Flow Over a Traveling Wavy Foil With a Passively Flapping Flat Plate

Flow over a traveling wavy foil with a passively flapping flat plate has been investigated using a multiblock lattice Boltzmann equation and the immersed boundary method. The foil undergoes prescribed undulations in the lateral direction and the rigid flat plate has passive motion determined by the fluid structure interaction. This simplified model is used to study the effect of the fish caudal fin and its flexibility on the locomotion of swimming animals. The flexibility of the caudal fin is modeled by a torsion spring acting about the pivot at the conjuncture of the wavy foil and the flat plate. The study reveals that the passively oscillating flat plate contributes half of the propulsive force. The flexibility, represented by the nondimensional natural frequency F, plays a very important role in the movement and propulsive force generation of the whole body. When the plate is too flexible, the drag force is observed. As the flat plate becomes more rigid, the propulsive force that is generated when the undulation is confined to last part of the wavy foil becomes larger. The steady movement occurs at F=5. These results are consistent with the observations of some swimming animals in nature. © 2012 American Physical Society

Hypericin enhances β-lactam antibiotics activity by inhibiting sarA expression in methicillin-resistant Staphylococcus aureus.

Bacteremia is a life-threating syndrome often caused by methicillin-resistant Staphylococcus aureus (MRSA). Thus, there is an urgent need to develop novel approaches to successfully treat this infection. Staphylococcal accessory regulator A (SarA), a global virulence regulator, plays a critical role in pathogenesis and β-lactam antibiotic resistance in Staphylococcus aureus. Hypericin is believed to act as an antibiotic, antidepressant, antiviral and non-specific kinase inhibitor. In the current study, we investigated the impact of hypericin on β-lactam antibiotics susceptibility and mechanism(s) of its activity. We demonstrated that hypericin significantly decreased the minimum inhibitory concentrations of β-lactam antibiotics (e.g., oxacillin, cefazolin and nafcillin), biofilm formation and fibronectin binding in MRSA strain JE2. In addition, hypericin significantly reduced sarA expression, and subsequently decreased mecA, and virulence-related regulators (e.g., agr RNAⅢ) and genes (e.g., fnbA and hla) expression in the studied MRSA strain. Importantly, the in vitro synergistic effect of hypericin with β-lactam antibiotic (e.g., oxacillin) translated into in vivo therapeutic outcome in a murine MRSA bacteremia model. These findings suggest that hypericin plays an important role in abrogation of β-lactam resistance against MRSA through sarA inhibition, and may allow us to repurpose the use of β-lactam antibiotics, which are normally ineffective in the treatment of MRSA infections (e.g., oxacillin)

Mechanical properties of in-situ synthesis of Ti-Ti3Al metal composite prepared by selective laser melting

Titanium composite strengthened by Ti3Al precipitations is considered to be one of the excellent materials that is widely used in engineering. In this work, we prepared a kind of Ti-Ti3Al metallic composite by in-situ synthesis technology during the SLM (selective laser melting) process, and analyzed its microstructure, wear resistance, microhardness, and compression properties. The results showed that the Ti-Ti3Al composite, prepared by in-situ synthesis technology based on SLM, had more homogeneous Ti3Al-enhanced phase dispersion strengthening structure. The grain size of the workpiece was about 1 μm, and that of the Ti3Al particle was about 200 nm. Granular Ti3Al was precipitated after the aluminum-containing workpiece formed, with a relatively uniform distribution. Regarding the mechanical properties, the hardness (539 HV) and the wear resistance were significantly improved when compared with the Cp-Ti workpiece. The compressive strength of the workpiece increased from 886.32 MPa to 1568 MPa, and the tensile strength of the workpiece increased from 531 MPa to 567 MPa after adding aluminum. In the future, the combination of in-situ synthesis technology and SLM technology can be used to flexibly adjust the properties of Ti-based materials

Comparative study on appropriate drought and flood index selection in a tropical farming island in China

