Surrogate Accelerated Bayesian Inversion for the Determination of the Thermal Diffusivity of a Material

Determination of the thermal properties of a material is an important task in many scientific and engineering applications. How a material behaves when subjected to high or fluctuating temperatures can be critical to the safety and longevity of a system's essential components. The laser flash experiment is a well-established technique for indirectly measuring the thermal diffusivity, and hence the thermal conductivity, of a material. In previous works, optimization schemes have been used to find estimates of the thermal conductivity and other quantities of interest which best fit a given model to experimental data. Adopting a Bayesian approach allows for prior beliefs about uncertain model inputs to be conditioned on experimental data to determine a posterior distribution, but probing this distribution using sampling techniques such as Markov chain Monte Carlo methods can be incredibly computationally intensive. This difficulty is especially true for forward models consisting of time-dependent partial differential equations. We pose the problem of determining the thermal conductivity of a material via the laser flash experiment as a Bayesian inverse problem in which the laser intensity is also treated as uncertain. We introduce a parametric surrogate model that takes the form of a stochastic Galerkin finite element approximation, also known as a generalized polynomial chaos expansion, and show how it can be used to sample efficiently from the approximate posterior distribution. This approach gives access not only to the sought-after estimate of the thermal conductivity but also important information about its relationship to the laser intensity, and information for uncertainty quantification. We also investigate the effects of the spatial profile of the laser on the estimated posterior distribution for the thermal conductivity

Using individual tracking data to validate the predictions of species distribution models

The authors would like to thank the College of Life Sciences of Aberdeen University and Marine Scotland Science which funded CP's PhD project. Skate tagging experiments were undertaken as part of Scottish Government project SP004. We thank Ian Burrett for help in catching the fish and the other fishermen and anglers who returned tags. We thank José Manuel Gonzalez-Irusta for extracting and making available the environmental layers used as environmental covariates in the environmental suitability modelling procedure. We also thank Jason Matthiopoulos for insightful suggestions on habitat utilization metrics as well as Stephen C.F. Palmer, and three anonymous reviewers for useful suggestions to improve the clarity and quality of the manuscript.Peer reviewedPostprintPostprintPostprintPostprintPostprin

Galactic Scale Feedback Observed in the 3C 298 Quasar Host Galaxy

We present high angular resolution multi-wavelength data of the 3C 298 radio-loud quasar host galaxy (z=1.439) taken using the W.M. Keck Observatory OSIRIS integral field spectrograph with adaptive optics, Atacama Large Millimeter/submillimeter Array (ALMA), Hubble Space Telescope (HST) WFC3, and the Very Large Array (VLA). Extended emission is detected in the rest-frame optical nebular emission lines H$\beta$, [OIII], H$\alpha$, [NII], and [SII], as well as molecular lines CO (J=3-2) and (J=5-4). Along the path of 3C 298's relativistic jets we detect conical outflows of ionized gas with velocities up to 1700 km s$^{-1}$ and outflow rate of 450-1500 M$_\odot$yr$^{-1}$. Near the spatial center of the conical outflow, CO (J=3-2) emission shows a molecular gas disc with a total molecular mass ($\rm M_{H_{2}}$) of 6.6$\pm0.36\times10^{9}$M$_{\odot}$. On the molecular disc's blueshifted side we observe a molecular outflow with a rate of 2300 M$_\odot$yr$^{-1}$ and depletion time scale of 3 Myr. We detect no narrow H$\alpha$ emission in the outflow regions, suggesting a limit on star formation of 0.3 M$_\odot$yr$^{-1}$kpc$^{-2}$. Quasar driven winds are evacuating the molecular gas reservoir thereby directly impacting star formation in the host galaxy. The observed mass of the supermassive black hole is $10^{9.37-9.56}$M$_{\odot}$ and we determine a dynamical bulge mass of 1-1.7$\rm\times10^{10}\frac{R}{1.6 kpc}$ M$_{\odot}$. The bulge mass of 3C 298 resides 2-2.5 orders of magnitude below the expected value from the local M$\rm_{bulge}-M_{BH}$ relationship. A second galactic disc observed in nebular emission is offset from the quasar by 9 kpc suggesting the system is an intermediate stage merger. These results show that galactic scale negative feedback is occurring early in the merger phase of 3C 298, well before the coalescence of the galactic nuclei and assembly on the local relationship.Comment: 23 pages, 11 figures, 4 tables, Accepted for publication in the Astrophysical Journa

