1,153 research outputs found
Mini-BRU/BIPS foil bearing development
The analysis revealed the failure agent to be a combination of poor teflon coating adhesion, a decrease in bearing sway space and, possibly, lack of flushing flow through the bearing. A change in Teflon coating vendors provided substantially improved coating quality and surface finish. The sway space was increased and the cooling bleed flow was adjusted to flush the bearing. These changes were included in a test conducted in the WHL from 6 April to 22 May 1978 which resulted in the completion of 1006.9 hours of operation at temperature and load. Post-test inspection revealed the bearings to be in excellent condition and capable of completing a much longer test
New insights into foreground analysis of the WMAP five-year data using FASTICA
In this paper, we present a foreground analysis of the WMAP 5-year data using
the FASTICA algorithm, improving on the treatment of the WMAP 3-year data in
Bottino et al 2008. We revisit the nature of the free-free spectrum with the
emphasis on attempting to confirm or otherwise the spectral feature claimed in
Dobbler et al 2008b and explained in terms of spinning dust emission in the
warm ionised medium. With the application of different Galactic cuts, the index
is always flatter than the canonical value of 2.14 except for the Kp0 mask
which is steeper. Irrespective of this, we can not confirm the presence of any
feature in the free-free spectrum. We experiment with a more extensive approach
to the cleaning of the data, introduced in connection with the iterative
application of FASTICA. We confirm the presence of a residual foreground whose
spatial distribution is concentrated along the Galactic plane, with pronounced
emission near the Galactic center. This is consistent with the WMAP haze
detected in Finkbeiner 2004. Finally, we attempted to perform the same analysis
on full-sky maps. The code returns good results even for those regions where
the cross-talk among the components is high. However, slightly better results
in terms of the possibility of reconstructing a full-sky CMB map, are achieved
with a simultaneous analysis of both the five WMAP maps and foreground
templates. Nonetheless, some residuals are still present and detected in terms
of an excess in the CMB power spectrum, on small angular scales. Therefore, a
minimal mask for the brightest regions of the plane is necessary, and has been
defined.Comment: Accepted for publication in MNRAS, 25 pages, 17 figures, 4 tables.
Version with full resolution figures available at:
http://www.mpa-garching.mpg.de/~bottino/downloads/bottino_etal.pd
Generation of femtosecond light pulses in the near infrared around λ = 850 nm
Femtosecond light pulses tunable between 840 nm and 880 nm are generated in a synchronously pumped ring dye laser. The laser emits nearly bandwidth-limited pulses (Δv tp = 0.45) with pulse durations down to 65 fs. At a pumping power of 450 mW of a mode-locked Ar-ion laser (λ = 514 nm) the infrared femtosecond dye laser has an output of up to 15 mW
Screw dynamo in a time-dependent pipe flow
The kinematic dynamo problem is investigated for the flow of a conducting
fluid in a cylindrical, periodic tube with conducting walls. The methods used
are an eigenvalue analysis of the steady regime, and the three-dimensional
solution of the time-dependent induction equation. The configuration and
parameters considered here are close to those of a dynamo experiment planned in
Perm, which will use a torus-shaped channel. We find growth of an initial
magnetic field by more than 3 orders of magnitude. Marked field growth can be
obtained if the braking time is less than 0.2 s and only one diverter is used
in the channel. The structure of the seed field has a strong impact on the
field amplification factor. The generation properties can be improved by adding
ferromagnetic particles to the fluid in order to increase its relative
permeability,but this will not be necessary for the success of the dynamo
experiment. For higher magnetic Reynolds numbers, the nontrivial evolution of
different magnetic modes limits the value of simple `optimistic' and
`pessimistic' estimates.Comment: 10 pages, 12 figure
Microlensing of Central Images in Strong Gravitational Lens Systems
We study microlensing of the faint images that form close to the centers of
strong gravitational lens galaxies. These central images, which have finally
begun to yield to observations, naturally appear in dense stellar fields and
may be particularly sensitive to fine granularity in the mass distribution. The
microlensing magnification maps for overfocussed (i.e., demagnified) images
differ strikingly from those for magnified images. In particular, the familiar
"fold" and "cusp" features of maps for magnified images are only present for
certain values of the fraction, f, of the surface mass density contained in
stars. For central images, the dispersion in microlensing magnifications is
generally larger than for normal (minimum and saddle) images, especially when
the source is comparable to or larger than the stellar Einstein radius. The
dispersion depends in a complicated way on f; this behaviour may hold the key
to using microlensing as a probe of the relative densities of stars and dark
matter in the cores of distant galaxies. Quantitatively, we predict that the
central image C in PMN J1632-0033 has a magnification dispersion of 0.6
magnitudes for Rsrc/Rein <~ 1, or 0.3 mag for Rsrc/Rein = 10. For comparison,
the dispersions are 0.5-0.6 mag for image B and 0.05-0.1 mag for image A, if
Rsrc/Rein <~ 1; and just 0.1 mag for B and 0.008 mag for A if Rsrc/Rein = 10.
(The dispersions can be extrapolated to larger sources sizes as sigma \propto
Rsrc^{-1}.) Thus, central images are more susceptible than other lensed images
to microlensing and hence good probes for measuring source sizes.Comment: 12 pages; accepted in MNRAS; many new magnification maps and
significantly expanded analysis of magnification map structur
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