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Stable System (stable + system)
Selected AbstractsStability and identification for rational approximation of frequency response function of unbounded soilEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2010Xiuli Du Abstract Exact representation of unbounded soil contains the single output,single input relationship between force and displacement in the physical or transformed space. This relationship is a global convolution integral in the time domain. Rational approximation to its frequency response function (frequency-domain convolution kernel) in the frequency domain, which is then realized into the time domain as a lumped-parameter model or recursive formula, is an effective method to obtain the temporally local representation of unbounded soil. Stability and identification for the rational approximation are studied in this paper. A necessary and sufficient stability condition is presented based on the stability theory of linear system. A parameter identification method is further developed by directly solving a nonlinear least-squares fitting problem using the hybrid genetic-simplex optimization algorithm, in which the proposed stability condition as constraint is enforced by the penalty function method. The stability is thus guaranteed a priori. The infrequent and undesirable resonance phenomenon in stable system is also discussed. The proposed stability condition and identification method are verified by several dynamic soil,structure-interaction examples. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis, Solution-State and Solid-State Structural Characterization of Monocationic Nitrido Heterocomplexes [M(N)(DTC)(PNP)]+ (M = 99Tc, Re; DTC = Dithiocarbamate; PNP = Heterodiphosphane)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2004Cristina Bolzati Abstract Mono-cationic nitrido heterocomplexes of general formula [M(N)(DTC)(PNP)]+ (where M is 99Tc or Re, DTC is the mono-anionic form of a dithiocarbamate ligand, and PNP is a diphosphane ligand with a tertiary amine-containing five-membered spacer) were prepared by ligand-exchange reactions with the labile precursors [M(N)Cl2(PPh3)2] in dichloromethane/alcohol mixtures. The molecular structure of the representative rhenium complex [Re(N)(dedc)(pnp2)][PF6] (1) displays a distorted, square-pyramidal geometry with the dithiocarbamate sulfur and the diphosphane phosphorus atoms spanning the four coordination positions on the equatorial plane. If the additional interactions between the nitrido nitrogen and the weakly bonded transN -diphosphane heteroatom, the molecular geometry can be viewed as pseudo-octahedral. The structure in solution, as established by multinuclear NMR spectroscopy and ESI spectrometry, is monomeric, and identical to that shown in the solid state. Replacement of the phenyl groups on the phosphorous atoms in complexes 1, 2, 5, and 6 with alkyl groups modified neither the course of the reaction nor the composition of the resulting complexes. These results, together with the observation that no symmetrical complexes containing two identical bidentate ligands were produced in these reactions, strongly supports the conclusion that a mixed coordination sphere, composed by a combination of ,-donor and ,-acceptor atoms around the [M,N]2+ group, constitutes a highly stable system. Compounds containing dangling alkyl-substituted groups in the outer sphere (3, 4, 7, and 8) were fully characterized by multinuclear NMR spectroscopy and ESI mass spectrometry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Stabilization of n integrators in cascade with bounded input with experimental application to a VTOL laboratory systemINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 10 2010G. Sanahuja Abstract This paper presents a global stabilization of a chain of n integrators in cascade. The control strategy is obtained using the Lyapunov approach and separated saturation functions. Moreover, the stability analysis is obtained using the recurrence theorem. This generalized control law is designed in order to quickly implement it on a system, as choosing a degree n gives all conditions to have a stable system. Moreover, in the proposed controller the saturation function bound only one state. This allows us to easily tune the control parameters. Simulations and real-time experiments are presented for the VTOL platform represented as a chain of two and four integrators in cascade. Copyright © 2009 John Wiley & Sons, Ltd. [source] Continuous Hydrogen Generation from Formic Acid: Highly Active and Stable Ruthenium CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Albert Boddien Abstract The ruthenium-catalyzed decomposition of formic acid was investigated with respect to continuous hydrogen generation and long-term stability of the catalytic systems. A highly active and stable system is presented, which was studied in batch and continuous modes for up to two months. The optimized catalyst system containing N,N -dimethyl- n -hexylamine with an in situ generated catalyst from (benzene)ruthenium dichloride dimer [RuCl2(benzene)]2 and 6 equivalents of 1,2-bis(diphenylphosphino)ethane (dppe) reached at room temperature a total turnover number (TON) of approximatly 260,000 with average turnover frequency (TOF) of about 900,h,1. Only hydrogen and carbon dioxide were detected in the produced gas mixture which makes this system applicable for direct use in fuel cells. [source] A novel lattice-spacing comparator with resolution of 10,8JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2003Xiaowei Zhang A novel, fast and stable system for measuring the lattice spacing of a silicon crystal with a precision of 10,8 is described. Self selection of monochromatic X-rays by a monolithic double channel-cut crystal monochromator (MDCM), producing silicon 264 and 624 diffraction, may lead to a stable, highly collimated and narrow-bandwidth beam. When utilizing the 264 and 624 Bragg reflections of a silicon sample, the angular distance between the two associated Bragg peaks must be extremely small, so that the diffraction angle can be determined with high precision and the traveling time from one peak to the other