Summary
Biological invasions are determined by interactions between resident plant communities and exotic plants. Time of invasion and species diversity of resident plant communities may greatly ...affect exotic plant invasions. We assembled low‐ and high‐diversity resident plant communities by sowing seeds of four and eight grassland species, respectively, and at each of three time periods (1, 4 and 7 weeks after sowing), the resident communities were invaded by Hydrocotyle vulgaris or not. We also constructed a plant community with H. vulgaris alone. Presence of H. vulgaris had no effect on biomass of the resident communities or biomass of each component species. Community age significantly affected biomass and evenness of the resident communities, and their competition with H. vulgaris, but the priority effect of the resident communities was slight. Increasing species richness did not change the interaction between H. vulgaris and the resident plant communities. These findings suggest a weaker competitive exclusionary effect of H. vulgaris on the resident communities with early germination, and H. vulgaris tended to have no significant impact on intact resident terrestrial plant communities. Thus, the potential risk of H. vulgaris invasion is low, especially in the communities with young age.
Maternal and paternal factors create considerable obstacles to the elimination of congenital syphilis (CS). A clear understanding of maternal and paternal factors is important in order to define ...interventions in every community. This study aimed to investigate the maternal and paternal factors associated with CS. A prospective cohort study was conducted from April 25, 2007 to October 31, 2012 at the Shenzhen Center for Chronic Disease Control and Prevention (SCCDC) in China. We screened 279,334 pregnant women and identified 838 women with syphilis. Finally, a total of 360 women with syphilis were included for analysis. At the end of follow-up, 34 infants 9.4 %, 95 % confidence interval (CI): 6.8–12.9 % were diagnosed with CS. Following adjustment for confounders, maternal history of syphilis adjusted risk ratio (aRR) = 0.21, prenatal care (aRR = 0.12), and complete treatment (aRR = 0.22) reduced the risk of infants being infected. Every two-fold increase of titer of non-treponemal antibodies (aRR = 1.88), early stage of syphilis (aRR = 9.59), a shorter length of time between the end of the first treatment to childbirth (aRR = 5.39), and every week of delay in treatment (aRR = 2.25) for maternal syphilis as well as paternal history of cocaine use (aRR = 6.28) and positive (aRR = 3.30) or unknown (aRR = 2.79) status of syphilis increased the risk of infants being infected. CS also increased the risk (aRR = 8.02) of neonatal death. Maternal and paternal factors constituted two separate profiles associated with CS. To become more effective, future strategies for the prevention of CS should be targeted to each profile.
The large deflections of slender ultralight sandwich beams with a metallic foam core are studied under transverse loading by a flat punch, in which interaction of bending and stretching induced by ...large deflections is considered. Firstly, a unified yield criterion for metallic sandwich structures considering the effect of core strength is proposed, which is valid for metallic sandwich cross-sections with various core strengths and geometries. This can reduce to the yield criterion for a solid monolithic cross-section and the classical yield criterion for sandwich cross-sections with a weak core, respectively. Then, analytical solutions for the large deflections of fully clamped and simply supported metallic foam core sandwich beams are derived under transverse loading by a flat punch, respectively. Comparisons of the present solutions with experimental results are presented and good agreements are found. The effects of the core strength, the size of loading punch and the boundary conditions on the structural response of sandwich beams are discussed in detail. It is shown that the axial stretching induced by large deflections has significant effect on the load-carrying and energy absorption capacities of sandwich structures in the post-yield regime, and the load-carrying and plastic energy absorption capacities of metallic foam core sandwich beams may be underestimated as the core strength is neglected in analysis, especially for the sandwich beams with a strong core.
► The combination influences of the various microstructural changes in thermally exposed K446 alloy on the mechanical properties are examined. ► μ phase evolves slower near the grain boundaries than ...within the grains due to the inhomogeneous distribution of elements. ► The μ precipitation is more detrimental to the mechanical properties than the γ′ coarsening in the present alloy. ► The combination of the beneficial and harmful considerations makes the elongations tend to present a peak value during exposure.
Microstructural evolution and microstructure-property relationship during long-term thermal exposure in K446 alloy are investigated in detail. The coarsening rate of γ′ precipitates increases with the rise of exposure temperature, yet decreases with the increment of exposure time. Primary MC carbides present an excellent stability and decompose to a tiny degree by two reaction forms, which have an insignificant influence on the properties. TCP-μ phase precipitates from the supersaturated matrix in the forms of needles and granules and experiences a remarkable evolution with prolonged exposure; the μ phase near the grain boundaries (GBs) evolves slower than that within the grains due to the inhomogeneous distribution of elements. In addition, the precipitation of μ phase is determined to be more detrimental to the mechanical properties than the γ′ coarsening in the present alloy.
•Dynamic response of geometrically asymmetric sandwich plates with aluminum hexagonal honeycomb core subjected to blast loading is investigated experimentally.•The analytical model is developed to ...predict the blast response of the geometrically asymmetric sandwich plate subjected to blast loading.•Some new deformation and damage modes are obtained for geometrically asymmetric sandwich plates.
