16,334 research outputs found
Symmetry breaking and clustering in a vibrated granular gas with several macroscopically connected compartments
The spontaneous symmetry breaking in a vibro-fluidized low-density granular
gas in three connected compartments is investigated. When the total number of
particles in the system becomes large enough, particles distribute themselves
unequally among the three compartments. Particles tend to concentrate in one of
the compartments, the other two having the (relatively small) same average
number of particles. A hydrodynamical model that accurately predicts the
bifurcation diagram of the system is presented. The theory can be easily
extended to the case of an arbitrary number of connected compartments
Emergence of simple patterns in many-body systems: from macroscopic objects to the atomic nucleus
Strongly correlated many-body systems often display the emergence of simple
patterns and regular behaviour of their global properties. Phenomena such as
clusterization, collective motion and appearance of shell structures are
commonly observed across different size, time, and energy scales in our
universe. Although at the microscopic level their individual parts are
described by complex interactions, the collective behaviour of these systems
can exhibit strikingly regular patterns. This contribution provides an overview
of the experimental signatures that are commonly used to identify the emergence
of shell structures and collective phenomena in distinct physical systems.
Examples in macroscopic systems are presented alongside features observed in
atomic nuclei. The discussion is focused on the experimental trends observed
for exotic nuclei in the vicinity of nuclear closed-shells, and the new
challenges that recent experiments have posed in our understanding of emergent
phenomena in nuclei.Comment: Invited contribution prepared for the special issue of "The tower of
effective (field) theories and the emergence of nuclear phenomen
Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers
Quantum nanomagnets can show a field dependence of the relaxation time very
different from their classical counterparts, due to resonant tunneling via
excited states (near the anisotropy barrier top). The relaxation time then
shows minima at the resonant fields H_{n}=n D at which the levels at both sides
of the barrier become degenerate (D is the anisotropy constant). We showed that
in Mn12, near zero field, this yields a contribution to the nonlinear
susceptibility that makes it qualitatively different from the classical curves
[Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to
finite dc fields showing how the bias can trigger the system to display those
quantum nonlinear responses, near the resonant fields, while recovering an
classical-like behaviour for fields between them. The analysis of the
experiments is done with heuristic expressions derived from simple balance
equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report
Global analysis of electromagnetic moments in odd near doubly magic nuclei
We use the nuclear DFT approach to determine nuclear electric quadrupole and
magnetic dipole moments in all one-particle and one-hole neighbors of eight
doubly magic nuclei. We align angular momenta along the intrinsic
axial-symmetry axis with broken time-reversal symmetry, which allows us to
explore fully the self-consistent charge, spin, and current polarizations.
Spectroscopic moments are determined for symmetry-restored wave functions and
compared with available experimental data. We find that the obtained
polarizations do not call for using quadrupole- or dipole-moment operators with
effective charges or effective g-factors.Comment: 15 LaTeX pages, 9 figure
Laser Spectroscopy for the Study of Exotic Nuclei
Investigation into the properties and structure of unstable nuclei far from
stability remains a key avenue of research in modern nuclear physics. These
efforts are motivated by the continual observation of unexpected structure
phenomena in nuclei with unusual proton-to-neutron ratios. In recent decades,
laser spectroscopy techniques have made significant contributions in our
understanding of exotic nuclei in different mass regions encompassing almost
the entire nuclear chart. This is achieved through determining multiple
fundamental properties of nuclear ground and isomeric states, such as nuclear
spins, magnetic dipole and electric quadrupole moments and charge radii, via
the measurement of hyperfine structures and isotope shifts in the atomic or
ionic spectra of the nuclei of interest. These properties, when measured with
sufficient precision for a long range of isotopes, offer prominent tests of
recently developed state-of-the-art theory and help to stimulate new
developments to improve the many-body methods and nucleon-nucleon interactions
at the core of these models. With the aim of exploring more exotic short-lived
nuclei located ever closer to the proton and neutron driplines, laser
spectroscopy techniques, with their continuous technological developments
towards higher resolution and higher sensitivity, are extensively employed at
current- and next-generation radioactive ion beam facilities worldwide. Ongoing
efforts in parallel promise to make even more exotic species available for
study at next-generation facilities. Very recently, an innovative application
of laser spectroscopy on molecules containing short-lived nuclei has been
demonstrated offering additional opportunities for several fields of research,
e.g. fundamental symmetry studies and astrophysics.Comment: 129 pages (bibliography 56 pages), 32 figures, invited review for
Progress in Particle and Nuclear Physics. Comments and suggestions are
welcom
Desarrollo de un instrumento de ayuda a la decisión para la mejora de las líneas de confección.
