Sampling the Variance-Covariance Matrix in the Bayesian Multivariate Probit Model

This paper is concerned with the Bayesian estimation of a Multivariate Probit model. In particular, this paper provides a method to sample the restricted variancecovariance matrix directly from its conditional posterior density. The method allows the application of a standard Gibbs sampling algorithm to sample from the posterior density of the parameters, and hence it avoids the use of a Metropolis step. The method uses a decomposition of the Inverted Wishart density and alternative identification restrictions

Estimating the Demand for Health Care with Panel Data: A Semiparametric Bayesian Approach

This paper is concerned with the problem of estimating the demand for health care with panel data. A random effects model is specifed in a semiparametric Bayesian fashion using a Dirichlet process prior. This results in a very exible mixture distribution with an in nite number of components for the random effects. Therefore, the model can be seen as a natural extension of prevailing latent class models. A full Bayesian analysis using Markov chain Monte Carlo (MCMC)simulation methods is discussed. The methodology is illustrated with an application using data from Germany

Detectors and Concepts for sub-100 ps timing with gaseous detectors

We give a short compendium of the main ongoing detectors and concepts capable of performing accurate sub-100 ps timing at high particle fluxes and on large areas, through technologies based on gaseous media. We briefly discuss the state-of-the-art, technological limitations and prospects, and a new bizarre idea

Tracing the Dynamics of Disk Galaxies with Optical and IR Surface Photometry: Color Gradients in M99

We present optical and IR surface photometry of M99 (NGC 4254) at g, r_S i, J and K'. We also present a K' image of M51 (NGC 5194) for comparison. Fourier decomposition of the disk light reveals that the radial distribution of power depends on wavelength, which in turn implies that the spiral structure traced in the visual (i.e. young population I and dust) is different from the one detected at 2 microns (i.e. old stellar disk). We observe radial modulation of the power and a dependency of power with wavelength that are consistent with modal theory of spiral structure. A central motivation for our research is the fundamental idea of density wave theory that the passage of a spiral density wave triggers star formation. We have found a stellar population age gradient consistent with this scenario in a reddening-free, red supergiant-sensitive, Q-like photometric parameter at 6 kpc galactocentric distance across one of the arms of M99. We rule out that the change in this parameter, Q(r_SJgi), across the arm is mainly due to dust. The difference in Q(r_SJgi) going from the interarm regions to the arms also indicates that arms cannot be due exclusively to crowding of stellar orbits. We present the first measurement of Omega_p, the angular speed of the spiral pattern, and of the location of the corotation radius, derived from the drift velocity of the young stars away from their birth site. The measured Q(r_SJgi) implies a star formation rate for M99 within the range of 10-20 M_odot/yr; a disk stellar mass surface density of ~80 M_odot/pc^2; and a maximum contribution of ~20 percent from red supergiants to the K' light in a small region, and much smaller on average. We measure a K' arm--interarm contrast of 2-3, too high for M99 to be a truly isolated galaxy.Comment: 25 pages of uuencoded, compressed Postscript (text only). To appear in 1 April 1996 issue of The Astrophysical Journal. Also available, together with 2 uuencoded, compressed PostScript files with 10 figures each, at http://astro.berkeley.edu/preprints.htm