Sines, steps and droplets: Semiparametric Bayesian modeling of arrival time series

I describe ongoing work developing Bayesian methods for flexible modeling of arrival time series data without binning, aiming to improve detection and measurement of X-ray and gamma-ray pulsars, and of pulses in gamma-ray bursts. The methods use parametric and semiparametric Poisson point process models for the event rate, and by design have close connections to conventional frequentist methods currently used in time-domain astronomy.Comment: 4 pages, 1 figure; to appear in the proceedings of IAU Symposium 285, "New Horizons in Time Domain Astronomy" (proceedings eds. Elizabeth Griffin, Bob Hanisch, and Rob Seaman), Cambridge University Press; see http://www.physics.ox.ac.uk/IAUS285

Absolute Timing of the Crab Pulsar with RXTE

We have monitored the phase of the main X-ray pulse of the Crab pulsar with the Rossi X-ray Timing Explorer (RXTE) for almost eight years, since the start of the mission in January 1996. The absolute time of RXTE's clock is sufficiently accurate to allow this phase to be compared directly with the radio profile. Our monitoring observations of the pulsar took place bi-weekly (during the periods when it was at least 30 degrees from the Sun) and we correlated the data with radio timing ephemerides derived from observations made at Jodrell Bank. We have determined the phase of the X-ray main pulse for each observation with a typical error in the individual data points of 50 us. The total ensemble is consistent with a phase that is constant over the monitoring period, with the X-ray pulse leading the radio pulse by 0.0102+/-0.0012 period in phase, or 344+/-40 us in time. The error estimate is dominated by a systematic error of 40 us in the radio data, arising from uncertainties in the variable amount of pulse delay due to interstellar scattering and instrumental calibration. The statistical error is 0.00015 period, or 5 us. The separation of the main pulse and interpulse appears to be unchanging at time scales of a year or less, with an average value of 0.4001+/-0.0002 period. There is no apparent variation in these values with energy over the 2-30 keV range. The lag between the radio and X-ray pulses may be constant in phase (rotational) or constant in time (linear pathlength). We are not (yet) able to distinguish between these two interpretations.Comment: 11 pages, 2 figure

Spin-density wave in Cr: nesting versus low-lying thermal excitations

It is well known that present versions of density functional theory do not predict the experimentally observed spin-density wave state to be the ground state of Cr. Recently, a so-called "nodon model" has been proposed as an alternative way to reconcile theory and experiment: the ground state of Cr is truly antiferromagnetic, and the spin-density wave appears due to low-lying thermal excitations ("nodons"). We examine in this paper whether the postulated properties of these nodons are reproduced by ab initio calculations

C1− Continuous crack propagation for mixed-mode fracture problems

In this work a C1− continuous crack propagation algorithm is proposed to improve the numerical simulation of localized deformation patterns, using higher order elements. The algorithm is applied for a standard smeared crack model and is validated by a mixed-mode fracture problem. From the results a reduction of mesh-induced directional bias is observed

Differentiated instruction in teacher education : a case study of congruent teaching

Teachers are supposed to use forms of differentiated instruction to anticipate the differences among their students. However, the adaptation of teaching to the diversity of the group often takes place with difficulty. Teacher education is blamed for not preparing student teachers adequately for differentiated instruction. Several authors suggest that congruent teaching in teacher education might be an adequate solution to this problem. This case study aims to investigate the (congruent) realization of differentiated instruction in teacher education using ethnographic tools. The results indicate that the observed teacher educator demonstrated limited forms of differentiation, largely without providing meta-commentary. Therefore, she is not a role model on the subject of differentiated instruction in the view of student teachers. These results are discussed in depth, and form a basis for further research and suggestions for practice in teacher education

Telescope Bibliographies: an Essential Component of Archival Data Management and Operations

Assessing the impact of astronomical facilities rests upon an evaluation of the scientific discoveries which their data have enabled. Telescope bibliographies, which link data products with the literature, provide a way to use bibliometrics as an impact measure for the underlying data. In this paper we argue that the creation and maintenance of telescope bibliographies should be considered an integral part of an observatory's operations. We review the existing tools, services, and workflows which support these curation activities, giving an estimate of the effort and expertise required to maintain an archive-based telescope bibliography.Comment: 10 pages, 3 figures, to appear in SPIE Astronomical Telescopes and Instrumentation, SPIE Conference Series 844

Learning and the market for housing

House prices have inertia, which may be because housing-market participants need time to recognize long booms and recessions. Within a dynamic stochastic general-equilibrium model with markets for housing and defaultable mortgages, I consider the case of imperfect knowledge and learning about the persistence of exogenous shocks. I evaluate the performance of the model against the last 40 years of key U.S. macroeconomic data. Bayesian comparison strongly favors the model with learning over the baseline case with perfect knowledge, although additional assumptions about the learning process may be necessary for an adequate account of house-price dynamics