The traditional drought and flood analysis method had not fully considered the proportion analysis of different drought and flood grades in the historical years of each rainfall station. This made results unconvincing and made it difficult to deeply understand the characteristics and applicability of various methods. Based on the daily rainfall data of 88 stations in Hainan Island from 1970 to 2019, the China-Z index and the Standardized Precipitation Index (SPI) were used to compare and analyze the spatial and temporal distribution characteristics of droughts and floods from three different time scales (flood season, non-flood season and the whole year). The results showed that both SPI and China-Z index can well reflect the actual drought and flood situations in Hainan Island. The analysis of the proportions of different drought and flood grades in the historical years of each rainfall station and regional historical drought and flood statistics suggested that the China-Z index had a better indication effect than SPI on the extreme drought and flood grades. The alternation of drought and flood between different eras were obvious. Hainan Island generally presented an east-west reverse drought-flood variation trend, as well as a north-south reverse drought-flood variation trend. The drought and flood in the central mountainous area of Hainan Island had been relatively stable. The distribution pattern of drought and flood had a good spatial consistency in the three periods. On the whole, Hainan Island had shown a trend of flood in the east and drought in the west in the past 50 years

Additive manufacturing of bio-inspired ceramic bone scaffolds: structural design, mechanical properties and biocompatibility

Ideal bone scaffolds require good biocompatibility and moderate mechanical properties, so as to promote the proliferation and differentiation of osteoblast cells, and achieve the good bone repair. Inspired by the porous structure of cancellous bone, 15 groups of bone scaffolds with variable irregularity (Ir1-5) and porosity (35.53-61.75%) were designed and fabricated by ceramic digital light processing (DLP) using 20 wt.% hydroxyapatite doped zirconia as the matrix material. The effects of structural parameters and material on mechanical properties and biocompatibility were studied. The shrinkage test results showed that the density of scaffolds was mainly affected by the porosity. The mechanical test results showed that Ir2 and Ir3 scaffolds had better compressive behaviors, and the compressive strength could be increased by 30% by regulating the irregularity. All scaffolds showed comparable mechanical properties to that of cancellous bone. Cell experiments showed that the effect of structure on cell proliferation, differentiation, and mineralization was most evident at the early stage of implantation. Meanwhile, the biocompatibility variation with the irregularity was consistent with mechanical properties. This study proved that a bio-inspired bone scaffold with excellent comprehensive properties could be obtained through reasonable design

Zn-doped chitosan/alginate multilayer coatings on porous hydroxyapatite scaffold with osteogenic and antibacterial properties

Porous hydroxyapatite (HA) scaffolds prepared by three-dimensional (3D) printing have wide application prospects owing to personalized structural design and excellent biocompatibility. However, the lack of antimicrobial properties limits its widespread use. In this study, a porous ceramic scaffold was fabricated by digital light processing (DLP) method. The multilayer chitosan/alginate composite coatings prepared by layer-by-layer method were applied to scaffolds and Zn2+ was doped into coatings in the form of ion crosslinking. The chemical composition and morphology of coatings were characterized by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Energy dispersive spectroscopy (EDS) analysis demonstrated that Zn2+ was uniformly distributed in the coating. Besides, the compressive strength of coated scaffolds (11.52 ± 0.3 MPa) was slightly improved compared with that of bare scaffolds (10.42 ± 0.56 MPa). The result of soaking experiment indicated that coated scaffolds exhibited delayed degradation. In vitro experiments demonstrated that within the limits of concentration, a higher Zn content in the coating has a stronger capacity to promote cell adhesion, proliferation and differentiation. Although excessive release of Zn2+ led to cytotoxicity, it presented a stronger antibacterial effect against Escherichia coli (99.4%) and Staphylococcus aureus (93%)

Untersuchung zur Lernkultur in Online-Kursen

Ausgehend von einer veränderten, durch Lern- und Kompetenzorientierung geprägten Lernkultur analysieren die Autorinnen zwölf mehrwöchige Online-Kurse mit insgesamt 130 Teilnehmer/innen. Die Autorinnen nehmen ein Klima der hohen Wertschätzung unter den Lernenden wahr sowie gegenseitiges Feedback in den Reflexions- und Diskussionsprozessen, welches das Lernen verstärkt. Die Hypothese, dass in rein virtuellen, mehrwöchigen Weiterbildungskursen eine veränderte Lernkultur gefördert und gelebt wird, wird mittels halbstrukturierter Interviews sowie qualitativer Inhaltsanalyse der Beiträge in den Diskussionsforen untersucht. (DIPF/ Orig.

