2,054,362 research outputs found
Distant FR I radio galaxies in the Hubble Deep Field: implications for the cosmological evolution of radio-loud AGN
Deep and high resolution radio observations of the Hubble Deep Field and
flanking fields have shown the presence of two distant edge-darkened FR I radio
galaxies, allowing for the first time an estimate of their high redshift space
density. If it is assumed that the space density of FR I radio galaxies at z>1
is similar to that found in the local universe, then the chance of finding two
FR I radio galaxies at these high radio powers in such a small area of sky is
1
than at present, effectively ruling out the possibility that FR I radio sources
undergo no cosmological evolution. We suggest that FR I and FR II radio
galaxies should not be treated as intrinsically distinct classes of objects,
but that the cosmological evolution is simply a function of radio power with FR
I and FR II radio galaxies of similar radio powers undergoing similar
cosmological evolutions. Since low power radio galaxies have mainly FR I
morphologies and high power radio galaxies have mainly FR II morphologies, this
results in a generally stronger cosmological evolution for the FR IIs than the
FR Is. We believe that additional support from the V/Vmax test for evolving and
non-evolving populations of FR IIs and FR Is respectively is irrelevant, since
this test is sensitive over very different redshift ranges for the two classes.Comment: LaTeX, 6 pages, 3 figs. To appear in MNRA
In vitro immunosuppressive effects of FR 900506 on human T lymphocyte alloactivation
FR 900506 (FR) is a new immunosuppressive drug which prolongs allograft survival. Our studies have compared the in vitro inhibitory effects of FR and cyclosporine (CsA) on human lymphocyte proliferation. Considerably lower doses of FR were required to induce inhibition of lymphocyte proliferation induced by concanavalin A (Con A) stimulation or in primary mixed lymphocyte reactions (MLR). Similar differences between FR and CsA were observed with the secondary stimulation of alloactivated T cells generated in MLR or propagated from liver transplant biopsies. These observations provide further evidence that FR is about 500 fold more potent than CsA and may be a useful immunosuppressive agent in organ transplantation
The Entrainment-Limited Evolution of FR II Sources: Maximum Sizes and A Possible Connection to FR Is
We construct a simple theoretical model to investigate how entrainment
gradually erodes high-speed FR II jets. This process is described by embedding
a mixing-layer model developed originally to describe FR I objects in a
self-similar model for the lobe structure of classical FR II sources. Following
the classical FR II models, we assume that the lobe is dominated by the
particles injected from the central jet. The entrainment produces a boundary
shear layer which acts at the interface between the dense central jet and the
less denser surrounding lobe, and the associated erosion of the jet places
interesting limits on the maximum size of FR II sources. The model shows that
this limit depends mainly on the initial bulk velocity of the relativistic jet
triggered. The bulk velocities of FR IIs suggested by our model are in good
agreement with that obtained from direct pc-scale observations on ordinary
radio galaxies and quasars. Finally, we discuss how FR IIs may evolve into FR
Is upon reaching their maximum, entrainment-limited sizes.Comment: 9 pages, 5 figures, accepted for publication in MNRA
An extended range of stable-symmetric-conservative Flux Reconstruction correction functions
The Flux Reconstruction (FR) approach offers an efficient route to achieving high-order accuracy on unstructured grids. Additionally, FR offers a flexible framework for defining a range of numerical schemes in terms of so-called FR correction functions. Recently, a one-parameter family of FR correction functions were identified that lead to stable schemes for 1D linear advection problems. In this study we develop a procedure for identifying an extended range of stable, symmetric, and conservative FR correction functions. The procedure is applied to identify ranges of such correction functions for various orders of accuracy. Numerical experiments are undertaken, and the results found to be in agreement with the theoretical findings
Laser spectroscopy of francium isotopes at the borders of the region of reflection asymmetry
The magnetic dipole moments and changes in mean-square charge radii of the
neutron-rich isotopes were measured with the
newly-installed Collinear Resonance Ionization Spectroscopy (CRIS) beam line at
ISOLDE, CERN, probing the to atomic
transition. The values for
and follow the observed increasing
slope of the charge radii beyond . The charge radii odd-even
staggering in this neutron-rich region is discussed, showing that
has a weakly inverted odd-even staggering while
has normal staggering. This suggests that both isotopes
reside at the borders of a region of inverted staggering, which has been
associated with reflection-asymmetric shapes. The value supports a shell model configuration for the
ground state. The values support the tentative
spin, and point to a intruder ground state configuration.Comment: Accepted for publication with Physical Review
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