874 research outputs found
Measurements of the Cerenkov light emitted by a TeO2 crystal
Bolometers have proven to be good instruments to search for rare processes
because of their excellent energy resolution and their extremely low intrinsic
background. In this kind of detectors, the capability of discriminating alpha
particles from electrons represents an important aspect for the background
reduction. One possibility for obtaining such a discrimination is provided by
the detection of the Cerenkov light which, at the low energies of the natural
radioactivity, is only emitted by electrons. In this paper, the results of the
analysis of the light emitted by a TeO2 crystal at room temperature when
transversed by a cosmic ray are reported. Light is promptly emitted after the
particle crossing and a clear evidence of its directionality is also found.
These results represent a strong indication that Cerenkov light is the main, if
not even the only, component of the light signal in a TeO2 crystal. They open
the possibility to make large improvements in the performance of experiments
based on this kind of material
Las reformas de la educación primaria actual : Las disciplinas mentales y su organización a base de nuevos principios
Con grandes vacilaciones he aceptado el honroso encargo de exponer a vuestra consideración algunas breves ideas acerca del sistema escolar vigente en las escuelas de la capital de la República, dependientes del Consejo Nacional de Educación. No pretendo corresponder fielmente a los anhelos en mí depositados. Mi limitada capacidad me veda enunciar la sentencia definitiva sobre el alcance de la reforma realizada, cuya eficacia práctica está sometida a un período de experimentación de resultados ya previsibles. En otra ocasión corresponderá apreciarlos; por el momento, he creído más oportuno y provechoso reseñaros, a grandes rasgos, las consideraciones de todo orden que han determinado la nueva orientación del trabajo escolar.Facultad de Humanidades y Ciencias de la Educació
Las reformas de la educación primaria actual : Las disciplinas mentales y su organización a base de nuevos principios
Con grandes vacilaciones he aceptado el honroso encargo de exponer a vuestra consideración algunas breves ideas acerca del sistema escolar vigente en las escuelas de la capital de la República, dependientes del Consejo Nacional de Educación. No pretendo corresponder fielmente a los anhelos en mí depositados. Mi limitada capacidad me veda enunciar la sentencia definitiva sobre el alcance de la reforma realizada, cuya eficacia práctica está sometida a un período de experimentación de resultados ya previsibles. En otra ocasión corresponderá apreciarlos; por el momento, he creído más oportuno y provechoso reseñaros, a grandes rasgos, las consideraciones de todo orden que han determinado la nueva orientación del trabajo escolar.Facultad de Humanidades y Ciencias de la Educació
Circumnuclear Star Clusters in the Galaxy Merger NGC 6240, Observed with Keck Adaptive Optics and HST
We discuss images of the central ~10 kpc (in projection) of the galaxy merger
NGC 6240 at H and K' bands, taken with the NIRC2 narrow camera on Keck II using
natural guide star adaptive optics. We detect 28 star clusters in the NIRC2
images, of which only 7 can be seen in the similar-spatial-resolution, archival
WFPC2 Planetary Camera data at either B or I bands. Combining the NIRC2 narrow
camera pointings with wider NICMOS NIC2 images taken with the F110W, F160W, and
F222M filters, we identify a total of 32 clusters that are detected in at least
one of these 5 infrared (lambda > 1 micron) bandpasses. By comparing to
instantaneous burst, stellar population synthesis models (Bruzual & Charlot
2003), we estimate that most of the clusters are consistent with being ~15 Myr
old and have photometric masses ranging from 7E5 M_sun to 4E7 M_sun. The total
contribution to the star formation rate (SFR) from these clusters is
approximately 10 M_sun/year, or ~10% of the total SFR in the nuclear region. We
use these newly discovered clusters to estimate the extinction toward NGC
6240's double nuclei, and find values of A_V as high as 14 magnitudes along
some sightlines, with an average extinction of A_V~7 mag toward sightlines
within ~3 arcsec of the double nuclei.Comment: 37 pages, 9 figures; Accepted for publication by Ap
Characterization of the KID-Based Light Detectors of CALDER
The aim of the Cryogenic wide-Area Light Detectors with Excellent Resolution
(CALDER) project is the development of light detectors with active area of
cm and noise energy resolution smaller than 20 eV RMS,
implementing phonon-mediated kinetic inductance detectors. The detectors are
developed to improve the background suppression in large-mass bolometric
experiments such as CUORE, via the double read-out of the light and the heat
released by particles interacting in the bolometers. In this work, we present
the characterization of the first light detectors developed by CALDER. We
describe the analysis tools to evaluate the resonator parameters (resonant
frequency and quality factors) taking into account simultaneously all the
resonance distortions introduced by the read-out chain (as the feed-line
impedance and its mismatch) and by the power stored in the resonator itself. We
detail the method for the selection of the optimal point for the detector
operation (maximizing the signal-to-noise ratio). Finally, we present the
response of the detector to optical pulses in the energy range of 0-30 keV
New application of superconductors: high sensitivity cryogenic light detectors
In this paper we describe the current status of the CALDER project, which is
developing ultra-sensitive light detectors based on superconductors for
cryogenic applications. When we apply an AC current to a superconductor, the
Cooper pairs oscillate and acquire kinetic inductance, that can be measured by
inserting the superconductor in a LC circuit with high merit factor.
