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America’s largest classroom: Expanding the role of education in our parks
An introduction to this issue's set of theme papers, which were inspired by the new book America’s Largest Classroom: What We Learn from Our National Parks (University of California Press, 2020). These papers explore innovations in education and interpretation in the US National Park Service
Marangoni bubble motion in zero gravity
It was shown experimentally that the Marangoni phenomenon is a primary mechanism for the movement of a gas bubble in a nonisothermal liquid in a low gravity environment. A mathematical model consisting of the Navier-Stokes and thermal energy equations, together with the appropriate boundary conditions for both media, is presented. Parameter perturbation theory is used to solve this boundary value problem; the expansion parameter is the Marangoni number. The zeroth, first, and second order approximations for the velocity, temperature and pressure distributions in the liquid and in the bubble, and the deformation and terminal velocity of the bubble are determined. Experimental zero gravity data for a nitrogen bubble in ethylene glycol, ethanol, and silicone oil subjected to a linear temperature gradient were obtained using the NASA Lewis zero gravity drop tower. Comparison of the zeroth order analytical results for the bubble terminal velocity showed good agreement with the experimental measurements. The first and second order solutions for the bubble deformation and bubble terminal velocity are valid for liquids having Prandtl numbers on the order of one, but there is a lack of appropriate data to test the theory fully
Finite element (MARC) solution technologies for viscoplastic analyses
A need for development of realistic constitutive models for structural components operating at high temperatures, accompanied by appropriate solution technologies for stress/life analyses of these components is studied. Viscoplastic models provide a better description of inelastic behavior of materials, but their mathematical structure is very complex. The highly nonlinear and stiff nature of the constitutive equations makes analytical solutions difficult. Therefore, suitable solution, finite element or other numerical, technologies must be developed to make these models adaptable for better and rational designs of components. NASA-Lewis has developed several solution technologies and successfully applied them to the solution of a number of uniaxial and multiaxial problems. Some of these solution technologies are described along with the models and representative results. The solution technologies developed and presented encompass a wide range of models, such as, isotropic, anisotropic, metal matrix composites, and single crystal models
Relation Between a Three Parameter Formula for Isotope Shifts and Staggering Parameters
It is noted that the staggering parameters used to describe even-odd effects
for isotope shifts can in some cases exhibit very rapidly varying behavior as a
function of neutron number. On the other hand a three parameter formula (3P)
with fixed coefficients can explain the same behaviour
Magnetar Spindown, Hyper-Energetic Supernovae, and Gamma Ray Bursts
The Kelvin-Helmholtz cooling epoch, lasting tens of seconds after the birth
of a neutron star in a successful core-collapse supernova, is accompanied by a
neutrino-driven wind. For magnetar-strength ( G) large scale
surface magnetic fields, this outflow is magnetically-dominated during the
entire cooling epoch.Because the strong magnetic field forces the wind to
co-rotate with the protoneutron star,this outflow can significantly effect the
neutron star's early angular momentum evolution, as in analogous models of
stellar winds (e.g. Weber & Davis 1967). If the rotational energy is large in
comparison with the supernova energy and the spindown timescale is short with
respect to the time required for the supernova shockwave to traverse the
stellar progenitor, the energy extracted may modify the supernova shock
dynamics significantly. This effect is capable of producing hyper-energetic
supernovae and, in some cases, provides conditions favorable for gamma ray
bursts. We estimate spindown timescales for magnetized, rotating protoneutron
stars and construct steady-state models of neutrino-magnetocentrifugally driven
winds. We find that if magnetars are born rapidly rotating, with initial spin
periods () of millisecond, that of order erg of
rotational energy can be extracted in seconds. If magnetars are born
slowly rotating ( ms) they can spin down to periods of
second on the Kelvin-Helmholtz timescale.Comment: 16 pages, 5 figures, emulateap
Structural response of SSME turbine blade airfoils
Reusable space propulsion hot gas-path components are required to operate under severe thermal and mechanical loading conditions. These operating conditions produce elevated temperature and thermal transients which results in significant thermally induced inelastic strains, particularly, in the turbopump turbine blades. An inelastic analysis for this component may therefore be necessary. Anisotropic alloys such as MAR M-247 or PWA-1480 are being considered to meet the safety and durability requirements of this component. An anisotropic inelastic structural analysis for an SSME fuel turbopump turbine blade was performed. The thermal loads used resulted from a transient heat transfer analysis of a turbine blade. A comparison of preliminary results from the elastic and inelastic analyses is presented
Design requirements and development of an airborne descent path definition algorithm for time navigation
The design requirements for a 4D path definition algorithm are described. These requirements were developed for the NASA ATOPS as an extension of the Local Flow Management/Profile Descent algorithm. They specify the processing flow, functional and data architectures, and system input requirements, and recommended the addition of a broad path revision (reinitialization) function capability. The document also summarizes algorithm design enhancements and the implementation status of the algorithm on an in-house PDP-11/70 computer. Finally, the requirements for the pilot-computer interfaces, the lateral path processor, and guidance and steering function are described
Diurnal variation in harbour porpoise detection – potential implications for management
Peer reviewedPublisher PD
Andreev Reflection in Heavy-Fermion Superconductors and Order Parameter Symmetry in CeCoIn_5
Differential conductance spectra are obtained from nanoscale junctions on the
heavy-fermion superconductor CeCoIn along three major crystallographic
orientations. Consistency and reproducibility of characteristic features among
the junctions ensure their spectroscopic nature. All junctions show a similar
conductance asymmetry and Andreev reflection-like conductance with reduced
signal (~ 10%-13%), both commonly observed in heavy-fermion superconductor
junctions. Analysis using the extended Blonder-Tinkham-Klapwijk model indicates
that our data provide the first spectroscopic evidence for
symmetry. To quantify our conductance spectra, we propose a model by
considering the general phenomenology in heavy fermions, the two-fluid
behavior, and an energy-dependent density of states. Our model fits to the
experimental data remarkably well and should invigorate further investigations.Comment: 4 pages, 4 figures; Phys. Rev. Lett., published versio
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