7,478 research outputs found
Detecting sound waves generated by leaks in buried water distribution pipes
It is common to use guided sound waves to detect leaks or cracks in pipelines. Applications include the nondestructive testing of oil and gas pipelines, which normally takes places at ultrasonic frequencies, as well as the detection of leaks and ruptures in water filled pipes at much lower audio frequencies. However, if the pipe is buried then sound leaks out of the pipe into the surrounding medium and this lowers the acoustic energy travelling along the pipe wall. This has the potential to limit the applications of this technology, and so it is necessary to develop knowledge of the acoustic properties of the guided waves in order to optimise detection techniques. Accordingly, this work examines the properties of sound waves propagating in an infinitely long fluid-filled buried pipe, with application to leak detection at low audio frequencies. A parametric study is undertaken to examine the sensitivity of sound propagation to the properties of the internal liquid, pipe walls and of the surrounding medium
Development of liquid oxygen cooled 110MM ROLLER and tandem ball bearings at up to .5 x 106 DN values for the oxidizer turbopump of the M-1 engine Technology report
Bearing package design suitability for M-1 liquid oxygen turbopum
Exotic Spaces in Quantum Gravity I: Euclidean Quantum Gravity in Seven Dimensions
It is well known that in four or more dimensions, there exist exotic
manifolds; manifolds that are homeomorphic but not diffeomorphic to each other.
More precisely, exotic manifolds are the same topological manifold but have
inequivalent differentiable structures. This situation is in contrast to the
uniqueness of the differentiable structure on topological manifolds in one, two
and three dimensions. As exotic manifolds are not diffeomorphic, one can argue
that quantum amplitudes for gravity formulated as functional integrals should
include a sum over not only physically distinct geometries and topologies but
also inequivalent differentiable structures. But can the inclusion of exotic
manifolds in such sums make a significant contribution to these quantum
amplitudes? This paper will demonstrate that it will. Simply connected exotic
Einstein manifolds with positive curvature exist in seven dimensions. Their
metrics are found numerically; they are shown to have volumes of the same order
of magnitude. Their contribution to the semiclassical evaluation of the
partition function for Euclidean quantum gravity in seven dimensions is
evaluated and found to be nontrivial. Consequently, inequivalent differentiable
structures should be included in the formulation of sums over histories for
quantum gravity.Comment: AmsTex, 23 pages 5 eps figures; replaced figures with ones which are
hopefully viewable in pdf forma
Diffusive transport in networks built of containers and tubes
We developed analytical and numerical methods to study a transport of
non-interacting particles in large networks consisting of M d-dimensional
containers C_1,...,C_M with radii R_i linked together by tubes of length l_{ij}
and radii a_{ij} where i,j=1,2,...,M. Tubes may join directly with each other
forming junctions. It is possible that some links are absent. Instead of
solving the diffusion equation for the full problem we formulated an approach
that is computationally more efficient. We derived a set of rate equations that
govern the time dependence of the number of particles in each container
N_1(t),N_2(t),...,N_M(t). In such a way the complicated transport problem is
reduced to a set of M first order integro-differential equations in time, which
can be solved efficiently by the algorithm presented here. The workings of the
method have been demonstrated on a couple of examples: networks involving
three, four and seven containers, and one network with a three-point junction.
