2,274 research outputs found
A theory of strongly orthotropic continuum mechanics
This paper presents a theory of continuum mechanics for strongly orthotropic materials that proposes a more informative asymmetric strain and rotation tensor. The infinitesimal strain tensor and, likewise, Green-Lagrange strains avoid rotational sensitivity by the use of effective shear strain averaging. The linear formulation of the proposed non-symmetric strain tensor field instead differentiates planar shear strains based on principal material direction and mechanical properties – adding determinacy to the otherwise geometric problem. The separation of in-plane shears also allows the formulation of a first order rotation tensor that gives change in principal property direction when applied to orthotropic materials – which is a new interpretation of rigid body rotation. Subsequent to the theory, a new extended Mohr’s plot and compliance tensor are presented. It is demonstrated in a numerical example that application of the proposed tensors yields the best solution when compared with an analytical model and three conventional solvers for a finite shear deformation
7.960 MC/S Observations of Radio Sources in the Sydney Catalogue
During March and September 1960, observations were made
with the Caltech interferometer of 739 sources listed in the
two catalogues of Mills, Slee and Hill^1,^2. The primary purpose
of the investigation was to provide this observatory
with a 960 Mc/s "finding list" for future measurements of
source sizes and precise positions.
The area covered in these observations was:
0: -50° to -20° a: 17 to 5 hours
o: -20° to +10° a: O to 24 hours.
In general, the observations were restricted to sources in the
MSH catalogues whose flux density at 86 Mc/s was greater than
15 x l0^(-26) watts m^-2 (c/s)^-l. All sources down to this level
were examined with the exception of those in the region 18h to
24h, between o^o and -10° .
Most sources were observed near transit for at least four
or five minutes at the position given in the Sydney catalogues.
This allowed us to observe one 10-degree declination zone each
night. The flux density of each source was measured relative to
the standard source Hydra A ( 09-14), which was observed each
night when possible. When Hydra A was not available, 22-11 was used as a secondary calibrator. All observations were made at
night to avoid effects of solar radiation
MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. VII. Blazar Jet Acceleration
We discuss acceleration measurements for a large sample of extragalactic
radio jets from the MOJAVE program which studies the parsec-scale jet structure
and kinematics of a complete, flux-density-limited sample of Active Galactic
Nuclei (AGN). Accelerations are measured from the apparent motion of individual
jet features or "components" which may represent patterns in the jet flow. We
find that significant accelerations are common both parallel and perpendicular
to the observed component velocities. Parallel accelerations, representing
changes in apparent speed, are generally larger than perpendicular acceleration
that represent changes in apparent direction. The trend for larger parallel
accelerations indicates that a significant fraction of these changes in
apparent speed are due to changes in intrinsic speed of the component rather
than changes in direction to the line of sight. We find an overall tendency for
components with increasing apparent speed to be closer to the base of their
jets than components with decreasing apparent speed. This suggests a link
between the observed pattern motions and the underlying flow which, in some
cases, may increase in speed close to the base and decrease in speed further
out; however, common hydro-dynamical processes for propagating shocks may also
play a role. About half of the components show "non-radial" motion, or a
misalignment between the component's structural position angle and its velocity
direction, and these misalignments generally better align the component motion
with the downstream emission. Perpendicular accelerations are closely linked
with non-radial motion. When observed together, perpendicular accelerations are
usually in the correct direction to have caused the observed misalignment.Comment: 17 pages, 11 figures, 1 table, accepted by the Astrophysical Journa
The milliarcsecond-scale jet of PKS 0735+178 during quiescence
We present polarimetric 5 GHz to 43 GHz VLBI observations of the BL Lacertae
object PKS 0735+178, spanning March 1996 to May 2000. Comparison with previous
and later observations suggests that the overall kinematic and structural
properties of the jet are greatly influenced by its activity. Time intervals of
enhanced activity, as reported before 1993 and after 2000 by other studies, are
followed by highly superluminal motion along a rectilinear jet. In contrast the
less active state in which we performed our observations, shows subluminal or
slow superluminal jet features propagating through a twisted jet with two sharp
bends of about 90 deg. within the innermost three-milliarcsecond jet structure.
Proper motion estimates from the data presented here allow us to constrain the
jet viewing angle to values < 9 deg., and the bulk Lorentz factor to be between
2 and 4.Comment: 11 pages, 12 figures. Accepted for publication in A&
Variability and Velocity of Superluminal Sources
We investigate the relation between the Doppler factor determined from
variations in total flux at 22 and 37 GHz, and the apparent transverse velocity
determined from VLBA observations at 2 cm. The data are consistent with the
relativistic beaming theory for compact radio sources, in that the distribution
of beta_{app}/delta_{var}, for 30 quasars, is roughly consistent with a Monte
Carlo simulation. The intrinsic temperature appears to be ~2x10^{10} K, close
to the "equipartition value" calculated by Readhead (1994). We deduce the
distribution of Lorentz factors for a group of 48 sources; the values range up
to about gamma=40.Comment: To be published in "Radio Astronomy at the Fringe", ASP Conf. Ser.
Vol. 300, J. A. Zensus, M. H. Cohen, & E. Ros (eds.), 8 pages, 3 figures,
needs rafringe.st
The Point of Origin of the Radio Radiation from the Unresolved Cores of Radio-Loud Quasars
Locating the exact point of origin of the core radiation in active galactic
nuclei (AGN) would represent important progress in our understanding of
physical processes in the central engine of these objects. However, due to our
inability to resolve the region containing both the central compact object and
the jet base, this has so far been difficult. Here, using an analysis in which
the lack of resolution does not play a significant role, we demonstrate that it
may be impossible even in most radio loud sources for more than a small
percentage of the core radiation at radio wavelengths to come from the jet
base. We find for 3C279 that percent of the core flux at 15 GHz must
come from a separate, reasonably stable, region that is not part of the jet
base, and that then likely radiates at least quasi-isotropically and is
centered on the black hole. The long-term stability of this component also
suggests that it may originate in a region that extends over many Schwarzschild
radii.Comment: 7 pages with 3 figures, accepted for publication in Astrophysics and
Space Scienc
Kinematics of parsec-scale structures in AGN: the 2cm VLBA Survey
We are investigating the kinematics of jets in active galactic nuclei on
parsec scales by studying a representative population of sources. This study is
being carried out using the Very Long Baseline Array at 15 GHz, with more than
800 images taken since 1994. In this contribution we present an overview of the
diversity of kinematics for a complete sample of sources.Comment: Proceedings of the 6th European VLBI Network Symposium, Ros E.,
Porcas R.W., Lobanov, A.P., & Zensus, J.A. (eds), MPIfR, Bonn, Germany. 2
pages, 3 figures, needs evn2002.cls style fil
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