43 research outputs found
The cosomological evolution of the environments of powerful radio galaxies
We present the results from the analysis of 26 extragalactic radio sources of
type FRII which were observed with the VLA at 5 GHz and around the 1.4 GHz
band. The sources were selected to have redshifts in the range ,
radio powers between and angular size . We found
that the depolarisation and the rms variations in the rotation measure
increased with redshift. The flux values obtained from the observations were
used to derive by means of analytical modelling the jet--power, density of the
central environment, age of the source and its lobe pressure and the results
were then compared with the observations. We find no significant correlations
with the density parameter suggesting that the depolarisation and the rms
variations in the rotation measure are indicative of the environment becoming
more disordered rather than denser. The age and size of a source are correlated
and both were found to be independent of redshift and radio--power. Jet--power
strongly correlated with the radio--power. The lobe pressure was found to be
anti--correlated with size which could explain why there are no sources beyond
a few Mpc in size. We found no significant correlation between size and density
which demonstrates that the sample is a fair representation of the population.Comment: 2 pages, Cozumel AGN 2003 conference proceeding
The depolarisation properties of powerful extragalactic radio sources as a function of cosmic epoch
We use the observed polarisation properties of a sample of 26 powerful radio
galaxies and radio-loud quasars to constrain the conditions in the Faraday
screens local to the sources. We adopt the cosmological redshift, low-frequency
radio luminosity and physical size of the large-scale radio structures as our
`fundamental' parameters. We find no correlation of the radio spectral index
with any of the fundamental parameters. The observed rotation measure is also
independent of these parameters. The difference between the rotation measures
of the two lobes of an individual source as well as the dispersion of the
rotation measure show significant correlations with the source redshift, but
not with the radio luminosity or source size. Thus the small-scale structure
observed in the rotation measure is caused by a Faraday screen local to the
sources. The observed asymmetries between the lobes of our sources show no
significant trends with each other or other source properties. Finally, we show
that the commonly used model for the depolarisation of synchrotron radio
emission by foreground Faraday screens is inconsistent with our observations.
We apply alternative models to our data and show that they require a strong
increase of the dispersion of the rotation measure inside the Faraday screens
with cosmological redshift. Correcting our observations with these models for
redshift effects, we find a strong correlation of the depolarisation measure
with redshift and a significantly weaker correlation with radio luminosity. All
our results are consistent with a decrease in the order of the magnetic field
structure of the Faraday screen local to the sources for increasing
cosmological redshift. (abridged)Comment: 14 pages, 16 eps figures, accepted by MNRA
Mechanisms of particles in sensitization, effector function and therapy of allergic disease
Humans have always been in contact with natural airborne particles from many sources including biologic particulate matter (PM) which can exhibit allergenic properties. With industrialization, anthropogenic and combustion-derived particles have become a major fraction. Currently, an ever-growing number of diverse and innovative materials containing engineered nanoparticles (NPs) are being developed with great expectations in technology and medicine. Nanomaterials have entered everyday products including cosmetics, textiles, electronics, sports equipment, as well as food, and food packaging. As part of natural evolution humans have adapted to the exposure to particulate matter, aiming to protect the individual's integrity and health. At the respiratory barrier, complications can arise, when allergic sensitization and pulmonary diseases occur in response to particle exposure. Particulate matter in the form of plant pollen, dust mites feces, animal dander, but also aerosols arising from industrial processes in occupational settings including diverse mixtures thereof can exert such effects. This review article gives an overview of the allergic immune response and addresses specifically the mechanisms of particulates in the context of allergic sensitization, effector function and therapy. In regard of the first theme (i), an overview on exposure to particulates and the functionalities of the relevant immune cells involved in allergic sensitization as well as their interactions in innate and adaptive responses are described. As relevant for human disease, we aim to outline (ii) the potential effector mechanisms that lead to the aggravation of an ongoing immune deviation (such as asthma, chronic obstructive pulmonary disease, etc.) by inhaled particulates, including NPs. Even though adverse effects can be exerted by (nano)particles, leading to allergic sensitization, and the exacerbation of allergic symptoms, promising potential has been shown for their use in (iii) therapeutic approaches of allergic disease, for example as adjuvants. Hence, allergen-specific immunotherapy (AIT) is introduced and the role of adjuvants such as alum as well as the current understanding of their mechanisms of action is reviewed. Finally, future prospects of nanomedicines in allergy treatment are described, which involve modern platform technologies combining immunomodulatory effects at several (immuno-)functional levels
Biotechnological synthesis of Pd/Ag and Pd/Au nanoparticles for enhanced SuzukiâMiyaura cross-coupling activity
Bimetallic nanoparticle catalysts have attracted considerable attention due to their unique chemical and physical properties. The ability of metal-reducing bacteria to produce highly catalytically active monometallic nanoparticles is well known; however, the properties and catalytic activity of bimetallic nanoparticles synthesized with these organisms is not well understood. Here, we report the one-pot biosynthesis of Pd/Ag (bio-Pd/Ag) and Pd/Au (bio-Pd/Au) nanoparticles using the metal-reducing bacterium, Shewanella oneidensis, under mild conditions. Energy dispersive X-ray analyses performed using scanning transmission electron microscopy (STEM) revealed the presence of both metals (Pd/Ag or Pd/Au) in the biosynthesized nanoparticles. X-ray absorption near-edge spectroscopy (XANES) suggested a significant contribution from Pd(0) and Pd(II) in both bio-Pd/Ag and bio-Pd/Au, with Ag and Au existing predominately as their metallic forms. Extended X-ray absorption fine-structure spectroscopy (EXAFS) supported the presence of multiple Pd species in bio-Pd/Ag and bio-Pd/Au, as inferred from PdâPd, PdâO and PdâS shells. Both bio-Pd/Ag and bio-Pd/Au demonstrated greatly enhanced catalytic activity towards SuzukiâMiyaura cross-coupling compared to a monometallic Pd catalyst, with bio-Pd/Ag significantly outperforming the others. The catalysts were very versatile, tolerating a wide range of substituents. This work demonstrates a green synthesis method for novel bimetallic nanoparticles that display significantly enhanced catalytic activity compared to their monometallic counterparts
A comparison of the algorithms for hypertext notes network linearisation
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