Already simple networks with relatively few containers exhibit interesting
transport behavior. For example, we showed that it is possible to adjust the
geometry of the networks so that the particle concentration varies in time in a
wave-like manner. Such behavior deviates from simple exponential growth and
decay occurring in the two container system.Comment: 21 pages, 18 figures, REVTEX4; new figure added, reduced emphasis on
graph theory, additional discussion added (computational cost, one
dimensional tubes
Absorption spectrum in the wings of the potassium second resonance doublet broadened by helium
We have measured the reduced absorption coefficients occurring in the wings
of the potassium 4S-5P doublet lines at 404.414 nm and at 404.720 nm broadened
by helium gas at pressures of several hundred Torr. At the experimental
temperature of 900 K, we have detected a shoulder-like broadening feature on
the blue wing of the doublet which is relatively flat between 401.8 nm and
402.8 nm and which drops off rapidly for shorter wavelengths, corresponding to
absorption from the X doublet Sigma+ state to the C doublet Sigma+ state of the
K-He quasimolecule. The accurate measurements of the line profiles in the
present work will sharply constrain future calculations of potential energy
surfaces and transition dipole moments correlating to the asymptotes He-K(5p),
He-K(5s), and He-K(3d).Comment: 2 figure
Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor
Current cosmological models indicate that the Milky Way's stellar halo was
assembled from many smaller systems. Based on the apparent absence of the most
metal-poor stars in present-day dwarf galaxies, recent studies claimed that the
true Galactic building blocks must have been vastly different from the
surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in
the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt
on this conclusion. However, verification of the iron-deficiency and
measurements of additional elements, such as the alpha-element Mg, are
mandatory for demonstrating that the same type of stars produced the metals
found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars
be conclusively linked to early stellar halo assembly. Here we report
high-resolution spectroscopic abundances for 11 elements in S1020549,
confirming the iron abundance of less than 1/4000th that of the Sun, and
showing that the overall abundance pattern mirrors that seen in low-metallicity
halo stars, including the alpha-elements. Such chemical similarity indicates
that the systems destroyed to form the halo billions of years ago were not
fundamentally different from the progenitors of present-day dwarfs, and
suggests that the early chemical enrichment of all galaxies may be nearly
identical.Comment: 16 pages, including 2 figures. Accepted for publication in Nature. It
is embargoed for discussion in the press until formal publication in Natur
The Molecular Line Opacity of MgH in Cool Stellar Atmospheres
A new, complete, theoretical rotational and vibrational line list for the A-X
electronic transition in MgH is presented. The list includes transition
energies and oscillator strengths for all possible allowed transitions and was
computed using the best available theoretical potential energies and dipole
transition moment function with the former adjusted to account for experimental
data. The A-X line list, as well as new line lists for the B'-X and the X-X
(pure rovibrational) transitions, were included in comprehensive stellar
atmosphere models for M, L, and T dwarfs and solar-type stars. The resulting
spectra, when compared to models lacking MgH, show that MgH provides
significant opacity in the visible between 4400 and 5600 Angstrom. Further,
comparison of the spectra obtained with the current line list to spectra
obtained using the line list constructed by Kurucz (1993) show that the Kurucz
list significantly overestimates the opacity due to MgH particularly for the
bands near 5150 and 4800 Angstrom with the discrepancy increasing with
decreasing effective temperature.Comment: 10 pages, 4 figures, 3 table
Working with Children with Learning Disabilities and/or who Communicate Non-verbally: Research experiences and their implications for social work education, increased participation and social inclusion
Social exclusion, although much debated in the UK, frequently focuses on children as a key 'at risk' group. However, some groups, such as disabled children, receive less consideration. Similarly, despite both UK and international policy and guidance encouraging the involvement of disabled children and their right to participate in decision-making arenas, they are frequently denied this right. UK based evidence suggests that disabled children's participation lags behind that of their non-disabled peers, often due to social work practitioners' lack of skills, expertise and knowledge on how to facilitate participation. The exclusion of disabled children from decision-making in social care processes echoes their exclusion from participation in society. This paper seeks to begin to address this situation, and to provide some examples of tools that social work educators can introduce into pre- and post-qualifying training programmes, as well as in-service training. The paper draws on the experiences of researchers using non-traditional qualitative research methods, especially non-verbal methods, and describes two research projects, focusing on the methods employed to communicate with and involve disabled children, the barriers encountered and lessons learnt. Some of the ways in which these methods of communication can inform social work education are explored alongside wider issues of how and if increased communication can facilitate greater social inclusion
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