1,617 research outputs found
Short-Baseline Active-Sterile Neutrino Oscillations?
We suggest the possibility that the anomalies observed in the LSND experiment
and the Gallium radioactive source experiments may be due to neutrino
oscillations generated by a large squared-mass difference of about 20 - 30
eV^2. We consider the simplest 3+1 four-neutrino scheme that can accommodate
also the observed solar and atmospheric neutrino oscillations. We show that, in
this framework, the disappearance of nu_e and nu_mu in short-baseline neutrino
oscillation experiments is mainly due to active-sterile transitions. The
implications of the first MiniBooNE results, appeared after the completion of
this paper, are discussed in an addendum.Comment: 12 pages. The implications of the first MiniBooNE results are
discussed in an addendu
Evaluation of resistive-plate-chamber-based TOF-PET applied to in-beam particle therapy monitoring
Particle therapy is a highly conformal radiotherapy technique which reduces the dose deposited to the surrounding normal tissues. In order to fully exploit its advantages, treatment monitoring is necessary to minimize uncertainties related to the dose delivery. Up to now, the only clinically feasible technique for the monitoring of therapeutic irradiation with particle beams is Positron Emission Tomography (PET). In this work we have compared a Resistive Plate Chamber (RPC)-based PET scanner with a scintillation-crystal-based PET scanner for this application. In general, the main advantages of the RPC-PET system are its excellent timing resolution, low cost, and the possibility of building large area systems. We simulated a partial-ring scannerbeam monitoring, which has an intrinsically low positron yield compared to diagnostic PET. In addition, for in-beam PET there is a further data loss due to the partial ring configuration. In order to improve the performance of the RPC-based scanner, an improved version of the RPC detector (modifying the thickness of the gas and glass layers), providing a larger sensitivity, has been simulated and compared with an axially extended version of the crystal-based device. The improved version of the RPC shows better performance than the prototype, but the extended version of the crystal-based PET outperforms all other options. based on an RPC prototype under construction within the Fondazione per Adroterapia Oncologica (TERA). For comparison with the crystal-based PET scanner we have chosen the geometry of a commercially available PET scanner, the Philips Gemini TF. The coincidence time resolution used in the simulations takes into account the current achievable values as well as expected improvements of both technologies. Several scenarios (including patient data) have been simulated to evaluate the performance of different scanners. Initial results have shown that the low sensitivity of the RPC hampers its application to hadro
Two-dimensional tunneling in a SQUID
Traditionally quantum tunneling in a static SQUID is studied on the basis of
a classical trajectory in imaginary time under a two-dimensional potential
barrier. The trajectory connects a potential well and an outer region crossing
their borders in perpendicular directions. In contrast to that main-path
mechanism, a wide set of trajectories with components tangent to the border of
the well can constitute an alternative mechanism of multi-path tunneling. The
phenomenon is essentially non-one-dimensional. Continuously distributed paths
under the barrier result in enhancement of tunneling probability. A type of
tunneling mechanism (main-path or multi-path) depends on character of a state
in the potential well prior to tunneling.Comment: 9 pages, 8 figure
Desarrollo y empleo de juegos educativos on-line destinados al auto-entrenamiento y auto-evaluación
La implantación del EEES, está originando cambios
en el modelo docente, cada vez más orientado al trabajo
autónomo del alumno. Los contenidos electrónicos
que apoyan el proceso de aprendizaje también
deben, por tanto, orientarse a facilitar el aprendizaje
autónomo, como por ejemplo los procesos de autoevaluación
y auto-entrenamiento por parte del estudiante.
Por ello, parece adecuado desarrollar contenidos
electrónicos que motiven y a la vez entretengan
de forma amena al alumnado durante su aprendizaje
autónomo. En esta contribución, proponemos
una serie de juegos educativos electrónicos como herramienta
que haga de la auto-evaluación y del autoentrenamiento
un proceso ameno y entretenido.Peer Reviewe
A Light Calibration System for the ProtoDUNE-DP Detector
A LED-based fiber calibration system for the ProtoDUNE-Dual Phase (DP) photon
detection system (PDS) has been designed and validated. ProtoDUNE-DP is a 6x6x6
m3 liquid argon time-projection-chamber currently being installed at the
Neutrino Platform at CERN. The PDS is based on 36 8-inch photomultiplier tubes
(PMTs) and will allow triggering on cosmic rays. The system serves as prototype
for the PDS of the final DUNE DP far detector in which the PDS also has the
function to allow the 3D event reconstruction on non-beam physics. For this
purpose an equalized PMT response is desirable to allow using the same
threshold definition for all PMT groups, simplifying the determination of the
trigger efficiency. The light calibration system described in this paper is
developed to provide this and to monitor the PMT performance in-situ.Comment: 15 pages, 5 figure
Computer Animation to teach interpolation
While mathematics courses are a basic topic in engineering studies, they are often considered as a dif- cult subject by students. In this work we present a learning experience based on computer animation and using the perspective of mathematical modelling. Our goal is to provide the students with a context that motivates the study of function interpolation. We present a problem statement that is intended to be solved by means of the Modeling Cycle. The development of the activity and the strategies identi ed during the process are presented and discussed
Light-induced instabilities in photo-oriented liquid crystal cells
In a planar liquid crystal sample sandwiched between a photosensitive and a
reference plate instabilities occurred, when the cell was illuminated from the
reference side. The instabilities were induced both by polarized white light
source and monochromatic laser beams. Static and dynamic regimes were found;
for laser irradiation dynamic instability was found only in a range of
polarization directions. A model, developed for monochromatic excitation,
predicts that at certain thicknesses dynamic instability is forbidden.
Experiments on a wedge-like cell confirmed this conclusion.Comment: to appear in Mol. Cryst. Liq. Crys
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