1,543 research outputs found
Majorana and the quasi-stationary states in Nuclear Physics
A complete theoretical model describing artificial disintegration of nuclei
by bombardment with alpha-particles, developed by Majorana as early as in 1930,
is discussed in detail alongside the basic experimental evidences that
motivated it. By following the quantum dynamics of a state resulting from the
superposition of a discrete state with a continuum one, whose interaction is
described by a given potential term, Majorana obtained (among the other
predictions) the explicit expression for the integrated cross section of the
nuclear process, which is the direct measurable quantity of interest in the
experiments. Though this is the first application of the concept of
quasi-stationary states to a Nuclear Physics problem, it seems also that the
unpublished Majorana's work anticipates by several years the related seminal
paper by Fano on Atomic Physics.Comment: latex, amsart, 13 page
Inert states of spin-S systems
We present a simple but efficient geometrical method for determining the
inert states of spin-S systems. It can be used if the system is described by a
spin vector of a spin-S particle and its energy is invariant in spin rotations
and phase changes. Our method is applicable to an arbitrary S and it is based
on the representation of a pure spin state of a spin-S particle in terms of 2S
points on the surface of a sphere. We use this method to find candidates for
some of the ground states of spinor Bose-Einstein condensates.Comment: 4 pages, 2 figures, minor changes, references added, typos correcte
Oral hygiene grade and quality of life in children with chemotherapy-related oral mucositis: A randomized study on the impact of a fluoride toothpaste with salivary enzymes, essential oils, proteins and colostrum extract versus a fluoride toothpaste without menthol
Effect of aggregates and ITZ on visco-damaged response of concrete at the meso scale level
A deep knowledge on the behavior of concrete materials at the mesoscale level
requires, as a fundamental aspect, to characterize aggregates and specifically, their thermal
properties if fire hazards (e.g. spalling) are accounted for. The assessment of aggregates
performance (and, correspondingly, concrete materials made of aggregates, cement paste and
ITZ –interfacial transition zone-) is crucial for defining a realistic structural response as well
as damage scenarios. Particularly, it is assumed that concrete creep is associated to cement
paste only and that creep obeys to the B3 model proposed by Bazant and Baweja since it
shows good compatibility with experimental results and it is properly justified theoretically.
The fully coupled 3D F.E. code NEWCON3D has been adopted to perform meso-scale
analyses of concrete characterized by aggregates of different types and different thermal
conductivities. Damage maps allows for defining an appropriate concrete mixture for
responding to spalling and for characterizing the coupled behaviour of ITZ as well
A simple test for hidden variables in spin-1 system
We resolve an old problem about the existence of hidden parameters in a
three-dimensional quantum system by constructing an appropriate Bell's type
inequality. This reveals a nonclassical nature of most spin- states. We
shortly discuss some physical implications and an underlying cause of this
nonclassical behavior, as well as a perspective of its experimental
verification.Comment: 4 pages, 1 figur
Nonlinear tunneling in two-dimensional lattices
We present thorough analysis of the nonlinear tunneling of Bose-Einstein
condensates in static and accelerating two-dimensional lattices within the
framework of the mean-field approximation. We deal with nonseparable lattices
considering different initial atomic distributions in the highly symmetric
states. For analytical description of the condensate before instabilities are
developed, we derive several few-mode models, analyzing both essentially
nonlinear and quasi-linear regimes of tunneling. By direct numerical
simulations, we show that two-mode models provide accurate description of the
tunneling when either initially two states are populated or tunneling occurs
between two stable states. Otherwise a two-mode model may give only useful
qualitative hints for understanding tunneling but does not reproduce many
features of the phenomenon. This reflects crucial role of the instabilities
developed due to two-body interactions resulting in non-negligible population
of the higher bands. This effect becomes even more pronounced in the case of
accelerating lattices. In the latter case we show that the direction of the
acceleration is a relevant physical parameter which affects the tunneling by
changing the atomic rates at different symmetric states and by changing the
numbers of bands involved in the atomic transfer
Majorana: from atomic and molecular, to nuclear physics
In the centennial of Ettore Majorana's birth (1906-1938?), we re-examine some
aspects of his fundamental scientific production in atomic and molecular
physics, including a not well known short communication. There, Majorana
critically discusses Fermi's solution of the celebrated Thomas-Fermi equation
for electron screening in atoms and positive ions. We argue that some of
Majorana's seminal contributions in molecular physics already prelude to the
idea of exchange interactions (or Heisenberg-Majorana forces) in his later
workson theoretical nuclear physics. In all his papers, he tended to emphasize
the symmetries at the basis of a physical problem, as well as the limitations,
rather than the advantages, of the approximations of the method employed.Comment: to appear in Found. Phy
In vitro inhibitory effect of two commercial probiotics on chromogenic actinomycetes
Black extrinsic discoloration is a common clinical and aesthetic problem. This study aims to evaluate the potential in vitro antagonistic activity of two commercial probiotics, Streptococcus salivarius M18 and Lactobacillus reuteri ProDentis, against microorganisms associated with black stains
Numerical modelling of ellipsoidal inclusions
Within the framework of numerical algorithms for the threedimensional
random packing of granular materials this work presents an
innovative formulation for polydispersed ellipsoidal particles, including
an overlapping detection algorithm for an optimized simulation of the
mesostructure of geomaterials, particularly concrete.
Granular composite cement-based materials can be so reconstructed with
adequate precision in terms of grain size distribution. Specifically, the
algorithm performance towards the assumed inclusion shape (ellipsoidal or
spheric) and degree of regularity (round or irregular) is here discussed.
Examples on real grading curves prove that this approach is effective.
The advantages of the proposed method for computational mechanics
purposes are also disclosed when properly interfaced with visualization
CAD (Computer Aided Design) tools
Landau-Zener problem in a three-level neutrino system with non-linear time dependence
We consider the level-crossing problem in a three-level system with
non-linearly time-varying Hamiltonian (time-dependence ). We study the
validity of the so-called independent crossing approximation in the
Landau-Zener model by making comparison with results obtained numerically in
density matrix approach. We also demonstrate the failure of the so-called
"nearest zero" approximation of the Landau-Zener level-crossing probability
integral.Comment: 11 pages, 3 figures. To be published in Physical Review
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