1,053 research outputs found
The Bayesian Decision Tree Technique with a Sweeping Strategy
The uncertainty of classification outcomes is of crucial importance for many
safety critical applications including, for example, medical diagnostics. In
such applications the uncertainty of classification can be reliably estimated
within a Bayesian model averaging technique that allows the use of prior
information. Decision Tree (DT) classification models used within such a
technique gives experts additional information by making this classification
scheme observable. The use of the Markov Chain Monte Carlo (MCMC) methodology
of stochastic sampling makes the Bayesian DT technique feasible to perform.
However, in practice, the MCMC technique may become stuck in a particular DT
which is far away from a region with a maximal posterior. Sampling such DTs
causes bias in the posterior estimates, and as a result the evaluation of
classification uncertainty may be incorrect. In a particular case, the negative
effect of such sampling may be reduced by giving additional prior information
on the shape of DTs. In this paper we describe a new approach based on sweeping
the DTs without additional priors on the favorite shape of DTs. The
performances of Bayesian DT techniques with the standard and sweeping
strategies are compared on a synthetic data as well as on real datasets.
Quantitatively evaluating the uncertainty in terms of entropy of class
posterior probabilities, we found that the sweeping strategy is superior to the
standard strategy
Systolic blood pressure reactions to acute stress are associated with future hypertension status in the Dutch Famine Birth Cohort Study
These analyses examined the association between blood pressure reactions to acute psychological stress and subsequent hypertension status in a substantial Dutch cohort. Blood pressure was recorded during a resting baseline and during three acute stress tasks, Stroop colour word, mirror tracing and speech. Five years later, diagnosed hypertension status was determined by questionnaire. Participants were 453 (237 women) members of the Dutch Famine Birth Cohort. In analysis adjusting for a number of potential confounders, systolic blood pressure reactivity was positively related to future hypertension. This was the case irrespective of whether reactivity was calculated as the peak or the average response to the stress tasks. The association was strongest for reactions to the speech and Stroop tasks. Diastolic blood pressure reactivity was not significantly associated with hypertension. The results provide support for the reactivity hypothesis. \ud
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Basin structure in the two-dimensional dissipative circle map
Fractal basin structure in the two-dimensional dissipative circle map is
examined in detail. Numerically obtained basin appears to be riddling in the
parameter region where two periodic orbits co-exist near a boundary crisis, but
it is shown to consist of layers of thin bands.Comment: published in J. Phys. Soc. Jpn., 72, 1943-1947 (2003
Grasslands - more important for ecosystem services than you might think
Extensively managed grasslands are recognized globally for their high biodiversity and their social and cultural values. However, their capacity to deliver multiple ecosystem services (ES) as parts of agricultural systems is surprisingly understudied compared to other production systems. We undertook a comprehensive overview of ES provided by natural and semiānatural grasslands, using southern Africa (SA) and northwest Europe as case studies, respectively. We show that these grasslands can supply additional nonāagricultural services, such as water supply and flow regulation, carbon storage, erosion control, climate mitigation, pollination, and cultural ES. While demand for ecosystems services seems to balance supply in natural grasslands of SA, the smaller areas of semiānatural grasslands in Europe appear to not meet the demand for many services. We identified three bundles of related ES from grasslands: water ES including fodder production, cultural ES connected to livestock production, and populationābased regulating services (e.g., pollination and biological control), which also linked to biodiversity. Greenhouse gas emission mitigation seemed unrelated to the three bundles. The similarities among the bundles in SA and northwestern Europe suggest that there are generalities in ES relations among natural and semiānatural grassland areas. We assessed tradeāoffs and synergies among services in relation to management practices and found that although some tradeāoffs are inevitable, appropriate management may create synergies and avoid tradeāoffs among many services. We argue that ecosystem service and food security research and policy should give higher priority to how grasslands can be managed for fodder and meat production alongside other ES. By integrating grasslands into agricultural production systems and landāuse decisions locally and regionally, their potential to contribute to functional landscapes and to food security and sustainable livelihoods can be greatly enhanced
A new method to measure Bowen ratios using high-resolution vertical dry and wet bulb temperature profiles
The Bowen ratio surface energy balance method is a relatively simple method
to determine the latent heat flux and the actual land surface evaporation.
