13,586 research outputs found
Simulated X-ray Cluster Temperature Maps
Temperature maps are presented of the 9 largest clusters in the mock
catalogues of Muanwong et al. for both the Preheating and Radiative models. The
maps show that clusters are not smooth, featureless systems, but contain a
variety of substructure which should be observable. The surface brightness
contours are generally elliptical and features that are seen include cold
clumps, hot spiral features, and cold fronts. Profiles of emission-weighted
temperature, surface brightness and emission-weighted pressure across the
surface brightness discontinuities seen in one of the bimodal clusters are
consistent with the cold front in Abell 2142 observed by Markevitch et al.Comment: Submitted to Monthly Notices Royal Astronomical Societ
Correction of non-linearity effects in detectors for electron spectroscopy
Using photoemission intensities and a detection system employed by many
groups in the electron spectroscopy community as an example, we have
quantitatively characterized and corrected detector non-linearity effects over
the full dynamic range of the system. Non-linearity effects are found to be
important whenever measuring relative peak intensities accurately is important,
even in the low-countrate regime. This includes, for example, performing
quantitative analyses for surface contaminants or sample bulk stoichiometries,
where the peak intensities involved can differ by one or two orders of
magnitude, and thus could occupy a significant portion of the detector dynamic
range. Two successful procedures for correcting non-linearity effects are
presented. The first one yields directly the detector efficiency by measuring a
flat-background reference intensity as a function of incident x-ray flux, while
the second one determines the detector response from a least-squares analysis
of broad-scan survey spectra at different incident x-ray fluxes. Although we
have used one spectrometer and detection system as an example, these
methodologies should be useful for many other cases.Comment: 13 pages, 12 figure
Hadamard States and Adiabatic Vacua
Reversing a slight detrimental effect of the mailer related to TeXabilityComment: 10pages, LaTeX (RevTeX-preprint style
Lyapunov exponents as a dynamical indicator of a phase transition
We study analytically the behavior of the largest Lyapunov exponent
for a one-dimensional chain of coupled nonlinear oscillators, by
combining the transfer integral method and a Riemannian geometry approach. We
apply the results to a simple model, proposed for the DNA denaturation, which
emphasizes a first order-like or second order phase transition depending on the
ratio of two length scales: this is an excellent model to characterize
as a dynamical indicator close to a phase transition.Comment: 8 Pages, 3 Figure
The effect of radiative cooling on scaling laws of X-ray groups and clusters
We have performed cosmological simulations in a ÎCDM cosmology with and without radiative cooling in order to study the effect of cooling on the cluster scaling laws. Our simulations consist of 4.1 million particles each of gas and dark matter within a box size of 100 h-1 Mpc, and the run with cooling is the largest of its kind to have been evolved to z = 0. Our cluster catalogs both consist of over 400 objects and are complete in mass down to ~1013 h-1 Mâ. We contrast the emission-weighted temperature-mass (Tew-M) and bolometric luminosity-temperature (Lbol-Tew) relations for the simulations at z = 0. We find that radiative cooling increases the temperature of intracluster gas and decreases its total luminosity, in agreement with the results of Pearce et al. Furthermore, the temperature dependence of these effects flattens the slope of the Tew-M relation and steepens the slope of the Lbol-Tew relation. Inclusion of radiative cooling in the simulations is sufficient to reproduce the observed X-ray scaling relations without requiring excessive nongravitational energy injection
Fisher-information condition for enhanced signal detection via stochastic resonance
Various situations where a signal is enhanced by noise through stochastic resonance are now known. This paper contributes to determining general conditions under which improvement by noise can be a priori decided as feasible or not. We focus on the detection of a known signal in additive white noise. Under the assumptions of a weak signal and a sufficiently large sample size, it is proved, with an inequality based on the Fisher information, that improvement by adding noise is never possible, generically, in these conditions. However, under less restrictive conditions, an example of signal detection is shown with favorable action of adding noise.Fabing Duan, François Chapeau-Blondeau, Derek Abbot
The Sunyaev-Zel'dovich temperature of the intracluster medium
The relativistic Sunyaev-Zel'dovich (SZ) effect offers a method, independent
of X-ray, for measuring the temperature of the intracluster medium (ICM) in the
hottest systems. Here, using N-body/hydrodynamic simulations of three galaxy
clusters, we compare the two quantities for a non-radiative ICM, and for one
that is subject both to radiative cooling and strong energy feedback from
galaxies. Our study has yielded two interesting results. Firstly, in all cases,
the SZ temperature is hotter than the X-ray temperature and is within ten per
cent of the virial temperature of the cluster. Secondly, the mean SZ
temperature is less affected by cooling and feedback than the X-ray
temperature. Both these results can be explained by the SZ temperature being
less sensitive to the distribution of cool gas associated with cluster
substructure. A comparison of the SZ and X-ray temperatures (measured for a
sample of hot clusters) would therefore yield interesting constraints on the
thermodynamic structure of the intracluster gas.Comment: This version accepted for publication in MNRAS following minor
revisio
Founders\u27 Day 1960
Founders\u27 Day 1960 with speakers President Harvey Rice, Professor O.T. Walter, as well as Edmund Wood, Kay Lorans, Fred Koch, and George Bonniwell.
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