624 research outputs found
Convergence of vector bundles with metrics of Sasaki-type
If a sequence of Riemannian manifolds, , converges in the pointed
Gromov-Hausdorff sense to a limit space, , and if are vector
bundles over endowed with metrics of Sasaki-type with a uniform upper
bound on rank, then a subsequence of the converges in the pointed
Gromov-Hausdorff sense to a metric space, . The projection maps
converge to a limit submetry and the fibers converge to
its fibers; the latter may no longer be vector spaces but are homeomorphic to
, where is a closed subgroup of ---called the {\em wane
group}--- that depends on the basepoint and that is defined using the holonomy
groups on the vector bundles. The norms converges to a map
compatible with the re-scaling in and the -action
on converges to an action on compatible with the
limiting norm.
In the special case when the sequence of vector bundles has a uniform lower
bound on holonomy radius (as in a sequence of collapsing flat tori to a
circle), the limit fibers are vector spaces. Under the opposite extreme, e.g.
when a single compact -dimensional manifold is re-scaled to a point, the
limit fiber is where is the closure of the holonomy group of the
compact manifold considered.
An appropriate notion of parallelism is given to the limiting spaces by
considering curves whose length is unchanged under the projection. The class of
such curves is invariant under the -action and each such curve preserves
norms. The existence of parallel translation along rectifiable curves with
arbitrary initial conditions is also exhibited. Uniqueness is not true in
general, but a necessary condition is given in terms of the aforementioned wane
groups .Comment: 44 pages, 1 figure, in V.2 added Theorem E and Section 4 on
parallelism in the limit space
Obtenção e caracterização de expandidos e farinha instantânea de sorgo no desenvolvimento de biscoitos doces.
Light yield determination in large sodium iodide detectors applied in the search for dark matter
Application of NaI(Tl) detectors in the search for galactic dark matter
particles through their elastic scattering off the target nuclei is well
motivated because of the long standing DAMA/LIBRA highly significant positive
result on annual modulation, still requiring confirmation. For such a goal, it
is mandatory to reach very low threshold in energy (at or below the keV level),
very low radioactive background (at a few counts/keV/kg/day), and high
detection mass (at or above the 100 kg scale). One of the most relevant
technical issues is the optimization of the crystal intrinsic scintillation
light yield and the efficiency of the light collecting system for large mass
crystals. In the frame of the ANAIS (Annual modulation with NaI Scintillators)
dark matter search project large NaI(Tl) crystals from different providers
coupled to two photomultiplier tubes (PMTs) have been tested at the Canfranc
Underground Laboratory. In this paper we present the estimates of the NaI(Tl)
scintillation light collected using full-absorption peaks at very low energy
from external and internal sources emitting gammas/electrons, and
single-photoelectron events populations selected by using very low energy
pulses tails. Outstanding scintillation light collection at the level of
15~photoelectrons/keV can be reported for the final design and provider chosen
for ANAIS detectors. Taking into account the Quantum Efficiency of the PMT
units used, the intrinsic scintillation light yield in these NaI(Tl) crystals
is above 40~photoelectrons/keV for energy depositions in the range from 3 up to
25~keV. This very high light output of ANAIS crystals allows triggering below
1~keV, which is very important in order to increase the sensitivity in the
direct detection of dark matter
VLT spectropolarimetry of two powerful radio galaxies at z~1.4: UV continuum, emission-line properties and the nature of high-redshift dust
(Abridged) Deep VLT spectropolarimetric observations are presented for two
powerful radio galaxies, 0850-206 and 1303+091. These observations cover the
rest-frame wavelength range ~ 1450 - 3750 A. New radio observations and
continuum images of the same sources are also presented. These galaxies are the
first two observed from a complete sample of nine radio sources with redshifts
in the range 1.3 < z < 1.5 (selected from the equatorial sample of powerful
radio sources of Best, Rottgering & Lehnert), as part of a project aimed to
investigate the multi-component nature of the UV continuum in radio galaxies
and any variations of the continuum properties with the radio source age.
The larger radio source of the two, 0850-206, presents a high continuum
fractional polarization, averaging 17% across the observed wavelength range and
reaching 24% at rest-frame wavelengths of <2000 A. The smaller radio source,
1303+091, shows a lower continuum polarization, averaging 8% and rising to 11%
for rest-frame wavelengths >3000 A. For both galaxies, the position angle of
the electric vector is generally constant with wavelength and within ~15
degrees of perpendicular to the radio axis. Both their total flux spectra and
polarized flux spectra reveal the 2200 A dust feature, and comparison with dust
scattering models suggests that the composition of the dust in these galaxies
is similar to that of Galactic dust. In 0850-206, scattered quasar radiation
dominates the UV continuum emission, with the nebular continuum accounting for
no more than ~22% and no requirement for any additional emission component such
as emission from young stars. By contrast, in 1303+091, unpolarized radiation
could be a major constituent of the UV continuum emission, with starlight
accounting for up to ~50% and the nebular continuum accounting for ~11%.Comment: 20 pages, including 14 figures. MNRAS accepte
Background analysis and status of the ANAIS dark matter project
ANAIS (Annual modulation with NaI Scintillators) is a project aiming to set
up at the new facilities of the Canfranc Underground Laboratory (LSC), a large
scale NaI(Tl) experiment in order to explore the DAMA/LIBRA annual modulation
positive result using the same target and technique. Two 12.5 kg each NaI(Tl)
crystals provided by Alpha Spectra took data at the LSC in the ANAIS-25 set-up.
The comparison of the background model for the ANAIS-25 prototypes with the
experimental results is presented. ANAIS crystal radiopurity goals have been
achieved for Th-232 and U-238 chains, but a Pb-210 contamination
out-of-equilibrium was identified, whose origin has been studied. The high
light collection efficiency obtained with these prototypes allows to anticipate
an energy threshold of the order of 1 keVee. A new detector, with improved
performances, was received in March 2015 and very preliminary results are
shown.Comment: 6 pages, 7 figure
Preliminary results of ANAIS-25
The ANAIS (Annual Modulation with NaI(Tl) Scintillators) experiment aims at
the confirmation of the DAMA/LIBRA signal using the same target and technique
at the Canfranc Underground Laboratory. 250 kg of ultrapure NaI(Tl) crystals
will be used as a target, divided into 20 modules, each coupled to two
photomultipliers. Two NaI(Tl) crystals of 12.5 kg each, grown by Alpha Spectra
from a powder having a potassium level under the limit of our analytical
techniques, form the ANAIS-25 set-up. The background contributions are being
carefully studied and preliminary results are presented: their natural
potassium content in the bulk has been quantified, as well as the uranium and
thorium radioactive chains presence in the bulk through the discrimination of
the corresponding alpha events by PSA, and due to the fast commissioning, the
contribution from cosmogenic activated isotopes is clearly identified and their
decay observed along the first months of data taking. Following the procedures
established with ANAIS-0 and previous prototypes, bulk NaI(Tl) scintillation
events selection and light collection efficiency have been also studied in
ANAIS-25.Comment: 4 pages, 6 Figure
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