43,261 research outputs found
Design and Construction of the 3.2 Mev High Voltage Column for Darht II
A 3.2 MeV injector has been designed and built for the Darht II Project at
Los Alamos Lab. The installation of the complete injector system is nearing
completion at this time. The requirements for the injector are to produce a 3.2
MeV, 2000 ampere electron pulse with a flattop width of at least 2-microseconds
and emittance of less than 0.15 p cm-rad normalized. A large high voltage
column has been built and installed. The column is vertically oriented, is 4.4
meters long, 1.2 meters in diameter, and weights 5700 kilograms. A novel method
of construction has been employed which utilizes bonded mycalex insulating
rings. This paper will describe the design, construction, and testing completed
during construction. Mechanical aspects of the design will be emphasized.Comment: 3 pages, 4 figures, Linac 200
The Way We Measure: Comparison of Methods to Derive Radial Surface Brightness Profiles
The breaks and truncations in the luminosity profile of face-on spiral
galaxies offer valuable insights in their formation history. The traditional
method of deriving the surface photometry profile for face-on galaxies is to
use elliptical averaging. In this paper, we explore the question whether
elliptical averaging is the best way to do this. We apply two additional
surface photometry methods, one new: principle axis summation, and one old that
has become seldom used: equivalent profiles. These are compared to elliptically
averaged profiles using a set of 29 face-on galaxies. We find that the
equivalent profiles match extremely well with elliptically averaged profiles,
confirming the validity of using elliptical averaging. The principle axis
summation offers a better comparison to edge-on galaxies.Comment: Accepted for publication by Monthly Notices of the R.A.S. A hi-res
version is available at http://www.astro.rug.nl/~vdkruit/Petersetal-VI.pd
Bayesian Cointegrated Vector Autoregression models incorporating Alpha-stable noise for inter-day price movements via Approximate Bayesian Computation
We consider a statistical model for pairs of traded assets, based on a
Cointegrated Vector Auto Regression (CVAR) Model. We extend standard CVAR
models to incorporate estimation of model parameters in the presence of price
series level shifts which are not accurately modeled in the standard Gaussian
error correction model (ECM) framework. This involves developing a novel matrix
variate Bayesian CVAR mixture model comprised of Gaussian errors intra-day and
Alpha-stable errors inter-day in the ECM framework. To achieve this we derive a
novel conjugate posterior model for the Scaled Mixtures of Normals (SMiN CVAR)
representation of Alpha-stable inter-day innovations. These results are
generalized to asymmetric models for the innovation noise at inter-day
boundaries allowing for skewed Alpha-stable models.
Our proposed model and sampling methodology is general, incorporating the
current literature on Gaussian models as a special subclass and also allowing
for price series level shifts either at random estimated time points or known a
priori time points. We focus analysis on regularly observed non-Gaussian level
shifts that can have significant effect on estimation performance in
statistical models failing to account for such level shifts, such as at the
close and open of markets. We compare the estimation accuracy of our model and
estimation approach to standard frequentist and Bayesian procedures for CVAR
models when non-Gaussian price series level shifts are present in the
individual series, such as inter-day boundaries. We fit a bi-variate
Alpha-stable model to the inter-day jumps and model the effect of such jumps on
estimation of matrix-variate CVAR model parameters using the likelihood based
Johansen procedure and a Bayesian estimation. We illustrate our model and the
corresponding estimation procedures we develop on both synthetic and actual
data.Comment: 30 page
The clinical effectiveness and cost-effectiveness of inhaler devices used in the routine management of chronic asthma in older children: a systematic review and economic evaluation
Background:
This review examines the clinical effectiveness and
cost-effectiveness of hand-held inhalers to deliver
medication for the routine management of chronic
asthma in children aged between 5 and 15 years.
Asthma is a common disease of the airways, with a
prevalence of treated asthma in 5–15-year-olds of
around 12% and an actual prevalence in the community
as high as 23%. Treatment for the condition
is predominantly by inhalation of medication. There
are three main types of inhaler device, pressurised
metered dose, breath actuated, and dry powder, with
the option of the attachment of a spacer to the first
two devices under some prescribed circumstances.
Two recent reviews have examined the clinical and
cost-effectiveness evidence on inhaler devices, but
one was for children aged under 5 years and the
comparison in the second was made between pressurised
metered dose inhalers and other types only.
Objectives:
This review examines the clinical effectiveness and
cost-effectiveness of manual pressurised metered
dose inhalers, breath-actuated metered dose
inhalers, and breath-actuated dry powder inhalers,
with and without spacers as appropriate, to deliver
medication for the routine management of chronic
asthma in children aged between 5 and 15 years.
Methods:
Two previous HTA reviews have compared the
effectiveness of inhaler devices, one focusing on
asthma in children aged under 5 years and the
other on asthma and chronic obstructive airways
disease in all age groups. For the current review, a
literature search was carried out to identify all
evidence relating to the use of inhalers in older
children with chronic asthma. A search of in-vitro
studies undertaken for one of the previous reviews
was also updated.
The data sources used were: 15 electronic bibliographic
databases; the reference lists of one of the
previous HTA reports and other relevant articles;
health services research-related internet resources;
and all sponsor submissions.
Studies were selected according to strict inclusion
and exclusion criteria, and relevant information
concerning effectiveness and patient compliance
and preference was extracted directly on to an
extraction/evidence table. Quality assurance
was monitored.
Economic evaluation was undertaken by reviewing
existing cost-effective evidence. Further economic
modelling was carried out, and tables constructed
to determine device cost-minimisation and
incremental quality-adjusted life-year (QALY)
thresholds between devices.
