Periodic solutions for a Lotka–Volterra mutualism system with several delays

In the present paper, a Lotka–Volterra type mutualism system with several delays is studied. Some new and interesting sufficient conditions are obtained for the global existence of positive periodic solutions of the mutualism system. Our method is based on Mawhin’s coincidence degree and novel estimation techniques for the a priori bounds of unknown solutions. Our results are different from the existing ones such as those in of Yang et al. [F. Yang, D. Jiang, A. Ying, Existence of positive solution of multidelays facultative mutualism system, J. Eng. Math. 3 (2002) 64–68] and Chen et al. [F. Chen, J. Shi, X. Chen, Periodicity in a Lotka–Volterra facultative mutualism system with several delays, J. Eng. Math. 21 (3) (2004) 403–409].     

Periodic solutions of a second order forced sublinear differential equation with delay

In this paper, existence criteria are established for the existence of periodic solutions of a second order sublinear differential equation with delay and forcing function. Our method is based on careful a priori estimation and continuation theorems, and our sublinear condition is an improvement of the boundedness condition in some recent results.     

Frequent oscillation in a nonlinear partial difference equation

This paper is concerned with a class of nonlinear delay partial difference equations with variable coefficients, which may change sign. By making use of frequency measures, some new oscillatory criteria are established. This is the first time oscillation of these partial difference equations is discussed by employing frequency measures.      

Synthesis of novel tetracyclic chromenes through carbanion chemistry of 4-methyl coumarins

Various substituents were introduced onto the methyl group in 4-methyl coumarins through lithiation, followed by reactions with a wide range of electrophiles. The presence of an alkoxy group on 6′-phenyl ring was found to be pivotal for the success of this reaction. This procedure provided a convenient synthetic pathway to elaborate the methyl group of 4-methylcoumarins. Application of this methodology was showcased with the synthesis of biologically important novel tetracyclic chromene ring systems (n = 1-3).     

A Minor New Flavone from Scutellaria baicalensis Georgi

A new flavone,6,2′-dihydroxy-5,7,8,6′-tetramethoxyflavone,was isolated from the roots of Scutellaria baicalensis. Its structure was established on the basis of spectral evidences.     

Enantioselective synthesis of (8S,13S,14R)-7-oxa-estra-4,9-diene-3,17-dione

The first enantioselective synthesis of (8S,13S,14R)-7-oxa-estra-4,9-diene-3,17-dione with the trans-C/D ring junction is described. Key features of the synthesis include Ag₂O-mediated C-O bond formation, thermodynamically controlled axial-equatorial inversion, one-pot of halogen exchange and Co/Cr-mediated C-C bond formation, and intramolecular aldol condensations.     

富勒烯及其衍生物的质谱研究

本文制备了一系列富勒烯及其衍生物，并利用多种质谱技术进行了鉴定、表征、揭示了它们在离子源条件下的稳定性及解规律。这些富勒烯及其省生物在ＦＤＭＳ、ＩＳＭＳ中均得到了较强的准分子离子峰且碎片峰很少。结果表昨ＦＤＭＳ，ＬＳＩＭＳ技术均适于富勒烯及其衍生物的定性分析，是目前富勒烯分析鉴定中较好的方法。     

Formation of ring calcium oxalate patterns induced by domains in DPPC Langmuir-Blodgett films

The ring patterns of calcium oxalate crystals were induced by domains in Langmuir-Blodgett （LB） films of dipalmitoylpho- sphatidylcboline （DPPC）. The result was explained by the defects at the ring boundaries of liquid condensed （LC） and liquid expanded （LE） phases of LB film. These boundaries could provide less free energy and much more nucleating sites for COM crystals.     

毒素蛋白ColicinE1与磷脂膜相互作用的荧光光谱研究临界摩尔比的测定

磷脂－蛋白相互作用的临界摩尔比是研究膜脂－蛋白相互作用的重要参数．本文利用荧光光谱技术首次测定了毒素蛋白ＣｏｌｉｃｉｎＥ１在不同条件下与不同磷脂膜相互作用的临界摩尔比并通过临界摩尔比的变化讨论了插膜蛋白与磷脂膜相互作用的规律，为进一步探讨毒素蛋白的插膜机制提供了重要的基础