A method for Bayesian regression modelling of composition data

Many scientific and industrial processes produce data that is best analysed as vectors of relative values, often called compositions or proportions. The Dirichlet distribution is a natural distribution to use for composition or proportion data. It has the advantage of a low number of parameters, making it the parsimonious choice in many cases. In this paper we consider the case where the outcome of a process is Dirichlet, dependent on one or more explanatory variables in a regression setting. We explore some existing approaches to this problem, and then introduce a new simulation approach to fitting such models, based on the Bayesian framework. We illustrate the advantages of the new approach through simulated examples and an application in sport science. These advantages include: increased accuracy of fit, increased power for inference, and the ability to introduce random effects without additional complexity in the analysis.Comment: 10 pages, 1 figure, 2 table

Stellar abundance analyses in the light of 3D hydrodynamical model atmospheres

I describe recent progress in terms of 3D hydrodynamical model atmospheres and 3D line formation and their applications to stellar abundance analyses of late-type stars. Such 3D studies remove the free parameters inherent in classical 1D investigations (mixing length parameters, macro- and microturbulence) yet are highly successful in reproducing a large arsenal of observational constraints such as detailed line shapes and asymmetries. Their potential for abundance analyses is illustrated by discussing the derived oxygen abundances in the Sun and in metal-poor stars, where they seem to resolve long-standing problems as well as significantly alter the inferred conclusions.Comment: Invited talk at IAU Symposium 210 "Modelling of Stellar Atmospheres", Uppsala, Sweden (12 pages

Numerical simulation of the mechanical response during strain path change: application to Zn alloys.

The microstructure-based hardening model (Beyerlein and Tome, 2007), that accounts for the dislocation reversal-related mechanisms and the cut-through effect, is extended to HCP metals. This model, which is embedded in the visco-plastic self-consistent framework, is applied in this work to predict the mechanical response of Zn alloy during strain path change. The predicted mechanical behavior and texture evolution during pre-loading and reloading is in good agreement with experimental observations. The change in hardening behavior after reloading is well reproduced by this model. The contributions of the different mechanisms are also analyzed. (C) 2014 Published by Elsevier Ltd.open1111Nsciescopu

Obliquity pacing of the western Pacific Intertropical Convergence Zone over the past 282,000 years

The Intertropical Convergence Zone (ITCZ) encompasses the heaviest rain belt on the Earth. Few direct long-term records, especially in the Pacific, limit our understanding of long-term natural variability for predicting future ITCZ migration. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferred from a marine sedimentary sequence collected off the eastern coast of Papua New Guinea. Unlike the precession paradigm expressed in its East Asian counterpart, our record shows that the western Pacific ITCZ migration was influenced by combined precession and obliquity changes. The obliquity forcing could be primarily delivered by a cross-hemispherical thermal/pressure contrast, resulting from the asymmetric continental configuration between Asia and Australia in a coupled East Asian-Australian circulation system. Our finding suggests that the obliquity forcing may play a more important role in global hydroclimate cycles than previously thought

Impact assessment of trade liberalisation between EU and Mercosur countries

Ongoing bilateral trade negotiations between the Mercosur group and the EU since 2000 on agricultural products served as incitement to analyse the impacts of possible outcomes. The objective of this paper is to quantitatively assess impacts of bilateral liberalisation scenarios on EU25 and Mercosur markets as well as their bilateral trade flows. For this purpose, the CAPRI model, which has already been applied to several multi- and bilateral trade liberalisation scenarios in the past, has been adopted in several ways. (1) Trading blocks in CAPRI have been expanded so that the Mercosur countries are now represented with country specific behavioural functions and explicit trade flows. (2) The parameters of these behavioural functions have been calibrated using recently estimated supply and demand elasticities (CAP, E. ET AL., 2006) as prior information in a constrained Bayesian framework (HECKELEI, T. ET AL., 2005). (3) Two different baselines scenarios varying in the assumed production potential of the Mercosur countries were defined with experts from these countries. This approach reflects that developments in Mercosur countries are very dynamic with lots of uncertainties. It also provides analysis of results dependent on baselines which is an innovation in CAPRI (technically and qualitatively). In this paper three selected scenarios are analysed. The first scenario reflects an unilateral partial liberalisation between the EU25 and the Mercosur countries by allocating additional Tariff Rate Quotas (TRQs) to the Mercosur countries for certain products based on an official EU proposal (USDA, 2005). The second scenario combines the partial unilateral liberalisation with the multilateral WTO G20 proposal. Sensitive products are defined according to JEAN, S. et al. (2006). The third comprises a bilateral full liberalisation between the EU25 and the Mercosur countries by allowing quota and duty free access in both directions for all agricultural products. The results focus on welfare effects and the market balances of seven key commodities (wheat, maize, rice, soybeans, bovine meat, chicken and pork). Furthermore, a sensitivity analysis on the elasticities of substitution between foreign and domestic produced goods that drive demand of trade flows is provided and shows that the choice of those elasticities is very crucial with respect to model results.Trade liberalisation, Mercosur, CAPRI, Armington., Demand and Price Analysis, International Relations/Trade,

