564 research outputs found
Using privileged information to manipulate markets: insiders, gurus, and credibility
Access to private information is shown to generate both the incentives and the ability to manipulate asset markets through strategically distorted announcements. The fact that privileged information is noisy interferes with the public's attempts to learn whether such announcements are honest; it allows opportunistic individuals to manipulate prices repeatedly, without ever being fully found out. This leads us to extend Sobel's [1985] model of strategic communication to the case of noisy private signals. Our results show that when truthfulness is not easily verifiable, restrictions on trading by insiders may be needed to preserve the integrity of information embodied in prices
Markov Chain Monte Carlo joint analysis of Chandra X-ray imaging spectroscopy and Sunyaev-Zeldovich Effect data
X-ray and Sunyaev-Zeldovich Effect data can be combined to determine the
distance to galaxy clusters. High-resolution X-ray data are now available from
the Chandra Observatory, which provides both spatial and spectral information,
and Sunyaev-Zeldovich Effect data were obtained from the BIMA and OVRO arrays.
We introduce a Markov chain Monte Carlo procedure for the joint analysis of
X-ray and Sunyaev-Zeldovich Effect data. The advantages of this method are the
high computational efficiency and the ability to measure simultaneously the
probability distribution of all parameters of interest, such as the spatial and
spectral properties of the cluster gas and also for derivative quantities such
as the distance to the cluster. We demonstrate this technique by applying it to
the Chandra X-ray data and the OVRO radio data for the galaxy cluster Abell
611. Comparisons with traditional likelihood-ratio methods reveal the
robustness of the method. This method will be used in follow-up papers to
determine the distances to a large sample of galaxy clusters.Comment: ApJ accepted, scheduled for ApJ 10 October 2004, v614 issue. Title
changed, added more convergence diagnostic tests, Figure 7 converted to lower
resolution for easier download, other minor change
Determination of the Cosmic Distance Scale from Sunyaev-Zel'dovich Effect and Chandra X-ray Measurements of High Redshift Galaxy Clusters
We determine the distance to 38 clusters of galaxies in the redshift range
0.14 < z < 0.89 using X-ray data from Chandra and Sunyaev-Zeldovich Effect data
from the Owens Valley Radio Observatory and the Berkeley-Illinois-Maryland
Association interferometric arrays. The cluster plasma and dark matter
distributions are analyzed using a hydrostatic equilibrium model that accounts
for radial variations in density, temperature and abundance, and the
statistical and systematic errors of this method are quantified. The analysis
is performed via a Markov chain Monte Carlo technique that provides
simultaneous estimation of all model parameters. We measure a Hubble constant
of 76.9 +3.9-3.4 +10.0-8.0 km/s/Mpc (statistical followed by systematic
uncertainty at 68% confidence) for an Omega_M=0.3, Omega_Lambda=0.7 cosmology.
We also analyze the data using an isothermal beta model that does not invoke
the hydrostatic equilibrium assumption, and find H_0=73.7 +4.6-3.8 +9.5-7.6
km/s/Mpc; to avoid effects from cool cores in clusters, we repeated this
analysis excluding the central 100 kpc from the X-ray data, and find H_0=77.6
+4.8-4.3 +10.1-8.2 km/s/Mpc. The consistency between the models illustrates the
relative insensitivity of SZE/X-ray determinations of H_0 to the details of the
cluster model. Our determination of the Hubble parameter in the distant
universe agrees with the recent measurement from the Hubble Space Telescope key
project that probes the nearby universe.Comment: ApJ submitted (revised version
Fast-Neutron Activation of Long-Lived Isotopes in Enriched Ge
We measured the production of \nuc{57}{Co}, \nuc{54}{Mn}, \nuc{68}{Ge},
\nuc{65}{Zn}, and \nuc{60}{Co} in a sample of Ge enriched in isotope 76 due to
high-energy neutron interactions. These isotopes, especially \nuc{68}{Ge}, are
critical in understanding background in Ge detectors used for double-beta decay
experiments. They are produced by cosmogenic-neutron interactions in the
detectors while they reside on the Earth's surface. These production rates were
measured at neutron energies of a few hundred MeV. We compared the measured
production to that predicted by cross-section calculations based on CEM03.02.