Dynamic response of geometrically asymmetric sandwich plates with aluminum hexagonal honeycomb core subjected to blast loading is investigated experimentally and theoretically. Specimens of various face sheet thicknesses are tested for three blast intensities which are varied by changing the weights of cyclotrimethylene trinitramine (RDX) explosive charges at a constant standoff distance. Four edges of sandwich plates are fully clamped. The deformation and damage modes of sandwich plates are obtained. The influences of the blast loading and the core density on the dynamic response of sandwich plates are analyzed. The analytical model is developed to predict the blast response of the geometrically asymmetric sandwich plate subjected to blast loading. It is shown that the theoretical predictions of the deflection of the center point at the rear face sheet is in good agreement with the experimental results. The geometrical asymmetry due to the thicknesses of the face sheets has a significant effect on the deformation and damage of sandwich plates.
The dynamic response of physically asymmetric rectangular sandwich plates with metal foam core subjected to blast loading is investigated analytically and numerically. The so-called ‘bounds’ of ...analytical solutions for the maximum central deflection of back face-sheets and the structural response time are obtained, respectively, by employing the yield criteria for an asymmetric sandwich structure including core compression. Furthermore, an improved membrane mode analysis considering the ‘residual’ bending moment for asymmetric sandwich plates is presented and the membrane mode solutions are given. It is shown that there is a good agreement between the theoretical predictions and the numerical results. Based on the analytical formulae, optimal design charts are constructed to maximize the impulsive resistance of physically asymmetric sandwich plates for a given mass. Finally, the performances of optimally designed sandwich plates with various face-sheet material combinations are discussed.
Pheochromocytomas and paragangliomas (PGL) are neuroendocrine tumors of sympathetic and parasympathetic paraganglia. This study investigated the relationships between genotype-specific differences in ...mitochondrial function and catecholamine content in PGL tumors.
Respiratory chain enzyme assays and (1)H-nuclear magnetic resonance (NMR) spectroscopy at 500 MHz were conducted on homogenates of 35 sporadic PGLs and 59 PGLs from patients with hereditary mutations in succinate dehydrogenase subunits B and D (SDHB, SDHD), succinate dehydrogenase assembly factor 2, von Hippel-Lindau (VHL), rearranged during transfection (RET), neurofibromatosis type 1 (NF1), and myc-associated factor X.
In SDHx-related PGLs, a significant decrease in complex II activity (P < 0.0001) and a significant increase in complex I, III, and IV enzyme activities were observed when compared to sporadic, RET, and NF1 tumors. Also, a significant increase in citrate synthase (P < 0.0001) enzyme activity was observed in SDHx-related PGLs when compared to sporadic-, VHL-, RET-, and NF1-related tumors. An increase in succinate accumulation (P < 0.001) and decrease in ATP/ADP/AMP accumulation (P < 0.001) was observed when compared to sporadic PGLs and PGLs of other genotypes. Positive correlations (P < 0.01) were observed between respiratory chain complex II activity and total catecholamine content and ATP/ADP/AMP and total catecholamine contents in tumor tissues.
This study for the first time establishes a relationship between determinants of energy metabolism, like activity of respiratory chain enzyme complex II, ATP/ADP/AMP content, and catecholamine content in PGL tumors. Also, this study for the first time successfully uses NMR spectroscopy to detect catecholamines in PGL tumors and provides ex vivo evidence for the accumulation of succinate in PGL tumors with an SDHx mutation.
The compressive strengths and dynamic response of corrugated sandwich plates with unfilled and foam-filled sinusoidal plate cores are investigated. The “effective” compressive strengths of the ...unfilled and foam-filled sinusoidal plate cores are derived and numerically analyzed. Finite element method is employed to analyze the dynamic response of fully clamped metal sandwich plates with unfilled and foam-filled sinusoidal plate cores subjected to impulsive loading. Moreover, a simplified plastic-string model is developed to analytically predict the large deflection and time responses of the clamped sandwich plates under impulsive loading. One can see a good agreement between the analytical and numerical predictions. It can be seen that the present analytical procedure is efficient and simple to evaluate the dynamic response of corrugated sandwich plates.
Tension–tension fatigue tests are carried out to investigate the fatigue of closed-cell aluminum alloy foam. The stress–life (S–N) curve of the foam is obtained, in which large scatter is observed ...and discussed in detail. To understand the scatter of fatigue life of the foam, fracture surface is examined. The fatigue life decreases as the number and the size of large cells increase. The irregularity of inner cell structure of the foam attributes to the scatter of fatigue life. Then, a statistical stress–life model is developed, and a series of statistical probability–stress–life (P–S–N) curves are obtained. The P–S–N curve is efficient in describing the fatigue of foam materials.
•Tensile fatigue tests are carried out for closed-cell aluminum alloy foam.•Large scatter of fatigue life is observed at each fatigue loading level.•Inner cell structure attributes to the scatter of fatigue life of foam.•Statistical P–S–N curves are established for foam material.
PDF
