The tubulin homolog FtsZ forms a polymeric membrane-associated ring structure (Z ring) at midcell that establishes the site of division and provides an essential framework for the localization of a multiprotein molecular machine that promotes division in Escherichia coli . A number of regulatory proteins interact with FtsZ and modulate FtsZ assembly/disassembly processes, ensuring the spatiotemporal integrity of cytokinesis. The Z-associated proteins (ZapA, ZapB, and ZapC) belong to a group of FtsZ-regulatory proteins that exhibit functionally redundant roles in stabilizing FtsZ-ring assembly by binding and bundling polymeric FtsZ at midcell. In this study, we report the identification of ZapD (YacF) as a member of the E. coli midcell division machinery. Genetics and cell biological evidence indicate that ZapD requires FtsZ but not other downstream division proteins for localizing to midcell, where it promotes FtsZ-ring assembly via molecular mechanisms that overlap with ZapA. Biochemical evidence indicates that ZapD directly interacts with FtsZ and promotes bundling of FtsZ protofilaments. Similarly to ZapA, ZapB, and ZapC, ZapD is dispensable for division and therefore belongs to the growing group of FtsZ-associated proteins in E. coli that aid in the overall fitness of the division process.

A square piezoelectric composite diaphragm was analyzed by the finite element method to enhance the sensitivity of a piezoelectric micromachined ultrasound transducer (pMUT). The structures of electrode and piezoelectric film were optimized and a centric electrode was designed to avoid the counteraction of stress in the centre and edges. In order to further improve the sensitivity; a pMUT with partially-etched piezoelectric film was adopted. The receive and transmit sensitivities of the pMUT were analyzed in details. The receive sensitivity of pMUT with partially-etched ZnO film is 3.3 dB or 6.8 dB higher than those with a centric and whole electrode, respectively; and the amplitude of a partially-etched ZnO film pMUT under a certain voltage is 5.5 dB and 30 dB higher than those with centric and whole electrode separately. Two pMUT-based ZnO films were fabricated by micromachining technology and their receive and transmit sensitivities were tested. The ZnO films deposited by direct current (DC) magnetron sputtering exhibit a densely packed structure with columnar crystallites. The test results show that the structure of the square diaphragm with partially-etched piezoelectric layer can significantly improve the transducer sensitivity. The receive sensitivity and transmit sensitivity are −238.35 dB (ref. 1 V/μPa) and 150.42 dB (ref. 1 μPa/V); respectively.

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