Hyperbranched
polysiloxane (HBPSi) is attracting increasing attention
due to its intrinsic fluorescence and good biocompatibility. However,
it is very challenging to explore its biological applications because
of the low fluorescence intensity and quantum yield. Herein, we introduced
rigid β-cyclodextrin to the end of flexible polysiloxane chain
to synthesize a novel fluorescent polymer (HBPSi-CD) and explore its
biological applications. Results showed that the fluorescence intensity
and quantum yield of HBPSi-CD, compared with HBPSi, were significantly
enhanced. Theoretical calculations and transmission electron microscopy
demonstrated that the synergy effect of intra/intermolecular hydrogen
bonds and hydrophobic effect promoted the formation of large supramolecular
self-assemblies and space electron delocalization systems, leading
to intense fluorescence. Notably, the biocompatible HBPSi-CD not only
lighted up mouse fibroblast cells, but also possessed high ibuprofen
loading capacity (160 mg g–1) and superior pH-responsive
drug release performance. This work promoted the development of biological
applications of HBPSi.
To prevent short-circuits between the upper and lower switches of power converters from over-current protection, the dead time is mandatory in the switching gating signal for voltage source converters. However, this results in many negative effects on system operations, such as output voltage and current distortions (e.g., increased level of fifth and seventh harmonics), zero-current-clamping phenomenon, and output fundamental-frequency voltage reduction. Many solutions have been presented to cope with this problem. First, the dead-time effect is analyzed by taking into account factors such as the zero-clamping phenomenon, voltage drops on diodes and transistors, and the parameters of inverter loads, as well as the parasitic nature of semiconductor switches. Second, the state-of-the-art dead-time compensation algorithms are presented in this paper. Third, the advantages and disadvantages of existing algorithms are discussed, together with the future trends of dead-time compensation algorithms. This article provides a complete scenario of dead-time compensation with control strategies for voltage source converters for researchers to identify suitable solutions based on demand and application.
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