2,088 research outputs found
Modeling and removal of optical ghosts in the PROBA-3/ASPIICS externally occulted solar coronagraph
Context: ASPIICS is a novel externally occulted solar coronagraph, which will
be launched onboard the PROBA-3 mission of the European Space Agency. The
external occulter will be placed on the first satellite approximately 150 m
ahead of the second satellite that will carry an optical instrument. During 6
hours per orbit, the satellites will fly in a precise formation, constituting a
giant externally occulted coronagraph. Large distance between the external
occulter and the primary objective will allow observations of the white-light
solar corona starting from extremely low heights 1.1RSun. Aims: To analyze
influence of optical ghost images formed inside the telescope and develop an
algorithm for their removal. Methods: We implement the optical layout of
ASPIICS in Zemax and study the ghost behaviour in sequential and non-sequential
regimes. We identify sources of the ghost contributions and analyze their
geometrical behaviour. Finally we develop a mathematical model and software to
calculate ghost images for any given input image. Results: We show that ghost
light can be important in the outer part of the field of view, where the
coronal signal is weak, since the energy of bright inner corona is
redistributed to the outer corona. However the model allows to remove the ghost
contribution. Due to a large distance between the external occulter and the
primary objective, the primary objective does not produce a significant ghost.
The use of the Lyot spot in ASPIICS is not necessary.Comment: 14 pages, 13 figure
Low-Altitude Reconnection Inflow-Outflow Observations during a 2010 November 3 Solar Eruption
For a solar flare occurring on 2010 November 3, we present observations using
several SDO/AIA extreme-ultraviolet (EUV) passbands of an erupting flux rope
followed by inflows sweeping into a current sheet region. The inflows are soon
followed by outflows appearing to originate from near the termination point of
the inflowing motion - an observation in line with standard magnetic
reconnection models. We measure average inflow plane-of-sky speeds to range
from ~150-690 km/s with the initial, high-temperature inflows being the
fastest. Using the inflow speeds and a range of Alfven speeds, we estimate the
Alfvenic Mach number which appears to decrease with time. We also provide
inflow and outflow times with respect to RHESSI count rates and find that the
fast, high-temperature inflows occur simultaneously with a peak in the RHESSI
thermal lightcurve. Five candidate inflow-outflow pairs are identified with no
more than a minute delay between detections. The inflow speeds of these pairs
are measured to be 10^2 km/s with outflow speeds ranging from 10^2-10^3 km/s -
indicating acceleration during the reconnection process. The fastest of these
outflows are in the form of apparently traveling density enhancements along the
legs of the loops rather than the loop apexes themselves. These flows could
either be accelerated plasma, shocks, or waves prompted by reconnection. The
measurements presented here show an order of magnitude difference between the
retraction speeds of the loops and the speed of the density enhancements within
the loops - presumably exiting the reconnection site.Comment: 31 pages, 13 figures, 1 table, Accepted to ApJ (expected publication
~July 2012
Scottish theme towns: have new identities enhanced development?
Three small towns in southwest Scotland have recently been branded as distinct theme towns, based on books, artists and food. This is an attempt to make them more attractive to visitors and thereby improve their economy. The objective of this research is to establish whether the new identities possessed by the towns have enhanced their development. It is argued, using data reviewing the past decade, that they have all developed, albeit at different rates, in terms of the economy and culture. Moreover, it is maintained that social capital has been enhanced and is a factor whose importance has been under-appreciated by planners and observers of this type of process. The relevance of the new identity to the pre-branding identity is also seen as a factor in successful development and ideas of authenticity and heritage are brought to bear on the relationship
The coupling of pathways and processes through shared components
<p>Abstract</p> <p>Background</p> <p>The coupling of pathways and processes through shared components is being increasingly recognised as a common theme which occurs in many cell signalling contexts, in which it plays highly non-trivial roles.</p> <p>Results</p> <p>In this paper we develop a basic modelling and systems framework in a general setting for understanding the coupling of processes and pathways through shared components. Our modelling framework starts with the interaction of two components with a common third component and includes production and degradation of all these components. We analyze the signal processing in our model to elucidate different aspects of the coupling. We show how different kinds of responses, including "ultrasensitive" and adaptive responses, may occur in this setting. We then build on the basic model structure and examine the effects of additional control regulation, switch-like signal processing, and spatial signalling. In the process, we identify a way in which allosteric regulation may contribute to signalling specificity, and how competitive effects may allow an enzyme to robustly coordinate and time the activation of parallel pathways.</p> <p>Conclusions</p> <p>We have developed and analyzed a common systems platform for examining the effects of coupling of processes through shared components. This can be the basis for subsequent expansion and understanding the many biologically observed variations on this common theme.</p
A Modeling of the Super-Eddington Luminosity in Nova Outbursts: V1974 Cygni
We have modeled nova light curves exceeding the Eddington luminosity. It has
been suggested that a porous structure develops in nova envelopes during the
super Eddington phase and the effective opacity is much reduced for such a
porous atmosphere. Based on this reduced opacity model, we have calculated
envelope structures and light curves of novae. The optically thick wind model
is used to simulate nova winds. We find that the photospheric luminosity and
the wind mass-loss rate increase inversely proportional to the reducing factor
of opacities, but the wind velocity hardly changes. We also reproduce the
optical light curve of V1974 Cygni (Nova Cygni 1992) in the super-Eddington
phase, which lasts 13 days from the optical peak 1.7 mag above the Eddington
luminosity.Comment: 8 pages, 4 figures, to appear in ApJ
Ultraviolet Spectra of CV Accretion Disks with Non-Steady T(r) Laws
An extensive grid of synthetic mid- and far-ultraviolet spectra for accretion
disks in cataclysmic variables has been presented by Wade and Hubeny (1998). In
those models, the disk was assumed to be in steady-state, that is T_eff(r) is
specified completely by the mass M_WD and radius R_WD of the accreting white
dwarf star and the mass transfer rate M_dot which is constant throughout the
disk. In these models, T_eff(r) is proportional to r^{-3/4} except as modified
by a cutoff term near the white dwarf.