Interactions in the superconductor can break the Cooper pairs, causing sizable
variations in the kinetic inductance and, thus, in the response of the LC
circuit. The continuous monitoring of the amplitude and frequency modulation
allows to reconstruct the incident energy with excellent sensitivity. This
concept is at the basis of Kinetic Inductance Detectors (KIDs), that are
characterized by natural aptitude to multiplexed read-out (several sensors can
be tuned to different resonant frequencies and coupled to the same line),
resolution of few eV, stable behavior over a wide temperature range, and ease
in fabrication. We present the results obtained by the CALDER collaboration
with 2x2 cm2 substrates sampled by 1 or 4 Aluminum KIDs. We show that the
performances of the first prototypes are already competitive with those of
other commonly used light detectors, and we discuss the strategies for a
further improvement
The Structure of Active Merger Remnant NGC 6240 from IRAC Observations
NGC 6240 is a rare object in the local universe: an active merger remnant
viewed at the point of merging where two active galactic nuclei are visible. We
present IRAC data of this object, providing high sensitivity maps of the
stellar and PAH distribution in this complicated system. We use photometry to
analyze the variation in these distributions with radius and provide an SED in
the four IRAC bands: 3.6 microns, 4.5 microns, 5.8 microns and 8.0 microns. We
fit the radial profiles of the 3.6 micron band to r^.25 and exponential
profiles to evaluate the structure of the remnant. Finally, we compare the IRAC
images with multi-wavelength data and examine how outflows in the X-ray, Halpha
and CO correlate with 8 micron emission. The results support the general
picture of NGC 6240 as a system experiencing a major merger and transitioning
from a disk galaxy to a spheroid. The sensitivity of IRAC to low surface
brightness mid-infrared features provides detailed information on the extended
distributions of stars and dust in this rare system.Comment: Accepted for publication in Ap
Measurements and optimization of the light yield of a TeO crystal
Bolometers have proven to be good instruments to search for rare processes
because of their excellent energy resolution and their extremely low intrinsic
background. In this kind of detectors, the capability of discriminating alpha
particles from electrons represents an important aspect for the background
reduction. One possibility for obtaining such a discrimination is provided by
the detection of the Cherenkov light which, at the low energies of the natural
radioactivity, is only emitted by electrons. This paper describes the method
developed to evaluate the amount of light produced by a crystal of TeO when
hit by a 511 keV photon. The experimental measurements and the results of a
detailed simulation of the crystal and the readout system are shown and
compared. A light yield of about 52 Cherenkov photons per deposited MeV was
measured. The effect of wrapping the crystal with a PTFE layer, with the aim of
maximizing the light collection, is also presented
Energy resolution and efficiency of phonon-mediated Kinetic Inductance Detectors for light detection
The development of sensitive cryogenic light detectors is of primary interest
for bolometric experiments searching for rare events like dark matter
interactions or neutrino-less double beta decay. Thanks to their good energy
resolution and the natural multiplexed read-out, Kinetic Inductance Detectors
(KIDs) are particularly suitable for this purpose. To efficiently couple
KIDs-based light detectors to the large crystals used by the most advanced
bolometric detectors, active surfaces of several cm are needed. For this
reason, we are developing phonon-mediated detectors. In this paper we present
the results obtained with a prototype consisting of four 40 nm thick aluminum
resonators patterned on a 22 cm silicon chip, and calibrated with
optical pulses and X-rays. The detector features a noise resolution
eV and an (182) efficiency.Comment: 5 pages, 5 figure
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