Exploratory spatiotemporal data analysis and modelling of public confidence in the police in central London

Improving public confidence in the police is one of the most important issues for the London Metropolitan Police Service (Met). Public confidence varies over geographic space and changes over time. Spatiotemporal analysis and modelling becomes more manageable with a thorough understanding of the underlying spatiotemporal autocorrelation structure of the phenomena under scrutiny. In this study, exploratory spatiotemporal analysis is conducted on repeated cross-sectional survey data from the Metropolitan Police Public Attitude Survey. This confirmed the presence of second order nonstationarity in public perceptions of the Met police

Predicting public confidence in the police with spatiotemporal Bayesian hierarchical modelling.

Public confidence in the police is crucial to effective policing. Estimating and predicting public confidence at the local level will better enable the police to conduct proactive confidence interventions to meet the concerns of the community. This work represents the first application of Bayesian spatiotemporal modelling to estimation and prediction of public confidence in the police at the local level. Three models of increasing spatiotemporal complexity were fitted by Markov chain Monte Carlo simulation using free software package WinBUGS. Public confidence was successfully predicted at the local level using a spatiotemporal model with an inseparable interaction structure

DNS and modeling of the interaction between turbulent premixed flames and walls

The interaction between turbulent premixed flames and walls is studied using a two-dimensional full Navier-Stokes solver with simple chemistry. The effects of wall distance on the local and global flame structure are investigated. Quenching distances and maximum wall heat fluxes during quenching are computed in laminar cases and are found to be comparable to experimental and analytical results. For turbulent cases, it is shown that quenching distances and maximum heat fluxes remain of the same order as for laminar flames. Based on simulation results, a 'law-of-the-wall' model is derived to describe the interaction between a turbulent premixed flame and a wall. This model is constructed to provide reasonable behavior of flame surface density near a wall under the assumption that flame-wall interaction takes place at scales smaller than the computational mesh. It can be implemented in conjunction with any of several recent flamelet models based on a modeled surface density equation, with no additional constraints on mesh size or time step

A spatiotemporal bayesian hierarchical approach to investigating patterns of confidence in the police at the neighbourhood level

Public confidence in the police is crucial to effective policing. Improving understanding of public confidence at the local l evel will better enable the police to conduct proactive confidence interventions to meet the concerns of local communities. Conventional approaches do not consider that public confidence varies across geographic space as well as in time. Neighbourhood leve l approaches to modelling public confidence in the police are hampered by the small number problem and the resulting instability in the estimates and uncertainty in the results. This research illustrates a spatiotemporal Bayesian approach for estimating an d forecasting public confidence at the neighbourhood level and we use it to examine trends in public confidence in the police in London, UK, for Q2 2006 to Q3 2013. Our approach overcomes the limitations of the small number problem and specifically , we inv estigate the effect of the spatiotemporal representation structure chosen on the estimates of public confidence produced. We then investigate the use of the model for forecasting by producing one - step ahead forecasts of the final third of the time - series . The results are compared with the forecasts from traditional time - series forecasting methods like naïve, exponential smoothing, ARIMA, STARIMA and others. A model with spatially structured and unstructured random effects as well as a normally distributed s patiotemporal interaction term was the most parsimonious and produced the most realistic estimates. It also provided the best forecasts at the London - wide, Borough and neighbourhood level

A Spatiotemporal Bayesian Hierarchical Approach to Investigating Patterns of Confidence in the Police at the Neighborhood Level

Public confidence in the police is crucial to effective policing. Improving understanding of public confidence at the local level will better enable the police to conduct proactive confidence interventions to meet the concerns of local communities. Conventional approaches do not consider that public confidence varies across geographic space as well as in time. Neighborhood level approaches to modeling public confidence in the police are hampered by the small number problem and the resulting instability in the estimates and uncertainty in the results. This research illustrates a spatiotemporal Bayesian approach for estimating and forecasting public confidence at the neighborhood level and we use it to examine trends in public confidence in the police in London, UK, for Q2 2006 to Q3 2013. Our approach overcomes the limitations of the small number problem and specifically, we investigate the effect of the spatiotemporal representation structure chosen on the estimates of public confidence produced. We then investigate the use of the model for forecasting by producing one‐step ahead forecasts of the final third of the time series. The results are compared with the forecasts from traditional time‐series forecasting methods like naïve, exponential smoothing, ARIMA, STARIMA, and others. A model with spatially structured and unstructured random effects as well as a normally distributed spatiotemporal interaction term was the most parsimonious and produced the most realistic estimates. It also provided the best forecasts at the London‐wide, Borough, and neighborhood level

Numerical simulations of turbulent premixed H2/O2/N2 flames with complex chemistry

Premixed stoichiometric H2/O2/N2 flames propagating in two-dimensional turbulence were studied using direct numerical simulation (simulations in which all fluid and thermochemical scales are fully resolved) including realistic chemical kinetics and molecular transport. Results are compared with earlier zero-chemistry (flame sheet) and one-step chemistry simulations. Consistent with the simpler models, the turbulent flame with realistic chemistry aligns preferentially with extensive strain rates in the tangent plane and flame curvature probability density functions are close to symmetric with near-zero means. By contrast to simple-chemistry results with non-unity Lewis numbers (ratio of thermal to species diffusivity), local flame structure does not correlate with curvature but rather with tangential strain rate. Turbulent straining results in substantial thinning of the flame relative to the steady unstrained laminar case. Heat release and H2O2 contours remain thin and connected ('flamelet-like') while species including H-atom and OH are more diffuse. Peak OH concentration occurs well behind the peak heat-release zone. The feasibility of incorporating realistic chemistry into full turbulence simulations to address issues such as pollutant formation in hydrocarbon-air flames is suggested

