A dense exopolysaccharide (EPS) matrix is crucial for cyanobacterial survival in terrestrial xeric environments, in which cyanobacteria undergo frequent expansion and shrinkage processes during environmental desiccation-rehydration cycles. However, it is unclear how terrestrial cyanobacteria coordinate the structural dynamics of the EPS matrix upon expansion and shrinkage to avoid potential mechanical stress while benefiting from the matrix. In the present study, we sought to answer this question by investigating the gene expression, protein dynamics, enzymatic characteristics, and biological roles of WspA, an abundantly secreted protein, in the representative terrestrial cyanobacterium Nostoc flagelliforme The results demonstrated that WspA is a novel β-galactosidase that facilitates softening of the EPS matrix by breaking the polysaccharide backbone under substantial moisture or facilitates the thickening and relinkage of the broken matrix during the drying process, and thus these regulations are well correlated with moisture availability or desiccation-rehydration cycles. This coordination of flexibility and rigidity of the cyanobacterial extracellular matrix may contribute to a favorable balance of cell growth and stress resistance in xeric environments.IMPORTANCE How the exopolysaccharide matrix is dynamically coordinated by exoproteins to cope with frequent expansion and shrinkage processes in terrestrial colonial cyanobacteria remains unclear. Here we elucidated the biochemical identity and biological roles of a dominant exoprotein in these regulation processes. Our study thus gained insight into this regulative mechanism in cyanobacteria to combat periodic desiccation. In addition, the filamentous drought-adapted cyanobacterium Nostoc flagelliforme serves as an ideal model for us to explore this issue in this study.
By a great deal of production practice,it discussed the three factors that influence the effect of the colour blended woollen fabrics,that is,raw material properties,colour matching and technology,and drew certain beneficial conclusion.
As a state-of-the-art method, the digital image correlation (DIC) technique is used to capture the fracture properties of wood along the longitudinal direction, such as the crack propagation, the strain field, and the fracture process zone (FPZ). Single-edge notched (SEN) specimens made of Douglas fir (Pseudotsuga menziesii) from Canada with different notch-to-depth ratios are tested by three-point-bending (3-p-b) experiment. The crack mouth opening displacements (CMOD) measured by the clip gauge and DIC technique agree well with each other, verifying the applicability of the DIC technique. Then, the quasi-brittle fracture process of wood is analyzed by combing the load-CMOD curve and the strain field in front of the preformed crack. Additionally, the equivalent elastic crack length is calculated using the linear superposition hypothesis. The comparison between the FPZ evolution and the equivalent elastic crack shows that specimens with higher notch-to-depth ratios have better cohesive effect and higher cracking resistance.
Abstract The use of bio-based biomass construction materials has the advantage of helping to reduce fossil energy demand, protecting the environment from carbon dioxide emission and reducing the production of non-degradable waste. This paper used resin-modified soy protein (SP) adhesive to combine rice straw stalks, and made straw-soy protein composites (SSPC) material. The physical properties, compressive behavior and stability during wetting drying cycles of SSPC were measured. Due to water evaporation, the SP matrix is full of connected pores, resulting to its physical properties of small density, high shrinkage ratio and low thermal conductivity, which are 0.24 g/cm 3 , 16.2%, and 0.065 W/(m•K), respectively. Adding straw is helpful to the physical properties of SP matrix, leading to an obvious decrease in shrinkage ratio and thermal conductivity of SSPC, which are 8.51% and 0.075 W/m•K. Furthermore, the compressive load–displacement curves of SSPC groups divide into two types: divergent and convergent. The compressive strength of divergent samples is decided by the critical displacement determined according to the convergent specimens. It shows that straw stalk proves the positive effect on the compressive property of SP matrix. As to the mass of SSPC samples during the wetting drying cycles, it drops apparently in the initial three cycles, and becomes negligible from the fifth cycle, meaning that the stability of SSPC during wetting drying cyclic process is quite good. The research result would be helpful for using SSPC as building material, especially as thermal insulation material.
The aim of the study was to evaluate the effect of radiation sterilization on biocompatibility of a disposable burette transfusion apparatus, in order to assess the safety of radiation sterilized medical devices. The initial bacteria burden of the burette transfusion apparatus was examed according to the ISO11737 standard, we combined cytotoxicity test, sensitization test and dermal irritation test to evaluate the tissue compatibility of the radiation sterilized samples, and the genotoxicity was investigated with chromosomal aberration test and micronucleus test. The study determined the verified sterilizing dosage at the level of 9.4kGy, results show the sample products had no cytotoxicity, no sensitization, no intracutaneous irritation, no genotoxicity in chromosome aberration test, and will not increase the micronucleus rate of PCE (p<;0.05). Disposable burette transfusion apparatus showed good tissue compatibility and had no genotoxicity after radiation sterilization. Radiation sterilization is a biologically safe method for sterilization of medical devices.
Triaxial tests were employed to investigate palm-fiber-reinforced sand under consolidated drained conditions in this study. Sixteen series of triaxial tests were carried out to investigate the properties of palm-fiber-reinforced sand. One series of pure sand was also employed for comparison. The deviator stress, stress path, shear strength, volume change, void ratio, and enhanced coefficient of fiber-reinforced sand were studied with different fiber lengths varying from 8 mm to 20 mm and fiber contents varying in mass from 0.3% to 0.9%. The test results indicate that palm fibers were beneficial for enhancing the shear strength of the sand. Compared to the peak shear strength increase of about 10% to 20%, the critical shear strength increased much more, by a little over 100%. Therefore, the fibers played a key role in enhancing the critical shear strength of the sand but not the peak shear strength of the sand. The addition of fiber to sand resulted in prolongation of the axial strain required to reach the critical void ratio and improved the sand’s ability to resist larger deformations, enhancing its toughness. Furthermore, the critical shear strength of the sand was positively correlated with both fiber content and fiber length, and the axial strain required to reach the critical shear strength increased with increasing fiber content and length. This study provides valuable experimental data and serves as a reference for temporary reinforcement in geotechnical engineering.
Abstract The cracking of fibrous composites is inevitable, and the cracking mode is depended on its fiber distribution. In this study, bamboo fibrous composites are selected to investigate the effect of fiber distribution on crack propagation. Glued-laminated bamboo (Glubam) is a bi-directional bamboo fibrous composites, usually used as a board member, its vertical thickness (V direction) is about 28 mm, and with the longitudinal fiber layers (L direction) to transverse fiber layers (T direction) setting a 4:1. Considering that there are fewer transverse fibers in glubam, it is more prone to cracking under transverse load, this study researches the mode-I fracture characteristics of glubam in the TV direction. The three-point bending (3-p-b) fracture test of glubam specimens with single-edge notches (SEN) was carried out in this study. The deformation curves show that the specimens still have the load-carrying capacity after reaching the maximum load, and the load shows a trend of step-like decrease, exhibiting a quasi-ductile fracture behavior. Overall, the fracture process can be divided into four stages, including linear, softening, quasi-ductile, and failure stages. In this study, the tensile strength f t and fracture toughness K IC of glubam in the softening and quasi-ductile stages are calculated using nonlinear elastic fracture mechanics (Non-LEFM) method, and the prefabricated crack length a 0 is modified according to the location of the transverse fibers. The deviations of the fracture parameters in the two stages are within 10%, which indicates that the modification of the prefabricated crack length is correct and indirectly demonstrates the correlation between the fracture parameters of the quasi-ductile stage and the transverse fiber position. On the other hand, quasi-ductile fractures exist in other materials and structures, and they all have staggered structures. This staggered structure makes the crack in the form of semi-stable propagation, while the load decreases in a step-like manner.
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