67 research outputs found
A mechanical coordinate converter
Mechanical converter for spherical coordinates used in polariscope balloon program
Measuring the Effect and Efficiency of City Marketing
AbstractCity marketing, defined as the interaction that exists in the management of the city policy areas, such as education, employment, or housing towards three target groups, viz. tourists, citizens and enterprises (Hospers, 2011), is increasingly becoming more important in the management of cities (Rennen, 2007) with raised budgets as a result. This research aims at gauging the effect and measuring the efficiency of city marketing, therefore designing a tool that is a combination of integrated performance rating (Jorissen, 1999) and return on investment (ROI) (Jacobson, 1987), based on widely available secondary data, spanning the time period 2008–2011
Reference prior for Bayesian estimation of seismic fragility curves
One of the crucial quantities of probabilistic seismic risk assessment
studies is the fragility curve, which represents the probability of failure of
a mechanical structure conditional to a scalar measure derived from the seismic
ground motion. Estimating such curves is a difficult task because for most
structures of interest, few data are available, whether they come from complex
numerical simulations or experimental campaigns. For this reason, a wide range
of the methods of the literature rely on a parametric log-normal model.
Bayesian approaches allow for efficient learning of the model parameters.
However, for small data set sizes, the choice of the prior distribution has a
non-negligible influence on the posterior distribution, and therefore on any
resulting estimate. We propose a thorough study of this parametric Bayesian
estimation problem when the data are binary (i.e. data indicate the state of
the structure, failure or non-failure). Using the reference prior theory as a
support, we suggest an objective approach for the prior choice to simulate a
posteriori fragility curves. This approach leads to the Jeffreys prior and we
prove that this prior depends only of the ground motion characteristics, making
its calculation suitable for any equipment in an industrial installation
subjected to the same seismic hazard. Our proposal is theoretically and
numerically compared to those classically proposed in the literature by
considering three different case studies. The results show the robustness and
advantages of the Jeffreys prior in terms of regularization (no degenerate
estimations) and stability (no outliers of the parameters) for fragility curves
estimation
PHASES Differential Astrometry and Iodine Cell Radial Velocities of the kappa Pegasi Triple Star System
kappa Pegasi is a well-known, nearby triple star system. It consists of a
``wide'' pair with semi-major axis 235 milli-arcseconds, one component of which
is a single-line spectroscopic binary (semi-major axis 2.5 milli-arcseconds).
Using high-precision differential astrometry and radial velocity observations,
the masses for all three components are determined and the relative
inclinations between the wide and narrow pairs' orbits is found to be 43.8 +/-
3.0 degrees, just over the threshold for the three body Kozai resonance. The
system distance is determined to 34.60 +/- 0.21 parsec, and is consistent with
trigonometric parallax measurements.Comment: Accepted for publication in ApJ, complete versions of tables 2 and 4
can be found at http://stuff.mit.edu/~matthew1/kapPegTables
Young stars and brown dwarfs surrounding Alnilam (eps Ori) and Mintaka (del Ori)
Aims: We look for new regions for the search of substellar objects. Methods:
Two circular areas, 45 arcmin-radius each, centred on the young massive star
systems Alnilam and Mintaka in the Orion Belt, have been explored. The regions
are very young (less than 10 Ma), have low extinction, and are neighbours to
sigma Orionis (~3 Ma), a young open cluster very rich in brown dwarfs and
planetary-mass objects. We have used Virtual Observatory tools, the
astro-photometric Tycho-2, DENIS and 2MASS catalogues, 10 control fields at
similar galactic latitudes, and X-ray, mid-infrared and spectroscopic data from
the literature. Results: We have compiled exhaustive lists of known young stars
and new candidate members in the Ori OB1b association, and of fore- and
background sources. A total of 136 stars display features of extreme youth,
like early spectral types, lithium in absorption, or mid-infrared flux excess.
Other two young brown dwarf and 289 star candidates have been identified from
an optical/near-infrared colour-magnitude diagram. We list additional 74 known
objects that might belong to the association. This catalogue can serve as an
input for characterisation of the stellar and high-mass substellar populations
in the Orion Belt. Finally, we have investigated the surface densities and
radial distributions of young objects surrounding Alnilam and Mintaka, and
compared them with those in the sigma Orionis cluster. We report a new open
cluster centred on Mintaka. Conclusions: Both regions can be analogs to the
sigma Orionis cluster, but more massive, more extended, slightly older, and
less radially concentrated.Comment: Accepted for publication in A&A. It will be published on line in
Sect. 14 (Catalogs and data). Tables in Appendix A will soon be available at
the CD
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