23,564 research outputs found
Bump-on-tail instability of twisted excitations in rotating cold atomic clouds
We develop a kinetic theory for twisted density waves (phonons), carrying a
finite amount of orbital angular momentum, in large magneto optical traps,
where the collective processes due to the exchange of scattered photons are
considered. Explicit expressions for the dispersion relation and for the
kinetic (Landau) damping are derived and contributions from the orbital angular
momentum are discussed. We show that for rotating clouds, exhibiting
ring-shaped structures, phonons carrying orbital angular momentum can cross the
instability threshold and grow out of noise, while the usual plane wave
solutions are kinetically damped.Comment: 5 pages, 5 figure
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
Tuned liquid dampers simulation for earthquake response control of buildings
This paper is focused on the study of an earthquake protection system, the Tuned Liquid Damper (TLD), which
can, if adequately designed, reduce earthquake demands on buildings. This positive effect is accomplished taking
into account the oscillation of the free surface of a fluid inside a tank (sloshing). The behaviour of an isolated
Tuned Liquid Damper, subjected to a sinusoidal excitation at its base, with different displacement amplitudes,
was studied by finite element analysis. The efficiency of the TLD in improving the seismic response of an existing building, representative of modern architecture buildings in southern European countries was also evaluated based on linear dynamic analyses
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