Actual disks may vary from the steady-state prescription for T_eff(r),
however, e.g. owing to outburst cycles in dwarf novae M_dot not constant with
radius) or irradiation (in which case T_eff in the outer disk is raised above
T_steady). To show how the spectra of such disks might differ from the steady
case, we present a study of the ultraviolet (UV) spectra of models in which
power-law temperature profiles T_eff(r) is proportional to r^{-gamma} with
gamma < 3/4 are specified. Otherwise, the construction of the models is the
same as in the Wade & Hubeny grid, to allow comparison. We discuss both the UV
spectral energy distributions and the appearance of the UV line spectra. We
also briefly discuss the eclipse light curves of the non-standard models.
Comparison of these models with UV observations of novalike variables suggests
that better agreement may be possible with such modified T_eff(r) profiles.Comment: 13 pages, 6 figures (one reduced quality), ApJ in pres
Restrictive antibiotic stewardship associated with reduced hospital mortality in gram-negative infection
Introduction: Antimicrobial stewardship has an important role in the control of Clostridium difficile infection (CDI) and antibiotic resistance. An important component of UK stewardship interventions is the restriction of broad-spectrum beta-lactam antibiotics and promotion of agents associated with a lower risk of CDI such as gentamicin. Whilst the introduction of restrictive antibiotic guidance has been associated with improvements in CDI and antimicrobial resistance evidence of the effect on outcome following severe infection is lacking.
Methods: In 2008, Glasgow hospitals introduced a restrictive antibiotic guideline. A retrospective before/after study assessed outcome following gram-negative bacteraemia in the 2-year period around implementation.
Results: Introduction of restrictive antibiotic guidelines was associated with a reduction in utilisation of ceftriaxone and co-amoxiclav and an increase in amoxicillin and gentamicin. 1593 episodes of bacteraemia were included in the study. The mortality over 1 year following gram-negative bacteraemia was lower in the period following guideline implementation (RR 0.852, P = 0.045). There was no evidence of a difference in secondary outcomes including ITU admission, length of stay, readmission, recurrence of bacteraemia and need for renal replacement therapy. There was a fall in CDI (RR 0.571, P = 0.014) and a reduction in bacterial resistance to ceftriaxone and co-amoxiclav but no evidence of an increase in gentamicin resistance after guideline implementation.
Conclusion: Restrictive antibiotic guidelines were associated with a reduction in CDI and bacterial resistance but no evidence of adverse outcomes following gram-negative bacteraemia. There was a small reduction in one year mortality
Risk factors for failure of outpatient parenteral antibiotic therapy (OPAT) in infective endocarditis
Objectives:
To identify risk factors for failure of outpatient antibiotic therapy (OPAT) in infective endocarditis (IE).
Patients and methods:
We identified IE cases managed at a single centre over 12 years from a prospectively maintained database. ‘OPAT failure’ was defined as unplanned readmission or antibiotic switch due to adverse drug reaction or antibiotic resistance. We analysed patient and disease-related risk factors for OPAT failure by univariate and multivariate logistic regression. We also retrospectively collected follow-up data on adverse disease outcome (defined as IE-related death or relapse) and performed Kaplan–Meier survival analysis up to 36 months following OPAT.
Results:
We identified 80 episodes of OPAT in IE. Failure occurred in 25/80 episodes (31.3%). On multivariate analysis, cardiac or renal failure [pooled OR 7.39 (95% CI 1.84–29.66), P = 0.005] and teicoplanin therapy [OR 8.69 (95% CI 2.01–37.47), P = 0.004] were independently associated with increased OPAT failure. OPAT failure with teicoplanin occurred despite therapeutic plasma levels. OPAT failure predicted adverse disease outcome up to 36 months (P = 0.016 log-rank test).
Conclusions:
These data caution against selecting patients with endocarditis for OPAT in the presence of cardiac or renal failure and suggest teicoplanin therapy may be associated with suboptimal OPAT outcomes. Alternative regimens to teicoplanin in the OPAT setting should be further investigated
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