18,247 research outputs found
The importance of community development for health and well-being
Public health - Economic aspects
A Stress/Displacement Virtual Element Method for Plane Elasticity Problems
The numerical approximation of 2D elasticity problems is considered, in the
framework of the small strain theory and in connection with the mixed
Hellinger-Reissner variational formulation. A low-order Virtual Element Method
(VEM) with a-priori symmetric stresses is proposed. Several numerical tests are
provided, along with a rigorous stability and convergence analysis
Emergent SU(N) symmetry in disordered SO(N) spin chains
Strongly disordered spin chains invariant under the SO(N) group are shown to
display random-singlet phases with emergent SU(N) symmetry without fine tuning.
The phases with emergent SU(N) symmetry are of two kinds: one has a ground
state formed of randomly distributed singlets of strongly bound pairs of SO(N)
spins (a `mesonic' phase), while the other has a ground state composed of
singlets made out of strongly bound integer multiples of N SO(N) spins (a
`baryonic' phase). The established mechanism is general and we put forward the
cases of and as prime candidates for experimental
realizations in material compounds and cold-atoms systems. We display universal
temperature scaling and critical exponents for susceptibilities distinguishing
these phases and characterizing the enlarging of the microscopic symmetries at
low energies.Comment: 5 pages, 2 figures, Contribution to the Topical Issue "Recent
Advances in the Theory of Disordered Systems", edited by Ferenc Igl\'oi and
Heiko Riege
Highly-symmetric random one-dimensional spin models
The interplay of disorder and interactions is a challenging topic of
condensed matter physics, where correlations are crucial and exotic phases
develop. In one spatial dimension, a particularly successful method to analyze
such problems is the strong-disorder renormalization group (SDRG). This method,
which is asymptotically exact in the limit of large disorder, has been
successfully employed in the study of several phases of random magnetic chains.
Here we develop an SDRG scheme capable to provide in-depth information on a
large class of strongly disordered one-dimensional magnetic chains with a
global invariance under a generic continuous group. Our methodology can be
applied to any Lie-algebra valued spin Hamiltonian, in any representation. As
examples, we focus on the physically relevant cases of SO(N) and Sp(N)
magnetism, showing the existence of different randomness-dominated phases.
These phases display emergent SU(N) symmetry at low energies and fall in two
distinct classes, with meson-like or baryon-like characteristics. Our
methodology is here explained in detail and helps to shed light on a general
mechanism for symmetry emergence in disordered systems.Comment: 26 pages, 12 figure
Massive Black Hole Binary Systems in Hierarchical Scenario of Structure Formation
The hierarchical scenario of structure formation describes how objects like
galaxies and galaxy clusters are formed by mergers of small objects. In this
scenario, mergers of galaxies can lead to the formation of massive black hole
(MBH) binary systems. On the other hand, the merger of two MBH could produce a
gravitational wave signal detectable, in principle, by the Laser Interferometer
Space Antenna (LISA). In the present work, we use the Press-Schechter
formalism, and its extension, to describe the merger rate of haloes which
contain massive black holes. Here, we do not study the gravitational wave
emission of these systems. However, we present an initial study to determine
the number of systems formed via mergers that could permit, in a future
extension of this work, the calculation of the signature in gravitational waves
of these systems.Comment: to match the published version in International Journal of Modern
Physics
Salt weathering of sandstone during drying : effect of primary and secondary crystallisation
ACTInternational audienc
Observational Study of the Multistructured Planetary Nebula NGC 7354
We present an observational study of the planetary nebula (PN) NGC 7354
consisting of narrowband Halpha and [NII]6584 imaging as well as low- and
high-dispersion long-slit spectroscopy and VLA-D radio continuum. According to
our imaging and spectroscopic data, NGC 7354 has four main structures: a quite
round outer shell and an elliptical inner shell, a collection of low-excitation
bright knots roughly concentrated on the equatorial region of the nebula, and
two symmetrical jet-like features, not aligned either with the shells' axes, or
with each other. We have obtained physical parameters like electron temperature
and electron density as well as ionic and elemental abundances for these
different structures. Electron temperature and electron density slightly vary
throughout the nebula. The local extinction coefficient c_Hbeta shows an
increasing gradient from south to north and a decreasing gradient from east to
west consistent with the number of equatorial bright knots present in each
direction. Abundance values show slight internal variations but most of them
are within the estimated uncertainties. In general, abundance values are in
good agreement with the ones expected for PNe. Radio continuum data are
consistent with optically thin thermal emission. We have used the interactive
three-dimensional modeling tool SHAPE to reproduce the observed morphokinematic
structures in NGC 7354 with different geometrical components. Our SHAPE model
is in very good agreement with our imaging and spectroscopic observations.
Finally, after modeling NGC 7354 with SHAPE, we suggest a possible scenario for
the formation of the nebula.Comment: Accepted for publication in AJ, 12 pages, 8 figure
Magnetically-controlled impurities in quantum wires with strong Rashba coupling
We investigate the effect of strong spin-orbit interaction on the electronic
transport through non-magnetic impurities in one-dimensional systems. When a
perpendicular magnetic field is applied, the electron spin polarization becomes
momentum-dependent and spin-flip scattering appears, to first order in the
applied field, in addition to the usual potential scattering. We analyze a
situation in which, by tuning the Fermi level and the Rashba coupling, the
magnetic field can suppress the potential scattering. This mechanism should
give rise to a significant negative magnetoresistance in the limit of large
barriers.Comment: 4 pages, 2 figure
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