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Function Technique (function + technique)

Distribution by Scientific Domains
Physics and Astronomy50%
Engineering30%

Kinds of Function Technique

  • green function technique
    		•

    Selected Abstracts

    Semi-adaptive control of convexly parametrized systems with application to temperature regulation of chemical reactors

    INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 4 2001
    Alexander Fradkov
    In this paper, we are interested in the problem of adaptive control of non-linearly parametrized systems. We investigate the viability of defining a stabilizing parameter update law for the case when the plant model is convex on the uncertain parameters. We show that, when the only prior knowledge is convexity, there does not exist an adaptation law,derivable from the standard separable Lyapunov function technique of Parks,applicable for all the state space. Therefore, we propose a semi-adaptive state feedback controller where adaptation takes place only in the region of the state space where convexity can be used to reduce parameter uncertainty. In the remaining part of the state space we freeze the adaptation and switch to a robust controller. This scheme ensures semi-global stability for convexly parametrized non-linear systems with matched uncertainty. The proposed controller is then applied to the problem of temperature regulation of continuous stirred exothermic chemical reactors where reaction heat is convex in the uncertain parameters. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Tuning of electron transport through molecular bridge systems: A study of shot noise

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2008
    Santanu K. Maiti
    Abstract We study electron transport characteristics through a single phenalenyl molecule attached with two nonsuperconducting electrodes by the use of Green's function technique. Parametric calculations are given based on the tight-binding model to characterize the electron transport through such molecular bridge system. It is observed that the electron transport properties are significantly influenced by (a) the interference effect and (b) the molecule-to-electrodes coupling strength. In this context we also describe the noise power of the current fluctuations that provides an important information about the electron correlation, which is obtained by calculating the Fano factor (F). The knowledge of this current fluctuations gives a key idea for fabrication of efficient molecular devices. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

    Cross-spectral analysis of the X-ray variability of Markarian 421

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002
    Y. H. Zhang
    ABSTRACT Using the cross-spectral method, we confirm the existence of the X-ray hard lags discovered with cross-correlation function technique during a large flare of Mrk 421 observed with BeppoSAX. For the 0.1,2 versus 2,10 keV light curves, both methods suggest sub-hour hard lags. In the time domain, the degree of hard lag, i.e. the amplitude of the 3.2,10 keV photons lagging the lower energy ones, tends to increase with the decreasing energy. In the Fourier frequency domain, by investigating the cross-spectra of the 0.1,2/2,10 keV and the 2,3.2/3.2,10 keV pairs of light curves, the flare also shows hard lags at the lowest frequencies. However, with the present data, it is impossible to constrain the dependence of the lags on frequencies even though the detailed simulations demonstrate that the hard lags at the lowest frequencies probed by the flare are not an artefact of sparse sampling, Poisson and red noise. As a possible interpretation, the implication of the hard lags is discussed in the context of the interplay between the (diffusive) acceleration and synchrotron cooling of relativistic electrons responsible for the observed X-ray emission. The energy-dependent hard lags are in agreement with the expectation of an energy-dependent acceleration time-scale. The inferred magnetic field (B, 0.11 G) is consistent with the value inferred from the spectral energy distributions of the source. Future investigations with higher quality data that show whether or not the time-lags are energy-/frequency-dependent will provide a new constraint on the current models of the TeV blazars. [source]

    Electric field control of magnetic properties in multiferroic thin films

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2010
    St. Kovachev
    Abstract The influence of the electric field E on the magnetic properties in multiferroic thin films is studied by a combination of modified Heisenberg and transverse Ising models (TIMs) using a Green's function technique. It is shown that the magnetization M, the Néel temperature TN and the spin-wave energies Em increase, whereas their damping decreases with increase in electric field E. This is an evidence for the strong intrinsic magnetoelectric (ME) coupling. [source]

    Quantum pumps formed of double walled carbon nanotubes

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009
    V. Zólyomi
    Abstract Using the Brouwer formula, we employ Green's function technique to study charge pumping in shuttle geometry double walled carbon nanotubes. We find strong chirality dependence, and that there is virtually no pumping if the chiral angle of the two walls is the same. We discuss which are the optimal chiralities that can be used for such quantum pumps. Furthermore, we argue that charge pumping with double walled tubes can be used to probe the strength of the inter-layer coupling between the inner and outer nanotube. [source]

