11,642 research outputs found
Speed of reaction diffusion in embryogenesis
Reaction diffusion systems have been proposed as mechanisms for patterning during many stages of embryonic development. While much attention has been focused on the study of the steady state patterns formed and the robustness of pattern selection, much less is known about the time scales required for pattern formation. Studies of gradient formation by the diffusion of a single morphogen from a localized source have shown that patterning can occur on realistic time scales over distances of a millimeter or less. Reaction diffusion has the potential to give rise to patterns on a faster time scale, since all points in the domain can act as sources of morphogen. However, the speed at which patterning can occur has hitherto not been explored in depth. In this paper, we investigate this issue in specific reaction diffusion models and address the question of whether patterning via reaction diffusion is fast enough to be applicable to morphogenesis
Complex pattern formation in reaction diffusion systems with spatially-varying parameters
Spontaneous pattern formation in reaction–diffusion systems on a spatially homogeneous domain has been well studied. However, in embryonic development and elsewhere, pattern formation often takes place on a spatially heterogeneous background. We explore the effects of spatially varying parameters on pattern formation in one and two dimensions using the Gierer–Meinhardt reaction–diffusion model. We investigate the effect of the wavelength of a pre-pattern and demonstrate a novel form of moving pattern. We find that spatially heterogeneous parameters can both increase the range and complexity of possible patterns and enhance the robustness of pattern selection
Resolving the large scale spectral variability of the luminous Seyfert 1 galaxy 1H 0419-577: Evidence for a new emission component and absorption by cold dense matter
An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in
September 2002, when the source was in an extreme low-flux state, found a very
hard X-ray spectrum at 1-10 keV with a strong soft excess below ~1 keV.
Comparison with an earlier XMM-Newton observation when 1H 0419-577 was `X-ray
bright' indicated the dominant spectral variability was due to a steep power
law or cool Comptonised thermal emission. Four further XMM-Newton observations,
with 1H 0419-577 in intermediate flux states, now support that conclusion,
while we also find the variable emission component in intermediate state
difference spectra to be strongly modified by absorption in low ionisation
matter. The variable `soft excess' then appears to be an artefact of absorption
of the underlying continuum while the `core' soft emission can be attributed to
recombination in an extended region of more highly ionised gas. We note the
wider implications of finding substantial cold dense matter overlying (or
embedded in) the X-ray continuum source in a luminous Seyfert 1 galaxy.Comment: 34 pages, 15 figures, submitted to Ap
A cross sectional study of organizational factors and their impact on job satisfaction and emotional burnout in a group of Australian nurses: infection control practitioners
Background
Infection control practitioners (ICPs) are a group of specialized nurses fundamental to effective healthcare infection prevention and control initiatives. Relative to other groups of nurses much less is known about their working conditions. Organizational factors may impact ICPs’ levels of job dissatisfaction and emotional job burnout and, subsequently, their quality of practice. We measure a range of organizational factors to document the working conditions of ICPs and show how these are linked to job satisfaction and emotional burnout in a sample of Australian ICPs.
Methods
We conducted a cross sectional study using an online survey. All employed ICPs in 50 of the largest public hospitals in Australia were invited to participate. One hundred and fifty three ICPs completed the survey.
Results
ICPs are moderately to highly satisfied with their job but show high levels of emotional burnout, time pressure and cognitive demands. Low job satisfaction was associated with less job control, low perceived organizational support and poor communication. In contrast, emotional burnout was associated with high time pressure and cognitive demands coupled with poor communication.
Discussion
This study provides new evidence about the organizational context of ICPs in Australia, and about the factors that impact on job satisfaction and emotional burnout. These findings may be used to modify national infection prevention and control programs to suit local organizational contexts. Further research is needed to determine the precise nature of these relationships and the downstream impacts on hospital-wide infection control outcomes.
Conclusions
Organizational context and factors are important to consider when evaluating the impact and implementation of infection control programs
An XMM-Newton observation of the Narrow Line Seyfert 1 Galaxy, Markarian 896
XMM-Newton observations of the NLS1 Markarian 896 are presented. Over the
2-10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is
just resolved and has an equivalent width of ~170 eV. The broad-band spectrum
is well modelled by a power law slope of gamma ~ 2.03, together with two
blackbody components to fit the soft X-ray excess. Using a more physical
two-temperature Comptonisation model, a good fit is obtained for an input
photon distribution of kT ~ 60eV and Comptonising electron temperatures of ~0.3
and 200 keV. The soft excess cannot be explained purely through the
reprocessing of a hard X-ray continuum by an ionised disc reflector.Comment: 6 pages, 4 figures, accepted by MNRA
Fe K emission and absorption features in XMM-Newton spectra of Mkn 766 - evidence for reprocessing in flare ejecta
We report on the analysis of a long XMM-Newton EPIC observation in 2001 May
of the Narrow Line Seyfert 1 galaxy Mkn 766. The 3-11 keV spectrum exhibits a
moderately steep power law continuum, with a broad emission line at ~6.7 keV,
probably blended with a narrow line at ~6.4 keV, and a broad absorption trough
above ~8.7 keV. We identify both broad spectral features with reprocessing in
He-like Fe. An earlier XMM-Newton observation of Mkn 766 in 2000 May, when the
source was a factor ~2 fainter, shows a similar broad emission line, but with a
slightly flatter power law and absorption at a lower energy. In neither
observation do we find a requirement for the previously reported broad 'red
wing' to the line and hence of reflection from the innermost accretion disc.
