Development of a Bird-like Flapping-wing Aerial Vehicle with Autonomous Take-off and Landing Capabilities

The lack of autonomous take-off and landing capabilities of bird-like flapping-wing aerial vehicles(BFAVs)seriously restricts their further development and application.Thus,combined with the current research results on the autonomous take-off and landing technology of unmanned aerial vehicles,four types of technologies are studied,including jumping take-off and landing technology,taxiing take-off and landing technology,gliding take-off and landing technology,and vertical take-off and landing(VTOL)technology.Based on the analytic hierarchy process(AHP)-comprehensive evaluation method,a fuzzy comprehensive evaluation model for the autonomous take-off and landing scheme of a BFAV is established,and four schemes are evaluated concretely.The results show that under the existing technical conditions,the hybrid layout VTOL scheme is the best.Furthermore,the detailed design and development of the prototype of a BFAV with a four-rotor hybrid layout are carried out,and the vehicle performance is tested.The results prove that through the four-rotor hybrid layout design,the BFAV has good autonomous take-off and landing abilities.The power consumption analysis shows that for a fixed-point reconnaissance mission,when the mission radius is less than 3.38 km,the VTOL type exhibits longer mission duration than the hand-launched type.     

Postmating Reproductive isolation between strains of Drosophila willistoni

Speciation can occur through the presence of reproductive isolation barriers that impede mating, restrict cross-fertilization, or render inviable/sterile hybrid progeny. The D. willistoni subgroup is ideally suited for studies of speciation, with examples of both allopatry and sympatry, a range of isolation barriers, and the availability of one species complete genome sequence to facilitate genetic studies of divergence. D. w. willistoni has the largest geographic distribution among members of the Drosophila willistoni subgroup, spanning from Argentina to the southern United States, including the Caribbean islands. A subspecies of D. w. willistoni, D. w. quechua, is geographically separated by the Andes mountain range and has evolved unidirectional sterility, in that only male offspring of D. w. quechua females × D. w. willistoni males are sterile. Whether D. w. willistoni flies residing east of the Andes belong to one or more D. willistoni subspecies remains unresolved. Here we perform fecundity assays and show that F1 hybrid males produced from crosses between different strains found in Central America, North America, and northern Caribbean islands are reproductively isolated from South American and southern Caribbean island strains as a result of unidirectional hybrid male sterility. Our results show the existence of a reproductive isolation barrier between the northern and southern strains and suggest a subdivision of the previously identified D. willistoni willistoni species into 2 new subspecies.     

An analysis of epiphytic lichen communities in Tasmanian cool temperate rainforest

A three-dimensional compositional pattern in the epiphytic lichen vegetation in Tasmanian cool temperate rainforest is demonstrated using the robust ordination technique, hybrid multidimensional scaling (HMDS). The first two dimensions are correlated with the age of the host tree (and the concomitant change in bark texture) and wetness of the substrate. No measured environmental variable is related to the third dimension, which is tentatively attributed to a gradient in the constancy of the microclimate. Patterns of richness of lichen growth forms and the cover of bryophytes are correlated with the three putative environmental gradients. Possible successional trends between 12 community groups derived by numerical classification are described with respect to changes in substrate age, wetness and microclimatic constancy. Temporal variation of these factors due to tree growth, together with the slow establishment and long persistence of some lichen species, make succession in epiphytic communities very complex. This study demonstrates the value of HMDS in identifying compositional patterns and generating hypotheses about the causal ecological factors. The existence of the postulated microclimatic constancy gradient was not appreciated before the analysis and its discovery illustrates the risk of relying on constrained ordination methods, such as canonical correspondence analysis.Abbreviations HMDS Hybrid multidimensional scaling - NMDS Non-metric multidimensional scaling     

Comparison of coligenoid formation by B subunits of porcine and human Escherichia coli heat-labile enterotoxins

A hybrid B subunit (coligenoid) of heat-labile enterotoxin could not be made from human heat-labile enterotoxin B subunit(LTh-B) and porcine LTp-B subunit(LTp-B). LTp-B monomer was able to form coligenoid by reassociation with homologous LTp-B monomer, but not with heterogeneous LTh-B monomer and vice versa. The dissociation of both coligenoids into monomers by SDS treatment occurred in a time-dependent manner, but the dissociation of LTh-B colligenoid was faster than that of LTp-B coligenoid. The association of LTp-B monomer is tighter than that of LTh-B monomer. The pI values of LTp-B coligenoid, LTp-B monomer and denatured LTp-B monomer were similar at 9.6-9.8, while the pI values of LTh-B coligenoid, LTh-B monomer and denatured LTh-B monomer were determined as 5.6-5.8, 9.2-9.6 and 9.2-9.6, respectively. All the ionic amino acids of LTp-B exist on the coligenoid surface. The difference in pI values between LTh-B coligenoid and LTh-B monomer suggests that some basic amino acids are located within the LTh-B coligenoid complex, but are exposed in the LTh-B monomer. These data suggest that the 4 amino acid substitutions between LTh-B and LTp-B result in a three dimensional structure difference and a less stable formation of LTh-B coligenoid compared to LTp-B coligenoid.