9,945 research outputs found
Experimental investigation of flow over a backward facing step-progress report
The sizes and arrangement of the wind tunnel used for the experimentation are described. The specifications for the cold-wire anemometers, hot-wire anemometers, cold-wire rakes, and miniature 3-wire probe are proveded. The results of the experiment are briefly discussed
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
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
Film annotation system for a space experiment
This microprocessor system was designed to control and annotate a Nikon 35 mm camera for the purpose of obtaining photographs and data at predefined time intervals. The single STD BUSS interface card was designed in such a way as to allow it to be used in either a stand alone application with minimum features or installed in a STD BUSS computer allowing for maximum features. This control system also allows the exposure of twenty eight alpha/numeric characters across the bottom of each photograph. The data contains such information as camera identification, frame count, user defined text, and time to .01 second
Model-independent assessment of current direct searches for spin-dependent dark matter
I evaluate the current results of spin-dependent weakly interacting massive
particle (WIMP) searches within a model-independent framework, showing the most
restrictive limits to date derive from the combination of xenon and sodium
iodide experiments. The extension of this analysis to the case of positive
signal experiments is elaborated.Comment: 4 pages, 4 figures, revised and accepted for publication on Phys.
Rev. Let
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.
The colour of the narrow line Sy1-blazar 0324+3410
Aims. We investigate the properties of the host galaxy of the blazar
J0324+3410 (B2 0321+33) by the analysis of B and R images obtained with the NOT
under good photometric conditions. Methods: The galaxy was studied using
different methods: Sersic model fitting, unsharp-masked images, B-R image and
B-R profile analysis. Results: The images show that the host galaxy has a
ring-like morphology. The B-R colour image reveals two bluish zones: one that
coincides with the nuclear region, interpreted as the signature of emission
related to the active nucleus, the other zone is extended and is located in the
host ring-structure. We discuss the hypothesis that the later is thermal
emission from a burst of star formation triggered by an interacting/merging
process
Vacuum structure of pure gauge theories on the lattice
We present results from simulations on two aspects of quark confinement in
the pure gauge sector. First is the calculation of the profile of the flux tube
connecting a static pair in . By using the Michael sum rules
as a constraint we give evidence that the energy density at the center of the
flux tube goes to a constant as a function of quark separation. Slow variation
of the width and energy density is not ruled out. Secondly in the confined
phase of lattice we calculate the curl of the magnetic monopole current
and show that the dual London equation is satisfied and that the electric
fluxoid is quantized.Comment: 14 pages (no figures, please request preprint), LSU HE NO. 130-199
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