WiggleZ Dark Energy Survey: Cosmological neutrino mass constraint from blue high-redshift galaxies

The absolute neutrino mass scale is currently unknown, but can be constrained by cosmology. The WiggleZ high redshift, star-forming, and blue galaxy sample offers a complementary data set to previous surveys for performing these measurements, with potentially different systematics from nonlinear structure formation, redshift-space distortions, and galaxy bias. We obtain a limit of ∑m_ν<0.60  eV (95% confidence) for WiggleZ+Wilkinson Microwave Anisotropy Probe. Combining with priors on the Hubble parameter and the baryon acoustic oscillation scale gives ∑m_ν<0.29  eV, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys

Eigenstrain-based reduced order homogenization models for polycrystal plasticity: addressing scalability

In this manuscript, accelerated, sparse and scalable eigenstrain-based reduced order homogenization models have been developed for computationally efficient multiscale analysis of polycrystalline materials. The proposed model is based on the eigenstrain based reduced order homogenization (EHM) approach, which takes the concept of transformation field theory that pre-computes certain microscale information and considers piece-wise constant inelastic response within partitions (e.g., grains) of the microstructure for model order reduction.The acceleration is achieved by introducing sparsity into the linearized reduced order system through selectively considering the interactions between grains based on the idea of grain clustering. The proposed approach results in a hierarchy of reduced models that recovers original EHM, when full range of interactions are considered, and degrades to the Taylor model, when all grain interactions are neglected. The resulting sparse system is solved efficiently using both direct and iterative sparse solvers, both of which show significant efficiency improvements compared to the full EHM. A layer-by-layer neighbor grain clustering scheme is proposed and implemented to define ranges of grain interactions. Performance of the proposed approach is evaluated by comparison with the original full EHM and crystal plasticity finite element (CPFE) simulations

Spatial variation of salt intake in Britain and association with socioeconomic status

Objectives: To evaluate spatial effects of variation and social determinants of salt intake in Britain. Design: Cross-sectional survey. Setting: Great Britain. Participants: 2105 white male and female participants, aged 19–64 years, from the British National Diet and Nutrition Survey 2000–2001. Primary outcomes: Participants’ sodium intake measured both with a 7-day dietary record and a 24-h urine collection. By accounting for important linear and non-linear risk factors and spatial effects, the geographical difference and spatial patterns of both dietary sodium intake and 24-h urinary sodium were investigated using Bayesian geo-additive models via Markov Chain Monte Carlo simulations. Results: A significant north–south pattern of sodium intake was found from posterior probability maps after controlling for important sociodemographic factors. Participants living in Scotland had a significantly higher dietary sodium intake and 24-h urinary sodium levels. Significantly higher sodium intake was also found in people with the lowest educational attainment (dietary sodium: coeff. 0.157 (90% credible intervals 0.003, 0.319), urinary sodium: 0.149 (0.024, 0.281)) and in manual occupations (urinary sodium: 0.083 (0.004, 0.160)). These coefficients indicate approximately a 5%, 9% and 4% difference in average sodium intake between socioeconomic groups. Conclusions: People living in Scotland had higher salt intake than those in England and Wales. Measures of low socioeconomic position were associated with higher levels of sodium intake, after allowing for geographic location