Genetic Variation of Promoter Sequence Modulates XBP1 Expression and Genetic Risk for Vitiligo

Our previous genome-wide linkage analysis identified a susceptibility locus for generalized vitiligo on 22q12. To search for susceptibility genes within the locus, we investigated a biological candidate gene, X-box binding protein 1(XBP1). First, we sequenced all the exons, exon-intron boundaries as well as some 5′ and 3′ flanking sequences of XBP1 in 319 cases and 294 controls of Chinese Hans. Of the 8 common variants identified, the significant association was observed at rs2269577 (p_trend = 0.007, OR = 1.36, 95% CI = 1.09–1.71), a putative regulatory polymorphism within the promoter region of XBP1. We then sequenced the variant in an additional 365 cases and 404 controls and found supporting evidence for the association (p_trend = 0.008, OR = 1.31, 95% CI = 1.07–1.59). To further validate the association, we genotyped the variant in another independent sample of 1,402 cases and 1,288 controls, including 94 parent-child trios, and confirmed the association by both case-control analysis (p_trend = 0.003, OR = 1.18, 95% CI = 1.06–1.32) and the family-based transmission disequilibrium test (TDT, p = 0.005, OR = 1.93, 95% CI = 1.21–3.07). The analysis of the combined 2,086 cases and 1,986 controls provided highly significant evidence for the association (p_trend = 2.94×10−6, OR = 1.23, 95% CI = 1.13–1.35). Furthermore, we also found suggestive epistatic effect between rs2269577 and HLA-DRB1*07 allele on the development of vitiligo (p = 0.033). Our subsequent functional study showed that the risk-associated C allele of rs2269577 had a stronger promoter activity than the non-risk G allele, and there was an elevated expression of XBP1 in the lesional skins of patients carrying the risk-associated C allele. Therefore, our study has demonstrated that the transcriptional modulation of XBP1 expression by a germ-line regulatory polymorphism has an impact on the development of vitiligo

Fabrication and properties of zirconia/hydroxyapatite composite scaffold based on digital light processing

Zirconia and hydroxyapatite(HA) are two typical implant materials, which have the advantages of excellent mechanical strength and good biological activity respectively. It was found that composite material had good biocompatibility and mechanical strength compared to the single material. In this paper, the porous scaffolds of ZrO2/HA composite were formed by digital light processing (DLP) technology and their performance were evaluated. Cell experiments showed that the addition of HA had a positive effect on cell proliferation and differentiation. Mechanical tests showed that the composite scaffold with 10 wt% HA had the best compressive capacity due to the pinning and bridging effect of a small amount of HA grains. When scaffolds were immersed in the simulated body fluid (SBF), the compressive strengths of the composite scaffolds decreased within the first 14 days and gradually increased after 14 days. The reason for this phenomenon was the degradation of calcium phosphate components and the deposition of apatite. By the 28th day, the compressive strengths of all the composite scaffolds increased to over 20 MPa, close to that of the zirconia scaffolds during the same period (25 MPa). The compressive strengths of all scaffolds met the requirement of cancellous bone during the entire soaking period, and the composite scaffolds have potential application value in bone repair

Improved proportionate FONLMS algorithm based direct adaptive Turbo equalization for MIMO underwater acoustic communications

In this paper, a novel normalized least mean squares (NLMS) algorithm that jointly updates the efficient of the linear equalizer and soft interference canceller (SIC) in an adaptive turbo equalizer for multiple-input multiple-output (MIMO) underwater acoustic (UWA) communications. To exploit the sparsity of MIMO UWA channels and enhance the convergence speed of adaptive equalization, improved proportionate fast self-optimized NLMS algorithm (IPFONLMS), is proposed to well adapt to sparse channel with the similar complexity as improve proportionate NLMS (IPNLMS) algorithm. Then we extend the proposed algorithm to the adaptive turbo equalization for MIMO UWA communications. The performance of the proposed adaptive algorithm is evaluated by numerical results. Simulation results show that the improved data efficiency and bit error ratio (BER) performance of the proposed receiver is achieved over adaptive turbo equalizer based on the IPNLMS algorithm