Effect of disjoining pressure in a thin film equation with\ud non-uniform forcing

We explore the effect of disjoining pressure on a thin film equation in the presence of a non-uniform body force, motivated by a model describing the reverse draining of a magnetic film. To this end, we use a combination of numerical investigations and analytical considerations. The disjoining pressure has a regularizing influence on the evolution of the system and appears to select a single steady-state solution for fixed height boundary conditions; this is in contrast with the existence of a continuum of locally attracting solutions that exist in the absence of disjoining pressure for the same boundary conditions. We numerically implement matched asymptotics expansions to construct equilibrium solutions and also investigate how they behave as the disjoining pressure is sent to zero. Finally, we consider the effect of the competition between forcing and disjoining pressure on the coarsening dynamics of the thin film for fixed contact angle boundary conditions

An in-flight investigation of ground effect on a forward-swept wing airplane

A limited flight experiment was conducted to document the ground-effect characteristics of the X-29A research airplane. This vehicle has an aerodynamic platform which includes a forward-swept wing and close-coupled, variable incidence canard. The flight-test program obtained results for errors in the airdata measurement and for incremental normal force and pitching moment caused by ground effect. Correlations with wind-tunnel and computational analyses were made. The results are discussed with respect to the dynamic nature of the flight measurements, similar data from other configurations, and pilot comments. The ground-effect results are necessary to obtain an accurate interpretation of the vehicle's landing characteristics. The flight data can also be used in the development of many modern aircraft systems such as autoland and piloted simulations

Elastic cavitation, tube hollowing, and differential growth in plants and biological tissues

Elastic cavitation is a well-known physical process by which elastic materials under stress can open cavities. Usually, cavitation is induced by applied loads on the elastic body. However, growing materials may generate stresses in the absence of applied loads and could induce cavity opening. Here, we demonstrate the possibility of spontaneous growth-induced cavitation in elastic materials and consider the implications of this phenomenon to biological tissues and in particular to the problem of schizogenous aerenchyma formation

Future beam experiments in the magnetosphere with plasma contactors: The electron collection and ion emission routes

Experiments where a high‐voltage electron beam emitted by a spacecraft in the low‐density magnetosphere is used to probe the magnetospheric configuration could greatly enhance our understanding of the near‐Earth environment. Their challenge, however, resides in the fact that the background magnetospheric plasma cannot provide a return current that balances the electron beam current without charging the spacecraft to such high potential that in practice prevents beam emission. In order to overcome this problem, a possible solution is based on the emission of a high‐density contactor plasma by the spacecraft prior to and after the beam. We perform particle‐in‐cell simulations to investigate the conditions under which a high‐voltage electron beam can be emitted from a magnetospheric spacecraft, comparing two possible routes that rely on the high‐density contactor plasma. The first is an “electron collection” route, where the contactor has lower current than the electron beam and is used with the goal of connecting to the background plasma and collecting magnetospheric electrons over a much larger area than that allowed by the spacecraft alone. The second is an “ion emission” route, where the contactor has higher current than the electron beam. Ion emission is then enabled over the large quasi‐spherical area of the contactor cloud, thus overcoming the space charge limits typical of ion beam emission. Our results indicate that the ion emission route offers a pathway for performing beam experiments in the low‐density magnetosphere, while the electron collection route is not viable because the contactor fails to draw a large neutralizing current from the background.Key PointsThe ion emission route is credible for beam experiments in the magnetosphereThe electron collection route is not viableThe background plasma facilitates beam emissionPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111985/1/jgra51700.pd

Importance of Flood Irrigation for Foraging Colonial Waterbirds

For a colonial-nesting bird, like the white-faced ibis (Plegadis chihi), the landscape surrounding the breeding colony can be important. White-faced ibis must rely on areas outside their breeding colony for foraging, but this part of their life history has received little attention, and the management of this landscape even less so. To address this knowledge gap, we conducted road-based driving surveys and a randomly selected, spatially balanced sample survey of agricultural fields within a 22-km radius of the 2 largest white-faced ibis breeding colonies in Idaho, USA: Market Lake Wildlife Management Area and Mud Lake Wildlife Management Area. Our study took place in 2012 and the primary objective was to quantify patterns of foraging habitat use of this marsh-nesting species, particularly associations with specific irrigation practices and crop types. We documented the majority of foraging birds in flood-irrigated and wheel-line sprinkler-irrigated agricultural fields (76%) and natural wetlands (13%), which were limited in our study area (3% of land cover). Even though 70% of the agricultural landscape included center pivot sprinkler irrigation, only 11% of foraging observations came from this irrigation type. Most agricultural fields (\u3e85%) used by foraging ibis were flood-irrigated and all had standing water or recent moisture at the time of use. Though ibis used many crop types when foraging in flooded agricultural fields, ibis use of alfalfa (58%) was greater than availability (38%). We also observed distinct distribution patterns around the 2 breeding colonies. Whereas birds foraged in all directions around Mud Lake (~80%) within a 12-km radius from the colony, we observed over half of birds around Market Lake foraging within 12–22 km, and almost exclusively to the south and southeast of the colony, reflecting the distribution of flood-irrigated agriculture in the area. The most common foraging distance (12–22 km) around Market Lake is greater than found in existing literature, suggesting that the foraging habitat is limited within 12 km of the colony and that the birds may need to travel farther to find adequate foraging habitat. Flood-irrigated agriculture and natural wetlands provide foraging habitats for white-faced ibis in eastern Idaho and should be considered in future management and conservation of wetland birds

Triangleland. I. Classical dynamics with exchange of relative angular momentum

In Euclidean relational particle mechanics, only relative times, relative angles and relative separations are meaningful. Barbour--Bertotti (1982) theory is of this form and can be viewed as a recovery of (a portion of) Newtonian mechanics from relational premises. This is of interest in the absolute versus relative motion debate and also shares a number of features with the geometrodynamical formulation of general relativity, making it suitable for some modelling of the problem of time in quantum gravity. I also study similarity relational particle mechanics (`dynamics of pure shape'), in which only relative times, relative angles and {\sl ratios of} relative separations are meaningful. This I consider firstly as it is simpler, particularly in 1 and 2 d, for which the configuration space geometry turns out to be well-known, e.g. S^2 for the `triangleland' (3-particle) case that I consider in detail. Secondly, the similarity model occurs as a sub-model within the Euclidean model: that admits a shape--scale split. For harmonic oscillator like potentials, similarity triangleland model turns out to have the same mathematics as a family of rigid rotor problems, while the Euclidean case turns out to have parallels with the Kepler--Coulomb problem in spherical and parabolic coordinates. Previous work on relational mechanics covered cases where the constituent subsystems do not exchange relative angular momentum, which is a simplifying (but in some ways undesirable) feature paralleling centrality in ordinary mechanics. In this paper I lift this restriction. In each case I reduce the relational problem to a standard one, thus obtain various exact, asymptotic and numerical solutions, and then recast these into the original mechanical variables for physical interpretation.Comment: Journal Reference added, minor updates to References and Figure

Dynamical derivation of Bode's law

In a planetary or satellite system, idealized as n small bodies in initially coplanar, concentric orbits around a large central body, obeying Newtonian point-particle mechanics, resonant perturbations will cause dynamical evolution of the orbital radii except under highly specific mutual relationships, here derived analytically apparently for the first time. In particular, the most stable situation is achieved (in this idealized model) only when each planetary orbit is roughly twice as far from the Sun as the preceding one, as observed empirically already by Titius (1766) and Bode (1778) and used in both the discoveries of Uranus (1781) and the Asteroid Belt (1801). ETC.Comment: 27 page