En este estudio se describe el software de simulación de daños en líneas de clasificación de fruta SIMLIN 2.0. Se refiere su empleo en la simulación de confección de melocotones Sudanell con una susceptibilidad intrínseca estimada mediante un modelo logístico, ajustado con esta misma herramienta, a partir de datos de Laboratorio SIMLIN 2.0 precisa la caracterización de las partidas de fruta mediante distribuciones de probabilidad, la cual puede llevarse a cabo con un interfaz de usuario de fácil utilización. El software permite evaluar los porcentajes de daño previstos para líneas de clasificación con distintos niveles de agresividad establecidos por medio de bases de datos generadas con frutos electrónicos tipo IS-100. Aporta distintas salidas gráficas que ayudan a definir las estrategias de mejora que más se adecúen a cada caso
A new beamline for laser spin-polarization at ISOLDE
A beamline dedicated to the production of laser-polarized radioactive beams
has been constructed at ISOLDE, CERN. We present here different simulations
leading to the design and construction of the setup, as well as technical
details of the full setup and examples of the achieved polarizations for
several radioisotopes. Beamline simulations show a good transmission through
the entire line, in agreement with observations. Simulations of the induced
nuclear spin-polarization as a function of atom-laser interaction length are
presented for Na, [1] and for Ar, which is studied in this
work. Adiabatic spin rotation of the spin-polarized ensemble of atoms, and how
this influences the observed nuclear ensemble polarization, are also performed
for the same nuclei. For Ar, we show that multiple-frequency pumping
enhances the ensemble polarization by a factor 1.85, in agreement with
predictions from a rate equations model.
[1] J. Phys. G: Nucl. Part. Phys./174408400
The evolution of H{\sc ii} galaxies: Testing the bursting scenario through the use of self-consistent models
We have computed a series of realistic and self-consistent models of the
emitted spectra of H{\sc ii} galaxies. Our models combine different codes of
chemical evolution, evolutionary population synthesis and photoionization. The
emitted spectrum of H{\sc ii} galaxies is reproduced by means of the
photoionization code CLOUDY, using as ionizing spectrum the spectral energy
distribution of the modelled H{\sc ii} galaxy, which in turn is calculated
according to a Star Formation History (SFH) and a metallicity evolution given
by a chemical evolution model that follows the abundances of 15 different
elements. The contribution of emission lines to the broad-band colours is
explicitly taken into account.
The results of our code are compared with photometric and spectroscopic data
of H{\sc ii} galaxies. Our technique reproduces observed diagnostic diagrams,
abundances, equivalent width-colour and equivalent width-metallicity relations
for local H{\sc ii} galaxies.Comment: 13 figures and 2 tables, accepted for publication in MNRAS Main
Journa
Ground-State Electromagnetic Moments of Calcium Isotopes
High-resolution bunched-beam collinear laser spectroscopy was used to measure
the optical hyperfine spectra of the Ca isotopes. The ground state
magnetic moments of Ca and quadrupole moments of Ca were
measured for the first time, and the Ca ground state spin was
determined in a model-independent way. Our results provide a critical test of
modern nuclear theories based on shell-model calculations using
phenomenological as well as microscopic interactions. The results for the
neutron-rich isotopes are in excellent agreement with predictions using
interactions derived from chiral effective field theory including three-nucleon
forces, while lighter isotopes illustrate the presence of particle-hole
excitations of the Ca core in their ground state.Comment: Accepted as a Rapid Communication in Physical Review
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