5,792 research outputs found
NO sub x deposited in the stratosphere by the space shuttle, phase 1
The results of calculations to determine the amount of NOx deposited in the stratosphere by space shuttle solid rocket motors (SRM) are presented. Flow properties and chemical composition in the exhaust nozzle and plume were analyzed. The nozzle calculations show that about 4.5 lbm/sec of NOx leaves the two SRMs. The total amount of NOx deposited in the stratosphere is related to the amount leaving the nozzle via an overall plume enhancement factor (OPEF), which depends upon the influence of afterburning and shocks in enhancing the exit plane NOx mole fraction. Calculations show that the OPEF is approximately 2, indicating the mass flow of NOx in the plume to be approximately l0 lbm/sec at 30 km altitude with a possible error factor of 4. For a vehicle velocity of 3750 ft/sec, therefore, the NOx deposition rate in the stratosphere is about 2.7 x 10(-3) lbm/ft
Influences on outdoor education teachers\u27 content selection
This study sought to identify what teachers perceive to be the major factors influencing their selection of content in outdoor education formal curricula in two Western Australian government senior high schools. The study uses comparative and descriptive measures, including a documentary analysis comparing Ministry of Education and school formal curricula. This analysis initially identified discrepancies with content selection, prompting the investigation, through interviewing, of teachers\u27 perceptions of their causes. From the perceptions investigated, five categories of factors were identified: Time, cost; expertise; needs; and resources. These categories were integrated to form a substantive theory for influences on content selection by outdoor education teachers
Computational models for the viscous/inviscid analysis of jet aircraft exhaust plumes
Computational models which analyze viscous/inviscid flow processes in jet aircraft exhaust plumes are discussed. These models are component parts of an NASA-LaRC method for the prediction of nozzle afterbody drag. Inviscid/shock processes are analyzed by the SCIPAC code which is a compact version of a generalized shock capturing, inviscid plume code (SCIPPY). The SCIPAC code analyzes underexpanded jet exhaust gas mixtures with a self-contained thermodynamic package for hydrocarbon exhaust products and air. A detailed and automated treatment of the embedded subsonic zones behind Mach discs is provided in this analysis. Mixing processes along the plume interface are analyzed by two upgraded versions of an overlaid, turbulent mixing code (BOAT) developed previously for calculating nearfield jet entrainment. The BOATAC program is a frozen chemistry version of BOAT containing the aircraft thermodynamic package as SCIPAC; BOATAB is an afterburning version with a self-contained aircraft (hydrocarbon/air) finite-rate chemistry package. The coupling of viscous and inviscid flow processes is achieved by an overlaid procedure with interactive effects accounted for by a displacement thickness type correction to the inviscid plume interface
NO sub X Deposited in the Stratosphere by the Space Shuttle Solid Rocket Motors
The possible effects of the interaction of the plumes from the two solid rocket motors (SRM) from the space shuttles and mixing of the rocket exhaust products and ambient air in the base recirculation region on the total nitrous oxide deposition rate in the stratosphere were investigated. It was shown that these phenomena will not influence the total NOx deposition rate. It was also shown that uncertainties in the particle size of Al2O3, size distributions and particle/gas drag and heat transfer coefficients will not have a significant effect on the predicted NOx deposition rate. The final results show that the total mass flow of NOx leaving the plume at 30 km altitude is 4000 g./sec with a possible error factor of 3. For a vehicle velocity of 1140 meter/sec this yields an NOx deposition rate of about 3.5 g./meter. The corresponding HCl deposition rate at this altitude is about a factor of 500 greater than this value
Model metadata report for a 3D model of Cirencester-Cricklade
This report publishes the metadata of a 3d modelling study by a BUFI student which
subsequently was then formalised by British Geological Survey (BGS) modelling staff. As the
model was created by a visiting student no accurate metadata was maintained during the project
set-up period. This document aims to publish all known metadata and indicates where
uncertainty of source arises. The model was given to BGS after the initial student completion phase to allow the in-house modelling team to bring the model into line with BGS best practice.
