19,514 research outputs found
Predictability of catastrophic events: material rupture, earthquakes, turbulence, financial crashes and human birth
We propose that catastrophic events are "outliers" with statistically
different properties than the rest of the population and result from mechanisms
involving amplifying critical cascades. Applications and the potential for
prediction are discussed in relation to the rupture of composite materials,
great earthquakes, turbulence and abrupt changes of weather regimes, financial
crashes and human parturition (birth).Comment: Latex document of 22 pages including 6 ps figures, in press in PNA
The ILIUM forward modelling algorithm for multivariate parameter estimation and its application to derive stellar parameters from Gaia spectrophotometry
I introduce an algorithm for estimating parameters from multidimensional data
based on forward modelling. In contrast to many machine learning approaches it
avoids fitting an inverse model and the problems associated with this. The
algorithm makes explicit use of the sensitivities of the data to the
parameters, with the goal of better treating parameters which only have a weak
impact on the data. The forward modelling approach provides uncertainty (full
covariance) estimates in the predicted parameters as well as a goodness-of-fit
for observations. I demonstrate the algorithm, ILIUM, with the estimation of
stellar astrophysical parameters (APs) from simulations of the low resolution
spectrophotometry to be obtained by Gaia. The AP accuracy is competitive with
that obtained by a support vector machine. For example, for zero extinction
stars covering a wide range of metallicity, surface gravity and temperature,
ILIUM can estimate Teff to an accuracy of 0.3% at G=15 and to 4% for (lower
signal-to-noise ratio) spectra at G=20. [Fe/H] and logg can be estimated to
accuracies of 0.1-0.4dex for stars with G<=18.5. If extinction varies a priori
over a wide range (Av=0-10mag), then Teff and Av can be estimated quite
accurately (3-4% and 0.1-0.2mag respectively at G=15), but there is a strong
and ubiquitous degeneracy in these parameters which limits our ability to
estimate either accurately at faint magnitudes. Using the forward model we can
map these degeneracies (in advance), and thus provide a complete probability
distribution over solutions. (Abridged)Comment: MNRAS, in press. This revision corrects a few minor errors and typos.
A better formatted version for A4 paper is available at
http://www.mpia.de/home/calj/ilium.pd
Cassini detection of Enceladus' cold water-group plume ionosphere
This study reports direct detection by the Cassini plasma spectrometer of freshly-produced water-group ions (O+, OH+, H2O+, H3O+) and heavier water dimer ions (HxO(2))(+) very close to Enceladus where the plasma begins to emerge from the plume. The data were obtained during two close ( 52 and 25 km) flybys of Enceladus in 2008 and are similar to ion data in cometary comas. The ions are observed in detectors looking in the Cassini ram direction exhibiting energies consistent with the Cassini speed, indicative of a nearly stagnant plasma flow in the plume. North of Enceladus the plasma slowing commences about 4 to 6 Enceladus radii away, while south of Enceladus signatures of the plasma interaction with the plume are detected 22 Enceladus radii away. Citation: Tokar, R. L., R. E. Johnson, M. F. Thomsen, R. J. Wilson, D. T. Young, F. J. Crary, A. J. Coates, G. H. Jones, and C. S. Paty ( 2009), Cassini detection of Enceladus' cold water-group plume ionosphere, Geophys. Res. Lett., 36, L13203, doi:10.1029/2009GL038923
Word-level Symbolic Trajectory Evaluation
Symbolic trajectory evaluation (STE) is a model checking technique that has
been successfully used to verify industrial designs. Existing implementations
of STE, however, reason at the level of bits, allowing signals to take values
in {0, 1, X}. This limits the amount of abstraction that can be achieved, and
presents inherent limitations to scaling. The main contribution of this paper
is to show how much more abstract lattices can be derived automatically from
RTL descriptions, and how a model checker for the general theory of STE
instantiated with such abstract lattices can be implemented in practice. This
gives us the first practical word-level STE engine, called STEWord. Experiments
on a set of designs similar to those used in industry show that STEWord scales
better than word-level BMC and also bit-level STE.Comment: 19 pages, 3 figures, 2 tables, full version of paper in International
Conference on Computer-Aided Verification (CAV) 201
Simple non-mydriatic retinal photography is feasible and demonstrates retinal microvascular dilation in Chronic Obstructive Pulmonary Disease (COPD).