The Bowen ratio method is based on the measurement of air temperature and
vapour pressure gradients. If these measurements are performed at only two
heights, correctness of data becomes critical. In this paper we present the
concept of a new measurement method to estimate the Bowen ratio based on
vertical dry and wet bulb temperature profiles with high spatial resolution.
A short field experiment with distributed temperature sensing (DTS) in a
fibre optic cable with 13 measurement points in the vertical was undertaken.
A dry and a wetted section of a fibre optic cable were suspended on a 6 m
high tower installed over a sugar beet trial plot near Pietermaritzburg
(South Africa). Using the DTS cable as a psychrometer, a near continuous
observation of vapour pressure and air temperature at 0.20 m intervals was
established. These data allowed the computation of the Bowen ratio with a
high spatial and temporal precision. The daytime latent and sensible heat
fluxes were estimated by combining the Bowen ratio values from the DTS-based
system with independent measurements of net radiation and soil heat flux. The
sensible heat flux, which is the relevant term to evaluate, derived from the
DTS-based Bowen ratio (BR-DTS) was compared with that derived from co-located
eddy covariance (<i>R</i><sup>2</sup> = 0.91), surface layer scintillometer
(<i>R</i><sup>2</sup> = 0.81) and surface renewal (<i>R</i><sup>2</sup> = 0.86) systems. By using
multiple measurement points instead of two, more confidence in the derived Bowen
ratio values is obtained
Three-dimensional modeling of acoustic backscattering from fluid-like zooplankton
Author Posting. Ā© Acoustical Society of America, 2002. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 111 (2002): 1197-1210, doi:10.1121/1.1433813.Scattering models that correctly incorporate organism size and shape are a critical component for the remote detection and classification of many marine organisms. In this work, an acoustic scattering model has been developed for fluid-like zooplankton that is based on the distorted wave Born approximation (DWBA) and that makes use of high-resolution three-dimensional measurements of the animal's outer boundary shape. High-resolution computerized tomography (CT) was used to determine the three-dimensional digitizations of animal shape. This study focuses on developing the methodology for incorporating high-resolution CT scans into a scattering model that is generally valid for any body with fluid-like material properties. The model predictions are compared to controlled laboratory measurements of the acoustic backscattering from live individual decapod shrimp. The frequency range used was 50 kHz to 1 MHz and the angular characteristics of the backscattering were investigated with up to a 1Ā° angular resolution. The practical conditions under which it is necessary to make use of high-resolution digitizations of shape are assessed.This work was supported
in part by the Woods Hole Oceanographic Institution
Education Office
Closed-Form Bayesian Inferences for the Logit Model via Polynomial Expansions
Articles in Marketing and choice literatures have demonstrated the need for
incorporating person-level heterogeneity into behavioral models (e.g., logit
models for multiple binary outcomes as studied here). However, the logit
likelihood extended with a population distribution of heterogeneity doesn't
yield closed-form inferences, and therefore numerical integration techniques
are relied upon (e.g., MCMC methods).
We present here an alternative, closed-form Bayesian inferences for the logit
model, which we obtain by approximating the logit likelihood via a polynomial
expansion, and then positing a distribution of heterogeneity from a flexible
family that is now conjugate and integrable. For problems where the response
coefficients are independent, choosing the Gamma distribution leads to rapidly
convergent closed-form expansions; if there are correlations among the
coefficients one can still obtain rapidly convergent closed-form expansions by
positing a distribution of heterogeneity from a Multivariate Gamma
distribution. The solution then comes from the moment generating function of
the Multivariate Gamma distribution or in general from the multivariate
heterogeneity distribution assumed.
Closed-form Bayesian inferences, derivatives (useful for elasticity
calculations), population distribution parameter estimates (useful for
summarization) and starting values (useful for complicated algorithms) are
hence directly available. Two simulation studies demonstrate the efficacy of
our approach.Comment: 30 pages, 2 figures, corrected some typos. Appears in Quantitative
Marketing and Economics vol 4 (2006), no. 2, 173--20
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