can be considerably reduced by the order of at least three compared with the established classical Bond method. This so-called self-reference comparator method can dramatically save measurement time and can provide an absolute measurement on the basis of the known X-ray wavelength available from the MDCM. Thus a lattice-spacing measurement with resolution of 10,8, within a few tens of seconds for an area of 1,mm2 on a silicon sample, has been realised. [source] Local forcing of a nonlinear surface reaction: CO oxidation on Pt(100)AICHE JOURNAL, Issue 1 2009Daniel Bilbao Abstract A novel spatiotemporal perturbation method for nonlinear surface reactions is reported, thus allowing the creation of new spatially localized structures. Forcing was achieved by dosing reactant gases through a capillary positioned near the catalyst surface, providing control over the local surface coverage and reaction rate. The emergence of localized concentration patterns and oscillations in an otherwise stable system is attributed to a local modification of the catalytic properties of the surface due to external forcing. Based on the spatial orientation, the temporal and thermal stability of the modified surface, as well as the affinity of CO toward the perturbed surface, subsurface O is proposed as a possible source of the observed localized patterning and surface memory effect. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Homogenous Synthesis of Hydroxyethylcellulose in NaOH/Urea Aqueous SolutionMACROMOLECULAR BIOSCIENCE, Issue 1 2006Jinping Zhou Abstract Summary: Hydroxyethylcellulose (HEC) was synthesized by a fully homogenous method from cellulose in 7.5 wt.-% NaOH/11 wt.-% urea aqueous solutions under mild conditions. HEC samples were characterized with NMR, SEC-LLS, solubility, and viscosity measurements. The MS and DS values of the obtained HEC samples are in the range from 0.54 to 1.44 and 0.45 to 1.14, respectively, and the relative DS values at C-2 and C-6 hydroxyl groups are slightly higher than those at C-3 hydroxyl groups. HEC samples are soluble in water starting from a MS of 0.57 and DS of 0.49, which display high viscosity in aqueous solutions. Moreover, a NaOH/urea aqueous solution is a stable system for cellulose etherification. In this way, we could provide a simple, pollution-free, and homogeneous aqueous solution system for synthesizing cellulose ethers. 13C NMR spectra of acetylated HEC (a) in CDCl3 at 40,°C and (b) in DMSO- d6 at 100,°C. [source] ,, model reduction for uncertain two-dimensional discrete systemsOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 4 2005Huijun Gao Abstract This paper investigates the problem of ,, model reduction for two-dimensional (2-D) discrete systems with parameter uncertainties residing in a polytope. For a given robustly stable system, our attention is focused on the construction of a reduced-order model, which also resides in a polytope and approximates the original system well in an ,, norm sense. Both Fornasini,Marchesini local state-space (FMLSS) and Roesser models are considered through parameter-dependent approaches, with sufficient conditions obtained for the existence of admissible reduced-order solutions. Since these obtained conditions are not expressed as strict linear matrix inequalities (LMIs), the cone complementary linearization method is exploited to cast them into sequential minimization problems subject to LMI constraints, which can be readily solved using standard numerical software. In addition, the development of zeroth order models is also presented. Two numerical examples are provided to show the effectiveness of the proposed theories. Copyright © 2005 John Wiley & Sons, Ltd. [source] A magnitude-robust control chart for monitoring and estimating step changes for normal process meansQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 6 2002Joseph J. Pignatiello Jr Abstract Statistical process control charts are intended to assist operators of a usually stable system in monitoring whether a change has occurred in the process. When a change does occur, the control chart should detect it quickly. If the operator can also be provided information that aids in the search for the special cause, then critical off-line time can be saved. We investigate a process-monitoring tool that not only provides speedy detection regardless of the magnitude of the process shift, but also supplies useful change point statistics. A likelihood ratio approach can be used to develop a control chart for permanent step change shifts of a normal process mean. The average run length performance for this chart is compared to that of several cumulative sum (CUSUM) charts. Our performance comparisons show that this chart performs better than any one CUSUM chart over an entire range of potential shift magnitudes. The likelihood ratio approach also provides point and interval estimates for the time and magnitude of the process shift. These crucial change-point diagnostics can greatly enhance special cause investigation. Copyright © 2002 John Wiley & Sons, Ltd. [source] On the sample-complexity of ,, identificationINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 7 2001S. R. Venkatesh Abstract In this paper we derive the sample complexity for discrete time linear time-invariant stable systems described in the ,, topology. The problem set-up is as follows: the ,, norm distance between the unknown real system and a known finitely parameterized family of systems is bounded by a known real number. We can associate, for every feasible real system, a model in the finitely parameterized family that minimizes the ,, distance. The question now arises as to how long a data record is required to identify such a model from noisy input,output data. This question has been addressed in the context of l1, ,2 and several other topologies, and it has been shown that the sample-complexity is polynomial. Nevertheless, it turns out that for the ,, topology the sample-complexity in the worst case can be infinite. Copyright © 2001 John Wiley & Sons, Ltd. [source] Estimation and forecasting in first-order vector autoregressions with near to unit roots and conditional heteroscedasticityJOURNAL OF