Modeling and Estimation for Self-Exciting Spatio-Temporal Models of Terrorist Activity

Spatio-temporal hierarchical modeling is an extremely attractive way to model the spread of crime or terrorism data over a given region, especially when the observations are counts and must be modeled discretely. The spatio-temporal diffusion is placed, as a matter of convenience, in the process model allowing for straightforward estimation of the diffusion parameters through Bayesian techniques. However, this method of modeling does not allow for the existence of self-excitation, or a temporal data model dependency, that has been shown to exist in criminal and terrorism data. In this manuscript we will use existing theories on how violence spreads to create models that allow for both spatio-temporal diffusion in the process model as well as temporal diffusion, or self-excitation, in the data model. We will further demonstrate how Laplace approximations similar to their use in Integrated Nested Laplace Approximation can be used to quickly and accurately conduct inference of self-exciting spatio-temporal models allowing practitioners a new way of fitting and comparing multiple process models. We will illustrate this approach by fitting a self-exciting spatio-temporal model to terrorism data in Iraq and demonstrate how choice of process model leads to differing conclusions on the existence of self-excitation in the data and differing conclusions on how violence is spreading spatio-temporally

An Extended Laplace Approximation Method for Bayesian Inference of Self-Exciting Spatial-Temporal Models of Count Data

Self-Exciting models are statistical models of count data where the probability of an event occurring is influenced by the history of the process. In particular, self-exciting spatio-temporal models allow for spatial dependence as well as temporal self-excitation. For large spatial or temporal regions, however, the model leads to an intractable likelihood. An increasingly common method for dealing with large spatio-temporal models is by using Laplace approximations (LA). This method is convenient as it can easily be applied and is quickly implemented. However, as we will demonstrate in this manuscript, when applied to self-exciting Poisson spatial-temporal models, Laplace Approximations result in a significant bias in estimating some parameters. Due to this bias, we propose using up to sixth-order corrections to the LA for fitting these models. We will demonstrate how to do this in a Bayesian setting for Self-Exciting Spatio-Temporal models. We will further show there is a limited parameter space where the extended LA method still has bias. In these uncommon instances we will demonstrate how a more computationally intensive fully Bayesian approach using the Stan software program is possible in those rare instances. The performance of the extended LA method is illustrated with both simulation and real-world data

Radio observations of the massive stellar cluster Westerlund 1

High-dynamic range radio observations of Westerlund 1 are presented that detect a total of 21 stars in the young massive stellar cluster, the richest population of radio emitting stars known for any young massive galactic cluster in the Galaxy. We will discuss some of the more remarkable objects, including the highly radio luminous supergiant B[e] star W9, with an estimated mass-loss rate ~10^{-3} solarmass/yr, comparable to that of eta Carina, along with the somewhat unusual detection of thermal emission from almost all the cool red supergiants and yellow hypergiants. There is strong supporting evidence from X-ray observations that each of the WR stars with radio emission are likely to be colliding-wind binariesComment: To appear in the proceedings of "Massive Stars: Fundamental Parameters and Circumstellar Interactions". 2 pages, 1 figur

Biochemical, endocrine, and hematological factors in human oxygen tolerance extension: Predictive studies 6

The Predictive Studies VI (Biochemical, endocrine, and hematological factors in human oxygen tolerance extension) Program consisted of two related areas of research activity, integrated in design and performance, that were each based on an ongoing analysis of human organ oxygen tolerance data obtained for the continuous oxygen exposures of the prior Predictive Studies V Program. The two research areas effectively blended broad investigation of systematically varied intermittent exposure patterns in animals with very selective evaluation of specific exposure patterns in man

Disc loss and renewal in A0535+26

This paper presents observations of the Be/X-ray binary system A0535+26 revealing the first observed loss of its circumstellar disc, demonstrated by the loss of its JHK infrared excess and optical/IR line emission. However optical/IR spectroscopy reveals the formation of a new inner disc with significant density and emission strength at small radii; the disc has proven to be stable over 5 months in this intermediate state.Comment: 4 pages, 4 figures, accepted by MNRAS, uses mn.st