Search results for "Linear system"
showing 10 items of 1558 documents
Characterization of Non-linear Inductors Including Thermal Effects for Power Applications
2018
This paper is focused on the behaviour of non-linear inductors employed in DC/DC switching converters considering the effects due to variations of both current and temperature. The characterization of the inductors is performed by a buck converter operated to stimulate the inductor under test by a constant current with superimposed a large signal. The measurements are carried out at several inductor’s temperature values. Data are automatically collected by a novel virtual instrument developed by the authors in LabVIEW® environment aiming to obtain a polynomial based analytical model. The deep knowledge of the inductor model allows its design to be optimized improving the power density of th…
Phonons in YBa2Cu3O7?x crystals with site-selective oxygen isotope substitution: Frequencies, normal vectors, non-linear properties
1995
Lattice vibrations of YBa2Cu3O7−x crystals with a site-selective isotope substitution18O→16O are investigated theoretically. It is shown that shifts of the frequencies of A1g oxygen vibrations due to this substitution are smaller than under complete one. However, phonon bands and normal vectors are changed much stronger, especially in the case when apical oxygens are substituted. On the basis of the presented analysis anharmonic properties and transition temperatures of the selectively substituted crystals are also briefly discussed.
On nonlinear behavior in brittle heterogeneous materials
2006
Abstract Many modern fiber-reinforced composite materials are ‘brittle’, in the sense that their strain to failure under quasi-static loading is typically of the order of 1% when loaded in directions generally controlled by fiber fracture, and the energy-to-failure under the quasi-static loading curve is typically small. For this reason, analysis of these materials is typically done under assumptions of linear elasticity, usually for homogeneous materials or material layers in a laminate. This is in contrast to ‘ductile’ metal behavior in which elastic–plastic behavior is widely discussed. What is most remarkable is the fact that for long-term behavior, the situation is nearly reversed in m…
Modelling of Cluster Formation in Optically Nonlinear Lithium Niobate Crystal
2011
Modelling of qualitative processes at formation of energetically stable clusters of oxygen octahedrons in the ferroelectric phase of lithium niobate (LiNbO3) crystal is considered with respect to composition. The structure of clusters arranged along the direction of crystallographic axis Y is shown to be the most ordered. The least ordered structures occur in clusters arranged along Z axis in the direction of which the values of ratio R = Li/Nb are most scattered.
Response of Cross-Ply Composite to Off-Axis Loading
2002
Polymer composites are known to exhibit nonlinear stress–strain response due to nonlinearly elastic or plastic deformation of the matrix and damage accumulation. Mechanistic modeling of material response explicitly accounting for these interacting factors often leads to complex theories. Plasticity theory formalism provides an alternative for nonlinear deformation description of composite material. We examine the applicability of an orthotropic plasticity model, developed by Sun et al. for unidirectionally reinforced composite, to composite laminate. The response of a symmetric and balanced cross-ply glass/epoxy laminate is studied under uniaxial tensile loading at different angles to the …
An Equivalent Orthotropic Representation of the Nonlinear Elastic Behavior of Multiwalled Carbon Nanotubes
2006
An equivalent orthotropic representation (EOR) of the nonlinear elastic behavior of multiwalled carbon nanotubes (MWCNTs) was developed based on a nested shell structural representation of MWCNTs. The EOR model was used together with the finite element method to simulate the large deformation of MWCNTs under bending, axial compression and radial compression. Results were compared with those of the nested shell model for four-, eight-, nine-, 14-, and 19-walled carbon nanotubes. The EOR model provides a dramatic improvement in computational efficiency and successfully quantitatively replicates the overall deformation behavior including the initial linear elastic behavior, the onset of local …
Electrostatic Control over Optically Pumped Hot Electrons in Optical Gap Antennas
2020
International audience; We investigate the influence of a static electric field on the incoherent nonlinear response of an unloaded electrically contacted nanoscale optical gap antenna. Upon excitation by a tightly focused near-infrared femtosecond laser beam, a transient elevated temperature of the electronic distribution results in a broadband emission of nonlinear photoluminescence (N-PL). We demonstrate a modulation of the yield at which driving photons are frequency up-converted by means of an external control of the electronic surface charge density. We show that the electron temperature and consequently the N-PL intensity can be enhanced or reduced depending on the command polarity a…
Nonlinear Transport in Hybrid Polypyrrole–Gold Nanostructures
2010
We have studied charge transport in nanometer scale films of polypyrrole (PPy) that were grown electrochemically onto discontinuous ultrathin films of gold. The gold films consisted of 100 nm size islands, separated from each other by nanometer-size gaps. The thickness of PPy can be varied from 30 to 200 nm. The I-V characteristics of these hybrid PPy-Au nanostructures show strong non-linearity at low temperatures, and in particular for the more insulating samples. The hopping transport is further verified from the log / versus V-1/4 plots. Furthermore, the I-V data follow an empirical relation dlog//dV(1/4) similar to T-1/2.
On the Use of L-shaped Granular Chains for the Assessment of Thermal Stress in Slender Structures
2014
Slender beams subjected to compressive load are common in civil engineering. The rapid in-situ measurement of this stress may help preventing structural anomalies. In this article, we describe the coupling mechanism between highly nonlinear solitary waves (HNSWs) propagating along an L- shaped granular system and a beam in contact with the gran- ular medium. We evaluate the use of these waves to measure stress in thermally loaded structures and to estimate the neutral temperature, i.e. the temperature at which the stress is null. We investigate numerically and experimentally one and two L- shaped chains of spherical particles in contact with a prismatic beam subjected to heat. We find that …
Characterization of different regimes in nonlinear liquid crystal models
2012
[EN] The range of validity of two models for nonlocal nonlinear optics in Nematic Liquid Crystals (NLC) is studied. Particularly the influence of the optical power and the initial position of the beam over its trajectory is studied when launching the beam with an offset in a planar cell. The main difference between both models is the dependence of the orientational angle with the optical field, either linear or nonlinear. The results demonstrate the critical role of the nonlinearity in the propagation of nematicons in NLC planar cells. © 2012 World Scientific Publishing Company.