Effect of boattail geometry on the acoustics of parallel baffles in ducts

Sound attenuation and total pressure drop of parallel duct baffles incorporating certain boattail geometries were measured in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. The baseline baffles were 1.56 m long and 20 cm thick, on 45-cm center-to-center spacings, and spanned the test section from floor to ceiling. Four different boattails were evaluated: a short, smooth (nonacoustic) boattail; a longer, smooth boattail; and two boattails with perforated surfaces and sound-absorbent filler. Acoustic measurements showed the acoustic boattails improved the sound attenuation of the baffles at approximately half the rate to be expected from constant-thickness sections of the same length; that is, 1.5 dB/n, where n is the ratio of acoustic treatment length to duct passage width between baffles. The aerodynamic total pressure loss was somewhat sensitive to tail geometry. Lengthening the tails to reduce the diffusion half-angle from 11 to 5 degrees reduced the total pressure loss approximately 9%. Perforating the boattails, which increased the surface roughness, did not have a large effect on the total pressure loss. Aerodynamic results are compared with a published empirical method for predicting baffle total pressure drop

High performance forward swept wing aircraft

A high performance aircraft capable of subsonic, transonic and supersonic speeds employs a forward swept wing planform and at least one first and second solution ejector located on the inboard section of the wing. A high degree of flow control on the inboard sections of the wing is achieved along with improved maneuverability and control of pitch, roll and yaw. Lift loss is delayed to higher angles of attack than in conventional aircraft. In one embodiment the ejectors may be advantageously positioned spanwise on the wing while the ductwork is kept to a minimum

Nonlinear optics of fibre event horizons

The nonlinear interaction of light in an optical fibre can mimic the physics at an event horizon. This analogue arises when a weak probe wave is unable to pass through an intense soliton, despite propagating at a different velocity. To date, these dynamics have been described in the time domain in terms of a soliton-induced refractive index barrier that modifies the velocity of the probe. Here, we complete the physical description of fibre-optic event horizons by presenting a full frequency-domain description in terms of cascaded four-wave mixing between discrete single-frequency fields, and experimentally demonstrate signature frequency shifts using continuous wave lasers. Our description is confirmed by the remarkable agreement with experiments performed in the continuum limit, reached using ultrafast lasers. We anticipate that clarifying the description of fibre event horizons will significantly impact on the description of horizon dynamics and soliton interactions in photonics and other systems.Comment: 7 pages, 5 figure

On the modulation instability development in optical fiber systems

Extensive numerical simulations were performed to investigate all stages of modulation instability development from the initial pulse of pico-second duration in photonic crystal fiber: quasi-solitons and dispersive waves formation, their interaction stage and the further propagation. Comparison between 4 different NLS-like systems was made: the classical NLS equation, NLS system plus higher dispersion terms, NLS plus higher dispersion and self-steepening and also fully generalized NLS equation with Raman scattering taken into account. For the latter case a mechanism of energy transfer from smaller quasi-solitons to the bigger ones is proposed to explain the dramatical increase of rogue waves appearance frequency in comparison to the systems when the Raman scattering is not taken into account.Comment: 9 pages, 54 figure

Factors Influencing Teachers in Engaging with University Outreach:Is it Just Cost?

A chemistry outreach day event was offered, free-of-charge, to schools in the south west of England who do not normally engage with Bristol ChemLabS outreach events delivered at the University of Bristol. The participating teachers were interviewed to find out their expectations of the day in terms of helping their students or in helping the teachers, whether the “free” aspect, or not, triggered the application to the event and whether finance or other barriers normally prevented engagement in such events. The value versus cost of such outreach an event is discussed. While finance was the biggest issue for the majority of the interviewed teachers they recognised the value of the inspiration rather than subject knowledge acquisition for their students. The advantages for the teachers were seen as better motivated students and the likelihood of more students taking their subject at higher levels. Having attended such an event and observing the quality and impact on their students, teachers were more inclined to engage in the future whether there was a financial charge or not.</jats:p

A simple and surprisingly accurate approach to the chemical bond obtained from dimensional scaling

We present a new dimensional scaling transformation of the Schrodinger equation for the two electron bond. This yields, for the first time, a good description of the two electron bond via D-scaling. There also emerges, in the large-D limit, an intuitively appealing semiclassical picture, akin to a molecular model proposed by Niels Bohr in 1913. In this limit, the electrons are confined to specific orbits in the scaled space, yet the uncertainty principle is maintained because the scaling leaves invariant the position-momentum commutator. A first-order perturbation correction, proportional to 1/D, substantially improves the agreement with the exact ground state potential energy curve. The present treatment is very simple mathematically, yet provides a strikingly accurate description of the potential energy curves for the lowest singlet, triplet and excited states of H_2. We find the modified D-scaling method also gives good results for other molecules. It can be combined advantageously with Hartree-Fock and other conventional methods.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Letter

A GIS Tool for Applying Habitat Suitability Models to Inform Management (Poster)