Discovery of a 500 au protobinary in the massive prestellar core G11.92-0.61 MM2

Funding: C.J.C. acknowledges support from the University of St Andrews Restarting Research Funding Scheme (SARRF), which is funded through the SFC grant reference SFC/AN/08/020. J.D.I. acknowledges support from the UK’s STFC under ST/T000287/1. S.Z. is funded by the China Scholarship Council–University of St Andrews Scholarship (PhD programmes, No. 201806190010). T.J.H. is funded by a Royal Society Dorothy Hodgkin Fellowship.We present high-resolution ( 24.7 L⊙ for MM2E and L* > 12.6 L⊙ for MM2W. The compact sources are connected by a "bridge" of lower-surface-brightness dust emission and lie within more extended emission that may correspond to a circumbinary disk. The circumprotostellar gas mass, estimated from ~0.2" resolution VLA 0.9 cm observations assuming optically thin emission, is 6.8 ± 0.9 M⊙. No line emission is detected towards MM2E and MM2W in our high-resolution 1.3 mm ALMA observations. The only line detected is 13CO J=2-1, in absorption against the 1.3 mm continuum, which likely traces a layer of cooler molecular material surrounding the protostars. We also report the discovery of a highly asymmetric bipolar molecular outflow that appears to be driven by MM2E and/or MM2W in new deep, ~0.5" resolution (1680 au) ALMA 0.82 mm observations. This outflow, traced by low-excitation CH3OH emission, indicates ongoing accretion onto the protobinary system. Overall, the super-Alfvenic models of Mignon-Risse et al. (2021) agree well with the observed properties of the MM2E/MM2W protobinary, suggesting that this system may be forming in an environment with a weak magnetic field.Publisher PDFPeer reviewe

'The Brick' is not a brick : A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.In this paper we provide a comprehensive description of the internal dynamics of G0.253+0.016 (a.k.a. 'the Brick'); one of the most massive and dense molecular clouds in the Galaxy to lack signatures of widespread star formation. As a potential host to a future generation of high-mass stars, understanding largely quiescent molecular clouds like G0.253+0.016 is of critical importance. In this paper, we reanalyse Atacama Large Millimeter Array cycle 0 HNCO $J=4(0,4)-3(0,3)$ data at 3 mm, using two new pieces of software which we make available to the community. First, scousepy, a Python implementation of the spectral line fitting algorithm scouse. Secondly, acorns (Agglomerative Clustering for ORganising Nested Structures), a hierarchical n-dimensional clustering algorithm designed for use with discrete spectroscopic data. Together, these tools provide an unbiased measurement of the line of sight velocity dispersion in this cloud, $\sigma_{v_{los}, {\rm 1D}}=4.4\pm2.1$ kms$^{-1}$, which is somewhat larger than predicted by velocity dispersion-size relations for the Central Molecular Zone (CMZ). The dispersion of centroid velocities in the plane of the sky are comparable, yielding $\sigma_{v_{los}, {\rm 1D}}/\sigma_{v_{pos}, {\rm 1D}}\sim1.2\pm0.3$. This isotropy may indicate that the line-of-sight extent of the cloud is approximately equivalent to that in the plane of the sky. Combining our kinematic decomposition with radiative transfer modelling we conclude that G0.253+0.016 is not a single, coherent, and centrally-condensed molecular cloud; 'the Brick' is not a \emph{brick}. Instead, G0.253+0.016 is a dynamically complex and hierarchically-structured molecular cloud whose morphology is consistent with the influence of the orbital dynamics and shear in the CMZ.Peer reviewedFinal Accepted Versio

Primality-testing Mersenne numbers

Report of a systematic review of Mersenne numbers 2^p-1 for p < 62982

Gravitational Instabilities in a proto-solar like disc I.: Dynamics and Chemistry

To date, most simulations of the chemistry in protoplanetary discs have used 1 + 1D or 2D axisymmetric α-disc models to determine chemical compositions within young systems. This assumption is inappropriate for non-axisymmetric, gravitationally unstable discs, which may be a significant stage in early protoplanetary disc evolution. Using 3D radiative hydrodynamics, we have modelled the physical and chemical evolution of a 0.17 M⊙ self-gravitating disc over a period of 2000 yr. The 0.8 M⊙ central protostar is likely to evolve into a solar-like star, and hence this Class 0 or early Class I young stellar object may be analogous to our early Solar system. Shocks driven by gravitational instabilities enhance the desorption rates, which dominate the changes in gas-phase fractional abundances for most species. We find that at the end of the simulation, a number of species distinctly trace the spiral structure of our relatively low-mass disc, particularly CN. We compare our simulation to that of a more massive disc, and conclude that mass differences between gravitationally unstable discs may not have a strong impact on the chemical composition. We find that over the duration of our simulation, successive shock heating has a permanent effect on the abundances of HNO, CN and NH3, which may have significant implications for both simulations and observations. We also find that HCO+ may be a useful tracer of disc mass. We conclude that gravitational instabilities induced in lower mass discs can significantly, and permanently, affect the chemical evolution, and that observations with high-resolution instruments such as Atacama Large Millimeter/submillimeter Array (ALMA) offer a promising means of characterizing gravitational instabilities in protosolar discs