1,184 research outputs found
Propagation front of correlations in an interacting Bose gas
We analyze the quench dynamics of a one-dimensional bosonic Mott insulator
and focus on the time evolution of density correlations. For these we identify
a pronounced propagation front, the velocity of which, once correctly
extrapolated at large distances, can serve as a quantitative characteristic of
the many-body Hamiltonian. In particular, the velocity allows the weakly
interacting regime, which is qualitatively well described by free bosons, to be
distinguished from the strongly interacting one, in which pairs of distinct
quasiparticles dominate the dynamics. In order to describe the latter case
analytically, we introduce a general approximation to solve the Bose-Hubbard
Hamiltonian based on the Jordan-Wigner fermionization of auxiliary particles.
This approach can also be used to determine the ground-state properties. As a
complement to the fermionization approach, we derive explicitly the
time-dependent many-body state in the noninteracting limit and compare our
results to numerical simulations in the whole range of interactions of the
Bose-Hubbard model.Comment: 16 pages, 7 figure
Comment on "Coherent Ratchets in Driven Bose-Einstein Condensates"
C. E. Creffield and F. Sols (Phys. Rev. Lett. 103, 200601 (2009)) recently
reported finite, directed time-averaged ratchet current, for a noninteracting
quantum particle in a periodic potential even when time-reversal symmetry
holds. As we explain in this Comment, this result is incorrect, that is,
time-reversal symmetry implies a vanishing current.Comment: revised versio
Edifícios pombalinos: comportamento e reforço
A análise estrutural de edifícios existentes é um desafio complexo por muitas razões, incluindo o desconhecimento sobre o comportamento dos materiais e componentes estruturais. Os edifícios pombalinos representam uma tipologia valiosa do nosso edificado, pelo contexto cultural do sismo de 1755 em Lisboa e de criação de uma cidade nova, bem como pelos aspetos tecnológicos inovadores. O presente artigo apresenta, inicialmente, um breve estado do conhecimento dos edifícios alvenaria-madeira. Posteriormente, são apresentados resultados de ensaios cíclicos recentes na Universidade do Minho sobre esta tipologia de paredes, que permitem caracterizar o seu comportamento e avaliar diferentes soluções de reforço
An overview on the seismic behaviour of timber frame structures
Traditional timber frame walls are an important structural element of many buildings and are usually composed of vertical posts and horizontal beams with bracing diagonal elements. In Portugal the timber frame walls, known as frontal walls, are usually part of Pombalino buildings, which were introduced by the Marquis of Pombal, who was responsible for the reconstruction of Downtown Lisbon after the great earthquake of 1755, which partially destroyed the city.
Given the increasing interest of the research community to this structural system, it is important to promote the discussion of the main findings that can contribute to the advance on the knowledge of the mechanical behaviour of timber frame buildings to seismic action.
Therefore, this paper intends: (1) to give an overview of the different solution of timber frame structures in different countries with special focus on the frontal walls characteristic of Pombalino buildings; (2) provide some examples of the reasonable behaviour of timber frame buildings in past earthquakes; (3) to summarize the experimental research carried out in the recent years in analysis of the behaviour to in-plane cyclic loading
Timber frames as an earthquake resisting system in Portugal
Timber frames are commonly adopted as a structural element in many countries with specific
characteristics varying locally, in termsof geometry and materials.Their diffusion in Southern European countries
is linked to their good seismic-resistant capacity, but only in the last decade interest has grown for this structural
typology, and studies have been performed to better understand their behaviour. In this contribution, a brief
state of the art on existing timber frame building typologies is presented, focusing on their seismic-resistant
characteristics. Additionally, an overview of possible strengthening solutions, adopted both in practice, and
tested experimentally are presented. Their performance when applied to walls and connections is also discussed.(undefined
Rotating Solution of Einstein-Maxwell Dilaton Gravity with Unusual Asymptotics
We study electrically charged, dilaton black holes, which possess
infinitesimal angular momentum in the presence of one or two Liouville type
potentials. These solutions are neither asymptotically flat nor (anti)-de
Sitter. Some properties of the solutions are discussed.Comment: 11 pages, Accepted (Int. J. Theor. Phys.
Charged Nariai Black Holes With a Dilaton
The Reissner-Nordstrom-de Sitter black holes of standard Einstein-Maxwell
theory with a cosmological constant have no analogue in dilatonic theories with
a Liouville potential. The only exception are the solutions of maximal mass,
the Charged Nariai solutions. We show that the structure of the solution space
of the Dilatonic Charged Nariai black holes is quite different from the
non-dilatonic case. Its dimensionality depends on the exponential coupling
constants of the dilaton. We discuss the possibility of pair creating such
black holes on a suitable background. We find conditions for the existence of
Charged Nariai solutions in theories with general dilaton potentials, and
consider specifically a massive dilaton.Comment: 20 pages, LaTeX, 4 figures, submitted to Phys. Rev.
Controlled transport of matter waves in two-dimensional optical lattices
We propose a method for achieving dynamically controllable transport of
highly mobile matter-wave solitons in a driven two-dimensional optical lattice.
Our numerical analysis based on the mean-field model and the theory based on
the time-averaging approach, demonstrate that a fast time-periodic rocking of
the two-dimensional optical lattice enables efficient stabilization and
manipulation of spatially localized matter wavepackets via induced
reconfigurable mobility channels.Comment: 4 pages, 4 figure
Numerical approaches for the analysis of timber frame walls
A numerical approach to simulate the behaviour of timber shear walls under both static and dynamic loading is proposed. Because the behaviour of timber shear walls hinges on the behaviour of the nail connections, the force-displacement behaviour of sheathing-to-framing nail connections are first determined and then used to define the hysteretic properties of finite elements representing these connections. The model nails are subsequently implemented into model walls. The model walls are verified using experimental results for both monotonic and cyclic loading. It is demonstrated that the complex hysteretic behaviour of timber shear walls can be reasonably represented using model shear walls in which nonlinear material failure is concentrated only at the sheathing-to-framing nail connections
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