The cross section calculations over-predict our measurements by approximately a
factor of three depending on isotope. We then use the measured cosmic-ray
neutron flux, our measurements, and the CEM03.02 cross sections to predict the
cosmogenic production rate of these isotopes. The uncertainty in extrapolating
the cross section model to higher energies dominates the total uncertainty in
the cosmogenic production rate.Comment: Revised after feedback and further work on extrapolating cross
sections to higher energies in order to estimate cosmic production rates.
Also a numerical error was found and fixed in the estimate of the Co-57
production rat
Dendrochronological dating of coal mine workings at the Joggins Fossil Cliffs, Nova Scotia, Canada
Joggins, Nova Scotia was one of the first places in North America where coal was mined. In this paper we employ dendrochronology to date timber pit props preserved within relic coal mine workings on the closely adjacent Fundy and Dirty seams. These remains comprise a system of adits created through ‘room and pillar’ mining. Of the seventy-three samples collected, forty-eight were successfully cross-dated against a local red spruce (Picea rubens Sarg.) master chronology thereby establishing the year in which each individual sample was cut as a live tree. Results indicate cut dates of 1849-1875 which are generally consistent with written archival records of mining activity on these coal seams. Our analysis of fourteen separate adits allows us to distinguish two phases of mining. Most adits (numbers 1-9 and 11-12 with cut dates of 1849-1868) are relics of an initial operation by the General Mining Association (1865-1871), which opened a mine entered at beach level. Dendrochronological dates preceding the opening of this mine may suggest that timber stockpiled from the nearby Joggins Mine (opened 1847) was used in its construction. The remaining adits (numbers 10 and 13-14 with cut dates of 1873-1875) are probably relics of a later mine opened by the Joggins Coal Mining Company (1872-1877). Although this mine was centered ~500 m inland, its western peripheral workings passed through the earlier workings to the shore. Findings improve knowledge of the industrial archaeology of the UNESCO World Heritage Site and help refine the regional master red spruce chronology for future dendrochronological studies
X-ray and Sunyaev-Zel'dovich Effect Measurements of the Gas Mass Fraction in Galaxy Clusters
We present gas mass fractions of 38 massive galaxy clusters spanning
redshifts from 0.14 to 0.89, derived from Chandra X-ray data and OVRO/BIMA
interferometric Sunyaev-Zel'dovich Effect measurements. We use three models for
the gas distribution: (1) an isothermal beta-model fit jointly to the X-ray
data at radii beyond 100 kpc and to all of the SZE data,(2) a non-isothermal
double beta-model fit jointly to all of the X-ray and SZE data, and (3) an
isothermal beta-model fit only to the SZE spatial data. We show that the simple
isothermal model well characterizes the intracluster medium (ICM) outside of
the cluster core in clusters with a wide range of morphological properties. The
X-ray and SZE determinations of mean gas mass fractions for the 100 kpc-cut
isothermal beta-model are fgas(X-ray)=0.110 +0.003-0.003 +0.006-0.018 and
fgas(SZE)=0.116 +0.005-0.005 +0.009-0.026, where uncertainties are statistical
followed by systematic at 68% confidence. For the non-isothermal double
beta-model, fgas(X-ray)=0.119 +0.003-0.003 +0.007-0.014 and fgas(SZE)=0.121
+0.005-0.005 +0.009-0.016. For the SZE-only model, fgas(SZE)=0.120 +0.009-0.009
+0.009-0.027. Our results indicate that the ratio of the gas mass fraction
within r2500 to the cosmic baryon fraction is 0.68 +0.10-0.16 where the range
includes statistical and systematic uncertainties. By assuming that cluster gas
mass fractions are independent of redshift, we find that the results are in
agreement with standard LambdaCDM cosmology and are inconsistent with a flat
matter dominated universe.Comment: ApJ, submitted. 47 pages, 5 figures, 8 table
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