8,504 research outputs found
Mixtures of Shifted Asymmetric Laplace Distributions
A mixture of shifted asymmetric Laplace distributions is introduced and used
for clustering and classification. A variant of the EM algorithm is developed
for parameter estimation by exploiting the relationship with the general
inverse Gaussian distribution. This approach is mathematically elegant and
relatively computationally straightforward. Our novel mixture modelling
approach is demonstrated on both simulated and real data to illustrate
clustering and classification applications. In these analyses, our mixture of
shifted asymmetric Laplace distributions performs favourably when compared to
the popular Gaussian approach. This work, which marks an important step in the
non-Gaussian model-based clustering and classification direction, concludes
with discussion as well as suggestions for future work
Unsupervised Learning via Mixtures of Skewed Distributions with Hypercube Contours
Mixture models whose components have skewed hypercube contours are developed
via a generalization of the multivariate shifted asymmetric Laplace density.
Specifically, we develop mixtures of multiple scaled shifted asymmetric Laplace
distributions. The component densities have two unique features: they include a
multivariate weight function, and the marginal distributions are also
asymmetric Laplace. We use these mixtures of multiple scaled shifted asymmetric
Laplace distributions for clustering applications, but they could equally well
be used in the supervised or semi-supervised paradigms. The
expectation-maximization algorithm is used for parameter estimation and the
Bayesian information criterion is used for model selection. Simulated and real
data sets are used to illustrate the approach and, in some cases, to visualize
the skewed hypercube structure of the components
Guaranteed energy-efficient bit reset in finite time
Landauer's principle states that it costs at least kTln2 of work to reset one
bit in the presence of a heat bath at temperature T. The bound of kTln2 is
achieved in the unphysical infinite-time limit. Here we ask what is possible if
one is restricted to finite-time protocols. We prove analytically that it is
possible to reset a bit with a work cost close to kTln2 in a finite time. We
construct an explicit protocol that achieves this, which involves changing the
system's Hamiltonian avoiding quantum coherences, and thermalising. Using
concepts and techniques pertaining to single-shot statistical mechanics, we
further develop the limit on the work cost, proving that the heat dissipated is
close to the minimal possible not just on average, but guaranteed with high
confidence in every run. Moreover we exploit the protocol to design a quantum
heat engine that works near the Carnot efficiency in finite time.Comment: 5 pages + 5 page technical appendix. 5 figures. Author accepted
versio
Parsimonious Shifted Asymmetric Laplace Mixtures
A family of parsimonious shifted asymmetric Laplace mixture models is
introduced. We extend the mixture of factor analyzers model to the shifted
asymmetric Laplace distribution. Imposing constraints on the constitute parts
of the resulting decomposed component scale matrices leads to a family of
parsimonious models. An explicit two-stage parameter estimation procedure is
described, and the Bayesian information criterion and the integrated completed
likelihood are compared for model selection. This novel family of models is
applied to real data, where it is compared to its Gaussian analogue within
clustering and classification paradigms
Understanding the enrolled nurse to registered nurse journey through a model adapted from Schlossberg's transition theory
Background
Substantial numbers of Enrolled Nurses (ENs) enrol in higher education programs to undergo the transition to Registered Nurse (RN) with the experience described as containing numerous challenges.
Objectives
This paper reports on a synthesis of the literature that explores the experiences of ENs undertaking a program of study to convert to RN. Consequently, a model is developed to identify educational interventions and resources to enable a successful transition for these students.
Design
A narrative review was completed with thematic synthesis of the literature guided by Schlossberg's Transition Theory, and Thomas and Harden's framework for systematic analysis of qualitative studies.
Data sources
CINAHL, Scopus, ProQuest Central and Health Collection were searched.
Review methods
The databases were searched for English language journal articles, theses and grey literature published from 1987 to 2016 from Australia, New Zealand, the United Kingdom, Canada and the USA. The key search words included truncations of: “enrolled nurse”, ‘licensed practical nurse’, “transition”, “conversion” and “experience”. This resulted in the identification of 33 related articles for review.
Results
Themes and sub-themes developed from the literature synthesis were integrated into an ‘EN to RN Transition model.’ The four stages of the model reflect the experiences of the ENs as they overcame the various challenges they encountered during their transition to RN. The model was used to develop recommendations that may improve their transition experience and decrease attrition.