The model was developed under the 3d Models for Teaching team, part of the Geological
Modelling Systems program at BGS. 3D geological models have great potential as a resource for
universities when teaching foundation geological concepts as it allows the student to visualise
and interrogate UK geology. They are especially useful when dealing with the conversion of 2D
field, map and GIS outputs into three dimensional geological units, which is a common problem
for all students of geology. Today’s earth science students use a variety of skills and processes
during their learning experience including the application of schema’s, spatial thinking, image
construction, detecting patterns, memorising figures, mental manipulation and interpretation,
making predictions and deducing the orientation of themselves and the rocks. 3D geological
models can reinforce spatial thinking strategies and encourage students to think about processes
and properties, in turn helping the student to recognise pre-learnt geological principles in the
field and to convert what they see at the surface into a picture of what is going on at depth
Algorithms for 3D rigidity analysis and a first order percolation transition
A fast computer algorithm, the pebble game, has been used successfully to
study rigidity percolation on 2D elastic networks, as well as on a special
class of 3D networks, the bond-bending networks. Application of the pebble game
approach to general 3D networks has been hindered by the fact that the
underlying mathematical theory is, strictly speaking, invalid in this case. We
construct an approximate pebble game algorithm for general 3D networks, as well
as a slower but exact algorithm, the relaxation algorithm, that we use for
testing the new pebble game. Based on the results of these tests and additional
considerations, we argue that in the particular case of randomly diluted
central-force networks on BCC and FCC lattices, the pebble game is essentially
exact. Using the pebble game, we observe an extremely sharp jump in the largest
rigid cluster size in bond-diluted central-force networks in 3D, with the
percolating cluster appearing and taking up most of the network after a single
bond addition. This strongly suggests a first order rigidity percolation
transition, which is in contrast to the second order transitions found
previously for the 2D central-force and 3D bond-bending networks. While a first
order rigidity transition has been observed for Bethe lattices and networks
with ``chemical order'', this is the first time it has been seen for a regular
randomly diluted network. In the case of site dilution, the transition is also
first order for BCC, but results for FCC suggest a second order transition.
Even in bond-diluted lattices, while the transition appears massively first
order in the order parameter (the percolating cluster size), it is continuous
in the elastic moduli. This, and the apparent non-universality, make this phase
transition highly unusual.Comment: 28 pages, 19 figure
Self-organization with equilibration: a model for the intermediate phase in rigidity percolation
Recent experimental results for covalent glasses suggest the existence of an
intermediate phase attributed to the self-organization of the glass network
resulting from the tendency to minimize its internal stress. However, the exact
nature of this experimentally measured phase remains unclear. We modify a
previously proposed model of self-organization by generating a uniform sampling
of stress-free networks. In our model, studied on a diluted triangular lattice,
an unusual intermediate phase appears, in which both rigid and floppy networks
have a chance to occur, a result also observed in a related model on a Bethe
lattice by Barre et al. [Phys. Rev. Lett. 94, 208701 (2005)]. Our results for
the bond-configurational entropy of self-organized networks, which turns out to
be only about 2% lower than that of random networks, suggest that a
self-organized intermediate phase could be common in systems near the rigidity
percolation threshold.Comment: 9 pages, 6 figure
Glider measurements of overturning in a Kelvin-Helmholtz billow train
The prospects for glider-based measurement of turbulence statistics are assessed using direct numerical simulation data representing breaking Kelvin-Helmholtz (KH) billows in a stratified, parallel shear flow. Transects tilted upstream against the shear tend to produce overestimates of overturning; those tilted with the shear produce underestimates. Low-angle transects can produce illusory overturning as the braid between the KH billows is crossed. Statistical features of the bias in displacement scales are related to geometrical aspects of KH billows. Results are interpreted in the context of a hypothetical effort to characterize overturning in a strongly sheared current (e.g. the Equatorial Undercurrent) using nonvertical profiles
Floppy modes and the free energy: Rigidity and connectivity percolation on Bethe Lattices
We show that negative of the number of floppy modes behaves as a free energy
for both connectivity and rigidity percolation, and we illustrate this result
using Bethe lattices. The rigidity transition on Bethe lattices is found to be
first order at a bond concentration close to that predicted by Maxwell
constraint counting. We calculate the probability of a bond being on the
infinite cluster and also on the overconstrained part of the infinite cluster,
and show how a specific heat can be defined as the second derivative of the
free energy. We demonstrate that the Bethe lattice solution is equivalent to
that of the random bond model, where points are joined randomly (with equal
probability at all length scales) to have a given coordination, and then
subsequently bonds are randomly removed.Comment: RevTeX 11 pages + epsfig embedded figures. Submitted to Phys. Rev.
The power of the feed-forward sweep
Vision is fast and efficient. A novel natural scene can be categorized (e.g. does
it contain an animal, a vehicle?) by human observers in less than 150 ms, and
with minimal attentional resources. This ability still holds under strong
backward masking conditions. In fact, with a stimulus onset asynchrony of about
30 ms (the time between the scene and mask onset), the first 30 ms of selective
behavioral responses are essentially unaffected by the presence of the mask,
suggesting that this type of “ultra-rapid” processing can rely on a sequence of
swift feed-forward stages, in which the mask information never “catches up” with
the scene information. Simulations show that the feed-forward propagation of the
first wave of spikes generated at stimulus onset may indeed suffice for crude
re-cognition or categorization. Scene awareness, however, may take significantly
more time to develop, and probably requires feed-back processes. The main
implication of these results for theories of masking is that pattern or
metacontrast (backward) masking do not appear to bar the progression of visual
information at a low level. These ideas bear interesting similarities to
existing conceptualizations of priming and masking, such as Direct Parameter
Specification or the Rapid Chase theory
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