Neural self-tuning adaptive control of non-minimum phase system

The motivation of this research came about when a neural network direct adaptive control scheme was applied to control the tip position of a flexible robotic arm. Satisfactory control performance was not attainable due to the inherent non-minimum phase characteristics of the flexible robotic arm tip. Most of the existing neural network control algorithms are based on the direct method and exhibit very high sensitivity, if not unstable, closed-loop behavior. Therefore, a neural self-tuning control (NSTC) algorithm is developed and applied to this problem and showed promising results. Simulation results of the NSTC scheme and the conventional self-tuning (STR) control scheme are used to examine performance factors such as control tracking mean square error, estimation mean square error, transient response, and steady state response

The Topological Relation Between Bulk Gap Nodes and Surface Bound States : Application to Iron-based Superconductors

In the past few years materials with protected gapless surface (edge) states have risen to the central stage of condensed matter physics. Almost all discussions centered around topological insulators and superconductors, which possess full quasiparticle gaps in the bulk. In this paper we argue systems with topological stable bulk nodes offer another class of materials with robust gapless surface states. Moreover the location of the bulk nodes determines the Miller index of the surfaces that show (or not show) such states. Measuring the spectroscopic signature of these zero modes allows a phase-sensitive determination of the nodal structures of unconventional superconductors when other phase-sensitive techniques are not applicable. We apply this idea to gapless iron based superconductors and show how to distinguish accidental from symmetry dictated nodes. We shall argue the same idea leads to a method for detecting a class of the elusive spin liquids.Comment: updated references, 6 pages, 4 figures, RevTex

Folding model study of the elastic α+α\alpha + \alpha scattering at low energies

The folding model analysis of the elastic $\alpha + \alpha$ scattering at the incident energies below the reaction threshold of 34.7 MeV (in the lab system) has been done using the well-tested density dependent versions of the M3Y interaction and realistic choices for the $^4$He density. Because the absorption is negligible at the energies below the reaction threshold, we were able to probe the $\alpha + \alpha$ optical potential at low energies quite unambiguously and found that the $\alpha + \alpha$ overlap density used to construct the density dependence of the M3Y interaction is strongly distorted by the Pauli blocking. This result gives possible explanation of a long-standing inconsistency of the double-folding model in its study of the elastic $\alpha + \alpha$ and $\alpha$-nucleus scattering at low energies using the same realistic density dependent M3Y interaction

Quantum Monte Carlo Study of Pairing Symmetry and Correlation in Iron-based Superconductors

We perform a systematic quantum Monte Carlo study of the pairing correlation in the $S_4$ symmetric microscopic model for iron-based superconductors. It is found that the pairing with an extensive s-wave symmetry robustly dominates over other pairings at low temperature in reasonable parameter region. The pairing susceptibility, the effective pairing interaction and the $(\pi,0)$antiferromagnetic correlation strongly increase as the on-site Coulomb interaction increases, indicating the importance of the effect of electron-electron correlation. Our non-biased numerical results provide a unified understanding of superconducting mechanism in iron-pnictides and iron-chalcogenides and demonstrate that the superconductivity is driven by strong electron-electron correlation effects.Comment: Accepted for publication as a Letter in Physical Review Letters, and more discussions are adde

Durability of MWCNT Composites under Electron and Neutron Irradiation

Electromagnetic interference shielding effectiveness and conductive properties of carbon nanotube containing composites intended for use as satellite surface materials have been investigated following electron and neutron irradiation. The MWCNT composites were irradiated to fluence levels of 1016 electrons/cm2 with 500 keV electrons. Increase in EMI-SE and conductivity was observed following electron irradiation in two of the samples. The sample with alternating layers of MWCNT and glass had a decrease in conductivity and an increase in EMI-SE post irradiation. This would suggest that the different layered configuration does play a role in the durability of the composite. Having multiple conductive layers of MWCNT composites provide increased durability against electron irradiation. Additional electron irradiations were conducted on three MWCNT composite with the two layers of MWCNT on the outside and 4 layers of glass sandwich in the center. The second set of MWCNT composites were irradiated with 1.0 MeV Si(eq) neutrons to a fluence level of 1014 neutrons/cm2 and 1015 neutrons/cm2. Minor changes in the conductivity and no change in EMI-SE was observed in the MWCNT composites. The overall changes observed; however, are inconsequential to MWCNT composites\u27 intended use as satellite surface structure. In addition, the different layered configurations did have an effect on the electrical properties and durability of the composite under irradiation. The sample with the alternating layer of MWCNT and glass had the least favorable configuration of the three designs

Equation of state of the neutron star matter, and the nuclear symmetry energy

The nuclear mean-field potentials obtained in the Hartree-Fock method with different choices of the in-medium nucleon-nucleon (NN) interaction have been used to study the equation of state (EOS) of the neutron star (NS) matter. The EOS of the uniform NS core has been calculated for the np$e\mu$ composition in the $\beta$-equilibrium at zero temperature, using version Sly4 of the Skyrme interaction as well as two density-dependent versions of the finite-range M3Y interaction (CDM3Y$n$ and M3Y-P$n$), and versions D1S and D1N of the Gogny interaction. Although the considered effective NN interactions were proven to be quite realistic in numerous nuclear structure and/or reaction studies, they give quite different behaviors of the symmetry energy of nuclear matter at supranuclear densities that lead to the \emph{soft} and \emph{stiff} scenarios discussed recently in the literature. Different EOS's of the NS core and the EOS of the NS crust given by the compressible liquid drop model have been used as input of the Tolman-Oppenheimer-Volkov equations to study how the nuclear symmetry energy affects the model prediction of different NS properties, like the cooling process as well as the gravitational mass, radius, and moment of inertia.Comment: To be published in Physical Review

Measurement of Refractive Index Change of Optical Fiber Core Induced by Femtosecond Laser Scanning

We report a new method to measure the refractive index change in optical fiber core induced by femtosecond (fs) laser exposure. An in-line Fabry-Perot interferometer, serving as the measurement platform, is constructed on a commercial single-mode optical fiber by onestep femtosecond (fs) laser fabrication. A positive refractive index change is observed and measured accurately as the laser pulse energy surpasses the ablation threshold