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The main challenges faced when detecting targets captured by UAVs include small target image size, dense target distribution, and uneven category distribution.In addition, the hardware limitations of UAVs impose constraints on the size and complexity of the model, which may lead to poor detection accuracy of the model. In order to solve these problems, a small target detection method based on the improved YOLOv8 algorithm for UAV viewpoint is proposed. The following improvements are made to the YOLOv8n model. Firstly, a bi-directional feature pyramid network (BiFPN) is introduced to enhance the fusion capability of the features. This improvement leads to better detection of small targets. Secondly, in the head part of the model, the original C2f module is replaced with the C3Ghost module. This change maintains the model's performance while significantly reducing the computational load. Lastly, the detection head adds a channel attention mechanism. This mechanism helps in filtering out unimportant information and enhancing the recognition of key features. The MPDIoU (Minimum Point Distance based IoU) loss function is improved, and the idea of inner-IoU loss function is adopted as a way to improve the model's learning ability for difficult samples. Experimental results on the VisDrone dataset show that the YOLOv8n model with these improvements improves 17.2%, 10.5%, and 16.2% in mean accuracy (mAP), precision (P), and recall (R), respectively, and these improvements significantly improve the performance of small target detection from the UAV viewpoint. [ABSTRACT FROM AUTHOR]

Aiming at the problems of low-frequency coverage, angle and polarization instability of ultra-wideband (UWB) frequency selective surface (FSS) in practical application, this paper introduces the additional circular parasitic patches and two-stage rectangular bent grids to enhance coupling, miniaturize geometry size, broaden bandwidth and suppress the drift of resonance frequencies based on the construction of a FSS unit cell by using a basic circular patch and a Jerusalem cross grid. The simulated and measured results show that the bandwidth of the FSS is 13.47 GHz, and its fractional bandwidth is 140.53%, which fully covers the UWB band (3.1–10.6 GHz). The UWB FSS has the flat transmission passband, and high transmission characteristics, and maintains stable performance at large incident angles and different polarization modes. The size of the UWB FSS unit cell is 0.25 λc × 0.25 λc × 0.12 λc. Therefore, the UWB FSS can be applied to electromagnetic stealth and the related fields of UWB communications. [ABSTRACT FROM AUTHOR]

As a homo‐oligomeric protein, the disassembly of Escherichia coli RbsD decamer produces a urea‐unfolded oligomeric intermediate structure, as the dissociation speed of the protein is lower than that of the unfolding process. There are five Lys2–Cl−–Lys2 salt linkages to connect these subunits. To explore the role of the salt linkages in these oligomeric intermediates, the Lys2Ala mutated in the N‐terminal of E. coli RbsD protein subunit was designed. It was found that the RbsD mutation protein (RbsD:K2A) loses its minor larger oligomers, which exist in RbsD, and displays other several oligomeric states (less than decamers), meanwhile the state of the oligomers depends on the protein concentration. It was also found that compared with RbsD, the crosslinking capability of the subunits of RbsD:K2A is weaker, while the crosslinking rate of dimers is higher, RbsD:K2A needs to substantially adjust its conformation to meet the space requirements when combined with d‐ribose. On the basis of these results, we suggest that Lys2–Cl−–Lys2 salt linkages in E. coli RbsD protein play an important role in stabilizing the intermediate products of oligomers and maintaining interaction between the intermediate products of oligomers, which may shed light on the study of these oligomeric proteins. [ABSTRACT FROM AUTHOR]

Indole is a very important signal molecule which plays multiple regulatory roles in many physiological and biochemical processes of bacteria, but up to now, the reasons for its wide range of functions have not been revealed. In this study, we found that indole inhibits the motility, promotes glycogen accumulation and enhances starvation resistance of Escherichia coli. However, the regulatory effects of indole became insignificant while the global csrA gene was mutated. To reveal the regulatory relationship between indole and csrA, we studied the effects of indole on the transcription level of csrA, flhDC, glgCAP and cstA, and also the sensing of the promoters of the genes on indole. It was found that indole inhibited the transcription of csrA, and only the promoter of the csrA gene can sense indole. Namely, indole indirectly regulated the translation level of FlhDC, GlgCAP and CstA. These data indicates that indole regulation is related with the regulation of CsrA, which may throw light on the regulation mechanism research of indole.

As a homo-oligomeric protein, the disassembly of Escherichia coli RbsD decamer produces a urea-unfolded oligomeric intermediate structure, as the dissociation speed of the protein is lower than that of the unfolding process. There are five Lys2-Cl - -Lys2 salt linkages to connect these subunits. To explore the role of the salt linkages in these oligomeric intermediates, the Lys2Ala mutated in the N-terminal of E. coli RbsD protein subunit was designed. It was found that the RbsD mutation protein (RbsD:K2A) loses its minor larger oligomers, which exist in RbsD, and displays other several oligomeric states (less than decamers), meanwhile the state of the oligomers depends on the protein concentration. It was also found that compared with RbsD, the crosslinking capability of the subunits of RbsD:K2A is weaker, while the crosslinking rate of dimers is higher, RbsD:K2A needs to substantially adjust its conformation to meet the space requirements when combined with d-ribose. On the basis of these results, we suggest that Lys2-Cl - -Lys2 salt linkages in E. coli RbsD protein play an important role in stabilizing the intermediate products of oligomers and maintaining interaction between the intermediate products of oligomers, which may shed light on the study of these oligomeric proteins., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)