1,781 research outputs found
Monte Carlo simulation of an experiment looking for radiative solar neutrino decays
We analyse the possibility of detecting visible photons from a hypothetical
radiative decay of solar neutrinos. Our study is focused on the simulation of
such measurements during total solar eclipses and it is based on the BP2000
Standard Solar Model and on the most recent experimental information concerning
the neutrino properties.Comment: 13 pages, 10 figures, accepted by Astropart. Phy
Surface-acoustic-wave driven planar light-emitting device
Electroluminescence emission controlled by means of surface acoustic waves
(SAWs) in planar light-emitting diodes (pLEDs) is demonstrated. Interdigital
transducers for SAW generation were integrated onto pLEDs fabricated following
the scheme which we have recently developed. Current-voltage, light-voltage and
photoluminescence characteristics are presented at cryogenic temperatures. We
argue that this scheme represents a valuable building block for advanced
optoelectronic architectures
Acoustic charge transport in n-i-n three terminal device
We present an unconventional approach to realize acoustic charge transport
devices that takes advantage from an original input region geometry in place of
standard Ohmic input contacts. Our scheme is based on a n-i-n lateral junction
as electron injector, an etched intrinsic channel, a standard Ohmic output
contact and a pair of in-plane gates. We show that surface acoustic waves are
able to pick up electrons from a current flowing through the n-i-n junction and
steer them toward the output contact. Acoustic charge transport was studied as
a function of the injector current and bias, the SAW power and at various
temperatures. The possibility to modulate the acoustoelectric current by means
of lateral in-plane gates is also discussed. The main advantage of our approach
relies on the possibility to drive the n-i-n injector by means of both voltage
or current sources, thus allowing to sample and process voltage and current
signals as well.Comment: 9 pages, 3 figures. Submitted to Applied Physics Letter
Nuclear Track Detectors. Searches for Exotic Particles
We used Nuclear Track Detectors (NTD) CR39 and Makrofol for many purposes: i)
Exposures at the SPS and at lower energy accelerator heavy ion beams for
calibration purposes and for fragmentation studies. ii) Searches for GUT and
Intermediate Mass Magnetic Monopoles (IMM), nuclearites, Q-balls and
strangelets in the cosmic radiation. The MACRO experiment in the Gran Sasso
underground lab, with ~1000 m^2 of CR39 detectors (plus scintillators and
streamer tubes), established an upper limit for superheavy GUT poles at the
level of 1.4x10^-16 cm^-2 s^-1 sr^-1 for 4x10^-5 <beta<1. The SLIM experiment
at the high altitude Chacaltaya lab (5230 m a.s.l.), using 427 m^2 of CR39
detectors exposed for 4.22 y, gave an upper limit for IMMs of ~1.3x10^-15 cm^-2
s^-1 sr^-1. The experiments yielded interesting upper limits also on the fluxes
of the other mentioned exotic particles. iii) Environmental studies, radiation
monitoring, neutron dosimetry.Comment: Talk given at "New Trends In High-Energy Physics" (experiment,
phenomenology, theory) Yalta, Crimea, Ukraine, September 27-October 4, 200
Surface acoustic wave-induced electroluminescence intensity oscillation in planar light-emitting devices
Electroluminescence emission from surface acoustic wave-driven light-emitting
diodes (SAWLEDs) is studied by means of time-resolved techniques. We show that
the intensity of the SAW-induced electroluminescence is modulated at the SAW
frequency (~1 GHz), demonstrating electron injection into the p-type region
synchronous with the SAW wavefronts.Comment: 4 pages, 3 figure
Search for possible neutrino radiative decays during the 2001 total solar eclipse
We present the results of the observations performed in the occasion of the
June 21, 2001 total solar eclipse, looking for visible photons emitted trough a
possible radiative decay of solar neutrinos. We establish lower limits for the
neutrino proper lifetimes larger than 1000 s/eV, for neutrino masses larger
than 0.01 eV.Comment: 18 pages, 11 figures, accepted by Astopart. Phys, updated reference
A Single Mechanism of Biogenesis, Initiated and Directed by PIWI Proteins, Explains piRNA Production in Most Animals [preprint]
In animals, piRNAs guide PIWI-proteins to silence transposons and regulate gene expression. The mechanisms for making piRNAs have been proposed to differ among cell types, tissues, and animals. Our data instead suggest a single model that explains piRNA production in most animals. piRNAs initiate piRNA production by guiding PIWI proteins to slice precursor transcripts. Next, PIWI proteins direct the stepwise fragmentation of the sliced precursor transcripts, yielding tail-to-head strings of phased pre-piRNAs. Our analyses detect evidence for this piRNA biogenesis strategy across an evolutionarily broad range of animals including humans. Thus, PIWI proteins initiate and sustain piRNA biogenesis by the same mechanism in species whose last common ancestor predates the branching of most animal lineages. The unified model places PIWI-clade Argonautes at the center of piRNA biology and suggests that the ancestral animal--the Urmetazoan--used PIWI proteins both to generate piRNA guides and to execute piRNA function
Walkability and street intersections in rural-urban fringes: a decision aiding evaluation procedure
We propose a decision-aiding evaluation procedure (i) for classifying road crossings based on their impact on walkability and, subsequently, (ii) for prioritising street improvements, in urban-rural fringe areas. In the peripheral urban-rural fringes, pedestrian mobility is usually less developed and people generally depend more on cars for their everyday chores. Partly this is inevitable given the structural features and supply of services and activities in such areas, but part is due to a frequent neglect of pedestrian mobility in planning and urban design. Measures to improve this state of affairs can include the design of more pedestrian-friendly environments offering to potential users a greater level of security, comfort and convenience when walking to their designated destinations. Our evaluation procedure combines a walkability assessment methodology with the ELECTRE TRI rating procedure, in order to assist planners and decision makers in designing physical streets to enhance the continuity, safety and quality of pedestrian paths. Improving the walking accessibility in the fringe areas of towns is a way to reduce the physical and perceptual distance which separates these contexts from the rest of the city, thus leading to a progressive integration of urban functions
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