A novel cyclodextrin (CD) derivative, mono-6-deoxy-benzimide-β-CD (MB-β-CD), in which a rigid substituent was linked to the narrow edge of the CD with a flexible H(2)C-N group, was successfully synthesized through the condensation of mono-6-deoxy-6-amino-β-cyclodextrin and benzaldehyde. To evaluate its enantioseparation abilities and investigate the role of the CD substituents and linkage in chiral recognition, MB-β-CD and mono-6-deoxyphenylimine-β-CD (MP-β-CD) with a rigid linkage were compared in the separation of 36 chiral compounds in a methanol/water mobile phase. The separation results showed that most of the analytes with rigid structures afforded better enantioresolutions on the MP-β-CD (with a rigid linkage) chiral stationary phase (CSP), while better enantioseparations for analytes with flexible structures and big steric hindrance were obtained on the MB-β-CD (with a flexible linkage) CSP. The former exhibited a specificity for the analyte structures, while the latter was more adaptable. Molecular dynamics simulations were performed to further understand the discrimination process and the function of the CD side arm.
Sulfur passivation of GaInAsSb photodetectors was studied in terms of Auger electron spectroscopy and x-ray photoelectron spectroscopy. The experimental results showed that Sb–S and In–S bonds exist on the sulfur-passivated GaInAsSb surfaces. The reverse dark current of the photodetectors was reduced and the peak detectivity reached 2.83×1010 cm Hz1/2 W−1 after passivation.
Compared with the results on the stability of switched systems, research on the H control for switched systems is not adequate yet. Attentions have been attracted to the H control 4 www.intechopen.com Switched Systems 66 for switched systems since 1998, when Hespanha considered the problem firstly. Similar to the stability problem, the H control problem can be classified into: Problem A. The H control under arbitrary switching signal; Problem B. The H control under a certain switching signal. Problem A means the internal stability and the L 2 gain of the switched systems are independent of the switching signal. Problem A is usually solved through the common Lyapunov method which is conservative in that the common Lyapunov function is not easy to choose. Wu and Meng (Wu & Meng, 2009) studied H model reduction for continuous-time linear switched systems with time-varying delay. By applying the average dwell time approach and the piecewise Lyapunov function technique, delay delay-dependent and delayindependent sufficient conditions are proposed in terms of linear matrix inequality (LMI) to guarantee the exponential stability and the weighted H performance for the error system.
Hydraulic fracturing (HF) is an effective technology to prevent and control coal dynamic disaster. The process of coal hydraulic fracturing (HF) induces a large number of microseismic/acoustic emission (MS/AE) waveforms. Understanding the characteristic of AE waveforms’ parameters is essential for evaluating the fracturing effect and optimizing the HF strategy in coal formation. In this study, laboratory hydraulic fracturing under true triaxial stress was performed on a cubic coal sample combined with AE monitoring. The injection pressure curve and temporal variation of AE waveforms’ parameters in different stages were analyzed in detail. The experimental results show that the characteristics of the AE waveforms’ parameters well reflect the HF growth behavior in coal. The majority of AE waveforms’ dominant frequency is distributed between 145 and 160 kHz during HF. The sharp decrease of the injection pressure curve and the sharp increase of the AE waveforms’ amplitude show that the fracture already runs through the coal sample during the initial fracture stage. The “trapezoidal” rise pattern of cumulative energy and most AE waveforms with low amplitude may indicate the stage of liquid storage space expansion. The largest proportion of AE waveforms’ energy and higher overall level of AE waveforms’ amplitude occur during the secondary fracture stage, which indicates the most severe degree of coal fracture and complex activity of internal fracture. The phenomenon shows the difference in fracture mechanism between the initial and secondary fracture stage. We propose a window-number index of AE waveforms for better response to hydraulic fracture, which can improve the accuracy of the HF process division.
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