30,752 research outputs found
Distributed Adaptive Attitude Synchronization of Multiple Spacecraft
This paper addresses the distributed attitude synchronization problem of
multiple spacecraft with unknown inertia matrices. Two distributed adaptive
controllers are proposed for the cases with and without a virtual leader to
which a time-varying reference attitude is assigned. The first controller
achieves attitude synchronization for a group of spacecraft with a leaderless
communication topology having a directed spanning tree. The second controller
guarantees that all spacecraft track the reference attitude if the virtual
leader has a directed path to all other spacecraft. Simulation examples are
presented to illustrate the effectiveness of the results.Comment: 13 pages, 11 figures. To appear in SCIENCE CHINA Technological
Science
A Forward-Looking Nash Game and Its Application to Achieving Pareto-Efficient Optimization
Recognizing the fact that a player’s cognition plays a defining role in the resulting equilibrium of a game of competition, this paper provides the foundation for a Nash game with forward-looking players by presenting a formal definition of the Nash game with consideration of the players’ belief. We use a simple two-firm model to demonstrate its fundamental difference from the standard Nash and Stackelberg games. Then we show that the players’ belief functions can be regarded as the optimization parameters for directing the game towards a much more desirable equilibrium
Theory of Interfacial Plasmon-Phonon Scattering in Supported Graphene
One of the factors limiting electron mobility in supported graphene is remote
phonon scattering. We formulate the theory of the coupling between graphene
plasmon and substrate surface polar phonon (SPP) modes, and find that it leads
to the formation of interfacial plasmon-phonon (IPP) modes, from which the
phenomena of dynamic anti-screening and screening of remote phonons emerge. The
remote phonon-limited mobilities for SiO, HfO, h-BN and
AlO substrates are computed using our theory. We find that h-BN
yields the highest peak mobility, but in the practically useful high-density
range the mobility in HfO-supported graphene is high, despite the fact
that HfO is a high- dielectric with low-frequency modes. Our
theory predicts that the strong temperature dependence of the total mobility
effectively vanishes at very high carrier concentrations. The effects of
polycrystallinity on IPP scattering are also discussed.Comment: 33 pages, 7 figure
Improved superlensing in two-dimensional photonic crystals with a basis
We study propagation of light in square and hexagonal two-dimensional
photonic crystals. We show, that slabs of these crystals focus light with
subwavelength resolution. We propose a systematic way to increase this
resolution, at an essentially fixed frequency, by employing a hierarchy of
crystals of the same structure, and the same lattice constant, but with an
increasingly complex basis.Comment: 16 Pages, 5 Figure
Electronic states and pairing symmetry in the two-dimensional 16 band d-p model for iron-based superconductor
The electronic states of the FeAs plane in iron-based superconductors are
investigated on the basis of the two-dimensional 16-band d-p model, where the
tight-binding parameters are determined so as to fit the band structure
obtained by the density functional calculation for LaFeAsO. The model includes
the Coulomb interaction on a Fe site: the intra- and inter-orbital direct terms
U and U', the exchange coupling J and the pair-transfer J'. Within the random
phase approximation (RPA), we discuss the pairing symmetry of possible
superconducting states including s-wave and d-wave pairing on the U'-J plane.Comment: 2 pages, 4 figures; Proceedings of the Int. Symposium on
Fe-Oxipnictide Superconductors (Tokyo, 28-29th June 2008
Spin Fluctuations and Unconventional Superconductivity in the Fe-based Oxypnictide Superconductor LaFeAsO_0.7 probed by 57Fe-NMR
We report Fe-NMR studies on the oxygen-deficient iron (Fe)-based
oxypnictide superconductor LaFeAsO ( 28 K) enriched by
Fe isotope. In the superconducting state, the spin component of
Fe-Knight shift decreases almost to zero at low temperatures
and the nuclear spin-lattice relaxation rate exhibits a
-like dependence without the coherence peak just below , which
give firm evidence of the unconventional superconducting state formed by
spin-singlet Cooper pairing. All these events below are consistently
argued in terms of the extended s-wave pairing with a sign reversal of
the order parameter among Fermi surfaces. In the normal state, we found the
remarkable decrease of upon cooling for both the Fe and As sites,
which originates from the decrease of low-energy spectral weight of spin
fluctuations over whole space upon cooling below room temperature.
Such behavior has never been observed for other strongly correlated
superconductors where an antiferromagnetic interaction plays a vital role in
mediating the Cooper pairing.Comment: 4 pages, 4 figures,Accepted for publication in J. Phys. Soc. Jpn.,
vol.78, No.1 (2009
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