22,833 research outputs found
The X-ray coronae of the two brightest galaxies in the Coma cluster
We use deep Chandra X-ray Observatory observations to examine the coronae of
the two brightest cluster galaxies in the Coma cluster of galaxies, NGC 4874
and NGC 4889. We find that NGC 4889 hosts a central depression in X-ray surface
brightness consistent with a cavity or pair of cavities of radius 0.6 kpc. If
the central cavity is associated with an AGN outburst and contains relativistic
material, its enthalpy should be around 5x10^55 erg. The implied heating power
of this cavity would be around an order of magnitude larger than the energy
lost by X-ray emission. It would be the smallest and youngest known cavity in a
brightest cluster galaxy and the lack of over pressuring implies heating is
still gentle. In contrast, NGC 4874 does not show any evidence for cavities,
although it hosts a well-known wide-angle-tail radio source which is visible
outside the region occupied by the X-ray corona. These two galaxies show that
AGN feedback can behave in varied ways in the same cluster environment.Comment: 11 pages, 11 figures, accepted by MNRA
Optimal Remote State Preparation
We prove that it is possible to remotely prepare an ensemble of non-commuting
mixed states using communication equal to the Holevo information for this
ensemble. This remote preparation scheme may be used to convert between
different ensembles of mixed states in an asymptotically lossless way,
analogous to concentration and dilution for entanglement.Comment: 4 pages, no figure
Optical Spectroscopy of the IRAS 1-Jy Sample of Ultraluminous Infrared Galaxies
This paper discusses the optical spectroscopic properties of the IRAS 1-Jy
sample of ultraluminous infrared galaxies (ULIGs). One hundred and eight of the
118 1-Jy ULIGs have been observed at dlambda = 8.3 AA resolution over the
wavelength range ~4500 A -- 8900 A. These data are combined with large,
previously published sets of optical spectroscopic data of lower luminosity
infrared galaxies to look for systematic trends with infrared luminosity over
the luminosity range L_ir ~ 10^{10.5}-10^{13} L_sun. As found in previous
studies, the fraction of Seyfert galaxies among luminous infrared galaxies
increases abruptly above L_ir ~ 10^{12.3} L_sun --- about 50% of the galaxies
with L_ir > 10^{12.3} L_sun present Seyfert characteristics. Many of the
optical and infrared spectroscopic properties of the Seyfert galaxies are
consistent with the presence of a genuine active galactic nucleus (AGN). About
30% of these galaxies are Seyfert 1s with broad-line regions similar to those
of optical quasars. The percentage of Seyfert 1 ULIGs increases with infrared
luminosity, contrary to the predictions of the standard unification model for
Seyfert galaxies. Comparisons of the broad-line luminosities of optical and
obscured Seyfert 1 ULIGs with those of optically selected quasars of comparable
bolometric luminosity suggest that the dominant energy source in most of these
ULIGs is the same as in optical quasars, namely mass accretion onto a
supermassive black hole, rather than a starburst. These results are consistent
with recently published ISO, ASCA, and VLBI data. (abridged)Comment: Text and 23 figures (45 pages), Tables 1 - 6 (16 pages
Nonclassical Fields and the Nonlinear Interferometer
We demonstrate several new results for the nonlinear interferometer, which
emerge from a formalism which describes in an elegant way the output field of
the nonlinear interferometer as two-mode entangled coherent states. We clarify
the relationship between squeezing and entangled coherent states, since a weak
nonlinear evolution produces a squeezed output, while a strong nonlinear
evolution produces a two-mode, two-state entangled coherent state. In between
these two extremes exist superpositions of two-mode coherent states manifesting
varying degrees of entanglement for arbitrary values of the nonlinearity. The
cardinality of the basis set of the entangled coherent states is finite when
the ratio is rational, where is the nonlinear strength. We
also show that entangled coherent states can be produced from product coherent
states via a nonlinear medium without the need for the interferometric
configuration. This provides an important experimental simplification in the
process of creating entangled coherent states.Comment: 21 pages, 2 figure
Monogamy and polygamy for multi-qubit entanglement using R\'enyi entropy
Using R\'enyi- entropy to quantify bipartite entanglement, we prove
monogamy of entanglement in multi-qubit systems for . We also
conjecture a polygamy inequality of multi-qubit entanglement with strong
numerical evidence for with
.Comment: 19 pages, 2 figure
Astrophysical Constraints on Modifying Gravity at Large Distances
Recently, several interesting proposals were made modifying the law of
gravity on large scales, within a sensible relativistic formulation. This
allows a precise formulation of the idea that such a modification might account
for galaxy rotation curves, instead of the usual interpretation of these curves
as evidence for dark matter. We here summarize several observational
constraints which any such modification must satisfy, and which we believe make
more challenging any interpretation of galaxy rotation curves in terms of new
gravitational physics.Comment: References added, submitted to Classical & Quantum Gravit
The Prediction of Biological Nitrogen Fixation
In organic farming systems, biological nitrogen (N) fixation is crucial for short-term productivity and long-term sustainability. However, the estimation of biological N fixation is fraught with difficulties, and many equations attempt to estimate the process. As part of an organic research programme, biological N fixation was measured by the 15N dilution technique in the ley phases of 2 experimental organic ley-arable rotations at 2 sites, between 1997 and 2000. Hence, N fixation has been determined on N partitioned to above-ground biomass. The measured values have been compared with N fixation estimates calculated from the equations proposed by Korsaeth & Eltun (2000) and Hogh-Jensen et al. (2004)
Complete Characterization of Quantum-Optical Processes
The technologies of quantum information and quantum control are rapidly
improving, but full exploitation of their capabilities requires complete
characterization and assessment of processes that occur within quantum devices.
We present a method for characterizing, with arbitrarily high accuracy, any
quantum optical process. Our protocol recovers complete knowledge of the
process by studying, via homodyne tomography, its effect on a set of coherent
states, i.e. classical fields produced by common laser sources. We demonstrate
the capability of our protocol by evaluating and experimentally verifying the
effect of a test process on squeezed vacuum.Comment: 5 pages, 4 figure
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