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

A literature survey on sideslip angle estimation using vehicle dynamics based methods

The vehicle sideslip angle or lateral velocity is a measure both for driving stability and for occupant’s subjective perception of safety. With the introduction of vehicle dynamics control systems and automated driving functions, knowledge of this vehicle motion state is required for many control strategies. This article gives an overview on the state of the art on sideslip angle estimation. In contrast to other literature studies on this topic, it focuses on vehicle dynamics based algorithms. The following types of observers are discussed: Kalman Filter-type, recursive least squares (RLS), sliding mode observers (SMO) or nonlinear observers (NLO). Eventually, cascaded observers are used that first estimate some states, which then act as input to the sideslip angle estimator. Since the choice of an observer strategy always depends on the application, this article provides a brief insight into the work of selected research groups that have studied the topic. These examples will help to clarify the presence of many different approaches in the literature. A detailed discussion on vehicle and tire models is not included but referenced to other sources. Finally, this article provides recommendations for two main target groups: First, researchers and engineers that plan to design an algorithm for sideslip angle estimation using deterministic vehicle dynamics based approaches. Second, researchers and engineers planning to include an existing algorithm in an automated driving function that want to learn about advantages and limitations of these types of algorithms. Author

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

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

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

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 $5\times5$ cm$^2$ 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

Measurements and optimization of the light yield of a TeO2_2 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$_2$ 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