Petiolate wings: effects on the leading-edge vortex in flapping flight

The wings of many insect species including crane flies and damselflies are petiolate (on stalks), with the wing planform beginning some distance away from the wing hinge, rather than at the hinge. The aerodynamic impact of flapping petiolate wings is relatively unknown, particularly on the formation of the lift-augmenting leading-edge vortex (LEV): a key flow structure exploited by many insects, birds and bats to enhance their lift coefficient. We investigated the aerodynamic implications of petiolation P using particle image velocimetry flow field measurements on an array of rectangular wings of aspect ratio 3 and petiolation values of P = 1–3. The wings were driven using a mechanical device, the ‘Flapperatus’, to produce highly repeatable insect-like kinematics. The wings maintained a constant Reynolds number of 1400 and dimensionless stroke amplitude Λ* (number of chords traversed by the wingtip) of 6.5 across all test cases. Our results showed that for more petiolate wings the LEV is generally larger, stronger in circulation, and covers a greater area of the wing surface, particularly at the mid-span and inboard locations early in the wing stroke cycle. In each case, the LEV was initially arch-like in form with its outboard end terminating in a focus-sink on the wing surface, before transitioning to become continuous with the tip vortex thereafter. In the second half of the wing stroke, more petiolate wings exhibit a more detached LEV, with detachment initiating at approximately 70% and 50% span for P = 1 and 3, respectively. As a consequence, lift coefficients based on the LEV are higher in the first half of the wing stroke for petiolate wings, but more comparable in the second half. Time-averaged LEV lift coefficients show a general rise with petiolation over the range tested.This work was supported by an EPSRC Career Acceleration Fellowship to R.J.B. (EP/H004025/1)

The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing

Insect wing shapes are diverse and a renowned source of inspiration for the new generation of autonomous flapping vehicles, yet the aerodynamic consequences of varying geometry is not well understood. One of the most defining and aerodynamically significant measures of wing shape is the aspect ratio, defined as the ratio of wing length (R) to mean wing chord ($\bar{c}$). We investigated the impact of aspect ratio, AR, on the induced flow field around a flapping wing using a robotic device. Rigid rectangular wings ranging from AR = 1.5 to 7.5 were flapped with insect-like kinematics in air with a constant Reynolds number (Re) of 1400, and a dimensionless stroke amplitude of $6.5\bar{c}$ (number of chords traversed by the wingtip). Pseudo-volumetric, ensemble-averaged, flow fields around the wings were captured using particle image velocimetry at 11 instances throughout simulated downstrokes. Results confirmed the presence of a high-lift, separated flow field with a leading-edge vortex (LEV), and revealed that the conical, primary LEV grows in size and strength with increasing AR. In each case, the LEV had an arch-shaped axis with its outboard end originating from a focus-sink singularity on the wing surface near the tip. LEV detachment was observed for $\mathrm{AR}\gt 1.5$ around mid-stroke at $\sim 70\%$ span, and initiated sooner over higher aspect ratio wings. At $\mathrm{AR}\gt 3$ the larger, stronger vortex persisted under the wing surface well into the next half-stroke leading to a reduction in lift. Circulatory lift attributable to the LEV increased with AR up to AR = 6. Higher aspect ratios generated proportionally less lift distally because of LEV breakdown, and also less lift closer to the wing root due to the previous LEV's continuing presence under the wing. In nature, insect wings go no higher than $\mathrm{AR}\sim 5,$ likely in part due to architectural and physiological constraints but also because of the reducing aerodynamic benefits of high AR wings

Hellinger Distance Trees for Imbalanced Streams

Classifiers trained on data sets possessing an imbalanced class distribution are known to exhibit poor generalisation performance. This is known as the imbalanced learning problem. The problem becomes particularly acute when we consider incremental classifiers operating on imbalanced data streams, especially when the learning objective is rare class identification. As accuracy may provide a misleading impression of performance on imbalanced data, existing stream classifiers based on accuracy can suffer poor minority class performance on imbalanced streams, with the result being low minority class recall rates. In this paper we address this deficiency by proposing the use of the Hellinger distance measure, as a very fast decision tree split criterion. We demonstrate that by using Hellinger a statistically significant improvement in recall rates on imbalanced data streams can be achieved, with an acceptable increase in the false positive rate.Comment: 6 Pages, 2 figures, to be published in Proceedings 22nd International Conference on Pattern Recognition (ICPR) 201

Restorative practice and behaviour management in schools: discipline meets care.

The history of restorative practices in New Zealand schools is directly related to projects such as the Suspension Reduction Initiative (SRI) and the more recent Student Engagement Initiative (SEI); thus the origins of restorative practices in schools are linked with behaviour management and school discipline. During the same period, teachers' work has become more complex: They are working with an increasingly diverse range of students, which in turn requires epistemologically diverse teaching and relationship-building approaches to ensure maximum participation for all. Teachers are looking for new and better ways to interact with students in their classrooms, and those responsible for disciplinary systems are looking to restorative practice for new ways to resolve the increasing range and number of difficulties between teachers and students, students and other students, and between the school and parents. Restorative practices (RP) are currently seen as a way of achieving all this, so they carry a huge burden of hope. Relationship skills are a key competency in the new curriculum, and the philosophy of restoration offers both a basis for understanding and a process for putting this agenda into practice. In effect, it means educating for citizenship in a diverse world, including teaching the skills of conflict resolution. If we accept this philosophy, the curriculum for teacher education will require significant changes in what students are taught about behaviour and classroom management

