31,998 research outputs found
Rapidity and pt dependence of identified-particle elliptic flow at RHIC
Elliptic flow has been measured by the BRAHMS experiment as a function of
transverse momentum and pseudorapidity for the Au+Au reaction at sqrt[s_{NN}] =
200 GeV. Identified-particle v2 (eta, pt) values were obtained with the two
BRAHMS spectrometers at pseudorapidities eta approximately equal to 0, 1, and
3.4. The results show that the differential v2(eta, pt) values for a given
particle type are essentially constant over the covered pseudorapidity range.
It is suggested that the dominant cause of the observed fall-off of the
integral v2 values going away from mid-rapidity is a corresponding softening of
the particle spectra .Comment: 4 pages, 2figure, Quark Matter 2006 parallel session contributio
Passive Mode-Locking of Monolithic InGaAs/AlGaAs Double Quantum Well Lasers at 42GHz Repetition Rate
Pulse trains with a 42GHz repetition rate were generated by monolithic InGaAs/AlGaAs double quantum well lasers at a wavelength of 985 [angstroms]. The cavity was electrically divided into three regions, one providing gain and the other two providing saturable absorption. The optical modulation has a depth greater than 98% and full-width at half-maximum under 6ps, and bias conditions for sustained mode-locking are determined
Isothermal shocks in Abell 2199 and 2A 0335+096?
We report on a partially circular X-ray surface brightness discontinuity
found at about 55 kpc from the centre of Abell 2199 with Chandra X-ray
observatory observations. Unlike cold fronts found in other clusters, the
feature shows no significant temperature change across it but has an apparent
density jump. We therefore identify it as a weak isothermal shock associated
with the central AGN and the inflation of its radio bubbles, as found in the
Perseus cluster. We examine a similar feature at 40 kpc radius found by
Mazzotta et al in 2A 0335+096, and conclude that it too may be an isothermal
shock. The change in density if these are shocks implies a Mach number of ~1.5.
If the isothermal nature of these features is confirmed by deeper observations,
the implication is that such shocks are common in clusters of galaxies, and are
an important mechanism for the transport of energy from a central supermassive
black hole into the cluster core.Comment: 5 pages, accepted by MNRAS, includes minor changes suggested by
refere
A deeper X-ray study of the core of the Perseus galaxy cluster: the power of sound waves and the distribution of metals and cosmic rays
We make a further study of the very deep Chandra observation of the X-ray
brightest galaxy cluster, A426 in Perseus. We examine the radial distribution
of energy flux inferred by the quasi-concentric ripples in surface brightness,
assuming they are due to sound waves, and show that it is a significant
fraction of the energy lost by radiative cooling within the inner 75-100 kpc,
where the cooling time is 4-5 Gyr, respectively. The wave flux decreases
outward with radius, consistent with energy being dissipated. Some newly
discovered large ripples beyond 100 kpc, and a possible intact bubble at 170
kpc radius, may indicate a larger level of activity by the nucleus a few 100
Myr ago. The distribution of metals in the intracluster gas peaks at a radius
of about 40 kpc and is significantly clumpy on scales of 5 kpc. The temperature
distribution of the soft X-ray filaments and the hard X-ray emission component
found within the inner 50 kpc are analysed in detail. The pressure due to the
nonthermal electrons, responsible for a spectral component interpreted as
inverse Compton emission, is high within 40 kpc of the centre and boosts the
power in sound waves there; it drops steeply beyond 40 kpc. We find no thermal
emission from the radio bubbles; in order for any thermal gas to have a filling
factor within the bubbles exceeding 50 per cent, the temperature of that gas
has to exceed 50 keV.Comment: Accepted by MNRAS. Now includes evidence for further ancient bubble
at 170 kpc radius, and minor changes suggested by referee. A version with
good quality figures is available from
http://www-xray.ast.cam.ac.uk/papers/perdetail2.pd
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