17,010 research outputs found
Radio and optical orientations of galaxies
We investigate the correlations between optical and radio isophotal position
angles for 14302 SDSS galaxies with magnitudes brighter than 18 and which
have been associated with extended FIRST radio sources. We identify two
separate populations of galaxies using the colour, concentration and their
principal components. Surprisingly strong statistical alignments are found:
late-type galaxies are overwhelmingly biased towards a position angle
differences of and early-type galaxies to . The
late-type alignment can be easily understood in terms of the standard picture
in which the radio emission is intimately related to areas of recent
star-formation. In early-type galaxies the radio emission is expected to be
driven by accretion on to a nuclear black hole. We argue that the observed
correlation of the radio axis with the minor axis of the large-scale stellar
distribution gives a fundamental insight into the structure of elliptical
galaxies, for example, whether or not the nuclear kinematics are decoupled form
the rest of the galaxy. Our results imply that the galaxies are oblate
spheroids with their radio emission aligned with the minor axis. Remarkably the
strength of the correlation of the radio major axis with the optical minor axis
depends on radio loudness. Those objects with a low ratio of FIRST radio flux
density to total stellar light show a strong minor axis correlation while the
stronger radio sources do not. This may reflect different formation histories
for the different objects and we suggest we may be seeing the different
behaviour of rationally supported and non-rotationally supported ellipticals.Comment: Version to appear in MNRA
The Curci-Ferrari model with massive quarks at two loops
Massive quarks are included in the Curci-Ferrari model and the theory is
renormalized at two loops in the MSbar scheme in an arbitrary covariant gauge.Comment: 8 latex page
Improving efficiency in radio surveys for gravitational lenses
Many lens surveys have hitherto used observations of large samples of
background sources to select the small minority which are multiply imaged by
lensing galaxies along the line of sight. Recently surveys such as SLACS and
OLS have improved the efficiency of surveys by pre-selecting double-redshift
systems from SDSS. We explore other ways to improve survey efficiency by
optimum use of astrometric and morphological information in existing
large-scale optical and radio surveys. The method exploits the small position
differences between FIRST radio positions of lensed images and the SDSS lens
galaxy positions, together with the marginal resolution of some larger
gravitational lens systems by the FIRST beam. We present results of a small
pilot study with the VLA and MERLIN, and discuss the desirable criteria for
future surveys.Comment: Accepted by MNRAS. 9 pages, 5 figure
Interaction of Ising-Bloch fronts with Dirichlet Boundaries
We study the Ising-Bloch bifurcation in two systems, the Complex Ginzburg
Landau equation (CGLE) and a FitzHugh Nagumo (FN) model in the presence of
spatial inhomogeneity introduced by Dirichlet boundary conditions. It is seen
that the interaction of fronts with boundaries is similar in both systems,
establishing the generality of the Ising-Bloch bifurcation. We derive reduced
dynamical equations for the FN model that explain front dynamics close to the
boundary. We find that front dynamics in a highly non-adiabatic (slow front)
limit is controlled by fixed points of the reduced dynamical equations, that
occur close to the boundary.Comment: 10 pages, 8 figures, submitted to Phys. Rev.
Influence of wear algorithm formulation on computational-experimental corroboration
Experimental wear testing is well-established as an important part of the TKR design process. Recently, in-silico models have proved their value to corroborate long-term in-vitro results on a much shorter timescale [1]. Both FE-based models & multi-body dynamics can be used to predict contact pressures, sliding distances and cross-shear (CS). The precise mechanisms of wear are not sufficiently understood to permit analytical calculations, and so empirical formulations are used to estimate wear depths & volumes.Most early simulations were based on a modified Archard/Lancaster formulation; more recently a number of alternative formulations for cross shear have been proposed; it is unclear which is the most robust or accurate for the widest range of activities. The aim of this study was to develop and corroborate a fast in-silico wear model, and use this to compare different wear formulations
First Principles LCGO Calculation of the Magneto-optical Properties of Nickel and Iron
We report a first principles, self-consistent, all electron, linear
combination of Gaussian orbitals (LCGO) calculation of a comprehensive
collection of magneto-optical properties of nickel and iron based on density
functional theory. Among the many magneto-optical effects, we have studied the
equatorial Kerr effect for absorption in the optical as well as soft X-ray
region, where it is called X-ray magnetic linear dichroism (X-MLD). In the
optical region the effect is of the order of 2\% while in the X-ray region it
is of the order of 1\% for the incident angles considered. In addition, the
polar Kerr effect, X-ray magnetic circular dichroism (X-MCD) and total X-ray
absorption at the L edges, soft X-ray Faraday effect at the L
edges have also been calculated. Our results are in good agreement with
experiments and other first principles methods that have been used to calculate
some of these properties.Comment: 22 pages RevTex. 8 figures submitted separately as a uuencoded,
compressed tar fil
- …