Providing stringent star formation rate limits of z∼\sim2 QSO host galaxies at high angular resolution

We present integral field spectrograph (IFS) with laser guide star adaptive optics (LGS-AO) observations of z=2 quasi-stellar objects (QSOs) designed to resolve extended nebular line emission from the host galaxy. Our data was obtained with W. M. Keck and Gemini-North Observatories using OSIRIS and NIFS coupled with the LGS-AO systems. We have conducted a pilot survey of five QSOs, three observed with NIFS+AO and two observed with OSIRIS+AO at an average redshift of z=2.15. We demonstrate that the combination of AO and IFS provides the necessary spatial and spectral resolutions required to separate QSO emission from its host. We present our technique for generating a PSF from the broad-line region of the QSO and performing PSF subtraction of the QSO emission to detect the host galaxy. We detect H$\alpha$ and [NII] for two sources, SDSS J1029+6510 and SDSS J0925+06 that have both star formation and extended narrow-line emission. Assuming that the majority of narrow-line H$\alpha$ is from star formation, we infer a star formation rate for SDSS J1029+6510 of 78.4 M$_\odot$yr$^{-1}$ originating from a compact region that is kinematically offset by 290 - 350 km/s. For SDSS J0925+06 we infer a star formation rate of 29 M$_\odot$yr$^{-1}$ distributed over three clumps that are spatially offset by $\sim$ 7 kpc. The null detections on three of the QSOs are used to infer surface brightness limits and we find that at 1.4 kpc distance from the QSO that the un-reddened star formation limit is $<$ 0.3 M$_\odot$yr$^{-1}$kpc$^{-2}$. If we assume a typical extinction values for z=2 type-1 QSOs, the dereddened star formation rate for our null detections would be $<$ 0.6 M$_\odot$yr$^{-1}$kpc$^{-2}$. These IFS observations indicate that if star formation is present in the host it would have to occur diffusely with significant extinction and not in compact, clumpy regions.Comment: 17 pages, 7 figures, 7 tables, Accepted to Ap

Optics: general-purpose scintillator light response simulation code

We present the program optics that simulates the light response of an arbitrarily shaped scintillation particle detector. Predicted light responses of pure CsI polygonal detectors, plastic scintillator staves, cylindrical plastic target scintillators and a Plexiglas light-distribution plate are illustrated. We demonstrate how different bulk and surface optical properties of a scintillator lead to specific volume and temporal light collection probability distributions. High-statistics optics simulations are calibrated against the detector responses measured in a custom-made cosmic muon tomography apparatus. The presented code can also be used to track particles intersecting complex geometrical objects.Comment: RevTeX LaTeX, 37 pages in e-print format, 12 Postscript Figures and 1 Table, also available at http://pibeta.phys.virginia.edu/public_html/preprints/optics.p

Variable direct and indirect effects of a habitat-modifying invasive species on mortality of native fauna

Habitat-modifying invasive species can influence rates of predation on native prey either directly by providing protective structure or indirectly by modifying traits of prey species responding to the habitat. The alga Caulerpa taxifolia is one of the most successful invasive species of shallow-water marine systems globally, often provisioning habitat in areas previously lacking in vegetated structure. We experimentally evaluated the direct effect of Caulerpa to provide refuge for the native clam Anadara trapezia and how this balances with its influence on two trait-mediated indirect interactions that may increase Anadara\u27s susceptibility to predators. Specifically, Caulerpa\u27s alteration of physical and chemical properties of the surrounding water and sediment deteriorate Anadara\u27s condition and predator resistance properties and also cause Anadara, though normally buried, to project from beneath the sediment, exposing it to predators. Our results show that Anadara are somewhat (but not consistently) protected from predators by living among Caulerpa. Shallow burial depth did not counteract this protective effect. However at times of year when predator activity diminishes and conducive environmental conditions develop, negative effects of Caulerpa habitat such as hypoxia and lowered flow may dominate. Under such situations, poor clam condition accentuates Anadara\u27s susceptibility to mortality. Ultimately, a slight and inconsistent positive effect of Caulerpa to protect Anadara from predators is exceeded by the strong negative effect of Caulerpa on clam mortality, which is heightened by clams\u27 weakened condition produced by chronic exposure to Caulerpa. Our results show that invasive habitat-modifying species can affect mortality of native species not simply through obvious positive direct effects of their protective structure, but indirectly through contrasting negative modification of the traits of prey species responding to the habitat