1,567 research outputs found
Lost in translation: a multi-level case study of the metamorphosis of meanings and action in public sector organisational innovation
This paper explores the early implementation of an organisational innovation in the UK National Health Service (NHS) - Treatment Centres (TCs) - designed to dramatically reduce waiting lists for elective care. The paper draws on case studies of eight TCs (each at varying stages of their development) and aims to explore how meanings about TCs are created and evolve, and how these meanings impact upon the development of the organisational innovation. Research on organisational meanings needs to take greater account of the fact that modern organisations like the NHS are complex multi-level phenomena, comprising layers of interlacing networks. To understand the pace, direction and impact of organisational innovation and change we need to study the interconnections between meanings across different organisational levels. The data presented in this paper show how the apparently simple, relatively unformed, concept of a TC framed by central government, is translated and transmuted by subsequent layers in the health service administration, and by players in local health economies and, ultimately in the TCs themselves, picking up new rationales, meanings, and significance as it goes. The developmental histories of TCs reveal a range of significant re-workings of macro policy with the result that there is considerable diversity and variation between local TC schemes. The picture is of important disconnections between meanings, that in many ways mirror Weickâs (1976) âloosely coupled systemsâ. The emergent meanings and the direction of micro-level development of TCs appear more strongly determined by interactions within the local TC environment, notably between what we identify as groups of âidealistsâ, âpragmatistsâ, âopportunistsâ and âscepticsâ than by the framing (Goffman 1974) provided by macro and meso organisational levels. While this illustrates the limitations of top down and policy-driven attempts at change, and highlights the crucial importance of the front-line local âmicro-systemsâ (Donaldson & Mohr, 2000) in the overall scheme of implementing organisational innovations, the space or headroom provided by frames at the macro and meso levels can enable local change, albeit at variable speed and with uncertain outcomes
A discontinuity in the low-mass initial mass function
The origin of brown dwarfs (BDs) is still an unsolved mystery. While the
standard model describes the formation of BDs and stars in a similar way recent
data on the multiplicity properties of stars and BDs show them to have
different binary distribution functions. Here we show that proper treatment of
these uncovers a discontinuity of the multiplicity-corrected mass distribution
in the very-low-mass star (VLMS) and BD mass regime. A continuous IMF can be
discarded with extremely high confidence. This suggests that VLMSs and BDs on
the one hand, and stars on the other, are two correlated but disjoint
populations with different dynamical histories. The analysis presented here
suggests that about one BD forms per five stars and that the BD-star binary
fraction is about 2%-3% among stellar systems.Comment: 14 pages, 11 figures, uses emulateapj.cls. Minor corrections and 1
reference added after being accepted by the Ap
Global Models for the Evolution of Embedded, Accreting Protostellar Disks
Most analytic work to date on protostellar disks has focused on those in
isolation from their environments. However, observations are now beginning to
probe the earliest, most embedded phases of star formation, during which disks
are rapidly accreting from their parent cores and cannot be modeled in
isolation. We present a simple, one-zone model of protostellar accretion disks
with high mass infall rates. Our model combines a self-consistent calculation
of disk temperatures with an approximate treatment of angular momentum
transport via two mechanisms. We use this model to survey the properties of
protostellar disks across a wide range of stellar masses and evolutionary
times, and make predictions for disks' masses, sizes, spiral structure, and
fragmentation that will be directly testable by future large-scale surveys of
deeply embedded disks. We define a dimensionless accretion-rotation parameter
which, in conjunction with the disk's temperature, controls the disk evolution.
We track the dominant mode of angular momentum transport, and demonstrate that
for stars with final masses greater than roughly one solar mass, gravitational
instabilities are the most important mechanism as most of the mass accumulates.