Results:
Number and quality of studies, and
direction of evidence:
Fourteen randomised controlled studies were
identified relating to the clinical effectiveness of
inhaler devices for delivering β2-agonists. A further
five were on devices delivering corticosteroids and
one concerned the delivery of cromoglicate.
Overall, there were no differences in clinical
efficacy between inhaler devices, but a pressurised
metered dose inhaler with a spacer would appear
to be more effective than one without. These
findings endorse those of a previous HTA review
but extend them to other inhaler devices.
Seven randomised controlled trials examined the
impact on clinical effectiveness of using a nonchlorofluorocarbon
(CFC) propellant in place of
a CFC propellant in metered dose inhalers, both
pressurised and breath activated, although only one
study considered the latter type. No differences were
found between inhalers containing either propellant.
A further 30 studies of varying quality, from 12 randomised
controlled trials to non-controlled studies,
were identified that concerned the impact of use
by, and preference for, inhaler type, and treatment
adherence in children. Differences between the
studies, and limitations in comparative data between
various inhaler device types, make it difficult to draw
any firm conclusions from this evidence.
Summary of benefits:
No obvious benefits for one inhaler device type
over another for use in children aged 5–15 years
were identified.
Costs and cost per quality-adjusted
life-year:
Two approaches have been taken: cost-minimisation
and QALY threshold. In the QALY threshold
approach, additional QALYs that each device must
produce compared with a cheaper device to achieve
an acceptable cost per QALY were calculated. Using
the cheapest and most expensive devices for delivering
200 μg of beclometasone per day, assuming no
cost offset for any device, and a threshold of £5000,
the largest QALY needed was 0.00807. With such
a small QALY increase, no intervention can be
categorically rejected as not cost-effective.
Conclusions:
Generalisability of findings:
On the available evidence there are no obvious
benefits for one inhaler device over another
when used by children aged 5–15 years with
chronic asthma. However, the evidence, in the
majority of cases, was compiled on children
with mild to moderate asthma and restricted
to a limited number of drugs. Therefore the
findings may not be generalisable to those at
the more severe end of the spectrum of the
disease or to inhaler devices delivering some
of the drugs used in the management of asthma.
Need for further research:
Many of the previous studies are likely to
have been underpowered. Further clinical
trials with a robust methodology, sufficient
power and qualitative components are needed
to demonstrate any differences in clinical
resource use and patients’ asthma symptoms.
Further studies should also include the
behavioural aspects of patients towards their
medication and its delivery mechanisms.
It is acknowledged that sufficient power may
prove impractical owing to the large numbers
of patients required
Nonconventional screening of the Coulomb interaction in FexOy clusters: An ab-initio study
From microscopic point-dipole model calculations of the screening of the
Coulomb interaction in non-polar systems by polarizable atoms, it is known that
screening strongly depends on dimensionality. For example, in one dimensional
systems the short range interaction is screened, while the long range
interaction is anti-screened. This anti-screening is also observed in some zero
dimensional structures, i.e. molecular systems. By means of ab-initio
calculations in conjunction with the random-phase approximation (RPA) within
the FLAPW method we study screening of the Coulomb interaction in FexOy
clusters. For completeness these results are compared with their bulk
counterpart magnetite. It appears that the onsite Coulomb interaction is very
well screened both in the clusters and bulk. On the other hand for the
intersite Coulomb interaction the important observation is made that it is
almost contant throughout the clusters, while for the bulk it is almost
completely screened. More precisely and interestingly, in the clusters
anti-screening is observed by means of ab-initio calculations
The Shape of Dark Matter Haloes IV. The Structure of Stellar Discs in Edge-on Galaxies
We present optical and near-infrared archival observations of eight edge-on
galaxies. These observations are used to model the stellar content of each
galaxy using the FitSKIRT software package. Using FitSKIRT, we can
self-consistently model a galaxy in each band simultaneously while treating for
dust. This allows us to accurately measure both the scale length and scale
height of the stellar disc, plus the shape parameters of the bulge. By
combining this data with the previously reported integrated magnitudes of each
galaxy, we can infer their true luminosities. We have successfully modelled
seven out of the eight galaxies in our sample. We find that stellar discs can
be modelled correctly, but have not been able to model the stellar bulge
reliably. Our sample consists for the most part of slow rotating galaxies, and
we find that the average dust layer is much thicker than what is reported for
faster rotating galaxies.Comment: Accepted for publication by Monthly Notices RAS. Hi-res. version
available at www.astro.rug.nl/~vdkruit/Petersetal-IV.pd
The Shape of Dark Matter Haloes II. The Galactus HI Modelling & Fitting Tool
We present a new HI modelling tool called \textsc{Galactus}. The program has
been designed to perform automated fits of disc-galaxy models to observations.
It includes a treatment for the self-absorption of the gas. The software has
been released into the public domain. We describe the design philosophy and
inner workings of the program. After this, we model the face-on galaxy NGC2403,
using both self-absorption and optically thin models, showing that
self-absorption occurs even in face-on galaxies. It is shown that the maximum
surface brightness plateaus seen in Paper I of this series are indeed signs of
self-absorption. The apparent HI mass of an edge-on galaxy can be drastically
lower compared to that same galaxy seen face-on. The Tully-Fisher relation is
found to be relatively free from self-absorption issues.Comment: Accepted for publication by Monthly Notices RAS. Hi-res. version
available at www.astro.rug.nl/~vdkruit/Petersetal-II.pd
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