14,549 research outputs found
Do Individuals Learn To Maximise Expected Utility?
Violations of expected utility theory are sometimes attributed to imprecise preferences interacting with a lack of learning opportunity in the experimental laboratory. This paper reports a test of whether conditions which facilitate objective probability learning yield decisions better described by expected utility theory than is the case in experiments devoid of learning opportunity. The data show that expected utility maximising behaviour increases with the learning opportunity, but so too do systematic violations. Learning, therefore, may exacerbate choice anomalies.
Narrow Band X-ray Photometry as a Tool for Studying Galaxy and Cluster Mass Distributions
We explore the utility of narrow band X-ray surface photometry as a tool for
making fully Bayesian, hydrostatic mass measurements of clusters of galaxies,
groups and early-type galaxies. We demonstrate that it is sufficient to measure
the surface photometry with the Chandra X-ray observatory in only three (rest
frame) bands (0.5--0.9 keV, 0.9--2.0 keV and 2.0--7.0 keV) in order to
constrain the temperature, density and abundance of the hot interstellar medium
(ISM). Adopting parametrized models for the mass distribution and radial
entropy profile and assuming spherical symmetry, we show that the constraints
on the mass and thermodynamic properties of the ISM that are obtained by
fitting data from all three bands simultaneously are comparable to those
obtained by fitting similar models to the temperature and density profiles
derived from spatially resolved spectroscopy, as is typically done. We
demonstrate that the constraints can be significantly tightened when exploiting
a recently derived, empirical relationship between the gas fraction and the
entropy profile at large scales, eliminating arbitrary extrapolations at large
radii. This "Scaled Adiabatic Model" (ScAM) is well suited to modest
signal-to-noise data, and we show that accurate, precise measurements of the
global system properties are inferred when employing it to fit data from even
very shallow, snapshot X-ray observations. The well-defined asymptotic
behaviour of the model also makes it ideally suited for use in
Sunyaev-Zeldovich studies of galaxy clusters.Comment: 15 pages, 6 figures. Accepted for Publication in MNRA
Nucleation in a Fermi liquid at negative pressure
Experimental investigation of cavitation in liquid helium 3 has revealed a
singular behaviour in the degenerate region at low temperature. As the
temperature decreases below 80 mK, the cavitation pressure becomes
significantly more negative. To investigate this, we have extrapolated the
Fermi parameters in the negative pressure region. This allowed us to calculate
the zero sound velocity, which we found to remain finite at the spinodal limit
where the first sound velocity vanishes. We discuss the impact on the
nucleation of the gas phase in terms of a quantum stiffness of the Fermi
liquid. As a result we predict a cavitation pressure which is nearer to the
spinodal line than previously thought.Comment: 6 pages, 2 figures. To be published in Journal of Low Temperature
Physics, Proceedings of the International Symposium on Quantum Fluids and
Solids QFS200
The ELIXR Galaxy Survey. II: Baryons and Dark Matter in an Isolated Elliptical Galaxy
The Elliptical Isolated X-ray (ElIXr) Galaxy Survey is a volume-limited
(<110Mpc) study of optically selected, isolated, Lstar elliptical galaxies, to
provide an X-ray census of galaxy-scale (virial mass, Mvir < 1e13 Msun)
objects, and identify candidates for detailed hydrostatic mass modelling. In
this paper, we present a Chandra and XMM study of one such candidate, NGC1521,
and constrain its distribution of dark and baryonic matter. We find a
morphologically relaxed hot gas halo, extending almost to R500, that is well
described by hydrostatic models similar to the benchmark, baryonically closed,
Milky Way-mass elliptical galaxy NGC720. We obtain good constraints on the
enclosed gravitating mass (M500=3.8e12+/-1e12 Msun, slightly higher than
NGC\thin 720), and baryon fraction (fb500=0.13+/-0.03). We confirm at 8.2-sigma
the presence of a dark matter (DM) halo consistent with LCDM. Assuming a
Navarro-Frenk-White DM profile, our self-consistent, physical model enables
meaningful constraints beyond R500, revealing that most of the baryons are in
the hot gas. Within the virial radius, fb is consistent with the Cosmic mean,
suggesting that the predicted massive, quasi-hydrostatic gas halos may be more
common than previously thought. We confirm that the DM and stars conspire to
produce an approximately powerlaw total mass profile (rho \propto r^-alpha)
that follows the recently discovered scaling relation between alpha and optical
effective radius. Our conclusions are insensitive to modest, observationally
motivated, deviations from hydrostatic equilibrium. Finally, after correcting
for the enclosed gas fraction, the entropy profile is close to the self-similar
prediction of gravitational structure formation simulations, as observed in
massive galaxy clusters.Comment: Accepted for publication in the Astrophysical Journal. Minor
modifications to match accepted version. Conclusions unchanged. 18 pages, 11
figures and 3 table
Liquid ethylene-propylene copolymers
Oligomers are prepared by heating solid ethylene-propylene rubber in container that retains solid and permits liquid product to flow out as it is formed. Molecular weight and viscosity of liquids can be predetermined by process temperature. Copolymers have low viscosity for given molecular weight
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