We predict that binary formation through disk fission, fragmentation of the
disk into small objects, and spiral arm strength all increase in importance to
higher stellar masses.Comment: 17 pages, 9 figures, accepted for publication in ApJ. Model updated
to better reflect simulations in the literature; discussion of key
assumptions and strategy clarifie
STUDY OF DISPERSANT AGENTS FOR THORIUM OXIDE
S>A preliminary study of dispersing agents for thorium oxide was completed and several of the dispersants have possible uses. Also many of the industrial dispersing agents tested are not usable with thorium oxide due to induced behavior causing balling and caking. The effects of nitric acid concentration were observed to also effect each dispersing agent. (auth
The Formation of the First Stars. I. The Primordial Star Forming Cloud
To constrain the nature of the very first stars, we investigate the collapse
and fragmentation of primordial, metal-free gas clouds. We explore the physics
of primordial star formation by means of three-dimensional simulations of the
dark matter and gas components, using smoothed particle hydrodynamics, under a
wide range of initial conditions, including the initial spin, the total mass of
the halo, the redshift of virialization, the power spectrum of the DM
fluctuations, the presence of HD cooling, and the number of particles employed
in the simulation. We find characteristic values for the temperature, T ~ a few
100 K, and the density, n ~ 10^3-10^4 cm^-3, characterising the gas at the end
of the initial free-fall phase. These values are rather insensitive to the
initial conditions. The corresponding Jeans mass is M_J ~ 10^3 M_sun. The
existence of these characteristic values has a robust explanation in the
microphysics of H2 cooling, connected to the minimum temperature that can be
reached with the H2 coolant, and to the critical density at which the
transition takes place betweeb levels being populated according to NLTE, and
according to LTE.
In all cases, the gas dissipatively settles into an irregular, central
configuration which has a filamentary and knotty appearance. The fluid regions
with the highest densities are the first to undergo runaway collapse due to
gravitational instability, and to form clumps with initial masses ~ 10^3 M_sun,
close to the characteristic Jeans scale. These results suggest that the first
stars might have been quite massive, possibly even very massive with M_star >
100 M_sun.Comment: Minor revisions. 26 pages, including 24 figures and 5 tables. ApJ, in
press. To appear in the Dec. 20, 2001 issue (v563
Analysing Astronomy Algorithms for GPUs and Beyond
Astronomy depends on ever increasing computing power. Processor clock-rates
have plateaued, and increased performance is now appearing in the form of
additional processor cores on a single chip. This poses significant challenges
to the astronomy software community. Graphics Processing Units (GPUs), now
capable of general-purpose computation, exemplify both the difficult
learning-curve and the significant speedups exhibited by massively-parallel
hardware architectures. We present a generalised approach to tackling this
paradigm shift, based on the analysis of algorithms. We describe a small
collection of foundation algorithms relevant to astronomy and explain how they
may be used to ease the transition to massively-parallel computing
architectures. We demonstrate the effectiveness of our approach by applying it
to four well-known astronomy problems: Hogbom CLEAN, inverse ray-shooting for
gravitational lensing, pulsar dedispersion and volume rendering. Algorithms
with well-defined memory access patterns and high arithmetic intensity stand to
receive the greatest performance boost from massively-parallel architectures,
while those that involve a significant amount of decision-making may struggle
to take advantage of the available processing power.Comment: 10 pages, 3 figures, accepted for publication in MNRA
A laboratory-based beam tracking x-ray imaging method achieving two-dimensional phase sensitivity and isotropic resolution with unidirectional undersampling
Beam tracking X-ray Phase Contrast Imaging is a âShack-Hartmannâ type approach which uses a pre-sample mask to split the x-rays into âbeamletsâ which are interrogated by a detector with sufficient resolution. The ultimate spatial resolution is determined by the size of the mask apertures, however achieving this resolution level requires âsteppingâ the sample or the mask in increments equal to the aperture size (âditheringâ). If an array of circular apertures is used (which also provides two-dimensional phase sensitivity) instead of long parallel slits, this stepping needs to be carried out in two directions, which lengthens scan times significantly. We present a mask design obtained by offsetting rows of circular apertures, allowing for two-dimensional sensitivity and isotropic resolution while requiring sample or mask stepping in one direction only. We present images of custom-built phantoms and biological specimens, demonstrating that quantitative phase retrieval and near aperture-limited spatial resolutions are obtained in two orthogonal directions
DETERMINATION OF Li IN AQUEOUS SOLUTION BY NEUTRON ACTIVATION ANALYSIS
A method for determining the concentration of Li/sup 6/ in aqueous solution was tested using the nuclear reactions Li/sup 6/(n, alpha )H and O/sup 16/(H/sup 3/,n)F/sup 18/. Annihilation gamma radiation of induced 1.87-hr F/ sup 18/ radioactivity was counted with a welltype scintillation counter, and the radioactivity per millimole of lithium was found to be independent of lithium concentration below about 0.2 moles/liter. The sensitivity limit for detecting lithium is less than 0.1 micromole (0.0075 micromole Li/sup 6/). (auth
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