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Hydrogel is an emerging material widely used in the biological field. The tensile properties of hydrogel mainly depend on its polymer network, but due to the complex microstructure of the network, some properties of the hydrogel have yet to be quantitatively analyzed. In this article, we built a three-dimensional random fiber network to characterize the microstructure of a hydrogel. The fibers were simplified as elastic beams, and the cross-links were regarded as "hinges." Combined with the macroscopic experimental results, the influence of the change of fiber length and the relationship between the polymer content and the cross-link density were studied. The model was verified by the quasi-static tensile test results of real PVA hydrogel materials with different fiber contents. The results show that the model can well match the tensile stress–strain curve and tensile strength of the PVA hydrogels with different fiber contents. The change in microstructure of the fiber network induces nonlinear behaviors, and although the cross-link number increases with the increase in polymer content, the cross-link density (per unit PVA chain length) of the PVA hydrogel slightly decreases as the content increases. [ABSTRACT FROM AUTHOR]

The increase in population, the development of industry and agriculture, and the exploitation and utilization of natural resources have inevitably caused a series of ecological and environmental problems, including trace metal pollution. Quantifying the influence of human activities on the metal concentrations of an aqueous environment is helpful for understanding the process and the relationship between socioeconomic development and ecological environmental quality at the macro level. We investigated how human activities and natural variabilities influence the concentrations and distributions of trace metals in the aquatic environment of the heavily sediment-laden Yellow River (> 5000 km). The results showed that the relevant indicators of human activities, such as the population density, average GDP, the number of industrial enterprises above a designated size, percent cropland, percent impervious surface, and the proportion of total crops sown area, had significant positive effect on the concentrations and distributions of some metals in the water environment with a weight of 33∼64%. Moreover, percent grassland and percent wetland exhibited a significant negative correlation with metals. Rapid population growth and socioeconomic development have accelerated the production of metals and other pollutants, that eventually enter the aquatic environment via runoff or other methods through a series of migrations and transformations; thus, the scope of pollution has gradually increased. Some artificially constructed prevention, control and repair measures have played a role in mitigating the effects of environmental pollutants, including metals. This study contributes to the development of effective strategies for controlling metal pollution in the Yellow River basin. [Display omitted] • Distributions of trace metals were investigated in the sediment-laden Yellow River. • Concentration of most metals in water environment showed a significant difference. • Human activities positively affect metal concentrations with a weight of 33∼64%. • Grassland and wetland mitigated metal pollution load into the sediment-laden river. [ABSTRACT FROM AUTHOR]

As increasing numbers of people run VoIP softphones on their laptops and smartphones, vulnerabilities in VoIP protocols and systems introduce new threats to the computer systems that run VoIP softphones. This paper investigates key threats that target VoIP hosts and techniques for mitigating the threats. In particular, this paper shows that crafted SIP traffic can disable a Windows XP host that runs a Vonage VoIP softphone or a Linphone by consuming almost all the free memory within minutes. While this “noisy attack” can be effectively mitigated by threshold-based filtering, the paper demonstrates that a “stealthy attack” can be launched to defeat threshold-based filtering and disable the host computer without ever ringing the softphone. To mitigate the stealthy attack, the paper describes a limited context aware filtering approach that leverages the context and SIP protocol information to ascertain the intentions of a SIP message on behalf of the client. Experiments demonstrate that limited context aware filtering can effectively defeat a stealthy attack while allowing legitimate VoIP traffic and calls to go through. [ABSTRACT FROM AUTHOR]

Litters of three dominant shrubs were chosen to assess the influence of habitat and litter quality on litter decomposition rates in Horqin Sandy Land, Northern China. Litter in 20 x 25 cm litter bags of 2 x 2 mm mesh size were added to the depth of 0 cm and 10 cm in the sand soil along a habitat gradient of sand dune stabilization and restoration: mobile dune, semi-mobile dune, semi-fixed dune and fixed dune. Litter mass loss was measured five times to evaluate changes in decomposition rates. Results showed that litter decomposition rates increased along the habitat gradient of sandy dune restoration, and litter in fixed dune decomposed significantly faster than that in mobile dune. A. halodendron litter decomposed significantly faster than C. microphylla and S. gordejevii litter in sandy dunes. Litter decomposition rates increased about 5% per month from May to September. Litters buried 10 cm deep decomposed much faster than that on the soil surface. Pearson's correlation analysis showed that residual lignin content and the lignin:C ratio were significantly and positively correlated with decomposition rates, indicating that lignin content plays an important role in litter decomposition rates. [ABSTRACT FROM AUTHOR]