12,292 research outputs found
H∞ control for networked systems with random communication delays
Copyright [2006] IEEE. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.This note is concerned with a new controller design problem for networked systems with random communication delays. Two kinds of random delays are simultaneously considered: i) from the controller to the plant, and ii) from the sensor to the controller, via a limited bandwidth communication channel. The random delays are modeled as a linear function of the stochastic variable satisfying Bernoulli random binary distribution. The observer-based controller is designed to exponentially stabilize the networked system in the sense of mean square, and also achieve the prescribed H∞ disturbance attenuation level. The addressed controller design problem is transformed to an auxiliary convex optimization problem, which can be solved by a linear matrix inequality (LMI) approach. An illustrative example is provided to show the applicability of the proposed method
Split Two-Higgs-Doublet Model and Neutrino Condensation
We split the two-Higgs-doublet model by assuming very different vevs for the
two doublets: the vev is at weak scale (174 GeV) for the doublet \Phi_1 and at
neutrino-mass scale (10^{-2} \sim 10^{-3} eV) for the doublet \Phi_2. \Phi_1 is
responsible for giving masses to all fermions except neutrinos; while \Phi_2 is
responsible for giving neutrino masses through its tiny vev without introducing
see-saw mechanism. Among the predicted five physical scalars H, h, A^0 and
H^{\pm}, the CP-even scalar h is as light as 10^{-2} \sim 10^{-3}eV while
others are at weak scale. We identify h as the cosmic dark energy field and the
other CP-even scalar H as the Standard Model Higgs boson; while the CP-odd A^0
and the charged H^{\pm} are the exotic scalars to be discovered at future
colliders. Also we demonstrate a possible dynamical origin for the doublet
\Phi_2 from neutrino condensation caused by some unknown dynamics.Comment: version in Europhys. Lett. (discussions added
Numerical evidences of spin-1/2 chain approaching spin-1 chain
In this article, we study the one dimensional Heisenberg spin-1/2 alternating
bond chain in which the nearest neighbor exchange couplings are ferromagnetic
(FM) and antiferromagnetic (AF) alternatively. By using exact diagonalization
and density matrix renormalization groups (DMRG) method, we discuss how the
system approaches to the AF uniform spin-1 chain under certain condition. When
the ratio of AF to FM coupling strength}
\textit{is very small, the physical quantities of the alternating bond chain
such as the spin-spin correlation, the string correlation function and the spin
density coincide with that of the AF uniform spin-1 chain. The edge state
problem is discussed in the present model with small}\textit{limit. In
addition, the Haldane gap of the AF uniform spin-1 chain is 4-times of the gap
of the system considered.Comment: 9pages,8page
Rank 3 permutation characters and maximal subgroups
In this paper we classify all maximal subgroups M of a nearly simple
primitive rank 3 group G of type L=Omega_{2m+1}(3), m > 3; acting on an L-orbit
E of non-singular points of the natural module for L such that 1_P^G <=1_M^G
where P is a stabilizer of a point in E. This result has an application to the
study of minimal genera of algebraic curves which admit group actions.Comment: 41 pages, to appear in Forum Mathematicu
Spin-resolved correlation kinetic energy of the spin-polarized electron gas
URL:http://link.aps.org/doi/10.1103/PhysRevB.70.205126
DOI:10.1103/PhysRevB.70.205126We give an exact formula, based on differentiation with respect to the electron mass, for the spin resolution of the kinetic energy (KE) of a general many-electron system, including the correlation KE. We evaluate the spin-resolved correlation KE for a uniform three dimensional electron gas of arbitrary spin polarization at metallic densities, using the Singwi-Tosi-Land-Sjolander formalism. We give a very accurate scaling relation for the data thus obtained. Our results are expected to be relevant in the analysis of spintronic systems.J.F.D. acknowledges support from an Australian Research Council Large Grant. G.V. acknowledges NSF Grant No. DMR-0313681. Computer time was provided by Research Computing Services at Griffith University
Cosmo MSW effect for mass varying neutrinos
We consider neutrinos with varying masses which arise in scenarios relating
neutrino masses to the dark energy density in the universe. We point out that
the neutrino mass variation can lead to level crossing and thus a cosmo MSW
effect, having dramatic consequences for the flavor ratio of astrophysical
neutrinos.Comment: 8 pages, 1 figure, more detailed discussions, version to be published
by Mod. Phys. Lett.
Experimental verification of a self-consistent theory of the first-, second-, and third-order (non)linear optical response
We show that a combination of linear absorption spectroscopy, hyper-Rayleigh
scattering, and a theoretical analysis using sum rules to reduce the size of
the parameter space leads to a prediction of the two-photon absorption
cross-section of the dye AF455 that agrees with two-photon absorption
spectroscopy. Our procedure, which demands self-consistency between several
measurement techniques and does not use adjustable parameters, provides a means
for determining transition moments between the dominant excited states based
strictly on experimental characterization. This is made possible by our new
approach that uses sum rules and molecular symmetry to rigorously reduce the
number of required physical quantities.Comment: 10 pages, 9 figure
Activities of methionine-γ-lyase in the acidophilic archaeon “Ferroplasma acidarmanus” strain fer1
Biogeochemical processes on exposed pyrite ores result in extremely high levels of sulfuric acid at these locations. Acidophiles that thrive in these conditions must overcome significant challenges, including an environment with proton concentrations at pH 3 or below. The role of sulfur metabolism in the archaeon “Ferroplasma acidarmanus” strain fer1’s ability to thrive in this environment was investigated due to its growth-dependent production of methanethiol, a volatile organic sulfur compound. Two putative sequences for methionine- γ-lyase (EC 4.4.1.11), an enzyme known to carry out α,γ-elimination on L-methionine to produce methanethiol, were identified in fer1. Bioinformatic analyses identified a conserved pyridoxal-5′-phosphate (PLP) binding domain and a partially conserved catalytic domain in both putative sequences. Detection of PLP-dependent and L-methionine-dependent production of α-keto compounds and thiol groups in fer1 confirmed the presence of methionine-γ-lyase activity. Further, fer1 lysate was capable of processing related substrates, including D-methionine, L-cysteine, L-cystathionine, and L/D-homocysteine. When the two putative fer1 methionine-γ- lyase gene-coded proteins were expressed in Escherichia coli cells, one sequence demonstrated an ability to carry out α, γ-elimination activity, while the other exhibited γ-replacement activity. These fer1 methionine-γ-lyases also exhibited optimum pH, substrate specificity, and catalytic preferences that are different from methionine-γ-lyases from other organisms. These differences are discussed in the context of molecular phylogeny constructed using a maximum likelihood algorithm based on methionine-γ-lyase sequences from a diverse selection of organisms
- …