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Antimicrobial resistance has been seriously threatening human health, and discovering new antimicrobial agents from the natural resource is still an important pathway among various strategies to prevent resistance. Guanidine-containing polyhydroxyl macrolides, containing a polyhydroxyl lactone ring and a guanidyl side chain, can be produced by many actinomycetes and have been proved to possess many bioactivities, especially broad-spectrum antibacterial and antifungal activities. To explore the potential of these compounds to be developed into new antimicrobial agents, a review on their structural diversities, spectroscopic characterizations, bioactivities, acute toxicities, antimicrobial mechanisms, and the structure-activity relationship was first performed based on the summaries and analyses of related publications from 1959 to 2019. A total of 63 guanidine-containing polyhydroxyl macrolides were reported, including 46 prototype compounds isolated from 33 marine and terrestrial actinomycetes and 17 structural derivatives. Combining with their antimicrobial mechanisms, structure-activity relationship analyses indicated that the terminal guanidine group and lactone ring of these compounds are vital for their antibacterial and antifungal activities. Further, based on their bioactivities and toxicity analyses, the discovery of guanidyl side-chain targeting to lipoteichoic acid of Staphylococcus aureus indicated that these compounds have a great potency to be developed into antimicrobial and anti-inflammatory drugs.

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An output‐only multiple‐crack localization method is proposed in this paper to detect and localize breathing cracks in a stepped rotor, which utilizes the crack‐induced local shape distortions in super‐harmonic characteristic deflection shapes (SCDSs). To minimize the noise effects on SCDSs and improve the accuracy of SCDS‐based crack localization, singular value decomposition is adopted to estimate the SCDS as the dominant singular vector of output power spectral density matrix at a super‐harmonic frequency. Then, in order to better reveal shape distortions in the SCDSs, an after‐treatment technique called gapped smoothing method is applied to derive a damage index. Numerical experiments are carried out to investigate the performance of the proposed method based on a two‐disc stepped rotor‐bearing system with breathing cracks established by the finite element method. Results show that the method is effective for single and multiple crack localization in stepped rotors and interference of steps can be excluded. Furthermore, the method is robust to noise. Influences of crack depths and rotating speeds are also investigated, and how to choose the rotating speed for better crack localization is discussed.

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Collagen/nano-hydroxyapatite (collagen/nHA) scaffolds were successfully prepared on carbon/carbon composites as bioactive films using the layer-by-layer coating method. Surface characterizations of collagen/nHA scaffolds were detected by scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. Compressive strengths of the scaffolds were evaluated by a universal test machine. In vitro biological performances were determined using scaffolds seeded with MC3T3-E1 osteoblasts-like cells and cultured in mineralization medium for up to 21 days. In addition, cellular morphologies and several related gene expressions of MC3T3-E1 cells in the scaffolds were also evaluated. Chemical and morphological analysis showed that the scaffolds had uniform pore sizes and unified phase composition. Mechanical testing indicated that the collagen/nHA scaffolds had the highest compressive strength in 50% of strain condition when the proportion of collagen and nano-hydroxyapatite was 1:3. Cellular morphology observations and cytology tests indicated that MC3T3-E1 cells were adhered on these scaffolds and proliferated. SEM photographs and gene expressions showed that mineralized MC3T3-E1 cells and newly formed extra cellular matrix (ECM) filled up the pores of the scaffolds after the 3-week mineralization inducement. Nano-sized apatite particles were secreted from MC3T3-E1 cells and combined with the reconstructed ECM. Collectively, collagen/nHA scaffolds provided C/C composites with a biomimetic surface for cell adhesion, proliferation and mineralized extra cellular matrices formation.

Structural characteristic deflection shapes (CDSs) such as mode shapes which contain spatial knowledge of structures are highly sensitive for damage detection and localization. Nevertheless, CDSs are vulnerable to measurement noise, which degrades the accuracy of damage identification. In order to enhance CDS-based damage identification, contributions are made in three aspects. First, a robust CDS estimation approach is proposed based on common principal component analysis, which estimates the CDSs as the common diagonalizer of a set of covariance matrices by joint approximation diagonalization (JAD). Second, an adaptive gapped smoothing method (GSM) is proposed and validated to be more accurate than the traditional GSM. Third, a new damage identification index capable of localizing damage and indicating relative damage severity is defined without requiring information of healthy structures. Finally, numerical and experimental examples of beams and a frame with cracks are studied to demonstrate the advantages of the proposed damage identification method in terms of noise robustness and accuracy.