22,448 research outputs found
Co-ordinating distributed knowledge: An investigation into the use of an organisational memory
This paper presents an ethnographically informed investigation into the use of an organisational memory, focusing in particular on how information was used in the performance of work. We argue that understanding how people make use of distributed knowledge is crucial to the design of an organisational memory. However, we take the perspective that an ‘organisational memory’ is not technology dependant, but is an emergent property of group interaction. In this sense, the technology does not form the organisational memory, but provides a novel means of augmenting the co-ordination of collaborative action. The study examines the generation, development and maintenance of knowledge repositories and archives. The knowledge and information captured in the organisational memory enabled the team members to establish a common understanding of the design and to gain an appreciation of the issues and concerns of the other disciplines. The study demonstrates why technology should not be thought of in isolation from its contexts of use, but also how designers can make use of the creative flexibility that people employ in their everyday activities. The findings of the study are therefore of direct relevance to both the design of knowledge archives and to the management of this information within organisations
Surveyor ejecta detector model ML 256-1 and 185-1 and Surveyor ejecta detector ground support equipment model ML 260-1 Final engineering report
Engineering analyses on Surveyor lunar dust particle detector instrumentation, and ground support equipmen
Large-scale anisotropy in stably stratified rotating flows
We present results from direct numerical simulations of the Boussinesq
equations in the presence of rotation and/or stratification, both in the
vertical direction. The runs are forced isotropically and randomly at small
scales and have spatial resolutions of up to grid points and Reynolds
numbers of . We first show that solutions with negative energy
flux and inverse cascades develop in rotating turbulence, whether or not
stratification is present. However, the purely stratified case is characterized
instead by an early-time, highly anisotropic transfer to large scales with
almost zero net isotropic energy flux. This is consistent with previous studies
that observed the development of vertically sheared horizontal winds, although
only at substantially later times. However, and unlike previous works, when
sufficient scale separation is allowed between the forcing scale and the domain
size, the total energy displays a perpendicular (horizontal) spectrum with
power law behavior compatible with , including in the
absence of rotation. In this latter purely stratified case, such a spectrum is
the result of a direct cascade of the energy contained in the large-scale
horizontal wind, as is evidenced by a strong positive flux of energy in the
parallel direction at all scales including the largest resolved scales
Investigation of the fiber reinforcement of a cobalt base alloy for application at elevated temperature
Technique developed for incorporating alumina and silicon carbide fibers in cobalt base alloy for application at high temperature
Evidence for Bolgiano-Obukhov scaling in rotating stratified turbulence using high-resolution direct numerical simulations
We report results on rotating stratified turbulence in the absence of
forcing, with large-scale isotropic initial conditions, using direct numerical
simulations computed on grids of up to 4096^3 points. The Reynolds and Froude
numbers are respectively equal to Re=5.4 x 10^4 and Fr=0.0242. The ratio of the
Brunt-V\"ais\"al\"a to the inertial wave frequency, N/f, is taken to be equal
to 4.95, a choice appropriate to model the dynamics of the southern abyssal
ocean at mid latitudes. This gives a global buoyancy Reynolds number
R_B=ReFr^2=32, a value sufficient for some isotropy to be recovered in the
small scales beyond the Ozmidov scale, but still moderate enough that the
intermediate scales where waves are prevalent are well resolved. We concentrate
on the large-scale dynamics, for which we find a spectrum compatible with the
Bolgiano-Obukhov scaling, and confirm that the Froude number based on a typical
vertical length scale is of order unity, with strong gradients in the vertical.
Two characteristic scales emerge from this computation, and are identified from
sharp variations in the spectral distribution of either total energy or
helicity. A spectral break is also observed at a scale at which the partition
of energy between the kinetic and potential modes changes abruptly, and beyond
which a Kolmogorov-like spectrum recovers. Large slanted layers are ubiquitous
in the flow in the velocity and temperature fields, with local overturning
events indicated by small Richardson numbers, and a small large-scale
enhancement of energy directly attributable to the effect of rotation is also
observed.Comment: 19 pages, 9 figures (including compound figures
Galactic Globular Cluster Relative Ages
Based on a new large, homogeneous photometric database of 35 Galactic
globular clusters (GGCs), a set of distance and reddening independent relative
age indicators has been measured. The observed D(V-I)_2.5 and D(V)(HB-TO) vs.
metallicity relations have been compared with the relations predicted by two
recent updated libraries of isochrones. Using these models and two independent
methods, we have found that self-consistent relative ages can be estimated for
our GGC sample. Based on the relative age vs. metallicity distribution, we
conclude that: (a) there is no evidence of an age spread for clusters with
[Fe/H]<-1.2, all the clusters of our sample in this range being old and coeval;
(b) for the intermediate metallicity group (-1.2<=[Fe/H]<-0.9) there is a clear
evidence of age dispersion, with clusters up to ~25% younger than the older
members; and (c) the clusters within the metal rich group ([Fe/H]>=-0.9) seem
to be coeval within the uncertainties (except Pal12), but younger (~17%) than
the bulk of the Galactic globulars. The latter result is totally model
dependent. From the distribution of the GGC ages with the Galactocentric
distance, we can present a possible scenario for the Milky Way formation: The
GC formation process started at the same zero age throughout the halo, at least
out to ~20 kpc from the Galactic center. According to the present stellar
evolution models, the metal-rich globulars are formed at a later time (~ 17%
lower age). And finally, significantly younger halo GGCs are found at any
R(GC)>8 kpc. For these, a possible scenario associated with mergers of dwarf
galaxies to the Milky Way is suggested.Comment: 47 pages, 9 figures. To be published in the Astronomical Journal,
November issu
Adaptive mesh refinement with spectral accuracy for magnetohydrodynamics in two space dimensions
We examine the effect of accuracy of high-order spectral element methods,
with or without adaptive mesh refinement (AMR), in the context of a classical
configuration of magnetic reconnection in two space dimensions, the so-called
Orszag-Tang vortex made up of a magnetic X-point centered on a stagnation point
of the velocity. A recently developed spectral-element adaptive refinement
incompressible magnetohydrodynamic (MHD) code is applied to simulate this
problem. The MHD solver is explicit, and uses the Elsasser formulation on
high-order elements. It automatically takes advantage of the adaptive grid
mechanics that have been described elsewhere in the fluid context [Rosenberg,
Fournier, Fischer, Pouquet, J. Comp. Phys. 215, 59-80 (2006)]; the code allows
both statically refined and dynamically refined grids. Tests of the algorithm
using analytic solutions are described, and comparisons of the Orszag-Tang
solutions with pseudo-spectral computations are performed. We demonstrate for
moderate Reynolds numbers that the algorithms using both static and refined
grids reproduce the pseudo--spectral solutions quite well. We show that
low-order truncation--even with a comparable number of global degrees of
freedom--fails to correctly model some strong (sup--norm) quantities in this
problem, even though it satisfies adequately the weak (integrated) balance
diagnostics.Comment: 19 pages, 10 figures, 1 table. Submitted to New Journal of Physic
Space - Single Precision Cowell Trajectory Program
Single Precision Cowell Trajectory program - digital computer program for trajectory computatio
SFPRO - Single Precision Cowell Trajectory Processor
Digital computer program for IBM 7094 computer to generate spacecraft tracking station calculation
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