264,782 research outputs found
Optimal feedback control infinite dimensional parabolic evolution systems: Approximation techniques
A general approximation framework is discussed for computation of optimal feedback controls in linear quadratic regular problems for nonautonomous parabolic distributed parameter systems. This is done in the context of a theoretical framework using general evolution systems in infinite dimensional Hilbert spaces. Conditions are discussed for preservation under approximation of stabilizability and detectability hypotheses on the infinite dimensional system. The special case of periodic systems is also treated
Analysis of test system misalignment in the creep test
Sheet type rectangular 1100-0 aluminum specimens were tested. The creep strain at the geometric centerline of the specimen is different than that at the neutral axis, and decreases with time. The effect of misalignment, which decreases with creep time, is minimized when creep tests are conducted with long pullrods and large initial strain level (high creep stress)
Conductance spectra of metallic nanotube bundles
We report a first principles analysis of electronic transport characteristics
for (n,n) carbon nanotube bundles. When n is not a multiple of 3, inter-tube
coupling causes universal conductance suppression near Fermi level regardless
of the rotational arrangement of individual tubes. However, when n is a
multiple of 3, the bundles exhibit a diversified conductance dependence on the
orientation details of the constituent tubes. The total energy of the bundle is
also sensitive to the orientation arrangement only when n is a multiple of 3.
All the transport properties and band structures can be well understood from
the symmetry consideration of whether the rotational symmetry of the individual
tubes is commensurate with that of the bundle
Influence of doping level on the Hall coefficient and on the thermoelectric power in
Hall coefficient and thermoelectric power TEP are studied
systematically in the single crystals (NCCO) with
different x from underdoped to overdoped regime. With increasing doping level,
both and TEP decrease and change their sign from negative to positive. A
striking feature is that the temperature dependence of the Hall angle follows a
behavior in the underdoped regime, while a in the overdoped regime.
These behaviors are closely related to the evolution of Fermi surface with
doping level observed by ARPES.Comment: 4 pages, 4 figures, to be published in PR
Topology of Entanglement in Multipartite States with Translational Invariance
The topology of entanglement in multipartite states with translational
invariance is discussed in this article. Two global features are foundby which
one can distinguish distinct states. These are the cyclic unit and the
quantised geometric phase. Furthermore the topology is indicated by the
fractional spin. Finally a scheme is presented for preparation of these types
of states in spin chain systems, in which the degeneracy of the energy levels
characterises the robustness of the states with translational invariance.Comment: major revision. accepted by EPJ
Angle-Resolved Photoemission Spectroscopy of the Antiferromagnetic Superconductor Nd1.87Ce0.13CuO4: Anisotropic Spin-Correlation Gap, Pseudogap, and the Induced Quasiparticle Mass Enhancement
We performed high-resolution angle-resolved photoemission spectroscopy on
Nd1.87Ce0.13CuO4, which is located at the boundary of the antiferromagnetic
(AF) and the superconducting phase. We observed that the quasiparticle (QP)
effective mass around (pi, 0) is strongly enhanced due to the opening of the AF
gap. The QP mass and the AF gap are found to be anisotropic, with the largest
value near the intersecting point of the Fermi surface and the AF zone
boundary. In addition, we observed that the QP peak disappears around the Neel
temperature (TN) while the AF pseudogap is gradually filled up at much higher
temperatures, possibly due to the short-range AF correlation.Comment: 4 pages, 4 figure
High- superconductivity in undoped ThFeAsN
Unlike the widely studied ReFeAsO series, the newly discovered iron-based
superconductor ThFeAsN exhibits a remarkably high critical temperature of 30 K,
without chemical doping or external pressure. Here we investigate in detail its
magnetic and superconducting properties via muon-spin rotation/relaxation
(SR) and nuclear magnetic resonance (NMR) techniques and show that ThFeAsN
exhibits strong magnetic fluctuations, suppressed below 35 K, but no magnetic
order. This contrasts strongly with the ReFeAsO series, where stoichiometric
parent materials order antiferromagnetically and superconductivity appears only
upon doping. The ThFeAsN case indicates that Fermi-surface modifications due to
structural distortions and correlation effects are as important as doping in
inducing superconductivity. The direct competition between antiferromagnetism
and superconductivity, which in ThFeAsN (as in LiFeAs) occurs at already zero
doping, may indicate a significant deviation of the -wave superconducting
gap in this compound from the standard scenario.Comment: 6 pages, 5 figure
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