FORECASTING, Issue 7 2009Theologos Pantelidis Abstract This paper investigates the effects of imposing invalid cointegration restrictions or ignoring valid ones on the estimation, testing and forecasting properties of the bivariate, first-order, vector autoregressive (VAR(1)) model. We first consider nearly cointegrated VARs, that is, stable systems whose largest root, lmax, lies in the neighborhood of unity, while the other root, lmin, is safely smaller than unity. In this context, we define the ,forecast cost of type I' to be the deterioration in the forecasting accuracy of the VAR model due to the imposition of invalid cointegration restrictions. However, there are cases where misspecification arises for the opposite reasons, namely from ignoring cointegration when the true process is, in fact, cointegrated. Such cases can arise when lmax equals unity and lmin is less than but near to unity. The effects of this type of misspecification on forecasting will be referred to as ,forecast cost of type II'. By means of Monte Carlo simulations, we measure both types of forecast cost in actual situations, where the researcher is led (or misled) by the usual unit root tests in choosing the unit root structure of the system. We consider VAR(1) processes driven by i.i.d. Gaussian or GARCH innovations. To distinguish between the effects of nonlinear dependence and those of leptokurtosis, we also consider processes driven by i.i.d. t(2) innovations. The simulation results reveal that the forecast cost of imposing invalid cointegration restrictions is substantial, especially for small samples. On the other hand, the forecast cost of ignoring valid cointegration restrictions is small but not negligible. In all the cases considered, both types of forecast cost increase with the intensity of GARCH effects. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preparation and Characterisation of Pd Nanoclusters in Hyperbranched Aramid Templates to be used in Homogeneous CatalysisMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 12 2003Daniela Tabuani Abstract In the present paper the potential use of hyperbranched (HB) aramids as metallic solution stabilisers and carriers for homogeneous catalysis is outlined. Aramids, synthesised either from A2,+,B3 reagents [namely, p -phenylenediamine (PPD) and trimesic acid (TMA)] or from an AB2 monomer [i.e., 5-(4-aminobenzamido)isophtalic acid, named ABZAIA], have been used to stabilise palladium nanoclusters dispersed in two solvent media, namely N,N, -dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The influence of the nature of the polymeric support as well as of the solvent medium on both cluster dimensions and stability of the solutions has been investigated. Indeed, the interactions between the polymeric support and the metallic precursor (PdCl2), as revealed by 1H NMR spectroscopy, involve only the amino groups of the HB aramids. Metal nanocluster dimensions and stability are strongly dependent on the polymer used as a stabilizer. Transmission electron microscopy (TEM) analysis has shown that the presence of HB polymer in the solution reduces cluster dimensions and allows the obtaining of stable systems. The low concentration of NH2 end groups in the poly(AB2) system leads to the formation of Pd particles of rather low dimensions with a high tendency to aggregate. All prepared solutions are stable under inert atmosphere for at least a month, with an improved stabilisation when using the poly(A2,+,B3) system for more than five months. A TEM micrograph of poly(ABZAIA)/Pd from a DMSO solution. [source] Minimum effort dead-beat control of linear servomechanisms with ripple-free responseOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 3 2001Abstract A new and systematic approach to the problem of minimum effort ripple-free dead-beat (EFRFDB) control of the step response of a linear servomechanism is presented. There is specified a set of admissible discrete error feedback controllers, complying with general conditions for the design of ripple-free dead-beat (RFDB) controllers, regardless of the introduced degree of freedom, defined as the number of steps exceeding their minimum number. The solution is unique for the minimum number of steps, while their increase enables one to make an optimal choice from a competitive set of controllers via their parametrization in a finite-dimensional space. As an objective function, Chebyshev's norm of an arbitrarily chosen linear projection of the control variable was chosen. There has been elaborated a new, efficient algorithm for all stable systems of the given class with an arbitrary degree of freedom. A parametrized solution in a finite space of polynomials is obtained through the solution of a standard problem of mathematical programming which simultaneously yields the solution of a total position change maximization of servomechanism provided that a required number of steps and control effort limitation are given. A problem formulated in this way is consecutively used in solving the time-optimal (minimum-step) control of a servomechanism to a given steady-state position with a specified limitation on control effort. The effect of EFRFDB control on the example of a linear servomechanism with torsion spring shaft, with the criterions of control effort and control difference effort, is illustrated and analysed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Stochastic Model Reduction by Maximizing IndependenceASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2005Hui Zhang By analysing information descriptions in state space models of linear stochastic systems, this paper proposes two model reduction methods via principles of maximizing independence and conditional independence among the reduced state vector, respectively. These methods are based on state aggregation. The independence and conditional independence are measured by the Kullback-Leibler information distance. It is demonstrated that the maximum conditional independence method is not only applicable to stable systems, but also applicable to unstable systems. Simulation results illustrate the efficiency of the present methods. 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