346 research outputs found
Radio Jet-Ambient Medium Interactions on Parsec Scales in the Blazar 1055+018
As part of our study of the magnetic fields of AGN we have recently observed
a large sample of blazars with the Very Long Baseline Array. Here we report the
discovery of a striking two-component jet in the source 1055+018, consisting of
an inner spine with a transverse magnetic field, and a fragmentary but distinct
boundary layer with a longitudinal magnetic field. The polarization
distribution in the spine strongly supports shocked-jet models while that in
the boundary layer suggests interaction with the surrounding medium. This
behavior suggests a new way to understand the differing polarization properties
of strong- and weak-lined blazars.Comment: LaTex; 10 pages; 6 figures; reference fix; to appear in ApJL, 518,
1999 June 2
Utilizing x-ray computed tomography for heritage conservation : the case of megalosaurus bucklandii
Of key importance to any cultural institution is the practice of conservation, the method by which specimens at risk of severe degradation or destruction are treated to ensure that they survive into the future. However, surface inspection is often insufficient to properly inform conservators of the best treatment approach, and where there is little to no record of the conservational history of an object it can be difficult to identify exactly what form of conservation has been undertaken. X-Ray Computed Tomography (XCT) grants a way to overcome these issues by allowing conservators to non-destructively investigate the subsurface details of an artefact to provide essential information on condition of a specimen. Here, the potential of this approach is demonstrated using the first XCT scans of the iconic dentary of Megalosaurus bucklandii Mantell, 1827 (1); the first dinosaur ever named and described scientifically. XCT analysis reveals that the degree of repair is less extensive than previously thought and also elucidates two different material types, M1 and M2, thought to be representative of at least two phases of repair. Finally the potential of this approach is further explored, highlighting its importance for conservation practice, identifying forgeries and hoaxes in addition to potential applications in public engagement
Resonant Kelvin-Helmholtz modes in sheared relativistic flows
Qualitatively new aspects of the (linear and non-linear) stability of sheared
relativistic (slab) jets are analyzed. The linear problem has been solved for a
wide range of jet models well inside the ultrarelativistic domain (flow Lorentz
factors up to 20; specific internal energies ). As a distinct
feature of our work, we have combined the analytical linear approach with
high-resolution relativistic hydrodynamical simulations, which has allowed us
i) to identify, in the linear regime, resonant modes specific to the
relativistic shear layer ii) to confirm the result of the linear analysis with
numerical simulations and, iii) more interestingly, to follow the instability
development through the non-linear regime. We find that very high-order
reflection modes with dominant growth rates can modify the global, long-term
stability of the relativistic flow. We discuss the dependence of these resonant
modes on the jet flow Lorentz factor and specific internal energy, and on the
shear layer thickness. The results could have potential applications in the
field of extragalactic relativistic jets.Comment: Accepted for publication in Physical Review E. For better quality
images, please check
http://www.mpifr-bonn.mpg.de/staff/mperucho/Research.htm
Faraday rotation in the MOJAVE blazars: 3C 273 a case study
Radio polarimetric observations of Active Galactic Nuclei can reveal the
magnetic field structure in the parsec-scale jets of these sources. We have
observed the gamma-ray blazar 3C 273 as part of our multi-frequency survey with
the Very Long Baseline Array to study Faraday rotation in a large sample of
jets. Our observations re-confirm the transverse rotation measure gradient in
3C 273. For the first time the gradient is seen to cross zero which is further
indication for a helical magnetic field and spine-sheath structure in the jet.
We believe the difference to previous epochs is due to a different part of the
jet being illuminated in our observations.Comment: 6 pages, 3 figures. To appear in the proceedings of "Beamed and
Unbeamed Gamma-rays from Galaxies", held in Muonio, Finland, April 11-15,
2011. Journal of Physics: Conference Serie
Interleukin 21 inhibits cancer-mediated FOXP3 induction in naïve human CD4 T cells
IL-21 is known to promote anti-tumour immunity due to its ability to promote T cell responses and counteract Treg-mediated suppression. It has also been shown to limit Treg frequencies during tumour-antigen stimulations. However, whether this represents inhibition of FOXP3 induction in naïve CD4 T cells or curtailed expansion of natural Treg remains unclear. Moreover, whether this effect is maintained in an environment of tumour-derived immunosuppressive factors is not known. Here, we show that in the context of a number of cancers, naïve CD45RA+ CD4 T cells are induced to express high levels of FOXP3, and that FOXP3 expression correlates with inhibition of T cell proliferation. FOXP3 expression was most potently induced by tumours secreting higher levels of total and active TGFβ1 and this induction could be potently counteracted with IL-21, restoring T cell proliferation. We conclude that Treg induction in naïve T cells is a common phenomenon amongst a number of different cancers and that the ability of IL-21 to counteract this effect is further evidence of its promise in cancer therapy
Evidence for early disk-locking among low-mass members of the Orion Nebula Cluster
We present high-resolution spectroscopic observations for 91 PMS stars in ONC
with masses in the range 0.10-0.25Msun carried out with the multi-fiber
spectrograph FLAMES@ESO. Our aim is to better understand the disk-locking
scenario in very low-mass stars. We have derived radial velocities, vsini, and
full width at 10% of the Halpha emission peak. Using published measurements of
infrared excess as disk tracer, and equivalent width of the NIR CaII line
lambda8542, mid-IR difference [3.6]-[8.0]micron derived by Spitzer data, and
10% Halpha width as diagnostic of the level of accretion, we have looked for
any correlation between vsini divided by the radius and presence of disk and
accretion. Four low-mass stars are SB2 systems. The distribution of rotation
periods derived from our vsini measurements is unimodal with a peak of few
days. Our is lower than the one expected for a random distribution. We
find no evidence for a population of fast rotators close to the break-up
velocity. A clear correlation between vsini/R and Delta(Ic-K) has been found.
While for stars with no circumstellar disk a spread in the rotation rates is
seen, stars with a circumstellar disk show an abrupt drop in their rotation
rates by a factor of ~5. On the other hand, only a partial correlation between
vsini and accretion is observed when other indicators are used. The X-ray
coronal activity level shows no dependence on vsini/R suggesting that all stars
are in a saturated regime limit. The critical velocity is probably below our
vsini detection limit of 9 km/s. The ONC low-mass stars in our sample at
present seem to be not locked, but the clear correlation we find between
rotation and IR color excess suggests that they were locked once. In addition,
the percentage of accretors seems to scale inversely to the stellar mass.Comment: 16 pages, 2 Tables, 17 figures. Accepted by Astronomy and
Astrophysics. Full version of abstract is available in the manuscrip
'Caught Between a Rock and a Hard Place': Anti-discrimination Legislation in the Liberal State and the Fate of the Australian Disability Discrimination Act
This article offers a critical analysis of some of the practical implications for disabled people of the Disability Discrimination Act of 1992. Specifically, it raises questions about politics and the role of the law as an instrument of social change?taking greater account of the interests of disabled people?on the one hand, and of the reliance of the social model of disability on a strategy based upon legal rights on the other. The article also suggests that the constraining effects of Australia's constitutional protections of rights and its federal system of government hinder the mildly progressive elements of the Disability Discrimination Act. To illustrate this, the paper employs empirical evidence to suggest that these effects have been exacerbated by the passage of the Human Rights Legislation Amendment Act in 1999
Review Article: Rethinking Holder
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68947/2/10.1177_096394709800700104.pd
- …