Brown's enantioselective allylation reactions and ring-closing metathesis reaction are key steps.     

Temporal variability of the telluric sodium layer

The temporal variability of the telluric sodium layer is investigated by analyzing 28 nights of data obtained with the Colorado State University LIDAR experiment. The mean height power spectrum of the sodium layer was found to be well fitted by a power law over the observed range of frequencies, 10 microHz to 4 mHz. The best-fitting power law was found be be 10(beta)nu(alpha), with alpha=-1.79+/-0.02 and beta=1.12+/-0.40. Applications to wavefront sensing require knowledge of the behavior of the sodium layer at kilohertz frequencies. Direct measurements at these frequencies do not exist. Extrapolation from low-frequency behavior to high frequencies suggests that this variability may be a significant source of error for laser guide star adaptive optics in large-aperture telescopes.     

Electrically controlled transfer of spin angular momentum of light in an optically active medium

Spin is an intrinsic property of the photon. A method for using an externally applied dc electric field to manipulate the transfer of spin angular momentum of light in an optically active medium is presented. To discuss this, we first develop a wave coupling theory of the mutual action of natural optical activity and the linear electro-optic effect. Besides being used for analyzing the electrically controlled transfer of spin angular momentum of light, the theory can also be used to describe the propagation of light traveling along an arbitrary direction in any optically active medium with an external dc electric field along an arbitrary direction.     

Mesoporous silica nanorods toward efficient loading and intracellular delivery of siRNA

The technology of RNA interference (RNAi) that uses small interfering RNA (siRNA) to silence the gene expression with complementary messenger RNA (mRNA) sequence has great potential for the treatment of cancer in which certain genes were usually found overexpressed. However, the carry and delivery of siRNA to the target site in the human body can be challenging for this technology to be used clinically to silence the cancer-related gene expression. In this work, rod shaped mesoporous silica nanoparticles (MSNs) were developed as siRNA delivery system for specific intracellular delivery. The rod MSNs with an aspect ratio of 1.5 had a high surface area of 934.28 m²/g and achieved a siRNA loading of more than 80 mg/g. With the epidermal growth factor (EGF) grafted on the surface of the MSNs, siRNA can be delivered to the epidermal growth factor receptor (EGFR) overexpressed colorectal cancer cells with high intracellular concentration compared to MSNs without EGF and lead to survivin gene knocking down to less than 30%.     

钻井完井液浸泡弱化页岩脆性机制

页岩脆性是页岩地层钻井、水力压裂设计的关键参数之一,目前针对钻井过程中工作液浸泡对页岩脆性的影响还未引起关注.通过开展钻井完井液浸泡前后页岩三轴力学实验,利用脆性评价模型分析了页岩脆性变化特征.结果表明,延长组页岩脆性强于龙马溪组页岩;油基和水基钻井完井液浸泡均能导致页岩脆性降低,且油基钻井完井液浸泡后的页岩脆性降低幅度更大;龙马溪组页岩浸泡后脆性减弱幅度较延长组页岩大.页岩脆性弱化机制包括:(1)由层理面胶结强度不同引起的脆性强弱差异;(2)由毛管自吸作用导致的高孔压、高应力强度因子、低临界断裂韧性;(3)由碱液侵蚀导致的页岩溶蚀孔形成及矿物颗粒碎裂;(4)由黏土矿物水化膨胀产生的膨胀应力;(5)由钻井完井液滤液润滑导致的页岩破裂面摩擦系数降低.延长组页岩层理面强度较龙马溪组页岩低,导致延长组页岩脆性强于龙马溪组页岩.其次,和水基钻井完井液相比,油基钻井完井液具有更大的自吸量、更高的pH值、更强的润滑性,因此,油基钻井完井液浸泡降低页岩脆性幅度更大.另外,由于龙马溪组页岩具有更小的润湿角、更强的毛管自吸和碱液侵蚀作用,相同浸泡条件下,龙马溪组页岩脆性降低幅度更大.本研究可为页岩地层钻井液性能优化、井壁稳定控制、水力压裂设计等提供理论指导.      

Spectroscopic properties of Yb~(3+)-doped TeO_2–BaO–BaF_2–Nb_2O_5-based oxyfluoride tellurite glasses

A series of oxyfluoride glasses with the compositions of 75 mol% TeO2, 10 mol% Nb2O5,(15 mol%-x) BaO, x BaF2(x = 0 mol%, 5 mol%, 10 mol%, 15 mol%) doped with Yb2O3 were prepared by the melt-quenching method. Their emission cross-sections, fluorescence lifetimes, and gain properties were investigated by using the absorption spectra and the fluorescence decay curves. The results show that by substituting BaF2 for BaO, the emission cross-section decreases from 1.37 pm2 to 1.21 pm2, and the fluorescence lifetime increases from 0.71 ms to 0.96 ms. These properties indicate that this oxyfluoride tellurite glass may have potential uses as the Yb2O3-doped gain medium in a solid laser.     

线形离子阱囚禁199Hg＋实验的光学系统设计

利用Zemax软件为线形离子阱囚禁199 Hg＋实验设计了一套光学系统,该系统包括两部分,即光学激发系统和荧光收集系统。光学激发系统由202 H g无极谱灯和激发透镜组组成。激发透镜组将202 Hg无极谱灯的直径为15 mm的圆形面光源整形成23 mm ×4 mm的矩形光去激发199 H g＋能级跃迁,从而使其辐射出荧光,再利用荧光收集系统去收集该荧光。荧光收集系统由收集透镜组、滤波片和光电倍增管组成。设计结果表明：该收集透镜组可以很好地将荧光发光面成像在直径为23 m m的光电倍增管上,具有较高的荧光收集效率,约3％。经物理系统实验,结果表明,该光学系统满足实验要求且具有较高的信噪比,其值约为20。这为高性能线形199 H g＋微波频标的工程应用提供了基础。     

Analysis of rectangular-core waveguide structures and directional couplers by an iterated moment method

Using an iterated moment method (weighted index method), formulae are derived for the accurate calculation of the dispersion characteristics and field distributions of guided modes in strip dielectric waveguides and strip-loaded waveguides, and for the calculation of the coupling length of rectangular-core dual-channel directional couplers. The formulae are simple and the results obtained by the present analysis agree well with computer-aided exact numerical analysis. This method can be readily extended to the analysis of other dielectric waveguide structures.