7,477 research outputs found
A Far-Infrared Survey of Molecular Cloud Cores
We present a catalogue of molecular cloud cores drawn from high latitude,
medium opacity clouds, using the all-sky IRAS Sky Survey Atlas (ISSA) images at
60 and 100~m. The typical column densities of the cores are cm and the typical volume densities are cm. They are therefore significantly less dense than
many other samples obtained in other ways. Those cloud cores with IRAS point
sources are seen to be already forming stars, but this is found to be only a
small fraction of the total number of cores. The fraction of the cores in the
protostellar stage is used to estimate the prestellar timescale - the time
until the formation of a hydrostatically supported protostellar object. We
argue, on the basis of a comparison with other samples, that a trend exists for
the prestellar lifetime of a cloud core to decrease with the mean column
density and number density of the core. We compare this with model predictions
and show that the data are consistent with star formation regulated by the
ionisation fraction.Comment: 13 pages, 7 figure
The initial conditions of isolated star formation: IV - C18O observations and modelling of the pre-stellar core L1689B
We present C18O observations of the pre-stellar core L1689B, in the (J=3-2)
and (J=2-1) rotational transitions, taken at the James Clerk Maxwell Telescope
in Hawaii. We use a lambda-iteration radiative transfer code to model the data.
We adopt a similar form of radial density profile to that which we have found
in all pre-stellar cores, with a `flat' inner profile, steepening towards the
edge, but we make the gradient of the `flat' region a free parameter. We find
that the core is close to virial equilibrium, but there is tentative evidence
for core contraction. We allow the temperature to vary with a power-law form
and find we can consistently fit all of the CO data with an inverse temperature
gradient that is warmer at the edge than the centre. However, when we combine
the CO data with the previously published millimetre data we fail to find a
simultaneous fit to both data-sets without additionally allowing the CO
abundance to decrease towards the centre. This effect has been observed
qualitatively many times before, as the CO freezes out onto the dust grains at
high densities, but we quantify the effect. Hence we show that the combination
of mm/submm continuum and spectral line data is a very powerful method of
constraining the physical parameters of cores on the verge of forming stars.Comment: 10 pages. Accepted for publication in MNRA
Role of hydrogen peroxide in intra-operative wound preparation based on an in vitro fibrin clot degradation model
Three per cent hydrogen peroxide (H2O2) is widely used to irrigate acute and chronic wounds in the surgical setting and clinical experience tells us that it is more effective at removing dried-on blood than normal saline alone. We hypothesise that this is due to the effect of H2O2 on fibrin clot architecture via fibrinolysis. We investigate the mechanisms and discuss the clinical implications using an in vitro model. Coagulation assays with normal saline (NaCl), 1% and 3% concentrations of H2O2 were performed to determine the effect on fibrin clot formation. These effects were confirmed by spectrophotometry. The effects of 1%, 3% and 10% H2O2 on the macroscopic and microscopic features of fibrin clots were assessed at set time intervals and compared to a NaCl control. Quantitative analysis of fibrin networks was undertaken to determine the fibre length, diameter, branch point density and pore size. Fibrin clots immersed in 1%, 3% and 10% H2O2 demonstrated volume losses of 0.09-0.25mm3/min, whereas those immersed in the normal saline gained in volume by 0.02±0.13 mm3/min. Quantitative analysis showed that H2O2 affects the structure of the fibrin clot in a concentration-dependent manner, with the increase in fibre length, diameter and consequently pore sizes. Our results support our hypothesis that the efficacy of H2O2 in cleaning blood from wounds is enhanced by its effects on fibrin clot architecture in a concentration- and time-dependent manner. The observed changes in fibre size and branch point density suggest that H2O2 is acting on the quaternary structure of the fibrin clot, most likely via its effect on cross-linking of the fibrin monomers and may therefore be of benefit for the removal of other fibrin-dependent structures such as wound slough
The Big Society and the Conjunction of Crises: Justifying Welfare Reform and Undermining Social Housing
The idea of the “Big Society” can be seen as culmination of a long-standing debate about the regulation of welfare. Situating the concept within governance theory, the article considers how the UK coalition government has justified a radical restructuring of welfare provision, and considers its implications for housing provision. Although drawing on earlier modernization processes, the article contends that the genesis for welfare reform was based on an analysis that the government was forced to respond to a unique conjunction of crises: in morality, the state, ideology and economics. The government has therefore embarked upon a programme, which has served to undermine the legitimacy of the social housing sector (most notably in England), with detrimental consequences for residents and raising significant dilemmas for those working in the housing sector
The concept of solidarity: emerging from the theoretical shadows?
The concept of solidarity has been relatively neglected by social scientists since Durkheim's pioneering work in the late 19th century. The discipline of politics has been guilty of overlooking this 'subjective' element of community life, but recent works by Stjernø and Brunkhorst reflect a growing awareness of the theoretical significance of the concept. Whereas early liberal attempts to theorise solidarity took the nation state to be the appropriate community for its realisation, the emergence of globalisation raises the possibility of human solidarity developing in the global community. Traditional forms of solidarity have been dissipated by the social changes accompanying globalisation, but they were often locked into the defence of particular interests. New forms may be emerging to rekindle the broader vision of human solidarity. Recent work by writers such as Habermas, Honneth, Rorty and Touraine focuses on widening and deepening democratic participation and/or the articulation of our ethical obligations in various ways. It is argued here that these perspectives need to be supplemented by a radical humanist approach grounded in a normative theory of human self-realisation
Exclusive Hadronic D Decays to eta' and eta
Hadronic decay modes and
are studied in the generalized
factorization approach. Form factors for transitions
are carefully evaluated by taking into account the wave function normalization
of the eta and eta'. The predicted branching ratios are generally in agreement
with experiment except for and
; the calculated decay rates for the first two decay modes
are too small by an order of magnitude. We show that the weak decays and followed by resonance-induced final-state
interactions (FSI), which are amenable technically, are able to enhance the
branching ratios of and dramatically
without affecting the agreement between theory and experiment for and . We argue that it is difficult to understand
the observed large decay rates of and
simultaneously; FSI, W-annihilation and the production of excess eta' from
gluons are not helpful in this regard. The large discrepancy between the
factorization hypothesis and experiment for the ratio of
and remains as an enigma.Comment: 15 pages, 1 figure, to appear in Phys. Rev. D. Form factors for D to
eta and eta' transitions are slightly change
Towards the automated reduction and calibration of SCUBA data from the James Clerk Maxwell Telescope
The Submillimetre Common User Bolometer Array (SCUBA) instrument has been
operating on the James Clerk Maxwell Telescope (JCMT) since 1997. The data
archive is now sufficiently large that it can be used to investigate
instrumental properties and the variability of astronomical sources. This paper
describes the automated calibration and reduction scheme used to process the
archive data with particular emphasis on `jiggle-map' observations of compact
sources. We demonstrate the validity of our automated approach at both 850- and
450-microns and apply it to several of the JCMT secondary flux calibrators. We
determine light curves for the variable sources IRC+10216 and OH231.8. This
automation is made possible by using the ORAC-DR data reduction pipeline, a
flexible and extensible data reduction pipeline that is used on UKIRT and the
JCMT.Comment: 9 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
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