More detailed examination of the longer XMM-Newton observation reveals evidence
for rapid spectral variability in the Fe K band, apparently linked with the
occurrence of X-ray 'flares'. A reduction in the emission line strength and
increased high energy absorption during the X-ray flaring suggests that these
transient effects are due to highly ionised ejecta associated with the flares.
Simple scaling from the flare avalanche model proposed for the luminous QSO PDS
456 (Reeves etal. 2002) confirms the feasibility of coherent flaring being the
cause of the strong peaks seen in the X-ray light curve of \mkn.Comment: 9 pages, 11 figures, submitted to MNRA
A simultaneous XMM-Newton and BeppoSAX observation of the archetypal Broad Line Seyfert 1 galaxy NGC 5548
We report the spectral analysis of a long XMM-Newton observation of the
well-studied, moderate luminosity Broad Line Seyfert 1 galaxy NGC 5548. The
source was at an historically average brightness and we find the hard (3-10
keV) spectrum can be well fitted by a power law of photon index gamma ~ 1.75,
together with reflection. The only feature in the hard X-ray spectrum is a
narrow emission line near 6.4 keV, with an equivalent width of ~ 60 eV. The
energy and strength of this line is consistent with fluorescence from `neutral'
iron distant from the central continuum source. We find no evidence for a broad
Fe K line, with an upper limit well below previous reports, suggesting the
inner accretion disc is now absent or highly ionised. The addition of
simultaneous BeppoSAX data allows the analysis to be extended to 200 keV,
yielding important constraints on the total reflection. Extrapolation of the
hard X-ray power law down to 0.3 keV shows a clear `soft excess' below ~ 0.7
keV. After due allowance for the effects of a complex warm absorber, measured
with the XMM-Newton RGS, we find the soft excess is better described as a
smooth upward curvature in the continuum flux below ~ 2 keV. The soft excess
can be modelled either by Comptonised thermal emission or by enhanced
reflection from the surface of a highly ionised disc.Comment: 9 pages, 11 figures, accepted by MNRAS; minor changes to text and
figure
Numerical modeling of dynamic powder compaction using the Kawakita equation of state
Dynamic powder compaction is analyzed using the assumption that the powder behaves, while it is being compacted, like a hydrodynamic fluid in which deviatoric stress and heat conduction effects can be ignored throughout the process. This enables techniques of computational fluid dynamics such the equilibrium flux method to be used as a modeling tool. The equation of state of the powder under compression is assumed to be a modified version of the Kawakita loading curve. Computer simulations using this model are performed for conditions matching as closely as possible with those from experiments by Page and Killen [Powder Metall. 30, 233 (1987)]. The numerical and experimental results are compared and a surprising degree of qualitative agreement is observed
Conditional probabilities with Dirac observables and the problem of time in quantum gravity
We combine the "evolving constants" approach to the construction of
observables in canonical quantum gravity with the Page--Wootters formulation of
quantum mechanics with a relational time for generally covariant systems. This
overcomes the objections levied by Kucha\v{r} against the latter formalism. The
construction is formulated entirely in terms of Dirac observables, avoiding in
all cases the physical observation of quantities that do not belong in the
physical Hilbert space. We work out explicitly the example of the parameterized
particle, including the calculation of the propagator. The resulting theory
also predicts a fundamental mechanism of decoherence.Comment: 4 pages, no figures, RevTe
What is a hospital bed day worth? A contingent valuation study of hospital Chief Executive Officers.
BACKGROUND: Decreasing hospital length of stay, and so freeing up hospital beds, represents an important cost saving which is often used in economic evaluations. The savings need to be accurately quantified in order to make optimal health care resource allocation decisions. Traditionally the accounting cost of a bed is used. We argue instead that the economic cost of a bed day is the better value for making resource decisions, and we describe our valuation method and estimations for costing this important resource. METHODS: We performed a contingent valuation using 37 Australian Chief Executive Officers' (CEOs) willingness to pay (WTP) to release bed days in their hospitals, both generally and using specific cases. We provide a succinct thematic analysis from qualitative interviews post survey completion, which provide insight into the decision making process. RESULTS: On average CEOs are willing to pay a marginal rate of 436 for an Intensive Care Unit (ICU) bed day, with estimates of uncertainty being greater for ICU beds. These estimates are significantly lower (four times for ward beds and seven times for ICU beds) than the traditional accounting costs often used. Key themes to emerge from the interviews include the importance of national funding and targets, and their associated incentive structures, as well as the aversion to discuss bed days as an economic resource. CONCLUSIONS: This study highlights the importance for valuing bed days as an economic resource to inform cost effectiveness models and thus improve hospital decision making and resource allocation. Significantly under or over valuing the resource is very likely to result in sub-optimal decision making. We discuss the importance of recognising the opportunity costs of this resource and highlight areas for future research
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