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Effective species management and conservation require knowledge of species distribution and status. We used pointtransect distance sampling surveys of the endangered palila (Loxioides bailleui), a honeycreeper currently found only on the Island of Hawai’i, USA, to generate robust estimates of total abundance and simultaneously model the distribution, abundance, and spatial correlation of the species as a density surface model (DSM). Point-transect distance sampling is a widely applied method to estimate bird densities accounting for imperfect detection probability. For the DSM we used a generalized additive model framework and soap film smoothers to control the effects of boundary features. This modeling approach allowed us to account for imperfect detection and propagate detection probability uncertainty. We compared the uncertainty in palila abundance estimates using standard point-transect distance sampling to estimates from the DSM. The DSM, accounting for both distance-sampling-derived detection probability variance and the generalized additive model density estimate variance, did not improve population estimator precision; however, it provided insight into the species’ distribution, density, and uncertainty. We also applied excursion sets analysis to objectively identify areas where the species occurs in high densities. The 2017 global population of <2,000 individuals was limited to an excursion area of 1,500 ha. Our findings can help management and regulatory agencies by simultaneously mapping a species’ distribution and density, improving survey protocols, and providing information important to species conservation.

Key messageBark stripping wounds by red deer (Cervus elavus L.) were assessed on 9026 Norway spruce trees. Wound variables (length, width, area, relative width, height above ground, and angle) were analysed using generalized additive models with spatial soap film smoothers. Wounds located at the uphill side of trees were larger in summer than winter, and wound size depended on the diameter at breast height (DBH) and was spatially clustered.ContextIn Austria, red deer (Cervus elaphus L.) is the main species causing bark stripping wounds. In winter, they often gnaw at the bark because of food scarcity; in summer, large pieces of bark are detached to help digestion, water, and nutrient uptake or as social behaviour.AimsThe aim of this study was to analyse wound size (length, width, area, relative width (i.e., width divided by stem circumference)) and wound position (height above ground, angle (i.e., deviation between wound azimuth from slope line)) for winter and summer bark stripping wounds by red deer depending on stand attributes and to describe the spatial patterns of wound size within stands.MethodsA total of 3832 wounds on 9026 trees in nine experimental stands of Norway spruce (Picea abies (L.) Karst.) located at 47° 19’ N and 14° 46’ E at an elevation of 1009–1622 m were analysed. A linear regression model was fit for wound length over wound width for each season. For all wound variables (wound length, width, area, relative width, position, height above ground, and angle) generalized additive models (GAM) with soap film smoothers, which predict spatial patterns, were fitted.ResultsOf all wounds, 79.5 % were inflicted in winter and 20.5 % in summer. Wound length (31.9 cm ± 31.2 SD), width (11.7 cm ± 6.0 SD), area (446.5 cm2± 558.1 SD), and relative wound width (0.177 cm ± 0.098 SD) were modelled depending on summer or winter bark peeling, DBH, and tree coordinates. For wound height above ground (119.4 cm± 26.8 SD) and angle (− 1.9 ± 97.3 SD), no meaningful GAM could be calculated. Seasonal differences between wound length and area were more pronounced than for wound width; differences in height above ground were minimal, but significant. Analyses further showed that wounds were mainly located at the uphill side of the trees.ConclusionThe spatial clustering of wound sizes might reduce the efficiency of thinning to remove heavily damaged trees in bark-peeled stands and might increase the number of sample points required to assess deer impact in forest inventories. Also, the uphill location of damages is an important information in inventories.

Bark stripping is a key topic in forestry because of economic losses due to associated fungal infections of wood, finally resulting in growth decrease and the loss of ecosystem services. Numerous studies identified factors influencing the spatial distribution of bark stripping damage between stands or at the landscape scale. However, patterns within single stands are not yet reported. In this research, we performed a terrestrial laser scanning supported census of nine stands in Austria (9026 trees in total). A generalised additive model with a binomial distribution (link = logit) and soap film smoother was fitted to the data. The probability of bark stripping on the single tree level depended on the following covariates: Spruce was more vulnerable than larch, damage probability decreased with DBH and the local slope and increased with the Epanechnikov Kernel (bandwidth = 15 m) estimate of tree density. At the nearest neighbour distance of two metres, there was a damage maximum. The spatial distribution of bark stripping damage was clumped, and its intensity decreased with increasing distance to forest roads. In 67.7% of the cases, the model predicted the right outcome for the total population (overall model accuracy). This percentage varied between 55.3 and 79.1% between stands. In conclusion, the spatial distribution should be considered in inventory designs for bark stripping damages to mitigate bark stripping effects on the forests.

Gravity governs the large-scale structure of the Universe, driving the formation and interactions of galaxies. These interactions generate distinctive features–such as complex orbits, tidal spiral arms and bridges–that are commonplace at astrophysical scales but rarely observed at human scales. Multi-body dynamics can be observed at laboratory scale with particles at liquid interfaces interacting via the “Cheerios effect”, but such systems have limited ability to reproduce gravity-shaped structures because of their short-range interactions, strong dissipation, and a limited number of rigid bodies. Here, we show that miscible milimetric water lenses on a soap film can sustain long-lived orbital motion, collisions, and mergers, producing tidal arms and bridges reminiscent of interacting galaxies. These dynamics arise from a Newton-like gravito-capillary attraction, low dissipation, and lens deformability. A quantitative model of film deformation accurately predicts both static lens shapes and orbital trajectories for single and multiple bodies. This controllable, time-resolved platform enables direct experimental study of the gravity-driven formation of complex, deformable structures, paving the way for laboratory gravitational analogues.