Active heat exchange system development for latent heat thermal energy storage

Active heat exchange concepts for use with thermal energy storage systems in the temperature range of 250 C to 350 C, using the heat of fusion of molten salts for storing thermal energy are described. Salt mixtures that freeze and melt in appropriate ranges are identified and are evaluated for physico-chemical, economic, corrosive and safety characteristics. Eight active heat exchange concepts for heat transfer during solidification are conceived and conceptually designed for use with selected storage media. The concepts are analyzed for their scalability, maintenance, safety, technological development and costs. A model for estimating and scaling storage system costs is developed and is used for economic evaluation of salt mixtures and heat exchange concepts for a large scale application. The importance of comparing salts and heat exchange concepts on a total system cost basis, rather than the component cost basis alone, is pointed out. The heat exchange concepts were sized and compared for 6.5 MPa/281 C steam conditions and a 1000 MW(t) heat rate for six hours. A cost sensitivity analysis for other design conditions is also carried out

Nesting Ecology of the Northern Goshawk in the Black Hills of South Dakota

The nesting ecology of northern goshawks (Accipiter gentilis) was studied in the Black Hills of western South Dakota from 2003 to 2009. Goshawk nest territories were found by broadcasting alarm calls, intensive searches of potential nesting habitat, and visiting historic nesting territories based on information from the USDA Forest Service. During this 7- yr period, 30 active goshawk nesting territories were studied. There were 53 nesting attempts sufficiently monitored to establish that 35 nests fledged young (66% successful). Among these monitored nests, there was an average of 1.1 chicks fledged/nesting attempt and 1.6 chicks fledged/successful nest. Goshawks frequently used alternative nests from one year to the next, and we were not always successful at finding new alternative nests. Alternative nests ranged from 50 yds to 0.7 mi apart. The average number of alternative nests found per nesting territory was 2.2, and in 1 territory there were six nests. Ponderosa pine (Pinus ponderosa) was the preferred nest tree with 65 goshawk nests in pine trees and one nest found in a white spruce tree (Abies glauca). The average diameter (dbh) of nest trees was 16.8 in dbh. Nest stand characteristics were measured at 21 nest tree sites. Average nest stand dbh was 10.2 in, average nest stand tree density was 266 trees/ac, and the average nest stand basal area was 128 ft2/ac

Unstable Elastic Materials and the Viscoelastic Response of Bars in Tension

Some homogeneous elastic materials are capable of sustaining finite equilibrium deformations with discontinuous strains. For materials of this kind, the energetics of isothermal, quasi-static motions may differ from those conventionally associated with elastic behavior. When equilibrium states involving strain jumps occur during such motions, the rate of increase of stored energy in a portion of the body may no longer coincide with the rate of work of the external forces present. In general, energy balance now includes an additional effect due to the presence of moving strain discontinuities. As a consequence, the macroscopic response of the body may be dissipative. This fact makes it possible to model certain types of inelastic behavior in solids with the help of such "unstable" elastic materials; see, for example, Abeyaratne and Knowles (1987a,b,c)

A note on the driving traction acting on a propagating interface: Adiabatic and non-adiabatic processes of a continuum

An expression for the driving traction on an interface is derived for an arbitrary continuum undergoing an arbitrary thermomechanical process which may- or may not be adiabatic

A Potential Representation for Two-Dimensional Waves in Elastic Materials of Harmonic Type

In the present note we consider two-dimensional finite dynamical deformations for the class of homogeneous, isotropic elastic materials introduced by F. John in [1] and referred to by him as materials of harmonic type. The theory of such materials, developed in [1] and [2], appears to be simpler in many respects than that of more general elastic materials, and it may offer the possibility of investigating some features of nonlinear elastic behavior more explicitly than is possible in general. For plane motions of such materials, we derive here a representation for the displacements in terms of two potentials which is analogous to the theorem of Lamé in classical linear elasticity (see [3]) for the case of plane strain. The two nonlinear differential equations satisfied by the potentials reduce upon linearization to the wave equations associated with irrotational and equivoluminai waves in the linear theory. In the following section we state without derivation the equations governing two-dimensional waves in an elastic material of harmonic type. The reader is referred to [1] for details. In Sec. 3 we derive the representation in terms of potentials described briefly above

Barro's fertility equations: the robustness of the role of female education and income

Barro and Lee (1994) and Barro and Sala-i-Martin (1995) find that real per-capita GDP and both male and female education have important effects on fertility in their cross-country empirical studies. In order to assess the robustness of their results, their estimated models are subjected to specification and diagnostic testing, the effects on the model of using the improved Barro and Lee (1996) cross-country data on educational attainment of the population aged 15 and over are examined, and the different specifications used by Barro and Lee and by Barro and Sala-i-Martin compared. The results obtained suggest that their fertility equations do not perform well in terms of diagnostic testing, and are very sensitive to the use of different vintages of the educational attainment proxies and of the Summers-Heston cross-country income data. A robust explanation of fertility, to link with empirical growth equations, has, therefore, not yet been found; further work is required in this area