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The dynamic compressive responses of a multi–layer sandwich structures with the truss core were studied experimentally and numerically under the underwater explosion shock loading. A three–layer truss-core sandwich specimen was designed and fabricated from the stainless steel. The density gradient between core layers is realized by changing the cross-sectional size of the truss members in the core layer. A water tank explosion testing device was employed to carry out the underwater explosion experiment. The finite element method was used to investigate the influences of the layered strategy of structures and the density gradient between core layers on the dynamic response. The results reveal that the density–decreasing sandwich panels CBA has the optimal underwater explosion resistance, and the explosion resistance increases as the decrease of the density gradient ratio. [ABSTRACT FROM AUTHOR]

The parvorder Rhynchopthirina contains three currently recognised species of lice that parasitize elephants (both African savanna elephant Loxodonta africana and Asian elephant Elephas maximus), desert warthogs (Phacochoerus aethiopicus) and Red River hogs (Potamochoerus porcus), respectively. The Asian elephant lice and the African savanna elephant lice are currently treated as the same species, Haematomyzus elephantis (Piaget, 1869), based on morphology despite the fact that their hosts diverged 8.4 million years ago. In the current study, we sequenced 23 mitochondrial (mt) genes of African savanna elephant lice collected in South Africa and analysed the sequence divergence between African savanna elephant lice and previously sequenced Asian elephant lice. Sequence comparisons revealed >23% divergence for the 23 mt genes as a whole and ~17% divergence for cox1 gene between African savanna and Asian elephant lice, which were far higher than the divergence expected within a species. Furthermore, the mt gene sequence divergences between these lice are 3.76–4.6 times higher than that between their hosts, the African savanna and Asian elephants, which are expected for the co‐divergence and co‐evolution between lice and their elephant hosts. We conclude that (1) H. elephantis (Piaget, 1869) contains cryptic species and (2) African savanna and Asian elephant lice are different species genetically that may have co‐diverged and co‐evolved with their hosts. [ABSTRACT FROM AUTHOR]

A multilayer gradient double-corrugated sandwich plate was designed, and the finite element method was employed to investigate numerically the dynamic responses of the sandwich plate subjected to underwater blast loads. ALE modeling method was adopted to simulate the fluid-structure interaction between the water and sandwich plate. TNT explosive was modeled by the JWL model, and the 304 stainless steel used for the double-corrugated sandwich plate was modeled by Johnson-Cook constitutive model. The peak deflection of the back face sheet, the support reaction at the edge of the sandwich plate, and the energy absorption of the structure were discussed to assess the underwater blast resistance of the double-corrugated sandwich structure. The results show that the configuration P2 with the increasing core relative density has a better blast resistance ability and the weakest upper core layer of the configuration P2 has the greater contribution to reducing the impulse transmission to the sandwich structure. [ABSTRACT FROM AUTHOR]

The anti-penetration performance of the composite armor structures, which are composed of steel, Kevlar composite, and ultra-high molecular weight polyethylene (UHMWPE) composite, were investigated numerically. The effects of composite armor configurations, the thickness of back plates, the shapes and incident angles of projectile on the anti-penetration performance were analyzed. The results indicate that the configuration with steel, Kevlar and UHMWPE on the first, second and third layers of the composite armor have the better anti-penetration performance. As the thickness of the composites back plate increases, the specific energy absorption of the composite armor decreases while the anti-penetration performance of the composite armor increases. In addition, it can be also found that the ball-headed projectile has stronger penetration ability than the flat-headed projectile of the same weight, and the penetration ability of projectile decreases with the increase in the impact angle of projectile. [ABSTRACT FROM AUTHOR]

The dynamic responses of layered polyvinyl chloride (PVC) foam sandwich panels under air blast loads were investigated by employing 3D numerical simulation method. PVC foam of different densities and Kevlar composite were selected, respectively, as core and face sheets of sandwich panels. The quasi-static mechanical behavior of PVC foam was tested by a quasi-static compression experiment. Two types of density-graded panels (three-layer foam core and six-layer foam core) were analyzed under different explosive charge to explore the effect of gradient arrangement and the layer number of foam core. The validation of the simulation approach was studied by a comparison of simulation results with the existing experimental results from the literature. The deformation characteristics, support reactions and energy absorption of sandwich panels were analyzed to explore the blast resistance of the graded foam sandwich structures. It can be found that the gradient strategy of foam core has a significant influence on the PVC foam sandwich panel under air blast loads, and increasing the thickness of the back sheet is an effective measurement to improve the blast resistance of PVC foam sandwich panel with Kevlar face sheet. [ABSTRACT FROM AUTHOR]

