Stress-corrosion coupled damage localization induced by secondary phases in bio-degradable Mg alloys:phase-field modeling

In this study,a phase-field scheme that rigorously obeys conservation laws and irreversible thermodynamics is developed for modeling stress-corrosion coupled damage(SCCD).The coupling constitutive relationships of the deformation,phase-field damage,mass transfer,and electrostatic field are derived from the entropy inequality.The SCCD localization induced by secondary phases in Mg is numerically simulated using the implicit iterative algorithm of the self-defined finite elements.The quantitative evaluation of the SCCD of a C-ring is in good agreement with the experimental results.To capture the damage localization,a micro-galvanic corrosion domain is defined,and the buffering effect on charge migration is explored.Three cases are investigated to reveal the effect of localization on corrosion acceleration and provide guidance for the design for resistance to SCCD at the crystal scale.

Similarities and differences in gastrointestinal microbiomes between wild and human-cared spotted dolphins(Stenella attenuata)in natural waters

Despite the growing awareness on the importance of gut microbiomes,understanding marine mammal gut microbiomes remains limited due to difficulties in sampling.Spotted dolphins(Stenella attenuata)are widely spread oceanic cetaceans,and there is a gap in knowledge regarding their gut microbiology.In this study,we opportunistically collected samples from both wild and human-cared spotted dolphins in the southern waters of Hainan Island,China.This provided the opportunity to examine the composition and diversity of the gut microbial communities of this cetacean species.Since these dolphins inhabit a similar water environment,different food sources might be the primary factor distinguishing the gut microbiomes of wild and human-cared populations,offering valuable experimental material to investigate potential differences in gut microbial community structure among marine mammals in similar environments but with varying food sources.We found that the gastrointestinal microbial community structure of wild and human-cared dolphins demonstrated significant differences,both overall and at specific locations.However,no significant difference was observed in the microbial diversity of their gastrointestinal tracts,indicating that the disparities primarily lie in microbiota composition.Additionally,we detected numerous potentially pathogenic bacteria,suggesting a comprehensive future study of marine mammal gut microbiology.Such a study might involve determining health indicator factors associated with these microbiomes.Our study not only supplements information on the gut microbiology of spotted dolphins but also delves into the similarities and differences in gastrointestinal microbial communities within the same marine mammal species when food source variations play a significant role in their lives.

Microbial diversity and structure in the gastrointestinal tracts of two stranded short-finned pilot whales(Globicephala macrorhynchus)and a pygmy sperm whale(Kogia breviceps)

Information on the gut microbiome composition of different mammals could provide novel insights into the evolution of mammals and succession of microbial communities in different hosts.However,there is limited information on the gut microbiome composition of marine mammals,especially cetaceans because of sampling constraints.In this study,we investigated the diversity and composition of microbial communities in the stomach,midgut,and hindgut of 2 stranded short-finned pilot whales(Globicephala macrorhynchus)and hindgut of a stranded pygmy sperm whale(Kogia breviceps)by using 16S rRNA gene amplicon sequencing technology.On the basis of the 50 most abundant operational taxonomic units,principal coordinate analysis,and non-metric multidimensional scaling analysis,we confirmed that the gut microbial communities of the 3 whales were different.Our results revealed that the gut microbiome of 1 stranded short-finned pilot whale GM16 was dominated by Firmicutes(mainly Clostridium)and Fusobacteria;whereas that of the other pilot whale GM19 was composed of Gammaproteobacteria and Bacteroidetes(mainly Vibrio and Bacteroides,respectively),probably caused by intestinal disease and antibiotic treatment.The gut microbiome of the pygmy sperm whale was dominated by Firmicutes and Bacteroidetes.Moreover,different gastrointestinal tract regions harbored different microbial community structures.To our knowledge,this is the first report of the gut microbiome of short-finned pilot whales,and our findings will expand our current knowledge on microbial diversity and composition in the gastrointestinal tract of cetaceans.