The swimming locomotion of fish involves a complex interplay between a deformable body and induced flow in the surrounding fluid. While innovative robotic devices, inspired by physicomechanical designs evolved in fish, have been created for underwater propulsion of large swimmers, scaling such powerful locomotion into micro-/nanoscale propulsion remains challenging. Here, a magnetically propelled fish-like artificial nanoswimmer is demonstrated that emulates the body and caudal fin propulsion swimming mechanism displayed by fish. To mimic the deformable fish body for periodic shape changes, template-electrosynthesized multisegment nanowire swimmers are used to construct the artificial nanofishes (diameter 200 nm; length 4.8 μm). The resulting nanofish consists a gold segment as the head, two nickel segments as the body, and one gold segment as the caudal fin, with three flexible porous silver hinges linking each segment. Under an oscillating magnetic field, the propulsive nickel elements bend the body and caudal fin periodically to generate travelling-wave motions with speeds exceeding 30 μm s . The propulsion dynamics is studied theoretically using the immersed boundary method. Such body-deformable nanofishes exhibit a high swimming efficiency and can serve as promising biomimetic nanorobotic devices for nanoscale biomedical applications.

No abstract

The coronavirus disease 2019 (COVID‐19) is a pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). However, little is known about the durability of the antibody response during COVID‐19 convalescent phase. We investigated the prevalence of anti‐SARS‐CoV‐2 specific antibodies including immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies and the dynamic changes in antibody levels in convalescent COVID‐19 patients. A total of 159 blood samples were collected from 52 recovered COVID‐19 patients up to six months after symptom onset for longitudinal serological tests. The positive rate of IgG and IgM antibodies was 92.3% and 90.4% in the first month after symptom onset, and the seropositivity of IgG antibody remained high at all follow‐up time points, whereas the seropositivity of IgM antibody decreased to 22.73% by the sixth months after symptom onset. The level of IgG antibody was stable, the level of IgM antibody decreased slightly in the early convalescent phase and was detected in only five patients in the sixth month after symptom onset. The level of IgG antibody was higher in the severe and critical group than in the moderate group. The anti‐SARS‐CoV‐2 specific antibodies have a long‐term persistence in convalescent COVID‐19 patients, whether they have long‐term protection need to be further investigated.

No abstract

Background and AimsDifferences in local abundance and ploidy level are predicted to impact the direction of introgression between species. Here, we tested these hypotheses on populations of Betula albosinensis (red birch) and Betula platyphylla (white birch) which were thought to differ in ploidy level, the former being tetraploid and the latter diploid.MethodsWe sampled 391 birch individuals from nine localities in China, and classified them into species based on leaf morphology. Twelve nuclear microsatellite markers were genotyped in each sample, and analysed using principal coordinates analysis and STRUCTURE software. We compared the effects of two different methods of scoring polyploid genotypes on population genetic analyses. We analysed the effect of ploidy, local species abundance and latitude on levels of introgression between the species.Key ResultsLeaf morphology divided our samples into red and white birch, but genetic analyses unexpectedly revealed two groups within red birch, one of which was tetraploid, as expected, but the other of which appeared to have diploid microsatellite genotypes. Five individuals were identified as early-generation hybrids or backcrosses between white birch and red birch and five were identified between red birch and ‘diploid’ red birch. Cline analysis showed that levels of admixture were not significantly correlated with latitude. Estimated genetic differentiation among species was not significantly different between determined tetraploid and undetermined tetraploid genotypes.ConclusionsLimited hybridization and gene flow have occurred between red birch and white birch. Relative species abundance and ploidy level do not impact the direction of introgression between them, as genetic admixture is roughly symmetrical. We unexpectedly found populations of apparently diploid red birch and this taxon may be a progenitor of allotetraploid red birch populations. Incomplete lineage sorting may explain patterns of genetic admixture between apparently diploid and allotetraploid red birch.