100,197 research outputs found
ASAP : towards accurate, stable and accelerative penetrating-rank estimation on large graphs
Pervasive web applications increasingly require a measure of similarity among objects. Penetrating-Rank (P-Rank) has been one of the promising link-based similarity metrics as it provides a comprehensive way of jointly encoding both incoming and outgoing links into computation for emerging applications. In this paper, we investigate P-Rank efficiency problem that encompasses its accuracy, stability and computational time. (1) We provide an accuracy estimate for iteratively computing P-Rank. A symmetric problem is to find the iteration number K needed for achieving a given accuracy ε. (2) We also analyze the stability of P-Rank, by showing that small choices of the damping factors would make P-Rank more stable and well-conditioned. (3) For undirected graphs, we also explicitly characterize the P-Rank solution in terms of matrices. This results in a novel non-iterative algorithm, termed ASAP , for efficiently computing P-Rank, which improves the CPU time from O(n 4) to O( n 3 ). Using real and synthetic data, we empirically verify the effectiveness and efficiency of our approaches
Photodissociation of interstellar ArH+
Aims. Following the recent detection of 36ArH+ in the Crab nebula spectrum,
we have computed the photodissociation rate of ArH+ in order to constrain the
physical processes at work in this environment. Methods. Photodissociation
cross sections of ArH+ are computed in an ab initio approach including explicit
account of spin-orbit coupling. Results. We report the photodissociation cross
section of ArH+ as a function of wavelength. Photodissociation probabilities
are derived for different impinging radiation fields.The photodissociation
probability of for a very small unshielded cloud surrounded on all sides by the
unshielded InterStellar Radiation Field (ISRF) model described by Draine (1978)
is equal to 9.9e-12 s-1 and 1.9e-9 s-1 in the Crab nebula conditions. The
dependence on the visual extinction is obtained by using the Meudon Photon
Dominated Region (PDR) code and corresponding analytical fits are provided.
Conclusions. These data will help to produce a realistic chemical network to
interpret the observations. Photodissociation of ArH+ is found to be moderate
and the presence of this molecular ion is mainly dependent on the molecular
fractionComment: 11 pages, 6 Figures, Accepted in Astronomy Astrophysic
Dissociation energy and long-range potential of diatomic molecules from vibrational spacings - The halogens
Dissociation energy and long-range potential of diatomic molecules from vibrational spacings, halogen
Shape resonances and rotationally predissociating levels - The atomic collision time delay functions and quasibound level properties of H2 /Chi /1 Sigma g plus//
Atomic collision time delay functions and quasibound level properties of ground state of molecular hydroge
Adaptive Optics observations of LBQS 0108+0028: K-band detection of the host galaxy of a radio-quiet QSO at z=2
We report the first unambiguous detection of the host galaxy of a normal
radio-quiet QSO at high-redshift in K-band. The luminosity of the host
comprises about 35% of the total K-band luminosity. Assuming the average colour
of QSOs at z=2, the host would be about 5 to 6 mag brighter than an unevolved
L* galaxy placed at z=2, and 3 to 4 mag brighter than a passively evolved L*
galaxy at the same redshift. The luminosity of the host galaxy of the QSO would
thus overlap with the highest found in radio-loud QSOs and radio-galaxies at
the same redshift.Comment: Accepted to be published in MNRAS. 4 pages, 2 postscript figures.
Also available at http://www.mpa-garching.mpg.de/~itzia
Roche-lobe filling factor of mass-transferring red giants - the PIONIER view
Using the PIONIER visitor instrument that combines the light of the four
Auxiliary Telescopes of ESO's Very Large Telescope Interferometer, we measure
precisely the diameters of several symbiotic and related stars: HD 352, HD
190658, V1261 Ori, ER Del, FG Ser, and AG Peg. These diameters - in the range
of 0.6 to 2.3 milli-arcseconds - are used to assess the filling factor of the
Roche lobe of the mass-losing giants and provide indications on the nature of
the ongoing mass transfer. We also provide the first spectroscopic orbit of ER
Del, based on CORAVEL and HERMES/Mercator observations. The system is found to
have an eccentric orbit with a period of 5.7 years. In the case of the
symbiotic star FG Ser, we find that the diameter is changing by 13% over the
course of 41 days, while the observations of HD 352 are indicative of an
elongation. Both these stars are found to have a Roche filling factor close to
1, as is most likely the case for HD 190658 as well, while the three other
stars have factors below 0.5-0.6. Our observations reveal the power of
interferometry for the study of interacting binary stars - the main limitation
in our conclusions being the poorly known distances of the objects.Comment: A&A, in pres
A ring galaxy at z=1 lensed by the cluster Abell 370
We present a study of a very peculiar object found in the field of the
cluster-lens Abell 370. This object displays, in HST imaging, a spectacular
morphology comparable to nearby ring-galaxies. From spectroscopic observations
at the CFHT, we measured a redshift of based on the identification of
[O ii] 3727 \AA and [Ne v] 3426 \AA emission lines. These emission lines are
typical of starburst galaxies hosting a central active nucleus and are in good
agreement with the assumption that this object is a ring-galaxy. This object is
also detected with ISO in the LW2 and LW3 filters, and the mid Infra-Red (MIR)
flux ratio favors a Seyfert 1 type. The shape of the ring is gravitationally
distorted by the cluster-lens, and most particularly by a nearby cluster
elliptical galaxy. Using the cluster mass model, we can compute its intrinsic
shape. Requiring that the outer ring follows an ellipse we put constraints on
the M/L ratio of the nearby galaxy and derive a magnification factor of 2.5
0.2. The absolute luminosities of the source are then $L_B = 1.3 \
10^{12} L_{B \odot}\nu_\nu \simeq 4. 10^{10}_\odot$ in the
mid-IR.Comment: 5 pages, 5 figures, uses aa.cls, accepted to A&A Letters. Minor
changes, Figure 1 revisited and typos adde
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