    Influence of substrates on the statical and dynamical properties of ferroelectric thin films

    PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007
    J. M. Wesselinowa
    Abstract Based on the transverse Ising model using a Green's function technique it is shown that the influence of the substrate induces strong changing of various statical and dynamical properties due to different exchange interactions between the ferroelectric thin film and the substrate. Properties such as the phase transition temperature, the polarization, the soft-mode energy, the damping and the dielectric function were found to be highly dependent upon the magnitude and the kind (tensile or compressive) of the stress due to the substrate. There is some competition between the surface and substrate effects. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Spin-polarized resonant tunneling through two coupled quantum dots

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2006
    P. Trocha
    Abstract Resonant electronic transport through two coupled non-interacting single-level quantum dots attached to ferromagnetic leads with collinear magnetizations is analyzed theoretically. Coupling of the dots to external leads as well as the inter-dot coupling are assumed to be spin dependent. Basic transport characteristics, including current-voltage curves, linear and nonlinear conductance, and tunnel magnetoresistance associated with magnetization rotation are calculated using the Green function technique. The relevant Green functions have been calculated by the equation of motion method. Variation of the transport characteristics with such system parameters like energy level position, spin polarization of the leads, and coupling between the dots has been calculated numerically. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Observer-based controller design of discrete-time piecewise affine systems

    ASIAN JOURNAL OF CONTROL, Issue 4 2010
    Ya-Hui Gao
    Abstract This paper presents a novel observer-based controller design method for discrete-time piecewise affine (PWA) systems. The basic idea is as follows: at first, a piecewise linear (without affine terms) state feedback controller and a PWA observer are designed separately, and then it is proved that the output feedback controller constructed by the resulting observer and state feedback controller gains can guarantee the stability of the closed-loop system. During the controller design, the piecewise-quadratic Lyapunov function technique is used. Moreover, the region information is taken into account to treat the affine terms, so the controller gains can be obtained by solving a set of linear matrix inequalities, which are numerically feasible with commercially available software. Three simulation examples are given finally to verify the proposed theoretical results. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source]

    Tracking control for switched linear systems with time-delay: a state-dependent switching method,

    ASIAN JOURNAL OF CONTROL, Issue 5 2009
    Qing-Kui Li
    Abstract Tracking control for switched linear systems with time-delay is investigated in this paper. Based on the state-dependent switching method, sufficient conditions for the solvability of the tracking control problem are given. We use single Lyapunov function technique and a typical hysteresis switching law to design a tracking control law such that the H, model reference tracking performance is satisfied. The controller design problem can be solved efficiently by using linear matrices inequalities. Since convex combination techniques are used to derive the delay independent criteria, some subsystems are allowed to be unstable. It is highly desirable that a non-switched time-delay system can not earn such property. Simulation example shows the feasibility and validity of the switching control law. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source]

    Group functions approach based on the combination of strictly local geminals and molecular orbitals

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2006
    A. M. Tokmachev
    Abstract Thegroup functions technique is a natural way to introduce local description into quantum chemistry. It can also be a basis for construction of numerically effective computational schemes having almost linear growth of computational costs with that of the size of the system. Previously, we constructed a family of computationally efficient semiempirical methods based on the variationally determined strictly local geminals (SLGs). It was implemented with four popular parameterization schemes (MINDO/3, MNDO, AM1, and PM3). Because of construction details, its applicability was restricted only to compounds with well-defined two-electron two-center chemical bonds and lone pairs. We generalize the previous treatment to make the electronic structure calculations possible for a wider class of compounds without loss of computational efficiency. The proposed scheme (SLG/SCF) is based on the general group function approach combining different descriptions for different electron groups: essentially local two-electron ones are described by geminals, while those with other numbers of electrons are described in the one-electron approximation. We implement the RHF, UHF, and ROHF approaches for the groups with delocalized electrons. This approach is tested for a series of radicals and molecules with extended ,-electron systems. It is shown that the SLG/SCF-based methods describe the experimental data not worse than the corresponding SCF procedures and provide a good starting point for calculations of polyatomic molecular systems. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]