Bayesian hierarchical modelling of bacteria growth

Bacterial growth models are commonly used in food safety. Such models permit the prediction of microbial safety and the shelf life of perishable foods. In this paper, we study the problem of modelling bacterial growth when we observe multiple experimental results under identical environmental conditions. We develop a hierarchical version of the Gompertz equation to take into account the possibility of replicated experiments and we show how it can be fitted using a fully Bayesian approach. This approach is illustrated using experimental data from Listeria monocytogenes growth and the results are compared with alternative models. Model selection is undertaken throughout using an appropriate version of the deviance information criterion and the posterior predictive loss criterion. Models are fitted using WinBUGS via R2WinBUGS.Predictive microbiology, Growth models, Gompertz curve, Bayesian hierarchical modelling

Optical properties of chalcopyrite-type intermediate transition metal band materials from first principles

The optical properties of a novel potential high-efficiency photovoltaic material have been studied. This material is based on a chalcopyrite-type semiconductor (CuGaS2) with some Ga atom substituted by Ti and is characterized by the formation of an isolated transition-metal band between the valence band and the conduction band. We present a study in which ab-initio density functional theory calculations within the generalized gradient approximation are carried out to determine the optical reflectivity and absorption coefficient of the materials of interest. Calculations for the host semiconductor are in good agreement with experimental results within the limitations of the approach. We find, as desired, that because of the intermediate band, the new Ti-substituted material would be able to absorb photons of energy lower than the band-gap of the host chalcopyrite. We also analyze the partial contributions to the main peaks of its spectrum

Metastability and paramagnetism in superconducting mesoscopic disks

A projected order parameter is used to calculate, not only local minima of the Ginzburg-Landau energy functional, but also saddle points or energy barriers responsible for the metastabilities observed in superconducting mesoscopic disks (Geim et al. Nature {\bf 396}, 144 (1998)). We calculate the local minima magnetization and find the energetic instability points between vortex configurations with different vorticity. We also find that, for any vorticity, the supercurrent can reverse its flow direction on decreasing the magnetic field before one vortex can escape.Comment: Modified version as to appear in Phys. Rev. Let

Thermohaline instability and rotation-induced mixing. III - Grid of stellar models and asymptotic asteroseismic quantities from the pre-main sequence up to the AGB for low- and intermediate-mass stars at various metallicities

The availability of asteroseismic constraints for a large sample of stars from the missions CoRoT and Kepler paves the way for various statistical studies of the seismic properties of stellar populations. In this paper, we evaluate the impact of rotation-induced mixing and thermohaline instability on the global asteroseismic parameters at different stages of the stellar evolution from the Zero Age Main Sequence to the Thermally Pulsating Asymptotic Giant Branch to distinguish stellar populations. We present a grid of stellar evolutionary models for four metallicities (Z = 0.0001, 0.002, 0.004, and 0.014) in the mass range between 0.85 to 6.0 Msun. The models are computed either with standard prescriptions or including both thermohaline convection and rotation-induced mixing. For the whole grid we provide the usual stellar parameters (luminosity, effective temperature, lifetimes, ...), together with the global seismic parameters, i.e. the large frequency separation and asymptotic relations, the frequency corresponding to the maximum oscillation power {\nu}_{max}, the maximal amplitude A_{max}, the asymptotic period spacing of g-modes, and different acoustic radii. We discuss the signature of rotation-induced mixing on the global asteroseismic quantities, that can be detected observationally. Thermohaline mixing whose effects can be identified by spectroscopic studies cannot be caracterized with the global seismic parameters studied here. But it is not excluded that individual mode frequencies or other well chosen asteroseismic quantities might help constraining this mixing.Comment: 15 pages, 11 figures, accepted for publication in A&

Organic vs Conventional Suckling Lamb Production: Product Quality and Consumer Acceptance

Samples of suckling lambs (n=40) of two breeds reared under conventional and organic conditions were analysed to asses physico-chemical characteristics, including instrumental texture, and nutritional quality in terms of fatty acid composition. Consumer acceptance was also studied using the home-use test. Results revealed that organic suckling lamb meat is healthier as shown by the lower saturated fatty acid levels, the higher polyunsaturated fatty acid contents and the higher 6/3 ratiko. The organic meat had lower instrumental hardness, received higher scores in all sensory parameters, and had statistically better fat sensation and higher ratings for overall liking. These results lend support to the notion among consumers that organic products are healthier and tastier

Consumer Appreciation of Carcass Quality of Organic vs Conventional Suckling Lamb Production

Carcass characteristics of sucking lambs (n= 40) of two breeds reared under conventional and organic conditions were analysed including objective and subjective parameters for fatness and conformation, meat and fat colour. Consumer acceptance was also studied using the home-use test. Results showed that the characteristics of the carcass of suckling lamb were similar for both types of production systems pointing out that organic production system did not affect fatness or muscle development. However, organic meat was darker (higher L* and a* values) probably related with the higher amount of exercise, although fat was not more yellow. In contrast consumers did not consider organic meat darker and there were not significant differences in appearance related with the similar conformation. These results reflect that consumer perceive organic meat as at least as good as conventional production not only regarding environmental quality but also regarding carcass quality

Vortices in a rotating BEC under extreme elongation

We investigate a non-axisymmetric rotating BEC in a limit of rotation frequency for which the BEC transforms into a quasi-one-dimensional system. We compute the vortex lattice wavefunction by minimizing the Gross-Pitaevskii energy functional in the lowest Landau level approximation for different confinement potentials. The condensate typically presents a changing number of vortex rows as a function of the interaction strength or rotation-confinement ratio. More specifically, the vortex lattices can be classified into two classes according to their symmetry with respect to the longitudinal axis. These two classes correspond to different local minima of the energy functional and evolve independently as a function of the various parameters.Comment: 8 pages, 12 figure

Aerostructural topology optimization using high fidelity modeling

We investigate the use of density-based topology optimization for the aeroelastic design of very flexible wings. This is achieved with a Reynolds-averaged Navier–Stokes finite volume solver, coupled to a geometrically nonlinear finite element structural solver, to simulate the large-displacement fluid-structure interaction. A gradient-based approach is used with derivatives obtained via a coupled adjoint solver based on algorithmic differentiation. In the example problem, the optimization uses strong coupling effects and the internal topology of the wing to allow mass reduction while maintaining the lift. We also propose a method to accelerate the convergence of the optimization to discrete topologies, which partially mitigates the computational expense of high-fidelity modeling approaches

Experimental Investigation of Supercooled Water Droplet Breakup near the Leading Edge of an Airfoil

This paper presents the results of an experimental study on supercooled droplet deformation and breakup near the leading edge of an airfoil. The results are compared to prior room-temperature droplet deformation results to explore the effects of droplet supercooling. The experiments were conducted in the Adverse Environment Rotor Test Stand at The Pennsylvania State University. An airfoil model placed at the end of the rotor blades mounted onto the hub in the Adverse Environment Rotor Test Stand chamber was moved at speeds ranging between 50 and 80 ms. The temperature of the chamber was 20C. A monotonic droplet generator was used to produce droplets that fell perpendicular to the airfoil path. High-speed imaging was employed to observe the interaction between the droplets and the airfoil. Cases with equal slip and initial velocity were selected for the two environmental conditions. The airfoil velocity was 60 ms, and the slip velocity for both sets of data was 40 ms. The deformation of the weakly supercooled and warm droplets did not present different trends. The similar behavior for both conditions indicates that water supercooling has no effect on particle deformation for the range of supercooling of the droplets tested and the selected impact velocity