12,285 research outputs found
Luminosity function, sizes and FR dichotomy of radio-loud AGN
The radio luminosity function (RLF) of radio galaxies and radio-loud quasars
is often modelled as a broken power-law. The break luminosity is close to the
dividing line between the two Fanaroff-Riley (FR) morphological classes for the
large-scale radio structure of these objects. We use an analytical model for
the luminosity and size evolution of FRII-type objects together with a simple
prescription for FRI-type sources to construct the RLF. We postulate that all
sources start out with an FRII-type morphology. Weaker jets subsequently
disrupt within the quasi-constant density cores of their host galaxies and
develop turbulent lobes of type FRI. With this model we recover the slopes of
the power laws and the break luminosity of the RLF determined from
observations. The rate at which AGN with jets of jet power appear in the
universe is found to be proportional to . The model also roughly
predicts the distribution of the radio lobe sizes for FRII-type objects, if the
radio luminosity of the turbulent jets drops significantly at the point of
disruption. We show that our model is consistent with recent ideas of two
distinct accretion modes in jet-producing AGN, if radiative efficiency of the
accretion process is correlated with jet power.Comment: 13 pages, 1 figure, accepted by MNRA
Erratum: Luminosity function, sizes and FR dichotomy of radio-loud AGN
This erratum corrects a number of formulae containing mistakes in the paper
'Luminosity function, sizes and FR dichotomy of radio-loud AGN', 2007, MNRAS,
v. 381, p.1548. The corrections do not alter any of the conclusions in the
original paper.Comment: single page, no figures, erratum to MNRAS, 2007, v. 381, p. 154
Tracking Midwest manufacturing and productivity growth
Federal Reserve District, 7th ; Manufactures
Characterization of a thermally imidized soluble polyimide film
A soluble aromatic poly(amic acid) film was converted to a soluble polyimide by staging at 25 deg intervals to 325 C and characterized at each interval by several analytical methods. The behavior observed was consistent with an interpretation that a reduction occurred in molecular weight of the poly(amic acid) during the initial stages of cure before the ultimate molecular weight was achieved as a polyimide. This interpretation was supported by the results of solution viscosity, gel permeation chromatography, low angle laser light scattering photometry and infrared spectroscopy analysis. The results serve to increase the fundamental understanding of how polyimides are thermally formed from poly(amic acids)
Stability Properties of Strongly Magnetized Spine Sheath Relativistic Jets
The linearized relativistic magnetohydrodynamic (RMHD) equations describing a
uniform axially magnetized cylindrical relativistic jet spine embedded in a
uniform axially magnetized relativistically moving sheath are derived. The
displacement current is retained in the equations so that effects associated
with Alfven wave propagation near light speed can be studied. A dispersion
relation for the normal modes is obtained. Analytical solutions for the normal
modes in the low and high frequency limits are found and a general stability
condition is determined. A trans-Alfvenic and even a super-Alfvenic
relativistic jet spine can be stable to velocity shear driven Kelvin-Helmholtz
modes. The resonance condition for maximum growth of the normal modes is
obtained in the kinetically and magnetically dominated regimes. Numerical
solution of the dispersion relation verifies the analytical solutions and is
used to study the regime of high sound and Alfven speeds.Comment: 42 pages includes 7 figures, to appear in Ap
Crystal Structures of Influenza A Virus Matrix Protein M1: Variations on a Theme
Matrix protein 1 (M1) of the influenza A virus plays multiple roles in virion assembly and infection. Interest in the pH dependence of M1\u27s multiple functions led us to study the effect of subtle pH changes on M1 structure, resulting in the elucidation of a unique low-pH crystal structure of the N1-165-domain of A/WSN/33 (H1N1) M1 that has never been reported. Although the 2.2 Å crystal structure of M1 N-terminus shows a dimer with the two monomers interacting in a face-to-face fashion at low pH as observed earlier, a 44° rotation of the second monomer has led to a significantly different dimer interface that possibly affects dimer stability. More importantly, while one of the monomers is fully defined, the N-terminal half of the second monomer shows considerable disorder that appears inherent in the protein and is potentially physiologically relevant. Such disorder has not been observed in any other previously reported structure at either low or high pH conditions, despite similar crystallization pH conditions. By comparing our novel N1-165-domain structure with other low-pH or neutral-pH M1 structures, it appears that M1 can energetically access different monomer and dimer conformations, as well as oligomeric states, with varying degree of similarities. The study reported here provides further insights into M1 oligomerization that may be essential for viral propagation and infectivity
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