BACKGROUND: Chronic Obstructive Pulmonary Disease (COPD) is associated with an increased risk of myocardial infarction and stroke but it remains unclear how to identify microvascular changes in this population. OBJECTIVES: We hypothesized that simple non-mydriatic retinal photography is feasible and can be used to assess microvascular damage in COPD. METHODS: Novel Vascular Manifestations of COPD was a prospective study comparing smokers with and without COPD, matched for age. Non-mydriatic, retinal fundus photographs were assessed using semi-automated software. RESULTS: Retinal images from 24 COPD and 22 control participants were compared. Cases were of similar age to controls (65.2 vs. 63.1 years, p = 0.38), had significantly lower Forced Expiratory Volume in one second (FEV1) (53.4 vs 100.1% predicted; p < 0.001) and smoked more than controls (41.7 vs. 29.6 pack years; p = 0.04). COPD participants had wider mean arteriolar (155.6 ±15 uM vs. controls [142.2 ± 12 uM]; p = 0.002) and venular diameters (216.8 ±20.7 uM vs. [201.3± 19.1 uM]; p = 0.012). Differences in retinal vessel caliber were independent of confounders, odds ratios (OR) = 1.08 (95% confidence intervals [CI] = 1.02, 1.13; p = 0.007) and OR = 1.05 (CI = 1.01, 1.09; p = 0.011) per uM increase in arteriolar and venular diameter respectively. FEV1 remained significantly associated with retinal vessel dilatation r = -0.39 (p = 0.02). CONCLUSIONS: Non-mydriatic retinal imaging is easily facilitated. We found significant arteriole and venous dilation in COPD compared to age-matched smokers without COPD associated with lung function independent of standard cardiovascular risk factors. Retinal microvascular changes are known to be strongly associated with future vascular events and retinal photography offers potential to identify this risk. TRIAL REGISTRATION: clinicaltrials.gov NCT02060292
Discovery of Aboriginal remains at Mt Cameron West, Tasmania
The recent discovery of an incomplete skeleton
initially identified as that of a Tasmanian aboriginal
adds to the limited number of osteological remains
of the extinct race
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The artistry of conversation
This thesis proposes a new way of thinking about conversation as a methodology and argues that conversation itself can be considered as an art practice. The practice research has been developed through a body of five artworks produced between 2012-14, each of which directly engaged with communities and residents of the city of Nottingham, UK, and emerged in relation to the specificity of this location. The doctoral research has been presented within the international contexts of art and social science through several seminars and conferences, including the researcher's co-founding and co-curation of InDialogue (2012 – present), a biannual interdisciplinary symposium.
The research engages with existing work on conversation and the dialogic by Allan Kaprow, David Bohm, Mikhail Bakhtin, Grant H. Kester and Hubert Hermans, from which it develops a socio-artistic and philosophical framework to theoretically underpin a body of dialogic practice. For the purpose of this thesis, PhD stands for Practice in High Definition: the body of work produced has been tested and analysed to develop an original methodology, which has been termed APSSL, to describe its five key features: architactics, performativity, storyteller, social activism and legacy.
The thesis sets out the framework for a performative and experiential approach, providing examples of the orchestration of space and the dialogic architectures of site and body. Conversation is considered as a methodological producer and as the instigator of practice. Aesthetic in approach, the methodology is recognised for its socializing power in terms of generating the opportunity for a public presentation of self and other, and for the mobility of voices in spaces. It establishes that there can be an artistry of conversation
The expected performance of stellar parametrization with Gaia spectrophotometry
Gaia will obtain astrometry and spectrophotometry for essentially all sources
in the sky down to a broad band magnitude limit of G=20, an expected yield of
10^9 stars. Its main scientific objective is to reveal the formation and
evolution of our Galaxy through chemo-dynamical analysis. In addition to
inferring positions, parallaxes and proper motions from the astrometry, we must
also infer the astrophysical parameters of the stars from the
spectrophotometry, the BP/RP spectrum. Here we investigate the performance of
three different algorithms (SVM, ILIUM, Aeneas) for estimating the effective
temperature, line-of-sight interstellar extinction, metallicity and surface
gravity of A-M stars over a wide range of these parameters and over the full
magnitude range Gaia will observe (G=6-20mag). One of the algorithms, Aeneas,
infers the posterior probability density function over all parameters, and can
optionally take into account the parallax and the Hertzsprung-Russell diagram
to improve the estimates. For all algorithms the accuracy of estimation depends
on G and on the value of the parameters themselves, so a broad summary of
performance is only approximate. For stars at G=15 with less than two
magnitudes extinction, we expect to be able to estimate Teff to within 1%, logg
to 0.1-0.2dex, and [Fe/H] (for FGKM stars) to 0.1-0.2dex, just using the BP/RP
spectrum (mean absolute error statistics are quoted). Performance degrades at
larger extinctions, but not always by a large amount. Extinction can be
estimated to an accuracy of 0.05-0.2mag for stars across the full parameter
range with a priori unknown extinction between 0 and 10mag. Performance
degrades at fainter magnitudes, but even at G=19 we can estimate logg to better
than 0.2dex for all spectral types, and [Fe/H] to within 0.35dex for FGKM
stars, for extinctions below 1mag.Comment: MNRAS, in press. Minor corrections made in v
Planning For 5G: A Problem Structuring Approach for Survival in the Telecoms Industry
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordThis paper examines the application of systemic problem structuring methods to the development of a research strategy in response to the challenges of fifth generation (5G). The paper proposes a methodology for strategic decision making. The key stakeholders, objectives, technologies, and boundaries from existing literature are identified and problem structuring based on hierarchical process modeling is used to explore the dependency of certain features of 5G on specific technologies, giving an indication of the importance of certain technologies over others and thus insight into where to place research effort. The hard technical challenges of 5G are discussed and equally the importance of the soft social and business challenges explored. For context, we explain how 5G will provide a platform for innovations and discuss how new and existing businesses may use this to their advantage. Problem structuring is used to explore how the challenges and opportunities of future wireless systems are related to the process of developing new business models
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