66 research outputs found
On the existence of supersolid helium-4 monolayer films
Extensive Monte Carlo simulations of helium-4 monolayer films adsorbed on
weak substrates have been carried out, aimed at ascertaining the possible
occurrence of a quasi-two-dimensional supersolid phase. Only crystalline films
not registered with underlying substrates are considered. Numerical results
yield strong evidence that helium-4 will not form a supersolid film on {any}
substrate strong enough to stabilize a crystalline layer. On weaker substrates,
continuous growth of a liquid film takes place
A novel method for the absolute fluorescence yield measurement by AIRFLY
One of the goals of the AIRFLY (AIR FLuorescence Yield) experiment is to
measure the absolute fluorescence yield induced by electrons in air to better
than 10% precision. We introduce a new technique for measurement of the
absolute fluorescence yield of the 337 nm line that has the advantage of
reducing the systematic uncertainty due to the detector calibration. The
principle is to compare the measured fluorescence yield to a well known process
- the Cerenkov emission. Preliminary measurements taken in the BFT (Beam Test
Facility) in Frascati, Italy with 350 MeV electrons are presented. Beam tests
in the Argonne Wakefield Accelerator at the Argonne National Laboratory, USA
with 14 MeV electrons have also shown that this technique can be applied at
lower energies.Comment: presented at the 5th Fluorescence Workshop, El Escorial - Madrid,
Spain, 16 - 20 September 200
Temperature and Humidity Dependence of Air Fluorescence Yield measured by AIRFLY
The fluorescence detection of ultra high energy cosmic rays requires a
detailed knowledge of the fluorescence light emission from nitrogen molecules
over a wide range of atmospheric parameters, corresponding to altitudes typical
of the cosmic ray shower development in the atmosphere. We have studied the
temperature and humidity dependence of the fluorescence light spectrum excited
by MeV electrons in air. Results for the 313.6 nm, 337.1 nm, 353.7 nm and 391.4
nm bands are reported in this paper. We found that the temperature and humidity
dependence of the quenching process changes the fluorescence yield by a
sizeable amount (up to 20%) and its effect must be included for a precise
estimation of the energy of ultra high energy cosmic rays.Comment: presented at the 5th Fluorescence Workshop, El Escorial - Madrid,
Spain, 16 - 20 September 2007, to appear in Nuclear Instruments and Methods
Bedforms produced by fine, cohesionless, granular and flakey sediments under subcritical water flows
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