5,544 research outputs found
Crystalline droplets with emergent topological color-charge in many-body systems with sign-changing interactions
We introduce a novel type of self-bound droplet which carries an emergent
color charge. We consider a system of particles hopping on a lattice and
interacting via a commensurately sign-changing potential which is attractive at
a short range. The droplet formation is heralded by spontaneous crystallization
into topologically distinct domains. This endows each droplet with an emergent
color charge governing their mutual interactions: attractive for equal colors
and repulsive otherwise. The number of allowed colors is fixed only by the
discrete spatial symmetries of the sign-changing part of the interaction
potential. With increasing interaction range, the droplets become progressively
more mobile, with their color charge still being energetically protected,
allowing for nontrivial viscous dynamics of the interacting droplet plasmas
formed during cooling. Sign-changing potentials with a short-range attraction
appear quite naturally for light-mediated interactions and we concretely
propose a realization in state-of-the-art experiments with cold atoms in a
multimode optical cavity.Comment: version similar to published, including supplementary material
Heat wave propagation in a nonlinear chain
We investigate the propagation of temperature perturbations in an array of
coupled nonlinear oscillators at finite temperature. We evaluate the response
function at equilibrium and show how the memory effects affect the diffusion
properties. A comparison with nonequilibrium simulations reveals that the
telegraph equation provides a reliable interpretative paradigm for describing
quantitatively the propagation of a heat pulse at the macroscopic level. The
results could be of help in understanding and modeling energy transport in
individual nanotubes.Comment: Revised version, 1 fig. adde
Behaviour of traditional Portuguese timber roof structures
The aim of this paper is to present the results of a structural analysis of common trusses traditionally used in roof construction in Portugal. The study includes the results of a preliminary survey intending to assess the geometry, materials and on site pathologies, as well as a twodimensional linear elastic static and dynamic analysis. The trusses behaviour under symmetric and non-symmetric loads, the king post/tie-beam connection, the stiffness of the joints and the incorrect positioning of the purlins, were some of the structural aspects that have been investigated
Experimental analysis of original and strengthened traditional timber connections
Tests on full-scale unstrengthened connections were performed under monotonic and cyclic loading. Attention has been principally focused on the birdsmouth joint, because of its common use in practice. Different strengthening solutions with metal elements have been evaluated
Modelling of timber joints in traditional structures
Original unstrengthened timber connections and the effects of different strengthening techniques
have been evaluated experimentally with tests on full-scale birdsmouth joints. Experimental results
show that structural response of traditional timber connections under cyclic loading cannot be
represented by common constraint models, like perfect hinges or rigid joints, but should be using
semi-rigid and friction based models. A research program has investigated the behaviour of old
timber joints and examined strengthening criteria. The main parameters affecting the mechanical
behaviour of the connection have been singled out. A synthetic model of cyclic behaviour has been
adapted on the basis of experimental results
Discrete Breathers in a Realistic Coarse-Grained Model of Proteins
We report the results of molecular dynamics simulations of an off-lattice
protein model featuring a physical force-field and amino-acid sequence. We show
that localized modes of nonlinear origin (discrete breathers) emerge naturally
as continuations of a subset of high-frequency normal modes residing at
specific sites dictated by the native fold. In the case of the small
-barrel structure that we consider, localization occurs on the turns
connecting the strands. At high energies, discrete breathers stabilize the
structure by concentrating energy on few sites, while their collapse marks the
onset of large-amplitude fluctuations of the protein. Furthermore, we show how
breathers develop as energy-accumulating centres following perturbations even
at distant locations, thus mediating efficient and irreversible energy
transfers. Remarkably, due to the presence of angular potentials, the breather
induces a local static distortion of the native fold. Altogether, the
combination of this two nonlinear effects may provide a ready means for
remotely controlling local conformational changes in proteins.Comment: Submitted to Physical Biolog
Demonstration of an electrostatic-shielded cantilever
The fabrication and performances of cantilevered probes with reduced
parasitic capacitance starting from a commercial Si3N4 cantilever chip is
presented. Nanomachining and metal deposition induced by focused ion beam
techniques were employed in order to modify the original insulating pyramidal
tip and insert a conducting metallic tip. Two parallel metallic electrodes
deposited on the original cantilever arms are employed for tip biasing and as
ground plane in order to minimize the electrostatic force due to the capacitive
interaction between cantilever and sample surface. Excitation spectra and
force-to-distance characterization are shown with different electrode
configurations. Applications of this scheme in electrostatic force microscopy,
Kelvin probe microscopy and local anodic oxidation is discussed.Comment: 4 pages and 3 figures. Submitted to Applied Physics Letter
A Simple Algebraic Derivation of the Covariant Anomaly and Schwinger Term
An expression for the curvature of the "covariant" determinant line bundle is
given in even dimensional space-time. The usefulness is guaranteed by its
prediction of the covariant anomaly and Schwinger term. It allows a parallel
derivation of the consistent anomaly and Schwinger term, and their covariant
counterparts, which clarifies the similarities and differences between them. In
particular, it becomes clear that in contrary to the case for anomalies, the
difference between the consistent and covariant Schwinger term can not be
extended to a local form on the space of gauge potentials.Comment: 16 page
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