16 research outputs found
<Contributed Talk 11>Chaos in Thermo-visco-elastic Systems Subject to Laser Irradiation
[Date] November 28 (Mon) - December 2 (Fri), 2011: [Place] Kyoto University Clock Tower Centennial Hall, Kyoto, JAPA
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Nonlinear oscillations, bifurcations and chaos in ocean mooring systems
Complex nonlinear and chaotic responses have been recently observed in various
compliant ocean systems. These systems are characterized by a nonlinear mooring
restoring force and a coupled fluid-structure interaction exciting force. A general class
of ocean mooring system models is formulated by incorporating a variable mooring
configuration and the exact form of the hydrodynamic excitation. The multi-degree of
freedom system, subjected to combined parametric and external excitation, is shown to
be complex, coupled and strongly nonlinear.
Stability analysis by a Liapunov function approach reveals global system
attraction which ensures that solutions remain bounded for small excitation.
Construction of the system's Poincare map and stability analysis of the map's fixed
points correspond to system stability of near resonance periodic orbits. Investigation of
nonresonant solutions is done by a local variational approach. Tangent and period
doubling bifurcations are identified by both local stability analysis techniques and are
further investigated to reveal global bifurcations. Application of Melnikov's method to
the perturbed averaged system provides an approximate criterion for the existence of
transverse homoclinic orbits resulting in chaotic system dynamics. Further stability
analysis of the subharmonic and ultraharmonic solutions reveals a cascade of period
doubling which is shown to evolve to a strange attractor.
Investigation of the bifurcation criteria obtained reveals a steady state
superstructure in the bifurcation set. This superstructure identifies a similar bifurcation
pattern of coexisting solutions in the sub, ultra and ultrasubharmonic domains. Within
this structure strange attractors appear when a period doubling sequence is infinite and
when abrupt changes in the size of an attractor occur near tangent bifurcations.
Parametric analysis of system instabilities reveals the influence of the convective inertial
force which can not be neglected for large response and the bias induced by the
quadratic viscous drag is found to be a controlling mechanism even for moderate sea
states.
Thus, stability analyses of a nonlinear ocean mooring system by semi-analytical
methods reveal the existence of bifurcations identifying complex periodic and aperiodic
nonlinear phenomena. The results obtained apply to a variety of nonlinear ocean
mooring and towing system configurations. Extensions and applications of this research
are discussed
Theory of Edge Effects and Conductance for Applications in Graphene-Based Nanoantennas
In this paper, we present a theory of edge effects in graphene for its applications to nanoantennas in the THz, infrared, and visible frequency ranges. The novelty of the presented model is reflected in its self-consistency, which is reached due to the formulation in terms of dynamical conductance instead of ordinary surface conductivity. The physical model of edge effects is based on using the concept of the Dirac fermion and the Kubo approach. In contrast with earlier well-known and widely used models, the surface conductance becomes non-homogeneous and non-local. The numerical simulations of the spatial behavior of the surface conductance were performed in a wide range of values, known from the literature, for the graphene ribbon widths and electrochemical potential. It is shown that if the length exceeds 800 nm, our model agrees with the classical Drude conductivity model with a relatively high degree of accuracy. For rather short lengths, the conductance exhibits a new type of spatial oscillations, which are not present in the ordinary conductivity model. These oscillations modify the form of effective boundary conditions and integral equations for electromagnetic field at the surface of graphene-based antenna. The developed theory opens a new way for realizing electrically controlled nanoantennas by changing the electrochemical potential via gate voltage. The obtained results may be applicable for the design of different carbon-based nanodevices in modern quantum technologies
Erratum: Top-down silicon microcantilever with coupled bottom-up silicon nanowire for enhanced mass resolution (2015 Nanotechnology 26 145502)
Vidal-Álvarez, Gabriel et al.© 2015 IOP Publishing Ltd. A stepped cantilever composed of a bottom-up silicon nanowire coupled to a top-down silicon microcantilever electrostatically actuated and with capacitive or optical readout is fabricated and analyzed, both theoretically and experimentally, for mass sensing applications. The mass sensitivity at the nanowire free end and the frequency resolution considering thermomechanical noise are computed for different nanowire dimensions. The results obtained show that the coupled structure presents a very good mass sensitivity thanks to the nanowire, where the mass depositions take place, while also presenting a very good frequency resolution due to the microcantilever, where the transduction is carried out. A two-fold improvement in mass sensitivity with respect to that of the microcantilever standalone is experimentally demonstrated, and at least an order-of-magnitude improvement is theoretically predicted, only changing the nanowire length. Very close frequency resolutions are experimentally measured and theoretically predicted for a standalone microcantilever and for a microcantilever-nanowire coupled system. Thus, an improvement in mass sensing resolution of the microcantilever-nanowire stepped cantilever is demonstrated with respect to that of the microcantilever standalone.This work has been partially funded by the Spanish government and the European Union FEDER program under project TEC2012-32677 (NEMS-in-CMOS), the Gicserv-6 NGG-193 program, the Israel Science Foundation (1475/09), and the Technion Russell Berrie Nanotechnology Institute.Peer reviewe
Top-down silicon microcantilever with coupled bottom-up silicon nanowire for enhanced mass resolution
Vidal-Álvarez, Gabriel et al.© 2015 IOP Publishing Ltd. A stepped cantilever composed of a bottom-up silicon nanowire coupled to a top-down silicon microcantilever electrostatically actuated and with capacitive or optical readout is fabricated and analyzed, both theoretically and experimentally, for mass sensing applications. The mass sensitivity at the nanowire free end and the frequency resolution considering thermomechanical noise are computed for different nanowire dimensions. The results obtained show that the coupled structure presents a very good mass sensitivity thanks to the nanowire, where the mass depositions take place, while also presenting a very good frequency resolution due to the microcantilever, where the transduction is carried out. A two-fold improvement in mass sensitivity with respect to that of the microcantilever standalone is experimentally demonstrated, and at least an order-of-magnitude improvement is theoretically predicted, only changing the nanowire length. Very close frequency resolutions are experimentally measured and theoretically predicted for a standalone microcantilever and for a microcantilever-nanowire coupled system. Thus, an improvement in mass sensing resolution of the microcantilever-nanowire stepped cantilever is demonstrated with respect to that of the microcantilever standalone.This work has been partially funded by the Spanish government and the European Union FEDER program under project TEC2012-32677 (NEMS-in-CMOS), the Gicserv-6 NGG-193 program, the Israel Science Foundation (1475/09), and the Technion Russell Berrie Nanotechnology Institute.Peer Reviewe