22,291,437 research outputs found
Backbending phenomena in light nuclei at A~60 mass region
Recent studies of the backbending phenomenon in medium light weight nuclei
near A~60 expanded greatly our interest about how the single particle orbits
are nonlinearly affected by the collective motion. As a consequence we have
applied a modi…ed version of the exponential model with the inclusion of
paring correlation to describe the energy spectra of the ground state bands
and/or the backbending phenomenon in mass region at A~60. A firm conclusion is
obtained concerning the successful validity of the proposed modified model in
describing the backbending phenomenon in this region. Comparison with different
theoretical descriptions is discussed.Comment: 4 pages, 1 figure
Study on cosmogenic activation above ground for the DarkSide-20k project
The activation of materials due to the exposure to cosmic rays may become an
important background source for experiments investigating rare event phenomena.
DarkSide-20k is a direct detection experiment for galactic dark matter
particles, using a two-phase liquid argon time projection chamber filled with
49.7 tonnes (active mass) of Underground Argon (UAr) depleted in 39Ar. Here,
the cosmogenic activity of relevant long-lived radioisotopes induced in the
argon and other massive components of the set-up has been estimated; production
of 120 t of radiopure UAr is foreseen. The expected exposure above ground and
production rates, either measured or calculated, have been considered. From the
simulated counting rates in the detector due to cosmogenic isotopes, it is
concluded that activation in copper and stainless steel is not problematic.
Activation of titanium, considered in early designs but not used in the final
design, is discussed. The activity of 39Ar induced during extraction,
purification and transport on surface, in baseline conditions, is evaluated to
be 2.8% of the activity measured in UAr from the same source, and thus
considered acceptable. Other products in the UAr such as 37Ar and 3H are shown
to not be relevant due to short half-life and assumed purification methods
Production of pions, kaons and protons in pp collisions at GeV with ALICE at the LHC
The production of , , , , p, and pbar at mid-rapidity
has been measured in proton-proton collisions at GeV with the
ALICE detector. Particle identification is performed using the specific energy
loss in the inner tracking silicon detector and the time projection chamber. In
addition, time-of-flight information is used to identify hadrons at higher
momenta. Finally, the distinctive kink topology of the weak decay of charged
kaons is used for an alternative measurement of the kaon transverse momentum
() spectra. Since these various particle identification tools give
the best separation capabilities over different momentum ranges, the results
are combined to extract spectra from = 100 MeV/ to 2.5 GeV/.
The measured spectra are further compared with QCD-inspired models which yield
a poor description. The total yields and the mean are compared with
previous measurements, and the trends as a function of collision energy are
discussed.Comment: 24 pages, 18 captioned figures, 5 tables, published version, figures
at http://aliceinfo.cern.ch/ArtSubmission/node/388
Ultra-sensitive graphene membranes for microphone applications
Microphones exploit the motion of suspended membranes to detect sound waves.
Since the microphone performance can be improved by reducing the thickness and
mass of its sensing membrane, graphene-based microphones are expected to
outperform state-of-the-art microelectromechanical (MEMS) microphones and allow
further miniaturization of the device. Here, we present a laser vibrometry
study of the acoustic response of suspended multilayer graphene membranes for
microphone applications. We address performance parameters relevant for
acoustic sensing, including mechanical sensitivity, limit of detection and
nonlinear distortion, and discuss the trade-offs and limitations in the design
of graphene microphones. We demonstrate superior mechanical sensitivities of
the graphene membranes, reaching more than 2 orders of magnitude higher
compliances than commercial MEMS devices, and report a limit of detection as
low as 15 dBSPL, which is 10 - 15 dB lower than that featured by current MEMS
microphones.Comment: 34 pages, 6 figures, 7 supplementary figure
Persistent random walk with exclusion
Modelling the propagation of a pulse in a dense {\em milieu} poses
fundamental challenges at the theoretical and applied levels. To this aim, in
this paper we generalize the telegraph equation to non-ideal conditions by
extending the concept of persistent random walk to account for spatial
exclusion effects. This is achieved by introducing an explicit constraint in
the hopping rates, that weights the occupancy of the target sites. We derive
the mean-field equations, which display nonlinear terms that are important at
high density. We compute the evolution of the mean square displacement (MSD)
for pulses belonging to a specific class of spatially symmetric initial
conditions. The MSD still displays a transition from ballistic to diffusive
behaviour. We derive an analytical formula for the effective velocity of the
ballistic stage, which is shown to depend in a nontrivial fashion upon both the
density (area) and the shape of the initial pulse. After a density-dependent
crossover time, nonlinear terms become negligible and normal diffusive
behaviour is recovered at long times.Comment: Revised version accepted for publication in Europ. Phys. J.
Clusterized nuclear matter in the (proto-)neutron star crust and the symmetry energy
Though generally agreed that the symmetry energy plays a dramatic role in
determining the structure of neutron stars and the evolution of core-collapsing
supernovae, little is known in what concerns its value away from normal nuclear
matter density and, even more important, the correct definition of this
quantity in the case of unhomogeneous matter. Indeed, nuclear matter
traditionally addressed by mean-field models is uniform while clusters are
known to exist in the dilute baryonic matter which constitutes the main
component of compact objects outer shells. In the present work we investigate
the meaning of symmetry energy in the case of clusterized systems and the
sensitivity of the proto-neutron star composition and equation of state to the
effective interaction. To this aim an improved Nuclear Statistical Equilibrium
(NSE) model is developed, where the same effective interaction is consistently
used to determine the clusters and unbound particles energy functionals in the
self-consistent mean-field approximation. In the same framework, in-medium
modifications to the cluster energies due to the presence of the nuclear gas
are evaluated. We show that the excluded volume effect does not exhaust the
in-medium effects and an extra isospin and density dependent energy shift has
to be considered to consistently determine the composition of subsaturation
stellar matter. The symmetry energy of diluted matter is seen to depend on the
isovector properties of the effective interaction, but its behavior with
density and its quantitative value are strongly modified by clusterization.Comment: A contribution to the upcoming EPJA Special Volume on Nuclear
Symmetry Energ
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