5,449 research outputs found
Integral relations and the adiabatic expansion method for 1+2 reactions above the breakup threshold: Helium trimers with soft-core potentials
The integral relations formalism introduced in \cite{bar09,rom11}, and
designed to describe 1+ reactions, is extended here to collision energies
above the threshold for the target breakup. These two relations are completely
general, and in this work they are used together with the adiabatic expansion
method for the description of 1+2 reactions. The neutron-deuteron breakup, for
which benchmark calculations are available, is taken as a test of the method.
The s-wave collision between the He atom and He dimer above the
breakup threshold and the possibility of using soft-core two-body potentials
plus a short-range three-body force will be investigated. Comparisons to
previous calculations for the three-body recombination and collision
dissociation rates will be shown.Comment: To be published in Physical Review
General integral relations for the description of scattering states using the hyperspherical adiabatic basis
In this work we investigate 1+2 reactions within the framework of the
hyperspherical adiabatic expansion method. To this aim two integral relations,
derived from the Kohn variational principle, are used. A detailed derivation of
these relations is shown. The expressions derived are general, not restricted
to relative partial waves, and with applicability in multichannel
reactions. The convergence of the -matrix in terms of the adiabatic
potentials is investigated. Together with a simple model case used as a test
for the method, we show results for the collision of a He atom on a \dimer
dimer (only the elastic channel open), and for collisions involving a Li
and two He atoms (two channels open).Comment: Accepted for publication in Physical Review
Variational description of continuum states in terms of integral relations
Two integral relations derived from the Kohn Variational Principle (KVP) are
used for describing scattering states. In usual applications the KVP requires
the explicit form of the asymptotic behavior of the scattering wave function.
This is not the case when the integral relations are applied since, due to
their short range nature, the only condition for the scattering wave function
is that it be the solution of in the internal region.
Several examples are analyzed for the computation of phase-shifts from bound
state type wave functions or, in the case of the scattering of charged
particles, it is possible to obtain phase-shifts using free asymptotic
conditions. As a final example we discuss the use of the integral relations in
the case of the Hyperspherical Adiabatic method.Comment: 34 pages, 7 figures, accepted in Phys. Rev.
Three-body structure of low-lying 12Be states
We investigate to what extent a description of 12Be as a three-body system
made of an inert 10Be-core and two neutrons is able to reproduce the
experimental 12Be data. Three-body wave functions are obtained with the
hyperspherical adiabatic expansion method. We study the discrete spectrum of
12Be, the structure of the different states, the predominant transition
strengths, and the continuum energy spectrum after high energy fragmentation on
a light target. Two 0+, one 2+, one 1- and one 0- bound states are found where
the first four are known experimentally whereas the 0- is predicted as an
isomeric state. An effective neutron charge, reproducing the measured B(E1)
transition and the charge rms radius in 11Be, leads to a computed B(E1)
transition strength for 12Be in agreement with the experimental value. For the
E0 and E2 transitions the contributions from core excitations could be more
significant. The experimental 10Be-neutron continuum energy spectrum is also
well reproduced except in the energy region corresponding to the 3/2- resonance
in 11Be where core excitations contribute.Comment: 16 pages, 9 figures. Accepted for publication in Physical Review
Integral relations for three-body continuum states with the adiabatic expansion
Application of the Hyperspherical Adiabatic expansion to describe three-body
scattering states suffers the problem of a very slow convergence. Contrary to
what happens for bound states, a huge number of hyperradial equations has to be
solved, and even if done, the extraction of the scattering amplitude is
problematic. In this paper we show how to obtain accurate scattering phase
shifts using the Hyperspherical Adiabatic expansion. To this aim two integral
relations, derived from the Kohn Variational Principle, are used. The
convergence of this procedure is as fast as for bound states.Comment: 4 pages, 1 figur
Isomeric 0- halo-states in 12Be and 11Li
We predict the existence of an isomeric 0-state in Be at an
excitation energy of about 2.5 MeV, and a 0-resonance in Li with
both energy and width of about 1 MeV corresponding to two-neutron emission. The
structure of these halo-like states are like the 1-states which means
essentially a core surrounded by two neutrons in single-particle and
p-states. The life-time of the Be state is determined by or
-emission, s or s
estimated for photon energies of 0.1 MeV and 0.6 MeV, respectively.Comment: to be published in Physics Letters
The helium trimer with soft-core potentials
The helium trimer is studied using two- and three-body soft-core potentials.
