4,906 research outputs found
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
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
Elastin is Localised to the Interfascicular Matrix of Energy Storing Tendons and Becomes Increasingly Disorganised With Ageing
Tendon is composed of fascicles bound together by the interfascicular matrix (IFM). Energy storing tendons are more elastic and extensible than positional tendons; behaviour provided by specialisation of the IFM to enable repeated interfascicular sliding and recoil. With ageing, the IFM becomes stiffer and less fatigue resistant, potentially explaining why older tendons become more injury-prone. Recent data indicates enrichment of elastin within the IFM, but this has yet to be quantified. We hypothesised that elastin is more prevalent in energy storing than positional tendons, and is mainly localised to the IFM. Further, we hypothesised that elastin becomes disorganised and fragmented, and decreases in amount with ageing, especially in energy storing tendons. Biochemical analyses and immunohistochemical techniques were used to determine elastin content and organisation, in young and old equine energy storing and positional tendons. Supporting the hypothesis, elastin localises to the IFM of energy storing tendons, reducing in quantity and becoming more disorganised with ageing. These changes may contribute to the increased injury risk in aged energy storing tendons. Full understanding of the processes leading to loss of elastin and its disorganisation with ageing may aid in the development of treatments to prevent age related tendinopathy
Mind the Gap
Mind the Gap sought to improve the metacognition and academic attainment of pupils in Year 4. There were two aspects to the intervention. The first involved training teachers in how to embed metacognitive approaches in their work, and how to continue to effectively and strategically involve parents. This training took place over a day and was provided by a consultant. The second component focused on parental engagement and offered families the opportunity to participate in a series of facilitated workshops where children and parents work together to create an animated film. Sessions were coordinated by a practitioner who helped participants to think about how they are learning, create learning goals and reflect on their progress; to be metacognitive about the learning process they were engaged in together. The families were offered 2 hours of workshops per week for 5 weeks (10 hours in total).
The project targeted schools in four areas of England: Birmingham, Devon, London and Manchester. It was delivered by the Campaign for Learning, with assessments carried out by Durham University. Delivery started in September 2012 and finished in October 2013. The project was evaluated using a randomised controlled trial, which compared the interventions to a ‘business-as-usual’ control group. It is important to note that it was eligibility for the animation course, not participation, that was randomised, so the results must be regarded as estimating the effect of being offered the animation course (alone or in combination with teacher training, as appropriate) rather than participating in it
Gas permeation through a polymer network
We study the diffusion of gas molecules through a two-dimensional network of
polymers with the help of Monte Carlo simulations. The polymers are modeled as
non-interacting random walks on the bonds of a two-dimensional square lattice,
while the gas particles occupy the lattice cells. When a particle attempts to
jump to a nearest-neighbor empty cell, it has to overcome an energy barrier
which is determined by the number of polymer segments on the bond separating
the two cells. We investigate the gas current as a function of the mean
segment density , the polymer length and the probability
for hopping across segments. Whereas decreases monotonically with
for fixed , its behavior for fixed and increasing
depends strongly on . For small, non-zero , appears to increase
slowly with . In contrast, for , it is dominated by the underlying
percolation problem and can be non-monotonic. We provide heuristic arguments to
put these interesting phenomena into context.Comment: Dedicated to Lothar Schaefer on the occasion of his 60th birthday. 11
pages, 3 figure
Sediment Sorting and Rounding in a Basaltic Glacio-Fluvio-Aeolian Environment: hrisjkull Glacier, Iceland
Sediments and sedimentary rocks preserve a rich history of environment and climate. Identifying these signals requires an understanding of the physical and chemical processes that have affected sedimentary deposits [1]. Such processes include sorting and rounding during transport and chemical alteration through weathering and diagenesis. Although these processes have long been studied in quartz-dominated sedimentary systems [2], a lack of studies of basaltic sedimentary systems limits our interpretations of the environment and climate where mafic source rocks dominate, such as on Mars [3,4]. As part of the SAND-E: Semi-Autonomous Navigation for Detrital Environments project [5], which uses robotic operations to examine physical and chemical changes to sediments in basaltic glacio-fluvialaeolian environments, this research studies changes in sorting and rounding of fluvial-aeolian sediments along a glacier-proximal-to-glacier-distal transect in the outwash-plain of the risjkull glacier in SW Iceland (Fig. 1
Pressure Raman effects and internal stress in network glasses
Raman scattering from binary GexSe1-x glasses under hydrostatic pressure
shows onset of a steady increase in the frequency of modes of corner-sharing
GeSe4 tetrahedral units when the external pressure P exceeds a threshold value
Pc. The threshold pressure Pc(x) decreases with x in the 0.15 < x < 0.20 range,
nearly vanishes in the 0.20 < x < 0.25 range, and then increases in the 0.25 <
x < 1/3 range. These Pc(x) trends closely track those in the non-reversing
enthalpy, DHnr(x), near glass transitions (Tgs), and in particular, both
DHnr(x) and Pc(x) vanish in the reversibility window (0.20 < x < 0.25). It is
suggested that Pc provides a measure of stress at the Raman active units; and
its vanishing in the reversibility window suggests that these units are part of
an isostatically rigid backbone. Isostaticity also accounts for the non-aging
behavior of glasses observed in the reversibility window
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