Habitat suitability models are used to guide habitat management for species of conservation concern. Models quantify relationships between known species locations and environmental attributes, which are used to identify and map areas most likely to support species of concern. Managers can then restrict human activities with negative impacts on habitat suitability in these areas. Application of habitat suitability models, however, typically requires technical expertise not available to most land managers. We developed a prototype GIS tool that facilitates application of habitat suitability models to guide management of habitat for woodpecker species of conservation concern. The tool operates within an ArcGIS environment, which is readily available to most managers, and will be capable of generating habitat suitability maps for several species of concern (i.e., Black-backed Woodpecker [Picoides arcticus], Three-toed Woodpecker [P. dorsalis], Lewis’s Woodpecker [Melanerpes lewis], and White-headed Woodpeckers [P. albolvartus]). The tool also automates much of the model application process, reducing requisite technical expertise, and making habitat suitability models widely available. The tool will be accompanied by a manual describing implementation and interpretation of resulting habitat suitability maps. The tool will be especially helpful for informing management of post-disturbance forests (i.e. after wildfire and beetle infestations) to identify suitable habitat for disturbance specialists (e.g., Black-backed, Three-toed, and Lewis’s Woodpeckers).  Identification of suitable habitat is necessary to effectively develop management plans that incorporate the needs of habitat specialists in post-disturbance landscapes. Our prototype is currently being tested by U.S. Forest Service biologists

Landscape Heterogeneity at White-Headed Woodpecker Nest Sites in West-Central Idaho

The white-headed woodpecker (Picoides albolarvatus) is a regional endemic species of dry conifer forests in the Inland Pacific Northwest, where forest restoration activities are increasingly common. Recent efforts to mitigate severe fire effects and restore ecological function in these forests have prompted land managers to consider the implications of forest management actions on a range of resources, including wildlife. Identifying the associations of sensitive wildlife species with the structure and distribution of resources across landscapes is necessary for scientifically-sound management decisions. We examined the heterogeneity and proportion of open- and closed- canopy forest patches surrounding white-headed woodpecker nest sites during 2012 and 2013. We used logistic regression to compare differences between nest (n = 34) and non-nest (n = 184) sites. We found a stronger positive relationship with low canopy closure within 1-ha of nest sites compared with non-nest sites (nests: x? = 0.49, SD = 0.43; non-nests: x? = 0.06, SD = 0.16; P &lt; 0.001). We also measured a stronger positive relationship with the edge density between low and moderate canopy patches within a 1-km radius of nest sites compared with non-nest sites (nests: x? = 30.0 meters/ha, SD = 14.6; non-nests: x? = 18.4 m/ha, SD = 14.9; P &lt; 0.001). Our results are consistent with studies of nesting white-headed woodpeckers in Oregon. These data will help further validate and refine habitat suitability models across their northern range and contribute towards effective management decisions that will benefit the white-headed woodpecker

Relativistic diffusion processes and random walk models

The nonrelativistic standard model for a continuous, one-parameter diffusion process in position space is the Wiener process. As well-known, the Gaussian transition probability density function (PDF) of this process is in conflict with special relativity, as it permits particles to propagate faster than the speed of light. A frequently considered alternative is provided by the telegraph equation, whose solutions avoid superluminal propagation speeds but suffer from singular (non-continuous) diffusion fronts on the light cone, which are unlikely to exist for massive particles. It is therefore advisable to explore other alternatives as well. In this paper, a generalized Wiener process is proposed that is continuous, avoids superluminal propagation, and reduces to the standard Wiener process in the non-relativistic limit. The corresponding relativistic diffusion propagator is obtained directly from the nonrelativistic Wiener propagator, by rewriting the latter in terms of an integral over actions. The resulting relativistic process is non-Markovian, in accordance with the known fact that nontrivial continuous, relativistic Markov processes in position space cannot exist. Hence, the proposed process defines a consistent relativistic diffusion model for massive particles and provides a viable alternative to the solutions of the telegraph equation.Comment: v3: final, shortened version to appear in Phys. Rev.

Home-Range Size of White-Headed Woodpeckers in W est- Central Idaho

The white-headed woodpecker (Picoides albolarvatus) is a species of management concern in dry-conifer forests of the Inland Northwest, where forest restoration and fuels reduction treatments are increasingly common.  This species may be vulnerable to forest management treatments because it occupies a limited distribution and has narrow habitat requirements.  Forest treatments could negatively affect this species if foraging and nesting resources are removed or could benefit the species through creation of more heterogeneity across the landscape.  Studies of other woodpecker species have identified resource availability and habitat composition as a key influence on the variation of home range size within a population.  We examined home range size of white-headed woodpeckers in a landscape historically managed for timber harvest and is currently receiving extensive forest restoration treatments.  In our first field season, we obtained relocations on 7 radio-tagged woodpeckers (5 males and 2 females, all from different breeding pairs), from late nesting through fledgling periods (late June to early September).  We obtained direct foraging observations at the radio locations.  Estimated home range sizes were quite variable(24 - 180 ha), based on the minimum convex polygon (MCP) method.  We will also estimate home range sizes using the fixed-kernel method.  Identifying habitat spatial attributes that account for variation in home range size will contribute towards effective management decisions for the persistence of white-headed woodpecker populations