A Water Tank Cerenkov Detector for Very High Energy Astroparticles

Extensive airshower detection is an important issue in current astrophysics endeavours. Surface arrays detectors are a common practice since they are easy to handle and have a 100% duty cycle. In this work we present an experimental study of the parameters relevant to the design of a water Cerenkov detector for high energy airshowers. This detector is conceived as part of the surface array of the Pierre Auger Project, which is expected to be sensitive to ultra high energy cosmic rays. In this paper we focus our attention in the geometry of the tank and its inner liner material, discussing pulse shapes and charge collections.Comment: Accepted in Nucl. Instr. and Meth. A, LaTex 18 pages, 7 figure

Limited metacognitive access to one’s own facial expressions

As humans we communicate important information through fine nuances in our facial expressions, but because conscious motor representations are noisy, we might not be able to report these fine but meaningful movements. Here we measured how much explicit metacognitive information young adults have about their own facial expressions. Participants imitated pictures of themselves making facial expressions and triggered a camera to take a picture of them while doing so. They then rated confidence (how well they thought they imitated each expression). We defined metacognitive access to facial expressions as the relationship between objective performance (how well the two pictures matched) and subjective confidence ratings. Metacognitive access to facial expressions was very poor when we considered all face features indiscriminately. Instead, machine learning analyses revealed that participants rated confidence based on idiosyncratic subsets of features. We conclude that metacognitive access to own facial expressions is partial, and surprisingly limited

Dense plasma interferometry with a tabletop soft X-ray laser and an amplitude division interferometer based on diffraction gratings

Includes bibliographical references (page 486).We have demonstrated a novel Mach-Zehnder soft x-ray interferometer that uses diffraction gratings as beam splitters. The interferometer was used together with a 46.9nm tabletop soft x-ray laser, to map the evolution of the electron density distribution of a large-scale laser created plasma

Dense plasma diagnostics with an amplitude-division soft-x-ray laser interferometer based on diffraction gratings

Includes bibliographical references (page 358).We report the demonstration of an amplitude-division soft-x-ray interferometer that can be used to generate high-contrast interferograms at the wavelength of any of the saturated soft-x-ray lasers (5.6-46.9 nm) that are available at present. The interferometer, which utilizes grazing-incidence diffraction gratings as beam splitters in a modified Mach-Zehnder configuration, was used in combination with a tabletop 46.9-nm laser to probe a large-scale (~2.7-mm-long) laser-created plasma

Phase transformations induced by implantation of ¹²C⁻ ions into α-Fe and AISI 304 and 316 stainless steels studied by CEMS and SEM

Samples of AISI 304 and 316 stainless steels, initially in austenitic (first set) and martensitic states (second set) and α-Fe (third set), were implanted with 180 keV¹²C⁻ to a dose of 10¹⁷ atoms/cm² at room temperature. Surfaces were examined by SEM (scanning electron microscopy) and the crystalline-phase fractions were estimated through CEMS (conversion electron Mossbauer spectroscopy). Different grades of etching were produced by sputtering during the implantations on the stainless steel samples depending on the previous crystallographic states. CEMS data reveal the γ → α′ transformation in the initially martensitic samples and no noticeable modifications as a result of the implantation on α-Fe and austenitic samples.Facultad de Ciencias Exacta

Estudio de superficie de α - FE y aceros inoxidables implantados con ¹²C⁻

Se han implantado iones ¹²C⁻ con una energía de 180 keV y una dosis del orden de 10¹⁷ at / cm² en a - Fe y en aceros inoxidables AISI304 y 316 en distintas fases en equilibrio. Se estudian las modificaciones superficiales que tienen lugar atendiendo a sus anteriores estados cristalinos. Se observaron cambios importantes en las superficies de las muestras implantadas tales como la formación de ampollas (blisters), escamas (flakes), y ataque preferencial producidos por el impacto de los iones sobre la superficie. Se relacionan las modificaciones superficiales con las estructuras cristalinas de las muestras previas a la implantación.Facultad de Ciencias Exacta

Applications of high repetition rate tabletop soft X-ray lasers become a reality in several fields

Includes bibliographical references (page 468).For many years researchers have envisioned the development of compact high repetition rate tabletop soft x-ray laser, that could be routinely used in application in numerous disciplines. With demonstrated average powers of several mW and millijoule-level pulse energy at 46.9nm, the Ne-like Ar capillary discharge-pumped laser is the first compact laser to reach this goal. In this paper we summarize the development status of high repetition rate tabletop soft x-ray lasers based on capillary discharge excitation, and give examples of their successful use in several applications. Results of the use of a caprllary discharge pumped 46.9nm laser m dense plasma interferometry, soft x-ray reflectometry for the determination of optical constants, characterization of diffraction gratings, laser ablation of materials, and plasma generation are described. The observation of lasing at 52.9nm line in Ne-like Cl with output pulse energy up to 10 μJ is also reported

Extremely compact soft X-ray lasers based on capillary discharges

Includes bibliographical references (page 522).Extremely compact high repetition rate soft X-ray lasers based on capillary discharge excitation have demonstrated average powers of a few milliWatt at 46.9 nm, milli-Joule-level pulse energy, peak spectral brightness several orders of magnitude larger than third-generation synchrotron beam lines, and excellent spatial coherence. Examples of the use of a capillary discharge soft X-ray laser in dense plasma diagnostics and laser ablation of materials are summarized

Low-frequency plasma conductivity in the average-atom approximation

Low-frequency properties of a plasma are examined within the average-atom approximation, which presumes that scattering of a conducting electron on each atom takes place independently of other atoms. The relaxation time tau distinguishes a high-frequency region omega tau > 1, where the single-atom approximation is applicable explicitly, from extreme low frequencies omega tau < 1, where, naively, the single-atom approximation is invalid. A proposed generalization of the formalism, which takes into account many-atom collisions, is found to be accurate in all frequency regions, from omega =0 to omega tau >1, reproducing the Ziman formula in the static limit, results based on the Kubo-Greenwood formula for high frequencies, and satisfying the conductivity sum-rule precisely. The correspondence between physical processes leading to the conventional Ohm's law and the infrared properties of QED is discussed. The suggested average-atom approach to frequency-dependent conductivity is illustrated by numerical calculations for the an aluminum plasma in the temperature range 2--10 eV.Comment: 9 pages 3 figure

Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory

The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects related to the angles of incidence of the particles into the detectors. The magnitude of the effect depends upon the zenith angle and state of development of the shower and thus provides a novel observable, $(\sec \theta)_\mathrm{max}$, sensitive to the mass composition of cosmic rays above $3 \times 10^{18}$ eV. By comparing measurements with predictions from shower simulations, we find for both of our adopted models of hadronic physics (QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass increases slowly with energy, as has been inferred from other studies. However, the mass estimates are dependent on the shower model and on the range of distance from the shower core selected. Thus the method has uncovered further deficiencies in our understanding of shower modelling that must be resolved before the mass composition can be inferred from $(\sec \theta)_\mathrm{max}$.Comment: Replaced with published version. Added journal reference and DO