8,712 research outputs found
INLA or MCMC? A Tutorial and Comparative Evaluation for Spatial Prediction in log-Gaussian Cox Processes
We investigate two options for performing Bayesian inference on spatial
log-Gaussian Cox processes assuming a spatially continuous latent field: Markov
chain Monte Carlo (MCMC) and the integrated nested Laplace approximation
(INLA). We first describe the device of approximating a spatially continuous
Gaussian field by a Gaussian Markov random field on a discrete lattice, and
present a simulation study showing that, with careful choice of parameter
values, small neighbourhood sizes can give excellent approximations. We then
introduce the spatial log-Gaussian Cox process and describe MCMC and INLA
methods for spatial prediction within this model class. We report the results
of a simulation study in which we compare MALA and the technique of
approximating the continuous latent field by a discrete one, followed by
approximate Bayesian inference via INLA over a selection of 18 simulated
scenarios. The results question the notion that the latter technique is both
significantly faster and more robust than MCMC in this setting; 100,000
iterations of the MALA algorithm running in 20 minutes on a desktop PC
delivered greater predictive accuracy than the default \verb=INLA= strategy,
which ran in 4 minutes and gave comparative performance to the full Laplace
approximation which ran in 39 minutes.Comment: This replaces the previous version of the report. The new version
includes results from an additional simulation study, and corrects an error
in the implementation of the INLA-based method
Can âNew Welfareâ Address Poverty through More and Better Jobs?
New welfare has been prominent in recent European social policy debates. It involves mobilising more people into paid work, improving human capital and ensuring fairer access to opportunities. This programme is attractive to business (more workers, better human capital and reduced social conflict to enhance productivity and profitability) and to citizens (more widely accessible job-opportunities with better rewards): a relatively low-cost approach to the difficulties governments face in maintaining support and meeting social goals as inequalities widen. The general move towards ânew welfareâ gathered momentum during the past two decades, given extra impetus by the 2007-9 recession and subsequent stagnation. While employment rates rose during the prosperous years before the crisis, there was no commensurate reduction in poverty. Over the same period the share of economic growth returned to labour fell, labour markets were increasingly de-regulated and inequality increased. This raises the question of whether new welfareâs economic (higher employment, improved human capital) and social (better job quality and incomes) goals may come into conflict. This paper examines data for 17 European countries over the period 2001 to 2007. It shows that new welfare is much more successful at achieving higher employment than at reducing poverty, even during prosperity, and that the approach pays insufficient attention to structural factors, such as the falling wage share, and to institutional issues, such as labour market deregulation
Contributions of Repulsive and Attractive Interactions to Nematic Order
Both repulsive and attractive molecular interactions can be used to explain
the onset of nematic order. The object of this paper is to combine these two
nematogenic molecular interactions in a unified theory. This attempt is not
unprecedented; what is perhaps new is the focus on the understanding of
nematics in the high density limit. There, the orientational probability
distribution is shown to exhibit a unique feature: it has compact support on
configuration space. As attractive interactions are turned on, the behavior
changes, and at a critical attractive interaction strength, thermotropic
behavior of the Maier-Saupe type is attained.Comment: 14 pages, 4 figure
An ab initio study of the C3(+) cation using multireference methods
The energy difference between the linear 2 sigma(sup +, sub u) and cyclic 2B(sub 2) structures of C3(+) has been investigated using large (5s3p2d1f) basis sets and multireference electron correlation treatments, including complete active space self consistent fields (CASSCF), multireference configuration interaction (MRCI), and averaged coupled-pair functional (ACPF) methods, as well as the single-reference quadratic configuration interaction (QCISD(T)) method. Our best estimate, including a correction for basis set incompleteness, is that the linear form lies above the cyclic from by 5.2(+1.5 to -1.0) kcal/mol. The 2 sigma(sup +, sub u) state is probably not a transition state, but a local minimum. Reliable computation of the cyclic/linear energy difference in C3(+) is extremely demanding of the electron correlation treatment used: of the single-reference methods previously considered, CCSD(T) and QCISD(T) perform best. The MRCI + Q(0.01)/(4s2p1d) energy separation of 1.68 kcal/mol should provide a comparison standard for other electron correlation methods applied to this system
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Adapting the International System of Units to the twenty-first century
We review the proposal of the International Committee for Weights and Measures
(ComitĂŠ International des Poids et Mesures, CIPM), currently being considered by
the General Conference on Weights and Measures (ConfĂŠrences GĂŠnĂŠrales des Poids et
Mesures, CGPM), to revise the International System of Units (Le Système International
dâUnitès, SI). The proposal includes new definitions for four of the seven base units of
the SI, and a new form of words to present the definitions of all the units. The objective
of the proposed changes is to adopt definitions referenced to constants of nature, taken
in the widest sense, so that the definitions may be based on what are believed to be
true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and
mole are linked to exact numerical values of the mass of the international prototype of the
kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature
of water and the molar mass of carbon-12, respectively, in the new SI these units are linked
to exact numerical values of the Planck constant, the elementary charge, the Boltzmann
constant and the Avogadro constant, respectively. The new wording used expresses the
definitions in a simple and unambiguous manner without the need for the distinction
between base and derived units. The importance of relations among the fundamental
constants to the definitions, and the importance of establishing a mise en pratique for
the realization of each definition, are also discussed
Plans for the first balloon flight of the gamma-ray polarimeter experiment (GRAPE)
We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), has been successfully demonstrated in the lab using partially polarized gamma-ray sources and using fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model, consisting of a single detector module, was flown on a high altitude balloon flight to further demonstrate the design and to collect background data. We are currently preparing a much larger balloon payload for a flight in the fall of 2011. Using a large (16-element) array of detector modules, this payload is being designed to search for polarization from known point sources of radiation, namely the Crab and Cygnus X-1. This first flight will not only provide a scientific demonstration of the GRAPE design (by measuring polarization from the Crab nebula), it will also lay the foundation for subsequent long duration balloon flights that will be designed for studying polarization from gamma-ray bursts and solar flares. Here we shall present data from calibration of the first flight module detectors, review the latest payload design and update the predicted polarization sensitivity for both the initial continental US balloon flight and the subsequent long-duration balloon flights
GRAPE: a balloon-borne gamma-ray polarimeter
The Gamma-RAy Polarimeter Experiment (GRAPE) is a concept for an astronomical hard X-ray Compton polarimeter operating in the 50 - 500 keV energy band. The instrument has been optimized for wide-field polarization measurements of transient outbursts from energetic astrophysical objects such as gamma-ray bursts and solar flares. The GRAPE instrument is composed of identical modules, each of which consists of an array of scintillator elements read out by a multi-anode photomultiplier tube (MAPMT). Incident photons Compton scatter in plastic scintillator elements and are subsequently absorbed in inorganic scintillator elements; a net polarization signal is revealed by a characteristic asymmetry in the azimuthal scattering angles. We have constructed a prototype GRAPE module that has been calibrated at a polarized hard X-ray beam and flown on an engineering balloon test flight. A full-scale scientific balloon payload, consisting of up to 36 modules, is currently under development. The first flight, a one-day flight scheduled for 2011, will verify the expected scientific performance with a pointed observation of the Crab Nebula. We will then propose long-duration balloon flights to observe gamma-ray bursts and solar flares
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