Influence of wing flexibility on the aerodynamic performance of a tethered flapping bumblebee

The sophisticated structures of flapping insect wings make it challenging to study the role of wing flexibility in insect flight.In this study,a mass-spring system is used to model wing structural dynamics as a thin,flexible membrane supported by a network of veins.The vein mechanical properties can be estimated based on their diameters and the Young's modulus of cuticle.In order to analyze the effect of wing flexibility,the Young's modulus is varied to make a comparison between two different wing models that we refer to as flexible and highly flexible.The wing models are coupled with a pseudo-spectral code solving the incompressible Navier–Stokes equations,allowing us to investigate the influence of wing deformation on the aerodynamic efficiency of a tethered flapping bumblebee.Compared to the bumblebee model with rigid wings,the one with flexible wings flies more efficiently,characterized by a larger lift-to-power ratio.

Thinking about worry:A systematic review and meta-analysis on the assessment of metacognitions in children and adolescents

BACKGROUND The metacognitive model of generalized anxiety disorder identifies three forms of metacognition:Positive metacognitive beliefs about worry(POS),negative metacognitive beliefs about worry(NEG),and meta-worry.Though this model was originally developed relying on adult samples,it has since been applied to children and youth in different studies,and results mostly support its validity for this group.As the roles of POS,meta-worry,and age-effects do not appear to be fully clarified for children and adolescents yet,an integration of studies on children and adolescents and the metacognitive model is both timely and worthwhile.AIM To summarize the current research on relationships,age-effects,and measurements for POS,NEG,and meta-worry in childhood and youth.METHODS We carried out a literature search in the electronic databases PsycINFO,PubMed,PSYNDEX,and ERIC in 2017 and updated in 2020.Empirical research in German or English language on metacognition was included with child and adolescent samples diagnosed with anxiety disorders or healthy controls if POS,NEG,or meta-worry were measured.Studies were included for meta-analysis if they reported correlations between these metacognitions and anxiety or worry.Consensus rating for eligibility was done for 20.89% of full-texts with 90.32% agreement.Risk of bias was assessed with the appraisal tool for cross-sectional studies and consensus rating of appraisal tool for cross-sectional studies for 20.83% of included studies attaining agreement of intraclass correlation=0.898.Overall,correlations between metacognitions,anxiety and worry were calculated with RevMan 5.4.1,assuming random-effects models.Meta-regressions with mean age as the covariate were performed via the online tool MetaMar 2.7.0.PROSPERO-ID:CRD42018078852.RESULTS Overall,k=763 records and k=78 additional records were identified.Of those,k=48 studies with 12839 participants were included and of those,k=24 studies were included for meta-analysis.Most studies showed consistent NEG correlations with worry and anxiety,as well as higher values for clinical than for nonclinical samples.POS findings were less consistent.Meta-analysis revealed large effects for NEG correlating with worry and anxiety,small to medium effects for POS correlating with worry and anxiety,as well as small to medium effects for POS correlating with NEG.Meta-regressions did not reveal mean age as a significant covariate.Meta-worry was assessed in only one study.We identified eight questionnaires and one interview-format that assess metacognition about worry in children and adolescents.CONCLUSION POS and NEG are measurable from the age of seven upwards and correlate with anxiety and worry without influences by age.Meta-worry requires further investigation.

Carbon Fibre Reinforced Concrete: Dependency of Bond Strength on T_gof Yarn Impregnating Polymer

In this paper, a method for the evaluation of the influence of different polymer suspensions and environmental conditions on adhesion between an impregnated carbon fibre heavy tow and concrete for reinforcement will be proposed. For this purpose, the impregnation material itself was investigated as a polymer film before and after incubation in water and aqueous suspensions, such as NaOH and a cementitious solution, in terms of its thermal properties, swelling behaviour and morphology. Thin polymer films were manufactured and subsequently investigated with quantification of the swelling for 28 d by thermal and scanning electron microscope analysis. The effect of pull-out shear stress was evaluated to investigate parameters such as high temperature and moisture on adhesion to concrete. Contact angle measurements were used to determine the surface energy of the polymer films. All incubated polymer films yielded a change in both surface morphology and specific residues on the polymer film surface, e.g. in the form of calcium carbonate, but no change in glass-transition temperature. A high correlation between glass-transition temperature and measured shear stress was shown during single yarn pull-out tests. Furthermore, the water treatment of pull-out samples strengthened the influence for the glass-transition temperature during the adhesion test. No influence of the surface energy of the used polymer impregnation for carbon fibres on the pull-out test was detected.

Numerical simulation of vortex-induced drag of elastic swimmer models

We present numerical simulations of simplified models for swimming organisms or robots, using chordwise flexible elastic plates. We focus on the tip vortices originating from three-dimensional effects due to the finite span of the plate. These effects play an important role when predicting the swimmer＇s cruising velocity, since they contribute significantly to the drag force. First we simulate swimmers with rectangular plates of different aspect ratios and compare the results with a recent experimental study. Then we consider plates with expanding and contracting shapes. We find the cruising velocity of the contracting swimmer to be higher than the rectangular one, which in turn is higher than the expanding one. We provide some evidence that this result is due to the tip vortices interacting differently with the swimmer.