Conclusion
This paper reports on a synthesis of the literature, and presents a four stage model, that reflects the experiences of ENs in their transition to RN. Recognising the elements within each stage can assist educators develop strategies and provide educational resources to enhance the EN journey
The Cosmic Lens All-Sky Survey parent population - I. Sample selection and number counts
We present the selection of the Jodrell Bank Flat-spectrum (JBF) radio source
sample, which is designed to reduce the uncertainties in the Cosmic Lens
All-Sky Survey (CLASS) gravitational lensing statistics arising from the lack
of knowledge about the parent population luminosity function. From observations
at 4.86 GHz with the Very Large Array, we have selected a sample of 117
flat-spectrum radio sources with flux densities greater than 5 mJy. These
sources were selected in a similar manner to the CLASS complete sample and are
therefore representative of the parent population at low flux densities. The
vast majority (~90 per cent) of the JBF sample are found to be compact on the
arcsecond scales probed here and show little evidence of any extended radio jet
emission. Using the JBF and CLASS complete samples we find the differential
number counts slope of the parent population above and below the CLASS 30 mJy
flux density limit to be -2.07+/-0.02 and -1.96+/-0.12, respectively.Comment: 10 pages, 4 figures, accepted for publication in MNRA
A meta-analysis of variables that predict significant intracranial injury in minor head trauma.
BACKGROUND: Previous studies have presented conflicting results regarding the predictive effect of various clinical symptoms, signs, and plain imaging for intracranial pathology in children with minor head injury. AIMS: To perform a meta-analysis of the literature in order to assess the significance of these factors and intracranial haemorrhage (ICH) in the paediatric population. METHODS: The literature was searched using Medline, Embase, Experts, and the grey literature. Reference lists of major guidelines were crosschecked. Control or nested case-control studies of children with head injury who had skull radiography, recording of common symptoms and signs, and head computed tomography (CT) were selected. OUTCOME VARIABLE: CT presence or absence of ICH. RESULTS: Sixteen papers were identified as satisfying criteria for inclusion in the meta-analysis, although not every paper contained data on every correlate. Available evidence gave pooled patient numbers from 1136 to 22 420. Skull fracture gave a relative risk ratio of 6.13 (95% CI 3.35 to 11.2), headache 1.02 (95% CI 0.62 to 1.69), vomiting 0.88 (95% CI 0.67 to 1.15), focal neurology 9.43 (2.89 to 30.8), seizures 2.82 (95% CI 0.89 to 9.00), LOC 2.23 (95% CI 1.20 to 4.16), and Glasgow Coma Scale (GCS) <15 of 5.51 (95% CI 1.59 to 19.0). CONCLUSIONS: There was a statistically significant correlation between intracranial haemorrhage and skull fracture, focal neurology, loss of consciousness, and GCS abnormality. Headache and vomiting were not found to be predictive and there was great variability in the predictive ability of seizures. More information is required about the current predictor variables so that more refined guidelines can be developed. Further research is currently underway by three large study groups
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Fast three dimensional r-adaptive mesh redistribution
This paper describes a fast and reliable method for redistributing a computational mesh in three dimensions which can generate a complex three dimensional mesh without any problems due to mesh tangling. The method relies on a three dimensional implementation of the parabolic Monge–Ampère (PMA) technique, for finding an optimally transported mesh. The method for implementing PMA is described in detail and applied to both static and dynamic mesh redistribution problems, studying both the convergence and the computational cost of the algorithm. The algorithm is applied to a series of problems of increasing complexity. In particular very regular meshes are generated to resolve real meteorological features (derived from a weather forecasting model covering the UK area) in grids with over 2×107 degrees of freedom. The PMA method computes these grids in times commensurate with those required for operational weather forecasting
Lensing galaxies: light or dark?
In a recent paper, Hawkins (1997) argues on the basis of statistical studies
of double-image gravitational lenses and lens candidates that a large
population of dark lenses exists and that these outnumber galaxies with more
normal mass-to-light ratios by a factor of 3:1. If correct, this is a very
important result for many areas of astronomy including galaxy formation and
cosmology. In this paper we discuss our new radio-selected gravitational lens
sample, JVAS/CLASS, in order to test and constrain this proposition. We have
obtained ground-based and HST images of all multiple-image lens systems in our
sample and in 12 cases out of 12 we find the lensing galaxies in the optical
and/or near infrared. Our success in finding lensing galaxies creates problems
for the dark lens hypothesis. If it is to survive, ad hoc modifications seem to
be necessary: only very massive galaxies (more than about one trillion solar
masses) can be dark, and the cutoff in mass must be sharp. Our finding of lens
galaxies in all the JVAS/CLASS systems is complementary evidence which supports
the conclusion of Kochanek et al. (1997) that many of the wide-separation
optically-selected pairs are physically distinct quasars rather than
gravitational lens systems.Comment: 4 pages, 2 included figures, accepted for publication in Astronomy
and Astrophysics. Paper version available on request. This replacement amends
the text to allow more discussion of the overlap with astro-ph/971016
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