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Abstract

This paper proposes a new dc-side active filter for wind generators that combines 12-pulse polygon auto-transformer rectifier with dc-side current injection method and dual-buck full-bridge inverter having not the “shoot-through” problem in conventional bridge-type inverters, and therefore this system with the character low harmonic distortion and high reliability. The proposed dc-side active filter is realized by using dual-buck full bridge converter, which directly injects compensation current at dc-side of two six-pulse diode bridges rectifiers. Compared with the conventional three-phase active power filter at ac-side, the system with the dc-side active filter draws nearly sinusoidal current by shaping the diode bridges output current to be triangular without using the instantaneous reactive power compensation technology, only using simple hysteretic current control, even though under load variation and unbalanced voltage disturbances, and while an acceptable linear approximation to the accurate waveform of injection current is recommended. The perfor- mance of the system was simulated using MATLAB/Simulink, and the possibility of the dc-side active filter eliminating current harmonics was confirmed in steady and transient states. The simulation results indicate, the system has a total harmonic distortion of current reduced closely to 1%, and a high power factor on the wind generator side.
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Abstract

MDAP-2 is a new antibacterial peptide with a unique structure that was isolated from house- flies. However, its biological characteristics and antibacterial mechanisms against bacteria are still poorly understood. To study the biological characteristics, antibacterial activity, hemolytic activi- ty, cytotoxicity to mammalian cells, and the secondary structure of MDAP-2 were detected; the results showed that MDAP-2 displayed high antibacterial activity against all of the tested Gram-negative bacteria. MDAP-2 had lower hemolytic activity to rabbit red blood cells; only 3.4% hemolytic activity was observed at a concentration of 800μg/ml. MDAP-2 also had lower cytotoxicity to mammalian cells; IC50 values for HEK-293 cells, VERO cells, and IPEC-J2 cells were greater than 1000 μg/ml. The circular dichroism (CD) spectra showed that the peptide most- ly has α-helical properties and some β-fold structure in water and in membrane-like conditions. MDAP-2 is therefore a promising antibacterial agent against Gram-negative bacteria. To deter- mine the antibacterial mechanism(s) of action, fluorescent probes, flow cytometry, and transmis- sion electron microscopy (TEM) were used to study the effects of MDAP-2 on membrane perme- ability, polarization ability, and integrity of Gram-negative bacteria. The results indicated that the peptide caused membrane depolarization, increased membrane permeability, and destroyed membrane integrity. In conclusion, MDAP-2 is a broad-spectrum, lower hemolytic activity, and lower cytotoxicity antibacterial peptide, which is mainly effective on Gram-negative bacteria. It exerts its antimicrobial effects by causing bacterial cytoplasm membrane depolarization, increas- ing cell membrane permeability and disturbing the membrane integrity of Gram-negative bacte- ria. MDAP-2 may offer a new strategy to for defense against Gram-negative bacteria.
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