A new type of composite armor, which is composed of the front steel plate, medium dual-layer piecewise ceramic tiles separated by steel grid and the Kevlar back plate, was designed based on the bio-inspiration. The failure mechanism, energy absorption, and the effect of the geometric parameters on ballistic response of composite armors were analyzed. The results show that the damage area of ceramic layer can be remarkably decreased by replacing a monolithic ceramic plate by the piecewise ceramic tiles, and the ballistic properties of armors can be enhanced by using multiple ceramic tiles separated by metal grids in composite armors. [ABSTRACT FROM AUTHOR]

The dynamic responses of multi-layer gradient pyramid lattice sandwich plates subjected to blast loadings were investigated by employing numerical simulation method in this paper. The relative densities of core layers were adjusted by varying cross-sectional dimensions of lattice truss. Six kinds of gradient configurations were proposed based on the arrangement of various lattice core layers. The mechanical properties of 304 stainless steel used in this analyses were simulated using rate-dependent JC constitutive model, and the blast loadings were imposed to the sandwich structures using CONWEP loading mode. The validation of the simulation approach was studied by a comparison of simulation results with the existing experimental results from the literature. The back sheet deflection and the support reaction were analyzed to evaluate the blast resistance of multi-layer gradient sandwich structures. It can be found that the gradient configuration, of which relative density of core layer increases layer by layer from front sheet to back sheet, has the most excellent blast resistance. The dynamic response of gradient lattice sandwich structures in the case of different standoff distances and different explosive charges were calculated. And the relationships between intensity of load and blast resistance of the gradient sandwich structures with pyramid lattice core were analyzed. [ABSTRACT FROM AUTHOR]

AbstractA hybrid sandwich panel with lightweight core composed of corrugated core and metallic foam were designed. The dynamic responses of this hybrid sandwich panels were numerically investigated under combined loading of blast and fragments by LS-DYNA software. To simulate this loading condition, the TNT charge was used to drive prefabricated fragments. The developed numerical approach was validated by using the existing experimental results. The effects of foam layer location, foam density, back plate configuration and stand-off distance on the dynamic response were systematically analyzed. The results indicate that the hybrid sandwich panels with corrugated and foam separation demonstrate higher protective capability. Compared with the foam-filled corrugated sandwich panels, the energy absorption is increased by up to 16.3%. Increasing the foam density can enhance the impact resistance of the structure under combined loading of blast and fragments. The back plate with composite plate has better anti-fragmentation ability than the steel plate. [ABSTRACT FROM AUTHOR]

The importance of selenium (Se) in biology and health has become increasingly clear. Hydrogen selenide (H 2 Se), the biologically available and active form of Se, is suggested to be an emerging nitric oxide (NO)-like signaling molecule . Nevertheless, the research on H 2 Se chemical biology has technique difficulties due to the lack of well-characterized and controllable H 2 Se donors under physiological conditions, as well as a robust assay for direct H 2 Se quantification. Motivated by these needs, here, we demonstrate that selenocyclopropenones and selenoamides are tunable donor motifs that release H 2 Se upon reaction with cysteine (Cys) at pH 7.4 and that structural modifications enable the rate of Cys-mediated H 2 Se release to be tuned. We monitored the reaction pathways for the H 2 Se release and confirmed H 2 Se generation qualitatively using different methods. We further developed a quantitative assay for direct H 2 Se trapping and quantitation in an aqueous solution, which should also be operative for investigating future H 2 Se donor motifs. In addition, we demonstrate that arylselenoamide has the capability of Cys-mediated H 2 Se release in cellular environments. Importantly, mechanistic investigations and density functional theory (DFT) calculations illustrate the plausible pathways of Cys-activated H 2 Se release from arylselenoamides in detail, which may help understand the mechanistic issues of the H 2 S release from pharmacologically important arylthioamides. We anticipate that the well-defined chemistries of Cys-activated H 2 Se donor motifs will be useful for studying Se biology and for development of new H 2 Se donors and bioconjugate techniques.