86,467 research outputs found
Dual frequency VSOP imaging of the jet in S5 0836+710
The luminous high-redshift (z=2.17) quasar S50836+710 has been observed in
October 1997 with the VSOP at 1.6 GHz and 5 GHz. We report here a previously
unpublished image made from the data at 1.6 GHz and compare the structure of a
relativistic jet in this quasazr at the two frequencies. We present a spectral
index image tracing spectral properties of the jet up to ~40 milliarcsecond
distance from the nucleus. The curved jet ridge line observed in the images and
the spectral index distribution can be described by Kelvin-Helmholtz
instability developing in a relativistic outflow with a Mach number of ~6. In
this description, the overall ridge line of the jet is formed by the helical
surface mode of Kelvin-Helmholtz instability, while areas of flatter spectral
index embedded into the flow correspond to pressure enhancements produced by
the elliptical surface mode of the instability. An alternative explanation
involving a sequence of slowly dissipating shocks cannot be ruled out at this
point.Comment: 7 pages, 4 figures, pasj00.cls. Submitted to PASJ. (Corrected figure
orientation
Observation of the nonlinear Wood's anomaly on periodic arrays of nickel nanodimers
Linear and nonlinear magneto-photonic properties of periodic arrays of nickel
nanodimers are governed by the interplay of the (local) optical response of
individual nanoparticles and (non-local) diffraction phenomena, with a striking
example of Wood's anomaly. Angular and magnetic-field dependencies of the
second harmonic intensity evidence Wood's anomaly when new diffraction orders
emerge. Near-infrared spectroscopic measurements performed at different optical
wavelengths and grating constants discriminate between the linear and nonlinear
excitation mechanisms of Wood's anomalies. In the nonlinear regime the Wood's
anomaly is characterized by an order-of-magnitude larger effect in intensity
redistribution between the diffracted beams, as compared to the linear case.
The nonlinear Wood's anomaly manifests itself also in the nonlinear magnetic
contrast highlighting the prospects of nonlinear magneto-photonics.Comment: 8 pages, 6 figure
Polly's Polyhedral Scheduling in the Presence of Reductions
The polyhedral model provides a powerful mathematical abstraction to enable
effective optimization of loop nests with respect to a given optimization goal,
e.g., exploiting parallelism. Unexploited reduction properties are a frequent
reason for polyhedral optimizers to assume parallelism prohibiting dependences.
To our knowledge, no polyhedral loop optimizer available in any production
compiler provides support for reductions. In this paper, we show that
leveraging the parallelism of reductions can lead to a significant performance
increase. We give a precise, dependence based, definition of reductions and
discuss ways to extend polyhedral optimization to exploit the associativity and
commutativity of reduction computations. We have implemented a
reduction-enabled scheduling approach in the Polly polyhedral optimizer and
evaluate it on the standard Polybench 3.2 benchmark suite. We were able to
detect and model all 52 arithmetic reductions and achieve speedups up to
2.21 on a quad core machine by exploiting the multidimensional
reduction in the BiCG benchmark.Comment: Presented at the IMPACT15 worksho
The Core Mass Function in the Massive Protocluster G286.21+0.17 revealed by ALMA
We study the core mass function (CMF) of the massive protocluster
G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array via 1.3~mm
continuum emission at a resolution of 1.0\arcsec\ (2500~au). We have mapped a
field of 5.3\arcmin5.3\arcmin\ centered on the protocluster clump. We
measure the CMF in the central region, exploring various core detection
algorithms, which give source numbers ranging from 60 to 125, depending on
parameter selection. We estimate completeness corrections due to imperfect flux
recovery and core identification via artificial core insertion experiments. For
masses , the fiducial dendrogram-identified CMF can be fit
with a power law of the form
with , slightly shallower than, but still consistent with, the
index of the Salpeter stellar initial mass function of 1.35.
Clumpfind-identified CMFs are significantly shallower with
. While raw CMFs show a peak near ,
completeness-corrected CMFs are consistent with a single power law extending
down to , with only a tentative indication of a shallowing
of the slope around . We discuss the implications of these
results for star and star cluster formation theories.Comment: 11 pages, accepted by Ap
Molecular Gas and Star formation in ARP 302
We present the Submillimeter Array observation of the CO J=2-1 transition
towards the northern galaxy, ARP 302N, of the early merging system, ARP 302.
Our high angular resolution observation reveals the extended spatial
distribution of the molecular gas in ARP 302N. We find that the molecular gas
has a very asymmetric distribution with two strong concentrations on either
side of the center together with a weaker one offset by about 8 kpc to the
north. The molecular gas distribution is also found to be consistent with that
from the hot dust as traced by the 24 micro continuum emission observed by the
Spitzer. The line ratio of CO J=2-1/1-0 is found to vary strongly from about
0.7 near the galaxy center to 0.4 in the outer part of the galaxy. Excitation
analysis suggests that the gas density is low, less than 10 cm, over
the entire galaxy. By fitting the SED of ARP 302N in the far infrared we obtain
a dust temperature of =26-36 K and a dust mass of M=2.0--3.6 M. The spectral index of the radio
continuum is around 0.9. The spatial distribution and spectral index of the
radio continuum emission suggests that most of the radio continuum emission is
synchrotron emission from the star forming regions at the nucleus and
ARP302N-cm. The good spatial correspondance between the 3.6 cm radio continuum
emission, the Spitzer 8 & 24 m data and the high resolution CO J=2-1
observation from the SMA shows that there is the asymmetrical star forming
activities in ARP 302N.Comment: 19 pages, 8 figures, accepted by A
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