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91.
92.
<正>负离子表面活性剂混合体系曾被认为是表面活性剂配方的禁忌,但通过增大表面活性剂头基的面积,正负混合体系在很宽的物质的量比下都不会产生沉淀,而且还会产生显著的增效效应。头基大的离子型表面活性剂甚至能够用来增溶难溶的反电荷表面活性剂。 相似文献
93.
Dr. Kathrin I. Mohr Dr. Carsten Volz Dr. Rolf Jansen Dr. Victor Wray Dr. Judith Hoffmann Dipl.‐Ing. Steffen Bernecker Priv.‐Doz. Dr. Joachim Wink Dr. Klaus Gerth Prof. Dr. Marc Stadler Prof. Dr. Rolf Müller 《Angewandte Chemie (International ed. in English)》2015,54(38):11254-11258
Lantibiotics (lanthionine‐containing antibiotics) from Gram‐positive bacteria typically exhibit activity against Gram‐positive bacteria. The activity and structure of pinensin A ( 1 ) and B ( 2 ), lantibiotics isolated from a native Gram‐negative producer Chitinophaga pinensis are described. Surprisingly, the pinensins were found to be highly active against many filamentous fungi and yeasts but show only weak antibacterial activity. To the best of our knowledge, lantibiotic fungicides have not been described before. An in‐depth bioinformatic analysis of the biosynthetic gene cluster established the ribosomal origin of these compounds and identified candidate genes encoding all of the enzymes required for post‐translational modification. Additional encoded functions enabled us to build up a hypothesis for the biosynthesis, export, sensing, and import of this intriguing lantibiotic. 相似文献
94.
Dr. Luke A. Clifton Dr. Stephen A. Holt Dr. Arwel V. Hughes Dr. Emma L. Daulton Dr. Wanatchaporn Arunmanee Dr. Frank Heinrich Dr. Syma Khalid Damien Jefferies Dr. Timothy R. Charlton Dr. John R. P. Webster Dr. Christian J. Kinane Prof. Jeremy H. Lakey 《Angewandte Chemie (International ed. in English)》2015,54(41):11952-11955
Gram‐negative bacteria are an increasingly serious source of antibiotic‐resistant infections, partly owing to their characteristic protective envelope. This complex, 20 nm thick barrier includes a highly impermeable, asymmetric bilayer outer membrane (OM), which plays a pivotal role in resisting antibacterial chemotherapy. Nevertheless, the OM molecular structure and its dynamics are poorly understood because the structure is difficult to recreate or study in vitro. The successful formation and characterization of a fully asymmetric model envelope using Langmuir–Blodgett and Langmuir–Schaefer methods is now reported. Neutron reflectivity and isotopic labeling confirmed the expected structure and asymmetry and showed that experiments with antibacterial proteins reproduced published in vivo behavior. By closely recreating natural OM behavior, this model provides a much needed robust system for antibiotic development. 相似文献
95.
随机结构正交展开分析的Ritz动力聚缩法 总被引:1,自引:0,他引:1
针对随机结果正交展开理论计算上的弱点 ,本文在分析扩阶矩阵特性的基础上 ,于 Ritz模态向量子空间中对扩阶方程实现动力聚缩 ,大大提高了正交展开理论对实际工程问题的分析能力。分析实例表明 :即使结构参数具有很大变异性 (如δ =0 .4 )时 ,该算法依然能理想地与 Monte Carlo法模拟结果相吻合 ,计算时间则远远小于 Monte Carlo模拟法。同时 ,分析例证再一次强化了在结构动力分析中考虑结构参数随机性的必要性 相似文献
96.
文献〔1〕给出了等距时间序列的灰色预测GM(1,N)模型,本文把它推广到非等距时间序列,得到了相应模型,并应用于地下工程的几个实例 相似文献
97.
Yinyan Gong Yong Zhou Huacheng Wu Danping Wu Yongli Huang Chang Q. Sun 《Journal of Raman spectroscopy : JRS》2016,47(11):1351-1359
The solute–solvent interaction of salts has a striking impact on various biological and industrial processes but its mechanism remains yet mysterious despite intensive studies since 1888 when Franz Hofmeister established the salt series. A combination of confocal Raman spectroscopy and contact angle measurements has enabled us to resolve the hydrogen bond relaxation (O:H―O, HB) and the associated charge polarization dynamics at different molecular site because of alkali halides hydration. Results show consistently that salt hydration softens the O:H phonon but stiffens H―O phonon cooperatively. The extent of HB relaxation and polarization is proportional to the electronegativity difference and ionic radius, following the order of Hofmeister series: X (R/η) = I (2.2/2.5) > Br (1.96/2.8) > Cl (1.81/3.0) > F (1.33/4.0) ≈ 0 for anions, and Y(R/η) = Na (0.98/0.9) > K (1.33/0.8) > Rb (1.49/0.8) > Cs (1.65/0.8) for cations. Observations suggest that ions create each an electric field that aligns, stretches, and polarizes water molecules, which relaxes the O:H―O bond cooperatively, depresses the molecular dynamics, and enhances the hydration shell viscosity and the skin stress. Exercises also demonstrate that Raman spectroscopy performs as a powerful tool for probing the molecular‐site‐resolved HB network relaxation dynamics in terms of phonon stiffness, molecular fluctuation dynamics, and phonon abundance transition under external stimulus. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
98.
Presented here is an L-leap method for accelerating stochastic simulation of well-stirred chemically reacting systems,in which the number of reactions occurring in a reaction channel with the largest propensity function is calculated from the leap condition and the number of reactions occurring in the other reaction channels are generated by using binomial random variables during a leap.The L-leap method can better satisfy the leap condition.Numerical simulation results indicate that the L-leap method can obtain better performance than established methods. 相似文献
99.
Michael C. Mackey Irina G. Nechaeva 《Journal of Dynamics and Differential Equations》1994,6(3):395-426
We study the stability of linear stochastic differential delay equations in the presence of additive or multiplicative white and colored noise. Using a stochastic analog of the second Liapunov method, sufficient conditions for mean square and stochastic stability are derived. 相似文献
100.
First-Passage Time of Duffing Oscillator under Combined Harmonic and White-Noise Excitations 总被引:1,自引:0,他引:1
The first-passage time of Duffing oscillator under combined harmonic andwhite-noise excitations is studied. The equation of motion of the system is firstreduced to a set of averaged Itô stochastic differential equations by using thestochastic averaging method. Then, a backward Kolmogorov equation governing theconditional reliability function and a set of generalized Pontryagin equationsgoverning the conditional moments of first-passage time are established. Finally, theconditional reliability function, and the conditional probability density and momentsof first-passage time are obtained by solving the backward Kolmogorov equation andgeneralized Pontryagin equations with suitable initial and boundary conditions.Numerical results for two resonant cases with several sets of parameter values areobtained and the analytical results are verified by using those from digital simulation. 相似文献