6,655 research outputs found
Thermal behaviour of single ply triaxial woven fabric composites
This paper studies the complex thermal deformation of single-ply triaxial weave com- posites. This behaviour is studied experimentally, by testing ?at plates and narrow strips of TWF, and numerically, by carrying out ?nite-element simulations that capture the e?ects of the thermo-mechanical anisotropy of the individual tows that make up the composite. It is shown that the dominating e?ect is the development of a thermally-induced twist
Quasi-Static Folding and Deployment of Ultrathin Composite Tape-Spring Hinges
Deployable structures made from ultrathin composite materials can be folded elastically and are able to selfdeploy
by releasing the stored strain energy. This paper presents a detailed study of the folding and deployment of a
tape-spring hinge made from a two-ply plain-weave laminate of carbon-fiber reinforced plastic. Aparticular version
of this hinge was constructed, and its moment-rotation profile during quasi-static deployment was measured. The
present study is the first to incorporate in the simulation an experimentally validated elastic micromechanical model
and to provide quantitative comparisons between the simulations and the measured behavior of an actual hinge.
Folding and deployment simulations of the tape-spring hinge were carried out with the commercial finite element
package Abaqus/Explicit, starting from the as-built unstrained structure. The folding simulation includes the effects
of pinching the hinge in the middle to reduce the peak moment required to fold it. The deployment simulation fully
captures both the steady-state moment part of the deployment and the final snap back to the deployed configuration.
An alternative simulation without pinching the hinge provides an estimate of the maximum moment that could be
carried by the hinge during operation. This is about double the snapback moment
Modulated phases of graphene quantum Hall polariton fluids
There is growing experimental interest in coupling cavity photons to the
cyclotron resonance excitations of electron liquids in high-mobility
semiconductor quantum wells or graphene sheets. These media offer unique
platforms to carry out fundamental studies of exciton-polariton condensation
and cavity quantum electrodynamics in a regime in which electron-electron
interactions are expected to play a pivotal role. Focusing on graphene, we
present a theoretical study of the impact of electron-electron interactions on
a quantum Hall polariton fluid, that is a fluid of magneto-excitons resonantly
coupled to cavity photons. We show that electron-electron interactions are
responsible for an instability of graphene integer quantum Hall polariton
fluids towards a modulated phase. We demonstrate that this phase can be
detected by measuring the collective excitation spectra, which soften at a
characteristic wave vector of the order of the inverse magnetic length.Comment: 26+17 pages, 5+3 figure
Resonant modes in strain-induced graphene superlattices
We study tunneling across a strain-induced superlattice in graphene. In
studying the effect of applied strain on the low-lying Dirac-like spectrum,
both a shift of the Dirac points in reciprocal space, and a deformation of the
Dirac cones is explicitly considered. The latter corresponds to an anisotropic,
possibly non-uniform, Fermi velocity. Along with the modes with unit
transmission usually found across a single barrier, we analytically find
additional resonant modes when considering a periodic structure of several
strain-induced barriers. We also study the band-like spectrum of bound states,
as a function of conserved energy and transverse momentum. Such a
strain-induced superlattice may thus effectively work as a mode filter for
transport in graphene
Cavity QED of Strongly Correlated Electron Systems: A No-go Theorem for Photon Condensation
In spite of decades of work it has remained unclear whether or not
superradiant quantum phases, referred to here as photon condensates, can occur
in equilibrium. In this Letter, we first show that when a non-relativistic
quantum many-body system is coupled to a cavity field, gauge invariance forbids
photon condensation. We then present a microscopic theory of the cavity quantum
electrodynamics of an extended Falicov-Kimball model, showing that, in
agreement with the general theorem, its insulating ferroelectric and exciton
condensate phases are not altered by the cavity and do not support photon
condensation.Comment: Reference list updated and minor typos correcte
Statistical correlations of an anyon liquid at low temperatures
Using a proposed generalization of the pair distribution function for a gas
of non-interacting particles obeying fractional exclusion statistics in
arbitrary dimensionality, we derive the statistical correlations in the
asymptotic limit of vanishing or low temperature. While Friedel-like
oscillations are present in nearly all non-bosonic cases at T=0, they are
characterized by exponential damping at low temperature. We discuss the
dependence of these features on dimensionality and on the value of the
statistical parameter alpha.Comment: to appear in Phys. Chem. Liquid
Utilização da ferramenta Idrisi Taiga: Módulo ETM na análise espacializada de tendências climáticas no Brasil.
Baseado na demanda por estudos científicos objetivos que descrevam o contexto atual das interações entre mudanças climáticas globais e assuntos de interesse público, este trabalho avalia o potencial da ferramenta IDRISI Taiga – módulo ETM (Earth Trends Modeler) na análise espacializada de tendências climáticas.Trabalho apresentado na V Mostra de Trabalhos de Estagiários e Bolsistas, Campinas, out. 2009
Deployment Dynamics of Composite Booms with Integral Slotted Hinges
This paper considers a lightweight boom with an integral hinge consisting of a thin-walled tube made of carbon fibre reinforced plastic with two longitudinal slots. The dynamic deployment of this boom is studied both experimentally and by means of detailed finite-element simulations. The deployment of the boom can be divided into three phases: deployment; incomplete latching, buckling of the tape springs and large rotation of the boom; and vibration of the boom in latched configuration. The simulations show that the most critical phase is the second one, as the highest strains in both the fibres and the matrix occur at this stage. Through the simulations it is found that the deployment of the particular boom design studied in this paper is quite sensitive to the details of the gravity offload system
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