8,373 research outputs found
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.
Protocolo de actuación ante hemangiomas y/o malformaciones vasculares
When facing any vascular lesion present in the first
moments of life, it is necessary to determine whether
one is dealing with a tumour or a vascular malformation,
given the different evolution of both processes and,
hence, the different treatments they require.
Diagnosis is basically clinical, based on a correct
anamnesis and a detailed physical exploration. The
first thing is to establish whether the lesion was present
at birth and has changed size significantly, which
would lead one to think of a haemangioma or, on the
contrary, whether it is congenital and of very slow
growth, such as vascular malformations. Facing dubious
lesions, it is recommendable to carry out a biopsy
with immunohistochemistry for the GLUT-1 antibody,
specific to haemangiomas.
Amongst the image tests, the first choice is usually
ecography-Doppler, which makes it possible to determine
whether the lesion is of high or low flow and to
distinguish whether one is dealing with a haemangioma
or a vascular malformation. Depending on the type of
lesion, its localisation and degree of affectation it might
be necessary to carry out radiography, magnetic resonance,
phlebography, angio-resonance, arteriography
or lymphoscintigraphy to complete the study.
In more particular cases, such as multiple haemangiomatosis,
it is necessary to carry out an hepatic
echography, blood concealed in faeces, gastroscopy
and colonoscopy, as well a determination of thyroid
hormones; and in venous or combined extensive malformations,
a haemogram and coagulation tests.
On the other hand, the possible repercussions on
other organs make a multidisciplinary approach essential,
with the participation of different specialists.
Due to the wide spectrum covered by vascular
anomalies, treatment must be individualised
An experimental model of mixing processes generated by an array of top-heavy turbulent plumes
The mixing process of two fluids of unequal density generated by the evolution of an array of forced turbulent plumes is studied in the laboratory. The corresponding qualitative conclusions and the quantitative results based on measures of the density field and of the height of the fluid layers are described. The partial mixing process is characterized and analyzed, and the conclusions of this analysis are related to the mixing efficiency and the volume of the final mixed layer as functions of the Atwood number, which ranges from 0.010 to 0.134. An exponential fit is used to evaluate the mixing efficiency versus the Atwood showing the role of initial conditions on mixing efficiency variability
Induced structures under seasonal flow conditions in the Ebro delta shelf. Laboratory and numerical models
The characteristic induced length scale produced by a river flow in its outlet is studied. Two experimental methods are compared: a) Physical modeling in laboratory and b) numerical mesoscale diffusion model; under low tidal and
realistic seasonal flow conditions from Spring, Summer, Fall and Winter field data from the Ebro delta shelf. The physical laboratory experiences were performed on a
five-meter diameter turntable, using the Froude-Rossby similarity. This paper shows complementary results from both methods investigating the vortex characteristic and the dynamics of the flow. The experimental results under rotating conditions show coherent vortex dynamics in the large-meso scale coastal boundary. The numerical model, on the other hand, lacks the mesoscale vortex dynamics and
its induced diffusion but gives reasonable flow conditions in the close region (15–20 km) around the river mouth. Both the experiments and numerical simulations show river plume diffusion smaller than D2 ∝ t3
Particle dispersion processes in two-dimensional turbulence: a comparison with 2-D kinematic simulation.
International audienceWe study numerically the comparison between Lagrangian experiments on turbulent particle dispersion in 2-D turbulent flows performed, on the one hand, on the basis of direct numerical simulations (DNS) and, on the other hand, using kinematic simulations (KS). Eulerian space-time structure of both DNS and KS dynamics are not comparable, mostly due to the absence of strong coherent vortices and advection processes in the KS fields. The comparison allows to refine past studies about the contribution of non-homogeneous space-time 2-D Eulerian structure on the turbulent absolute and relative particle dispersion processes. We particularly focus our discussion on the Richardson's regime for relative dispersion
Predicting the spread of epidemiological diseases by using a multi-objective algorithm
The epidemiological models are able to predict the spread of diseases, but a previous work on calibrating some involved parameters must be done. In this work, we propose a methodology to adjust those parameters based on solving a multi-objective optimization problem whose objective functions measure the accuracy of the model. More precisely, we have considered the Between-Countries Disease Spread model because it involves a set of countries taking into account the migratory movements among them. As a result, using some real data about the number of detected cases and the number of deaths for the Ebola virus
disease, we have shown that the methodology is able to find a set of values for the parameters so that the model fits the outbreak spread for a set of countries
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
Application of Resonance Perturbation Theory to Dynamics of Magnetization in Spin Systems Interacting with Local and Collective Bosonic Reservoirs
We apply our recently developed resonance perturbation theory to describe the
dynamics of magnetization in paramagnetic spin systems interacting
simultaneously with local and collective bosonic environments. We derive
explicit expressions for the evolution of the reduced density matrix elements.
This allows us to calculate explicitly the dynamics of the macroscopic
magnetization, including characteristic relaxation and dephasing time-scales.
We demonstrate that collective effects (i) do not influence the character of
the relaxation processes but merely renormalize the relaxation times, and (ii)
significantly modify the dephasing times, leading in some cases to a
complicated (time inhomogeneous) dynamics of the transverse magnetization,
governed by an effective time-dependent magnetic field
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