Realistic helium-helium potentials present an extremely strong short-range
repulsion and support a single, very shallow, bound state. The description of
systems with more than two helium atoms is difficult due to the very large
cancellation between kinetic and potential energy. We analyze the possibility
of describing the three helium system in the ultracold regime using a gaussian
representation of a widely used realistic potential, the LM2M2 interaction.
However, in order to describe correctly the trimer ground state a three-body
force has to be added to the gaussian interaction. With this potential model
the two bound states of the trimer and the low energy scattering helium-dimer
phase shifts obtained with the LM2M2 potential are well reproduced.Comment: 15 pages, 3 figures, submitted to Few-Body System
Three-body structure of low-lying 18Ne states
We investigate to what extent 18Ne can be descibed as a three-body system
made of an inert 16O-core and two protons. We compare to experimental data and
occasionally to shell model results. We obtain three-body wave functions with
the hyperspherical adiabatic expansion method. We study the spectrum of 18Ne,
the structure of the different states and the predominant transition strengths.
Two 0+, two 2+, and one 4+ bound states are found where they are all known
experimentally. Also one 3+ close to threshold is found and several negative
parity states, 1-, 3-, 0-, 2-, most of them bound with respect to the 16O
excited 3- state. The structures are extracted as partial wave components, as
spatial sizes of matter and charge, and as probability distributions.
Electromagnetic decay rates are calculated for these states. The dominating
decay mode for the bound states is E2 and occasionally also M1.Comment: 17 pages, 5 figures (version to appear in EPJA
Estenosis de la arteria renal unilateral de diagnóstico neonatal
La estenosis de la arteria renal es una causa rara de hipertensión arterial neonatal de origen renovascular. Hay muy pocos casos descritos en la literatura en esta etapa. La mayor parte de los pacientes con esta afectación permanecen asintomáticos, y la hipertensión se detecta en las revisiones pediátricas rutinarias. El diagnóstico puede realizarse mediante la combinación de hallazgos bioquímicos y radiológicos. El manejo inicial del paciente se basa en terapia farmacológica hasta alcanzar un crecimiento adecuado para evaluar la reparación definitiva de la lesión vascular o la nefrectomía en caso de supresión funcional del riñón afecto.
Se presenta a una paciente femenina recién nacida a término, con hipertensión arterial e importante falla cardíaca congestiva, originada por una estenosis unilateral de la arteria renal, con supresión funcional y atrofia del riñón afecto, que precisó importante soporte inotrópico y antihipertensivo durante los primeros días de vida, con importante mejoría clínica posterior.
Renal artery stenosis represents a rare cause of neonatal arterial hypertension of renovascular origin, having been described few cases in the literature at this stage of life. Most patients with this disease remain asymptomatic; hypertension can be detected in routine pediatric revisions. Diagnosis can be performed by combining biochemical and radiological findings. The initial management consists of pharmacological therapy in order to achieve adequate growth. Subsequently, it is necessary to assess definitive repair of the vascular lesion or nephrectomy in the case of functional abolition of the affected kidney. We present a term newborn female, with arterial hypertension and an important congestive heart failure, caused by a unilateral renal artery stenosis, with functional abolition and atrophy of the affected kidney, which required an important inotropic and antihypertensive support during her first days of life, with significant clinical improvement subsequently
Metadiffusers : deep-subwavelength sound diffusers
We present deep-subwavelength diffusing surfaces based on acoustic metamaterials, namely metadiffusers. These sound diffusers are rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators. Strong dispersion is produced in the slits and slow sound conditions are induced. Thus, the effective thickness of the panel is lengthened introducing its quarter wavelength resonance in the deep-subwavelength regime. By tuning the geometry of the metamaterial, the reflection coefficient of the panel can be tailored to obtain either a custom reflection phase, moderate or even perfect absorption. Using these concepts, we present ultra-thin diffusers where the geometry of the metadiffuser has been tuned to obtain surfaces with spatially dependent reflection coefficients having uniform magnitude Fourier transforms. Various designs are presented where, quadratic residue, primitive root and ternary sequence diffusers are mimicked by metadiffusers whose thickness are 1/46 to 1/20 times the design wavelength, i.e., between about a twentieth and a tenth of the thickness of traditional designs. Finally, a broadband metadiffuser panel of 3 cm thick was designed using optimization methods for frequencies ranging from 250 Hz to 2 kHz
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