19,438 research outputs found
Bound state techniques to solve the multiparticle scattering problem
Solution of the scattering problem turns to be very difficult task both from
the formal as well as from the computational point of view. If the last two
decades have witnessed decisive progress in ab initio bound state calculations,
rigorous solution of the scattering problem remains limited to A4 case.
Therefore there is a rising interest to apply bound-state-like methods to
handle non-relativistic scattering problems. In this article the latest
theoretical developments in this field are reviewed. Five fully rigorous
methods will be discussed, which address the problem of nuclear collisions in
full extent (including the break-up problem) at the same time avoiding
treatment of the complicate boundary conditions or integral kernel
singularities. These new developments allows to use modern bound-state
techniques to advance significantly rigorous solution of the scattering
problem.Comment: To appear in Progress in Particle and Nuclear Physic
The ion motion in self-modulated plasma wakefield accelerators
The effects of plasma ion motion in self-modulated plasma based accelerators
is examined. An analytical model describing ion motion in the narrow beam limit
is developed, and confirmed through multi-dimensional particle-in-cell
simulations. It is shown that the ion motion can lead to the early saturation
of the self-modulation instability, and to the suppression of the accelerating
gradients. This can reduce the total energy that can be transformed into
kinetic energy of accelerated particles. For the parameters of future
proton-driven plasma accelerator experiments, the ion dynamics can have a
strong impact. Possible methods to mitigate the effects of the ion motion in
future experiments are demonstrated.Comment: 11 pages, 3 figures, accepted for publication in Phys. Rev. Let
Seismic vulnerability of Modern Architecture building's: Le Corbusier style: a case study
In Portugal, at the end of the World War II, a new generation of architects emerged, influenced by the Modern
Movement Architecture, born in Central-Europe in the early twenties but now influenced also by the Modern
Brazilian Architecture.
They worked with new typologies, such as multifamily high-rise buildings, and built them in the most important
cities of the country, during the fifties, reflecting the principles of the Modernity and with a strong formal conception
inspired in the International Style’s codes.
Concrete, as material and technology, allowed that those “Unity Centre” buildings become modern objects,
expressing the five-point formula that Le Corbusier enounced in 1927 and draw at the “Unité d’Habitation de
Marseille”, namely: the building lifted in pilotis, the free design of the plan, the free design of the façade, the
unbroken horizontal window and the roof terrace.
In Lisbon, late forties urban plans transformed and expanded the city, creating modulated buildings repeated in
great extensions – that was a progressist idea of standardization. The Infante Santo complex is a successful adaptation
to the Lisbon reality of the Modern Urbanism and Architecture.
In the fifties, it was built a large number of Modern housing buildings in Lisbon, with structural characteristics
that, in certain conditions, can induce weaknesses in structural behaviour, especially under earthquake loading. For
example, the concept of buildings lifted in pilotis can strongly facilitate the occurrence of soft-storey mechanisms,
which turns these structures very vulnerable to earthquake actions.
The development and calibration of refined numerical tools, as well as, assessment and design codes makes
feasible the structural safety assessment of existing buildings. To investigate the vulnerability of this type of
construction, one building representative of the Modern Architecture, at the Infante Santo Avenue, was studied. This
building was studied with the non-linear dynamic analysis program PORANL, which allows the safety evaluation
according to the recently proposed standards
Four-nucleon scattering: Ab initio calculations in momentum space
The four-body equations of Alt, Grassberger and Sandhas are solved for \nH
scattering at energies below three-body breakup threshold using various
realistic interactions including one derived from chiral perturbation theory.
After partial wave decomposition the equations are three-variable integral
equations that are solved numerically without any approximations beyond the
usual discretization of continuum variables on a finite momentum mesh. Large
number of two-, three- and four-nucleon partial waves are considered until the
convergence of the observables is obtained. The total \nH cross section data
in the resonance region is not described by the calculations which confirms
previous findings by other groups. Nevertheless the numbers we get are slightly
higher and closer to the data than previously found and depend on the choice of
the two-nucleon potential. Correlations between the deficiency in \nd
elastic scattering and the total \nH cross section are studied.Comment: Corrected Eq. (10
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