13,890 research outputs found
The hybrid SZ power spectrum: Combining cluster counts and SZ fluctuations to probe gas physics
Sunyaev-Zeldovich (SZ) effect from a cosmological distribution of clusters
carry information on the underlying cosmology as well as the cluster gas
physics. In order to study either cosmology or clusters one needs to break the
degeneracies between the two. We present a toy model showing how complementary
informations from SZ power spectrum and the SZ flux counts, both obtained from
upcoming SZ cluster surveys, can be used to mitigate the strong cosmological
influence (especially that of sigma_8) on the SZ fluctuations. Once the strong
dependence of the cluster SZ power spectrum on sigma_8 is diluted, the cluster
power spectrum can be used as a tool in studying cluster gas structure and
evolution. The method relies on the ability to write the Poisson contribution
to the SZ power spectrum in terms the observed SZ flux counts. We test the toy
model by applying the idea to simulations of SZ surveys.Comment: 12 pages. 11 plots. MNRAS submitte
Study of the glass transition in the amorphous interlamellar phase of highly crystallized poly(ethylene terephthalate)
Poly(ethylene terephthalate) (PET) is a semi--crystalline polymer that can be
crystallized to different degrees heating from the amorphous state. Even when
primary crystallization has been completed, secondary crystallization can take
place with further annealing and modify the characteristics of the amorphous
interlamellar phase. In this work we study the glass transition of highly
crystallized PET and in which way it is modified by secondary crystallization.
Amorphous PET samples were annealed for 4 hours at temperatures between 140C
and 180C. The secondary crystallization process was monitored by differential
scanning calorimetry and the glass transition of the remaining interllamelar
amorphous phase was studied by Thermally Stimulated Depolarization Currents
measurements. Non--isothermal window polarization is employed to resolve the
relaxation in modes with a well--defined relaxation time that are subsequently
adjusted to several standard models. Analysis of experimental results, show
that cooperativity is reduced to a great extend in the interlamellar amorphous
regions. The evolution of the modes on crystallization temperature reveals that
large scale movements are progressively replaced by more localized ones, with
higher frequency, as crystallization takes place at higher temperatures. As a
consequence, the glass transition temperature of the amorphous interlamellar
phase tends to lower values for higher annealing temperatures. Evolution of
calorimetric scans of the glass transition are simulated from the obtained
results and show the same behaviour. The interpretation of these results in
terms of current views about secondary crystallization is discussed.Comment: 30 pages, 5 tables, 12 figures; figure 5 modifie
Observing the Sunyaev-Zel'dovich Effect Closer to Home
Hot gas trapped in a dark matter halo will produce a decrement in the surface
brightness of the microwave background, the Sunyaev-Zel'dovich (SZ) effect.
While massive clusters produce the strongest central SZ decrements, we point
out that a local galaxy halo, specifically the halo of M31, may be one of the
brightest integrated SZ sources in the sky. For various realistic gas
distributions consistent with current X-ray limits, we show that the integrated
SZ decrement from M31 will be comparable to decrements already detected in more
distant sources, provided its halo contains an appreciable quantity of hot gas.
A measurement of this decrement would provide direct information on the mass,
spatial distribution and thermodynamic state of hot gas in a low-mass halo, and
could place important constraints on current models of galaxy formation.
Detecting such an extended (~ 10 degree), low-amplitude signal will be
challenging, but should be possible with all-sky SZ maps from satellite
missions such as the Wilkinson Microwave Anisotropy Probe or the Planck
Surveyor.Comment: 5 pages, 3 figures; submitted to MNRA
Radiative capture reaction for Ne formation within a full three-body model
Background: The breakout from the hot Carbon-Nitrogen-Oxigen (CNO) cycles can
trigger the rp-process in type I x-ray bursts. In this environment, a
competition between and the
two-proton capture reaction is
expected.
Purpose: Determine the three-body radiative capture reaction rate for
formation including sequential and direct, resonant and
non-resonant contributions on an equal footing.
Method: Two different discretization methods have been applied to generate
Ne states in a full three-body model: the analytical transformed
harmonic oscillator method and the hyperspherical adiabatic expansion method.
The binary --O interaction has been adjusted to reproduce the known
spectrum of the unbound F nucleus. The dominant contributions to
the reaction rate have been
calculated from the inverse photodissociation process.
Results: Three-body calculations provide a reliable description of Ne
states. The agreement with the available experimental data on Ne is
discussed. It is shown that the
reaction rates computed within the two methods agree in a broad range of
temperatures. The present calculations are compared with a previous theoretical
estimation of the reaction rate.
Conclusions: It is found that the full three-body model provides a reaction
rate several orders of magnitude larger than the only previous estimation. The
implications for the rp-process in type I x-ray bursts should be investigated.Comment: 10 pages, 10 figures. Corrected versio
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