174 research outputs found
Adaptive Variable Selection for Sequential Prediction in Multivariate Dynamic Models
We discuss Bayesian model uncertainty analysis and forecasting in sequential
dynamic modeling of multivariate time series. The perspective is that of a
decision-maker with a specific forecasting objective that guides thinking about
relevant models. Based on formal Bayesian decision-theoretic reasoning, we
develop a time-adaptive approach to exploring, weighting, combining and
selecting models that differ in terms of predictive variables included. The
adaptivity allows for changes in the sets of favored models over time, and is
guided by the specific forecasting goals. A synthetic example illustrates how
decision-guided variable selection differs from traditional Bayesian model
uncertainty analysis and standard model averaging. An applied study in one
motivating application of long-term macroeconomic forecasting highlights the
utility of the new approach in terms of improving predictions as well as its
ability to identify and interpret different sets of relevant models over time
with respect to specific, defined forecasting goals.Comment: 23 pages, 11 figure
Bayesian Computation in Dynamic Latent Factor Models
Bayesian computation for filtering and forecasting analysis is developed for
a broad class of dynamic models. The ability to scale-up such analyses in
non-Gaussian, nonlinear multivariate time series models is advanced through the
introduction of a novel copula construction in sequential filtering of coupled
sets of dynamic generalized linear models. The new copula approach is
integrated into recently introduced multiscale models in which univariate time
series are coupled via nonlinear forms involving dynamic latent factors
representing cross-series relationships. The resulting methodology offers
dramatic speed-up in online Bayesian computations for sequential filtering and
forecasting in this broad, flexible class of multivariate models. Two examples
in nonlinear models for very heterogeneous time series of non-negative counts
demonstrate massive computational efficiencies relative to existing
simulation-based methods, while defining similar filtering and forecasting
outcomes.Comment: 21 pages, 7 figure
Southern Folkways Journal Review Number 7
This collection of articles relating to Bulloch County begins with an report about a project on Statesboro history done by second graders at Trinity Christian School, followed by an account of the Martin Pittman Laboratory School, âOther Bulloch County Tales,â a record of the family of James R. Bird, and memories of the life of Rubye Akins Anderson by Mary Lawrence Anderson. Also included are two accounts on Brooklet, âHow âSix Jugâ Became Atlantaâs First Automotive Star,â and research on the Dixon family.https://digitalcommons.georgiasouthern.edu/bchs-pubs/1035/thumbnail.jp
Recent trends in UK insects that inhabit early successional stages of ecosystems
Improved recording of less popular groups, combined with new statistical approaches that compensate for datasets that were hitherto too patchy for quantitative analysis, now make it possible to compare recent trends in the status of UK invertebrates other than butterflies. Using BRC datasets, we analysed changes in status between 1992 and 2012 for those invertebrates whose young stages exploit early seral stages within woodland, lowland heath and semi-natural grassland ecosystems, a habitat type that had declined during the 3 decades previous to 1990 alongside a disproportionally high number of Red Data Book species that were dependent on it. Two clear patterns emerged from a meta-analysis involving 299 classifiable species belonging to ten invertebrate taxa: (i) during the past 2 decades, most early seral species that are living near their northern climatic limits in the UK have increased relative to the more widespread members of these guilds whose distributions were not governed by a need for a warm micro-climate; and (ii) independent of climatic constraints, species that are restricted to the early stages of woodland regeneration have fared considerably less well than those breeding in the early seral stages of grasslands or, especially, heathland. The first trend is consistent with predicted benefits for northern edge-of-range species as a result of climate warming in recent decades. The second is consistent with our new assessment of the availability of early successional stages in these three ecosystems since c. 1990. Whereas the proportion and continuity of early seral patches has greatly increased within most semi-natural grasslands and lowland heaths, thanks respectively to agri-environmental schemes and conservation management, the representation of fresh clearings has continued to dwindle within UK woodlands, whose floors are increasingly shaded and ill-suited for this important guild of invertebrates
A variety of Levitrons : a review
After a brief history and critique of some older instruments, several new Levitron geometries are described. As a result of their greater stability these devices can be used as analogues of a number of phenomena and applications, including magnetic resonance techniques, atom traps and accelerator rings. In particular, the notion of the spinning magnet (or spignet) in a linear trap is similar to the mechanism underpinning the confinement of antihydrogen in a magnetic minimum trap, as achieved in experiments at CERN
- âŠ