Analogical physical models are a preferred technique to intuitively grasp complex engineering problems. It is well-known that the equilibrium minimal-surface configuration of membranes under equibiaxial tension can be visually represented by the surface of a soap film under equivalent boundary conditions, but this analogy fails when the stress state is not uniform equibiaxial. We extend to this situation the analogy with soap films. The equilibrium state of an orthotropically tensioned membrane is found by geometrically stretching the shape of a soap film, in a precise manner depending upon the applied state of stress. The procedure is easily done by elaborating digital pictures. The method is mathematically justified under the kinematic hypotheses of small strains and large rotations, and further verified in a parametric design environment. It can also provide an insight into the equilibrium configuration of cable-nets, when the stresses in the warp and weft directions are considerably different. Furthermore, this visualization favors implementing transformable shapes for membranes or orthogonal cable nets, as a consequence of a modification of the ratio of the principal stress components.

Flapping wing micro-air-vehicles (FWMAVs) animate the small-space dexterous flight, hovering, and energy-saving characteristics of birds and insects, and are believed to have enlightenment for the development of bionic flight in the future. When designing FWMAVs, detailed unsteady aerodynamic information is required. Besides the computational fluid mechanics (CFD) technology study, the flow visualization is also needed to assist this research. This article innovatively used soap film visualization with high-speed photography to record two kinds of the 2D flow fields laterally and longitudinally, respectively, generated by a flapping wing of 10 cm span. Different from the qualitative comparison of soap film imaging with the conventional smoke tracing method, the subsequent processing of the soap film images was demonstrated. This work explains how to quantify the soap film imaging into lift and thrust forces, and the corresponding results are compared with the wind tunnel force measurement data preliminarily.

The evolution of a polygonal helium cylinder impacted by a planar weak shock wave is investigated experimentally. Three different polygonal interface shapes including a square, an equilateral triangle and a diamond are formed by the soap film technique, where thin pins are used as edges to connect the adjacent sides of soap films. Shock tube experiments are conducted to obtain sequences of schlieren images using a high-speed video camera. In each case, the development of the wave system and the evolution of the polygonal helium cylinder subjected to a planar shock wave with a Mach number of 1.21±0.03 are obtained in a single test. For comparison, numerical simulations are also performed using the two-dimensional and axisymmetric vectorized adaptive solver (VAS2D). The variations of the interface properties including the displacement, the length and the height of the distorted interfaces in the three cases are given. For the square helium cylinder, two counter-rotating vortices connected by a thin link can be observed. The height of the distorted interface always increases, and its length first decreases and then increases. In the triangle case, an air jet is formed quickly and moves downwards within the volume and eventually encounters the downstream interface, resulting in a bulge on the downstream interface. In the diamond case, the upstream interface quickly forms a re-entrant air jet similar to that in the triangle case, and the downstream interface becomes flat. The circulation in the three cases is calculated numerically, revealing the main driving mechanism of the development of the shocked polygonal interface. This work exhibits the great potential of the experimental method in studying shock–polygonal interface interactions in the case of slow/fast (air/helium) situations.

AbstractThis paper deals with a simple, fast and economical visualization method to validate two-dimensional large eddy simulations (LES) of the flow over a foil. This technique exploits the optical properties of soap film and relies on the wake patterns and the frequency at which these are shed at the trailing edge of the foil.Graphical Abstract

AbstractIn this article, we study the dynamic response of a soap film under continuous electromagnetic forcing. The dynamics presented here describe the forcing of a monopole vortex during its generation at the center of the film. This response is quantified by the dimensionless Reynolds and Chandrasekhar numbers. When Chandrasekhar number reaches values near 800, Reynolds number reaches a damping rate. An analysis of the kinetic energy throughout the film shows that its response can be explained by Gibbs and Marangoni elasticity. Upon small forcing, the film shows an fast response after which it maintains its initial speed at all times (Marangoni). For a large forcing however, the speed of the film increases continuously throughout the experiment (Gibbs).Graphical Abstract

Ensembles of particles rotating in a two-dimensional fluid can exhibit chaotic dynamics yet develop signatures of hidden order. Such rotors are found in the natural world spanning vastly disparate length scales — from the rotor proteins in cellular membranes to models of atmospheric dynamics. Here we show that an initially random distribution of either driven rotors in a viscous membrane, or ideal vortices with minute perturbations, spontaneously self assemble into a distinct arrangement. Despite arising from drastically different physics, these systems share a Hamiltonian structure that sets geometrical conservation laws resulting in prominent structural states. We find that the rotationally invariant interactions isotropically suppress long-wavelength fluctuations — a hallmark of a disordered hyperuniform material. With increasing area fraction, the system orders into a hexagonal lattice. In mixtures of two co-rotating populations, the stronger population will gain order from the other and both will become phase enriched. Finally, we show that classical 2D point vortex systems arise as exact limits of the experimentally accessible microscopic membrane rotors, yielding a new system through which to study topological defects. Rotor-like dynamics is observed in many natural systems, from the rotor proteins in cellular membranes to atmospheric models. Here, the authors uncover geometrical conservation laws that limit distribution of driven rotors in a membrane or a soap film and allow to predict their structural states.