9,792 research outputs found
An implicit finite-difference solution to the viscous shock layer, including the effects of radiation and strong blowing
An implicit finite-difference scheme is developed for the fully coupled solution of the viscous, radiating stagnation-streamline equations, including strong blowing. Solutions are presented for both air injection and injection of carbon-phenolic ablation products into air at conditions near the peak radiative heating point in an earth entry trajectory from interplanetary return missions. A detailed radiative-transport code that accounts for the important radiative exchange processes for gaseous mixtures in local thermodynamic and chemical equilibrium is utilized in the study. With minimum number of assumptions for the initially unknown parameters and profile distributions, convergent solutions to the full stagnation-line equations are rapidly obtained by a method of successive approximations. Damping of selected profiles is required to aid convergence of the solutions for massive blowing. It is shown that certain finite-difference approximations to the governing differential equations stabilize and improve the solutions. Detailed comparisons are made with the numerical results of previous investigations. Results of the present study indicate lower radiative heat fluxes at the wall for carbonphenolic ablation than previously predicted
The design of a research water table
A complete design for a research water table is presented. Following a brief discussion of the analogy between water and compressible-gas flows (hydraulic analogy), the components of the water table and their function are described. The major design considerations are discussed, and the final design is presented
A modified method of integral relations approach to the blunt-body equilibrium air flow field, including comparisons with inverse solutions
Numerical calculation of inviscid adiabatic flow field around blunt bodies at hypersonic speed
Kentucky River Basin Water Quality Assessment Study
The current report summarizes the work associated with the construction, calibration, and application of the CE-QUAL-W2 water quality model to the Kentucky River. In applying the model to the Kentucky River System, the primary objective was to assess the impact of the operation of low-level control valves on water quality of the Kentucky River. This was accomplished by modeling the impact of the valves for low flow conditions associated with the 1930 drought of record along with projections for the year 2020. The results of this study indicate that for the modeled scenario, the proposed valves can be used to draw down the individual pools on the Kentucky River a maximum of 4 feet without causing significant chronic or acute impacts to the biota of the river
Kentucky River Modeling and Monitoring Needs Assessment
This report outlines the responsibilities of the Kentucky River Authority in the planning, operation, and management of river monitoring
Raman Scattering Signatures of Kitaev Spin Liquids in A IrO Iridates
We study theoretically the Raman scattering response in the
gapless quantum spin liquid phase of the Kitaev-Heisenberg model. The dominant
polarization-independent contribution reflects the density of
states of the emergent Majorana fermions in the ground-state flux-sector. The
integrability-breaking Heisenberg exchange generates a second contribution,
whose dominant part has the form of a quantum quench
corresponding to an abrupt insertion of four gauge fluxes. This results
in a weakly polarization dependent response with a sharp peak at the energy of
the flux excitation accompanied by broad features, which can be related to
Majorana fermions in the presence of the perturbed gauge field. We discuss the
experimental situation and explore more generally the influence of
integrability breaking for Kitaev spin liquid response functions.Comment: 9 pages including supp. ma
Magnetic excitations in vanadium spinels
We study magnetic excitations in vanadium spinel oxides AVO (A=Zn,
Mg, Cd) using two models: first one is a superexchange model for vanadium S=1
spins, second one includes in addition spin-orbit coupling, and crystal
anisotropy. We show that the experimentally observed magnetic ordering can be
obtained in both models, however the orbital ordering is different with and
without spin-orbit coupling and crystal anisotropy. We demonstrate that this
difference strongly affects the spin-wave excitation spectrum above the
magnetically ordered state, and argue that the neutron measurement of such
dispersion is a way to distinguish between the two possible orbital orderings
in AVO.Comment: accepted in Phys. Rev.
Wheels within wheels: Hamiltonian dynamics as a hierarchy of action variables
In systems where one coordinate undergoes periodic oscillation, the net
displacement in any other coordinate over a single period is shown to be given
by differentiation of the action integral associated with the oscillating
coordinate. This result is then used to demonstrate that the action integral
acts as a Hamiltonian for slow coordinates providing time is scaled to the
``tick-time'' of the oscillating coordinate. Numerous examples, including
charged particle drifts and relativistic motion, are supplied to illustrate the
varied application of these results.Comment: 7 pages, 3 figure
Looking to the Future: Key Points for Sustainable Management of Northern Great Plains Grasslands
The grasslands of the northern Great Plains (NGP) region of North America are considered endangered ecosystems and priority conservation areas yet have great ecological and economic importance. Grasslands in the NGP are no longer self-regulating adaptive systems. The challenges to these grasslands are widespread and serious (e.g. climate change, invasive species, fragmentation, altered disturbance regimes, and anthropogenic chemical loads). Because the challenges facing the region are dynamic, complex, and persistent, a paradigm shift in how we approach restoration and management of the grasslands in the NGP is imperative. The goal of this article is to highlight four key points for land managers and restoration practitioners to consider when planning management or restoration actions. First, we discuss the appropriateness of using historical fidelity as a restoration or management target because of changing climate, widespread pervasiveness of invasive species, the high level of fragmentation, and altered disturbance regimes. Second, we highlight ecosystem resilience and long-term population persistence as alternative targets. Third, because the NGP is so heavily impacted with anthropogenic chemical loading, we discuss the risks of ecological traps and extinction debt. Finally, we highlight the importance of using adaptive management and having patience during restoration and management. Consideration of these four points will help management and restoration of grasslands move toward a more successful and sustainable future. Although we specifically focus on the NGP of North America, these same issues and considerations apply to grasslands and many other ecosystems globally
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